Use of high carbon coal ash
AssigneeLafarge Canada Inc.
InventorsDavid Bridson Oates, John Graham Whellock, Philip Souza Zacarias
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Abstract
A synthetic slag is produced by a high temperature combustion reaction between coal ash having a high carbon content, and a source of lime such as cement kiln dust. The carbon content of the coal ash is oxidized by oxygen gas, which typically is derived from air or an air/oxygen combination in an exothermic reaction and the heat generated is exploited in the melting process. In this way the gaseous products will typically comprise nitrogen, unreacted oxygen and carbon dioxide, and heat energy can be readily recovered from the hot off gas products evolving during the combustion reaction. The synthetic slag may be pelletized and employed as lightweight mineral aggregate or milled to cement fineness to provide slag cement.
Claims22
A method of producing a calcium aluminosilicate synthetic slag from a source of lime and coal ash comprising:
- a) melting an inorganic material providing a source of lime and a coal ash at a temperature of 1200° C. to 1650° C. and reacting lime and coal ash to form a molten calcium aluminosilicate synthetic slag,
- b) adding additional amounts of said inorganic material and said coal ash having a carbon content of 5 to 30% by weight to said molten slag,
- c) jetting an oxygen containing gas into said molten slat to anitate said molten slag and disperse the gas therein and oxidising the carbon content of said coal ash in said molten slat with said gas in an exothermic reaction with generation of heat and carbon dioxide and exploiting the generated heat in the melting and reacting of said additional amounts to produce a melt of molten calcium aluminosilicate synthetic slat and
- d) recovering said synthetic slaa from said melt, said inorganic material and coal ash being employed to provide a molar ratio of SiO2and Al2O3 to CaO of 1 to 2.5:1 to form said calcium aluminosilicate synthetic slag.
A method of producing a cement from industrial inorganic byproducts comprising:
- a) melting and reacting a charge consisting essentially of cement kiln dust and fly ash in amounts to provide a molar ratio of SiO2 and Al2O3 to CaO of 1 to 2.5:1, at a temperature of 1200° C. to 1650 ° C. to form molten calcium aluminosilicate slat;
- b) adding additional amounts of said cement kiln dust and fly ash having a carbon content of 3 to 30% by weight, based on the weight of fly ash, to said molten slag;
- c) jetting an oxygen containing gas into said molten slaR to agitate the molten slat and disperse the gas therein and oxidising the carbon content of said fly ash in said molten slag with said gas in an exothermic reaction with generation of heat and by-product carbon dioxide and exploiting the generated heat in the melting of said fresh additional amounts to produce melt of molten calcium aluminosilicate material, and
- d) recovering a calcium aluminosilicate cement from said enlarged melt.
Dependencies are inferred from the claim text.