Recovery Section

The urea solution leaving the stripper bottom contains about 12 wt% of NH and is further purified in the 1.8 MPa (18 bar) and 0.2 MPa (2 bar) recovery sections of the plant. The resultant NH and CO2 separated in the decomposers is absorbed and returned to the synthesis section by the high pressure centrifugal carbamate pump. 

Dialkylphenols are also produced in specialized plants. These plants combine complex batch reactors with vacuum distillation trains or other recovery systems. Alkenes with carbon numbers between 4 and 9 react with phenol to make an unrefined alkylphenol mixture, which is fed into the recovery section where very high purity product is isolated. The product is stored, handled, and shipped just as are the monoalkylphenols. 

Although there are minor differences in the HCl—vinyl chloride recovery section from one vinyl chloride producer to another, in general, the quench column effluent is distilled to remove first HCl and then vinyl chloride (see Eig. 2). The vinyl chloride is usually further treated to produce specification product, recovered HCl is sent to the oxychlorination process, and unconverted EDC is purified for removal of light and heavy ends before it is recycled to the cracking furnace. The light and heavy ends are either further processed, disposed of by incineration or other methods, or completely recycled by catalytic oxidation with heat recovery followed by chlorine recovery as EDC (76). 

Examination of this equation will show that the required heat transfer area for the heat recovery section per unit mass of distillate produced, increases significantly when PR is increased, and decreases slightly as the number of heat recovery stage, is increased. 

Of the four commercial processes for the purification of carbon monoxide two processes are based on the absorption of carbon monoxide by salt solutions, the third uses either low temperature condensation or fractionation, and the fourth method utilizes the adsorption of carbon monoxide on a soHd adsorbent material. AH four processes use similar techniques to remove minor impurities. Particulates are removed in cyclones or by scmbbing. Scmbbing also removes any tars or heavy hydrocarbon fractions. Acid gases are removed by absorption in monoethanolamine, hot potassium carbonate, or by other patented removal processes. The purified gas stream is then sent to a carbon monoxide recovery section for final purification and by-product recovery. 

The overhead temperatures of both the absorber and stripper are kept as low as possible to minimise solvent carryover. A temperature of about 311 K is typically used ia the high pressure absorber. The overhead temperature ia the stripper is set by the boiling poiat of the saturated complex solution and by the operating pressure of the stripper. At a stripping pressure of 0.166 MPa (1.7 atm), a temperature of 378 Kis used. The solvent-rich gas from the stripper is cooled to recover as much solvent as possible by condensation prior to the final aromatics-recovery section. Fiaal solvent recovery is accomphshed by adsorption on activated carbon (95). 

An ethylene plant contains more than 300 equipment items. Traditionally, operators were trained at the site alongside experienced co-workers. With the advent of modem computers, the plant operation can be simulated on a real-time basis, and the results displayed on monitors (107). Computers are used in a modem plant to control the entire operation, eg, they are used to control the heaters and the recovery section (108). A weU-controUed plant is much more profitable than a poorly controlled plant. For the heaters, a model-based control system is gaining importance (109). Instead of simply controlling the coil outlet temperature (COT), severity is actually controlled. The measurement of severity (either or C H /CH ratio) requires on-line effluent... 

Coal properties influence pulverizer capacity and the sizing of the air heater and other heat-recovery sections of a steam generator. Furnace size and heat-release rates are designed to control slagging characteristics. Consequently, heat-release rates in terms of the ratio of net heat input to plan area range from 4.4 MW/m" (1.4 X 10 Btii/[h ft ]) for severely slagging coals to 6.6 MW/m (2.1 X 10 Btii/[h ft ]) for low-slagging fuels. 

Heat recovery section of an AHU The part of an AHU in which a sensible or latent heat gain or loss takes place by means of a heat-transfer medium. 

