Adiabatic operations absorption

For further design and optimization of absorption units with countercurrent flow and solvent regeneration, see [3.4, 3.25-3.30]. The calculations for adiabatic operated absorbers, in which large heat effects have to be considered, are described in [3.31]. Process control of absorption columns can be found in [3.32]. The dynamic behavior of absorption tray columns is discussed in [3.33]. 

The simplifying assumption found useful in gas absorption, that the temperature of the fluid remains substantially constant in adiabatic operations, will be satisfactory only in solute collection from dilute liquid solutions and is unsatisfactory for estimating temperatures in the case of gases. Calculation of the temperature effect when heats of adsorption are large is very complex [2, 89]. The present discussion is limited to isothermal operation. 

Estimation of operating data (usually consisting of a mass and energy in which the energy balance decides whether the absorption balance can be considered isothermal or adiabatic)... 

The thermal efficiency of the process (QE) should be compared with a thermodynamically ideal Carnot cycle, which can be done by comparing the respective indicator diagrams. These show the variation of temperamre, volume and pressure in the combustion chamber during the operating cycle. In the Carnot cycle one mole of gas is subjected to alternate isothermal and adiabatic compression or expansion at two temperatures. By die first law of thermodynamics the isothermal work done on (compression) or by the gas (expansion) is accompanied by the absorption or evolution of heat (Figure 2.2). 

The gas leaving an ammonia oxidation unit in a continuous process is cooled rapidly to 20°C and contains 9 mol % NO, 1% N02, 8% O2, and 82% N2 (all the water formed by reaction is assumed to be condensed). It is desirable to allow oxidation of NO to N02 in a continuous reactor to achieve a molar ratio of N02 to NO of 5 before absorption of the N02 to make HNO3. Determine the outlet temperature of the reactor, if it operates adiabatically (at essentially 6.9... 

The motion of the electrons is treated in the adiabatic approximation. For absorption in the infrared, the electrons remain in the ground state. The electric dipole moment of the complex of two molecules is the expectation value of the dipole moment operator over the ground electronic state, which is a function of the nuclear coordinates only. Specifically, the dipole moment of a complex of n molecules is dependent on the vibrational (r,) and orientational ( ,) coordinates, and on the position (J ,-) of the mass centers of the molecules i, for 1 < i < n,... 

The reactor system may consist of a number of reactors which can be continuous stirred tank reactors, plug flow reactors, or any representation between the two above extremes, and they may operate isothermally, adiabatically or nonisothermally. The separation system depending on the reactor system effluent may involve only liquid separation, only vapor separation or both liquid and vapor separation schemes. The liquid separation scheme may include flash units, distillation columns or trains of distillation columns, extraction units, or crystallization units. If distillation is employed, then we may have simple sharp columns, nonsharp columns, or even single complex distillation columns and complex column sequences. Also, depending on the reactor effluent characteristics, extractive distillation, azeotropic distillation, or reactive distillation may be employed. The vapor separation scheme may involve absorption columns, adsorption units,... 

With lean gas feeds, only relatively small amounts of feed components pass into the liquid. Hence, the heats of solution of these components are relatively small, and the absorption column operates approximately isotherrmlly. For significant amounts of absorption, the exothermic heats of solution become important. In the latter case, the temperature of the liquid phase can increase measurably, resulting in lower solubility of solutes and more solvent required. For this adiabatic case, the exit solvent temperature can be calculated from heats of absorption and the heat capacity of the solvent. As the solvent temperature rises, two approaches can be used ... 

Gas cooling, cleaning, and sulfur dioxide removal is accomplished by adiabatically cooling flue gas with quench water, passing into a venturi-type water scrubber to remove fly ash, followed by absorption of the sulfur dioxide in an aqueous solution of sodium citrate and citric acid. The pilot plant has demonstrated the feasibility of a commercial plant consistently to remove more than 95% of the sulfur dioxide in the inlet gas. The pilot unit has operated for prolonged periods with exit gas of 25-50 ppm sulfur dioxide. 

One kmol/s of a gas consisting of 75 mol% methane and 25% n-pentane at 300 K and 1 atm is to be scrubbed with 2 kmol/s of a nonvolatile paraffin oil entering the absorber free of pentane at 308 K. Estimate the number of ideal trays for adiabatic absorption of 98.6% of the pentane. Neglect the solubility of methane in the oil, and assume operation to be at constant pressure. The pentane forms ideal solutions with the paraffin oil. The average molecular weight of the oil is 200 and the heat capacity is 1.884 kJ/kg-K. The heat capacity of methane over the range of temperatures to be encountered is 35.6 kJ/kmol-K for liquid pentane, is 177.5 kJ/kmol-K for pentane vapor, is 119.8 kJ/kmol-K. The latent heat of vaporization of n-pentane at 273 K is 27.82 MJ/kmol (Treybal, 1980). 

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