Principle of biomass gasification

There are 4 main stages in the gasification process:

  • A drying phase integrated or not into the gasification reactor,
  • A pyrolysis phase which produces, under the effect of heat and in the absence of oxidizing agent, volatile materials (CO, CO2, H2CH, CH4, H2Ovap and gaseous hydrocarbons called "tars") and coal,
  • A combustion phase, sometimes called partial oxidation, which by injection of an oxidizing agent (air, O2, H2Ovap) oxidizes the volatile materials produced during the pyrolysis phase and sometimes part of the coal. This phase provides the heat required for the entire process and destroys the tar fraction.
  • A gasification phase itself, also called reduction, closely linked to the combustion phase, which converts coal (carbon) into a fuel gas rich in CO and H2 called « synthesis gas » or « syngas » in English.

These four steps are always present, but their spatial and temporal sequence and configuration may differ depending on the biomass introduction mode, the gasifying agent and the reactor technology. They may take place in the same reactor or in separate chambers in the case of tiered gasification.

The synthesis gas is then ready to be recovered in several uses:

  • cogeneration allowing the simultaneous recovery of electricity and heat (possibility of significantly improving electrical efficiency compared to a conventional process by direct combustion of biomass);
  • direct substitution of natural gas for certain industrial applications such as glass melting;
  • production of bio-methane (also known as synthetic natural gas) through the methanation process.

Tars produced by pyro-gasification

The synthesis gas obtained carries with it, under the effect of high temperatures and in an uncontrolled way, heavy organic compounds generated by thermal decomposition and called tars. These tars condense easily on cold spots, causing pipe fouling and loss of heat exchange efficiency. In addition, tars can form coke by coking or soot by polymerization.

Although tars are not the only source of poisoning (particles, metal salts, inorganic sulphur, chlorine and nitrogen compounds), they are still the only source of poisoning. most difficult pollutant to remove.
There are different definitions of tars. In general, the tars or « Tars » refer to a complex mixture of aliphatic or aromatic hydrocarbons from one to several rings which may or may not contain a heteroatom.
The tar composition in a synthesis gas depends directly on the operating conditions (temperature, pressure, oxidizing or non-oxidizing atmosphere, residence time), the type of reactor used and the nature of the biomass.

However , tar analysis and more specifically their extreme environment sampling (high temperatures and pressures, high humidity) are proving to be a major factor in difficult task. The difficulty is to have a sample that, under laboratory conditions, either representative as much as possible of the « synthetic gas ».


The reference method for tar sampling is called the « Tar Protocol »


tar protocol principle



This technique is based on   discontinuous sampling of synthesis gases containing particles and tars under isokinetic conditions.

The sampling system consists of several trapping devices A heated particle filter, a condenser and a series of bubblers containing solvents. A heating device for the sampling lines partially prevents the condensation of tars before the devices provided for this purpose.

The sampling process consists of 4 modules and sub-modules.








The module 1 consists of a sampling valve system and a heated isokinetic probe that allows the gas sampling, whether in a pressurized reactor or not. Sampling lines are generally maintained at temperatures above 350°C to minimize the condensation of heavy tars.

The module 2 is composed of a gravimetric filter that allows to recovering particles at the exit of the reactor. Indeed, these particles could lead to clogging of the sampling supports located downstream (condenser and bubblers).

In the module 3, the bubblers of tar collection are placed in different baths with temperatures ranging from 20 to -20 °C. The baths absorb the heat generated by the cooling of the gases and their condensation. Direct condensation of liquid effluents without dilution medium (only by cold trap) can cause reactions between the trapped compounds, so a solvent is placed in each of the bubblers to absorb these compounds and thus avoid any parasitic reaction.

Isopropanol has been determined as the solvent most appropriate for the collection of tars due to its low toxicity and its ability to solubilize tars for their collection.

Immediately after sampling, the contents of the bubblers are stored in a bottle which is kept hermetically sealed at a temperature below 5°C for further analysis.

The module 4, as for him, allows to measure and settle the gas parameters.

The sampled gas flow rate is kept constant by means of a vacuum pump. It is important to ensure that the sampling rate is not too high in relation to the cooling and adsorption capacity of the bubblers.

Biomass gasification projects

The pyro-gasification sector is under construction in France with the emergence of the first commercial units. Indeed, companies are increasingly confronted with the problem of energy management and are forced to replace their use of fossil fuels with cleaner energies.

Since one of the solutions is the gasification of various biomasses, many projects are emerging. Here are some major examples for each application of gasification.

... For heat production

The CAVALE (Coopérative Agricole des Viticulteurs et Agriculteurs de Limoux et des Environs) has a distillery located in the commune of Limoux (France). This distillery recycles 10,000 tonnes of grape marc each year to produce potable alcohol, colourings, polyphenols, grape seeds, tartars and essential oils. In 2016, the cooperative decided to investigate a project to valorize spent marc in gasification at its industrial site at the Pont du Sou in Pieusse (11). The principle is to produce a syngas by gasification of the marc and then to burn this gas via a burner to supply heat to the pome dryer used in the distillery process.

The company Verallia (formerly Saint Gobain Emballage) in Champagne (France) designs and manufactures glass packaging, including champagne bottles. In 2018, Verallia produced nearly 16 billion bottles and jars. The glass furnace of the hollow glass production site in Oiry (Epernay), where champagne bottles are made, formerly supplied with natural gas, is now partly supplied with syngas produced by gasification of by-products of the wine-growing operation (vine shoots, vines, etc.).

