(357b) Refinery Vacuum Towers - State of the Art

Refinery vacuum towers present difficult challenges for mass transfer internals. They combine severe mechanical constraints, difficult process conditions, and large economic consequences of being wrong in any direction. This is a service that often lacks a clear-cut conservative or safe answer. This paper reviews the state of the art for internals in refinery vacuum columns. Equipment must meet both service and mechanical requirements.

Services commonly include heat transfer (pumparounds), de-entrainment (feed entry and overhead) and stripping (trays). Less often, fractionation services may be included. In modern vacuum towers the dominant heat-transfer and fractionation choices include grid-packing and structured packing. The major driving force is the low pressure drop of the structured packing. Additional benefits also come from the good performance of packing at low liquid loads.

Mechanical difficulties come from large equipment diameters and severe mechanical loads during upsets.

Auxiliary equipment to make the packing works include collectors, liquid distributors, and vapor distributors. These must also meet the service and mechanical requirements imposed by the process.