[0001] The present invention relates to a device and a method for controlling the injection
of an operating fluid in an evolving fluid of a plant for the production of electrical
energy and to a plant for the production of electrical energy comprising said control
device. In particular, the present invention relates to a device and to a method for
controlling the injection of an operating fluid in an evolving fluid of a combined-cycle
electrical energy production plant.
[0002] Energy-production plants, and in particular combined-cycle energy-production plants,
usually comprise a device for controlling the injection of an operating fluid into
the fluid evolving in the plant. In the case of the combined-cycle plant, the evolving
fluid is initially water, then vapour, and finally condensate.
[0003] The operating fluid is injected into the evolving fluid in different portions of
the plant in order to protect from electrochemical corrosion and from the deposition
of encrusting salts the circuit of the plant within which the evolving fluid flows.
[0004] Known devices for controlling the injection of the operating fluid substantially
comprise means for calculation of a flowrate of operating fluid to be injected, and
means for driving at least one pump for injection of the operating fluid on the basis
of the flowrate of operating fluid calculated. In particular, the calculation means
are configured for calculating the flowrate of operating fluid to be injected on the
basis of the difference between a value of a detected parameter of the evolving fluid
modified by the operating fluid and a reference value set beforehand.
[0005] Said control devices generally use a PID (proportional integral derivative) control
mode, which requires identification of appropriate control constants.
[0006] However, the identification of the control constants is particularly problematical,
in so far as it is very difficult to identify control constants such as to determine
a control of the injection that is precise, stable, and fast. The choice of the control
constants has repercussions on the stability of the control of the injection above
all in emergency situations, such as, for example, pollution of the condensate, where
it is necessary to intervene rapidly maintaining the stability of the control.
[0007] Frequently, it is necessary to entrust control of the injection of the operating
fluid to an operator, who, on the basis of the measurements of the detected parameter
of the evolving fluid, regulates directly the pumps for injection of the operating
fluid.
[0008] An aim of the present invention is to provide a device for controlling the injection
of an operating fluid that is free from the drawbacks highlighted of the known art.
In particular, an aim of the invention is to provide a device for controlling the
injection of an operating fluid that is reliable and simple to use.
[0009] In accordance with said aims, the present invention relates to a device for controlling
the injection of at least one operating fluid in an evolving fluid of a plant for
the production of electrical energy, said device comprising:
calculation means for calculating at least one flowrate of operating fluid to be injected
into the evolving fluid on the basis of a detected parameter of the evolving fluid
modified by the operating fluid;
the device being
characterized in that the calculation means are configured for calculating the flowrate of operating fluid
to be injected according to a first mode when the detected parameter is lower than
a given threshold value and according to a second mode when the detected parameter
is higher than said threshold value.
[0010] The present invention moreover relates to a method for controlling the injection
of at least one operating fluid in an evolving fluid of a plant for the production
of electrical energy. In accordance with said purposes, the present invention relates
to a method for controlling the injection of at least one operating fluid in an evolving
fluid of a plant for the production of electrical energy comprising the step of calculating
at least one flowrate of operating fluid to be injected into the evolving fluid on
the basis of a detected parameter of the evolving fluid modified by the operating
fluid; the method being
characterized in that the flowrate of operating fluid to be injected is calculated according to a first
mode when the detected parameter is lower than a given threshold value and according
to a second mode when the detected parameter is higher than said threshold value.
[0011] The present invention moreover relates to a plant for the production of electrical
energy. In accordance with said aims the present invention relates to an electrical
energy production plant comprising at least one steam-turbine unit flowing within
which is an evolving fluid; the plant being characterized by comprising a device for
controlling the injection of at least one operating fluid into the evolving fluid
as claimed in any one of Claims 1 to 18.
[0012] Further characteristics and advantages of the present invention will be clear from
the following description of a non-limiting example of embodiment thereof, with reference
to the attached figure, which is a schematic representation of a plant for the production
of energy according to the present invention.
[0013] In Figure 1 designated by the reference number 1 is a plant for the production of
energy. In the non-limiting example described and illustrated herein, the plant 1
is a plant for the combined-cycle production of electrical energy and comprises a
gas-turbine unit 2, a steam-turbine unit 3, two alternators 5, 6, respectively coupled
to the gas-turbine unit 2 and to the steam-turbine unit 3 and connected to a distribution
network (not illustrated), a steam generator 7, a condenser 8, an assembly for injection
of a first operating fluid 10, an assembly for injection of a second operating fluid
11, and an operating fluid injection control device 12. Alternatively, the plant comprises
a gas-turbine unit, a steam-turbine unit, and an alternator all set on one and the
same axis.
[0014] The exhaust fumes of the gas-turbine unit 2 are channelled along a duct 13 and provide
a source of heat for the steam generator 7.
