Targeted reagent injection for slag control from combustion of coals high in iron and/or calcium

Abstract

Disclosed is a process that increases the output of a combustor fired with coal having high iron and/or calcium content, by reducing the tendency of slag to form on heat exchange surfaces and changing the nature of the slag to make it easier to remove. The process includes combusting a slag-forming coal, having high iron and/or calcium content, with an overall excess of oxygen; moving the resulting combustion gases though heat exchange equipment under conditions which cause cooling of slag formed by burning the fuel; and prior to contact with said heat exchange equipment, introducing aqueous aluminum trihydroxide in amounts and with droplet sizes and concentrations effective to decrease the rate of fouling, and preferably, increase the friability of the resulting slag. Desirably, the aluminum trihydroxide reagent is introduced in the form of an aqueous liquid and computational fluid dynamics is employed to determine flow rates and select reagent introduction rates, reagent introduction location(s), reagent concentration, reagent droplet size and/or reagent momentum. In a preferred aspect, the feed rate will up to about 6 pounds ATH per ton and preferably with up to about 2 pounds Mg(OH) 2 per ton of coal. A process is also provided for cleaning and maintaining cleanliness of a combustor.

1 . A process for reducing slag cohesiveness and/or adhesiveness in a combustor, thereby decreasing the rate of fouling, comprising:
 combusting a slag-forming coal, having high iron and/or calcium content, with an overall excess of oxygen;   moving the resulting combustion gases though heat exchange equipment under conditions which cause cooling of slag formed by burning the fuel; and   prior to contact with said heat exchange equipment, introducing aqueous aluminum trihydroxide in amounts and with droplet sizes and concentrations effective to decrease the rate of fouling by slag.   
     
     
         2 . A process according to  claim 1 , wherein the treatment is effective to increase the friability of resulting slag. 
     
     
         3 . A process according to  claim 1 , wherein, the aluminum trihydroxide reagent is introduced in the form of an aqueous liquid and computational fluid dynamics is employed to determine initial flow rates and select reagent introduction rates, reagent introduction location(s), reagent concentration, reagent droplet size and/or reagent momentum. 
     
     
         4 . A process according to  claim 1 , wherein the treatment further includes introducing magnesium hydroxide in amounts and with droplet sizes and concentrations effective to decrease the rate of fouling by slag. 
     
     
         5 . A process according to  claim 1 , wherein the treatment comprises introducing up to about 6 pounds of aluminum trihydroxide slurry per ton of coal and up to about 2 pounds of Mg(OH) 2  per ton of coal. 
     
     
         6 . A process for removing slag deposits in a combustor burning coal, comprising:
 introducing into hot combustion gases in the combustor, aqueous aluminum trihydroxide in amounts and with droplet sizes and concentrations effective to remove slag deposits.   
     
     
         7 . A process according to  claim 6 , wherein the treatment further includes introducing magnesium hydroxide in amounts and with droplet sizes and concentrations effective to decrease the rate of fouling by slag. 
     
     
         8 . A process according to  claim 6 , wherein the treatment comprises introducing up to about 6 pounds of aluminum trihydroxide slurry per ton of coal and up to about 2 pounds of Mg(OH) 2  per ton of coal. 
     
     
         9 . A process a cleaning and maintenance of a boiler comprising a regimen of initial dosing of from about 3 to 6 pounds of ATH per ton of coal and about 1 to 2 pounds of Mg(OH) 2  per ton of coal for a time sufficient to reduce slag, followed by a reduced reducing the dosing of from about 10 to about 50% of the initial values for maintaining the combustor clean and operating efficiently. 
     
     
         10 . A process according to  claim 9 , wherein the treatment further includes introducing magnesium hydroxide in amounts and with droplet sizes and concentrations effective to decrease the rate of fouling by slag.