Chemical conditioning process of a heat transfer fluid in a circuit of a power generation plant.
A two-point chemical conditioning process adjusts the pH-Eh pair in the heat transfer fluid circuit to enhance solubility, addressing wall thinning and deposition issues, thereby improving the longevity and efficiency of power generation plants.
Patent Information
- Application Number
- FR2023014323
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-12-15
- Publication Date
- 2025-11-07
- Estimated Expiration
- 2043-12-15
Smart Images
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Abstract
Description
Title of the invention: Chemical conditioning process for a heat transfer fluid in a circuit of a power generation plant. Technical field of the invention
[0001] The invention relates to the field of chemical conditioning of a heat transfer fluid in a circuit of a power generation plant.
[0002] The invention may, for example, relate to a circuit in a heat production plant conveying a heat transfer fluid in single-phase (liquid) form between a hot source and a cold source. The invention may also relate to a secondary circuit in a power generation plant conveying a heat transfer fluid in two-phase form between a hot source (steam generator) and a cold source (condenser). Technical background
[0003] Fig. 1 schematically represents a secondary circuit CS of a power generation plant.
[0004] This secondary circuit comprises various components, namely a hot source, here a steam generator, a cold source, here a condenser, a pipeline connecting the steam generator to the condenser, incorporating one or more turbines intended to be driven by the flow of heat transfer fluid (in the form of steam generated by the steam generator) and another pipeline connecting the condenser to the steam generator and incorporating a pump to drive the heat transfer fluid (in liquid form from the outlet of the condenser) and heaters.
[0005] The heat transfer fluid is generally water in a power generation plant.
[0006] In this type of circuit, we encounter phenomena of wall thinning in certain places and phenomena of material deposition on the circuit walls in other places.
[0007] The phenomena of wall thinning in a circuit are known as dissolution and erosion-corrosion, preferentially located in the portions of the circuit carrying a heat transfer fluid in single-phase vapor form (pipe connecting the steam generator to the condenser and turbine). In the portions of the circuit carrying a heat transfer fluid in single-phase liquid form, corrosion also contributes to wall thinning and the generation of species in the aqueous phase.
[0008] The phenomena of material deposition on the walls of a circuit are known under the The terms fouling and clogging refer primarily to the sections of single-phase liquid circuits (pipe connecting the condenser to the steam generator and pump) and two-phase liquid-vapor circuits (steam generator, condenser). Fouling refers to the precipitation of oxides or metals on all surfaces, for example, of the steam generator, from species present in the aqueous phase, while clogging refers to localized precipitation on thermohydraulic singularities, for example, fluid passages in tube sheets or distribution plates.
[0009] The term dissolution-precipitation refers to a chemical action that modifies the passive film that may be present on the wall by decreasing its thickness by dissolution (which activates corrosion) or by increasing it by precipitation (which slows down corrosion).
[0010] The term erosion-corrosion refers more to a mechanical action which removes part of the oxide and which has the effect of accelerating the corrosion of the metal (loss of the passive film).
[0011] To limit these phenomena, which are detrimental in the long term to the proper functioning of the power plant, chemical conditioning of the heat transfer fluid is carried out. Thus, as shown in [Fig. 1], the secondary circuit includes a chemical conditioning device, generally installed at the outlet of the condenser.
[0012] This chemical conditioning method allows reducing and acid-base species to be injected into the pipe connecting the condenser to the steam generator (liquid phase) to define a reference solubility of the different phases of iron in the heat transfer fluid. Iron is indeed an element present in the different types of alloys constituting the various components of the secondary circuit.
[0013] The injection of reducing and acid-base species makes it possible to adjust a hydrogen potential - redox potential (pH-Eh) pair to a given reference value. It should be recalled that the hydrogen potential (pH) measures, by the logarithm of the activity of the solvated proton, the acid-base character of the water, and that the redox potential (Eh) measures the oxide-reducing character of the water with respect to the species present in the water or the materials in contact with it (oxidation reaction of a metal to an oxidized form, change in the degree of oxidation of a solvated chemical species, etc.).
