Absorber gas

Spectral discrimination (9) and specific gas detection can be modeled if one assumes the gas absorbs photons of a specific wavelength exponentially with distance into the gas (Beet s law). When the absorption distance is x (cm), the incident it power density at the detector in the spectral band pass is J (W/cm ) and the power density incident on the gas is the gas concentration, C (ppm) is given by ... 

Fig. 1. Absorption column arrangement with a gas absorber A and a stripper S to recover solvent.

For the liquid-phase mass-transfer coefficient /cl, the effects of total system pressure can be ignored for all practical purposes. Thus, when using Kq and /cl for the design of gas absorbers or strippers, the primary pressure effects to consider will be those which affect the equilibrium curves and the values of m. If the pressure changes affect the hydrodynamics, then Icq, and a can all change significantly. 

Generahzed prediction methods for fci and Hi do not apply when chemical reaction occurs in the liqmd phase, and therefore one must use ac tual operating data for the particular system in question. A discussion of the various factors to consider in designing gas absorbers and strippers when chemical reac tious are involved is presented by Astarita, Savage, and Bisio, Gas Treating with Chemical Solvents, Wuey (1983) and by Kohl and Ricseufeld, Gas Purification, 4th ed., Gulf (1985). 

FIG. 14-1 Gas absorber using a solvent regenerated by stripping, a) Absorber, (h) Stripper. 

Use of HTU and K a Data In estimating the size of a commercial gas absorber or hquid stripper it is desirable to have data on the... 

Heat effects that may cause temperatures to vaiy from point to point in a gas absorber are (1) the heat of solution of the solute... 

Temperature and Humidity of Rich Gas Cooling and consequent dehumidification of the feed gas to an absorption tower can be very beneficial. A high humidity (or relative saturation with solvent) limits the capacity of the gas phase to take up latent heat and therefore is unfavorable to absorption. Thus, dehumidification of the inlet gas prior to introducing it into the tower is worth considering in the design of gas absorbers with large heat effects. 

There are a number of different types of experimental laboratory units that could be used to develop design data for chemically reacting systems. Charpentier [ACS Symp. Sen, 72, 223-261 (1978)] has summarized the state of the art with respect to methods of scaUng up lab-oratoiy data and tabulated typical values of the mass-transfer coefficients, interfacial areas, and contact times to be found in various commercial gas absorbers as well as in currently available laboratoiy units. 

Absorbers and strippers frequently operate with a liquid having essentially the same physical characteristics regardless of the pressure. An example of this is a gas absorber. The same lean oil is used if the tower is operating at 100 or l,000psi. This type of system is excluded from the CAFq limiting value. 

VOC Removal efficiencies for gas absorbers vary for each pollutant-solvent system and with the type of absorber used. Most absorbers have removal efficiencies in excess of 90 percent, and packed-tower absorbers may achieve efficiencies greater than 99 percent for some pollutant-solvent systems. The typical collection efficiency range is from 70 to greater than 99%. 

Another property of importance is the pore volume. It can be measured indirectly from the adsorption and/or desorption isotherms of equilibrium quantities of gas absorbed or desorbed over a range of relative pressures. Pore volume can also be measured by mercury intrusion techniques, whereby a hydrostatic pressure is used to force mercury into the pores to generate a plot of penetration volume versus pres- sure. Since the size of the pore openings is related to the pressure, mercury intrusion techniques provide information on the pore size distribution and the total pore volume. 

The LPG stream containing a mixture of C s and C4 s must be treated to remove hydrogen sulfide and mercaptan. This produces a noncorrosive, less odorous, and less hazardous product. The C s and C4 s from the debutanizer accumulator flow to the bottom of the H S contactor. The operation of this contactor is similar to that of the fuel gas absorber, except that this is a liquid-liquid contactor. 

Carbon dioxide is absorbed first using a potassium hydroxide solution. Oxygen is the next gas absorbed, using pyrogallol (the same oxygen scavenger produced from quebracho tannins). The glass absorption chamber also contains steel wool as a catalyst. 

Rich gas entering at bottom Gas absorbed Lean gas leaving absorber Gas leaving bottom tray Gas leaving tray 2 from top Lean oil... 

Kato, M., K. Nakagawa, T. Ohashi, S. Yoshikawa, and K. Essaki, Carbon Dioxide Gas Absorbent Containing Lithium Silicate, U.S. Patent No. 6,387845 Bl, May 2002. 

---