Method and apparatus for operating a solar thermal power plant

Abstract

A solar thermal power plant, wherein, in an intermediate superheater in the water-steam circuit, steam is heated to a settable setpoint temperature value at the outlet by a heat carrier medium which has been heated solar-thermally, wherein, for the heating of the steam to a set setpoint temperature value, a mass flow of the heat carrier medium entering the intermediate superheater is controlled as a function of a determined enthalpy difference of the heat carrier medium between the entry and exit thereof into and out of the intermediate superheater and as a function of a determined enthalpy difference of the steam between the exit and entry thereof out of and into the intermediate superheater is provided.

1 . A method for operating a solar thermal power plant in which steam is heated in an intermediate superheater in a water/steam circuit by a solar-thermally heated heat transfer medium to an adjustable setpoint temperature value at an exit, comprising:
 in order to heat the steam to an adjusted setpoint temperature value, regulating a mass flow of the solar-thermally heated heat transfer medium entering the intermediate superheater as a function of an ascertained enthalpy difference of the solar-thermally heated heat transfer medium between its entry and exit into and out of the intermediate superheater and an ascertained enthalpy difference of the steam between its exit and entry out of and into the intermediate superheater.   
     
     
         2 . The method as claimed in  claim 1 , wherein actual pressure values and actual temperature values respectively measured at an entry and the exit are used in order to ascertain the enthalpy of the steam at the entry and the enthalpy of the solar-thermally heated heat transfer medium at the entry and the exit, and a measured actual pressure value of the steam at the exit and the adjusted setpoint temperature value of the steam exit are used in order to ascertain the enthalpy of the steam at the exit. 
     
     
         3 . The method as claimed in  claim 1 , wherein, in order to regulate the mass flow of the solar-thermally heated heat transfer medium entering the intermediate superheater, a mass flow setpoint value is determined from the ratio of the product of the enthalpy difference of the steam and a parameter characterizing a mass flow of the incoming steam to the enthalpy difference of the solar-thermally heated heat transfer medium. 
     
     
         4 . The method as claimed in  claim 1 , wherein thermal energy stored in or released from tube walls of the intermediate superheater is also taken into account in order to regulate the mass flow of the solar-thermally heated heat transfer medium. 
     
     
         5 . The method as claimed in  claim 1 , wherein thermal energy stored in or released from the solar-thermally heated heat transfer medium is also taken into account in order to regulate the mass flow of the solar-thermally heated heat transfer medium. 
     
     
         6 . The method as claimed in  claim 1  wherein an actual temperature value measured at the exit of the steam from the intermediate superheater is also taken into account in order to regulate the mass flow of the solar-thermally heated heat transfer medium. 
     
     
         7 . An apparatus for operating a solar thermal power plant in which steam is heated in an intermediate superheater in a water/steam circuit by a solar-thermally heated heat transfer medium to an adjustable setpoint temperature value at an exit, comprising:
 a regulating device for a mass flow of the solar-thermally heated heat transfer medium entering the intermediate superheater;   a mass flow setpoint value control device for controlling the regulating device as a function of an ascertained enthalpy difference of the solar-thermally heated heat transfer medium between its entry and exit into and out of the intermediate superheater and an ascertained enthalpy difference of the steam between its exit and entry out of and into the intermediate superheater; and   a first module and a second module for ascertaining the enthalpy of the solar-thermally heated heat transfer medium at an entry and the exit, and a third module and a fourth module for ascertaining the enthalpy of the steam at the entry and the exit.   
     
     
         8 . The apparatus as claimed in  claim 7 , wherein the mass flow setpoint value control device has a controlling element by which a selected setpoint temperature value of the steam at the exit is specified for the fourth module. 
     
     
         9 . The apparatus as claimed in  claim 7 , wherein a plurality of pressure sensors and temperature sensors for measuring the pressure and the temperature of the steam and of the solar-thermally heated heat transfer medium are provided in order to ascertain the enthalpies at the entries and/or exits of the steam and/or of the solar-thermally heated heat transfer medium out of and into the intermediate superheater. 
     
     
         10 . The apparatus as claimed in  claim 7 , wherein the mass flow setpoint value control device includes:
 a first subtractor element for subtracting the ascertained steam entry enthalpy from the ascertained steam exit enthalpy,   a second subtractor element for subtracting the ascertained heat transfer medium exit enthalpy from the ascertained heat transfer medium entry enthalpy,   a fifth module for ascertaining a parameter characterizing a mass flow of the incoming steam,   a multiplier element for multiplying the parameter by a difference from the first subtractor element, and   a divider element for dividing a product from the multiplier element by a difference from the second subtractor element.   
     
     
         11 . The apparatus as claimed in  claim 10 , further comprising a sixth module to take into account thermal energy stored in or released from tube walls of the intermediate superheater, an output value of which is added to the product from the multiplier element by an adder element before the divider element. 
     
     
         12 . The apparatus as claimed in  claim 10 , further comprising a seventh module to take into account thermal energy stored in or released from the solar-thermally heated heat transfer medium, an output value of which is added to the product from the multiplier element by an adder element before the divider element. 
     
     
         13 . The apparatus as claimed in  claim 10 , further comprising a control module superordinate to a mass flow setpoint value guide device, which corrects a ratio at the output of the divider element by means of a further multiplier element in the event of steady state deviations between the measured steam exit temperature and the adjusted setpoint temperature value. 
     
     
         14 . A parabolic trough power plant having a solar-thermally heated heat transfer medium, an intermediate superheater in a water/steam circuit, in which steam is heated by the solar-thermally heated heat transfer medium to an adjustable setpoint temperature value at an exit, and an apparatus formed as claimed in  claim 7  for regulating a mass flow of the solar-thermally heated heat transfer medium entering the intermediate superheater. 
     
     
         15 . The parabolic trough power plant as claimed in  claim 14 , wherein the solar-thermally heated heat transfer medium is thermal oil.