[0015] The steam generator 7 comprises a high-pressure element 14, a medium-pressure element
15 and a low-pressure element 16, each of which comprises an economizer 17, a cylindrical
body ("drum") 18, an evaporator 19 and a super-heater 20, operation of which is known
and will not be discussed in detail.
[0016] The economizers 17 of the high-pressure element 14 and of the medium-pressure element
15 receive water from the low-pressure drum 18 by means of a supply pump 21, whilst
the economizer 17 of the low-pressure element 16 receives water from a collection
tank of the condenser 8, by means of an extraction pump 22.
[0017] The steam-turbine unit 3 comprises a high-pressure section 24, a medium-pressure
section 25, and a low-pressure section 26 circulating within which is steam coming,
respectively, from the high-pressure element 14, the medium-pressure element 15, and
the low-pressure element 16. In a different embodiment (not illustrated) the steam
turbine comprises the high-pressure section and a medium-low-pressure section.
[0018] Basically, within the plant 1 an evolving fluid flows, which is initially water supplied
by the pump 21, becomes vapour (steam) within the steam generator 7, and is transformed
into condensate after the expansion in the low-pressure section 26 of the steam-turbine
unit 3.
[0019] The injection assembly 10 of the first operating fluid comprises a tank 28 containing
the first operating fluid, and an injection pump 32 for injecting the first operating
fluid. The injection pump 32 injects the first operating fluid into the evolving fluid
upstream of the supply pump 21 under the control of the control device 12 as will
be described in detail hereinafter. The evolving fluid, in this situation, is water
coming from the low-pressure drum 18.
[0020] The first operating fluid comprises a de-oxygenating fluid diluted in water, for
example, an amine-based de-oxygenating organic fluid.
[0021] The de-oxygenating fluid has a given concentration of active principle, commonly
referred to as de-oxygenating power P
deox.
[0022] The assembly 11 for injection of the second operating fluid comprises a tank 35 containing
the second operating fluid, and an injection pump 36 for injection of the second operating
fluid. The injection pump 36 injects the second operating fluid into the evolving
fluid downstream of the pump 22 for extraction of the condensate under the control
of the control device 12 as will be described in greater detail hereinafter. The evolving
fluid, in this situation, is condensate coming from the condenser 8.
[0023] The second operating fluid comprises an alkalinizing fluid diluted in water, for
example an amine-based or ammoniac-based alkalinizing fluid, to maintain the pH of
the evolving fluid in the limits set by the standards.
[0024] The alkalinizing fluid has a given concentration of alkalinizing agent C
flop.
[0025] The control device 12 comprises a calculation module 38 for calculating the flowrates
Q
1 , Q
2 of operating fluid to be injected into the fluid evolving in the plant 1 and a driving
module 39 for driving the injection pumps 32 and 36 on the basis of the calculated
flowrates Q
1 , Q
2 of operating fluid.
[0026] The calculation module 38 is configured for calculating the flowrate Q
1 of the first operating fluid to be injected into the evolving fluid upstream of the
supply pump 21 on the basis of a detected parameter of the evolving fluid modified
by the first operating fluid. In the example described and illustrated herein, the
detected parameter of the evolving fluid modified by the first operating fluid is
the concentration of oxygen C
1 in the evolving fluid detected in the portion of plant 1 into which the operating
fluid is injected, in particular upstream of the supply pump 32.
[0027] In particular, the calculation module 38 is configured for calculating the flowrate
Q
1 of the first operating fluid to be injected according to a first mode when the concentration
of oxygen C
1 is lower than a given threshold value C
TS and according to a second mode when the concentration of oxygen C
1 is higher than said threshold value C
TS.
[0028] The threshold value C
TS of the detected parameter of the evolving fluid modified by the first operating fluid
defines the type of treatment that it is intended to adopt. In the case where it is
intended to adopt a reducing type treatment, the threshold value C
TS is comprised between 4 and 6 ppb, preferably 5 ppb. In the case where it is desired
to adopt an oxidizing type treatment, the threshold value C
TS is comprised between 19 and 20 ppb, preferably 20 ppb.
[0029] In the case where the reducing treatment is chosen, the calculation module 38 calculates
the flowrate Q
1 according to a formula independent of the concentration of oxygen C
1 in the first mode, whilst in the second mode adds to the independent term calculated
in the first mode, a term depending upon the concentrations of oxygen C
1.
[0030] In particular, in the first mode, i.e., when the value of the concentration of oxygen
C
1 is lower than the threshold value C
TS, the calculation module 38 calculates the flowrate Q
1 of the first operating fluid according to the following formula:
where:
K1 is a conversion factor depending upon the measure units used;
Qflev1 is the flowrate of evolving fluid upstream of the supply pump 21;
Dflop is the dilution in water of the de-oxygenating fluid in the tank 28; and
DoseRif is a reference dose of the operating fluid established beforehand and such as to
maintain the concentration of oxygen C1 below the threshold value CTS.
