1、 ANSI/ISA77.13.011999 (R2008) Fossil Fuel Power Plant Steam Turbine Bypass System Reaffirmed 30 December 2008 Copyright 2008 ISA. All rights reserved. ANSI/ISA77.13.011999 (R2008) Fossil Fuel Power Plant Steam Turbine Bypass System ISBN: 978-1-934394-74-8 Copyright 2008 by ISA. All rights reserved.
2、Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher.- 3
3、 - ANSI/ISA77.13.011999 (R2008) Copyright 2008 ISA. All rights reserved. Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA77.13.011999 (R2008). This document has been prepared as part of the service of ISA towards a goal of u
4、niformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alex
5、ander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Unit
6、s (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this en
7、d, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Soc
8、iety for Testing the firebox area, including burners and dampers; the convection area, consisting of any superheater, reheater, and/or economizer sections as well as drums, generating tubes, and headers. 3.4 condenser backpressure elements: a multiple breakdown diffuser, normally installed in the st
9、eam condenser neck, used to generate a positive back pressure upstream of the condenser vacuum and to reduce the kinematic energy of steam from an external source other than the turbine exhaust. 3.5 controller: any automatic, semi-automatic, or manual device or system of devices used to regulate the
10、 boiler turbine, or any other equipment within defined parameters. If automatic, the device or system responds to variations in temperature, pressure, water level, flow, or other control variables. 3.6 differential producer: a measuring element that is inserted in a process flow path and used to cre
11、ate a pressure drop that is proportional to the square of the volumetric flow rate. ANSI/ISA77.13.011999 (R2008) - 10 - Copyright 2008 ISA. All rights reserved. 3.7 fail safe: the capability to go to a predetermined safe state in the event of a specific malfunction. 3.8 fault tolerant: built-in capa
12、bility of a system to provide continued, correct execution of its assigned function in the presence of a hardware and/or software fault. 3.9 integral windup: the saturation of the integral controller output, in the presence of a continuous error, which may cause unacceptable response in returning th
13、e process to its setpoint within acceptable limits of time and overshoot. 3.10 load: a device that receives power or that power which is delivered to such a device, as in the rate of output, lb/hr (kg/s) of steam or megawatts (kilowatts) of electrical generations. 3.11 logic system: decision-making
14、logic equipment with its associated power supplies, I/O hardware, and sensing devices. 3.12 mode (submode): a particular operating condition of a control system, such as manual, automatic, remote, or coordinated. 3.13 redundant (redundancy): the duplication or repetition of elements in electrical or
15、 mechanical equipment to provide alternative functional channels in case of failure of one channel. 3.14 severe duty valve: a mission-critical valve, typically seeing high-pressure drop service, which may see cavitating or flashing fluids, or if not properly designed, may see early trim erosion, vib
16、ration, or excess noise. 3.15 shall, should, and may: the word “SHALL” is to be understood as a REQUIREMENT; the word “SHOULD” as a RECOMMENDATION; the word “MAY” as a PERMISSIVE, neither mandatory nor recommended. 3.16 steam quality: the ratio of the vapors mass to the mixtures mass. 3.17 turbine:
17、a machine that converts energy from a moving fluid into rotating mechanical energy that drives a load. In a power plant, a turbine converts energy in the steam into mechanical energy to drive an electric generator (the mechanical load). 3.18 turbine governor valves: the primary control valves used t
18、o regulate the flow of steam through the turbine during normal operation. 3.19 turn-down ratio: the ratio from maximum operating to minimum operating conditions, providing a controllable or measurable span. The device must perform over this range. - 11 - ANSI/ISA77.13.011999 (R2008) Copyright 2008 I
19、SA. All rights reserved. 4 Bypass systems 4.1 General requirements The steam turbine bypass system requirements are defined for those components and logic systems necessary to handle steam to and around the turbine. The design of systems to prevent water damage to steam turbines is covered by the Am
