Gas Compression in the Refrigeration and Process Gas Industry

It is possible to design customized gas transport and compression solutions for the process gas and refrigeration industry only if the design of the machine chosen for the task is completely in alignment with the client’s particular requirements. The following two considerations must precede any purchase decisions.

Firstly, the requirements of the process as seen from the vantage point of the person who will be operating the plant is important, and secondly, the design of the selected machine is important in terms of the equipment supplier. This combination is only fulfilled if the manufacturer of the equipment has sufficient expertise and a wide array of devices for the customer to select from.

In the case of Aerzen Maschinenfabrik, the specialist knowledge stems from its long history of manufacturing rotary displacement blowers (from 1868 onwards) and screw compressors (from 1943 onwards).

It has also been involved in the supply of compressors and blowers for use in gas compression by the process gas and refrigeration industry for more than six decades and has shot to prominence as a phenomenally successful equipment supplier. Its machines are now in demand in petrochemicals, chemicals, soda, steel, and biogas industries, among others.

Aerzen focuses firstly on, “The detailed analysis of the current situation at the customer before any other considerations. The essential criteria include the composition of the gas to be compressed, the inlet pressure and temperature, the required outlet pressure and temperature, the ambient temperature, the expected flow rates and the quantities of cooling water available for cooling.”

Aerzen also explains that, “These and other parameters are essential prerequisites for a customized quotation, which also takes account of particular requirements such as special motors, frequency inverters and sound insulation measures etc.”

It is known that exacting specifications must be met for gas compression machinery, whatever the context. These devices must be completely gas-tight, as flammable, or toxic gases may be used. All relevant regulations and certifications must be complied with for the customer in question, such as the ATEX regulations or Ex specifications. The materials may vary, such as nodular cast iron, stainless steel or cast steel, depending on what is to be pumped and the kind of process taking place on-site.

Three Compressor Systems for Customized Solutions

Despite the global presence of Aerzen, it is at heart a small firm, with a few handpicked members of staff. This, coupled with its impressive range of equipment manufacture, allows it to offer customers the rare privilege of choosing the right machines for each application, after considering the range available and the requirements of the specific process.

When it comes to customized gas compression equipment for use by the refrigeration or process gas industry, Aerzen has a large array of oil-free rotary displacement blowers, as well as screw compressors with oil-free compression, or with oil injection. Some are presented below:

Rotary Displacement Blowers, Oil-free Compression

  • The GR Series
    • They achieve pressure differences of up to 1.5 bar
    • They are capable of handling intake volume flows between 100 and 50,000 m³/h
  • The GQ Series
    • These handle pressure differences of up to 1.5 bar
    • Their intake volume flows are larger, and range between 15,000 to 100,000 m³/h

Screw Compressor

Compressors with oil injection include:

  • The VMY 36 Series (used in refrigeration and process gas)
    • These can cope with a single step of pressure difference of up to around 20 bar
    • They can handle intake volume flows between 500 and 8,900 m³/h
  • The VMY 56 Series (also for refrigeration and process gas)
    • They can handle a pressure difference up to 25 bar
    • They can cope with intake volume flows of between 300 to 2,700 m³/h

Compressors which are oil-free include the VR Series:

  • These have the capacity to cope with a pressure difference of up to 52 bar
  • Their intake volume flows go from about 650 to 120,000 m³/h

Though the system is complex, carefully prepared quotations, well-conceived engineering, as well as actual project phases, coupled with extreme care in the brief period of actual commission, results in a highly tailored and powerful solution with low maintenance and a strong build. Aerzen compressors are of the top quality and use little fuel, with a legendary trouble-free life of over 30 years having been achieved in some applications.

GR Series Rotary Displacement Blowers

The GR series is made up of oil-free compressors with a double-leaf design, which can be used in process gas industries for pressure differences going up to 1,500 bar and intake flow rates of 100-50,000 m³/h. They are positive displacement type compressors and change their working characteristics with the operating conditions.

Some common uses include steel manufacture-related gas blowers for coke ovens and blast furnaces; a compression of mixed gases containing hydrogen, hydrocarbon and carbon monoxide, water vapor or any toxic or critical gases. These may be produced from nodular cast iron, cast steel, or cast stainless steel as Aerzen can vary the material depending on the specific process.

The same material will be used for the rotors and for each type of conveying chamber seal. A neutral chamber is here used to separate the conveyor from the oil chamber. With a strong build, these are not susceptible to gas impurities including tar, dirt or dust, or liquid molecules. They are designed to allow the injection of water or solvents, as well as cleaning or cooling agents.

GQ Series Rotary Displacement Blowers

The GQ series is also oil-free but operates on the rotary displacement principle, for applications which may generate pressure differences of up to 1.2 bar. In specialized processes this may go up to 1.5 bar in a single-stage unit, or up to 3.0 bar for a double-stage unit. These have air intake flow rates between 15,000 and 100,000 m³/h.

