High-temperature syngas is produced by entrained-flow coal gasification. A traditional quenching process has the drawback of low heat recovery efficiency, and the cleaning of convective syngas cooler is a big problem. Thus, the combination of a radiant syngas cooler and a quench chamber is a more promising way for heat recovery and syngas preliminary purification. In this study, based on the traditional radiant syngas cooler, sixteen radiation screens are added to increase the heat exchange area, so as to further improve heat recovery efficiency of the radiant syngas cooler. Heat transfer and structure analysis of a forging plate on the top of the radiation screen are carried out by numerical simulation. The radiation screen changes the internal spatial structure of the radiant syngas cooler, which also affects the heat transfer characteristics of the membrane wall. The circumferential temperature distribution of the cylinder membrane wall is not uniform, and the temperature is the highest at the central pipe. The surface heat flux of the cooling pipes on the radiation screen reaches the maximum value at the position with a distance of about 6 m from the top. The slag and fly ash carried in the gas flow deposit on the wall surface and form deposition layers, which protects the forging plate and cooling pipes, but reduces the heat transfer efficiency.
The high-temperature syngas and molten slag droplets discharged from entrained-flow coal gasifiers contain a large amount of heat energy, which can be efficiently recovered by radiant syngas coolers (RSCs). However, it is hard to know the solidification degree of molten slag droplets at the outlet of an RSC during industrial operations. In this work, the industrial-scale RSC and molten slag droplet models are established to predict the solidification degree of slag droplets at the outlet of the RSC. Then, the effects of slag diameter, syngas flow field, slag initial temperature, slag porosity, and slag pore structure are investigated by numerical simulations, and residence time as well as complete solidification time are calculated by coupling of a discrete-phase model and a solidification model. The results indicate that as the slag droplet diameter increases, the residence time of the slag droplet shortens, but the complete solidification time increases. When the slag droplet diameter is greater than or equal to 3.0 mm, the complete solidification time is larger than the residence time, and the slag droplet cannot solidify completely at the outlet of the RSC. The solidification degree in the windward zone is greater than that in the leeward zone. Although the slag initial temperature has little effect on the solidification, a lower slag initial temperature is still conducive to a greater solidification degree. Additionally, the pore structure facilitates solidification, and the promoting effect of penetrated pores is more remarkable than that of closed pores. A larger porosity is also beneficial to accelerate the solidification of molten slag droplets and increase the solidification degree.
Radiant syngas cooler (RSC) is an important piece of equipment for heat recovery and steam generation in the gasification plant. In this work, the industrial RSC model of an opposed multi-burner coal-water-slurry gasification device is established, and the heat recovery performance of RSC is studied by numerical simulation method. The simulation result of the total heat transfer rate is compared with the industrial operation data. The effect of different operating parameters on RSC is further studied, including the operating load, inlet syngas temperature, and ash deposition thickness. The results show that there is a spindle-shaped high-temperature zone on the circumferential membrane wall surface with a distance of 6.5 m from the top under the basic operating conditions. There is also an obvious high-temperature zone in the mid-upper section
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