Figure 2. API plans 52, 53A and 54
This is an effective method for reducing the energy footprint of sealing systems in general. The elimination of cooling water reduces the cost to operate the seal and pump. The drawbacks of air cooling include its limited capacity and typical restriction to outdoor installations. Another method for eliminating the cooling water is to use product cooling. In this case, the process fluid is circulated through a coil in the barrier fluid reservoir or heat exchanger to remove the heat from the seal. This method is limited to process temperatures up to 50 deg C (122 deg F), and the fluid must be free of solids. The energy required to re-pump the process fluid back to discharge must be considered as the flow rates may be fairly high in this scenario.
- The energy footprint for controlling process or barrier fluid temperature can be estimated for any flush plan application. Meaningful comparisons can be made to determine the most energy-efficient system.
- Reliability, emissions and safety aspects of the seal must be considered during the evaluation and selection process.
- For the majority of seal applications, the energy footprint for controlling process or barrier fluid temperature is small compared with the overall footprint of the pump. Exceptions apply in services involving high temperatures and/or dirty fluids.
- For single seal and dual unpressurized seals in a high-temperature environment, the footprint for API Plan 23 is smaller than that for Plan 21. Plan 21 should be used only when Plan 23, for some reason, cannot be applied.
- Heat soak losses can be reduced significantly by having a close clearance bushing at the bottom of the seal chamber.
- For dual seals in a high-temperature environment, API Plans 52 and 53 consume less energy than Plan 54.
- Air cooling and product cooling may be effective methods for reducing the energy foot print in specific applications.
In next month's article we will focus on the energy required to remove external fluids or diluents from a process stream.
September 2010, Pumps & Systems
Next Month: What is the Sealing System Energy Footprint for removing diluents from the process stream?