Industrial drying facility using drying fluid

Abstract

The invention relates to a method for heating a fluid to be heated, and to a drying facility using a drying fluid, the method comprising the following steps: - heating the working fluid of a boiler (7), which comprises a tank containing this working fluid in a liquid / vapour phase equilibrium at a pressure lower than atmospheric pressure, and producing vapour in a vapour circuit (10) by means of a boiling heat exchanger (62) mounted on a heat recovery circuit and arranged in the tank; - increasing the pressure, and therefore the temperature, of the vapour circulating in the vapour circuit (10), and maintaining a vacuum in the tank of the boiler (7) by means of at least one compressor (11.1, 11.2) arranged on the vapour circuit (10); - condensing the vapour from the at least one compressor (11.1, 11.2), and heating the fluid to be heated by means of at least one heat injection exchanger (12, 14.1, 14.2).

Description

[0001] Description

[0002] Industrial drying installation using drying fluid

[0003] FIELD OF THE INVENTION

[0004] The invention relates to the field of drying wet products using drying fluid in industry. It potentially targets any drying installation capable of being implemented, such as spray dryers, belt dryers, heating cylinders, ovens, drying furnaces, flash dryers, fluidized bed dryers, paddle dryers, screw dryers, silos, rotary drums or tunnel dryers. These dryers are present in various industrial sectors such as food processing, chemicals, paper and cardboard, and non-metallic materials. This installation uses, for example, air as a drying fluid (a drying fluid is defined as a fluid that allows the evacuation of evaporated water from the dryer and the supply of heat to the dryer to facilitate this evaporation), which serves as a vector for transporting the evaporated water as well as a means for supplying calories to the dryer.

[0005] The invention aims more particularly at optimizing energy consumption in the context of such installations by recovering heat from the drying fluid extracted from the drying enclosure in particular, for reinjection into the intake air circuit or into said drying enclosure.

[0006] STATE OF THE ART

[0007] Drying installations are very widespread equipment in industry and represent a significant part of industrial consumption: 10 to 20% of total energy consumption in industry in industrialized countries (according to the literature "Modern Drying Technology", Volume 4 by Evangelos Tsotsas and Arun S. Mujumdar - 2007), they generally consist of a drying chamber through which the wet product to be dried passes, said chamber being crossed by a drying fluid, usually hot, which becomes loaded with moisture upon contact with the wet product. The extraction drying fluid thus loaded with moisture is evacuated from the chamber. This extraction drying fluid has a relatively high temperature and humidity.

[0008] It is therefore easy to understand the loss in terms of energy, resulting from the temperature and humidity in the extraction drying fluid, and consequently, the energy consumption necessary to ensure the effective evaporation of the humidity present in the product to be dried. It is in fact known that the enthalpy of vaporization at atmospheric pressure Ahvap is of the order of 630 kWh per ton of evaporated water, requiring in such a configuration where the extraction drying fluid is simply released into the atmosphere, an energy consumption 2 to 4 times higher (according to the literature "Drying processes in industry", ADEME, CETIAT, 2017), often fossil gas or coal, possibly via a heat transfer fluid such as steam, superheated water or hot water.

[0009] In other words, this mode of operation is a source of energy and exergy inefficiency.

[0010] In order to reduce this consumption, solutions exist to recirculate part of the extraction drying fluid at the level of the drying fluid introduction circuit, in order to transfer part of the relative heat of the extraction drying fluid to it. This recirculation certainly allows an energy gain, however very limited.

[0011] Drying installations have also been described which combine the introduction of hot air on the one hand, as described above, but also heating cylinders arranged within the drying chamber. These heating cylinders are typically heated by steam or hot air.

[0012] Other solutions allow heat recovery by preheating the inlet drying fluid with the extraction drying fluid, via an air / extraction drying fluid heat exchanger.

