Method of reducing hydrogen cyanide and ammonia in synthesis gas

A method for reducing the hydrogen cyanide and ammonia content of a gas stream exiting a gasifier comprising:

• (a) admixing an iron-containing compound selected from the group consisting of iron-rich flyash, iron-rich slag fines, and mixtures thereof obtained from step (e) with a nitrogen-containing dry coal feed, wherein the iron-containing compound has at least about 35 percent by weight iron, and wherein the mixture of iron-containing compound and coal feed comprises finely divided particles;
• (b) injecting the mixture into an entrained flow gasifier having opposed burners, each said opposed burner comprising a pair of burner outlets arranged substantially opposite one another wherein streams from each said opposed burner outlet impinge to form a flame zone substantially where the streams impinge, said flame zone having a temperature greater than about 1650.degree. C.;
• (c) gasifying the coal feed in the resulting mixture under gasifying conditions, thereby producing a gas stream comprising hydrogen, carbon monoxide and flyash, and producing slag fines;
• (d) collecting said flyash in a solids separation unit and collecting said slag fines in a water bath, wherein said flyash and slag fines are iron-rich;
• (e) magnetically recovering at least a portion of said iron-rich flyash and iron-rich slag fines;
• (f) admixing at least a portion of said iron-rich flyash, iron-rich slag fines, or mixtures thereof with the coal feed in step (a);
• and
• (g) recovering the gas stream having at least about 80 volume percent reduced amounts of hydrogen cyanide and ammonia;
• (h) wherein the iron in said iron-containing compound does not substantially react to form metal sulfides in the gasifier.

A method for reducing the hydrogen cyanide content of a gas stream exiting a gasifier comprising:

• (a) admixing in a coal pulverizing stage a recycled iron-rich flyash with a nitrogen-containing dry coal feed wherein the amount of iron in the mixture is less than about 5 percent by weight iron based on the coal feed, and wherein the mixture of iron-rich flyash and dry coal feed comprises finely divided particles;
• (b) injecting the mixture into a dry-feed entrained flow gasifier having a opposed burners, each said opposed burner comprising a pair of burner outlets arranged substantially opposite one another wherein streams from each said opposed burner outlet impinge to form a flame zone substantially where the streams impinge, said flame zone having a temperature greater than about 1650.degree. C.;
• (c) gasifying the coal feed in the resulting mixture under gasifying conditions, wherein said gasifier is at a pressure greater than about 300 psig and a temperature outside of said flame zone from about 1100.degree. C. up to about 2200.degree. C., thereby producing a gas stream comprising hydrogen, carbon monoxide and flyash, wherein at least about 95 percent of the nitrogen in the coal is converted to gaseous molecular nitrogen, and wherein substantially no sulfides are formed in said flame zone by reaction with the iron in said iron-containing compound;
• (d) collecting said flyash in a solids separation unit, wherein said flyash is iron-rich;
• (e) magnetically recovering at least a portion of said iron-rich flyash and mixing at least a portion of said iron-rich flyash with the coal feed in step (a);
• and
• (f) recovering the gas stream having at least about 95 volume percent reduced amounts of hydrogen cyanide;
• (g) wherein said iron-containing compound does not substantially react to form metal sulfides in the gasifier.

In a method for gasification of coal in an entrained flow gasifier having opposed burners, each said opposed burner comprising a pair of burner outlets arranged substantially opposite one another wherein streams from each said opposed burner outlet impinge to form an impinging flame zone, the improvement which yields lower hydrogen cyanide levels in a gas stream exiting said gasifier, said improvement comprising:

• (a) admixing an iron-containing compound with a coal nitrogen-containing dry coal feed to produce an iron compound-coal mixture having not more than about 5 percent by weight iron based on the coal feed, wherein the mixture comprises finely divided particles, and wherein said mixture is dry;
• (b) injecting said dry mixture into said entrained flow gasifier, wherein the temperature generated in said impinging flame zone is significantly high that iron present will not combine with sulfur present to form iron sulfides;
• (c) gasifying the coal in said iron compound-coal mixture in the impinging flame zone, thereby producing a gas stream comprising hydrogen, carbon monoxide and flyash, and producing slag fines;
• (d) recovering said flyash and said slag fines, wherein said flyash and slag fines are iron-rich and comprise substantially no iron sulfides formed by reaction with iron in said iron-containing compound;
• (f) mixing at least a portion of said iron-rich flyash or iron-rich slag fines with the coal feed in step (a);
• and
• (g) recovering the gas stream having reduced amounts of hydrogen cyanide.