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Author Topic: Gravity feed max heat input running oil boiler on veg  (Read 10733 times)
martin W
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« on: November 04, 2017, 09:35:36 AM »

Hello all,

I'm looking at running an old oil boiler on waste oil (usually veg oils, but might have some fish oil content - the oil is really just leftovers, as opposed to waste).

I'm about to do some trials, connecting the oil boiler to an IBC as a storage tank (for now).

Ideally I would like to gravity feed from the boiler to the IBC so I do not need to pump. Both oil boiler and IBC will be next to each other so around 1m-2m pipe run on both flow and return in 22mm copper pipe..

The oil boiler is a 12-14kW model.

Can you gravity feed 14kW of heat?, at best I would have 0.5m head above the boiler, probably 0.25m



I've looked on web and can't seem to find anything about how much heat you can gravity flow. For trial puposed I could pump, but long term if successfull trials I do not want to pump (less electrical energy used).

thanks

Martin


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« Reply #1 on: November 04, 2017, 09:57:13 AM »

Normal heating oil produces about 10-11 kWh per litre, and hopefully your oil will be in the same ball-park. So you might need to get a flow of about 1.5 litres/hr to the boiler.
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« Reply #2 on: November 04, 2017, 10:01:32 AM »

By "old oil boiler" do you mean an old kerosene/28 sec type boiler. To burn any type of waste oil, cooking veg or even old motor oil you need a new head that goes on the front because to burn the thicker oil they have a different pump and high pressure air to vaporise the old oil. These heads are available on ebay then you can burn anything. Any oil boiler will work on 50cm head but you will need thicker pipes to get the thicker oil through. I have tried even adding just 5% old oil to my heating tank and it gummed everything up and filled the boiler full of soot. NEVER again.

https://www.ebay.co.uk/itm/Waste-Oil-Burner-10-50-kw-Best-Prices-on-Ebay/162684085451?hash=item25e0ba24cb:g:iVsAAOSwTuJYq1Uh



* waste oil.jpg (218.6 KB, 1600x900 - viewed 360 times.)
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dhaslam
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« Reply #3 on: November 04, 2017, 10:40:14 AM »

There  should'nt be much difficulty in feeding heat by gravity to the BIG but you would probably need to raise it a bit and use at least 28mm pipe.   You will need a thermostat on the tank  to avoid overheating.  Without using a loading valve the temperature will be fairly uniform all over.
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« Reply #4 on: November 04, 2017, 11:51:02 AM »

I read some info about burning thicker oils in a standard boiler, iirc they preheated the oil to reduce the viscosity so the standard burner could be used.To achieve that  they used an electric oil preheater at startup, the copper oil feed pipe from the preheater was then wrapped around the flu, when the flu came up to temp a stat switched off the preheater.  The advantage is you can switch over to  burn commercial heating oil if you run out of  veg oil....

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« Reply #5 on: November 04, 2017, 07:12:10 PM »

I think 12kW should be ok with a gravity circuit, if as D Haslam suggests you use 28mm pipe and keep the horizontals as short as possible. Why not stick a couple of gate valves in the pipework so that you could insert a pump between them without draining down if the boiler cycles too much?

Desp
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martin W
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« Reply #6 on: November 05, 2017, 07:54:33 AM »

Thanks for the reply's all,

I am planing on pre heating the 'waste' oil before it entering the boiler. Short term, I am planing to start the boiler on kerosene, then change over to the heaitng oil.

The oil boiler was free, as I removed it fully working when someone upgraded to a mains gas boiler. Its an old Trianco TRO12/16.

Originally I was going to make a waste oil burner (ala youtube) and make a flue boiler from scrap, then I had this given to me for free so thought I'd give it a go as it had all the electronic controls on it anyway.

I managed to plumb it up to the IBC yesterday, so time and weather allowing I will fire it up on Tuesday. I used 22mm pipe as I didn't have any 28mm - 1" BSP compresison fittings. Plus it was scrapp 22mm pipe I used. Return is around 1m long with a drop of around 3". it has 2 bends made with pipe bender. Flow is aorund 400mm and has one 90 de gbend and a 30 deg bend, both again made with a  pipe bender. If I used 28mm I would have had to use solder elbows so a tight 90 anyway. The flow pipe work rises around 6".



