Glen Farrow boiler smokey

[aspenarb]

I have a few friends running wood boilers and the smokey ones seem to be the ones that are over sized for the application. The oversized ones spend extended periods damped down and smouldering between calls for heat. I suppose the trade off is the capacity of the burn box and time spent loading. Just an observation which has no scientific basis

 

Bob

[cornish wood burner]

I have a few friends running wood boilers and the smokey ones seem to be the ones that are over sized for the application. The oversized ones spend extended periods damped down and smouldering between calls for heat. I suppose the trade off is the capacity of the burn box and time spent loading. Just an observation which has no scientific basis

 

Bob

Absolutely correct Bob except for the last bit. It has a very good scientific basis. Low fire box/ furnace temperature will give poor combustion. The large wood burners I run burn best/cleanest if they are run hard and I don't see any different principle for the smaller ones. I'm sure that is what Andrew (openspaceman) was endeavoring to find out but his query was not answered.

[Duffryn]

Hi Duffryn

Thanks for your input.

When you say secondary air input are you talking about the two side boxes that the fan pushes air through? And then am I right in thinking that the primary air in put is the bigger box section running up the middle on the floor.

Does anyone manage to burn these effectively without any smoke. It's quite odd some days it's smokes a lot and then others hardly not so much.

Thanks Grant

 

Yes the secondary air tubes are the highest tubes on the left and right hand side. Lifting the tubes themselves will improve boiler performance significantly ( been there , done that ) but will invalidate RHI accreditation. Having said this if the smoke only occurs on some days and not others then there have to others factors contributing. These could be load height, moisture content, heat demand placed on the boiler and potentially wind. What is the boiler being used to heat ?

Edited November 7, 2015 by Duffryn
Spelling

[BARNSLEY BOB]

when was timber felled, is it french import stuff.

variation in tannin and tar content and hence smokeyness .

[openspaceman]

Absolutely correct Bob except for the last bit. It has a very good scientific basis. Low fire box/ furnace temperature will give poor combustion. The large wood burners I run burn best/cleanest if they are run hard and I don't see any different principle for the smaller ones. I'm sure that is what Andrew (openspaceman) was endeavoring to find out but his query was not answered.

 

Yes you have both got the correct reason. There are many mechanisms that make it difficult to achieve a goo turn down ration with a wood burner compared with a gas flame, lower emissivity being one.

 

One can make a fair judgement of the reason for the smoke (which is just products of incomplete combustion) by its colour. Mostly we are probably talking about a mild blue haze and this is generally caused by the secondary flame being quenched before the offgas has been fully oxidised, what has happened is the flame has stripped the easy to burn hydrogen component from the mixture of compounds and the remaining carbon has reformed as a microscopic graphene based soot before it can be oxidised as it has moved beyond the flame into a cooler area, often the cooling will be by excess air or the aforementioned loss by radiation. These tiny particles then form a sol in the exhaust gas and the weak forces that hold them apart act over similar distances to the wavelength of light such that they pass all but the blue component which we see reflected as a blue haze.

[Celtictimber]

when was timber felled, is it french import stuff.

variation in tannin and tar content and hence smokeyness .

 

 

Yea it's French beams felled probably two year ago however it's all been kiln dried

[Celtictimber]

Yes the secondary air tubes are the highest tubes on the left and right hand side. Lifting the tubes themselves will improve boiler performance significantly ( been there , done that ) but will invalidate RHI accreditation. Having said this if the smoke only occurs on some days and not others then there have to others factors contributing. These could be load height, moisture content, heat demand placed on the boiler and potentially wind. What is the boiler being used to heat ?

 

 

The boiler is heating a container which we use to dry beams and also heating our office building about 7 radiators

[Duffryn]

The boiler is heating a container which we use to dry beams and also heating our office building about 7 radiators

 

Ok , try filling the fuel chamber with fuel up to the secondary air tubes, set the fan speed to 7. If you have clear emissions from the flue after the first 15-20 mins then the problem will be the height of the secondary air tubes. I presume your boiler is located outside so there is no restriction on air inflow to the boiler fans ? If so and the boiler still smokes after the test above then the issue will almost certainly be the fuel.

[BARNSLEY BOB]

has the tar condensed on the inside of the boiler.

 

may need some dry beech and sycamore to burn it off.

[Celtictimber]

Ok , try filling the fuel chamber with fuel up to the secondary air tubes, set the fan speed to 7. If you have clear emissions from the flue after the first 15-20 mins then the problem will be the height of the secondary air tubes. I presume your boiler is located outside so there is no restriction on air inflow to the boiler fans ? If so and the boiler still smokes after the test above then the issue will almost certainly be the fuel.

 

 

Thanks Duffryn I'll give this a go over the next few days and let you know how it goes.

Grant