Seeking reasons for ash collapse in calcination furnaces and countermeasures

Reason: The furnace load is too high, the ore is fine, and the residual sulfur level is high, all of which lead to the collapse of the ash layer that has built up. Solution: Adjust the furnace load and promptly introduce air to remove the slag.

I fully agree with Wuwei’s view. It’s also necessary to test the ingredients of the raw materials again; high lead content is another factor.

Excess residual sulfur in the slag, overly dark color of the furnace sand, too fine ore, high levels of lead and zinc in the ore, excessively high temperature in the upper part of the furnace, and an excessive diffusion angle can all cause ash collapse.

Could you please provide detailed information on the raw materials, the baking strength, and the temperatures at the top, middle, and bottom of the furnace? Only then can our colleagues help you conduct a thorough analysis.

Seeking advice on the causes and solutions for ash collapse in the roasting furnace. Reply: Our factory has experienced similar incidents of cold ash collapse (from the top and surrounding areas of the furnace), with such collapses occurring 3-4 times in a row, resulting in the furnace becoming inoperable and requiring re-ignition to resume operation. The reason is simple: severe stratification of the raw materials fed into the furnace led to this stratification phenomenon, which in turn caused the aforementioned accident of collapsed cold ash and furnace shutdown

Thank you for the guidance. Our analysis leads to similar conclusions. However, it’s very difficult to reduce the production workload, so improvements can only be made by adjusting the slag removal schedule

The raw material contains about 40% sulfur and about 9% water; its roasting strength is 10 t/m2·h, the temperature at the top of the furnace is 1060°C, the temperature in the boiling layer is 900°C, and the temperature at the bottom is 880°C

Where is the mineral mined from? Is the secondary air supply to the furnace turned up to full? The top temperature of the furnace should not exceed 1000 degrees. Conduct another full analysis of the raw materials, especially for lead.

:L This issue is easy to handle. We have a system for dealing with it; it has occurred frequently in the past, and the main cause is the problem with the raw materials – high lead content. Our approach: 1: Mix lead sand and copper sand to control the lead content in the ore fed into the furnace. 2: Add enough bottom air at once, without using secondary air. 3: Maintain an appropriate pressure at the furnace bottom, keeping it at a slightly higher level. Our furnace used to burn pyrite, but later it directly burned sulfur concentrate, with a roasting intensity of 35 t/m2·h

What’s the furnace temperature like in your company? Could you provide more details on that? What is the scale of production there? Is no secondary air used when burning sulfur-rich sand? That’s really impressive!!!! I guess it must be a small furnace. If burning sulfur-rich sand can achieve a roasting strength of 35 t/m2·h as you mentioned, then our design concepts will need to be completely revised. A furnace capable of handling 200,000 tons per day doesn’t require 20 square meters of space. The existing facilities capable of processing 200,000 tons per day can be expanded to handle 500,000 tons per day

In addition to excessive lead and zinc content in the ore, factors such as the ore being too fine, low roasting intensity, and overly dark color of the slag resulting from weak oxygen roasting can all easily lead to ash collapse.

The reason for the collapse of the ash layer is the formation of lumps of slag on the top or walls of the boiling furnace. Over time, these slag lumps grow larger, and when they become too heavy to be supported by their own structure, they fall down. The reason for the formation of slag lumps in a fluidized bed furnace may be that too much fine powder material is fed into the furnace, making it easy for this powder to be carried to the upper part of the furnace. At the same time, if the moisture content of the feed material is too high, this moisture evaporates and reaches the upper part of the furnace, where it combines with the powder that has been carried there. When this mixture comes into contact with the top or walls of the furnace, it solidifies. Another likely reason is that the air velocity through the small holes in the wind cap is too high, which can easily blow the powdered ore to the upper part of the fluidized bed furnace, or result in an excessive amount of powdered ore reaching the top of the furnace. To deal with nodulation in boiling furnaces, it is important to ensure that the particle size of the material fed into the furnace is appropriate, that the content of fine ore is not too high, and that the moisture level does not exceed 7%; this way, nodulation will not be severe. Additionally, during the annual maintenance of the fluidized bed furnace, or when replacing the air nozzles on it, a long rake can be used to remove the mineral deposits from the top or walls of the furnace. This ensures that mineral deposits will not grow too large in the future, and it also prevents injuries caused by the falling of such deposits during the maintenance of the boiling furnace.

