Topic: Gas burner jet heat outputs (Read 7813 times)

gondolier88 · « **on:** February 18, 2013, 11:05:40 am »

Does anyone here know where I could see a chart listing heat outputs of the different sizes of gas jets (Kw/hr or Btu's, doesn't matter which)?

I can't seem to find one anywhere!!

Greg

dreadnought72 · « **Reply #1 on:** February 18, 2013, 01:23:06 pm »

Greg, I'd tend towards a more practical calculation. Can you work it out from propane's ~46MJ/kg?

Weigh the use of gas (in kg) in a known time (in seconds), and then the output in watts would be:

watts = 46*10^6 * gas used / time

gondolier88 · « **Reply #2 on:** February 18, 2013, 02:36:48 pm »

Hi dreadnought,

Thanks, let me explain a little more clearly; I am designing a gas burner and have come to the conclusion that I require 15,500btu's or 4Kw of gas per hour at full tilt, using butane/propane.

I now need to see which gas jets would give me the desired heat output (technically I should be saying heat input, but you get used to saying things so often...!).

I have now since discovered that BSS can supply gas jets rated to 7400btu's/hr, and I wanted to run a split line burner system anyway, so that is a good result. I know there is a shortfall there, but I have a margin of 25% to play with anyway, so 14,800btu's/hr would be more than enough.

A chart with gas input per hour would certainly be of use to modellers however, perhaps someone is sitting on one somewhere?

Thanks again.

Greg

AlexC · « **Reply #3 on:** February 18, 2013, 04:03:21 pm »

Hi Greg,

Gas jets are usually rated for flow/hr; Not a specific BTU rating.

The flow rate is determined by several factors, such as temperature, pressure, specific gravity, jet profile, jet angle etc.

You can only correlate the Heat value (BTU's) per unit volume of a specific gas providing you know it's calorific value and take into account all the variables as above.

A good reference relating to gas, and several other types of fuel, jets can be obtained from the following: -

www.peconet.com/products/eclipse.htm

Scroll down towards the bottom and download the Engineering design PDF. It has several tables for gas jets... and lots of other good stuff.

Calorific values for Propane is 21,660 Btu's per lb
Calorific value for Butane is 21,300 Btu's per lb

Providing they are burned completely.

Hope this helps.

Regards.

AlexC

gondolier88 · « **Reply #4 on:** February 18, 2013, 10:37:19 pm »

Hi Alex,

So you'll know where there is a chart listing flow rates....?

Sorry to be so direct, being a gas engineer I usually work on the other side of the calculation so CV's and flow rates are fine, but mean nothing if I can't see a listing comparing jet sizes.

Greg

AlexC · « **Reply #5 on:** February 18, 2013, 11:46:15 pm »

AlexC.

AlexC · « **Reply #6 on:** February 19, 2013, 12:04:30 am »

Hi Greg,

As a gas enjineeer I'd have thought you had such info at your fingertips.

I do have a chart giving average Btu per orifice dia, after the necessary conversion Maths has been done for you... but it is not jet manufacturer specific.

Best I can do.

Take it or leave it.

AlexC

gondolier88 · « **Reply #7 on:** February 19, 2013, 07:58:00 am »

Quote from: AlexC on February 19, 2013, 12:04:30 am

Hi Greg,

As a gas enjineeer I'd have thought you had such info at your fingertips.

I do have a chart giving average Btu per orifice dia, after the necessary conversion Maths has been done for you... but it is not jet manufacturer specific.

Best I can do.

Take it or leave it.

AlexC

Hi Alex,

Yes I thought so too, but it appears not, even mighty Google wouldn't stump up with an answer.

Btu per orifice dia. sounds perfect to me, would you be able/willing to post it on here for everyone to see?

Thanks for your help.

Greg

AlexC · « **Reply #8 on:** February 19, 2013, 11:10:56 am »

Eh?...

Quote

would you be able/willing to post it on here for everyone to see?

I already have, in my last post, and anyone can download it.

AlexC

gondolier88 · « **Reply #9 on:** February 19, 2013, 08:05:44 pm »

Sorry, still getting used to the 'new' forum layout!

Thanks Alex!

