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1.1* Scope. This code applies to the following: A.1.1 Technological advances in recent years and, in particular, the pervasiveness of microprocessor-based hardware make it even more important that only highly qualified individuals be employed in applying the requirements of this code to operating systems. Each type of hardware has its own unique features and operational modes. It is vital that the designer of the safety system be completely familiar with the features and weaknesses of the specific hardware and possess a thorough understanding of this code and its intent. It is not possible for this code to encompass all specific hardware applications, nor should this code be considered a “cookbook” for the design of a safety system. In applying any type of equipment to a safety system, the designer should consider carefully all the possible failure modes and the effect that each might have on the integrity of the system and the safety of the unit and personnel. In particular, no single point failure should result in an unsafe or uncontrollable condition or a masked failure of a microprocessor-based system that could result in the operator unwittingly taking action that could lead to an unsafe condition. In this code, the sections that apply to all fuels should be used in conjunction with those sections covering the specific fuel utilized. (1) Single burner boilers, multiple burner boilers, stokers, and atmospheric fluidized bed boilers with a fuel input rating of 3.7 MWt (12.5 million Btu/hr) or greater (2) Pulverized fuel systems at any heat input rate (3) Fired or unfired steam generators used to recover heat from combustion turbines [heat recovery steam generators (HRSGs)] and other combustion turbine exhaust systems at any heat input rate 1.1.1 This code covers design, installation, operation, maintenance, and training. 1.1.2 This code covers strength of the structure, operation and maintenance procedures, combustion and draft control equipment, safety interlocks, alarms, trips, and other related controls that are essential to safe equipment operation. 1.1.3 This code does not cover process heaters used in chemical and petroleum manufacture in which steam generation is incidental to the operation of a processing system. 1.1.4 Chapter 5 covers single burner boilers that fire the following fuels: (1) Fuel gas as defined in 3.3.74. (2)*Other gas having a calorific value and characteristics similar to natural gas A.1.1.4(2) This can include some heavier-than-air gases. (3) Fuel oil as defined in 22.214.171.124 (4) Fuel gas and fuel oil that are fired simultaneously for fuel transfer (5) Fuel gas and fuel oil that are fired simultaneously and continuously 1.1.5 Chapter 6 covers multiple burner boilers firing one or more of the following: (1) Fuel gas, as defined in 3.3.74 (2) Fuel oil, as defined in 126.96.36.199 (3) Pulverized coal, as defined in 188.8.131.52.1 (4) Simultaneous firing of more than one of the fuels stated in 1.1.5(1) through 1.1.5(3) 1.1.6 Chapter 7 covers atmospheric fluidized bed boilers. 1.1.7* Chapter 8 covers HRSG systems and other combustion turbine exhaust systems. A.1.1.7 It is not possible for this code to encompass the specific hardware applications, nor should it be considered a cookbook for the design of a safe HRSG system. A HRSG is a complex system, often involving numerous components, multiple steam pressure levels, emission control systems, and augmented air or supplementary firing. The simplest combined cycle plant automatically has certain hazards that are common to all designs. Coupling various designs of heat recovery units with combustion turbines of varying characteristics in different configurations (such as varying damper arrangements) can produce unique hazards. The potential ineffective use of the combustion turbine as the source of the purge and potential sources of substantial fuel entering the HRSG from normal and false starts are major considerations that need to be addressed. Other concerns are special provisions, for example, automatic transfer during transients, multiple stacks that can create reverse flows, internal maintenance of the HRSG with the combustion turbine in operation, multiplicity of cross connections between units to prevent shutdown, and fitting the HRSG into a small space using finned tubes that are more sensitive to temperature and subject to iron fires. Insufficient failure analysis of arrangements, configurations, and equipment can increase the number of damaging incidents, lost production, and the possibility of personal injury or death. It is vital that the designer of the combustion turbine and any burner safety system(s) be completely familiar with the features, characteristics, and limitations of the specific hardware and also possess a thorough understanding of this code and its intent. 1.1.8 Chapter 9 covers pulverized fuel systems, beginning with the raw fuel bunker, which is upstream of the pulverizer and is the point at which primary air enters the pulverizing system, and terminating at the point where pressure can be relieved by fuel being burned or collected in a device that is built in accordance with this code. The pulverized fuel system shall include the primary air ducts, which are upstream of the pulverizer, to a point where pressure can be relieved. 1.1.9 Chapter 10 covers boilers that use a stoker to fire the following fuels: (1) Coal (2) Wood (3) Refuse-derived fuel (RDF) (4) Municipal solid waste (MSW) (5) Other solid fuels 184.108.40.206 Where solid fuel is fired simultaneously with other fuels (e.g., a solid fuel stoker fired in combination with fuel gas, fuel oil, or pulverized auxiliary fuel), additional controls and interlocks shall include those covered in Chapters 5, 6, and 9. Exception No. 1: The purge requirements of Chapters 5 and 6 shall not be required when the stoker is firing and the boiler is on-line. In those cases, if no cooling air is being provided to the auxiliary burners, a purge of their associated air supply ducts shall be provided. Exception No. 2: Where fuel oil or fuel gas is fired in a supervised manual system in accordance with Chapter 5, the excessive steam pressure interlock shall not be required.
NFPA 85 contributes to operating safety and prevents explosions and implosions in boilers with greater than 12.5 MMBTUH, pulverized fuel systems, and heat recovery steam generators.
Provisions apply to boiler design, installation, operation, maintenance, and training for the full range of large boiler installations and pulverized fuel systems. Among topics covered are strength of the structure, combustion and draft control equipment, safety interlocks, alarms, trips, and other related controls that are essential to safe equipment operation.
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