Optimising Sulphur Recovery Rate versus Carbon Dioxide Footprint Figure 4: Principle of a Thermoplate Heat Exchanger Figure 5: Point-welding Thermoplates
Blue = flow of cooling medium, e.g. boiler feed water; red = flow of reaction gas.
2. Closed loop steam systems with air coolers to condense the steam raised are preferably used for cooling each of the two reactors. This system is very similar to the coolers of car engines.
3. The two switchover valves required in the process are reliable four-way valves with a rotating cock. Patent for these valves is pending.
Thermoplates for Internally Cooled Catalytic Reactors Internally cooled catalytic reactors have proved themselves in many applications. They are applied primarily for selective reactions, where a rigorous temperature control is required, or in reactions where the chemical equilibrium is strongly temperature-dependent. The Claus reaction for sulphur recovery is of this second kind. So far, mostly tubular heat exchangers were used for reactor cooling, mostly with the catalyst in the tubes. In a few cases also, spiral wound tubular heat exchangers were applied, with the tubes submerged in the catalyst. However, these types of reactors had a number of features which are disadvantageous. Primarily, often the heat exchangers’ buildable geometry forced conditions on the catalytic reactions that were not optimal. For example, the straight tube reactors had to be built slim and high in order not to have too high a thermal stress on the tube sheets. That means necessarily high pressure drop, high linear gas velocity and mechanical stress on the lower catalyst particles. The spiral wound exchangers avoid these disadvantages to some degree. But they require many manufacturing steps and a high level of skill and therefore typically are rather expensive. All these features of tubular reactors are rather unfavourable for sulphur recovery plants.
The new generation of catalytic reactors in SMARTSULF applies thermoplate heat exchangers. They avoid all the disadvantages of the tubular reactors named above.
The catalyst is embedded between the thermoplates, while boiler feed water as the cooling medium flows within the thermoplates. Several thermoplates are combined to form the total heat exchanger surface required. The basic element of the heat exchangers is the thermoplate. The principle is shown in Figure 4.
A thermoplate consists of two equally thick metal sheets that are combined by point welding (see Figure 5 and Figure 6). At their
HYDROCARBON WORLD – VOLUME 6 ISSUE 2
edges these sheets are welded together by a resistance roller seam. These welding steps are done by robots that facilitate production of a lot of exchanger surface at low cost. Both the point welds and
43 Figure 6: Thermoplate
Figure 7: Thermoplates with Header
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