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Changchun Dongshi Technology (Group) Co., Ltd., which has been active in the field of gas purification and desulfurization for over a decade, has always remained at the forefront of industry technology. Over the years, the company has maintained close exchanges and cooperation with universities and research institutions, working together on public relations efforts for various scientific and technological projects. By anticipating the needs of the industry and addressing its challenges, the company has managed to overcome many difficult technical problems in this field. Key products include the wet 888 desulfurization technology, the JNT series of advanced desulfurization technologies, as well as the DS-type vacuum filter dedicated for sulfur foam, and the QYD-type mass transfer internals. Products such as the “QYD-type mass transfer internal component technology,” “wet 888 desulfurization technology,” “sulfur recovery technology,” “by-product salt extraction technology,” and “dry advanced desulfurization technology” have been granted **patents. Next, we will mainly discuss the DS-type vacuum filter specialized for sulfur foam. 1 Introduction to the DS-type vacuum filter specialized for sulfur foam. The sulfur foam vacuum filter is a high-efficiency DS-type filtering device that combines sulfur foam separation with the treatment of desulfurization liquid. It was independently designed and developed by Changchun Dongshi Technology (Group) Co., Ltd. in response to the requirements of the desulfurization process and the characteristics of sulfur foam. In 2008, the DS-type sulfur foam vacuum filter was recognized by the Energy and Environment Committee of the China Environmental Protection Federation as a \"key new technology and product for energy conservation and emission reduction in China\". In 2009, the DS environmentally friendly sulfur recovery process was also recognized by the China Fertilizer Industry Association as a \"technology supporting the development of the fertilizer industry\". Currently, the vacuum filters developed by Dongshi Company are widely used in industries such as fertilizers, coking, pharmaceuticals, and natural gas. 2 Characteristics of the DS-type special vacuum filter for sulfur foam in wet desulfurization 2.1 Ability to reduce steam consumption Generally, the sulfur foam liquid content in the regeneration overflow is around 90%; when using continuous sulfur melting, 9 tons of desulfurization liquid are recycled from the sulfur melting tank for every ton of sulfur produced ； After filtration using the DS-type filter dedicated for sulfur foam, the filter cake contains 30% moisture. Assuming that the solids in the filter cake are 100% sulfur, 1.43 tons of filter cake (with 30% moisture) are required to produce 1 ton of sulfur. In other words, only 0.43 tons of desulfurization solution enter the sulfur melting tank along with the filtered filter cake. Therefore, by using the DS-type filter for sulfur foam before melting, 8.57 tons less of solution need to be fed into the sulfur melting tank per ton of sulfur produced, compared to direct continuous melting. This solution usually needs to be heated from around 35°C to 70–90°C before exiting the sulfur melting tank, and the amount of steam required to raise its temperature is 821 kg, as calculated. The results show that using a vacuum filter designed specifically for DS-type sulfur foam filtration allows for the savings of 821 kg of steam per ton of sulfur processed, compared to continuous sulfur melting. Based on this, for a coke oven gas desulfurization system with a processing capacity of 60,000 Nm3/h, where the H2S level at the inlet is 5,000 mg/Nm3 and it needs to be kept below 100 mg/Nm3 at the outlet, with an sulfur recovery rate of 85%, 4,634 kg of steam can be saved per day. 2.2 Manufacturers that use continuous sulfur melting can reduce the temperature rise of the solution; it is impossible not to recycle the reflux liquid, as this would not only result in significant waste but also be unacceptable from an environmental perspective. It is certainly better to cool the liquid first before returning it to the system, but natural cooling requires a long time, as well as specific equipment and space; an increase in the volume of the solution also presents problems. If a cooling medium is used for cooling, this **increases operating costs, and issues such as salt precipitation and blockages can occur during the cooling process. Therefore, especially in large-scale coking plants with high gas volumes and high H2S levels in the