Traditional ash fusion
behavior is described by four characterization
temperatures determined by shape of variation ash cone, cylinder,
or cubes. The results by thermomechanical analysis (TMA) describe
the whole fusion process, which supports the better understanding
of the ash fusion process. However, the interaction between slags
and the crucible at high temperatures is the key factor on the accuracy
of the TMA measurement. In this work, the influence of the interaction
between slags and different crucible materials, including platinum
(Pt), alumina (Al2O3), zirconia (ZrO2), graphite (C), and molybdenum (Mo), on TMA results and its mechanism
was investigated. The slag–crucible interaction includes diffusion
and reaction mechanisms, and the interaction with Al2O3 and ZrO2 crucibles is controlled by the diffusion
process of slags into the crucible wall. The Al2O3 crucible is as stable as Pt and has no obvious effect on the ash
fusion process as a result of its compact structure and stable crystal
form. The ZrO2 crucible becomes porous during heating and
cooling as a result of crystal transition, which results in the penetration
of melted slags into the crucible. ZrO2 can also diffuse
into slags, and the diffusion rate is enhanced by sodium in slags.
Both C and Mo crucibles are reactive with iron-containing slags; the
interaction with the C crucible is related to the iron content of
ashes; and the interaction with the Mo crucible is accelerated by
the basic oxides (e.g., Na2O, CaO, and Fe2O3) in coal ashes. To obtain an accurate result of ash fusion
behavior by TMA, especially for ashes with high basic oxide contents,
the Al2O3 crucible is strongly recommended to
avoid the slag–crucible interaction.
Gasification kinetic parameters of coal char based on the random pore (RPM) model are obtained with CO2 and H2O using a high-pressure thermogravimetry analysis (TGA) under atmospheric pressure and 4.0 MPa pressure, considering the influence of internal diffusion and particle structure varying with carbon conversion. The Chemical Percolation Devolatilization (CPD) model is used to modify the actual volatile content. Through the coupling of the gasification kinetic reaction model, a comprehensive numerical simulation method of the entrained flow gasification process is established. This method is used to simulate the typical gasifier of HTL (a gasification technology of Changzheng Engineering Co.) in an industrial plant. The research shows that the intrinsic reaction parameters obtained by TGA under high pressure can give a more reasonable reaction state of coal char particles in the gasifier than that measured under atmospheric pressure, and the simulation results are in good agreement with the industrial data. In addition, HTL adopts a single top-fired burner and multi-channel swirling feed type. The particles are entrained and mixed with swirling oxygen, and the combustion reaction is completed quickly in the upper part of the gasifier. In contrast, the gasification reactions are relatively slow and mostly dominate in the recirculation zone and pipe flow zone, leading to high carbon conversion.
The research object in this paper is an industrial HTL gasifier in a plant. A three-dimensional model is built. The chemical percolation devolatilization (CPD) model is used to calculate the pyrolysis reaction. Considering the gas diffusion in the inner pores of the particle and the evolution of pore structure, the random pore model (RPM) was used to simulate the chemical reaction on the particle surface, and the gasification reaction kinetic parameter of char was measured by high-pressure thermogravimetry analysis. The slag model was constructed to describe the formation process and distribution of slag. Through the coupling of the above models, a simulation method that combines several submodels for the entrained flow gasifier is built, and the results from simulation are in good agreement with the industrial data. Furthermore, the effect of the uniformity of pulverized coal injection was analyzed by this method. The simulation results reflect that the asymmetric feed of coal will affect gas-solid mixing and reduce carbon conversion, and it leads to a higher local wall temperature and a lower ratio of crude slag to fine slag.
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