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Safeguard packed column efficiency with proper liquid distribution

Initial liquid distribution directly affects the efficiency of structured and random packing beds. As such, some form of flow test should be conducted to validate distributor performance prior to column startup. Steady state water flow testing is the most common method of testing distributors. It can be conducted in the shop or in the field to verify the design, manufacture and installation.

Three Common Types of Liquid Distributor Flow Tests
• Liquid Range Test with Level Measurement: Water is fed to the distributor at the maximum and minimum design operating rates. At each rate, level measurements are taken at various locations within the distributor, typically at the end of each trough. Relative standard deviation of the level measurements must fit within the manufacturer specifications (normally 5-10% of the calculated flow rates). The flow patterns within the distributor should appear uniform, without excessive localized momentum. Sulzer conducts this mandatory flow test for all distributors.

• Area Measurement: This test is more common for large diameter and spray header distributors. Identical pans are placed at several locations under the distributor to collect flows from multiple distribution points over a constant timed collection period. The liquid flow rate is then calculated for each pan (area). The standard deviation of the flows to each pan is used to determine the macroscale uniformity of liquid distribution across the distributor. These tests are typically conducted at minimum, design, and maximum flow rates.

• Point Measurement: This test is similar to the area measurement test except that flows are measured from individual distribution points at predetermined locations for a micro-scale evaluation. The standard deviation calculated from these samples must be within design standards. Typically, a minimum of 10% of the total number of individual distribution points are measured.

Conclusions
Flow tests can quickly reveal maldistribution that could adversely impact column performance. By identifying issues early, simple adjustments can be directly made to the equipment while on the test stand, prior to column startup, avoiding costly shutdowns.

Final Note – Installation
No matter how well a distributor is designed and verified during manufacture, poor installation can substantially compromise column performance. All distributors must be properly oriented and leveled within the tolerances shown on the assembly drawings provided by the equipment manufacturer. Always verify distributor installation in the field prior to startup.

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