EP3475638B1 - Method and facility for recovering thermal energy on a furnace with tubular side members and for converting same into electricity by means of a turbine producing the electricity by implementing a rankine cycle - Google Patents

Description

The invention relates to the field of the recovery of heat energy from furnaces with tubular spars and its conversion into electricity by means of an expansion cycle turbine using a fluid other than water vapor.

The invention relates in particular to steel reheating furnaces intended to reheat products, in particular slabs, blooms, blanks or billets, operating at a temperature suitable for their hot rolling, and more particularly furnaces with mobile beams. A reheating furnace makes it possible to bring the products to high temperatures, for example to a temperature of about 1200 ° C. for a carbon steel. The heating of the furnace is commonly carried out by burners supplied with preheated air and fuel and operating with a slight excess of air.

EP0971192 describes an example of a longitudinal beam furnace equipped with fixed beams and mobile beams. The products are placed on the beams and are heated by burners placed above and below the products. The spars are made of andirons and cooled keels. The movable side members allow the transport of the products in the oven by following a cycle comprising a first phase of ascent by the movable side members, from an initial position, which allows the products to be lifted. The first phase is followed by a second phase of horizontal transport by the mobile spars, then a third phase of depositing the products on the fixed spars. The products are thus moved by one step on the fixed side members before the fourth phase of moving the moving side members back to their initial position. The andirons of the fixed side members are carried by pins integral with the oven floor. The andirons of the mobile side members are carried by pins passing through the floor of the oven and fixed, under the oven, on a translation frame. The translation frame is based on a mechanism which ensures a rectangular cycle by the horizontal and vertical displacement of the frame assembly, keels and andirons of the mobile side members.

The structure of the side members is produced by tubes or hollow sections which are cooled by a circulating heat transfer fluid, which is traditionally water at low temperature and low pressure, for example 30 to 55 ° C. and 5 bars. The quantity of energy evacuated per unit of time by the heat transfer fluid is important in order to limit the temperature and to have sufficient mechanical strength of the structure of the side members. The evacuated power is for example 10 MW _th for a furnace with a capacity of 450 t / h. The hot water recovered at the outlet of the longitudinal members can then be used in the plant, for example for sanitary use, for heating buildings, or for processes for which relatively low temperatures are necessary. It is known that the water at low temperature and low pressure cooling the spars can be replaced by superheated high pressure water, which is partially transformed into saturated steam in the andirons. The resulting steam can be used in the plant for different needs. The cooling of the structure of the side members by a mixture of water and saturated steam is advantageous, in particular because it makes it possible to ensure the operation of the structure of the side members at a stable temperature. Indeed, the change of state from the liquid phase to the vapor phase taking place at a substantially constant temperature, the outlet temperature of the cooling fluid from the spars is constant, whatever the operating speed of the furnace, only the quantity of water passing in evolving vapor phase. The outlet temperature of the cooling fluid is, for example, 215 ° C. for a fluid pressure of 21 bars absolute.

A heat recuperator is traditionally placed in a flue of combustion fumes from the furnace. It enables energy recovery from these fumes by preheating the combustion air from the burners and sometimes the fuel. Downstream of this recuperator, the temperature of the flue gases is still relatively high, for example 300 ° C. It is known to add other heat exchangers, or a recovery boiler, in flues to further exhaust the fumes. In the case where the cooling of the structure of the side members is carried out by superheated water with production of steam, it may for example be a superheated water saver or a steam superheater.

The steel reheating furnaces operate continuously and have large production capacities, for example 450 t / h. Their operating regime frequently varies, in particular according to the nature and temperature of the products placed in the oven and the timing of the oven. As a result, the volume of the combustion fumes also varies frequently, the latter being substantially proportional to the hourly tonnage of the products heated in the oven. The changes in the flow of fumes are also accompanied by a variation in the temperature of said fumes. These fluctuations in the temperature of the flue gases lead to a significant variation in the performance of the exchangers placed in flues or in recovery boilers. At reduced tonnage, the flue gas temperature no longer allows the residual energy of the flue gases to be used in steam.

The products to be heated in the oven must always be heated to the rolling temperature, and this being relatively constant, the temperature of the oven walls vary little. As the heat losses through the side members fluctuate little, the generation of steam by a cooling system for the side members structure is less dependent on the hourly tonnage of the furnace.

