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Other Internal Projects

Variable Frequency Drives

photo of variable frequency drives

Installation of variable frequency drives (VFDs) on the pumps and fans for our Cooling Tower Number 1 were completed in the summer of 2008. In addition to providing much smoother operation and control, integrating the VFDs into the system saves us about $500,000 annually.

Boiler Upgrades

In August 2003, UEM applied for a Voluntary Emission Reduction Permit (VERP) and was approved by the Texas Commission on Environmental Quality (TCEQ) in December 2003. The VERP provided significant upgrades to our boilers, mostly Boiler 3 and 7. The overarching expectation of the project was that the energy savings resulting from the emission retrofits to Boiler 3 and 7 would pay for the cost of the retrofits in less than two years.

The retrofit to Boiler 3 began in December 2004 and took about two months to complete. In the end, the results of the retrofit met or surpassed the goals and requirements in the following ways:

  • Nox emissions were reduced more than 85% to 25 ppm.
  • Forced draft fan horsepower at 20% load was 17 HP and O2 went from a high of 4% at minimum load (15,000 pounds per hour) to just a little more than 1% at full load.
  • We also discovered that the boiler could be “banked” (remain on hot standby) consuming approximately only 1 MMBtuh (essentially a 100:1 turndown). From this “banked” condition the boiler can achieve full load of 150,000 pounds per hour in approximately two minutes.

The retrofit to Boiler 7 was more complex than Boiler 3 and consisted of two phases. The first phase of the project began in July 2005 and completed in November 2005. This phase consisted of:

  • A complete rewiring of the burner management system and combustion control system.
  • Installation of a 600 HP VFD and a 150 HP VFD
  • Programming logic changes and replacement of the majority of the fuel gas side valves, instrumentation and control wiring
  • The scanner air blowers for Boiler 3 and Boiler 7 were disconnected and plant compressed air was used in their place. This provided horsepower savings and a considerable reduction in noise. (The scanner air blowers were once the loudest pieces of equipment in the plant).

The second phase consisted of the installation of the economizer, installation of the fuel gas recirculation duct and fan, along with modifications to the burner air registers similar to Boiler 3. This phase was completed in February 2007.

The results of the first phase were very similar to the results of the Boiler 3 retrofit:

  • At a boiler load of 300,000 pounds per hour the fans consume only 123 HP, the stack O2 is at 1.4% and boiler efficiency increased 10%. The original system used 600 HP, and had a stack O2 of over 4% at the same load.
  • The boiler showed the same improvement in responsiveness as Boiler 3.
  • The retrofit also provided the ability to “bank” Boiler 7. This is significant in that it has the potential to allow the entire Power Plant system to operate in a combined cycle mode.

Plant-Wide Optimization

screenshot of PE-Advisor

In the summer of 2002, UEM decided to solicit proposals to develop and implement a real-time, supply-side energy optimization system for our central utilities plants. This is because we wanted a tool that could perform timely “what-if” scenarios to examine potential cost-savings opportunities and the potential side effects of changing the way the plant operated as a whole.

We selected LightRidge Resources to design, develop, and implement a real-time optimization (RTO) system. The LightRidge Resources PE-Advisor™ system has multiple operating levels and modes. In a broad sense, the system status level is focused on presenting a consolidated and integrated view of the status of systems, conditions, and financial elements in the plant while the scenarios level provides the user the ability to compare alternative scenarios to situations in the real world.

The PE-Advisor™ system also tracks current equipment performance and compares it to design or baseline performance. Below are the results from the RTO system:

  • Savings of an estimated minimum of $1.3-1.6 million, most of which is annually recurring. These savings exceed the implementation cost of the RTO system.
  • The system currently imports and monitors more than 900 critical plant data points.
  • The validity of the data flow for these points is collectively and continually verified.
  • PE-Advisor™ flags those calculated values that do not agree with measured values. This provides our department with the information needed to start troubleshooting problems, resolving any internal conflicts in data interpretation along the way and thus also ensuring that decisions are made based on valid information.