Compressor in applications

Applications

Gas compressors are used in various applications where either higher pressures or lower volumes of gas are needed:
- in pipeline transport of purified natural gas to move the gas from the production site to the consumer.
- in petroleum refineries, natural gas processing plants, petrochemical and chemical plants, and similar large industrial plants for compressing intermediate and end product gases.
- in refrigeration and air conditioner equipment to move heat from one place to another in refrigerant cycles: see Vapor-compression refrigeration.
- in gas turbine systems to compress the intake combustion air
- in storing purified or manufactured gases in a small volume, high pressure cylinders for medical, welding and other uses.
- in many various industrial, manufacturing and building processes to power all types of pneumatic tools.
as a medium for transferring energy, such as to power pneumatic equipment.
- in pressurised aircraft to provide a breathable atmosphere of higher than ambient pressure.
- in some types of jet engines (such as turbojets and turbofans) to provide the air required for combustion of the engine fuel. The power to drive the combustion air compressor comes from the jet's own turbines.
- in SCUBA diving, hyperbaric oxygen therapy and other life support devices to store breathing gas in a small volume such as in diving cylinders.
- in submarines, to store air for later use in displacing water from buoyancy chambers, for adjustment of depth.
- in turbochargers and superchargers to increase the performance of internal combustion engines by increasing mass flow.
- in rail and heavy road transport to provide compressed air for operation of rail vehicle brakes or road vehicle brakes and various other systems (doors, windscreen wipers, engine/gearbox control, etc).
- in miscellaneous uses such as providing compressed air for filling pneumatic tires.

Compressor: Gas laws

Temperature
Compression of a gas naturally increases its temperature.
In an attempt to model the compression of gas, there are two theoretical relationships between temperature and pressure in a volume of gas undergoing compression. Although neither of them model the real world exactly, each can be useful for analysis. A third method measures real-world results:

Isothermal - This model assumes that the compressed gas remains at a constant temperature throughout the compression or expansion process. In this cycle, internal energy is removed from the system as heat at the same rate that it is added by the mechanical work of compression. Isothermal compression or expansion more closely models real life when the compressor has a large heat exchanging surface, a small gas volume, or a long time scale (i.e., a small power level). Compressors that utilize inter-stage cooling between compression stages come closest to achieving perfect isothermal compression. However, with practical devices perfect isothermal compression is not attainable. For example, unless you have an infinite number of compression stages with corresponding intercoolers, you will never achieve perfect isothermal compression.

Adiabatic - This model assumes that no energy (heat) is transferred to or from the gas during the compression, and all supplied work is added to the internal energy of the gas, resulting in increases of temperature and pressure. Theoretical temperature rise is T2 = T1·Rc(k-1)/k, with T1 and T2 in degrees Rankine or kelvins, and k = ratio of specific heats (approximately 1.4 for air). R is the compression ratio; being the absolute outlet pressure divided by the absolute inlet pressure. The rise in air and temperature ratio means compression does not follow a simple pressure to volume ratio. This is less efficient, but quick. Adiabatic compression or expansion more closely model real life when a compressor has good insulation, a large gas volume, or a short time scale (i.e., a high power level). In practice there will always be a certain amount of heat flow out of the compressed gas. Thus, making a perfect adiabatic compressor would require perfect heat insulation of all parts of the machine. For example, even a bicycle tire pump's metal tube becomes hot as you compress the air to fill a tire.

Polytropic - This model takes into account both a rise in temperature in the gas as well as some loss of energy (heat) to the compressor's components. This assumes that heat may enter or leave the system, and that input shaft work can appear as both increased pressure (usually useful work) and increased temperature above adiabatic (usually losses due to cycle efficiency). Compression efficiency is then the ratio of temperature rise at theoretical 100 percent (adiabatic) vs. actual (polytropic).
In the case of the fire piston and the heat pump, people desire temperature change, and compressing gas is only a means to that end.

Types of compressors

The main types of gas compressors are illustrated and discussed below:

1) Centrifugal compressors

A single stage centrifugal compressor
Centrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants. Their application can be from 100 hp (75 kW) to thousands of horsepower. With multiple staging, they can achieve extremely high output pressures greater than 10,000 psi (69 MPa).
Many large snow-making operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium sized gas turbines.

2) Diagonal or mixed-flow compressors

Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to the axial direction. The diagonal compressor has a lower diameter diffuser than the equivalent centrifugal compressor.

3) Axial-flow compressors

Axial-flow compressors are dynamic rotating compressors that use arrays of fan-like aerofoils to progressively compress the working fluid. They are used where there is a requirement for a high flows or a compact design.
The arrays of aerofoils are set in rows, usually as pairs: one rotating and one stationary. The rotating aerofoils, also known as blades or rotors, accelerate the fluid. The stationary aerofoils, also known as a stators or vanes, turn and decelerate the fluid; preparing and redirecting the flow for the rotor blades of the next stage. Axial compressors are almost always multi-staged, with the cross-sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number. Beyond about 5 stages or a 4:1 design pressure ratio, variable geometry is normally used to improve operation.
Axial compressors can have high efficiencies; around 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Axial-flow compressors can be found in medium to large gas engines, in natural gas pumping stations, and within certain chemical plants.

4) Reciprocating compressors

A motor-driven six-cylinder reciprocating compressor that can operate with two, four or six cylinders.
Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors well over 1000 hp are still commonly found in large industrial and petroleum applications. Discharge pressures can range from low pressure to very high pressure (>5000 psi or 35 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, noisier, and more costly than comparable rotary units.

5) Rotary screw compressors

Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space. These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 hp (2.24 kW) to over 500 hp (375 kW) and from low pressure to very high pressure (>1200 psi or 8.3 MPa).

6) Rotary vane compressors

Rotary vane compressors consist of a rotor with a number of blades inserted in radial slots in the rotor. The rotor is mounted offset in a larger housing which can be circular or a more complex shape. As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing. Thus, a series of decreasing volumes is created by the rotating blades. Rotary Vane compressors are, with piston compressors one of the oldest of compressor technologies.
With suitable port connections, the devices may be either a compressor or a vacuum pump. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Dry vane machines are used at relatively low pressures (e.g., 2 bar) for bulk material movement whilst oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about 13 bar in a single stage. A rotary vane compressor is well suited to electric motor drive and is significantly quieter in operation than the equivalent piston compressor.

7) Scroll compressors

A scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases. The vane geometry may be involute, archimedean spiral, or hybrid curves. They operate more smoothly, quietly, and reliably than other types of compressors in the lower volume range
Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid or gas between the scrolls.

8) Diaphragm compressors

A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in touch with the gas being compressed.
Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications.

9) A three-stage diaphragm compressor

The photograph included in this section depicts a three-stage diaphragm compressor used to compress hydrogen gas to 6,000 psi (41 MPa) for use in a prototype compressed hydrogen and compressed natural gas (CNG) fueling station built in downtown Phoenix, Arizona by the Arizona Public Service company (an electric utilities company). Reciprocating compressors were used to compress the natural gas.
The prototype alternative fueling station was built in compliance with all of the prevailing safety, environmental and building codes in Phoenix to demonstrate that such fueling stations could be built in urban areas.

Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible, so the main action of a pump is to transport liquids.

Advantage and disadvantage of gas turbine engines

Advantages of gas turbine engines

Very high power-to-weight ratio, compared to reciprocating engines;
Smaller than most reciprocating engines of the same power rating.
Moves in one direction only, with far less vibration than a reciprocating engine.
Fewer moving parts than reciprocating engines.
Low operating pressures.
High operation speeds.
Low lubricating oil cost and consumption.

Disadvantages of gas turbine engines
Cost is much greater than for a similar-sized reciprocating engine since the materials must be stronger and more heat resistant. Machining operations are also more complex;
Usually less efficient than reciprocating engines, especially at idle.
Delayed response to changes in power settings.
These disadvantages explain why road vehicles, which are smaller, cheaper and follow a less regular pattern of use than tanks, helicopters, large boats and so on, do not use gas turbine engines, regardless of the size and power advantages imminently available.

