Case Histories
Boosting hydrogen compressor capacity
A Gulf Coast refinery needed 15% to 20% more hydrogen when their new ULSG unit went on stream. However, the existing four compressor suction drums could not handle the additional throughput without liquid carryover that could eventually damage the compressors.
Amistco engineers performed an in-depth study of the suction drums. Advanced computational fluid dynamics (CFD) was used to predict velocity profiles upstream and downstream of the mist eliminators. Results indicated that although the space available inside the vessels was tight, all of them could be retrofitted instead of replaced. The refinery required that this work be done without welding to the vessel walls or altering the inlet and outlet nozzles.
Amistco recommended using mesh agglomerators with Double-Pocket Vanes for high capacity and high efficiency in all four suction drums. One would have a vertical double-bank system as shown before in Figure 6. Two others would have a similar arrangement with a single bank as shown in Figure 14, and the last needed a four-bank system.
To avoid welding on the wall of each vessel, the new internals would be secured by Amistco’s double expansion rings as shown before in Figure 7. Finally, to ensure proper flow distribution in this tight retrofit, inlet diffusers would be installed in all the vessels, as illustrated in Figure 14.
After the retrofit was completed, the hydrogen compressor train was able to operate at 122% of its former capacity without evidence of liquid carryover.
Curing product haze in a ULSG hydrotreater
An East Coast refinery had recently installed an ultra-lowsulfur gasoline treater. Although the product met the low-sulfur specification, it was very hazy and could not be immediately used for blending products. The existing coalescer was incapable of removing the haze, so that the gasoline had to be stored for up to 5 days to settle the entrained water to the bottom of the tank. This situation created a major logistics problem for the refinery. Storage capacity was scarce, and on-line blending facilities were used for the final gasoline product. Thus the refinery was unable to supply gasoline to all of its customers on time.
Engineers from Amistco studied the hydrotreater and the tank farm. They then installed a special type of coalescer that is able to remove the haze from gasoline. In addition, a large portable coalescer was provided for the tank farm, allowing treatment of any tank that might have hazy distillate products. These provisions totally cured the problem. Now the refinery is considering similar coalescers for removing product haze in its diesel hydrotreater and other locations.
Eliminating excessive sulfur in anime off gas
After adding an ultra-low-sulfur diesel treater, a Caribbean refinery was faced with excessive sulfur content in their amine treater off gas. In addition, they experienced substantial amine losses, and burner tips in heaters fueled by the off gas were plugging more frequently.
Amistco engineers reviewed the process conditions at the amine treater and found that the original absorber tower internals were inadequate to handle the increased H2S content in the feed from the ULSD plant. Although the absorber solvent had already been switched from MEA to MDEA, there was insufficient vapor-liquid contacting surface. Consequently not all of the H2S was absorbed by the solvent, so that part of it went with the off gas. In addition, the gas load was higher than before, and the existing mist eliminator could not handle that increase. Thus, amines carried over with the off gas. The amine mist gradually plugged the burner tips as the amine turned into a powder when the fuel gas was burned.
To provide enough surface area for the solvent to absorb all the H2S, Amistco supplied high-capacity structured packing for the amine treater absorber and regenerator. In addition, the mist eliminator in the absorber overhead knockout drum was replaced with a high-capacity, high-efficiency Double-Pocket Vane unit with mesh agglomerator.
After these changes were made, the off gas from the amine treater was low in sulfur content and contained no amine mist. The burner plugging problem disappeared, and the refinery began saving $125,000 per year in amine recovery.
Debottlenecking a sulfur plant
A large refinery in South America was bottlenecked for capacity in the sulfur plant condensers. Due to high content of liquid sulfur in the feed to each condenser, liquid was flooding the mesh pad and carrying over with the excess gas. The sulfur was plugging the converter catalyst, causing shorter operating time between shutdowns. In addition, the mesh mist eliminators were frequently becoming fouled with solidified sulfur.
After reviewing the sulfur plant’s operating conditions, Amistco revamped each condenser, replacing the old mesh mist eliminator with a high-efficiency vane-mesh combination located below the condenser gas outlet as in Figure 13. This upgrade yielded three advantages:
- Condenser capacity was increased by 15 to 20 percent.
- The vane-mesh combination provided a higher efficiency, extending the catalytic converter run length due to less sulfur contamination.
- The vane unit prevented the mesh pad from flooding with liquid sulfur, minimizing occurrences of plugging.
For information and consultation, call Bernhard Kalis, Technical Director, or any other separation specialist at Amistco’s headquarters in Alvin, Texas: 800-839-6374 or 281-331-5956, fax 281-585-1780, e-mail Amistco@amistco.com.
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