[0014] The advantage of adjusting the torque value (pH-Eh) can be understood from [Fig.2],
[0015] Figure 2 shows the Pourbaix diagram (Eh as a function of pH) of iron in water at 150 °C and atmospheric pressure. The two lines (a) and (b) represent the thermodynamic stability domain of water (outside these lines (a) and (b), Water decomposes through oxidation-reduction to produce dioxygen or dihydrogen, depending on the case. Depending on the values of the hydrogen potential (pH) and the redox potential (Eh) of the solution, different oxides and aqueous species will appear. For example, at a temperature of 150 °C, magnetite (Fe3O4) can only form at pH values between 6 and 14 and Eh values between -0.3 V and -1.2 V, that is, in basic and reducing environments. Thus, for a given temperature, a stability range for magnetite is defined (the possible form or oxidation state of iron in water).
[0016] In general, a Pourbaix diagram highlights three domains for a metal: a corrosion domain where the metal oxidizes rapidly, an immunity domain where the metal does not corrode, and a passivity domain where corrosion is prevented by the formation of an oxide layer.
[0017] In the context of the chemical conditioning carried out on the heat transfer fluid of a secondary circuit of a power plant, we therefore seek to define an Eh-pH pair in the passivity range of a given oxide (magnetite in our example) among all the possible oxides of the metal concerned (Iron) in order to protect against corrosion.
[0018] The stability range of the oxide is, however, relatively extensive and leaves a wide range of possible values for the pH - Eh pair. This is all the more true since, in a secondary circuit of a power generation plant, the pressure is typically around 70 bars which allows the stability range of water to be extended (in particular the curve (a) is shifted downwards compared to the representation in [Fig.2]).
[0019] To fix the most suitable pH-Eh couple value, we seek in parallel to limit the solubility of the oxide thus formed.
[0020] Figure 3 shows the solubility diagram of magnetite at 150°C as a function of pH. This diagram shows that a minimum solubility of magnetite in water exists and is obtained for a pH between 9 and 11.
[0021] This range of pH values shown on the Pourbaix diagram in [Fig. 2] allows us to define a more restricted range for the redox potential Eh, approximately between -500 mV and -900 mV (at 150°C). In practice, Eh is typically set to a value of -600 mV for a temperature of 25°C.
[0022] It is therefore this dual condition on the stability range of a given oxide ([Fig.2]) and its minimum solubility ([Fig.3]) that allows us to define an optimum pH-Eh pair. Since the value of this pair varies with temperature, and therefore as the heat transfer fluid moves within the circuit, it should be noted that a typical standard is assumed, at 25°C, such that (pH, Eh) = (10, -600mV).
[0023] This limits the phenomena of dissolution-precipitation and erosion-corrosion the walls of the secondary circuit components.
[0024] In practice, and as previously stated, the pH-Eh couple is adjusted by injecting reducing and acid-base species into the (single-phase) liquid phase.
[0025] In a secondary circuit (which operates in two phases), ammonia (NH3), ethanolamine (C2H7NO) or morpholine (C4H9NO) can be chosen to regulate the hydrogen potential pH and hydrazine to regulate the redox potential Eh. All these species are soluble and volatile and can therefore be present in both the liquid and vapor phases encountered in the secondary circuit.
[0026] Fig. 4 schematically represents what happens in the secondary circuit when the heat transfer fluid is in motion, in terms of temperature (top), the solubility of an element M (typically the iron contained in the alloys of the different components of the secondary circuit) in the chemically conditioned heat transfer fluid (middle) and the resulting thickness of material deposit or thinning (dissolution of oxides, erosion-corrosion) on the walls of the secondary circuit (bottom).
[0027] Thus, on the upper curve, we note that the heat transfer fluid alternately sees its temperature increase in the steam generator (hot source) then decrease in the condenser (cold source) and remain relatively constant in the pipes.
