combustion calorimetry; high ash coal; effectivity of combustion

Modelová řada směsí černého uhlí s minerální látkou byla proměřena ve spalovacím kalorimetru s cílem upřesnit maximální obsah nehořlavých, minerálních příměsí, kdy ještě není snížena účinnost spalování uhlí. Sledování prokázala, že snížení účinnosti spálení/shoření lze očekávat u uhlí převyšujících obsah minerálních látek 50 %. Tehdy již vzorek v kalorimetru nevyhoří v celém svém objemu a účinnost spálení tak klesá.

A series of coal-mineral matter mixtures was inves-tigated by bomb combustion calorimetry (IKA C4000, Germany) to elucidate boundary for ash content in coal at which combustion proceeds with lowered efficiency. For the experiments, a high rank bituminous coal was mixed with particles of mine stone, both being milled to size below 0.2 mm. Before the usage, the sample of stone was heated at 900°C for 2 hours in air to stabilize mineral matter composition. Mixtures 5, 10, 15, 20, 25, 30, 40 and 50% of coal were used, with sample weights both of 1 g and/or 2 grams being applied. The efficien-cy of the combustion process at the bomb test was assessed of the measured calorific value and that of “theoretically” calculated. The “theoretical” calorific value of the mixture was determined from the actual content of the coal proving known specific calorific value (36.6 MJ/kg). Based on the measurements, mineral matter content of about 50% was found as limiting for fully efficient combustion of coal in the bomb calorimeter. At content of 90% of mineral matter, the efficiency of combustion is about 70% (sample weight 1 g) and/or 50% (sample weight 2 g). Afterwards, the combustion efficiency steeply decreases to zero.