SIEMENS SIMATIC S7 + WINCC

Desuperheater Temperature Control

This mesh allows steam temperature control at the boiler outlet through water injection between the primary/secondary superheaters. Control is carried out through the steam temperature transmitter at the boiler outlet (TT300), which sends a signal to the controller. The controller output signal acts directly on the desuperheat valve (TCV300), controlling the flow of water for injection into the steam desuperheater.

When the steam temperature decreases (PV drops), the valve (MV) must close to maintain the temperature at the indicated SP. When the steam temperature increases (PV increases), the valve (MV) must close to maintain the temperature at the indicated SP.

• Create Function FC8 CTR_TT300 Superheated Steam Temperature Control. Right-click on the Blocks folder and select Insert New Object > Function menu item.

• Create a variable for opening the steam desuperheater valve in the symbol table.

Name	Address	Type	Description	S7_m_c
TCV300_RB	MD44	Real	Desuperheadter Valve READBACK	True

• Open CTR_TIC300 function and insert FB_PID function block.

TIC300

FB_PID

DB58

• Move the PID output to the TCV300 control valve on the Profibus-PA network.

• Read the opening value of the TCV300 control valve via the Profibus-PA network.

• Force PID action. When the steam temperature decreases (PV drops), the valve (MV) must close to maintain the temperature at the indicated SP. When the steam temperature increases (PV increases), the valve (MV) must close to maintain the temperature at the indicated SP.

• Move multiplication factor to convert PV and SP (0 to 500 oC) to 0 to 100% at the PID input.

• Call FC8 CTR_TIC300 in OB1.

• Select Operator Control and Monitoring for DB58 TIC300.

• Compile AS and OS.

• Create front for PID Steam Temperature Control Overheated in Controle_Temperatura.pdl.

C script to show the picture window PW_PID object in the current picture.

The Picture Name property of the PW_PID picture window receives the name of the PID.PDL.

The TagPrefix property of the picture window PW_PID is set to CALD/TIC300. This instruction adds the text “CALD/TIC300” at the beginning of all object dynamizations within the picture window.