Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 220

Feedstock requirements for a biomass power facility are dependent upon the capacity of the facility and, to a lesser extent, the efficiency of a specific technology. Dramatic reductions in demand, on a normalized basis, are achievable with increased size of the facility. A 5-MW direct combustion (stoker) power plant has a much higher heat rate than a larger facility. Indeed the larger plant may be approximately 50% more efficient than the smaller installation. The major reason for the higher efficiencies at larger sizes is the increased temperature and pressure that can be economically accommodated in the big facilities to supply larger turbines.

Fuel characteristics greatly affect the combustion process and therefore the decision process for choosing combustion technologies. The most common problems associated with the direct combustion of wood are boiler slagging and fouling, erosion and corrosion, combustion instability, and particulate carryover.

Fuel characteristics that should be analyzed include heating value, moisture content, ash content, sodium and potassium quantities, particle size distribution, ash fusion temperature, and sulfur content. Physical fuel characteristics such as density and particle size affect combustion as well as material handling considerations. Changes in fuel density could cause combustion to occur in the wrong place in the boiler, upsetting the heat transfer scheme and therefore the boiler efficiency.