Cooking.pdf

Hydrogen

Cookin’ On

Hydrogen

Stove Burner Conversion

Figure 1 shows the principal parts of a typical range top

burner used with conventional gaseous fuels. Usually the

fuel streams in through a gas orifice with a delivery

pressure between 3-15 inches of water column. Primary

air is then drawn in with the gas stream through an

air-gas mixer. Secondary air openings to mix in more air

may or may not be present. Finally, as the mixture exits

through the burner ports, combustion occurs, if a spark

ignition source or pilot light is present.

Horse of a Different Color

This burner design will not suffice for hydrogen in an

unaltered state. Burners optimized for hydrogen

combustion require that undiluted hydrogen be delivered

directly to the burner ports without primary or secondary

air mixing. So, if we are trying to work with an existing

burner in a typical gas appliance, we will have to find a

suitable method to seal off any openings that were

installed for this purpose. There’s no method that will

work in all instances. The actual openings we are

referring to may be an integral part of a cast iron body. Or

the primary air openings may be a modest distance from

the burner head in an aluminum delivery tube with an

adjustable closure. We used silicon sealant with stainless

steel tape and ring clamps in one recent alteration, but

this simple Coleman stove conversion hasn’t been

subjected to long term use as yet.

From Scratch

One might opt to build a simple hydrogen burner and

direct fuel delivery apparatus from the ground up, rather

than deal with the problem of sealing off a nagging

assortment of useless holes.

Burners and their attached

parts get hot, and transfer

heat readily through

conduction. Sorry, duct tape

and chewing gum won’t cut it.

Our first attempt at a simple

hydrogen conversion utilized

a rudimentary two burner

range of cast iron

construction. See Figure 2.

After we tossed the existing

burner assembly, and

removed the screwed-on

brass orifice, a threaded

adaptor was exposed. To this

we attached a 1/4 inch NPT

straight coupling followed by a

short length of black iron pipe

David Booth and Walt Pyle

onverting conventional stove top

burners to run on hydrogen is a

simple process. Knowing the

proper handling procedures of hydrogen

will make your installation safe and

efficient.

Theory Before Practice

Hydrogen burns differently than either propane or natural

gas. In particular, hydrogen’s rate of diffusion and flame

velocity are roughly ten times or greater than that of

propane or natural gas. Diffusion rate measures how long

it takes a gas introduced in one side of a room to be

detected on the other side. Flame speed is how fast a

flame travels to burn available fuel-air mixture.

Flashback of the flame into the primary mixture of fuel gas

and air must be prevented in all burners. This is typically

achieved with natural gas and propane by adjusting

the fuel velocity so that it is higher than the normal

flame velocity. The flame velocity of hydrogen is too

high for this technique to be practical. Another

flashback control strategy employs burner ports with

a minimum quenching diameter which theoretically

will not allow the flame to pass back through the

port. In practice, however, it is very difficult to make

the holes small enough to quench a hydrogen flame.

Fortunately, flashback can be

minimized by preventing

hydrogen from mixing

with air before the

burner port.

Some flashback

may still occur

creating a loud

popping sound

but this noise is

usually harmless.

Figure 1: A conventional burner for natural

gas and propane (not for hydrogen).

Diagram by Chris Greacen

Home Power #33 • February / March 1993

Hydrogen

Stainless steel wool surrounds burner assembly

Burner ports bored on drill

press with smallest bit that

wouldn't break

3/8" I. D.

Plumber's cross

On-off

knob

1/4" straight coupling

Plumber's cross

bored and taped

to receive 1/4"

I. D. nipple

1/4" I. D. nipple

1/4" I. D.

elbow

"Stock" brass valve

body with male

1/4" I. D. threads

1 1/2" x 3/8" I. D.

Pipe nipples

3/8" I. D. End caps

Figure 2: Pure hydrogen is delivered to burner ports

without primary or secondary air mixing.

Diagram by David Booth

Figure 3: Top view of radial burner made from scratch

using black iron pipe fittings.

Diagram by David Booth

of the same diameter. Don’t use galvanized pipe, because

of the fumes that will be released at high temperatures.

Then we installed a 90 degree elbow followed by a short

vertical nipple of more pipe. Next a 3/8 inch NPT fitting

shaped like a cross with four female threaded openings

was drilled and tapped to create a fifth hole. See Figure 3.

This threaded onto the short vertical nipple, and four

slightly longer nipples of equal length extended out

radially from the remaining holes. Finally, these

terminated in threaded end caps. A drill press is almost

essential for drilling a series of very fine holes which line

up along the top of the radial burner arms, and through

the top of the cross. Ideally, these burner ports would

have a 0.057 cm (0.0225 inch) diameter or less, which is

the approximate minimum quenching diameter.