Greg

SteamboatPhil · « **Reply #10 on:** February 19, 2013, 08:26:14 pm »

Just a quick thought and those in the know will correct me (I use petrol in my burners) but the heat you require and the discharge rate of the gas you must surely have huge problems in gas container size (giving the run time you are after) and frezzing of the pipes must also be a consideration.
happy to be corrected, as I say we use vaporising petrol, so gas to me is still "dark magic"

P

gondolier88 · « **Reply #11 on:** February 19, 2013, 09:23:04 pm »

Hi Phil,

Not my problem as such, just doing some calc's for a burner. The boat is 7ft long and 15" wide, so space isn't too much of a premium. The CampingGaz R904 cylinder is 170mm dia. and around 220mm high, plus regulator, and has a max. draw-off rate of 1300g/hr- a good margin more than is required.

Although, now we've done all this, it looks like a new engine is going to be used instead of the large 1"+1"x1" engine as was, it looks like a modest ST Twin Launch is going to be used- although only 1/8" less stroke (quite a lot in model terms), it's valve gear is a lot better than the last engine, so operating margins don't have to be quite so large!

Having fun with larger than normal marine model engineering anyway, even if it is just on paper at the moment.

Greg

kiwimodeller · « **Reply #12 on:** February 20, 2013, 08:17:19 am »

Greg, if temperature drop and consequent drop in gas pressure becomes a problem simply connect two, three or even four gas cannisters in parallel, all turned on at the same time. I was taught this many years ago when working in the hire business and renting out LPG heaters to heat workshops etc. Running multiple gas cylinders was the only way to keep the heater output up. It is all to do with the ratio of surface area to volume of gas being drawn off. The greater the area the less the temperature drop. I have now got two of my bigger boats running two cylinders and the flame now remains constant for a much longer range. Hope this helps, Ian.

derekwarner · « **Reply #13 on:** February 20, 2013, 11:54:06 am »

OK Guys........
Ian....you have shown images of twin gas containers in a previous build .....the squat tubby ones with the EN16 threaded connection
My question is ...

what is the nominal gas pressure in these disposable gas canisters prior to discharge ?

I am not after a lesson on the Boyles & Charles gas equation.........just a simple answer............Derek

gondolier88 · « **Reply #14 on:** February 20, 2013, 08:36:08 pm »

Thanks Ian, I try to keep connections to a minimum on gas supply where possible. Also, the cost of replacing 3-4 small cylinders for every 1hr run would be prohibitive, the R904 cylinder is a welded steel cylinder that you pay to own, only paying a nominal re-fill fee when empty- works out a lot cheaper in the long run.

Also, being able to use a commercially available gas regulator allows me to rate the burners properly, as well as making spares an easy option for the owner, rather than having to hunt around for fittings that are model specific.

Thanks for your help though, and you are right, coupling cylinders can be a great way to combat draw-off problems.

Greg

steamboatmodel · « **Reply #15 on:** February 21, 2013, 01:06:34 am »

Have you looked at converting a camp stove or portable BBQ unit to run this? Another possibility is to check with the ride on Model Train guys and see what they are using.
Regards,
Gerald.

flashtwo · « **Reply #16 on:** February 21, 2013, 11:13:08 am »

Hi Greg,

With my Stuart D10 driving a 5 inch prop at 500RPM, the gas consumption has been in the order of 4 g/min.

As you know with my monotube boiler set up (see flash steam boiler control thread) the system would freeze up if it wasn't for drawing off the liquid fuel from the inverted gas cylinder (460g type), passing it through the fuel evaporator coil located around the burner and sending back to the servo gas valve. A feed water cooled attemperator is used between the fuel evaporator coil and the servo gas valve to prevent high temperature fuel gas from heating the valve.

I've used my own jet which has a 0.7mm diameter. The biggest factor in gas throughput is still the ambient temperature, which governs the gas boil-off and subsequent fuel delivery pressure. The servo gas valve compensates a lot for the changes in delivery pressure. The pressure v. ambient of the gas cylinder has been roughly about 1.5Bar at 10degC, 3Bar at 20degC and 4Bar at 35degC, although I'd have to go through all my old notes for the exact figures.

