Boiler Appurtenances

In almost all countries today, safety codes and regulations exist for the construction, operation, and inspection of all boilers and associated pressure vessels and boiler systems. Both HW and steam-raising plants are provided with several vital boiler appurtenances (appliances or fittings) and various subsystems containing auxiliaries (accessories) that must be maintained, monitored, and controlled. However, for small HW and LP steam boiler plants the inspection process may be rather cursory with regard to the pressure vessel internals and tends to concentrate primarily on ensuring the proper operation of the various appurtenances that provide for boiler safety. 

Appurtenances are primarily the fittings that enable boilers to operate safely. They control the FW supply, boiler pressure, BW level, and steam supply. Appurtenances include  

NOTE Soot blowers are typically employed only on WT boilers and may be regarded as appurtenances because boiler safety and reliability is directly related to the cleanliness of the heat transfer surfaces. Boiler performance and efficiency also depend on the same heat-transfer cleanliness factors. 

The pressure gauge and associated shut-off valve, the boiler vent cock valve, main steam stop valve, and safety valve can be observed rising above the crown sheet of a FT boiler (the highest point of the boiler), normally in a line running the length of the boiler. 

Water tube boilers have a pressure gauge, vent cock, and drum safety valve on the top of the steam drum. Where superheaters are fitted, the steam takeoff line leads to the superheater, which is followed by a superheater safety valve, automatic nonreturn valve, and stop valve with a pressure-equalizing line and valve. 

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One of several codes written by the American Society of Mechanical Engineers. Some codes provide controls for the construction, repairs, and the operation of boilers and other types of PV and boiler appurtenances in the United States. 

Appurtenances, see Boiler appurtenances AQtm Total, nonchemical technology 340... 

Less than 10 MW 24 0 29fj Including condenser, heaters, and all other necessary appurtenances but not boiler... 

Today boiler vessels are usually fabricated from special boiler plate and firebox steels of varying thickness, while their auxiliaries (supplementary equipment) and appurtenances (boiler accessories and instruments, especially those employed for safety reasons) may be produced from any of several different constructional metals, alloys, and other materials, including cast iron, copper alloys, stainless steels, and so forth. Tubes and tube plates may be variously constructed of carbon steel, low-alloy steels, or special alloy steels, with each design providing for particular required levels of thermal and mechanical stress and corrosion resistance. The overall boiler plant system may have a life expectancy in excess of 50 to 60 years, although individual components may need to be replaced periodically during this period. 

Pressure vessels and appurtenances should be constructed of stainless steel or other corrosion-resistant materials. Ideally, these steam generators should receive hot demineralized FW to minimize chemical treatment requirements. Alternatively, where a main boiler plant is installed, 100% steam condensate provides a good source of FW. In practice, it is very difficult to accurately control the correct amount of chemical feed. Chemicals are typically restricted to potable grade, deposit control agents such as polyacrylates, and other materials listed under the Code of Federal Regulations, CFR 21 173.310, or National Sanitary Foundation (NSF International) approval system. These boilers may be electrically heated or gas-fired. 

Modem HW-generating and steam-raising facilities comprise a number of often complex, interdependent boiler plant subsystems, appurtenances, and auxiliaries, with large process, utility, and cogeneration boiler plants being especially complex. This chapter provides notes on many of the various boiler plant subsystems and types of equipment employed as an introduction to considering the waterside problems that may be encountered therein. 

The boiler steam generation system primarily covers the boiler itself, the boiler surfaces (the primary heat-transfer and steam-generating surfaces within the boiler proper), and all necessary appurtenances. 

Vital periodic testing and maintenance of safety valves, pressure relief valves, stop valves, and other items is usually carried out on a 12-month cycle. Boiler plant equipment fitted with such appurtenances (and thus requiring regular checks), include boilers, heaters, deaerators, evaporators, and economizers. 

Preparing a boiler for inspection requires the operator to first follow a sequence of specific boiler shutdown procedures, including cooling the boiler slowly to prevent undue stress to the metal and refractory. The primary purpose of the inspection process is to ensure continued boiler safety, and therefore a thorough inspection of all appurtenances is mandatory. 

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