Chicken farm manure used to generate power and heat

http://www.engineerlive.com/content/21081

Sean Ottewell reports on how chicken manure is the latest fuel to benefit from advanced technology heat and power generation, while a process used in the manufacture of coffee could boost biomass energy content by 20 per cent.

Waste from chicken farms has long been used as a fuel, but tougher regulations are forcing the manufacturers to turn to more advanced solutions.

For example, GE Energy's ecomagination-certified Jenbacher gas engines will use biogas created from chicken manure to generate needed power and heat at a large chicken farm north of the China's capital city of Beijing.

The plant is the first of its type in China and could pave the way for similar applications in the future.

The Beijing Deqingyuan chicken farm waste utilisation plant comes as the country seeks innovative ways to meet its energy and environmental requirements. Providing 14600MWh of electricity per year, the project is designed to help reduce sub-urban electricity shortages.

By using the biogas for power generation in place of previously used coal-fired power, the new project is expected to reduce the equivalent of about 95,000 tons of CO2 per year, qualifying the project for the UN-sanctioned clean development mechanism (CDM) programme.

The Beijing Deqingyuan project is also reducing the farm's dust levels, further enhancing the area's air and water quality by controlling odours and improving the work environment for the farm's employees. The improvements support the guidelines of several Chinese government initiatives including the underground water conservation law, the new rural construction plan and the distributed energy solution policy.

Located in YanQing district, about 50km north of Beijing, the farm owns three million chickens, producing 220tons of manure and 170tons of wastewater each day. The farm's new cogeneration system features an anaerobic digester system to treat the waste material, producing enough biogas to fuel two GE's Jenbacher JMS 320 GS-BLgas engines. The plant has an installed electric capacity of more than 2MW for use at the chicken farm. Additionally, the plant's thermal output is used to support the chicken waste fermentation process and also heat the chicken farm in the winter.

"This biogas project will quickly pay for itself by meeting the customer's demand for cost-effective electricity and heat," said Jack Wen, president and ceo of GE Energy China. "We estimate that the customer will save more than US$1.2million a year in electricity costs alone."

A similar project has been underway in Milan since June following the decision of commercial farmers and cattle breeders Azienda Agricola di Giuseppe and Paolo Gomiero to install similar technology at the Baita del Latte farm's first biogas plant.

The power plant uses biogas created by the digestion of a wet mixture of animal waste, or slurry, as well as agricultural biomass materials such as corn and rye. By using the biogas for power generation in place of fossil fuels, the project is expected to result in the reduction of the equivalent of about 5000 tons of CO2 per year, thus providing significant environmental benefits.

The new biogas project allows Gomiero to address two common farming challenges: obtaining energy at sustainable prices and properly disposing of agricultural and animal wastes like cow manure and chicken dung, which presents an ecological and regulatory challenge for farmers due to its high content of nitrates.

"This project is an excellent example of an advanced solution to an ecological issue," said Gomiero, who owns the Baita del Latte plant along with his two brothers, Roberto and Lorenzo. "In fact, the EEC's Nitrates Directive provides for very restrictive regulations in terms of chicken dung disposal. Thus the biogas plant actively contributes to the correct use of such substances. The anaerobic digestion of organic substances optimises the initial product by making it more stable and odorless. Moreover, the remaining substrate is useful as an excellent fertiliser - eliminating the use of chemical substances."

GE Energy supplied a Jenbacher type J320GS cogeneration unit for this plant, which went into operation in June. The plant has an installed electric capacity of 1.06MW, with an efficiency of 40.8 per cent. The power plant is equipped with a heat recovery system that utilises the waste heat from the jacket water. The electricity produced is supplied to the Italian power distribution network, while thermal energy is recovered and used to power the biomass digestion process, the farm's housing facilities and cattle sheds.

The Jenbacher engine is fuelled by biogas created from 20m3 of cattle effluent and approximately 50tons of biomass each day. By delivering the electricity generated by the biogas engine to the public grid, Baita del Latte is able to obtain "green certificates" provided by Italian legislation. These certificates are negotiable instruments that prove electricity is being produced using renewable energy sources.

"The project is rewarding in terms of its economic return," Gomiero added. "The plant is seen as a successful demonstration project. We expect many other farms will follow us because this territory in the Veneto region has been chronically troubled with energy demands that traditional sources, like fossil fuels, have not been able to fulfill."

"Public programmes that support the exploitation of organic waste and require the increased contribution of renewable energy are leading to new opportunities that may be of interest to the farming world," said Mario Artoni, general manager of GE Energy's Jenbacher gas engine business for Italy. "In Italy, legislation on the incentives for on-site electrical power from renewable sources has aroused great interest in biogas plants. Today, more than ever, the practical and economic answers to Italy's energy and environmental challenges can be found in initiatives like this one - especially if they produce the outcomes we expect."

Energy crops take a roasting

Meanwhile, new research in the UK could help to increase the energy content of other biomass fuels by up to 20 per cent.

The study, carried out by engineers from the University of Leeds, examined the combustion behaviour of crops grown specifically for energy creation when put through a mild thermal process called torrefaction - a process more usually associated with coffee production.

Torrefaction is increasingly seen as a desirable treatment for biomass because it creates a solid product which is easier to store, transport and mill than raw biomass.

The study examined the energy crops willow, canary grass and agricultural residue wheat straw to see what happened when they went through the torrefaction process and how they behaved at a range of temperatures when they were heated to create an energy-enhanced fuel.

Results showed that the treated materials needed less time and energy to heat to burning point, and also that they offered increased energy yields upon burning.

Willow emerged as having the most favourable properties, in that it retained more of its mass in the torrefaction process and also performed best in terms of its energy yield. As an example, willow was shown to have an 86 per cent energy yield, compared with 77 per cent for wheat straw and 78 per cent for reed canary grass.

"Raw biomass takes up a lot of space and has a low energy density which makes it costly - environmentally and economically - to transport. Plus you need more of it than say, coal, to produce energy efficiently," says professor Jenny Jones who worked on this study with PhD student Toby Bridgeman.

"Torrefaction is not currently used in the UK in either the agricultural or the energy sectors," says Bridgeman. "But our paper shows that it has a lot of benefits, besides those to do with fuel handling, so we feel it's definitely something we'd like to explore further."