Reduce the resistance of the desulfurization system

Adjust the pressure booster fan! Reduce the liquid-to-gas ratio! Hehe! For reference

Please, the original poster, explain clearly where the resistance is mainly concentrated: in the desulfurization tower? Cooling tower? Gas-water separator? Or is the resistance distribution throughout the entire system relatively even? It would be better if information such as gas flow rate, main pipe specifications, and equipment specifications could be provided. The preliminary estimate is that either the resistance in the desulfurization tower is high, or the resistance in the system’s piping and equipment is high.

What LZ might be referring to is an increase in the resistance of the desulfurization tower; managing desulfurization has become increasingly important these days. Regeneration management is regarded as a top priority, and some companies assign a dedicated role to handle regeneration. When the resistance increases, our approach is to raise the temperature to 40 degrees and artificially adjust the gas-to-air ratio to cause significant fluctuations. However, this method becomes ineffective when the resistance is too high

Reply to the post by 4th floor, 740412: Regeneration is of paramount importance in desulfurization management, as determined by the underlying mechanisms. There must be some resistance on the desulfurization tower there; raise the temperature to 40 degrees and artificially vary the liquid-to-gas ratio. I think Tewin has some merit to his argument; firstly, it reduces the viscosity of the solution, thereby decreasing the adhesion of sulfur particles to the filler ； Secondly, it increases the solubility of the by-products, allowing them to dissolve back into the solution from the filler. However, raising the temperature can strengthen the adhesion of sulfur particles to the filler; the fundamental solution to salt clogging lies in taking measures to prevent the accumulation of salts from reaching a level at which they precipitate. As for artificially adjusting the liquid-gas ratio, it’s of no use; it’s just an illusion.

It’s not necessarily just a blockage in the desulfurization tower; it depends on the process and equipment setup in the plant in question. Generally, plants have a packed ammonia purification tower after the desulfurization tower, and that too can cause blockages. The person in question should carefully check the resistance levels in each tower, identify where the resistance lies, and then analyze and address the issue accordingly. As for the causes of blockages, it is not possible to generalize, as there are too many variable factors in actual production. What the people above mentioned are just situations that may occur under normal circumstances. However, if blockages are caused by improper selection of towers or packing, poor quality of cooling water in the desulfurization system, or issues with desulfurization temperature control, the methods for dealing with such blockages cannot be generalized and require targeted approaches. I agree with what was said on floor 3: the original poster should provide detailed information on the desulfurization process, as well as the resistance distribution throughout the system. Information on the gas supply volume, specifications of the main pipes, the equipment used, specifications of the packing materials, and the levels of oxygen and carbon dioxide in the gas supply is also necessary. Additionally, it’s important to know whether there are any blockages in the regeneration system and what the results of any analysis of such blockages are. Of course, the conditions of the system’s cooling water and make-up water cannot be ignored either. I once worked in a factory where, due to poor management, the operators used hard water as makeup water for the system throughout production. As a result, the regeneration system became severely clogged and the system resistance increased...

Thank you all. I think the pipes here might be too small, so we plan to make minor repairs to enlarge the connection pipes between the towers. One more question: Does the secondary water used in parallel with the gas generation in the cooling tower ahead of the desulfurization tower affect the regeneration of the desulfurization solution?

I feel that the use of desulfurization agents affects the resistance of the desulfurization tower to a certain extent. We have been using TTS desulfurization agents here for 4 years, and there is not yet a significant pressure difference between the inlet and outlet of the desulfurization tower. Additionally, the regeneration system must be properly managed; otherwise, the system resistance will change significantly.

What method do you use for desulfurization? What kind of packing is used in the desulfurization tower? Can you upload the system process flow diagram? What is the inlet hydrogen sulfide concentration? Can you upload the analysis of the solution’s components? What is the amount of suspended sulfur? What is the size of the tower? What is the gas flow rate? What is the circulation volume? It’s difficult to analyze this for you! Generally speaking, high resistance is closely related to the parameters mentioned above.

