Optimising Sulphur Recovery Rate versus Carbon Dioxide Footprint Figure 8: Thermoplate Exchanger in Shell
Since thermoplate heat exchangers can be put together in modules, one can realise virtually any diameter and height of the heat exchanger. This in turn facilitates the adjustment of the heat exchanger according to the optimal operating conditions of the catalyst, so that the process conditions are best suited with respect to linear gas velocity, space velocity, pressure drop and temperature.
Figure 9: Sketch of Four-way Valve 2
The Switch-over Procedure in SMARTSULF Once the SubDewPoint reactor has been fully charged with sulphur it has to be switched to the position of the hot reactor for regeneration. The switchover is started fully automatically after a pre-determined flow of gas to the SRU has been reached. The complete procedure is then controlled and executed by the reactor sequence control program. No operator action is required in any of the steps.
1 3
In SMARTSULF the switchover of the process gas is done by two four-way valves (see Figure 9) and in that respect again takes an approach different from the former technology. The valves are as simple as possible, containing only the cock which separates the gas streams. That makes these valves robust, easy to maintain and to operate. Only one drive is required to switch the two valves, which are connected
In general, processes that 4 A patent is pending for the valves.
reduce CO2 emissions also save fuel, thus reducing operating costs.
the seam welds of the thermoplates are gap-free. After welding, the plates are expanded by injecting high-pressure liquid between the metal sheets. This opens the channels shown schematically in Figure 4.
Usually, the welding points form rectangles. By the expansion, results the typical form of a stitch cushion, as can be seen in Figure 6. Several thermoplates aligned in parallel form a thermoplate stack (see Figure 7), which is then incorporated in a shell (see Figure 8).
More than a thousand of such thermoplate heat exchangers have been built and installed in plants worldwide. The services included extremely
difficult ones, such as condensers for COCl2, which is both highly toxic and corrosive when in contact with water. The sizes delivered reached up to several thousand m2 per unit. This type of heat exchanger is certainly a mature and tested technology.
Thermoplate heat exchangers are compact, lightweight, low-pressure drop and thermally efficient. These features make these fully welded plate heat exchangers suitable for sulphur recovery converters. The thermoplates are self-contained and pass no forces onto the next adjacent thermoplate. Therefore, catalyst can be inserted between the plates without mechanical stress on the particles. The thermoplate heat exchangers have a higher heat transfer rate in comparison to tubular heat exchangers, though the difference is not very large.
1.
Heisel M, Rameshni M, Minimise carbon footprint from Claus tailgas units, Hydrocarbon Processing, 2011;90:(2):71.
44
by a drive shaft. This also ensures that all ways are switched at exactly the same time.
For switchover, the blocking element is rotated by 90°. In the position shown in Figure 9, the gas streams 1 plus 4 are connected and 2 plus 3. After switchover, the gas streams 1 plus 2 are connected and 3 plus 4.
Conclusions
With respect to CO2 emission, most tail gas treatment processes were not optimised when they were introduced. At that time, CO2 was not seen as an environmental issue. Presently, it is. The tailgas
treatment processes considered generate very different CO2 emissions to withhold SO2. While SMARTSULF produces surplus energy and thus a CO2 credit of ca 70 kg/h per kg of SO2 emitted, SCOT consumes energy and generates emissions of up to ca 45 kg
CO2 per kg SO2 emitted. The CO2 emissions of SUPERCLAUS and SULFREEN are inbetween SCOT and SMARTSULF, with the
SO2 emissions slightly higher. In general, processes that reduce CO2 emissions also save fuel, thus reducing operating costs. Often, however, CapEx justification for reduced OpEx is
marginal. Increasing concern over CO2 emissions will shift those economics. This article compares Claus tail gas treating options from
that perspective. n
2. Hydrocarbon Processing, Gas Processing Handbook 2009, Houston/TX, 2009.
HYDROCARBON WORLD – VOLUME 6 ISSUE 2
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