Turning wood into gas


On 24 November, Xylowatt will begin operating a gas generator at CHU UCL Namur. Fuelled by biomass, it will supply the hospital with heat and electricity. This is a direct consequence of 20 years of research at the Louvain School of Engineering.

When it came time in 2001 to christen the young spin-off born of research conducted by Professor Martin and his team, one name quickly stuck: Xylowatt. The combination of ‘xylo’, the prefix relating to wood, and ‘watt’, the unit of power or energy flow, perfectly captured the company’s goal: creating energy out of biomass, mainly wood. But what kind of energy and how? ‘I was a researcher at UCL on Professor Martin’s team in the 1990s’, recalls Frédéric Bourgois, one of the company’s co-founders. ‘I worked on gasification processes. But our goal wasn’t just scientific, it was also to exert an economic and environmental impact. We developed our technology over the seven years prior to Xylowatt’s creation. Then we continued working on two aspects: research at the university and industrial development at the company.’

Wood is an attractive fuel because it’s abundant and locally available, making it a significant energy source. But it has one major drawback: it’s a solid, which limits direct use. Indeed, it’s difficult to use it as fuel for an engine. ‘The value of gasification,’ explains Hervé Jeanmart, Professor at the Louvain School of Engineering (EPL) and member of the iMMC (Institute of Mechanics, Materials and Civil Engineering), ‘is converting solid biomass into gas. The conversion itself is efficient: the resulting gas contains nearly the same amount of energy as wood. It’s an energy-neutral process long used to convert coal into what’s called mains gas, originally used for street lighting. But converting from wood is more complex.’

No tar

Wood is composed of cellulose and lignin chains, or, in chemical terms, carbon (about 50%), oxygen (42%), hydrogen (6%), nitrogen and minerals. To understand how tars form, combustion in a fireplace is a good starting point. Burning a log in a fireplace breaks these chains and produces natural gas, a process takes place in phases: first, it decomposes under the effect of heat (pyrolysis: when tall flames appear), which releases gaseous compounds as the log turns to charcoal; next, owing to the supply of oxygen, both the gas and charcoal burn (combustion: fewer flames but more intense heat). The released energy (heat) comes from the simultaneous combustion of pyrolytic gases and charcoal. One problem: imperfect pyrolytic product combustion produces tars that stick to the flue and cause chimney fires. Their polluting presence is far beyond anecdotal: tars can represent up to 50% of the initial dry mass. In gasification, they must be destroyed in order to obtain a clean gas.

‘Xylowatt developed the Notar process, whose name (“no tar”) is self-explanatory’, Mr Bourgois says. ‘Within the gas generator we physically separated the phases of pyrolysis, combustion and reduction of carbon combustion products. This is what sets Xylowatt apart from other gasification boiler companies.’ In concrete terms, in the pyrolysis zone of the gas generator, the wood decomposes into volatile matter (CHyOx pyrolytic gas) and charcoal (C). In the second part of the generator, the combustion or oxidation zone, air is injected in order to oxidize the gas into CO2 and H2O. Any tars are completely destroyed. Finally, in the third part of the generator, the reduction zone, the glowing charcoal reacts with the preceding stage’s combustion products (CO2 and H2O) to produce hydrogen (H2) and carbon monoxide (CO): the wood has become gas.



The CHU UCL Namur gas generator – or boiler – is the most powerful that Xylowatt has ever built. It will fuel a first-of-its-kind trigeneration system, combining cooling, heating and electricity generation. In the short term, however, only electricity and heat will be produced. The gas produced by the Notar process (called ‘syngas’, short for ‘synthetic gas’) will fuel a gas-powered generator that will produce electricity and hot water. The power of the syngas is about 2MW; the electrical power is about 620 kW and that of the heat is 1.1 MW. This satisfies the hospital’s needs, excepting spikes in demand. But the designers wanted to go further and take advantage of the reduced need for heat in summer in order to produce air conditioning (with power of 680 kW). This will make the university hospital the only one of its kind.

‘In this industrial project,’ Professor Jeanmart observes, ‘the university’s research involvement is logically minimal. But we’re of course continuing to work on thermal chemical biomass conversion processes in the broader sense. We’re trying to improve the technology from different directions. The first is the source of biomass. We’re testing biomass of lower and lower quality such as rubbish, ashes, straw, sewage sludge. These are economically advantageous because they’re worth less. We’re also looking to improve the pyrolytic phase, which can still pose problems when certain parameters change such as the percentage of biomass moisture. Finally, we’re working in sub-Saharan Africa to develop locally manufactured gasification technologies.’


Burkina Faso

The team of Professor Jeanmart and Mr Bourgois, who is the project’s research collaborator, just began a five-year programme in Burkina Faso focusing on heat generation, which may seem paradoxical in hot country. And why focus on producing gas instead of burning biomass to produce heat? Because the goal is to use agricultural residues including rice husks, which are difficult to burn cleanly in a boiler. The heat will be used in agri-food processes, including the required pre-sale blanching of rice, or drying facilities for food preservation. ‘And all this must be achieved in a sustainable manner,’ Professor Jeanmart insists, ‘it must be possible to locally build and maintain everything. This is also why we’re starting with heat generation and not electricity, which will come in the next phase but is more complex to implement and requires currently non-existent distribution networks.’

The programme owes much of its support to the French Community of Belgium’s Coopération universitaire pour le développement (ARES-CCD).

Henri Dupuis.



A glance at Frédéric Bourgois's bio

1990                              Civil and Mechanical Engineering, energy orientation, UCL

1990 -1991                   Researcher, Underground Gasification Modelling, Faculty of Applied Sciences, UCL

1992 -1994                   Research Associate, Institut Burkinabé de l'Énergie (Burkina Faso)

1994 -1995                   Willow Gasification Pilot Study Coordinator, Faculty of Applied Sciences, UCL

1995 -2001                   Project Leader, TtCR-gazel (coppiced willow gasification interuniversity project); Project Leader, REGAL (development of a
                                       cogeneration unit via gasification), Faculty of Applied Sciences, UCL

2001 -2014                   Xylowatt sa

2007 -2014                   Administrator, Fédération Inter Environnement Wallonie des associations au service de l’environnement

Since 2015                   Scientific Collaborator, Louvain School of Engineering, UCL

Since 2015                   Founder and Managing Director, COOPEOS scrl, cooperative targeting sustainable energy biomass development


A glance at Hervé Jeanmart's bio

1991-1996                  Civil and Mechanical Engineering, UCL

1996-2002                  PhD Teaching Assistant, Department of Mechanical Engineering, UCL

2002- 2003                 Postdoctoral Researcher, ITLR (Institut für Thermodynamik der Luft-und Raumfahrt), Stuttgart

2004                            Postdoctoral Researcher, UCL

Since 2004                  Professor, Louvain School of Engineering, UCL

Since 2008                  Coordinator for exact sciences in cooperation with Université de Kinshasa

Since 2013                  Professor of Energetics, ICHEC (Brussels Management School)

Since 2016                  Vice President, iMMC (Institute for Mechanics, Materials and Civil Engineering), UCL

Published on November 24, 2017