Gas turbine in commercial use

There have been a number of experiments in which gas turbines were used to power seagoing commercial vessels. The earliest of these experiments may have been the oil tanker "Aurus" (Anglo Saxon Petroleum) - circa 1949.
The United States Maritime Commission were looking for options to update WWII Liberty ships and heavy duty gas turbines were one of those selected. In 1956 The "John Sergeant" was lenghened and installed with a General Electric 6600 SHP HD gas turbine, reduction gearing and a variable pitch propeller. It operated for 9700 hours using residual fuel for 7000 hours. The success of this trial opened the way for more development by GE on the use of HD gas turbines for marine use with heavy fuels. The "John Sergeant" was scrapped in 1972 at Portsmouth PA.
Between 1970 and 1982, Seatrain Container Lines operated a scheduled container service across the North Atlantic with four 26,000 tonne dwt. container ships. Those ships were powered by twin Pratt & Whitney gas turbines of the FT 4 series. The four ships in the class were named "Euroliner", "Eurofreighter", "Asialiner" and "Asiafreighter". They operated a transatlantic container service between ports on the eastern seaboard of the United States and ports in north west Europe. Following the dramatic OPEC price increases of the mid-nineteen seventies, operations were constrained by rising fuel costs. Some modification of the engine systems on those ships was undertaken to permit the burning of a lower grade of fuel (i.e. marine diesel). The modifications were partially successful. It was proved that particular fuel could be used in a marine gas turbine but, savings made were less than anticipated due to increased maintenance requirements. After 1982 the ships were sold, then re-engined with more economical diesel engines. Because the new engines were much larger, there was a consequential loss of some cargo space.
The first passenger ferry to use a gas turbine was the GTS Finnjet, built in 1977 and powered with two Pratt & Whitney FT 4C-1 DLF turbines, generating 55000 kW and propelling the ship to a speed of 31 knots. However, the Finnjet also illustrated the shortcomings of gas turbine propulsion in commercial craft, as high fuel prices made operating her unprofitable. After just four years of service additional diesel engines were installed on the ship to allow less costly operations during off-season. Another example of commercial usage of gas turbines in a passenger ship are Stena Line's HSS class fastcraft ferries. HSS 1500-class Stena Explorer, Stena Voyager and Stena Discovery vessels use combined gas and gas (COGAG) setups of twin GE LM2500 plus GE LM1600 power for a total of 68,000 kW. The slightly smaller HSS 900-class Stena Charisma, uses twin ABB–STAL GT35 turbines rated at 34,000 kW gross. The Stena Discovery was withdrawn from service in 2007, another victim of too high fuel costs.
In July 2000, the Millennium became the first cruise ship to be propelled by gas turbines, in a Combined Gas and Steam Turbine configuration. The RMS Queen Mary 2 uses a Combined Diesel and Gas Turbine configuration.

Gas turbine in naval use

Naval use
Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961.
The Swedish Navy produced 6 Spica class torpedoboats between 1966 and 1967 powered by 3 Bristol Siddeley Proteus 1282, each delivering 4300 hp. They were later joined by 12 upgraded Norrköping class ships, still with the same engines. With their aft torpedo tubes replaced by antishipping missiles they served as missile boats until the last was retired in 2005.
The Finnish Navy issued two Turunmaa class corvettes, Turunmaa and Karjala, in 1968. They were equipped with one 16 000 shp Rolls-Royce Olympus TMB3 gas turbine and two Wärtsilä marine diesels for slower speeds. Before the waterjet-propulsion Helsinki class missile boats, they were the fastest vessels in the Finnish Navy; they regularly achieved 37 knot speeds, but they are known to have achieved 45 knots when the restriction mechanism of the turbine was geared off. The Turunmaas were paid off in 2002. Karjala is today a museum ship in Turku, and Turunmaa serves as a flotating machine shop and training ship for Satakunta Polytechnical College.
The next series of major naval vessels were the four Canadian Iroquois class helicopter carrying destroyers first commissioned in 1972. They used 2 ft-4 main propulsion engines, 2 ft-12 cruise engines and 3 Solar Saturn 750 kW generators.
The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines. The marine gas turbine operates in a more corrosive atmosphere due to presence of sea salt in air and fuel and use of cheaper fuels.

Gas turbine in Tank use

Tank use
The first use of a gas turbine in an armoured fighting vehicle was in 1954 when a unit, PU2979, specifically developed for tanks by C. A. Parsons & CO., was installed and trialled in a British Conqueror tank. Since then, gas turbine engines have been used as auxiliary power units (APUs) in some tanks and as main powerplants in Soviet/Russian T-80s and U.S. M1 Abrams tanks, among others. They are lighter and smaller than diesels at the same sustained power output but the models installed to date are less fuel efficient than the equivalent diesel, especially at idle, requiring more fuel to achieve the same combat range. Different models of M1 have addressed this problem with battery packs or secondary generators to power the tank's systems while stationary, saving fuel by reducing the need to idle the main turbine. T-80s can mount three large external fuel drums to extend their range. Russia has stopped production of the T-80 in favour of the diesel-powered T-90 (based on the T-72), while Ukraine has developed the diesel-powered T-80UD and T-84 with nearly the power of the gas-turbine tank.
A turbine is theoretically more reliable and easier to maintain than a piston engine, since it has a simpler construction with fewer moving parts but in practice turbine parts experience a higher wear rate due to their higher working speeds. The turbine blades are highly sensitive to dust and fine sand, so that in desert operations air filters have to be fitted and changed several times daily. An improperly fitted filter, or a bullet or shell fragment that punctures the filter can damage the engine. Piston engines also need well-maintained filters, but they are more resilient if the filter does fail.
Like most modern diesel engines used in tanks, gas turbines are usually multi-fuel engines.

Gas turbine in vehicles

Gas turbines in vehicles

The 1950 Rover JET1

The 1967 STP Oil Treatment Special on display at the Indianapolis Motor Speedway Hall of Fame Museum, with the Pratt & Whitney gas turbine shown.

A 1968 Howmet TX, the only turbine-powered race car to have achieved victory.
Gas turbines are used on ships, locomotives, helicopters, and in tanks. A number of experiments have been conducted with gas turbine powered automobiles.
In 1950, designer F.R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car, and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum.
Rover and the British Racing Motors (BRM) Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 Hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km/h) and had a top speed of 142 mph (229 km/h). American Ray Heppenstall joined Howmet Corporation and McKee Engineering together to develop their own gas turbine sports car in 1968, the Howmet TX, which ran several American and European events, including two wins, and also participated in the 1968 24 Hours of Le Mans. The cars used Continental gas turbines, which eventually set six FIA land speed records for turbine-powered cars.
For open wheel racing, 1967's revolutionary STP Oil Treatment Special four-wheel drive turbine-powered special fielded by racing and entrepreneurial legend Andy Granatelli and driven by Parnelli Jones nearly won the Indianapolis 500; the STP Pratt & Whitney powered turbine car was almost a lap ahead of the second place car when a gearbox bearing failed just three laps from the finish line. In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney gas turbine. Chapman had a reputation of building radical championship-winning cars, but had to abandon the project because there were too many problems with turbo lag.
The original General Motors Firebird was a series of concept cars developed for the 1953, 1956 and 1959 Motorama auto shows, powered by gas turbines.
American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars. Their turbines employed unique rotating recuperator that significantly increased efficiency.
Japanese car manufacturer Toyota demonstrated several gas turbine powered prototype vehicles such as the Century gas turbine hybrid in 1975, the Sports 800 GT in 1977 and the GTV in 1985. No production vehicles were made.
The fictional Batmobile is often said to be powered by a gas turbine or a jet engine. In fact, in 1989s filmed Batman, the production department built a working turbine vehicle for the Batmobile prop. Its fuel capacity, however, was reportedly only enough for 15 seconds of use at a time.
In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1 series hybrid. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator. Later on in 2006 GM went into the EcoJet concept car project with Jay Leno.
The arrival of the Capstone Microturbine has led to several hybrid bus designs from US and New Zealand manufacturers, starting with HEV-1 by AVS of Chattanooga, Tennessee in 1999, and closely followed by Ebus and ISE Research in California, and Designline in New Zealand. AVS turbine hybrids were plagued with reliability and quality control problems, resulting in liquidation of AVS in 2003. Today, the most successful design by Designline is now operated in 5 cities in 6 countries, with over 30 buses in operation worldwide.
It is worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important.
Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. In hybrids, gas turbines reduce the responsiveness problem, and the emergence of the continuously variable transmission may also help alleviate this. A recent idea is the 'Multi-Pressure' turbine proposed by Robin Mackay of Agile Turbines. This concept is expected to provide three different power level ranges - each of them exhibiting high efficiency and low emission levels. The engine has two compressor spindles and an intercooler. By a system of three-way valves, it can be operated with both 'wings' in super atmospheric pressure mode (high power) or one 'wing' super atmospheric and the other sub atmospheric (cruising power) or both 'wings' in sub atmospheric mode (idling). Since there is no change in direction or speed of gas flow at transition from one power level to another (only mass flow changes) transition is almost instantaneous - thus overcoming the slow throttle response characteristic of gas turbines in land vehicle applications.
Turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small gas turbine engines are rarities; but turbines are mass produced in the closely related form of the turbocharger.
The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a turbine engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283 kW (380 bhp). Speed-tested to 365 km/h or 227 mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.
Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See gas turbine-electric locomotive for more information.

