Crystallization issue at the pump inlet of the hydrodesorption tower
Thread Content
The stripping tower in the coking gasoline and diesel hydrogenation unit tends to form crystals at the inlet of the standby pump and at the reflux valve assembly (white crystals that disappear when heated by steam). How can such crystallization be prevented?
The white crystals are likely various hydrosulfides and ammonium sulfides formed as a result of the reaction between hydrogen sulfide and ammonia. Method to avoid crystal formation: Slightly increase the temperature after air cooling, that is, raise the temperature of the liquid in the reflux tank to around 45 degrees Celsius (I haven’t been able to find out the exact crystallization temperature). I’m not sure if what I said is correct.
Do you actually do this?
We usually keep it at 35 degrees Celsius. Crystals appeared in the bypass line of the control valve for the reflux tank level (sulfur-containing wastewater). Since this bypass line was not used frequently, crystals accumulated and caused blockages in it. When the plant was shut down for maintenance, the bypass line was replaced, and it was found that the entire line was filled with white crystals. Solution to prevent blockage in the secondary line: Keep the valve of the secondary line at a certain opening degree to maintain continuous flow and prevent crystal deposition.
Handling suggestions: 1. Increase the emission of waste hydrogen； ⒉Increase the dosage of corrosion inhibitor injected at the top of the tower appropriately ； ⒊Steam tracing is applied to the discharge line for low-acidity water from the reflux tank and the reflux pump pipelines, while steam purging lines are used for salt removal and salt treatment.
This substance should be an ammonium salt crystal, and crystallization accumulation occurred at the inlet of the standby pump due to lack of flow. Solution: First, increase the water flow rate for high-pressure air cooling to keep the temperature after cooling below 50°C. Second, if crystallization occurs, it can be dissolved by directly heating with steam. Additionally, the corrosion inhibitor mentioned on the 5th floor can only prevent hydrogen sulfide corrosion; does it also have any effect on preventing ammonium salt crystallization? Furthermore, the corrosion inhibitor was injected into the overhead oil-gas outlet pipeline and did not enter the stripping tower.
I have encountered situations where the inlet filter froze; raising the temperature and enhancing dehydration resolved the issue, but I have not faced any problems with ammonia crystallization.
Raising the inlet temperature to 40 degrees will suffice.