Combustion with reduced carbon in the ash
Combustion of coal in which oxygen is injected into the coal as it emerges from burner produces ash having reduced amounts of carbon.
1. A method for combusting coal and producing ash which has a reduced carbon content, comprising providing a combustion device, feeding air and a nonaqueous stream of coal through a burner into said device, and combusting the coal in the combustion device, while
feeding one or more gaseous streams that contain at least 35 vol. % O 2 into said coal as the coal emerges from said burner so that said O 2 combusts with said coal in a flame, in an amount of said O 2 which is less than 20% of the stoichiometric amount required for complete combustion of said coal, wherein the carbon content of the ash generated by said combustion is lower than the carbon content of ash generated by combustion carried out without said O 2 feeding step but under otherwise identical conditions.
2. A method according to claim 1 further comprising reducing the amount of air fed through said burner so that the total amount of O 2 fed into said device is between 100% and 130% of the stoichiometric amount needed for complete combustion of said coal.
3. A method according to claim 1 further comprising adding air from a source other than said burner into a region within said combustion device outside said flame, in an amount containing sufficient O 2 that the total amount of O 2 fed into said device is at least the stoichiometric amount needed for complete combustion of said coal.
4. A method according to claim 1 wherein the amount of O 2 fed is less than 10% of the stoichiometric amount required for complete combustion of said coal.
5. A method according to claim 1 wherein the amount of O 2 fed is less than 5% of the stoichiometric amount required for complete combustion of said coal.
6. A method according to claim 1 wherein a stream of coal is fed through said burner and said one or more gaseous streams that contain at least 35 vol.% O 2 is fed into said coal by injecting it through a hollow lance, positioned in said stream, into the coal as the coal emerges from the burner.
7. A method according to claim 1 wherein a stream of coal is fed through an annular coal passage of said burner, and said one or more gaseous streams that contain at least 35 vol.% O 2 is fed into said coal by injecting it through an annular passage surrounding or surrounded by said annular coal passage.
8. A method according to claim 1 wherein said said one or more gaseous streams that contain at least 35 vol.% O 2 is injected directly into said coal through a lance having a closed end and multiple nozzles near the end of the lance.
9. A method for reducing the carbon content of ash formed by combustion of coal in a combustion device, comprising providing a combustion device that has a primary combustion zone and a burnout zone, feeding air and a nonaqueous stream of coal through a burner into said primary combustion zone and combusting the coal in the primary combustion zone in a flame that contains a fuel-rich zone, while
feeding said one or more gaseous streams that contain at least 35 vol.% O 2 into said coal as it emerges from said burner so that said O 2 combusts with said coal in said fuel-rich zone, wherein the amount of O 2 fed is less than 20% of the stoichiometric amount required for complete combustion of said coal and keeps the fuel-rich zone fuel-rich, while reducing the amount of air fed into said fuel-rich zone through said burner so that the total amount of O 2 fed into said device is between 100% and 130% of the stoichiometric amount needed for complete combustion of said coal, wherein the carbon content of the ash generated by said combustion is lower than the carbon content of ash generated by combustion carried out without said O 2 feeding step but under otherwise stoichiometrically identical conditions.
10. A method according to claim 9 wherein the amount of O 2 fed is less than 15% of the stoichiometric amount required for complete combustion of said coal.
11. A method according to claim 9 wherein the amount of O 2 fed is less than 10% of the stoichiometric amount required for complete combustion of said coal.
12. A method according to claim 9 wherein the amount of O 2 fed is less than 5% of the stoichiometric amount required for complete combustion of said coal.
13. A method according to claim 9 wherein a stream of coal is fed through said burner and said one or more gaseous streams that contain at least 35 vol.% O 2 is fed into said coal by injecting it through a hollow lance, positioned in said stream, into the coal as the coal emerges from the burner.
14. A method according to claim 9 wherein a stream of coal is fed through an annular coal passage of said burner, and said one or more gaseous streams that contain at least 35 vol.% O 2 is fed into said coal by injecting it through an annular passage surrounding or surrounded by said annular coal passage.
15. A method according to claim 9 wherein said said one or more gaseous streams that contain at least 35 vol.% O 2 is injected directly into said coal through a lance having a closed end and multiple nozzles near the end of the lance.
16. A method for operating a combustion device, comprising feeding air and a nonaqueous stream of coal through a burner into said device, and combusting said coal in said device in a flame that has a fuel-rich zone, while feeding said one or more gaseous streams that contain at least 35 vol.% O 2 into said coal as it emerges from said burner so that said O 2 combusts with said coal in said fuel-rich zone, wherein the amount of O 2 fed is less than 20% of the stoichiometric amount required for complete combustion of said coal and keeps the fuel-rich zone fuel-rich, while feeding air from a source other than said burner into a region within said device, outside said fuel-rich zone, in an amount containing sufficient O 2 that the total amount of O 2 fed into said device is at least the stoichiometric amount needed for complete combustion of said coal, wherein the carbon content of the ash generated by said combustion is lower than the carbon content of ash generated by combustion carried out without said O 2 feeding step but under otherwise stoichiometrically identical conditions.
17. A method according to claim 16 wherein the amount of O 2 fed is less than 15% of the stoichiometric amount required for complete combustion of said coal.
18. A method according to claim 16 wherein the amount of O 2 fed is less than 10% of the stoichiometric amount required for complete combustion of said coal.
19. A method according to claim 16 wherein the amount of O 2 fed is less than 5% of the stoichiometric amount required for complete combustion of said coal.
20. A method according to claim 16 wherein a stream of coal is fed through said burner and said one or more gaseous streams that contain at least 35 vol.% O 2 is fed into said coal by injecting it through a hollow lance, positioned in said stream, into the coal as the coal emerges from the burner.
21. A method according to claim 16 wherein a stream of coal is fed through an annular coal passage of said burner, and said one or more gaseous streams that contain at least 35 vol.% O 2 is fed into said coal by injecting it through an annular passage surrounding or surrounded by said annular coal passage.
22. A method according to claim 16 wherein said said one or more gaseous streams that contain at least 35 vol.% O 2 oxygen is injected directly into said coal through a lance having a closed end and multiple nozzles near the end of the lance.