Improving Boiler Operations with Better Measurements

Emerson’s Bob Sabin, Tim Badger and Scott Pettigrew teamed up on the presentation, Fix Tough Measurement Problems to Improve Boiler Operation. Their abstract:

While boilers are crucial to plant/mill business results, many times their performance is lacking. Poor combustion causes higher fuel costs and increased emissions. Lack of reliability and response hurts site production throughput and quality. A root cause of poor boiler operation is often inadequate process measurement due to the fact that some process parameters are difficult to measure reliably and repeatably. This session will provide guidance on how to overcome tough boiler measurement challenges including where to place devices, preferred technology choices, and installation methods.

Bob opened by describing the key boiler control requirements safety, reliability and optimized performance. Optimized performance he described was in terms of response, fuel cost and emissions. Reliable boiler control begins with a strong base from the mechanical aspects of the unit to the measurement instrumentation and final control devices.

Key boiler instrumentation includes oxygen analyzers, airflow sensors, variable frequency drive (VFD) fan, damper drive, furnace temperature and furnace pressure.

For the water side instrumentation key instrumentation includes steam flow, boiler drum level, feedwater temperature, feedwater flow rate, feedwater pressure, VFD-driven pump, feedwater flow valve, and drum pressure.

For the gas side, key instrumentation includes:

Tim then presented on drum level considerations. Managing the drum level is critical for safe and reliable operations. High drum level can cause carryover and lead to damage to steam turbines and reduced heat transfer efficiency. For the drum level, considerations include low-level risks exposure of tubes to excessive heat and tube damage, leading to unplanned shutdowns.

Tim describes advantages of guided wave radar (GWR) technology for drum level measurements. GWR is independent of density, but steam dielectric (DC) can cause up to 20% error and varies with pressure changes, Applications for guided wave radar include boiler drums, high pressure feed water heaters and steam separators.

In the GWR, dynamic vapor compensation (DVC) automatically compensates for varying steam DC. It Uses a reference reflector to measure steam dielectric and reduces errors to less than 2%.

Scott described some considerations for fuel flow. These include:

  • Mass versus volumetric flow
  • Accuracy, turndown requirements
  • Types of fuel & their variability
  • Installed performance
  • Installation costs
  • Control combustion, monitor boiler efficiency, monitor plant energy use, environmental reporting
  • Pressure loss allowances/meter location relative to regulator
  • Straight pipe requirements

Steam flow considerations include:

  • Accuracy, turndown requirements
  • Installed performance
  • Indoor/outdoor, weatherization
  • Installation cost
  • Operating cost
  • Control drum level, monitor boiler efficiency, balance plant steam use
  • Technology preferences

Steam flow meter technology includes differential pressure (DP) flow and vortex meters.

Airflow considerations include unique duct geometries and installation considerations. For duct geometries, considerations include:

  • Fans and dampers
  • Expansion joints
  • Man-way doors
  • Internal structural restrictions
  • Conditioning vanes
  • Service access restrictions

Installation considerations include:

  • Thin-wall
  • Mounting to flat, round or transition shaped ducts
  • Internal structural supports and conditioning vanes
  • Undocumented internal structure additions
  • Fiberglass duct material
  • Manway and internal service access requirements
  • External installation clearance and service access requirements

They closed the presentation by making the points that a good working base of instrumentation and end devices is needed to support safe, reliable, and optimal boiler operation and boiler measurement and actuation can sometimes be challenging, but proven technologies exist to deliver desired business results. You can find more information from the Emerson Industrial Energy Solution team.

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