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Condensate drains tanks
A typical condensate tank is shown in Figure 5. Critical issues include vent sizing, redundancy of controls and redundancy of pumping equipment, including independent power supplies. The following recommendations apply:
- The cross-sectional area of the drain tank vent should be large enough to make certain that the tank internal pressure, with all simultaneous drains open, will be lower than that of the lowest pressure drain into the tank under all operating conditions, including start-up and shutdown.
- When the drain tank is connected to the condenser, the drain tank should provide separation of entering condensate and steam from the drain source(s). The vent line to the condenser should be large enough so that the tank pressure will be less than the source pressures of all drains connected to the tank under all conditions. Under startup and shutdown conditions, some of the drains might be close to condenser pressure.
- The tank drain line should be sized for the maximum service conditions. When a drain pump is
required, it should be actuated automatically based on drain tank level. If a drain pump is required and its failure could possibly lead to water entering the turbine, redundant drain pumps (supplied with power from separate power sources) should be furnished, each controlled by an independent level controller actuated automatically based on drain tank level. Independent level signals indicating a high-high alarm condition in the tank should be provided in the control room.Advertisement - Connections for incoming drains on the tank should be located above the maximum water level in the tank.
Axial or side turbine exhaust
- Avoid discharging high-energy bypass steam into the area between the condenser hotwell and the tube bundle
- Locate the curtain spray and bypass sparger a safe distance from the condenser tube bundles to allow a sufficient reduction in kinetic energy, so that high-energy steam does not reach areas above and below the tube bundles and cause a recirculation backflow with entrained water toward the turbine.
- Determine an incidence angle of high-energy steam jets that will avoid reflected velocity vectors toward the turbine exhaust.
Integrated control systems (ICS)
In the standard, an integrated control system (ICS) is defined as, "a control system featuring multiple processors, input/output (I/O) modules and memory storage interconnected through a communication network and equipped with redundant power supplies. Normally, a distributed control system (DCS) or redundant programmable logic controllers (PLCs) will meet this requirement."
The minimum ICS features to meet the reliability and redundancy needs addressed in this standard are:
- Dual processors
- Uninterruptible power supply
- I/O associated with redundant plant equipment, and that instruments should not be connected to the same I/O cards.
- Outputs that fail to know position during processor or internal communication failure.
Conclusion
TDP-1-2006 was revised to include recent experience, modern instrumentation and technology and combined-cycle systems. The overriding philosophy remains constant: "No single failure of equipment, device or signal, or loss of electrical power, should result in water or cold steam entering the turbine."
The Committee is currently working on TDP-2 for nuclear power plants. Look for it in the near future.
This article was published with permission of the ASME Power Division. For more information, visit www.asme.org.
Larry Kielasa is presently retired after serving 38 years with DTE Energy. During his career, Kielasa served in a variety of engineering and management roles. He is a past chair of the ASME Power Division, and is the current vice president of Financial Operations at ASME and chairman of the ASME Turbine Water Damage Prevention Committee. He has a bachelor's degree in Nuclear Engineering from the University of Michigan and a master's degree in Administration from Central Michigan University. You may contact him by e-mailing editorial@woodwardbizmedia.com.
John Boyle is a senior engineering technical specialist at FM Global, a business property insurer, where he works with companies in the power generation industry to help protect their facilities from property-related risks. He is a member of the ASME Turbine Water Damage Prevention Committee. He has a bachelor's degree in Engineering Science and a master's degree in Chemical Engineering from the University of Rhode Island. You may contact him by e-mailing editorial@woodwardbizmedia.com.
Ram G. Narula has more than 48 years of experience in the power industry, including 37 years with Bechtel Power Corporation, where he is vice president and chief technology officer. He is a Fellow of the ASME International and the Vice Chair of the ASME Turbine Water Induction Prevention Committee. Narula served on the ASME Codes & Standards Board of Directors for 8 years. He has a B.S. degree in Mechanical Engineering, an M.S. degree in Nuclear Engineering, and an M.B.A. degree. He has published more than 100 technical papers and traveled to more than 60 countries. You may contact him by e-mailing editorial@woodwardbizmedia.com.
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