Investigation on the deposition failure of a reactor effluent air cooler in hydrocracking unit

• Deposition failure is investigated via technical and multiphase flow simulation.
• High temperature H2S-H2 corrosion occurs in the upstream heat exchangers.
• Technical simulation determines crystallization temperature of ammonium salts.
• Deposition process of particles is analyzed by multiphase flow simulation.
• Thermal stress is produced and induces the bending deformation of air cooler tubes.

The deposition failure of a reactor effluent air cooler (REAC) is investigated by the technical analysis and multiphase flow simulation. The blockages of REAC tubes are mainly induced by the corrosion products come from the upstream heat exchangers, a result of the high temperature H2S-H2 corrosion. Meanwhile, NH4Cl salts crystallize upstream the air coolers and enter into the REAC tubes, flowing along with the corrosion products. Through analyzing the residence times and deposition rates of salts, it is found that the corrosion products tend to deposit on two sides of the header box, the third row of tubes and the regions of low velocities. The temperatures inside the REAC tubes significantly decrease once the tubes are blocked. Fouling of NH4HS salts occurs when the temperature falls below 30 °C. The expansion and contraction of carbon steel with large difference in temperature lead to the bucking of tubes. The regions with high risk deposition are obtained from simulation, which agree well with the actual failure phenomenon.