How do you handle the clear liquid that is filtered out during the operation of continuous sulfur melting tanks?

It cannot be returned directly to the system; instead, it can be processed in this way: the material is fed into a vertical cooler with an open top for cooling, and then sent to a tank where it is filtered using sacks or brown pads (the raw sulfur paste is packaged and taken away, or the sulfur is melted and taken away). The filtered liquid is then returned to the regeneration tank.

It cannot be returned directly to the system; you can handle it in the following way: 1. The liquid is sent to a filtration and sedimentation tank (the sedimentation tank can have two to three stages of filtration). 2. The filter screen in the sedimentation tank can be a 60-mesh stainless steel mesh. 3. The filtered clear liquid is recovered to the system after heat exchange (at a temperature below 40 degrees). 4. The sulfur content in the precipitate from the first stage is relatively high, allowing for secondary sulfur extraction through melting. 5. The volume of each stage of the sedimentation and filtration tank is approximately 20–30 cubic meters. :P: handshake

I’m not sure what desulfurization agent you use. If the material is sent directly back into the system, a large amount of sulfur paste will adhere to the surface of the desulfurization tower fillers, resulting in an increase in the pressure difference within the tower and thus preventing liquid flow. First, you need to adjust the feeding rate of the sulfur melting tank, as well as the amount of steam and the temperature inside the tank, in order to melt as much sulfur as possible from the sulfur paste fed into the tank. The temperature inside the tank should not be too high, as this can lead to various side reactions that alter the composition of the desulfurization solution. Additionally, the clear liquid coming out of the sulfur melting tank must go through processes such as cooling, sedimentation, and filtration before it can be returned to the system; it cannot be sent back to the regeneration tank, but rather to the rich liquid tank, where it can be regenerated via spraying before being reintroduced into the system

I agree with what was said upstairs. If the liquid from the sulfur melting tank is not cooled, filtered, and subjected to precipitation and regeneration, then the sulfur ions in it will undergo partial oxidation and regeneration reactions in the desulfurization tower, resulting in the formation of sulfur. This sulfur adheres to the surface of the packing, leading to an increase in the pressure difference within the tower, and may even cause liquid retention

What everyone is saying makes sense; I’m also worried about the sulfur melting furnace. It’s been very enlightening

Some companies precipitate the overflow from the regeneration tank; the portion containing more sulfur paste at the bottom is melted, while the clearer liquid from the top is sent directly to an underground sedimentation tank, thereby reducing the amount of sulfur-melting waste liquid. In my opinion, a temperature higher than 120 degrees during sulfur melting leads to various side reactions, which is a serious flaw. Centrifugation can be considered for separation, with absolutely no side reactions.

As long as the liquid discharged from the sulfur melting tank is clear enough, it can be directly returned to the lean liquid system by simply lowering the temperature. However, it is not easy to achieve sufficiently clear drainage; the key lies in the selection of the sulfur melting tank – careful calculation is required, along with the right model and manufacturer. If it is a sulfur melting kettle from Shijiazhuang Precision Chemical Technology Co., Ltd., you can contact the manufacturer for assistance.

