Read the 10 questions and answers about the SEWGS technology
Almost all organic substances – both fossil fuels and, for example, agricultural waste streams – can be gasified into synthesis gas, a mixture of carbon monoxide (CO) and hydrogen gas (H2). Synthesis gas is also a by-product of steel production and oil refining. Until now, industry has been using the gas as a fuel or feedstock for other processes. The disadvantage of this is that the carbons in the gas are released into the atmosphere in the form of CO2.
It is also possible to transform and separate synthesis gas such that blue hydrogen and CO2 remain. Blue hydrogen is hydrogen from hydrocarbons but without CO2 emissions, which industry can use as a raw material or fuel. Carbon dioxide is a raw material for various chemical products and can be stored underground.
TNO has developed the Sorption Enhanced Water Gas Shift (SEWGS) process, a revolutionary combination technology that converts synthesis gas into hydrogen and carbon dioxide. In addition, the SEWGS process separates the carbon dioxide from the hydrogen gas in the same reactor. The combination ensures a more energy-efficient conversion and almost complete CO2 removal.
The SEWGS process combines two process steps in one reactor. The first process is known as the water-gas shift reaction in which steam (H2O) converts carbon monoxide into carbon dioxide and hydrogen. Because this is a so-called equilibrium reaction, parts of the desired substances (hydrogen and carbon dioxide) will react back into the undesired substances (water and carbon monoxide); the reaction keeps itself in balance and it is impossible to achieve complete conversion. In order to prevent this undesired reverse reaction as much as possible, conventional processes usually use a lot of steam.
However, this is not necessary if a company uses the SEWGS process. The second process prevents this undesired reaction. The reactor contains a solid adsorbent material (hydrotalcite enriched with potassium carbonate) that selectively binds acidic substances. Carbon dioxide, also known as carbonic acid, therefore adheres to the surface of the adsorbent material. As a result, the carbon dioxide can no longer react with hydrogen. An additional advantage is that other acidic substances, such as hydrogen sulphide, also bind to the surface of the adsorbent.
The combination of these processes in one reactor results in a much more efficient process, which means that less energy is lost. Most of the captured carbon dioxide is released simply when the pressure in the reactor is reduced, but the last bit of CO2 that remains in the adsorbent material requires a steam flush. The heat from the process is suitable for this. And because the solid adsorbent can tolerate high temperatures, such a steam flush is quite possible.
TNO has already successfully demonstrated the SEWGS process on an industrial scale at SSAB in Sweden. This steel producer generates blast furnace gas, or synthesis gas, when converting iron ore to steel. Normally, the company uses part of the gas to heat its own processes. What remains goes to a power station.
In the European Union-supported STEPWISE project, a SEWGS installation processed 800 cubic metres of blast furnace gas per hour from one of the steel mills. Every day, the pilot installation captured 14 tonnes of CO2. The demonstration project shows that industry can save a lot of costs by using SEWGS technology to capture CO2. The SEWGS process delivers a 25% cost reduction compared to other CO2 capture technologies, which brings the cost price down to around 33 euros per tonne of CO2 captured.
The BOF2UREA project, completed in 2020, also showed that industry can cost-effectively produce urea from another type of steel gas: Basic Oxygen Furnace (BOF) gas. The INITIATE project builds on this with a prototype demonstration on an industrial scale and in an industrial environment. SEWGS plays a crucial role in this.
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