How to boost column performance with the right random packings
Mr. Vinit KaleManager Sales
Sulzer Chemtech Bahrain

NeXRing high performance random packings are already in use in many applications. The main advantages of the seven-membered family of packings are high separation efficiency, low pressure drop and small tendency to fouling. Due to their special shape, NeXRing packings have a relatively large, freely accessible surface with high mechanical stability at the same time. Mr. Vinit Kale, Manager Sales at Sulzer Chemtech Bahrain, looks at how NeXRing can improve column performance and boost plant productivity.

Random packings are column internals used for distillation, absorption and stripping in chemical, fertilizer, refining, petrochemical, and gas processing plants. The main advantage of random packings is that they can be easily replaced when the separation efficiency of a column has to be improved due to fouling or other reasons.

The performance of Sulzer NeXRing packings is provided by a relatively large and accessible ring surface on which the separation process can take place, the special shape of the rings, which allows for a higher packing density and thus a larger available surface and the open design of the rings, which reduces the pressure drop compared to conventional rings by up to 50%.

NeXRing packings distribute themselves evenly within the column packing section, while the structure of the rings provides for uniform liquid and gas flow through the column. The shape of the packing appears fragile, but the ring structure can be hardly deformed. The end flanges and the reinforced ribs give the NeXRing a high mechanical strength. The packing family includes seven sizes.

Comparison of different ring types
Before a product enters the market, Sulzer's research and development (R & D ) engineers conduct in-house testing to reliably determine the range of application. The tests are verified by an independent institute in the USA. shows the relative efficiencies and relative capacities for different versions of the established P-Ring (equivalent to Pall Ring), I -Ring(equivalent to IMTP Ring) and NeXRing packings. The P-Ring #2 packing is a standard in the industry, so it is used as a reference value (100% efficiency and 100% capacity). The data presented clearly indicates that NeXRing packings provide higher capacity and efficiency compared to P-Ring and I-Ring.

The ring size affects the flow and therefore the capacity. The larger the rings, the lower the flow resistance. A more open ring structure (I-Ring and NeXRing) increases the flow, while a smaller ring size increases the efficiency of the separation process, as a larger surface is available for the separation process. Good contact with liquid and gas increases the process efficiency and thus the quality of the process. As a result, the NeXRing has a much better efficiency than the P-Ring and the I-Ring.

Packing for CO2 absorbers
Due to their special properties, NeXRing packings are used in many industrial sectors, e.g. for the removal of carbon dioxide (CO2) and hydrogen sulfide (H2S) from natural gas or biogas. For this purpose, the gas is brought into contact with amine-based solvents such as monoethanolamine (MEA), diethanolamine(DEA), methyldiethanolamine (MDEA) or MDEA/piperazine solutions (activated MDEA).

A common feature of these solvents is their strong tendency to foam, which affects the flow of the gas through the separation column. Compared to conventional random packings such as P-Ring and I-Ring, NeXRing packings provide a high surface exposure to liquid and vapor. The largely open area allows separation with less pressure drop and thereby reduces the hydraulic effect of foaming. The example provided in is based on calculations for one of Sulzer's European customers and shows how the use of NeXRing can reduce the pressure drop or increase the column capacity, increasing the overall column efficiency.

Methane separation
A significant increase in global coal gasification capacity is expected in the near future. This is especially true for regions like the Far East and Asia. The actual coal gasification step is usually followed by a methane separation process. The raw gas produced from coal consists mainly of carbon monoxide (CO), hydrogen (H2) and methane (CH4). In the methane separation column, the three constituents are separated into two streams: CO and H2, and liquid methane, which is easily transported in condensed form and sold as liquefied natural gas (LNG). Refer Figure 2 show working principle of methane separation

A customer in China operated a methane separation column with four different sections (Figure 3), designed for operation with a feed of 24.5% CO, 58.5% H2 and 17% CH4. However, the customer changed the coal type for the gasification, which significantly changed the composition of the feed to the methane separation column.

In fact, the new raw gas composition was actually 24.5% CO, 51.5% H2 and 24% CH4. In view of the increased load in the lower column sections, the capacity of the existing column was insufficient to process gas with this composition. Sulzer retrofitted the column and replaced the Nutter Ring #2 random packings in the two lower sections with NeXRing #2 packings.

The customer was very satisfied with the result. The replacement increased the capacity of the entire system by 20%. The replacement of the existing liquid distributor in the lowest section could yield to an even higher increase in capacity.

Treatment of acid wastewater
Sour water and sour gas are produced in oil refineries as waste products from atmospheric and vacuum columns. Hydrogen sulphide (H2S), ammonia (NH3) and hydrogen cyanide (HCN) are typical components of sour water that must be removed before the water can be used elsewhere in the plant. This happens in so-called stripping columns. By supplying heat in the form of steam, H2S and NH3 are removed from the sour water and withdrawn as gases from the top of the column.

An integrated power plant of a refinery in Asia was unable to meet government wastewater treatment requirements for the existing plant. Sour water and sour gas from the upstream process were fed to the stripping column. Particles and dust from the sour water accumulated in the packed bed and led, after a short time, to an increase in the pressure drop in the column. The company turned to Sulzer's specialists for help. They recommended upgrading the random packings in the two lower sections of the three-part column (Refer Figure 4), where the fouling occurred. In 2017, the customer replaced the P-Ring #2 type packings in both sections with NeXRing #2 packings. Even after half a year of operation, no increase in pressure drop could be detected.

Compared to the P-Ring, the NeXRing has a very open design. This allows the small particles to flow through unhindered without getting stuck. In addition, in all three column sections, the overall pressure drop in the column is lower than in the previous P-Ring arrangement. The customer regularly checks the pressure drop for quality assurance in order to ensure compliance with the state's requirements.

Optimized emission control
Governments around the world have adopted stringent regulations to reduce global air pollution from sulfur dioxide (SO2) emissions. An Asian customer and operator of a refinery, was unable to meet the new government regulations with its existing equipment. To reduce the SO 2content in the flue gas, a new column had to be built. Sulzer performed calculations and developed a concept that allowed the customer to meet government regulations using Sulzer's products and a new process arrangement.

According to this, SO2 is removed in several stages using water and alkaline solutions. The goal was a reduction of the SO2 content in the exhaust gas below 50 ppm. While the original column design used Type I-Ring #40 packings, the new design featured NeXRing #1 packings. Although they provide the same capacity as the I-Ring #40 packings, they offer greater efficiency. Since a certain amount of dust is to be expected during the process, the resistance of NeXRing to contamination was also an advantage .

The calculations convinced the customer, which opted for a column equipped exclusively with NeXRing packings. The column is now successfully in operation and the SO2 content has been reduced to 35 ppm. The total pressure drop is 40% less than required, resulting in significant energy savings over the service life of the column.

Design the column yourself
Sulzer has gained experience and test data for hydraulic capacity of separation columns over many years. Based on this know-how, Sulzer engineers have developed a design program called Sulcol that gives customers the ability to design their own columns. Columns of different sizes can be configured with various types of internals. The Sulcol program then determines the hydraulic capacity of the system. Columns can be configured with different types of trays, random or structured packing. Interested customers can download the latest version of Sulcol from the Sulzer website.