An excellent question, M. Dellil! Although you still need to supply enough thermal energy to overcome the activation energy threshold for the reaction, Note that the Claus reaction is maximized at lower temperatures, meaning that the lower you go, the more conversion you get. You just don’t want to go below the sulphur dewpoint unless your bed is specifically designed for that; sulphur dewpoints are usually determined by simulations. However, most plants dedicate their first converter bed to hydrolyzing COS and CS2, which if left alone slip right through the Claus unit. This hydrolysis requires a much higher inlet bed temperature. Many plants find their overall recovery efficiency is higher when they assign the first bed to go after these “renegade” sulphur atoms, rather than focus on maximizing Claus conversion. In summary, the first Claus reactor inlet temperature is chosen to give a suitable catalyst temperature for optimal COS and CS2 conversion. The second and third Claus reactor inlet temperatures are chosen to provide a catalyst temperature marginally above the sulphur dewpoint. - Leah Goettler
Thank you Leah, well explained about the conversion and the recovery. what about the H2S/SO2 analyzer readings in the condenser outlet and its control on trim air control to Rx Furnace. what is the ideal value H2S/SO2 for best conversion to be maintained.
No - fuel gas co-firing won’t help minimize tail gas analyzer fluctuations. These can only be minimized by adding an acid gas analyzer and by proper tuning of the air flow control loops. Fuel gas co-firing is usually only used either to increase flame temperature or to add volume for plants that are at high turndown rates.
What if hydrocarbons enter with acid gas feed, should you increase the reaction furnace temperature in order to deal with the tail gas analyzer from hunting ?
If you have periodic small hydrocarbon concentration changes, then the tail gas H2S:SO2 analyzer will eventually correct for these hydrocarbons. For regular or large acid gas hydrocarbon changes, then it is recommended to add hydrocarbon measurement along with H2S measurement for an acid gas analyzer. The analyzer would constantly adjust the required feed-forward air:acid gas ratio based on the H2S and hydrocarbon contents. The feedback H2S:SO2 analyzer would then have a lot less work to do, and would be better able to keep the tail gas ratio at 2:1.
The dewpoint is defined as the temperature at which the equilibrium vapor pressure equals the partial pressure of the sulphur at the process pressure. As the sulphur partial pressure increases, the temperature at which the first liquid droplet forms will also increase. You can also think of it in the reverse, in the example of a water knockout drum. The colder you go, the more water condenses and the partial pressure of water in the process gas decreases. It’s the same principle.
Hi Umang! The tail gas analyzer is actually one of the most critical pieces of running an SRU effectively. The feedback control is what keeps the plant stable. All sulphur plant designs include a tail gas analyzer, and if it is out of operation then we recommend that it be repaired and returned to service as soon as possible. If you do have to run the sulphur plant for a brief period without a working tail gas analyzer, then we have the following recommendations: - The control system should have a feed forward air:acid gas flow ratio and (if you are at a refinery) a feed-forward air:sour water stripper gas ratio. These should be used to provide the “best guess” air flow rates until the tail gas analyzer is fixed. - If you only have a modified-Claus sulphur plant (no tail gas unit), then you can recognize that the best overall efficiency (lowest overall emissions) occur when you have the optimal amount of air to the sulphur plant reaction furnace. If your emissions go up / efficiency goes down then you can try adding or subtracting air from the reaction furnace (usually 1% of flow at a time) to see if this improves the efficiency. Any reaction furnace air flow change that improves your efficiency is the right thing to do. - If you have an amine-based tail gas unit, then you can adjust the air flow to the sulphur plant reaction furnace until you get a “normal” temperature rise across the tail gas unit catalyst bed. The temperature rise across the bed is mostly a function of the SO2 concentration in the sulphur plant tail gas; as the SO2 goes up or down, so does the tail gas unit catalyst temperature rise. If you know your historical “normal” temperature rise across this reactor, then you can adjust the sulphur plant air flow (again maybe 1% changes at a time) to make more or less SO2 in the tail gas until the reactor temperature rise reaches this “normal” value. Please let us know if you have any further questions!
Could you please talk about the liquid sulphur volume expansion and associated line rupture?
Hello. How can i calculate amount of catalysts in reactors, to make process go work good?
Thanks a lot, what is the effect of reactors inlet temperature on sulfur recovery?
