Process for removing halogen gases from a gas stream containing carbon dioxide

Abstract

A process for removing halogen gases from a gas stream containing carbon dioxide such as flue gas from an industrial waste incinerator burning chlorinated organic wastes, the process includes seven steps. The first step is to flow fresh absorption liquor to a gas-liquid contactor (such as a column packed with pall rings) the fresh absorption liquor containing water, base and thiosulfate (such as sodium carbonate and sodium thiosulfate). The second step is to flow the gas stream to the gas-liquid contactor. The third step is to contact the fresh absorption liquor and the gas stream in the gas-liquid contactor to form a contacted gas stream and a contacted absorption liquor. The fourth step is to flow the contacted gas stream from the gas-liquid contactor to form an exhaust gas stream from the process. The fifth step is to flow the contacted absorption liquor from the gas-liquid contactor to form used absorption liquor. The exhaust gas must have a concentration of halogen gases that is less than half the concentration of halogen gases in the original gas stream and the exhaust gas must have a concentration of carbon dioxide that is more than half the concentration of carbon dioxide in the original gas stream.

What is claimed is: 
     
       1. A process for removing halogen gases from a gas stream containing a concentration of halogen gases and a concentration of carbon dioxide, the process comprising the steps of: (a) flowing fresh absorption liquid to a gas-liquid contactor at a flow rate, the fresh absorption liquor comprising soft water, a concentration of base and a concentration of thiosulfate;   (b) flowing the gas stream to the gas-liquid contactor at a flow rate:   (c) contacting the fresh absorption liquor and the gas stream in the gas-liquid contactor to form a contacted gas stream and a contacted absorption liquor, the flow rate of fresh absorption liquor, the concentration of base in the fresh absorption liquor and the concentration of thiosulfate in the fresh absportion liquor relative to the flow rate of the gas stream, the concentration of halogen gases in the gas stream and the concentration of carbon dioxide in the gas stream being sufficient to remove more than half of the halogen gases from the gas stream by a chemical reaction with the fresh absorption liquor, more than half of the carbon dioxide from the gas stream not being removed from the gas stream;   (d) flowing the contacted gas stream from the gas-liquid contactor to from an exhaust gas stream from the process, the exhaust gas stream containing less than half the halogen gas than the gas stream contained, the exhaust gas stream containing more than half the carbon dioxide than the gas stream contained; and   (e) flowing the contacted absorption liquor from the gas-liquid contactor to form a stream of used absorption liquor, the stream of used absorption liquor having a thiosulfate concentration of about 100 parts per million.   
     
     
       2. The process of claim 1, especially suitable when it is desired to increase the flow rate of fresh absorption liquor but not the flow rate of liquid waste, further comprising the steps of: (f) flowing a portion of the used absorption liquor to waste thereby leaving a remaining portion of used absorption liquor; and   (g) adding soft water, thiosulfate and base to the remaining portion of used absorption liquor to form fresh absorption liquor.   
     
     
       3. The process of claim 2, especially suitable when the concentration of halogen gases in the gas stream varies substantially, further including the steps of: (h) analyzing the used absorption liquor for residual thiosulfate; and   (i) controlling the adding of thiosulfate to the remaining portion of used absorption liquor of step (g) according to the analyses of step (h).