Fuel & Power Station - Generate electricity & biofuel in one plant

Sheps,

Sounds good to me. I'm employed in a small (15 Meg) 3 GT dual fuel CC cogen. We mostly fire on NG but have the option of using ultra low sulfur diesel when NG is not available. We use our waste heat to supply a 370 F hot water loop that is 6 miles or so in length. We also have the option of using duct burners to increase the turbine exhaust heat if we need more BTU's going into the heat recovery. The heat is utilized to heat buildings and research areas such as greenhouses. The high temp hot water is also used to generate steam via heat exchangers and is used for many purposes. I have often wondered if it would be feasible to have heating coils in place when we are constructing (for lack of a better term) landfills. Then when the landfill reaches a certain height we could turn on the heat and "cook" the methane out at a much faster rate. We could also investigate if if would make economic sense to retrofit existing mature landfills. Sewage plant sludge is another possible feed stock for methane production. In my area we have many methane recovery operations and some of them inject oxygen to increase methane production. The gas could then be filtered and scrubbed of CO2 and used to fuel the combustion turbines ( as could the pyrolysis oil in your senario) to generate more power or sold to one of the utility companies. Power and natural gas demand is seasonal in my area. Decisions would need to be made as to when to burn or sell the methane based on economics. All in all I like your idea. We need more out of the box ideas and solutions if we want to sustain our present lifestyle in a more eco friendly manner. Ed

Your point about seasonal availability of NG in some industies could also impact on thiis design, especially with the option to fire on Diesel. Economically it could be worth firing on Biofuel at times of higher NG cost.

370F sounds a bit low for efficient pyrolysis, but as you say the exhaust temps could be boosted. There may still be enough residual heat left after the pyrolysis stage for local hot water & raising steam.

I like the landfill idea: Maybe an on-site solar furnace could be used for your landfill 'cooking'.

The typical range of my combustion turbine exhaust gas temperatures (into the hi temp heat recovery units) are from 800F without the duct burners to 1250F or so with them on. The hi temp shut down setpoint is 1450F so there is a lot of room here to make changes. The heat recovery units could be using oil instead of water to transfer the heat as is often done in oil refineries.This would allow much higher temps without the need for really high pressures as is the case in hi temp hot water or steam systems. You would also have the option of impounding this oil in insulated storage tanks for other uses. Internal pipe, tank and heat exchanger corrosion would be virtually zero because or no entrained oxygen in the system. You would also save money on chemicals for feed water treatment and condensate recovery equipment. The typical efficiencies of combustion turbines like mine are around 30%. There are some much larger units out there that use some of the exhaust heat to preheat the air before the combustor. These guys claim to have efficiencies in the 60% range so it is possible to nearly double our electric production. I am not sure of how large an impact that these higher temps would have on turbine life but it would most likely shorten it. One limiting factor to running these units really hot is the production of higher NOx levels. We use a wet system ( deionized water injection into the combustor) to keep our flame front temperatures at 1250F. There are better systems out there. It is with out a doubt that we need better more integrated systems to squeeze out every possible BTU from the fuels we use and to lessen our environmental impact. You mentioned solar furnaces. I read about a peaking plant in the southwest (CA I think) that uses a mirror array to focus solar heat on a large oil filled recovery unit. We need more of this type of plant to eliminate brownouts and service interruptions. Ed

Regarding your suggestion of using exhaust heat to drive out methane from landfills, I was curious if such pyrolysis did not require dry heat conditions? The reasoning is that with a landfill, there just might be the issue of soil-water/humidity as a result of the water flowing from the surrounding into the landfill.

If the power generator is to be built from scratch then then I would think that it would be more cost-effective to start-off with the biomass gasifiers at once, instead of incurring the additional capital expense of an NG burner. then calculate the cost advantage relative to the prevailing system.

Hi.

Yes, this type of development may only make economic sense when retrofitted.

That said, my inspiration came from the belief that natural gas via pipeline is wonderful for stationary power sources, whereas liquid fuels can be better used on 'the move'.

We have petrol giants like BP trying to re-sell us Gas-to-Liquid technology as a 'green' solution (a pre-WWII concept). I much prefer some system that can give us bio-fuels on an economically viable scale, whilst using tryed & tested GT equipment on the 'front-end'.

I had been thinking, although from the stand point of sustainability the recovery of the energy contents of biomass would be advantageous, I think that the capital cost which would be required for implementation versus the continued used of an existing secondary heat recovery system would argue against the idea every time.

However, several farmers are beginning to install at their expense, individual "wood-burners" which actually are of the form of Biomass Gasifier you have in mind. perhaps a better way would be to sell the exhaust gas and have the gas distributed to the various farmers for use in their own Biomass Gasifiers. This would enable the Utility company to still make money from the farmers, support the sustainability programs, and reduce the operations and related overheads. this approach just might be a win win situation.

Just a thought.