Dilemma – refractory bricks and tuyere pressure difference
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There are many dilemmas in logic, and unfortunately I’ve encountered one recently. To produce gas, coal is essential; the boss has provided us with fairly good conditions, but lately that’s no longer possible – we can’t get enough coal as usual, so we had to find alternatives in the market. As a result, new coal has started to arrive at the factory. The quality of this new coal isn’t bad at all; it has a ash content of around 8%, an ash fusion point of 1200°C, and a high calorific value. Once it was used, the output of useful gas increased significantly, leaving the boss beaming with joy. . . . But here’s the problem: although the concentration of active gas components is high, the pressure difference at the slag outlet gradually increases over time. The temperature control is also good; in fact, the slag samples taken on site show that the furnace temperature isn’t low. So why does the pressure difference at the slag outlet remain high? So, as the temperature was increased gradually and the pressure difference at the slag outlet stabilized, the composition of the slag suddenly dropped. Upon analyzing the chromium content in the slag, it was astonishingly high – more than ten times higher than before. Won’t these refractory bricks be used up very quickly then? Feeling worried and troubled – it’s clear that this coal has poor slag adhesion properties. Yet it still has to be used. The key question is how to address the conflict between maintaining normal production (by keeping the pressure difference at the slag outlet stable) and reducing wear on the refractory bricks Please, fellow sailors, help me analyze this.
Why not try adding a flux?
This post was last edited by pyp222 on 2011-4-27 at 10:24. This problem cannot be solved simply by adding a cosolvent. Adding a cosolvent can improve the acid-base ratio in the composition of coal ash, thereby reducing its melting point; currently, the melting point of the new coal ash mentioned by the poster is not high, at around 1200°C only. The cosolvent can be omitted. The viscosity-temperature properties of the new coal used by the poster are likely inferior to those of the previous coal, so the range within which the furnace temperature can be controlled is narrower than with the old coal, making operation more difficult. Xu Qinger, I think the severe erosion of the refractory bricks might be due to the replacement with new coal; the ash melting point of this new coal is lower than that of the previous coal. During operation, it’s possible that the expected furnace temperature was not properly estimated, and the furnace temperature became a bit too high when switching to the new coal. As a result, the slag that was previously present in the furnace melted and flowed down to the slag outlet, which led to a reduced resistance to erosion and an increased pressure difference at the slag outlet. My personal suggestion is to reduce the load, slightly decrease the oxygen supply at the center, and increase the thickness of the slag layer in the furnace. After increasing this slag layer thickness, gradually restore the load while adjusting the furnace temperature and the oxygen supply at the center, so as to optimize the operation of the gasification furnace while protecting the refractory bricks. But it’s easier said than done; patience and courage are needed to attempt such actions. These are my personal opinions; please point out any mistakes so we can improve together
This post was last edited by Fengqing888 on 2011-4-25 at 10:07. The viscosity-temperature properties of coal also have a direct impact on the operating temperature of gasification furnaces. Sometimes, coal with a low ash melting point can still have ash with a high viscosity. The T4 temperature of the Yima coal used in Huainan is generally less than 1300°C; when the temperature exceeds 1400°C, the viscosity of the ash is low, but below 1400°C, its viscosity increases sharply, resulting in reduced fluidity. 1. The application of coal blending technology requires relatively low technical standards. It can be accomplished through simple experiments. Based on the operational experience of units such as the Wei River, Huaihua, and Southern Shandong regions, blending coal with other fuels can expand the sources of raw materials. Improve operating parameters. 2. Burner modification requires high technical standards; it involves changing the atomization angle and increasing mixing within the furnace, while balancing between elevated temperature and the composition of the effective gas. 3. From your operations, the increase in effective gas components is also related to the increased backmixing of materials inside the furnace caused by the rising pressure difference. If the increase in pressure difference remains within acceptable limits, the pressure difference requirement can be relaxed appropriately. It is possible to observe the size of the slag outlet after the furnace is shut down to determine whether it is necessary to maintain the original pressure difference requirement. Since your ash content is relatively low and the amount of slag is small, the slag outlet will not get blocked during normal operation. There is no need to be fixated on the taphole pressure difference metric.
This post was last edited by logo911 on 2011-4-25 at 13:30. It’s just a suggestion: 1. Adding a cosolvent does not help to reduce the viscosity temperature of the ash; this method can be used if the ash has a high melting point. 2. Increase the proportion of the previously used coal type in blending for combustion. 3. The operating temperature should be maintained at a level where the pressure difference at the slag outlet remains stable, and this can be achieved by the operator. 4. Observe the changes in the slag in a timely manner. One should not solely focus on short-term production volumes or cheap coal types; instead, priority should be given to the stable operation of the gasification furnace, as only long-term stable operation can yield benefits.
What all the fellow sailors above have said makes a lot of sense. I would like to add that the original poster could also reduce the oxygen-coal ratio, which is responsible for the sudden drop in effective gas pressure, in order to find a suitable ratio that prevents the slag port pressure difference from becoming too large. It’s sufficient as long as this pressure difference doesn’t keep increasing once it reaches a certain level. Of course, this requires the original poster to keep exploring over time. I know it’s easy to talk about but difficult to put into practice; I hope the original poster can resolve the issue soon.
After changing the type of coal, the operating conditions still need to be gradually explored and adjusted.
Reply to 1# xuqinger: Hello. I have just started working in the coal chemical industry, specifically with Texaco’s reactors. I have a question for you: our shift stripper is constantly experiencing overpressure issues, and it’s difficult to control the liquid level; sometimes the pump located at the bottom of the stripper ends up running without any liquid to pump Could you give some guidance? ?
This post was last edited by zhlfwxx on 2011-5-3 at 17:24. Only stable operation can bring benefits; if the tuyere becomes blocked and prevents the gasification furnace from functioning properly, it causes significant losses to the company, and sacrifices must be made – in the form of refractory bricks. I have time to check the forum today; wish it runs smoothly!
Conduct a slag composition analysis to determine whether it is an acidic slag or an alkaline slag
1. Due to the low ash content of coal, if the operating temperature is too high, slag does not tend to form inside the furnace, thereby preventing the furnace lining from being maintained. This is also why furnace types such as SHELL and GSP require a certain level of ash content. Of course, GE, FourSpray, and Multiverse are no exception. 2. The type of coal used by the poster’s unit may be a low-ash coal, which has a relatively narrow operating temperature range. Slagging does not occur when the temperature is slightly above the flow temperature, but slag forms when the temperature is slightly below it. These two temperature ranges are also relatively narrow. 3. Due to the differences in the operation of the four nozzles compared to GE and other systems, it is not possible to adjust the temperatures at the top and bottom of the gasification furnace quickly simply by controlling the amount of oxygen at the center. In other words, the method of using four nozzles to increase the slag notch temperature is not as direct as that of GE and multi-nozzle systems (which can achieve this by increasing the central oxygen level); when using four nozzles to raise the slag notch temperature, the temperature at the upper part of the gasification furnace also increases accordingly. Since I have never operated a four-nozzle system, I can’t say much, but the key to operating it is to increase the temperature at the slag outlet without allowing the temperature in the upper part of the furnace to rise accordingly. Consider starting with the gasifier load and oxygen distribution ； Considerations such as coal blending are taken into account. I also hope the original poster will share their experience.....