Temperature of residue hydrogenation hot fraction before air cooling and water injection?

Ammonium chloride levels below 230 are also possible

It’s too late to inject water at 150 degrees; the crystallization temperature of ammonium chloride is ≤220 degrees, and that of ammonium hydrosulfide is ≤120 degrees

I would like to ask everyone: Is it feasible to keep injecting water at a rate of 150 after the replacement, and to inject water intermittently at a rate of 240 before the replacement (for half a month)? . Also, are there any requirements regarding the feed temperature of the mixed hydrogen and the temperature of the mixed hydrogen? How is it controlled, roughly? Will an excessively large cross-line distance for the raw materials affect the results after hydrogen mixing? Thank you!

Generally, continuous water injection is used before air cooling, while intermittent water injection is employed before the heat exchanger. The frequency of intermittent water injection depends mainly on the upward trend in system pressure drop; a decision to switch to intermittent injection is made based on the conditions of that pressure drop.

Next, let’s analyze the reasons for the formation of ammonium salts crystals: The sulfur, nitrogen, and chlorine compounds contained in the crude oil are converted into H2S, HCl, and NH3 through hydrogenation reactions. Under suitable conditions, these substances react to form NH4Cl and NH4HS. At appropriate temperatures, NH4Cl and NH4HS can directly change from gaseous state to solid crystals. Such ammonium salt crystals can quickly block the tubes. When the process medium contains water, NH4Cl and NH4HS form corrosive aqueous solutions, which then cause crystalline deposits to form again in areas with low flow rates or dead zones, leading to under-scale corrosion; in areas with high flow rates, especially those with turbulent flow, erosion occurs. NH4HS crystallizes into a solid at temperatures below about 120°C; therefore, crystallization of NH4HS leading to blockages and corrosion is commonly observed in the air coolers used to treat reaction products. The crystallization temperature of NH4Cl is between 180 and 220°C; therefore, crystallization of NH4Cl can cause blockages as well as under-scale corrosion in the heat exchanger tubes.

Within the tube bundle of the heat exchanger, as the temperature decreases, the vapor pressures of NH3 and HCl in the process fluid increase accordingly. When their product Kp exceeds the equilibrium constant K1, ammonium salts begin to crystallize. The formation of crystals increases the pressure drop at that location, reduces the flow area, and lowers the temperature there, which in turn leads to more crystallization. This creates a vicious cycle that results in the gradual complete blockage of that section of the tube bundle. When water is present in the raw material or when water is injected, NH4CL undergoes deliquescence, producing HCL and forming concentrated hydrochloric acid, which causes severe corrosion to the tube bundles.

Therefore, intermittent water injection is generally used before the heat exchanger, while continuous water injection is used before air cooling. Furthermore, due to the high temperature at the injection point before the heat exchanger, it is necessary to ensure that there is 25% liquid phase remaining after vaporization, so as to provide sufficient liquid water for flushing at that point.