1、 STANDARD ANSI/ISA-77.41.01 Fossil Fuel Power Plant Boiler Combustion Controls Revised November 2010 ANSI/ISA77.41.01-2010 Fossil Fuel Power Plant Boiler Combustion Controls ISBN: 978-1-936007-69-1 Copyright 2010 by the International Society of Automation (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-77.41.01-2010 Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA-77.41.01-2010. The standards referenced within this document may contain provi
4、sions 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 encouraged to investigate the possibility of applying the
5、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 document has been prepared as part of the service of ISA, the Internat
6、ional 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. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secreta
7、ry, 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 Standards and Practices Department is aware of the growing need for attention to the metric system of units i
8、n 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 standards of incorporating suitable references to the SI (and the metric system) in their business and professiona
9、l 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 reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Mode
10、rn 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 sections or any combination thereof, as well as drums and headers. 3.6 burner: A device or group of devices for th
11、e introduction of fuel and air into a combustion chamber at the velocity, turbulence, and concentration required to maintain ignition and combustion of fuel. 3.7 combustion: the rapid chemical combination of oxygen with the combustible elements of a fuel, resulting in the production of heat. Copyrig
12、ht 2010 ISA. All rights reserved. ANSI/ISA-77.41.01-2010 - 12 3.8 combustible: the heat-producing constituent of a fuel, flue gas, or fly ash. 3.9 controller: any manual or automatic device or system of devices used to regulate a process within defined parameters. If automatic, the device or system
13、responds to variations in a process variable. 3.10 control loop: a combination of field devices and control functions arranged so that a control variable is compared to a setpoint and returns to the process in the form of a manipulated variable. 3.11 convection: the transmission of heat by the circu
14、lation of a liquid or a gas, such as air. Convection may be natural or forced. 3.12 draft: the difference between atmospheric pressure and some lower pressure existing in the furnace or gas passages of a steam-generating unit. 3.13 efficiency: the ratio of energy output to the energy input. The effi
15、ciency of a boiler is the ratio of heat absorbed by water and steam to the heat equivalent of the fuel fired. 3.14 excess air: air supplied for combustion in excess of theoretical combustion air. 3.15 fail safe: the capability to go to a predetermined safe state in the event of a specific malfunctio
16、n. 3.16 final control element: the component of a control system (such as a control valve) that directly regulates the flow of energy or material to or from the process. 3.17 flue gas: the gaseous products of combustion in the flue to the stack. 3.18 forced draft fan: a fan supplying air under press
17、ure to the fuel-burning equipment. 3.19 fuel: a substance containing combustible material used for generating heat; coal, oil, and gas are fuels referenced in this standard. 3.20 furnace: an enclosed space provided for the combustion of fuel. 3.21 furnace pressure: the pressure of gases in the furna
18、ce (see also draft). 3.22 induced draft fan: a fan exhausting flue gases from the furnace. 3.23 instrument: a device used directly or indirectly to measure and/or control a process variable. The term includes Copyright 2010 ISA. All rights reserved. - 13 ANSI/ISA-77.41.01-2010 primary elements, fina
19、l control elements, measuring devices, computing devices, and electrical devices, such as annunciators, switches, and push buttons. The term does not apply to parts that are internal components of an instrument (e.g., a receiver bellows or a resistor). 3.24 integral windup: the saturation of the int
20、egral 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. 3.25 load: the rate of energy output, usually expressed as lb/hr (kg/s) of steam or megawatts of electrical g
21、eneration. 3.26 logic system: decision-making logic equipment with its associated power supplies, I/O hardware, and sensing devices. 3.27 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
22、 transport the coal from the pulverizers to the burners. 3.28 redundant (redundancy): duplication or repetition of elements in electronic or mechanical equipment to provide alternative functional channels in case of failure of element. 3.29 secondary air: combustion air introduced on the edge of the
23、 burning zone to supplement the primary air for support of the combustion process. 3.30 secondary combustion: combustion that occurs as a result of ignition at a point beyond the furnace. 3.31 setpoint: the desired operating value of the process variable. 3.32 shall, should, and may: the word “SHALL
24、” is to be understood as a REQUIREMENT; the word “SHOULD” as a RECOMMENDATION; the word “MAY” as a PERMISSIVE, neither mandatory nor recommended. 3.33 tertiary air: the air supplied to certain types of burners for cooling the burner metal or to improve the combustion process. 3.34 theoretical (stoic
25、hiometric) combustion air: the chemically correct amount of air required for complete combustion of a given quantity of a specific fuel. 3.35 tracking: forcing an inactive control function to follow the active control function so that upon a mode transfer, no process upset occurs. Copyright 2010 ISA
26、. All rights reserved. ANSI/ISA-77.41.01-2010 - 14 4 Minimum design requirements for combustion control system The combustion control system shall meet operational requirements and correctly interface with the process. To accomplish this objective, the following requirements are defined for minimum
27、system design: a) Process measurement requirements b) Control and logic requirements c) Final control device requirements d) System reliability and availability e) Alarm requirements f) Operator interface 4.1 Process measurement requirements 4.1.1 Instrument installation for combustion control Proce
28、ss sensing devices should be installed as close as practical to the source of the measurement with consideration being given to excessive vibration, temperature, and access for periodic maintenance. Dedicated isolation valves and impulse lines should be run to each pressure-sensing device used for c