The thermal energies contained in the flue gases and the cooling fluid of the spars each represent approximately 10 MW _th on a 450 t / h furnace with temperatures respectively of the order of 300 ° C and 200 ° C. The use of a water-steam cycle for the production of electricity from these energies is difficult to implement and is not economically profitable with these levels of temperature and thermal power, as well as these amplitudes of power variations.

KR20140036363 describes an energy recovery solution on a steel reheating furnace making it possible to recover the energy losses of the furnace contained in the fumes and in the cooling system of the spars, by using them in a common electricity production installation, while overcoming the problems of variability thereof. It implements an installation for generating electricity by a thermodynamic Rankine cycle using an organic fluid as working fluid. An organic Rankine cycle machine, called "ORC" for the acronym of the English terms Organic Rankine Cycle, converts medium or low temperature heat into electricity, thanks to the use of an organic working fluid of density greater than that of water. In the ORC machine, the working fluid in the liquid state is compressed and then vaporized. The organic fluid vapor is then expanded before being condensed. The machine comprises in particular an evaporator, an expansion turbine, a condenser and a booster pump. The expansion turbine is for example of the radial or axial type, with one or two stages, the rotation of which drives an alternator which produces electricity.

The organic fluid has a low boiling point, for example less than 50 ° C at atmospheric pressure, and is of the wetting type, that is to say that it is not necessary to superheat the vapor of this. fluid after evaporation to avoid creating droplets in the turbine during expansion. This type of fluid can thus allow, despite a low temperature of the hot source, to extract a maximum of work in the turbine and thus to have a better efficiency than a water vapor cycle at low temperatures, for example below 350 ° C.

Thus the choice of the ORC technology, among the various thermodynamic cycles making it possible to produce electricity, makes it possible to obtain a better thermodynamic machine efficiency, that is to say the ratio between available thermal energy and net electricity produced.

The calories necessary for the vaporization of the organic fluid of the ORC machine are provided by the energy recovered from the reheating furnace, partly from the cooling fluid of the side members and partly from the combustion fumes.

In the solution disclosed by KR20140036363 , the coolant for andirons and keels is a mixture of molten salts. This mixture is for example composed, by mass, of 52% of KNO ₃ , 18% of NaNO ₃ and 30% of LiNO ₃ . To maintain these molten salts in the temperature range required for proper operation of the furnace, and in particular for their maintenance in the liquid phase, the installation comprises a recirculation loop 40 with additional equipment, which makes the installation more expensive and relatively complex to operate compared to a solution in which the cooling fluid is water or a water / steam mixture. Calories from the molten salts are transmitted to the organic fluid of the ORC by means of an exchanger 21. In the event of deterioration of this exchanger, the molten salts may come into contact with the organic fluid of the ORC, which represents a risk. for installation. In addition, this solution does not make it possible to modulate the calorific input of the molten salts to the organic fluid of the ORC. If the ORC is stopped, the continuous supply of calories by the molten salts can lead to a very significant rise in the temperature of the organic fluid, hence a risk for the installation.

Otherwise, KR20140036363 describes a solution in which part of the fumes directly exchange calories with the organic fluid of the ORC by means of an exchanger 51. In the event of deterioration of this exchanger, there is a risk of fire if the organic fluid of the ORC comes into contact with the fumes.

The state of the art therefore does not allow a double recovery of energy from the fumes from the reheating furnace and from the cooling fluid of the andirons and keels under conditions allowing optimal energy performance, flexibility in regulating the operation of the 'ORC and safe operating conditions.

This objective is achieved with, according to a first aspect of the invention, a method for recovering energy by an energy recovery installation, able to be connected to at least one longitudinal heating furnace equipped with burners, said furnace. heating system comprising a cooling circuit for said side members, in which water circulates, the latter being in the liquid state at the inlet of the side members and in the liquid / vapor mixture state at the outlet of the side members, said mixture being separated downstream of the side members into liquid water on one side and steam on the other, the steam directly or indirectly yielding calories to a first intermediate recirculation loop, and furthermore a recovery system energy making it possible to absorb part of the calories from the fume circuit evacuated by the oven, said calories being transferred to a second intermediate recirculation loop, said first and second intermediate recirculation loops directly or indirectly transferring calories to an organic fluid loop arranged so as to supply a turbine producing electricity by the implementation of a cycle of organic Rankine.

In a configuration in which the cooling of the andirons and keels is carried out by water and a water / steam mixture, the condensation of the vapors in the exchanger allows a significant transfer of calories between the steam and the organic fluid of the ORC .