Blockages in the desulfurization tower lead to an increase in its resistance; in severe cases, liquid can be carried along with the gas, which affects production. This is an inevitable issue in desulfurization systems (including variable desulfurization), and it is also a problem that receives considerable attention in the desulfurization industry. Although the development of catalyst technology has led to the creation of many new catalysts that possess the ability to clear blockages in towers (such as the Dongshi 888 catalyst), thereby alleviating the problem of tower blockages, this issue remains a focal point in the desulfurization industry due to factors related to each company’s process conditions, operations, and management. The blockage of the tower is mainly caused by sulfur and salt buildup. The reasons for this include the following: (1) The quality of the gas entering the tower is poor; ash, coal tar, and other impurities carried in the gas accumulate over time on the packing, leading to an increase in tower resistance and thus tower blockage. (2) The desulfurization absorption and sulfur precipitation reactions take place 80% of the time within the desulfurization tower. The sulfur that precipitates inside the tower cannot be carried out of the tower along with the desulfurization fluid in a timely manner; it tends to stick to the surface of the packing, causing gas flow to deviate from its normal path. Over time, this can lead to blockages in the tower. (3) The circulation volume of the solution is insufficient; a low circulation volume leads to a decrease in the pressure of the desulfurization liquid as it enters the tower, resulting in a reduced spraying density. The desired spraying density is generally 35–50 cubic meters per square meter per hour. A low spraying density can cause dry areas to form within the tower’s packing, leading to poor gas-liquid contact and a decrease in desulfurization efficiency. Over time, this can result in local blockages, uneven gas-liquid distribution, an increase in tower resistance, and ultimately tower blockage. (4) There are issues with the equipment in the desulfurization system: firstly, the filler material used in the desulfurization tower is inappropriate, and the gas-liquid distributor, redistributor, and demister in the tower have unreasonable designs or are installed incorrectly. During the maintenance of the desulfurization tower, only the packing inside the tower was removed for cleaning; the broken packing and sulfur deposits that were blocked in the demister and between the two humps of the baffle plate were not removed in a timely manner. This resulted in obstructions in the liquid drop holes of the demister and baffle plate, causing gas to flow unevenly after the tower was restarted and an increase in the tower resistance. Secondly, there are issues with solution regeneration; the sulfur flotation effect is poor, suspended sulfur levels increase, and the desulfurization efficiency declines. This is mainly reflected in the lack of appropriate regeneration equipment and defects in the design of the oxidation regeneration tank. There are no distribution plates in the oxidation regeneration tank; for example, at a chemical company in Henan with an annual synthetic ammonia production capacity of 45,000 tons, the oxidation regeneration tanks have a diameter of 8000/9000/10000 mm and are 9 meters high – quite large indeed – yet there are no distribution plates inside them (at least two layers should be present). In some plants, the pore size of the distribution plates in the oxidation and regeneration tanks is too large; generally, the pore size of these distribution plates is 8–15 mm, with a pore spacing of 20–25 mm. The air self-priming ejector was selected and installed improperly, resulting in a low amount of air drawn in and insufficient amount of air for regeneration; the typical blowing intensity is 50–80 cubic meters per square meter per hour. The distance between the tail pipe of the air-suction jet and the bottom of the regeneration tank is too large; generally, this distance is 400–600 mm, with a maximum of no more than 800 mm. If this distance is too great, it can lead to the formation of too many dead zones within the tank, thereby affecting the effectiveness of regeneration. In some factories, the distance between the tail pipe of the air-suction jet and the tank bottom is even over 1500 mm. During the installation of air-self-priming injectors, it is required that the central axes of the nozzle, suction pipe, contraction pipe, and mixing pipe be aligned with each other, with a concentricity of ≤1.0 mm. (5) Inadequate operation and management: During operation, the temperature of the desulfurization solution should be kept at an appropriate level, generally between 38–42°C; if it exceeds 45°C, the bubbles tend to break easily, resulting in poor flotation of elemental sulfur and an increase in the formation of by-products. The total amount of these three by-products (Na2S2O3, Na2SO4, NaCNS) should generally be less than 250 g/L. Side reactions increase, crystals tend to precipitate, leading to salt buildup. Once salt buildup occurs, it not only raises the resistance in the tower but, more importantly, causes severe corrosion of the equipment. Once salt clogging occurs, even the best catalysts are ineffective; the Dongshi 888 catalyst can only achieve satisfactory results in removing sulfur clogs ； The sulfur bubbles floated up in the oxidation and regeneration tank cannot overflow in a timely manner; they remain on the surface of the liquid for too long. Once these bubbles break, they sink, causing suspended sulfur in the solution to rise. This sulfur is then carried by the desulfurization pump into the tower, where it deposits on the packing. Over time, this leads to sulfur blockages ； The solution circulation rate cannot be kept stable; adjustments are made too frequently. When a reduction is required, some adjustments can be made to the components of the solution ； After some trial and error, the blowing intensity can be stabilized at the optimal level; excessive adjustments are generally not advisable, as this may affect the flotation of elemental sulfur and result in poor regeneration efficiency. (6) Improper selection of catalysts: Although low-quality catalysts are cheaper, during use, the elemental sulfur that precipitates inside the