MAN Gas Engines for wood gas CHP

MAN Gas Engines for Power Generation in Cogeneration Plants

Powerhouses in every sense: MAN engines impress in wood gas CHPs

In today’s energy sector we are seeing a transition away from nuclear and fossil fuels as energy sources. As a result, power producers are placing a greater focus on ensuring a reliable, clean supply of energy to the market. MAN Engines has already been offering ideal solutions to overcome this challenge for decades, supplying robust and clean gas engines to CHP manufacturers. The use of special gases such as biogas and sewage gas has proven to be a particularly sustainable and popular method. Wood gasification is less well known, but is now also coming to the fore. Here too, MAN Engines and its partners are servicing this small but steadily growing market by supplying powerful gas engines.

Wood gas CHP with MAN E0836
CHP with MAN E0836, which was specially engineered for operation with natural gas and special gas.

“In Germany, we currently have annual forest growth of around 128 million m3, but our wood consumption is 99 million m3,” comments Günther Zibes, Head of Sales Power at MAN Engines, discussing the sustainability of the forestry industry. From his perspective one thing is certain: “Against the backdrop of the current energy transition, wood gasification is certainly a technology that can play an interesting part in the energy mix, using wood as a renewable commodity.” The principle of obtaining a flammable gas from this solid commodity, and then using it to run combined heat and power plants (CHPs), is a highly promising proposition. In order to do so, the wood first needs to be transformed into a gas in what is known as a gasifier. As part of this, the wood is transformed in a multi-stage thermochemical process, ultimately producing wood gas as fuel. This can then be used to run an internal combustion engine for direct mechanical power generation. To meet these requirements, MAN Engines currently offers special gas engines with power outputs from 54 kW to 320 kW. It has also been following the development of wood gasification technology with partners such as the Austrian boiler manufacturer Fröling for some time. Wolfgang Aichinger, authorised representative and sales manager at Fröling Heizkessel- und Behälterbau Ges.m.b.H., summarises the advantages of wood gasification as follows: “The process is simpler and faster than gasifying biomass to produce biogas. The process also takes place directly on site in the gasifier, meaning there is no need to first bring the fuel to the internal combustion engine via lines.” As such, wood energy plants have the potential to make an important contribution to ensuring the local energy supply, in particular in rural areas.

The idea of using wood as an energy source is almost as old as humankind itself. For thousands of years now, people have particularly valued the heat released during combustion. However, the use of wood gas as a fuel is not a modern invention either. Wood gasifiers were the most widely used alternative drive systems in times when commodities were in short supply, such as during the Second World War or the oil crises. At the end of the 1930s, wood gasifiers were already being installed in MAN trucks and tractors, for example. However, wood gas could never compete in the long run with more affordable fuels such as crude oil or natural gas. Nevertheless, thanks to improved methods for producing wood gas and more efficient engines, the technology has now become an interesting alternative.

Wood gas CHP with MAN E0836
Wolfgang Aichinger, authorised representative at Fröling: “Our gasification process enables us to achieve an extraordinarily pure quality of gas for biomass.”

Robust MAN engines as a cornerstone of wood gasification

Fröling Ges.m.b.H. identified this trend early on. The Upper Austrian company is one of the pioneers in wood gasification technology, and has constantly refined the gasification process further. It relies on gas engines from MAN Engines to convert the wood gas into electricity: “The engines that we use must be able to cope with the particular properties of lean gases – a category of gases that includes wood gas. They also need to emit minimal emissions, be easy to service, and operate with maximum efficiency. The engines made by MAN fulfil these requirements and are the best fit for our system,” explains Wolfgang Aichinger.

The biggest challenge facing the engines is dealing with the high proportion of carbon monoxide and hydrogen in wood gas. This differentiates wood gas clearly from other fuel gases such as natural gas and biogas, as these consist mainly of methane. Moreover, the quality of the gas fluctuates more heavily with wood gasification than it does with natural gas or biogas, which creates difficult conditions for internal combustion engines. “MAN Engines produces particularly robust engines which are able to meet even special requirements, such as use with gases containing a high proportion of hydrogen. As a basic principle, our engines developed specifically for natural gas and special gas applications are designed such that they can be used for almost any application without the need for major modifications,” comments Günther Zibes. For this reason, the units from MAN’s centre of excellence for engines in Nuremberg are not just used with natural gas and biogas, but are also deployed in more specialised applications such as wood gas CHPs.