[0028] On the right-hand curve in the middle, it can be seen that the solubility CMjeq of element M decreases with temperature (the composition of reducing and acid-base species, determined by the quantity of these species injected by the chemical conditioning method of the secondary circuit, remains constant, but the pH and Eh vary with temperature). In this case, it can be seen on the middle curve that the solubility CM of element M in the heat transfer fluid decreases in the steam generator (hot source), then increases in the condenser (cold source), and remains relatively constant in the pipes.
[0029] This reflects the fact that the flow of material from element M is directed from the heat transfer fluid towards a wall in the steam generator (hot source). It is therefore precisely here that the secondary circuit is likely to encounter precipitation phenomena leading to fouling and / or clogging. Conversely, a flow of material from element M is directed from a wall towards the heat transfer fluid in the condenser (cold source). It is therefore precisely here that the secondary circuit is likely to undergo dissolution and / or erosion phenomena at the level of its walls, also activating corrosion of these walls containing element M (typically iron).
[0030] On the lower curve, the location of the deposit (hot spring) and the location are also indicated. corrosion (cold source).
[0031] The chemical conditioning currently carried out makes it possible to greatly limit the phenomena of dissolution-precipitation (fouling, clogging) and also of erosion-corrosion.
[0032] However, these phenomena nevertheless exist and remain observable over long time scales, but nevertheless shorter than the operating periods of the electricity production plants.
[0033] The comments made previously in the case of a secondary circuit of a power generation plant can be generalized to various power generation plant circuits.
[0034] One objective of the invention is therefore to reduce or even eliminate deposits fouling or clogging the walls of a circuit in a power generation plant.
[0035] Another objective of the invention is to be able to further limit the erosion-corrosion of the metallic alloys present in such a circuit.
[0036] Furthermore, another objective is to reduce the amount of toxic products used in such a circuit. Summary of the invention
[0037] To achieve at least one of the aforementioned objectives, the invention proposes a method for chemically conditioning a heat transfer fluid in a circuit of a power generation plant, the circuit comprising the following components: - a hot spring, - a cold source, - a first pipe connecting the outlet of the hot spring to the inlet of the cold spring, - a second pipeline connecting the outlet of the cold source to the inlet of the hot source GV, each of said components being made of a metallic alloy containing iron, the process comprising a step consisting of: A) inject reducing and acid-base species into the second pipe to define, at a given temperature, a reference hydrogen potential - redox potential pair in the heat transfer fluid, characterized in that the process includes the following additional steps: B) inject a reducing species at the inlet of the hot source to decrease the redox potential of the heat transfer fluid, thereby increasing the solubility of the different phases of iron in the heat transfer fluid, and C) either remove the reducing species injected in step B at the inlet of the cold source, or inject an oxidizing species at the inlet of the cold source to compensate for the effects of the reducing species injected in step B, thereby increasing the redox potential of the heat transfer fluid and decreasing the solubility of the different phases of iron in the heat transfer fluid.
