Compressors valve losses

White, K. H., Prediction and Measurement of Compressor Valve Loss, ASME 72-PET-4, New York, NY American Society of Mechanical Engi neers, 1972. 

Bauer has studied losses in compressor cylinder performance associated with valve losses as they relate to overall efficiency. Bunn examines poppet valves for retrofitting cylinders. 

Figure 12-6G. AJAX APV-1000, high-efficiency compressor valve. Suction and discharge losses are 4-8% compared to conventional valves with losses of 6-20% as a percentage of the total indicated horsepower. (Used by permission Bui. 2-214. Cooper-...

The control systems enabled in the simulation were i) the IHX flow balance controller, which acts through primary compressor speed to maintain equal flow rate on the hot and cold sides of the IHX ii) the bypass flow controller which acts through bypass valve loss coefficient to maintain a shaft speed set point. Additionally the pre-cooler and intercooler cold side flow rates are supplied as forcing functions. The flow rates were roughly matched to decay heat level. The PCU shaft set point is decreased from 60 Hz over time to have the shaft speed more or less track the decreasing reactor energy production rate. 

The performance of reciprocating (piston) compressors with large valve area, or where valve losses are evaluated, is considered as close to... 

One cost-effective means of reducing compression valve losses and enhancing compressor efficiency is to replace valve plates with thermoplastic plates equipped with additional flow ports (i.e., openings in the plates for gas passage). Modifying valve plates in this manner will reduce horsepower valve losses due to the frictional pressure drop. 

For example, for one machine equipped with plastic poppet valves (i.e., compressor cylinder valves designed for high capacity but low compression ratios), valve losses as measured by a Beta Scan were reduced from 25% to 10% when the compression ratio was reduced from 1.42 to 1.28. This occurred even though the gas volume moved through the compressor increase by 50%. 

Indications and plant response will vary depending on whether the affected valve is associated with a Brayton unit turbine/compressor, or alternator cooling line (for multiple Brayton unit configurations). Closure of an inlet or outlet valve to a Brayton unit turbine or compressor causes loss of loop flow and consequent loss of the Brayton unit. Closure of a valve in the alternator cooling line will cause overheating of the alternator and potential loss of delivered electrical power. Evaluations have been performed for a two loop plant with one loop operating and the other is an installed spare, and for a three loop plant with two operating and one spare loops. 

The first method is used most frequently. The next preference is for the last method, mostly used in small compressors due to problems with speed control of electrical motors. Other means of capacity control are very seldom utilized due to thermodynamic inefficiencies and design difficulties. Energy losses in a compressor, when capacity regulation is provided by lifting the suc tion valves, are due to fric tion of gas flowing in and out the unloaded cylinder. This is shown in Fig. 11-84 where the comparison is made for ideal partial load operation, reciprocating, and screw compressors. 

The most versatile arrangement, from an operations point of view, is individual transfer valves, one for the twin coolers and one for the twin filters. The use of one valve for both the filter and cooler results in a loss in flexibility, as the cooler maintenance interval is usually somewhat longer term than a filter changeout. Should one cooler be out of service, and the filter that is paired with the operating cooler be fouled, the compressor will have to shutdown. Each user will have to review the extra cost oi a second valve against the operation limit. 

Report the total of all releases to the air that are not released through stacks, vents, ducts, pipes, or any other confined air stream. You must include (1) fugitive equipment leaks from valves, pump seals, flanges, compressors, sampling connections, open-ended lines, etc. (2) evaporative losses from surface impoundments and spills (3) releases from building ventilation systems and (4) any other fugitive or non-point air emissions. 

In addition to failure as a result of their utihty supply, items of equipment are subject to individual failure through mechanical malfunction. Such items include pumps, fans, compressors, mixers, instruments and control valves. The process upset resulting from such malfunctions (e.g., loss of a reflux pump) may in turn result in emergency conditions and the potential for overpressure. These contingencies should be examined and evaluated. 

A speed controller does not ehminate the need for a recycle valve, flare valve, or suction throttling valve, but it will minimize their use. The recycle valve and suction throttling valve add arbitrary loads to the compressor and thus increase fuel usage. The flare valve leads to a direct waste of reservoir fluids and tlius loss of income. For this reason, engine speed control is rec-... 

A greater difficulty arises where the compressor may go down to 33% or 25% capacity and the thermostatic expansion valve is called upon to control a much reduced flow Under such conditions, the thermostatic expansion valve maybe unstable and hunt , with slight loss of evaporator efficiency Since the required duty is less, this is of no great importance. It is possible to fit two expansion valves in parallel, one for the minimum load and both for the full load, but this arrangement is not usually necessary... 

In the event of quick disconnect a torque imbalance occurs and the PCU shaft begins to over speed. If no control action is taken the terminal speed is a function of PCU loop friction losses and the turbo-machine performance curves. To prevent damage from the over speed condition, a bypass valve is opened to redirect flow from the high pressure compressor to the outlet of the turbine. 

To avoid shaft over speed on loss of load, the bypass valve is opened to raise the outlet pressure of the turbine so that it is closer to the inlet pressure thereby reducing the shaft work performed by the turbine. A bypass line containing the bypass valve serves to divert high pressure compressor outlet coolant around the reactor and turbine. The bypass line connects the compressor outlet to the recuperator hot side inlet as shown in Figure 12. 

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