WO2013113714A1

WO2013113714A1 - Installation and method for recovering energy using supercritical co2

Info

Publication number: WO2013113714A1
Application number: PCT/EP2013/051716
Authority: WO
Inventors: Guy Monfort; Pierre BERGIERS
Original assignee: Centre de Recherches Métallurgiques asbl - Centrum voor Research in de Metallurgie vzw
Priority date: 2012-01-31
Filing date: 2013-01-30
Publication date: 2013-08-08
Also published as: BE1020489A3

Abstract

The present invention relates to an installation for recovering energy lost in a high-speed factory line producing parts (3) carried at a high temperature which then need to be treated at a low temperature, comprising pressurised and sealed compartments or boxes (4, 4', 4'' etc.) wherein said parts (3) carried at high temperature are deposited and cooled to said low temperature, each pressurised and sealed compartment (4, 4', 4'' etc.) being supplied by a closed cooling circuit (1) containing a supercritical fluid, and a heat recovery system (2).

Description

INSTALLATION AND METHOD OF ENERGY RECOVERY USING SUPERCRITICAL CQ ₂ Object of the invention

The present invention relates to a new method for recovering lost energy in industrial facilities operating at high speed and preferably continuously, and in particular in the steel or metallurgical industry.

The invention also relates to an installation for implementing the method.

State of the art and position of the problem

In heavy industry, and particularly in the steel industry, there are many sources of heat whose energy is lost. The main reasons are essentially:

- the difficulty of transforming this energy in a usable way. This is particularly the case for relatively low temperature sources and large or distributed sources;

- the time lost to recover this energy. This would hurt productivity. This is particularly the case in mass production where thermal exchanges with hot products in order to recover energy would introduce a too long delay in the rate of production;

- the high additional cost of energy recovery, often linked to the low yields that can be drawn from it. At present, in the steel industry, when a coil (or "coil") is hot rolled (coiled at 600-650 ° C), it must be cooled to about 100 ° C before to be cold rolled. These reels are stored on park, more rarely in pools, to cool them. The heat thus dissipated is lost in all cases.

However, the amount of energy that is thus spent is enormous. Thus, for a plant producing 5 x 10 ⁶ tonnes of steel a year, more than 300 x 10 ⁶ kWh / year could be recovered. By counting on a return of 16 ~ 6 for the transformation in electricity, that corresponds to 10 wind turbines of 2 MW (with a yield of use of 25%), which would allow to feed 40 000 people in electricity.

Aims of the invention

The present invention aims to overcome the disadvantages of the state of the art.

In particular, the invention aims to provide a means of energy recovery from hot products, preferably manufactured continuously or at least at high speed, without unduly increasing the production time and allowing a efficient recovery.

The invention is more particularly to provide a method for recovering heat from hot coils and slabs in the steel industry.

Main characteristic elements of the invention

[0009] A first aspect of the present invention relates to an installation for the recovery of energy lost in a high-speed industrial line. producing high-temperature parts to be subsequently treated at low temperature, comprising pressurized and sealed compartments, wherein said high temperature parts are deposited and cooled to said low temperature, each pressurized and sealed compartment being fed with a closed cooling circuit containing a supercritical fluid. The installation also includes a heat recovery system. The supercritical fluid is advantageously supercritical CO 2. The parts to be cooled are preferably coils or slabs produced in the metallurgical or hot-iron industry.

According to preferred embodiments of the invention, the installation further comprises one or a suitable combination of the following characteristics:

- the closed cooling circuit contains the heat recovery system;

the installation comprises a circuit in which the heat recovery system, isolated from the cooling circuit, is located via a heat exchanger transferring the energy recovered in the cooling circuit to the heat recovery system;

the heat recovery system is associated with means for generating electricity;

each compartment comprises input means for the cold supercritical fluid, means for distributing the fluid at the level of the part or parts to be cooled, a watertight box proper that can contain the part or parts to be cooled, means for recovering the fluid; and other gases and means for outputting the hot supercritical fluid and other gases from the compartment; - The waterproof case is removable or has a lid, to allow the insertion and removal of the part or parts to be cooled;

each compartment is connected to a plurality of pipes in parallel each containing the supercritical fluid in a certain temperature range, the temperatures being increasing from one pipe to the other, from the input fluid temperature to the inlet at its temperature at the outlet, a system of valves for modifying the connections between each compartment and the pipes, so that the or parts to be cooled pass from one temperature range to another gradually, in the decreasing direction from an initial temperature to a final temperature, lower than the initial temperature;

each compartment is designed so that air introduced at the same time as a room to be cooled in a compartment is driven under the pressure of the supercritical fluid into the pipes and discharged through an outlet.

