ASME PTC 12.1:2015 pdf free download – Closed Feedwater Heaters
(a) For the purpose of this Code, a closed feedwater heater is a power plant heat exchanger designed to heat a given quantity of feedwater through a specified tem- perature range. The heating medium is steamor conden- sate at a specified temperature and pressure. In feedwater heaters, the feedwater and heating medium typically are routed through the tubes and shell, respec- tively. Feedwater heaters are typically designed to be configured in one of the following ways:
(1) horizontal
(2) vertical channel down
(3) vertical channel up
(4) duplex (two separate tube bundles in a single divided shell)
(b) In some cases, more than one feedwater heater is required fora givenfeedwaterflow and extractionsteam source. Insuchinstances, the feedwaterheateris divided into two or three parallel heaters, which constitute a multiple string arrangement. The shell side of the heater may be constructed with one, two, or three independent zones and arranged in various combinations:
(1) desuperheating zone
(2) condensing zone
(3) drain cooling zone
Each zone is considered to be an independent heat transfer entity contained within the same shell. Extraction steam from the turbine is the heating medium in the desuperheating zone. Depending on the heater design, extraction steam from the turbine together with other possible energy sources such as incoming drains are the heating medium in the condens- ing zone. Condensate is the heating medium in the drain cooling zone.
(c) This Code is written in accordance with the ASME PTC 1, General Instructions. ASME PTC 2, Definitions and Values, defines certain technical terms and numerical constants which are used in this Code with the significance and value therein established. The PTC 19 Series, Supplements on Instruments and Apparatus, which covers the instruments prescribed in this Code, should be used for reference. 1-2 OBJECT The object of this Code is to provide the procedures, direction, and guidance for determining the thermo- hydraulic performance of a closed feedwater heater. It can be utilized to verify contractual performance for a new heater or to calculate performance of an existing heater in comparison to the design point. The overall performance parameters utilized to accomplish this are the following:
(a) terminal temperature difference (TTD), which is the difference between the saturation temperature cor- respondingto the steaminletpressure and the feedwater outlet temperature
(b) drain cooler approach (DCA), which is the differ- ence between drain outlet temperature and feedwater inlet temperature
(c) tube-side (feedwater) pressure loss through the heater
(d) shell-side pressure loss through the desuperheat- ing zone
(e) shell-side pressure loss through the drain cool- ing zone The Code methodology adjusts the manufacturer’s guaranteed performance parameters to the actual test conditions, for a comparison to as-tested performance.
This Code applies to all horizontal and vertical heaters except those with partial pass full-length drain cooling zones. The heater design is based on a specific operating condition that includes flow, temperature, and pressure. This specific condition constitutes the design point that is found on the manufacturer’s feedwater heater specifi- cation sheet.