After operating biogas-fuelled CHP systems for a decade using agricultural waste, GF-Bio-Energie has now replaced its three engine-based units with one 1.2 MWe engine from MTU Onsite Energy, and redeployed the smaller units to provide heat and power to buildings in the local town. Christoph Bendzko tells the story.

In 2008, GF-Bio-Energie Hasetal in Löningen, Germany, replaced its dual fuel engines with biogas-powered Otto cycle engines from MTU Onsite Energy.

Maize is among the crops being used by GF-Bio-Energie to produce biogas, used to supply electricity to the local grid and to heat building in the town of Löningen

To maximize cost effectiveness, the company aims for high performance from each combined heat and power (CHP) system. In light of the experience gathered with the 370 kW engines, the company was very interested to test a pilot series model of the 4000 Series with nearly 1.2 MW of electrical power in a 12-month trial involving 7500 hours of duty.

Since October 2009, this pre-trial unit has been operating as the baseload engine supplying heat to the biogas plant and most of the public buildings in the small town of Löningen in the German state of Lower Saxony. After exhaustive trials of the new biogas engine, its market introduction followed in March 2011.

THE SWITCH FROM FARMING TO BIOGAS

As the profit margins for corn, grain and potatoes shrank towards the end of the 1990s, many farmers started looking for alternative sources of income, and interest grew in CHP systems powered with biogas. Brothers Reinhard and Hermann Gross, who grow maize and grain on roughly 1800 hectares of arable land and already operated a liquid manure exchange, recognized a great opportunity in the exploitation of biogas.

Converting agricultural waste, crops grown for fuel, liquid manure or even chicken manure into electricity and heat promised higher profits than selling crops on the food and feed market because electricity generated from biogas is sold at fixed rates in Germany.

The heat produced in the CHP systems can be used in the fermentation process or for community heating in the immediate vicinity.

MTU’s 4000 Series engine generates nearly 1.2 MW of electrical power

In 2001, the brothers went ahead with their plans and set up a biogas plant with ten 80 kW dual fuel engines in the machinery hall of the specially founded company called GF-Bio-Energie Hasetal GmbH.

The electrical power – altogether 800 kW – was fed into the local power grid and heat supplied to a school campus that includes three schools and two gymnasiums as well as an indoor swimming pool and a meeting hall in Löningen.

For the heat transfer, a 1.8 km district heating pipeline was built. Thus, GF-Bio-Energie Hasetal provides permanent power of about 500 kW to the city of Löningen for heating the school campus. The remaining need of about 1600 kW is covered by existing boiler plants in the respective buildings.

NEW CHP SYSTEMS

Servicing and maintaining ten engines was becoming very expensive. In addition, stricter emission controls and the need for reliable, powerful units and higher efficiency led the operators of the plant to rethink their approach seven years later. They reshuffled their cards and chose Otto cycle engines. Three CHP modules from MTU Onsite Energy using 400 Series engines, each producing 370 kW of electricity and heat replaced the dual fuel engines. The reliability of these modules of the 400 Series was the deciding factor.

Brothers Reinhard and Hermann Gross have switched from growing maize and grain for the food market to operating a biogas-fuelled CHP plant

But the operators were not satisfied with successes so far achieved. Their plan for the future was one large engine to cover the baseload demand and a few smaller ones to cope with the demand peaks. ‘The positive experience with MTU Onsite Energy and the Series 400 engines were instrumental in our decision to look for new solutions together,’ relates Reinhard Gross. And MTU Onsite Energy made them a special offer: a pilot series model of the new Series 4000 biogas engine. ‘At first we had serious doubts whether it was the right decision. A pilot series model that nobody had any experience with was clearly a risk,’ admits Gross. Nevertheless, the team around the brothers and engineer Wilfried Förster stuck by their decision – and they haven’t regretted it so far.

They built a new generator shed and, in 2009, MTU Onsite Energy engineers installed the CHP module with the new 12-cylinder biogas engine. Now they only have one engine to service in their plant and, in addition, save space. With an electrical output of 1166 kW and more than 1300 kW of heat output, this single engine replaces all three of the smaller Series 400 units.

In its trial period between October 2009 and October 2010, the new biogas engine completed over 7500 hours of duty. Monthly averages for duty and downtimes show that the engine was in use for nearly 90% of the time. ‘That is certainly better than we expected,’ adds Gross.

Low maintenance costs are one of the major benefits of these large engines. A large machine only requires a single oil change and the replacement of one set of spark plugs, for example. Producing the same power would require three 400 Series machines, which would need correspondingly more time for maintenance and inspection.

BIOGAS ENGINE IMPRESSES

The new biogas engines are based on the modular concept of the Series 4000 engine family, which covers both diesel and gas engines and is available in various versions for more than 20 different applications. MTU Onsite Energy first marketed natural gas-fuelled systems based on Series 4000 engines eight years ago. The design and control technology of these gas-fuelled, spark ignition engines which had already proved themselves in the field, were then modified to suit the peculiarities of operation with biogas.

