RUNNING SRUs AT LOW THROUGHPUT EFFECTS & CONSIDERATIONS
Middle East Sulphur 2017
Abu Dhabi, UAE
February 14, 2017
GASCO: Khaleelullah Nizamuddin Syed
UniverSUL Consulting: Abdulkader Al Kasem
Cicerone & Associates, LLC: Doug Cicerone
AGENDA
Introduction
Effects of running
SRUs at Habshan plant
˃
˃
˃
˃
Feed control
Reaction furnace
Reaction furnace skin temperature
Incinerator performance
Effects of running SRUs
at low throughput
Upstream
considerations
GASCO HABSHAN SRUs
GASCO HABSHAN SRUs
Habshan-0
Habshan-1
Habshan-2
Habshan-HGCE
Habshan-5
50
51
52
53
54
57
58
59
152
153
550
551
552
553
97.0
Acid gas
3-stage Claus
Acid gas
1-stage Claus with
2 parallel CBA beds
99.0
Acid gas
1-stage Claus with
2 parallel CBA beds
99.0
Enriched acid gas with
natural gas co-firing
3-stage Claus with
1-stage SUPERCLAUS®
99.9
2-stage Claus with amineAcid gas with natural gas cobased TGTU
firing
(FLEXSORB®)
98.8
99.0
TYPICAL CBA UNIT
T: 245 C
T: 950 C
WHB
Fuel Gas
Incinerator
Reheater
RF
Acid Gas
T: 143 C
Converter
T: 128 C
T: 600 C
Air
Air
T: 258 C
T: 155 C
Condenser
Sulfur
T: 143 C
Condenser
Condenser
Sulfur
T: 127 C
T: 151 C
Condenser
Sulfur
T: 130 C
T: 325 C
T: 171 C
T: 315C
Stack
Condenser
Sulfur
Sulfur
EFFECTS OF RUNNING SRUs
AT LOW THROUGHPUT
COMBUSTION AIR BLOWERS
ADVANTAGES
˃ None
DISADVANTAGES
˃ because centrifugal blowers
need a minimum air flow to
prevent surge:
 Excess air is blown-off at
low throughput  wasted
energy (electricity or steam)
 Inlet guide vanes can help
reduce this inefficiency
REACTION FURNACE
ADVANTAGES
Residence time increases as throughput decreases  helps increase sulfur
conversion & improves destruction of BTEX
REACTION FURNACE
DISADVANTAGES
˃ Controlling the air and acid gas flows to RF can be difficult:
 Manual control can help to stabilize flow
 Split range control can be used to get 10% throughput or below
˃ Some reaction furnace burners won’t turn down below 30%:
 Can cause damage as the flame backs up against the burner face
> Reaction Furnace operating temperatures decrease (particularly in
smaller furnaces)
> Skin temperatures decrease as operating temperature decreases:
 Possibility for low temperature acidic corrosion
CONDENSERS & RUNDOWN LINES
ADVANTAGES
DISADVANTAGES
˃ Sulphur fogging may occur at low
gas velocities
˃ None
˃ Plugging may occur at low sulfur
flow rates (catalyst and/or
refractory dust can accumulate
since the liquid velocities are low)
˃ Rundown lines are sensitive to
small disturbances in the steam
jacket heat transfer (inadequate
insulation, cold weather, etc.)
