Reducing mercury emissions from the burning of coal

• US 20060210463A1
• Filed: 03/16/2006
• Published: 09/21/2006
• Est. Priority Date: 03/17/2005
• Status: Active Grant

• Current Assignee: Nox Ii Ltd. (Arthur J Gallagher & Company)
• Original Assignee: Nox Ii Ltd. (Arthur J Gallagher & Company)
• Inventors: Comrie, Douglas C.
• Granted Patent: US 7,507,083 B2
• Time in Patent Office: Days
• US Class Current: 423/215.500
• CPC Class Codes: B01D 2253/104 Alumina
• CPC Class Codes: B01D 2253/11 Clays
• CPC Class Codes: B01D 2257/30 Sulfur compounds
• CPC Class Codes: B01D 2257/602 Mercury or mercury compounds
• CPC Class Codes: B01D 53/04 with stationary adsorbents B01D53/025 takes precedence
• CPC Class Codes: B01D 53/30 Controlling by gas-analysis apparatus regulating non electrical variables in general G05D
• CPC Class Codes: B01D 53/485 containing only one sulfur compound other than sulfur oxides or hydrogen sulfide
• CPC Class Codes: B01D 53/64 Heavy metals or compounds thereof, e.g. mercury
• CPC Class Codes: B01D 53/78 with gas-liquid contact
• CPC Class Codes: B01J 20/041 Oxides or hydroxides
• CPC Class Codes: B01J 20/043 Carbonates or bicarbonates, e.g. limestone, dolomite, aragonite
• CPC Class Codes: B01J 20/046 containing halogens, e.g. halides
• CPC Class Codes: B01J 20/06 comprising oxides or hydroxides of metals not provided for in group B01J20/04
• CPC Class Codes: B01J 20/12 Naturally occurring clays or bleaching earth
• CPC Class Codes: B01J 20/16 Alumino-silicates B01J20/12 takes precedence
• CPC Class Codes: B01J 2220/42 Materials comprising a mixture of inorganic materials materials coated or impregnated on a carrier B01J20/32
• CPC Class Codes: C10L 10/00 Use of additives to fuels or fires for particular purposes additives for liquid carbonaceous fuels characterised by their chemical nature C10L1/10; using binders for briquetting solid fuels C10L5/10; using additives to improve the combustion of solid fuels C10L9/10
• CPC Class Codes: C10L 10/02 for reducing smoke development
• CPC Class Codes: C10L 9/10 by using additives
• CPC Class Codes: F23J 15/00 Arrangements of devices for treating smoke or fumes
• CPC Class Codes: F23J 15/025 : using filters
• CPC Class Codes: F23J 15/04 : using washing fluids scrubbers for removing solids only F23J15/022
• CPC Class Codes: F23J 7/00 : Arrangement of devices for supplying chemicals to fire
• CPC Class Codes: F23K 1/00 : Preparation of lump or pulverulent fuel in readiness for delivery to combustion apparatus
• CPC Class Codes: F23K 2201/505 : with additives
• CPC Class Codes: Y02P 40/10 : Production of cement, e.g. improving or optimising the production methods; Cement grinding
• CPC Class Codes: Y10S 423/05 : Automatic, including computer, control

Abstract

Processes and compositions are provided for decreasing emissions of mercury upon combustion of fuels such as coal. Various sorbent compositions are provided that contain components that reduce the level of mercury and/or sulfur emitted into the atmosphere upon burning of coal. In various embodiments, the sorbent compositions are added directly to the fuel before combustion; are added partially to the fuel before combustion and partially into the flue gas post combustion zone; or are added completely into the flue gas post combustion zone. In preferred embodiments, the sorbent compositions comprise a source of halogen and preferably a source of calcium. Among the halogens, iodine and bromine are preferred. In various embodiments, inorganic bromides make up a part of the sorbent compositions.

Claims

1. A process for burning coal to reduce the amount of mercury released into the atmosphere comprising

applying a sorbent composition comprising calcium bromide onto the coal;

delivering the coal into a coal burning furnace;

combusting the coal containing the sorbent in the coal burning furnace to produce ash and combustion gases;

measuring a mercury level in the combustion gases; and

adjusting the amount of sorbent composition applied to the coal based on the value of the mercury level.

2. A method according to claim 1, wherein the sorbent composition is a liquid.

3. A method according to claim 1, wherein the sorbent composition is a solid.

4. A method according to claim 1, wherein the sorbent composition further comprises a nitrate compound or a nitrite compound.

