Compressors pressure, increase

In the case of a liquid recycle, the cost of this pressure increase is usually small. Pumps usually have low capital and operating costs relative to other plant items. On the other hand, to increase the pressure of material in the vapor phase for recycle requires a compressor. Compressors tend to have a high capital cost and large power requirements giving higher operating costs. 

Compressors are used to handle large volumes of gas at pressure increases from 10.32 kPa (1.5lbg/in ) to several hundred kPa (lbg/in ). We can divide compressors into two major categories ... 

In this automatic thrust balancing system, the pressure behind the compressor wheel is controlled to a value between the compressor suction pressure and the wheel peripheral pressure. As the expander inlet pressure increases above the compressor suction pressure level, the resulting thrust force pushes the compressor wheel, and hence the rotor system, towards the compressor suction. In the reverse situation, when the pressure behind the compressor wheel is reduced below the wheel peripheral pressure level, the rotor system moves toward the expander. 

From this relationship, it is obvious that polytropic efficiency is the limiting value of the isentropic efficiency as the pressure increase approaches zero, and the value of the polytropic efficiency is higher than the corresponding adiabatic efficiency. Figure 3-6 shows the relationship between adiabatic and polytropic efficiency as the pressure ratio across the compressor increases. Figure 3-7 shows the relationship across the turbine. 

In an axiai flow compressor air passes from one stage to the next with each stage raising the pressure and temperature siightiy. By producing iow-pressure increases on the order of i.i i-i.4 i, very high efficiencies can be obtained. The use of muitipie stages permits overaii pressure increases up to... 

CONDITION MONITORING OUTPUTS Loss in Compressor Flow Through Put Loss in Compressor Pressure Ratio Fuel Cost Penalty Projected Increase in Fuel Cost After One Month Operation Surge Point Deterioration Trend and Anticipated Outage Date... 

The increase in compressor pressure ratio decreases the operating range of the compressor. The operating range of the compressor stretches from the surge line at the low flow end of the compressor speed line to the choke point... 

The cooling fraction obviously increases with combustion temperature, but the compressor pressure ratio (and hence the cooling air temperature Tj) is also critically important. It is seen that the arbitrary assumptions made for i/ in Chapter 4 (linearly increasing with the combustion temperature cot would be approximately valid for a cycle with a pressure ratio just below 30. 

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. 

Available horsepower from a gas turbine is a function of air compressor pressure ratio, combustor temperature, air compressor and turbine efficiencies, ambient temperature, and barometric pressure. High ambient temperatures and/or low barometric pressure will reduce available horsepower while low ambient temperatures and/or high barometric pressure will increase available horsepower. All industrial turbines will have high-temperature protection, but in areas subject to very low ambient temperatures horsepower limiting may be required. 

In a compressor, pressure is generated by pumping quantities of gas into a tank or other pressure vessel. Progressively increasing the amount of gas in the confined or fixed-volume space increases the pressure. The effects of... 

Increasing the gas plant pressure. A 10 psi increase in absorber pressure increases C3 recovery by 2% (Figure 9-10). However, this can reduce the wet gas compressor capacity. Fractionation efficiency decreases as the column pressure increases. 

To solve Equation 9.50, start by assuming a feed condition such that q can be fixed. Saturated liquid feed (i.e. q = 1) is normally assumed in an initial design as it tends to decrease the minimum reflux ratio relative to a vaporized feed. Liquid feeds are also preferred because the pressure at which the column operates can easily be increased if required by pumping the liquid to a higher pressure. Increasing the pressure of a vapor feed is much more expensive as it requires a compressor rather than a pump. Feeding a subcooled liquid or a superheated vapor brings inefficiency to the separation as the feed material must first return to saturated conditions before it can participate in the distillation process. 

If the polytropic efficiency of a centrifugal or axial compressor is assumed to be a function of volumetric flowrate, then the efficiency, in principle, will change from stage to stage. This is because the density changes between stages, even if the gas is cooled back to the same temperature as a result of the pressure increase. However, such effects are not likely to have a significant influence on the predicted power. 

GTs are constant-volume machines, such that a fixed-speed GT air compressor section draws a nearly constant volumetric flow of inlet air, independent of ambient air conditions. Air density drops with increased altitude (reduced barometric pressure), increased ambient temperature, and, to a lesser degree, increased water content (specific humidity). 

Increasing the average temperature during the heat-addition process with a reheater without increasing the compressor pressure ratio increases the net work of the Brayton cycle. A multistage turbine is used. Gas is reheated between stages. 

The centrifugal compressor, unless it is dirty or mechanically defective, has to operate on its curve. As the compressor discharge pressure increases, then Hp, the feet of polytropic head required, must also increase. Also, as can be seen from the compressor curve, the volume of gas compressed (ACFM) must decrease. When the volume of gas drops below a critical flow, the compressor will be backed up to its surge point. 

Let us refer again to Fig. 28.1. Suddenly, there is an increase in the molecular weight of the wet gas. This causes the density of the gas to increase. This results in an increase of the compressor AP. As the compressor AP increases, the compressor s suction pressure decreases. Why Well, if the discharge pressure is kept constant by the absorber backpressure control valve, then a bigger AP must drag down the suction pressure. The reduced suction pressure increases the suction vol-... 

A primary compressor increases the pressure of the entering ethylene gas (and propylene gas, which is added as a molecular weight control agent) from between 5 and 15 bar to about 250 bar. The secondary compressor further increases the gas pressure from 250 bar to the desired reactor pressure (approximately 2500 bar). An initiator is added to the gas as it enters the reactor. The reactor is operated to ensure a per-pass conversion of 15%-35% and is a wall-cooled reactor where the cooling water can be used to produce steam. The reaction mixture then enters the HP separator (-250 bar), where the mixture is flashed to produce two distinct phases a PE-rich melt phase and an ethylene-rich gas phase. The separated gas then enters the recycle loop. The ethylene gas is cooled before entering the secondary compressor. The PE enters the low-pressure separator. This low-pressure separator, also referred to as a hopper, performs the final degassing step. The separated ethylene gas is cooled and some components are removed. This step takes place... 

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