New Technology Helps To Reduce Capital Expenditure Of Coal Gasification Designs

For countries such as China that have little in the way of petroleum-based feedstocks, coal is an essential energy source; indeed, about 70% of the country’s energy comes from coal. As China’s economy continues to grow, so will its use of coal. Although far from being a clean fuel when burned to generate power, coal can be converted into synthesis gas (syngas), which is a mixture of carbon monoxide and hydrogen. As the conversion occurs at high pressures, which automatically implies smaller gas volumes, it offers an efficient way to remove pollutants and carbon dioxide from the syngas.

Shell is well known for its gasification technology, which it began developing in the 1950s. The Shell Coal Gasification Process was launched in the 1970s and the organisation has sold 21 licences in China: currently, 15 chemical plants are using Shell coal gasification technology to produce hydrogen and chemicals such as methanol and ammonia for fertilisers.

Shell has continued to develop its coal gasification process and has recently introduced a low-cost technology that uses a bottom water-quench process to cool the hot syngas exiting the reactor.

Rob van den Berg, Principal Process Engineer, Gasification, Shell GlobalSolutions International BV, explains the reasoning behind the new development. “One of the issues that is preventing wider uptake of gasification technology is cost,” he says. “Gasifiers can be expensive pieces of equipment, and, if the process is to be more widely adopted, the price needs to come down. The bottom water-quench option offers a lower-cost alternative to the traditional design.”

Shell Global Solutions has joined forces with Wison Engineering Ltd to build a demonstration plant in China to test the new technology. “Wison is an ideal partner for us because it has rich experience in engineering and considerable operational experience in gasification,” says van den Berg.

The new technology differs from the previous one in the way the syngas is cooled. In Shell’s traditional syngas cooler design, the hot gas passes along steel tubes through which water flows and releases its heat to the water. As the gas cools, steam is generated inside the tubes. However, this design is rather complex and requires a substantial amount of equipment.

In the new design, which uses the new bottom water-quench technology, the hot gas passes directly into a water bath. Van den Berg says, “Instead of raising steam separately using expensive equipment, the steam is now generated by mixing hot syngas with water. This is a very cost-effective solution for downstream plants that need a mixture of syngas and steam as feedstock. Good examples are synthetic natural gas, methanol and fertiliser plants.”

Shell Global Solutions has developed the technology and provided the basic design for the demonstration plant, and Wison is currently working on the detailed design. When the plant is completed, Shell will be on-site to help to ensure a smooth start-up.

Through the new design, Shell aims to strengthen its ties with China and continue to be a player in the gasification market. The new technology could be used in all future units that Shell designs, not just for China. “Once we have proved that this technology works, we can use it when gasifying alternative feedstocks in other parts of the world,” says van den Berg.

For more details on Shell Global Solutions’ coal gasification technologies.

For more information contact Rob van den Berg

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