[0031] In the second mode, i.e., when the value of the concentration of oxygen C
1 is higher than the threshold value C
TS, the calculation module 38 calculates the flowrate Q
1 of first operating fluid according to the following formula:
where:
K1 and K2 are conversion factors depending upon the measure units used;
Qflev1 is the flowrate of evolving fluid upstream of the supply pump 21;
Dflop is the dilution in water of the de-oxygenating fluid in the tank 28;
DoseRif is a reference dose of the operating fluid established beforehand and such as to
maintain the concentration of oxygen C1 below the threshold value CTS;
C1 is the concentration of oxygen detected upstream of the supply pump 21; and
Pdeox is the de-oxygenating power of the de-oxygenating fluid.
[0032] In the case where the oxidizing treatment is chosen, in the first mode, the calculation
module 38 determines a zero value of the flowrate Q
1. In the second mode, i.e., only when the value of the concentration C
1 is higher than the threshold value C
TS, the calculation module 38 calculates the flowrate Q
1 in accordance with Eq. (2) indicated above.
[0033] The calculation module 38 is moreover configured for calculating the flowrate Q
2 of second operating fluid to be supplied downstream of the pump 22 for intake of
the condensate on the basis of a detected parameter of the evolving fluid modified
by the second operating fluid. In the example described and illustrated herein, said
parameter is the pH of the evolving fluid detected in a portion of the plant in which
the operating fluid is injected, in particular downstream of the suction pump 22.
[0034] In particular, the calculation module 38 is configured for calculating the flowrate
Q
2 of the second operating fluid to be injected according to a first mode when the pH
of the evolving fluid downstream of the suction pump 22 is lower than a given threshold
value pH
TS and a second mode when the pH of the evolving fluid downstream of the suction pump
22 is higher than said threshold value pH
TS.
[0035] The threshold value pH
TS is comprised between 9 and 10, in particular the threshold value pH
TS is preferably 9.55 in the case where an amine-based operating fluid is used, whilst
it is preferably 9.85 in the case where an ammoniac-based operating fluid will be
used.
[0036] In the first mode, the calculation module 38 calculates the flowrate Q
2 according to a formula depending upon the pH detected, whilst in the second mode
the calculation module 38 calculates a zero flowrate Q
2. In detail, the formula for calculation of the flowrate Q
2 in the first mode is the following:
where:
PM is the molecular weight of the alkalinizing agent contained in the operating fluid;
Qflev2 is the flowrate of evolving fluid downstream of the extraction pump 22;
Cflop is the concentration of the alkalinizing agent in the second alkalinizing fluid;
Dflop is the dilution in water of the alkalinizing fluid in the tank 35;
pH is the value of the pH detected downstream of the pump 22 for extraction of the
condensate;
pHTS is the threshold value of the pH parameter detected.
[0037] The driving module 39, on the basis of the flowrates Q
1 , Q
2 of operating fluids calculated by the calculation module 38, sends to the injection
pumps 32 and 36 respective driving signals Sp
1 Sp
2 designed to drive the stroke of the pump in such a way as to determine an injection
of a flowrate of operating fluid equal to the flowrate calculated by the calculation
module 38.
[0038] Finally, it is evident that modifications and variations may be made to the device,
the method and the plant described herein without departing from the scope of the
annexed claims.
1. A device for controlling the injection of at least one operating fluid in an evolving
fluid of a plant (1) for the production of electrical energy comprising:
calculation means (38) for calculating at least one flowrate (Q1, Q2) of operating fluid to be injected into the evolving fluid on the basis of a detected
parameter (C1, pH) of the evolving fluid modified by the operating fluid;
the device (12) being characterized in that the calculation means (38) are configured for calculating the flowrate (Q1, Q2) of operating fluid to be injected according to a first mode when the detected parameter
(C1, pH) is lower than a given threshold value (CTS, pHTS) and according to a second mode when the detected parameter (C1, pH) is higher than said threshold value (CTS, pHTS).
2. A device according to Claim 1, characterized by comprising driving means (39) for driving at least one operating fluid injection
pump (32, 36) on the basis of the calculated flowrate (Q1, Q2) of operating fluid.
3. A device according to Claim 1 or Claim 2, characterized in that the operating fluid contains an alkalinizing fluid; the detected parameter of the
evolving fluid modified by the operating fluid being the pH.
4. A device according to Claim 3, characterized in that the evolving fluid in which the operating fluid is injected is condensed vapour.
5. A device according to Claim 3 or Claim 4, characterized in that the threshold value (pHTS) is comprised between 9 and 10.
