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

Abstract

A heat energy recovery installation installed on a beam reheating furnace equipped with burners includes a turbine that generates electricity by implementing a Rankine cycle on an organic fluid coming from calories derived partly from the fluid used for cooling the tubular beams via a first intermediate circuit, and in part from flue gases from the burners by way of a second intermediate circuit.

Claims

1. A method for recovering energy by an energy recovery installation configured to be connected to at least one beam reheating furnace equipped with burners, said beam reheating furnace configured to cool beams, in which water flows, the water being in a liquid state at an inlet of the beams and in a mixture of a liquid/vapor state at an outlet of the beams, said installation including a turbine that generates electricity by from an organic fluid used in a Rankine cycle, said method comprising: directly transferring thermal energy from the vapor to an intermediate heat transfer fluid by at least one first heat exchanger; directly transferring thermal energy of said intermediate heat transfer fluid to the organic fluid by at least one second heat exchanger; and directly transferring thermal energy of at least a portion of flue gases from the burners via another heat transfer fluid and a fourth heat exchanger to one of: (i) the organic fluid via a third heat exchanger, (ii) the intermediate heat transfer fluid via a third heat exchanger, and (iii) the intermediate heat transfer fluid via a valve system wherein the at least one second heat exchanger, the third heat exchanger, and the fourth heat exchanger are separate from one another.

2. The method according to claim 1, wherein the other heat transfer fluid is an organic fluid in liquid state.

3. The method according to claim 1, wherein the other heat transfer fluid and the intermediate heat transfer fluid are of a same type, the intermediate heat transfer fluid and the other heat transfer fluid being mixed upstream of the at least one second heat exchanger in which the heat transfer between the intermediate and other heat transfer fluids and the organic fluid is carried out.

4. The method of claim 1, wherein the intermediate heat transfer fluid is organic and in a liquid state.

5. The method of claim 2, wherein the organic fluid is a thermal oil.

6. The method according to claim 2, wherein the other heat transfer fluid and the intermediate heat transfer fluid are of a same type, the intermediate heat transfer fluid and the other heat transfer fluid being mixed upstream of the at least one second heat exchanger in which the heat transfer between the intermediate and other heat transfer fluids and the organic fluid is carried out.

7. A heat energy recovery installation configured to be connected to at least one beam reheating furnace equipped with burners, said beam reheating furnace configured to cool beams, in which water flows, the water being in a liquid state at an inlet of the beams and in a mixture of a liquid/vapor state at an outlet of the beams, said heat energy recovery installation comprising: a turbine configured to generate electricity from an organic fluid used in a Rankine cycle; at least one first heat exchanger functionally configured to directly transfer thermal energy from the vapor to an intermediate heat transfer fluid; at least one second heat exchanger configured to directly transfer heat energy from said intermediate heat transfer fluid to the organic fluid; and at least one third heat exchanger functionally configured to directly transfer at least a portion of calories contained in flue gases of the burners via another heat transfer fluid and a fourth heat exchanger to one of: (i) the organic fluid, and (ii) the intermediate heat transfer fluid and thereafter to the organic fluid, wherein the at least one second heat exchanger, the at least one third heat exchanger, and the fourth heat exchanger are separate from one another.

8. The installation according to claim 7, wherein the at least one beam reheating furnace comprises the fourth heat exchanger which is disposed in a flue gas discharge of said at least one beam reheating furnace to collect the calories from said flue gases and transmit the calories to the other heat transfer fluid flowing in said fourth heat exchanger.

9. The installation according to claim 7, wherein the other heat transfer fluid and the intermediate heat transfer fluid are of a same type.

10. The installation according to claim 7, further comprising a fifth heat exchanger functionally configured to directly or indirectly transfer heat energy from at least one other source to the organic fluid.

11. The installation of claim 7, wherein the intermediate heat transfer fluid is organic and in a liquid state.

12. The installation according to claim 8, wherein the other heat transfer fluid and the intermediate heat transfer fluid are of a same type.

