Method for the removal of mercury from a gas stream

Abstract

The present invention relates to a method for the removal of mercury from a gas stream. The method is characterized in that at a temperature above 170° C. the gas stream is contacted with a sorbent that as the active component is comprised of a mixture of substantially silica-alumina compounds and/or calcium compounds. According to a preference, the sorbent is kaolin, that may or may not be in the dehydrated form of meta-kaolin and is optionally obtained by thermal conversion of a material chosen from paper waste or residue from the paper industry. By this method it is possible to remove mercury at temperatures higher than room temperature. The invention also relates to a method for the removal of mercury from a gas stream, wherein the gas stream is contacted with a sorbent at a temperature above 50° C., which sorbent comprises as active substance a mixture of substantially silica-alumina compounds and/or calcium compounds, as well as with an oxidator. The invention also relates to a mercury-comprising sorbent obtained by this method and products manufactured therewith.

1 . A method for the removal of mercury from a gas stream, comprising the step of:
 contacting the gas stream at a temperature above 230° C. with a sorbent as the active component, the sorbent comprising a mixture of at least one of substantially silica-alumina compounds and calcium compounds, wherein said calcium compounds comprise at least one of calcium carbonate and calcium oxide.   
   
   
       2 . A method according to  claim 1 , wherein the sorbent comprises kaolin, that may or may not be in the dehydrated form of meta-kaolin. 
   
   
       3 . A method according to  claim 1 , wherein said calcium compounds comprise 60-70% of calcium carbonate and 40-30% of calcium oxide. 
   
   
       4 . A method according to  claim 1 , wherein the sorbent is obtained by thermal conversion of a material chosen from at least one of paper waste and residue from paper production. 
   
   
       5 . A method according to,  claim 1 , wherein during sorption the temperature is higher than 300° C. 
   
   
       6 . A method according to,  claim 1 , further comprising the step of activating the sorbent by means of an oxidator chosen from sulphate compounds, peroxides and chloride compounds. 
   
   
       7 . A method according to  claim 6 , wherein the activation of the sorbent and the oxidator is carried out prior to contacting the sorbent with the gas stream to be cleaned. 
   
   
       8 . A method according to  claim 7 , wherein after activation of the sorbent, the oxidator is removed. 
   
   
       9 . A method according to  claim 6 , wherein the oxidator and the sorbent are mixed together and as a mixture are added to the gas stream to be cleaned. 
   
   
       10 . A method according to  claim 6 , wherein the oxidator is added earlier to the gas stream, upstream from the sorbent. 
   
   
       11 . A method according to  claim 6 , wherein as oxidator a chlorine compound, preferably calcium hypochlorite is used. 
   
   
       12 . A method according to  claim 6 , wherein during sorption the temperature is higher than 50° C. 
   
   
       13 . A method according to  claim 1 , wherein the mercury is present in the metallic form. 
   
   
       14 . A sorbent comprising mercury adsorbed thereto, obtained by a method according to  claim 1 . 
   
   
       15 . A sorbent according to  claim 14 , wherein up to temperatures of more than 900° C. the mercury is irreversibly bound to the sorbent. 
   
   
       16 . Use of the mercury-comprising sorbent according to  claim 14  in a binding agent as hydraulic or pozzolanic compound. 
   
   
       17 . A moulded product obtained by using a sorbent according to  claim 14 . 
   
   
       18 . A method of improving a sorbent for the removal of mercury from a gas stream, comprising the steps of activating a compound comprised of a mixture of at least one of substantially silica-alumina compounds and calcium compounds, with an oxidator chosen from sulphate compounds, peroxides and chlorine compounds. 
   
   
       19 . A method according to  claim 5 , wherein during sorption the temperature is higher than 550° C. 
   
   
       20 . A method according to  claim 12 , wherein during sorption the temperature is higher than 400° C.