Hi Stuart, The goal in large-scale steam generation (powerplants as well as warships) is to produce steam above the critical point-steam with a pressure of 3206 psia (221 bar) and a corresponding saturation temperature of 705degF (374degC)-a region where there is no meaning to the words "vapor" or "liquid". There is only a single phase in this "supercritical" region. When this steam is expanded through power turbine nozzles it expands and the pressure is reduced. The result is very dry superheated steam which returns to the sub-critical realm and is recycled back to the steam generator.
Your Navy friend was talking about something much different than any of us are likely to encounter while trying to tap the energy from a biomass gasifier. The metallurgy itself is extremely important in these operating regions. 300 psig is another world altogether yet who of us feels totally at ease next to one of these boilers? (After 25-years I'm still squeamish.) Can't all of that high-entropy heat that needs to be "sunk" from an ORC system be used to dry a fuel source that would otherwise be completely unusable? Mark From: Gasification [mailto:[email protected]] On Behalf Of stuart mather Sent: Friday, February 1, 2013 5:18 PM To: Discussion of biomass pyrolysis and gasification Subject: Re: [Gasification] mycoremediation of tarry water Kevin Years ago, while I was in the Navy, during a tour of the engine room of a warship, one of the turbine boiler engineers warned us that if we encountered even a tiny high pressure/temp leak somewhere in the steam plumbing, we wouldn't see it, but it would instantly slice cleanly through whatever body part got in the way.. I'd forgotten about how dangerous steam can be. Clearly not an option for small scale set ups, although a small steam engine with a professionally designed boiler with multiple fail safe features probably warrants further consideration. But you obviously wouldn't be building one yourself. Whereas once the tar issue is addressed in an environmentally responsible way, the opportunities to lose life and limb would seem less with a gasifier/ICE approach to using biomass, and is a tinkerers dream. One further question, If the tars stay in biochar from low temp BM pyrolysis, and the soil bacteria/myccorhizal fungi deal with them, (are even beneficial I thought), why is the tarry water from a gasifier scrubber such an environmental hazard? Stuart. _____ From: Kevin <[email protected] <mailto:[email protected]> > To: Discussion of biomass pyrolysis and gasification <[email protected] <mailto:[email protected]> > Sent: Saturday, 2 February 2013 6:22 AM Subject: Re: [Gasification] mycoremediation of tarry water Dear Tom Certainly, what you say could be true for 2 MW and larger facilities that have the technical and economic economies of scale. Smaller gasifier and engine systems can deliver 1 HP for a heat rate of about 16,000 BTU/hp-hr. If powering a generator, this is a heat rate of about 24,000 BTU/kw-hr. I would doubt that small scale steam or ORC plants could meet this heat rate. Small gasification plants can be operated safely with a conscientious Operator, having very basic training. Steam power plants of any significant size and pressure, usually Stationary Engineers as Operators. With smaller steam Plants, the Operating labour Cost can be very significant. Best wishes, Kevin.
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