Regarding the relationship between the calculation of the overall conversion rate and the sampling points
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In the acid production process, sulfur dioxide in the flue gas is converted into sulfur trioxide through catalytic oxidation, and sulfur trioxide is then absorbed by the acid. The overall conversion rate is generally determined by measuring the sulfur dioxide concentrations at the inlet and outlet of the conversion process and calculating them. I would like to ask the senior experts and professionals here: 1. Taking the 3+1 two-stage conversion and two-stage absorption process as an example, should the gas concentration sampling point at the conversion outlet be at the exit of the fourth conversion stage or at the exit of the second absorption tower? 2. For the sulfur dioxide concentrations at these two sampling points, which is higher—the actual value or the theoretical value?
The actual sulfur dioxide concentration at the outlet of the second absorption tower is usually higher than the theoretical value (i.e., the actual emission concentration is higher than the theoretical zero-emission target), but efforts should be made to reduce this difference as much as possible through optimized operations such as controlling the acid temperature and increasing the amount of recycled acid.
Regarding the calculation of the overall conversion rate for the 3+1 two-stage reaction and two-stage absorption process, I understand that you are concerned about the impact of the choice of sampling points on data accuracy. Based on practical experience, it is generally recommended to take samples at the outlet of the fourth conversion stage, as the SO2 concentration at the outlet of the second absorption tower may be affected by the absorption efficiency and thus cannot fully reflect the effectiveness of catalytic conversion. Our factory conducted comparative tests last year, and the deviation of the data from the fourth-layer output compared to the theoretical values was more stable. The theoretical value is generally higher than the actual value, mainly due to factors such as catalyst activity degradation and uneven gas distribution. However, the specific level of difference depends on the catalyst model and operating conditions you are using. It is recommended to provide more details about the type of catalyst currently in use, so that a more accurate analysis can be conducted. This relates to process safety; it is recommended to rely on the actual measurement data provided by your factory’s technical department in the end.