Surge vessels

Because RPSA is appHed to gain maximum product rate from minimum adsorbent, single beds are the norm. In such cycles where the steps take only a few seconds, flows to and from the bed are discontinuous. Therefore, surge vessels are usuaHy used on feed and product streams to provide unintermpted flow. Some RPSA cycles incorporate delay steps unique to these processes. During these steps, the adsorbent bed is completely isolated and any pressure gradient is aHowed to dissipate (68). The UOP Polybed PSA system uses five to ten beds to maximize the recovery of the less selectively adsorbed component and to extend the process to larger capacities (69). 

The effluent from the reactor is a slurry of terephthaUc acid because it dissolves to a limited extent in almost all solvents, including the acetic acid—water solvent used here. This slurry passes through a surge vessel that operates at a lower pressure than the reactor. More terephthaUc acid crystallizes and the slurry is then ready to be processed at close to atmospheric conditions. The terephthaUc acid crystals are recovered by filtration, washed, dried, and conveyed to storage, from which they are in turn fed to the purification step. 

Reliable during power outage for short period of time, dependent on size of air surge vessel. 

Storage tanks and surge vessels for MEA must have inert blanket-gas systems. Sweet natural gas or nitrogen can be used as the blanket gas. This is required because MEA will oxidize when exposed to the oxygen in air. 

Surge vessels should operate about half full, not 90% full as in this case. 

Pressure surge can be controlled by the use of surge vessels connected to the pipeline with a gas space above the liquid. If a pressure surge passes along the pipeline, liquid flows into the vessel through a check valve and the gas is compressed. Another valve then lets out the liquid at a controlled rate. This type of arrangement is used in large hydraulic lines. 

For example, it is important to have large enough holdups in surge vessels, reflux drums, column bases, etc., to provide effective damping of disturbances (a much-used rule of thumb is 5 to 10 minutes). A sufficient excess of heat transfer area must be available in reboilers, condensers, cooling Jackets, etc., to be able to handle the dynamic changes and upsets during operation. The same is true of flow rates of manipulated variables. Measurements and sensors should be located so that they can be used for eflcctive control. 

The selected system comprises three direct-fired hot oil heaters, surge vessels ond circulation pumps. The hot oil is circulated in a closed loop through the tube bundles in the glycol reboilers. The system allows accurate control of the glycol tempercture ond by designing the fired heaters os a redundant utility system cvailoble to the three process troins the reliability of the system is thereby improved. 

In the combustor, coke is burned from the spent solid that is then separated from combustion gas in the surge vessel. The surge vessel circulates regenerated catalyst streams to the contractor inlet for feed vaporization, and to the combustor bottom for premixing. 

The degasser does just as its name signifies, it degasses the crude. It not only flashes off the gas but also serves as a surge vessel upstream of the atmospheric tanks. The degasser is generally a vertical vessel, 50... 

The swings in the vapor flowrate are typically quite significant to achieve tight pressure control. In an isolated column environment or when this vapor stream simply flows into a large vapor surge vessel or into a large pipeline (header), the variations in the flow cause no problem. But, if this vapor stream is the feed to a downstream unit, the flow variability can significantly disturb this unit and can result in poor plantwide control performance. 

In addition to discussing phase separators, it is also appropriate to eonsider the apphcation of accumulators in processes. Accumulators or surge vessels are necessary to reduce fluctuations in flow rate, pressure and composition and thereby improve process control. Although accumulators are not phase separators, they are discussed here because they are sometimes contained in the same vessel as a phase separator. For example, in a gas-liquid separator, the volume of liquid at the bottom of the separator is determined by the need to dampen fluctuations in flow rate. 

Before true continuous reactor trains became common, many were operated in a semi-continuous mode. Typically, there were three or four reactors in series and the styrene would be polymerized to a certain degree of conversion and transferred to the next vessel. This would allow reactants to be transferred into the vacated vessel and batch polymerization begun. This scheme was successful in normal operation, but a surge vessel was needed in case there was a problem with any of the reactors in sequence. 

Figure 76. Liquid film shaft seal with nlindrkwl hushing lor a high-pressure centrifugal compressor a) Shaft b) Bearing c) Pressure side d) Ambient side e) Floating seal rings f) Sea) oil surge vessel g) Sea) oil h) Lube oil i) Drain to gas-oil separaior k) Drain lo lube oil tank l) Elevation for seal oil head...

It is always desirable to have an immediate and convenient indication how a reaction is progressing. In this way, unproductive experiments can be aborted before much time is lost, and equipment failures etc. become immediately apparent. In a reaction that consumes a gas, this can be done by monitoring the gas consumption. In a gas reaction in a constant-volume batch reactor, the pressure drop is a direct measure of the reaction rate and can be followed at a glance on the pressure gauge or the strip chart of a pressure recorder. For a reaction at constant pressure, a set-up as shown in Figure 3.8 can be used A surge vessel at... 

Measurement of vapor pressure of low-boiling substances has already been treated in the discussion of Stock s apparatus. With substances boiling above room temperature, a heated manometer must be used. For instance, molten tin can be used as the manometer liquid and the flask containing the substance together with the short manometer lowered into the heated bath, while the second leg of the manometer is connected to a manometer and a surge vessel. The pressure is then compensated for imtil the tin in both legs is at the same level, and the pressure is read off on the manometer. 

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