ABATTOIRS handle products most people prefer not to think about as they tuck into their fillet steaks. The inedible parts of animals can be a health hazard if not properly handled, but are also a useful resource that abattoirs are increasingly learning to turn to their advantage.
If abattoirs don’t have large amounts of uninterrupted power for refrigeration and sterilisation, the consequences are disastrous. As Eskom power becomes more erratic and expensive, generating its own power makes increasing sense for the industry.
Several abattoirs have already opted for a biogas solution in terms of which animal waste — mainly meat unfit for human consumption and stomach contents — is put into a digester to generate methane to run a gas-fired power unit.
Country Meat abattoir in Kroonstad has taken an alternative route, employing specialist power company BioWaste Technologies to install a phase pyrolysis plant.
Country Meat is a halaal abattoir that can slaughter up to 275 head of cattle and sheep a day at peak periods but averages about 230 a day out of season. It generates about 11 tonnes of contaminated meat and stomach contents per day.
The pyrolysis machine is designed to run 24 hours a day and consume all the waste generated by the abattoir.
Joel Arcus, a director of BioWaste, says pyrolysis can be used to turn any waste with calorific value, including animal, agricultural and plastic waste, as well as coal fines, into syngas. The waste is heated to temperatures of about 900?C without oxygen, and a thermochemical reaction occurs that occurs in hydrocarbon gas or syngas.
AT COUNTRY Meat, animal waste is mixed to the most efficient ratio, fed through a dryer and then put into a closed system to generate gas. It requires a small amount of electricity or liquid petroleum gas to start the process, but once it is under way, the system becomes self-sufficient.
The gas is cleaned and then fed to a 150kVa gas generator to generate up to 120kW per hour of electricity.
The exhaust heat from the plant is used in a heat exchange system to partially heat water needed to clean the abattoir.
Arcus says there are three advantages to using the abattoir’s waste to generate heat. It saves the company the cost of a 500km round trip three times a week to the nearest waste disposal site.
The plant will also save about one-third of the abattoir’s Eskom demand, and heating the water reduces the amount of paraffin that is required to bring the water to the temperatures the abattoir needs.
About 95% of the energy in the solid waste is turned into useable syngas. The other 5% is used in the process and the residue can be used as a soil conditioner, as it contains large amounts of potassium.
Arcus says that for a relatively small abattoir like this one, carbon emissions are not a big issue, although it would be a factor that bigger companies might consider.
Compared with a coal-fired power station, pyrolysis produces about one-third less carbon emissions and no nitrogen oxide, sulphur oxide or other harmful emissions and byproducts.
By using its waste on site, the abattoir also cuts vehicle emissions and is not emitting the methane that would be released if the waste was sent to a landfill.
ARCUS says BioWaste Technologies decided to market pyrolysis as a technology solution rather than a biogas solution because anaerobic digestion of biomass is a relatively lengthy process, less efficient in converting waste to energy, and could be difficult to manage as bacteria die if temperature and nutrition are not held within strict limits.
Pyrolysis is a predictable and reliable science and a fully scaleable technology. The life of the plant is about 25 years.
Sean Thomas, the founder of Bio2Watt, which has two anaerobic digestion power plants — at Bronkhorstspruit and Cape Dairy — says the process is harder to manage if only abattoir waste is used because it contains quite a lot of nitrogen.
However, in Bio2Watt’s two projects, abattoir waste is combined with other waste streams, such as paper, fruit and vegetables and expired dairy products, and the process is working well.
Thomas agrees that it takes time to start up the anaerobic digestion process, but once it is working, it generates power continuously as long as it is fed with biomass.
Anaerobic digestion works best with economies of scale, he says.
Bio2Watt’s Bronkhorstspruit project is targeting about 4MW and Cape Dairy 3-4MW.
Arcus says private equity companies are willing to finance green energy projects with a guaranteed offtaker. Companies could use debt financing if their balance sheet is strong enough, or enter into a rental agreement with a third-party financier.
The Country Meat plant is BioWaste Technologies’ first installation in SA.
Arcus says it is looking at other waste-to-energy opportunities using various fuel sources that could generate between 1MW and 600MW per project.