How to deal with an increase in pressure difference in the desulfurization tower?

It mainly depends on the composition of your desulfurization solution, especially the level of suspended sulfur. What type of internals are used in your plant’s tower – packing? A bubble maker? Screen plate? Is there a possibility of liquid buildup? High resistance is basically caused by blockages in the tower that lead to liquid accumulation. What type of desulfurizer are you using? There is only one way to deal with consistently high resistance: stop the machine, dismantle the tower, and clean it up

One reason is the high level of suspended sulfur and the dirty desulfurization liquid； It’s also possible that there is a flow deviation of the liquid ； Increasing the flow rate of the desulfurization pump or starting the backup pump, as well as flushing the packing, might be effective. It is recommended to install a filter at the outlet of the desulfurization pump, which will yield better results.

Blockage in the desulfurization tower leads 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 our company’s 888 catalyst), thereby alleviating the problem of tower blockages, this issue remains a focal point in the desulfurization industry due to factors related to the process conditions, operations, and management practices of various companies. The blockage of the tower is mainly caused by sulfur and salt deposits. The main reasons for this are as follows: (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 solution as it enters the tower, resulting in a reduced spraying density. The desired spraying density is generally 35–80 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 selected for 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 wave plate were not removed in a timely manner. This resulted in obstructions in the liquid drainage holes of the demister and wave plate, which led to gas flow deviation 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 rise, and the desulfurization efficiency decreases. This is mainly manifested 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 factory in Henan with an annual synthetic ammonia production capacity of 45,000 tons, the oxidation regeneration tank has a diameter of 8000/9000/10000 mm and is 9 meters high – quite large indeed – yet it lacks distribution plates (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 800 mm. If this distance is too great, it can result in too many dead zones within the tank, which affects 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, converging 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 blockage occurs, even the best catalysts are ineffective; the 888 catalyst can only achieve satisfactory results in removing sulfur blockages ； 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 experimentation, 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, in addition to enhanced gas-water separation, 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 in equipment design or installation, seek an opportunity to carry out technical improvements. For example, when installing and selecting packing for the desulfurization tower, it is advisable to use three layers of packing, 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 become completely blocked, forcing shutdowns in order 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 spraying 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 means to address this issue. Attention should be paid to the recovery and processing of molten sulfur; the residual molten sulfur must undergo sequential processes of precipitation, filtration, cooling, oxidation, and impurity removal before it can be returned to the system. (5) Use catalysts of high quality. Our company’s 888 catalyst is a new version that has been improved upon the original PDS catalyst; it is non-toxic and highly efficient. It operates using the monocatalytic method, and is a catalyst based on ammonium trinuclear cobalt phthalocyanine sulfonate, which is a metal-organic polymer compound composed of multiple sulfonic groups. Due to its unique chemical structure, it possesses an extremely strong capacity 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, causing 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 secure, so the catalyst 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 (such as Na2S2O3 ≥ 150 g/L, Na2SO4 > 40 g/L, NaCNS ≥ 80 g/L), treatment is necessary. This generally involves removing portions of the solution sequentially, 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; the solution can then be added back to the system. This method is particularly effective for removing Na2SO4. The side reaction leading to 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 volume to flush the tower; at the same time, it is advisable to enhance the flotation of sulfur bubbles in the regeneration tank to ensure normal overflow, and efforts should also be made to improve sulfur recovery. 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. This post was last edited by Dongshi Zhang Tong on 2009-4-11 00:15.]

I think if the change with temperature is significant, it might be due to a high circulation rate or a high space velocity! Reason: The high temperatures during the day cause the volume of the washing solution to expand, increasing the contact area with the solution and thus raising the resistance ； At high temperatures, the gas volume expands, the space velocity increases, and the resistance rises. Have you recently increased the load or encountered issues with solution regeneration, which led to an increase in the circulation rate? 【Just my personal opinion; feel free to keep discussing! 】

1. We use PTS desulfurization based on tannin gum + cobalt phthalocyanine. 2. The solution circulation rate is 155–175 M3/h. 3. When the solution temperature is between 35 and 40 degrees, and does not exceed 45 degrees. 4. There are electrostatic precipitators and circulating cooling towers at the inlet of the gas desulfurization tower. 5. Polypropylene stepped rings are used in the desulfurization tower. 6. There are no nozzles inside the tower; a liquid distributor is used instead. 7. The suspended sulfur content in the desulfurization solution is below 1 g/l. The sodium thiosulfate content is virtually zero, while the sodium sulfate content is slightly higher, at around 45 g/l. 8. The regeneration pressure in the jet oxidation regeneration tank is 0.4–0.45 Mpa, and there is one layer of distribution plates inside the tank. That’s our specific situation; please analyze it based on this information. Thank you.

