Reasons for the spontaneous combustion of liquid sulfur filters
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:L: In the past few months, our liquid sulfur filters have experienced several instances of spontaneous combustion, all of which occurred after the machines were shut down and the filter elements were removed to clean the filter cake. Not every filter experienced such spontaneous combustion, and the temperature of the insulation steam was found to be normal. The possible reason for this is that there is FeS on the old filter screen; when it is pulled out, it reacts with air at high temperatures, resulting in even higher temperatures that ignite any remaining sulfur or other flammable substances. Later, by waiting for a longer period after shutting down the machine to allow its temperature to drop before pulling it out for cleaning, spontaneous combustion incidents became less frequent. :) Those who have encountered this phenomenon please share their experience; let’s help analyze it together.
We have not encountered spontaneous combustion in liquid sulfur filters here. However, spontaneous combustion did occur at the liquid sulfur storage tank and the cover of the clarification tank. At that time, I analyzed that the sulfur present in the pouring ceremony was formed by the condensation of sulfur vapor; it had a spiky shape and a large surface area, and it reacted with oxygen in the air to generate heat. As the temperature rose to the auto-ignition point of sulfur, spontaneous combustion occurred. Page 146 of Volume 1 of the book \"Production Process Flow, Equipment Installation and Construction Techniques, as well as Quality Inspection Standards for Sulfuric Acid\" provides an explanation of sulfur’s spontaneous combustion, but it is not clear.
FeS undergoes spontaneous combustion at low temperatures; does anyone know the ignition temperature of this substance?
Please refer to http://www.hjes.org.cn/anping/list.asp?id=570
Does that mean foam fire extinguishers should be installed on site at the liquid sulfur filter?
CO2 might be better, as it can also help cool things down. Since the filter elements of the filter are made of stainless steel mesh, using water to extinguish a fire will cause severe corrosion of the filter mesh; steam is slightly better for this purpose, while foam extinguishers may lead to even more severe corrosion.
Generally, liquid sulfur equipment such as sulfur melting tanks, filtration tanks, intermediate tanks, and liquid sulfur storage tanks are all equipped with fire-suppression steam nozzles, which are used for extinguishing fires. However, fire protection measures have not been taken into account in the design of liquid sulfur filters; this aspect needs to be considered in the future. A fire-suppression steam hose should be installed on site.
Sulfur vapor reacts with Fe to form a low-melting-point polymer, which has a very low ignition point of less than 100 degrees. Since there is O2 present at the vent openings, liquid sulfur can catch fire on its own. The solution is to coat the lid with aluminum, or to apply aluminum coating only to the vent openings
The same issue has occurred in our equipment as well. The main cause seems to be ferrous sulfide formation, as mentioned earlier. I believe it is primarily due to quality problems with the sulfur raw material – excessive acidity and moisture levels, along with the failure to add alkali in a timely manner, which increases the likelihood of ferrous sulfide forming. By increasing the amount of alkali added and replacing the sulfur supply, this problem no longer occurred. It is necessary to install steam fire suppression valves and water valves; be careful when using steam for fire suppression as it can cause injuries. Using fire extinguishers is not very effective!!
I think an explanation on the eighth floor would be better
The temperature of the resulting FeS is too high; once it is taken out and exposed to sufficient oxygen, it catches fire immediately
We have experienced similar situations as well, suspecting that sulfur is acidic and forms ferrous sulfide (which has a very low ignition point), leading to spontaneous combustion. It is recommended to analyze the acidity of sulfur, and if necessary, add quicklime at the source for neutralization. We have been adding quicklime at the source. Because pure sulfur is non-corrosive. When there is a lot of moisture or other impurities inside, sulfur becomes acidic after melting.
We have always used substances such as soda ash or lime to neutralize the acidity of liquid sulfur; sometimes it catches fire on its own, and this has happened several times this year, including twice last month. The measure we are taking now is to stop the filter machine, allow it to cool down for a while before proceeding with the slag removal process.
We also often encounter cases of spontaneous combustion after liquid sulfur is filtered and drawn out; we haven’t given this much thought, assuming it’s caused by a high content of organic substances in the sulfur, as well as hydrocarbons.
As for the reason related to the raw materials, it’s sometimes difficult to explain. We have four filters, and occasionally one of them catches fire on its own, while the other ones do not experience such issues. Sometimes it takes some time after being pulled out for cleaning before it catches fire on its own; the temperature must have dropped considerably. So I feel that FeS has a high possibility of oxidizing and self-igniting at high temperatures when exposed to air. After such an incident occurred again recently, a thorough inspection of the filter was carried out, and it was found that the insulation steam valve on the cylinder jacket could not be closed; as a result, the temperature of the cylinder might remain high even after it was shut down, increasing the risk of spontaneous combustion. There was an improvement after replacing the valve.