[0038] The process according to the invention may include at least one of the following additional steps, taken alone or in combination:
[0039] - during step B), a quantity of reducing species is injected ensuring that the solubility of the different phases of Iron over the entire area of the circuit going from the inlet of the hot source to the inlet of the cold source is greater than the solubility of the different phases of Iron at the inlet of the hot source;
[0040] - the reducing species injected at the inlet of the hot source in step B) is hydrazine or dihydrogen, preferably dihydrogen;
[0041] - the oxidant injected into the heat transfer fluid at the inlet of the cold source in step B) is dioxygen;
[0042] - step A) consists of imposing a pH between 9 and 11 and a redox potential in less than or equal to -550mV, for example between -650mV and -550mV, at a temperature of 25 °C;
[0043] - the acid-base species injected during step A) is chosen from ammonia (NH3), ethanolamine (C2H7NO) or morpholine (C4H9NO) or a mixture of these;
[0044] - the reducing species injected during step A) is hydrazine (N2H4);
[0045] - step A) is carried out at the outlet of the cold source;
[0046] - the circuit is a secondary circuit of a power generation plant in in which the hot source is a steam generator and the cold source a condenser, said circuit conveying a two-phase heat transfer fluid, in vapor form in the first pipe and in liquid form in the second pipe;
[0047] - the circuit is a circuit of a heat production plant, said circuit conveying a single-phase heat transfer fluid in liquid form. Brief description of the figures
[0048] Other objects and features of the invention will become clearer in the following description, made with reference to the accompanying figures, in which:
[0049] Figure 5 is a representative diagram of a secondary circuit of a power plant electricity production as planned to implement the process according to the invention;
[0050] Figure 6 represents what happens in the secondary circuit shown in Figure 6. [Fig.5] when the heat transfer fluid is in motion, in terms of temperature (top), solubility of an element M, Iron in this case (middle), and the resulting thickness of material deposit or thinning on the walls of the secondary circuit (bottom)
[0051] Fig. 7 shows the evolution of the redox potential (Eh, on the ordinates) as a function of the concentration of dihydrogen (on the abscissas, logarithmic scale) for several values of the dihydrogen pressure (curves mainly oriented vertically, lowest pressure on the left and highest on the right) and for several values of the temperature (curves mainly oriented horizontally, lowest temperature at the top and highest at the bottom);
[0052] Fig. 8 represents the evolution of the solubility of iron in the heat transfer fluid (water) of the secondary circuit of the installation shown in Fig. 5 as a function of temperature, this evolution being based, in accordance with the framework of the invention, on two operating points: a low temperature operating point PFbt and a high temperature operating point PFHT in the case of a reference conditioning based on ammonia;
[0053] Fig. 9 represents the evolution of the solubility of iron in a heat transfer fluid (water), always with a reference chemical conditioning based on ammonia, as a function of temperature and for different values of pH and for each pH, for different values of dihydrogen concentration;
[0054] Fig. 10 is a representation similar to that of Fig. 9, but for a reference chemical conditioning based on ethanolamine;
[0055] Fig. 11 is a representation similar to that of Fig. 9, but for reference chemical conditioning based on morpholine. Detailed description of the invention
[0056] The following description is made in support of the attached figures 5 to 11.
[0057] The [Fig.5] is a representative diagram of a secondary circuit of a power generation plant as provided for implementing the process according to the invention.
[0058] This secondary circuit CS includes, in particular, the various conventional components shown in Figure 1. Thus, the secondary circuit CS comprises a steam generator GV, a condenser COND, a first line CAI connecting the outlet of the steam generator GV to the inlet of the condenser COND, said first line CA being intended to carry the heat transfer fluid in the form of steam, and a second line CA2 connecting the outlet of the condenser COND to the inlet of the steam generator GV, said second line CA2 being intended to carry the heat transfer fluid in the form of liquid. It should be noted that each of the components of the secondary circuit is made of a metallic alloy containing iron.
[0059] This secondary circuit CS also includes a chemical conditioning MCC means conforming to that of the prior art. This conditioning MCC means Chemical conditioning (CC) allows for the implementation, in accordance with current prior art practices, of a step A) of chemical conditioning consisting of injecting reducing and acid-base species into the second pipe to define, at a given temperature, a reference hydrogen potential-redox potential (pH-Eh) pair in the heat transfer fluid. This CC means is generally located at the outlet of the COND condenser (cold source), to which it can then be considered equivalent. Consequently, step A) is then generally carried out at the condenser outlet.
[0060] However, the secondary circuit CS further includes a means MPI for introducing a product into the secondary circuit, this means MPI being located at the inlet of the steam generator GV (hot source). Moreover, the secondary circuit CS further includes a means MP2 for introducing or extracting a product from the secondary circuit CS, this means MP2 being located at the inlet of the condenser COND (cold source).
