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What is new in TDP-1?
TDP-1 includes several new items that address recent industry experience. These include the addition of combined-cycle units and the application of modern control systems and technology to turbine water damage protection.
The updated standard addresses the following:
- Combined-cycle configurations such as High Pressure, Intermediate Pressure and Low Pressure drums on Heat Recovery Steam Generators (HRSG)
- Cascading and direct turbine bypass systems
- Recommendations for process steam lines associated with co-generation configurations
- Recommendations on superheat attemperation at the outlet of the final superheater of HRSG
- Additional clarification of system drain requirements, including the use of drain flash tanks and pumped condensate drain tanks
Recommendations for draining side and axial turbine exhaust orientations into the condenser
Integrated control systems (ICS), such as distributed control system (DCS), into closed and open feedwater heater level instrumentation and
To facilitate the discussion of combined-cycle configurations, TDP-1-2006 introduces the concept of motive steam. Motive steam systems are systems that supply steam to a steam turbine for the primary purpose of power production or to an auxiliary turbine, such as a boiler feed pump drive turbine. The committee introduced the concept of motive steam to incorporate combined-cycle configurations: HP, IP and LP drums, in addition to the existing conventional steam (Rankine) cycle configurations.
Motive steam systems include:
- Main steam
- Hot and cold reheat steam
- High pressure (HP) steam
- Intermediate pressure (IP) steam
- Low pressure (LP) steam
- Admission steam
Motive steam systems do not include:
- Extraction steam
- Gland steam seal line
Recommendations for combined-cycle configurations
In this standard, a combined cycle is defined as a hybrid of the gas turbine (Brayton) and steam (Rankine) cycles. Waste heat contained in the gas turbine exhaust is fed through an HRSG that produces steam that is expanded through a condensing steam turbine to produce power.
HRSG system configurations typically include as many as three steam drums, each with level controlled by feedwater valve modulation and condensate or feed pump recirculation, or similar method of controlling inflows. The same plant design requirements that apply to other steam generators apply to HRSGs.
The use of attemperators external to the steam generator, downstream of the last superheating (or reheating) element, is discouraged; however, it is recognized that under some conditions it cannot be avoided. When this type of attemperator is required in the motive steam line to control the temperature of the steam entering a steam turbine, several additional features are recommended to provide adequate protection.
When a gas turbine cooling steam or power augmentation steam pipe is connected to a motive steam line, this pipe should not be connected at or near the low point of the motive steam pipe. If routing of this pipe creates a low point, a drain should be provided from the pipe.
Turbine bypass systems
Turbine bypass systems should be provided with the same level of protection as motive steam piping.
These should include drains and drain pots (if applicable) with power-operated drain valves.
Attemperators in bypass systems that discharge to the cold reheat system (or any other line connected back to the steam turbine) should be designed to the same requirements on motive steam system attemperators. Non-return valves should be provided in the cold reheat system to prevent the reverse flow of bypass steam into the steam turbine. Designers should carefully consider the location, design and orientation of large steam dumps (such as turbine bypasses) into the condenser.
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