FR2973866A1 - Heat treatment installation for drying of paper in paper production facility, has steam generation unit including heat exchanger comprising primary circuit supplied with hot gases, and secondary circuit crossed by fluid to be vaporized - Google Patents

Abstract

The installation has an infrared radiation system comprising a set of radiating elements (2) that is associated with a set of gas burners. A set of gas extraction units (3, 4, 16) is arranged for extraction of hot gases produced by the infrared radiation system. A steam generation unit includes a heat exchanger (5) i.e. steam generator or tubular heat exchanger with smooth walls, that is utilized for recovery of heat contained in the hot gases. The exchanger comprises a primary circuit supplied with hot gases. A secondary circuit of the exchanger is crossed by a fluid to be vaporized.

Description

The invention relates to a drying installation and will find a particular, non-limiting application for drying a web of material, for example paper in a paper production facility. The field of the invention is that of drying installations comprising infrared radiation devices comprising hot surfaces, such as ceramic plates, refractory metal surfaces, associated with burners, usually called infrared radiant burners. Platelets are called "radiant elements" in the rest of the application. In these devices, the combustion of a gas or oil makes it possible to wear at high temperature the radiant elements which then emit infrared radiation. From an energy point of view, 40% to 50% of the energy of combustion is transformed into infrared radiation, the rest of the energy being mainly in the form of hot combustion gases. Such devices are described in the documents FR-2.587.787, WO-0042356, EP-026.063 and FR-2.683.022 and are used to dry strip-like materials, at low temperature, such as paper, cloth and paper. steel for example. These infrared devices make it possible to dry or to perform a heat treatment without contact with the strip of material.

In thermal treatment plants, the infrared radiant elements are arranged in a set, one next to the other, in a fixed manner, to form a radiant surface placed parallel to the product to be treated. This set of radiant elements is usually called radiant vault. The strip product scrolls continuously along and across this radiant surface. The hot gases from the combustion of the fuel are diluted with the ambient air, then are collected by means of an extraction system comprising suction hoods and then discharged outside the buildings. Such installations are described in documents EP-1,721,109, EP-0,489,720, FR-2,771,161 and FR-2,758,575.

The efficiency of the heat transfer is less than 50% and most often between 25% and 40% depending on the operating conditions of the dried product. Much of the energy supplied to the facility is extracted and available as large volumes of hot gas, the temperature of which may exceed 300 ° C. This energy is released into the atmosphere and is lost.

One of the applications of infrared radiation devices is paper drying, without contact. Conventionally, the majority of the drying of the paper web is then carried out on heating cylinders, rotary, heated in saturated steam by means of a condensate / steam system of the installation. Such drying plants, with heating cylinders, are described in EP-0.530.164 and EP-1.918.452. The object of the present invention is to provide a drying installation comprising an infrared radiation system having at least one radiant element associated with a burner, improved energy efficiency compared to drying facilities of the state of the art. Other aims and advantages will appear during the description which is given for information only and which is not intended to limit it.

Also the invention relates to a drying installation, comprising: - a system of infrared radiation having at least one set of radiant elements, said radiant elements of the assembly being associated with one or more burners, adapted to bring these radiant elements to high temperature - Gas extraction means arranged for extracting hot gases produced by the infrared radiation system. According to the invention, said installation comprises steam generating means comprising at least one heat exchanger on the circuit of said means. extraction of gas in order to recover the heat contained in the hot gases, the primary of said at least one heat exchanger being supplied with hot gases collected by said extraction means, the secondary of said exchanger being traversed by a fluid to be vaporized. According to optional features taken alone or in combination: said steam generation means comprise a separator tank containing a condensate and steam, at least one pump and a pipe allowing the flow of condensate from said separator tank to at the secondary of said at least one heat exchanger, at least one return line for returning the superheated condensate to the separator tank, said separator tank being equipped with a steam outlet; said steam generating means comprises means for maintaining said controlled pressure separator flask comprising a pressure probe and an automatic valve on said steam outlet; said steam generating means comprise flow control means in said at least one heat exchanger, having at least one sensor and an automatic valve placed on said at least one return line; the steam generating means comprise means for maintaining the condensate level in the separator tank, comprising a measuring device for determining the condensate level in said separator tank and a booster device comprising a pump and an automatic valve, able to supply said separator balloon in condensate. According to one embodiment, said heat exchanger is a steam generator. According to one embodiment, said at least one heat exchanger 30 is chosen from: - smooth-walled tubular exchanger, finned tubular exchanger, - plate exchanger. According to one embodiment of said installation: - said infrared radiation system has a plurality of sets of radiant elements, - said gas extraction means comprise, for each set of radiant elements, a suction hood arranged in the vicinity of said set of radiant elements, for the suction of said hot gases produced by the assembly.

