BC: CORN VS WOOD PELLETS
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We had a discussion about wood pellets coal etc on RR;'s site last week, including how much you can grow per acre per year. Turns out there is more money in pellets than corn!;
consumerenergyreport.com.
A dry kg of wood has about 20Mj energy content.
The current best commercial energy return for a wood to liquid process, gasification and Fischer Tropsch, would give you 10MJ liquid fuel, but at quite some cost. You would also receive about 1MJ as electricity from the process heat.
Wood to methanol will give slightly better energy yield, up to 60%, but no one is doing this.
To make pellets, you use about 10% of the energy, so 18MJ, and then get 90% of that from the pellet stove/furnace/boiler, so 16MJ of heat.
We can also use the woodchips for electricity, by gasifier-then ICE (25% eff) and you will get 5MJ electricity PLUS 10MJ of waste heat from the engine (5MJ exhaust, 5MJ coolant) which you can use directly.
The 5MJ of electricity can be used to run a heat pump, and with CoP of 3:1, you will turn the 5Mj into 20MJ of heat, for a total of 30MJ.
The real question is the $$. Turning wood to liquid fuel is very expensive, and needs large scale plants - which means transporting the wood a long way. You can densify it first by pelleting, or torrefaction, which incurs more energy loss but saves on transport.
Wood to liquid yields 10MJ fuel, or 0.08gal, worth about 16c, and 1MJ elec (0.28kWh) worth about 2.8c, for a total of 18.8c
Wood pellets sell wholesale for $160/ton, and that is 8% moisture, so they are $174/ton, but you have used 10% of the energy to make them, so $157/ton, or 15.7c/kg - a better return. For the ton of pellets (8% moisture) you get 18.4GJ of energy, and 90% of that, from your furnace is 16.6GJ (16.3MMBTU), so you are paying near enough to $10/GJ - close to a residential NG rate.
Doing gasification-electricity route yields 5MJ electricity, worth 14c, plus 10MJ of heat, which we'll value at using what we get with pellets, $10/GJ=1c/MJ. So, the total is 14c+10c=24c/kg, or $240/ton.
Just for reference, the current futures market for 2x4 lumber is about $270per thousand board feet, or about $207per ton. But you need good straight wood for lumber, and some of the wood (20%) as energy to mill and kiln dry it. A ton of wood in the field yield 2/3 a ton of lumber, using the remainder as energy
So, a (dry)ton of wood, is worth;
$139 as lumber
$140 as electricity only
$174 as wood pellets
$188 as liquid fuel plus some energy
$240 as electricity and heat
What is wood being used for today?
The lumber industry is barely profitable, and is shrinking.
There are some stand alone wood to electricity plants, but they are only marginally profitable, and same for the cost of getting wood to co-fire with coal, unless subsidised.
The world pellet market has doubled in volume, twice, in the last decade, to ten million tons/yr. It is the fastest growing and most profitable wood products market. The equipment is simple, and any sawmill can be adapted to make them. It is even profitable to ship them from Vancouver through the Panama Canal to Europe!
There are a couple of demo wood to liquids (FT) plants in Europe, and one being built in Edmonton, Canada. They are VERY capital intensive, and seem to need to be paid to take wood (wood waste)
Doing electricity plus heat, needs a use for the heat. One of the largest consumers of wood pellets, Sweden, makes extensive use of CHP plants with district heating systems, and is building more of them.
I am working on a project to do wood CHP at a local commercial greenhouse - you can see the difference in value for an electricity project when there is a beneficial use for the heat!
The capital cost for wood to liquids is a big hurdle, as is the scale problem and even if there is a (new) cellulosic ethanol process, I doubt its economics will be much better.
Wood to electricity can be done at any scale, from as low as 10kW, and thus at any place. If you can do it anywhere, you can take it to a place that needs a lot of heat.
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