Pyrogasification or thermolysis of biomass is one of the most promising ways to produce hydrogen. Carbon-negative, it combines pyrolysis and gasification to produce renewable hydrogen and biochar.
Replacing fossil fuels is easy to say, but hard to do: using electricity is often not an option. This is one of the big issues in the energy transition. One of the most promising avenues is hydrogen, which can, for example, replace coal and coke in steel production or methane for thermal uses. The problem is that today, it is largely produced in a polluting way (steam reforming of methane or coal gasification), only 4% from potentially renewable sources (electrolysis). An absolutely fantastic solution is the pyrogasification of biomass.
In a nutshell, it consists in heating biomass in order to create a renewable synthetic gas (syngas) rich in hydrogen, which is then processed to extract the latter. The operation consumes little energy (it is self-powered: part of the syngas created is used as fuel), uses a material that has captured CO2 (a renewable biogas is produced) and, in addition, part of the latter remains in solid form (a product similar to coke: biochar). In the end, the process is therefore carbon-negative! For example, the HYNOCA process developed by Haffner Energy claims to store the equivalent of 16 kg of CO2 for each kg of hydrogen produced, i.e. 12 kg if we take into account the whole balance of the operation.
The pyrogasification process
Pyrogasification is a process that combines pyrolysis and gasification. First you dry the inputs, before pyrolyzing and gasifying them. Then, the fate of the syngas produced will depend on the desired purpose: it can be used as fuel, for cogeneration, to produce renewable heat, be transformed into methane by methanation or go through catalytic conversion (“water gas shift”) and then purified, to get dihydrogen.
Inputs: wood, agricultural waste and other biomass
The biggest problem and strength of pyrogasification is the material used as fuel. This varies, but in principle, many materials can be used:
- Crop residues and co-products of the food industry.
- Other wastes: “Solid Fuels of Recovery (CSR), used tires, dried sludge of STEP, etc” (ATEE)
There are millions of tons that are currently not valorized to exploit. The wood industry could thus provide colossal quantities of material. In Ivory Coast, the cocoa industry produces nearly a million tons of “pods”, which could be transformed into hydrogen to produce electricity, as the electricity network has many failures in this country. This is an extraordinary way to develop the energy transition.
Interesting point, according to ATEE.fr, this field would be complementary with methanization:
Many biomass resources do not “burn” well (ash fusion, for example lignocellulosic composting residues) but lend themselves well to pyrogasification (absence of oxygen avoiding ash fusion). On the waste, the pyrogasification field is positioned on homogeneous resources with strong calorific value, on small or average capacities, coherent with the radius of local supply and not on household waste with very big capacities (incineration).ATEE.fr
Nevertheless, beyond the variety of possible inputs, the characteristics of the material supplied must be particularly homogeneous:
Indeed, on the quality and the setting to the specifications of the inputs (moisture, granulometry, PCI, dust rate, etc.) will depend the good functioning of the processes and the quality of the produced energy compounds.ATEE.fr
This is the major weakness of the process, which concentrates a large part of the research and development efforts of the company.
What is pyrolysis ?
Pyrolysis consists in heating inputs at high temperatures in the absence of oxygen. It produces solid residues (“char”), liquid (tar, oil) and, of course, gases (CO2, H20 CO, CxHy, etc.). The predominance of the different substances varies according to the specific conditions. The ADEME distinguishes two types of pyrolysis:
- “Flash” pyrolysis, consisting of rapidly raising the temperature to 500-650°C, which creates mostly gas.
- Slow pyrolysis, consisting in slowly raising the temperature until 300-400°C, which favors the appearance of solid carbon (coke/biochar, the term seems to be used indifferently)
So there are several points on which my souces do not agree.
- Pyrolysis temperatures
According to Atee.fr, the temperature of the pyrolysis phase is between 400 and 1500°C. For Block et al (2019), it is between 300 and 800°C. It is still different for ADEME (see data retained).
- Pyrolysis or thermolysis?
I have a doubt about the use of the term pyrolysis or thermolysis. The company Haffner Energy speaks of “thermolysis” for the first stage of its HYNOCA process (which heats to 500°C). Another reliable source has repeated this distinction. According to a presentation by Suez, thermolysis would occur in the total absence of oxygen and pyrolysis in the presence of a small amount of oxygen (which would make combustion incomplete). They elaborate extensively on the distinction. This is also what emerges
According to the ADEME website, thermolysis “refers to pyrolysis where the heat required for the reactions is provided by a source external to the load to be pyrolyzed.”
I preferred to keep the more common term pyrolysis, but it is a point of caution.
Gasification occurs at high temperatures, between 900 and 1200°C, and involves the injection of a “gasifying agent”, which can be air, pure oxygen, water vapor or CO2. The heavy molecules become lighter and lighter, until they form “permanent” gases (CO, H2, CO2, CH4), tars, char and ashes. It can take place in the same reactor as pyrolysis.
To fuel these reactions, oxygen can be injected (pure or in air only), which triggers these reactions releasing large amounts of thermal energy, using the syngas as fuel:
There are several technologies to organize these processes on two topics:
- Are all these operations done in the same reactor?
- How the “bed” (= the material used) is “moved”. Classically, we distinguish between fixed bed, fluidized bed or entrained flow bed installations.
However, the variations are infinite.
Cleaning and use of the produced syngaz
Here, a syngas is obtained which consists mainly of H2 and CO and to a lesser extent of CH4, CO2, water and, occasionally, nitrogen. In principle, we have already finished the pyrogasification itself. Then, the ways vary according to the destination that one wants to give to the produced gas. If we want to extract hydrogen, we pass it through what is called the “water gas shift” (catalytic conversion), which makes it possible to extract H2 from the CO of the syngas, then we purify it.
