Oil drum incererator design

[Dave Baker]

Wanting to make one of these for myself to burn garden waste and household rubbish and maybe in time to make something to heat the garage in winter. Came across this web site with design details for a 900 degree C incinerator.

What puzzles me is why it needs such large air holes. 11 x 50mm air holes at the base and a further 8 x 60mm holes further up. As an airflow specialist in the design of car engine cylinder heads I know how fast enormous volumes of air gets through very small holes with just the 15 psi of our planet's atmospheric pressure pushing it.

It seems to me that a few half inch holes would feed any size of fire that could possibly burn in an oil drum. I imagine these people have done research and experiments before settling on the optimum design but it still stumps me. Any comments?

[Nthkentman]

Wanting to make one of these for myself to burn garden waste and household rubbish and maybe in time to make something to heat the garage in winter. Came across this web site with design details for a 900 degree C incinerator.

What puzzles me is why it needs such large air holes. 11 x 50mm air holes at the base and a further 8 x 60mm holes further up. As an airflow specialist in the design of car engine cylinder heads I know how fast enormous volumes of air gets through very small holes with just the 15 psi of our planet's atmospheric pressure pushing it.

It seems to me that a few half inch holes would feed any size of fire that could possibly burn in an oil drum. I imagine these people have done research and experiments before settling on the optimum design but it still stumps me. Any comments?

[docholliday93]

I don't think you're allowing for just how small the pressure differential is likely to be - if we assume that the air inside the drum has expanded so much it has negligible mass the differential will be about that between th e top and the bottom of the drum - somewhere around .03 psi (using a lot of handwaving, so I'd quite accept there may be a factor of 10 either way, bu t still pretty small).

[Tim Lamb]

In message , Nthkentman writes

I think that design was developed by students at Silsoe Agricultural College. The original purpose was the disposal of plastic chemical containers. This use is now banned:-)

Avoiding black smoke was probably part of the specification. Of course you won't get 15psi pressure differential anyway. I can confirm that they work but siting under or near overhanging trees is a huge mistake:-)

[Dave Liquorice]

Well the big difference is that the engine has a sealed piston "pulling" the air in, thus in effect as the full 15 psi across the opening. The incinerator is just using the convection from the fire, it has pretty much 15 psi both sides of the opening.

[The Other Mike]

Yes, you know nothing about airflow due to combustion :)

It's as near as dammit 15psi all round the combustion chanber. The only way to get the air to move is to heat some of it and then replace that air and heat it instantly and repeatedly. The differential pressure is very low. You *need* big holes or some means of achieving a forced draught like a fan or a compressor.

[Huge]

Dunno, but on the occasion I made an 'ad hoc' incinerator with an oil drum, every time I used it, I made the air holes bigger, until I more or less cut the bottom out of it, then it worked a treat.

[harryagain]

You don't have 15psi of air pushing it. At light up you have zero pressure difference. When it's up, running and warm you will only have natural convection, ie maybe 1/100psi.

Your information is I think long outof date, I don't think you are allowed to burn plastic in a device like this. These sort of incinerators are very ineffective and polluting, you may find there are local byelaws against their use for any purpose. If you have neighbours you will definitely piss them off with the stinking thing.

[JTM]

Dave Baker

I'd be interested to know how you would heat the garage in winter?

How to use the heat without using the carbon monoxide and other noxious fumes?

John

[Huge]

I assume he's talking about making a room sealed stove. A rather larger one than the ones customarily made from butane cylinders.

[Dave Baker]

Yep. Ain't no one within a couple of hundred yards to pay no nevermind to any smoke out here in the country and it sure would be nice to have a wood stove with a little chimbley out through the wall or the roof to sit around and jaw with friends when the snow and rain is lashing down outside.

Or I could just stay in the nice warm centrally heated house and leave doing stuff in the garage till summer.

[Tim Lamb]

In message , Dave Baker writes

There are modestly priced workshop stoves available. Apart from discomfort, the downside to unheated workshops is the restriction of

10deg. C for most commonly used wood glues. My carpenter gets round this by only heating a small, insulated office area and then carrying stuff in there.

Yes:-)

You would probably need to keep a stove ticking over to be able to reach

*comfort level* for an hour or so pottering.

[Dave Liquorice]

Why tick it over? Good burn and even a tiny stove will whack out the heat. I suspect that Mr Bakers "shed" is bit bigger than 6x8 or even single garage size. So a tiny stove might not be a good idea.

If Mr Baker would like a centrally heated "shed" there is an Coalbrookdale Much Wenlock stove with boiler not a million miles from me not doing a lot... Nominal 5 kW. Buyer collects, it's frigging heavy!

[Tim Lamb]

I was thinking how long it takes my stove to go from room temp to say

300 deg.C.

[Dave Liquorice]

I doubt your stove gets anything close to 300 C. Ours doesn't get much above 100 even flat out and measuring the iron parts away from the boiler.

"Ideal" woodburner flue gas temps are only in the low 100's to low

200's C.

Serious offer, it sat in the garage...

[Adrian]

Our woodburner hits 350degC on the outside, according to my IR thermometer.

[Grimly Curmudgeon]

Bingo. And I've found the best way to achieve quick, simple and easy smokeless combustion of some very horrible stuff is a forced air blower (like an old furnace fan or HVLP turbine - even a car blower) feeding tangentially into the drum. Using that, I can burn my waste and no bugger knows about it.

[Tim Lamb]

You're right. I've just checked the thermometer. Hot would be 200 deg. C and 300 is in the too hot range. Burning dry Oak, temperatures on the welded steel door frame reach in excess of 200.

[Dave Liquorice]

Of course, I thought I made a mistake once but I was wrong. B-)

Our stove has a socking great boiler fitted, nominal 10 kW output, but only 3 kW to the room so I expect the casing is a bit cooler than a non-boiler stove.

[Dave Baker]

Yes obviously the pressure differential is very low compared to an internal combustion engine but I think I've figured out why the design I referred to has such large air holes. It's to generate very high temperatures with massive oxygen supply and burn the contents as quickly and thoroughly as possible. In other words a pure incinerator rather than a heat source.

I've realised this is not what I'm after. I want a steady heat and for the fuel to last as long as possible so I clearly need much less air induction. I think I'll have to just suck it and see but I'll start off with a few 1/2" holes and I can always enlarge them later. I may even need to make flaps to control the air intake to regulate the burn speed.