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#190156 - 11/07/09 08:53 PM Experimental Oil Burner : Part One:
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
All images and information submitted by ECN Member Alan Belson:

Quote:
Heres some pics of an experimental 20kW+ nominal [75,000 btu/h] used-vegetable oil pressure-jet burner I built. The pics are self explanatory, I hope. It burns #2 diesel oil, vegetable-oil or mixes of the two.
See the schematic diagrams:









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The burner is shown operating, covers off, on neat vegetable oil preheated to c. 200C, with 10 bar indicated gauge:




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And at an estimated 13 bar[200psi] [gauge removed to avoid bending the needle ] Note the typical very long vegetable-oil flames. The estimated power, from fuel consumption figures, is 26 & 30 kW. I should add that I get an inexhaustible supply of old burners, some nearly new, from a friend who is retro-fitting wood-pellet burners locally:





Through a nozzle, a gear pump delivers a measured quantity of high-pressure oil, as a cone of micro-droplets, into a blast tube past electric ignition arcs. An air blower delivers all the combustion air to the blast tube. The process is sequenced by a Danfoss LOA 24 type Burner Controller. For #2 oil, the air and fuel are usually delivered at ambient temperature - other fuels may need to be pre-heated and supplied with heated air. Note: As oil pressure increases, droplet size reduces. As oil viscosity increases, both droplet size and, counter-intuitively, the flow rate both increase. As temperature of oil increases the viscosity reduces, as does the flow . These changes are not linear, for instance doubling the pump pressure does not double the flow rate.

This burner has 2 tandem electric air-heaters mounted inside an insulated copper-sheet muffle, inserted between the blower and the blast tube and carried in a welded steel support frame. Thermal-break gaskets are fitted at both ends. This allows the fuel and air to be heated to preset temperatures for trials. Oil is heated as the oil line is in the hot air stream.









Edited by Trumpy (11/09/09 05:16 PM)
Edit Reason: Having a little change around

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#190161 - 11/07/09 09:46 PM Re: Experimental Oil Burner : Part One: [Re: Trumpy]
homer Offline
Member

Registered: 09/30/04
Posts: 68
Loc: Vancouver, WA, USA
Trumpy,
Excellent job on the design! One comment - many boilers in the states are required to have a separate line voltage series of safety switches for over pressure, over temperature etc. which remove operating power to the fuel supply and blower and activate an input to the controller. (Very similar to centrifugal chiller safety circuits). These safety devices or limit switches are only manually resettable. The idea is that if the controller fails, a serious event is avoided.

You have obviously given this project a lot of thought and work. Congratulations!

Homer

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#190163 - 11/07/09 09:52 PM Re: Experimental Oil Burner : Part One: [Re: homer]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Homer,
It's not my work, I was only posting the thread here for Alan.
No way could I build anything this cool. whistle
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#190169 - 11/07/09 10:08 PM Re: Experimental Oil Burner : Part One: [Re: Trumpy]
homer Offline
Member

Registered: 09/30/04
Posts: 68
Loc: Vancouver, WA, USA
OOPs!
I should have read the whole post!

Good job Alan!

Homer

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#190251 - 11/09/09 05:39 PM Re: Experimental Oil Burner : Part One: [Re: Trumpy]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
{2nd part of the above post due to image count limitations}:

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Ignition HT enters the hot-air stream through porcelain bushes, using plain copper wires with air-gap insulation. When properly adjusted the ignition arcs emerge as ionised air 'flames' :




A 1.5kW triac [dimmer] switch controls one heater circuit. Option switches give between 0-3000W of
electrical heat and a 1400W adjustable control band on the dimmer. The heater units are from 1500W hot-air guns, butt silver-soldered in line, an inexpensive option. I used double-wound ceramic insulated conductors inside the muffle for the front heater, as the wires can be subjected up to c.220C [430F]. New electrical circuits interface with the existing burners LOA24 Controller and the 'call for heat' signal. A variable thermostat delays the burn start until the required ignition temperature is achieved.

