On line measurement of the lower heating value of waste and energetic efficiency of an existing waste to energy plant: Identification of uncertainty associated to probes and their influence on the results

An automatic system for calculating the lower heating value (LHV) of waste was implemented and analyzed 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 the gross and net efficiency of the plant. The main results indicated an average LHV ranging from about 7,300 to 10,000 kJ/kg. The composite uncertainty associated with this value was ±0.82% with p= 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 7%