Size of chip for biomass boiler

[Pierre_robbo]

i'm just having an eta woodchip burner fitted and intend to run it on homegrown wood chipped at 25% moisture at G30/50 sizing.

 

while hiring in a huge chipper to make this makes perfect sense i've also heaps of brash <50mm and less that i was considering putting through a small hired in chipper.

 

Obviously this will create a much finer chip, has anyone put such material through a woodchip burner? has anyone had any issues with such material?

[NI Tree]

a non biomass chipper will not have screen's and there for you will have a higher risk of blockages in the boiler, and the better wood you put through the better the chip quality

[farmer rod]

i'm just having an eta woodchip burner fitted and intend to run it on homegrown wood chipped at 25% moisture at G30/50 sizing.

 

while hiring in a huge chipper to make this makes perfect sense i've also heaps of brash <50mm and less that i was considering putting through a small hired in chipper.

 

Obviously this will create a much finer chip, has anyone put such material through a woodchip burner? has anyone had any issues with such material?

 

This afternoon my boiler stopped, cause;- one spiky twig that stuck in the opening of the rotary valve.

 

This is the first stoppage in two years of running, which I think is quite remarkable. We had our brash pile chipped through a Heizohack and compared with chipping good round wood the product is ugly. Having said that, the machinery has coped very well in the two months we have been burning this particular pile.

 

I would add, that I have removed a fair amount of "out of gauge" material from the feeder because the twigs and shards tend not to fall into the auger trough and build up into a birds nest, which if left for long enough would obstruct any chips.

 

If you are on site to sort out problems, then having imperfect chips is ok, an arb chipper, ie without a screen may well produce a better chip with twigs, but has it got enough output to make it worthwhile?

[openspaceman]

This afternoon my boiler stopped, cause;- one spiky twig that stuck in the opening of the rotary valve.

 

This is the first stoppage in two years of running, which I think is quite remarkable. We had our brash pile chipped through a Heizohack and compared with chipping good round wood the product is ugly. Having said that, the machinery has coped very well in the two months we have been burning this particular pile.

 

I would add, that I have removed a fair amount of "out of gauge" material from the feeder because the twigs and shards tend not to fall into the auger trough and build up into a birds nest, which if left for long enough would obstruct any chips.

 

If you are on site to sort out problems, then having imperfect chips is ok, an arb chipper, ie without a screen may well produce a better chip with twigs, but has it got enough output to make it worthwhile?

 

Rod is spot on, problems tend to build up so just one out of spec piece is unlikely to jam the system, I managed to lose a 13mm combination spanner and the auger passed that even though it was longer than the pitch of the flights. Over time we had more problem with fines packing in the auger trough than twigs jamming. Having said that I would advocate a simple oscillating screen to get over length stuff out of the heap but I have never had a budget to do it.

 

More of a problem is with fine material not having pore spaces to allow primary combustion air up from the grate. This is exacerbated with damp chip which needs much more primary air. Essentially burning wood with a <25% mc is a doddle because it really only needs over fire (secondary) air as worse case is you carry char over to the ash which is good for the soil (biochar). On the large scale very dry wood can cause problems with slagging on the grate or overheating the grate which meant some flue gas recirculation may be necessary.

 

Of course an arb chipper can be used, I've managed to stick a tonne of ash wood through a Forst into my hopper in less than an hour. With the roller speed set low it produces a fine chip.

[Pierre_robbo]

Thanks guys. Some important points for me to bare in mind. I'll start with some decent stuff and then maybe blend in a little finer chip later on.

[farmer rod]

How about some pictures of your installation

[Pierre_robbo]

this is the first install. Test fix. Concrete panels going in tomorrow!

[openspaceman]

[ATTACH]151930[/ATTACH][ATTACH]151931[/ATTACH][ATTACH]151932[/ATTACH] this is the first install. Test fix. Concrete panels going in tomorrow!

 

Probably too late to change but I had big problems with a bottom unloading silo. The drag arms being run off the auger sheared the auger after 4 years. The sloping auger will increase stress. I'd look to putting a second motor to drive the arms. This set up is fine for pellets but arb chips have a propensity to have a negative angle of repose i.e. a cavity will form rather than chips drop to the sweep arms.

[farmer rod]

nice place, is it just to heat your house? and what are you putting over the chips?

[Pierre_robbo]

Openspace - I was thinking about putting some bollards in the pit to almost reduce the down force in the agitator. Encourge a little bridging if you like. This should hopefully reduce the load on the gearbox and auger. I've 2 house, one I let out and adjoined a tiny village hall. This 50kw will be heating the lot. Just installed concrete panels today. Looks great I'll add pics tomorrow. With respect to chip type, I have endless ash and birch tree around so u was (the last I cut down was 140 years old). I intend to chip every last lb of the tree but how to economically chop the brash is my biggest concern. Pto chipper...? Crap Chinese 8'' on eBay start at £1500 or I could spend 20k