CATALYTIC CONVERTERS
ADVANTAGES
˃ Lower space velocities can
increase Sulphur conversion
˃ CBA cycle times can be
increased  Overall SRE will
increase
DISADVANTAGES
˃ Channeling of gas flow through
the catalyst can reduce Sulphur
conversion
˃ Heat losses to ambient become
more significant:
 Possible corrosion issues
(particularly at nozzles and
manways)
INCINERATOR
ADVANTAGES
DISADVANTAGES
˃ Burner controls (similar to reaction
furnace)
˃ Residence time increases
 increase the destruction
of all reduced sulfur species
 Controlling stack oxygen
content at natural draft
incinerators can be difficult 
excess fuel gas usage
˃ Damage to the burner (similar to
reaction furnace)
˃ Stack temperatures can get cold,
particularly if there is a WHB
 Potential stack corrosion &
inadequate dispersion of the
flue gases
HABSHAN CBA UNITS –
OPERATION AT TURNDOWN
FEED CONTROL
REACTION FURNACE
TEMPERATURE
ºC
RF Temp
1160
1140
1120
1100
1080
1060
1040
1020
1000
980
10
15
20
25
Feed Flow Knm3/h
30
35
H2S concentration (mole %)
Air Flow Knm3/h
REACTION FURNACE
60
455
405
355
305
255
205
155
105
55
5
50
40
30
20
10
0
10
15
20
25
Feed Flow Knm3/h
Air Flow H2S Conc FG to RF
30
35
REACTION FURNACE
SKIN TEMPERATURE
190
180
RF Skin Temp ºC
170
160
150
140
130
120
110
100
10
15
20
25
Feed Flow Knm3/h
30
35
40
Capacity Ratio = Actual(Press/Flow^2) /
Design(Press/Flow^2)
CONDENSERS
10
9
8
7
6
5
4
3
2
1
0
120
20
18
100
16
14
80
12
60
10
8
40
6
4
20
2
0
0
10
15
20
25
Feed Flow Knm3/h
Incin FG
O2 in Stack
30
35
Mole % O2 in stack
Nm3/h FG to Incini / Knm3/h AG Feed
INCINERATOR
UPSTREAM
CONSIDERATIONS
FEED STREAM PREHEAT
> All Habshan SRUs are equipped with air/acid gas preheaters
> Most preheaters in Habshan are indirect type (HP steam)
> Maximum achievable process temperature is ~225 to 235 oC
FEED STREAM PREHEAT
RF outlet temperature
1060
1040
1020
1000
980
960
940
50
100
150
200
250
CO-FIRING WITH FUEL GAS
> Fuel gas can be utilized to increase RF temperature
> Effective, but there are several disadvantages:
 CS2 production in the furnace is roughly proportional to the amount of
fuel gas added
 Recovery would suffer unless nearly all CS2 is hydrolyzed in the first
converter
 Potential for soot formation?
 Residence time in RF is reduced (but less of a concern at turndown)
In GASCO Habshan SRUs, fuel gas co-firing is used whenever acid gas
feed flow is lower than ~40% of the design capacity.
CO-FIRING WITH FUEL GAS
ºC
RF temperature
1140
1120
1100
1080
1060
1040
1020
0
1
2
3
4
5
6
Fuel gas flow (% of AG flow)
MOTHBALLING SRUs
> The oldest SRUs at Habshan were recently
mothballed, with the following objectives:
 Maximize feed flow to running SRUs
 Reduce operational costs & emissions
ACID GAS ENRICHMENT
> The purpose is to increase H2S content
of acid gas from AGRU
> The most common method is using a
separate absorber, with a selective
solvent, downstream of AGRU absorber
> Acid gas enrichment improves flame
stability, increases RF temperature and
improves BTEX destruction
Effect of acid gas quality on
furnace temperature
1080
1060
1040
1020
1000
980
H2S concentration mole%
In GASCO Habshan, there is only one aged unit, which employs MDEA. However,
this unit is not upstream of the CBA SRUs.
OXYGEN ENRICHMENT
> Oxygen enrichment is well known for SRU capacity enhancement – removes
N2 entering with combustion air
> Using oxygen enrichment can help when running SRU at low throughput by
improving reaction furnace performance
> this will lead to reduced mass flow which may make the situation worse if
burner has low turndown ratio
> increase the probability of channeling in converters and lower gas velocity in
condenser tubes
None of the Habshan SRUs are designed with oxygen enrichment.
CONCLUSIONS
> There are advantages and disadvantages to running SRUs at turndown – the
majority of the effects are disadvantages.
> Sometimes these effects are misleading - understanding the effects will help
operators identify the main causes of unstable conditions and will help in
energy conservation.
> Managing acid gas allocation among many SRUs (as in the 6 BSFCD
Habshan gas plant) is an important factor.
> Run above feed flow value that can effect SRU a lot in terms of smooth
operation, energy efficiency and environmental impact.
Thank You!