Biomass Boiler

Fully automated systems are exactly that a delivery truck drops off the chipped or ground up waste wood with a live bottom floor, and a series of augers and conveyers move the wood fuel from there to the boiler. With computer controls and a laser eye that measures the amount of fuel in the metering bin, the system automatically turns the augers and conveyers on and off as needed to maintain the amount of wood fuel to sustain the boiler's pressure and thus, the temperature demand of the thermostat. In other words, no handling of the wood fuel is required by the boiler operator.

Semi-automated or "surge bin" systems require somewhat more manpower than the fully automated system. Have installed a semi-automated system to handle the base heat load for four buildings totaling about 100,000 square feet, with a 1.2 million BTU per hour output. This system has a smaller storage bin, shorter, simpler fuel conveyance system, and is designed to meet less than the full heat load of the facility. The rationale behind this is that wood fired boilers operate most efficiently when they are working hard, and that the peak heat load in our region is significantly higher than the load required on most days of the year. The peak load may only be required on one or two days of the year, and sizing a boiler to meet the peak would necessarily compromise its efficiency for the majority of the time it is in use.

Pellets are a more processed fuel, and therefore, more expensive, but the tradeoff is that they are more condensed and uniform, which makes them much more efficient to transport and store. Recent rises in fossil fuel prices have driven up the demand for pellets rather dramatically, so this is an historic high. Because of their uniform nature, the conveyance system for pellets is even simpler and less expensive than a surge bin system. These systems essentially use a grain-type of storage silo and move the fuel to the boiler using gravity. The condensed nature of this fuel also makes the storage requirements considerably smaller, reducing up-front construction costs. Pellet fired systems are available and appropriate for a fairly wide range of facility sizes.

The fourth type of system is combined heat and power or CHP, in which wood waste is used to generate power, and heat is created as a byproduct of the power generation system. The capital investment required for high pressure steam generation associated with CHP systems is significantly higher, and due to the risks associated with their high pressure (from a minimum of 100 pounds per square inch up to hundreds of psi), the systems require a highly skilled and certified operator, which adds to the operating expense. Creating power also requires a great deal more fuel than creating heat, and as will be discussed in the fuel supply section below, wood fuel is bulky and difficult to transport. Requiring a great deal more fuel can enlarge the travel radius to the extent that the savings benefits of the system diminish. Finally, CHP systems create heat on a year-round basis, so if that heat is not desirable for certain seasons of the year, an additional expense of installing a cooling tower is required.