20、erican Society of Mechanical Engineers (ASME) standard TDP-1. The steam should be of a minimum quality of 92 percent to avoid impingement and corrosion. Figures E.1 and E.2 show a typical turbine steam bypass system to assist in explaining the design requirements of this clause. Other figures show s
21、pecific areas to help clarify the text materials. This standard will cover the following functions: a) Matching with an acceptable difference the metal to steam temperatures before steam is admitted to the turbine b) Handling the difference between the generated and consumed steam flows during trans
22、ient conditions 4.1.1 High-pressure (HP) bypass system The HP bypass system shall fulfill the following requirements: a) Control the pressure of the steam bypassing the HP turbine b) Control the pressure of the main steam from the boiler c) Control the flow and temperature of steam through the cold
23、reheat line to cool the boiler reheater tubing d) Control the flow of steam through the main steam line to cool the boiler final superheater in case of sliding pressure operation e) Prevent lifting of main steam and hot reheat safety valves during transient operations 4.1.2 Intermediate-pressure (IP
24、) and low-pressure (LP) bypass system The IP and LP bypass system shall fulfill the following requirements: a) Control the pressure of the steam bypassing the IP and LP turbines b) Control the pressure and temperature of the hot reheat steam from the boiler c) Prevent the lifting of hot reheat safet
25、y valves during transient operations d) Protect the condenser against excessive pressure, temperature, and steam kinematic energy ANSI/ISA77.13.011999 (R2008) - 12 - Copyright 2008 ISA. All rights reserved. 4.2 Elements The elements that make up the steam turbine bypass system are those added over t
26、he elements required for a system without the ability to bypass steam around the HP, IP, and LP turbines. Therefore, those elements that are added due to the bypass are shown in figures E.1 and E.2. 4.2.1 HP bypass elements a) HP bypass control valve (HPB) (see notes 1 and 3) b) Before HP bypass con
27、trol valve, block valve (B) (see note 3) c) HP bypass desuperheater (DES) (see note 1) d) HP bypass desuperheater spray water control valve (SPV) (see notes 2 and 3) e) HP bypass desuperheater spray water block valve (B) (see note 3) f) HP turbine cold reheat, non-return valve (NRV) g) HP turbine by
28、pass control system h) HP turbine bypass instrumentation i) HP turbine reverse flow valve (see note 4) NOTE 1 The pressure control valve and desuperheater may be combined into one HP turbine mainstream bypass pressure control and desuperheating valve as shown in figure E.2. NOTE 2 The desuperheater
29、may have an integral spray water control valve. NOTE 3 Block valves are usually required to assure that leakage does not occur through the control valve. This function could be integrated in a composite control valve, provided the block valves purpose is not compromised. NOTE 4 The reverse flow valv
30、e may be necessary to prevent excessive windage heating of the HP turbine blades during a hot restart if initial loading is accomplished using the LP/IP sections. 4.2.2 IP and LP elements a) IP/LP bypass control valve (IP/LPB) (see notes 1 and 3) b) Before IP/LP bypass control valve, block valve (B)
31、 (see note 3) c) IP/LP bypass desuperheater (DES) (see note 1) d) IP/LP bypass desuperheater spray water control valve (SPV) (see notes 2 and 3) e) IP/LP bypass desuperheater spray water block valve (B) (see note 3) f) Condenser back pressure elements (I) g) IP/LP pressure bypass control system h) I
32、P/LP bypass instrumentation - 13 - ANSI/ISA77.13.011999 (R2008) Copyright 2008 ISA. All rights reserved. NOTE 1 The pressure control valve and desuperheater may be combined into one IP and LP turbine hot reheat bypass pressure control and desuperheating valve as shown in figure E.2. NOTE 2 The desup
33、erheater may have an integral spray water control valve. NOTE 3 Block valves are usually required to assure that leakage does not occur through the control valve. This function could be integrated in a composite control valve, provided the block valves purpose is not compromised. 4.3 Capacity The st
34、eam flow capacity of the bypass system is governed by a number of other variables in the overall steam system. These are a) heat distribution in the boiler; b) turbine rotor diameter; c) condenser internals; d) startup, loading, unloading, and shutdown practices and requirements for the unit; e) saf
35、ety considerations; and f) economics. 4.3.1 System size There are a number of possibilities to size the bypass system. In this document the bypass system size or capacity to fulfill the two functions previously defined in 4.1 are as follows: a) A bypass system that matches the steam-to-turbine metal
