Regarding the issue of changing from washing to pickling

Very good; switching from water washing to acid washing is beneficial for both the country and its people. Our 100,000-ton system was due for renewal in 2004; I would like to provide a brief overview in the hope it will be helpful: At that time, the system consisted of a boiling furnace, a waste heat boiler, two stages of cyclones, an external scrubber tower, and an electrostatic precipitator. Modified to include an internal injection Venturi tube, fiberglass pipes, an inclined tube settler, a dilute acid circulation tank and pump; the sludge is pumped to the slag quencher using a slurry pump, with semi-circulation of the dilute acid and some of it being discharged after adding lime. The venturi tube uses circulating dilute acid, while the scrubber tower uses circulating liquid plus fresh water. The results are excellent, with an investment of just over 300,000. Wastewater can be used for flushing floors and as phosphorus fertilizer, etc.

The key is to make use of the existing framework by installing an internal fiberglass-reinforced plastic pipe. Inclined tube settler, two horizontal acid pumps, and a dilute acid circulation tank. Acid sludge tank, mixer, and sludge pump. The slag drum cooler was modified into a drum quencher; no water is required, and acid sludge and lime are used directly to adjust the pH value. The overall investment is low, requiring no significant effort. The design is being adjusted based on the actual conditions on site, which is of great value for the current washing process!

For a sulfuric acid plant with a capacity of 120,000 tons per year, it is quite troublesome to carry out pickling without using electrostatic dust collection, as the amount of dust generated is too large. The wastewater volume during the cleaning cycle is too high, and mud tends to accumulate in dead corners. For the second washing stage, if a plate heat exchanger is not used, an air cooling tower can only be employed; ordinary fiberglass cooling towers are not sufficient for this purpose. Moreover, the efficiency of the desorption tower has a significant impact on whether the air cooling tower manages to remove SO2 from the exhaust gases. In addition, high levels of air leakage in the system are also problematic, as they affect the volume of air flowing through the desorption tower, resulting in substantial losses in SO2 removal. Regarding the issues with the filter, the volume factor needs to be taken into account; it might not be suitable for use in this location.

There is a high amount of dust, but we can handle it; we have already tried this approach. There is a filter that works very well, and the desorption rate of sulfur dioxide in the desorption tower is now 98.5%. The acidic wastewater from the desorption tower is sent to the wastewater treatment plant for processing, and no odor is emitted during the cooling process. What we want now is to avoid using traditional acid washing processes, inclined plate sedimentation, plate heat exchangers, or electrostatic precipitators. I just don’t know how much sulfur dioxide is released from the purified water during the cooling process in the cooling tower Will it cause secondary pollution?

In fact, our idea is to keep the existing equipment and processes unchanged, as the purification system is sufficient to meet the requirements. The water coming out of the desorption tower is processed directly; after purification and cooling, most of this water is used in the venturi tube and foam tower, while another portion is directed to the dry absorption circulation tank for adding water. The water that is lost is replenished with fresh water, thereby enabling a closed-loop system.

The air-cooled tower process has been used. Whether there is secondary pollution depends on the desorption efficiency, but some amount of it always occurs; compared to the plate exchange process, secondary pollution is definitely greater.

The original poster’s idea is good, but I have some different opinions. If it is merely about treating the acidic wastewater in the purification stage, that is, carrying out solid-liquid separation, the effective process currently used in China is one that makes use of inclined plate settlers or CN filters ； But if the poster is considering adding water directly to the dry absorption stage after the wastewater from the purification stage has been filtered clean, then if the resulting acid is to be used as a fertilizer acid, there isn’t much of a problem. However, if the acid is intended for other purposes, then the contamination caused by heavy metal ions such as arsenic, fluorine, and iron in the wastewater becomes a significant issue. If possible, it would be advisable to completely purify this dilute acid solution by removing impurity ions, though the cost of doing so is likely to be high.

I heard that many people use CN filters.

If an air cooling tower is used directly, the odor in the environment remains quite strong

Secondary pollution from sulfur dioxide is difficult to avoid.

CN-type filters require polyacrylammonium, which incurs high operating costs; we have considered this option as well. However, there is a type of filter that does not have this drawback. The wastewater from the desorption towers undergoes a cooling process as it moves toward the wastewater treatment plant, during which sulfur dioxide is released. According to relevant environmental standards, the levels of sulfur dioxide in the air are within acceptable limits. Given the strict requirements for wastewater discharge under current environmental regulations, we came up with this idea. The function of inclined plate sedimentation is merely to settle solid particles, and we can achieve the same goal using filters, with better results. As for arsenic and fluoride, we have conducted tests and found that they will not have an impact on subsequent processes, as the raw materials we use allow for strict control over these substances.

Our sulfuric acid is used in the production of fertilizers; we are not considering using it for any other purposes at present.

It is recommended that you use electrostatic dust removal, as it will yield better results. Plate heat exchangers and fiberglass cooling towers are two devices with different functions. Plate heat exchangers are used to cool dilute acids with circulating water, while fiberglass cooling towers are used to cool circulating water; even when using a plate heat exchanger, a fiberglass cooling tower is still required.

Last time I was at Hubei Xiangyun Group Company, I saw that they had 14 CN filter units in operation; the production capacity for sulfuric acid was 400,000 tons. The cost of their flocculants wasn’t very high either – the concentration of the PAM flocculant was 1 ppm. None of the four systems are equipped with electrostatic dust removal devices, yet their performance is still satisfactory. However, it is recommended to install electrostatic precipitators when upgrading the sulfuric acid systems in the north; after all, temperatures are low in winter there, and the system should focus on drying the slag. This post was last edited by djg1208 on 2009-3-4 14:05.]

Everyone knows that electrostatic dust removal is good. But one costs money; a 100,000-ton system costs at least 1.5 million. Secondly, there may not be space for upgrading the old system. People can’t just discuss things in isolation; they need to take into account the conditions on site as well as those in the factory. In short, by doing a good economic calculation and ensuring that the manufacturing process is balanced, using one ton less of water and emitting one ton less of wastewater means doing something positive for future generations.

If plate heat exchangers are used, then we can carry out the modification without needing an electrostatic precipitator.

Perhaps my message wasn’t clear enough; what I mean is that the boiling furnace uses dry slag discharge, while the wastewater from the desorption tower is treated with a filter, cooled using a plate heat exchanger, and then sent back into a closed loop. The cooling water for the plate heat exchanger is circulated in a closed system through a fiberglass cooling tower, thereby enabling an internal closed-loop system.

It should be noted that our device uses wet slag discharge, and the purification process follows a Wen-Bao-Electric flow sequence.

Is such a filter really available? Could the original poster give some details? It’s also a cost saving if no flocculant is used.