13. The installation according to claim 8, further comprising a fifth heat exchanger functionally configured to directly or indirectly transfer heat energy from at least one other source to the organic fluid.

14. The installation according to claim 9, further comprising a fifth heat exchanger functionally configured to directly or indirectly transfer heat energy from at least one other source to the organic fluid.

15. The installation according to claim 12, further comprising a fifth heat exchanger functionally configured to directly or indirectly transfer heat energy from at least one other source to the organic fluid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages will become apparent in the light of the description of the preferred embodiments of the invention accompanied by the figures in which:

(2) FIG. 1 diagrammatically represents an installation according to a first embodiment in which the organic fluid of the ORC machine is preheated in series by the energy recovery on the two sources, steam and flue gases;

(3) FIG. 2 diagrammatically represents an installation according to a second embodiment similar to that of FIG. 1, but in which the organic fluid of the ORC machine is preheated in a single step, after the upstream addition of the two steam and flue gas sources;

(4) FIG. 3 diagrammatically represents an installation according to a third embodiment similar to that of FIG. 2 in which an additional intermediate circuit is added on the steam side; and

(5) FIG. 4 schematically represents an installation according to a fourth embodiment in which organic fluids collecting the calories from the beams and combustion flue gases are mixed upstream of the ORC machine and the energy is recovered at the same time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) These forms of embodiment being in no way exhaustive, it will be possible in particular to make variants of the invention comprising only a selection of the characteristics described hereinafter, 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.

(7) In FIG. 1, we can see schematically represented an installation according to a first example of embodiment of the invention. To simplify the description, only the equipment necessary for understanding the invention is shown in this figure. Essential equipment for the operation of the installation, such as pumps, valves, food cover, expansion tank, etc., is not shown in this figure and following, nor contained in this description, the skilled person should know how to define them, size them and optimally implement them on the installation.

(8) Products 1 are continuously heated in a beam reheating furnace 2. The movement and maintenance of the products in the furnace are provided by fixed beams and walking beams. The beams comprise skids 3a and posts 3b in which circulates a cooling fluid. Burners 5 heat the furnace 2 and the products 1. Flue gases from the burners 5 are discharged from the furnace by a flue pipe 6.

(9) At the inlet of the beams, the cooling fluid is, for example, superheated water at a temperature of 215° C. and a pressure of 21 bar absolute. During its flow in the beams, the superheated water is partially converted into saturated steam 4. At the outlet of the beams, the cooling fluid is composed of a mixture of superheated water and saturated steam 4. A balloon 7 enables the separation of liquid water and saturated steam 4.

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

(11) The installation comprises an intermediate recirculation loop 16 disposed between the steam circuit and the circuit 13 of the ORC machine. An intermediate heat transfer fluid 17 circulates in the intermediate recirculation loop 16, preferably organic, kept in liquid state.

(12) 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 gives calories to the intermediate coolant fluid 17 by means of the exchanger 18 in which it condenses, then the heat-transfer medium 17 in turn gives up calories to the organic fluid 21 of the ORC machine by means of the exchanger 8.

(13) The addition of the intermediate recirculation loop 16 can enhance the safety of the installation and use thermal fluids of different properties. Thus, the intermediate heat transfer fluid 17 may have a greater compatibility with the vapour than the organic fluid 21 of the ORC thus limiting the risk of fire or explosion.

(14) A heat exchanger 9 may be disposed in the chimney connector 6, possibly downstream, in the direction of the flue gas flow, with respect to other pieces of energy recovery equipment on the flue gases, for example a preheating recuperator of the combustion air of the burners.

(15) The heat exchanger 9 can be supplied with a heat transfer fluid 10, preferably organic in liquid state, circulating in a recirculation loop 11. The heat transfer fluid 10 can be of the same nature as the intermediate heat transfer fluid 17, on the steam side but it can also be of a different nature. The flue gases transfer part of their heat to the heat transfer fluid 10 in the heat exchanger 9. A second heat exchanger 12 is disposed on the recirculation loop 11. The second exchanger 12 enables the transfer of calories captured by the heat transfer fluid 10 to the organic fluid 21 of the ORC machine.