Gas turbine: External combustion

External combustion
Most gas turbines are internal combustion engines but it is also possible to build an external combustion gas turbine which is, effectively, a turbine version of a hot air engine.
External combustion has been used for the purpose of using pulverized coal or finely ground biomass (such as sawdust) as a fuel. External combustion gas has been used both directly and indirectly. In the direct system, the combustion products travel through the power turbine. In the indirect system, a heat exchanger is used and clean air travels through the power turbine. The thermal efficiency is lower in the indirect type of external combustion, however the blades are not subjected to combustion products.

Microturbines

Microturbines

A micro turbine designed for DARPA by M-Dot
Also known as:
Turbo alternators
MicroTurbine (registered trademark of Capstone Turbine Corporation)
Turbogenerator (registered tradename of Honeywell Power Systems, Inc.)
Microturbines are becoming widespread for distributed power and combined heat and power applications. They are one of the most promising technologies for powering hybrid electric vehicles. They range from hand held units producing less than a kilowatt, to commercial sized systems that produce tens or hundreds of kilowatts.
Part of their success is due to advances in electronics, which allows unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows the generator to be integrated with the turbine shaft, and to double as the starter motor.
Microturbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. Microturbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust, whereas the waste heat of recriprocating engines is split between its exhaust and cooling system. However, reciprocating engine generators are quicker to respond to changes in output power requirement and are usually slightly more efficient, although the efficiency of microturbines is increasing. Microturbines also lose more efficiency at low power levels than reciprocating engines.
They accept most commercial fuels, such as gasoline, natural gas, propane, diesel, and kerosene as well as renewable fuels such as E85, biodiesel and biogas.
Microturbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, space heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy.
Typical microturbine efficiencies are 25 to 35%. When in a combined heat and power cogeneration system, efficiencies of greater than 80% are commonly achieved.
MIT started its millimeter size turbine engine project in the middle of the 1990s when Professor of Aeronautics and Astronautics Alan H. Epstein considered the possibility of creating a personal turbine which will be able to meet all the demands of a modern person's electrical needs, just like a large turbine can meet the electricity demands of a small city. According to Professor Epstein current commercial Li-ion rechargeable batteries deliver about 120-150 Wh/kg. MIT's millimeter size turbine will deliver 500-700 Wh/kg in the near term, rising to 1200-1500 Wh/kg in the longer term.

Gas turbine: Turboshaft, Radial turbine, and scale jet engines

Turboshaft engines

Turboshaft engines are often used to drive compression trains (for example in gas pumping stations or natural gas liquefaction plants) and are used to power almost all modern helicopters. The first shaft bears the compressor and the high speed turbine (often referred to as "Gas Generator" or "N1"), while the second shaft bears the low speed turbine (or "Power Turbine" or "N2"). This arrangement is used to increase speed and power output flexibility.

Radial gas turbines

1963, Norway, Jan Mowill initiated the development at Kongsberg Våpenfabrikk. Various successors have made good progress in the refinement of this mechanism. Owing to a configuration that keeps heat away from certain bearings the durability of the machine is improved while the radial turbine is well matched in speed requirement

Scale jet engines

Scale jet engines are scaled down versions of this early full scale engine
Also known as miniature gas turbines or micro-jets.
Many model engineers relish the challenge of re-creating the grand engineering feats of today as tiny working models. Naturally, the idea of re-creating a powerful engine such as the jet, fascinated hobbyists since the very first full size engines were powered up by Hans von Ohain and Frank Whittle back in the 1930s.
Recreating machines such as engines to a different scale is not easy. Because of the square-cube law, the behaviour of many machines does not always scale up or down at the same rate as the machine's size (and often not even in a linear way), usually at best causing a dramatic loss of power or efficiency, and at worst causing them not to work at all. An automobile engine, for example, will not work if reproduced in the same shape at the size of a human hand.
With this in mind the pioneer of modern Micro-Jets, Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67. This engine can produce up to 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe. Its radial compressor, which is cold, is small and the hot axial turbine is large experiencing more centrifugal forces, meaning that this design is limited by Mach number. Guiding vanes are used to hold the starter, after the compressor impeller and before the turbine. No bypass within the engine is used.

Gas turbine: Compressed air energy storage

Compressed air energy storage

One modern development seeks to improve efficiency in another way, by separating the compressor and the turbine with a compressed air store. In a conventional turbine, up to half the generated power is used driving the compressor. In a compressed air energy storage configuration, power, perhaps from a wind farm or bought on the open market at a time of low demand and low price, is used to drive the compressor, and the compressed air released to operate the turbine when required.

Industrial gas turbines for electrical generation

Industrial gas turbines for electrical generation

GE H series power generation gas turbine. This 480-megawatt unit has a rated thermal efficiency of 60% in combined cycle configurations.
Industrial gas turbines differ from aeroderivatave in that the frames, bearings, and blading is of heavier construction. Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems. They can be particularly efficient——up to 60%——when waste heat from the gas turbine is recovered by a heat recovery steam generator to power a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling or refrigeration. A cogeneration configuration can be over 90% efficient. The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated enclosure, both to protect the engine from the elements and the operators from the noise.
Simple cycle gas turbines in the power industry require smaller capital investment than either coal or nuclear power plants and can be scaled to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for base load power plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Because they are less efficient than combined cycle plants, they are usually used as peaking power plants, which operate anywhere from several hours per day to a couple dozen hours per year, depending on the electricity demand and the generating capacity of the region. In areas with a shortage of base load and load following power plant capacity, a gas turbine power plant may regularly operate during most hours of the day and even into the evening. A typical large simple cycle gas turbine may produce 100 to 300 megawatts of power and have 35–40% thermal efficiency. The most efficient turbines have reached 46% efficiency.

Types of gas turbines

Types of gas turbines

1) Aeroderivatives and jet engines

Diagram of a gas turbine jet engine
Airbreathing jet engines are gas turbines optimized to produce thrust from the exhaust gases, or from ducted fans connected to the gas turbines. Jet engines that produce thrust primarily from the direct impulse of exhaust gases are often called turbojets, whereas those that generate most of their thrust from the action of a ducted fan are often called turbofans or (rarely) fan-jets.
Gas turbines are also used in many liquid propellant rockets, the gas turbines are used to power a turbopump to permit the use of lightweight, low pressure tanks, which saves considerable dry mass.
Aeroderivatives are also used in electical power generation due to their ability to startup, shut down, and handle load changes quicker than industrial machines. They are also used in the marine industry to reduce weight. The GE LM2500 and LM6000 are two common models of this type of machine.

2) Amateur gas turbines
A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur. See external links for resources.

3) Auxiliary power units
Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, such as those inside an aircraft. They supply compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power.

Gas turbine: Theory of operation

Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.
In practice, friction, and turbulence cause:
- non-isentropic compression: for a given overall pressure ratio, the compressor delivery temperature is higher than ideal.
- non-isentropic expansion: although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work.
pressure losses in the air intake, combustor and exhaust: reduces the expansion available to provide useful work.