An excellent question, M. Dellil! Although you still need to supply enough thermal energy to overcome the activation energy threshold for the reaction, Note that the Claus reaction is maximized at lower temperatures, meaning that the lower you go, the more conversion you get. You just don’t want to go below the sulphur dewpoint unless your bed is specifically designed for that; sulphur dewpoints are usually determined by simulations. However, most plants dedicate their first converter bed to hydrolyzing COS and CS2, which if left alone slip right through the Claus unit. This hydrolysis requires a much higher inlet bed temperature. Many plants find their overall recovery efficiency is higher when they assign the first bed to go after these “renegade” sulphur atoms, rather than focus on maximizing Claus conversion. In summary, the first Claus reactor inlet temperature is chosen to give a suitable catalyst temperature for optimal COS and CS2 conversion. The second and third Claus reactor inlet temperatures are chosen to provide a catalyst temperature marginally above the sulphur dewpoint.
- Leah Goettler
how about installing electrical coils in the demister instead of steam coils ?
Thank you Leah, well explained about the conversion and the recovery. what about the H2S/SO2 analyzer readings in the condenser outlet and its control on trim air control to Rx Furnace. what is the ideal value H2S/SO2 for best conversion to be maintained.
2:1
@@surajkanojia3583 4:1 is better.
how about using a nitrogen heater on the demister pad ?
Does fuel gas firing help to minimize the tail gas analyzer fluctuations when high CO2/H2S case 60/35 mole %
No - fuel gas co-firing won’t help minimize tail gas analyzer fluctuations. These can only be minimized by adding an acid gas analyzer and by proper tuning of the air flow control loops. Fuel gas co-firing is usually only used either to increase flame temperature or to add volume for plants that are at high turndown rates.
What if hydrocarbons enter with acid gas feed, should you increase the reaction furnace temperature in order to deal with the tail gas analyzer from hunting ?
If you have periodic small hydrocarbon concentration changes, then the tail gas H2S:SO2 analyzer will eventually correct for these hydrocarbons. For regular or large acid gas hydrocarbon changes, then it is recommended to add hydrocarbon measurement along with H2S measurement for an acid gas analyzer. The analyzer would constantly adjust the required feed-forward air:acid gas ratio based on the H2S and hydrocarbon contents. The feedback H2S:SO2 analyzer would then have a lot less work to do, and would be better able to keep the tail gas ratio at 2:1.
how about installing a gas liquid coalescer to minimize entrainment
how can we minimize Sulphur fog which is a problem in operating at low loads. After every shutdown, the RGG burner gets choked.
Why dew point of sulfur increases with increase in sulfur partial pressure?
The dewpoint is defined as the temperature at which the equilibrium vapor pressure equals the partial pressure of the sulphur at the process pressure. As the sulphur partial pressure increases, the temperature at which the first liquid droplet forms will also increase. You can also think of it in the reverse, in the example of a water knockout drum. The colder you go, the more water condenses and the partial pressure of water in the process gas decreases. It’s the same principle.
How to run sulphur plant without tail gas analyzer?
Hi Umang! The tail gas analyzer is actually one of the most critical pieces of running an SRU effectively. The feedback control is what keeps the plant stable. All sulphur plant designs include a tail gas analyzer, and if it is out of operation then we recommend that it be repaired and returned to service as soon as possible.
If you do have to run the sulphur plant for a brief period without a working tail gas analyzer, then we have the following recommendations:
- The control system should have a feed forward air:acid gas flow ratio and (if you are at a refinery) a feed-forward air:sour water stripper gas ratio. These should be used to provide the “best guess” air flow rates until the tail gas analyzer is fixed.
- If you only have a modified-Claus sulphur plant (no tail gas unit), then you can recognize that the best overall efficiency (lowest overall emissions) occur when you have the optimal amount of air to the sulphur plant reaction furnace. If your emissions go up / efficiency goes down then you can try adding or subtracting air from the reaction furnace (usually 1% of flow at a time) to see if this improves the efficiency. Any reaction furnace air flow change that improves your efficiency is the right thing to do.
- If you have an amine-based tail gas unit, then you can adjust the air flow to the sulphur plant reaction furnace until you get a “normal” temperature rise across the tail gas unit catalyst bed. The temperature rise across the bed is mostly a function of the SO2 concentration in the sulphur plant tail gas; as the SO2 goes up or down, so does the tail gas unit catalyst temperature rise. If you know your historical “normal” temperature rise across this reactor, then you can adjust the sulphur plant air flow (again maybe 1% changes at a time) to make more or less SO2 in the tail gas until the reactor temperature rise reaches this “normal” value.
Please let us know if you have any further questions!