PTQ Q1 2025 Issue

LP steam

Acid gas preheater

Combustion control

AAG KOD

AAG

LP steam

Cond

COPE ejector

To 1st preheater

SWS AG KOD

SWS AG

Waste heat boiler

Claus furnace

Burner

Liquid Sulphur

1st s ulphur condenser

Air

Figure 2 Simplified block flow diagram for Case 1

COPEII operation enhancements The amine acid feed gas (AAG) and sour water acid gas first pass through respective, existing knock-out drums to remove entrained liquid droplets before mixing. These gases are water-saturated and, when mixed, create the potential for condensation and salt formation. An AAG gas preheater is added in the design before the mixing point to preheat the AAG to achieve an outlet temperature of 180°C, using MP steam supplied from Claus waste heat boiler (WHB), avoiding condensation in the mixed stream and preventing potential condensation of elemental sul- phur when the COPEII recycle gas mixes with the feed acid gas. After mixing, the three combined gas streams are fed to the new, high-intensity COPEII main burner. The main burner ensures high-intensity mixing, a suf- ficiently high combustion temperature, and adequate residence time. The total O₂ required for combustion is sup- plied by the combination of pure oxygen and air from the combustion air blower. For this design, the normal oxygen enrichment level at design sulphur capacity is about 55%. COPEII operation allows for higher levels of oxygen enrichment without exceeding the temperature limits of the standard refractory linings by recycling process gas from the outlet of the first sulphur condenser to the COPE burner. The recycle gas flow rate is controlled to moderate the reaction furnace operating temperature. The expected temperature achieved in the reaction furnace is about 1,450°C during oxygen enrichment operation in this design. The recycle gas is routed to the burner using a new steam-driven COPE ejector. The recycle gas in COPEII operation is relatively cool and mostly inert. It acts as a heat sink that absorbs the required amount of the combustion heat release to maintain the reaction furnace temperature within design limits during oxygen-enriched operations. The COPE ejector motive steam is taken from the steam produced by the WHB downstream of the superheat coil. The balance of the first sulphur condenser outlet gas is processed normally through the catalytic portion of the SRU train in a similar fashion to the existing SRU train. No

further modification of the existing design is needed typi- cally in the rest of the unit. A new first sulphur condenser is required in this case to provide the necessary duty for processing 225 MTPD of sulphur capacity and to manage the higher flow rate of the process gas, which now includes the COPEII recycle gas. Additionally, a few modifications in the existing WHB are needed. The expected outlet temperature during oxygen enrichment is higher than the original outlet design tem- perature. The proposed modification is to add a new layer of castable refractory in the WHB outlet channel. At the same time, the piping from the WHB to the first sulphur condenser is replaced with stainless steel piping. Condensed sulphur from all sulphur condensers gravity drains through the existing sulphur seal pots and to the sul- phur pit. A new pit vent ejector, which sends the vent gases from the sulphur pit to the existing incinerator, is needed. The new ejector will be designed for the new unit design rate of elemental sulphur and higher amounts of devolving gases. Case study 1 summary For high levels of oxygen enrichment, the COPEII process offers several advantages. The key features of the process include: u Proven technology with demonstrated operation of high levels of oxygen enrichment. v Simple process equipment layout and straightforward process control. w High level of reliability and flexibility. The process pro- vides the benefit of online recycling for normal high-level oxygen-enrichment operation and irregular operations such as start-ups, shutdowns, and feed disturbance rejection. Case study 2: Processing lean gas The second case study looks at a SRU, which needed to process appreciable amounts of lean acid gas (LAG) after a refinery upgrade project. The SRU is a traditional unit designed for the typical AAG and the sour water stripper

PTQ Q1 2025