Hydrocarbon Processing - December 2020 - 43

Plant Design, Engineering and Construction
efit of revamp Option 2 is to reduce syngas usage and associated tail gas volumes
with the lowest CO shift capacity and the
lower total installed cost, which results
in a minor improvement in H2 recovery
and cycle time for PSA1. However, the
operational issue of switching valves is
still present in the PSA1 unit.
Option 3: Full CO shift unit in the
upstream of the existing PSA1. To address all operational challenges due to
the original PSA1 design deficiencies,
revamp Option 3 (full CO shift) routes

a small portion of HP syngas through a
new CO shift train with no bypass, as
shown in FIG. 7. The overall material balance and HP syngas capacities are sized
for the CO shift equipment to meet the
H2 demand.
The CO shift in this case is a single,
high-temperature shift reactor that
converts approximately 80% of the CO
feed, which is the simplest CO shift
configuration design. TABLE 4 shows
the anticipated performance. In this
case, the heating value of LP tail gas is

TABLE 2. Anticipated performance for revamp Option 1
Item

PSA1

PSA2

Total

349,000

53,510

402,510

Feed H2, mol%

45.6

Feed CO, mol%

51.6

H2 product/design, %

84.7

15.6

100.2

Feed capacity, sm3/hr

H2 product purity, mol%

99.8

H2 recovery, %

58.8

70.5

60.5

Tail gas ﬂow/design, %

102.4

14.6

117

Tail gas pressure, kPag

265

100
H2 recovery or feed/design and H2 product/design ratio, %

Option 1 is to add a new PSA2 train in
parallel to the existing PSA1 unit that is
designed to accept the incremental feed.
The balance of the additional H2 demand
will be delivered by the PSA2, in which
higher H2 recovery can be achieved by
lowering the tail gas pressure to 55 kPag.
In this case, a tail gas compressor is required to raise the tail gas to the main
head pressure. In addition, to debottleneck or restore PSA1 to its potential,
as suggested by the PSA1 licensor, the
existing PSA1 must be retrofitted by replacement of all switching valves and a
complete adsorbent charge.
Option 2: Partial CO shift unit with
bypass in PSA1. The CO shift process
is an economical way to debottleneck the
PSA-based H2 plant. The CO shift unit
converts CO and water to H2 and CO2 ,
a process in which not only additional H2
is generated but the H2 is also increased.
Compared to CO, the shifted CO2 is easier to separate using PSA technology.
Revamp Option 2 involves the installation of a partial CO shift unit with
bypass in the upstream of the existing
PSA1, as shown in FIG. 6. In this case,
only about 26% of the syngas load/design ratio are required to be processed in
a CO shift train to debottleneck the existing PSA1. The CO shift train is a single, high-temperature shift reactor that
converts approximately 80% of the CO
feed. The extent of CO shift in this case
is relatively moderate compared to a typical two-stage CO shift design. The same
modification of debottlenecking PSA1
as revamp Option 1 will be required for
all options in this study.
The following two notes should be
mentioned for this case and for revamp
Option 3:
* Only a portion of HP syngas must
be routed to the new CO shift unit
to meet H2 demand, while the
balance of the HP syngas can be
routed to the cogeneration unit
for power generation
* The new CO shift reaction
train consumes the pressure
drop, which must be recovered
through compression. It is
believed that the H2 makeup
compressor in the downstream
HCU can be revamped to
provide additional compression.
TABLE 3 outlines the anticipated performance for this case. The major ben-

90
80
70
60
50
40
H2 recovery
H2 product/design ratio
Average feed/design ratio
Feed/design ratio
Average H2 recovery

30
20
10
July-15

Aug.-15

Sept.-15

Oct.-15
Dates

Nov.-15

Dec.-15

Jan.-16

FIG. 4. H2 recovery, feed/design and H2 product/design ratios.
S90-tail gas

S96-tail gas

S92-cogeneration
S95-tail gas 2

Asphaltene

MIX-101

Sweet
syngas

Raw syngas
T

Asphaltene
gasiﬁcation

Acid gas
removal

S88-PSA

T
PSA 1

S89-H2

T 100
S97-H2
S93-PSA 2

T
New PSA 2

S94-H2

MIX-100

FIG. 5. Revamp Option 1: New PSA2 train in parallel.
Hydrocarbon Processing | DECEMBER 2020

Hydrocarbon Processing - December 2020

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