Simplified approximations for the accumulation value and time constant for an evaporator system in drum-type boilers

Abstract The storage capacity of the evaporator system of a boiler helps in minimizing the steam pressure fluctuations during load changes even before the combustion control comes into play. The quantitative representation of the storage capacity is usually expressed as an index known as the accumulation value and it quantifies the steam that can be additionally drawn for unit pressure drop. Further, the time constant of the evaporator system can be calculated using the accumulation value. The time constants calculated for varying load clearly indicates non-linear behaviour of the evaporator system. The time constant forms the basis for designing suitable controllers. The simplified approximate relationships for the calculation of the accumulation value of the evaporator of a boiler as a function of drum operating pressure, and of the time constant as a function of varying load, are given for different ratings of the boiler.