Analysis of Concentrated Solar Power Project Trace Heating Failures

Trace Heating

Electric Trace Heating is a system used to compensate for heat losses, using an electrical heating element, which is placed in physical contact with the surface of pipelines, tanks, vessels, equipment etc. It can also be fitted inside the pipe or vessel with suitable glanding.

In this way you can keep your manufacturing process alive and unfrozen by maintaining or raising temperatures. 

Concentrated Solar Power Trace Heating

Electric Trace Heating is critical to prevent freezing of molten salts (60% sodium nitrate and 40% potassium nitrate, from 207°C), Heat Transfer Fluid (Biphenyl ether mixture, from 12.3°C), synthetic oil (15°C) and water & condensates (0°C).

As such Trace Heating is vital to the Thermal Energy and Heat Transfer System as well as the Balance of Plant. If the materials in pipes, flanges etc. are not heated and the liquids solidify, the plant will be forced to stop creating significant down-time and cost to repair.

The operation temperature in CSP applications can be as high as 560°C, and as such only one type of Heating Cable can be used: Mineral Insulated Cable.

There have been numerous high profile failures in Concentrated Solar Power which have been a direct result of poor Design, Installation or Control of the Trace Heating units.

Common Mistakes

Design Choices

  • Wrong resistance chosen, and consequently not enough power to raise temperatures adequately. Conductor resistance should be within 10% of desired value, safety factor should be ≥ 1.2, and the suppler should be at least ISO9001 certified.
  • Wrong cable choices on shorter circuits which are more likely to burn out quicker
  • Using the minimum amount of cables but powering them to their limit – reducing their useable lifespan.
  • Using a cable that is providing too much power or using too many cables in one area (poor trace ratio) which is uneconomical.
  • Using a metal sheath that is unnecessary for the environment and consequently an uneconomical choice. Or using a metal sheath which is inappropriate for the environment. Does the manufacture meet international standards such as (ATEX, IECEx, CSA etc). Total traceability of materials is vital.
  • Using a cable that requires more accessories than necessary such as junction boxes, splice kits etc. which ramp up total costs.
  • Inaccurate measurement of cable runs which can lead to the wrong unit lengths with costly ramifications on site, or unnecessary crossing of cables with associated premature failure.

Installation Choices

  • Decide storage and SAT to international standards such as IEC62395 at project definition stage. One must agree suitable instruments to be procured for SAT inspection, agree training requirements for installers and request installation manual.
  • Supervision and quality control on site must be adequate. Without using trace heating installation experts easily avoided mistakes can occur.

Real Life Examples                                          

The following photos were taken on the site of CSP projects where MICC Group was called in to repair Trace Heating issues:

Overlapping MI Cables  Causing overheating on the pipe:

Overlap Overlap2

Band Over Joint – The Joint needs room to expand:

Band1 Band2

Heating cable off the edge/ Cables not touching pipe  Uneconomical use of Cable:

off1 Off2

 Cables too close together – Poor trace ratio and overheating likely:

Close1 Close2

Corrosion – Due to wrong metal sheath choice:

Corrosion1 Corrosion2

Weld Failure – Temperature Cycling and Overheating (likely from placing joints directly on the pipe  exposing it to high temperatures and creating unsuitable access for repair):

Weld1 Weld2

And saving the best till last… 

Mess

Whereas Good Installation from MICC Group looks like:

Good1 Good2

Conclusion

MI Cable though very robust needs to be handled and installed by properly trained and experienced installers. The production, handling, transport and storage in the field (when necessary) are important for the final quality in application.

FAT and SAT coordinated technically and document protocols (in production, storage, before installation, after installation, after insulation and cladding) are imperative. Through proper supervision from individuals with suitable expertise, these are easy mistakes to avoid. Without suitable expertise, the downtime caused from these simple errors can cause project catastrophes.

MICC Group are the world’s largest manufacture of Mineral Insulated Cable and can offer turn-key solutions in Trace Heating.

Click here to learn more about MICC’s work in CSP

Will Dooley

Key Account Manager

MICC Group

will@miccgroup.com

+44 (0) 7515 663836

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