Reduction of coal-fired combustion emissions
A process for mitigation of fouling deposits within a combustion zone, capturing of toxic metal emissions, and reduction of visible sulfur emissions attributable to sulfuric acid mist during coal combustion. SO 3 formed during coal combustion is reduced by the addition to the coal of raw, unprocessed magnesium-containing minerals such as magnesite ore or brucite ore. The minerals are pulverized to a fine particle size and combined with pulverized coal to provide a mixture of the particles. The mixture is combusted and the ore particles calcine and decrepitate to very fine magnesium oxide particles that have a significant particle surface area. The magnesium oxide particles react with the SO 3 produced during combustion of the coal and also capture toxic metals to reduce the quantity of undesirable stack discharge components.
1. A process for reducing visible sulfur emissions attributable to sulfuric acid mist during coal combustion, said process comprising the steps of:
mixing together a raw, unprocessed magnesium carbonate ore and coal to form a coal-ore mixture that results in a ratio of elemental magnesium to sulfur trioxide in flue gas of at least 1:1;
pulverizing the coal-ore mixture prior to combustion to provide coal-ore mixture particles that do not exceed −200 mesh; and
combusting the coal-ore mixture particles at a temperature sufficient to cause ore particles to calcine and decrepitate to magnesium oxide particles having a particle specific surface area of from about 200 m 2 /g to about 5 m 2 /g to absorb toxic metals and react with sulfur trioxides formed during combustion.
2. A process as claimed in claim 1 wherein the magnesium carbonate ore is pre-pulverized prior to mixing with the coal.
3. A process as claimed in claim 1 wherein the elemental magnesium in the ore to sulfur trioxide in the flue gas is from about 1:1 to about 10:1.
4. A process as claimed in claim 1 wherein the ore is intimately mixed with the coal and reacts with ash components to yield ash deposits that are friable and readily removed from furnace convective pass tubes.
5. A process as claimed in claim 1 wherein the toxic metals are selected from the group consisting of mercury, arsenic, lead, cadmium, and selenium.
6. A process as claimed in claim 1 wherein the magnesium carbonate ore is magnesite.
7. A process as claimed in claim 1 wherein the magnesium carbonate ore is brucite.