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Advanced Column Internals Support Energy Efficiency

| By Joy LePree

New packings and trays encourage effectiveness and energy efficiency in traditional and emerging applications

Equipment for distillation, absorption, stripping, extraction and phase separation plays a major role in the chemical process industries (CPI). However, separation processes are notoriously energy intensive, which is far from ideal with the current movement toward sustainability across all CPI sectors. Compounding the problem, operational challenges such as bottlenecks, fouling and corrosion often plague the towers and columns used for separations.

The good news is that today’s advanced column internals allow greater levels of energy efficiency, fewer operational challenges and more effective separations in traditional applications, while also paving the way for newer sustainability-based carbon capture, waste recovery and biofuel operations.

 

Efficiency and throughput

“The desire to reduce energy consumption is increasingly being expressed by operating companies worldwide,” says Neil Sandford, global technology leader — trays, with Koch-Glitsch, LP (Wichita, Kan.; www.koch-glitsch.com). “Separations are energy-intensive processes and the design and operation of the column internals can have a significant impact on overall energy consumption.”

Sandford continues: “New mass-transfer technologies provide improved performance and efficiency, so there are many opportunities in existing processing units to replace outdated equipment with newer technologies to achieve higher throughput with lower pressure drop and reduced energy requirements due to improved efficiency. These technologies can be applied in various ways to achieve the goals of the tower, unit and plant.”

Dean Segal, vice president of sales and marketing with Pope Scientific Inc., (Saukville, Wis.; www.popeinc.com) agrees that debottlenecking and retrofit projects are a growing trend. “The biggest challenge in these projects is the tradeoff between purity and yield and what that comes down to is the number of theoretical plates possible within a certain height and the inherent pressure drop that exists. In higher columns, the pressure drop can become so great that it is not viable,” Segal continues. “For this reason, there are various packings and trays that provide different characteristics and there are ways to be smarter about the design and operation of the overall system.”

Moize Turkey, vice president, engineering, with Amacs Process Tower Internals (Houston; www.amacs.com) adds, “In applications where we are retrofitting to achieve a 15 to 20% increase in capacity, there are two options: to increase the size of the tower or to use higher capacity, higher efficiency internals to keep the tower size smaller and reduce energy consumption. It is usually more economical to debottleneck towers with high capacity, high efficiency retrofit solutions as long as the entire system is looked at holistically.”

“Before focusing on the tray or packing, you need to understand the entire system and the constraints of the column, as well as the capacity target and other factors. Once you know what is needed and what issues may exist upstream and downstream of the unit, it becomes easier to develop a design and select high-efficiency, high-capacity internals that meet the end needs,” explains Babak Rafi, technology manager — mass transfer, with Amacs.

Fortunately, providers of column internals are developing a variety of high-efficiency, high-performance solutions, so there is likely to be a suitable option for most applications.

For example, Amacs offers its Scalloped Edge Mini Valve (SEMV) trays in which the scalloped edge feature splits the vapor into multiple smaller streams to enhance vapor-liquid contact, reducing entrainment and pressure drop (Figure 1). The valves can be fabricated as either fixed or float valves depending on application requirements.

FIGURE 1. Amacs’ Scalloped Edge Mini Valve (SEMV) trays feature scalloped edges that split the vapor into multiple smaller streams to enhance vapor/liquid contact, reducing entrainment and pressure drop

“They are designed in such a way that breaking the vapor stream into smaller jets reduces pressure drop and increases capacity, while also achieving a better efficiency, providing a double impact of reducing entrainment and increasing output while improving the efficiency of each tray,” explains Rafi. “This is why we can achieve a smaller footprint in diameter and tower height to achieve the efficiency and output that are needed.”

For packed columns, both structured and random packings are available to boost efficiency and performance, but the selection depends on many factors within the application.

“The advantage of random packings is a better redistribution due to sharp edges of the geometry itself,” says Daniel Borchardt, team leader of process technology with Raschig GmbH (Ludwigshafen, Germany; www.raschig.com). “In the past it was assumed that structured packings offer less redistribution property so a redistributor after a certain active column height was usually considered. However, the use of a redistributor eliminates the advantage of a structured packing reaching a higher specific capacity and wider operational range compared to a random packing with an equivalent specific surface due to directed flow guidance.”

He continues to say that Raschig executed pilot trials with the result that the outlet flow above the structured packing bed does not show a bigger droplet size distribution. Instead, it may be caused by the rotation of each packing element that takes place during installation. “Therefore, existing plants that are filled with random packing could be improved by using a structured packing and new commissions could have lower capital costs.”

