build my own prefurnace

[biffidum]

Hello, I am new here. I am trying to put together a plan for building a large prefurnace for a boiler. Is there any expertise here with these things?

I am working on the plans for a sloped grate rectangular prefurnace with primary under grate air and secondary air entering with the hot gases at the point of entry into the boiler vessel.

I am most curious about the ash and its removal. Currently I have the ash collecting in a trough at the base of the sloped grate with a small auger to drive it to one side. The whole affair is sealed off and would require the blowers to be powered down to remove the collected ash.

Also what type of steel would best suit as a grate or should I be going with a refractory grate?

 

[Singed Eyebrows]

Interesting, it appears your "boiler" is an air to water heat exchanger & you are just piping the hot furnace flue gas into it. If your prefurnace is not gasification I can see some possible creosote problems. As long as you have at least 300 to 350 F degrees out of your boiler this should be ok. I'm doing some guessing here as I haven't seen the plans. Can't tell what material you need without knowing the temps involved & design. Randy

 

[Singed Eyebrows]

OK, If you are doing what I think, you don't need gasification. You can see 2400 degrees+ flue gas coming off a furnace with primary under air. Only caution I have for you is DONT IDLE this. Grate material that will work is heavy cast iron, I can get items cast here pretty cheap, don't know about there. I know first hand the temps that can come off a wood fire with air blown under it. I think these temps can even exceed gasification temps at 2400 to 2700 degrees. Next best from cast iron would be heavy welded steel plate in my opinion, without making something out of inconel, the grate really doesn't see the high temps with air blowing through it, Randy

 

[biffidum]

The prefurnace is supposed to gasify the wood chips - small intense updraft (actually horizontal) type. At the entrance to the boiler secondary air is injected into the producer gas and combustion occurs. I have to figure out how to build the prefurnace to produce adequate gas for the boiler. The commercial gasifier prefurnaces I have seen use refractory for the grate, but it is not off the shelf stuff. I don't have a way to cast a grate. This may be way too much for me to do, although I do not easily shy away from complicated DIY projects.

I was wondering if anyone out there had any experience and wisdom to pass on.

 

[vvvv]

http://www.hernironworks.com/conifer.html