2. Side reactions during desulfurization regeneration: (1) During the desulfurization absorption process, in addition to the main reaction, there are also side reactions involving salts such as NaHCO3, Na2S2O3, Na2SO4, and sodium thiocyanate. ①CO2 in the feed gas is an acidic gas that can react with bases as follows: Na2CO3 + CO2 + H2O = 2NaHCO3. According to the mass transfer rate equation: NA = KG·F·ΔPM, where NA is the absorption rate, F is the absorption surface area, and KG is the overall gas-phase mass transfer coefficient. When other factors remain constant, increasing the Pco2 (in the gas phase) or decreasing the equilibrium partial pressure of PCO2 (in the liquid phase) increases the value of ΔPM, thereby increasing the absorption rate. ②When HS- comes into contact with oxygen, thiosulfate is formed: 2HS- + 2O2 = S2O32- + H2O. This reaction occurs mainly in the regeneration tank. Due to the ample amount of air in the tank and the high dissolved oxygen level in the liquid phase, when the production load is high and the regeneration effect is poor, the potential of the lean solution is low; as a result, the H2S absorbed does not get fully oxidized to elemental sulfur before entering the regeneration tank. A considerable amount of HS- enters the regeneration tank where it is oxidized by air to thiosulfate. This reaction accelerates significantly when the temperature is above 60°C and the pH is greater than 9. ③ Excessive dissolved oxygen in the solution, along with prolonged contact between the solution and air, leads to the formation of more sulfates. The reactions involved are:　　　HS-+H2O2=SO42-+H+　　　S2O32-+1/2O2=SO42-+S↓ The rate of these reactions increases when the solution temperature is high. ④The feed gas HCN has weak acidity; when it comes into contact with an alkaline solution, it is almost entirely absorbed to form sodium cyanide, which further reacts to produce sodium thiosulfate. ⑤ Suspended sulfur in the solution is also one of the factors that cause side reactions; the reaction equations are as follows:　　　S + SO32- = S2O32-　　　S + O2 = SO42- The extent of these reactions increases as the size of the sulfur particles decreases, as the amount of suspended sulfur increases, and as the temperature rises. ⑥ When sulfur is melted at high temperatures, it reacts more rapidly with alkalis and other substances, resulting in the formation of a large number of by-products, among which Na2S2O3 and sulfite ions are the most common. (2) Control and solutions for side reactions: The speed and rate at which side reactions occur can be improved and controlled. The general principle is to adjust the contents of the solution components appropriately, maintain suitable operating conditions, and enhance regeneration. Maintain the solution potential within an appropriate range, control the suitable operating temperature, and process the sulfur-melting recovery liquid for recovery. 3. Side reaction issues: In recent years, due to coal shortages, deteriorating coal quality, and increasing load, side reactions during the wet flue gas desulfurization process have become more severe, leading to higher consumption in the production process as well as equipment corrosion. In the desulfurization process, in addition to the main reaction, salts such as sodium bicarbonate, sodium thiosulfate, sodium sulfate, and sodium thiocyanate are also formed. 3.1 Reasons (1) Carbon dioxide in the feed gas is an acidic gas that can react with sodium carbonate to produce the following reaction: Na2CO3 + CO2 + H2O = 2NaHCO3. According to the mass transfer rate equation na = kG × F × △Pm, where: na – absorption rate ； F——Absorption surface area ； kG — total gas mass transfer coefficient ； △P — average driving force for CO2 partial pressures at the bottom and top of the tower. When all other factors remain constant, increasing the equilibrium partial pressure of Pco2 in the gas phase or decreasing it in the liquid phase increases its absorption rate due to an increase in △Pm. At the initial start-up of desulfurization, the solution consists entirely of Na2CO3; as the reaction of absorbing CO2 proceeds, NaHCO3 gradually increases in the solution. When the amount of CO2 absorbed is balanced by the amount of CO2 desorbed during regeneration, the concentrations of Na2CO3 and NaHCO3 in the liquid phase remain constant. In conventional atmospheric-pressure desulfurization, when the CO2 content in the feed gas is between 8% and 6%, and the total alkalinity of the solution is 0.4 N (equivalent to 21.2 g/L based on Na2CO3), then the concentration of Na2CO3 is around 5–6 g/L, while that of NaHCO3 is around 25 g/L. During the pressurized