Abstract:

Deisobutanizer reboiler is one of the key equipment in alkylation unit. It is usually horizontal thermosiphon reboiler. For a 300 kt/a alkylation unit, the inner diameter of the reboiler shell is approximately 1500mm under the condition that hot oil or low-pressure steam is the heat source. With the capacity expansion of the unit, the size of the reboiler will increase or several reboilers will be operated in parallel, which brings great difficulties to the piping design and field construction of equipment. Setting baffle in the column kettle can effectively reduce the inlet and outlet temperature of the reboiler shell side and improve the heat transfer temperature difference of the reboiler. The process simulation results show that after the baffle is set in the column kettle, the inlet and outlet temperature of the reboiler shell side decreases by 24.3℃ and 23.6℃ respectively, while the flow rates and specifications of the overhead and bottom products remain unchanged. The heat exchanger calculation results show that, after setting the baffle, the logarithmic average temperature difference increases by 47%, the heat exchange area decreases by 33%, and the inner diameter of the shell decreases by 300mm. In addition, the overflow of the baffle also provides a stable pressure head for the feed of the reboiler, which greatly improves the operational stability of the bottom reboiler system. For the effluent system of alkylation unit, there is no reboiler clogging problem in setting up the baffle due to the separation and removal of acid and alkali by coalescer before entering the deisobutanizer. This scheme can be regarded as a good optimization process for both new and modified alkylation units.

Key words: alkylation, deisobutanizer, reboiler