Flat Grate Vs. Underfeed Stoker Design

It seems that all the old school stokers were underfeed type that use a "bowl" to burn the coal, yet all the newer companies use a flat grate. Is there an inherent design flaw with the underfeed that required a re-engineering to solve? I've seen both burn and they both seem to do an equal job of heating and reliability.

The amount of iron, size of motors, auger screws and tubes, etc etc make the underfeed type much more expensive to build. But they are so heavy duty that I think they will last decades longer than the 'average' bed-type stoker.

The bed-type stoker with a gravity hopper is a much simpler design, and the size of the motors and gearbox needed for the stoker and combustion make this type much less expensive to build and repair.

I think it's all the economics of building and selling new units

I think both types burn coal just as effeciently.

Greg L

I'll agree with greg the reason most newer appliances are carpet or bed stokers is due to the higher manufacturing cost associated with making an underfed unit. If anything I think the underfed are slightly more efficient and definitely work better in warmer weather when your just using the boiler for domestic hot water purposes. However a new efm is about 60 to 75% more expensive than say a Keystoker of equal size.

e.alleg,
The underfeed or tulip type seems to work better then the flat grate. The reason being is that the coal rolls as it is burning, working itself in and out of the fire. As coal tumbles it burns on all sides, making for better efficienty to get the oxygen to all parts of the piece coal. But cost is out of site.
Jerry

LsFarm wrote: But they are so heavy duty that I think they will last decades longer than the 'average' bed-type stoker.

On the other hand they have a lot more moving parts to break and if you get something jammed in the auger a lot harder to service. The augers have shear pins so no fear of breaking them... As far as life span goes some of the oldest furnces I have seen wer made by Losch and they use a bed.

I think the greatest thing going for the old Keystoker design, the one used in their boilers, is the simplicity of it. Simplicity also comes with limitations. The EFM and similar designs outperform the Keystoker for holding fire in the summer months and during power outages. I agree with the others in that price probably has the biggest influence these days on boilers and furnaces. As far as radiant stoves go I have to wonder how would you build a stove like that around an underfed type stoker and still have a reasonably sized stove that does not weigh some ungodly amount?

gaw wrote:As far as radiant stoves go I have to wonder how would you build a stove like that around an underfed type stoker and still have a reasonably sized stove that does not weigh some ungodly amount?

Well, Harman pellet stoves are an underfed design (but not the coal stoves). But, looking at the pellet stove design, I don't think it would last 5 minutes as a coal stove......

It probably wouldn't be that hard to miniaturize an old fashioned underfeed stoker and design it to a Keystoker sized free standing stove. It could still use off-the shelf small gear motors to drive the auger, and blowers, etc wouldn't change. Only the burn pot, tuyeres, and auger would be the new parts.

Dang, that would be cool!

Chris

Sounds like a challenge for Greg L to me!

Probably a few others on here capable of such a feat....

OK guy's get busy!

BK

bksaun wrote: Probably a few others on here capable of such a feat....

Everyone spending the money they save on tinkering. Greg is probaly in the hole.