Hie High-Temperature Winkler (HTW) Process
The name “high-temperature Winkler” for the process developed by Rheinbraun primarily for lignite gasification is to some extent a misnomer. The most important development vis-a-vis the original Winkler process is the increase of pressure, which has now been demonstrated at 30 bar.
Rheinbraun, an important lignite producer in Germany, began work on the process in the 1970s. A Rheinbraun subsidiary, Union Kraftstoff, Wesseling, had operated atmospheric Winkler generators between 1956 and 1964, and Rheinbraun was able to build on the experience gained.
An important motivation for the initial development was to ensure the availability of a suitable process to utilize existing lignite reserves, should economic conditions (i. e., the price of oil) justify it. The focus was on methanol syngas and hydrogen generation for the parallel development of a hydrogenating gasifier for SNG production.
Development goals included raising the pressure so as to increase output and reduce compression energy, raising operating temperatures so as to improve gas quality and carbon conversion, and to include a solids recycle from the cyclone to the fluid-bed as a further measure to increase carbon conversion (Teggers and Theis 1980).
Figure 5-9. HTW Gasifier
The feed system uses a lock hopper and a screw feeder into the reactor from the high-pressure charge bin.
The HTW process includes heat recovery in a syngas cooler in which the raw synthesis gas is cooled from 900°C to about 300°C. Both fire tube and water tube concepts have been used in the demonstration plants, and selection is based on project specific criteria, such as desired steam pressure (Renzenbrink etal. 1998).
A ceramic candle filter is used downstream of the syngas cooler for particulate removal.
The 600 t/d, 10 bar demonstration unit in Berrenrath, which was operated over 12 years and achieved an availability of 84%, was used to supply gas to a commercial methanol plant. This provided the basis for a plant of similar size operating at 13.5 bar and gasifying mainly peat in Oulu, Finland. A further 160 t/d pilot plant was built in Wesseling to prove various aspects connected with IGCC applications, such as a higher pressure (25 bar). These three plants have now been shut down. Two 980 t/d units are currently under consideration for an IGCC facility at Vresova in the Czech Republic, where they will replace twenty-six existing fixed-bed gasifiers (Bucko etal. 2000).
In addition to the above, the HTW process can be applied to waste gasification (Adlhoch etal. 2000). A 20 t/d atmospheric demonstration unit has been built in Japan.