A second aspect of the present invention relates to a method for recovering energy lost in a high-speed industrial line producing high temperature parts to be treated at low temperature, using the installation according to one any of the preceding claims, characterized in that said parts brought to a temperature above 600 ° C are cooled in the case of coils, respectively 1200 ° C in the case of slabs, to a temperature below 150 ° C , respectively 800 ° C, for a period of less than 30 seconds, respectively 6 minutes, by placing said parts in the aforementioned compartments. Advantageously, the supercritical CO ₂ is mixed with hydrogen, the aforementioned energy recovery being combined with stripping and cleaning of said parts without acid or with a reduced amount of acid.

Brief description of the figures

[0013] FIG. 1 schematically represents a first circuit for cooling hot-rolled steel strip coils according to the present invention, intended to be associated with a second circuit, for heat recovery and electricity production. according to the state of the art, in a complete heat recovery installation of these coils in the production process.

[0014] Figure 2 schematically shows two possible embodiments for the second circuit mentioned above.

Figure 3 shows the detail of a compartment used for cooling coils according to the present invention.

Description of preferred embodiments of the invention

The principle of the invention is based on the use of carbon dioxide (CO ₂ ) in supercritical form. It is known that the CO ₂ in the supercritical state is in an intermediate state between the liquid and the gas, has a viscosity close to that of the gas, 10 times lower than that of the liquid, and especially a very high heat exchange coefficient. high (between 1 and 10 kW / m ² .K), which guarantees rapid cooling. On the other hand, unlike in the case of liquids, when the supercritical CO ₂ is brought into contact with a warmer body, it does not form a cauliflower layer which reduce the exchange coefficient. Another advantage of CO ₂ is that supercritical conditions are obtained for relatively low temperatures and pressures (31.1 ° C, 73.8 bar). It is therefore quite easy to reach the critical pressure and the low temperature guarantees a better performance in heat exchange. Finally, the supercritical CO ₂ is not corrosive and has properties of interest in use as a solvent. It is therefore possible to use it to combine surface cleaning with heat recovery.

Heat recovery according to a particular embodiment of the invention is illustrated below by the example of the cooling of hot coils produced in the steel industry (Figure 1).

The method according to the invention consists in placing the coils (or "coils") resulting from the winding of steel strips at the outlet of the hot rolling mill in a chamber (or compartment) under pressure into which is injected CO ₂ . By judiciously choosing the quantity injected, the increase in temperature will transform the gas into supercritical fluid, whose increased diffusivity should enable it to infiltrate between the turns of the coil and to cool it at high speed. An approximate calculation shows that a coil of 24 tons (strip thickness: 3 mm) initially raised to 640 ° C could see its temperature drop to less than 150 ° C in less than 30 seconds. Knowing that in general, a coil is produced every 6 minutes, it is possible to support the rate of production by using a countercurrent cooling circuit of the production, between several enclosures or compartments under pressure which make it possible to treat several coils more or less simultaneously. The increase in pressure and The temperature can then be exploited, by using an exchanger, to generate electricity or to provide useful energy in another form.

