Release of Alkali Metal, Sulfur, and Chlorine Species during High


Oct 5, 2012 - Abstract: The working hypothesis for the study was that the main part of the chlorine in biomass is in an inorganic form and therefore s...
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Release of Alkali Metal, Sulfur, and Chlorine Species during HighTemperature Gasification of Coal and Coal Blends in a Drop Tube Reactor Marc Blas̈ ing* and Michael Müller Institute for Energy Research (IEK-2), Leo-Brandt-Strasse 1, 52425 Jülich, Germany ABSTRACT: Investigations on the release of Na, K, S, and Cl species form a crucial element in designing control measures and developing hot-gas-cleaning strategies for coal gasification systems. A large body of useful data has already been delivered in this area, but the underlying reaction mechanisms are not yet sufficiently understood. To complement recently performed basic investigations with a flow tube furnace, a lab-scale drop tube reactor was used. The experiments were performed at 1300 °C in an atmosphere of He (carrier gas) and 5 vol % O2. Two hard coals and two blends of these coals were gasified during the experiments. In situ hot gas analysis of inorganic trace elements was performed by molecular beam mass spectrometry.

temperature. The ultimate analysis was performed by the central division of analytical chemistry (ZCH) of Forschungszentrum Jülich GmbH. The results are given in Table 1. The major elements of coal

1. INTRODUCTION Despite the increasing use of renewables, fossil fuels will be important for reliable energy production during the transformation of the energy economy. Therefore, the development of more efficient and more environmentally friendly techniques in next-generation coal power plants is becoming more and more important. A promising coal use process is the integrated gasification combined cycle (IGCC) process. The direct use of the raw gas requires gas cleanup to prevent downstream parts of the gasifier from several problems, e.g., poisoning of catalysts, inactivation of membranes, fouling, and corrosion. An increased efficiency and a decreased amount of harmful species, e.g., Na, K, S, and Cl species, can be achieved through hot fuel gas cleaning.1 This innovative cleanup technique requires comprehensive knowledge of the release characteristics of inorganic coal constituents. Previous work provided enhanced knowledge of the effect of key process parameters and the chemical constitution of coal on the release of Na, K, S, and Cl species from high-temperature gasification of coal.2−8 Because of the limited applicability of the previous batch experiments to a real high-temperature gasifier, this study used a drop tube furnace. The main difference of the present work in comparison to the mentioned previous work is the attempt to become closer to the conditions in an entrained flow gasifier. Therefore, we built a drop tube reactor and ran release experiments with continuous coal feed over a longer time. In previous batchscale experiments, the number of factors affecting the release reactions was reduced, e.g., interaction of the released species with the coal particles during different stages of the gasification process. Especially, the capture of the released species by the remaining coal ash is an important factor for the release of the species under investigation. The present results complement the recently published data sets based on batch experiments.

Table 1. Chemical Composition of the Coal Samples (Dry Basis) STD-1

STN-1

Ash and Water Content (Mass %) ash (water free) 6.77 9.14 water (as received) 6.75 1.49 Elemental Analysis (Mass %) C 83.6 78.8 H 4.22 5.54 N 1.72 1.61 O 6.26 8.86 S 0.75 0.64 Cl 0.116 0.015 Al 0.96 0.64 Ca 0.15 0.72 Fe 0.52 0.60 K 0.16 0.11 Mg 0.094 0.21 Na 0.053 0.25 Si 1.4 1.6 Elemental Ratios (Calculated on a Mole Basis) Cl/Na 1.4 0.04 S/Cl 7.1 47.3

2. EXPERIMENTAL SECTION

matter, including C, H, N, O, and S, were analyzed by a CHNS analyzer (system LECO). As such, coal samples of 2 mg were burned in oxygen. CO2, H2O, and SO2 were analyzed by infrared (IR) absorption. N2 was analyzed using heat conductivity, and O2 was determined by calculation. The content of Cl was analyzed using ion chromatography according to the Wickbold combustion method. Inorganic elements were analyzed by inductively coupled plasma

2.1. Fuel Preparation. Samples from two coals were collected, dried, and prepared for analysis. STD-1 is a German hard coal, and STN-1 is a Spitzbergen hard coal. The coals were ground and sieved. The fraction 1%, ±3%; for amounts 0.1−1%, ±10%; and for amounts