What is Structured Packing and How Is It Used in Process Plants?
Structured packing is a range of materials that are specially designed for use in distillation and absorption columns, as well as chemical reactors. They usually consist of thin corrugated metal plates or gauzes, designed to force fluids on complicated paths throughout the column. The design is intended to ultimately produce a large surface area for contact between different phases.
Structured packing is made from a variety of materials including corrugated sheets of perforated embossed metal, plastic, or wire gauze. The resulting product is an open honeycomb with inclined flow channels producing a high surface area coupled with a low gas flow resistance. Enhancements are often chosen to maximize liquid spreading which are ideal for applications with low pressure and irrigation rates.
How Structured Packing is Used in Process Plants
The uniformed arrangement of structured packing offers many advantages compared to other types of packing or trays. They are useful in many applications, such as those where precise liquid spreading is needed, such as offshore applications that are subject to permanent tilt and motion. There are several types of structured packing that can be used in process plants.
Gauze – It is the preferred packing for deep vacuum and low liquid rate applications. It has the lowest pressure drop per theoretical stage, making it the ideal choice for processing specialty chemicals, pharmaceuticals, and materials that are sensitive to temperature.
Knitted – Knitted packing can be rolled into one-piece layers to fit small diameter columns. It can also be wrapped back and forth to create rectangular bricks to be used in column manways. The multi-strand wires offer high surface area and high mass transfer efficiency at a higher-pressure drop than woven gauze.
Sheet Metal – This packing can handle a much wider range of vapor and liquid rates, as well as process services. Process applications range from low-pressure drop vacuum and atmospheric distillation services to medium high-pressure absorbers. Sheet metal packing can even handle a modest amount of fouling with adequate liquid loading to keep the packing wetted.
Grid – Grid packing can provide extended operation in fouling services. Corrugated sheet metal and stamped blades are considered grid packing. Both types are highly durable with large open areas to facilitate highly fouling process streams. Corrugated grid packing has a smooth surface to minimize fouling and is constructed of much thicker material than the normal sheet metal packing.
Structured Packing Versus Trays
Packing trays are generally used when a column is experiencing a bottleneck issue. These trays are replaced with structured packing for three reasons:
- They provide extra inter-facial area for contact between vapor and liquid.
- Better separation efficiency.
- Structured packed columns are shorter than trayed columns.
Structured packing is advantageous in applications that need constant contact, rather than the staged contact provided by trays.
Structured Packing Versus Random Packing
We’ve previously discussed the benefits of random packing. One such benefit is they are more cost efficient than structured packings and are less sensitive to misdistribution. However, structured packings tend to offer higher efficiency and capacity, as well as lower pressure drop than random packings. Structured packing also has a higher capacity and reduced liquid hold up compared to random packing and trays.
AMACS is a process internal manufacturer, replacing in kind equipment and manufacturing custom solutions, including structured packing. Feel free to call or e-mail us with your requirements to get a quick response and unsurpassed service.