Reducing fossil fuel use in hogged fuel power boilers

Tests were performed on ten operating power boilers producing 21 to 257 tonnes per hour of steam from hog fuel. Typical problems identified in baseline trials included inadequate air systems, non optimal air splits, unsuitable combustion air temperatures, inconsistent or poor hog delivery and distribution, and inadequate ash handling systems. Tests showed that it was often possible to increase steam generation from hog fuel and other wood wastes with adjustments to the air splits, hog feeding system and overfire air set up. In some boilers, it was possible to completely eliminate the use of supporting fossil fuels. Short term (1 - 2 day) tests at higher-than-normal firing rates were used to identify the limitations to running each boiler continuously at the higher firing rates, and low cost improvements to eliminate these limitations were then recommended. Long-term operating data subsequently provided by 4 different mills for 6 of these boilers indicated that a 457,500 t/yr increase in steam generation from hog was realized. The realized hog steam increase is equivalent to a reduction of 95,000 t/yr in CO2 emissions from combustion of fossil fuels. Total purchased fuel cost savings of $20 million/yr were achieved, ranging from $1.3 to 8.0 million per year for each of the optimized power boilers. These improvements were realized without increasing particulate emissions, while affecting reductions in greenhouse gas, NOx and SO2 emissions by displacing purchased fossil fuels.