…. For cogeneration


The power plant Synnov based in Villers-sous-sous-Montrond (France) recycles waste (building waste and refusal to sort) by gasification. The syngas produced by gasification drives five engines and a turbine to produce electricity that feeds into the EDF grid. The heat produced is recovered and fed to neighbouring industrial groups. The processing capacity of this plant is 45,000 tonnes of waste per year. It can thus produce 51,600 MWh of electricity and 90,000 MWh of thermal energy per year.

There are many other gasification cogeneration projects in our European neighbours where the economic context is more favourable (preferential electricity feed-in tariff), such as Germany and Italy, for example, which have hundreds of units in gasification cogeneration operation.

…. For the production of 2G biomethane

Other projects have chosen to convert syngas into biomethane for injection into the grid. These projects are generally of a larger size. Here are the main ones:

The power plant GOBIGAS, inaugurated in 2014 in the city of Gothenburg (Sweden), converts 90,000 tonnes/year of wood chips into biomethane. The latter is injected directly into the city's gas transmission network. The installation has a capacity of 20 MWbiomethane (34 MWbiomass).

The project was launched in 2006 and is part of Göteborg Energi's strategic plan to achieve 100% renewable gas in the city's grid by 2030. The network is also supplied with bio-methane by waste methanisation units.

The main target market in Sweden is the distribution of bio-methane fuel in the form of CNG. The city of Gothenburg already has more than 50 charging stations and is supported by strong demand from businesses and individuals.soclema_chariot sampling tar_tar protocol

In France, the project GAYA is a semi-industrial R&D platform managed by ENGIE and subsidized by ADEME. Its objective is to demonstrate the technical, economic and environmental feasibility of producing biomethane by biomass gasification followed by synthesis gas methanation (conversion of gas into methane). The results of this pilot project, which has been in operation since 2016, and the support of the government should enable the first industrial-scale installations to appear in France by 2021. SOCLEMA participated in this project by providing  A TAR PROTOCOL sampling trolley.

The demonstrator GoGreenGas is a project under development in Swindon, England. It is led by Advanced Plasma Power in partnership with Cadent (gas distribution network in the United Kingdom) and two other partners. It aims to demonstrate the technical, economic and environmental feasibility of producing biomethane for injection into the gas network. It will convert biomass and industrial waste into synthetic methane using a technology that couples a dense fluidized bed with a plasma torch. The latter is used to crack the tars contained in the syngas, and to vitrify the ashes into a material that can be reused in the construction sector. Currently, the pilot in place consumes 1.8 tonnes of waste per day (at 10% humidity) and the construction of an industrial unit is in progress. The capacity of a standard Gasplasma® industrial unit is 400 tonnes of waste per day.

The demonstrator Ambigo is a project under development in Alkmaar in the Netherlands. It aims to develop the production chain of biomethane from pyro-gasification for grid injection. Ambigo will be supplied with wood and recycled materials, which it will convert into methane using pyro-gasification technology combined with methanation. The unit will have a capacity of 2.6 MWbiomethane (4 MWbiomass) and will inject into the local gas network. The profitability of the project is partly based on the feed-in tariff negotiated with the Dutch government, in agreement with Gasunie, the natural gas infrastructure and transmission company in the Netherlands.

... For the production of biofuels

Syngas can also be converted into biofuels, notably via Fischer-Tropsch synthesis. Here are two projects under development in France and Germany:

The project BioTfuel , launched in Dunkirk, France, in 2010 by a consortium of major companies, including the Total, Axens and Avril groups, aims to convert lignocellulosic biomass (agricultural and forestry by-products or specific biomass) into second-generation biodiesel and biokerosene. The biomass is gasified to produce a synthesis gas which is then converted into biofuel by Fischer-Tropsch synthesis. The objective by 2020 is to produce 200,000 tonnes of biofuel per year (2/3 biodiesel and 1/3 biokerosene) from one million tonnes of biomass.

The pilot Bioliq II located in Germany aims to demonstrate the feasibility of a process for converting biomass (agricultural and forestry by-products) into biodiesel. The process consists of a rapid pyrolysis process that produces a high energy value oil called SynCrude. This oil is then carbonated to produce a syngas rich in CO and H2. This syngas is then purified and converted into biodiesel. Ultimately, this process should make it possible to produce 1 litre of diesel fuel from 7 kg of straw.

... For the production of bioH2

Finally, syngas can be used to produce hydrogen. Here are the two major projects in France:

The project «  Wood-Hy/Hy-boy », led by the community of municipalities of the Landes d'Armagnac, aims to produce green hydrogen from the crushing wood of the pines of the Landes forest via a gasification process. The site should go into production in 2022 and the hydrogen produced will be used for green mobility. Production is expected to reach 1,000 tonnes of hydrogen per year initially, enough to power more than 5,000 vehicles each year. It is a project that will create jobs while enhancing the local short circuit resource, with a limited wood supply radius of 30 km. The project was developed with the Toulouse-based company Enosis and is now supported by the Engie group. He is also one of the winners of the national call for projects « Hydrogen Territories ».

The project VitrHydrogenic aims to develop and optimize an industrial process, called Hynoca ® (HYdrogen NO CArbon) developed by the French company Haffner Energy. This is a process for converting biomass into hydrogen by pyrolysis followed by a Water Gas Shift. A first demonstrator should start in 2019 in Vitry-le-François (France) for a period of 4 years. At the beginning of 2020, the first commercial station will be commissioned on site. It will produce 120 kg of hydrogen per day from 500 tonnes of wood pellets per year. These pellets will gradually be replaced by forest chips and, in the long term, wood will only represent 20% of the input material, to favour the use of waste (agricultural waste, forest waste, pig slurry, poultry droppings, cereal straw, organic household waste, etc.). This station will supply 200 vehicles (base 20,000 km/year) each year.