Gas Stove Burner for Biogas and Methane Cooking

An in-depth article about biogas stoves covers everything from small-scale digesters to home cooking which, in India, is also known as “gobar gas”. So, read on for information on biogas stoves:

What is a Biogas Stove?

A biogas stove is a cooking appliance that uses biogas as its fuel source. Biogas is produced from the anaerobic digestion of organic matter, such as animal waste or food scraps, in the absence of oxygen.

These stoves are designed to efficiently use biogas for cooking, often requiring specific modifications, especially in their burner designs, to ensure proper (soot-free) combustion and energy utilization.

Biogas stoves are an eco-friendly alternative to traditional cooking methods, reducing reliance on fossil fuels and helping in waste management.

Biogas is the gaseous product of breaking down organic matter in the absence of oxygen. It can be used to meet the energy needs for cooking and baking in individual households as well as in small communities.

Biogas Stove Materials and Design

They are typically made from stainless steel or cast iron, with some designs suitable for small kitchens as built-in single-burner stoves specifically adapted for biogas.

The simplest option for home and small-scale biogas digester novices is to use a cooker that is either designed or modified to run on biogas (gobar gas). These stoves are compact, usually have only two burner rings, and are frequently portable. They can be repositioned to make room for other kitchen appliances on the countertop.

Biogas Use and Applications

Biogas is produced on-site through anaerobic digestion of the family's or community-generated organic kitchen waste. It is used to serve the energy needs of the kitchen for cooking and baking in households and small businesses.

If the digester is kept warm enough to be productive and fed with kitchen scraps daily or more frequently, it may provide 20 to 30 minutes of cooking before exhausting that day's supply.

Conventional Stoves Modified to Burn Biogas vs. Special Biogas Stoves

Stoves and ovens for biogas are the simplest to use because they can be coupled up and used immediately. They do not require modifications to the jets if the gas pressure they are designed for is similar to that of the biogas created. The burner design will be optimized to ensure efficient combustion and energy use.

Market Availability and Alternatives

Stoves and ovens for biogas applications are similar to conventional appliances that run on commercial fuels such as butane and propane.

However, there's limited market availability of biogas stoves in many countries, possibly due to low demand. Nevertheless, normal LPG stoves can be modified for biogas use. Videos may be available on YouTube to show you how to make the gas flow orifice diameter changes needed.

Initiatives and Adaptations

Nonprofit organizations are known to be working on biogas-fueled stove projects to support sustainable cooking and heating in impoverished communities (such as Heifer International and its partners). Look out for these in your locality.

CC BY by Sustainable sanitation

However, not many people are aware that you can use a normal LPG stove to run on biogas with simple modifications.

In fact, you will not find much difference if you look at both an LPG stove and a biogas stove normally.

Stoves for Small Scale and Home Biogas

By far the biggest demand for biogas stoves comes from the millions of small-scale domestic and smallholding-type biogas plants ranging in design from:

• small digesters based upon oil drum-sized vessels
• all the way up to the community (e.g. village) biodigesters built in-pits with masonry walls and covers.

The gas pressure at which these stoves must operate is low and highly variable, and the same goes for the proportion of methane present.

One thing that doesn't change though, is that biogas burns over a narrow range of mixtures containing 9% to 17% of biogas in the air. If the burning flame has too much gas, the burn will be poor and incomplete, giving off poisonous carbon monoxide and containing a lot of soot particles. via babiogas

A good biogas stove design aims to maximize the conversion of methane and reduce unburned methane and soot from incomplete combustion.

For this reason, a biogas stove should burn on the lean side with a small amount of air to avoid the flame becoming too rich.

In a good biogas stove design, the air is mixed with the gas before it is burned to ensure the correct air-gas mix is obtained. There are other problems to solve, which are known as:

• lighting back (flame blow-back),
• flame lift,
• and excessive pressure drop at the burner manifold.

A successful biogas stove design must avoid those problems and deliver the flame where the heat of combustion can efficiently conduct its warmth into the cooking vessel.

Potential Benefits of Using Biogas Stoves

Stoves and ovens using biogas have the potential to improve the well-being of marginalized people.

They offer an excellent opportunity to put an end to the indoor air pollution generated in the kitchens of many poor families around the world by wood burning.

As already mentioned, the use of biogas digesters also provides a benefit by treating organic waste that commonly represents health and environmental threats.

Local manufacturers of biogas stoves are, therefore, emerging in many countries. There appears to be significant potential to improve the combustion efficiency and overall quality of the stoves that are currently being offered on the market. It is hoped that as sales increase, sales competition will become greater, and the sellers will then match the quality of today's best gas stove brands.

