biogas -> light -> heat

Welcome David House.

I've looked at alternative energy sources and found biogas to be the one with the best potential for indoor lighting.  Considering the amount of gas that would need to be consumed, there would be considerable ancillary heat produced.  I've considered putting together some sort of lamp to take advantage of light and heat:  A glass mantle containing the lamp topped with a metal flu.  If suspended from the ceiling, a reflector can direct the lighting downward.  The metal flu would aid in dissipating heat, as well as directing exhaust to a central vent.  Does this make any sense?

Ken,

Ken Peavey wrote:
I've looked at alternative energy sources and found biogas to be the one with the best potential for indoor lighting.  Considering the amount of gas that would need to be consumed, there would be considerable ancillary heat produced.  I've considered putting together some sort of lamp to take advantage of light and heat:  A glass mantle containing the lamp topped with a metal flu.  If suspended from the ceiling, a reflector can direct the lighting downward.  The metal flu would aid in dissipating heat, as well as directing exhaust to a central vent.  Does this make any sense?

Sure, absolutely. It is hard to find biogas lights in production, excepting for sources in India and China, but depending on what parameters are applied, biogas can be used for lighting during the hours of dark, and is a very good alternative as compared with other things that might be available. For example, most of the world lives in villages, and in a village (or some other situation) where electricity is not available, kerosene, oil lamps and the like might be used, but most of those alternatives are either more expensive or provide less light, as compared with a well-designed biogas lamp. (By "well-designed", I mean that it will extract the maximum lumens out of the energy in the methane as possible. One means of doing this is by the use of regenerative heating, where the biogas itself is heated up before combustion by the heat from the biogas that has already been burned...)

As far as how much biogas would be needed, let me quote from The Complete Biogas Handbook, p. 99

Gas lamps of good design (inverted mantle, high pressure), can achieve 2.3 lumens per Calorie (of energy input as biogas) per hour (0.58 lumens per Btu per hour).

Compared to electric illumination, this is definitely not big potatoes. A 100-watt bulb will give 14.2 lumens per Calorie (of energy input as electricity) per hour. But even this is outclassed by fluorescent lamps, which can give up to 73 lumens per Calorie per hour. At 100% efficiency of conversion, heat into light, we would expect 721.5 lumens per Calorie per hour, so nobody can really brag.

At any rate, the light equivalent of a 100-watt bulb (using the above figures) will cost us 355 Cal (1,410 Btu) of heat energy per hour. At 5.8 Calories per liter of biogas (650 Btu per cubic foot), 100 watts of light would be obtained from 60 liters of biogas (2.2 cubic feet) burned each hour in a very good incandescent mantle lamp. This can, however, vary a great deal. One propane light was rated at 50-watts light output at a cost of 452 Cal per hour (1,800 Btu).

This is approximately a “best case” and “worst case,” and most inverted mantle manufactured natural gas or biogas lamps give light and burn gas in this range.

In a well-designed (and safe!) lamp, the biogas is burned completely, and the exhaust should contain nothing except carbon dioxide and water. Sometimes biogas has hydrogen sulfide in it (caused by conditions which are completely discussed in the book), and this can produce small quantities of hydrosulfuric acid. As implied by the statement, wherever there is incomplete combustion, then carbon monoxide can be produced. So it makes a great deal of difference regarding the design of the lamp, and the contaminants in the biogas.

Hydrogen sulfide (H2S) can often be detected by its odor, and there is a simple procedure described in one of the appendices to the book that describes how to find out with reasonable accuracy if and how much H2S might be present. That appendix, some others, and some chapters, are available for free download from the completebiogas site. (See the Table of Contents page: http://completebiogas.com/toc.html)

With the exception of H2S, and assuming complete combustion, however, the exhaust from burned biogas is quite safe, containing only carbon dioxide and water. The book describes how to determine if it will be safe not to vent the exhaust, and of course in a cold climate, one may want the heat to stay indoors.

To return to your initial point, however, I would say that if you are serious about designing and building such a light, you should do enough research to make sure that you understand both how to achieve complete combustion, and how to get the maximum amount of light out of that combustion. These are fairly technical issues, and for most folks, the better option will continue to be to purchase a well-designed light.

In any case, I would think it makes good sense to have a lamp that can be left up near the ceiling or lowered to allow maximum illumination for reading or close work.


d.

This was posted in its own thread, but should've been here:

I've thought along the same lines as Ken, but thought gas light s might do well in a greenhouse. The CO[sub]2[/sub] would also be appreciated, as well as the light and heat. But the spectrum was tweaked so that it looks balanced to the human eye. Presumably plants don't need so much green light. Do you think that would be worth exploring different sorts of mantle for use in a greenhouse?

Also, it would be nice to do without the thorium. A broken mantle shouldn't be a big deal, but if it's made of a radionuclide, I'd want to be careful.

I ask partly because I'll have my degree fairly soon, and while I don't know much about candoluminescence (the phenomenon that makes lantern mantles work), I have a fair amount of experience in several relevant fields.

Joel Hollingsworth wrote:
I've thought along the same lines as Ken, but thought gas light s might do well in a greenhouse. The CO[sub]2[/sub] would also be appreciated, as well as the light and heat. But the spectrum was tweaked so that it looks balanced to the human eye. Presumably plants don't need so much green light. Do you think that would be worth exploring different sorts of mantle for use in a greenhouse?

Also, it would be nice to do without the thorium. A broken mantle shouldn't be a big deal, but if it's made of a radionuclide, I'd want to be careful.

I ask partly because I'll have my degree fairly soon, and while I don't know much about candoluminescence (the phenomenon that makes lantern mantles work), I have a fair amount of experience in several relevant fields.

It's really outside my area of expertise, but if I were to pursue it I think a good place to start is to gain assurance that your assumptions about spectrum and materials are correct, and go from there. As I mentioned, the great majority of biogas lamps are from either India or China (and my impression is that there are a good many more manufactured in China), so if your university has connections in those countries-- and if you actually warm this up into a study-- then you may want to start by getting a small sample of the lamps and take them into a lab.

It should be easy in any case to get some biogas. Many universities generate mountains of degradable materials from their food services, and there is abundant literature on turning food waste or MSW into biogas.


d.