New applications of ‘Hess Law’ and comparisons with models for determining calorific values of municipal solid wastes in the Sri Lankan context

The present disposal methods of dumping municipal solid waste (MSW) are not acceptable in Sri Lanka. Therefore, the application of the concept of conversion of “waste to energy’ (WTE) required experimental validation of existing models and determination of the accuracy of the results. The results of models were different to experimental values due to high ash contents in the wastes. These differences were reduced by adjusting the reported elemental compositions which were applied to the modified Dulong model. However, not all the predictions were accurate and the Shafizadeh model was modified to give accurate predictions for biomass wastes, except for processed or non -carbohydrate polymerized materials. Accuracy improved when ‘Hess Law’ was applied to determine ‘energy of formation’, which was found to be inversely proportional to bomb calorimeter values. A further refinement was made with ‘formation coefficients’ which gave very accurate experimental values. A host of new information can be obtained from energy of formation, like improved characterization of wastes, validating experimental results. The latter led to the astonishing prediction of the possibility of replacing 2.5% of the present total energy consumptions or 42% of electricity consumption in Sri Lanka with efficient WTE plants. Thus, further extension of application of the Hess Law will have a futuristic outlook in improvement and development of efficient technologies while improving and protecting the environment.