To other plants
FC
SWS AG KOD
3
SWS AG
Preheater
LP steam
AAG
1
FC
AAG KOD
Cond
Claus burner
Claus furnace
To other plants
2
TGTU KOD
Recycle
FC
FC
To other plants
4
LAG KOD
FC
LAG
To other plants
O
Figure 3 Simplified block flow diagram for Case 2
acid gas from the upstream ARU and SWS units. The unit has a capacity of 150 MTPD of elemental sulphur production. The refinery has multiple Claus units, each with a dif - ferent capacity and design. All the individual Claus sec - tions were designed to operate with a common tail gas treatment unit (TGTU), with the TGTU recycle gas shared across all of the Claus plants. The feed gas streams were also shared between the multiple Claus plants. After the refinery upgrade project, a stream of lean sour gas will also be processed in the existing sulphur block. A single Claus unit was chosen to process this additional new LAG stream. Figure 3 presents the configuration of the unit, whereby the new feed steam of LAG is introduced in the unit. Like before, the items marked red are the new equipment or installations implemented as part of the revamp. Table 3 lists the feed gas flow rates and compositions for the pre- and post-revamp conditions. The base case data for 150 MTPD sulphur production corresponds to the con- ditions for which the unit had been designed. In general, the unit operated with lower normal flow rates of AAG. The major impact of processing lean feed gas in the exist - ing Claus furnace is that it reduces the reaction tempera - ture due to the presence of CO₂ in the LAG. In this case, the amount of LAG is considerable, leading to high amounts of CO₂ in the combined feed stream. Hence, the equilibrium Claus furnace temperature is very low. The furnace temper - ature is expected to be around 1,000°C when the mixture of AAG, SWS, and LAG is processed in the existing unit. Since the amount of elemental sulphur generated in the unit stays well below its design capacity, there is no need for any modification to the sulphur handling section, and the only design modification the unit demands is in pro - cessing the lean gas. Design options To manage the lean feed into the unit, design modifications
in the sulphur unit are needed to maintain the furnace tem- perature at an optimum value, above 1,260°C for this oper - ation. To increase the reaction temperature, the following design options were considered: Feed preheat Feed preheat includes heating up the acid gas streams and/ or the air stream supplied to the Claus furnace. Typically, low-pressure (LP) steam is used as a heating medium, but high-pressure (HP) steam (typically the 40-45 barg steam raised from the WHBs in Claus and Incinerator) can also be used under more unique cases. The steam level used The major impact of processing lean feed gas in the existing Claus furnace is that it reduces the reaction temperature due to the presence of CO₂ in the LAG defines the extent to which the streams can be preheated. With LP steam, it is limited to 120-130°C, while with 45 barg steam, preheating up to 230°C can be achieved. Unfortunately, the furnace temperature is only 1,100°C, even using 45 barg steam to preheat both the acid gas and the air streams. Co-firing Another method of increasing the furnace temperature is to implement co-firing of fuel gas on a continuous basis. The combustion of the hydrocarbons helps increase the furnace temperature to acceptable limits. For this unit to achieve a temperature of 1,260°C in the furnace, around 800 kg/h of fuel gas co-firing is required.
63
PTQ Q1 2025
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