gas, almost no cooling is done on the molten sulfur tank effluent before it is returned to the system – most of it is sent directly back to the system. This results in excessively high solution temperatures, especially in summer, causing significant problems for the operation of the system. Taking the desulfurization of coke oven gas with a gas volume of 60,000 Nm3/h and H2S content in the gas of 5 g/Nm3 as an example, using a continuous sulfur melting process that involves first filtering with a DS-type vacuum filter designed for sulfur foam and then melting the sulfur results in an additional 48.4 tons of reflux liquid being produced per day. According to the heat balance equation: M_hot·C_hot·(T2–T) = M_cold·C_cold·(T–T1), we have: T = (M_hot·T2 + M_cold·T1) / (M_hot + M_cold) = (48.4×10³×353 + 1050×10³×308) / (48.4×10³ + 1050×10³) = 310 K = 37°C. T–T1 = 37–35 = 2°C. In this formula, M_hot represents the daily amount of liquid returned to the sulfur melting tank, in kilograms ； M cold — Total system solution volume: 1000 m3 × 1050 kg/m3 = 1050 × 103 kg ； C_hot and C_cold represent the specific heat capacities of the return fluid and the system solution respectively; C_hot = C_cold ； T1—Initial temperature of the desulfurization liquid: K, 308 K ； T2—Temperature of the liquid returning to the sulfur melting tank: k, take 353 k ； T—Temperature of the desulfurization solution after mixing: k. As can be seen from the above calculations, compared to filtering with a vacuum filter designed specifically for DS sulfur foam and then remelting the sulfur, the reflux liquid from the melting tank on a daily basis will cause the temperature of the system solution to rise by 2°C. Continuous recycling of molten sulfur liquid, especially in summer, can cause the system temperature to rise extremely high, significantly affecting the normal operation of the system and even making it difficult to maintain production. If a DS sulfur foam filter is used for filtration before remelting sulfur. The problem of temperature rise in the solution no longer exists. 2.3 Reducing the formation rate of by-products: Excessively high temperatures facilitate the formation of by-products; in particular, when the temperature exceeds 50°C, the formation rate of Na2S2O3 increases almost linearly. The temperature of the reflux liquid in the sulfur melting tank is generally between 70–90°C. Although the oxygen content in the solution within the tank is not as high as that in the regeneration tank (column), sulfur foam and liquid coming out of the regeneration tank contain a certain amount of oxygen, and at the higher temperatures in the tank, this oxygen reacts rapidly with Na2CO3 and HS⁻ or elemental S present in the solution to form Na2S2O3. We have conducted multiple analyses of the Na2S2O3 content in plants with a gas capacity of 60,000 Nm3/h and an inlet H2S concentration of 5,000 mg/Nm3. The average value of Na2S2O3 levels in sulfur foam samples was 21.3 g/L, whereas the average value for Na2S2O3 in the clear liquid coming out of the sulfur melting tank was 51.4 g/L. It recovers 5.7 tons of sulfur per day, using continuous sulfur melting; as a result, at least 51.3 tons of liquid are discharged from the sulfur melting tank each day. If the DS-type sulfur foam filter is used first for filtration before melting, 49 tons less of liquid are discharged per day. This 49 tons of desulfurized liquid, after being subjected to high temperatures during sulfur melting, is recycled, which results in an increase in the amount of by-product Na2S2O3: (51.4–21.3) × 49 t / 1.05 = 1405 kg. With a total volume of 1000 m3 for the system’s solution, the use of the DS-type filter reduces the increase in the Na2S2O3 concentration in the entire system’s solution by 1405/1000 = 1.405 g/L per day. Furthermore, when a large amount of reflux liquid from the sulfur melting tank returns to the system, it causes localized overheating in a short period of time, accelerating side reactions and leading to a significant increase in the formation of by-products. Therefore, the formation rate of sulfur fusion by-products is **reduced** after filtration using a DS filter. 