Step 1:

This is the beginning of sequence A-B. The process gas entering the CBA section flows to the “A” reactor, and the process gas leaving the CBA sulfur condenser flows to the “B” reactor. The “A” is in the “lead” position and the “B” reactor is in the “lag” (final) position. The “A” reactor is operating in adsorption mode with the HP steam supply to the regen heaters blocked so that the feed to the. “A” reactor is not being heated.

Step 2:

When the adsorb cycle timer times out (set at 20 hours), the “A” reactor begins switching to heating mode by opening valve KV-4659 in the HP steam supply to slowly pressurize the shells of the regen heaters.

Step 3:

When the Pressurizing Timer times out (initially set at 15 minutes), the main HP steam valve, KV-4658, is opened and temperatura controller TIC-4642 is placed in “automatic”. The TIC-4642 setpoint is ramped up to 343 °C [650 °C] over a period of 5 minutes to switch the “A” reactor to heating mode.

Step 4:

When the Heating cycle timer times out (set at 10 hours), the “A” reactor begins switching to cooling mode by closing the two steam block valves, KV-4659. Temperature controller TIC-4642 is placed in “manual” and its output is set to 0% to close control valve TV-4642, to prevent wasting HP steam if KV-4658 or KV-4659 fails to close.

Step 5:

With the HP steam supply now blocked-in, temperatura controller TIC-4642 is placed in “manual” and its output is set to 50% to open control valve TV- 4642 and de-pressure the shells of the regen heaters to the LP steam header.

Step 6:

When the De-pressurizing Timer times out (initially set at 5 minutes), temperatura controller TIC-4642 is placed in “manual” and its output is set to 0%. This closes control valve TV-4642 so that the pressure in the shells of the regen heaters will continue to fall as the heaters cool to the temperatura of the incoming process gas. The “A” reactor is now in cooling mode.

Step 7:

When the overall cycle timer times out (set at 36 hours), the “lag” inlet and outlet valves for the “A” reactor, KV-4669A and KV-4671A, and the “lead” inlet and outlet valves for the “B” reactor, KV-4668B and KV-4670B, are opened. The process gas from the regen heaters will now flow in parallel through both the “A” and the “B” reactors, then out to the incinerator. The flowpath through the CBA sulfur condenser will be momentarily stagnant.