5. A method according to claim 1, comprising spraying an aqueous solution comprising calcium bromide onto the coal.

6. A method according to claim 5, wherein the solution comprises 20% to 60% by weight calcium bromide.

7. A method according to claim 1, comprising constant monitoring of the mercury level.

8. A method according to claim 1, comprising periodically sampling the mercury level.

17. A method according to claim 11, wherein the aluminosilicate clay comprises montmorillonite or kaolin.

19. A method according to claim 11, comprising applying a liquid composition comprising a bromine compound onto the coal pre-combustion.

20. A method according to claim 19, wherein the liquid composition comprises calcium bromide.

23. A method according to claim 1, comprising adding a liquid composition comprising calcium bromide onto the coal and a powder composition comprising aluminosilicate clay and any of portland cement, cement kiln dust, lime kiln dust, calcium oxide, calcium hydroxide, and calcium carbonate onto the coal.

9. A system for burning coal with reduced levels of mercury released outside the system comprising

a sorbent composition comprising calcium bromide;

a coal burning furnace comprising a burning chamber, a convection path for combustion gases leading from the burning chamber to an exit outside the convection path, and a particle collection device disposed in the convection path;

an apparatus for delivering coal to the furnace for combustion;

an apparatus disposed in the convection path for measuring the level of mercury in the convection path;

a sorbent delivery apparatus disposed to deliver the sorbent composition onto the coal before delivery of the coal into the furnace; and

a controller disposed to receive an output signal from the mercury measuring apparatus, and operationally connected to the sorbent delivery apparatus to adjust the delivery of the sorbent based upon the value of the output signal.

10. A method for reducing the amount of sulfur and mercury emitted during combustion of coal in a coal burning system comprising a furnace and convective pathways for the combustion gases, the method comprising applying a first sorbent composition and a second sorbent composition into the system,

wherein one of the first and second sorbent compositions is added to the coal prior to combustion and the other is injected into the coal burning system in a zone of the convective pathway downstream of the burning chamber, and

wherein the first sorbent composition comprises bromine and is added at an effective level to reduce mercury in the combustion gases and the second sorbent composition comprises calcium and is added at an effective level to reduce sulfur in the combustion gases.

11. A process for burning coal with reduced levels of undesirable elements escaping into the environment comprising

adding a mercury sorbent composition comprising a halogen into the coal burning process;

adding a sulfur sorbent composition comprising a calcium powder and an aluminosilicate clay into the coal burning process;

burning the coal to produce ash and combustion gases;

measuring the level of mercury in the combustion gases; and

adjusting the amount of halogen added to the coal based on the level of mercury.

12. A method according to claim 11, wherein the mercury sorbent composition comprises a bromine compound.

13. A method according to claim 11, comprising adding a sufficient amount of bromine onto the coal to capture in the ash 90% or more of the mercury in the coal

14. A method according to claim 11, wherein the mercury sorbent composition comprises calcium bromide.

15. A method according to claim 11, wherein the calcium powder comprises portland cement, cement kiln dust, and/or lime kiln dust.

16. A method according to claim 11, wherein the sulfur sorbent composition comprises 60-71% CaO, 12-15% SiO₂, 4-18% Al₂O₃, 1-4% Fe₂O₃, 0.5-1.5% MgO, and 0.1-0.5% Na₂O.

18. A method according to claim 11, wherein the sulfur sorbent composition comprises at least 2% silica and at least 2% alumina.

21. A method according to claim 11, comprising applying a powder sorbent comprising calcium onto the coal.

22. A method according to claim 21, wherein the powder sorbent comprises an aluminosilicate clay and at least one of portland cement, cement kiln dust, lime kiln dust, calcium oxide, calcium hydroxide, and calcium carbonate.

24. A method for reducing the level of mercury released into the atmosphere upon combustion of coal containing mercury in a coal burning system comprising a furnace and a convective pathway for combustion gases, the method comprising

adding a mercury sorbent and a sulfur sorbent onto pulverized coal;

burning the coal in the furnace;

burning the coal along with the sorbents to produce combustion gases and ash; and

adjusting the amount of mercury sorbent added depending on the measured level,

wherein the mercury sorbent comprises a halogen and the sulfur sorbent comprises a calcium compound and an aluminosilicate clay.

25. A method according to claim 24, wherein the halogen is bromine.

26. A method according to claim 24, wherein the mercury sorbent comprises calcium bromide.

27. A method according to claim 26, wherein the mercury sorbent is a liquid.

28. A method according to claim 24, comprising adding calcium bromide at a level of 0.01 to 5% by weight based on the weight of the coal.

29. A method according to claim 24, wherein the sulfur sorbent composition comprises one or more of portland cement, cement kiln dust, lime kiln dust, calcium oxide, calcium hydroxide, and calcium carbonate