A second combustion modification alternative, also in the demonstration plant stage, is to convert the coal to a synthetic fuel gas and then burn that in combination gas-turbine steam-turbine power plants. This seems complex and costly, but it has the advantage that in the synthetic fue sulfur is present as H2S; since no other acid gas is present, the sulfur can be easily removed from the gas by the methods described. The second, and more important, advantage is that modem gas-turbine steam-turbine plants have a much higher thermal efficiency than typical coal-fired steam plants(perhaps 45 percent vs. 33 percent). If the problems with this technology can be solved, it may offer a more efficient and economical way of converting coal to electricity than the systems currently used even though it is much more complex Don't Burn at All The majority of the SO derived from human activities comes from coal and oil combustion in electric power plants. If we can produce electricity in some other way or reduce our use of electricity, we will consequently reduce our emissions of So2. For this reason more efficient electric devices (lights, refrigerators, motors) are, in effect, SOz control devices. So also are nuclear, wind, solar, tidal, geothermal, and hydroelectric power plants. There is currently a serious effort by the U.S. EPA and by the electric util ity industry to improve the efficiency of electricity d to production of electricity from alternative reasons, including reduction of SO2 emissions 11.6S 1. SO emissions from human activities are mostly due to the combustion of sulfur-containing fossil fuels and the smelting of metal sulfide ores 2. The overall control strategy for SO2 emissions is to convert the sulfur to CaSO4 2H20 and eturn it to the ground in some kind of landfill, or use it to make wallboard 3. For liquid or gaseous fuels containing reduced sulfur, the most common approach is to use catalytic processes to convert the contained sulfur to H2S, remove that by scrubbing the gas with a weakly alkaline solution, convert the H S to elemental sulfur by the Claus process, and either sell that sulfur for sulfuric acid production or place it in a landfill. 4. For metal sulfide ore smelting which produces waste gases with 4 percent or more SOz, the common approach is to convert that SOz to sulfuric acid 5. For coal (or high-sulfur oil)used in a large power plant, the most common approach is to burn the coal and then treat the plant's exhaust gas(typically containing about 0. 1 percent SO2)with limestone or lime in a forced-oxidation wet scrubber or a spray dryer, to convert SOz to Caso 2H20, which will then go to a landfill or a wallboard plant 6. Other alternatives are being explored, some in large-scale demonstrations. They may replace those just listed in the future l1-1411－14 A second combustion modification alternative, also in the demonstration plant stage, is to convert the coal to a synthetic fuel gas and then burn that in combination gas-turbine steam-turbine power plants. This seems complex and costly, but it has the advantage that in the synthetic fuel gas the sulfur is present as H2S; since no other acid gas is present, the sulfur can be easily removed from the gas by the methods described. The second, and more important, advantage is that modem gas-turbine steam-turbine plants have a much higher thermal efficiency than typical coal-fired steam plants (perhaps 45 percent vs. 33 percent). If the problems with this technology can be solved, it may offer a more efficient and economical way of converting coal to electricity than the systems currently used even though it is much more complex. Don't Burn at All The majority of the SO2 derived from human activities comes from coal and oil combustion in electric power plants. If we can produce electricity in some other way or reduce our use of electricity, we will consequently reduce our emissions of SO2. For this reason more efficient electric devices (lights, refrigerators, motors) are, in effect, SO2 control devices. So also are nuclear, wind, solar, tidal, geothermal, and hydroelectric power plants. There is currently a serious effort by the U.S. EPA and by the electric utility industry to improve the efficiency of electricity usage, and to encourage production of electricity from alternative energy sources for a variety of reasons, including reduction of SO2 emissions. 11.6 Summary 1. SO2 emissions from human activities are mostly due to the combustion of sulfur- containing fossil fuels and the smelting of metal sulfide ores. 2. The overall control strategy for SO2 emissions is to convert the sulfur to CaSO4 .2H2O and return it to the ground in some kind of landfill, or use it to make wallboard. 3. For liquid or gaseous fuels containing reduced sulfur, the most common approach is to use catalytic processes to convert the contained sulfur to H2S, remove that by scrubbing the gas with a weakly alkaline solution, convert the H2S to elemental sulfur by the Claus process, and either sell that sulfur for sulfuric acid production or place it in a landfill. 4. For metal sulfide ore smelting, which produces waste gases with 4 percent or more SO2, the common approach is to convert that SO2 to sulfuric acid. 5. For coal (or high-sulfur oil) used in a large power plant, the most common approach is to burn the coal and then treat the plant's exhaust gas (typically containing about 0.1 percent SO2) with limestone or lime in a forced-oxidation wet scrubber or a spray dryer, to convert SO2 to CaSO4 . 2H20, which will then go to a landfill or a wallboard plant. 6. Other alternatives are being explored, some in large-scale demonstrations. They may replace those just listed in the future