If there is a temporary need to increase production while maintaining continuous and reliable operation, 3–4 atomization nozzles can be used in the middle of the furnace to reduce the temperature; after several months of actual use, this approach has proven effective in increasing production. Of course, whether to adopt this method or not depends on the specific circumstances. This post was last edited by zxg.wylton on 2008-4-25 15:56.]

A method of using 3 to 4 atomizing penshuiqiangs in the middle of the furnace to reduce the temperature – what kind of advanced trick is that you talking about? Could you introduce it? You produce sulfuric acid; do you also need this?

A full analysis of the raw materials should be conducted, with particular attention paid to controlling the lead content; high levels of lead can easily lead to the formation of nodules, which in turn causes the ash to collapse

The method of using 3 to 4 atomization guns in the middle of the furnace to reduce temperature has been used for sulfur concentrate. It is useful for reducing the furnace exit temperature and increasing production. However, the moisture content in the furnace gas will increase. Does typing in **（pen shui） keep appearing**? ? :o Last edited by zxg.wylton on 2008-4-26 14:37 ]

Excessively fine slag, high levels of lead and zinc in the ore, too high a temperature in the upper part of the furnace, and an excessive diffusion angle can all cause ash collapse. This phenomenon is likely related to improper settings of the bottom air and secondary air; furthermore, it is necessary to check whether the diffusion angle is suitable for burning sulfur-rich sand, and improvements should be made based on these factors

The methods for using ** to reduce boiling in furnaces are as follows: First, small sulfuric acid production units can be employed as a last resort, but this approach is not suitable for larger units. After using **, the moisture content in the furnace gases increases significantly, which raises the dew point temperature; this inevitably leads to corrosion in waste heat boilers and electrostatic precipitators. Second, it affects the efficiency of purification and adiabatic evaporation. Some experiences from the past may be useful, but their applicability must be considered. When helping others solve problems on forums, it’s important to provide valuable and applicable advice. Some traditional methods that worked well for smaller units can actually cause negative consequences when used to address certain problems. When working on technical issues, it’s necessary to analyze them comprehensively and come up with effective solutions – rather than trying to force things to fit a predetermined framework.

I think there are mainly two factors: one is the high lead content in the ore. Under high-temperature roasting, lead forms various salts, creating eutectic phases (liquid phases) at lower temperatures (900 to 1000 degrees). These phases tend to adhere to the top of the equipment due to the higher temperature there, eventually leading to the formation of lumps. Secondly, the temperature at the top of the furnace is too high; it may exceed the melting point of the mineral dust, causing the dust in the furnace gas to fuse together. Finally, there is nodulation. As for the water content, at the furnace top temperature the water is in vapor form and cannot condense; therefore, I believe its impact is minimal. Moreover, under conditions of a moderately high water content, the temperature of the boiling layer can be increased, the bottom air flow can be enhanced, the secondary air flow can be reduced, the reactions in the boiling layer can be intensified, and the secondary reactions in the upper part of the bubbling furnace can be minimized, thereby preventing the temperature in that upper area from becoming too high.

The main problems related to ash accumulation in the furnace are related to the raw materials: 1. The material is too fine, containing a high amount of dust, which forms lumps due to the high temperatures at the top of the furnace. 2. The ore contains excessive levels of lead and zinc. 3. Operational issues such as insufficient secondary air lead to the ash turning black over time. Our factory encountered such problems as soon as we started operating the furnace in February this year; not only was there ash accumulation in the furnace, but it also caused severe blockages in the system’s pipelines. Once the raw materials were changed, all these problems were resolved.