PTQ Q2 2025 Issue

Up to 30% more sieve bed utilisation

Figure 1 Shaped Support Grid

The thermal expansion of the assembly is only as great as the width and length of each panel. Such contained thermal expansion inside the ceramic ball bed avoids the creation of fines or ceramic breakage, ensuring the longevity and reliabil - ity of the molecular sieve bed. Also, the assembly expands and contracts under the bed without compromising an outer perimeter seal, which may happen in a cyclic gas dehydra - tion application. The enclosed stainless steel bottom surface panel ensures any bed material that might migrate under one of the panels will not leak into the flow of the process. Solution in action The Johnson Screens Shaped Support Grid design (see Figure 1 ) has been successfully deployed in numerous nat- ural gas processing plants worldwide, either in new instal - lations or in retrofits and expansions of existing ones. Its proven effectiveness in real-world applications serves as a testament to its reliability and the inspiration it provides for future advancements in the industry. An example of a successful deployment is in a liquefied natural gas (LNG) production plant in South America in 2017. One of its trains incurred significant production losses due to high differential pressure across the molecular sieve beds. This issue arose because of a restriction below the beds’ structural supports coupled with the fact that the sup- ports were grossly under-designed for load bearing. Additionally, the operator pursued reducing the fre - quency of planned turnarounds to once every four years, which was challenged by their bed design life of three years and potential pressure drop (dP) issues after two years. The SSGs replaced the then-current support grid during a planned turnaround. As per the design, they was installed directly onto the bottom head of the vessels, compared to the previous support grates, which were installed where the vessel’s cylindrical section meets the vessel head. The SSG installation increased the design dP of the bed supports by more than three times the original limit, reduc - ing the risk of production loss and bed support failure. To assure that the SSG’s technical design was acceptable and within the constraints of the existing facility, third-party computational fluid dynamics (CFD) analyses and finite element analyses (FEA) were performed to determine the flow patterns through the beds, SSG, and outlet nozzle and determine new loading and stress resultants on the lower vessel head and nozzle, respectively.

Traditional support grid conguration

Shaped support grid

Figure 2 More sieve bed utilisation

The increased bed depth available with the placement of the SSG allowed approximately 25% more molecular sieves to be loaded into the space created in the vessel head when the SSG was installed. The original regeneration parameters, i.e., regeneration gas flow/temperature, were adequate to effectively regenerate the beds within the same time period. After installing the SSG and increasing the amount of material in the beds, the start-up dP across the ‘fresh’ beds was approximately 45% greater. With the SSG enhance- ments, the operator then implemented a variable cycling regime in the train. Based on breakthrough testing, the adsorption time was increased from 18 to 29 hours. By adopting the new SSG design, the operator met the objectives of reducing the risk of production loss. The plant can now operate at full capacity without being restricted by high bed dP. The installation also reduced the molecular sieve bed change-out frequency from three to four years while reducing the risk of support grid failure leading to unplanned downtime. In addition, reducing the annual firing hours of the regeneration gas heaters increased the adsorption time by reducing the number of regeneration cycles, resulting in an approximately 13% reduction in greenhouse gas emis- sions. Another positive impact was reducing the quantity of molecular sieve material that must be disposed of, thanks to less frequent bed changes in the long term. Conclusion Upgrading to the SSG and implementing VCD have proven to be effective solutions for improving a plant’s processing capacity, production efficiency, and profitability. Kevin Chase Johnson Screens Contact: dan.fletcher@johnsonscreens.com

PTQ Q2 2025