As you know, once in the gaseous form, any fuel throttling will cause a temperature drop (this has been a good way of finding unintentional pipe blockages).

Despite all the success I've had with the above set-up, the very best performance last year was on a very hot day and I shall still be experimenting with the steam plant when it is installed in my 6ft 3inch Edwardian steam launch this year.

Ian

gondolier88 · « **Reply #17 on:** February 21, 2013, 08:59:09 pm »

Quote from: flashtwo on February 21, 2013, 11:13:08 am

Hi Greg,

With my Stuart D10 driving a 5 inch prop at 500RPM, the gas consumption has been in the order of 4 g/min.

As you know with my monotube boiler set up (see flash steam boiler control thread) the system would freeze up if it wasn't for drawing off the liquid fuel from the inverted gas cylinder (460g type), passing it through the fuel evaporator coil located around the burner and sending back to the servo gas valve. A feed water cooled attemperator is used between the fuel evaporator coil and the servo gas valve to prevent high temperature fuel gas from heating the valve.

I've used my own jet which has a 0.7mm diameter. The biggest factor in gas throughput is still the ambient temperature, which governs the gas boil-off and subsequent fuel delivery pressure. The servo gas valve compensates a lot for the changes in delivery pressure. The pressure v. ambient of the gas cylinder has been roughly about 1.5Bar at 10degC, 3Bar at 20degC and 4Bar at 35degC, although I'd have to go through all my old notes for the exact figures.

As you know, once in the gaseous form, any fuel throttling will cause a temperature drop (this has been a good way of finding unintentional pipe blockages).

Despite all the success I've had with the above set-up, the very best performance last year was on a very hot day and I shall still be experimenting with the steam plant when it is installed in my 6ft 3inch Edwardian steam launch this year.

Ian

Hi Ian,

Thanks for that, you can always be relied upon to put some figures up

Interesting figures they are too- it certainly shows the risks that await if gas cylinders are caught in a fire.

I was trying to white metal a bearing the other week in minus 2-3deg.C, with a large Butane torch- it took two hours!! I was about the same temperature as the cylinder by the time I had finished!

I could read back through your thread again, but, being a bit cheeky- what is your nearest estimate to efficiency of your flash plant? Just to give me some idea if my calculations are looking right for the larger Twin, I was hoping for somewhere near 40-55% on what will be a fairly large Yarrow three drum with feedwater heaters and steam dryer.

One idea I could be tempted with would be to take-off liquid Butane, pipe it into a reciever which has a coil from the engine exhaust in, from the receiver it would go through a boiler pressure controlled regulator, straight to the burner, as engine demand rises, so would gas temperature/efficiency?

Greg

frazer heslop · « **Reply #18 on:** February 21, 2013, 09:40:26 pm »

I made a burner that takes liquid gas from the tank and uses a pre heating tube within the burner I seem to remember the idea cam from Malcolm .It works very well and doesn't suffer from freezing.
best wishes
frazer

flashtwo · « **Reply #19 on:** February 22, 2013, 01:25:02 pm »

Hi Greg,

With your receiver idea I would put the gas through the coil and the steam into the open vessel where its expansion wouldn't be restricted, it wouldn't involve having a pressure vessel. I think the steam (at 100degC) would heat the liquid fuel less agressively than the burner's pilot flame that I use, which can result in temperatures in excess of 200degC (hence the need of the attemperator).

Regarding boiler efficiency, I think my monotube boiler with its 240 sq.in copper to water heating area (you have to be careful not to use the combustion gas to copper area which is much larger) has a very high efficiency of perhaps 90% or more.

This is based on knowing exactly the feed flow, feed flow inlet temperature and the steam outlet temperature. Also, the stack gas outlet temperature is about 160degC, which only about 25degC above the steam temperature.

The heat calculations on my spreadsheet seem to reflect the practical experience with the overall efficiency of heat input to shaft output of about 2%!

One thing I can't seem to get right is the steam consumption figures with the spreadsheet suggesting a value five times higher than expected. I know I'm using 1.7g/s (calibrated) of feed and the outlet steam temperature is 135degC (saturated)
but there is something I'm doing wrong. The Stuart D10, as you know, has 3/4in diameter with 3/4in stroke and has four power strokes per rev. I shall continue investigating my calcs and steam tables.