According to the invention, the calories coming from the steam and those coming from the flue gas circuit are transferred indirectly to the organic fluid of the ORC, via a first intermediate recirculation loop arranged between a circuit comprising the steam and the organic fluid, respectively via a second intermediate recirculation loop arranged between the flue gas circuit and the organic fluid.

The vapor circuit is isolated from the organic fluid by at least two pieces of equipment, for example two exchangers.

The flue gas circuit is isolated from the organic fluid by at least two pieces of equipment, for example two exchangers.

Thus, according to the invention, the calories coming from the steam are first transferred to a first intermediate recirculation loop before being transferred to the organic fluid used in the Rankine cycle. Also, although the steam has a very high pressure compared to that of the organic fluid, there is no significant risk of explosion if the exchanger is pierced, even if the organic fluid of the ORC is very often a hydrocarbon or flammable refrigerant, since the vapor cannot come into contact with said organic fluid.

Furthermore, according to the invention, the calories from the fumes are first transferred to a second intermediate recirculation loop before being transferred to the organic fluid used in the Rankine cycle. Also, there is no possible exchange between the organic fluid used in the Rankine cycle and the fumes, which avoids a risk of fire which is present in the prior art.

The method according to the invention therefore has more security than that according to the prior art.

The combination of the two energy sources coming from the fumes and the cooling system makes it possible on the one hand to be able to increase the annual global electricity production and on the other hand to be able to limit the investment. Indeed, this combination makes it possible to obtain a greater quantity of usable energy in a single ORC machine of great capacity (with a better efficiency and less expensive), than if the two heat sources were operated separately by two ORC machines of smaller capacity (lower efficiency and proportionately more expensive).

In addition, the combination of the two energy sources from the flue gases and the cooling system can stabilize the energy input supplied to the ORC machine. The combination of the two energy sources from the flue gases and the cooling system can allow the ORC machine to operate more often in its optimum operating range.

The sizing of the ORC machine makes it possible to limit the amount of the investment, and therefore the time necessary for the return on investment, thus increasing the economic interest of its implementation. During its design, a reheating furnace is dimensioned for a nominal production capacity corresponding to the heating of a number of tonnes per hour of a reference product from an initial temperature to a discharge temperature. From experience, in operation, the furnace operates on average at about 70% of its nominal capacity.

On the other hand, an ORC machine works well over a wide range of variations in the heat source, with the incoming thermal power typically varying between 30% and 100%. The maximum efficiency of the ORC machine is obtained for the maximum design power and it decreases with the incoming thermal power. An ORC machine must be stopped when the calorie supply to the organic fluid of the ORC machine is less than a minimum threshold generally between 20 and 30% of the maximum capacity allowed by the ORC machine.

By combining the two sources of thermal energy, the invention makes it possible, thanks to the stability and the capacity of the heat source coming from the side member cooling system, never to be less than 30% of the thermal load. Thus the ORC machine is always in operation, except in the event of shutdown of the installation, and does not require complex regulation.

According to another aspect of the invention, there is provided an energy recovery installation capable of being connected to at least one beam reheating furnace equipped with burners, said reheating furnace comprising a circuit for cooling said stringers, in which circulates water, this being in the liquid state at the entry of the side members and in the liquid / vapor mixture state at the outlet of the side members, said mixture being separated downstream of the side members into liquid water on one side and steam on the other, said installation comprising a turbine designed to produce electricity by implementing a Rankine cycle on an organic fluid, said installation further comprising at least exchangers functionally arranged heat so as to transfer to said organic fluid, at least part of the calories contained in combustion fumes from the burners, via a heat transfer fluid, and at least part of the calories contained in the steam, via a heat transfer fluid.

According to one possibility of the installation, at least one reheating furnace may include a heat exchanger which is arranged in a combustion fume discharge flue from said at least one reheating furnace in order to collect calories from said combustion fumes and transmit them to the heat transfer fluid circulating in said heat exchanger.

The exchanger placed in the flue for evacuation of the fumes according to the invention may optionally be placed downstream in the direction of flow of the fumes from other equipment for recovering energy from the fumes. The other energy recovery equipment can be, for example, a recuperator for preheating the combustion air of the burners.

According to one of the aspects of the invention, the installation comprises a first heat exchanger functionally arranged so as to directly or indirectly transfer energy from the steam to an intermediate heat transfer fluid, and a second heat exchanger arranged in so as to transfer thermal energy from said intermediate heat transfer fluid to the organic fluid of the ORC machine.

