Best practices for instrumentation

What is best practice to monitor the water side of a firetube boiler / ShellBoiler?


All FiretubeBoilersare at least equipped with a continuous level measurement (required in all control strategies for feedwater addition).

Guided WaveRadar and DPlevel are preferred because they are not susceptible to foam. Level switches are required to avoid priming (HL) and emergency shutdowns (or boiler explosions in the worst case).

3-element control strategy for feedwater addition requires flow measurements of feedwater and steam. These are also required to monitor direct fuel-to-steam efficiency.

When measuring steam flow (also at the flashsteam separator) , both degrees of superheat and dryness fraction should be monitored. (Superheated steam may indicate a half-open crown valve, too low a dryness fraction may lead to or indicate priming).

Delta T across the economizer should be monitored to check its efficiency. Pressure should be monitored to check for a leaking economizer.

Not only the feedwater quality should be checked, also the blowdown (e.g. pH, conductivity, TDS) and steam itself (pH, conductivity and Differential Conductivity ).

What is best practice to monitor the fire side of a firetube boiler/ shellBoiler?


FuelFlow measurement is important to determine the boiler’s fuel-to-steam (direct) efficiency :

  • For NaturalGas, typically ThermalMass flowmeters, ultrasonic or vortex flowmeters are used.

  • For liquid fuels, typically Coriolis flowmeters are used because of their high accuracy and their capability to measure density and viscosity as diagnostic parameters (Promass I 300).

  • For biogas, ultrasonic flowmeters like Prosonic Flow B200 are preferred because of their capability to measure the percentage of methane and GCV and NCV. CombustionAir flow is measured to check AirToFuel ratio. Combustion air temperature should be preferably high and monitored. FlueGas temperature is an important indicator for heat transfer issues inside the boiler: A rise indicates either problems on the fire side (soot) or on the water side (fouling). This value alongside flue gas analytics (%O2, %CO and %CO2 in larger boilers) is important to determine the combustion efficiency and the indirect efficiency of the boiler.