Etliylene production involves liigh temperatures (1500°F) in tlie pyrolysis section and cryogenic temperatures in tlie purification section. The feedstocks, products, and by-products of pyrolysis are flaimnable and pose severe fire liazards. Benzene, wliich is produced in small amounts as a byproduct, is a known carcinogen. Table 21.7.1 summarizes some of the properties of etliane (feedstock) and tlie product gases. Figure 21.7.1 shows a simplified schematic diagram of the pyrolysis and waste heat recovery section on an etliylene plant. 

Figure 21.7.1 Pyrolysis and waste recovery section of an etliylene production plant.

The process consists of a reactor section, continuous catalyst regeneration unit (CCR), and product recovery section. Stacked radial-flow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the CCR. The reactor feed consists solely of LPG plus the recycle of unconverted feed components no hydrogen is recycled. The liquid product contains about 92 wt% benzene, toluene, and xylenes (BTX) (Figure 6-7), with a balance of Cg aromatics and a low nonaromatic content. Therefore, the product could be used directly for the recovery of benzene by fractional distillation (without the extraction step needed in catalytic reforming). 

A test run is conducted to evaluate the performance of a 50,000 bpd (331 m /hr) FCC unit. The feed to the unit is gas oil from the vacuum unit. No recycle stream is processed however, the off-gas from the delayed coker is sent to the gas recovery section. Products from the unit are fuel gas, LPG, gasoline, LCO, and decanted oil (DO). Tables 5-2 and 5-3 contain stream flow rates, operating data, and laboratory analyses. The meter factors have been adjusted for actual operating conditions. 

Center-Fed Column Crystallizers Two types of center-fed column crystallizers are illustrated on Figs. 20-8 and 20-9. As in a simple distillation column, these devices are composed of three distinct sections a freezing or recovery section, where solute is frozen from the... 

Most investigators have focused their attention on a differential segment of the zone between the feed injection and the crystal melter. Analysis of crystal formation and growth in the recovery section has received scant attention. Table 20-4 summarizes the scope of the literature treatment for center-fed columns for both solid-solution and eutectic forming systems. 

Continuing further with the recovery aspects from coke oven gas reference may be drawn to the recovery of light oil (crude benzol). In a typical process used, the coke oven gas (from which benzol is to be recovered) after removal of tar, ammonia etc. is passed through the benzol scrubber where the benzol vapours are scrubbed by wash oil flowing countercurrent to the gas. Benzolised wash oil is then pumped to the recovery section where the crude benzol, absorbed in the wash oil is stripped off by steam. The steam vapour mixture, com-... 

Cost of instrumentation for control of recovery section Cost of electricity for pumps Pump costs (total)... 

Instead of the two-step, feedstock-to-add-to-anhydride, another process uses an organic solvent for continuous anhydrous (waterless) recovery of maleic anhydride coming from the reactor. In the recovery section of the process, a patented organic solvent removes the maleic anhydride from the reactor effluent gas. The solvent is separated from the MA later by distillation. 

The rhodium process is highly selective and operates under mild reaction pressure, 400 to 1000 psig. However, because of the high price of rhodium, an efficient recovery of the catalyst is essential. An expensive rhodium recovery section is an integral part of any new acetic acid plant (15-16). This can be a substantial financial burden, especially in a smaller plant. 

Nowhere is this effect more important than in the sulfur plant. In the sulfur recovery section, the air flow to the Claus reactor must be carefully proportioned to the sulfur flow in the feed even slight variations cause significant penalty in the sulfur plant efficiency and increased load on the tail-gas treating... 

Figure 12 is a simplified flow diagram of a chamber-type unit. In this instance the feed is taken only from the cracking plant stabilizer overhead although some plants also include the absorber overhead gas in the feed. If a predominantly C3-C4 charge is polymerized the recovery section can be modified to yield a propane stream for liquefied petroleum gas sale as well as butane by the use of a de-ethanizer (if required), a depropanizer, and a debutanizer. 

Resource Recovery Section Department of Natural Resources P.O. Box 30028 Lansing, MI 30241 (517) 373-0540... 

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