According to the invention, the heat transfer intermediate fluid can be an organic fluid in the liquid state, under the conditions of its use, for example a thermal oil. Advantageously, the heat transfer intermediate fluid is non-flammable at the temperature at which it is used, its ignition temperature being substantially higher than that of the organic fluid of the ORC.

This configuration makes it possible to improve the robustness of the equipment by limiting the sudden variations in temperature of exchange with the organic fluid of the ORC in the event of shutdown of the furnace thanks to the mass energy storage capacity. of intermediate fluid. It also makes it possible to improve the safety of the exchange system with the heat exchanger coming from the steam by locally controlling the behavior of this exchange without disturbing the loop supplying the ORC exchanger. The steam being at a pressure appreciably higher than that of the intermediate fluid (approximately 20 bars on the vapor side for approximately 4 to 7 bars on the intermediate fluid side), if the exchanger is pierced, the fluid will flow from the vapor circuit. towards the intermediate fluid circuit thus preventing the intermediate fluid from spilling into the andirons and keels.

Furthermore, the presence of an intermediate circuit between the steam circuit and the ORC circuit makes it possible to prevent steam from coming into contact with the organic fluid of the ORC, said contact possibly being a source of 'explosion.

This solution also allows the use of a robust technology exchanger for the exchange between the intermediate fluid and the organic fluid of the ORC, the two fluids having similar properties. It thus makes it possible to strengthen the operating safety of the ORC machine in the event of a problem with the steam circuit for cooling the side members.

To further enhance the safety of the installation, an additional intermediate loop can be added between the steam and the intermediate fluid described above.

The use of an intermediate organic fluid to recover calories from combustion fumes which remains in the liquid state, regardless of the fluctuations in temperature and volume of the combustion fumes in the flue, has the advantage of greatly facilitating the operation of the installation compared to the use of a recovery boiler in which a phase change in the exchanger takes place at higher pressure.

Advantageously according to the invention, regulation of the supply of calories to the ORC machine can be carried out on the flue gas circuit, by means of a partial bypass of the combustion fume exhaustion exchanger placed in the flue or dilution of the fumes with cold air to lower the temperature. Due to the sizing of the ORC for operation of the furnace at 70% of its nominal capacity, if the heat input to the ORC machine becomes too great, some of the fumes bypass the exchanger of the fume exhaustion circuit. combustion or the fumes will be diluted without this interfering with the operation of the furnace.

The heat transfer fluid used to collect calories from combustion fumes and that used indirectly to collect calories from andirons and keels can be of the same nature, but this method also makes it possible to use heat transfer fluids with different properties. This can make it possible to optimize energy recovery with fluids used at different temperature levels and to reinforce the safety of the installation by choosing fluids that minimize the risk of fire or explosion in the event of contact between them. fumes or steam and these fluids.

As an alternative embodiment, the addition of energy storage on the intermediate circuits makes it possible to improve the efficiency of the assembly without disturbing the main exchange circuit to the ORC.

Advantageously, the operation of the longitudinal members cooling circuit may not be modified by the presence of the ORC machine. The control of the installation can thus be simplified.

The calorific power transmitted to a thermal fluid used in the flue gas exhaustion circuit can be directly determined by the temperature rise of said fluid in an exchanger of the combustion fume exhaustion circuit.

If the ORC machine is shut down, a bypass of the fumes placed on the fume circuit can prevent the thermal fluid used in the fume exhaust system from heating up. Another method consists in using a heat transfer fluid operating at a higher temperature on the intermediate loop and / or in reducing the temperature of the flue gases by diluting them, for example with an air inlet upstream of the recuperator placed on the flue gas pipe. Air coolers can also be placed on the superheated water / steam circuit so as to evacuate the calories coming from the side members.

Advantageously according to the invention, the ORC machine is dimensioned according to the average operating speed of the reheating furnace and not according to the nominal capacity of the furnace. This has a double advantage: the ORC machine being smaller, the amount of the investment can be reduced, and the ORC machine can operate a maximum of the time on an optimal point (maximum efficiency) thus producing a maximum of electricity for a faster return on investment.

The installation according to the invention can furthermore comprise another heat exchanger functionally arranged so as to transfer thermal energy from at least one other source to the organic fluid.

