Multi-stage pyrolysis systems for treating chlorine contaminated wastes

Abstract

A method of decontaminating solids contaminated with chlorinated hydrocarbons includes a first step of heating the contaminated solids at a temperature high enough to volatize chlorine contaminates but below a temperature range favorable to the formation of the dioxins and furans to dechlorinate the contaminated solids. Volatilized chlorine contaminates are removed from the dechlorinated contaminated solids. The dechlorinated contaminated solids are then purged with an inert gas to remove oxygen from the dechlorinated contaminated solids. Thereafter the dechlorinated contaminated solids are heated in the absence of oxygen to a temperature sufficient to crack hydrocarbons contaminating the solids to lower molecular weight hydrocarbons.

1. A method of decontaminating solids contaminated with chlorinated hydrocarbons comprising:
 a) heating the contaminated solids at a temperature high enough to volatize chlorine contaminates but below a temperature range favorable to the formation of dioxins and furans to dechlorinate the contaminated solids;  
 b) removing the volatilized chlorine contaminates from the dechlorinated contaminated solids; and  
 c) cracking hydrocarbons contaminating the solids into lower molecular weight hydrocarbons by heating the dechlorinated contaminated solids in the absence of oxygen to a temperature sufficient to crack hydrocarbons.  
 
     
     
       2. The method of  claim 1  wherein step a) is performed in the absence of oxygen. 
     
     
       3. The method of  claim 1  wherein prior to step a) the contaminated solids are purged with an inert gas and the heating of step a) is conducted while purging the contaminated solids with an inert gas. 
     
     
       4. The method of  claim 1  wherein step b) is performed by purging the volatilized chlorine contaminates from the contaminated solids with an inert gas and then subjecting the purge gas containing the volatilized chlorine contaminates to means for removal of the chlorinated contaminates to produce a dechlorinated purge gas. 
     
     
       5. The method of  claim 4  further comprising flowing the dechlorinated purge gas to the heating step d) to subject any residual hydrocarbons in the dechlorinated purge gas to cracking. 
     
     
       6. The method of  claim 1  wherein the heating temperature of step a) is less than 400° F. 
     
     
       7. The method of  claim 1  wherein the heating temperature of step a) is between 300-400° F. 
     
     
       8. The method of  claim 1  wherein the heating temperature of step d) is at least 1000° F. and the dechlorinated solids are exposed to the temperature of at least 1000° F. for at least 15 minutes. 
     
     
       9. The method of  claim 1  wherein the solids reside in a container during steps a)-d). 
     
     
       10. The method of  claim 1  further comprising before step c) purging the dechlorinated contaminated solids with and inert gas to remove oxygen from the dechlorinated contaminated solids. 
     
     
       11. A method of decontaminating solids contaminated with chlorinated hydrocarbons comprising:
 a) purging the contaminated solids with an inert gas to substantially remove oxygen gas from the contaminated solids;  
 b) heating the contaminated solids at a first temperature high enough to volatilize chlorine contaminates but below a temperature range favorable to the formation of dioxins and furans to dechlorinate the contaminated solids;  
 c) purging the contaminated solids with an inert gas to remove the volatilized chlorine contaminates;  
 d) cracking hydrocarbons contaminating the solids into lower molecular weight hydrocarbons by heating the dechlorinated contaminated solids to a second temperature sufficient to crack hydrocarbons and  
 e) purging the dechlorinated contaminated solids with an inert gas to remove gaseous cracked lower molecular weight hydrocarbons.  
 
     
     
       12. The method of  claim 11  wherein the first temperature of step b) is less than 400° F. 
     
     
       13. The method of  claim 12  wherein the second temperature of step d) is greater than or equal to 1000° F. and the dechlorinated solids are heated for at least 15 minutes. 
     
     
       14. The method of  claim 11  further comprising subjecting the purge gas containing the volatilized chlorine contaminates to means for removal of the chlorinated contaminates to produce a dechlorinated purge gas. 
     
     
       15. The method of  claim 14  further comprising flowing the dechlorinated purge gas to the heating step d) to subject any residual hydrocarbons in the dechlorinated purge gas to cracking.