Refinery process up and downstream of heat exchangers and fired heaters
Refineries and petrochemical Chemical plants constitute of multiple functional units connected to each other. All these units perform their individual functions in order to deliver the desired output. In the case of a Refinery, it is the crude oil which is the input and the refinery produces various petroleum products as per the equipment installed. However, major processes in many refineries can be summed up as follows:
- Crude distillation
- Vacuum distillation
- Mid-distillation hydrotreating
- Naptha hydrotreating
- Catalytic Reforming
Certain processes might be absent due to the limitation of the particular refinery operations. All processes after the Vacuum distillation described above give their output in the form of a petroleum derived product be it LPG, Jet diesel, Gasoline, Hydrogen Gas, Aromatics, Petroleum Coke or Cycle oil for hydrotreating.
Among these processes the function of the Fired Heaters and Heat Exchangers is vital. They are critical to the success of the crude and vacuum distillation processes where they exchange heat with the fluid flowing through the unit in pipes. The purpose is to give the desired temperature to the crude passing through them so it can be properly distilled.
Upstream and Downstream processes in Crude and Vacuum Distillation units
For Distillation processes
In the case of crude distillation, upstream to the fired heaters are units that preheat the crude feed with heat recovered from the product itself and then desalt and dehydrate it using electrostatic enhanced liquid/liquid separation technique (Desalting process in a desalter). In the case of vacuum distillation, the upstream process consists of reducing the hydrocarbon partial pressure by using a vacuum and a stripping steam.
Downstream from these direct heaters in both types of distillation are cooling units that enable the various products to move to the top, sides or bottom of the units thus causing separation. Downstream process in case of crude distillation includes Flashing of the crude inside the atmospheric distillation column for crude distillation and in the Vacuum column in case of vacuum distillation, and in both cases using pump around cooling loops to create internal liquid reflux. The product is then drawn to the top, sides, and bottom of the unit.
In case of Delayed Coking process
Upstream to the fired heaters, the processes include preheating of the feed and providing primary condensing of coke drum vapors by introducing the feed to the bottom part of the main fractionator. The downstream process boils down to flashing the superheated feed in the large coke drum where the coke will remain while the vapors would leave from the top and/or go back to the fractionator. Another vital step is to drill the Off-line coke drum and removing of the petroleum coke through the process of hydro jetting.
In case of Hydrotreating process
Upstream to the fired heaters, the process involves preheating the feed by utilizing the reactor effluent and then the introduction of Hydrogen gas with the feed prior to its heating to the desired hydrotreating temperature in the fired heater. Downstream processes include Feed and hydrogen going down in a hydrogenation reactor packed with various types of catalysts depending upon desired reactions, cooling of reactor effluent and its entrance into the high-pressure separator which separates the liquid hydrocarbon from the hydrogen/hydrogen sulfide/ammonia gas (H2 / H2S/NH3). Here the amine absorber absorbs the acidic gases from hydrogen. Then this hydrogen gets recycled with make-up hydrogen. Separation of LPG (Liquid petroleum gases) gases occurs in the low-pressure separator prior to sending the hydrocarbon liquids to fractionation.
Thus we see the fired heaters form the crux of many of the Refinery and Petrochemical process and are integrated into the processes which occur both upstream and downstream of these fired heaters.
This video demonstrates heat exchanger cleaning..