Wood gas CHP with MAN E0836
CHP with MAN E0836, which was specially engineered for operation with natural gas and special gas.

Finding new value in waste wood

The use of wood gas CHPs makes particular economic sense in wood-processing facilities that require a lot of heat. One example of this is Hackgut Möslinger GmbH, an Austrian producer of wood chips, which operates a wood energy plant from Fröling. Four MAN E0836 LE202 industrial gas engines, each producing 50 kW at 1500 rpm, have been installed in the plant on the company’s premises in Gaspoltshofen. “The units used are very efficient anyway thanks to the optimised combustion processes, but this efficiency is boosted even further through the engine turbocharging,” highlights Günther Zibes as he explains the advantages of the MAN in-line six-cylinder engines.

The power generated by the plant flows into the Austrian power grid, generating feed-in remuneration, with the heat created when producing the power being used directly on site in the company’s work processes. The heat is used to dry wood chips on a belt dryer and in turn, these chips are used as fuel for the wood gasification plants. “Theoretically you could use any type of wood, but there are major differences in quality. Mixed wood with a high proportion of trunk wood and willow is best suited. It is particularly important that the wood is as dry as possible,” continues Wolfgang Aichinger. Newly harvested wood has a water content of 40 to 60 percent and thus offers heating power of just under 2 kWh/kg. In contrast, dried wood chips have a water content of less than 15 percent, meaning they offer heating power of around 4.5 kWh/kg.

Wood gas CHP with MAN E0836
The wood gasification plant on the Hackgut Möslinger premises. The wood gas that is produced is then used for electricity in CHPs.

Hackgut Möslinger is the perfect example of how a wood gasification plant can be used efficiently. However, Wolfgang Aichinger believes that other companies such as sawmills also stand to benefit from the new opportunities: “Residual wood is created in the wood-processing industry but has not been able to be used so far. Thanks to the wood gasification technology, however, it can be used as fuel and therefore generates added value.” Additionally, thanks to the use of the combined heat and power system, wood gasification plants with CHP achieve a peak overall efficiency of over 90%, roughly equating to 30% power and 60% heat.

A sustainable energy source with great prospects

In addition to their high levels of efficiency, CHPs that run on wood gas also impress with their favourable environmental impact. The energy is produced directly where it is required. Wood is also a natural, renewable commodity which can be found almost everywhere. As such, there is no need for long transportation routes. Moreover, the trees used for the wood gasification process will already have absorbed some of the carbon dioxide that is emitted. For Wolfgang Aichinger, the medium-term prospects for this technology look good: “Since the technology is relatively simple, we anticipate a large market for local plants. Wood gas would appear to be predestined for such applications.”

A sustainable energy source with great prospects

In addition to their high levels of efficiency, CHPs that run on wood gas also impress with their favourable environmental impact. The energy is produced directly where it is required. Wood is also a natural, renewable commodity which can be found almost everywhere. As such, there is no need for long transportation routes. Moreover, the trees used for the wood gasification process will already have absorbed some of the carbon dioxide that is emitted. For Wolfgang Aichinger, the medium-term prospects for this technology look good: “Since the technology is relatively simple, we anticipate a large market for local plants. Wood gas would appear to be predestined for such applications.”

Wood gasification is a thermodynamic process where wood is transformed from a solid biomass into a gaseous fuel. The wood is first dried at 100-200°C and the macromolecules undergo pyrolysis at 200-600°C, before the chemical processes of oxidation up to 1200°C and reduction at approx. 900°C take place. This results in hydrocarbon compounds, pyrolysis oils, and pyrolysis coke at temperatures in the range of 150-500°C. During oxidation, the hydrocarbon compounds are split into smaller molecules due to the reaction with oxygen. This produces carbon monoxide, hydrogen, water, carbon dioxide and methane. The subsequent reduction of carbon dioxide and water with carbon additionally produces carbon monoxide and hydrogen – the main share of the flammable components in the product gas.

Engine speed rpm (Hz) 1500 (50)
Engine length mm 1300
Engine width mm 740
Engine height mm 1030
Weight (dry) kg 605
Bore mm 108
Stroke mm 125
Displacement l 6.9
ISO standard power1 kW 110
Air-fuel ratio λ 1.4
Efficiency2    
-mechanical1 % 40.1
-thermal % 49.3
-total % 89.4
Combustion3   m
  1. in accordance with German Industrial Standard DIN ISO 3046, Part 1
  2. at 100% load
  3. m = lean, st = stoichiometric