1、 AMERICAN NATIONAL STANDARD ANSI/ISA-77.44.01-2007 (R2013) Fossil Fuel Power Plant Steam Temperature Controls Reaffirmed 7 March 2013 ANSI/ISA-77.44.01-2007 (R2013) Fossil Fuel Power Plant Steam Temperature Controls ISBN: 978-0-876640-21-0 Copyright 2013 by ISA. All rights reserved. Not for resale.
2、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. ISA 67 Alexander D
3、rive P. O. Box 12277 Research Triangle Park, North Carolina 27709 USA- 3 - ANSI/ISA-77.44.01-2007 (R2013) Copyright 2013 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/ISA-77.44.01-2007 (R2013). The s
4、tandards referenced within this document may contain provisions which, through reference in this text, constitute requirements of this document. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this document are
5、encouraged to investigate the possibility of applying the most recent editions of the standards indicated within this document. Members of IEC and ISO maintain registers of currently valid International Standards. ANSI maintains registers of currently valid U.S. National Standards. This edition of A
6、NSI/ISA-77.44.01-2007 (R2013), Fossil Fuel Power Plant Steam Temperature Controls, was prepared by the individuals on subcommittee ISA77.44 who contributed to the production of ANSI/ISA-77.44.012000, Fossil Fuel Power Plant Steam Temperature Control System Drum Type, and ANSI/ISA-77.44.022001, Fossi
7、l Fuel Power Plant Steam Temperature Control System Once Through Type. The purpose of combining these two documents was to consolidate related text. The content has been organized and updated per current practices. This document has been prepared as part of the service of ISA toward a goal of unifor
8、mity 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 Alexander
9、 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 Units (SI
10、) 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 end, th
11、is 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 Society
12、for Testing the firebox area, including burners and dampers; the convection area, consisting of any superheater, reheater, economizer sections or any combination thereof, as well as drums and headers. 3.4 cascade control system: a control system in which the output of one controller (the outer loop)
13、 is the setpoint for another controller (the inner loop). The outer loop is normally a slower responding process than the inner loop. 3.5 control loop: a combination of field devices and control functions arranged so that a control variable is compared to a setpoint, and its output returns to the pr
14、ocess in the form of a manipulated variable. 3.6 controller: any manual or automatic device or system of devices used to regulate a process within defined parameters. If automatic, the device or system responds to variations in a process variable. 3.7 desuperheater (direct contact type): a device in
15、 which the steam and the cooling medium (water) are mixed. 3.8 deviation: the difference between the loop setpoint and the process variable (also called error). ANSI/ISA-77.44.01-2007 (R2013) - 14 - Copyright 2013 ISA. All rights reserved. 3.9 error: see 3.8 deviation. 3.10 feedback: a concept in wh
16、ich a process measurement is used to determine whether the control variable is at the desired value. A signal is produced by a measuring device that is proportional to the magnitude of a controlled variable or position of a control element. 3.11 final control element: component of a control system (
17、such as a control valve) that directly regulates the flow of energy or material to or from the process. 3.12 gas pass: an arrangement in which the convection banks of a boiler are separated by gas-tight baffles into two or more parallel gas paths isolating portions of the superheater and reheater su
18、rfaces. The proportion of total gas flow through each gas pass may be varied by regulating dampers. 3.13 gas recirculation: a method by which flue gas from the boiler, economizer, or air heater outlet is reintroduced to the lower furnace to reduce furnace heat absorption while increasing convection
19、pass heat absorption or to reduce NOx emission. 3.14 integral control action: an action in which the controllers output is proportional to the time integral of the error input. It is also called reset action. 3.15 integral windup: the saturation of the integral controller output in the presence of a
20、 continuous error, which may cause unacceptable response in returning the process to its setpoint within acceptable limits of time and overshoot. 3.16 interlock: a device or group of devices (hardware or software) arranged to sense a limit or off-limit condition, or improper sequence of events, and
21、to shut down the offending or related piece of equipment, or to prevent proceeding in an improper sequence in order to avoid an undesirable condition. 3.17 linearity: the nearness with which the plot of a signal or other variable plotted against a prescribed linear scale approximates a straight line
22、. 3.18 master fuel trip: an event resulting in the rapid shutoff of all fuel including igniters. 3.19 primary air: combustion air that enters the fuel-burning zone and directly supports initial combustion. On pulverized coal-fired units, the primary air is used to transport the coal from the pulveri
23、zers to the burners. 3.20 reheater: a heating surface receiving steam returning to the boiler from the high-pressure turbine exhaust. 3.21 secondary air: combustion air introduced on the edge of the burning zone to supplement the primary air for support of the combustion process. - 15 - ANSI/ISA-77.