According to this last embodiment, the steam generation means comprise a heat exchanger, common to said plurality of radiant elements, each extraction hood comprising, optionally, a flow cutter and means for controlling said flow control member. flow cut-off to said set of corresponding radiant elements, or alternatively, the steam generating means comprise, for each set of radiant elements, a heat exchanger placed in the corresponding hood of said extraction means in order to recover the heat contained in the hot gases of said set of corresponding radiant elements.

According to one embodiment, said installation is a drying installation of a strip of material, having means for scrolling said strip of material under the action of infrared radiation of said infrared radiation system. According to one embodiment, the installation comprises heating cylinders, rotary, on which is intended to be plated said strip of material, and a condensate-steam system for supplying said heating rolls with heating steam, said installation having means for injecting the vapor produced by said steam generating means into said condensate-vapor system of said heating rolls.

The invention will be better understood on reading the following description accompanied by the appended drawings, in which: FIG. 1 is a schematic view of an installation according to the invention, according to a first embodiment; - Figure 2 is a schematic view of an installation according to the invention, according to a second embodiment; FIG. 3 is a diagrammatic view of a detail of a suction hood of the extraction means of the installation of FIG. 1; - Figure 4 is a schematic view of an installation according to the invention, according to a third embodiment; FIG. 5 is a diagrammatic front view of a set of radiant elements of an installation of FIGS. 1, 2 or 4. Also, the invention relates to a drying installation, comprising: a system of infrared radiation exhibiting at least one set of radiant elements, said radiant elements of the assembly being associated with one or more burners, capable of bringing said radiant elements 200 up to a high temperature; means 3, 4, 16 for extracting gases arranged for extraction of the hot gases produced by the infrared radiation system.

The burner or burners associated with said set of radiant elements are preferably gas burners and allow each radiant element to be heated at high temperature so that the latter emits infrared radiation. By high temperature is meant a temperature of between 500 ° C and 1,500 ° C. The radiant elements 200 may each comprise a ceramic wafer or a wafer in a refractory metal. The radiant elements 200 of the same set 2 are arranged side by side, preferably in the same plane, to form a radiant surface, as illustrated in FIG. 5. According to one embodiment, each radiant element 200 of the assembly 2 is associated with a burner. According to another embodiment, a burner, common to the radiant elements 200 of the assembly makes it possible to bring all the radiant elements 200 of the assembly 2 to a high temperature. Said extraction means have, for said set of radiant elements, 2, a fume hood 3, the gases collected by the fume hood being conveyed along a pipe 16 by means of an extractor 4 of said extraction means. According to the invention, said installation comprises steam generating means comprising at least one heat exchanger 5; 23 on the circuit of said gas extraction means for recovering the heat contained in the hot gases, the primary of said at least one heat exchanger 5; 23 being supplied with hot gases collected by said extraction means. The secondary of the at least one exchanger 5; 23 is crossed by the fluid to be vaporized. According to an embodiment of the invention illustrated in the example of FIGS. 1 or 2, said steam generating means comprise a separator tank 8 containing a condensate and steam, at least one line 6 and a pump 7 allowing the circulation of the condensate from said separator tank 8 to the secondary of the at least one heat exchanger 5, at least one return line 17 allowing the return of the superheated condensate to the separator tank 8, said separator tank being equipped with a steam outlet. According to this embodiment, the steam is generated by superheating a condensate and expanding this superheated condensate in said separator tank 8.

Advantageously, said steam generating means comprise means for maintaining said separator flask 8 under controlled pressure comprising a pressure sensor 11 and an automatic valve 12 on said steam outlet. When the pressure measured by the pressure sensor 11 in the separator tank 8 exceeds a predetermined pressure, the automatic valve 12 is controlled at the opening, releasing steam by said steam outlet. When the measured pressure becomes lower than said determined pressure, said automatic valve 12 is controlled on closing. According to one embodiment, said steam generating means comprise flow control means in said at least one heat exchanger 5, having at least one sensor 10 and an automatic valve 9 placed on said at least one return line 17. The sensor 10 is for example a temperature sensor, a pressure sensor or a flow sensor. Said automatic valve is slaved according to the signal of the sensor 10.