The R&D target was to achieve an optimum balance between competing aims (maximum performance with simultaneously low pollution operation) while using biogas – a fuel with less volatility than natural gas. To ensure that the lean mixture used to achieve low emissions does not lead to a reduction in power, the engines are equipped with turbochargers.

With a rate of electrical efficiency above 42%, Series 4000 biogas engines achieve almost the same level as comparable natural gas engines. And to ensure that fluctuations in gas quality have no negative effects on either engine performance or engine service life, MTU engineers developed and optimized an engine management system that facilitates operation with biogas with methane content as low as only 45%.

In line with customer demand for high electricity revenues, design engineers placed particular emphasis on reliability and adopted a robust design and a defensive engine set-up that deliver long-term, low-fault operation to minimize downtime and reduce maintenance costs.

To keep investment costs low, wherever practical the biogas engine incorporates components also used in natural gas and diesel units. These include the diesel engine block, which is designed for the highest dynamic loads, and the robust crankshaft, which has already performed extremely well in continuous operation in gas applications. Design features from natural gas applications, such as uncooled exhaust lines, have also been adopted.

The piston/cylinder liner assembly was developed from scratch. Instead of aluminium pistons, forged steel components are used in the biogas combustion system. Research on the lubrication characteristics of the pistons and the cylinder liners led to optimization of the system whilst biogas-specific valve timing and valve stroke were also adopted. These features maximize utilization of the biogas fuel, which has a lower calorific value than natural gas, and also facilitate low-pollution combustion.

Handling agricultural waste, the feedstock for GF-Bio-Energie biogas CHP operation

The well-known and proven Advanced Diesel Engine Control system (ADEC) was adapted for use in the biogas sector. This unit controls the engine in line with prevailing operating conditions and communicates with the higher-level MTU Module Control (MMC) via a bus system. All engine operation and diagnostic statistics can be accessed by the operator or MTU Onsite Energy Customer Services either on site or via a remote maintenance system.

The 4000 Series engine has proven itself at GF-Bio-Energie Hasetal and has also shown its quality in the laboratory. After six months of operation, the engine was dismantled and analyzed at MTU’s Friedrichshafen facility. Measurements revealed that even the newly designed components performed well, showing extremely low wear. Now reassembled, this engine is once again operating in the biogas plant.

MORE HEAT FOR LÖNINGEN

The Gross brothers were always confident their concept would bear fruit. Even before looking for a large-scale engine like the Series 4000, they and their managing director Wilfried Förster had decided, together with Mayor Thomas Städtler, that the existing Series 400 engines should be relocated as satellite CHP modules. As part of the new district heating scheme for the town of Löningen, work has been going on since October 2010 to install them in the vicinity of public buildings to supply electricity and heat close to the point of consumption.

The necessary biogas fuel from the plant is delivered to the satellite CHP modules via newly installed pipelines. That means that less heat is lost in transit. What is more, with the new district heating system, the people of Löningen will need less gas for heating and reduce the town’s carbon footprint by 1225 tonnes of carbon dioxide per year. To provide additional capacity, three more Series 400 engines will be installed in satellite CHP plants. ‘In that way, we will be able to bring in each engine individually as required and always guarantee sufficient electricity and heat,’ explains Förster.

In future, three more schools, a sports hall, the hospital, the retirement home plus a garden centre, two banks, the town hall and the open air swimming baths will be supplied. The heat with a thermal output of 1200 kW per hour covers the basic energy need of these public buildings. Additional heat demands are covered by redundancy boiler or existing boiler plants in the schools.

As they would have to pay compensation if they failed to supply heat, and they do not want to repair broken-down engines themselves, one thing was important to the operators from the start: ‘We need a reliable partner who deals with and solves any problems. We found that partner in MTU Onsite Energy,’ says Reinhard Gross. The robust design and conservative tuning of the new biogas engine enable long-term trouble-free operation. In other words, the engine is idle much less of the time. A complete overhaul of the basic engine is not scheduled until around 64,000 hours of duty have been completed. That is more than seven years if the engine runs 24 hours a day.

BENEFITS FOR ALL SIDES

Both GF-Bio-Energie Hasetal and the town of Löningen benefit from the business relationship. Under German law, the supplier receives payment for the electricity it feeds into the power grid. A total of about 2.1 MW electrical output is provided to the power supply company. The town of Löningen, the hospital and other consumers benefit from the heat supply by saving on heating costs. And there are environment benefits as well – the operators have retrofitted all their engines with catalytic converters that lower formaldehyde emission.

Further investment in their biogas plant by GF-Bio-Energie Hasetal will depend on acquiring new heat consumers. ‘Responsible use of renewable energy crops such as maize and grain is very important to us. So we will only expand when the demand is there,’ explains Wilfried Förster. As long as the company has no need for itself, it will again sell most of what the farmers sow this spring, because they have always grown and harvested their own raw materials for producing biogas.

Christoph Bendzko is the Senior Manager for Strategic Development at MTU in Augsburg, Germany. Email: christoph.bendzko@mtu-online.com

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