openspaceman

This is about right for biomass in general and hardwoods but pine has higher lignin and if we are talking chipped wood rather than whole trees I think it would be 5.2 @10% mc wwb They base their working on 18.6MJ/kg oven dry, a figure used in the stove community for biomass in general. It's so specific a figure that I think the writer trawled it from past papers or an internet search rather than anything empirical.

The key is to burn smokelessly, which means maintaining a flame. Failing that you are right, the smoke needs to be exhausted before it can condense onto the flue walls. This means keeping the temperature above the dew point of any condensible tars in the smoke (just about impossible) and water (a bit more than 100C) all the way up the flue. As the flue has a thermal mass it's always going to be cold enough at start up. A thin SS flue which is insulated will get to temperature faster than a brick flue. I've seen single skin ss perforated by corrosion from being run too cool, the solution was to insulate it. It's the need to prevent condensation in the flue that makes one reason a woodburner less efficient than a condensing gas boiler.

Even then the energy used to do the drying is always more than necessary to just evaporate the water. Some of the water in wood is "free" water and some weakly "bonded", as wood dries the free water migrates out quite easily and the wood does not change size or shape much. After that (aka the fibre saturation point) the moisture removed is associated with the cell structure and its loss causes the structure to shrink. most of the shrinkage is tangential, which is why you see radial splits in a round log, then a lesser amount of radial shrinkage and very little longitudinal shrinkage. The ratio of the tangential to radial shrinkage is an indication of how stable the wood in a plank will be and is why woods like oak are better quarter sawn to avoid the differential. As wood dries below 25% mc wwb this bonded water is in equilibrium with moisture in the surroundings. As the capacity of the air to absorb moisture goes up ( i.e. its relative humidity goes down) moisture migrates through the wood and is evaporated. There is an equilibrium established between the wood and the air. In my house the rh in summer is around 55% and the temperature now is 18C, the equilibrium moisture content of wood will be around 10% on a wet weight basis on a wet day with no heating in the winter it will be around 15% ( given time for the moisture to migrate through the wood to the surface) An interesting side effect of the water bound to the cell structure having a weak bond is that there is a small energy change in addition to that needed to evaporate the water, this shows up in a hysteresis in the equilibrium moisture content depending on whether the relative humidity is increasing of decreasing. For most of our burning purposes these effects are insignificant and drying to the fibre saturation point is the most bang for buck. If we make some simple assumptions, like ignoring the ash produced and allowing a flue gas exit temperature of 150+C to avoid chimney problems then a simple formula for the energy we release and have available for heating will be: hardwood 5.2kWh/kg oven dry wood-0.75kWh/kg of moisture softwood 5.5kWh/kg dry wood -0.75kWh/kg moisture So a cubic metre of scots pine weighing 1 kg green with 0.4kg of dry wood in it and 60% mc will yield about 1.88kWh from the stove if burned efficiently, dry it to 30% mc wwb and it should give 2.6kWh, a 17% difference. As others have pointed out the advantages of drying below the fibre saturation point are largely to do with clean burning rather than energy gains. Whilst advocating burning wood as dry as possible I don't think much of a burner that cannot cope with 25-30% mc wwb wood.

I agree totally but some allowances have to be made for all technology. I live in a suburb which is mildly attractive and I did think hard about this. Locally there is a development with solar tiles and they are only conspicuous because they are slightly shinier than the rest of the roof (mock slates). Had this house still had a slate roof I'd have considered them.

It's 100% efficient compared with the roof tiles its covering. 8 today from 3.9kW installed capacity.

but I'll bet by then the wood had already noticeably deteriorated I guessed volume wasn't a consideration, so the extra 25% or so from the branches isn't much value. Are the trees up to above 0.05m3 to 50mm top? When I did pine thinnings for psr in the 80s i'd managed to fell and sned about 150 poles/day in these sizes of pine first thinnings but I think the trees were 20 years old and that was 600 miles south of you. Lodgepole pine is probably a nightmare to sned in comparison to scots. How do your costs compare between whole tree chipping at stump and shortwood harvesting to yard then chipping? BTW in djbobbins original calc of 28m3 of wood chipped that would make an awkward heap of 80m3. Stacked as poles it only occupies 40m3. Removing the bark at harvest retains more minerals on the land and reduces ash from the boiler.

This is known as sour felling, allowing transpiration to continue and remove moisture. Will the needles drop off? I've not noticed a lot of needle dropping off lop and top after a thinning, at least not in a season. I suppose you intend just motor manual felling and chipping? Stuff dries much better if harvested with a machine set so it takes strips out of the bark and then it can be stored near point of use, seasoning. Small pine doesn't season well in its bark.

Nowadays I try and stick with kWhr all the way but your figures look well within the ball park. Actually on a mass for mass basis softwoods are higher cv than hardwood (because of higher lignin content). We imported softwood pellets that were over 20MJ/kg even with 10% moisture, they were douglas fir I think. whole tree chips will be lower.

The good places I knew seem to have disappeared. Last time I had a brake band relined the chap said that it was asbestos based material that needed rivets and modern stuff was bonded, modern stuff also had lower friction coefficient.

Probably better just to blow air through the heat and let the heat from the microbes lower the rh of the air directly. Most big chip consumers just take the hit and lose the vapour (and enthalpy of vapour) up the flue it's only small boilers that don't cope with high moisture. Local firm to me just stockpiles logs in the round during the summer as chip heaps respire energy and the mould clumps the chips.

