Post on 02-Jun-2018
8/11/2019 sunfur recovery process.pdf
1/7
8/11/2019 sunfur recovery process.pdf
2/7
284 Petroleum Refining Technologyand Economics
TREATED
GAS
CW
C
W
ACID
GAS
TOSULFUR
PLAN
T
O
FUEL
SOURGAS
STEA
M
ABSORBER
FLASH
TANK
STILL
FIGURE
13.5
Aminetreatingunit.
8/11/2019 sunfur recovery process.pdf
3/7
285 Petroleum Refining Technologyand Economics
2005U.S.GulfCoastcost,
MM$
10080
60
40
20
108
6
4
2
1
0.8
0.6
0.4
0.2
0.1
2 4 6 8 20 40 60 80 200 400 600 8001 10 100 1000
Amine Solution CirculationU.S. GPM
FIGURE 13.6 Amine gas treating unit investment cost: 2005 U.S. Gulf Coast (see Figure 13.5).
Present refinery practice generally provides for removal of hydrogen sulfide from
refinery gas streams by solvent absorption, as discussed in the previous section. The
acid gas stream recovered from these treating processes contains some carbon dioxide
and minor amounts of hydrocarbons, but in most cases, the hydrogen sulfide content
is over 50%. Therefore, the once-through Claus process is used in most sour crude
refineries to convert the hydrogen sulfide to elemental sulfur.
In the partial combustion (once-through) process, the hydrogen sulfide-rich gas
stream is burned with one third the stoichiometric quantity of air, and the hot gases
are passed over an alumina catalyst to react sulfur dioxide with unburned hydrogensulfide to free sulfur. The reactions are
Burner: 2H2S + 3O2 2H2O + 2SO2
Reactor: 2H2S + SO2 2H2O + 3S (13.4)
8/11/2019 sunfur recovery process.pdf
4/7
286 Petroleum Refining Technologyand Economics
TABLE 13.3
Amine Gas Treating Unit Cost Data
Costs included
1. Conventional, single flow, MEA, or DEA treating system
2. Electric motor-driven pumps
3. Steam-heated reboiler
4. Water-cooled reflux condenser and solution cooler
Costs not included
1. Acid gas disposal
2. Cooling water supply
3. Steam (or hot oil) supply for regenerator reboiler
Utility data
Power,a kWh/gal solution circulated 0.01kWh/M3 2.64
Fuel,b BTU/gal solution circulated 1,000.00MJ/M3 280.00
Cooling water,c gal/gal (m3/m3) solution circulated 4.40Amine makeup,d lb/MMscf inlet gas 2.50
kg/MMNm3 0.04
a Assumes amine pumps driven by electric motors and cooling done with water.b Reboiler heat usually supplied as 60 psig steam.c 30F (17C) rise.d In actual practice, amine solution circulation varies in the range of 0.15 to 0.40 gal
per scf of acid gas (H2S plus CO2) removed. For preliminary estimates, a value of 0.30 gal
of solution circulation per scf of acid gas can be assumed.
Note: See Figure 13.5.
The burner is located in a reaction chamber, which may be either a separate
vessel or a part of the waste heat boiler. The purpose of the reaction chamber is to
allow sufficient time for the combustion reaction to be completed before the gastemperature is reduced in the waste heat boiler.
Ammonia frequently is present in the Claus unit feed streams and must be
completely destroyed in the reaction furnace to avoid plugging of equipment with
ammonium salts. Specially designed burners and combustion zones have been devel-
oped for this purpose [13].
The waste heat boiler removes most of the exothermic reaction heat from gases
by steam generation. Many types of waste heat boilers are in use. Usually they are
arranged so that the gas flows through several tube passes in series with chambers,
or channels, where a portion of the gases many be withdrawn at elevated temper-atures to use for reheating the main gas flow stream prior to the catalytic converters.
Some elemental sulfur is often condensed and removed from the gas in the waste
heat boiler. In some plants, a separate condenser is used after the waste heat boiler.
