What is the Net Energy Yield for Wood Syngas?

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Discussion Overview

The discussion revolves around the net energy yield of wood syngas produced from wood gasification, specifically using softwood chips. Participants are exploring the feasibility of using wood gas as an energy source compared to traditional electrical utility prices, while also considering factors such as wood chip quality, moisture content, and gasifier efficiency.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Adam calculates the cost of wood chips and compares it to electrical utility prices, estimating a cost of $0.0155/kWh after accounting for engine efficiency.
  • One participant questions the moisture content of the wood chips, noting that it significantly affects energy yield and gasification efficiency.
  • Another participant challenges the feasibility of transporting wood chips at the stated price, suggesting that typical prices in certain regions are much higher.
  • Adam confirms the low quality and moisture content of the wood chips, estimating an energy density of 5 MJ/kg, while noting that dry wood chips yield higher energy densities of 15-20 MJ/kg.
  • There is a discussion about the efficiency of gasifiers, with one participant mentioning a figure of 70% efficiency and questioning whether this is accurate.
  • Adam expresses uncertainty about the net energy yield from gasification and seeks input on how much gas energy is produced from heating wood chips in a gasifier.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the net energy yield of wood gasification or the accuracy of the efficiency figures discussed. Multiple viewpoints regarding the cost and quality of wood chips, as well as the efficiency of gasifiers, remain contested.

Contextual Notes

Participants express uncertainty regarding the assumptions made about wood chip quality, moisture content, and the efficiency of gasification processes. The discussion includes varying claims about costs and energy densities, which may depend on specific conditions and definitions.

Adam9393
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Hello,

My name is Adam and I am experimenting with wood gas. I recently came across a really cheap wood chip source and would like to compare it against electrical utility prices. I am curious if running an old generator would be cheaper than off peak rates of $0.065/kwh.

As of right now, I have calculated that wood chips would cost around $0.0006/MJ (assuming 5 MJ/kg and $3.00/1000kg)

0.0006 x 3.6 MJ= $0.00216 / kwh

Efficiency of internal combustion engine is 0.14. I would need 7x the amount of energy to get 1 kwh.

0.00216 x 7.2 = $0.0155 / kwh.

This is where I am stuck. Does anyone know the net energy yield of wood gasification (softwood chips). If I could factor that into my price will I be pretty close...? Thanks!
 
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Do you know how dry the chips are? That makes a big difference.

https://en.wikipedia.org/wiki/Wood_gas_generator#Design said:
the humidity of the wood (usually 15 to 20%) and the water vapor created by the O- and H-atoms of the dry wood itself (about 0.4 liters of water loaded with organic substances per kg of dry wood) condenses during the gas cooling and filtering procedure and yields a liquid (see also wood tar), which needs specific waste water treatment. This treatment requires about 25 to 35% of the created wood gas energy.

There seems to be a large number of suppliers. https://en.wikipedia.org/wiki/Wood_gas_generator#List_of_commercially_available_systems
If you visit their sites, there might be some efficiency claims.

You should also read the accounts of others who did the same thing.
https://en.wikipedia.org/wiki/Wood_gas_generator#Media_coverage
 
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Adam9393 said:
My name is Adam and I am experimenting with wood gas. I recently came across a really cheap wood chip source and would like to compare it against electrical utility prices. I am curious if running an old generator would be cheaper than off peak rates of $0.065/kwh.

As of right now, I have calculated that wood chips would cost around $0.0006/MJ (assuming 5 MJ/kg and $3.00/1000kg)

0.0006 x 3.6 MJ= $0.00216 / kwh

Efficiency of internal combustion engine is 0.14. I would need 7x the amount of energy to get 1 kwh.
I don't understand; are you saying you would use the electricity for electric resistance heat? Why wouldn't you just use the fuel for heat directly like you plan to do with the wood gassification?
This is where I am stuck. Does anyone know the net energy yield of wood gasification (softwood chips). If I could factor that into my price will I be pretty close...? Thanks!
Googling "wood gassification energy density" yielded this:
The heat of combustion of "producer gas" — a term used in the United States meaning wood gas produced for use in a combustion engine — is rather low compared to other fuels. Taylor[13]reports that producer gas has a lower heat of combustion of 5.7 MJ/kg versus 55.9 MJ/kg for natural gas and 44.1 MJ/kg for gasoline. The heat of combustion of wood is typically 15-18 MJ/kg.
https://en.wikipedia.org/wiki/Wood_gas
 
Adam9393 said:
As of right now, I have calculated that wood chips would cost around $0.0006/MJ (assuming 5 MJ/kg and $3.00/1000kg)

Is it really $3 per ton? Even if it were free, it's hard to believe you can even haul it to your place of use for that.
 
phyzguy said:
Is it really $3 per ton?

Good catch. I missed that. In the south and PNW the prices are $30-$55 per ton.
 
The price really is $3 per tonne. Yes hard to believe..that is why I am super interested. The chips are not great quality and definitely will not be dry. That is why I assume a conservative energy density of 5 MJ/kg. Dry wood chips are around 15-20 MJ/kg. The distance to transport is not far...max 30 kilometers. I will have to factor this in.

For every unit of heat supplied to the gasification process how much gas energy is yielded. In some documents I have read that gasifier efficiencies are 70%. It has been a while since chemistry class... does this value make sense. If I were to use 1 kg of wood chips to heat up 1 kg of the same wood chips in a gasifier, I would be left with 0.7 kg of gas fuel?
 

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