Interview Waste-to-energy : Ole Hedegaard Madsen: "Chemical looping has the potential to get really big"

Decarbonisation is the buzzword of the moment. One of the emerging technologies is chemical looping, which utilizes a reduction reaction to allow combustion without air. This could help various industries, waste to energy among them, to drastically reduce their CO2 emissions. Ole Hedegaard Madsen, Senior Director of Technology and Business Development at Babcock & Wilcox, explains the new technology.

How long have scientists been working on chemical looping?

Research has been ongoing for 20 to 25 years. Babcock & Wilcox has been active in this field of research for nearly two decades.

To start at the beginning: what is chemical looping?

The idea of avoiding air as an oxidiser in the combustion process is a really old one. We need the oxygen but we don’t need the 80 per cent nitrogen. Chemical looping is a way to bring oxygen to a fuel by having the oxygen connected to a particle. Typically, this particle is a metal. After you have added a number of oxygen molecules to the metal particles, you bring them in contact with your fuel. And then you oxidise the fuel the same way you do in normal combustion processes. But in this process, you have oxygen only in the reaction. So, the outcome from the oxidation is basically 100 per cent CO2. Of course, this is a big advantage when we talk about greenhouse gases because you don’t have to capture the CO2. What you get is CO2 and some water, which is easy to remove; you can just cool it out of the process. And the CO2 can be used for power-to-X processes or stored underground.

After combustion, the particle leaves the reactor and circles back to an oxidiser, a fluidised bed, to add oxygen back on the particles, which is done simply with air. During this process you actually get a lot of heat. In cooling down the fluidised bed, steam is produced, which also can be used for various processes.

You have a process where in one way you are producing CO2 but you are still producing energy in a conventional way – but without the involvement of any nitrogen.

Why are you now launching your BrightLoop technology?

The basic principle of chemical looping was quite quickly understood by everybody in the combustion industry. But one of the challenges is that the metal particles in the past have had a limited lifetime and were quite expensive to make. That’s what Babcock & Wilcox have developed together with Ohio State University, which is one of the leading universities involved in research and development of chemical looping for the combustion industry. The unique particle developed by Ohio State and B&W has a lifetime of at least two years before it needs to be replaced. So that makes it economically viable to do chemical looping.

We have also developed a two-step chemical looping system. The first step is isolation of CO2. And then we have an extra step where we add some steam to be able to produce hydrogen while the metal particle still goes back to the oxidiser and round, like I explained earlier. So by making CO2 and making hydrogen you get a very flexible process.

What fuels are suitable for chemical looping?

We are testing different types of fuels. We started with coal, and now are testing gaseous fuels like natural gas. We also are going to test different biomass fuel stocks, including waste wood. But there are some constraints. You cannot use municipal solid waste (MSW) in the BrightLoop process; it would be simply too inhomogeneous. This type of waste can only be combusted in a conventional waste-to-energy plant. But I think the technology can benefit from the sorting of the waste too. So it could be rubber, waste wood – different types of cleaner waste streams. At the moment we are testing the requirements of the fuel to be able to go into the process.

Within this closed loop, are there still emissions?

Yes; there will still be some emissions. Looking towards the future, there will be more source separation of waste. We have more advanced sorting technology. We are investing a lot of money in the waste upstream and one of the positive things about that is that it gives you more opportunities downstream, because out of these processes you get cleaner waste streams and some of them will be feasible to put into a system like chemical looping. But of course, it’s still waste. Also, with other technologies like pyrolysis: even if the plastic goes in a loop, the additives to the plastic don’t magically disappear. It’s similar with the fuel for our chemical looping process: we typically used wood waste that will contain small amounts of chloride, sulphur and also some metals. These minor substances will still be there after combustion. So, the CO2 flue gas coming out of the reactor still has to be cleaned, but now the flow is only 20 per cent instead of 100 per cent because we don’t have all this nitrogen.

But it’s much more economically efficient to clean the flue gas without nitrogen.

So for most fuels you still have to clean the flue gas for those substances because the fuel itself contains them, but it’s much easier to remove.

When did Babcock & Wilcox get involved in the project with Ohio State University?

Ohio State started chemical looping research around 2004 with a laboratory scale project, and built a pilot plant in 2008. In 2014 B&W built a more industrial standard pilot plant, and in 2016 the testing was done with the new particles. Our next step is to build a demonstration plant at 2.5 to 25 megawatts thermal input, probably at an existing site to benefit from the existing auxiliary equipment. It’s a modular system so it’s quite easy to go up in size. Also, all the technology used is well-known and tested. So, the thermal input can go up to 100 megawatts.

How important will chemical looping be for waste to energy in the future?

It could be quite big, because in Europe and to some extent in North America, a lot of effort is put into sorting the waste. Out of that a lot of waste will actually be recycled. But a certain amount of waste will remain unrecyclable. So, this waste stream can be treated with new technologies like chemical looping or pyrolysis.

Even if we recycle 50 per cent, there will be a certain amount that cannot be recycled. If you look at Europe, 25 per cent of waste still goes to landfill. So there are opportunities for new technologies.

Can all combustion-based energy production systems use chemical looping?

If you look at chemical looping and fossil fuels, there is still much that can be done. When we started on the project with Ohio State back in 2014, we talked about climate change but not on the same scale as today. In that time the biggest problem with coal was the huge amount of CO2 coming from the process.

The good thing about coal is that it is found all over the world, so there is no monopoly on fuel. If you could use the coal and reduce the CO2 using chemical looping, then from a greenhouse gas point of view you have a good power plant. And I think to some extent that argument is still valid, because of course you still need to remove sulphur and chlorine from the flue gases. But in doing that and removing the CO2, you have a very stable source for power production. Also if you look at natural gas you could produce and use hydrogen.

There are good reasons to look at all sorts of fuels. We need to get rid of the CO2
as a greenhouse gas. And if we could get some hydrogen in the process, this could be really interesting because we need hydrogen and other fuels for the future.

When could this technology be used on a commercial scale?

The plan is to build and start operation of the demo unit next year. Then you need one or two years of operation. So in 2025 the technology could be ready for commercial operation.

Do you see chemical looping more as a niche technology or do you think it could become a gold standard?

When we talk about using it for WtE, the sorting of the waste is essential to have a waste stream that is fit for chemical looping. It will start as a niche but it has the potential to be really important. Highly sorted waste streams are coming into the market and that is where chemical looping fits in.

But I think that conventional WtE plants will be around for many years because they are very efficient, especially when they are increasingly combined with carbon capture.

There are many technologies dealing in decarbonisation. But which one will be the winner, that’s hard to tell.