BHSL fluidised bed technology has been uniquely designed to combust poultry litter. Industrial ‘wet woodchip’ boilers have been available for many years, and these use a ‘grate’ system rather than a bed of sand. As these systems are based on fuels that follow known woody biomass specifications, they may not readily combust poultry manure with the considerable variations in moisture content present.
The floor of a traditional furnace chamber uses mechanical ‘fingers’ or ‘chains’ to move the fuel through the combustion process. Often these arrangements must be water cooled to stop the mechanisms overheating. By contrast the only moving part in the BHSL furnace chamber is sand. This abrades the manure and handles slag and clinkers without the need for complicated moving parts.
Clinkers and slag can occur if molten minerals quickly cool down as a result of a variable moisture content fuel. A fluidised bed of sand operates at lower temperatures, so minerals do not melt in the first place, and the rapid movement within the bed helps spread wet fuel among the sand without it cooling specific sections too much. The sand is automatically reconditioned and any clinkers that do form are removed so they do not cause problems. By contrast, grate based systems often use higher temperatures to support combustion, so when wet fuel is presented it can quickly turn into clinker, requiring a full shutdown to permit manual cleaning of the furnace.