HTW™-gasification of high volatile bituminous coal in a 500 kWth pilot plant

Abstract

Processing of difficult feedstock’s like high-ash coal or biogenic residues poses a challenge for most common gasification technologies. The High-Temperature-Winkler (HTW™) gasifier, as part of the fluidized bed gasification technologies might very well provide a solution for these feedstock’s. Gasification takes place in the two characteristic zones of the gasifier (bubbling fluidized bed zone and post gasification zone) enabling dry ash removal, while the majority of heavy hydrocarbons like tars are converted. A semi industrial HTW™ pilot plant was erected at the Institute for Energy Systems and Technology by retrofitting a circulating fluidized bed reactor in cooperation with thyssenkrupp Industrial Solutions AG (former ThyssenKrupp Uhde GmbH). Commissioning was successfully carried out in June 2015 using pre-dried lignite. This study shows the usability of the HTW™ technology for an increased variety of feedstocks, by means of high volatile bituminous coal (HVBC). Furthermore, significant workload was put into identification of optimizations for the pilot plant in order to increase performance, handling and quality of the gasification process. During the 5 days of continuous operation, 7.4 tons of HVBC were gasified to examine the gasifier behavior depending on the feedrate, temperature and distribution of gasification agents. During these tests syngas containing more than 50 vol% CO and H2 was produced. The syngas quality significantly increases with the temperature, while the gasifier load and the particle size showed mixed results. Increasing the load (feedrate) of the gasifier resulted in decreasing temperatures. More particles were entrained into and through the post gasification zone, reducing efficiency and carbon conversion rate as well as syngas quality.Optimizations of the gasifier include removal of the loop seal from the return leg, reducing the overall CO2 injection by at least 20%. Furthermore, an optimized cyclone was developed to significantly increase separation efficiency and carbon conversion rate. Increased temperature of the gasification agents will benefit the overall energy balance of the gasifier increasing performance and syngas quality and decreasing freeboard velocity. The temperature dependence of the gasification of HVBC indicate significant improvement in syngas quality for this feed by an increase of gasifier temperatures. The evaluation and verification of these optimizations will be done during the next longterm tests of the gasifier using pre-dried lignite.