A new wave of technology for clean energy conversion
Innovative looping technology may pave the way for industrial applications. Gas switching combustion may be used for power generation or hydrogen production.
THE REASON THAT CARBON CAPTURE technology has not been commercialized as expected, is that they all carry a significant energy penalty. If industrial companies want to capture CO2, they will have to spend more energy. And the costs will soar.
“There is simply no off-shelf technology that companies can buy, without having to burn more fuel and spend more energy to capture CO2 ,” says project director Shahriar Amini at SINTEF. “So today, implementation hinges on incentives and funding from governments.”
Amini heads a project called GaSTech – Demonstration of Gas Switching Technology for Accelerated Scale-up of Pressurized Chemical Looping Applications. The aim of this research effort is to develop cost-effective, affordable CCS-technology.
The point of departure for the project is conventional postcombustion processes. In chemical looping combustion, there are two reactors. In the first reactor, an oxygen carrier material (i.e. a metal oxide), is oxidized by air. The next step, in the second reactor, the oxide is reduced by natural gas.
The solid metal or metal oxide exists in the shape of powders. Hence, the oxygen carrying material – whether in the form of metal or metal oxide– keeps looping between the two reactors. The chemical reaction in the oxidation stage creates a very high temperature in the stream of gas, which can be used in power plants to create electricity.
LIMITATIONS OF CONVENTIONAL TECHNOLOY
However, there are certain limitations to the conventional process. “If you want to scale up this reactor system in very large units, the circulation of solids is very difficult”, explains Amini.
“You would need to apply very high pressure for higher efficiency–and operating two pressurized units complicates the industrial design and operation.”
Consequently, Amini and his group of researchers have taken this technology one step further. The gas switching combustion process uses one single reactor. Instead of moving the oxygen career materials from one reactor to another, a valve in the reactor inlet switches between injecting natural gas and air into the reactor.
SMALLER MODULES ARE CONNECTED
“Let’s assume that the metal powder oxide in the reactor is iron oxide, FeO,” explains Amini.. “At the inlet of the reactor, a valve is adjusted so that natural gas flows into the reactor. The natural gas will react with the oxygen of the FeO, reducing the oxide to metal (Fe). The outlet gas coming out of this reaction is a pure stream of CO2 with water vapor. After separation of water vapor easily through condensation, a very pure stream of CO2 is created, which then can be compressed and transported for storage.
Then, the valve is set to inject air. The Fe reacts with the oxygen of the air, converting the iron to iron oxide. This is an exothermic reaction that creates a stream of gas with temperatures up to 1000 °C. The air, deprived of its oxygen, now consists mainly of nitrogen that can be led into a thermal power plant to produce electricity.
“It’s about simplicity,” says Amini. “It’s much easier to scale up a concept with one single reactor. And the beauty of this process, is that we don’t necessarily need to build very large units. We can have smaller plants modules connected to each other to work in a cluster.”
One advantage of the technology is that it’s able to produce both power aswell as hydrogen.
RELEVANT FOR NORWEGIAN INDUSTRY
“This technology can be very relevant for Norwegian industry, because in hydrogen production, natural gas is used as a feedstock, and you can separate CO2 with no energy penalty.” Over the last decade, in a number of projects funded by Research Council of Norway, European Commission and ACT*, Amini and his colleagues have tested this reactor extensively. The next step will be to put the technology to work in a pilot. Hopefully, that will be the next project.