Author(s)

M Mahamud, P Corte & H Sastre

Abstract

High ash-content coals, previously rejected by industry, are becoming a complementary energy source. Hence, the evaluation of their heating values is of capital importance. When the determination of heating values of very high ash- content coals is carried out by means of a calorimetric pump, the problem of incomplete combustion often arises, thus making the determination of the heating values a difficult task. In the present study, several techniques for evaluating the heating value of very high ash-content coals are tested, appraised and optimised. A common strategy for overcoming incomplete combustion is to mix the sample with a combustible substance of known heating value. This technique may, however, present an important pitfall, as the heat generated by the sample is usually much lower that the heat from the combustion of the auxiliary fuel. An alternative method for the determination of heating values is proposed, namely the calculation of the actual heating value of the coal by means of a mass-energy balance. Ash determination after calorimetric experiments leads to the determination of the unburned amount of coal. It is possible to estimate the actual heating value of the sample if experimental data are carefully correlated. The determination of the heating values of bituminous coals with ash contents ranging from 50 to 85% was carried out. The experiments revealed that the influence of other parameters needs to be highlighted. The degree of sample compaction, sample layout and certain other variables are of capital importance in order to achieve satisfactory combustion of the materials.

Keywords