Defining mathematical models of biomass combustion products recirculation | Određivanje matematičkih modela pri recirkulaciji produkata sagorevanja bala pšenične slame

The paper reviews test results for a biomass-fired hot water boiler, located at Mitrosrem agricultural company from Sremska Mitrovica (Serbia), work unit Kuzmin. Nominal boiler power is 120 kW. As a fuel, there were used wheat straw bales. The impact of the quantity of inlet air (150, 220, 290, 360 and 430 cubic meter/h) fed to the boiler firebox was continuously monitored. We examined correlation between boiler thermal power, energy efficiency rate and bale combustion time, as well as mass decreasing during the bale combustion and we gave corresponding mathematical models. These correlation were given in the case of no recirculation of combustion products and in the case of recirculation 16.5 %. In the case of no combustion products recirculation, average boiler thermal power rate ranges from 63.47 to 90.90 kW (from 43.00 to 88.12 kW for 16.5 % recirculation). Maximum boiler thermal power is 130.94 kW in the case of no recirculation (122.44 kW for 16.5 % recirculation). Increasing the air throughput in the firebox, increases the thermal capacity of the boiler, while the bale combustion time is reduced. In the case of no recirculation, total combustion time ranges between 587 and 1,175 (from 698 to 1485 s for 16.5 % recirculation). It is given the excessive air coefficient values at maximal boiler thermal power and maximal boiler energy efficiency rate. Excessive air coefficient values are between 0.4 and 12.4 (during wheat straw bale combustion with no recirculation), and from 0.8 to 12.8 (for wheat straw bale combustion with 16.5 % recirculation). Bale mass decreasing is slower during the combustion process with recirculation of 16.5 %. One can conclude that it is better to use recirculation of 16.5 % because the same number of straw bales can be used for longer period than when there is no recirculation of combustion products. All examinations are covered by suitable mathematical models and graphic presentatition of those models.