Brayton cycle
As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, nickel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (co-generation) uses waste heat for hot water production.
Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft/compressor/turbine/alternative-rotor assembly (see image above), not counting the fuel system.
More sophisticated turbines (such as those found in modern jet engines) may have multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast system of complex piping, combustors and heat exchangers.
As a general rule, the smaller the engine the higher the rotation rate of the shaft(s) needs to be to maintain tip speed. Turbine blade tip speed determines the maximum pressure that can be gained, independent of the size of the engine. Jet engines operate around 10,000 rpm and micro turbines around 100,000 rpm.
Thrust bearings and journal bearings are a critical part of design. Traditionally, they have been hydrodynamic oil bearings, or oil-cooled ball bearings. These bearings are being surpassed by foil bearings, which have been successfully used in micro turbines and auxiliary power units.

Gas turbine

A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.)
Energy is added to the gas stream in the combustor, where air is mixed with fuel and ignited. Combustion increases the temperature, velocity and volume of the gas flow. This is directed through a (nozzle) over the turbine's blades, spinning the turbine and powering the compressor.
Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.

Boiler: Controlling draft

Most boilers now depend on mechanical draft equipment rather than natural draft. This is because natural draft is subject to outside air conditions and temperature of flue gases leaving the furnace, as well as the chimney height. All these factors make proper draft hard to attain and therefore make mechanical draft equipment much more economical.
There are three types of mechanical draft:
Induced draft: This is obtained one of three ways, the first being the "stack effect" of a heated chimney, in which the flue gas is less dense than the ambient air surrounding the boiler. The more dense column of ambient air forces combustion air into and through the boiler. The second method is through use of a steam jet. The steam jet oriented in the direction of flue gas flow induces flue gasses into the stack and allows for a greater flue gas velocity increasing the overall draft in the furnace. This method was common on steam driven locomotives which could not have tall chimneys. The third method is by simply using an induced draft fan (ID fan) which sucks flue gases out of the furnace and up the stack. Almost all induced draft furnaces have a negative pressure.
Forced draft: Draft is obtained by forcing air into the furnace by means of a fan (FD fan) and ductwork. Air is often passed through an air heater; which, as the name suggests, heats the air going into the furnace in order to increase the overall efficiency of the boiler. Dampers are used to control the quantity of air admitted to the furnace. Forced draft furnaces usually have a positive pressure.
Balanced draft: Balanced draft is obtained through use of both induced and forced draft. This is more common with larger boilers where the flue gases have to travel a long distance through many boiler passes. The induced draft fan works in conjunction with the forced draft fan allowing the furnace pressure to be maintained slightly below atmospheric.

Boiler fittings and acessories

Safety valve: It is used to relieve pressure and prevent possible explosion of a boiler.
Water level indicators: They show the operator the level of fluid in the boiler, also known as a sight glass, water gauge or water column is provided.
Bottom blowdown valves: They provide a means for removing solid particulates that condense and lay on the bottom of a boiler. As the name implies, this valve is usually located directly on the bottom of the boiler, and is occasionally opened to use the pressure in the boiler to push these particulates out.
Continuous blowdown valve: This allows a small quantity of water to escape continuously. Its purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the steam - a condition known as priming.
Hand holes: They are steel plates installed in openings in "header" to allow for inspections & installation of tubes and inspection of internal surfaces.
Steam drum internals, A series of screen, scrubber & cans (cyclone separators).
Low- water cutoff: It is a mechanical means (usually a float switch) that is used to turn off the burner or shut off fuel to the boiler to prevent it from running once the water goes below a certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure.
Surface blowdown line: It provides a means for removing foam or other lightweight non-condensible substances that tend to float on top of the water inside the boiler.
Circulating pump: It is designed to circulate water back to the boiler after it has expelled some of its heat.
Feedwater check valve or clack valve: A nonreturn stop valve in the feedwater line. This may be fitted to the side of the boiler, just below the water level, or to the top of the boiler. A top-mounted check valve is called a top feed and is intended to reduce the nuisance of limescale. It does not prevent limescale formation but causes the limescale to be precipitated in a powdery form which is easily washed out of the boiler.
Desuperheater tubes or bundles: A series of tubes or bundle of tubes, in the water drum but sometime in the steam drum that De-superheated steam. This is for equipment that doesn't need dry steam.
Chemical injection line: A connection to add chemicals for controlling feedwater pH.

Steam accessories
Main steam stop valve:
Steam traps:
Main steam stop/Check valve: It is used on multiple boiler installations.

Combustion accessories
Fuel oil system:
Gas system:
Coal system:

Other essential items
Pressure gauges:
Feed pumps:
Fusible plug:
Inspectors test pressure gauge attachment:
Name plate:
Registration plate:

Hydronic boilers

Hydronic boilers are used in generating heat for residential and industrial purposes. They are the typical power plant for central heating systems fitted to houses in northern Europe (where they are commonly combined with domestic water heating), as opposed to the forced-air furnaces or wood burning stoves more common in North America. The hydronic boiler operates by way of heating water/fluid to a preset temperature (or sometimes in the case of single pipe systems, until it boils and turns to steam) and circulating that fluid throughout the home typically by way of radiators, baseboard heaters or through the floors. The fluid can be heated by any means...gas, wood, fuel oil, etc, but in built-up areas where piped gas is available, natural gas is currently the most economical and therefore the usual choice. The fluid is in an enclosed system and circulated throughout by means of a motorized pump. Most new systems are fitted with condensing boilers for greater efficiency. The name can be a misnomer in that, except for systems using steam radiators, the water in a properly functioning hydronic boiler never actually boils. These boilers are referred to as condensing boilers because they condense the water vapor in the flue gases to capture the latent heat of vaporization of the water produced during combustion.
Hydronic systems are being used more and more in new construction in North America for several reasons. Among the reasons are:
They are more efficient and more economical than forced-air systems (although initial installation can be more expensive, because of the cost of the copper and aluminum).
The baseboard copper pipes and aluminum fins take up less room and use less metal than the bulky steel ductwork required for forced-air systems.
They provide more even, less fluctuating temperatures than forced-air systems. The copper baseboard pipes hold and release heat over a longer period of time than air does, so the furnace does not have to switch off and on as much. (Copper heats mostly through conduction and radiation, whereas forced-air heats mostly through forced convection. Air has much lower thermal conductivity and higher specific heat than copper; however, convection results in faster heat loss of air compared to copper. See also thermal mass.)
They do not dry out the interior air as much.
They do not introduce any dust, allergens, mold, or (in the case of a faulty heat exchanger) combustion byproducts into the living space.
Forced-air heating does have some advantages, however. See forced-air heating.

Boiler: Supercritical steam generators

Supercritical steam generators (also known as Benson boilers) are frequently used for the production of electric power. They operate at "supercritical pressure". In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3200 PSI, 22 MPa, 220 bar) that actual boiling ceases to occur, and the boiler has no water - steam separation. There is no generation of steam bubbles within the water, because the pressure is above the "critical pressure" at which steam bubbles can form. It passes below the critical point as it does work in the high pressure turbine and enters the generator's condenser. This is more efficient, resulting in slightly less fuel use. The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" actually occurs in this device.

History of supercritical steam generation
Contemporary supercritical steam generators are sometimes referred as Benson boilers. In 1922, Mark Benson was granted a patent for a boiler designed to convert water into steam at high pressure.
Safety was the main concern behind Benson’s concept. Earlier steam generators were designed for relatively low pressures of up to about 100 bar, corresponding to the state of the art in steam turbine development at the time. One of their distinguishing technical characteristics was the riveted drum. These drums were used to separate water and steam, and were often the source of boiler explosions, usually with catastrophic consequences. However, the drum can be completely eliminated if the evaporation process is avoided altogether. This happens when water is heated at a pressure above the critical pressure and then expanded to dry steam at subcritical pressure. A throttle valve located downstream of the evaporator can be used for this purpose.
As development of Benson technology continued, boiler design soon moved away from the original concept introduced by Mark Benson. In 1929, a test boiler that had been built in 1927 began operating in the thermal power plant at Gartenfeld in Berlin for the first time in subcritical mode with a fully open throttle valve. The second Benson boiler began operation in 1930 without a pressurizing valve at pressures between 40 and 180 bar at the Berlin cable factory. This application represented the birth of the modern variable-pressure Benson boiler. After that development, the original patent was no longer used. The Benson boiler name, however, was retained.
Two current innovations have a good chance of winning acceptance in the competitive market for once-through steam generators:
A new type of heat-recovery steam generator based on the Benson boiler, which has operated successfully at the Cottam combined-cycle power plant in the central part of England,
The vertical tubing in the combustion chamber walls of coal-fired steam generators which combines the operating advantages of the Benson system with the design advantages of the drum-type boiler. Construction of a first reference plant, the Yaomeng power plant in China, commenced in 2001.