36、 temperatures should be sized for 15 percent of maximum continuous rated (MCR) flow at valves wide open. This system reduces the startup time by about 30 minutes. b) A bypass system that handles the difference between the generated and consumed steam flows during upset or transient conditions should
37、 handle 40 percent of MCR flow at valves wide open or should have a greater size range. c) A bypass system that keeps the steam generator running at full load without blowing the safety valves in case of a turbine or generator trip at full load should handle 100 percent of MCR flow at valves wide op
38、en. 4.4 Design requirements The design requirements for each of the elements are as follows. 4.4.1 HP and IP/LP turbine bypass control valve a) Design criteria The design criteria for the bypass system valves shall be specified as shown in tables 4.4.1(a) and 4.4.1(b). ANSI/ISA77.13.011999 (R2008) -
39、 14 - Copyright 2008 ISA. All rights reserved. Table 4.4.1(a) HP turbine bypass control valve Severe duty, pressure type or pressure- and temperature-reducing type (see note 2) Operating Conditions The coordinated inlet and outlet pressure, temperature, and flow conditions for all distinct service s
40、ituations Inlet and Outlet Design Pressure The maximum design pressure for the inlet and outlet Inlet and Outlet Design Temperature The maximum design temperature for the inlet and outlet Inlet Pipe Size (Internal Diameter ID) and Material The same as the piping just before the valve Outlet Pipe Siz
41、e (Internal Diameter ID) and Material The same as the piping just after the valve Noise Level The desired maximum noise level at 1.0 meter (3.28 feet) from the valve (see ISA-75.07-1997) Shutoff Leakage Class The desired shutoff class at the design pressure and temperature rating of the valve usuall
42、y Class V of ANSI/FCI 70.2 Travel Time The desired minimum travel time from any position including fully closed at the maximum operating pressure Fail State The HP bypass valve is normally a fail-closed valve (see note 1.) Modulating Time The maximum time for full stroke operation Turndown Ratio The
43、 full range of coordinated operating parameters of flow, pressure, and temperature Quick Opening Time The travel time for a valve that is provided with quick opening devices NOTE 1 If the applicable pressure vessel code permits, this valve can also be used as a fail-open safety relief. An “HP to con
44、denser” valve is preferably fail closed. NOTE 2 If the control valve has an integral water injection system, the average droplet size and distribution and the evaporation length (90% of total droplet mass) shall be provided by the manufacturer. - 15 - ANSI/ISA77.13.011999 (R2008) Copyright 2008 ISA.
45、 All rights reserved. Table 4.4.1(b) IP and LP turbines hot reheat bypass control valve Severe duty, pressure type or pressure- and temperature-reducing type with stem sealing for condenser vacuum if required (see note 2 from previous page) Operating Conditions The coordinated inlet and outlet press
46、ure, temperature, and flow conditions for all distinct service situations Inlet and Outlet Design Pressure The maximum design pressure for the inlet and outlet Inlet and Outlet Design Temperature The maximum design temperature for the inlet and outlet Inlet Pipe Size (Internal Diameter ID) and Mater
47、ial The same as the hot reheat piping just before the valve Outlet Pipe Size (Internal Diameter ID) and Material The same as the hot reheat piping just after the valve Noise Level The desired maximum noise level at 1.0 meter (3.28 feet) from the valve (see ISA-75.07-1997) Shutoff Leakage Class The d
48、esired shutoff class at the desired design pressure and temperature rating of the valve usually Class V of ANSI/FCI 70.2 Travel Time The desired minimum travel time from any position, including fully open, at the maximum operating pressure Fail State The IP and LP turbines bypass valve is preferably
49、 a fail-closed design Modulating Time The maximum time for full-stroke operation Turndown Ratio The full range of coordinated operating parameters of flow, pressure, and temperature Condenser Back Pressure The maximum back pressure for valve operation at a specified pressure, temperature, and Flow NOTE If the code permits, this valve can also be used as a fail-open safety relief. An “HP to condenser” valve is preferably fail closed. b) Control valve actuator The type, motive power, material, function, and design of the actuator des
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