Water-removal trays dehydrating

Determine How much water is removed from the overhead accumulator and the intermediate dehydrator or water removal tray No water is removed from the bottoms due to the use of superheated steam. 

Mols liquid water collected on dehydrator tray and removed at that point up tower above ivhere reflux returns below this tray = 777.7 - 268... 

Insufficient absorption or off-specification for exit scrubbed gas feed gas concentration off spec/feed gas temperature or pressure outside operating window for amine absorbers > 50 °C for H2S and < 24 °C for C02/feed gas pressure has de-creased/[solvent flowrate too low] for glycol dehydration 12.5 to 25 L TEG per kg water removed/[solvent incorrect] /incorrect feed tray location/[column operation faulty] /absorber operating conditions differ from design/[absorber malfunction]. ... 

Ordinary rectification for the dehydration of acetic acid requires many trays if the losses of acid overhead are to be restricted, so that azeotropic processes are used exclusively. Among the entrainers that have been found effective are ethylene dichloride, n-propyl acetate, and n-butyl acetate. Water contents of these azeotropes are 8, 14, and 28.7 wt %, respectively. Accordingly, the n-butyl acetate is the most thermally efficient of these agents. The n-propyl acetate has been used in large installations, in the first stage as solvent for extraction of acetic acid and then as azeotropic entrainer to remove the accompanying... 

The liquid effluent from the flash drum is first degassed. The vapors consisting of methyl iodide and formate, acetaldehyde and methyl acetate, are dissolved in the azeotrope produced by the subsequent acetic add dehydration column. The degassed arid mixture is then distilled to remove the light components and the cobalt iodide, which is recycled to the reactor in the form of an aqueous slurry. This mixture is then dehydrated and purified by azeotropic distillation. The third compound employed is one of the reaction products (methyl acetate, bp10l3 = 70.4°C, water content 8.5 per cent weight). The column has about 60 trays.. ... 

Product separation and purification the first distillation column is designed to produce a cut enriched with acetic acid by the removal of the lighter and heavier components (methyl iodide, methyl acetate, etc.. This-cut is then dehydrated by heteroazeotropic distillation. The aqueous fraction recovered at the top is refractionated to remove excess water. The heavy stream is treated in a finishing column which produces glads acetic add in the distillate, while the residual acetic add at the bottom is also recovered in a complementary fractionation that separates the heavy products such as propionic add. These high-alloy steel columns each have between 35 and 45 actual trays. 

Purification. The effluent is sent to a series of distillations. The first (30 to 35 trays) separates a methanol/water mixture at the top, which is then sent to a dehydration tower (25 to 30 trays), while the bottom is sent to a column in winch the ester is fractionated under partial vacuum (40 to 45 trays). Methyl toluate and excess p-xylene leave at the top and are recycled to the oxidation reactor. The withdrawal, consisting of crude terephthalate, is redistilled under vacuum to remove heavy compounds (20 trays), and then sent to a vacuum crystallizer (40 to 50 kPa absolute) using methanol as solvent. This may be followed by a second crystallization, or a countercurrent washing with methanol to complete the purification. The dimethyl terephthalate is finally centrifuged, melted to remove residual methanol, and vacuum distilled (30 trays). The molar yield of the operation in relation to p-xylene is about 87 per cent... 

The purification unit consists of three valve-tray columns. The production medium for AA in the purification stage at 130-200 °C contains up to 16% water, 26% methyl iodide, and other components, such as methyl acetate (MA), methanol (MeOH), hydrogen iodide (HI), formic acid (FA), and propionic acid (PA) (PEP Report, 1994). The fractionation column removes the light components and portions of water in the mixture, and the dehydration column treats both water and FA. The last column, which is an SSC, produces the final AA product from the side draw by cutting off the remaining light and heavy components from... 

A few prunes are still sun dried, but most are dehydrated. Sun drying requires more than 1 week for completion, and may be hampered by bad weather. Prior to dehydration, plums are immersed in hot water for a few seconds to remove the natural wax, and then dipped in lye to prevent fermentation. Next, the plums (prunes) are placed in single layers on trays, and placed in the dehydrator where temperature, air movement, and humidity are controlled. In efficient operations drying in a dehydrator is completed in 3 to 4 days, when the fruit reaches 18 to 19% moisture. Some larger dehydrators may only require 12 to 24 hours. The drying ratio is approxi-mately2 1/2 lb (1.13 kg) of fresh fruit to 1 lb (0.45 kg) of dried fruit. 

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