Problems with the molten sulfur axe solution

With the current high pressure to protect the environment and strict requirements regarding energy conservation and reduction of consumption, it is essential to recycle the clear liquid. During the recycling process, care must be taken to keep the suspended sulfur level below 10 g/l. Two phenomena may occur during recovery (observed in actual work): 1. Severe foaming of the solution after it is introduced into the system. It is mainly caused by the excessively high temperature of the recycled liquid; the problem can be resolved by cooling the liquid before feeding it back into the system ； 2. After the clear liquid is recovered, there is no foam or less foam in the regeneration tank. This situation is mainly caused by the high content of sodium thiocyanate in the clear liquid. Conduct analysis first to reduce the amount of liquid to be recovered.

Sulfur foam that has just been separated by flotation from the desulfurization liquid system contains about 90% desulfurization liquid; if a large amount of liquid is carried along with the foam when it overflows, this will result in a high concentration of desulfurization liquid in the sulfur foam tank. If separation by heating and stratification is carried out, the desulfurization liquid at a temperature of 60 degrees accelerates the rate of side reactions ； If it is fed directly into the sulfur melting tank without stratified separation, the side reactions in the desulfurization solution will intensify and accelerate under the high-temperature conditions of the tank; therefore, in either case, the desulfurization solution returning to the system will have a high content of by-products.

Share this article with everyone: The Impact of Sulfur Melting Residues on Desulfurization Systems and Treatment Measures 1. Introduction In the desulfurization systems of enterprises such as nitrogen fertilizer plants, methanol plants, and coking plants, most of the hydrogen sulfide is removed using the wet oxidation method for desulfurization. Although the process equipment conditions vary among different plants, the entire desulfurization process consists of three main stages: absorption, regeneration, and sulfur recovery. Among them, absorption is key, regeneration is central, and the recovery of molten sulfur is essential. The three influence each other. In the past, due to various factors such as limited production capacity, low hydrogen sulfide levels, and lax environmental regulations, some companies did not pay enough attention to sulfur recovery. In recent years, due to the expansion of enterprise scale, tight coal supplies have led to the rapid use of high-sulfur coal in these enterprises; meanwhile, the diversification of their products has increased the precision requirements for hydrogen sulfide in subsequent processing steps. Under these circumstances, sulfur recovery and sulfur melting also become more important as the role of the desulfurization system in the entire production process increases. 2. Impact of molten sulfur residue on the desulfurization system: Desulfurization is centered around regeneration to maintain a healthy cycle in the system. Removing as much sulfur as possible is essential to maintain the quality of the circulating solution; otherwise, an increasing accumulation of sulfur within the system will lead to high levels of suspended sulfur, reduced absorption capacity of the solution, and a decline in desulfurization efficiency. During the process of recovering molten sulfur, if the residual liquid is directly recycled and reintroduced into the system, it will cause sulfur to float, reducing the separation efficiency and decreasing the amount of sulfur foam – or even eliminating it altogether – which deteriorates operating conditions and affects normal production. If not recovered, significant losses of absorbent and catalyst occur, leading to serious waste and negative impacts on the environment. In particular, as production scales continue to expand and high-sulfur coal is used, the amount of hydrogen sulfide that can be processed per unit of time increases, resulting in more residual liquid after sulfur melting. This not only makes it difficult to handle the residue remaining after sulfur melting during cooling, temperature reduction, and precipitation processes, but it also **increases the chances** of HS being converted to S2O32- during these processes. The excessive formation of these by-products makes the solution turbid and reduces its quality; this not only directly affects the desulfurization efficiency but, in severe cases, the crystallization of these by-products within the desulfurization solution can also block the equipment pipes and fillers, forcing shutdowns and disrupting normal production. 3. Solutions: Since traditional sulfur recovery processes can hardly meet the requirements of large-scale production, finding an effective solution has become an urgent task for the desulfurization industry. Currently, the generally accepted view in the industry is that sulfur foam should be filtered. This is because 80% of the sulfur foam coming out of the regeneration tank consists of desulfurization liquid, with only 20% being elemental sulfur. Moreover, due to the use of different catalysts, variations in the quality of regeneration, as well as differences in operational controls, the content of elemental sulfur in the sulfur foam also varies; in many plants, it is less than 10%. All these sulfur foams are fed into the sulfur melting tank for heating; this not only **increases steam consumption but also makes it more difficult to handle the residual liquid. Therefore, by first subjecting the sulfur foam to pressure filtration to convert it into a sulfur cake and then melting the sulfur, many problems can be easily resolved. Although the concepts are unified, in practical application, there is a great variety of approaches, each showing its own strengths. Taking filtration equipment alone as an example, there are those that use centrifuges, vacuum drum filters, pressure filters, Gore membrane filtration, as well as those that employ sedimentation tanks for filtered or unfiltered processing, and so on. Objectively speaking, the use of these filtration devices does provide a certain level of assurance for the stable operation and continuous functioning of the manufacturers that use them. However, there are also many common problems, such as large size of the equipment, complex operation requirements, the need for dedicated personnel to monitor it, frequent replacement of filter fabrics, high labor intensity, poor working conditions, and suboptimal filtration performance. Under these circumstances, our Changchun Dongshi Science and Trade Co., Ltd. developed a specialized filter for DS-type sulfur foam, which fundamentally addresses the many shortcomings of previous filtering devices. 4. DS-type sulfur foam filter: The DS-type vacuum filter designed specifically for sulfur foam is a new type of efficient, energy-saving, and environmentally friendly solid-liquid separation device that integrates nanometric inorganic membrane technology, ultrasonic technology, and automated control. It utilizes different ultra-fine pores, based on the components of the desulfurization solution and their specific physical and chemical properties, to filter out elemental sulfur from the sulfur foam without affecting the composition of the solution. The resulting filter cake can be packaged for sale or fed into a sulfur melting tank for further processing ； Due to the use of nanofiltration, the desulfurized solution after filtration contains very low levels of sulfur (the removal efficiency of elemental sulfur can exceed 99.9%). The filtered solution has low turbidity and is clear and transparent (with a total solid content of <50 PPm). Moreover, since it is a physical filtration process, the physicochemical properties of the solution remain unchanged after filtration. It can be directly reused in the desulfurization system, thereby greatly saving energy consumption and reducing environmental pollution as well as damage to the system. The working principle of the DS desulfurization vacuum filter is as follows: By utilizing nanoceramic technology, under the action of vacuum pressure, the filtering medium allows only the desulfurization solution to pass through the pores of the ultra-fine ceramic membrane, while mechanical impurities, elemental sulfur, and bubbles in the solution cannot pass through. This mechanism, which prevents any loss of vacuum, significantly reduces the energy consumption of the vacuum filter as well as the solid content in the filtered solution. Compared with traditional filtration equipment, the DS-type sulfur foam filter has the following advantages: 4.1 A clean working environment with no pollution. 4.2 The vacuum level is high, resulting in a filter cake with lower moisture content compared to traditional filters. The filtration efficiency can reach over 70%. 4.3 It has a compact structure, occupies little space, and is easy to install and maintain. 4.4 Low energy consumption – it saves over 90% more energy compared to other filtration devices. 4.5 The filtrate is clear and transparent; solid content

