Yongseung Yun

Performance of a pilot-scale gasifier for Indonesian Baiduri coal

An entrained-bed slagging gasifier of 3 ton/day-class was constructed in 1995 and has operated in Korea ever since. A total of nine imported coals were tested to distinguish the gasification performance with coal characteristics under high pressure conditions. Through the tests, Indonesian Baiduri coal was selected as one of the most suitable coals for the gasifier due to its high reactivity, suitable ash fusion temperature, and low ash content. For the Baiduri coal, the gasifier yields more than 98% carbon conversion efficiency and above 80% cold gas efficiency while producing about 60% CO and 30% H2 in the nitrogen-free basis. Results show that none of the heavy metal constituents in the produced slags by the gasification is leached out by water, which is a major advantage over any combustionbased processes where ash normally contains many leachable heavy components that may contaminate the under-ground water eventually.

Effects of Pressure in Coal Pyrolysis Observed by High Pressure TGA

High-pressure thermogravimetric analyzer was employed to investigate the effects of pressure on the thermal decomposition process, which is the very first step in most coal utilizing processes, and pyrolyzates from TGA were analyzed by on-line GC/MS. Results showed that pyrolysis of coal with steam under high-pressure conditions exhibited a slower reaction rate compared to the lower pressure conditions, and the effect is more evident at the high temperature region. Coal rank also exhibited a distinct effect on the pyrolysis rate such that a subbituminous coal showed a bigger effect by steam-addition and pressure than bituminous coals. Weathered coal sample illustrated a slower reaction rate compared to the unoxidized coal. In addition, the implication of pressure effects on pyrolysis has been described.

Operation performance of a pilot-scale gasification/melting process for liquid and slurry-type wastes

A gasification/melting facility that can operate up to 10 bar and 1,550 °C with a maximum 1 ton/day capacity was developed for liquid and slurry-type combustible wastes. The main focus of the system development was minimal use of expensive fuel for maintaining the reaction temperature by replacing it with cheap waste oil for energy input. The carbon conversion obtained was 97% while the cold gas efficiency reached 77.6% for the refined waste oil. When the feed was refined oil mixed with fly ash from a municipal waste incinerator, the carbon conversion and cold gas efficiency were 93% and 71.9%, respectively, with a slag conversion ratio of 0.93. The slag produced from fly ash exhibited environmentally acceptable heavy-metal leaching values and thus can be applicable as road material and for other purposes. The optimal O2/feed ratio was 0.9–1.0 when only the refined waste oil was gasified, whereas the O2/feed ratio had to be higher than 1.2 when fly ash was mixed. In addition, data showed that gasifier temperature can be estimated by on-line methane concentration measurements.

Corrosion behavior of Hastelloy® C–4® Ni–Cr–Mo–Fe alloys for coal gasification syngas plants

Abstract A mechanistic exposure experiment was performed on welded samples of the commercially available Haynes® Hastelloy® C–4® Ni-Cr-Mo-Fe alloy (65 wt.-% Ni, 16 wt.-% Cr, 16 wt.-% Mo, 3 wt.-% Fe, 2 wt.-% Co, 1 wt.-% Mn, 0.7 wt.-% Ti, 0.5 wt.-% Cu, 0.08 wt.-% Si and 0.01 wt.-% C) at coal gasification pilot plant facilities affiliated with the Institute for Advanced Engineering in Yongin-si, South Korea. The alloy samples were preoxidized at 400 °C under a stagnant air atmosphere for 24 h prior to exposure to the corrosive environment (60 % CO, 28.4 % H2, 2.5 % CO2, 0.8 % CH4, 600 ppm H2S and 110 ppm carbonyl sulfide under 2.005 MPa pressure and 170 °C). Thermodynamic Ellingham-Pourbaix stability diagrams were constructed to provide insight into the mechanism of the observed corrosion behavior prevailing in the piping materials between the particulate removal unit and water scrubber of the coal gasification pilot plant. The thermodynamic inference of the corrosion mechanism was supplemented with morphological, compositional and microstructural analyses of the exposed samples using scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy analyses performed on the external and cross-sectional surfaces of the recovered corrosion test samples to comprehensively examine the corrosion scale. The X-ray diffraction results revealed stable corrosion products of NiO, MoNi4 and Cr4.6MoNi2.1 after a total accumulated exposure duration of 139 h to the corrosive atmosphere. Scanning electron microscopy and energy dispersive X-ray spectroscopy positively identified the formation of rather continuous and adherent preoxidation corrosion products in the alloy samples, although extensively peeled off oxides were eventually observed as corrosion scale on the post-exposure alloy samples, which were attributed to the combined effects of the evaporation of the hydrated Fe, Al and Cr chlorides and their subsequent transformation into thin (spalled) oxides.

Corrosion behavior of welded Ni-Co-Cr-Si alloys during exposure in integrated coal gasification combined cycle syngas plants

Abstract The corrosion behavior of commercially available and welded Haynes® 160® Ni-Co-Cr-Si alloy samples was investigated by exposure to coal-gasifying integrated coal gasification combined cycle pilot plant facilities under typical conditions as 2.005 MPa and 160 to 300 °C. The morphological and microstructural analyses of the exposed samples were conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy analysis on the external surface of the recovered corrosion test samples to obtain information of the corrosion scale. These analyses based on the pre- and post-exposure corrosion test samples combined with thermodynamic Ellingham-Pourbaix stability diagrams provided preliminary insight into the mechanism of the observed corrosion behavior prevailing in the piping materials that connected the particulate removal unit and the water scrubber of the integrated coal gasification combined cycle pilot plant. Uniform material wastage was observed after 46 hours of operation, and a preliminary corrosion mechanism was suggested: the observed material waste and corrosion behavior of the Haynes® 160® Ni-Co-Cr-Si alloy samples cut off from the coal syngas integrated coal gasification combined cycle plant were explained by the formation of discontinuous (complex) oxide phases and subsequent chlorine-induced active oxidation under the predominantly reducing environment encountered. This contribution supplements the already published studies of Haynes® 556® Fe-Ni-Cr-Co alloys and Haynes® 230® nickel-based superalloys and completes the comprehensive series of such coal-gasifying integrated coal gasification combined cycle pilot plant exposure tests using the facilities affiliated with the Institute for Advanced Engineering.