Marcos Buenijo wrote:Just sharing one of my wacky ideas. I like the idea of using a modernized piston steam engine with good thermal efficiency and fueled by biomass as an off grid power plant. One of the main benefits of a piston steam engine in this setting is the ability to operate at very low power for extended periods while providing heat in a convenient package. Steam is an excellent heat transfer medium. Unfortunately, these systems are not available. So, I considered, why not a biomass fueled steam generator for heating applications? Furthermore, since my recent research shows that charcoal gasifiers can power very small engines cleanly and with impressive energy density, then how about a system that chars wood chips at a controlled rate while generating steam on demand? The charcoal produced from the system can then be stored for use as required in fueling small engines.
I'll describe a basic configuration to get the reader thinking on the topic. Particulate biomass like wood chips is gravity fed through a vertical pipe section. A hopper is connected to the top. A lower section of the pipe is surrounded by a combustion chamber fueled by pyrolysis gases generated from the heated wood chips. A key point to consider is that pyrolysis occurs at a rate directly proportional to the rate at which the biomass feeds through the system (within limits). So, it's possible to govern the steam rate with a motorized auger tha removes charcoal from the base of the system. A steam generator tubing coil is placed above the combustion chamber in the annular space between the pipe and exterior shroud used to form the combustion chamber. The draft draws air into the base of the system to cool the lower pipe (and charcoal within) and combust the pyrolysis gases escaping from a ring of holes in the inner pipe at the base of the combustion chamber. These hot combustion gases pass over the steam generator coil before heating the hopper that contains the fuel (thereby drying and/or preheating the fuel before it enters the pipe).
The steam generated is sent through an insulated line to a high point in the system, then distributed to various heating applications. This is controlled in two ways. First, each load has a valve to control flow. Second, the final pass of the steam/condensate is through an insulated water storage tank. The temperature of the water in this tank is used as a control for the auger motor.