[0061] The following steps can then be implemented.
[0062] A step B) consisting of injecting a reducing species at the inlet of the steam generator, to decrease the redox potential (-AEh) of the heat transfer fluid and thus increase the solubility of the different phases of iron in the heat transfer fluid. It is understood that this step B) is implemented by means of the MPI located at the inlet of the steam generator, an inlet to which said MPI can be considered equivalent.
[0063] A step C) consisting of removing, at the condenser inlet, the reducing species injected in step B), thereby increasing the redox potential (+AEh) of the heat transfer fluid and thus decreasing the solubility of the different phases of iron in the heat transfer fluid. Alternatively or in addition, step C) may also consist of injecting, at the condenser inlet, an oxidizing species to compensate for the effects of the reducing species injected in step A). In all cases, it is understood that this step C) is implemented by means MP2 located at the condenser inlet, an inlet to which said means MP2 can be considered equivalent.
[0064] The implementation of steps B) and C) makes it possible to reduce the deposits fouling or clogging the walls of the secondary circuit.
[0065] Furthermore, advantageously, during step B) a quantity of reducing species can be injected such that the solubility of the different phases of Iron over the entire area of the secondary circuit going from the inlet of the steam generator GV to the inlet of the condenser COND is greater than the solubility of the different phases of Iron at the inlet of the steam generator.
[0066] This also helps to limit the dissolution-precipitation and erosion-corrosion of the metallic alloys present in the secondary circuit.
[0067] A situation that allows both the reduction or even the elimination of fouling deposits or sealing the walls of the secondary circuit while limiting the erosion-corrosion of the metallic alloys present in this circuit is explained in support of [Fig.6].
[0068] Fig. 6 schematically represents what happens in the secondary circuit CS shown in Fig. 5 when the heat transfer fluid is in motion, in terms of temperature (top), solubility of an element M (Iron in this case) (middle) and the resulting thickness of material deposit or thinning (dissolution-precipitation, erosion-corrosion) on the walls of the secondary circuit (bottom).
[0069] Thus, on the upper curve of [Fig. 6], it can be seen that the heat transfer fluid alternately increases in temperature in the steam generator (hot source) and then decreases in the condenser (cold source), remaining relatively constant in the pipes. This upper curve of [Fig. 6] is identical to the corresponding curve in [Fig. 4].
[0070] On the right-hand curve of [Fig. 6], it is noted that there are two operating points PFht, PFbt, unlike what occurs for the corresponding curve of [Fig. 4]. The transition from one operating point to the other is achieved through the implementation of steps B) and C). For each operating point, the solubility CM,eq of element M decreases with temperature.
[0071] On the mid-curve of [Fig.6], we note, just before the inlet of the steam generator (point A), that the solubility CM of the element M in the heat transfer fluid is that provided by the chemical conditioning of step A). We are then in a completely classic operating point.
[0072] Step B) is then implemented at the inlet of the steam generator (hot source), which has the effect of immediately increasing the solubility of element M in the heat transfer fluid (point B). We then move from a first operating point PFBT, conventional, to a second operating point PFHT.
[0073] The solubility of element M then decreases in the steam generator (hot source) with increasing temperature, but with values linked to this second operating point until the outlet of the steam generator (point C).
[0074] The solubility remains substantially constant in the first pipe up to the inlet of the condenser (point D).
[0075] At the condenser inlet, step C) of the process according to the invention is implemented. The solubility of element M in the heat transfer fluid then decreases immediately (point E). The process then transitions from the second operating point PFHt to the first, conventional operating point PFBt.
[0076] Then, the solubility of element M in the heat transfer fluid increases in the condenser until its outlet (point F) with the decrease in temperature.
[0077] This solubility ultimately remains substantially constant in the second channel lisation up to point A.