Superheated steam boilers

A superheated boiler on a steam locomotive.

Most boilers heat water until it boils, and then the steam is used at saturation temperature (i.e., saturated steam). Superheated steam boilers boil the water and then further heat the steam in a superheater. This provides steam at much higher temperature, and can decrease the overall thermal efficiency of the steam plant due to the fact that the higher steam temperature requires a higher flue gas exhaust temperature. However, there are advantages to superheated steam. For example, useful heat can be extracted from the steam without causing condensation, which could damage piping and turbine blades.
Superheated steam presents unique safety concerns because, if there is a leak in the steam piping, steam at such high pressure/temperature can cause serious, instantaneous harm to anyone entering its flow. Since the escaping steam will initially be completely superheated vapor, it is not easy to see the leak, although the intense heat and sound from such a leak clearly indicates its presence.
The superheater works like coils on an air conditioning unit, however to a different end. The steam piping (with steam flowing through it) is directed through the flue gas path in the boiler furnace. This area typically is between 1300-1600 degrees Celsius (2500-3000 degrees Fahrenheit). Some superheaters are radiant type (absorb heat by radiation), others are convection type (absorb heat via a fluid i.e. gas) and some are a combination of the two. So whether by convection or radiation the extreme heat in the boiler furnace/flue gas path will also heat the superheater steam piping and the steam within as well. It is important to note that while the temperature of the steam in the superheater is raised, the pressure of the steam is not: the turbine or moving pistons offer a "continuously expanding space" and the pressure remains the same as that of the boiler. The process of superheating steam is most importantly designed to remove all droplets entrained in the steam to prevent damage to the turbine blading and/or associated piping.

Boiler: Safety

Historically, boilers were a source of many serious injuries and property destruction due to poorly understood engineering principles. Thin and brittle metal shells can rupture, while poorly welded or riveted seams could open up, leading to a violent eruption of the pressurized steam. Collapsed or dislodged boiler tubes could also spray scalding-hot steam and smoke out of the air intake and firing chute, injuring the firemen that loaded coal into the fire chamber. Extremely large boilers providing hundreds of horsepower to operate factories could demolish entire buildings.
A boiler that has a loss of feed water and is permitted to boil dry can be extremely dangerous. If feed water is then sent into the empty boiler, the small cascade of incoming water instantly boils on contact with the superheated metal shell and leads to a violent explosion that cannot be controlled even by safety steam valves. Draining of the boiler could also occur if a leak occurred in the steam supply lines that was larger than the make-up water supply could replace. The Hartford Loop was invented in 1919 by the Hartford Steam Boiler and Insurance Company as a method to help prevent this condition from occurring, and thereby reduce their insurance claim.

Boiler: Configuration

Boilers can be classified into the following configurations:
"Pot boiler" or "Haycock boiler": a primitive "kettle" where a fire heats a partially-filled water container from below. 18th Century Haycock boilers generally produced and stored large volumes of very low-pressure steam, often hardly above that of the atmosphere. These could burn wood or most often, coal. Efficiency was very low.
Fire-tube boiler. Here, water partially fills a boiler barrel with a small volume left above to accommodate the steam (steam space). The heat source is inside a furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the temperature of the heating surface just below boiling point. The furnace can be situated at one end of a fire-tube which lengthens the path of the hot gases, thus augmenting the heating surface which can be further increased by making the gases reverse direction through a second parallel tube or a bundle of multiple tubes (two-pass or return flue boiler); alternatively the gases may be taken along the sides and then beneath the boiler through flues (3-pass boiler). In the case of a locomotive-type boiler, a boiler barrel extends from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly increase the heating surface compared to a single tube and further improve heat transfer. Fire-tube boilers usually have a comparatively low rate of steam production, but high steam storage capacity. Fire-tube boilers mostly burn solid fuels, but are readily adaptable to those of the liquid or gas variety.
Water-tube boiler. In this type,the water tubes are arranged inside a furnace in a number of possible configurations: often the water tubes connect large drums, the lower ones containing water and the upper ones, steam; in other cases, such as a monotube boiler, water is circulated by a pump through a succession of coils. This type generally gives high steam production rates, but less storage capacity than the above. Water tube boilers can be designed to exploit any heat source including nuclear fission and are generally preferred in high pressure applications since the high pressure water/steam is contained within narrow pipes which can withstand the pressure with a thinner wall.

Boiler for steam locomotive
Flash boiler. A specialized type of water-tube boiler.
Fire-tube boiler with Water-tube firebox. Sometimes the two above types have been combined in the following manner: the firebox contains an assembly of water tubes, called thermi syphons. The gases then pass through a conventional firetube boiler. Water-tube fireboxes were installed in many Hungarian locomotives, but have met with little success in other countries.
Sectional boiler. In a cast iron sectional boiler, sometimes called a "pork chop boiler" the water is contained inside cast iron sections. These sections are assembled on site to create the finished boiler.

Boiler

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.

Application
Boilers have many applications. They can be used in stationary applications to provide heat, hot water, or steam for domestic use, or in generators and they can be used in mobile applications to provide steam for locomotion in applications such as trains, ships, and boats. Using a boiler is a way to transfer stored energy from the fuel source to the water in the boiler, and then finally to the point of end use.

Materials
Construction of boilers is mainly in steel, stainless steel, and wrough iron. In liive steam models, copper or brass is often used. Historically copper was often used for fireboxes (particularly for steam locomotives), because of its better thermal conductivity. The price of copper now makes this impractical.
Cast iron is used for domestic water heaters. Although these are usually termed "boilers", their purpose is to produce hot water, not steam, and so they run at low pressure and try to avoid actual boiling. The brittleness of cast iron makes it impractical for steam pressure vessels.
For much of the Victorian "age of steam", the only material for boilermaking was the highest grade of wrought iron, with assembly by rivetting. This iron was often obtained from specialist ironworks, such as Cleator Moor (UK), noted for the high quality of their rolled plate and its suitability for high reliability use in critical applications, such as high pressure boilers. 20th century practice moved towards steel and welding.

Fuel
The source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas. Electric steam boilers use resistance or immersion type heating elements. Nuclear fission is also used as a heat source for generating steam. Heat recovery steam generators (HRSGs) use the heat rejected from other processes such as gas turbines.

Mechanism of metallocene catalysts

Mechanism of metallocene catalysts requires a co catalyst for activation. One of the most common co catalysts for this purpose is Methylalmuinoxane (MOA). Other catalysts include, Al(C2H5)3. There are numerous metallocene catalysts that can be used for propylene polymerization. Some metallocene catalysts are used for industrial process, while others are not, due to their high cost. One of simplest is Cp2ZrCl. Different catalyst can lead to polymers with different molecular weights and properties. Active research is still being conducted on metallocene catalyst. In the mechanism the metallocene catalyst first reacts with the co catalyst. If Metylalmuinoxane (MAO) is the co catalyst, the first step is to replace one of the Cl atoms on the catalyst with a methyl group from the Metylalmuinoxane (MAO). The methyl group on the MAO is replaced by the Cl from the catalyst. The MAO then removes another Cl from the catalyst. This makes the catalyst positively charged and susceptible to attack from propylene. Once the catalyst is activated, the double bond on the propylene coordinates with the metal of the catalyst. The methyl group on the catalyst then migrates to the propene, and the double bond is broken. This starts the polymerization. Once the methyl migrates the positively charged catalyst is reformed and another propene can coordinate to the metal. The second propene coordinates and the carbon chain that was formed migrates to the propene. The process of coordination and migration continues and a polymer chain is grown off of the metallocene catalyst.