29、ontrol in accordance with ISA-77.70.02 Instrument Piping Installation and ASME B31.1 Power Piping. 4.1.2 Measurement and conditioning Filtering techniques used to condition process measurements shall not adversely affect stability or reduce control system response. 4.1.3 Process measurements 4.1.3.1
30、 Mass airflow measurement The mass airflow measurement shall be a repeatable signal that is representative of the air entering the furnace. When volumetric airflow-rate measurement techniques are employed and the air temperature at the flow- measuring element varies 50F (28C) or more, the measured (
31、indicated) flow shall be compensated for flowing air density to determine the true mass airflow rate. 4.1.3.2 Furnace pressure measurement Furnace pressure shall be measured with three furnace pressure transmitters, each on a separate pressure-sensing tap. 4.1.3.3 Fuel measurement The fuel-flow meas
32、urement shall be a representative measure of the total fuel energy entering Copyright 2010 ISA. All rights reserved. - 15 ANSI/ISA-77.41.01-2010 the furnace. 4.1.3.4 Gas analysis measurement a) A representative flue-gas oxygen measurement shall be provided. b) A representative flue-gas measurement o
33、f equivalent combustibles should be provided for monitoring under low excess-air firing conditions. 4.2 Control and logic requirements 4.2.1 Automatic tracking Automatic tracking shall be provided for bumpless control-mode transfer. 4.2.2 Combustion control The combustion control, which responds to
34、the boiler energy demand, shall be accomplished with the following: a) Furnace pressure (balanced draft systems) control b) Air demand and air control c) Fuel demand and fuel control d) Excess air The development of the boiler energy demand is covered in ANSI/ISA-77.43.01, Fossil Fuel Power Plant Un
35、it/Plant Demand DevelopmentDrum Type. 4.2.2.1 Furnace pressure (draft) control The furnace pressure control shall regulate flue gas flow to maintain furnace pressure at the desired set point in compliance with the requirements of NFPA 85. The furnace pressure control shall utilize a feedforward sign
36、al representative of the boiler airflow demand. 4.2.2.2 Air demand and air control Airflow demand shall be developed from the boiler energy demand and used to control airflow to the furnace. There shall be a minimum airflow demand limit to prevent air from being reduced below the unit purge rate whe
37、n the air control is in automatic. Suitable provisions shall be included to prevent controller windup under minimum air limit conditions. The minimum airflow limit shall be in compliance with the requirements of NFPA 85. The following are prerequisites for the airflow control in automatic: a) Furnac
38、e pressure control in automatic (balanced draft systems) b) One or more forced draft fans (or other air source) in service and the associated regulating device(s) in automatic control Copyright 2010 ISA. All rights reserved. ANSI/ISA-77.41.01-2010 - 16 Provision shall be made to ensure that the auto
39、matic regulation of air shall result in a fuel-to-air ratio that provides safe boiler operation. This shall include limiting of fuel flow or airflow to ensure that fuel flow never exceeds the safe combustion limit that the airflow will support. 4.2.2.3 Fuel demand and fuel control Fuel demand shall
40、be developed from the boiler energy demand and used to control fuel flow to the furnace. Total fuel input shall be determined from one or a combination of calculated values, fuel measurements, or characterized fuel demand outputs. The fuel demand/fuel input relationship shall be used to control ener
41、gy balance on a Btu (kJ) basis. When the fuel control is in automatic, there shall be a minimum fuel demand limit to prevent fuel from being reduced below the level required to support stable flame conditions in the furnace. Suitable provisions shall be included to prevent controller windup under mi
42、nimum fuel limit conditions. The following are prerequisites for fuel controller in automatic: a) Air control in automatic b) One fuel source in service and the associated regulating device(s) in automatic control Provision shall be made to ensure that the automatic regulation of fuel shall result i
43、n a fuel-to-air ratio that provides safe boiler operation. This shall include limiting of fuel flow or airflow under all conditions to ensure that fuel flow never exceeds the safe combustion limit that the airflow will support. 4.2.2.4 Excess air Excess air shall be maintained at all loads to assure
44、 proper combustion of the fuel entering the furnace and should not allow the furnace to operate at an oxygen level in the flue gas below the boiler or burner manufacturers requirements. Suitable provisions shall be included to prevent excess air controller windup under airflow limit conditions. 4.2.
45、3 Burner management interface requirements Any interface between the combustion control system and the burner management system shall comply with NFPA 85. 4.3 Final control device requirements All final control elements shall be designed to fail safe on loss of demand signal or motive power, i.e., o
46、pen, closed, or lock in place. The fail-safe position shall be determined by the user and be based upon the specific application to meet all boiler purge and interlock requirements of NFPA 85. 4.4 System reliability and availability In order to establish minimum criteria, the combustion control syst
47、em specification shall include the following as part of the system design base: a) Maximum and minimum unit load (steaming capacity) b) Normal operating load range c) Anticipated load changes Copyright 2010 ISA. All rights reserved. - 17 ANSI/ISA-77.41.01-2010 d) Start-up and shutdown frequency e) D
48、egree of automation f) Boiler auxiliary maximum and minimum capacities Field transmitting device redundancy should be provided to the extent necessary to achieve desired system reliability. When only one transmitter is used, and the control system can detect a bad signal, the control loop shall be t
49、ransferred to manual when a signal is detected as bad. When two transmitters are used, the minimum, maximum, or average can be selected. If both transmitters are good signals and excessive deviation between the transmitters exist, then an alarm shall be generated, and the associated control loop shall be transferred to manual. If one transmitter is a bad signal, then the selection shall transfer to the good signal. If both transmitters are bad signals, then transfer the loop to manual. When three transmitters are used, the median signal shall be selected
