The HTWTM- fluidized-bed process
On the basis of preliminary tests in a bench-scale plant at Aachen Technical University, a pilot plant was set up by Rheinbraun in its coal processing factory Wachtberg at Frechen near Cologne in order to test the HTW™ process. This project was subsidized by the Federal Ministry for Research and Technology (BMFT). thyssenkrupp Industrial Solutions was responsible for the engineering, supervision of civil works and erection activities and for commissioning the plant. thyssenkrupp Industrial Solutions and Rheinbraun engineers jointly performed the tests and evaluated the results. The pilot plant was commissioned in summer 1978. The test program covered the evaluation of the process design in particular:
- Gasification under pressure
- Gasification at elevated temperature
- Improving the carbon conversion rate
- Improving the gas quality"
In view of the good results obtained in the pilot plant, Rheinische Braunkohlewerke AG decided to install a demonstration plant for the gasification of lignite. The plant started up in 1986 to produce synthesis gas suitable for methanol production, which was transported by pipeline to the methanol synthesis plant of Union Rheinische Braunkohlen Kraftstoff AG to demonstrate the feasibility of methanol production from lignite. The Berrenrath plant demonstrated excellent performance, high availability, a robust operation and the ability to co-feed solid waste up to 50%.
INPUT: low rank and high reactive feedstocks, such as lignite, peat, biomass, waste, with high ash content or high ash softening point.
OUTPUT: synthetic natural gas or chemicals as well as power
Main process data
up to 700 MWth single train capacity
Main process features
- Fluidized bed
- Operates below ash softening point
- Dry feeding system
- Post-gasification zone for tar destruction
- Multiple oxygen nozzles for optimum distribution
In the fluidized bed, a high material and energy transfer rate is achieved and this ensures a uniform temperature distribution throughout the gasifier. The temperature is maintained below the ash softening point.
Screw conveyers or gravity pipes are used for supplying the feedstock to the HTW™ gasifier. Due to the gasifier pressure, both feeding and bottom ash removal have to be performed by lock-hopper systems. The gasification agents, steam and oxygen (or air) are injected at the bottom of the gasifier (here they serve simultaneously as fluidizing agents for the fluidized bed) and they are also introduced into the fluidized bed as well as above the fluidized bed, into the so-called post-gasification zone in order to improve the gas quality and the conversion rate due to the temperature increase.
Process flow diagram
The fluidized-bed gasification process was developed in the 1920s in Germany by Fritz Winkler. Commercial-scale Winkler gasifiers were operated in over 40 applications around the world. In the 1970s, thyssenkrupp Industrial Solutions together with Rheinische Braunkohlewerke AG commenced the development of a pressurized version of the Winkler gasifier – the High Temperature Winkler (HTW™) gasification process. The HTW™ process enables shorter residence time, higher reaction velocity, higher reactor throughput for larger plant capacity, higher carbon conversion rate, higher plant efficiency and improved syngas quality. In 1978, the HTW™ pilot plant started-up in Frechen, Germany, with a pressure of 10 bar. "
The operating experience gained there laid the foundation for the design and construction of the HTW™ commercial-scale plant in Berrenrath, which started up in 1986 to convert Rhenish brown coal into methanol. The Berrenrath plant achieved plant availabilities of over 8,000 hours per year. In 1988, another commercial HTW™ gasification plant started up for Kemira in Oulu, Finland.
This plant converted 100% biomass (peat) into ammonia. Within the further development of the HTW™ process for IGCC applications, and the later engineering for the KoBra IGCC plant at Hürth, an additional 25 bar HTW™ gasification plant started operation in 1989 at Wesseling. In the mid-1990’s the HTW™ plant at Wesseling was operated using air instead of oxygen as reactant. Carbon conversion efficiencies up to 95% could be achieved. Around the same time, the HTW™ plant at Berrenrath ran a program to add up to 30% of MSW / plastic wastes as feedstock to the gasifier. Due to the excellent results, Sumitomo Heavy Industries selected the HTW™ process for a municipal solid waste gasification plant that started up in Japan in Niihama in 2000.