Effect of feedstock moisture content  on biomass boiler operation, TAPPI JOURNAL October 2015

Please Note: This document will be available in PDF format in the "My Electronic Documents" link on the home page once your order has been completed. Please make sure you have the latest version of Acrobat Reader. Click on the Acrobat Reader icon to check for the latest version, it’s FREE. To print a hardcopy of a PDF file correctly you must have a postscript printer. If you are not sure if your printer is a postscript printer please refer to your owner’s manual.

Purchase of electronic (downloadable) documents made at www.tappi.org by credit cards, followed by instant download CANNOT be cancelled. We do not offer refunds on electronic download documents.

TAPPI and the TAPPI JOURNAL (TJ) editorial staff would like to welcome a new member to the TJ editorial board, Marc F. Foulger, Global Business Manager Headboxes, for GL&V USA Inc.

ABSTRACT: Burning feedstock with high and constantly varying moisture content is a challenge in the operation of the stoker-grate type biomass boilers in pulp and paper mills. A fundamental study was performed, using a thermogravimetric combustor controlled at different temperatures, to systematically investigate the effect of moisture content on the combustion behavior of several woody biomasses. The results show that combustion occurred through three stages: drying, devolatilization, and char burning. Increasing the moisture content of the sample above 30% significantly increased the drying time and the time to ignition of the sample. Moisture content, however, had only a small effect on the devolatilization rate and virtually no effect on the char burning rate. Furnace temperature had a great effect on combustion. Samples containing 40% moisture could still ignite and burn readily at 800°C, but they took a much longer time to ignite at 500°C and did not ignite at 400°C. These results imply that in biomass boiler operation, the high moisture content in feedstock delays combustion and causes the furnace temperature to decrease. The low temperature, in turn, suppresses combustion, further decreasing the furnace temperature and causing more delay in combustion. This downward spiral will eventually lead to a boiler blackout unless the biomass feed rate is significantly reduced or the auxiliary fuel (natural gas and fuel oil) flow rate cofired in the boiler is increased to keep the furnace temperature high.