Kiln Drying Firewood - Yourself

[Duffryn]

I cannot see it worth burning 20% mc fuel in a boiler as large as this, nor would I expect to get to 85% of the wood energy into water but the figures are fairly straightforward, first need to clear up the differece between power and energy, power is the amount of heat the boiler will give out in a unit of time, so we'll say a 175kW(thermal) boiler. Run this flat out for an hour and it will have released 175kWh(t) of heat, some of this heat will be lost up the flue or out of the sides but accepting the 85% into water figure that means the water receives 3.57MWh of heat over the 24 hours running, in practice the boiler has to modulate to an average figure less than this or something tends to blow off.

 

Of the 20% mc (wet weight basis) wood that needs to be burned each kg burned perfectly yields about 4kWh of heat and we need 4200kWh so fractionally over a tonne as Duffryn says. Logs are far to valuable to burn doing this.

 

Next you must consider the conversion of energy in the heated water to drying the logs. This will vary enormously with many factors like insulation, saturation of air and temperature of moisture laden air leaving the kiln. We aimed for a coefficient of performance of 1.11kWh per kg of water removed from wood on a simple system. One could do better but with much increase capital cost.

 

Short cycle times are entirely dependent on temperature as once you pass enough air over the log surface to evapourate moisture it's the time that takes for the water to move out of the log that limits you.

 

I don't disagree. Just to clarify the RHI emission certificate will be based on wood at a certain m/c . In this case that is 20%. More fuel will be required at a higher m/c and the boiler will fail the RHI emissions by an even greater margin. I agree you should not use logs to fuel a batch fed boiler, in fact few would recommend doing so.

 

The issue with the Glenn Farrow boiler and Kiln is that it will not deliver anywhere near 85% efficiency or meet the RHI emissions in practical use

[Duffryn]

Please correct me if I am wrong - 50 tonnes for circa 7.5 tonnes of fuel. Is this not 50 m3 of loose fill containerised logs.

 

Yes I corrected the post the 50- tonnes should have been 50m3

[arboriculturist]

Absolutely spot on ! In Germany there are annual tests on biomass boilers and it would not surprise me if the UK followed.

 

There is a significant correlation between emissions and fuel load. On a batch fed boiler the emissions test is difficult to pass and so the temptation to use a totally unrealistically low fuel load is high. Whilst the boiler may have "passed" the manufacturers RHI emissions test owners will need to be happy of the potential risk they run in using a boiler that will not be RHI compliant in every day use. Your comparison to the MOT emissions test is a great analogy.

 

The test itself is carried out by the manufacturer and an independent test house. It is not currently a requirement for the boiler to be tested in use or after commissioning.

 

There is some interesting points here. However I know someone close to where I live who has imported a boiler themselves and OFGEM are requiring that the have the NOx and Particulates independantly tested on site and the results to be submitted as part of their RHI application!

 

The boiler was supplied with the correct certification when delivered, so is OFGEM's request 'reasonable' / justifiable?

[Duffryn]

There is some interesting points here. However I know someone close to where I live who has imported a boiler themselves and OFGEM are requiring that the have the NOx and Particulates independantly tested on site and the results to be submitted as part of their RHI application!

 

The boiler was supplied with the correct certification when delivered, so is OFGEM's request 'reasonable' / justifiable?

 

Interesting. This rather shows the direction that Ofgem are going in and supports the risks I highlighted above

[difflock]

I suspect that OFGEM could argue a very "reasonable" case at Law, that despite CE conformity compliant certificates being supplied with the Euro imported boiler, the entirely different UK fuelwood, necessitates an "installed" test.

I do also suspect that ALL the major boiler manufacturers use absolutly prime dry wood(e.g. clean beech at 12-15% moisture) for their testing regime/published output figures.

Would that suspision be a tad cynical?

PS

Fascinating stuff above.

I could only(in my head)justify burning difficult to process/minimally processed/low grade/commercially unsalable wood to dry firewood for sale.

Or simplistically run through a chipper/chip fed boiler(as I believe was alluded to somewhere above)

Though this would of course make the boiler even less likely to pass emmissions tests.

cheers

marcus

[Duffryn]

I suspect that OFGEM could argue a very "reasonable" case at Law, that despite CE conformity compliant certificates being supplied with the Euro imported boiler, the entirely different UK fuelwood, necessitates an "installed" test.

I do also suspect that ALL the major boiler manufacturers use absolutly prime dry wood(e.g. clean beech at 12-15% moisture) for their testing regime/published output figures.

Would that suspision be a tad cynical?

PS

Fascinating stuff above.

I could only(in my head)justify burning difficult to process/minimally processed/low grade/commercially unsalable wood to dry firewood for sale.

Or simplistically run through a chipper/chip fed boiler(as I believe was alluded to somewhere above)

Though this would of course make the boiler even less likely to pass emmissions tests.

cheers

marcus

 

 

Probably a bit cynical (but I understand your train of thought !) The wood used as fuel in the rhi emissions test is sampled as part of the test and the resultant certificate will be based on the m/c of the fuel tested. If they used 10% beech then the RHI certificate would be limited to 10% m/c wood.

[openspaceman]

Ah thanks for the reply. The timber I tested was fresh felled, crosscut, split and centre of log tested. However I know internal moisture levels can vary a lot.

 

I don't use that method, I dry a sample in the microwave and then spend a few days watching its weight increase.

 

You must use use the full 40ft of container to get in 36M3 in stillages. Are you running a chip/pellet boiler?

 

Ours was for a client and it was freshly milled 2.5" reject boards, even so I think it would have lost weight between milling and kilning. It was over 10 years ago, I am not active in that field now.

[renewablejohn]

Keeping out of this thread after my comments last time where ridiculed but now appear to have come home to roost. I will stay smug in the knowledge that my solar kiln comes up with the RHI goods without the need to burn my stock in the process.

[Mortimer Firewood]

Probably a bit cynical (but I understand your train of thought !) The wood used as fuel in the rhi emissions test is sampled as part of the test and the resultant certificate will be based on the m/c of the fuel tested. If they used 10% beech then the RHI certificate would be limited to 10% m/c wood.

 

Hi mate been hearing good things about you from some of the local land owners would like to discuss a few things regarding the log pro and where your going with it. I was very interested at the time but had other things to attend to. Can you pm me your number please.

 

Regards Mike

[arboriculturist]

Keeping out of this thread after my comments last time where ridiculed but now appear to have come home to roost. I will stay smug in the knowledge that my solar kiln comes up with the RHI goods without the need to burn my stock in the process.

 

Sorry I missed the posting a while back. Sorry to hear that your post was not well recieved by some. Do you have a Solar Kiln that you dry in bulk with? I am a great supporter of using the power of the elements, but of course not everyone is able to.