[0078] Thus, between point D (condenser inlet) and point A (steam generator inlet), we are in a first operating point PFLT, which is classical and is represented in [Fig. 4]. Conversely, between point A (steam generator inlet) and point D (condenser inlet), we are in a second operating point PFHT, radically different from the first operating point due to the introduction of a reducing species into the secondary circuit at the steam generator inlet.
[0079] On the lower curve of [Fig. 6], and unlike the corresponding curve in [Fig. 4], it can be seen that there is neither deposition of matter (no precipitation) at the steam generator (hot source) nor thinning (no dissolution) at the condenser (cold source). This means that precipitation of element M in the steam generator becomes impossible and that dissolution of element M in the condenser also becomes impossible.
[0080] In the case where there is a partial overlap of solubilities between the two states PFht and PFbt (contrary to what is shown in [Fig. 6]), for example because the quantity of reducing species introduced at the inlet of the steam generator is insufficient, the efficiency is not maximized. Nevertheless, this is still advantageous for the secondary circuit because there remains a reduction in the quantity of matter displaced between the condenser (dissolution, erosion) and the steam generator (precipitation, but also deposition, which corresponds to the sedimentation of solid particles on the walls) compared to conventional single-point conditioning.
[0081] From a practical point of view, it is important to determine the quantity of reducing species to be introduced at the inlet of the steam generator during step B) of the process according to the invention in order to change the redox potential as desired.
[0082] By definition, the evolution of the redox potential depends directly on the evolution of the dihydrogen concentration in the heat transfer fluid (a chemical species electrochemically equivalent to all reducing species, including hydrazine, with the formula N2H4, is equivalent to 2 H2). Reference can be made, for example, to [Fig. 7], which shows this relationship for different temperature values (substantially horizontal lines) ranging from 25°C to 300°C and for different dihydrogen pressure values (substantially vertical lines, lowest pressure on the left and increasing pressure towards the right) ranging from 103 bar to 10 bar. Also by definition, the dihydrogen concentration will depend on the additional mass flow rate of dihydrogen added to or removed from the heat transfer fluid, taking into account the mass flow rate of the heat transfer fluid circulating in the secondary circuit.The mass flow rate of heat transfer fluid present in the secondary circuit depends on . the installation in question, but it is known.
[0083] We will first present an example for a given installation and therefore a given (known) mass flow rate of heat transfer fluid. Examples
[0084] In this example, conventional chemical conditioning (step A) is carried out with ammonia and hydrazine. The addition of reducing agent at the inlet of the steam generator (at a temperature of 200 °C in this example) decreases the redox potential from -519 mV / ENH to -553 mV / ENH. At the inlet of the condenser (at a temperature of 30 °C in this example), the redox potential is increased from -535 mV / ENH to -514 mV / ENH. Under these conditions, no precipitation of iron oxides will occur in the steam generator since the solubility of the oxides remains consistently greater than that of iron in the heat transfer fluid.
[0085] Hydrazine can be chosen as a reducing agent added at the inlet of the steam generator.
[0086] However, another molecule with reducing character can also be used, including dihydrogen. Indeed, as can be seen from the values provided above as an example, since the change in redox potential is small at each transition from one operating point to another, the amount of dihydrogen required to achieve this change at the inlet of the steam generator is also small. Specifically, a change of -34mV in the redox potential at a temperature of 200 °C (i.e., a change from -519mV / ENH to -553mV / ENH) is obtained by adding dihydrogen to the heat transfer fluid in order to increase the concentration of dihydrogen dissolved in the heat transfer fluid (water) by +52.4 pmol.kg1 (i.e., the equivalent of 1.3 cm3 TPN).kg 1 of gaseous dihydrogen, where TPN designates standard temperature and pressure conditions - this equivalence aims to give the volume of gaseous dihydrogen under TPN conditions that would need to be introduced into the heat transfer fluid to obtain +52.4 pmol.kg1 of dihydrogen dissolved in the heat transfer fluid). The link between the desired evolution of the redox potential and the concentration of dihydrogen to be added is shown in [Fig.7].
