Instrumentation & Controls

Tubing manufacturers have many alternatives for manufacturing and testing stainless steel tubing for feedwater heater and condenser applications. ASTM specifications are fairly generic in nature and only specify the minimum tube design and testing requirements—which may not be sufficient to provide the appropriate quality for a critical power plant application. To make the right material selections, it’s helpful to understand how welded stainless steel tubing is manufactured and its quality is checked.

Ongoing research into experience with plant- and fleet-level software reveals that these applications work side by side but do not necessarily function as an integrated “knowledge management” system. On the supplier side, the industry continues to be fragmented, with individual programs governing a narrow part of the overall plant.

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By design, combined HP-IP turbines have a small amount of internal leakage from the high-pressure turbine to the intermediate-pressure turbine. As turbines age, the leakage increases considerably and becomes excessive, creating a heat rate penalty and possibly a reliability problem. Last month we explored the symptoms and causes of steam leakage within GE steam turbines and how to correct the problem. In Part II, we examine the same issues for Westinghouse and Allis-Chalmers turbines from both theoretical and practical angles.

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.