One can also want to transform the syngas into CH4 (see Gaya below) or into biofuel by the Fischer-Tropsch synthesis (e.g. BioTfuel), but I don’t know precisely how it is done.
Biomass pyrogasification projects
Motivated by the oil shocks of the 70’s, research was interested in pyrogasification and many projects were born between 90 and 2005 for waste management. Nevertheless, the expected performances were not reached, the treatment being too expensive compared to incineration. Today, the focus is not so much on an alternative to waste incineration as on biogas production. The objective is now to demonstrate the feasibility of the technology. Two main types of projects can be distinguished: those aiming at producing H2 and those aiming at producing biomethane or biofuels. I put aside those intended to produce only heat or cogeneration, which seem to me less interesting.
Hydrogen production by pyrogasification of biomass
Hydrogen has many interests for the environment. In addition to the fact that we already use large quantities of it, the production of which must be replaced by environmentally friendly processes, it could be used as a fuel for mobility and to decarbonize several sectors of industry (notably cement and steel) and to stabilize electricity networks. While water electrolysis using renewable energy sources (RE) is attractive, it faces difficulties that call into question its viability. On the contrary, pyrogasification is clearly a hope for the energy transition. It allows the valorization of otherwise unexploited materials and absorbs CO2.
Haffner Energy and the HYNOCA process
The HYNOCA process developed by Haffner Energy promises to produce hydrogen from biomass, by thermolysis, then gasification (they call it “steam cracking”, but it’s the same thing I think). The company was successfully floated on the stock exchange earlier this year and a demonstrator of their modules is being installed in Strasbourg. They promise a cost of dihydrogen production competitive with steam reforming of methane, down to 1.5€/kg H2 and a carbon-negative process, capturing the equivalent of 12kg of CO2 per kg of H2 produced.
Energy&+, the Breton project
Energy&+ is a rather extraordinary company: started in 2006 as a plumber-heater, it turned to the valorization of biomass, especially with methanization. Recently, it has been developing wood pyrogasification. It has created W&nergy, a holding company that will carry 5 projects and pyrogasification and has received an investment of 7 million euros Eiffel Investment Group. They announce 2 projects in service from 2022. (rq doubt: they do not mention the production of hydrogen ôo)
They would participate “within the framework of the FORETS project (Training, Research and Environment in Tshopo) financed by the European Union, and executed by the Center for International Forestry Research (CIFOR), in the design of a cogeneration plant in Yangambi, in the Tshopo Province (DRC).” (source) The Breton company is expected to deliver a wood pyrogasification unit offering 150kW electrical and 250kW thermal. The hydrogen produced would be immediately converted into electricity and heat (to be verified).
Wood-Hy/Hy-boy carried by the Landes d’Armagnac community of municipalities
Wood-Hy/Hy-Boy aims, as its name suggests, to transform wood into hydrogen. The project is supported by the Landes d’Armagnac community of communes. The site, installed in Losse, is supposed to start production in 2022 and produce 1000 tons of H2 per year. There seems to be very little news apart from the announcements.
Production of renewable synthetic methane
Many projects are intended to produce biomethane by gasification (e.g. Gobigas (Gothenburg, Sweden, 2014), Gogreengas (Swindon, England), Ambigo (Alkmaar, Netherlands)). We can also note the BioTfuel project, launched in Dunkirk in 2010, which aimed to transform biomass into a synthesis gas that is then converted into biofuel by the Fischer-Tropsch synthesis. In France, the best known project is GAYA. The commercial scale is potentially reached and industrial installations are under development: Salamandre, from Engie, and the projects of Qairos Energies and HYMOOV.
GAYA: transforming wood into biomethane through pyrogasification
Gaya is a semi-industrial research and development platform based in Saint-Fons. Its purpose is to test the feasibility of solutions based on gasification. The project, which brings together several partners, is led by Engie. Initiated in 2010 and launched in 2016, the initiative aimed to transform dry wood into biomethane by gasification, then methanation of the syngas. The initial budget was €47 million, with €19 million coming from ADEME. It had produced its first cubic meters of gas in 2019. The renewable CH4 produced can be injected into the gas network or used as CNG (Natural Gas for Vehicles).
The plan originally focused on forest biomass, but recently the facility has also been using solid recovered fuels (SRF), such as paper, cardboard or even some plastics, which would otherwise have been destined for landfill. It began production in November 2020, which would be a “world first.”
Building on this experience, Engie plans to deploy an industrial unit in Le Havre: the Salamandre project. Starting in 2023, the facility would produce up to 150 GWh of gas and 45 GWh of heat from 70,000 tons of waste per year (CSR).
To dig further:
- Chantal Block, Augustina Ephraim, Elsa Weiss-Hortala, Doan Pham Minh, Ange Nzihou, et al.. Copyrogasification of Plastics and Biomass: a Review. Waste and Biomass Valorization, Springer, 2019, 10 (3), pp.483-509
- Atee.fr : La pyrogazéification : comment ça marche ?
- Atee.fr : Les intrants en pyrogazéification
- ADEME: https://www.ademe.fr/expertises/dechets/passer-a-laction/valorisation-energetique/dossier/pyrolyse-gazeification/principes-pyrolyse-gazeification
- Soclema : https://soclema.com/applications/gaz-renouvelables/syngaz-issu-de-la-gazeification-de-la-biomasse/