Gas Production Technologies
Gasification is a thermochemical conversion process and the core technology of the Biomass-to-Liquid (BtL) pathway. In this process, solid carbon-containing materials - such as coal, wood, or other lignocellulosic biomass—are converted into a combustible gas mixture known as synthesis gas (syngas) at high temperatures, typically above 700°C. This gas consists primarily of hydrogen and carbon monoxide and can be used to produce electricity, heat, or synthetic fuels. There are three main categories of gasification technology, each with several subtypes:
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In fixed-bed gasification, the solid feedstock rests on a grate inside the reactor while air or oxygen flows upward through the material from below. As heat moves through the reactor, the feedstock is gradually converted into syngas, ash, and charcoal from the bottom upward. The resulting syngas typically exits the reactor at the top.
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In fluidized-bed gasification, biomass in the form of wood chips or similarly sized particles is mixed with hot sand and suspended by an upward flow of air or steam. This creates a fluid-like, "boiling" bed that ensures efficient heat transfer and uniform gasification. The produced syngas is withdrawn from the side or top of the reactor, while the dry ash is separated and removed from the system.
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In entrained-flow gasification, the feedstock is finely ground and injected into a high-temperature reactor together with oxygen or steam. The reaction takes place extremely rapidly at temperatures exceeding 1,200°C, producing a very clean syngas that exits the reactor directly. Due to these high temperatures, the ash melts into a vitrified slag, which must also be removed from the system.
How the dual fluidized bed technology works
The choice of gasification technology depends largely on the characteristics of the feedstock—such as particle size and ash composition—as well as on the intended end product. For the production of high-quality fuels such as Sustainable Aviation Fuel (SAF), the quality and composition of the syngas are particularly critical.
At Solarbelt, we conducted a comprehensive technology assessment with a particular focus on identifying solutions suitable for the residual biomass resources available in countries of the Global South.
Although fixed-bed gasifiers are robust, cost-effective, and well suited for simpler applications such as electricity and heat generation in isolated grids, they do not meet the technological requirements for liquid fuel production. They cannot provide the syngas quality and composition required for fuel synthesis, and their limited scalability makes them unsuitable for producing the large volumes of synthetic fuels needed.
Entrained-flow gasifiers produce a very clean, tar-free syngas with high energy efficiency. However, they are technically complex and require finely ground feedstock as well as large amounts of oxygen. In addition, these systems are only economically viable at very large scales—typically processing several hundred thousand tonnes of biomass per year. Collecting such large quantities of sustainable biomass is a major challenge in countries of the Global South.
The production of synthetic fuels via the Biomass-to-Liquid (BtL) pathway has so far been successfully demonstrated only with entrained-flow and fluidized-bed gasification technologies. Because fluidized-bed gasifiers require less intensive feedstock preparation than entrained-flow systems and can operate economically at smaller scales, Solarbelt focuses on the dual fluidized-bed gasification technology also used at the Syngas Platform Vienna. This process uses two interconnected reactors to convert residual biomass into an energy-rich synthesis gas. Sand circulates continuously between the reactors,
transferring heat through fluidized sand beds—hence the name. In the first reactor, the gasifier, biomass is heated to around 850°C and mixed with steam, causing it to decompose into syngas and biochar. The biochar is then transferred to the combustion reactor, where it is burned to heat the
circulating sand. The hot sand carries this heat back to the gasifier, enabling gasification without the need for direct oxygen injection. The result is a low-tar syngas rich in hydrogen and carbon monoxide, making it well suited for synthetic fuel production. Several commercial plants for the production of electricity and synthetic energy carriers based on dual fluidized-bed gasification technology have already been built worldwide.