Domestic Appliances Running on Biogas

As a gaseous fuel, biogas can be used for many domestic tasks. A common practice is the adaptation of commercial appliances that originally ran on fossil fuel gases, such as liquefied petroleum gas (LPG) or natural gas.

Biogas from small digesters may contain carbon dioxide and water vapour and is at low pressure when it flows out of burner holes. It flows through stoves with less volition and, therefore has a lower calorific value than LPG (or natural gas). It therefore cannot be used in normal LPG gas appliances.

Regular appliances can be modified to run on biogas by enlarging apertures (theoretically a simple process, but a lot more tricky in practice).

There are several domestic appliances, in addition to stoves and cookers which can be fuelled biogas. These are:

• Biogas Lamps
• Radiant Heaters
• Incubators
• Refrigerators
• Biogas-fuelled Engines including modified:
  • Four-stroke Diesel Engines
  • Four-stroke spark-ignition engines.

Cost of Household Biogas Systems

The cost of any sort of process equipment includes an initial investment as well as ongoing operating costs.

Considering the initial capital cost versus the financial and environmental benefits is important.

In the following case study it is estimated that an 8 m³ household biogas tank can treat the manure from 4 to 6 pigs, yielding around 385 m³ of biogas annually.

That suggests that such a plant can save 847–1,200 kg of coal based on the calculation of the effective heat equivalent.

According to the methodology recommended by IPCC in 2006, if a household biogas digester treats the manure of four pigs, it can reduce greenhouse gas (GHG) emissions by 1.5~5.0 tonnes of CO2e annually.

The initial equipment purchase and installation costs of each household biogas digester (8–16 m³) range from US$750 to US$1,250, depending on the digester size.

Most rural households in developing countries have low disposable income and weak financial capacity for such a large investment as above for a plastic or steel tank-based digester. In addition, the household will, during the use of any digester, incur a biogas digester maintenance cost burden.

By contrast, the current practice of the deep-pit treatment method is by far considered the most attractive option for manure treatment, given that it requires very limited additional investment beyond the labour input. via www.ctc-n.org

According to one research group, the cost functions for a biogas plant are as follows:

1. The economies of scale
2. The ratio of the cost of a given size of plant to the cost of a reference plant (this remains almost constant over time)
3. The effect of retention time and other factors on the capital cost
4. The cost of the material (if it must be brought in from outside the farm or home).

Using a Biogas Stove

Biogas can be used in gas appliances for energy production, which is then used for heating, lighting, the supply of steam plants, water boilers, gas stoves, infrared radiators, and internal combustion engines.

The simplest method of biogas utilization is using it in burners (gas rings), as it can be directly supplied from low-pressure gas holders.

The best biogas stove sellers offer designs that are specifically developed for the low-pressure gas burners needed to burn biogas directly from small digesters or from storage holders containing biogas.

Gas pipes are also needed that can effectively connect the point where you collect the accumulated biogas and the stored gas through gas lines to the home stove.

The stainless steel, built-in single-burner stove is specially adapted to cook with biogas.

The stoves made by the Israeli-owned Homebiogas™ firm are designed to slide into an existing stove “range” or be built into a countertop and are perfect for those who have limited kitchen space.

After selecting the type of digester, the retention time, which is a key parameter in determining digester size, is chosen to maximize the percentage of biogas production concerning the retention time.

An average retention time of 10 to 30 days is often chosen as the minimum amount of time for sufficient bacterial action to take place to produce biogas and to destroy many of the toxic pathogens found in human waste.

At the household level, biogas systems can also be used to produce fertilizer, not just to provide energy for cooking and lighting.

Safety “pilot”

Air filter Biogas-fueled radiant heaters should always be equipped with a safety pilot, which turns off the gas supply if the temperatures go low, i.e., the biogas does not burn any longer.

Biogas consumption can be calculated by assuming that:

• household burners consume 0.2 to 0.45 m³ of biogas per hour and
• Industrial burners burn from 1 m³ to 3 m³ of biogas per hour.

The biogas volume necessary for food preparation can be determined from the time spent on daily cooking.

Using a Regular LPG Stove

Using 1-2 burners for biogas in addition to your current LPG stove is a good way to set up a kitchen to use biogas whenever possible. If a user chooses to connect a “HomeBiogas”™ digester to a regular stove, the user should be aware of the energy requirement of the stove.

The Biogas stove is different from the LPG regular stove since low-compressed bio-methane is a far less compressed gas than LPG, and the gas burner flame openings need to be wider for better combustion.

