Steam turbine plant
Provided are a main steam piping connecting a steam generator and a steam turbine, a bypass piping branched from the main steam piping and bypassing the steam turbine, a bypass valve provided in the bypass piping, a warming piping branched from the bypass valve, a warming valve provided in the warming piping, and a control system. The control system controls the warming valve in such a manner that bypass valve temperature t is brought to within a temperature range satisfying the three conditions: (1) being equal to or higher than the saturated temperature of steam flowing into the bypass valve; (2) having a temperature difference from the flowing-in steam of equal to or less than an allowable value; and (3) being equal to or lower than a temperature at which the formation rate of steam oxidation scale rises.
1. A steam turbine plant comprising:
a steam generator;
a steam turbine;
a condenser;
a main steam piping connecting the steam generator and the steam turbine;
a bypass piping branched from the main steam piping and bypassing the steam turbine;
a bypass valve provided in the bypass piping;
a warming piping branched from a portion of the bypass piping upstream of the bypass valve or from a main body of the bypass valve and joining the main steam piping;
a warming valve provided in the warming piping; and
a control system that controls the warming valve,
wherein the control system is configured to output a signal for controlling the warming valve in such a manner as to control a metal temperature of the bypass valve to within predetermined temperature ranges as follows:
(1) being equal to or higher than a saturated temperature of steam flowing into the bypass valve, the saturated temperature being a saturated temperature of the flowing-in steam at a steam pressure during a normal operating;
(2) having a temperature difference from the flowing-in steam of equal to or less than a first allowable value set in advance as an allowable value for thermal shock or thermal deformation produced on a material of the bypass valve; and
(3) being equal to or lower than a second allowable value set in advance based on a relationship between the material of the bypass valve, the metal temperature of the bypass valve, and a formation rate of steam oxidation scale.
2. The steam turbine plant according to claim 1 , comprising:
a temperature measuring instrument that measures the metal temperature of the bypass valve by detection or through calculation,
wherein the control system generates a signal for opening the warming valve when a value measured by the temperature measuring instrument is equal to or lower than a set temperature a satisfying the temperature ranges (1) and (2), the control system generates a signal for closing the warming valve when the value measured by the temperature measuring instrument is equal to or higher than a set temperature b satisfying the temperature range (3), and the control system outputs the thus generated signal to the warming valve.
3. The steam turbine plant according to claim 2 ,
wherein the material of the bypass valve is chrome steel, the saturated temperature of the flowing-in steam is 366° C., the first allowable value is 200° C., and the second allowable value is 550° C., and
wherein the set temperature a is 400° C., and the set temperature b is 500° C.
4. The steam turbine plant according to claim 1 , comprising:
a temperature measuring instrument that measures the metal temperature of the bypass valve by detection or through calculation,
wherein the control system generates a signal for opening or closing the warming valve in such a manner that a value measured by the temperature measuring instrument approaches a target temperature c that is a value between the set temperature a satisfying the temperature ranges (1) and (2) and the set temperature b satisfying the temperature range (3), and the control system outputs the thus generated signal to the warming valve.
5. The steam turbine plant according to claim 4 ,
wherein the material of the bypass valve is chrome steel, the saturated temperature of the flowing-in steam is 366° C., the first allowable value 200° C., and the second allowable value is 550° C., and
wherein the set temperature a is 400° C., and the set temperature b is 500° C.
6. The steam turbine plant according to claim 1 ,
wherein the control system closes the warming valve when a plant shut-down signal is inputted.
7. A steam turbine plant comprising:
a steam generator;
a steam turbine;
a condenser;
a main steam piping connecting the steam generator and the steam turbine;
a bypass piping branched from the main steam piping and bypassing the steam turbine;
a bypass valve provided in the bypass piping;
a warming piping branched from a portion of the bypass piping upstream of the bypass valve or from a main body of the bypass valve and joining the main steam piping;
a warming valve provided in the warming piping; and
a control system that controls the warming valve,
wherein the control system is configured to output a signal for controlling the warming valve in such a manner as to control a metal temperature of the bypass valve to within predetermined temperature ranges as follows:
(1) being equal to or higher than 366° C. that is a saturated temperature of steam flowing into the bypass valve;
(2) having a temperature difference from the flowing-in steam of equal to or less than 200° C. set in advance as a first allowable value; and
(3) being equal to or lower than 550° C. set in advance as a second allowable value.