According to another aspect of the invention, there is provided a beam reheating furnace equipped with burners, characterized in that it is equipped with an energy recovery installation according to the invention, said energy installation being connected to said oven.

• la Figure 1 représente schématiquement une installation selon un premier mode de réalisation dans laquelle le fluide organique de la machine ORC est préchauffé en série par la récupération d'énergie sur les deux sources, vapeur et fumées,
• la Figure 2 représente schématiquement une installation selon un second mode de réalisation similaire à celui de la figure 1, mais dans lequel le fluide organique de la machine ORC est préchauffé en une seule étape, après l'addition en amont des deux sources vapeur et fumées,
• la Figure 3 représente schématiquement une installation selon un troisième mode de réalisation similaire à celui de la figure 2 dans lequel un circuit intermédiaire supplémentaire est ajouté coté vapeur, et,
• la Figure 4 représente schématiquement une installation selon un quatrième mode de réalisation dans lequel des fluides organiques collectant les calories provenant des longerons et des fumées de combustion sont mélangés en amont de la machine ORC et l'énergie est récupérée parallèlement.

Other characteristics and advantages will appear in the light of the description of the preferred embodiments of the invention accompanied by the figures in which:

• the Figure 1 schematically represents an installation according to a first embodiment in which the organic fluid of the ORC machine is preheated in series by the recovery of energy from the two sources, steam and smoke,
• the Figure 2 schematically shows an installation according to a second embodiment similar to that of the figure 1 , but in which the organic fluid of the ORC machine is preheated in a single step, after the upstream addition of the two sources of steam and smoke,
• the Figure 3 schematically shows an installation according to a third embodiment similar to that of the figure 2 in which an additional intermediate circuit is added on the steam side, and,
• the Figure 4 schematically shows an installation according to a fourth embodiment in which organic fluids collecting the calories from the longitudinal members and combustion fumes are mixed upstream of the ORC machine and the energy is recovered in parallel.

These embodiments are in no way limiting, it is in particular possible to produce variants of the invention comprising only a selection of characteristics described below, as described or generalized, isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention from the state of the art.

On the Figure 1 , one can see schematically represented an installation according to a first exemplary embodiment of the invention. To simplify the description, only the equipment items necessary for understanding the invention are shown in this figure. Equipment essential for the operation of the installation, such as pumps, valves, food tank, expansion vessel, etc., are not shown in this figure and the following, nor described in this description, the person skilled in the art knowing define them, size them and locate them as best as possible on the installation.

Products 1 are continuously heated in a reheating furnace 2 with tubular spars. The movement and maintenance of the products in the oven are ensured by fixed beams and mobile beams. The spars comprise andirons 3a and keels 3b in which a cooling fluid circulates. Burners 5 heat the furnace 2 and the products 1. Combustion fumes from the burners 5 are evacuated from the furnace via a flue gas 6.

At the entry of the side members, the cooling fluid is, for example, water superheated at a temperature of 215 ° C. and at a pressure of 21 bars absolute. During its flow in the side members, the superheated water is partially transformed into saturated steam 4. On leaving the side members, the cooling fluid is composed of a mixture of superheated water and saturated steam 4. A tank 7 allows separation of liquid water and saturated steam 4.

The installation comprises an ORC machine implementing a Rankine cycle on an organic fluid 21 circulating in a circuit 13.

The installation comprises an intermediate recirculation loop 16 arranged between the steam circuit and the circuit 13 of the ORC machine. An intermediate fluid coolant 17 circulates in the intermediate recirculation loop 16, preferably organic, maintained in the liquid state.

The intermediate recirculation loop 16 comprises in particular two heat exchangers 8 and 18 and a circulation pump, not shown. Thus, the saturated steam 4 transfers calories to the intermediate heat transfer fluid 17 by means of the exchanger 18 in which it condenses, then the intermediate heat transfer fluid 17 in turn transfers calories to the organic fluid 21 of the ORC machine by means of the 'exchanger 8.

The addition of the intermediate recirculation loop 16 can make it possible to reinforce the safety of the installation and to use thermal fluids of different properties. Thus the intermediate heat transfer fluid 17 may have greater compatibility with the vapor than the organic fluid 21 of the ORC, thus limiting the risk of fire or explosion.

A heat exchanger 9 can be placed in the flue gas 6, possibly downstream, in the direction of flow of the fumes, relative to other equipment for recovering energy from the fumes, for example a preheating recuperator combustion air from the burners.

