Sulphur in coal

Sulphur content of coals generally varies from 0.5 to 3%, with some exceptions of higher amounts. It occurs principally in two fonns  

Although sulphur does have some heating value (2240 kcal/kg), SO2 and SO3 formed during the combustion of sulphur-containing coals are extremely harmful. 

CaS04 + Si02 (usually present in coals in small amounts) 

The gases cause environmental pollution and in moist atmosphere produce acids (H2SO3 and H2SO4) which cause corrosion of the metallic equipment around. 

We can have an idea of the pollutional hazards from the fact that sulphur oxides equivalent to 3 tons of concentrated H2SO4 are discharged daily into atmosphere by a small Thennal Power Plant bunting per day 100 tons of coal that contains only 1% sulphur. 

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For these reasons, the determination of sulphur in coal is of considerable importance and a representative selection of a wide range of industrial coals has been made with the aim to establish them as coal reference materials (CRMs 331, 332, 333, 334, 335 and 336) [12]. 

Combustion of sulphur in coal, petroleum and oils, treatment of sulphur ores... 

A. Attar, Chemistry, thermodynamics and kinetics of reactions of sulphur in coal-gas reactions a review. Fuel 57(14), 201-212 (1978). 

A known weight of powdered coal is fused with Eschka-mixture in presence of air. The sulphur in coal is oxidised to SO2 which is absorbed by Eschka-mixture to produce the corresponding sulphites ... 

Sulphur attack on nickel-chromium alloys and nickel-chromium-iron alloys can arise from contamination by deposits resulting from the combustion of solid fuels, notably high-sulphur coals and peat. This type of corrosion, which has been observed on components of aircraft, marine and industrial gas turbines and air heaters, has been associated with the presence of metal-sulphate and particularly sodium sulphate arising directly from the fuel or perhaps by reaction between sodium chloride from the environment with sulphur in the fuel. Since such fuels are burned with an excess of air, corrosion occurs under conditions that are nominally oxidising although the deposits themselves may produce locally reducing conditions. 

Fig. 7.76 Superimposed simplified thermodynamic stability diagrams for three elements with oxygen and sulphur at 871°C. The shaded rectangle indicates possible activity ranges in coal gasification atmospheres (after Stringer )...

Energy recovery from packaging waste is discussed, with particular reference to the co-combustion of mixed plastics with other conventional fuels such as wood, coal and peat. Experimental work is described in which a project was established to evaluate the possibility of energy recovery from a circulating fluidised bed boiler using packaging from different sources as fuel. The role of sulphur in the formation of PCDD/F in the combustion process was also studied. 

Thus it will be necessary to exploit other more abundant resources of hydrocarbons. In the United Kingdom there are large reserves of coal which could satisfy demand for at least two hundred and fifty years. The National Coal Board currently mines approximately 120 million tons of coal per annum of which 65% is used for generating electricity (JO. (Combustion of the low sulphur British coals does not result in excessive atmospheric pollution.) To satisfy the increased demand for coal the National Coal Board has undertaken an investment programme which includes the development of a mining complex at Selby in Yorkshire which, it is estimated, will produce in excess of 10-million tons when full production is reached in 1988. 

Chandra, D. Roy, P. Mishra, A.K., et al., Removal of Sulphur From Coal by Thiobacillus Ferroxidans and by Mixed Acidophilic Bacteria Present in Coal. Fuel, 1979. 59(4) pp. 249-252. 

Occurrence. Native sulphur occurs in deposits around volcanoes and hot springs. It occurs in numerous sulphides minerals, in sulphates, in crude oils, in coal and as H2S in natural gas. 

In removal of sulphur from coal gas In nonferrous smelting industries In mineral separations (e.g. coal-washing)... 

Casagrande, D. j. 1987. Sulphur in peat and coal. In Scott, A. C. (ed) Coal and Coal-Bearing Strata Recent Advances. Geological Society, London, Special Publications, 32, 87-105. 

Thiophene is found in small amounts in coal tar, and commercially it is prepared from the cyclization of butane or butadiene with sulphur at 600 °C. 

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