Effluent depressurization

Pressure equalization steps are used to conserve gas and compression energy. They are appHed to reduce the quantity of feed or product gas needed to pressurize the beds. Portions of the effluent gas during depressurization, blowdown, and purge can be used for repressurization. 

Additional stripping of the adsorbates from the adsorbent and purging of them from the voids can be accomplished by the addition or a purge step. The purge can begin toward the end of the depressurization or immediately afterward. Purging is accomphshed with a flow of produc t countercurrent to adsorption to provide a lower residual at the product effluent end of the bed. 

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. 

Once the extraction is complete, the dead-ended valve is repositioned to allow flow. Subsequently, pressure and density are rapidly reduced to prevent significant losses of the supercritical fluid and the extraction effluent is transferred for collection. With a non-restricted transfer, the flow of supercritical fluid effluent is rapid. This rapid depressurization was made possible by the invention of a delivery nozzle which would ensure collection of the extracted solutes without losses. It consists of a small inverted polyethylene delivery funnel, a few common stainless steel fittings and a spring. No loss of the extracted solutes and modifier has been observed with the use of this nozzle. 

Effluent from the hydrogenation reactor is depressured to about 400 psig. This level of hydrogen is required to prevent the reverse reaction, diethylaluminum hydride decomposition, which results in plating of aluminum on the process equipment. Product diethylaluminum hydride, unreacted aluminum, and solvent are charged to the ethylation reactor. Ethylene is introduced and undergoes a rapid, exothermic reaction to form triethylaluminum. A tubular reactor with high heat transfer capabilities is required to control this reaction (12). 

In both types, a pressure restriction is needed somewhere after the column in order to keep the pressure above the critical value. In some cases it comes after the detector, which is then operated much as it is in LC, except that it has to have the capability of withstanding the higher pressure. If it comes before the detector, some problems have arisen as the depressurized effluent enters the detector. Noise is generated and is believed to originate with the formation of small nonvolatile particles that can also plug the transfer lines. 

Hydrogen gas was preheated and mixed with feed liquid before entering the reactor. The reactor effluent was cooled to transfer-line temperature in a heat exchanger and passed to a separator. Both liquid and gas streams were depressurized through separate control valves to 30 psig. The liquid stream is degassed at the lower pressure. 

A standard arrangement for sampling gaseous products downstream of the reactor is shown in Fig. 5. In a needle valve (or a similar device), the reactor effluent is depressurized and the flow rate is controlled. In the vast majority of cases, the analytical instrument of the choice will be a gas chromatograph equipped with a capillary column, because such an instrument often allows a good separation of the products and, if equipped with an appropriate detector, a reliable quantitative analysis of these products. The working principle of gas chromatography, however, is inherently... 

Reaction products leave the reactor and are cooled in two countercurrent heat exchangers with water. Effluent is then depressurized to atmospheric pressure. Samples are collected for the analysis. 

General Reeerences API Report 521, Guide for Pressure Relieving and Depressurizing Systems, American Petroleum Institute, Washington, D.C., March 1997. AIChE-CCPS, Guidelines for Pressure Relief and Effluent Han-... 

This study is on the development of high-purity isobutane production from isobutane-enriched stream by gaseous adsorption technology. Isobutane purification from Ci mixture, in which not only isobutane, but also n-butane and several kinds of Ct olefins in small or in trace are involved, is very difficult by a traditional distillation method because of their close relative volatilities between constituting components. The continuous layered 3-bed process in which was comprised of six steps as follows pressurization-1 by the cocurrent effluent gas from the other bed, pressurization-2 by isobutane (noduct, adsorption, cocurrent depressurization, countercurrent blowdown, and low pressure purge by isobutane product, was applied. From the experiment, isobutane product with over 99.9% purity and with the trace levels of olefin components could be obtained at ambient temperature. Silver impregnated cliq prefers to CMS for the removal of Ci olefins... 

The unit intended to collect the effluent from the extractor following depressurization is only included in an SFE assembly when the extractor is not coupled on-line to another unit, whether a chromatograph or detector, and is located after the depressurization unit. There are three main ways of collecting solutes, namely solvent bubbling, collection on a sorbent material and cryogenic trapping. 

Figure 22.3(b) is a schematic drawing of a two-column embodiment of a PSA process for solvent vapor recovery, (i) The solvent-laden feed gas is passed through the carbon column at a superambient pressure level (P ) in order to produce a solvent-free effluent gas at pressure P. (ii) The column is then countercurrently depressurized to a near ambient pressure level (Pp) to desorb a part of the adsorbed solvents. It is then (iii) countercurrently purged at pressure Pd with a part of the solvent-free gas produced by step (i) in order to further desorb the solvent, (iv) Finally, the column is countercurrently pressurized from Pp to P with another part of the solvent-free gas produced during step (i). The... 

---