SORBENTS FOR COAL COMBUSTION

Abstract

Sorbent compositions containing halogen and either nitrates or nitrites are added to coal to mitigate the release of mercury and/or other harmful elements into the environment during combustion of coal containing natural levels of mercury.

Claims

1. A method for reducing emissions of mercury that arise from combustion of mercury-containing fuels, comprising applying a mercury sorbent directly onto the fuel before combustion or directly into a gaseous stream after combustion where the temperature is 1500 F. to 2700 F., wherein the mercury sorbent comprises a halogen compound and at least one of a nitrate compound and a nitrite compound.

2. The method of claim 1, wherein the mercury sorbent comprises a nitrite compound and a nitrate compound.

3. The method of claim 1, wherein the halogen compound comprises a bromine compound.

4. The method of claim 1, wherein the halogen compound comprises an iodine compound.

5. The method of claim 1, wherein the mercury sorbent comprises a source of calcium.

6. The method of claim 1, wherein the mercury sorbent comprises calcium bromide, calcium iodide, calcium nitrate, or calcium nitrite.

7. The method of claim 1, further comprising applying a calcium containing sulfur sorbent directly onto the fuel before combustion or directly into a gaseous stream after combustion where the temperature is 1500 F. to 2700 F.

8. The method of claim 7, wherein the sulfur sorbent comprises calcium oxide, calcium hydroxide, calcium carbonate, calcium bicarbonate, calcium nitrate, calcium nitrite, calcium acetate, calcium citrate, calcium phosphate, calcium hydrogen phosphate, apatite, calcium alkoxylates, or organocalcium compounds.

9. The method of claim 7, wherein the sulfur sorbent comprises cement kiln dust, lime kiln dust, or portland cement.

10. The method of claim 7, wherein the sulfur sorbent comprises an aluminosilicate clay.

11. The method of claim 10, wherein the clay comprises montmorillonite or kaolin.

12. The method of claim 1, wherein the fuel is coal.

13. The method of claim 12, wherein the mercury sorbent is applied onto the coal at a coal burning facility.

14. The method of claim 12, wherein the mercury sorbent is applied onto the coal at a coal producer.

Description

EXAMPLES

[0054] In the Examples, coals of varying BTU value, sulfur, and mercury content are burned in the CTF furnace at the Energy Environmental Research Center (EERC) at the University of North Dakota. Percent mercury and sulfur reductions are reported based on the total amount of the element in the coal prior to combustion.

Example 1

[0055] This example illustrates the mercury sorption ability of a calcium bromide/water solution when applied to a Powder River basin sub-bituminous coal. The as-fired coal has a moisture content of 2.408%, ash content of 4.83%, sulfur content of 0.29%, a heating value of 8,999 BTU and a mercury content of 0.122 g/g. Combustion without sorbent results in a mercury concentration of 13.9 g/m.sup.3 in the exhaust gas. The fuel is ground to 70% passing 200 mesh and blended with 6% of a sorbent powder and 0.5% of a sorbent liquid, based on the weight of the coal. The powder contains by weight 40-45% Portland cement, 40-45% calcium oxide, and the remainder calcium or sodium montmorillonite. The liquid is a 50% by weight solution of calcium bromide in water.

[0056] The sorbents are mixed directly with the fuel for three minutes and then stored for combustion. The treated coal is fed to the furnace. Combustion results in a 90% mercury (total) removal at the bag house outlet and a 80% removal of sulfur as measured at the bag house outlet.

Example 2

[0057] This example illustrates the use of powder and liquid sorbents applied to three bituminous coals of varying mercury content. All coals are prepared as in Example #1, with the same addition levels of sorbents.

TABLE-US-00001 % of Mercury % Sulfur Parameter Coal Removal Removal % Moisture 8.48 Pittsburgh, 97.97 40.0 % Sulfur 2.28 Seam, Bailey Mercury 16.2 g/m.sup.3 Coal BTU value 13,324 % Moisture 10.46 Freeman Crown 97.9 36.0 % Sulfur 4.24 III Mercury 8.53 g/m.sup.3 BTU value 11,824 % Moisture 1.0 Kentucky Blend 90.1 52.0 % Sulfur 1.25 Mercury 5.26 g/m.sup.3 BTU value 12,937

Example 3

[0058] This example illustrates addition of a mercury sorbent post-combustion. Pittsburgh Seam-Bailey Coal is ground to 70% passing 200 mesh. No sorbent was added to the fuel pre-combustion. Liquid sorbent containing 50% calcium bromide in water is duct injected into the gaseous stream of the furnace in the 2200 F.-1500 F. zone. The liquid sorbent is injected at the rate of approximately 1.5% by weight of the coal.

TABLE-US-00002 Sorbent % S # Hg Coal Type Composition reduction Reduction Pittsburgh 50% CaBr.sub.2 28.13 96.0 SeamBailey 50% H20 Coal

Example 4

[0059] This example illustrates addition of a liquid and a powder sorbent post-combustion. No sorbent was added directly to the fuel. Both fuels are bituminous and noted as Freeman Crown III and Pittsburgh Seam-Bailey Coal. In both cases the coal was ground to 70% minus 200 mesh prior to combustion. The powder and liquid sorbents are as used in Example 1. Rates of liquid and powder addition (percentages based on the weight of the coal being burned), as well as mercury and sulfur reduction levels, are presented in the table.

TABLE-US-00003 Liquid sorbent Powder sorbent S Hg Coal Type injection rate injection rate Reduction Reduction Freeman 1.0 4.0 36.27 97.89 Crown III Pittsburgh SeamBailey 1.5 6.10 33.90 96.00 Coal

Example 5

[0060] Pittsburgh Seam Bailey Coal is prepared as in Example 1. The powder sorbent of Example 1 is added to the coal pre-combustion at 9.5% by weight. The liquid sorbent of Example 1 (50% calcium bromide in water) is injected post-combustion in the 1500 F.-2200 F. zone at a rate of 0.77%, based on the burn rate of the coal. Sulfur reduction is 56.89% and mercury reduction is 93.67%.

Example 6

[0061] Kentucky Blend Coal is prepared as in Example 1. The powder sorbent of Example 1 is added to the coal pre-combustion at 6% by weight. The liquid sorbent of Example 1 (50% calcium bromide in water) is injected post-combustion in the 1500 F.-2200 F. zone at a rate of 2.63%, based on the burn rate of the coal. Sulfur reduction is 54.91% and mercury reduction is 93.0%.

[0062] Although the invention has been set forth above with an enabling description, it is to be understood that the invention is not limited to the disclosed embodiments. Variations and modifications that would occur to the person of skill in the art upon reading the description are also within the scope of the invention, which is defined in the appended claims.