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February 2015 · Energy-Tech Magazine
March 2010 Go to Page 1 2 3 4
Heat exchanger O&M practices
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Figure 1. Shell and tube heat exchanger
Figure 1. Shell and tube heat exchanger

The balance of plant (BOP) category of utility power plant heat exchangers is often overlooked when maintenance managers evaluate the need for preventive maintenance. The sound, reliable operation of the turbine, generator, pumps, fans, air compressors, etc., is often directly linked to the proper care and maintenance of these various types of BOP heat exchangers. Taking proper care of your BOP heat exchangers can often help avoid suffering more costly consequences as a direct result of inadequate cooling, due to clogged or fouled tubes, or from cross-contamination caused by heat exchanger tube or tube joint failures.

This article aims to provide a basic understanding of the thermal, hydraulic and chemical (metallurgical) issues that challenge the responsible system engineer who is charged with their proper care, and offers specific guidelines for operational and maintenance practices to help establish a successful preventative maintenance program.

References for the basics
Two references are strongly recommended as required reading to gain a working knowledge of the various types and configurations of shell and tube heat exchangers. The first is the Standards of the Tubular Exchanger Manufacturers Association (TEMA). Secondly, the Heat Exchanger Institute guidelines for Power Plant Heat Exchangers, which complements the TEMA standards because it specifically deals with and contains information about utility power-generating heat exchanger applications.

Common BOP heat exchangers
BOP heat exchangers are of various types and configurations, from basic shell and tube exchangers to plate and frame exchangers, finned coils, double-pipe exchangers and many others. Each has its own advantages and disadvantages and each can require different maintenance approaches.

These auxiliary exchangers differ widely, using various fluids to be heated or cooled, as well as which medium is on the tube side and which is on the shell side. It also is important to know which side is operating at the higher pressure, since any failures will result in leakage from the higher to the lower side. Because of this, each exchanger offers different challenges in the operation and maintenance programs. The approach to corrective maintenance also varies based on the specifics of the exchanger.

Common BOP coolers include: main turbine lube oil coolers, station air compressor inter-coolers, condensate coolers, auxiliary lube oil coolers, hydrogen coolers, air ejector/gland steam condensers and others. Common BOP heaters include: fuel gas or fuel oil heaters, auxiliary boilers, reboilers, air and glycol heaters, as well as other applications.

Service water systems
Now that we have introduced some of the most common BOP heat exchangers, we need an understanding of the systems that they’re an integral part of. Since the most popular BOP’s are auxiliary coolers, we will continue our discussions with examples of equipment coolers that utilize service water as the cooling medium. Station service water systems are either “closed loop” (cooling tower) or “open” (river, lake or pond) systems. Open systems can be either fresh or brackish water consistency, and as one would expect, different environments demand different water chemical treatments, and yield different fouling and corrosion potentials.

Categories of typical problems and susceptibilities
The following outlines some of the more common problems associated with BOP heat exchangers:

  • Designs with poor/marginal performance
  • Configurations with poor maintainability
  • Corrosion susceptibility based on materials of construction
  • Lack of on-line performance monitoring
  • Propensity for fouling/clogging
  • Improper maintenance procedures
  • Lack of Preventative Maintenance plans

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