Hydrocarbon Processing - December 2020 - 31

Plant Design, Engineering and Construction
* It can be measured with a
high degree of accuracy.
Sulfur recovery efficiency is used here as
the key performance index for the sulfur
process.
A second performance parameter that
is related directly to, and used in tandem
with, the recovery efficiency is the conversion efficiency. Conversion efficiency
is the fraction of input compound sulfur
that is converted to elemental sulfur. Recovery is always less than conversion for
two reasons:
1. The elemental sulfur vapor
produced in the catalytic reactors
is recovered by condensation
to the liquid in the condensers.
The equilibrium sulfur vapor
at the condenser outlet is not
recovered. While this vapor loss
can be minimized by using the
lowest practicable condenser

temperature, it cannot be
eliminated unless another method
of removing the elemental sulfur
from the gas stream is developed.
2. Liquid sulfur in the form of fog
or mist often becomes entrained
in the condenser outlet gas
stream and may not be recovered.
This mechanism of efficiency
loss can be eliminated by careful
condenser and coalescer design
and good operation.
The sulfur recovery efficiency is calculated using the carbon-to-sulfur ratio.
This method is based on the principle that
the carbon contained in the gas remains
constant at any point of time of the unit,
whereas the sulfur amount in the gas decreases along the unit as liquid sulfur is recovered. This method can be applied only
for the units, including indirect reheaters
or steam heaters, instead of direct-fired

100
Feed + air, no sulfur removal
(data from Sulsim 5)

95
90

100% H2S, P = 1
50% H2S, 50% N2, P = 1
100% H2S, P = 2

Conversion to sufur, %

85
80
75

Catalytic
region

70
Furnace
region

65
60
Main form of sulfur
liquid

55

S8

S2

50
200

0

400

600
800
Temperature, °C

1,000

1,200

1,400

FIG. 2. Claus process thermodynamics: Equilibrium conversion of H2S to sulfur.
100

CV2

Feed + air, no sulfur removal
(data from Sulsim 5)

95
CD2

90

CV1
89% sulfur removed
75% sulfur removed
No sulfur removed

85
Conversion to sufur, %

According to the conversion curve in
thermal conversion of H2S to sulfur is thermodynamically limited to less
than 75% at the high operating temperature of the reaction furnace in the thermal
stage. Higher conversions are obtained
by low-temperature catalytic reactions
in subsequent reactors. The catalyst, the
low temperature and the removal of sulfur product by the condensers all enhance
the attainment of an overall conversion
efficiency of 96%-98% (FIG. 3). Although
the lower temperature is ideally desirable
to obtain better conversion, realistic operation should be performed with a dewpoint margin of 8°C-10°C to avoid liquid
sulfur deposition on the catalyst, which
causes temporary catalyst deactivation.
Therefore, the conventional Claus process operates subsequent catalytic reactors at lower temperatures, but all above
the sulfur dewpoint.
The incremental conversion efficiency
to be gained by using more than four reactors is not justified since the expense
and operating problems associated with
a fourth stage outweigh the advantage
of the extra 0.1%-0.2% conversion attainable. However, conversion through
only the SRU is not enough to meet the
emissions limit. Tail gas from the SRU
goes to the subsequent TGTU for further
removal of sulfur. The treated gas from
the amine absorber is transferred to the
incinerator, where all remaining sulfur
species are oxidized and then emitted to
atmosphere. Regenerated H2S from the
amine regenerator is recycled to the SRU.
Ultimately, the overall sulfur conversion
efficiency will be more than 99.9%.
The main performance parameters
for a sulfur plant are sulfur conversion
efficiency and sulfur recovery efficiency.
In an environmental view, SO2 emissions
levels can be an important key parameter.
The objective of the Claus process is
the recovery of elemental sulfur from the
input of sulfur compounds (chiefly H2S).
Therefore, the logical performance of capability index is sulfur recovery efficiency.
It is also a suitable index for a number of
other reasons:
* It is a direct measure of process
performance
* It is dependent on all significant
process operating conditions,
both thermodynamic and kinetic
* It is independent of plant size
and feed composition
FIG. 2,

80

RF

CD1
75
Catalytic
region

70

Furnace
region

65
60
55
50
0

200

400

600
800
Temperature, °C

1,000

1,200

1,400

FIG. 3. Claus thermodynamics with sulfur removal.
Hydrocarbon Processing | DECEMBER 2020

31



Hydrocarbon Processing - December 2020

Table of Contents for the Digital Edition of Hydrocarbon Processing - December 2020

