Modeling of Multiphase Flow and Heat Transfer in Radiant Syngas Cooler of an Entrained-Flow Coal Gasification

Abstract

A comprehensive model has been developed to analyze the multiphase flow and heat transfer in the radiant syngas cooler (RSC) of an industrial-scale entrained-flow coal gasification. The three-dimensional multiphase flow field and temperature field were reconstructed. The realizable k−ϵ turbulence model is applied to calculate the gas flow field, while the discrete random walk model is applied to trace the particles, and the interaction between the gas and the particle is considered using a two-way coupling model. The radiative properties of syngas mixture are calculated by weighted-sum-of-gray-gases model (WSGGM). The Ranz−Marshall correlation for the Nusselt number is used to account for convection heat transfer between the gas phase and the particles. The discrete ordinate model is applied to model the radiative heat transfer, and the effect of ash/slag particles on radiative heat transfer is considered. The model was successfully validated by comparison with the industrial plant measurement data, which demonstrated the ability of the model to optimize the design. The results show that a torch shape inlet jet was formed in the RSC, and its length increased with the diameter of the central channel. The recirculation zones appeared around the inlet jet, top, and bottom of the RSC. The overall temperature decreased with the heat-transfer surface area of the fins. The concentration distribution, velocity distribution, residence time distribution, and temperature distribution of particles with different diameters have been discussed. Finally, the slag/ash particles size distribution and temperature profile at the bottom of the RSC have been presented.

Modeling and analysis of a syngas cooler with concentric evaporator channels in a coal gasification process

“…The turbulence was solved by the realizable k-ε model [18], which has a more fundamental foundation for jet and circulating flows. The model was found the most appropriate for simulations in a RSC [10]. The radiation was predicted by the discrete ordinate method with an angular discretization of five divisions and three pixels both in the polar and azimuthal directions.…”

“…An RSC can be combined with a convective heat exchanger downstream. Several experimental and numerical studies have been conducted for flow patterns of gas and particles in this type of SGC [4,9,10]. The SGC adopted in Shell coal gasification processes consists of a series of concentric heat exchangers made of helical coil tubes.…”

Simulation of Radiant Syngas Coolers and Comparison with Various Arrangements of the Entrained‐Flow Gasifier

“…In our original papers 5, 8, the surface temperature of each membrane wall was set a constant which was estimated using the heat flux balance equation. In this paper, the surface temperature of deposits T a was calculated using heat flux balance equations (8)–(10) by user‐defined functions (UDFs).…”

“…For entrained‐flow slagging gasifiers, the syngas leaves the gasifiers at a temperature above the ash fusion temperature 2. The slag viscosity must be sufficiently lower than 25 Pa s, optimally at 15 Pa s at the tapping temperature which is usually varied from 1200 to 1600 °C to ensure that the slag can be tapped 3–5. Thus, the raw syngas exiting the gasifier must be cooled and cleaned before final use.…”

“…In our original papers 5, 8, 9, attempts have been made to develop a numerical model for predicting the multiphase flow and temperature field of an industrial‐scale RSC, and four different syngas cooling types have been compared with the numerical model. It was validated that the numerical model is the best choice for investigating the flow field and temperature field of the RSC under high‐temperature and high‐pressure conditions.…”