According to one embodiment, the steam generating means comprise condensate level holding means in the separator tank 8, comprising a measuring device 18 for the determination of condensate level in said separator tank 8 and a device booster comprising a pump 14 and an automatic valve 13, able to supply said separator tank 8 in condensate. The means for maintaining the condensate level in the separator tank 8 serves to maintain the condensate level at a determined value. The condensate level drop is explained by the steam escaping from the separator tank 8 by said steam outlet. When the measuring device 18 detects a drop in condensate level, said means make it possible to compensate for the loss of mass by opening said automatic valve 13 and by actuating the pump 14 of the booster device. When the level of the condensates detected by the measuring device 18 returns to normal, the pump 14 is stopped and the automatic valve 13 is closed. According to one embodiment of the invention illustrated in FIG. 1 or 2: said infrared radiation system has a plurality of sets of radiant elements 2, said gas extraction means comprise, for each set of radiant elements 2, a suction hood 3 arranged near said set of radiant elements 2 for the suction of said hot gases produced by the set of radiant elements 2. According to the embodiment of FIG. steam generating apparatus comprises, for each set of radiant elements 2, a heat exchanger 5 placed in the corresponding suction hood 3 of said extraction means in order to recover the heat contained in the hot gases of said set of radiant elements 2 corresponding. Preferably, each heat exchanger 5 is associated with an automatic valve 9 and with a sensor 10 in order to allow independent regulation of the superheated condensate flow rate, in particular as a function of the temperature reached, measured by said sensor, downstream of said heat exchanger 5. Alternatively, according to the embodiment of FIG. 2, the steam generating means may comprise a heat exchanger 5, common to said plurality of sets of radiant elements 2. Optionally, each suction hood 3 comprises an element 25 and, if appropriate, means for controlling said flow-off device 25 against said set of corresponding radiant elements 2. In this embodiment, said flow cutoff member 25 works all or nothing. This member 25 is controlled to close when said set of radiant elements 2 of the corresponding hood is stopped and opening when said set of radiant elements 2 is in operation. This arrangement makes it possible to avoid dilution of the hot gases in said extraction means if one or some of the sets of radiant elements 2 are not in operation. According to an embodiment illustrated in Figure 4, said at least one heat exchanger 23 is a steam generator whose secondary is supplied with condensate. This heat exchanger 23 operates in boiling. A level of condensate in said exchanger 23 is measured by a sensor 22 and continuously maintained, for example by means of a pump 20 and an automatic valve 21. The condensates can come from a separator tank 15. Said exchanger 23 operating in boiling, the steam produced is controlled by means of a pressure sensor 24 and an automatic valve 26.

According to a preferred embodiment, said installation is a drying installation of a strip of material 1, having means for scrolling said strip of material under the action of infrared radiation of said infrared radiation system. When the infrared radiation system is placed above the material strip, and when said heat exchangers are placed in the suction hoods 3, as illustrated in FIG. 1, there is a risk of condensation of the hot gases. contacting the walls of the heat exchangers 5. In order to prevent condensation droplets from falling on the strip of material 1, baffles 19 may be provided, in line with the heat exchanger 5, between said heat exchanger 5 and the mouth of the suction hood 3. These baffles 19, illustrated in Figure 3, have the function of collecting the condensation droplets and to evacuate them. According to one embodiment, said installation comprises heating cylinders (not illustrated), rotating, on which is intended to be plated said strip of material, and a condensate-steam system for supplying said heating rolls with heating steam. Conventionally, the heating cylinders, rotating, are located downstream of the infrared radiation system in the direction of travel of the material strip. Advantageously, said installation may have means for injecting the steam produced by said steam generating means into said condensate-vapor system of said heating cylinders. Said at least one heat exchanger 5; 23 is an exchanger comprising said primary and said secondary preventing cross contaminations between the fluid passing through the primary and the fluid passing through the secondary. Said heat exchanger 5; 23 may be chosen from: - a smooth-walled tubular exchanger, - a finned tubular exchanger, - a plate exchanger. We now describe in detail the example of Figure 1. In this example of Figure 1, heat exchangers 5 are disposed within each hood 3 suction hot gases. These heat exchangers 5 are supplied with condensates by means of a pump 7 and 10 ducts 6. These condensates are superheated in the heat exchangers 5, then the superheated condensates are returned by individual return lines 17 to the storage tank. Separator 8. Each return line 17 is equipped with a sensor 10 (ie temperature, pressure or flow) and an automatic valve 9 for adjusting the flow rate of the condensates flowing in each heat exchanger 5. The separator balloon 8 is equipped with a pressure sensor 11 and an automatic valve 12 controlling the pressure level in the separator balloon. A level measuring device 18 in the separator tank 8 makes it possible to control an automatic valve 13 and a pump 14 20 and to continuously supply a quantity of condensate that compensates for the mass of vapor produced, escaping from the separator tank 8 The return temperature of the condensates can be measured using the sensor 10 and kept continuously above the temperature of the saturating vapor corresponding to the operating pressure in the separator tank 8.