The fourth floor has already provided detailed explanations. It is recommended that the original poster take the following actions: 1. Improve the regeneration process to minimize the content of suspended sulfur. 2. Operate the electrostatic dust removal and cooling dust removal equipment properly to ensure clean gas quality; the temperature should not be too high. 3. Reduce the oxygen content in the gas as much as possible. 4. Increase the circulation volume of the liquid appropriately. 5. Control the ratio of gum to alum in the tannin solution; cobalt phthaloquinone-based desulfurizing agents can be added as appropriate. 6. It is best to use filtration along with intermittent sulfur melting processes.

Strictly control the suspended sulfur content in the desulfurization solution to less than 1 g/l; additionally, the tower can be flushed once a week by increasing the circulation volume of the desulfurization solution to wash the packing.

Is it because the ethanolamine solution is too dirty, causing clogging of the trays?

Zhang Tong from the East Lion team on the fourth floor is a subordinate of Boss Wang and Boss Liang. The 888 desulfurization catalyst they produce is quite good; adding it can reduce resistance.

Through analysis, it seems to have little to do with Zhang Tong’s analysis; the main factor is the change in pressure differences between day and night. From a temperature perspective, the view expressed upstairs is valid in practical terms, but it shouldn’t have such a significant impact, as the temperature of the solution remains relatively stable; through heat exchange, the expansion of the gas should not be substantial, so a difference of 2 KPa should not occur. I personally believe it is the effect of regenerated and absorbed air, as well as differences in oxygen content, that cause variations in the concentration of the solution. This, in turn, affects the amount of oxygen present in the tower (mainly in the lower packing layers). Regeneration within the tower leads to a short-term accumulation of sulfur paste; at night, the concentration decreases, which reduces the resistance resulting from the sulfur paste that has accumulated during the day. Thus, the above situation arises. Furthermore, the analysis shows that the resistance was already high initially; this may be due to characteristics such as large size of the tannin sulfur particles and their ease of regeneration, as well as the result of prior accumulation. You can try adding some PDS; if that doesn’t work, then the tower needs to be cleaned. After cleaning it, there will be no pressure difference between day and night. Furthermore, adding PDS is only a short-term measure; it should be stopped as soon as it shows no effect, and the tower should be cleaned promptly. And it’s as effective as Zhang Tong says every day.

I believe the main factor contributing to the increased tower resistance is the high content of by-products salts, the presence of precipitated crystals, along with severe corrosion of the equipment. Impact of side reaction products on desulfurization ● The accumulation of by-products increases the viscosity of the desulfurization liquid, affecting mass transfer and the formation of sulfur foam. ●The accumulation of by-products will precipitate out of the solution, disrupting normal operating conditions and increasing the resistance in the desulfurization tower; in worse cases, it can completely block the tower and pipelines, bringing production to a standstill. ●Soda ash (ammonia) consumption increases, the washing efficiency of the desulfurization liquid drops sharply, and the sulfur recovery rate declines. ●High concentrations of (NH4)2SO4 can also cause corrosion of carbon steel equipment. I believe that, based on the selection of more mature desulfurization agents, the main factor affecting the stability of the desulfurization system is the continuous increase in side reactions and their resulting by-products. No matter how carefully such reactions are controlled, they are still inevitable; what is referred to as stability is only short-term stability. The true solution lies in completely eliminating the amount of by-products generated by these unavoidable side reactions! The desulfurization liquid can be subjected to crude salt (mixed salt) extraction, and the desalted desulfurization liquid can be reused. This not only addresses the issue of increased by-products, keeping the content of by-products in the desulfurization solution stable, but also generates economic benefits. Low investment, small land footprint, easy operation – it completely solves the problems of environmental protection and low desulfurization efficiency. Other methods are neither thorough nor free of negative effects; they only provide temporary solutions rather than addressing the root cause. Speak up if you have something to say! My email address is: zhp1389@126.com

First, determine whether it is sulfur blockage or salt blockage. If increasing the PDS tower washing does not work, it is recommended to consider dismantling the tower if possible, while also cleaning all tanks and the bottom of the tower vessel!

The fog suppression layer became clogged, creating a local water seal.

It’s a very common problem; you just need to find someone with solid technical skills to handle it

Tower blockage is mainly caused by sulfur; inadequate routine maintenance leads to poor regeneration efficiency, resulting in high levels of suspended sulfur, or poor cleaning efficiency of the injectors.