The theoretical electrical heat required is c.1600W when burning neat vegetable oil at 200C preheat and supplying 115% fully heated stoichiometric air, [ 15% excess over the theoretical air needed to burn all the oil supplied ], to a 0.5GPH nozzle at 10 bar [150psi], plus losses - say 1800W.

Why preheat to this level? When burning heavy oils, it's vital that an absolute minimum of unburned fuel enters the firebox. Unburned heavy fuel will not evaporate like diesel oil if it gets in the firebox - it will polymerise to varnish, spoil the heat exchanger performance and would eventually become a fire risk. 0.5mm [20 thousandths of an inch] of oil resin/ash on a boiler tube will cut heat transfer by up to 50%. This burner was designed to have clean, near-instant ignition and near instant flame-out at cycle end, by preheating the burner head to the full working temperature before firing and by sophisticated valve-work inside the pump and nozzle. A special pressure cut-off valve is fitted inside the burner nozzle [Delavan Protec 135 psi] and a separate drive motor runs a special Danfoss LE oil pump, divorced from the blower motor for trials purposes. This pump relieves the injection line pressure at burner shutdown. In fact, in its latest version, this burner has three motors fitted, so I can run RH or LH pumps recycled from scrap burners, as the whim takes me.

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A 120-second run-on timer, [arrived at by experiment ], is fitted to the blower so it continues blowing air after flame-out. This protects components and wiring upstream from residual heat. Trials established the temperatures of preheat obtained from various Dimmer adjustment positions on the bezel, see pic:







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As part of my setup, I have built a centrifugal oil-filtration plant. It's essential that used oil is cleaned to 20 microns or better to avoid clogging the nozzle. Actually, I found in practice that if used VO is left to stand for a month or so in 20 litre sealed plastic jugs and carefully decanted, it requires minimum filtration to clean it up. All additional electrical components have been fitted into an auxiliary box. Relays have been fitted to carry the increased amperage imposed by the air heaters and for circuit logic requirements. I found it very difficult to get flexible wiring to lay neatly, so in the end, I didn't bother!:





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All the safety features of the donor burner have been retained. I also retro-fitted a reclaimed higher voltage transformer,[7500v+7500v], for fatter ignition arcs.
All the other modifications are concerned with the elevated temperatures and the strength of the assembly.

A steel frame supports the additional weight of the new machine. The fuel injection line has been moved outside the chassis and the photo-resistance cell has been
relocated, because the heater elements would interfere with it's function. Temperature is now limited to 200C, as I found a Viton rubber O seal is fitted in the Delavan Protec nozzle assembly:






The electrical diagrams show only those circuits added to my standard burner. The main modification to the regular burner circuit is to create and intercept a 'call' signal before it gets to Pin 1 on the LOA24 and to interpose my own control, logic and power circuitry. Minor
modifications are to lead out neon feeds from the Controller Pins, rewire the blower to be independent of the Controller, wire in pump motor #2 to Pins 1 and 2 and to put in switches to Pin 7 [ignition] and the 'Call' signal to have 'disable operation' features. I also have the igniters running 100% of the burn, normally they shut off after successful ignition.

Note that some of the pics are already outdated, as detail changes occured during the build and trials.

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#190252 - 11/09/09 05:45 PM Experimental Oil Burner: Part Two: [Re: Trumpy]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
My experiments on burning neat vegetable oil in this machine were not a complete success. I'll be honest, I had hoped to fit this burner to our boiler but despite all the hard work and careful design, other problems appeared.

Ignition could be adjusted to be 100% reliable from about 150C electrical preheat upwards. The flame is instantly stable with a clean, frighteningly sharp cutoff with the Protec valve fitted, but the pump pressure and air setting have to be increased substantially to get a good clean flame, which of course increases the oil consumption, flame length and power.

