Heating with agricultural biomass
By EduTransfer Design Associates and Haywire Creative
For many years, some agricultural producers have experimented with straw bales or wood heating in simple, single combustion-chamber boilers. While this approach has been relatively successful, it had drawbacks, including high particulate emissions, poor energy recovery, and early failure of the combustion chamber due to acids in the combustion components.
An innovative technology from Germany, the HERLT Gasifier, eliminates some of these problems and improves energy performance.
“The units can be used in any agricultural applications that require heat. They can be used for hydronic heating, provide heat for low pressure steam applications, produce hot air to dry grain, or power a multi-blade vapor turbine to generate electricity,” says Don Murray, President of EMISPEC, the Quebec company that markets the technology in Canada.
Here’s how the HERLT Gasifier works:
- Agricultural biomass, such as straw bales, whole wood logs, or other baled energy crops like willow or switchgrass is fed into the first gasification chamber where the heat is 400 degrees Celsius. At this temperature, the biomass releases CO (carbon monoxide), H2 (hydrogen) and CH4 (methane) combustible gases.
- The gas is channeled to a second, post-combustion chamber where the internal combustion produces clean, hot gas at a temperature in excess of 1000 degrees Celsius.
- An appropriate heat exchanger captures the heat for use in various applications.
Murray explains that the high combustion temperature of the gas provides very low emissions and increases the efficiency of the boiler:
- Emissions tests, conducted by TÜV Nord on gasifiers fueled with whole straw bales, yield average emission levels in the range of 50 mg/Nm3 CO; 300 mg/Mm3 NO2 (Nitrogen dioxide) and 20-120 mg/Mm3 fine particles. These results are better than current government regulations.
- The flue gas emission temperatures are under 200 degrees Celsius. The heat radiation losses of the larger boiler are about 2.5%. This results in a boiler efficiency of 85%.
- Straw contains about 5% of ash; wood has less than 1%. Ash is removed from the gasification chamber through the discharge doors.
- The consumption of five whole, round straw bales per day provides 1,300 MBTU (one million British thermal units) per hour of thermal heat or approximately 30,000 MBTU per day.
Various sizes of HERLT Gasifiers are available, ranging from 85 to 2500 kilowatts (kW), equivalent to 300,000 to 8 million BTU per hour. Murray says a 500 kW unit provides the thermal heat requirements for a 3000 square metre chicken broiler farm operation complete with adjacent living quarters and warehouses.
“A single 1.6 metre diameter, 485 kilogram whole round straw bale produces thermal energy equivalent to the combustion of 115 litres of Class 2 fuel oil,” says Murray.
Potential applications include:
- Hydronic heating (hot water / forced air)
– Greenhouses,
– Chicken broiler farms,
– Pig farms
– Dairies,
– District heating
– Drying chambers
– Thermal oil heat
– Low pressure steam <120 psi
- Micro electric production < 100 kWe
Setting capital costs aside, Murray says that the cost of energy generation is roughly 2.5 cents per kWh. This is based on a landed price of $20 per big round bale of roadside non-saleable old or grey straw. A 500 kW unit costs in the range of $230,000.
Over 50 industrial size systems are operating throughout Europe, and 500 systems of 100 kW or lower are used in residential and SME applications.
Murray says burning biomass is considered near carbon neutral, since growing crops and forests recaptures CO2 gas given off during combustion. Considering the process cycle as a whole, low levels of net CO2 emissions are released back to the atmosphere.
