New gas engine improves efficiency by 20%

MAN Energy Solutions was contracted in August 2017 to supply a 7.5 MW 12V35/44G TS reciprocating gas engine to replace the plant’s two existing 3 MW units. The new engine’s two-stage turbocharged design is said to render the 7.5 MW unit particularly efficient. As a result, the Schwa¨bisch Hall CHP plant now achieves a fuel efficiency of up to 90%.

“Schwa¨bisch Hall Municipal Utilities are pioneers in the field of the energy transition and decentralised generation,” said Hajo Hoops, senior sales manager in the Power Plants division of MAN Energy Solutions. “The decision to order from MAN was made on the basis of the ... flexibility of the system. It will also be possible to participate in the energy balancing market as the existing district-heating storage components allow the decoupling of electrical and thermal energy-generation.”

MAN PrimeServ will service and maintain the engine under a ten year contract.

Efficiency

“The new engine will achieve an electrical efficiency of 47%, compared to the 39% of  the previous units,” stated Gebhard Gentner, managing director of Schwa¨bisch Hall Municipal Utilities. “This means a 20% increase in the efficiency of the plant as a whole, thereby fulfilling the requirements stipulated in the German CHP Act for the plant to be operated commercially.”

Gentner concluded: “High-efficiency technologies, such as heat and power cogeneration, make an important contribution to controllable power generation in the context of the energy transition. Schwa¨bisch Hall Municipal Utilities operates more than 50 cogeneration units at over 30 sites.”

Engine specification

The engine is described by its maker as a ‘superior efficient spark ignited two-stage turbocharged gas engine’. It is available in 12V and 20V-cylinder versions with electrical outputs of 6.9 MW to 12.4 MW. The engine’s improved power and efficiency mean a higher power density and hence a more compact plant design. The two-stage turbocharging design has two turbochargers upstream from the engine, arranged in series, to increase air charge pressure across the range, resulting in a significant increase in efficiency and output.

“The turbochargers are the core of this innovation and MAN Energy Solutions is the only large engine manufacturer that designs and builds its own turbochargers. This enables us to achieve the perfect matching of engine and turbochargers leading to the superior performance of the MAN 35/44G TS.”

Aside from efficiency, the major benefits of the engine, which are shared by other two-stage turbocharged gas engines made by the company, are said to be:

• Short start-up and power ramp up times, thus suitable for peak load applications.
• Excellent load response.
• Easy maintenance/ high availability.

Gas engines vs turbines

A study conducted by the Essen-Duisburg University in co-operation with MAN compared reciprocating engines and turbines in CHP applications and concluded that for the production of district heating from combined heat and power facilities, gas engine power plants offer a number of advantages over gas turbine based plants. Recip based plants were found to be operationally superior, both in terms of energy efficiency and cost- effectiveness.

For the study, a gas turbine based plant and two different configurations of a recip based power plant were compared. In the latter technology, multiple gas engines are arranged in combination, and can be individually switched on or off as required.

Apart from industrial CHP, the main area of application for CHP plants in the multi-digit megawatt range is the supply of district heating. “Industrial CHP applications tend to be very specific in their requirements for heat supply”, said Tobias Vogel, research assistant in the Department for Environmental Process and System Technology at the Essen-Duisburg University. “For this reason, we focused on district heating applications, and specifically the district heating network of a small city, which represents a typical example for district heating production in Germany.”

A multitude of parameters were compared, such as the heat yield, electricity production, fuel consumption, fuel utilisation and financial yield of the systems.

“All of the systems provided the necessary heat demand and met the legally required efficiency of more than 80 %”, said Vogel. “But ... the [recip based] combined heat and power systems have proved themselves superior to gas turbine based power plants and showed better energy efficiency and cost-effectiveness. The economic optimum was shown to be achieved with a mix of engines in simple cycle CHP mode and others with downstream coupled water- or steam-cycles.”

The full study is available for download from: English: http://powerplants.man.eu/docs/ librariesprovider7/brochures/man-gas-engine-study_en