We'll see if it cycles too much without a pump. First run will be on kerosene, then heat the waste oil in a tin (with blowtorch) and then turn over to waste oil. I am more concerned if it will actually run on heated waste oil thnad the gravity, but I don't wan tit kettling and just could not find a ready reconner on gravity feed and kW's

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martin W
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« Reply #7 on: November 05, 2017, 08:02:23 AM »

On gravity flow and heat input I seem to remember seeing a calc on engineering toolbox where it would show how much water flow rate you would get with a given head and temperature difference.


I seem to remember I get around a 6-8 deg C difference on my thermal store when heating with the wbs boiler.

What do others get as a temperature difference?

from this flow rate I think I can work out how many kWs it will handle.

edit,

for some more info her on converting pascal to m/s flow rate

https://sciencing.com/how-7562015-convert-kpa-liters-per-minute.html

also engineering toolbox shows a table of heat height to flow rates with temp
https://www.engineeringtoolbox.com/gravity-heating-systems-d_189.html

so I should get somewhere around 41- 48 pascals per meter head.. ive got about a third of that..

so around 16 pascals

so 16/983=0.01627
square root it = 0.01627"5 = 0.1276 gives fluid velocity in meters per second

find volume of 1m of pipe
22mm = 0.32 lites

so 0.32x0.1276 = 0.0401 litres per second

=0.0704 x 60 = 2.44 litres per minute
= 0.0704 x 3600 = 147 litres per hour.

So how much flow to get rid of 12-14kW of heat at delta T of 10 deg C... (although its probablt going to be around 5 deg c)




« Last Edit: November 05, 2017, 09:44:52 AM by martin W » Logged

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« Reply #8 on: November 05, 2017, 10:11:02 AM »

hello,

So how much flow to get rid of 12-14kW of heat at delta T of 10 deg C... (although its probablt going to be around 5 deg c)

- It takes 1.16kWh to lift 1000litres by 1C so 11.6kWh will lift it by 10C. You have to pump the 1000litres in 60minutes, therefore 1000/60 = 16.67litres/minute
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martin W
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« Reply #9 on: November 05, 2017, 07:37:22 PM »

hello,

So how much flow to get rid of 12-14kW of heat at delta T of 10 deg C... (although its probablt going to be around 5 deg c)

- It takes 1.16kWh to lift 1000litres by 1C so 11.6kWh will lift it by 10C. You have to pump the 1000litres in 60minutes, therefore 1000/60 = 16.67litres/minute

Funnily enough I had a ball park figure of 10kW needed around 1m3 flow per hour..

thanks for that A.L.

So it looks like its going to cycle a lot... oh the joy of tinkering...

Smiley
 
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« Reply #10 on: November 06, 2017, 07:27:32 AM »

You can always try fitting a smaller jet in the burner, that way the output of the boiler will be reduced and could reduce the boiler cycling significantly. Using a higher temperature delta between boiler and tank would also help as that would reduce the rate of fuild transfer required (double the temperature delta and half the flow rate). Fitting larger pipes would also help though maybe more involved I guess. If it is just the cycling you need to reduce you might also try fitting a local tank/store/buffer close to the boiler so it could take the heat for a longer run and then transfer that to the main tank over a longer period.
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martin W
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« Reply #11 on: November 10, 2017, 10:08:24 AM »

I have a 300 watt towel rail heater which I am fitting to a tank which will heat the oil up to 75-80 degrees. Rough working out the 300 watt can heat around 2.5-3 litres per hour from 0-70 degs C. I will insulate the first bit of 10mm copper pipe, before it enters boiler. The 300 watt heater will be thermostat controlled

Long term I will probably need a local heater right next to burner. I might make a heat box with the 300 watt heater in next to burner and 2 litres or so oil capacity and use the oil boiler flow pipe work to heat the main oil tank.

Sorry this is going off topic of gravity flow...

Will post if it gravity flows ok when I get to test it out... might be this weekend..

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martin W
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« Reply #12 on: November 15, 2017, 05:52:54 PM »

Well finally fired it up on Tuesday.... no go on the gravity flow... Heinz! 22mm pipe and 0.2m head didn't work... boiler got up to max temp with almost no heat coming up the pipe from top of boiler... Fork.

Bit the bullet and had to buy a pump (at least I can reuse it for other factory trials). I will start a new thread on the oil boiler running on the vegi/fish oil once it sit running and when I got more questions. Stuff I've read so far sugguests heatign oil to 70-80 Deg C and also uppin gpum pressure and using a smaller nozzle (also probably a solid cone as oposed to ring cone).

Thanks all for the help/



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Woodstove owner since Feb 2011 Tongue (yes it's finally off the pallet)
Solar Water Heating since 17th March 2009, 2.94kW PV since Dec 2011
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