Steam Load
The steam load to a vacuum overhead ejector system is going to be a combination of steam from multiple sources. All of the steam that enters the vacuum tower is going to end up being a load to the vacuum system. Unlike the hydrocarbon loads, the make-up of the steam load does not consist of multiple components and therefore only needs to be concerned with the overall flow. The steam load is often a combination of the following:
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Column Stripping Steam – Steam introduced in tower’s stripping section.
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Side Strippers – Steam introduced to the flow into any side strippers.
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Furnace Steam / Velocity Steam – Steam used to maintain velocity in the various heater passes.
In almost all cases, the steam flows at these points are metered and controlling their flow rate has performance and reliability implications for the tower. All of the steam load from the tower to the vacuum system will end up condensed in the hotwell alongside all of the condensed motive steam. Any tube leaks into the system will also add to the hotwell flow. With these conditions, determining the steam load to the vacuum system from the hotwell condensed water flow is difficult and lacks accuracy. The steam consumption of the ejectors can be calculated and subtracted from the overall hotwell water flow rate, however a summation of metered steam flow rates is preferred.