Compressors operation

For air compressors Operating safety Thermal stability, Volatility Resistance to oxidation Extreme pressure and anti-wear (compressors) properties Low coking tendency (hot reciprocating compressors)... 

Since most compressors operate along a polytropic path approaching the adiabatic, compressor calculations are generally based on the adiabatic cui ve. 

The compressors operating range is between two major regions as seen in Fig. 10-74, which is a performance map of a centrifugal compressor. These two regions are. surge, which is the lower flow limit of... 

The thermocycle system can be operated only when condensing water is available at a temperature lower than the required chilled-water-supply temperature. Modifications for a centrifugal refrigeration unit include the installation of a small liqmd-refrigerant pump, cooler spray header nozzles, and a vapor bypass line between the cooler and the condenser. Without the compressor operating, a thermocycle capacity up to 35 percent of the refrigeration-unit rating can be produced. 

The turboexpander in combination with a compressor and a heat exchanger functions as a heat pump and is analyzed as follows In Fig. 29-44 consider the compressor and aftercooler as an isothermal compressor operating at To with an efficiency and assume the working fluid to be a perfect gas. Further, consider the removal of a quantity of heat by the tumoexpander at an average low temperature Ti-This requires that it dehver shaft work equal to Q. Now, make the reasonable assumption that one-tenth of the temperature drop in the expander is used for the temperature difference in the heat exchanger. If the expander efficiency is and this efficiency is mul-... 

Consider a reciprocating compressor operating in a process plant and using a motor of 110 kW, 980 r.p.m. The compressor is required to operate at 825 r.p.m. through V-belts. The approximate centre distance between the motor and the compressor may be considered as 1 m. 

In 1985, the first active magnetic bearing in a pipeline compressor for continuous use was installed on the Alberta Gas Transmission System of NOVA Corporation. Tlie bearings have been running smoothly, with a noted improvement in compressor operation and efficiency. 

Capacity control is more complex in compressor networks where two or more compressors operate in series or parallel. Automatic distribution of the load between compressors is required. The antisurge and load sharing control loops must be coordinated to ensure surge protection while tlie load distribution and energy consumption are optimized. 

The main power source is a 2,200 kW rated motor, which drives two high-speed pinions through integral gears. The first stage of the compressor operates at 17,900 rpm, while the second and third stages operate at 21,800 rpm. The unit is controlled by a local control system, but operators can also monitor the operating parameters from the plant control room. 

Figure 3-16 shows the effeet of efficiency as a function of the load for both the compressor and turbine. Part-load turbine efficiencies are affected more than compressor efficiencies. The discrepancy results from the compressor operating at a relatively constant inlet temperature, pressure, and pressure ratio, while the turbine inlet temperature is greatly varied (Figure 3-17). 

Gas compressors operating on highly toxic or flammable gases may require redundant systems to assure no leakages. In many applications, such as refrigeration gas, buffer seals are required with the liquid-buffered face seal. A popular technique is to use a buffered labyrinth seal with a liquid seal. 

Verifying temperature is the second most important aspect of any compressor operation. As with pressure, the basic form of measurement is a simple temperature gauge. The construction of the gauges is quite varied, ranging from a bimetallic device to the filled systems. When transmis sion is involved, the sensor becomes quite simple, taking the form v)l a thermocouple or a resistance temperature detector (RTD). The monitor does the translation from the native signal to a temperature readout ()r signal proportional to temperature. 

Almost all compressor operations will be more satisfactory if a control system is included. Hence, it should always be considered during the ong inai planning phase. Manual operation will result in an operating pattetn that differs considerably from a controlled one. Proper evaluation cif pat terns is required before the need for a control system can be established. 

Each installation will have a series of startup checks that should be made prior to going into operation. These will vary for each compressor. A little extra time to record the overall compressor operation will he valuable if problems arise. 

Most of the compressors are of the pressure lubricated type and need some sort of lubrication system. For critical service, the API 614 lubrication system should be used. These systems were covered in Chapter 8. Since lubrication systems are key to the reliable compressor operation, a few things important to a reliable lubrication system seem in order. First... 

A process engineer s task is often to evaluate the performance of a compressor unit based on gas throughputs and terminal pressures. Since compressor stations are complex machines and operations, the analysis required is sophisticated and goes well beyond simple computations on a personal computer, although some preliminary evaluations can certainly be made. In this section we summarize the working expressions for standard compressor operations. Compressor operations can be categorized under three thermodynamic categories ... 

Figure 12-50B. A forced-feed lube system ensures that journal and thrust bearings are properly lubricated. The system is basicaiiy designed in accordance with APi 614 and is suitabie for continuous compressor operation. (Used by permission Bui. PROM 526/i-5/95-ii. Nuovo Pignone, S.p.A., Fiorence, itaiy New York Los Angeies and Houston, Texas. Aii rights reserved.)...

More recently, the Southern Gas Association s Gas Machinery Research Council and Pipeline and Compressor Research Council cooperated with Southwest Research Institute to develop a software package that enhances reciprocating compressor operation. Several major American and foreign compressor manufacturers (and some other interested companies) have cooperated with Southwest Research Institute or developed their own proprietary pulsation-reduction design computer programs. 

Newcomb, W. K, Improving Gas Compressor Operation by Testing and Research, Form 254, Ingersoll-Rand Co. 

If the back pressure on the outlet side of the compressor is below the fixed output pressure, the compressed gas will simply expand in an expansion tank or in the initial portion of the pipeline attached to the outlet side of the compressor. Figure 3-74 shows the pressure versus volume plot for a typical rotary compressor operating against a back pressure below the design pressure of the compressor. 

Figure 3-75 shows the pressure versus volume plot for a typical rotary compressor operating against a back pressure equal to the design s pressure of the compressor. 

Screw compressors operate at rather high speeds. Thus, they are rather high volumetric flowrate compressors with relatively small exterior dimensions. 

Figure 3-79. Straight lobe rotary compressor operating cycle [4,23].

In compressor operation, part of the heat given off by the compressor and motor is transmitted to the surrounding air. For plants located in closed rooms, this heat must be removed to limit the rise in temperature of the ambient air. Some of the heat dissipates through walls, windows, floor and roof, but this heat removal is seldom sufficient. The compressor room should be ventilated and the heat removed with the ventilating air. Sometimes the heat can be recovered and used for heating purposes. In an entirely water-cooled compressor installation, the heat to be removed by ventilation is relatively small, since the cooling water takes the major part away. 

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