The Influence of Burning Ratios Based on Coal Characteristics on its Combustion in the Boiler Furnace

The need of switch to burn non-design fuel arises during the thermal power plants long-term operation. The choice of replacing coal is quite complicated and currently being solved by various non-design fuels experimental combustion on a specific power boiler. The aim of the work is to develop criteria assessing non-design coal burning possibility in a specific furnace before experimental combustion. The stated goal is achieved with the help of numerical combustion modeling regarding various coals at the pre-critical parameters boiler furnace with an average composition ranking by the lower calorific value. 2 burning ratios have been proposed based on foreign experience: the fuel ratio and the degree of fuel burnout. The first is the ratio of the fuel carbon to volatile substances contents, which in this work are taken as an analytical mass. The second is calculated with the proposed formula, which, instead of the combustible content in fly ash, use mechanical underburning widely included in the technical calculations. Combustion zones with the degree of the acceptable fuel burnout according to the standards and with its excess are distinguished. The limit of possible coal combustion according to the fuel coefficient is found as well. It is shown that this furnace is quite universal for burning a wide range of coals, although it was originally designed for burning brown coal. It is not recommended to burn only lean and low-caking bituminous coals, anthracites and brown coals with calorific value less than 11.5 MJ/kg or humidity more than 40%. The obtained results are significant for the preliminary assessment of non-design fuel combustion and narrowing the range of fuels under consideration. Other the boiler conversion consequences for non-design fuel should be taken into account for the final decision, and above all, the probability of the heating surfaces slagging.