The dependence of COx and NOx emission concentrations on the excess air coefficient during combustion of selected agricultural briquetted by-products
Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamýcká 129, CZ165 21 Prague, Czech Republic
The issue of CO, CO2 and NOx emissions is very extensive and important. The aim of the paper is the experimental determination of the CO, CO2 and NOx emission dependencies on the amount of excess air. Materials used for the experiments were several types of briquetted biomass. Crops used were Czech knotweed (Reynoutria × bohemica), Rumex hybrid OK 2 (Rumex patientia × Rumex tianschanicus), meadow hay and timothy grass (Phleum pratense). For all samples proximate and elemental analyses were performed (semiautomatic calorimeter LECO AC-600 elemental analyser CHN628 + S and analyser LECO TGA-701) and stoichiometric calculations of combustion were made. Combustion device used in combustion tests was a hot air stove with a grate fireplace and with manual fuel supply. The combustion process was monitored by analyser Madur GA-60. Parameters monitored during the combustion tests were primarily the flue gas temperature and the emission levels of carbon monoxide, carbon dioxide and nitrogen oxides.
Analyses and calculations of plant biomass samples indicate their good properties for energy use. The gross calorific value was as high as 19.55 MJ.kg-1 in the sample of Rumex OK 2. Limiting factor is the high quantity of ash in plant material. The briquettes from timothy grass achieved 5.77% wt. ash in the dry matter. The excess combustion air had positive influence during combustion test. On the other hand, this caused heat loss by departing flue gases, wherein the flue gas temperature reached high values. The excess air coefficient also significantly affected the emission levels of carbon dioxide and monoxide and nitrogen oxides in the flue gases. Results were statistically analysed and complemented by regression equations, which in practice can be used to optimize the combustion process in boilers with manual fuel supply.