Control of the top temperature in the absorption tower for catalytic stabilization units
Thread Content
Stable process flow: Compressor outlet → where the compressed rich gas and desorbed gas meet → air cooling → cooler → gas-liquid separation tank → to the absorption tower. There are many factors that affect the temperature at the top of the absorption tower; here, I would like to focus on the issue of controlling the temperature after cooling in the cooler. It is well known that in a stabilizer tower, liquefied gas is a multi-component mixture, and minor changes in the composition at the tower top are not reflected sensitively in terms of temperature. Therefore, the stabilizer tower cannot regulate the reflux flow by controlling the top temperature of the tower. Practical operation also shows that when adjusting the reflux volume, there is always a slight delay in temperature changes~~~ In the aforementioned process, I observed that when adjusting the temperature of the cooler, there is as well a slight delay in the response of the temperature at the top of the absorption tower. For example, when the temperature at the top of the absorption tower is 30 degrees, if the outlet valve for the cooling water in the cooler is reduced by half, the temperature at the top of the absorption tower changes little. Then, if the outlet valve of the cooler is further tightened to just three notches left, the temperature at the top of the absorption tower starts to change, and it can gradually rise to 42 degrees. I wonder whether the temperature of the cooling water in everyone’s coolers also needs to be adjusted frequently? In our plant, even when the outlet valve of the cooler is fully open, the temperature after cooling doesn’t drop very low; the lowest temperature achievable in this case is 36 degrees. The workshop management requires that the temperature at the top of the absorption tower be kept between 34 and 39 degrees to prevent excessive absorption. Now that the weather has turned colder, the temperature at the top of the absorption tower often falls below 34 degrees. In such situations, we have no choice but to reduce the opening of the cooler’s outlet valve. Due to delays, the valve often has to be closed quite tightly, and as a result, the temperature in the absorption tower rises to 42 degrees. Then we are forced to reopen the outlet valve fully. This back-and-forth adjustment, in my opinion, disrupts the gas-liquid distribution in the absorption tower, and it’s also frustrating and exhausting. I’d like to ask everyone: is it correct to make such frequent adjustments to the temperature after cooling? It’s cold now; what is the minimum temperature allowed at the top of everyone’s absorption towers? How to adjust it?
The purpose of controlling the temperature of the absorption tower is to ensure effective absorption while also taking into account the risk of excessive absorption and energy consumption. The leadership in charge of the installation has set this temperature range, presumably for these very reasons. The regulations are correct; the reason the original poster raised the issue is due to difficulties in controlling them. Why not adjust it in advance? Does it have to wait until the temperature reaches the lower limit before taking action? Is there an indication for the total amount of circulating water? It can be adjusted according to the water volume. And knowing full well that temperature regulation is delayed, why not wait a bit? The adjustment range is too large! By the way, air cooling must have a fan, right? The control of air cooling is much more sensitive than that of circulating water.
First, ensure stability in the feed temperature, the pressure in the stabilizer, and the temperature at the bottom of the stabilizer. The top temperature can be easily controlled by adjusting the reflux rate; on the other hand, adjusting water usage is troublesome and results in large fluctuations. Generally, once the water level is adjusted to a certain level, there’s no need to adjust it anymore
No frequent adjustments are needed; we aim to keep it between 35 and 45 degrees, and it’s fine if it’s 1–2 degrees higher or lower. As long as the difference is not too large, no adjustment is usually made; adjustments are mainly made to the fan, specifically the variable-frequency one. Water is adjusted only when all fans have stopped
The lower the temperature at the top of the absorption tower, the better; it is generally sufficient to keep it below 40 degrees. In winter, this temperature can usually be maintained around 35 degrees, while in summer it is typically around 40 degrees. If absorption is excessive, the pressure in the tower can be reduced. Additionally, the temperature at the top of the absorption tower is also related to the amount of reflux in the middle section, as well as the temperatures of the crude steam and the warm steam used as absorbents. Higher temperatures of these steams result in a higher temperature at the top of the absorption tower. :lol:loveliness:
In the operation of an absorption tower, absorption is an exothermic reaction; the lower the temperature in the absorption tower, the better. It is ideal to keep this temperature below 40 degrees. When absorption is excessive, the pressure at the top of the absorption tower can be reduced. Additionally, the temperature at the top of the absorption tower needs to be well controlled, and the amount of reflux in the middle section is also related to the temperatures of the crude steam and the warm steam along with the absorbent； The temperature of the crude steam and warm steam, as well as that of the absorbent, is high, resulting in a high temperature at the top of the absorption tower, which hinders its operation
The absorption process is exothermic, and as the absorption proceeds, the temperature in the absorber increases from top to bottom. Therefore, a mid-stage reflux heat extraction is installed in the middle of the absorption tower to reduce the temperature during the absorption process. The temperature of the process medium after cooling is generally 40°C. The use of refrigeration methods can reduce the temperature of the medium after cooling, thereby replacing the need for additional absorbents and intermediate heat extraction systems.
We also adjust things in this way often, but we have plenty of experience at it, so it comes naturally to us, haha!
It’s mainly because the adjustment is too rapid; if it’s done more slowly, a balance point will be achieved.
It is best to control the temperature at the top of the absorption tower using a fan. If no fan is available, the temperature of the entire tower can be adjusted accordingly; for example, if the temperature is currently a bit low, the flow rates of the first and second recirculation streams can be reduced slightly, or the temperature of the rich gas can be adjusted
For controlling the temperature at the top of the absorption tower, air cooling has the most significant effect. As for adjusting the feed temperature, mid-stage reflux, and the temperature of the gasoline supplied from the distillation process, there is limited room for adjustment. However, we can adjust the temperature of the supplementary absorbent, which makes it easy to stabilize the operation
We generally control the top temperature by regulating the temperature of the crude steam and the heated steam. The temperature is lower, so absorption is better; less absorbent is needed.
Anything from 25 to 45 is fine; it mainly depends on the absorption effect, so the absorbent needs to be adjusted accordingly
In the south, the value is below 45, which is normal; the values for the upper and lower parts of the tower are more or less the same, around 42