6. A device according to any one of Claims 3 to 5,
characterized in that in the first mode the calculation means (38) are configured for calculating a flowrate
(Q2) of operating fluid as a function of the pH detected.
7. A device according to Claim 6,
characterized in that in the first mode the calculation means (38) are configured for calculating a flowrate
(Q
2) of operating fluid as follows:
where:
PM is the molecular weight of the alkalinizing agent contained in the operating fluid;
Qflev2 is the flowrate of evolving fluid in the portion of plant in which the operating
fluid is injected;
Cflop is the concentration of the alkalinizing agent in the alkalinizing fluid;
Dflop is the dilution in water of the alkalinizing fluid;
pH is the value of the pH detected in the portion of plant in which the operating
fluid is injected; and
pHTS is the threshold value of the pH parameter detected.
8. A device according to one of Claims 3 to 7, characterized in that in the second mode the calculation means (38) are configured for calculating a zero
flowrate (Q2) of operating fluid.
9. A device according to Claim 1 or Claim 2, characterized in that the operating fluid contains a de-oxygenating fluid; the detected parameter of the
evolving fluid modified by the operating fluid being a concentration of oxygen (C1).
10. A device according to Claim 9, characterized in that the evolving fluid into which the operating fluid is injected is water.
11. A device according to Claim 9 or Claim 10, characterized in that the threshold value (CTS) is comprised between 4 and 6 ppb.
12. A device according to one of Claims 9 to 11, characterized in that in the first mode the calculation means (38) are configured for calculating a flowrate
(Q1) of operating fluid independent of the concentration of oxygen (C1).
13. A device according to Claim 12,
characterized in that in the first mode the calculation means (38) are configured for calculating a flowrate
(Q
1) of operating fluid as follows:
where:
K1 is a conversion factor depending upon the measure units used;
Qflev1 is the flowrate of evolving fluid in the portion of plant in which the operating
fluid is injected;
Dflop is the dilution in water of the de-oxygenating fluid; and
DoseRif is a reference dose of the operating fluid established beforehand and such as to
maintain the concentration of oxygen (C1) below the threshold value (CTS).
14. A device according to one of Claims 9 to 13, characterized in that in the second mode the calculation means (38) are configured for calculating a flowrate
(Q1) of operating fluid as a function of the concentration of oxygen (C1).
15. A device according to Claim 14,
characterized in that in the second mode the calculation means (38) are configured for calculating a flowrate
(Q
1) of operating fluid as follows:
where:
K1 and K2 are conversion factors depending upon the measure units used;
Qflev1 is the flowrate of evolving fluid in the portion of plant in which the operating
fluid is injected;
Dflop is the dilution in water of the de-oxygenating fluid;
DoseRif is a reference dose of the operating fluid established beforehand and such as to
maintain the concentration of oxygen (C1) below the threshold value (CTS) ;
C1 is the concentration of oxygen detected in the portion of plant in which the operating
fluid is injected; and
Pdeox is the de-oxygenating power of the de-oxygenating fluid.
16. A device according to Claim 9, characterized in that the threshold value(CTS) is comprised between 19 and 21 ppb.
17. A device according to Claim 16, characterized in that in the first mode the calculation means (38) are configured for calculating a flowrate
(Q1) of operating fluid as a function of the concentration of oxygen (C1).
18. A device according to Claim 17,
characterized in that in the second mode the calculation means (38) are configured for calculating a flowrate
(Q
1) of operating fluid as follows:
where:
K1 and K2 are conversion factors depending upon the measure units used;
Qflev1 is the flowrate of evolving fluid in the portion of plant in which the operating
fluid is injected;
Dflop is the dilution in water of the de-oxygenating fluid;
DoseRif is a reference dose of the operating fluid established beforehand and such as to
maintain the concentration of oxygen (C1) below the threshold value(CTS) ;
C1 is the concentration of oxygen detected in the portion of plant in which the operating
fluid is injected; and
Pdeox is the de-oxygenating power of the de-oxygenating fluid.
19. A method for controlling the injection of at least one operating fluid in an evolving
fluid of a plant (1) for the production of electrical energy comprising the step of
calculating at least one flowrate (Q1, Q2) of operating fluid to be injected into the evolving fluid on the basis of a detected
parameter (C1, pH) of the evolving fluid modified by the operating fluid; the method being characterized in that the flowrate (Q1, Q2) of operating fluid to be injected is calculated according to a first mode when the
detected parameter (C1, pH) is lower than a given threshold value (CTS, pHTS) and according to a second mode when the detected parameter (C1, pH) is higher than said threshold value (CTS, pHTS).
20. An electrical energy production plant comprising at least one steam-turbine unit (3)
within which an evolving fluid flows; the plant (1) being characterized by comprising a device for controlling (12) the injection of at least one operating
fluid into the evolving fluid as claimed in any one of Claims 1 to 18.