2.4 Reducing alkali consumption: In recent years, whether in the nitrogen fertilizer industry or in the coking industry, high alkali consumption has been a common issue during desulfurization processes. Most production managers in enterprises are aware of the reasons why the increase in by-products leads to higher alkali consumption, as well as why sulfur melting results in an increase in by-products. However, few people really care about just how much the increase in alkali consumption occurs as a result of continuous sulfur melting; when high alkali consumption is observed, efforts are made to find causes in other areas, only to find that these efforts yield little result. In the solution of the desulfurization system, regardless of the reaction pathway by which Na2S2O3 is formed, its Na+ ions originate solely from Na2CO3. Therefore, for every 1 mol of Na2S2O3 produced, 1 mol of Na2CO3 is consumed; in other words, to produce 1 kg of Na2S2O3, 0.67 kg of Na2CO3 is required. For example, in a plant with a gas flow rate of 60,000 Nm3/h and an inlet H2S concentration of 5,000 mg/Nm3, which recovers 5.7 tons of sulfur per day, at least 51.3 tons of liquid must be discharged from the sulfur melting tank. The concentration of Na2S2O3 in the clear liquid increased from 21.3 g/L to 51.4 g/L. The increase in alkali consumption per day due to the accumulation of by-products resulting from continuous sulfur melting was: (51.4 – 21.3) × 51.3 t / 1.05 × 0.67 = 985 kg. The amount of alkali consumed due to the formation of by-products when sulfur is remelted after filtration using a DS-type sulfur foam filter is: (51.4 – 21.3) × 2.45 t / 1.05 × 0.67 = 47 kg, resulting in a direct savings of 938 kg of alkali. For a plant with a gas flow rate of 60,000 Nm3/h and an inlet H2S concentration of 5,000 mg/Nm3, the savings of 938 kg of Na2CO3 per day are self-evident. 2.5 The DS-type vacuum filter dedicated for sulfur foam is used for filtering salts; by employing this filter, it is possible to **reduce the amount of by-products formed during the sulfur melting process, which not only lowers consumption but is also beneficial for environmental protection. However, in system solutions, by-products are an inevitable presence; no matter how well they are controlled, they will gradually accumulate. The specialized DS-type filters for sulfur foam result in a significant reduction in the amount of by-products after filtration, compared to before filtration. Based on the experiences of several users, these filters can reduce by-products by 20%–30% during summer, and by 40%–50% during winter. Below are a set of data from a manufacturer in Shandong: It can be seen that some by-products are carried away during the filtration process due to adhesion to the sulfur paste, thereby enabling effective filtration of these by-products in the solution. This is also confirmed by the fact that, after the factory adopted a specialized vacuum filter for DS sulfur foam, the amount of solution discharged decreased from 80 tons per month to 60 tons per month. 2.6 The DS-type vacuum filter dedicated for sulfur foam has low operating costs; its energy consumption during operation is reduced by over 90% compared to other filtering equipment. Compared to direct continuous sulfur melting, its energy consumption increases only by a negligible amount in the form of electrical power usage. Under normal conditions, this filter can handle 0.6–1.2 m3/m2·h of sulfur foam per hour. Taking the enterprise mentioned above as an example, with a gas flow rate of 60,000 Nm3/h and an H2S concentration at the inlet of 5,000 mg/Nm3, we can choose a DS-15 type filter. Its operating power is only 9 kW; including cleaning time, assuming it operates for 16 hours per day, the daily electricity cost would be: 9 kW × 16 × 0.76 (local electricity price) = 109 yuan. This results in savings of around 2,000 yuan per day. 3 Performance comparison of the DS-type vacuum filter dedicated for sulfur foam with other filtration equipment: Compared to other devices, the DS-type vacuum filter designed for sulfur foam exhibits clear advantages in terms of automation level, energy consumption, filtrate purity, moisture content in the filter cake, and filtration speed. The performance comparison of the DS-type vacuum filter dedicated for sulfur foam with other types of filters is as follows: 3.1 Comparison with plate and frame filter presses – Although not widely used in the desulfurization industry, some companies do employ them. Their operation is intermittent, with loading, filtering, slag removal, and cleaning constituting one working cycle. Although automation control has now been implemented in such filters, some versions are equipped with an automatic plate-removal system, a curved-arm-assisted slag removal system, a single-bar water flushing system, a flip-plate liquid collection system, and a PLC system. However, when used in sulfur foam filtration, we encounter a common problem: due to the high viscosity of the sulfur foam, the filter media stick together, requiring manual assistance to