Compressor drivers

This chapter will describe all common compressor drivers, but as a practical consideration, details on selection or sizing, hazardous area... 

The condensing steam turbine has a relatively low thermal efficiency because about two-thirds of the steam enthalpy is lost to cooling water in the condenser. Expensive boiler feedwater treatment is required to remove chlorides, salts, and silicates, which can be deposited on the blades causing premature failure. The blades are already under erosion conditions because of water drops present in the condensing steam. Even with these disadvantages, the condensing turbine is still selected, especially in a process that requires very large compressor drivers and relatively low amounts of process steam. 

Compressor, Driver ond Speed Gears See Specification Sheet. 

In establishing specifications, the first important items to identify from the plant process material balance are normal, maximum, and minimum intake or suction flow rates together with corresponding conditions of temperature and pressure. The required discharge pressure must be established. If it is necessary or important to be able to operate at reduced or over-normal flow rates, these should be identified for the manufacturer, together with the length of time of such expected condition e.g., full time at one-half rate, 20 minutes out of every hour at 10% over normal, etc. These operating requirements may separate the types of equipment. Because it is uneconomical to purchase horsepower that cannot be used by the fluid system, ask that the manufacturer state the maximum load and/or conditions that will fully load the available horsepower of the compressor-driver unit. 

Oil coolers for bearing oil (and often sized for turbine oil requirements when turbine is used) must be a part of the system and are usually mounted on or in the compressor-driver base plate (s). This makes a compact arrangement but is sometimes so congested as to give poor maintenance conditions. The cooler, oil filter, and regulator can also be mounted adjacent to the unit. For some sizes, the compres-... 

Usually, dual oil pumps are included, so that one pump failure will not shut down the compressor-driver unit. The first or main pump may be driven by electric motor, and the standby steam or gas may be driven by turbine. Any combination is acceptable as long as the selection takes into account the specific local conditions and service reliability. Figures 12-50A-C show an overall assembly, including accessories. 

Steam, oil and water piping directly associated with connecting the compressor-driver unit. 

Compressors with drivers over 150 kW that handle flammable gases (the compressor driver should be shutdown through the interlock system before the valves are closed). 

Control Devices In many installations the use of gas is intermittent, and some means of controlling the output of the compressor is therefore necessary. In other cases constant output is required despite variations in discharge pressure, and the control device must operate to maintain a constant compressor speed. Compressor capacity, speed, or pressure may be varied in accordance with requirements. The nature of the control device will depend on the function to be regulated. Regulation of pressure, volume, temperature, or some other factor determines the type of regulation required and the type of the compressor driver. 

An obvious method of controlling the capacity of a compressor is to vary the speed. This method is applicable to units driven by variable-speed drivers such as steam pistons, steam turbines, gas engines, diesel engines, etc. In these cases the regulator actuates the steam-admission or fuel-admission valve on the compressor driver and thus controls the speed. 

A very large percentage of refrigeration systems are not limited by either the compressor driver horsepower, the condenser, or the evaporator. Many refrigeration systems are limited by either ... 

For example, adding lighter propane to heavier isobutane in a refinery alkylation unit is a common practice to increase refrigerant circulation. But this will work only when the compressor driver has spare... 

If the compressor driver is an electric motor, then divide the compressor power by an electric-motor efficiency to size the electric motor. 

Compressors Driver type, inlet flow, suction and discharge presstures, temperature, shaft power, MOC... 

Heat recovery from gas turbine generators and gas turbine compressor drivers to generate steam or use heat directly in low temperature heater application. The steam generated via Heat Recovery Steam Generators (HRSGs) can be used for ... 

Pneumatic supply. Since the loss of air supply can result in the final element moving to the safe state, these systems should be evaluated with the same scrutiny as power for electrical devices. Redundancy of air supply (bottle or backup compressors), diversity in air compressor drivers (steam/electric), air accumulators, and low-pressure alarms can be used to increase air supply integrity. 

When a compressor is running at its maximum rated speed, it is speed-limited. The maximum rated speed is stamped on the compressor nameplate. There is no physical restraint to prevent operation of the compressor above its nameplate speed. However, compressors are equipped with overspeed trips, which automatically shut the compressor driver down when the compressor reaches a preset speed. Certainly, compressors that run well above their nameplate speed can self-destruct in a dramatic and tragic fashion. 

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