Method and arrangement for purifying gases

Abstract

A gaseous substance such as a flue gas or a combustion gas contains an adsorbable impurity which is capable of undergoing an exothermic reaction in the presence of oxygen. The gaseous substance is passed into an adsorber via an inlet conduit. In the adsorber, the impurity in the gaseous substance is adsorbed therefrom. The purified gaseous substance is withdrawn from the adsorber therefrom. The purified gaseous substance is withdrawn from the adsorber via an outlet conduit and conveyed to an exhaust stack. The adsorption of the impurity, as well as the reaction thereof with oxygen in the adsorber, liberate heat. The liberated heat is conveyed from the adsorber by the gaseous substance which is being purified and, accordingly, no undue temperature increase, which may harm or even cause combustion of the adsorbent, occurs in the adsorber. The operation of purifying the gaseous substance is carried out at an underpressure so that, when passage of the gaseous substance through the adsorber is interrupted for some reason, currents of air tend to be drawn through the adsorber due to the suction effects generated in the inlet and outlet conduits. The currents of air constitute sources of fresh oxygen and, as a result, reaction of the adsorbed impurity can continue. The liberated heat is no longer removed, however, so that a drastic temperature increase will then occur in the adsorber. To avoid this, a pair of spaced butterfly valves is provided in both the inlet and outlet conduits. The butterfly valves close, although not with absolute gastightness, when the passage of the gaseous substance through the adsorber is interrupted. This reduces the suction effects. Air or an inert gas is admitted into the regions between the respective pairs of butterfly valves until a pressure on the order of atmospheric pressure has been reached in these regions. The air or inert gas serves as a sort of buffer which prevents the suction effects generated by the source of the gaseous substance and the exhaust stack from acting on the adsorber. Although the air or inert gas may leak into the adsorber until atmospheric pressure has been reached in the latter, any oxygen introduced in this manner is quickly used up so that only minimal temperature increases occur in the adsorber.