remove the material. Moreover, cleaning the filter fabric is very difficult, and the issue of needing manual cleaning cannot be truly resolved, which significantly reduces the level of automation and increases the labor intensity. The DS-type vacuum filter dedicated for sulfur foam automatically draws in the material, dries it, discharges it, and performs backwashing under the action of vacuum pressure. After use for a period of time, it should be cleaned using a mixture of ultrasonic waves and a low-concentration alkaline solution. The entire process takes place automatically and continuously, without the need for human intervention. In terms of degree of automated control, the DS-type vacuum filter dedicated for sulfur foam is far superior to plate and frame filters. 3.2 Compared to drum centrifuges, plate and frame filter presses are used less frequently in the desulfurization industry. Centrifuges rely on inertial centrifugal force for separation; their main component is a drum that rotates at high speed around a vertical or horizontal axis. The side walls of the drum are equipped with numerous small holes, and the inner surface of the drum is covered with a filter cloth. The rotation of the drum generates centrifugal force, which causes the filtrate to be discharged through the pores, while the sulfur paste remains trapped on the filter cloth. The higher the drum speed, the higher the separation efficiency. Therefore, to achieve a high separation efficiency, a motor with higher power is required to drive it. The operating power of a WG---1500 scraper discharge centrifuge is between 25 and 30 kilowatts, whereas for a DS-type vacuum filter designed specifically for sulfur foam, a area of 15 square meters is sufficient; its vacuum pump requires only two motors of 2.35 kilowatts each, resulting in an overall operating power of less than 9 kilowatts. Therefore, the DS-type vacuum filter designed for sulfur foam has a clear advantage in terms of power consumption. 3.3 Comparison of filter media: Both plate and frame filtration and centrifugal filtration primarily use filter cloths. During the filtration process, clogging of these filter cloths can hinder an increase in productivity. The causes of clogging include mechanical blockage by sulfur particles, as well as the accumulation of carbonates and sulfates formed through chemical reactions on the surface of the filter cloth. Cleaning or replacing it requires a lot of effort. Moreover, the filter pores in the filter cloth are prone to deformation. The DS-type vacuum filter dedicated for sulfur foam uses ceramic filter plates. The internal structure is gradient-shaped. It features low filtration resistance, high strength, and no deformation. The pore size is small, and the material is hydrophilic; during filtration, surface tension arises between water and the hydrophilic ceramic, creating a capillary effect that keeps the pores filled with liquid. When a vacuum is created, the filtrate passes through the pores, while air and sulfur particles cannot do so, thereby ensuring no loss of vacuum. This principle significantly reduces energy consumption and the moisture content in the materials, as well as the solid content in the filtrate. 3.4 Comparison of filtration effects: Based on the data from various manufacturers, under normal operating conditions, the moisture content in the filter cake obtained through plate and frame filter presses and centrifuges is 30–40%, while the solid content in the filtrate is 50 ppm ； The filter cake obtained after filtration using the DS-type vacuum filter dedicated for sulfur foam has a moisture content of 30% or less, while the solid content in the filtrate is 30 ppm or less. 3.5 Comparison of processing capacity: In terms of filtration rate, the DS-type vacuum filter designed for sulfur foam processing far exceeds plate and frame filters as well as centrifuges; its processing capacity for sulfur foam is 0.6–1.2 m3/m2·h ； The plate and frame filter press has a rate of only 0.4–0.5 m3/m2·h. The separation efficiency of a centrifuge is determined by the drum diameter and rotational speed; the larger the drum diameter, the higher the efficiency, but the greater the stress, making it difficult to ensure sufficient strength ； As the rotational speed increases, the separation efficiency improves, but there is a limit to this, and it also leads to increased power consumption. Therefore, for enterprises with a large production scale, if a DS-type sulfur foam filter is chosen for the system, one unit will suffice; whereas if centrifuges are used, two or more units will be required.