24、44.01-2007 (R2013) Copyright 2013 ISA. All rights reserved. 3.22 setpoint: the desired operating value of the process variable. 3.23 superheater: boiler heating surface that is not part of the boiler enclosure, which receives only steam already at or above its saturation temperature. (See Figure 3.2
25、3.a and Figure 3.23.b for typical steam and gas flow paths.) Figure 3.23.a Typical superheater steam flow path Figure 3.26.b Typical superheater gas flow path 3.23.1 intermediate superheater: section or sections of superheating surface located between primary and secondary superheaters. 3.23.2 plate
26、n superheater: intermediate superheater surface, which is also a radiant superheater. 3.23.3 primary superheater: first boiler heating surface to receive steam at or slightly above saturation temperature. 3.23.4 secondary superheater: final stage of boiler superheating surface. ANSI/ISA-77.44.01-200
27、7 (R2013) - 16 - Copyright 2013 ISA. All rights reserved. 3.23.5 radiant superheater: steam superheating surface where the primary means of heat transfer to the steam is by radiation rather than convection; typically, an intermediate superheater section. 3.24 trip: the automatic removal from operati
28、on of specific equipment or the automatic discontinuance of a process action or condition as the result of an interlock or operator action. 3.25 transient correction: a control action specifically applied to minimize any process error resulting from a temporary process change; e.g., temperature cont
29、rol action applied to counter the effects of over- or under-firing during load changes. 4 Process measurement requirements 4.1 Instrument installations for superheat and reheat steam temperature control Instruments should be installed as close as practical to the source of the measurement, with cons
30、ideration given to excessive vibration, ambient temperature, and accessibility for periodic maintenance. Temperature measurement should be located at least 20 pipe diameters downstream of any attemperator. 4.2 Design of thermocouples and temperature sensors Design of thermocouples and temperature se
31、nsors shall meet the requirements of ASME Power Test Code PTC19.3 “Temperature Measurements.” Design of the attachment of the thermowell to the pipe shall meet the requirements of either ASME Boiler Pressure Vessel Code Section I “Power Boilers” for Boilers or ASME B31.1 “Power Piping” Code, dependi
32、ng on the code jurisdiction for the pipe. Thermowell installations shall consider location, mounting, and velocity criteria in making a proper interface with the process. 4.3 Isolation valves and impulse lines Separate isolation valves and impulse lines shall be provided for head-type instrumentatio
33、n. 4.4 Process measurements for superheat and reheat steam temperature control Process measurements for superheat temperature control are listed below. For location of these measurements, see Figures C.1a, C.1b, C.1c, and C.1d. 4.4.1 Secondary (final) superheater outlet steam temperature measurement
34、 A temperature measurement, taken at the outlet of the secondary (final) superheater, is required for superheat steam temperature control strategies. 4.4.2 Secondary superheater inlet temperature measurement A temperature measurement, taken at the attemperator outlet(s) for single-stage or multiple-
35、stage attemperation and followed by a superheater section, is required as the secondary variable in a cascade loop with feedforward control strategy. 4.4.3 Primary (initial, platen) inlet temperature measurement A temperature measurement, taken at the primary superheater inlet (or outlet of the firs
36、t stage attemperator of multiple-stage attemperation), is required as the secondary variable in a cascade loop with feedforward control strategy. - 17 - ANSI/ISA-77.44.01-2007 (R2013) Copyright 2013 ISA. All rights reserved. 4.4.4 Primary (initial, platen) outlet temperature measurement A temperatur
37、e measurement, taken at the outlet of the primary superheater section before the first stage attemperator, is required in a single- or multiple-stage attemperator control strategy. 4.4.5 Primary (initial, platen, intermediate) inlet pressure measurement A pressure measurement is required in a multip
38、le-stage attemperator control strategy to prevent saturation following first-stage spray attemperation. Typically, this pressure is measured at the inlet of the primary superheater. A pressure measurement is required in a two-stage attemperator control strategy to prevent saturation following first-
39、stage spray attemperation. Typically, this pressure is measured at the inlet of the intermediate superheater; however, drum pressure may be used if the primary superheaters pressure loss is considered. 4.4.6 Intermediate inlet temperature measurement A temperature measurement, taken at the intermedi
40、ate superheater inlet (or outlet of the first stage attemperator of two-stage attemperation), is required as the secondary variable in a three-element control strategy. 4.4.7 Intermediate outlet temperature measurement A temperature measurement, taken at the outlet of the intermediate superheater se
41、ction before the second stage attemperator, is required in a two-stage attemperator control strategy. 4.4.8 Reheat steam temperature measurement A temperature measurement, taken at the outlet of the final reheater, is required for single loop and single loop with feedforward reheat steam temperature
42、 control strategies for modulation of the reheat steam temperature control mechanisms provided by the boiler manufacturer. 4.4.9 Attemperator spray water-flow measurement An attemperator spray water, mass-flow signal provides an alternative to the use of the attemperator outlet steam temperature as
43、the secondary variable in a cascade loop with feedforward control strategy. 4.4.10 Waterwall (convection pass) outlet temperature measurement A temperature measurement, taken at the outlet of the furnace walls (convection pass) section and followed by a superheater section, is required in a multiple
44、-stage attemperator control strategy. 5 Attemperation methods Control and logic requirements for an attemperator control system for control of steam temperatures The function of the superheat temperature control system is to maintain superheat steam temperature within the boiler manufacturers specif
45、ied limits. Generally, the goal is to obtain a specified final superheat steam temperature over the specified boiler-load range. Control strategy must be based on the particular control mechanisms used and the boiler manufacturers philosophy for controlling steam temperature. Although the strategies
46、 in this standard use conventional PID control techniques, it is not the intention to preclude the use of advanced control strategies. Refer to Table B.1 for a summary of typical control systems. For the control of superheat steam temperature, this standard addresses single-stage attemperation and t
47、wo-stage attemperation. For typical boiler superheater attemperation arrangements, see Figures C.1a and C.1b. Single-loop steam temperature control is the minimum control strategy for reheat steam temperature leaving the boiler and shall be used only for application where reheat spray is the seconda
48、ry means of reheat temperature control. ANSI/ISA-77.44.01-2007 (R2013) - 18 - Copyright 2013 ISA. All rights reserved. Referring to Figure C.9, reheat steam temperature is measured and compared to a setpoint. The setpoint bias in Figures C.5-C.8, which is used to slightly increase the setpoint above
49、 the setpoint of the primary controlling mechanism, is summed with the reheat temperature error to develop the final error signal. Proportional and integral control action, along with an automatic/manual station function, completes the control scheme to regulate the valve. Single loop with feedforward and cascade loop with feedforward steam temperature control strategy should be used in applications where reheat spray is the primary method of reheat temperature control; with variable steam pres
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