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Modular sulphur plant has high recovery rate (TIA)

The early production facilities (EPF) for Kuwait’s Jurassic gas field involved the treatment of fairly sour feed gas streams with, for each EPF phase, a sulphur production capacity of 2x100 t/d.

Pauline Weber
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Article Summary
Spetco, as build-
operate-transfer (BOT) operator of such a phase, selected Prosernat with its SmartSulf technology for the delivery of the equipment, completely modularised for easy and fast track site installation. SmartSulf is a compact, low cost SRU technology to achieve high sulphur recoveries with the minimum number of equipment items.

Local environmental regulations required for this kind of SRU an overall sulphur recovery of at least 99.4%. This level can be guaranteed with the process without the need for installation of any downstream tail gas treatment process. The concept of SmartSulf is based on the use of a Claus unit with two catalytic stages, differentiated from conventional Claus by the fact that the catalytic reactors are operated under isothermal conditions and the second catalytic stage is operated under sub-dew point conditions in order to achieve much higher sulphur yields than in a conventional Claus process. This concept is illustrated in Figure 1.

 The acid gas is fed into a thermal section, similar to what is found in a conventional Claus design. After sulphur condensation and reheating, the tail gas from the thermal stage is fed to the first catalytic stage. Both catalytic reactors are equipped with an internal heat exchanger in order to control the temperature in the reactors. The heat of the Claus catalytic reaction is removed by circulating water counter-currently in the heat exchanger inside the reactor. The first catalytic reactor is operated at temperatures above sulphur sub-dew point. However, by controlling the temperature at the outlet of the first reactor, higher catalytic conversions are already being achieved compared with a conventional first stage Claus reactor. After sulphur condensation, the gas from the first reactor is then fed to the second catalytic reactor. This reactor is operated at temperatures below sulphur sub-dew point, thus achieving much higher conversions. Because the temperature is controlled until the outlet of the reactor, the conversions achieved are in fact even higher than those obtained in conventional sub-dew point tail gas treatment processes. For a typical acid gas in a refinery, overall sulphur recoveries are above 99.5%. Tail gas from the SmartSulf unit can therefore in most cases be sent directly to the incinerator without the need for any downstream tail gas treatment unit. This is the case for the early production facilities in Kuwait.

Once the second catalytic reactor is loaded with liquid sulphur, a couple of automatic four-way valves are rotated so that the first reactor originally operated in ‘hot mode’ is now operated in sub-dew point mode. The second catalytic reactor is now operated in ‘hot mode’ and therefore regenerated by vaporising all the accumulated sulphur which is then condensed in the external sulphur condenser.

The process is a breakthrough in sulphur recovery technology, enabling high sulphur recovery without the need for a tail gas treatment unit. To summarise, the key reasons for selecting Prosernat and its SmartSulf process for this EPF project have been:
• The capacity of the process to meet local environmental regulations
• The compactness of the process with a minimum amount of equipment items compared to other technologies
• The low cost of this technology compared to alternative Claus plus tail gas treatment options
• The capacity of Prosernat to supply the unit fully modularised within a tight time frame
• The capacity of Prosernat to support its customer for such a BOT project through financing and continuous operational support.

Construction of the unit
Each of the SmartSulf 100 t/d trains will be delivered in the following modularised form (see Figure 2):
• One module for feed gas pretreatment (knockout drum and air preheater)
• Three modules for the whole catalytic section (including a sulphur condenser and four-way valves)
• One package for the thermal section with reaction furnace, burner and waste heat boilers with base 
plates and access platform supplied loose for site installation
• One incinerator conditioning skid (for tail gas and combustion air)
• One loose incinerator and burner.

Modularisation is an answer to many specific challenges faced by the oil and gas industry, such as harsh site conditions, size limitations at site or for transport as well as tight project schedule. Prosernat has experience with more than 400 modular units being successfully applied to sulphur recovery and installed worldwide.

SmartSulf technology, with its limited number of equipment items, is a technology of choice when fast track modular delivery is required for a sulphur recovery plant with high sulphur recoveries up to 99.5%.

This short case study originally appeared in PTQ's Technology In Action feature - Q2 2017 issue.

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