Optimising Sulphur Recovery Rate versus Carbon Dioxide Footprint
downstream heat exchanger. This controls the temperature at the outlet of the catalyst bed within a narrow range. The heat exchanger applied is a thermoplate stack with large clearances. The space between the thermoplates is filled with catalyst that is in this way efficiently cooled. As this type of heat exchanger is not yet so well known it will be discussed in more detail below. But first the process needs to be described.
The first converter of a Claus plant is always a compromise between two competing targets: the reaction temperature has to be high
enough for maximum COS and CS2 hydrolysis and as low as possible for a favourable equilibrium of the Claus reaction and thus maximum
The fundamental idea of SMARTSULF is the removal of reaction heat of the Claus reaction directly in the catalyst bed
conversion. The internally cooled reactor can solve this conflict as the top layer of the catalyst remains without cooling. The feed temperature to this section is typically 220 °C to 240 °C and reaction heats it up to approximately 320 °C. That is the temperature required
for COS and CS2 hydrolysis. The second section downstream in the same reactor is cooled and a fixed outlet temperature slightly above the sulphur dewpoint can be reached by evaporating boiler feed water. This combination of an adiabatic and a cooled section in one reactor reaches conversion rates comparable to a two-stage Claus plant.
Downstream of the first reactor follows a sulphur condenser and then a second identical reactor that is operated at a lower temperature. This shifts the chemical equilibrium towards more sulphur formation. The outlet temperature is chosen in the range 100 to 125 °C, i.e. it may be even below the sulphur solidification point.
During the operation below the sulphur dew point the sulphur produced accumulates on the catalyst and deactivates it slowly. Therefore, it has to be regenerated and this is done by switching it into the position of the first reactor. There, at the high temperature of up to approximately 320 °C the sulphur is desorbed and the catalyst thus regenerated. The former first reactor is switched at the same time into the position as the cold second reactor. This procedure is repeated typically once every 24 hours. The treated gas finally is sent to the incinerator and then to stack.
Discussion of SMARTSULF versus more Conventional Sulphur Recovery Processes
Conventional sulphur recovery processes with better than 99.0 % recovery rates have one disadvantage in common: they add tailgas clean-up processes to the Claus process. This makes the whole system rather complex and thus prone to much maintenance, increased downtime, higher capital and operating cost. SMARTSULF takes a
HYDROCARBON WORLD – VOLUME 6 ISSUE 2
Table 1: Conversion of Main Utilities to CO2 Equivalent Thermal energy
Fuel Electric power
1 m³/h of CH4 generates 35,200 kJ/h which is 9.78 kWh/h. With this value can be calculated the CO2 emission of thermal sources, e.g. of steam
1 m³/h of CH4 generates 1 m³/h of CO2
1 kW electric power was assumed to be generated from thermal power with an efficiency of 40 % which
results in 9.78 x 40 % = 3.76 kWh/m³ CO2 or 0.26 m³ CO2/kWh
N2 Instrument air Cooling water Demin water HP steam LP steam Hydrogen
Requires ~ 0.2 kW/m³ which results in 0.2/3.79 = 0.05 m³ CO2
Compression energy to 10 bar plus 10 % for purification: 0.15 kWh/m³ ≡ 0.15/3.79 = 0.06 m³ CO2
Pumping energy up to 20 bar = 0.75 kWh/m³ ≡ 0.2 m³ CO2/m³ CW
Cooling water + 20 % = 0.24 m³ CO2/m³ demin water
Requires thermal energy of 1,685 kJ/kg steam ≡ 1,685/35,200 = 0.05 m³ CO2
Requires thermal energy of 2,000 kJ/kg steam ≡ 2,000/35,200 = 0.06 m³ CO2
From steam reformer, 0.75 m³ CO2/m³ H2 CW = cooling water; HP = high pressure; LP = low pressure.
Table 2: Comparison of the CO2 and SO2 Footprints of Various Claus Tailgas Treatment Processes
Import
Electrical energy Cooling water
H2 Fuel
Instrument air N2
Demin water
HP steam, 45 bar sat LP steam, 4.5 bar sat
Export HP steam, 45 bar sat LP steam, 4.5 bar sat SRR (%)
SO2 emissions (kg/h)
SCOT SUPERCLAUS SULFREEN SMARTSULF CO2 emissions (m3/h)
189 120 80 42
0 0
384 335 3 6
10
3 0 4
115 220 179 13
-721 -562 -109 -377 99.9 98.6 8
117
Total CO2 emissions (kg/h) 349.6 -479.0 HP = high pressure; LP = low pressure; SRR = sulphur recovery rate.
Figure 1: Process Flow Diagram of SMARTSULF SWS gas MP steam
Acid gas plus
E04A V01A
MP BFW MP steam MP steam
140 0 0
323 3 3 4
156 13
-626 -309 99.0 83
-577.5
135 0 0
356 2 0 4
73 13
-864 -195 99.8 13
-932.1
E04B
Fuel
Air
D03A R01A
F01/ E01
D01 P01A V01B D02 E02
Plant air
MP BFW supply
Sulphur
BFW = boiler feed water; D01 = sulphur separator; D02 = sulphur separator; D03 A/B = steam drums; E02 = sulphur condenser; E03 = reheat; F01/E01 = reaction furnace and waste heat boiler; F02 = incinerator; MP = medium pressure; R01A/B = catalytic reactors with internal cooling; SWS = sour water stripper; V01A/B = switch-over valves.
MP BFW P01B
E03
D03B R01B F01
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