Algorithmic Temperature Control
Algorithmic temperature control is utilized for accurate temperature control at or close to steam saturationtemperatures. Conventional temperature sensing via insertion, thermowells cannot accurately measure
steam temperatures within 10°F (5°C) of saturation. This is due to unevaporated water droplets collecting
on the thermowell leading to erroneous temperature readings and loss of control of the cooling water
control valve. Taking advantage of the rapid advance in electronic technology, Copes-Vulcan can offer a
preprogrammed logic module to interface with the DCS or panel mounted with local controllers.
Drain/Warming Valve
Control ValveSteam
Dump TubeCondenserOutlet Steam PressureWater Flow Inlet SteamTemperatureInlet SteamPressureBypass Valve PTX TTX PTX FTX Command SignalPosition Transmitter Algorithmic temperature control logic diagram.
Operating Philosophy
The amount of cooling water supplied to the combined turbine bypass valve or separate desuperheatingelement is determined by a heat balance calculation performed within the algorithm module. The module
receives several inputs.
Input: Output: • Inlet steam temperature — T
1 • Cooling water flow rate — Q
w .The algorithm has preprogrammed steam tablesand instantly calculates the required coolingwater quantity. This analog output is directedto the temperature controller which constantlymonitors required water flow against actualwater flow. The actual water flow is measured either froman orifice plate or valve position feed back.This extremely rapid and accurate method oftemperature control negates the temperature sensor problems encountered when bypassing to condensers, especially when utilizing dump tubes or where there are only short distances from the bypass valve to the condenser inlet. (required to calculate inlet steam enthalpy — h
1 ).• Inlet steam pressure — P
1 (required to calculate inlet steam enthalpy — h
1 ). • Inlet steam flow — Q
1 (the steam flow into the bypass valve is measured either by an orifice plate or valve position feed back).• Outlet or condenser pressure — P
2 (required to determine saturation enthalpy — h
2 ).• (The cooling water temperature and hence cooling water enthalpy — h
w is an adjustable constant within the algorithm. Even relatively large changes in water temperature have only very small effects in overall enthalpy.)Cooling water quantity Q
w = Q
1 x h
1 - h
2 h
2 - h
w 9 9
