Pressure discharge

The capacity of an ejector is expressed as pounds per hour total of non-condensable plus condensables to the inlet flange of the unit. For multistage units, the total capacity must be separated into pounds per hour of condensables and non-condensables. The final stages are only required to handle the non-condensable portion of the load plus the saturation moisture leaving the intercondensers. 

The non-condensables leaving a surface condenser are saturated with water vapor at the temperature corresponding to the pressure. For a process condenser the vapor corresponds to the process fluid. 

To provide for sufficient total capacity, the temperature at Lhe air outlet of a well designed surface condenser is generally assumed to be about 7.5°F below the temperature of saturated steam at the absolute pressure in the condenser [12]. 

In this case the temperature at the air outlet of this type condenser is generally assumed to be 5°F above the inlet temperature of the cooling water. In addition to the normally expected air leakage, an allowance must be made for air liberated from the injection waLer [10]. 

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The principle of operation of the hydraulic reciprocating pump is similar to the beam pump, with a piston-like sub-surface pump action. The energy to drive the pump, however, is delivered through a hydraulic medium, the power fluid, commonly oil or water. The power fluid drives a downhole hydraulic motor which in turn drives the pump. A separate surface pump delivers the hydraulic power. The power fluid system can be of the closed loop or of the open type. In the latter case, the power fluids are mixed with the produced fluid stream. The performance of the hydraulic pump is primarily monitored by measuring the discharge pressures of both surface and sub-surface pumps. 

Hypercompressors. In an LDPE plant a primary compressor, usually of two stages, is used to raise the pressure of ethylene to about 25—30 MPa and a secondary compressor, often referred to as a hypetcomptessot, is used to increase it to 150—315 MPa (22,000—45,700 psi). The thermodynamic properties of ethylene ate such that the secondary compressor requires only two stages and this results in a large pressure difference between the second stage suction and discharge pressures. 

A compressor is typically a specially designed device, and comes with far less surplus capacity than other process components. As a result compressors merit great care in specification of flow, inlet pressure, and discharge pressure. Similarly, the control system and equipment need to be carefully matched to provide turndown with maximum efficiency. 

Equation (6-128) does not require fric tionless (isentropic) flow. The sonic mass flux through the throat is given by Eq. (6-122). With A set equal to the nozzle exit area, the exit Mach number, pressure, and temperature may be calculated. Only if the exit pressure equals the ambient discharge pressure is the ultimate expansion velocity reached in the nozzle. Expansion will be incomplete if the exit pressure exceeds the ambient discharge pressure shocks will occur outside the nozzle. If the calculated exit pressure is less than the ambient discharge pressure, the nozzle is overexpanded and compression shocks within the expanding portion will result. 

Motor running backward or impeller of double suction design is mounted backward. Discharge pressure developed in both cases is about one-half design value. 

Backward-Curved Blade Blowers These blowers are used when a higher discharge pressure is needed. It is used over a wide range of applications. Both the forward and backward curved blades do have much higher stresses than the radial bladed blower. 

Positive Displacement Compressors Positive displacement compressors are machines that are essentially constant volume machines with variable discharge pressures. These machines can be divided into two types ... 

High-Pressure Compressors There is a definite trend in the chemical industry toward the use of high-pressure compressors with discharge pressures of from 34.5 to 172 MPa (5000 to 25,000 IbFin ) and wim capacities from 8.5 X 10 to 42.5 X 10 mVh (5000 to 25,000 ftVmin). These require special design, and a complete knowledge of the characteristics of the gas is necessary. In most cases, these types of applications use the barrel-type centrifugal compressor. 

Ejector Performance The performance of any ejec tor is a function of the area of the motive-gas nozzle and venturi throat, pressure of the motive gas, suction and discharge pressures, and ratios of specific heats, molecular weights, and temperatures. Figure 10-102, based on the assumption of constant-area mixing, is useful in evaluating single-stage-ejector performance for compression ratios up to 10 and area ratios up to 100 (see Fig. 10-103 for notation). 

Dead-heading A blockage on the discharge side of an operating pump which results in the flow reducing to zero and an increase in the discharge pressure. The energy input from the deadheaded pump increases the temperature and pressure of the fluid in the pump. 

Suction pressure is the pressure at the pump s suction nozzle as measured on a gauge. The suction pressure is probably the most important pressure inside the pump. All the pump s production is based on the suction pressure. The pump takes suction pressure and converts it into discharge pressure. If the suction pressure is inadequate, it leads to cavitation. Because of this, all pumps need a gauge at the suction nozzle to measure the pressure entering the pump. 

In the graphie below (Figure 1-5), these three pumps arc developing the same discharge pressure. In this ease they develop different heads inversely proportional to the specific gravity of the fluids. 

The measure of the pump s ability to develop a given discharge pressure. 

Change the pipe sehedule. If there is a designated schedule, you can bet it was ba.sed on discharge pressures and not suction pre.ssures. 

Any pump will generate more flow as the discharge pressure is reduced. 

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