The issue of optimizing the regeneration degree of the regeneration tower

1 The regeneration condition is poor, but the desulfurization efficiency remains stable. Overall, the regeneration condition in the variable-desulfurization process is not as good as that in the conventional desulfurization process, and more problems occur; phenomena such as bubbles, weak bubbles, floating bubbles, and no bubbles appear in the variable-desulfurization process. The desulfurization efficiency is also unstable; manufacturers with high efficiency can achieve over 95%, while those with lower efficiency fall short of 50%. In some cases, there is even the strange phenomenon where the levels of hydrogen sulfide at the inlet and outlet are identical. Through summary, we found that the phenomenon of low desulfurization efficiency is mainly concentrated in variable degassing desulfurization at low pressure levels, with the highest incidence occurring at a pressure of 0.8 MPa. The poor regeneration condition is mainly observed in degassing and desulfurization processes under high pressure levels, with the highest incidence occurring at pressures of 2.0–3.0 MPa. This is characterized by poor sulfur foam flotation, sparse foam, and a high level of suspension. This phenomenon has sparked considerable controversy within the industry. The focus of the debate is that many believe the main cause of this issue is the CO2 dissolved in the desulfurization solution; in the injectors and regeneration tanks, the extensive desorption of CO2 interferes with the normal suction process of the injectors, thereby affecting flotation. But many people firmly oppose this view. In actual production, in order to avoid the effects of CO2, most manufacturers install flash tanks at the outlet of the stripping tower to mitigate these effects; however, this measure does not yield satisfactory results. We found that a production process without a flash tank isn’t as poor as we thought; in other words, some manufacturers manage to do it quite well ； In production processes that use flash tanks, the regeneration effect is not as good as we had expected; in some cases, it is even very poor. Another phenomenon, one that we certainly do not want to see, is that some manufacturers, in an effort to completely eliminate the impact of CO2, operate their regeneration systems by reducing the pressure of the desulfurization liquid at the outlet of the desulfurization tower from a high level to atmospheric pressure, and then repressuring it to 0.4–0.5 MPa in order to regenerate it in the regeneration tank. According to data from the field, this approach is working quite well at present. One can imagine that if it is indeed CO2 affecting regeneration, then using this method might be acceptable (of course, there are better ways to address the issue). But if there is another cause, the company’s losses can be severe. Not to mention anything else, the electricity consumption alone results in a considerable loss each year. Therefore, when making decisions in this area, a company must be extremely cautious and must not act recklessly; after all, the losses involved are huge and long-lasting. The issues raised above have not yet been resolved, nor has the essence of the problems been identified. Ultimately, there is no appropriate theory to explain it, so it is not possible to arbitrarily propose some solutions. 2. There is a significant temperature difference between the inlet and outlet gases in the converter. This phenomenon has always existed; it’s just that many manufacturers do not pay attention to this variation. Moreover, this phenomenon is not very noticeable in the desulfurization of converter gases at lower pressure levels. According to our on-site measurements, for the desulfurization of conversion gas at pressures below 1.5 MPa, the temperature difference between the inlet and outlet is on average 2–3°C. At pressures above 1.5 MPa, especially in the range of 2.0–3.0 MPa, the temperature difference is much larger; it can be around 10°C in some cases, and even exceed 20°C in others. Moreover, the higher the pressure level, the higher the hydrogen sulfide content at the inlet, and thus the greater the temperature difference. In engineering design, special attention must be paid to heat balance in this regard, with efforts to reduce the temperature of the inlet shift gas; otherwise, the regeneration system will not be able to maintain normal operation. Regenerative flotation is already not effective, and higher temperatures make it even less suitable for regeneration. Many people don’t understand such a large temperature difference, but it can actually be explained theoretically. It mainly comes from the heat of reaction, as can be seen from the following reaction. (1) The enthalpy change for the reaction CO32–(aq) + H2S(g) = HS–(aq) + HCO3–(aq) is: 12.68 KJ/mol. (2) The enthalpy change for the reaction CO32–(aq) + CO2 = HCO3–(aq) is: 330. 48 kJ/mol. Here, only the reactions in which alkaline solutions absorb hydrogen sulfide and carbon dioxide are listed; in fact, all desulfurization reactions, whether primary or secondary, are exothermic reactions. Therefore, it is normal for there to be a certain temperature difference in the gas exiting the desulfurization tower. Then why is it not obvious in the semi-detached state? The reason is actually quite simple. On the one hand, the amount of solution involved in the semi-deprotonation process is large; even though the reaction releases some heat, it’s difficult for the temperature of such a large volume of solution to rise significantly. On the other hand, since the ejector absorbs a large amount of air, this also leads to a decrease in the solution’s temperature. Additionally, during semi-deprotonation, the main exothermic reaction is the absorption of hydrogen sulfide and carbon dioxide by the alkaline solution. The heat released during the absorption of H2S is actually very small, at only 12.68 kJ/mol. Although the heat release associated with CO2 absorption is high (330.48 kJ/mol), its concentration in the gas is low – around 6% to 8% – and the pressure is low, resulting in a small amount of CO2 dissolving in the solution. Therefore, only a small amount of CO2 participates in the reaction, and consequently, the amount of heat released is also low. But the situation is very different for the desulfurization reaction of pressurized shift gas. Firstly, the amount of solution involved in the desulfurization process is smaller, which is a factor that can lead to an increase in temperature. On the other hand, compared to partial desulfurization, the CO2 content in the shift gas is higher – almost 4 to 5 times greater – which increases the likelihood of CO2 participating in the reaction. Additionally, as pressure rises, the partial pressure of CO2 increases as well, thereby accelerating its diffusion and dissolution rate. This results in a significant increase in the amount of CO2 that participates in the reaction. This is precisely why higher pressure leads to a larger temperature difference. Taking these factors into account, it is not difficult to understand why there is a large temperature difference between the gas entering and leaving the tower in the pressure-swapped gas desulfurization process. This also provides a solid theoretical foundation for us who work in engineering design.

Problems with tower blockage: (1) Insufficient circulation leads to an inadequate spraying density in the tower, resulting in the formation of \"dry zones\" that cause tower blockage. (2) The regeneration effect is poor, with a high level of suspended sulfur in the lean solution. (3) The packing layer is relatively high (over 6m) and no distributor is installed, resulting in solution skew flow. (4) The structure of the tower internals (distributor, redistributor, and packing support devices) is unreasonable. (5) Improper selection of packing (due to the special physical and chemical properties of desulfurization liquid and elemental sulfur, many packing materials with a large surface area are not suitable as packing for desulfurization towers; this is especially true at high pressure levels, where careful attention must be paid to the choice of packing). (6) Filler lodging or damage