With pressure differences of up to 2.0 bar, it is possible to operate multiple systems in parallel and also as double-stage systems, as is the case when Midrex® processes are underway in the manufacture of steel.

These are also constructed on the positive displacement design and change their functioning with the operating conditions at the time. Their main uses lie in the compressing process and when cooling gas. For this reason, they are then fitted with specially designed combination seals for the conveying chamber.

To showcase the Aerzen experience and to comply with the highest standards, the GR series have met the KTA regulations, being certified as water vapor compression blowers of rotary displacement type, suitable for secondary circuits in nuclear power plants. They thus fit the top category regarding their manufacture, their inspection and quality control procedures, and their test standards.

For such extreme orders it may take three years from the first step of preparation, through to the early testing, and raw material procurement, from the first production line to start. GQ Series blowers are notable for being more durable than most others when there are gas line impurities, such as liquid, dirt or dust. Water injection at a constant rate can be introduced by injection to clean the conveying chamber or to cool the gas.

VMY Series Oil Injection Screw Compressor - Refrigeration

This series is an oil injection type manufactured for the refrigeration industry. Aerzen brought out compressor stages for screw compressors for several years using oil injection technology. These were taken advantage of by other manufacturers to produce refrigeration systems based on these compressor stages.

However, an Aerzen subsidiary, Aerzen Hungária KFT. in Esztergom, Hungary, has become a center of excellence to distribute, design, engineer and package refrigeration systems from 2012 onwards. It sells VMY Series screw compressors for this purpose all over the world. This series of refrigeration systems offers output adjustment from 100% to 200%, by regulating the flow rate due to an inbuilt valve.

This allows for very economical gas compression for natural gas, ammonia, hydrocarbons, inert gas, hydrogen chloride, helium, process gas and gas mixtures. The oil-injection type compressor has the advantage of resisting volume changes, as well as coping with shifts in temperature and pressures. The screw compressors are applied in closed circuits for cooling, using helium, ammonia, or Freon.

VMY Series Oil Injection Screw Compressors – Process Gases

The VMY screw compressors for the compression of process gases are specially designed for the process gas industry which is characterized by fluctuating requirements. They are used to compress all kinds of gases, including inert or natural gases, hydrocarbons, and other process gas mixtures, for chemical, petrochemical, power generation and various other equipment areas.

They resist shifts in gas volume, pressure, and temperatures. They can achieve residual levels as low as 5 to 1 ppm by their inbuilt oil separation capability at the supply limit.

VR Series Oil-free Screw Compressors - Process Gas

Aerzen VR series screw compressors use oil-free technology and if required, optional injections of water, to compress gases which vary in their molecular weights. They use both upper and lower gas inlet or outlet orifices. They can handle gases which are impure, polymerize easily, or for processes which must be oil-free.

The machine can operate up to the pressure and temperature limits and speed permitted for the compressor. They can handle pressure differences of up to 12 bar, or even 25 bar if high pressure equipment is used, at a discharge temperature up to 250 °C (while the stainless steel compressor stage is limited to 160 °C).

Both single and multiple compressor stages are available with intercooling capability. The flow rates are between 600 m³/h and 120,000 m³/h. The main rotor rotates between 2000 and 20000 1/min. These process gas compressors have a 4 + 6 - rotor profile, with an asymmetrical arrangement of a male rotor with four and a female rotor with six teeth, so that the rotor core diameter is stronger than expected for the permitted fall in pressure.

The compressor unit complies with API 619,613,614,671 and other international guidelines, as well as acid gas regulations (NACE) and can also vary with customer specifications. Some important applications include petrochemical refineries, chemical plants, coking plants, coke oven gas, soda factories and steel mills for conveying flare gas, lime kiln gas, mixed gases, and gases with hydrogen sulphide concentrations (sour gas).

Water can be injected to reduce operating temperatures when required to prevent butadiene polymerization during the manufacture of styrene-butadiene rubber, for instance. Solvent injection can also be carried out for purifying the chamber. This type of compressor thus allows cleaning by water injection as well as sealing water leakage when polymerized molecules, and gas impurities such as naphthalene or tar, could spoil the rotors or on the housing walls.

Conclusion

While ready-made gas compressors are hard to find in the refrigeration and process gas industry, custom-built solutions can be made by coordinating the planning and purchase phases between the customer and the equipment supplier.

Aerzen makes it easier to do this by offering a large range of different compressor types. Its cost-effective and rugged designs are also made possible by the vast technical knowledge and over six decades of experience. It thus helps evolve specialized setups for each individual customer which offer exceptionally low power consumption during gas compression in these areas of industry.

This information has been sourced, reviewed and adapted from materials provided by Aerzener Maschinenfabrik GmbH.

For more information on this source, please visit Aerzener Maschinenfabrik GmbH.

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