Heating your home with manure may seem like an unusual idea, but it can be a cost-effective and eco-friendly way to provide warmth and cut your energy bills. Manure contains methane, which can be used as a renewable biofuel to produce heat and energy. In this comprehensive guide, I will walk you through everything you need to know about heating your home with manure, from how manure produces methane to constructing your own manure-fueled furnace or boiler.
How Manure Produces Methane Gas
Manure contains high levels of organic matter such as undigested plant material and microbes. As this organic matter decomposes anaerobically (without oxygen), it produces biogas – a mixture of gases including methane, carbon dioxide, and small amounts of other gases.
Methane is the main component of natural gas that is used for heating and cooking in many homes. Manure can produce substantial quantities of this valuable fuel. For example, dairy cows can generate 15-20 gallons of manure per day and beef cattle generate 11-13 gallons daily. Swine and poultry also produce significant amounts of manure. This manure contains about 7-10 cubic feet of methane per animal per day when handled as a liquid or semi-solid.
The process of anaerobic digestion by microbes is what releases the methane from manure. This occurs naturally in places like manure lagoons or deep stack manure piles. However, the methane can be captured much more efficiently through anaerobic digesters.
Anaerobic Digesters Capture Methane from Manure
Anaerobic digesters are systems designed to optimize the anaerobic digestion process for methane production. There are several types of digesters:
- Covered lagoon digesters – A flexible cover captures biogas from an anaerobic treatment lagoon.
- Complete mix digesters – Manure is mixed with microbes to produce biogas which is collected under a fixed cover.
- Plug flow digesters – Manure moves through a heated, underground concrete tank and biogas is collected.
- Fixed film digesters – Manure flows over a fixed surface area containing anaerobic microbe colonies.
Digesters usually consist of a large heated tank where manure is mixed and decomposed. The methane and other biogases produced bubble up and are collected in pipes or flexible covers on top of the tank.
Benefits of anaerobic digesters include:
- Capturing 3-10 times more methane than uncontrolled systems.
- Reducing manure odor by 60-90%.
- Killing pathogens like E. coli in the manure.
- Producing a nutrient-rich fertilizer byproduct.
Using Methane for Heating
The methane produced in digesters can be used to fuel furnaces, boilers, and other heating systems. Here are some key steps in utilizing manure methane for home heating:
Raw biogas from digesters contains about 60% methane, 38% CO2, and 2% other gases. To use it for heating, the gas needs to be processed to increase the methane content to around 90%. This involves removing CO2, moisture, and trace gases.
Common biogas clean-up methods include water scrubbing, pressure swing adsorption, membrane separation, and cryogenic upgrading. The processed biomethane can then be compressed to fuel pressure for heating systems.
Heating System Requirements
To run on methane, heating systems need to be designed for gaseous biofuels. Key components include:
- A blower to move the methane from the digester to the heating system.
- Gas control valves and air-to-gas ratio controls.
- A biogas ** burner designed for methane**.
- Exhaust vents for combustion gases.
- Safety gas detectors and shut-off valves.
Many new systems are available to help adapt conventional furnaces, boilers, and heaters to run on methane.
Sizing the Digester and Heating System
To heat a home with manure methane, the digester and heating unit need to be properly sized. Factors like climate, home size, insulation, and energy needs determine capacity.
As a rule of thumb, one mature dairy cow can generate enough manure to produce 40-60 cubic feet of methane per day – equal to 40-60,000 BTUs. A plug-flow digester for a small home would need 10-20 cows, though more may be needed in cold climates.
Constructing a Small Manure Methane Heating System
With the right materials, skills, and permits, you can construct a home-scale methane digester and heating system. Here are the main steps involved:
1. Digester Construction
A basic plug flow digester consists of a long concrete or lined pit filled with manure and heated to 95-100°F. The digestion chamber needs an airtight cover to collect methane. A ramp and conveyor loads new manure while effluent drains remove digested material.
2. Biogas Piping
PVC or HDPE pipes collect biogas from the digester and transfer it to the clean-up and heating system. Include a moisture trap and pressure relief valves. The gas line should slope up from the digester.
3. Biogas Clean-Up
A water or amine scrubber can be constructed to remove CO2 and hydrogen sulfide from the methane prior to burning. This involves bubbling the gas through a chemical solution.
4. Furnace or Boiler Retrofit
A qualified technician needs to adapt a furnace or boiler to run on methane. This includes adjusting the burners, adding methane controls and safety features, and testing combustion.
5. Permitting and Inspection
Check local building codes and obtain required construction, electrical, and plumbing permits. Have the completed system inspected before use.
Key Considerations for Heating with Manure
Heating your home with manure methane can work well if done properly, but here are some important factors to consider:
- Sufficient steady manure supply and herd size – at least 10-20 cows needed.
- Adequate digester heating – electricity or solar heat may be required.
- Meeting local zoning and permitting requirements.
- Handling the effluent – digested manure needs to be spread or treated.
- Safety – methane and hydrogen sulfide are hazardous.
- Maintenance – digesters and equipment need upkeep.
Proper training in construction, operation, and maintenance is highly recommended when installing a manure methane system. Overall, capturing energy from manure can be a worthwhile renewable heating strategy given the right circumstances.
Heating a home with manure offers an innovative way to offset fossil fuel use by utilizing the methane emissions from livestock waste. While unconventional, manure methane can serve as a viable renewable fuel when the right digestion, processing, and heating systems are in place. With some knowledge and effort, the manure produced on farms and homesteads can provide heat and energy independence. If designed and operated safely, a manure methane furnace or boiler can be a smart heating solution.