[0013] Recently, there has been a growing interest in heat recovery from the extraction drying fluid using high-temperature heat pumps (whose condenser has a temperature below 100°C), or even very high-temperature heat pumps (whose condenser has a temperature above 100°C), for reinjection into the intake air or into other heat supply means, for example injector exchangers, in the dryer (for example heating cylinders).

[0014] Also, some manufacturers are working on closed-loop drying installations, in which a heat pump condenses the water from the extraction drying fluid at the heat pump evaporator, and then reheats the dried extraction drying fluid via the heat pump condenser.

[0015] Finally, superheated steam dryers make it possible to approach the minimum energy required by the change of drying fluid, and can be coupled with mechanical steam compressors to approach the minimum exergy required by the drying process, with consumptions lower than 200 kWh / tonne of evaporated water. These types of dryers and configurations are the most efficient, but their intrinsic characteristics limit their scope of application, particularly with regard to the thermosensitivity of the products to be dried as well as the management of seals.

[0016] It follows from these findings, particularly in a context where energy is becoming a particularly high cost item for manufacturers and where industry is strongly encouraged, or even forced, to reduce its CO2 emissions to stop global warming, that an increasingly pressing need exists in terms of rationalization of such drying installations and more particularly in terms of reducing energy consumption at source.

[0017] This is the object of the present invention.

[0018] BRIEF STATEMENT OF THE INVENTION

[0019] To this end, the invention relates to an installation for drying a wet product using a drying fluid, comprising a drying enclosure within which the wet product to be dried and the drying fluid ensuring the drying pass, said enclosure comprising at least one circuit for introducing the inlet drying fluid, and at least one circuit for discharging the drying fluid resulting from the exchange of water and energy with the wet product to be dried, this installation comprising:

[0020] • at least one boiler operating with a working fluid suitable for producing steam in a steam circuit, and comprising:

[0021] ° a tank containing the working fluid in liquid / vapor phase equilibrium at a pressure lower than atmospheric pressure in nominal operation, connected to the steam circuit;

[0022] ° a boiling exchanger adapted to heat the working fluid of the boiler, mounted on a heat recovery circuit and arranged in said tank;

[0023] • at least one compressor placed on the steam circuit, capable of increasing the pressure, and therefore the temperature, of the steam circulating in the steam circuit, and adapted to maintain the boiler tank under vacuum;

[0024] • at least one heat injector exchanger capable of condensing the steam from said at least one compressor, and of ensuring heat transfer to a heat injection circuit.

[0025] The invention also aims at such a configuration with a first temperature increase by a heat pump. In this embodiment, the intermediate heat transfer loop comprises:

[0026] - a low temperature recovery loop with a heat recovery exchanger arranged on said heat source (said low temperature recovery loop can also supply heat sinks via other heat injector exchangers);

[0027] - a high temperature recovery loop on which the boiling exchanger is placed, and a heat pump adapted to raise the temperature of the low temperature recovery loop to reinject the heat into the high temperature recovery loop.

[0028] The high temperature recovery loop can also, for example:

[0029] - use available heat through recovery exchangers;

[0030] - exploit the heat available at this temperature level on injector exchangers for heat requirements on the dryer or on other industrial processes. According to another object, the invention relates to a method for heating a fluid to be heated, comprising the following steps:

[0031] - heating the working fluid of a boiler which comprises a tank containing this working fluid in a liquid / vapour phase equilibrium at a pressure lower than atmospheric pressure, and producing vapour in a vapour circuit, using a boiling exchanger mounted on a heat recovery circuit and arranged in said tank;

[0032] - increase the pressure, and therefore the temperature, of the steam circulating in the steam circuit, and maintain a depression in the boiler tank using at least one compressor placed on the steam circuit;

[0033] - condense the steam from said at least one compressor, and ensure the heating of said fluid to be heated, using at least one heat injector exchanger.

[0034] The boiler tank is maintained under vacuum, i.e. at a pressure which is lower than atmospheric pressure during nominal operation. Nominal operation of the installation is understood here as the normal and stabilized operating phases of the installation during drying, excluding shutdown, start-up, maintenance, etc.

