Energy escapes the system when heated process fluid leaks, making seals a critical component for conservation.
by Richard Smith
November 17, 2016
API Plan 62Figure 5. A diagram showing API Plan 62

API Plan 62: API Plan 62 is an atmospheric plan commonly used on hot-oil-type applications for a single seal. With Plan 62, steam is taken across the atmospheric side of the seal and down to a drain system.

The steam is not used for cooling but instead carries away any hydrocarbon particles that congeal on the atmospheric side of the face, removing them before they start carbonizing and causing the seal and faces to “hang up.”

Plan 62 is a relatively energy-efficient method of sealing a hot-oil pump. Generally, only a small amount of steam is required; however, controlling the steam flow on a steam quench can be difficult.

For example, in some installations the steam escapes to the atmospheric side of the seal, which dramatically increases the energy requirement, quickly making the system inefficient. Most issues with the API Plan 62 steam quench’s energy efficiency are a result of poor maintenance.

Applying the Plans

Applying the previously mentioned API plans to a hypothetical hot-oil pumping application illustrates the relative energy efficiency of each (see Table 1).

Single-Seal Flush PlansTable 1. A comparison of single-seal flush plans

The configuration of this example application is a single-stage, end-suction centrifugal pump (API 610 compliant), based on the following characteristics and factors.

Pumped fluid: Hydrocarbon at 600 F (315 C)
Specific gravity: 0.8
Specific heat: 1.67 kJ-C (0.4 BTU/lb-C)
System pressure: 345 kPag (50 psig) in seal chamber
Pump driver: 50 hp (typical)
Sealing devices: Compression packing, mechanical seals
Assumptions:Heat lost at the pump must be replaced at the system boiler/heat exchanger

To put the figures in Table 1 into context, if a pump is running 24 hours a day, 365 days a year, the difference between flushing a seal using API Plan 32 and API Plan 23 can mean around 400,000 kW of energy saved each year. When these savings, which equate to a 96 percent reduction in energy costs, are spread across multiple pumps and multiple locations, the potential overall savings are huge.

Potential sealing system savings can exceed the energy savings obtained from switching to variable frequency drives, improving pump hydraulics, trimming impellers or resizing pumps in many applications. Selection of inappropriate sealing systems can have a significant impact on the thermal efficiency of a plant and a plant’s utilities.

Sealing systems found in many industrial applications, even when functioning as intended, are extremely wasteful of energy.

However, the sealing industry has technologies that can overcome some of this energy waste, and there is increased awareness about these solutions. Improved sealing technologies available today can reduce the need for energy-wasting systems that result in cooling/dilution of the process and the need for downstream separation/evaporation, re-heating and/or effluent treatment.

Being able to choose between different sealing systems or flush plans requires a good understanding of the principles of their operation and why they each are used. The best way to access this knowledge is to work with a sealing partner that has an understanding of this specialized area.

References

  1. youtube.com/watch?v=FvPRTowCK-E
  2. maintenancetechnology.com/2010/01/saving-energy-with-sealing-systems-344/
  3. pumpsystemsmatter.org/uploadedFiles/Pumps/Membership/Member_Services/Meetings/AZIBERT%20-%20Sealing%20Systems%20Energy%20Efficiency.pdf
  4. api.org
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