Feed pressure

The temperature and composition of each feed stream and the stream ratios are specified along with a common feed pressure (significant only for the vapor stream) and the flash pressure. For an isothermal flash the flash temperature is also specified. Resulting vapor and liquid compositions, phase ratios, vaporization equilibrium ratios, and, for an adiabatic flash, flash temperature are returned. 

The carbamate solution from the scmbber flows to a high pressure ejector. The NH feed pressure induces enough head to convey the carbamate solution from the scmbber to the carbamate condenser. 

The repressurization step returns the adsorber to feed pressure and completes the steps of a PSA cycle. Pressurization is carried out with product and/or feed. Pressurizing with product is done countercurrent to adsorption so that purging of the product end continues indeed it may be merely a continuation of the purge step but with the bed exit valve closed. Pressurizing with feed cocurrent to adsorption in effect begins adsorption without producing any product. 

The second type of hoUow-fiber module is the bore-side feed type illustrated in Figure 23b. The fibers in this type of unit are open at both ends, and the feed fluid is usually circulated through the bore of the fibers. To minimize pressure drops inside the fibers, the fibers often have larger diameters than the very fine fibers used in the shell-side feed system and are generally made by solution spinning. These so-called capillary fibers are used in ultrafiltration, pervaporation, and in some low to medium pressure gas appHcations. Feed pressures are usually limited to less than 1 MPa (150 psig) in this type of module. 

The repressurization step that returns the adsorber to feed pressure and completes the steps of a PSA cycle should be completed with pressure equalization steps to conserve gas and compression energy. Portions of the effluent gas during depressurization, blowdown, and enrichment purge can be used for repressurization to reduce the quantity of feed or product gas needed to pressurize the beds. The most efficient cycle is one that most closely matches available pressures and adsorbate concentration to the appropriate portion of the bed at the proper point in the cycle. 

The power input from a liquid stream injected with a hydraulic spray nozzle may usually be taken as approximately equal to the product of the nozzle feed pressure pf and the volumetric hquid rate. The liquid-phase contacting power Pe may then be calculated from the following formulas ... 

DisK Presses Figure 18-157 shows a disk press. The two disks, or press wheels, converge to a veiy narrow space at the bottom. This is the point of maximum compression, which can be more than 14 times the feed pressure. The press wheels have channels to cany the hquid from the dewatered product, and they are covered with a screen plate. Wheels 1.5 m (5 ft) in diameter are used on a large press that requires about 80 connected horsepower and produces just under 1 tonne/h (0.9 ton/h) of sohds (diy basis). Typical apphcations are fibrous materials such as coffee grounds, pineapple and citrus peels and wastes, alfalfa, and brewers spent grain. 

Roll presses provide a mechanical advantage in amphfying the feed pressure Pq to some maximum value P, . This maximum pressure... 

The reactor feed may be preheated and the feed pressure may alter. The volumetric flowrate of gases depends on the reactor temperature and pressure at fixed mass flowrate. In many cases, the feed is liquid at room temperature, while the reaction mixture is a gas at the higher temperature in the reactor. In these instances, the performance of the reactor is represented as conversion and selectivity against the liquid hourly space velocity (LHSV). This is defined as... 

Process Retentate Permeate Common range of feed pressure (atm) Membrane type Typical iqrplications/ species... 

Feed pressure, Pf, and consequently size of booster pump. 

As can be seen from the plots, the minimum TAC is about 55,OOQ/yr. The opdmal permeate composition is about 0.0005 kmol/m which conesponds to a feed pressure of 48 atm. It is interesting to note that the optimum value of Cp is significantly less than the required target composition (0.0012 kmol/m ). In other words, more separation can be obtained for less cost It is also worth mentioning that in some cases, environmental regulations tnay allow the bypass of a fraction of the feed and later mix it with the over-separated permeate to attain the requited target composition. In such cases, lower costs than the ones shown in Figs. 11.5 and 11.6 can be accomplished. 

The driving force for the separation is differential pressure. CO2 tends to diffuse quickly through membranes and thus can be removed from the bulk gas stream. The low pressure side of the membrane that is rich in CO2 is normally operated at 10 to 20% of the feed pressure. 

Oil differential cutout (oil feed pressure to be above the crankcase pressure) ... 

Osmotic Pinch As the feed travels along the feed channels, friction losses lower the feed pressure. Solvent flux along the feed channel dewaters the feed and increases solute concentration and osmotic pressure. For a recovery or conversion ratio CR, a module solute retention R, and an inlet solute concentration of c , the bulk concentration cj, is... 

The electricity requirement for large-scale hydrogen liquefaction amounts to about 0.3 MJei per MJ of LH2 today (suction pressure typically 2 to 3 MPa, which corresponds to the outlet pressure of the PSA of a typical steam reforming plant), but can be reduced to about 0.16 MJel per MJ of LH2, if the feed pressure can be increased (Quack, 2001). 

In certain cases, if feeding pressures are low, tools can be formed in lighter grades of metals. 

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