Polypropylene (PP): Synthesis

An important concept in understanding the link between the structure of Polypropylene (PP) and its properties is tacticity. The relatives orientation of each methyl group relative to the methyl groups on neighbouring monomers has a strong effect on the finished polymer's ability to form crystals, because each methyl group takes up space and constrains backbone bending. Like most other vinyl polymers, useful polypropylene cannot be made by radical polymerization due to the higher reactivity of the allytic hydrogen (leading to dimerization) during polymerization. Moreover, the material that would result from such a process would have methyl groups arranged randomly, so called atactic Polypropylene (PP). The lack of long range order prevents any crystallinity in such a material, giving an amorphous material with very little strength and only specialized qualities suitable for niche end uses. A Ziegler-Natta catalyst is able to limit incoming monomers to a specific orientation, only adding them to the polymer chain if they face right direction. Most commercially available Polypropylene (PP) is made with such Ziegler-Natta catalysts, which produce mostly isotactic polypropylene (the upper chain in the figure above). With the methyl group consistenly on one another to form the crystals that give commercial polypropylene many of its desirable properties. More precisely engineered Kaminsky catalysts have been made, which offer a much greater level of control. Based on metallocene molecules, these catalst use organic groups to control the monomers being added, so that a proper molecules, these catalysts use organic groups to control the monomers being added, so that a proper choice of catalyst can produce isotactic, syndiotactic, or atactic polpropylene, or even a combination of these. Aside from this quantitative control, they allow better quantitative control, with a much greater ratio of the desired tacticity than previous Ziegler-Natta techniques. They also produce narrower molecular weight distributions than tradisional Ziegler-Natta catalyst, which can further improve properties. Tproduce a rubbery polypropylene, but with the organic groups that influence tacticity held in place by a relatively weak bond. After the catalyst has produced a short length of polymer which is capable of crystallization, light of the proper frequency is used to break this weak bond, and remove the selectivity of the catalyst so that the remaining length of the chain is atactic. The result is a mostly amorphous material with small crystals embedded in it. Since each chain has one end in a crystal but most of its length in the soft, amorphous bulk, the crystalline regions serve the same purpose as vulcanization.

Polypropylene (PP): Degradation

Degradation

Polypropylene (PP) is liable to chain degradation from exposure to Ultra Violett (UV) radiation such as that present in sunlight. This is one main reason for not using it transparent instead of glass. For external applications, Ultra Violett (UV)-absorbing additives must be used. Carbon black also provides some protection from UV attack. The polymer can also be oxidised at high temperatures, a common problem during moulding operations. Anti oxidants are normally added to prevent polymer degradation.

Polypropylene (PP): Chemical and physical properties

Most commercial polypropylene (PP) is isostatic and has an intermediate level crystallinity between that of low density polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate. Through the incorporation of rubber particles, Polypropylene (PP) can be made both tough and flexible, even at low temperatures. This allows Polypropylene (PP) to be used as a replacement for engineering plastics, such as ABS. Polypropylene (PP) is rugged, often somewhat stiffer than some some other plastics, reasonably economical, and can be made transparent as polystyrene, acrylic or certain other plastics. It can be also be made opaque and have many kinds of colors through the use of pigments. Polypropylene (PP) has very good resistance to fatique, so that most plastic living hinges, such as those on flip top bottles, are made from this material. Very thin sheets of Polypropylene (PP) are used as a dielectric within certain high performance pulse and low RF capasitors.

Polypropylene(PP) has melting point of about 160 degree Celcius, as determined by Differential Scanning Calorimetry (DSC). Many plastic items for medical or laboratory use can be made from Polypropylene (PP) because it can withstand the heat in an autoclave. Food containers provide a good hands on example of difference in modulus, since the rubbery (softer, more flexible) feeling of Linear density polyethylene (LDPE) with respect to Polypropylene (PP) of the same thickness is readily apparent. Rugged, translucent, reuseable plastic containers made in a wide variety of shapes and sizes for consumers from various companies such as Rubbermaid and Sterilite are commonly made of polypropylene, although the lids are often made of somewhat more flexible Linear density polyethylene (LDPE) so they can snap on to the container to close it. Polypropylene can also be made into disposable bottles to contain liquid, powdered or similar consumer products, although High density polyethylene (HDPE) and Polyethylene terephthlate (PET) are commonly also used to make bottles. Plastic pails, car batteries, wastebaskets, cooler containers, dishes and pitchers are often made of Polypropylene (PP) or High density polyethylene (HDPE), both of which commonly have rather similar appearance, feel, and properties at ambient temperature.

The Melt Flow Rate (MFR) or Melt Flow Index (MFI) is an indication of polypropylene's (PP's) molecular weight. This helps to determine how easily the melted raw material will flow during processing. Higher Melting Flow Rate (MFR) Polpropylenes (PPs) fill the plastic mold more easily during the injection or blow molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease. There are three general types of Polypropylene (PP): homopolymer, random copolymer and impact or block copolymer. The comonomer used is typically ethylene. Ethylene-propylene rubber added to Polypropylene (PP) homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to Polypropylene (PP) homopolymer decreases the polymer crystallinity and makes the polymer more transparent.

Polypropylene (PP)

Polypropylene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g., ropes, thermal underwear and carpets), stationary, plastic parts and reuseable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids. Polypropylene is commonly recycled, and has the number"5" as its recycling symbol. Melt processing of polypropylene can be achieved via extrusion and molding. Common extrusion methods include production of melt blown and spun bond fibers to form long rolls for future conversion into a wide range of useful products such as face masks, filters, nappies and wipes. The most common shaping technique is injection molding, which is used for parts such as cups, cutlery, vials, caps, containers, housewares and automotive parts such as batteries. The related techniques of blow molding and injection strech blow molding are also used, which involve both extrusion and moulding. The large number of end use applications of polypropylene (PP) are often possible because of the ability to tailor grades with specific molecular properties and additives during its manufacture. For example, antistatic additives can added to help Polypropylene (PP) surface resist dust and dirt. Many physical finishing techniques can be applied to Polypropylene (PP) parts in order to promote adhesion of printing ink and paints.

Linear density polyethylene (LDPE), Very low density polyethylene (VLDPE) and Ethylene copolymers

Linear density polyethylene (LDPE) is defined by a density range of 0.910-.0940 g/cm3. Linear density polyethylene (LDPE) has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous dipole induced dipole attraction is less. This results in a lower tensile strength and increased ductility. Linear density polyethylene (LDPE) is created by free radical polymerization. The high degree of branching with long chains gives molten Linear density polyethylene (LDPE) unique and desireable flow properties. Linear density polyethylene (LDPE) is used for both rigid containers and plastic film applications such as plastic bags and film wrap.

Very low density polyethylene (VLDPE) is defined by a density range of 0.880-0.915 g/cm3. Very low density polyethylene (VLDPE) is substantially linear polymer with hogh levels of short chain branches, commonly made by copolymerization of ethylene with short chain alpha olefins (for example, 1-butene, 1-hexene and 1-octene). Very low density polyethylene (VLDPE) is most commonly produced using metallocene catalysts due to the greater co-monomer incorporation exhibited by these catalysts. Very low density polyethylenes (VLDPEs) are used for hose and tubing, ice and frozen food bags, food packaging and strech wrap as well as impact modifiers when blended with other polymers. Recently much research activity has focused on the nature and distribution of long chain branches in polyethylene. In High density polyethylene (HDPE) a relatively small number of these branches, perhaps 1 in 100 or 1000 branches per backbone carbon, can significantly affect the rheological properties of the polymer.

Ethylene coplymers

In addition to copolymerization with alpha olefins, ethylene can also be copolymerized with a wide range of other monomers and ionic composition that creates ionized free radicals. Common examples include vinyl acetate (the resulting product is ethylene vinyl acetate copolymer, or EVA, widely used in atheletic shoe sole foams) and variety of acrylates (applications include packaging and sporting goods).

Linear low density polyethylene (LLDPE)

Linear low density polyethylene (LLDPE) is defined by a density range of 0.915-0.925 g/cm3. Linear low density polyethylene (LLDPE) is substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with sort chain alpha olefins (for example, 1-butene, 1-hexene and 1-octene). Linear low density polyethylene (LLDPE) has higher tensile strength than Linear density polyethylene (LDPE), it exhibits higher impact and puncture resistance than Linear density polyethylene (LDPE). Lower thickness (gauge) films can be blown, compared with Linear density polyethylene (LDPE), with better enviromental stress cracking resistance but is not as easy to process. Linear low density polyethylene (LLDPE) is used in packaging, particularly film for bags and sheets. Lower thickness may be used compared to Linear density polyethylene (LDPE). Cable covering, toys, lids, buckets, containers and pipe. While other applications are available, Linear low density polyethylene (LLDPE) is used predominantly in film applications due to its toughness, flexibility and relative transparency.

