4-stage equilibrium conversion rate of 800,000-ton sulfur-based acid production plant
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Recently, I came across two 800,000-ton sulfuric acid production plants (temporarily referred to as Plant A and Plant B), both of which use imported catalysts and operate under a \"3+1\" two-turn two-absorption process; their overall conversion efficiency has remained very high after several years of operation. Further investigation revealed that the conversion efficiency of each of these two systems in a single run did not reach the designed values, being 92% and 93% respectively; however, the overall conversion efficiency could exceed 98.5%, and even reach 99.9%! During testing of Unit A, it was found that the sampling point at the 4th stage outlet of this unit was located above the demister of the second absorption tower; a pipeline was installed from the sampling point to the ground to facilitate laboratory analysis. During sampling and analysis on the secondary absorption tower platform, the secondary conversion rate was relatively close to the design value (99.6% overall conversion), indicating that some air was mixed in during sampling through the sampling pipes at ground level. Device B has a similar situation as well: there is a sampling pipe that runs from above the demister of the second suction tower down to the ground, and a vacuum pump is used to assist with sampling. The conversion rate of layer 4 in Device B is as high as 97%. According to Device B, the exit temperature at the fourth stage is 449°C; the composition of the flue gas is SO2: 0.888%, O2: 5.486%, and the local atmospheric pressure is 81.43 KPa. Using the trial-and-error method, the equilibrium conversion rate was calculated to be 96.6%, while the actual conversion rate determined through testing was higher than this equilibrium value! This post was last edited by in the blink of an eye on 2009-3-25 22:58.]
It’s called not knowing until you calculate it – then you’re shocked!
Based on the conditions you provided, the inlet temperature is 423°C, the outlet temperature is 449°C, and the equilibrium conversion rate is 96.88%. The concentration here is low (~280 ppm); considering the analysis errors (including your own errors) and the possible absorption effect of the two absorption towers, this difference should be acceptable, right? However, the conversion rate remains high even after several years of operation (it could be even higher with optimization); in any case, this catalyst is indeed quite good.
The main problem is that the conversion rate at one stage deviates from the designed value, causing the reaction to shift backward. The drawback of this catalyst is that it tends to become powdery when used in one-stage or four-stage processes, resulting in high screening losses and a significant decline in activity.
Leaving the first paragraph aside, let’s talk about the fourth one. If, as you say, \"a deviation in the conversion rate at one stage from the designed value causes the reaction to shift backward,\" then it seems unlikely that the fourth stage can achieve a high degree of segmented conversion while experiencing a significant drop in activity; thus, it would be impossible to maintain such a high overall conversion rate even after several years of operation :o
I. Layer 4 is most affected due to its position at the forefront in terms of process configuration; however, compared to Layer 1, it is less impacted. Please calculate the equilibrium conversion rate and check whether local atmospheric pressure has been taken into account; if no correction for atmospheric pressure is made, the result will be on the high side. The initial focus on this issue came from users who reported that the results were exceptionally good, with a total accuracy rate of 99.9%, which they found incredible! It has a bit of a mythological flavor.
A transfer efficiency of 99.9% is truly incredible; ordinary device designs don’t achieve such high conversion rates, let alone after operating for several years – I just can’t believe it. But even if, as you say, the conversion rate is around 99.6%, that’s still quite good. :Lol, when I calculated the equilibrium conversion rate, I used 85 kPa(a) for the pressure at the four inlet stages; there shouldn’t be any problems with that, right? It seems that this pressure has little effect on the equilibrium conversion rate. :)
I did the calculation too; it’s 96.6%
Experts, could you tell me what value you have calculated for the heat loss at the fourth layer? The data comes from there, thank you
Personal opinion: If it is a \"3+1\" dual conversion dual absorption system, and the total conversion rate comes out to 99.8% when each conversion step achieves 93% or 92%, then the sampling issue should be investigated, as the four stages cannot reach such a high conversion rate (i.e., above the equilibrium conversion rate).
You mean the temperature rise across four layers, right? The inlet temperature is 422 and the outlet temperature is 449; if an adiabatic temperature rise of 300 is used, and the calculation is based on one rotation and one suction per layer, then the resulting temperature rise is roughly consistent. However, considering it is a double-rotation double-suction type, the temperature rise at the four layers should be higher than that calculated above.
Master! So you all know how to calculate too; I heard it from someone else.
It seems unlikely to achieve 99.9% in terms of transmission rates; it’s already difficult for us to reach 98%
I heard others say it’s better to calculate it yourself! So as not to be deceived by others! My calculations aren’t complicated either; I found the formulas in a manual (I looked them up in \"Inorganic Chemical Engineering – Sulfuric Acid and Nitric Acid\"), and then used Excel to enter those formulas for semi-automated calculations. In fact, Excel has very powerful functions, and I’ve only used its basic features; I recommend that everyone give it a try when they have time. It turns out that when I did the calculations manually, on paper, I could only process a few sets of data per day – it was too slow. By using the above method, efficiency is greatly improved; once the formulas are established, only the data needs to be entered for subsequent calculations, eliminating the need for repetitive manual calculations.
Hehe, I heard it from authoritative people, so it should be correct, right? Listening to multiple perspectives helps one see things more clearly. If one only listens to you, there’s a chance of being deceived, because to me, you also belong to the category of \"others\". :Perhaps the constants you use are different, which is why the conclusions vary slightly. :)
This of yours must be at the level of 30 years ago, right? It is entirely possible to achieve a total conversion rate of over 99.9%; I’ve heard that the total conversion rate at Shandong Yanggu Xiangguang Copper Industry is well above 99.9%.
I suggest you do the calculation; calculating the balanced conversion rate is not complicated. Or simply substitute the result into the formula and see. Note: Equation (3-10) on P102 of \"Inorganic Chemical Engineering Technology – Sulfuric Acid and Nitric Acid\"
Thank you, I’ll try to find it and study it* study it*. :)
Using the automatic calculation table for equilibrium conversion rate, with a pressure of 85 kPa(a), an exit temperature of 449°C in the fourth stage, and concentrations of SO2 at 0.888% and O2 at 5.486%, the equilibrium conversion rate was calculated to be 96.76%. :o If the temperature is reduced to 448°C, the equilibrium conversion is 96.83% ； When the temperature is reduced to 447°C, the equilibrium conversion is 96.90%. It is also possible that the so-called higher measured conversion rate than the equilibrium conversion rate is due to errors in temperature measurement. :lol Last edited by boqing_zh on 2009-4-10 13:47 ]
The problem is that the overall conversion rate of this device is 99.83%, while the conversion rate for stage two is 97.5%, which is already higher than the equilibrium conversion rate. :L Last edited by in the blink of an eye on 2009-4-10 14:53 ]