Ch E 452: Process Design, Analysis, and Simulation Tracing Chemicals through the Process Flow Diagra

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Ch E 452 Process Design,Analysis, and
SimulationTracing Chemicals through the Process
Flow Diagram

• David A. Rockstraw, Ph.D., P.E.
• New Mexico State University
• Chemical Engineering

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Tracing Primary Chemicals

• Reactants start with the feed (LHS of PFD) and
  trace chemicals forward toward reactor.
• Products start with the product (RHS of PFD) and
  trace chemicals backward toward reactor.

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Tactics applicable to non-reactors

• (1) Any unit operation, or group of operations,
  that has a single or multiple input stream(s) and
  a single output stream is traced in a forward
  direction. If chemical A is present in any input
  stream, it must appear in the single output
  stream.

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Tactics applicable to non-reactors

• (2) Any unit operation, or group of operations,
  that has a single and single or multiple output
  stream(s) is traced in a backward direction. If
  chemical A is present in any output stream, it
  must appear in the single input stream.

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Tactics applicable to non-reactors

• (3) Systems such as distillation columns are
  composed of multiple unit operations with a
  single input or output stream. It is sometimes
  necessary to consider such equipment combinations
  as blocks before implementing Tactics (1) and (2).

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Reactors

• Only in reactors are feed chemicals transformed
  into product chemicals.

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Toluene Hydrodealkylation
Toluene Feed Tactic 1 is applied to each unit
operation in succession
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Toluene Hydrodealkylation
a. Toluene feed Stream 1 mixes with Stream 11 in
V-101l. A single unidentified stream leaves Tank
V-101, and goes to pump P-101. All the toluene
feed is in this stream
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Toluene Hydrodealkylation
b. Stream 2 leaves pump P-101 and goes to mixer
m-102. All the feed toluene is in this stream
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Toluene Hydrodealkylation
c. A single unidentified stream leaves mixer
m-102 ,and goes to exchanger E-101. All the feed
toluene is in this stream.
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Toluene Hydrodealkylation
d. Stream 4 leaves exchanger E-101, and goes to
heater H-101. All the feed toluene is in this
stream.
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Toluene Hydrodealkylation
e. Stream 6 leaves heater H-101 and goes to
reactor R-101. All the feed toluene is in this
stream.
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Toluene Hydrodealkylation
Benzene Product Tactic 2. Applied to each unit
operation in succession.
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Toluene Hydrodealkylation
a. Product Stream 15 leaves exchanger E-105
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Toluene Hydrodealkylation
b. Entering exchanger E-105, is an undesignated
stream from s-103 of the distillation system. It
contains all of the benzene product.
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Toluene Hydrodealkylation
c. Apply Tactic 3 and treat the tower T-101, pump
P-102 exchangers E-104 and E-106, vessel V-104,
and splitter s-103 as a system.
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Toluene Hydrodealkylation
d. Entering this distillation unit system is
Stream 10 from exchanger E-103. It contains all
the benzene product.
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Toluene Hydrodealkylation
e. Entering exchanger E-103, is Stream 18 from
vessel V-l03. It contains all the benzene product.
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Toluene Hydrodealkylation
f. Entering vessel V-103, is an undesignated
stream from vessel V-102. It contains all the
benzene product.
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Toluene Hydrodealkylation
g. Entering vessel V-102, is an undesignated
stream from exchanger E-102. It contains all the
benzene product.
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Toluene Hydrodealkylation
h. Entering exchanger E-102 is Stream 9 from
reactor R-101. It contains all the benzene
product.
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Process Description propylene oxidation to
acrylic acid
Propylene is supplied as a saturated vapor from
storage at 11.5 bar, Stream 3. After throttling
to 4.3 bar, this stream is mixed with
low-pressure stream, Stream 2, and air, Stream 1,
which is compressed in compressor C-301 prior to
mixing. The resulting mixture, Stream 4, is fed
to fluidized bed catalytic reactor R-301.
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Process Description propylene oxidation to
acrylic acid
The fluidized bed operates close to isothermally
at 310C with a single pass conversion of
propylene of about 88. The heat of reaction is
removed by a circulating stream of molten salt,
which is cooled externally in exchanger E-301 by
cooling water. Three primary reactions take
place in the reactor, giving rise to two organic
acid products acrylic and acetic acids.
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Process Description propylene oxidation to
acrylic acid
Reaction 1
Reaction 2
Reaction 3
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Process Description propylene oxidation to
acrylic acid
The reactor effluent, Stream 6, is rapidly
quenched by a circulating stream of water, Stream
8, in the Quench Tower, T-301. Most of the
organic acids dissolve in the water. The
non-condensable gases plus small amounts of
acrylic acid and acetic acid leave the top of
T-301 and are fed to the Quench Cooler, T-302,
where they are contacted with a countercurrent
stream of deionized water, Stream 10.
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Process Description propylene oxidation to
acrylic acid
Most of the remaining acid is absorbed into the
water stream, Stream 7, which leaves the bottom
of T-302 and is mixed with the quench water. The
gases leaving T-302 contain the non-condensable
gases, including the unreacted propylene, and
these are sent off site to an incinerator for
disposal.
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Process Description propylene oxidation to
acrylic acid
A slipstream, Steam 9, of the circulating quench
water is sent to the solvent tower, T-303. Here
the organic acids are extracted from the water
using diisopropyl ether in a rotating disk
extractor. The organic phase leaving T-303
contains virtually all of the acid, Stream 13.
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Process Description propylene oxidation to
acrylic acid
This stream is sent to two distillation towers,
T-304 and T-305. In the first tower, the solvent
is separated from the acids and is taken overhead
as Stream 16. Stream 16 is mixed with a small
amount of recovered solvent from T-306 and
recycled back to E-309 where it is heated with
low-pressure steam prior to returning to T-303.
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Process Description propylene oxidation to
acrylic acid
The bottom product from T-304, Stream 14,
contains nearly all of the acid produced in
R-301. This stream is fed to tray 23 of tower
T-305. Overhead product from T-305, stream 19,
consists of 95 wt acetic acid at 47C and is
sent to off-site storage. The bottoms, Stream
17, consists of 99.9wt acrylic acid, which is
cooled to 40C in E-310 using cooling water prior
to being pumped to off-site storage.
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Process Description propylene oxidation to
acrylic acid
The aqueous phase leaving T-303, Stream 12, is
fed to tray 6 of the Waste Tower, T-306, where a
small amount of dissolved solvent is recovered as
overhead product and recycled. The bottom
product from this column, Stream 20, contains
water with very small amounts of organic
material. This material is cooled off-site prior
to being fed to the wastewater treatment facility