2# Luo Hu 15185080221: When using the low-temperature (room temperature) sulfur melting axe cleaning solution, bubbles still form in the regeneration tank; similar bubble formation occurs at high temperatures (around 50 degrees)

I’ve also seen what was mentioned upstairs, but I think it’s a system issue and has little to do with Qingye. Firstly, if the sulfur melting residue is not removed properly, as they have already analyzed, this has a significant impact on the system. Why then, when environmental regulations are not strict, is this residue not removed? Leaks in the system are ignored. Apart from cost issues, problems with the desulfurization system occur rarely; this is due to the continuous replacement of the solution. Environmental regulations are strict, and especially in recent years, various odd problems have arisen with desulfurization systems, keeping the staff at desulfurizer manufacturers extremely busy without being able to resolve these issues. The reason lies in the inherent complexity of the regeneration process, as well as the interactions and interdependencies among different salts; currently, there is no clear conceptual framework within the industry to address this issue. But that’s not a problem either; I think as long as proper filtering is done at night, it certainly won’t have an impact on the system. Secondly, in my opinion, factors such as the quality of the gas (primarily influenced by the raw coal, such as hydrocarbons, thiocyanates, and humic acids), as well as the quality of the chemicals introduced by the catalyst (such as the degree of ripening of tannins and the breakdown and derivatives of the main reducing agents), all play a role. Once these factors accumulate to a certain extent, foaming in the solution becomes inevitable. Even the quality of the alkali added to the solution can have an impact on the system; there are many such reasons. Still, I agree with Zhang Tong from Dongshi: it is necessary to separate as much solution as possible from the foam before pressure cooking, so as to minimize the impact on the system.

It is best to lower the temperature to near the system temperature, and the level of suspended sulfur should also be as low as possible. Otherwise, high temperatures during system regeneration can easily lead to the formation of by-products, while high levels of suspended sulfur can cause blockages in the desulfurization tower.