On time measurement of the efficiency of a waste-to-energy plant and evaluation of the associated uncertainty

An automatic system for calculating the lower heating value (LHV) of waste was implemented and analysed for an existing waste-to-energy plant. The calorific value was determined by the indirect method using the whole combustion chamber and heat recovery steam generator as the calorimeter. On the basis of this fundamental information it was also possible to evaluate on time the gross and net efficiency of the plant. The main results indicated that the LHV varied daily, from 4000 to 13,000 kJ/kg, even if the average monthly values ranged from about 7300 to 10,000 kJ/kg. The uncertainty associated with these values was ±0.82% with a confidence interval of 95%. The corresponding gross and net efficiencies were about 18% and 8%, respectively, with an associated uncertainty < 1.4%. The LHVs of waste were in good agreement with those measured by a calorimetric bomb, even if they had a higher uncertainty level of about 5.6%.