Page 61 - Chemical Process Equipment - Selection and Design

Appendix 2.1

escriptions of Example Process Flowsheets

These examples ask for the construction of flowsheets from the vacuum gas oil (HVGO) is charged to the top plate of zone 2,
given process descriptions. Necessary auxiliaries such as drums and removed at the bottom tray and charged to furnace no. 2 that
pumps are to’ be included even when they are not mentioned. operates at 500 psig and 925°F.
Essential control instrumentation also is to be provided. Chapter 3 Effluents from both furnaces are combined and enter the
has examples. The processes are as follows: soaker; this is a large vertical drum designed to provide additional
residence time for conversion under adiabatic conditions. Effluent
n. visbreaker operation, at 500psig and 915°F enters the bottom zone of the main frac-
2. cracking of gas oil, tionator.
3. olefin production from naptha and gas oil, Bottoms from zone 1 goes to a stripping column (5psig).
propylene oxide synthesis, Overhead from that tower is condensed, returned partly as reflux
5. phenol by the chlorobenzene process, and partly to zone 3 after being cooled in the first condenser of the
5. manufacture of butadiene sulfone, stripping column. This condensing train consists of the preheater for
a. detergent manufacture, the stream being returned to the main fractionator and an air
8. natural gas absorption, cooler. The cracked residuum from the bottom of the stripper is
tall oil distillation, cooled to 170°F in a steam generator and an air cooler in series.
recovery of isoprene, Live steam is introduced below the bottom tray for stripping.
I. AU of the oil from the bottom of zone 3 (at 700”F), other than
vacuum distillation,
Be the portion that serves as feed to furnace no. 1, is withdrawn
air separation.
through a cooler (500°F) and pumped partly to the bop tray of zone
1. VISBREAKER OPERATION 2 and partly as spray quench to zone 1. Some of the bottoms of
zone 1 likewise is pumped through a filter and an exchanger and to
Visbreaking is a mild thermal pyrolysis of heavy petroleum fractions the same spray nozzle.
whose object is to reduce fuel production in a refinery and to make Part of the liquid from the bottom tray of zone 4 (at 590°F) is
s0me gasoline. pumped to a hydrogenation unit beyond the battery limits. Some
The oil of 7.2API and 700°F is supplied from beyond the light material is returned at 400°F from the hydrogenation unit to
battery limits to a surge drum F-1. From there it is pumped with the middle of zone 4, together with some steam.
J-1ABE to parallel furnaces B-lA&B firom which it comes out at Overhead from the top of the column (zone 4) goes to a partial
890°F and 200 psig. Each of the split streams enters at the bottom of condenser at 400°F. Part of the condensate is returned to the top
its own evaporator T-1.4BB that has five trays. Overheads from the tray as reflux; the rest of it is product naphtha and proceeds beyond
evaporators combine and enter at the bottom of a 30-tray the battery limits. The uncondensed gas also goes beyond the
fractionator T-2. A portion of the bottoms from the fractionator is battery limits. Condensed water is sewered.
fed to the top trays of T-lA&B; the remainder goes through
exchanger E-5 and is pumped with J-2A&B back to the furnaces 3. OLEFIN PRODUCTION
B-lA&B. The bottoms of the evaporators are pumped with
J4A&E through exchangers E-5, E-3A (on crude), and E-3B (on A gaseous product rich in ethylene and propylene is made by
cooling water) before proceeding to storage as the fuel product. pyrolysis of crude oil fractions according to the following
A side stream is withdrawn at the tenth tray from the top of description. Construct a flowsheet for the process. Use standard
T-2 and proceeds to steam stripper T-3 equipped with five trays. symbols for equipment and operating conditions. Space the symbols
Steam is fed below the bottom tray. The combined steam and oil and proportion them in such a way that the sketch will have a
vapors return to T-2 at the eighth tray. Stripper bottoms are pleasing appearance.
pumped with J-6 through E-2A (on crude) and E-2B (on cooling Crude oil is pumped from storage through a steam heated
water) and to storage as “heavy gasoline.” exchanger and into an electric desalter. Dilute caustic is injected
Overhead of the fractionator T-2 is partially condensed in E-1A into the line just before the desalting drum. The aqueous phase
(on crude) and E-113 (on cooling water). A gas product is collects at the bottom of this vessel and is drained away to the
withdrawn overhead of the reflux drum which operates at 15 psig. sewer. The oil leaves the desalter at 190”F, and goes through heat
The “light gasoline” is pumped with J-5 to storage and as reflux. exchanger E-2 and into a furnace coil. From the furnace, which it
Oil feed is 322,48Opph, gas is 3370, light gasoline is 5470, leaves at 600”F, the oil proceeds to a distillation tower.
heavy gasoline is 9940, and fuel oil is 103,700 pph. After serving to preheat the feed in exchanger E-2, the bottoms
Include suitable control equipment for the main fractionator proceeds to storage; no bottoms pump is necessary because the
T-2. tower operates with 65psig at the top. A gas oil is taken off as a
sidestream some distance above the feed plate, and naphtha is
2. CRACKING OF GAS taken off overhead. Part of the overhead is returned as reflux to the
tower, and the remainder proceeds to a cracking furnace. The gas
A gas oil cracking plant consists of two cracking furnaces, a soaker, oil also is charged to the same cracking furnace but into a separate
a main fractionator, and auxiliary strippers, exchangers, pumps, and coil. Superheated steam at 800°F is injected into both cracking coils
drums. The main fractionator (15Opsig) consists of four zones, the at their inlets.
bottom zone being no. 1. Effluents from the naphtha and gas oil cracking coils are at
A light vacuum gas oil (LVGO) is charged to the top plate of 1300°F and 1200”F, respectively. They are combined in the line just
zone 3, removed from the bottom tray of this zone and pumped to before discharge into a quench tower that operates at 5psig and
furnace no. 1 that operates at 1OOOpsig and 1000°F. A heavy 235°F at the top. Water is sprayed into the top of this tower. The
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