(16) The organic fluid circulates in the ORC machine in the recirculation loop 13 including, preferably successively in the direction of the fluid flow, the heat exchangers 8 and 12, an expansion turbine 14, an organic fluid 21 condensation exchanger 15 of the ORC machine and a booster pump 24. The heat energy transferred to the organic fluid 21 of the ORC machine in the heat exchangers 8 and 12 enables the latter to be brought into the vapour phase. The expansion of the steam rotates the expansion turbine 14 which is coupled to an alternator that generates electricity. At the outlet of the expansion turbine 14, the exchanger 15 makes it possible to condense the organic fluid 21, 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 flowing in a circuit 22.

(17) A set of registers 23 makes it possible to bypass the heat exchanger 9, by all or part of the flue gases.

(18) 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. According to the invention, the installation thus makes it possible to also upgrade one or more other heat sources for increased overall efficiency of the industrial site on which it is installed.

(19) FIG. 2 schematically represents an alternative embodiment of the invention in which the flue gas calories are supplied to the intermediate fluid 17 and not directly to the fluid 21 of the ORC. Likewise, the complementary supply of calories of the fluid 26 is made to the intermediate fluid 17 and not directly to the fluid 21 of the ORC. This configuration allows a simplified control of the ORC, and increases its safety, with a single heat exchanger in which all the heat gains to the fluid 21 and its vaporization is achieved.

(20) FIG. 3 schematically represents another embodiment of the invention in which an intermediate loop 30 is added on the vapour side in which a heat transfer fluid 31 circulates. The steam 4 gives calories to the heat transfer fluid 31 by condensing in the exchanger 18, then the heat transfer fluid 31 in turn yields these calories to the heat transfer fluid 17 by means of a heat exchanger 32. This configuration makes it possible to reinforce the safety of the installation, and the flexibility of its control, the technology of the heat exchangers 8, 18, 31 and the nature of the heat transfer fluids 31, 17, 21 being chosen so as to have tested technologies on the heat exchangers and to limit the risk of fire or explosion in case of contact between the fluids in case the fluids exchangers get burst.

(21) FIG. 4 diagrammatically represents another variant embodiment of the invention in which a mixture is produced between 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 made by means of three-way valves 20, then flows to a heat exchanger 19 in which it transfers calories to the organic fluid 21 of the ORC machine. At the outlet of 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.

(22) The amount of energy available on the flue gases and the beam coolants is generally around the same magnitude, for example 10 MWth on the flue gases and on the beams for a furnace with a capacity of 450 t/h.

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

(24) On the heat exchanger 9, the flue gas temperature 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 heat transfer fluid 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 a temperature of 225° C. to 215° C. and a flow rate of from 70 kg/s to 50 kg/s respectively according to the two cases of operation described above. For such temperatures, the organic fluid 21 of the most suitable ORC machine is pentane, since it is carried upstream of the expansion turbine 14 at a temperature for example of between 135° C. and 160° C., respectively, according to two cases of operation, so that the net power delivered by the ORC machine be maximum, of 1.2 MW.sub.e and 0.9 MW.sub.e, respectively.

(25) 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 may be disposed in the chimney connector of each furnace or of a single furnace. Likewise, calories can be recovered from steam coming from the beams of both furnaces or from one.

(26) As we have just seen, the invention enables an efficient energy recovery on the heat losses of the furnace by the flue gases and the beams, thanks to a dimensioning of the ORC machine that is well adapted to the operating regime of the furnace and its operating stability resulting from the combination of two heat sources.

(27) Of course, the invention is not limited to the examples which have just been described and many adjustments can be made to these examples without departing from the scope of the invention. In addition, the various features, shapes, variants and embodiments of the invention may be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other.