Instrumentation & Controls

With U.S. mercury regulations pending and control technologies in the full-scale demonstration stage, accurate and reliable measurement of mercury in flue gas is becoming more important than ever. This article compares the results of field measurements of commercially available mercury monitors to approved reference methods. A key but not-so-surprising finding: Not all mercury monitors are created equal.

Several states have mandated faster and/or deeper reductions in plant mercury emissions than those called for by the Clean Air Mercury Rule. Unfortunately, differences between plants make accurate evaluation of control options difficult. In most cases, even statistically based Hg emission models don’t pass muster because they don’t account for the dynamic chemical behavior of Hg species in gas cleaning systems. This article describes one system evaluation tool that has been validated using Hg field test data from 50 full-scale flue gas cleaning systems. It is already being used by TVA and other utilities.

By design, combined HP-IP turbines have a small amount of internal leakage from the high-pressure turbine to the intermediate-pressure turbine. When turbines are new, the amount of this leakage is close to the design heat balance. But as turbines age, the leakage increases considerably, causing a heat rate penalty and possibly a reliability problem. In Part I, we explore the symptoms and causes of excessive leakage within GE steam turbines and how to correct the problem. Part II, in next month’s issue, will examine the same issues for Westinghouse and Allis-Chalmers turbines.

Keeping coal-fired steam plants running efficiently and cleanly is a daily struggle. An article in the February 2007 issue of POWER explained that one way to improve the combustion and emissions performance of a plant is to optimize the performance of its coal pulverizers. By adding a dynamic classifier to the pulverizers, you can better control coal particle sizing and fineness—and increase pulverizer capacity to boot.

Since 1999, the Texas grid operator ERCOT has given plant owners economic incentives to upgrade and extend the life of their generating units. Lower Colorado River Authority has seized the opportunity to modernize the control systems of its 1970s-vintage Sim Gideon natural gas–fired steam plant. Sophisticated control schemes now calculate the toll taken by running units under severe service conditions—including the high ramp rates that a plant must execute to sell ancillary services.

On-line temperature monitoring of steam turbine rotors must be based on modeling thermodynamic processes—not direct temperature measurements. Good operating decisions can significantly extend the life of aging turbines, particularly those that are routinely cycled or operated at their maximum ramp rates.

Operators of combined-cycle plants that have been pressed into cycling service should make sure that the aqueous diet of their steam generators—especially heat-recovery steam generators—fits the plants’ more active lifestyle. Following are some tips for keeping your HRSGs’ water treatment regimen in tip-top shape. These prescriptions can keep the units vital longer and make them subject to fewer unexpected failures.

The state of interconnection standards for distributed generation plants remains disconcerting to many prospective owners of such plants. IEEE 1547 has been in place for several years and appears to be the best option in a field of competing standards. But IEEE 1547 is an imperfect standard; it holds at least six holes. Here are some suggestions for filling them.

Contrary to public belief, the most common electrical phenomenon produced by a power plant’s steam turbines, turbine-driven compressors, and pumps isn’t sparks or lightning bolts. It’s static electricity. The physical effects of static electricity—greater vibration and higher temperatures—can damage bearings, shaft journals, couplings, and gears enough to cause a forced outage. A few inexpensive instruments in the hands of a well-trained technician can prevent "frosting" and "worm tracks" in your babbitt bearings. We’ll start the training right now.

Arc flash is arguably the most deadly and least understood hazard faced daily by plant personnel. Research indicates that even the best safety plan, training regimen, and protective equipment may be no match for the heat and blast effects of an arc flash. Consider this article a wakeup call to retrofit every switchgear cubicle in your plant with a properly designed remote racking system. Forewarned is forearmed.