Ian

gondolier88 · « **Reply #20 on:** February 22, 2013, 08:24:14 pm »

Hi Ian,

Yes, that is a better idea- it would certainly negate needing a pressure vessel. I agree, the burner flame is a little over-egging the matter.

I expected between 80-90% for your boiler, 90% is certainly very impressive, I'm glad you realised I meant the efficiency of the boiler, rather than the plant- oh dear, 2%- it's really quite depressing at model sizes isn't it! Although I think my estimate on 40-55% efficiency for the Yarrow boiler might not be too far off.

Could I suggest your spreadsheet is set up for steam input for 100% of the stroke, whereas cut-off will be at around 20-25% of the stroke?

Thanks for your help.

Greg

flashtwo · « **Reply #21 on:** February 23, 2013, 09:44:06 am »

Hi Greg,

I've amended my spreadsheet to incorporate the cut-off figure - thank you very much for your insight.

I've recalculated the consumption, but still get large consumption figures. It makes me think that I'm passing wet steam to the engine. Water in the steam of only 34mg/stroke would account for the discrepancy between theory and practice.

In the past I have experimented with a super heater tube in the monotube boiler, but I have read somewhere that you can't have superheat in the presence of water, i.e. a steam separator is required.

SteamboatPhil does a very good demonstration of superheating steam just by directing a cirgarette lighter flame onto the steam pipe and speeding up the engine.

Anyhow, this means I've got lots more experimenting to do, which is great! The object now is to obtain very dry steam and in doing so, reduce the feed to a quarter of the current value.

Ian

steamboatmodel · « **Reply #22 on:** February 23, 2013, 02:52:26 pm »

I wonder if at our scale if we can really produce Superheated Steam or are we just drying it? I came across a site that has some information that may help.
http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/what-is-steam.asp
Regards,
Gerald.
PS I will not be held responsible for any headaches resulting from gray matter exercise from reading on above site. I am now off to find my headache meds.

gondolier88 · « **Reply #23 on:** February 24, 2013, 11:20:00 am »

Quote from: flashtwo on February 23, 2013, 09:44:06 am

Hi Greg,

I've amended my spreadsheet to incorporate the cut-off figure - thank you very much for your insight.

I've recalculated the consumption, but still get large consumption figures. It makes me think that I'm passing wet steam to the engine. Water in the steam of only 34mg/stroke would account for the discrepancy between theory and practice.

In the past I have experimented with a super heater tube in the monotube boiler, but I have read somewhere that you can't have superheat in the presence of water, i.e. a steam separator is required.

SteamboatPhil does a very good demonstration of superheating steam just by directing a cirgarette lighter flame onto the steam pipe and speeding up the engine.

Anyhow, this means I've got lots more experimenting to do, which is great! The object now is to obtain very dry steam and in doing so, reduce the feed to a quarter of the current value.

Ian

I think you are probably onto something with assuming your getting carry-over. It does beg the question, even though you have worked out the water injection properly, is it worth reducing the amount you are injecting; a smaller amount of steam, but containing more energy? A smaller amount of water initially would also cool your boiler down less as well perhaps?

You are right with saying that you can't have superheated steam in the presence of water; not that it is because the water is there and is somehow stopping the steam being superheated, but water is an indication that true superheat isn't really occurring.

As Gerald says, it is very difficult to produce true superheat at model sizes- some of the larger miniature loco's manage to, but they can have around 10ft of stainless superheater flue off high pressure boilers with massive grate area and sharp and aggressive draught through the
boiler- which is great on a train, but isn't what you want in a sedate, quiet and elegant steam launch.

That said, would it be possible to arrange a model version of commercial processing setups, where sat. steam was put through a secondary heat exchanger with it's own heat source? A high heating surface, low flow rate heat exchanger, with a ceramic burner of it's own, gas controlled by a high temperature thermistor on the steam output line. Ian, one for you I think, especially as electrickery is involved!

Greg

News:

Author Topic: Gas burner jet heat outputs (Read 7813 times)