Figure 1 shows an example of a cooling circuit according to the invention. It is a continuous circuit containing supercritical CO ₂ (P> 74 bar and T> 31 ° C) which makes it possible to feed different compartments or caissons 4, 4 ', 4 ", etc. containing hot coils 3 for example of increasing temperature, from the first to the last compartment, from left to right in the figure, that is to say, cooled "against the current" of the arrival of cold fluid 7. A " Countercurrent "means that the supercritical fluid gradually warms up by coming into contact with increasingly hot coils. As shown in FIG. 1, each compartment 4 can advantageously be connected by valves to a series of pipes or pipes 5 themselves connectable in parallel, according to all possible combinations. Each of these pipes 5 corresponds to a certain range of CO ₂ temperature, e.g. ranging from 50 to 550 ° C, the temperature increasing in steps ΔΤ = 500 / Nstep, where Nstep is the number of pipes (see Figure 1). As a given coil cools, the valve control system (not shown) changes the connections to connect the proper piping system to each coil in the line. Since the coils can not be moved easily, once enclosed in a box, the above-mentioned pipe and valve system is used flexibly so that the fluid has a temperature difference with the lowest coil possible, which will lead to the best thermal efficiency. So that the fluid can have a constant flow, it is necessary to have more bobbins than there are intermediate steps and some boxes are paralleled. Each driving temperature range can be considered a step.

This is valid for all the boxes in the system, except for the incoming box, which contains air and the outgoing box, which contains the supercritical CO2 at "low temperature". In fact, the well 4, which contains the coldest coil and the supercritical CO2 at high pressure, is advantageously connected by a set of pipes 5, in parallel with the caisson 4 ^<n) containing the hottest coil (c '). that is to say that has just been put in a compartment) and inevitably air. The supercritical CO2 pressure is then used to expel the air that will be evacuated via an outlet 6. This operation makes it possible to purge the CO2, that is to say to obtain a box containing a hot coil and CO2, without air inlet into the system. It also reduces the consumption of compressed CO2 (decrease in the amount of material consumed, as well as compression energy).

According to the invention, the heat recovered by the supercritical CO2 circuit 1 is then transferred to a heat recovery circuit 2, in particular for the production of electricity, as represented for example in FIG. This may be for example a gas turbine system operating according to the supercritical cycle of Rankine or Brayton.

The supercritical CO2 at the outlet 8 after the last compartment 4 of the circuit 1 is at high temperature. According to a first embodiment, this hot supercritical fluid can be used to produce electricity by passing directly through a turbine 9 and then a cooler 10 (Figure 2a). According to a second embodiment, this can also be done in passing through a heat exchanger 11 which will transfer the heat to a conventional system turbine 9 - condenser 12 - steam generator, the heat exchanger 11 advantageously acting as a steam generator (Figure 2b). The supercritical fluid which has given up its calories then returns in a closed circuit to the cooling compartments 4 of the supercritical CO ₂ circuit 1 via the inlet 7.

An example of compartment 4 is shown in FIG. 3. Each compartment 4 is composed of a "cold" supercritical CO ₂ inlet 41 (at temperature T _n -1), of a gas distribution system 42 on the coil, preferably in a ring, so that the CO ₂ can diffuse into the coil by its wafer, between the strips, the box itself containing the coil 43, a gas recovery system 44 and finally an outlet supercritical CO ₂ "hot" 45 (at temperature T _n such that T _n > T _n _i). For reasons of mechanical strength, pipes in which the supercritical CO ₂ transits must be fixed, so the entry and exit will not be mobile. The box 43 of the compartment is therefore advantageously mobile in order to effect the coil changes. It can also be provided with a pivoting lid or not, for inserting and removing the coil, with a sealed closure.

Still in the steel industry, the method can also find application to the cooling slabs whose higher temperature than that of the coils would allow even higher yield. Calculations have shown that slab cooling of 56 tons from 1200 to 800 ° C can be achieved in 6 minutes, with energy recovery of 10,000 MJ. The disadvantage is that the thickness of the product increases the cooling time. However, speeds remain compatible with the production, especially in the case where the half-products are intended for export and remain then several days on park.

[0025] Finally, since the supercritical CO ₂ is miscible with hydrogen, a combination of the two fluids can make it possible to associate the energy recovery with stripping and cleaning of the products, which makes it possible to eliminate, or In any case, the acids used for this purpose, as well as the effluent treatment problems associated with them, must be greatly reduced.

It appears, following the examination of existing patents, that the supercritical CO ₂ has never been proposed for energy recovery. On the other hand, there are applications where it is used as heat transfer fluid in electricity production circuits and applications have been envisaged (but probably not realized) for the cooling of engines or for air conditioning of cars.