[0087] The addition of dihydrogen at such (very low) concentrations is advantageous because it will most often be spontaneously purged (step C) of the process according to the invention) from the heat transfer fluid at the condenser without the addition of oxidizing species. Indeed, the condenser typically has vacuum pumping. However, for installations without vacuum pumping at the condenser, a simple addition of an oxidant such as dioxygen (step C) of the process according to the invention), in our example at a concentration of +26.2 pmol.kg1 of dioxygen, will eliminate the dihydrogen introduced into the secondary circuit during step A), and this before a new fluid path in the circuit.
[0088] Figure 8 shows more clearly what happens with this conditioning example. Figure 8 represents the solubility of iron in the heat transfer fluid as a function of temperature when following the heat transfer fluid through a cycle in the secondary circuit shown in Figure 5. Two curves, PFHT and PFBT, are shown for a high-temperature operating point and a low-temperature operating point, respectively. Points A to F are the same as those shown in Figure 5 (in the middle).
[0089] At point A, we are just before the inlet of the steam generator but before the injection of the reducer into the heat transfer fluid.
[0090] At point B, the reducer has been injected and we are just after the inlet of the steam generator.
[0091] Between points A and B, we therefore observe the effect of adding the reducer according to step B) at the inlet of the steam generator which results in a drastic increase in the solubility of Iron in the heat transfer fluid.
[0092] Then, between point B and point C, we move from the inlet of the steam generator to its outlet. We observe that the solubility decreases with increasing temperature within the steam generator.
[0093] At the outlet of the steam generator, the temperature then decreases until the inlet of the condenser and this describes the passage from point C to point D (first pipe).
[0094] The reducer is then removed in accordance with step C) of the process at the inlet of the condenser, which results in the passage from point D to point E and therefore in a drastic decrease in the solubility of Iron in the heat transfer fluid.
[0095] The condenser reduces the temperature and at its outlet, we arrive at point F.
[0096] Finally, from point F, we return to point A by going from the outlet of the condenser to the inlet of the steam generator (second pipe).
[0097] End of example.
[0098] Of course, beyond this example, ammonia (NH3) can be used under other conditions. Reference can be made to the nomograph in [Fig. 9], which provides the solubility of iron in the heat transfer fluid (on the y-axis) as a function of temperature (on the x-axis), for different values of hydrogen potential (pH), namely pH = 9, pH = 9.5, and pH = 10 (taken at 25°C each time), and, for each of the aforementioned pH values, for different concentrations of dihydrogen, respectively 1, 10, and 100 pmol / kg. [Fig. 9] allows the quantities of reducing agent and / or oxidizing agent to be used for two-point operating conditioning according to the invention to be adapted to the specific operating conditions of the secondary circuit (temperatures within the steam generator and the condenser, etc.). acid-base operation used on the installation, etc). The conversion of the dihydrogen concentrations indicated on [Fig.9] into redox potential can be carried out using [Fig.7].
[0099] It is also possible with other conventional conditioning methods than that carried out with ammonia (NH3), and therefore with ethanolamine (C2H7NO) or morpholine (C4H9NO) to regulate the pH, with hydrazine being able to be retained to regulate the redox potential (Eh).
[0100] The nomograms given in [Fig. 10] and [Fig. 11] correspond to the one provided in [Fig. 9], respectively for ethanolamine ([Fig. 10]) and morpholine ([Fig. 11]). These figures allow the quantities of reducing agent and / or oxidizing agent to be used for two-point operating condition according to the invention, depending on the specific operating conditions of the circuit. The conversion of the dihydrogen concentrations indicated in these figures into redox potential can also be carried out using [Fig. 7].