The gas temperature entering the first catalytic converter is controlled at about 425 to
475F (218 to 246C), which is necessary to maintain the catalyst bed above sulfur
dewpoint in order to avoid saturating the catalyst with sulfur and thereby deactivating
8/11/2019 sunfur recovery process.pdf
5/7
Supporting
Processes
287
REHEAT GAS
GAS 7 -10PSIG
STM
450F
560F
BFW
BFW
350F
400F
440F
BFW
BFW
250F
TAIL
AIR S S S
BURNER WASTE HEAT FIRST FIRST SECOND SECONDAND BOILER CONVERTER CONDENSER CONVERTER CONDENSER
REACTION
NOTE:
BFW = BOILER FEED WATER
FIGURE 13.7 Once-through Claus sulfur process.
8/11/2019 sunfur recovery process.pdf
6/7
Supporting Processes 289
2005U.S.GulfCoastcost,
MM$
100
80
60
40
20
Basis is 93% sulfur recovery by Clausunit from refinery gas.
For 98% recover multiply cost by a factor 2.0
10
8
6
4
2
1
2 4 6 8 20 40 60 80 200 400 600 800
Sulfur Production, Long Tons/Day
FIGURE 13.8 Claus sulfur plant investment cost: 2005 U.S. Gulf Coast (see Table 13.4).
the catalyst. The reaction between hydrogen sulfide and sulfur dioxide in the con-
verter is also exothermic. Gases from the converter are cooled in the following
condenser for removal of most of the elemental sulfur as liquid.
The condenser outlet temperatures must be maintained above about 275F
(135C) to avoid solidifying the sulfur. Two converters and condensers in series are
indicated in Figure 13.7, but most plants have three converters.
Modifications of the once-through process include various reheat methods for
the converter feed temperature control, such as heat exchange with converter outlet
gases, in-line burners, and fired reheaters. Overall recovery is usually not over 96%
and is limited by thermodynamic considerations, as described in the literature [11].
When refineries process crude oils with sulfur contents higher than design, it is
necessary to recover more sulfur in the Claus unit. An economical method for increas-
ing the capacity of Claus units is the substitution of oxygen for a portion of the
combustion air needed in the reaction furnace. This modification can increase the
capacity for sulfur production by 50% or more at a relatively small capital cost [14].
8/11/2019 sunfur recovery process.pdf
7/7
Supporting Processes 289
TABLE 13.4
Claus Sulfur Recovery Unit Cost Data
Costs included
1. Once-through modified Claus unit designed for 94 to 96% recovery
2. Three converters (reactors) with initial charge of catalyst
3. Incinerator and 150-ft (46-m)-tall stack
4. Sulfur receiving tank and loading pump
5. Waste heat boiler
Costs not included
1. Boiler feed water treating
2. Boiler blowdown disposal
3. Solid sulfur storage or reclaiming
4. Sulfur loading facilities (except for loading pump)
5. Supply of power and water
6. Tail gas clean-up process unit
Utility data
Power, kWh/long ton of sulfur 100
kWh/MT 98
Boiler feed water, gal/long ton of sulfur 820
M3/MT 3
Waste heat steam production at 250 psia (1740 kPa)
lb/long ton sulfur 6500
kg/MT 2900
Fuel None
Cooling water None
Note: See Figure 13.8
13.4.2 CARBON-SULFUR COMPOUNDS
Carbonyl sulfide (COS) and carbon disulfide (CS2) have presented problems in many
Claus plant operations due to the fact that they cannot be converted completely to
elemental sulfur and carbon dioxide. These compounds may be formed in the
combustion step by reaction of hydrocarbons and carbon dioxide, as shown below:
CH4 + SO2 COS + H2O + H2
CO2 + H2 COS + H2O
CH4 + 2S2 CS2 + 2H2S (13.5)
Many more complex reactions are possible. These compounds, if unconverted,
represent a loss of recoverable sulfur and an increase in sulfur emission to the
atmosphere. Special alumina catalyst is significantly more effective in converting
both COS and CS2 to elemental sulfur than the conventional bromide catalyst [6].