Reasons for the decline in efficiency of the catalytic cracking fractionator top heat exchanger

The top of the tower or the bottom? Can coking occur at the top of the tower?

The poster might be referring to scaling in the heat exchanger. The decrease in heat exchanger efficiency is due, in addition to fouling or coking (not referring to the top of the tower) which leads to an increase in the thermal resistance caused by fouling, to the flow pattern of the fluid passing through the heat exchanger. A decrease in the heat transfer coefficient on either the tube side or the shell side will result in a decrease in the overall heat transfer coefficient, thereby leading to a reduction in the efficiency of the heat exchanger. Regarding the top of the catalytic fractionation tower mentioned by the original poster, oil and gas condense there; hence there is a question of whether condensation occurs in a film form or in droplet form. The heat transfer coefficient for film-type condensation is higher than that for droplet-type condensation. Therefore, when the amount of oil and gas at the tower top changes, the condition of condensation may change as well, which leads to a decrease in the heat transfer coefficient.

The decline in the efficiency of the heat exchanger at the top of the catalytic cracking fractionator is most likely due to coking; other possible causes include: 1. An increase in the amount of non-condensable gas at the top of the tower, which reduces the heat transfer coefficient and thus lowers the efficiency of the heat exchanger. 2. Uneven condensation leads to flow deviation, reducing the efficiency of the heat exchanger. 3. An increase in the flow rate at the top of the tower leads to a greater cooling load; if cooling is not sufficient, it may also reduce the efficiency of the heat exchanger. 4. The flow rate at the top of the tower decreases, and the Reynolds number drops, which leads to a reduction in the heat transfer coefficient and thus a decrease in the efficiency of the heat exchanger. There might be other reasons too!

The heat exchanger at the top of the catalytic cracking fractionator can also become fouled: any fluid can cause fouling, to varying degrees. Light materials suffer less from scaling, while heavier materials experience more severe issues. This post was last edited by upca on 2008-1-9 13:27.]

The reasons for this phenomenon are multifaceted: 1. It is caused by salt deposition in the heat exchanger, with ammonia salts being the main cause. 2. Scaling is another factor; there are various reasons for this, but it is primarily due to the quality of the circulating water. 3. Another factor is the volume of water being processed – changes in this volume can lead to changes in flow velocity, which in turn affects the heat transfer efficiency. 4. Changes in the temperature of the circulating water also play a role; the temperature of the water entering the system affects the heat transfer coefficient as well

Does the heat exchanger at the top of the tower recombine salts? I have only heard of salt deposition on the trays at the top of the tower; could you please explain the mechanism of salt deposition in the heat exchanger at the top of the tower? Thank you

I agree with what was said on the seventh floor; in our plant, salt builds up on the pump and heat exchangers located on the top circulation side, which reduces the efficiency of these pumps and heat exchangers.

The heat exchange efficiency of the overhead oil-gas condenser is low: 1. There is a large amount of non-condensable gas in the oil and gas; 2. The quality of the circulating water is poor, leading to scaling; 3. Salts accumulate on the heat exchanger, mainly sodium salts or ammonia salts; 4. The pressure of the circulating water is insufficient, resulting in inadequate water supply to the heat exchanger.

The issue of reduced efficiency in the heat exchanger at the top of the catalytic cracking distillation column. A decrease in the efficiency of this heat exchanger is most likely due to coking; other possible causes include: 1. An increase in the amount of non-condensable gas at the column top, which leads to a reduction in the heat transfer coefficient and thus a decline in the heat exchanger’s efficiency. 2. Uneven condensation leads to flow deviation, reducing the efficiency of the heat exchanger. 3. An increase in the flow rate at the top of the tower leads to a greater cooling load; if cooling is not sufficient, it may also reduce the efficiency of the heat exchanger. 4. The flow rate at the top of the tower decreases, and the Reynolds number drops, which leads to a reduction in the heat transfer coefficient and thus a decrease in the efficiency of the heat exchanger. This guy’s analysis is quite comprehensive. :lol :victory:

Top replacement coking is possible, but it will not be as severe as in the slurry heat exchanger. I agree with what everyone has said about coking and scaling; when the circulating water is dirty and contains rust, etc., backwashing can yield good results

The low-temperature heat exchanger at the top of the tower suffers from scaling rather than coking; pay attention to whether the quality of the hot water used is satisfactory.

An increase in the temperature of the circulating cold water or an increase in atmospheric temperature can also lead to a deterioration in the heat exchange efficiency at the bottom of the distillation tower. Generally, an increase in gas load or an increase in the amount of non-condensable gas causes the heat exchange to fail to meet the requirements. A decrease in flow rate also leads to a poorer heat exchange effect. The heat exchanger leads to a deterioration in heat exchange efficiency, and this usually happens over a certain period of time; it does not increase suddenly or within a very short timeframe.

Coking at the top of the tower is entirely possible; apart from coking and scaling, flow deviation also has a significant impact, and then there’s what that gentleman explained

Agree with what was said on floor 10; it’s the most common situation.

As a supplementary point, dirty circulating water can also cause blockages in the pipe system, affecting the cooling efficiency.