Improving Combustion for a Wood Shavings-Fired Boiler

I would also look into a way to put a catalitic converter in the system as it will clean and add more heat.

From the design of some rockets used by the German military during the Great War, vibration was a method used to increase the power output, and obviously made more power from the available fuel, hence more efficient combustion. But, I don't think this is a solution for a boiler, as the refractory would not stand the vibration.

You are obviously burning scrap, and probably have no choice as to the type of wood and its moisture content. Can the chips be pretreated (perhaps made dryer) prior to combustion? Probably not because of the additional price. Can they be blended with other fuel types to burn more efficiently and produce fewer regulated emissions? That would depend on the design of the boiler's firebox.

For example, a famous distillery not very far from me has boilers whose fuel sources are many: Nr. 2 Diesel, black coal, natural gas, scrap wooden pallets, barrel parts, etc.. How do they burn the wood products and maintain their emissions level at an acceptable rate? I don't know. Past the design of the boiler, the most critical component is the diameter, length, straightness, and smoothness of the exhaust stack. There is the area where I think a good boiler designer could help you.

Ing. Robert Forbus

It honestly sounds as if th ecombustion chamber is to big.

Combustion engineering makes round bottom fed retorts-or at least they did for coal stoker boilers and they burned wood pellets too.

I think you would bew money ahead by contacting them about an auger fed retort for this as this would be a perfect match for even the smallest pelletizer feeding a retort combustion chamber and you would not have the particulate problems in my opinion due to the very high burn temperatures acheived through the retort as the air is blown right through the auger to the base of the retort and they have clean clear exhaust gas.

Burning this type of fuel on a fluidized sand hearth has demonstrated great improvement in efficiency and emissions. Combustion air is pumped up thru sand that the fuel burns on top of. Energy products of Idaho manufactures and markets this equipment.

I would see if there is a way to cut the wood into smaller sized pieces for better and more uniform combustion - when coal is burned, it is first ground and then pulverized into a powder as fine or smaller than talcum powder - more surface area, more uniform sized particles for uniform combustion, etc. Once finely powdered, it is blown into the fireball with an air stream which helps with the oxygen content for combustion. I know you can't likely pulverize your wood chips, but I have seen in saw mills where they are run through chippers to get pretty small particle sizes - again, more surface and more uniformly sized makes for better control.

Plan B would be to investigate the catalytic option in the discharge stream.

My $.02.

The product we are burning is pretty fine--and very dry, being planer shavings from lumber that has been kiln-dried. The lumber is targeted at a 19% moisture content, but the shavings are probably more like 6%, since they are from the surface of the lumber. The shavings are fine, looking more like sawdust than shavings, since the lumber is sawn nearly to size in the sawmill and the planing process takes off only about 0.030".

My questions are posed because we are limited on the amount of money I can spend. I could definitely go to the big guys who do this work every day, with a sackful of cash and have a combustion chamber designed and built so fast my head would spin. But the paybacks I could show to install an "over the counter" new combustor would be pretty skinny so it would not fly for us.

My window of opportunity exists because we have budgeted significant maintenance money early next year to redo the refractory in the firebox. If I can come up with a better design, meaning: better firebox shape/airflow pattern/etc., then I could likely get a bit of additional money to rework the firebox into something better.

That makes the challenge for me. There are a few design parameters that I know I need to meet: maximize residence time in the firebox, ensure that the oxygen levels are met but not significantly exceeded (excess air beyond the stoichiometric ideal cools the hot gasses), ensure adequate mixing of combustion air in the combustion chamber, etc.

By the way, the existing system puts out about 15 million BTU. I think a properly-designed combustor might add a few more percents to the "British Thermal Underwears" that we are happily churning out now.

Opinions or points of view?

Thanks,

Jon.

Convert to wood chips & saw dust and brequett them.

You can also mix them with garbage or any agro waste and brequett them.

This way yyou will not only improve combustion but also save up to 50% wood/fuel

plus you can sell the berquetts as fuel to anybody for winter fire-places.

Look up the google for Brequetting machines.