Compressors heads

The expander equation (Equation 1) is generated from the standard compressor head calculation (see Compressors, Horsepower Calculation) by ... 

Theoretical work or compressor head is the heart and substance of compressor design. Some basic form of understanding must be devel oped even if involvement with compressors is less than that of design of the machine itself. Proper applications cannot be made if this understanding is absent. The following theoretical evaluations will be abbreviated as much as possible to reduce the length and still present the philosophy. For the reader with the ambition and desire, the presentation will be an outline to which the reader can fill in the spaces. 

The up-rate looks feasible considering that none of the inlet nozzle guidelines have been exceeded, the Mach number is still a low value, and the pressure drop is not significant. If the pressure drop had been significant, the effect of the drop could have been evaluated with respect to the compressor head and possibly a usable compromise worked out. 

If the suction pressure decreases, and discharge pressure remains constant, the compressor head must increase, approaching the surge point in the process. 

As suction pressure increases or discharge pressure decreases, the compressor head requirement will decrease and the flow rate will increase. A flare valve will avoid stonewalling or overranging driver horsepower. 

End clearance is required to keep the piston from striking the compressor head or crank end. Some small clearance is also required under suc-... 

If an air compressor head is available, increase regenerator pressnre, reducing cyclone vapor and solids loadings. 

When properly designed, installed, and operated, these compressors serve well. However, there are stories about problems with liquids from condensation of saturated vapor streams entering the suction side of the compressor. The typical reciprocating compressor design is not very tolerant of an accumulation of liquids in the suction. There is the possibility of blowing the compressor heads off if the compressors are subjected to incompressible fluids. 

The propellant was simply pent-up water and steam pressure. The destructive pressure buildup occurred as the compressor operated for over five hours with no cooling water flow. Cooling water was trapped in the water jacket on the compression head as the compressor piston continued operating. The team concluded that the fragmentation of the compressor water jacket was a consequence of the operating condition, and a metal failure analysis of the compressor head was not necessary. The damage was immediate and limited, there was no release of gas, and the incident did not require the attention of the available on-site emergency squad. Fortunately, there were no personnel injuries due to this incident. 

All the problems associated with chlorine compression apply to diaphragm compressors. They must be protected against combustion of metal parts in dry chlorine. Since the compressor head usually is carbon steel, this means a maximum temperature of about 120°C. There must be no contact between chlorine and a combustible lubricant. Double separation between the two, as was the case with reciprocating compressors, can prevent this contact. Two diaphragms with an inert intermediate fluid are standard. The oil can be a chlorinated fluorocarbon that does not react with chlorine. The space between diaphragms should have a leak detector that sounds an alarm and shuts down the compressor when either diaphragm fails. 

In Figure 19-9, the compressor head-capacity curve follows none of the system characteristics. Variation of the compressor outlet to meet the demand of the system, therefore, requires controls to regulate the volume, pressure, or a combination. 

In the early hours of the morning, a compressor head water jacket violently raptured and blew apart. A hand-sized fragment of metal was propelled about 50 yards. This chunk of metal flew across an in-plant road and an open area before striking a storage... 

An example of gas detector protection is found in unattended cold stores and cooling plants which use ammonia as the refrigerant. There is practically no risk in attended plants because a few parts per million of ammonia in air is easily detectable by the pungent smell, so the attendant is aware that there is a leak and can take remedial action before the concentration becomes dangerous. The lower explosive limit is comparatively high at 16% this concentration is only likely under abnormal conditions, such as a blown compressor head gasket, and is intolerable for the eyes and respiratory system. 

Most centiifiigal compressor is operated at speed greater than 3,DOO rpm. Fiom Figure 7a, it shows that compressor head can be increased by Increasing its operating speed. However, increase compressor operating spe is a limited by the maximum impeller stress, rotor critical speed, and surge line. [5J... 

The values of compressibility factor and isentropic exponent (k or heat capacity latio) arc usually decreased as gas is compressed. It is usually use average compressibility factor to caJcuIaie compressor head and power. Compressor head calculation is not sensitive to isentropic or polytropic exponent. Therefore, isentropic or polytropic exponent at compressor inlet or its average ean be used for compressor head and power calculation. 

The TRACE power plant model (Section 12.4.1) includes two parallel identical Brayton loops. In this transient the first loop Brayton (B1) is assumed to fail (sudden stop) at time zero. The loss of Brayton is initiated using a TRACE code restart from the steady state condition defined in Table 12-3, Figure 12-13, and Figure 12-14. The loss of Brayton transient is initiated in TRACE by resetting the turbine and compressor head and torque to zero. This action effectively stops Brayton loop flow within one second. Other models have used a more gradual Brayton flow coastdown for this transient. A variety of events could cause a Brayton to shutdown or be isolated. These events may be control actions (e.g., valve closure) or mechanical failures in the turbine, compressor, or alternator. While some failures could result in a gradual coastdown, others could rapidly stop flow. The TRACE transient models the most rapid loss of flow. 

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