To that end, the company offers Super-Pak structured packing. Unlike previous structured packing designs, there are no sharp directional flow changes within the Raschig Super-Pak element. Rows of sinusoidal waves within the vertical packing sheets are surface enhanced to encourage greater turbulent radial spread of thin liquid-film flows on the front and back of the waves on each sheet within a packing element.

The open structure achieves improved hydraulic and mass-transfer efficiency characteristics and loading capacity is high, with improved separation, while pressure drop remains low during normal operation.

To accommodate the need for higher capacities and better efficiency in a variety of applications, Koch-Glitsch offers several options: Flexipak HC structured packing (Figure 2), Proflux severe service grid and Intalox Ultra random packing, which can provider higher capacities, lower pressure drops and increased efficiency compared to conventional structured, grid and random packing types that may still be used in processing units. “Sometimes simply changing the packing can achieve higher throughput or higher product quality in existing processing units, while in new towers, these can be applied to reduce column diameter and height to lower the capital cost of the project.”

FIGURE 2. To accommodate the need for higher capacities and better efficiency, Koch-Glitsch offers Flexipak HC structured packing, which can provide higher capacities, lower pressure drops and increased efficiency compared to conventional structured, grid and random packing types

And, Performance Distillation Solutions (PDS; Bellefonte, Pa.; www.pdspropak.com) offers its Pro-Pak random packing (Figure 3) in applications where space is limited or high numbers of theoretical plates are required. “The small height equivalent to theoretical plates (HETPs) provided by the packing allows columns to be much shorter for a similar number of theoretical stages,” says Jason Paloskey, technical sales manager with PDS.

FIGURE 3. Pro-Pak random packing from Performance Distillation Solutions is used where high purity, space saving, energy saving and/or low loading design are critical considerations.

Pro-Pak is used where high purity, space saving, energy saving and low-loading design are critical considerations, because they provide greater efficiencies for better separation and higher free space to ensure lower pressure drop.

 

Solving operational challenges

While efficiency and throughput are indeed significant challenges, fouling, corrosion and ultra-low liquid load conditions are often prevalent in chemical separations. Fortunately, advanced technologies are available to reduce these issues.

Koch-Glitsch offers a range of solutions to lessen the impact of fouling, including fouling-tolerant tray designs using large, fixed valves like the Provalve tray, which offers a strong forward pushing action to keep the potential foulants moving down the tower.

Corrosion is also a major challenge in chemical separations and internals made of stainless steel or certain plastics will not work within highly corrosive media, says Rainald Pabst, sales product manager, columns and internals, with DeDietrich Process Systems GmbH (Mainz, Germany; www.dedietrich.com). For this reason, DeDietrich offers high-performance column internals made of high-corrosion-resistant materials, such as borosilicate glass, glass-lined steel, Tantalum, Si-ceramics and fluorinated plastics like polytetrafluoroethylene (PTFE) (Figure 4).

column internals

FIGURE 4. DeDietrich offers high-performance column internals made of high-corrosion-resistant materials like borosilicate glass, glass-lined steel, Tantalum, Si-ceramics and fluorinated plastics, like PTFE. This cross-section illustration showcases various technology offerings

“These materials are more corrosion resistant in difficult, heavy chemical industries, such as mineral acid recovery plants than Hastelloy or other metallic packings, but offer nearly the same pressure drop and behavior as metallic structured packings,” says Pabst. “We can combine highly corrosion-resistant materials with structured packings to solve the challenges of new separation processes but also find that customers who have been operating columns for 30 or 40 years with older packing styles come to us for these modern packings with higher efficiency and throughput, as well as corrosion resistance.”

Raschig also offers its Raschig-Pak Ceradur (Figure 5), a special ceramic packing with a unique chemical composition that results in superior chemical resistance and provides an alternative to more expensive packings.

FIGURE 5. Raschig-Pak Ceradur is a special ceramic packing with a unique chemical composition that results in superior chemical resistance and provides an alternative to more expensive packings

And, Sulzer Chemtech (Winterthur, Switzerland; www.sulzer.com) has developed a unique hybrid gauze structured packing, AYPlus DC (Figure 6), to overcome the issues associated with ultra-low liquid load operating conditions. In these conditions, it is challenging to have adequate liquid spreading and wettability on the surface of structured packings, which leads to a significant drop in efficiency. Sulzer’s packing AYPlus DC offers excellent wettability even for an aqueous system with high surface tension, the company says.

