The term ‘biomass’ covers all organic materials with the potential to be broken down and used in an energy recovery process to generate heat, power, natural gas and biofuel. So, for example, biomass can be used to fuel urban heating plants, district heating and cooling networks and cogeneration plants.
Over a period of years, ENGIE has conducted a number of pioneering R&D projects to improve the combustion process and make it possible to use resources other than wood. In carrying out this work, it has tested a diverse range of materials in its facilities, including olive stones and pulp, vegetable oils, coffee grounds, crop residues and wastewater treatment plant sludge… The results have been more than encouraging.
Waste or ‘plant biomass’ offers the major advantage of being carbon neutral. In practical terms, burning plant waste releases a quantity of CO2 equivalent to that absorbed via photosynthesis when the plants were alive. To achieve this, two processes are used: direct combustion and gasification.
As well as its carbon neutrality, biomass offers two more significant benefits: it is an inexhaustible source of energy and it is available everywhere in the world. Both are priceless assets in responding effectively to the energy needs of emerging countries and isolated regions.
The usual method of converting ligneous biomass (mostly logging slash, but also straw or energy crops) into energy is through direct combustion. In other words, it is burned in a boiler to generate heat, electricity, or electricity and heat (cogeneration).
Gasification is an innovative alternative that entails converting biomass into fuel, which can then be used in many different ways. The biomass is dried before being reduced to charcoal through pyrolysis (thermal decomposition). The next step is gasification, to produce a gaseous mixture containing primarily carbon monoxide, hydrogen and methane. The resulting synthetic fuel gas is then cleaned, ready to put to several uses:
- The cogeneration process recovers power and heat simultaneously, and offers the possibility of significantly improving electrical efficiency compared to using biomass in a conventional direct combustion process
- Direct substitution of natural gas for certain industrial uses such as glass fusion
- Production of biomethane (also called synthetic natural gas) by means of methanation