Wherever a gasification unit is not cost-justified, pellet boilers are evolving as a viable technology to produce heat for small to medium scale applications. Multiple units can serve large-scale applications, making the technology of particular interest to the greenhouse sector.
The pellet boiler furnace works by circulating water around an insulated heating box, which can burn pellets produced from other ZWES processes. In particular, the char resulting from the pyrolysis of municipal waste and waste wood will be used to make high-energy briquettes for boilers.
Units are installed on the exterior of a home or business, and once the water reaches a certain temperature, it is pumped back inside through a heat exchanger. A small, one-amp blower stokes the fire, keeping it at optimal temperatures. Biomass is loaded into a chute on the furnace and fed into the burning chamber by an electronically controlled augur.
Greenhouse heating is an example of a larger pellet boiler application. Rather than using a single large burner, multiple furnaces can be chained together to pump heat into larger buildings or water storage tanks. A single hopper can be designed to feed multiple units. Some units are currently designed to burn different types of biomass, such as soybeans, olive and cherry pits, oats, wheat and barley.