Absorption reboiled

Procedures, General Design Concept, Choice of Solvent, Selection of Column Diameter, Physical Absorption, Solvent Absorption, Natural Gas Dehydration, Gas Drying, Sulfuric Acid Manufacture, Formaldehyde Absorption, Absorption with Chemical Reaction, Cracked Gas Scrubbing, Amine Systems, Hot Carbonate Systems, Multicomponent Absorption, Reboiled Absorbers, Example Problem, Notation, References... 

If a relatively sharp separation is required between two components of adjacent volatihty, but either an undesirably low temperature is required to produce reflux at the column-operating pressure or an undesirably high temperature is required to produce boil-up, then refluxed stripping as shown in Fig. I3-7g or reboiled absorption... 

FIG. 13-7 Separation operations related to distillation, (a) Flush vaporization or partial condensation, (h) Absorption, (c) Rectifier, (d) Stripping, (e) Reboded stripping, (f ) Reboiled absorption, (g) Refluxed stripping, (h) Extractive distillation. ( ) Azeotropic distillation. 

Overhead vapors and gases Liquid products Absorption oils Alkylation trace acid streams Reboiler streams... 

In this case, the reactions can be reversed at a regeneration stage in a stripping column by the input of heat in a reboiler. If the solvent is to be recovered by stripping the solute from the solvent, the chemical absorption requires more energy than physical absorption. This is because the energy input for chemical absorption must overcome the heat of reaction as well as the heat of solution. However, chemical absorption involves smaller solvent rates than physical absorption. 

S Entropy (kJ-K-1, kJkg-1-K-1, kJkmol-1-K-1), or number of streams in a heat exchanger network (-), or reactor selectivity (-), or reboil ratio for distillation (-), or selectivity of a reaction (-), or slack variable in optimization (units depend on application), or solvent flowrate (kg s-1, kmol-s-1), or stripping factor in absorption (-)... 

Ammonia absorption refrigeration is particularly applicable when low level heat is available for operation of the stripper reboiler and power costs are high. Steam jet refrigeration is the large scale system of choice when chilled water is cold enough, that is above 40T or so. 

The most widely used is ammonia absorption in water. A flowsketch of the process is in Figure 8.27. Liquid ammonia at a high pressure is obtained overhead in a stripper, and then is expanded through a valve and becomes the low temperature vapor-liquid mixture that functions as the refrigerant. The low pressure vapor is absorbed in weak liquor from the bottom of the stripper. Energy input to the refrigeration system is primarily that of the steam to the stripper reboiler and a minor amount of power to the pump and the cooling water circulation. 

Only a few modifications of the algorithm were required to make it applicable to absorption and reboiled absorption. The changes were mainly in the handling of the enthalpy and total mass balance equations to accommodate different specification combinations involving the reflux, heat duties, and top and bottom product flow rates. The results of two example problems, one each for absorption and reboiled absorption, are shown in Table II. 

Reboiled absorption methane-butane (5 components) octane solvent 25 8 3.5 3.6... 

Multiple equilibrium stage processes simulated in this program are distillation, absorption, and stripping. Both simple and reboiled absorbers are included, and multiple feed plus side-stream products are possible from the fractionators. Matrix- and short-cut-type solution methods are provided in separate subroutines. 

Another multistage method included in the program is the absorption and stripping factor method of Edmister (25). ASFPH, as it is called, can simulate simple and reboiled absorbers and also fractionators. The method used does not have very good convergence characteristics however, it is of value in studying plant performance data. 

The separation section will change accordingly (Figure 10.11). The lean gas with only 25% VAM from the initial gas and free of acetic acid is sent to the absorption column (C-l). The column (C-2) is no longer necessary. The bottom from (T-l) is led directly to (C-3). Less water means lower reflux from the three-phase decanter. In consequence, the duty of the column (C-3) can be reduced from 30 MW to about 8.5 MW, which represents a considerable energy saving of about 70%. In this way the reboiler duty of (C-3) can be covered entirely by the steam produced in the reactor. 

The process for absorbing acid gas takes place in two stages (1) absorption and (2) regeneration. The absorption takes place in a column where the sour gas is contacted with the lean solvent. The rich solvent is sent to a second column where the solvent is regenerated. Heat is applied to the system via a reboiler and the overheads are condensed, typically in an aerial cooler. The solvent regeneration is done not only at higher temperature, but also at lower pressure. Figure 1.1 is a schematic of the process. 

A rectification zone in which the dissolved bntenes fraction is displaced from the solvent in countercurrent flow with butadiene t apdr, which is obtain by controlled reboiling of the extract. These butenes, which contain butadiene, are returned to the absorption zone. A sidestream is drawn off at a level where the olefin content is practically nil, the acenlene content low, and the 1,3-butadiene content a maximum. Separation takes place in a column with about 45 travs operatins at the bottom around 75 C at 0.7. 10 Pa. 

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