It's chlorosis, possibly from canker in the graft unions

and even that's 50 more than I was taught it was when in school. Good job you're not darker or we'd be in bigger trouble

25 years ago I got a tp960 on account of the better chip it produced from roundwood, it's up in Norfolk but with you and Farmer Rod both asking in the same area... The friend who borrowed it is now gone over to biogas to run the farm, and put electricity in the grid, so it and his two boilers are surplus: "One boiler is a Baxi Multifuel 35 kW with a 600 litre hopper. The other is a Gejs with a bigger hopper for tractor bucket filling, over 2 m3. It is 50 kW. Both have oxygen sensing."

Yes and watch for a vinegary smell which indicates one bit has got over hot I should have refreshed the thread before replying, I hadn't seen your reply as I was trying to fathom the "check engine" light on daughter's vitara which I'm borrowing tomorrow.

Fill an oven proof container, weigh, stick in electric oven for 24 hours at 120C, weigh, empty container, weigh it. Difference between the container weight and when full of oven dry chips is the oven dry weight (ODT). Diffence between the container and green weight is wet weight. wet weight-ODT is water, water divided by wet weight times 100 is moisture content wet weight basis. You can do the same much quicker using the defrost setting of a microwave but the temperature can easily run away . you need to monitor till there is no change in weight. probably but drying a thin layer then heaping it may be safer, you'll need it below 25% to stop it sweating/mould.

350.org

Yes but the proof is in the eating and a good practitioner with a 3 stone fire is hard to beat. The priority is to improve indoor air pollution but this was probably not properly recognised until Kirk Smith pointed out the problems. Me too though I always hoped to be more involved I think it was Tom Reed that first used the term for discarded tin cans used for raw materials. I first heard how important it was from a chap with a trekkasaw who worked on ships, he said that in the pacific people dived after the waste that was thrrown overboard, that would be around86. That's funny, me too, I nearly gave up and went to bed, off again in 7.

Yes but they are high mass stoves, these were promoted in the 80s especially in South America, as improved stoves, the lorena was one but whilst they do control air supply to some extent they soak up a lot of energy in heating the stove. This is why there is a move to lighter weight, tincanium, stoves that can be fabricated locally by blacksmiths from old oil drums and such but also using mixtures of clays that are lighter and better insulators. The first picture shows the woman using a blowpipe to fan the flames, the fire vents to the room in which a young child is sitting. The flames are touching the pot which is blackened with soot, the pot is a good shape but there will be greater heat losses with no lid. Interestingly the woman does not have the blowpipe to her mouth, intuitively this makes sense until you wonder that we inhale 21% oxygen and exhale 18%. Similar comments on the second picture, is she removing a pot from a steamer? Note the soot stained upper walls. Some say the smoke preserves the thatch by killing bugs but it's a high price to pay breathing the air inside. I'm not sure of the third picture, are they burning rushes? And a coil to heat water in a sunken two pot stove? Last picture indicates some sort of drying or smoking of stuff hanging from the ceiling. What country? Nepal? We discussed cooking and lighting in Nepal and I was appalled to be told the average life expectancy was about 45, this when I was 50 and no a decade later I still don't feel I'm ready to shuffle off. The site is down atm but if you are interested visit BioEnergy Discussion Lists when it comes back online.

That's a three stone fire with a tin can pot. It does demonstrate some of the problems with a three stone fire though, the uncontrolled combustion air and, more importantly the cold pot being in the flame. This quenches the flame and that means the flame has not burned out, hence the sooty deposit on the can. This is an inconvenience but in the rural third world the cooking may be taking place indoors, sooty particles then circulate in the room and are a source of Indoor Air Pollution, because these particulates are a complex of carbon and phenolic based organic compounds, they are not only carcinogenic, like Benzo-a-pyrene in tobacco smoke also, but are implicated in susceptibility to acute respiratory infecting in youngsters. This and unsanitary water supply are the biggest child killers. The rocket is in effect 1/3 of a three stone fire with a bit more length for combustion to complete, it still has the problem of allowing too much excess air through the stove which other designs try to control. The kelly kettle is a precursor to the rocket and I did notice one being used in some of the early footage of the young princess Elizabeth.

Are you sure you don't mean tincanium? Most of these designs started off life as coffee, paint tins etc.

Length of a piece of string question, when I packed up as Sudbrook closed I was forwarding 2.5m hardwood pulp onto trailers at 58 tonne/day over 1km for £4/tonne and using about 30 litres of diesel. It was OK if nothing went wrong. I can get woodchip to you for cheaper than you could fell and chip it if you take it in the summer and in 25 tonne loads.

I dug mine out on Monday and the rope and harness, all worked as I remembered it, section felling an old Lawsons, rope management left a bit to be desired but it's been 10 years or so. I always found it a bit low powered for anything but early softwood thinnings, preferring a 262 for most work.

Yes but never is a long time, highways authorities change and lose records which is why my advice, and that of the NFU last I heard, is in addition to yours and is to re affirm regularly.

Arrgh! Not in my bailiwick if I see the application. I won't oppose a sensible diversion round a headland or away from a yard or dwelling but hemming in a prevously open path will get me going. In fact when a land owner wishes to change the route of a currently fenced in path one of the conditions I strive for is the open aspect. Now where are you

Yes and the 18 ton trailer bit is a bit hard to achieve with regard to axle spacings and it means the tractor must weigh less than 6190kg What taxation class are these mogs used under?