Operating data of a Bubbling Fluidized Bed (BFB) boiler and three Stoker Grate (SG) biomass boilers from different pulp mills were analyzed over a two-year period. The results show that in all cases, the thermal performance decreases markedly from 5.5 to 4 lb steam/lb dry biomass as the feedstock moisture content increases from 40 to 60%. The BFB boiler had better thermal performance, although it operated in a higher moisture content range compared to the SG boilers. Multivariate analysis (MVA) was also performed on one of the SG boilers to determine operating parameters that affect thermal performance. The results show that furnace temperature, oil flow rate and ID fan current positively correlate with thermal performance, while the feedstock moisture content, total air flow, and excess O_2 negatively correlate with thermal performance. This implies that when modifying an operating parameter to improve thermal performance, it is important to take into account correlations among various parameters. In some cases one positively correlated parameter may cause an increase in a negatively correlated parameter. The net effect may be a decrease in thermal performance.
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