[0101] It should be noted that an additional and important effect of the two-point operating condition according to the invention is expected on the precipitation of oxides in so-called "single-pass" steam generators, that is, steam generators that vaporize all of the water they receive. By delaying and / or shifting the zone of oxide precipitation towards higher temperatures in the steam generator, these oxides will have a high probability of being carried away in the steam rather than adhering to the various walls. Indeed, in "single-pass" steam generators, the complete transformation of liquid water into steam inevitably leads to an increase in the concentration of aqueous species, and ultimately, to the reaching of a solubility limit for each element before the heat transfer fluid exits the steam generator.Carrying the solids formed in the steam (solubility limit reached) is also a way to limit fouling and / or clogging, even if in this particular case of "single pass" steam generators, it is impossible to completely avoid the precipitation of oxides in the water vaporization zone.
[0102] The preceding description, made with reference to a secondary circuit of a power generation plant, applies equally to a heat generation plant, in which the circuit carries a single-phase heat transfer fluid in liquid form between the hot source (for example a boiler, or a heat exchanger recovering heat from a heat source) and the cold source (for example a heat exchanger).
Claims
Demands
1. A method for chemically conditioning a heat transfer fluid in a circuit of a power generation plant, the circuit (CS) comprising the following components: - a hot source (GV), - a cold source (COND), - a first pipe (CAI) connecting the outlet of the hot source (GV) to the inlet (MP2) of the cold source (COND), - a second pipe (CA2) connecting the outlet of the cold source (COND) to the inlet (MPI) of the hot source (GV), each of said components being made of a metallic alloy containing iron, the method comprising a step consisting of: A) injecting reducing and acid-base species into the second pipe (CA2) to define, at a given temperature, a reference hydrogen potential - redox potential (pH-Eh) pair in the heat transfer fluid,characterized in that the process comprises the following additional steps: B) injecting a reducing species at the inlet (MPI) of the hot source to decrease the redox potential (Eh) of the heat transfer fluid, thereby increasing the solubility of the different phases of iron in the heat transfer fluid, and C) removing, at the inlet (MP2) of the cold source, the reducing species injected in step B) or injecting, at the inlet (MP2) of the cold source, an oxidizing species to compensate for the effects of the reducing species injected in step B), thereby increasing the redox potential (Eh) of the heat transfer fluid and decreasing the solubility of the different phases of iron in the heat transfer fluid.
2. A method according to claim 1, characterized in that during step B), a quantity of reducing species is injected ensuring that the solubility of the different phases of Iron over the entire area of the circuit going from the inlet of the hot source to the inlet of the cold source is greater than the solubility of the different phases of Iron at the inlet of the hot source.
3. A method according to any one of the preceding claims, characterized in that the reducing species injected at the inlet of the hot source at the stage B) is hydrazine or dihydrogen, preferably dihydrogen.
4. A process according to any one of the preceding claims, characterized in that the oxidant injected into the heat transfer fluid at the inlet of the cold source in step C) is dioxygen.
5. A method according to any one of the preceding claims, characterized in that step A) consists of imposing a pH between 9 and 11 and a redox potential less than or equal to -550mV, for example between -650mV and -550mV, at a temperature of 25°C.
6. A method according to any one of the preceding claims, characterized in that the acid-base species injected during step A) is selected from ammonia (NH3), ethanolamine (C2H7NO) or morpholine (C4H9NO) or a mixture thereof.
7. 7. A process according to any one of the preceding claims, characterized in that the reducing species injected during step A) is hydrazine (N2H4).
8. A method according to any one of the preceding claims, characterized in that step A) is carried out at the outlet (MCC) of the cold source (COND).
9. 9. A method according to any one of the preceding claims, characterized in that the circuit is a secondary circuit of a power generation plant in which the hot source is a steam generator and the cold source is a condenser, said circuit conveying a two-phase heat transfer fluid, in vapor form in the first pipe and in liquid form in the second pipe.
10. 10. A method according to any one of claims 1 to 8, characterized in that the circuit is a circuit of a heat production plant, said circuit conveying a single-phase heat transfer fluid in liquid form.