Recycle Week: a second life for coke oven gases

Since the Fridays for Future climate strikes inspired by Greta Thunberg, the discussions about sustainability and the demands on industry have become louder and louder. And rightly so. That’s why we’re looking forward to focusing on a project that consumes CO2 – and doesn’t produce it – as part of Recycle Week 2019.

Sebastian Riethof is familiar with complex processes. He has developed, together with his team, a process in which coke oven gases can be recycled, and which forms part of his doctoral thesis at the TU Berlin. Riethof was not only in charge of the pilot project, but is now also coordinator of process engineering at our coking plant in Schwelgern. So nobody can explain better how his process can help the steel industry to become more sustainable.

For his PhD thesis at the TU Berlin, our process engineer Sebastian Riethof tackled a very special question: How can coke oven gases be turned into something valuable?

“We wash out environmentally harmful components from the coke oven gas that are converted into recyclable materials. The washed-out components – such as ammonia – are then mixed with water and CO2. If this happens in the right proportion, the mixture crystallizes and a salt is formed. This can then be used for other purposes.”

In this process, reusable materials are recycled from components of the coke oven gas. Another major advantage is that CO2 is consumed and not produced.

The process is an extension of the gas cleaning in coking plants

From 2015 to 2016, this expansion was tested in a pilot plant on our steel mill site in Duisburg. The plant was the first of its kind in the world. Right from the start, the aim of the project was to convert recyclable materials in a way that conserved resources.

Project manager Dr. Holger Thielert sees the future in such projects: “You always have to be one step ahead. So we are already considering what will be important in 2030, and are taking the right steps now.” This also fits in with the company philosophy: “Basically, of course, we are interested in building our plants as environmentally friendly as possible.”

The Schwelgern coking plant is located directly on the banks of the Rhine in the north of Duisburg and is recognized as one of the most modern coking plants in the world. Most of the coke produced on-site finds its way into the blast furnaces of our neighboring steel plant in Bruckhausen

The process starts with the production of coke, which, along with iron ore, is the main feedstock for the production of pig iron in the blast furnace. “Coal is ‘baked’ at high temperatures in the coking plant. The hot gases produced in this process carry a number of substances with them. In the pilot plant, the coke oven gas is now washed in a complex process. The addition of carbon dioxide produces ammonium hydrogen carbonate,” is how Dr. Thielert describes the process.

Process gases are turned into foam mattresses or fertilizers

The salt extracted can be used to produce a wide variety of end products. As a fertilizer, it can be used outside Europe for fertilization in agriculture. “The salt can also be used as a foaming agent because it corresponds to the technical quality level. It is then used, for example, in the manufacture of foam mattresses,” explains Sebastian Riethof.

This means that certain process gases, which are produced anyway during the production of coke, are converted into new products in an environmentally friendly way.

“The process supports CO2 reduction. More important than ever for our future.”

Overall, the project was very successful – and important. CO2, which is not produced, is needed to create the salt. “The project is ready for series production. If an interested customer approaches us, we can implement it,” says Dr. Thielert.

At thyssenkrupp, Dr. Holger Thielert (on the left) is the project manager for the sustainable coking plant process. The process is all set for industrial application – customer inquiries are very welcome

The process can therefore reduce the steel industry’s footprint by binding non-emitting CO2 molecules in salts. According to Sebastian Riethof, this is a forward-looking step: “The process supports CO2 reduction. This is more important than ever for our future.”