1、 STANDARD ANSI/ISA77.82.01-2011 Selective Catalytic Reduction (SCR) Control Systems Approved 17 January 2011 ANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 2ANSI/ISA77.82.01-2011 Selective Catalytic Reduction (SCR) Control Systems ISBN: 978-1-936007-79-0 Copyright 2011 by ISA, The I
2、nternational Society of Automation. All rights reserved. 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), w
3、ithout the prior written permission of the Publisher. ISA 67 Alexander Drive P. O. Box 12277 Research Triangle Park, North Carolina 27709 USAANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 3Preface This preface, as well as all footnotes and annexes, is included for information purpos
4、es and is not part of ANSI/ISA77.82.01-2011. The standards 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, an
5、d parties to agreements based on this document are 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 current
6、ly valid U.S. National Standards. This document has been prepared as part of the service of ISA, The International Society of Automation, toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Tow
7、ard 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 Drive; P. O. Box 12277; Research Triangle Park, NC, 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA
8、 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) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA stan
9、dards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical
10、 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 for Testing the firebox area, including burners and dampers; the convection area, consisting of any superheater, reheater, economizer sect
11、ions or any combination thereof, as well as drums and headers. ANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 103.8 burner a device or group of devices for the introduction of fuel and air into a combustion chamber at the velocity, turbulence, and concentration required to maintain
12、ignition and combustion of fuel. 3.9 cascade control system a control system in which the output of one controller (the outer loop) is the setpoint for another controller (the inner loop). The outer loop is normally a slow responding process as compared to the inner loop. 3.10 catalyst a substance t
13、hat initiates a chemical reaction and enables it to proceed under milder conditions than otherwise possible. 3.11 combustion the rapid chemical combination of oxygen with the combustible elements of a fuel, resulting in the production of heat. 3.12 combustible the heat-producing constituent of a fue
14、l, flue gas, or fly ash. 3.13 control loop a control structure in which the controlled variable is measured and compared to the setpoint to create a deviation signal, which is processed through the control algorithm and outputted to a control actuator to drive the controlled variable to the setpoint
15、. 3.14 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. 3.15 deviation the difference between the loop setpoint and the process variable. 3.16 differen
16、tial pressure flow element a measuring element that is inserted in a process flow path and used to create a pressure drop that is proportional to the square of the rate of flow. 3.17 drum (steam) a closed vessel designed to withstand internal pressure. A device for collecting and separating the stea
17、m/water mixture circulated through the boiler. 3.18 error see 3.15 deviation. 3.19 excess air air supplied for combustion in excess of theoretical combustion air. 3.20 fail safe the capability to go to a predetermined safe state in the event of a specific malfunction. 3.21 feedback a signal produced
18、 by a measuring device that is proportional to the magnitude of a controlled variable or position of a control element. ANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 113.22 final control element the component of a control system (such as a control valve) that directly regulates the
19、 flow of energy or material to or from the process. 3.23 firing rate the rate of fuel combustion in a boiler. 3.24 flue gas the gaseous products of combustion in the flue to the stack. 3.25 fuel a substance containing combustible material used for generating heat; coal, oil, and gas are fuels refere
20、nced in this standard. 3.26 fuel trip the automatic shutoff of a specific fuel as the result of an interlock or operator action. 3.27 furnace an enclosed space provided for the combustion of fuel. 3.28 furnace pressure the pressure of gases in the furnace (see also draft). 3.29 induced draft fan a f
21、an exhausting flue gases from the furnace. 3.30 instrument a device used directly or indirectly to measure and/or control a process variable. The term includes primary elements, final control elements, measuring devices, computing devices, and electrical devices, such as annunciators, switches, and
22、push buttons. The term does not apply to parts that are internal components of an instrument (e.g., a receiver bellows or a resistor). 3.31 integral control action an action in which the controllers output is proportional to the time integral of the error input. When used in combination with proport
23、ional action, it previously was called reset action. 3.32 integral windup the saturation of the integral controller output in the presence of a continuous error, which may cause unacceptable response in returning the process to its setpoint within acceptable limits of time and overshoot. 3.33 interl
24、ock a device or group of devices (hardware or software) arranged to sense a limit or off-limit condition, or improper sequence of events, and 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. 3.34 lo
25、ad the rate of energy output, usually expressed as lb/hr (kg/s) of steam or megawatts of electrical generation. 3.35 load index signal representative of desired output energy flow rate. 3.36 master fuel trip (MFT) an event resulting in the rapid shutoff of all fuel. (See 3.26 fuel trip.) ANSI/ISA-77
26、.82.01-2011 Copyright 2011 ISA. All rights reserved. 123.37 mode (submode) a particular operating state of a control system, such as manual, automatic, remote, coordinated, etc. A mode is usually designed to achieve a desired control strategy. 3.38 molar ratio the ratio of the number of molecules of
27、 each substance involved in a balanced chemical reaction. 3.39 nitrogen oxides the nitrogen oxides controlled by SCRs are mainly NO and NO2and are products of combustion. 3.40 protective logic circuits logic circuits designed to prevent damage to equipment by related system equipment malfunctions, f
