Coal is widely used as a source of power and heat by the chemical, paper, cement, and metal industries. In the U.S., there are some 900 coal preparation plants and coal-fired power plants, and some 100 coal analyzers have already been installed in them. One key consideration in operating coalburning facilities is the control of SO 2 emissions to the atmosphere from coal-fired power plants. Because the most economical method of reducing the sulfur content of coal is through the blending of various coals, on-line coal analyzers are often needed. The characteristics of coal are monitored for environmental protection, quality assurance, and process control.Gross calorific value is determined by burning a weighed sample of coal. A calibrated isoperibol oxygen bomb calorimeter is used for that purpose under controlled conditions (Figure 8.14c). The bucket, which holds the oxygen bomb, provides good circulation and rapid thermal equilibrium for the bomb. Thermal jacketing is provided by a circulating water system, which maintains cooling water flow around the bucket. A microprocessor control system monitors and controls the jacket temperature, fires the bomb, and monitors the temperature in the bucket. The test continues until the controller determines that equilibrium has been reached. A microcomputer uses the sample weight and temperature data—applying correction for acid, sulfur, fuse, and any added combustion aids—to calculate the gross calorific value.An ASTM method for determining sulfur in coal uses the washings from the oxygen bomb calorimeter. Sulfur is precipitated as barium sulfate from the washings. The precipitate is filtered, ashed, and weighed. An automatic titrimetric system is also available for rapid sulfur determination using the oxygen bomb washings. The washings are titrated with a lead perchlorate solution to obtain a lead precipitate.