The heat exchanger 9 can be supplied with a heat transfer fluid 10, preferably organic in the liquid state, circulating in a recirculation loop 11. The heat transfer fluid 10 can be of the same type as the intermediate heat transfer fluid 17, on the vapor side. , but it can also be of a different nature. The fumes yield part of their calories to the heat transfer fluid 10 in the heat exchanger 9. A second heat exchanger 12 is placed on the recirculation loop 11. The second exchanger 12 allows the transfer of the calories captured by the heat transfer fluid 10. to the organic fluid 21 of the ORC machine.

The organic fluid 21 circulates in the ORC machine in the recirculation loop 13 comprising in particular, preferably successively in the direction of the flow of the fluid, the heat exchangers 8 and 12, an expansion turbine 14, a condensation exchanger 15 organic fluid 21 of the ORC machine and a booster pump 24. The thermal energy transferred to the organic fluid 21 of the ORC machine in the heat exchangers 8 and 12 makes it possible to bring it to the vapor phase. The expansion of the steam drives the expansion turbine 14 in rotation which is coupled to an alternator which produces electricity. At the outlet of the expansion turbine 14, the exchanger 15 allows the organic fluid 21 to be condensed, before it is returned to the heat exchangers 8 and 12 to undergo a new Rankine cycle. The organic fluid 21 transfers calories in the exchanger 15 to a heat transfer fluid circulating in a circuit 22.

A set of registers 23 allows the heat exchanger 9 to be bypassed by all or part of the combustion fumes.

A heat exchanger 25 makes it possible to capture calories from a fluid 26 available on the site and to transmit them to the organic fluid 21 of the ORC machine. The installation according to the invention thus also makes it possible to upgrade one or more other heat sources for increased overall performance of the industrial site on which it is installed.

The Figure 2 shows schematically an alternative embodiment of the invention in which the calories of the fumes are supplied to the intermediate fluid 17 and not directly to the fluid 21 of the ORC. Likewise, the additional supply of calories from the fluid 26 is made to the intermediate fluid 17 and not directly to the fluid 21 of the ORC. This configuration allows simplified control of the ORC, and reinforces its safety, with a single exchanger in which all the heat inputs to the fluid 21 and its vaporization are made.

The Figure 3 schematically represents another variant embodiment of the invention in which an intermediate loop 30 is added on the steam side in which a heat transfer fluid 31 circulates. The steam 4 transfers calories to the heat transfer fluid 31 by condensing in the exchanger 18, then the heat transfer fluid. heat transfer fluid 31 in turn transfers these calories to the heat transfer fluid 17 by means of a heat exchanger 32. This configuration makes it possible to strengthen the safety of the installation, and the flexibility of its regulation, the technology of exchangers 8, 18, 31 and the nature of the heat transfer fluids 31, 17, 21 being chosen so as to have proven technologies on the exchangers and to limit the risks of fire or explosion in the event of contact between the fluids following the drilling of the exchangers.

The Figure 4 schematically shows another variant embodiment of the invention in which a mixture is produced between a part of the heat transfer fluid 10 circulating in the recirculation loop 11 and a part of the intermediate heat transfer fluid 17, preferably organic, circulating in the recirculation loop 16, the fluids 10 and 17 being of the same nature. This mixture, for example produced by means of three-way valves 20, is then led to a heat exchanger 19 in which it transfers calories to the organic fluid 21 of the ORC machine. At the outlet from the exchanger 19, the fluid mixture is again distributed between the two recirculation loops 11 and 16, for example by means of three-way valves.

The quantity of energy available on the flue gases and the cooling fluid of the side members is generally of the same order of magnitude, for example 10 MW _th on the flue gases and on the side members for a furnace with a capacity of 450 t / h.

On the heat exchanger 18, the temperature of the saturated steam 4 being substantially constant, for example 215 ° C for a pressure of 21 bars absolute, the heat exchange with the intermediate coolant 17 of the recirculation loop 16 is always optimum.

On the heat exchanger 9, the temperature of the flue gases can vary, for example from 300 ° C., for a maximum capacity of the furnace, to 280 ° C. for 70% of its capacity. Thus, the heat exchange with the coolant 10 of the recirculation loop 11 is variable and the operating conditions of the common fluid of the loop 20 entering the ORC machine can vary, in the case of a thermal oil, from 225 ° C to 215 ° C in temperature and from 70 kg / s to 50 kg / s in flow rate respectively according to the two operating cases described above. For such temperatures, the most suitable organic fluid 21 of the ORC machine is pentane, the latter being brought upstream of the expansion turbine 14 to a temperature for example between 135 ° C and 160 ° C respectively depending on the requirements. two operating cases, so that the net power delivered by the ORC machine is maximum, respectively 1.2 MW _e and 0.9 MW _e .

