Removal Of Hydrogen Sulfide In Pressurized Coal Gasification With Calcium-Based Sorbents And Oxidation Of Calcium Sulfide

2G PFBC-CC and IGCC, including coal gasification, are considered to be the potential technologies that would meet the energy and environmental demands of the future. Sulfur in the coal is converted to, for the most part, H2S, which must to be removed from the hot gas in order to protect the equipment in the later stages of the process from its corrosive effects and also in order to meet strict regulations for sulfur emissions. The spent sorbent, composed mainly of CaS, is chemically unstable when piled at the open air and must to be stable before direct disposal. As the key technologies, these processes will be important to the industrial application of 2G PFBC-CC and IGCC. Based on this background, the research on the sulfidation with calcium-based sorbents and the oxidation of CaS were carried out in a pressurized thermogravimetric analyzer (PTGA) and the bench-scale hot gas cleanup tests were performed in a 0.1MWth thermal input pressurized fluidized bed with a jet.Sulfur capture reactions of CaCO3-H2S and CaO-H2S, together with the reaction of oxidation of CaS, were investigated in the PTGA, the effects of such parameters as pressure, temperature, reactant gas concentration, particle diameter, gas composition and sorbent type on the sorbent conversion were determined and the reaction mechanism and reaction model were constructed. The results show that the total pressure has two sides: increasing pressure at the constant reacted gases (H2S or O2) partial pressure leads to a reduction in the conversion; on the other hand, the rise in pressure at a constant volume fraction of reacted gases gives rise to an increase in the chemical reaction rate. Temperature is the most important factor. The enhanced temperature benefits to the sulfidation, however, the sintering at higher temperature will occur and thus leading to the lower reactivity. All the reactions are the first order for partial pressure of reaction gases. The larger particles, the lower sulfidation rate is obtained. The reaction conditions and sorbent type affect the reaction greatly. All the calcined sorbents can reach high conversion due to its large porosity. However, at the noncalcining conditions, the original limestones with little porosity have poor reactivity; while at the half-calcining conditions, the reactivity of dolomites are much higher than that of limestone, and also higher than that of calcined limestones. In order to mimic the real"in gasifier"conditions, the coinstantaneous processes of calcinations and sulfidation of calcium-based sorbents were investigated. The results show that these reactions are interactional. The reaction mechanism of the sulfidation and oxidation are brought forward, the reactions occur by solid-state diffusion of reactant species through the product layer at the later stage. In view of the coarseness and roughness of the particle surface, the fractal theory, which describes the abnormity degrees of solid substances, was introduced to the classical models and the fractal reaction models, named fractal unreacted shrinking core model and fractal grain model were constructed after the fractal modification. Good agreement between the model predictions and experimental results is found.The Fourier Transform Infrared (FTIR) spectrum technique coupled with PTGA was used to the oxidation of CaS for the first time, the compositions of reacted samples were measured by virtue of FTIR successfully. The SEM-EDS analyses also indicate that the reaction between CaS and CaSO4 will occur when the temperature exceeds 870℃during the oxidation of CaS. In addition, the reaction of CO2 and CaS was studied at high pressure for the first time, the composition of product was varied with the content of CO2 in the flue gas. The oxidation experiments with different sulfidation degrees show that the conversion of CaS decreases with the rise in the S/Ca.The effect of reacting conditions on the fractal dimension, which represents the degree of irregularity of the porous materials, and influence of fractal dimension on the reaction properties were also investigated. The experimental results show that the calcining conditions and particle diameter affect the fractal dimension greatly, and the fractal dimension has different values with different materials (calcium-based sorbents or CaS). The effect of fractal dimension on the sulfidation and oxidation reactions is also obvious, and the different fractal dimension has different influencing extent on the reactions mentioned previously.The bench-scale experiments for the hot gas cleanup with limestones were carried out successfully in a 0.1MWth thermal input pressurized fluidized bed with a jet. The experimental results show that with the...