Contents
Hydrocarbon Processing - December 2020 - Intro
Hydrocarbon Processing - December 2020 - Cover1
Hydrocarbon Processing - December 2020 - Cover2
Hydrocarbon Processing - December 2020 - Contents
Hydrocarbon Processing - December 2020 - 4
Hydrocarbon Processing - December 2020 - 5
Hydrocarbon Processing - December 2020 - 6
Hydrocarbon Processing - December 2020 - 7
Hydrocarbon Processing - December 2020 - 8
Hydrocarbon Processing - December 2020 - 9
Hydrocarbon Processing - December 2020 - 10
Hydrocarbon Processing - December 2020 - 11
Hydrocarbon Processing - December 2020 - 12
Hydrocarbon Processing - December 2020 - 13
Hydrocarbon Processing - December 2020 - 14
Hydrocarbon Processing - December 2020 - 15
Hydrocarbon Processing - December 2020 - 16
Hydrocarbon Processing - December 2020 - 17
Hydrocarbon Processing - December 2020 - 18
Hydrocarbon Processing - December 2020 - 19
Hydrocarbon Processing - December 2020 - 20
Hydrocarbon Processing - December 2020 - 21
Hydrocarbon Processing - December 2020 - 22
Hydrocarbon Processing - December 2020 - 23
Hydrocarbon Processing - December 2020 - 24
Hydrocarbon Processing - December 2020 - 25
Hydrocarbon Processing - December 2020 - 26
Hydrocarbon Processing - December 2020 - 27
Hydrocarbon Processing - December 2020 - 28
Hydrocarbon Processing - December 2020 - 29
Hydrocarbon Processing - December 2020 - 30
Hydrocarbon Processing - December 2020 - 31
Hydrocarbon Processing - December 2020 - 32
Hydrocarbon Processing - December 2020 - 33
Hydrocarbon Processing - December 2020 - 34
Hydrocarbon Processing - December 2020 - 35
Hydrocarbon Processing - December 2020 - 36
Hydrocarbon Processing - December 2020 - 37
Hydrocarbon Processing - December 2020 - 38
Hydrocarbon Processing - December 2020 - 39
Hydrocarbon Processing - December 2020 - 40
Hydrocarbon Processing - December 2020 - 41
Hydrocarbon Processing - December 2020 - 42
Hydrocarbon Processing - December 2020 - 43
Hydrocarbon Processing - December 2020 - 44
Hydrocarbon Processing - December 2020 - 45
Hydrocarbon Processing - December 2020 - 46
Hydrocarbon Processing - December 2020 - 47
Hydrocarbon Processing - December 2020 - 48
Hydrocarbon Processing - December 2020 - 49
Hydrocarbon Processing - December 2020 - 50
Hydrocarbon Processing - December 2020 - 51
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Hydrocarbon Processing - December 2020 - 53
Hydrocarbon Processing - December 2020 - 54
Hydrocarbon Processing - December 2020 - 55
Hydrocarbon Processing - December 2020 - 56
Hydrocarbon Processing - December 2020 - 57
Hydrocarbon Processing - December 2020 - 58
Hydrocarbon Processing - December 2020 - 59
Hydrocarbon Processing - December 2020 - 60
Hydrocarbon Processing - December 2020 - 61
Hydrocarbon Processing - December 2020 - 62
Hydrocarbon Processing - December 2020 - 63
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Hydrocarbon Processing - December 2020 - 65
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Hydrocarbon Processing - December 2020 - 67
Hydrocarbon Processing - December 2020 - 68
Hydrocarbon Processing - December 2020 - 69
Hydrocarbon Processing - December 2020 - 70
Hydrocarbon Processing - December 2020 - 71
Hydrocarbon Processing - December 2020 - 72
Hydrocarbon Processing - December 2020 - 73
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Hydrocarbon Processing - December 2020 - 76
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Hydrocarbon Processing - December 2020 - 78
Hydrocarbon Processing - December 2020 - 79
Hydrocarbon Processing - December 2020 - 80
Hydrocarbon Processing - December 2020 - 80A
Hydrocarbon Processing - December 2020 - 80B
Hydrocarbon Processing - December 2020 - 81
Hydrocarbon Processing - December 2020 - 82
Hydrocarbon Processing - December 2020 - Cover3
Hydrocarbon Processing - December 2020 - Cover4
Hydrocarbon Processing - December 2020 - GP-1
Hydrocarbon Processing - December 2020 - GP-2
Hydrocarbon Processing - December 2020 - GP-3
Hydrocarbon Processing - December 2020 - GP-4
Hydrocarbon Processing - December 2020 - GP-5
Hydrocarbon Processing - December 2020 - GP-6
Hydrocarbon Processing - December 2020 - GP-7
Hydrocarbon Processing - December 2020 - GP-8
Hydrocarbon Processing - December 2020 - GP-9
Hydrocarbon Processing - December 2020 - GP-10
Hydrocarbon Processing - December 2020 - GP-11
Hydrocarbon Processing - December 2020 - GP-12
Hydrocarbon Processing - December 2020 - GP-13
Hydrocarbon Processing - December 2020 - GP-14
Hydrocarbon Processing - December 2020 - GP-15
Hydrocarbon Processing - December 2020 - GP-16
Hydrocarbon Processing - December 2020 - GP-17
Hydrocarbon Processing - December 2020 - GP-18
Hydrocarbon Processing - December 2020 - GP-19
Hydrocarbon Processing - December 2020 - GP-20
Hydrocarbon Processing - December 2020 - GP-21
Hydrocarbon Processing - December 2020 - GP-22
Hydrocarbon Processing - December 2020 - GP-23
Hydrocarbon Processing - December 2020 - GP-24
Hydrocarbon Processing - December 2020 - GP-25
Hydrocarbon Processing - December 2020 - GP-26
Hydrocarbon Processing - December 2020 - GP-27
Hydrocarbon Processing - December 2020 - GP-28
Hydrocarbon Processing - December 2020 - GP-29
Hydrocarbon Processing - December 2020 - GP-30
Hydrocarbon Processing - December 2020 - GP-31
Hydrocarbon Processing - December 2020 - GP-32
Hydrocarbon Processing - December 2020 - GP-33
Hydrocarbon Processing - December 2020 - GP-34
Hydrocarbon Processing - December 2020 - GP-35
Hydrocarbon Processing - December 2020 - GP-36
Hydrocarbon Processing - December 2020 - GP-37
Hydrocarbon Processing - December 2020 - GP-38
Hydrocarbon Processing - December 2020 - GP-39
Hydrocarbon Processing - December 2020 - GP-40
Hydrocarbon Processing - December 2020 - GP-41
Hydrocarbon Processing - December 2020 - GP-42
Hydrocarbon Processing - December 2020 - GP-43
Hydrocarbon Processing - December 2020 - GP-44
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