According to an exemplary embodiment of the invention, the energy recovery installation makes it possible to collect calories from at least two furnaces. A heat exchanger 9 can be placed in the flue gas pipe of each oven or of a single oven. Likewise, calories can be recovered from the steam coming from the longitudinal members of the two furnaces or of only one.

As we have just seen, the invention allows efficient energy recovery from the thermal losses of the furnace by the combustion fumes and the longitudinal members, thanks to a dimensioning of the ORC machine well adapted to the operating speed of the furnace and a stability of operation thereof resulting from the combination of two heat sources.

Claims (7)

1. A method for recovering energy by means of an energy recovery installation that can be connected to at least one beam reheating furnace (2) equipped with burners (5), said beam reheating furnace comprising a cooling system for said beams, in which water flows, being in liquid state at the inlet of the beams and in a mixture of liquid/vapour state at the outlet of the beams, said mixture being separated downstream of the beams in the form of liquid water on the one side and steam (4) on the other, said installation comprising a turbine (14) generating electricity by performing a Rankine cycle on an organic fluid (21), said method comprising a step of directly or indirectly transferring thermal energy from the vapour (4) to an intermediate heat transfer fluid (17), preferably organic in liquid state, by means of a heat exchanger (18), a step of thermal energy transfer of said intermediate heat transfer fluid to the organic fluid (21) by means of a heat exchanger (8, 19), and a step of direct or indirect thermal energy transfer of at least a portion of the flue gases from the burners (5) to the organic fluid (21) by means of a heat exchanger (12, 19) functionally arranged to transfer to said organic fluid (21) at least a portion of the calories contained in the flue gases of the burners (5) via a heat transfer fluid (10) and an exchanger (9).
2. Method according to Claim 1, wherein the heat transfer fluid (10) for transferring at least a portion of the calories contained in flue gases from the burners (5) to the organic fluid (21) is an organic fluid in liquid state, preferably a thermal oil.
3. Method according to Claim 1 or 2, wherein the heat transfer fluid (10) for transferring at least a portion of the calories contained in flue gases from the burners (5) to the organic fluid (21) and the intermediate heat transfer fluid (17) for transferring thermal energy to the organic fluid (21) are of the same nature, these two heat transfer fluids (10, 17) being mixed upstream of the exchanger (19) in which the heat transfer between these fluids and the organic fluid (21) is carried out.
4. Heat energy recovery installation that can be connected to at least one beam reheating furnace (2) equipped with burners (5), said beam reheating furnace comprising a cooling system for said beams, in which water flows, being in liquid state at the inlet of the beams and in a mixture of liquid/vapour state at the outlet of the beams, said mixture being separated downstream of the beams in the form of liquid water on the one side and steam (4) on the other, said installation comprising a turbine (14) arranged to generate electricity by implementing a Rankine cycle on an organic fluid (21), said installation comprising a heat exchanger (18) functionally arranged to directly or indirectly transfer thermal energy from the vapour (4) to an intermediate heat transfer fluid (17), preferably organic in liquid state, the at least one heat exchanger (8, 19) being arranged to transfer heat energy from said intermediate heat transfer fluid to the organic fluid (21), said installation further comprising at least one heat exchanger (12, 19) functionally arranged to transfer to said organic fluid (21) at least a portion of the calories contained in the flue gases of the burners (5) via a heat transfer fluid (10) and an exchanger (9).
5. Installation, according to Claim 4, wherein the at least one beam reheating furnace (2) comprises the heat exchanger (9) which is arranged in a flue gas discharge of said at least one beam reheating furnace to collect calories from said flue gases and transmit them to the heat transfer fluid (10) flowing in said heat exchanger.
6. Installation according to Claims 4 or 5, wherein the heat transfer fluid (10) and the intermediate heat transfer fluid (17) are of the same nature.
7. Installation according to any one of Claims 4 to 6, further comprising another heat exchanger (25) functionally arranged to directly or indirectly transfer heat energy from at least one other source (26) to the organic fluid (21).

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