Cross linked polyethylene (PEX) and Medium density polyethylene (MDPE)

Cross linked polyethylene (PEX) is a medium to high density polyethylene containing cross link bonds introduced into the polymer structure, changing the thermoplast into an elastomer. The high temperature properties of the polymer are improved, its flow is reduced and its chemical resistance is enhanced. Cross linked polyethylene (PEX) is used in some potable water plumbing systems because tubes made of material can expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water tight, connection.

Medium density polyethylene (MDPE) is defined by a density range of 0.926-0.940 g/cm3. Medium density polyethylene can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. Medium density polyethylene has good shock and drop resistance properties. It also is less notch sensitive than High density polyethylene (HDPE), stress cracking resistance is better than High density polyethylene (HDPE). Medium density polyethylene (MDPE) is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures.

Ultra high molecular weigh polyethylene (UHMPE) and High density polyethylene (HDPE)

Ultra high molecular weight polyetyhlene (UHMWPE) is polyethylene with a molecular weight numbering in millions, usually between 3.1 and 5.67 million. The high molecular results in less efficient packing of the chains into the crystal structure as evidenced by densities of less than high density polyethylene (for example, 0.930-0.935 g/cm3). The high molecular weigh results in a very tough material. Ultra high molecular weight polyethylene (UHMWPE) can be made through any catalyst technology, although Ziegler catalyst are most common. Because of its outstanding toughness and its cut, wear and excellent chemical resistance, Ultra high molecular weight polyethylene (UHMWPE) is used in a wide diversity of applications. These include can and bottle handling maschine parts, moving parts on weaving maschines, bearings, gears, artificial joints, edge protection on ice rinks and butcher's chopping boards. It competes with Aramid in bulletproof vests, under tradenames Spectra and Dyneema, and is commonly used for the construction or articular portions of implants used for hip and knee replacements.

High density polyrthylene (HDPE) is defined by a density of greater or equal to 0.941 g/cm3. High density polyethylene has a low degree of branching and thus stronger intermolecular forces and tensile strength. High density polyethylene (HDPE) can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler-Natta catalysts) and reaction conditions. High density polyethylene (HDPE) is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes.

Polyethylene: Classification

Polyethylene is classified into several different categories based mostly on its density and branching. The mechanical properties of Polyethylene depend significantly on variables such as the extent and type of branching, the crystal structure and the molecular weight.

- Ultra high molecular weight polyethylene (UHMWPE)

- Ultra low molecular weight polyethylene (ULMWPE or PE-WAX)

- High molecular weight polyethylene (HMWPE)

- High density polyethylene (HDPE)

- High density cross linked polyethylene (HDXLPE)

- Cross linked polyethylene (PEX OR XLPE)

- Medium density polyetyhlene (MDPE)

- Low density polyethylene (LDPE)

- Linear low density polyethylene (LLDPE)

- Very low density polyethylene (VLDPE)

Special purpose plastics

Special purpose plastics:

- Polymetyl methacrylate (PMMA): Contact lenses, glazing (best known in this form by its various trade names around the world, e.g., Perspex, Oroglas, Plexiglas), aglets, fluoroscent light diffusers, rear light covers for vehicles.

- Polytetrafluoroethylene (PTFE, trade name Teflon): Heat resistant, low friction coatings, used in things like non stick surfaces for frying pans, plumber's tape and water slides.

- Polyethereketone (PEEK) (Polyetherketone): Strong, chemical- and heat resistant thermoplastic, biocompatibility allows for use in medical implant applications, aerospace mouldings. One of the most expensive commersial polymers.

- Polyetherimide (PEI) (Ultem): A high temperature, chemically stable polymer that does not crystallize.

- Phenolics (PF) or (Phenol formaldehydes): High modulus, relatively heat resistant, and excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper laminated products (e.g. "Formica"), thermally insulation foams. It is a thermosetting plastic, with the familiar trade name Bakelite, that can be moulded by heat and pressure when mixed with a filler like wood flour or can be cast in its unfilled liquid form or cast as foam, e.g. "Oasis". Problems include the probability of mouldings naturally being dark colours (red,green,brown), and as thermoset difficult to recycle.

- Urea formaldehyde (UF): One of the aminoplasts and used as a multi colorable alternative to Phenolics. Used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housing.

- Melamine formaldehde (MF): One of the aminoplasts, and used as a multi colorable alternative to phenolics, for instance in mouldings (e.g. break resistance alternatives to ceramic cups, plates and bowls for children) and the decorated top surface layer of the paper laminates (e.g."Formica").

- Polyactic acid: A biodegradble, thermoplastic, found converted into variety of aliphatic polyesters derived from lactic acid which in turn can be made by fermentation of various argricultural products such as corn starch, once made from diary products.

- Plastarch material: Biodegradable and heat resistant, thermoplastic composed of modified corn starch.

Common plastics and uses

Common plastics uses:

- Polypropylene (PP): Food containers, appliances, car fenders (bumpers)
- Polystyrene (PS): Packaging foam, food containers, disposable cups, plates, cutlery, CD and cassette boxes.
- High Impact Polystyrene (HIPS): Fridge liners, food packaging, vending cups.

- Acrylonitrile butadiene styrene (ABS): Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe.

- Polyetylene terephthlate (PET): Carbonated drinks bottles, jars, plastic film, microwavable packaging.

- Polyester (PES): Fibers, textiles.

- Polyamides (PA) (Nylons): Fibers, toothbrush bristle, fishing line, under the hood car engine mouldings.

- Polyvinyl chloride (PVC): Plumbing pipes and guttering, shower curtains, window frames, flooring.

- Polyurethanes (PU): Cushioning foams, thermal insulation foams, surface coatings, printing rollers. (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic found in cars.)

- Polycarbonate (PC): Compact discs, eyeglases, riot shields, security windows, traffic lights, lenses.

- Polyvinylidene chloride (PVDC) (Saran): Food packaging

- Polyethylene (PE): Wide range of inexpensive uses including supermarket bags, plastic bootles.

- Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS): A blend or PC and ABS that creates a stronger plastic. Car interior and exterior parts.

Plastic: Price, environment, and the future

The biggest threat to the conventional plastics industry is most likely tobe environmental concerns, including the release of toxic pollutants, greenhouse gas, litter, biodegradable and non biodegradable landfill impact as a result of the production and disposal of petroleum and petroleum based plastics. Of particular concern has been the recent accumulation of enormous quantities of plastic trash in ocean gyres, particular the North Pacific Gyre, now known informally as the Great Pacific Garbage Patch or the Pacific Trash Vortex. For decades one of the great appeals of plastics has been their low price. Yet in recent years the cost of plastics has been rising dramatically. A major cause is the sharply rising cost of petroleum, the raw material that is chemically altered to form commercial plastics. With some observers suggesting that future oil reserves are uncertain, the price of petroleum may increase further. Therefore, alternatives are being sough. Oil shale and tar oil are alternatives for plastic production but are expensive. Scientists are seeking cheaper and better alternatives to petroleum based plastics, and may candidates are in laboratories all over the world. One promising alternative may be fructose.

Pastic: Identification code

1. PET (Polyetylene terephthlate): Commonly found on 2 liter soft drink bottle, cooking oil bottles, peanut butter jars.

2. HDPE (High density Polyethylene): Commonly found on detergent bottles, milk jugs.

3. PVC (Polyvinyl chloride): Commonly found on plastic pipes, outdoor furniture, siding, floor titles, shower curtains, clamshell packaging.

4. LDPE (Low Density Polyethylene): Commonly found on dry cleaning bags, produce bags, trash can liners, food storage containers.

5. PP (Polypropylene): Commonly found on bottle caps, drinking straws, yogurt containers.

6. PS (Polystyrene): Commonly found on "packing peanuts", cups, plastic tableware, meat trays, take away food clamshell containers.