tower cannot be carried away with the solution in a timely manner. Over time, this leads to blockages in the tower, which can severely affect production. The following focuses on several measures to take after tower blockage occurs: (1) Ensure proper purification of the gas before it enters the tower; the gas must be washed to remove dust and subjected to electrostatic desulfurization, and gas-water separation should be enhanced to prevent impurities such as coal tar and fly ash from entering the desulfurization system. (2) Thoroughly investigate the root cause of tower blockage. If it is due to issues with equipment design or installation, seek an opportunity to carry out technical improvements. For example, when filling and selecting the packing for the desulfurization tower, it is advisable to use a three-layer arrangement, with each layer having a height of 5–6 meters; the total height of the packing should be 15–18 meters. The packing should mainly consist of loose polypropylene with a diameter of 50–70 mm, and larger-sized packing should be used in the lower sections to prevent blockages ； Components such as gas-liquid distributors, redistributors, and degasifiers should be designed properly, with an appropriate gas-liquid distribution surface ； The packing supports are usually hump-shaped plates, and various companies have experienced blockages in these humps to some extent; in severe cases, the hump channels get completely blocked, forcing shutdowns to remove the packing for cleaning. It is recommended to replace these hump-shaped plates with grid-shaped plates ； 2-3 layers of distribution plates should be installed in the oxidation regeneration tank. The function of these plates is to ensure that the gas-liquid mixture is mixed and stirred as it passes through them, thereby improving the efficiency of regeneration; if the pore size is too large, the mixing and stirring effect is reduced ； To ensure the quality of maintenance, a thorough inspection of the tower should be carried out after the packing inside it is removed, and any issues found should be addressed promptly. (3) Strictly control the process parameters: ensure proper flotation and overflow of sulfur foam in the regeneration tank, maintain a stable regeneration pressure (usually between 0.40–0.45 MPa), and keep the liquid level stable to prevent large fluctuations that could cause sediment to be carried into the tower ； Control the regeneration temperature carefully; if it is too high, side reactions accelerate, leading to the formation of excessive amounts of by-products. The crystallization of these by-products can cause blockages in the tower. (4) Ensure an adequate circulation rate and spray density so that the sulfur deposits on the surface of the packing can be washed away. It is not advisable to adjust the circulation rate; instead, reducing the overall alkalinity of the solution should be used as a method. Attention should be paid to the recovery and processing of molten sulfur; the residual molten sulfur must undergo successive stages of precipitation, filtration, cooling, oxidation, and impurity removal before it can be returned to the system. (5) Choose a catalyst of high quality; the Dongshi Brand 888 catalyst is an improved version of the original PDS product. It is non-toxic and highly efficient, and operates using a single-catalyst method. This catalyst is based on a metal-polymeric-organic compound composed of ammonium trinuclear cobalt phthalocyanine sulfonate, created through the combination of multiple sulfonic groups. Due to its unique chemical structure, it possesses an extremely strong ability to absorb and carry oxygen. During the desulfurization process, it continuously releases highly active atomic oxygen, which enables the rapid conversion of H2S and some organic sulfur compounds into elemental sulfur. This **improves the efficiency of desulfurization; over 50% of the organic sulfur can be removed. During oxidation and regeneration, the sulfur particles formed are large in size, making them easy to separate and recover. As a result, the viscosity of the desulfurization solution decreases, the amount of suspended sulfur is reduced, and the solution becomes clearer. Furthermore, the 888 catalyst can not only adsorb and activate oxygen but also has a certain activating effect on sulfur, enabling it to form polysulfides. When these polysulfide compounds are regenerated, sulfur is released, thereby gradually reducing the amount of suspended sulfur in the solution. The sulfur adhered to the filler also becomes less bonded, so it serves a certain function in cleaning the tower. (6) Strengthen the analysis of solution components to ensure that all components of the solution meet the specified standards. When the concentration of by-products in the solution is too high (e.g., Na2S2O3 ≥ 150 g/L, Na2SO4 > 40 g/L, NaCNS ≥ 80 g/L), treatment is necessary. This usually involves removing portions of the solution in successive batches, heating it under vacuum to cause concentration, and then cooling it to allow the by-product crystals to precipitate. It is also possible to discharge a certain amount of solution when the temperature is low, thereby lowering the temperature and causing Na2SO4 to precipitate as crystals; after that, the solution can be added back to the system. This method is particularly effective for removing Na2SO4. The side reaction resulting in the formation of sodium thiocyanate cannot be eliminated at present, but hydrogen cyanide in the gas should be removed. (7) Treatment for the increase in resistance after tower blockage and the occurrence of liquid carryover in the gas exiting the tower. Based on the author’s many years of experience in operation and management, it is possible to increase the circulation rate to flush the tower; at the same time, increasing the circulation rate of the solution helps enhance the flotation of sulfur bubbles in the regeneration tank, ensuring normal overflow. It is also necessary to improve the recovery of molten sulfur. In short, there are many reasons for tower blockage; when the tower resistance increases, it is necessary to conduct a thorough analysis to identify the cause of the blockage. Only by taking appropriate measures can the underlying problem be resolved.

Be sure to keep a close eye on the liquid levels in the desulfurization tower and the cooling gas washing tower!