Discussion on slag hanging in the quenching ring
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Some time ago, after the Texaco gasifier was in operation for a period of time, it was observed that the temperature of the slag holding tray increased, as well as the pressure difference at the slag outlet. Subsequent attempts to address the issue by adjusting the oxygen-to-coal ratio, regulating the central oxygen level, and reducing the load yielded little improvement; eventually, the furnace had to be shut down. Inspection later revealed slag accumulation in the quenching ring. I believe it might be that the initial control of the furnace temperature was too low, which led to slag accumulation in the quenching ring and even at the slag outlet; various adjustments were made later, and these did have some effect, as the absence of slag accumulation at the slag outlet is good evidence of this. But why didn’t the temperature of the slag holding tray decrease? The key issue is that the slag attached to the quenching ring does not melt; the quenching ring is a region with relatively low temperatures, and it is difficult for the slag there to melt once it has attached itself. Therefore, in normal operation, one should not keep the furnace temperature too low in an attempt to increase the effective gas production, as this can lead to slag accumulation at the slag outlet, on the quenching ring, and even in the downcomer – and such consequences are far from beneficial. These are just my personal opinions; I welcome everyone’s criticism and suggestions. Please join the discussion too!
Mainly, the furnace temperature is too low, below the ash melting point of the coal fed into the furnace! The slag has high flow viscosity; it accumulates in the quenching ring, causing slag adhesion!
Temperature control in Texaco gasifiers is indeed very important and quite complex. Because it is affected by many factors, especially changes in coal (such as ash content, ash fusion point, and other properties), and these changes occur frequently. A high temperature control is certainly detrimental to the furnace, but a low one can also lead to severe slag accumulation on the furnace walls and blockages at the slag outlet; it is therefore necessary to make adjustments based on the gas composition as well as the shape and characteristics of the slag
Frequently checking the slag sample helps in determining the operating temperature and the performance of the gasification furnace; if it is observed that the slag level rises and there is stringy ash, the slag should be melted promptly.
It’s good that you, Xiao Sheng, are willing to carefully observe the various parameters of the gasification furnace; the fact that you’re able to discuss these topics in depth with others shows that you are quite humble. However, operating a gasification furnace is something that cannot be easily explained by theory, and this may be related to our current level of theoretical knowledge – we are not yet able to provide genuine guidance for production processes. Therefore, to operate a gasification furnace effectively, long-term experience accumulation and learning in various aspects are required, as well as extensive discussion with others to make progress. From your post, I know you are from HL; otherwise, how could everyone outside have heard about the issues with their gasification process so quickly and even called to ask questions? What I want to say to you is: it’s good to make progress by communicating and discussing more, but it’s important to truly understand what Chairman Mao said – \"Sing the song appropriate for the mountain you’re on.\" Which one did you say? This post was last edited by Tianya Langji on 2009-2-4 22:09.]
There are many reasons for slag formation in gasifiers, the most important of which are the viscosity-temperature properties of the coal. The operating temperature of the gasifier is determined based on these viscosity-temperature properties; if it is too high, fluxes must be added to adjust it. By regularly monitoring the slag samples and the pressure difference at the slag outlet of the gasifier, and by analyzing the operational data to determine the oxygen-to-coal ratio as well as the corresponding temperature for methane in the gases, this phenomenon can basically be prevented. A lot of detailed work needs to be done. It is important that there be no significant changes in the type of coal.
What are the reasons for the increase in the temperature of the slag tray? It’s not the case that slag accumulation in the quenching ring or downcomer will cause an increase in the temperature of the slag holding tray. Is it also because the slag holding tray is already severely eroded?