28、ailure, or operator errors. 3.41 redundant (redundancy) duplication or repetition of elements in electronic or mechanical equipment to provide alternative functional channels in case of failure of the primary device. 3.42 selective catalytic reduction (SCR) a process for reducing the NOx emissions f
29、rom power plants by passing the flue gas over a catalyst in the presence of ammonia and oxygen. 3.43 setpoint the desired operating value of the process variable. 3.44 shall, should, and may the word “SHALL“ is to be understood as a REQUIREMENT; the word “SHOULD“ as a RECOMMENDATION; and the word “M
30、AY“ as a PERMISSIVE, neither mandatory nor recommended. 3.45 steam header pipe in which steam output from multiple boilers is collected and then distributed to various steam loads. 3.46 theoretical (stoichiometric) combustion air the chemically correct amount of air required for complete combustion
31、of a given quantity of a specific fuel. 3.47 tracking forcing an inactive control function to follow the active control function so that upon a mode transfer, no process upset occurs. 3.48 trip the automatic removal from operation of specific equipment or the automatic discontinuance of a process ac
32、tion or condition as the result of an interlock or operator action. 3.49 turbine a machine that converts energy from a moving fluid into rotating mechanical energy to drive a load. In a power plant, a turbine converts energy in the steam into mechanical energy to drive an electric generator (the loa
33、d) or an auxiliary, such as a boiler feedpump. 3.50 two-out-of-three logic circuit (2/3 logic circuit) a logic circuit that employs three independent inputs and whose output of the logic circuit is the same state as any two matching input states. 3.51 urea an organic compound which can be decomposed
34、 into ammonia. Urea is sometimes used as a precursor of ammonia for an SCR. ANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 134 Minimum design requirements for SCR control systems In order to establish minimum criteria, the SCR control systems specification shall include the followin
35、g as part of the system design basis: Maximum and minimum unit load (steaming capacity) Normal operating load range Anticipated load changes Start-up and shutdown frequency Degree of automation Boiler auxiliary maximum and minimum capacities Type of fuel Flue-gas temperatures leaving the boiler Seas
36、onal requirements of the SCR, if any The SCR control systems shall meet operational requirements and correctly interface with the process. To accomplish this objective, the following requirements are defined for minimum system design: Process measurement requirements Control and logic requirements F
37、inal control device requirements System reliability and availability requirements Alarm requirements Operator interface requirements 4.1 Process measurement requirements 4.1.1 Instrument installation for SCR controls Process sensing devices should be installed as close as practical to the source of
38、the measurement with consideration being given to excessive vibration, temperature, and access for periodic maintenance. Separate isolation valves and impulse lines should be run to each pressure-sensing device used for control. No copper or copper-based alloy shall be used for any ammonia-wetted fi
39、ttings, tubing, or instrumentation. For measurements in flue-gas ducts, multiple sensors may be required to get a representative measurement. ANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 144.1.2 Measurement conditioning Filtering techniques used to condition process measurements s
40、hall not adversely affect stability or reduce control system response. 4.1.3 Process measurements 4.1.3.1 Ammonia storage and delivery subsystem Ammonia storage tank level One local measurement is required, and one remote measurement separate from and independent of the local measurement is also req
41、uired. This is used to compute the quantity in percent of tank capacity of ammonia liquid in the tank. Ammonia storage tank pressure Two redundant measurements are required. The sensor should measure both pressure and vacuum. Ammonia storage tank temperature Fogging system supply pressure Safety sho
42、wer activation sensor Supply header suction pressure Supply header discharge pressure Forwarding pump suction strainer differential pressure 4.1.3.2 Dilution air and ammonia flow control subsystem Inlet NOxconcentration or calculated index for inlet NOxconcentration Outlet NOxconcentration Flue-gas
43、flow rate or calculated index for flue-gas flow rate Ammonia-mass flow rate Dilution air-mass flow rate (for anhydrous systems) Dilution air temperature (for anhydrous systems) Dilution air pressure (for anhydrous systems) Heater (air/gas) flow Heater (air/gas) temperature Heater (air/gas) pressure
44、ANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 15 Ammonia filter differential pressure Ammonia flow-control valve discharge pressure Ammonia vaporizer sump temperature Ammonia and diluent mixture temperature SCR flue-gas inlet temperature 4.1.3.3 Startup and shutdown subsystem Econo
45、mizer outlet temperature SCR flue-gas inlet temperature SCR flue-gas outlet temperature Catalyst (or reactor steel) temperature 4.1.3.4 Flue-gas bypass and isolation subsystem Inlet and outlet damper-seal, air-differential pressure Dehumidifier heater inlet temperature (if required). (Depending on d
46、uct size and arrangement, a grid of temperature sensors may be required to obtain a representative measurement.) Dehumidifier heater outlet temperature Warming medium temperature (e.g., air or flue gas) SCR outlet temperature. (Depending on duct size and arrangement, a grid of temperature sensors ma
47、y be required to obtain a representative measurement. The lowest of these readings should be used.) 4.1.3.5 Catalyst cleaning subsystem Overall SCR differential pressure Each catalyst layer differential pressure Sootblowing medium (steam or air) supply pressure Sootblowing medium (steam only) supply
48、 temperature Sonic air-horn supply pressure Sootblowing steam-header drain temperature 4.1.3.6 Ammonia leak-detection systems Ambient ammonia concentration ANSI/ISA-77.82.01-2011 Copyright 2011 ISA. All rights reserved. 164.2 Control and logic requirements Automatic tracking shall be provided for bu
49、mpless control-mode transfer for all modulating control systems described in sections 4.2.1 through 4.2.5 below. 4.2.1 Ammonia storage and delivery subsystem 4.2.1.1 Truck or train unloading The train or truck unloading control system shall include a manually initiated emergency automatic shutdown function. In addition an automatically initiated shutdown shall occur when a high-ambient ammonia concentration (50-100 ppm) is detected. For anhydrous ammonia systems, the unloading
