Vent gas recovery

Low-strength NH3-Solutions from vent gas Recovery scrubbers and Aqua storage spheres... 

VS = vent gas scrubber EC = ethylbenzene recovery column DC = diethylbenzene recovery column. 

Both air and oxygen processes can be designed to be comparable in the following areas product quaUty, process flexibiUty for operation at reduced rates, and on-stream rehabiUty (97,182). For both processes, an on-stream value of 8000 h/yr is typical (196). The rehabiUty of the oxygen-based system is closely linked to the rehabiUty of the air-separation plant, and in the air process, operation of the multistage air compressor and power recovery from the vent gas is cmcial (97). 

Control of ga.s movement by recovery. The movement of gases in landfills can also be controlled by instadhng gas-recovery wells in completed landfills (see Fig. 25-74b). This is considered an active venting system. Clay and other hners are used when landfill gas is to be recovered. In some gas-recovery systems, leachate is collected and recycled to the top of the landfill and reinjected through perforated lines located in drainage trenches. Typically, the rate of gas production is greater in leachate-recirculation systems. 

Gas Phase Olefin Polymerization Process with Recovery of Monomers from Reactor Vent Gas by Absorption, U.S. Patent 5,521.264, May 28, 1996. 

Pressure control will be necessary for most systems handling vapour or gas. The method of control will depend on the nature of the process. Typical schemes are shown in Figures 5.17a, b, c, d (see p. 230). The scheme shown in Figure 5.17a would not be used where the vented gas was toxic, or valuable. In these circumstances the vent should be taken to a vent recovery system, such as a scrubber. 

Absorption is a commonly applied operation in chemical processing. It is used as a raw material or a product recovery technique in separation and purification of gaseous streams containing high concentrations of organics (e.g., in natural gas purification and coke by-product recovery operations). In absorption, the organics in the gas stream are dissolved in a liquid solvent. The contact between the absorbing liquid and the vent gas is accomplished in countercurrent spray towers, scrubbers, or packed or plate columns. 

After recovery of the EDC, the vent gas contains both oxygen and fuels (ethane and uncondensed EDC) that would be a flammable mixture and a serious safety hazard if the plant were not designed and operated correctly. 

At the end of the washing step, the liquid is drained to the operative tank by the pump, and through the button filter, FB, then the gas-recovery step takes place to recover most of the vapour or gaseous CO2 from the chamber. As the gas-recovery can be assumed to be like an adiabatic process, the fluid in the chamber is pre-heated by an electric resistance heat exchanger, HE2, to contain the reduction in temperature. The CO2 vapour is compressed by the oil-free compressor CV and fed to HE1 to condense before being stored in the operative tank. Finally, the chamber is vented and the door can be opened to recover the cleaned garments. 

This calorific value is very low compared to 37 MJ/m (1000 Btu/ft ) for natural gas. The vent gas is barely worth recovery, but if the gas has to be burnt to avoid pollution, it could be used in an incinerator such as that shown in Figure 3.15, giving a useful steam production to offset the cost of disposal. 

An electronics company wants to fit a solvent recovery system on the vent gas from its circuit board manufacturing line. The solvent recovery system consists of a chiller, a knockout drum, and an adsorbent bed. The adsorbent is periodically regenerated by circulating hot air over the bed and to the chiller and knockout. After consultation with equipment vendors, the following purchased prices are estimated for the major plant equipment ... 

There are other options for recovering C02 from SMROG. It can be removed by using an amine scrubber prior to its introduction (C02 free) into a PSA system for the production of H2 in order to reduce the size of the PSA unit and to improve the H2 recovery.22 It is also possible to recover the C02 from the vent gas of an existing H2 PSA process by using an additional PSA system, which uses nearambient pressure adsorption of C02 followed by its desorption by evacuation.23 NaX or NaY zeolite can be conveniently used to adsorb about 60% C02 from a gas stream at near-ambient pressure and produce a high-purity C02 stream as the desorbed gas by evacuation. 

The conditions at the top of the absorber are often design variables that also have to be set considering the balance between equipment and operating costs. For example, if tentative specifications call for 98 percent recovery of a product from a gas stream, the designer might calculate how much taller the column would have to be to get 99 percent recovery. If the value of the extra product recovered exceeds the extra costs, the optimum recovery is at least 99 percent, and the calculation should be repeated for even higher recovery. If the unremoved solute is a pollutant, its concentration in the vent gas may be set by emission standards, and the required percent recovery may exceed the optimum value based on product value and operating costs. 

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