How to evaluate the performance of the acid distributor in the drying and absorption tower of a acid-making plant
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The dry absorption tower of the acid production unit is a packed tower, and the performance of the acid splitter is crucial for the moisture levels in the drying tower as well as the SO3 absorption efficiency of the absorption tower. Generally speaking, there are the following ways to assess the performance of the acid separator in a dry absorption tower: 1. The moisture levels in the drying tower; of course, sometimes it is necessary to rule out issues related to the packing. For newly built acid production plants, generally speaking, the likelihood of problems with the packing is relatively low. 2. SO3 absorption rate of the absorber. It should be noted that the acid retention in the fiber bed of the demister also contributes to SO3 absorption; if there are abnormalities in the SO3 absorption rate, the first thing the user should check is the acid distributor. 3. Measure the temperature distribution across the tower cross-section at the location of the acid splitters; in most cases, the temperature distribution across the tower cross-section above these splitters takes on a funnel-shaped pattern, which is mainly due to the effect of wall flow. 4. Measurement of the SO3 content in the tower cross-section at the location of the acid distributor: Monmouth once conducted acid mist tests on absorption towers equipped with tubular acid distributors. The results showed that the closer to the tower wall, the higher the SO3 content. The distribution of SO3 content on the acid separators of many manufacturers also follows a bell-shaped pattern. 5. The temperature of the flue gas exiting the tower is close to the temperature of the acid in the tower; for example, when a Menck splitter is used in the dry absorption tower of an acid production plant, this temperature difference is often only 1 degree Celsius.
Currently, in China, the measurement of the SO3 absorption rate in absorption towers involves measuring the SO3 content at both the inlet and outlet of the towers. This is because the acid retained by the mist eliminators has a certain masking effect on the acid distribution performance of the acid distributors.
In production, it is primarily determined that when the acid flow rate is sufficient, a temperature difference of 1–2 degrees between the temperature of the incoming acid and the temperature of the flue gas exiting the tower indicates good spraying efficiency
There should be no acid leakage at the connection of the acid splitter; the temperature difference between the exhaust gas temperature and the acid temperature in the tower should be within 1 degree. This ensures uniform acid distribution by the splitter, as well as a sufficiently high height for the packing layer. In my opinion, structured packing is prone to wall flow phenomenon, while the wall flow effect of random packing is minimal. If wall flow occurs, the acid mist concentration on the tower walls should be lower than that inside the tower; the distribution of acid is uneven. The spraying volume increases gradually from top to bottom along the tower walls, while it decreases gradually in the middle part of the tower. As the flue gas moves upward from the bottom, it is easier for acid mist to be carried upward from the middle. The temperature of the tower walls should be lower than that in the middle – just my personal opinion{:9011:}
It’s a clever idea; existing acid distributors are optimized based on random-packed packing. In fact, many of the problems that occur with random-packed packing do not arise with structured packing. Random packings may not induce large-scale wall flow, which can result in the possible formation of vertical cavities along the tower walls. This is also in line with the design concept of previous acid separators: more acid should be distributed near the tower wall to ensure that gas-liquid exchange can still occur even in the event of a cavity forming. However, with structured packings, wall flow inevitably occurs. The resistance to liquid flow through the vertical channels along the tower walls must be lower than that in the diagonal channels at the center of the packing. Under such circumstances, the phenomenon you described will occur: the flow rate along the tower walls increases, while the flow rate at the center of the packing decreases. So what should we do? A liquid collection ring is placed around the outer diameter of each layer of packing or every few layers, to collect the wall-flowing liquid and allow it to continue moving back and forth through the packing.