Rapid sulfuric-acid absorbers

Abstract

fuming sulfuric-acid absorption of SO3; monohydrate absorption of SO3 in the first and second stages; and desorption of SO2 from the product sulfuric acid. The following characteristic features must be considered in building apparatus for these processes: • the mass-transfer rate is determined primarily by diffusion and thermal processes in the gaseous phase, and the H2O and SO3 vapors above the acid possess low tension; • the reactions that take place are distinguished by high thermal effects; • accompanying processes occur during formation of the sulfuric-acid fog; • the working environments are toxic ecologically dangerous liquid and gaseous media; • high corrosion activity of the production media with respect to basic metallic structural materials; and • the production rate can be achieved with a small number of degrees of contact (up to five). Counterflow packed absorbers (towers) with nonmetallic (ceramic, porcelain) contact elements (Rashig rings, Intalocks seats, etc.), or direct-flow Venturi-tube apparatus are traditionally used for the execution of these processes. These apparatuses do not, however, correspond to the modern level of mass-exchange equipment. Their use in heavy-duty sulfuric-acid systems is inexpedient due to cumbersomeness and large material outlays. A new generation of sulfuric-acid absorbers, which are distinguished by high rates, compactness, and low material consumption, has been developed. Moreover, energy expenditures have not been increased. The apparatus include tubular and hollow sections. The tubular sections can be oriented horizontally and vertically. The gas in the tubes moves at a velocity of 5–30 m/sec. The liquid is delivered in the form of a spray via injectors in the gaseous flow directly ahead of the inlet to the working tubes. The hollows sections may be operated in a counterflow, direct-flow, or crossing regime at gas velocities of 2–10 m/sec. Alternation of hollow and tubular sections can provide for a high degree of component absorption with a moderate pressure loss. Intensification of the process is achieved in a combined apparatus as a result of the formation of a fresh phase-contact surface as the flows proceed from one section to another (from a hollow to a tubular section, and conversely). Let us consider examples of individual solutions of combined apparatus for specific operating conditions. 1. Fuming sulfuric-acid absorber – a vertical cylindrical vessel with a flat bottom and conical cover. The gas moves along a spiral path and exits via all-jet swirl injectors mounted in the cover of the vessel. The initial gas concentration is 8% of SO3. The degree of SO3 absorption by fuming sulfuric acid (22–25%) amounts to 80–90%, and the loss of gas pressure is 300 Pa. The dwell time of the gas in the vessel is 2.5–3.5 sec. The material outlays and volume of the vessel are three to five times lower as compared with traditional packed vessels. Chemical and Petroleum Engineering, Vol. 37, Nos. 7–8, 2001