The efficiency of bark and wood fuel utilization in the hot water boilers

Abstract

The commissioning of a hot water boiler house at SJSC “Sawmill 25” was another major step in increasing of efficiency of the integrated use of wood raw in the enterprise. It required efficiency assessment of burning bark and wood fuel in the combustion chambers of PR 8000 boilers. For this purpose, the comprehensive energy audit of boiler house equipment was carried out, the biofuel mixture as fired and the residues of combustion were analyzed. The moister content of bark and wood fuel was 50.83–54.82 %. The proportion of bark in the fuel varied in the range from 55 to 77 %. As a result of the energy audit, the components of boilers heat balance were calculated. In this case, combined relative and calorimetric method supplemented with thermal imaging was used to determine external heat loss. Gaseous and particulate emissions were determined with electrochemical and weight methods. Distribution of combustibles in fly ash fractions was analyzed. The overall separation efficiency of gas cleaning plants was determined. Gas-entrained soot particles were studied with an electronic scanning microscope. Based on the analysis, recommendations were elaborated to improve the energy-ecological performance of the tested boiler house and to reduce the emission of particulate matter. Measures for partial or complete removal of restrictions on the furnace draft when burning bark and wood fuel with a relative moister content of more than 55% were proposed. The energy audit showed that the design characteristics of the main and auxiliary equipment of PR-8000 boiler provide sufficiently high energy-ecological performance if the grates surfaces are used effectively and the vacuum in the combustion chambers is close to the optimum values.