In the whole wet desulfurization process, some process conditions are contradictory from absorption to regeneration and then to sulfur recovery. Generally, the newly designed desulfurization unit will comprehensively consider various interactive factors, and take the desulfurization, regeneration and sulfur recovery of the system as a systematic project, comprehensively consider and solve it as a whole. However, there are often various mismatched factors for the continuous expansion and transformation of production or the use of old equipment, so we must correctly understand and give reasonable consideration to these indicators.
1. Blowing intensity and regeneration air volume
We know that regeneration has several functions. First, supply the oxygen for the chemical reaction required for desulfurization. Second, HS - in the rich liquid continues to be oxidized during regeneration and restores the activity of the catalyst. Third, under the bubbling and stirring of air, sulfur particles gather into sulfur foam and float on it, which is convenient for flotation to separate sulfur. Fourth, the CO2 gas absorbed in the solution while desulfurization is carried out, so as to improve the alkalinity of the solution and reduce the consumption of alkali. It can be seen from this that the greater the blowing intensity is, the more complete and thorough the regeneration is if only from the perspective of regeneration. However, excessive blowing intensity will bring adverse effects on the normal flotation of sulfur foam. Excessive air volume will cause large liquid level churning, unstable sulfur foam layer and poor sulfur flotation separation, resulting in high suspended sulfur. If the air volume is too large for a long time, the solution potential will be high, which will accelerate the side reaction. Excessive oxidation will also cause the rise of sodium sulfate and equipment corrosion. Therefore, the blowing intensity of the regeneration tank should be appropriate. Generally, the blowing intensity of the jet regeneration process is 60m3 / m2 h～100m3/m2. h。 In production practice, enterprises can find out the best air volume suitable for their own working conditions according to their own equipment and process conditions.
2 solution circulation volume and regeneration residence time
溶液的循环量与再生停留时间是反比关系。在其它条件不变的情况下，当气量大，H2S含量高时，为保证脱硫效率，应适当增加溶液循环量，即增大液气比和喷淋密度。但是，在增加循环量的同时，一定要考虑溶液在再生槽中的停留时间。否则，因为循环量的增加，缩短了溶液在再生槽的停留时间，造成再生不完全，溶液质量差，同样达不到较高的脱硫效率。以前我公司做过一个方案，脱硫塔直径为φ4800，原有的贫液泵额定流量为420m3/h，其喷淋密度20m3/m2.h多，明显偏小了。所以，必须增加溶液的循环量。如果单纯从喷淋密度考虑，以增加至800 m3/h为佳，此时喷淋密度为44 m3/m2.h。但是该厂再生槽容积是为循环量400 m3/h左右而设计，如果流量增加至800 m3/h，则溶液在再生槽中的停留时间太短，无法满足再生需求，再生槽容积肯定要做相应调整，这样就给施工带来很大的工作量。考虑到该厂脱硫塔进口硫含量不高，脱硫负荷不大，所以，建议把流量增加到600 m3/h，这样喷淋密度为33 m3/m2.h，基本能满足要求，而且，该流量下再生槽内溶液的停留时间为12分钟。
The circulation amount of solution is inversely proportional to the regeneration residence time. When other conditions remain unchanged, when the gas volume is large and the H2S content is high, in order to ensure the desulfurization efficiency, the solution circulation volume should be appropriately increased, that is, the liquid-gas ratio and spray density should be increased. However, while increasing the circulation volume, the residence time of the solution in the regeneration tank must be considered. Otherwise, the residence time of the solution in the regeneration tank is shortened due to the increase of the circulation volume, resulting in incomplete regeneration and poor solution quality, which also can not achieve high desulfurization efficiency. Our company has made a scheme before, and the diameter of desulfurization tower is φ 4800, the rated flow of the original lean solution pump is 420m3 / h, and its spray density is 20m3 / m2 H is too much, which is obviously too small. Therefore, the circulation amount of solution must be increased. If only considering the spray density, it is better to increase to 800 m3 / h, and the spray density is 44 m3 / m2 h。 However, the volume of the regeneration tank in the plant is designed for the circulation volume of about 400 m3 / h. If the flow increases to 800 m3 / h, the residence time of the solution in the regeneration tank is too short to meet the regeneration demand. The volume of the regeneration tank must be adjusted accordingly, which will bring a lot of work to the construction. Considering that the sulfur content at the inlet of the desulfurization tower of the plant is not high and the desulfurization load is small, it is recommended to increase the flow to 600 m3 / h, so that the spray density is 33 m3 / m2 h. Basically meet the requirements, and the residence time of the solution in the regeneration tank under this flow is 12 minutes.
The amount of solution circulation is also closely related to the amount of regeneration air. Because the process of spraying oxidation regeneration tank depends on the rich liquid to inhale air through the ejector, and the amount of air inhaled by the rich liquid is basically constant. If the circulation volume is too small, the intake air volume is insufficient, which may not meet the air volume required by the regenerative oxidation tank. Soon after start-up, there may be problems such as unsatisfactory regeneration effect, high suspended sulfur, low sulfur recovery rate, high consumption of absorbent and catalyst, and even tower blockage.
3 total alkalinity and pH value of solution
The total alkalinity of the solution is directly proportional to its sulfur capacity. Therefore, increasing the total alkalinity is an effective way to improve the sulfur capacity. In other words, in the process of neutralization reaction, increasing the total alkalinity can better ensure the desulfurization efficiency under the condition that other working conditions remain unchanged. However, if the total alkalinity is too high, the consumption of raw materials will increase and the side reactions will accelerate.
PH value is the basic index of desulfurization solution. Too low pH value is not conducive to the absorption of hydrogen sulfide, will reduce the solubility of low oxygen, and the regeneration effect of solution is poor; If the pH value is too high, the side reaction will be accelerated, the generation rate of side salt will be high, the sulfur separation speed will be affected, the sulfur recovery will be poor, and the alkali consumption will be increased.
As for the relationship between total alkalinity and pH value, generally speaking, pH value increases with the increase of total alkalinity, but strictly speaking, pH value is mainly affected by NaHCO3 / Na2CO3, pH is inversely proportional to the ratio, and there is the influence of sulfate ion.
In the actual production, due to the different conditions of each plant, the H2S content in the desulfurization inlet gas varies greatly, and the rationality of process and equipment configuration also varies greatly. Therefore, the control principle and guiding ideology for the total alkalinity should be: on the premise of ensuring the appropriate solution circulation and high desulfurization efficiency, ensure the outlet hydrogen sulfide, control the total alkalinity of the solution at the low limit, and reduce the production consumption and the generation of side reactants, So as to maintain the stability of working conditions.
4 attach importance to analysis
The analysis data is our eyes. We reasonably adjust the consumption and guide the work, so we establish, improve and standardize the desulfurization analysis, so as to make better use of these analysis data to guide the production and ensure the continuous and stable operation of the production.
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