Pressure inlet

Inlet pressure and pressure drop (gas-phase reactions)... 

The rich oil from the absorber is expanded through a hydrauHc turbiae for power recovery. The fluid from the turbiae is flashed ia the rich-oil flash tank to 2.1 MPa (300 psi) and —32°C. The flash vapor is compressed until it equals the inlet pressure before it is recycled to the inlet. The oil phase from the flash passes through another heat exchanger and to the rich-oil deethanizer. The ethane-rich overhead gas produced from the deethanizer is compressed and used for produciag petrochemicals or is added to the residue-gas stream. 

Most gas-fired, heavy-duty gas turbines installed as of 1996 operate at gas pressures between 1.2 and 1.7 MPa (180—250 psig). However, aero derivative gas turbines and newer heavy-duty units can have such high air-inlet compression ratios as to require booster compressors to raise gas inlet pressures, in some cases as high as 5.2 MPa (750 psig). 

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. 

A reaction A 3B takes place in a tubular flow reactor at constant temperature and an inlet pressure of 5 atm. The rate equation is... 

Steam pressure. The main boosters can operate on steam pressures from as low as 0,15 bar up to 7 bar gauge. The quantity of steam required increases rapidly as the steam pressure drops (Fig, 11-106), The best steam rates are obtained with about 7 bar. Above this pressure the change in quantity of steam required is prac tically negligible. Ejectors must be designed for the highest available steam pressure, to take advantage of the lower steam consumption for various steam-inlet pressures. 

Mechanical Expanders Reciprocating expanders are very similar in concept and design to reciprocating compressors. Generally these units are used with inlet pressures of 4 to 20 MPa. These machines operate at speeds up to 500 rpm. The thermal efficiencies (actual enthalpy difference/maximum possible enthalpy difference) range from about 75 percent for small units to 85 percent for large machines. 

TABLE 29-9 Typical Stage Efficiencies for Steam Turbines at 600 psi Inlet Pressure and 750 F Inlet Temperature... 

Typically an inlet pressure decrease of one inch of water column reduces the power output by 0.4 percent and increases the heat rate by 0.125 percent. Similarly, an exhaust pressure increase of one inch of water reduces the power output by 0.15 percent and the heat rate by 0.125 percent. 

Economics Power-recoveiy units have no operating costs in essence, the energy is available free. Furthermore, there is no incremental capital cost for energy supply. Incremental installed energy-system costs for a steam-turbine driver and supply system amount to about 800 per kilowatt, and the incremental cost of an electric-motor driver plus supply system is about 80 per kilowatt. By contrast, even the highest-inlet-pressure, largest-flow power-recoveiy machines will seldom have an equipment cost of more than 140 per kilowatt, and costs frequently are as low as 64 per kilowatt. However, at bare driver costs (not including power supply) of 64 to 140 per kilowatt for the power-recovery driver versus about 30 to 80 per Idlowatt for... 

Tube side—ethyiene gas 190°F (88°C) inlet, pressure 6000 psig (41,400 kPa)... 

Ion-exchange chromatography involves an electrostatic process which depends on the relative affinities of various types of ions for an immobilised assembly of ions of opposite charge. The stationary phase is an aqueous buffer with a fixed pH or an aqueous mixture of buffers in which the pH is continuously increased or decreased as the separation may require. This form of liquid chromatography can also be performed at high inlet pressures of liquid with increased column performances. 

Inlet Pressure, 1012 kPa Inlet Temperature, 473K Inlet Composition, 0.772 Kg mol/cu m carbon monoxide, 1.801 Kg mol/cu m hydrogen. 

Hydroearbon gas expanders range in the order of 100 hp to 8,000 and more hp. The majority of these maehines are usually designed for power reeovery duty, with a proeess eompressor direetly driven by the expander. The gas is usually expanded from an inlet pressure in the 100 bar to 50 bar range, down to outlet pressures in the 50 to 15 bar range. This results in an expansion ratio of 2 1 to 4 1, a very suitable expansion for a single-stage expander. Typieal effieieneies range from 84% to 86%. 

Inlet pressure 40 bai- a (575 psia) Temperature 95°C (203°F) Back pressure ... 

A few separation plants have reeiproeating expanders for 2,000 to 3,000 psi (13,800-20,700 kN/m ) inlet pressure. The ineoming pressurized gas is about -40°F (-40°C) and is not elean enough to operate satisfaetorily in small turhoexpanders. However, several turboexpanders have been put into air serviee during the last deeades at 1,500 psia (10,300 kN/m ) for liquid produetion. 

Figure 2-11 illustrates the potential severity of three problems that tend to eorrelate turboexpander inlet pressure thrust bearings, erosion of rotor and nozzles, and radial bearings. 

Figure 2-11. Potential frequency of problems without benefit of modern improvements, statistically related to inlet pressure (1 atm = 101.3 kNm ).

Pressures Turboexpanders ean be designed to operate at up to 3,000 psi and higher inlet pressures as required by eonditions. Expansion pressure ratios ean also be adjusted for eaeh proeess over a wide range. A majority of effieient expansion ratios are below 5 1, although pressure ratios up to 10 1 ean be aeeommodated with reasonable effieieney. Smaller, lower pressure units are popular for air separation and helium liquefaetion. Intermediate pressure (100-1,000 psi) and high pressure expanders (1,000-3,000 psi) are widely used in natural gas proeessing and industrial gas liquefaetion. 

In post-boost applications, the turboexpander operates under generally equalized pressure conditions (i.e., the turboexpander discharge pressure is approximately the same as the compressor inlet pressure). 

In pre-boost applications, the turboexpander discharge pressure is considerably lower than the compressor inlet pressure. This situation requires special consideration when designing the turboexpander and auxiliary systems. In pre-boost designs, compressing the gas to a higher pressure produces more refrigeration in the turboexpander. Figure 3-9 shows a cross-section of an expander-compressor unit. 

The maehine must aeeommodate a wide inlet pressure range. 

Example 1 shows the expander inlet conditions typical of past FCC applications with an expander inlet pressure of 30 psia and inlet temperature of 1,200°F. Example 2 shows the conditions prevalent in more recent FCC regenerator technology, where most of the CO is... 

Plotting these pressures and temperatures on a Mollier diagram (Figure 4-115), makes it possible to compare the amount of available energy for both examples. The available energy of Example 1 is 71.5 Btu/lb as compared to 110.4 Btu/lb for Example 2. In other words, increasing the inlet pressure from 30 to 42 psia and the temperature from 1,200 to 1,300°F results in over a 50% increase in available energy, which translates directly into recoverable power. 

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