Burning wood directly or making wood gas

[faslan]

is Burning wood directly or making wood into wood gas more energy efficient ?

 

i made a wood gasifier in home but i read some articles saying syn gas have very low heating value and i'm little bit confused

which process can give more heat

burning 1 kg air dry wood or making 1 kg wood into wood gas then burn

Edited May 20, 2014 by faslan

[CaptainPanic]

It really depends what you want to do.

 

If you make a gasifier wood stove, you avoid some smoke problems, and you burn the wood cleaner than when you use a normal stoves. But you must burn the gas directly. When you use a gasifier wood stove, or if you burn the wood in a conventional stove, you essentially burn all the wood on the spot, and create only CO2, water vapor and little other gases and ash. The efficiency will be roughly the same, but the gasifier will produce less soot.

 

Below, I also briefly discuss larger scale applications. This is not very relevant for you, since your home-made gasifier is much too small for that.

If you want to transport the fuel through a pipeline, it may be more convenient to make a gas, since logs don't travel through pipes very well. There are plenty initiatives worldwide to create methane (natural gas) from biomass. And I believe that very few, if any, are economically profitable. Gas and shale gas are just too cheap. You can make methane from the gasifier's syngas with an additional process step similar to Fischer Tropsch synthesis.

 

Also, the syngas you make will have a higher heating content (in "energy per mass") than the original wood, but you will lose some of the energy in the process (in absolute terms), because you obviously have to heat the wood to make the gas. So, for some applications it is better to have syngas.

Finally, if you want to make electricity, it may have an advantage to make gas, because it enables you to use a Combined Cycle Gas Turbine (CCGT), which has a much higher efficiency of electricity from fuel (55-59% according to wikipedia) than thermal systems which typically don't go much higher than 42%. That advantage may offset the losses in the gasification.