BTU Question

[PelletBoy]

Hi,

I am looking into setting up a CHP project on my residential rural property to provide heat and electricity to my home and sell approximately 50 kWe to the grid. I will need to provide 310,000 BTU / h to the furness and will be using wood pellets as the fuel ( I will be manufacturing the pellets myself from softwood on my property and clean 2x4 construction waste, I work for a large construction company and could have access to tons of clean softwood waste). How much wood biomass will I need to produce 310,000 BTU / h?

Thanks.

PelletGuy

 

[Ugly]

Hi,

I am looking into setting up a CHP project on my residential rural property to provide heat and electricity to my home and sell approximately 50 kWe to the grid. I will need to provide 310,000 BTU / h to the furness and will be using wood pellets as the fuel ( I will be manufacturing the pellets myself from softwood on my property and clean 2x4 construction waste, I work for a large construction company and could have access to tons of clean softwood waste). How much wood biomass will I need to produce 310,000 BTU / h?

Thanks.

PelletGuy

I'm scratching my head because I have no idea what kind of device is going to give you 50KW of generation capacity on only 310,000 BTU per hour energy.
50KW /.746 =67.02 HP
67.02HP x 2,544 BTU/h = 170,499 BTU/h

The above example is at 100% per cent efficiency. Not possible even with steam generation (engines or turbine). Keep in mind, you still need to heat the house and that takes BUT/h as well. Practical examples I've looked at say you will get much less efficeincey during conversion from BTU/h to KW

anyhow figure 7000 BTU/h per pound of wood at 100% conversion of wood to BTU/h. Again, not possible but some get low 90's % apparently.
So you need 44 pounds at a 100% for 310,000 BTU/h

 

[pybyr]

Any reason you're going to make pellets instead of woodchips?

Seems like woodchips would be easier to make- and there are already units out there that have had success at using them as feeds for gasification.

 

[sparke]

I was thinking the same thing. the amount of energy you waste converting to the soft wood to pellets does not make sense. Unless... you are also in the pellet business?

Why not use a furnace that will burn your soft wood efficiently instead? Without the hassle of converting to pellets...

 

[jebatty]

Thermo-dynamic efficiency on all but the highest tech coal fired electrical generation plants is just under 50% average, if I recall correctly from prior research, and electrical generation output efficiency is about 30%. I doubt you could expect greater than 30% btu conversion efficiency from your wood input btu, and if you get that high, you are equaling commercial.

 

[jebatty]

Addendum: the 50% relates to conversion of heat to mechanical energy and follows from the second law of thermodynamics.

 

[PelletBoy]

Hi Guys,

Thanks for your speedy replies, I am planing to sell wood pellets so using the pellets were in my plans but nothing is written in stone at this point as I am still in the planing stage with all of this. The product I was going to use for generation is the Stirling Bio Power CHP unit here is the link, (broken link removed) I have been waiting a long time for a commercial capacity Stirling Engine to come to the market. What excites me about these units is the fact that it is the thermal differential between hot and cold that gives the power so if you increase the cooling capacity it is like adding additional BTU's to the action. My basic plan is to build a electrical generation capacity that will pay for all of my basic living expenses (mortgage, installation costs on the generation equipment, taxes, etc.). My provincial government has a procurement project that offers Standard Offering Contracts with a premium on bio-power paid for twenty years and I can see myself setting up a lifestyle where I have reduced what I need to do to survive to feeding wood into a chipper and maintaining equipment that is very maintenance free for the most part. With a twenty year contract through the government that makes the local distributers buy power from me at a good price I would never have an issue finding customers or clients or care what the stock-market was doing its just wood goes in power comes out and thank you very much for the check. The reason I am going to scale the operation down to the minimum to pay my basic expenses is not to take to much of the wood available. I hope if this works out I will document every step in great detail and start to develop procedures that any other person could create the same situation for themselves. So long as governments will secure long term contracts for procurement banks will lend money to small operators with bulletproof business models I would think.

I'll post any updates that come along and will answer any questions that I can if your interested.

PelletBoy...

 

[jebatty]

For almost taking a stab in the dark when I posted that I doubted that you could expect more than about 30% electrical generation efficiency, I hit it pretty close. The Stirlingbiopower website posts an estimated 27-28% net electrical efficiency with 75-80% CHP efficiency. This is right inline with estimates from other CHP applications.

How much of the excess heat will you be able to use in your H application? Can you use the H year round? What about the summer? Without being able to use most of the heat or distributing it to others, isn't your only real economic gain resulting from a an inexpensive fuel source? Nothing wrong with that, so long as inexpensive fuel is readily available. Is it likely that other markets for the fuel will develop which will impact the fuel economy you are forecasting?

If you proceed on this, keep us posted. I too would like to consider a CHP option.

 

[Ugly]

Pelletboy: How much are the stirling units ?