Squeeze Capacity Out of Design Margin

The lesson learned was that the OSBL cost could be a major cost component for a retrofit project. It should be included in the cost estimate at the early stage because this could avoid rework and surprise in the later stage. 

To understand the plant design margins and constraints, it is recommended to conduct a rating survey for key equipment, and the results can be shown in a plot with rankings and indications of which equipment are limiting and which ones have spare capacity with how much. 

Some design margins are hidden, but can be discovered. For example, many process furnaces are designed based on radiant flux or tube wall temperature (TWT) limit. If the furnace of interest is operating below the design limit, the gap provides 

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