Feed/Effluent Exchangers
Via a series of feed/effluent shell-and-tube exchangers, the reactor effluent preheats
the reactor charge before entering the reactor charge heater. This recovers as much
heat as possible from the heat of reaction and the sensible and latent heats of the
reactor effluent. Liquid feed may be preheated separately with reactor effluent
exchange before combining with the recycle (treat) gas, depending on the heat
integration scheme.
Reactor Charge Heater
In most units, the fresh feed and recycle gas are heated together as “combined feed”
to the desired reactor inlet temperature in a combined feed charge heater. In units
processing heavy feed, especially the atmospheric residue units, the liquid feed is
preheated separately in the reactor feed/reactor effluent exchange, and only the
recycle gas is heated in the heater upstream of the reactor.
Makeup Hydrogen System
Makeup hydrogen is typically obtained from hydrogen manufacturing plants, naphtha
cracking complexes, and/or naphtha catalytic reforming units. Depending on the
pressure of the hydrotreating unit, the makeup hydrogen might have to be compressed
before introduction into the unit. Reciprocating compressors are typically used for
this service. The makeup gas is introduced into the recycle gas system.
Feed
filter
Fresh
feed
Reactor
charge
pump
To stripper
column
To
stripper
column
Water
injection
Sour
water
Sour
water
Cold
separator
Cold
flash
drum
To off gas
scrubber
Feed
surge
drum
Reactor
charge
heater
Reactor
Hot
separator
Vgo unionfining unit
(Reactor section)
schematic flow diagram
Hot flash
drum
Recycle gas
compressor
Gas
makeup
Recycle gas
scrubber
Fig. 2 Schematic flow diagram of a reactor section
Hydrotreating in Petroleum Processing
367