At 10 bar [150psi] , occasional Roman Candles, [ larger, slower-burning droplets emerging from the flame tip, too big to burn in time inside the flame] occurred. These are furnace varnishers! Increases in oil pressure solved that problem, only to create another. A very fine haze of unburned microscopic 'motes' of oil appeared, [clearly visible in the darker 20 bar flame pic, where I deliberately increased the pressure to get a good pic ] , as a 'halo' surrounding the flame.



Theoretically, the oil droplets need to be between 20 and 40 microns in diameter. The very nature of the vegetable oil appears to be the problem, for even when heated [to 150C or over] to obtain a viscosity similar to diesel oil, the long-chain molecular nature of the fuel seems to produce droplets in a wider range of sizes than the ideal and they take longer to burn. Above 40 microns, tendency for Roman Candles. Below 20 microns and the micro droplets are travelling so fast they can go right through the flame without burning at all!

The killer problem, however, is the necessary burner idle times, when vegetable oil can set like varnish on or in the nozzle itself. I lost two nozzles within days, clogged with resin overnight. Even though I get my nozzles from the States legally tax and duty free via the internet at US$4 each, [ US $8 for a Protec insert ] such losses are unacceptable. I took to cleaning out the Vegetable Oil from the burner to conserve nozzles by running a neat diesel wash through the pump at the end of each experiment, which turned out to be a EUREKA MOMENT!

Accidentally burning a small can of wash-oil, [after my carefully annotated oil-soaked tape labels all fell off, the story of my life!], I found that vegetable and diesel mixtures can be burned without preheating at all. Trials, using cleaned dog-meat cans as fuel tanks, with the pump flexibles dunked in them, established: 10% VO in diesel burns superbly; no changes in pressure or air required. 20%; a slightly longer flame, air up a tad. 30% required further slight increase in air. 40% produced rare Roman Candles, but increased pump and air pressure solved that, even longer flame.

50% and 60% VO required slight [80C] preheating or an initial 15 second neat diesel burn to ignite, produced either a smattering of Candles and/or a slight oil haze. At 70% VO, 100C preheating was essential for assured ignition, both candles and/or haze a lot worse. Within wide adjustments, up to a 40% VO cut can be burned consistently, with no ejection of unburned oil.

Back at the Drawing Board, a cunning plan began to evolve. I now intend to use a regular, unmodified pressure jet burner, with a regular off-the-shelf, low power [150W] Danfoss FBHB5 inline 70C oil preheater lifted from a doner burner [for consistent fuel supply parameters] and to burn a mix of VO and #2 diesel at about a 33%-40% VO cut. Fitting the Danfoss LE pump and Protec anti-drip valve will aid cleaner burns. I reckon I'll need to increase pump pressure slightly to about 11-12 bar, but have ordered some 0.4GPH x 80 hollow-cone nozzles from my supplier in the States to cut back the power slightly.

This is because a VO/#2 flame is longer and there is a limit to the size of flame that can be accomodated in a given boiler firebox. The visible flame should not impinge on boiler tubes or furnace plates, btw, as this causes sooting. To mix the oils, I am building an insulated, 150W heated [@ 50C] 30-liter 'day-tank' in stainless steel for the VO, [to prevent any fat granules in the used oil clogging filters], supplying a small variable-output washing-machine grade peristaltic pump. This will accurately dose about 10-15 ml of VO per minute, teeing into the Burner's oil pump diesel inlet line, via a small additional 200 mesh filter = a 33-40% mix at c. 20kW power.

The Danfoss pump will be reconfigured to run single-pipe supply, to avoid pumping VO back to the diesel tank from the LE pump's relief valve. The day-tank will need refilling about every 7 days or so. A simple delay circuit at burn-end will allow the burner to run on for about 60 seconds on diesel only, thus flushing the system at each burn, allowing an assured diesel-only start and preventing nozzle varnishing. Plus, 100% #2 oil can be burned if required at the press of a switch.

Here's the schematic:



Hopefully, the new burner will be fitted and running our heating this winter. More pics and results anon....

Alan"


Edited by Trumpy (11/09/09 05:47 PM)
Edit Reason: Formatting

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