The first time that a new digester set-up is used, the gas in the tank won't burn as it contains Carbon Dioxide gas. If, fortunately, it burns then good, or else wait for the second time after draining the first tank-load of gas.

The second use will be likely to be much better quality biogas, and thereafter will usually be good methane. You can detect how much gas there is in the system when the gas holder tank rises up as the gas is produced.

The “Clean Gas” Benefit

Biogas combustion is so much cleaner than other fuels, such as solid biomass and kerosene, that its use must always be considered for health reasons.

However, for these advantages to make it worth buying a biogas stove, it depends on the quality of the biogas stove (particularly the burner) to provide a good, hot, and clean burn.

How to Modify a Normal LPG Stove to Run on Biogas

So it is very difficult for biogas stoves in big cities. However, you can use a normal LPG stove to run on biogas with simple modifications. You will not find much difference if you look at both LPG stoves and biogas stoves normally.

The biogas burner I am showing has 3 mm holes in it. Take an LPG stove, unscrew it, and remove the nozzle, and this may be enough.

Also,  close any air-entraining or mixing gap provided for LPG use. You can control the pressure and required amount of biogas with the gas control knob provided.

Check, by comparison with the existing burner, the operation of it with biogas after removing the nozzle.

If it is burning properly, then leave it as it is otherwise necessary to search for a burner of the same diameter. Burners are of different sizes. So take your LPG burner when searching. In our locality, hardware stores are fabricating and selling locally-made stoves for biogas use.

Once you have done the modifications, Connect the Biogas pipeline to your stove and check your stove and it should run on biogas properly. via ww.instructables.com

Do not add anything other than cow dung slurry and organic waste. Once gas formation starts, you can feed organic waste in small quantities. Make sure there is no leakage. Also, be aware that the initial gas produced will not burn as it will be mostly carbon dioxide.

Release the gas 2 to 3 times before testing. Use a Bunsen burner to test, and do not use a lighted matchstick for testing.

If the gas pressure is too low to fuel the Bunsen burner, try adding some weight on top of the gas holder to get better (higher) pressure.

LPG Stoves Versus Biogas Stoves

Almost any gas stove can be converted to support biogas by removing the pressure nozzle. However, one stove cannot supply both LPG and biogas.

For an LPG stove versus a Biogas stove, the LPG stove wins for its low cost for a high-quality product. Lightweight and portable. Check that the one you buy has easy-to-use heat adjustment dials.

Against this background, for the biogas stove, you will most likely need a match to light the stove. In addition, heat adjustment is not precise.

If you're looking for something simple on holiday, a butane stove can be perfect for you. It's our favourite, for a solo camper looking to make a simple but delicious meal, is a cheap LPG stove.

However, for the poor and any environmentally aware person, the biogas stove is considered far better with its wonderfully “green” environmental benefits. Plus its value in reducing the unhealthy smoke found in the homes of so many developing nations where wood would otherwise be the only economically feasible alternative cooking fuel.

Biogas is not perfect, and LPG can be easier to use, but biogas can be so much cheaper and is always a renewable fuel with so many benefits over the alternative use of a fossil fuel such as LPG.

Methane Used in Puxin Biogas Stoves

To begin explaining biogas stoves, it is probably useful to first think about what “biogas” is?

Biogas is essentially another word for methane gas (although it usually is only just over half methane and half other gases).

In its first decade, the Puxin methane program was a success. The company installed more than 20,000 biogas stoves (or biodigesters) in that period.

The biogas that fuels the Puxin biogas stove and similar products is produced in biodigesters that enable rural households to turn the waste of their cows and pigs into a methane-rich gas suitable for both:

• cooking and lighting, as well as
• the output product known as bio-slurry (predominantly used as a substitute for fertilizer).

For instance, the 5,000l biogas digester package from Puxin comes with:

• the digester which produces the biogas (a gas mixture that is predominantly made up of methane (CH₄) and carbon dioxide (CO₂))
• a method for purifying biogas (methane purifier) MP 12 135 (PVC),
• a gas holder with a capacity of 5 m³,
• a generator bg 2500 w (biogas power generator 2500 watts),
• bacterial methane activators gp-7 for 1 month,
• installation of equipment, and
• stoves.

Puxin Biogas Oven

Cookstoves and ovens for biogas applications are made by Chinese manufacturers such as Puxin. They are similar to those of conventional appliances running on commercial gas fuels.

A biogas stove usually has a single or double burner with varying gas consumption rates, which is influenced by the pressure provided by the biogas plant and the diameter of the inlet pipe.

Stoves and ovens for biogas applications are similar to conventional appliances that run on commercial fuels such as butane and propane.

[First published 7 September 2020.]