In the version illustrated according to the example of FIG. 2, a single heat exchanger 5 is placed on the common exhaust pipe 16 of said hot gas extraction means which comprise a plurality of suction hoods 3. This heat exchanger 5 is preferably located upstream of the extractor 4, in the direction of flow of the hot gases. In order to optimize the thermal recovery, each extraction hood 3 is equipped with a disconnecting member 25, such as for example a valve operating in all or nothing, slaved to the operation of said radiant element 2 corresponding to said hood. 3. Figure 3 is a detailed view of a suction hood of the installation as shown in Figure 1. Advantageously, each suction hood has baffles 19 for the collection of condensed water on said heat exchanger 5. The collected water may be rejected outside the edges of the material web 1. Naturally, other embodiments could have been envisaged for the skilled person without departing from the scope of the invention defined by the claims below.

Claims (13)

REVENDICATIONS1. Heat treatment installation, in particular for drying, comprising: an infrared radiation system having at least one set of radiant elements (2), said radiant elements (200) of the assembly being associated with one or more burners, capable of carrying at high temperature said radiant elements (200), gas extraction means (3, 4, 16) arranged for extracting the hot gases produced by the infrared radiation system, characterized in that it comprises steam generating means comprising at least one heat exchanger (5; 23) on the circuit of said gas extraction means (3, 4, 16) for recovering the heat contained in the hot gases, said at least one heat exchanger ( 5; 23) having a primary and a secondary, the primary of said at least one heat exchanger (5 23) being supplied with hot gases, the secondary of said exchanger (5; 23) being traversed by a fluid to be vaporized. 2. Installation according to claim 1, wherein said steam generating means comprise a separator tank (8) containing a condensate and steam, at least one pump (7) and a pipe (6) allowing the circulation of the condensate. condensate from said separator tank (8) to the secondary of said at least one heat exchanger (5), at least one return line (17) for returning the superheated condensate to the separator tank (8), said balloon separator being equipped with a steam outlet. The plant of claim 2, wherein said steam generating means comprises means for maintaining said separator tank (8) under controlled pressure comprising a pressure probe (11) and an automatic valve (12) on said steam outlet. . 30 4. Installation according to claim 2 or 3, wherein said steam generating means comprise flow control means in said at least one heat exchanger (5), having at least one sensor (10) and an automatic valve (9). placed on said at least one return line (17). 5. Installation according to one of claims 2 to 4, wherein the steam generating means comprise means for maintaining condensate level in the separator tank (8), comprising a measuring device (18) for determining condensate level in said separator tank (8) and a booster device comprising a pump (14) and an automatic valve (14), able to supply said separator tank (8) with condensate. 6. Installation according to claim 1, wherein said heat exchanger (23) is a steam generator. 7. Installation according to one of claims 1 to 6, wherein said at least one heat exchanger is selected from: - smooth-walled tubular exchanger, finned tubular exchanger, - plate exchanger. 8. Installation according to one of claims 1 to 7, wherein: - said infrared radiation system has a plurality of sets of radiant elements (2), - said gas extraction means comprise, for each set of radiant elements, a suction hood (3) arranged close to said set of radiant elements (2), for the suction of said hot gases produced by said set of corresponding radiant elements (2), and in which the means steam generating means comprise a heat exchanger (5), common to said plurality of sets of radiant elements (2). 9. Installation according to claim 8, wherein each suction hood (3) comprises a flow cutter member (25) and means for controlling said flow cutter member (25) to said set of radiant elements (2). corresponding. 10. Installation according to one of claims 1 to 7, wherein: - said infrared radiation system has a plurality of sets of radiant elements (2), - said gas extraction means comprise, for each set of radiant elements (2), a suction hood (3) arranged in the vicinity of said set of radiant elements for suction of said hot gases produced by said set of corresponding radiant elements (2), and wherein the means for steam generation comprises, for each radiant element (2), a heat exchanger (5) placed in the corresponding suction hood (3) of said extraction means in order to recover the heat contained in the hot gases of said corresponding radiant element. 11. Installation according to one of claims 1 to 10, wherein said installation is a drying plant of a strip of material (1), having means for scrolling said strip of material under the action of infrared radiation of said infrared radiation system. 12. Installation according to claim 11, comprising rotating heating cylinders, on which is intended to be plated said material web, and a condensate-steam system for supplying said heating rolls with heating steam, said installation having means for injecting the steam produced by said steam generating means in said condensate-steam system of said heating rolls. 13. Use of the heat treatment plant according to one of claims 1 to 12 for drying paper.