The Catalytic Advantage

It has been observed in early experiments that the flame

combustion of hydrogen/air mixtures can lead to

unacceptable levels of nitrogen oxide (NO x ) pollutant

emissions. The primary end product of hydrogen

combustion is simply water vapor. However, if the

temperature of combustion exceeds a threshold level of

about 1315°C (2400°F), a significant amount of oxygen

and nitrogen from the air may react and form this

unwanted byproduct. This also occurs with natural gas

(primarily methane), propane, and other hydrocarbon fuel

combustion.

The first approach is based on Billings and his associates’

work with flame assisted catalytic burners. Their

conversions utilized the catalytic properties of stainless

steel at elevated temperatures. Later, in another article,

we’ll describe the conversion of a catalytic space heater

which optimizes “flameless” combustion with a small

amount of platinum.

Flame Assisted Catalysis

The technique developed by the Billing’s research team to

reduce NO x formation relies on controlling two interacting

phenomena. First, as has already been described,

hydrogen/air mixing is inhibited by blocking off any

primary air openings. Second, a stainless steel wire mesh

is arranged tightly around the circular burner head or

radial burner arms, as shown in Figure 2.

Where does one find stainless steel wool or wire mesh?

Look for stainless steel pot scrubbers in a large,

thoroughly stocked supermarket in the housewares

section.

Getting our NO x Off

This stainless steel wool blanket around the burner

actually serves two complementary functions. It inhibits

the mixing of air and hydrogen thus producing a zone

immediately surrounding the burner head where the

concentration of hydrogen is very high and the

concentration of air is very low. The wire mesh should be

thick enough so that the flame does not radiate above it

or out too far laterally.

Fortunately, you can use a catalyst to lower the

combustion temperature thus preventing the formation of

nitrogen oxides. The catalytic material is not used up or

altered in any fashion in the process.

There are two catalytic conversion techniques which

succeed in producing negligible levels of NO x emissions.

Stainless steel also works as an excellent catalyst for

hydrogen combustion. If there isn’t a sufficient amount of

stainless steel mesh, the catalytic capability and ability to

Home Power #33 • February / March 1993

Hydrogen

prevent NO x production could be lost. Hydrogen and

oxygen are thus combined on the surface of the catalyst

at a lower temperature than would occur without the

catalyst. The result of the lowered combustion

temperature is that nitrogen oxides are virtually

eliminated. The steel wool proceeds to glow bright red

even at these temperatures, indicating that the otherwise

invisible hydrogen flame is present.

spread the word about hydrogen’s unique advantages. It

is clearly the hands-down winner among the possible

candidates of alternative fuels for the future in our

environmentally beleaguered world.

A Note on Safety

Remember that storing pure hydrogen can be regarded

as a relatively safe procedure, but storing hydrogen /air or

hydrogen/oxygen mixtures is foolhardy and strictly

inadvisable.

According to Roger Billings in The Hydrogen World View,

the flame-assisted catalytic technique can lower NO x

emission from hydrogen combustion in range burners,

ovens, and space heaters to negligible levels. The

resulting data showed NO x emission levels between 1 and

5 parts per million (ppm) for a catalytic assisted burner.

This can be compared with 40 ppm for conventional range

burners operated on natural gas and up to 250 ppm for a

hydrogen burner without a catalyst. These burner

emission levels are all quite low, however, compared to

internal combustion engine exhaust gas NO x production.

More to Come

We need to build a sound understanding, before we can

confidently proceed to implement hydrogen for scores of

potential uses. If you’d like more information, dig into the

references at the end of the article.

In the next issue, we will delve into a technique for

transforming the chemical energy stored in hydrogen to

available heat energy without the presence of a flame.

This form of combustion is possible when hydrogen is

oxidized in the presence of certain specific catalysts such

as platinum. This is considered “pure” catalytic

combustion. Water vapor is the only byproduct along with

heat, so no venting of the appliance may be necessary (if

means to prevent oxygen depletion for the room air is

assured). At this time, most city and county building

codes require an exhaust flu for stoves running all

gaseous fuels, and we recommend that the room where

the stove is being used be vented to the outdoors.

We’re in the process of putting together a system that will

convert renewable solar electricity into the storable

chemical energy of hydrogen through the process of

electrolysis. The process is still underway but we will offer

detailed accounts of our endeavors in forthcoming issues.

Much of the research that we referred to in this article was

performed by Roger Billings, N. R. Baker, and their

associates of the now defunct Billings Energy

Corporation. This pioneering work was done mostly in the

1970s. An early research endeavor involved conversion

of all the gas appliances on a Winnebago recreational

vehicle from propane to hydrogen operation. To

demonstrate hydrogen’s practicality even further, five

natural gas appliances were converted to hydrogen. This

multi-phased project in Provo, Utah was called the

Hydrogen Homestead. Included among the appliances

converted for this home were an oven, a range, a

barbeque, a fireplace log burner, and the booster heater

for the home’s heat pump system.

Access

Authors: David Booth, Alternative Energy Engineering,

POB 391, Miranda, CA 95553 • 707-923-4336

Walt Pyle, WA6DUR, Richmond, CA • 510-237-7877

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