Should a county jail make its own heat and power from forest residues? The El Dorado County Board of Supervisors in California thinks the idea deserves a proper look. On 27 October it gave conceptual approval to move ahead with planning and a feasibility study for a woody biomass combined heat and power (CHP) system at the Placerville Jail, Wood Bioenergy reported on 3 November. The aim is to cut the site's reliance on propane and steady its long-term energy costs.
The proposal, developed by FLOYD BioEnergy, uses two modular gasification units of about 70 kW peak electrical output each. Together they would burn around 950 bone-dry tons of wood chips a year. The wood is turned into syngas, which is cleaned and fed to engines that make electricity and recoverable heat, all used on site behind the meter. Biochar from the process could bring carbon-credit income.
A county study found about 106,000 bone-dry tons of reliable forest residues within El Dorado County. Equipment for the two modules is estimated at $1.8 million, which expected federal incentives could bring down to about $1.2 million; with around $400,000 for permitting and planning, the preliminary net estimate is about $1.6 million. The supervisors asked for more detail on financing and procurement before any final commitment, and want room kept on the site for planned transitional housing.
Small engines, real heat recovery
At this size the value of a CHP plant depends heavily on how much of the engine heat is actually used. The jacket water and exhaust heat are normally passed to the building's heating and hot-water circuits through a plate heat exchanger, so that the engine coolant never mixes with the site water. On a gasifier plant, where tar and dust are part of daily life, it pays to place that exchanger where it can be reached and opened without draining half the system.
Sources: Wood Bioenergy