Biodegradeable plastics

Research has been done on biodegradable plastics that break down with exposure to sunlight (e.g. ultra violet radiation), water or dampness, bacteria, enzymes, wind abrasion and some instances rodent pest or insect attack are also included as forms of biodegradation or environmental degradation. It is clear some of these modes of degradation will only work if the plastic is exposed at the surface, while other modes will only be effective if certain conditions are found in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is expensive at present. The German chemical company BASF makes Ecoflex, a fully biodegradable polyester for food packaging applications. Apotential disadvantage of biodegradeable plastics is that the carbon that is locked up in them is released into the atmosphere as a greenhouse gas carbon dioxide when they degrade, though if they are made from natural materials, such as vegetable crop derivatives or animal products, there is not net gain in carbon dioxide emissions, although concern will be for a worse greenhouse gas, methane release. Of course, increasing non-biodegradable plastics will release carbon dioxide as well, while disposing of it in landfills will release methane when plastic does eventually break down. So far, these plastics have proven too costly and limited for general use, and critics have pointed out that the only real problem they address is roadside litter, which is regarded as a secondary issue. When such plastic materials are dumped into landfills, they can become "mummified" and persist for decades even if they are supposed to be biodegradable. There have been some success stories. The Courtauld concern, the original producer of rayon, came up with a revised process for the material in the mid 1980s to produce "Tencel". Tencel has many superior properties over rayon, but still produced from "biomass" feedstocks, and its manufacture is extraordinarily clean by the standards of plastic production. Researchers at the University of Illinois at Urbana have been working on developing biodegradable resins, sheets and films made with zei (corn protein). Recently, however, a new type of biodegradable resin has made it debut in the United States, called Plastarch Material (PSM). It is heat, water, and oil resistant and sees a 70% degradation in 90 days. Biodegradable plastics based on polylactic acid (once derived from dairy products, now from cereal crops such as maize) have entered the marketplace, for instance as polylactates as disposable sandwich packs. An alternative to starch based resins are additives such as Bio-Batch an additive that allows the manufacturers to make PE, PS, PP, PET, and PVC totally biodegradable in landfills where 94.8% of most plastics end up, according to EPA's latest MSW report located under "Municipal Solid Waste in the United States": 2003 Data Tables. It is also possible that bacteria will eventually develop the ability to degrade plastics. This has already happened with nylon: two types of nylon eating bacteria, Flavobacteria and Pseudomonas, were found in 1975 to possess enzymes (nylonase) capable of breaking down nylon. While not a solution to the disposal problem, it is likely that bacteria will evolve the ability to use others synthetic plastics as well. In 2008, a 16 years old reportedly isolatedly two plastic cosuming bacteria.

Best perfume: Preserving perfume

Fragnance compounds in perfumes will degrade or break down if improperty stored in the presence of:

- Heat

- Light

- Oxygen

- Extraneous organic materials

Proper presevation of perfumes involve keeping them away from sources of heat and storing them where they will not be exposed to light. An opened bottle will keep its aroma intact for several years, as long as it is well stored. However the presence of oxygen in the head space of the bottle and environmental factors will in the long run alter the smell of the fragnance. Perfumes are best preserved when kept in light-tight aluminium bottles or in their original packaging when not in use, and refrigerated at a relatively low temperatures between 3-7 degrees Celcius. Although it is difficult to completely remove oxygen from the headspace of a stored flask of fragnance, opting for spray dispensers instead of rollers and "open" bottles will minimize oxygen exposure. Sprays also have the advantage of isolating fragnance inside a bottle and preventing it from mixing with dust, skin, and detritus, which would degrade an alter the quality of a perfume.

Best perfume: Health issues

Perfume ingredients, regardless of natural or synthetic origin, may all cause health problems when used or abused in substantial quantities. Although the areas are under active research, much remains to be learned about the effects of fragnance on human health.

Immunological

Evidence in peer-reviewed journals show that some fragnances can cause asthmatic reaction even when the participants could not actually smell the fragnances. Many fragnance ingredients can cause allergic skin reactions or nausea. In some cases, an excessive use of perfumes may cause allergic reactions of the skin. For more instance, acetophenone, ethyl acetate and acetone while present in many perfumes, are also known or potential respiratory allergens. Nevertheless this may be misleading, since the harm presented by many of these chemicals (either natural or synthetic) is dependent on environmental conditions and their concentrations in a perfume. For instance, linalool, which is listed as an irritant, causes skin irritation when it degrades to peroxides, however the use of antioxidants in perfumes or reduction in concentrations can prevent this. Some research on natural aromatics have shown that many contain compounds that cause skin irritation, however some studies, such as IFRA's research claim that opoponax is too dangerous to be used in perfumery, still lack scientific consensus. It is also true that sometimes inhalation alone can cause skin irritation.

Carcinogenicity

There is scientific evidence that some common ingredients, like certain synthetic musks, can disrupt the ballance of hormones in human body (endocrine disruption) and even cause cancer (nitro-musk). Some natural aromatics, such as oakmoss absolutes, contain allergens and carcinogenic compounds.

Best perfume: Reverse engineering

Creating perfumes through reverse engineering with analytical techniques such as Gas Chromatography (GC)/Mass Spectroscopy (MS) can reveal the "general" formula for any particular perfume. The difficult of GC/MS analalysis arises due to the complexity of a perfume's ingredients, this is particularly due to pesence of natural essential oils and other ingredients consisting of complex chemical mixtures. However, "anyone armed with good Gas Chromatography (GC)/Mass Spectroscopy (MS) equipment and experienced in using this equipment can today, within days, find out a great deal about the formulation of any perfume.....customers and competitors can analyze most perfumes more or less precisely. Antique or badly preserved perfumes undergoing this analysis can also be difficult due to the numerous degradation by-products and impurities that may have resulted from breakdown of the odorous compounds. Ingredients and compounds can usually be ruled out or identified using gaschromatography (GC) smellers, which allow individual chemical components to identified both through their physical properties and their scent. Reverse engineering of best selling perfumes in the market is a very common practice in the fragnance industry due to the relative simplicity of operating Gas Chromatography (GC) equipment, the pressure to produce marketable fragnances, and the highly lucrative nature of perfume market.

Best perfume: Fragnance bases

Instead of building a perfume from "ground up", many modern perfumes and colognes are made using fragnance bases or simply bases. Each base is essentially modular perfume that is blended from essential oils and aromatic chemicals, and formulated with a simple concept such as "fresh cut grass" or "juicy sour apple". Many of Guerlain's Aqua Allegoria line, with their simple fragnance concepts, are good examples of what perfume fragnance bases are like. The effort used in developing bases by fragnance companies or individual perfumers may equal that of a marketed perfume, since they are useful in that they are reuseable. On top of its reusability, the benefit in using bases for construction are quite numerous:

1. Ingredients with "difficult" or "overpowering" scents that are tailored into a blended base may be more easily incoporated into a work of perfume.

2. A base may be better scent approximation of a certain thing than the extract of the thing itself. For example, a base made to embody the scent for "fresh dewy rose" might be a better approximation for the scent concept of a rose after rain than plain rose oil. Flowers whose scents cannot be extracted, such as gardenia or hyacinth, are composed as bases from data derived from headspace technology.

3. Aperfumer can quickly rough out a concept from a brief by cobbling together multiple bases, then present it for feedback. Smoothing out the "edges" of the perfume can be done after a positive response.

Best perfume: Basic framework

Perfume oils usually contain tens to hundreds of ingredients and these are typically organized in a perfume for the specific role they will play. These ingredients can be roughly grouped into four groups:

- Primary scents

Can consist of one or a few main ingredients for a certain concepts, such as "rose". Alternatively, multiple ingredients can be used together to create an "abstract" primary scent that does not bear a resemblance to a natural ingredient. For instance, jasmine and rose scents are commonly blends for abstract floral fragnances. Cola flavourant is good exampleof an abstract primary scent.

- Modifiers

These ingredients alter the primary scent to give the perfumer a certain desired character: for instance, fruit esters may be included in a floral primary to create a fruity floral; calone and citrus scents can be added to create a "fresher" floral. The cherry scent in cherry cola can be considered a modifier.

- Blenders

A large group of ingredients that smooth out the transitions of a perfume between different "layers" or bases. Common blending ingredients include linalool and hydroxycitronellal

- Fixatives

Used to support the primary scent by bolstering it. Many resins and wood scents, and amber bases are used as fixatives.

The top, middle, and base notes of a fragnance may have seperate primary scents and supporting ingredients. The perfumer's fragnance oils are then blended with ethyl alcohol and water, aged in tanks for several weeks and filtered through processing equipment to, respectively allow the perfume ingredients in the mixture to stabilize and remove any sediment and particles before the solution can be filled into the perfume bottles.