desulfurization process (such as modified desulfurization), due to the high operating pressure, the CO2 concentration is also high, which increases the driving force of △Pm. As a result, the concentration of Na2CO3 in the liquid phase decreases significantly, accounting for only 5% to 10% of the total alkalinity, with the majority being NaHCO3. (2) When hydrogen sulfide comes into contact with oxygen, thiosulfate is formed: 2HS—+2O2＝S2O32- +H2O. This reaction occurs mainly in the regeneration tank, where there is an abundance of air and a high concentration of dissolved oxygen in the liquid phase. When the production load is high and the regeneration effect is poor, the potential of the lean solution becomes low; as a result, the hydrogen sulfide absorbed cannot be completely oxidized to elemental sulfur in the reaction tank, and a considerable amount of hydrogen sulfide is oxidized by air to thiosulfate. When the solution temperature is above 60°C and the pH value is greater than 9, the rate of this side reaction increases significantly (generally, the liquid temperature is around 40±2°C and the pH value is about 8.5, so there is no major problem). The feed gas contains a small amount of oxygen, and sodium thiosulfate is also formed in the absorption tower (the oxygen content is generally 0.4%, so the impact is minimal). (3) If the dissolved oxygen level in the solution is too high, or if the solution is in contact with air for too long, more sulfates will be formed. The reactions are as follows: HS—+H2O2＝SO42-+H+, and S2O32-+1/2O2＝SO42-+S↓. This side reaction occurs more rapidly at higher solution temperatures. (4) The raw material gas, hydrogen cyanide, has weak acidity; when it comes into contact with an alkaline solution, it is almost entirely absorbed to form sodium cyanide, which further converts into sodium thiocyanate. The reaction equations are as follows: 2HCN + Na2CO3 = 2NaCN + H2O + CO2; 2HS— + 2CN— + 1/2O2 = 2CNS— + H2O; Na2CO3 + 2HCN + 2S = 2NaCNS + H2O + CO2. The severity of these side reactions depends mainly on the concentration of HCN in the feed gas. (5) Suspended sulfur in the solution is also one of the causes of side reactions. The reaction equations are as follows: S + SO32- → S2O32-; S + O2 → SO42-; S + 6OH- → 2S2- + S2O32- + 3H2O. The extent of these reactions increases as the size of the sulfur particles decreases (smaller sulfur particles are more easily charged and have a larger surface area, resulting in higher reactivity), as the amount of suspended sulfur increases, and as the liquid temperature rises. 4H2O2 + 2HS— = S2O32- + 5H2O; S2O32- + H2O2 = SO32- + H2O. (6) During the regeneration oxidation process, phenols in the solution are oxidized to quinones by air, and a certain amount of hydrogen peroxide is generated as well. If the amount of catalyst in the solution is low at this time, the following side reactions occur due to an excess of hydrogen peroxide: 4H2O2 + 2HS— = S2O32- + 5H2O; S2O32- + H2O2 = SO42- + H2O (7). During high-temperature sulfur melting, sulfur reacts rapidly with alkalis and other substances, resulting in the formation of numerous by-products, among which sodium thiosulfate and sulfite are the main ones. 2Na2S2O3 + S → Na2S + Na2S4O6; S0 + 6OH− → 2S2− + S2O32− + 3H2O. 4Na2S2O3 → 3Na2SO4 + Na2S + 4S. 3.2 Effects and hazards of side reactions: (1) Since the absorption of H2S is carried out by Na2CO3, if the carbonation reaction is severe and the concentration of Na2CO3 in the solution is too low, it will affect the desulfurization efficiency. Additionally, a decrease in the solution’s pH makes it difficult for the regenerated solution to absorb oxygen, which is unfavorable for sulfur precipitation. (2) If side reactions are severe, alkali consumption increases dramatically; sometimes, even with large amounts of alkali added, it is difficult to keep the alkalinity within the specified range, which directly affects absorption and regeneration, leading to production disruptions and increased production costs. (3) When the sodium sulfate concentration reaches a certain level, the corrosion of the equipment by the solution increases. Due to the low solubility of sodium sulfate, crystals tend to form when it is cold, thereby blocking the pipelines. (4) When the total amount of by-products in the solution is very high, the viscosity and specific gravity of the solution increase, leading to higher power consumption. This also affects mass and heat transfer, thereby hindering absorption and regeneration. (5) A high level of by-products in the solution can also accelerate the formation of thiosulfate, thereby reducing the sulfur recovery rate. 3.3 Solutions