Pressure services downcomer

Downcomer support bars should be compatible with conunercial downcomer adapters. DoAvncomer adapters allow downcomer enlargement in a future revamp without the need to weld new downcomer support bars to the shell. These adapters are clamped to the existing downcomer support bars and to the new downcomer panels (274), and their use can dramatically lower the cost of a future revamp. Downcomer enlargement is one of the most effective and most popular revamp techniques in foaming, high-liquid-load, and high-pressure services. 

If a trayed column in high pressure service does not have sufficient downcomer residence time to clarify the liquid phase, the vapor/liquid mixture will be carried down to the next lower tray. This recycling of vapor lowers the capacity, as well as the separation efficiency, of the trays. Conditions preventing rapid disengagement of vapor and liquid in a tray downcomer are high liquid viscosity, low surface tension, and a small density difference between liquid and vapor. Also, any tendency for the liquid to foam will increase the downcomer residence time required. 

Downcomer sealing. While pressure drop and fouling considerations set the minimum values for downcomer clearance, sealing considerations set the maximum value for downcomer clearance. If the service... 

Problems of establishing a liquid seal in the column downcomers are common in low-liquid-rate services during startup. In such services, the downcomer liquid seal may also occasionally be lost during operation. Symptoms of these problems are excessive entrainment and poor separation. As distinct from flooding, column pressure drop may remain low. These problems, and cures that can be implemented at the design stage, are described in Sec. 6.18. 

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