For safety reasons, it may be envisaged to place the pressurized CO ₂ enclosures in the basement of industrial facilities. In the event of a leak, the CO ₂ being heavier than air, it would then remain confined long enough to take the necessary measures.

Reference symbols

1. supercritical CO ₂ closed circuit

2. heat recovery circuit

3. coil

, 4 ', 4' ', ... coil cooler (several compartments)

5. cooling pipes in parallel

6. air evacuation

7. supercritical fluid inlet in the cooler

8. supercritical fluid outlet from the cooler

9. turbine

10. cooler

11. exchanger

12. condenser

41. arrival of cold supercritical fluid in the compartment

42. gas distribution system

43. box containing the coil to be cooled

44. gas recovery system

45. Hot supercritical fluid outlet

Claims

1. Installation for the recovery of energy lost in a high-speed industrial line producing parts (3) carried at high temperature which must then be treated at low temperature, comprising pressurized compartments or caissons (4, 4 ', 4 '', ...), where are deposited said parts (3) carried at high temperature and cooled to said low temperature, each compartment under pressure and sealed (4, 4 ', 4' ', ...) being fed by a closed cooling circuit (1) containing a supercritical fluid, the installation also comprising a heat recovery system (2).

2. Installation according to claim 1, characterized in that the closed cooling circuit

(1) contains the heat recovery system (2).

3. Installation according to claim 1, characterized in that it comprises a circuit which is the heat recovery system (2), isolated from the cooling circuit (1), via a heat exchanger (11) ensuring the transfer energy recovered in the cooling circuit (1) to the heat recovery system (2).

4. Installation according to claim 1, characterized in that the heat recovery system (2) is associated with means for generating electricity.

5. Installation according to claim 1, characterized in that each compartment (4, 4 ', 4'', ...) comprises input means (41) of the cold supercritical fluid, fluid distribution means (42). ) at the level of the part (s) to be cooled (3), a waterproof box proper (43) that can contain the part (s) to be cooled (3), fluid recovery means and other gases (44) and output means (45) of the hot supercritical fluid and other compartment gases (4,4 ', 4'', ...).

6. Installation according to claim 5, characterized in that the waterproof case (43) is removable or has a cover, to allow insertion and removal of the or parts (3) to be cooled.

7. Installation according to claim 1, characterized in that each compartment (4, 4 ', 4' ', ...) is connected to a plurality of parallel pipes (5) each containing the supercritical fluid in a certain range of temperatures, the temperatures being increasing from one pipe to the other, from the input fluid temperature of the inlet (7) to its temperature at the outlet (8), a valve system for changing the connections between each compartment (4, 4 ', 4' ', ...) and the pipes (5), in such a way that the piece or pieces to be cooled pass from one temperature range to the other gradually, in the direction decreasing, from an initial temperature to a final temperature, lower than the initial temperature.

8. Installation according to claim 7, characterized in that each compartment (4, 4 ', 4' ', ...) is designed so that air introduced at the same time as a room to cool (3) in a compartment (4, 4 ', 4' ', ...) is removed under pressure from the supercritical fluid in the pipes and discharged through an outlet (6).

9. A method for recovering energy lost in a high-speed industrial line producing high temperature parts (3) to be further processed at low temperature using the plant according to any one of the preceding claims, characterized in that said parts are cooled (3) brought to a temperature above 600 ° C, respectively 1200 ° C, up to a temperature below 150 ° C, respectively 800 ° C, for a period of less than 30 seconds, respectively 6 minutes, by placing said parts (3) in the aforementioned compartments (4).

10. The method of claim 9, characterized in that the supercritical fluid is supercritical CO ₂ .

11. The method of claim 9, characterized in that said parts to be cooled (3) are coils, respectively slabs, produced in the metallurgical industry or steel hot.

12. The method of claim 9, characterized in that the supercritical CO ₂ is mixed with hydrogen, the aforementioned energy recovery being combined with etching and cleaning of said parts (3) without acid or with a reduced amount. acid.