FIGURE 6. Sulzer’s AYPlus DC offers excellent wettability to overcome issues associated with ultralow liquid-load operating conditions, where it is challenging to have adequate liquid spreading and wettability on the surface of structured packings

The performance has been tested in Sulzer’s R&D test center in Winterthur, witnessed by an independent research institute, and has been successfully proven in the field in nearly 100 installations. In combination with Sulzer’s MellaTech ultra-low liquid load distributor, AYPlus DC outperforms equivalent metal-sheet structured packings with up to three times more efficiency while meeting requirements in terms of capacity and pressure drop. The packing improves the performance and reduces energy consumption of various highly relevant aqueous applications with low liquid load, such as the drying column in an ethylene glycol plant.

 

Sustainability projects

Thanks to these advancements in column internals, mass-transfer equipment will continue to play a critical role in sustainable and green applications. “Columns, packing and internals are very important for decarbonization efforts and mass transfer has been used to capture CO2 for years in various applications such as gas processing, hydrogen production, ammonia production and fertilizer plants,” says Koch-Glitsch’s Zack Bondley, global technology leader — packing. “The solvent technology is very mature in these applications and it is a common and effective process. The units operate at higher pressures and have higher concentrations of CO 2 than the post-combustion carbon-capture units to capture CO2 from fluegases.”

According to Bondley, post-combustion carbon capture units operate close to atmospheric pressure. The amount of fluegas at the low operating pressure results in very large absorber towers and the energy required from the blower in these large units requires a low-pressure-drop media in the absorber tower to make it economically viable. “While traditional structured packing was typically used in these applications, there was a need for improved packing to help reduce the absorber column size, both in height and diameter without increasing the pressure drop.”

Koch-Glitsch developed Flexipak CP structured packing specifically for the needs of CO2 absorber towers. “The structured packing provides options to tower height due to its improved capture efficiency and reduces the diameter due to increased capacity and lower pressure drop, allowing the capital cost of the CO2 absorber tower to be greatly reduced,” says Bondley. “Alternatively, the same-sized tower can also be used for a dramatic reduction in the pressure drop to reduce the operating cost of the carbon-capture unit.”

Sulzer’s packing AYPlus DC finds use in post-combustion carbon capture plants. In these applications, a once-through design in the water wash section of a CO2 absorber to reduce the solvent emissions to sub-ppm (parts per million) and even down to parts per billion (ppb) levels is made possible with this packing. Compared to the traditional design, which requires two pump-around units, the advanced design offers better efficiency and lower capital costs. In combination with MellapakCC structured packings and tailored MellaTech column internals, the performance of the CO2 absorber is maximized while the plant’s capital and operational expenses are minimized.

MellapakCC is Sulzer’s structured packing family for carbon capture. This packing family has performed in numerous industrial-scale columns across various carbon-capture plants, including power plants, cement, steel, petroleum-refinery and petrochemical facilities, with the largest column diameter exceeding 7.5 m.

And, PDS’s Pro-Pak packing and column internals have been used as a mass-transfer medium in both scrubbing columns and stripping columns, allowing the transfer of gases into a waste stream and aiding in the transfer out of a carrier fluid, according to Paloskey. “Further, applications involving cryogenic distillation of CO2 and/or CO 2-rich streams can benefit from the high efficiency of Pro-Pak, reducing size and, thus, the amount of energy needed to cool the system — a double win!”

In addition to carbon-capture applications, trays, packings and column internals are required for applications such as sustainable biofuels and waste-to-chemical applications.

For example, Raschig developed a unit to turn plastic waste to chemicals using advanced structured packing. “In this customer’s application, the pyrolysis-oil upgrade unit improves the quality of the produced pyrolysis oil, which is a liquid that is made from hard-to-recycle plastic waste that would otherwise end up in a landfill,” explains Raschig’s Borchardt. “The cleaned and treated pyrolysis oil raffinate/product is used in an ethylene cracker to produce a wide range of chemicals, closing the recycle loop. This plant is already built and expected to be in operation by the third quarter of 2024. All the extraction columns are equipped with structured packings without a redistributor in the active section.”

And, high-efficiency and high-capacity trays or packings can significantly enhance separation and purification of biofuels, such as bioethanol and biodiesel, says Amacs’ Rafi. “Using advanced internals reduces energy consumption in these applications and makes these energy sources more reliable and more common, which is essential because energy consumption is a critical factor in the production of biofuels and makes it most cost-efficient. There is a direct relationship between unit performance and the use of more alternative energy sources, such as biofuels. Advanced internals can help make this possible.”