[0035] The heat injection circuit consists of one or more elements which are heated by the heat injector exchanger(s).

[0036] In one embodiment, within the boiler, the working fluid is at a pressure less than about 1 Bar, preferably less than about 0.9 Bar, preferably less than 0.8 Bar, preferably less than about 0.7 Bar, preferably less than 0.6 Bar, preferably less than about 0.5 Bar, preferably less than 0.4 Bar, preferably less than about 0.3 Bar, preferably less than 0.2 Bar, preferably less than about 0.1 Bar. As used herein, "Bar" means "absolute Bar".

[0037] In one embodiment, said drying fluid is selected from the group consisting of air, nitrogen, carbon dioxide, and mixtures thereof.

[0038] Depending on the situation, the initial heat input within the boiler(s) occurs directly in said boiler(s) by external input, or indirectly by heating the inlet drying fluid by an external source when initiating heat recovery.

[0039] In other words, the invention makes it possible to recover the heat contained in the drying fluid loaded with moisture and in the other heat sources present in the environment of the dryer, and, from this heat, to generate steam under depression within the boiler, said steam then undergoing an increase in its pressure and its temperature using a compressor so as to supply a heat injector exchanger to heat a fluid to be heated, such as the drying fluid, upstream of the drying enclosure, in the drying enclosure and / or in the environment of the dryer.

[0040] For the purposes of the invention:

[0041] - a boiler is defined as comprising: a tank containing a working fluid under vacuum in a liquid / vapour phase equilibrium in which a heat input allows boiling of the working fluid; and a boiling exchanger positioned in this boiler tank, and allowing boiling to be generated, i.e. a phase change from a liquid phase to a vapour phase of the working fluid;

[0042] - a working fluid is defined as a fluid that carries heat from a source to a sink, through liquid / vapor phase changes;

[0043] - a heat recovery exchanger is defined as equipment allowing heat to be recovered by heating the working fluid of the boiler, this heat being recovered from the evacuation circuit (5) (directly or indirectly), or from any other available heat source that one wishes to use;

[0044] - a heat injector exchanger is defined as equipment capable of supplying heat to a fluid.

[0045] According to a variant of the invention, the drying chamber can itself integrate means for supplying additional heat, which are part of the heat injector exchangers, supplied with steam from the compressor mentioned above. These means for supplying additional heat are conventionally heating cylinders, double walls of the drying chambers, screws, pallets or even steam radiators.

[0046] According to a variant of the invention, the surrounding industrial processes can themselves integrate heat supply means, which are part of the heat injector exchangers, supplied with steam from the previously mentioned compressor.

[0047] The boiler is managed so that its internal pressure (the pressure in the tank) is lower than atmospheric pressure. The boiler is thus in a negative pressure state. This negative pressure is the result of a balance between the power required by the heat injector exchangers and the available power, which is higher the lower the temperature. Indeed, the lower the heat recovery temperature on the heat recovery circuit, the more energy will be recovered. Also, the pressure in the boiler depends on the working fluid, and the balance between the power required to supply the heat injector exchangers and the power available at the heat sources on the heat recovery circuit.The invention allows self-regulation in which, when there is a decrease in the heat requirement at the heat injector exchangers (in the drying enclosure, on the inlet drying fluid or any other heat requirement), little steam is produced by the boiler. If the availability of heat in the sources is not decreased at the recovery temperature level, then the temperature and pressure in the boiler increase by increasing the boiling point of the working fluid, and the compressor decreases its compression ratio in order to supply steam to the heat injector exchanger (or heat injector exchangers if there are several) at the pressure level of the requirement set by the process.If the boiler pressure rises too high (while remaining under negative pressure) and a compressor becomes obsolete (when several compressors are used), a compressor can for example be slowed down or bypassed during these phases of low heat demand and high heat availability. Conversely, when the steam demand increases, the compressor(s) accelerate, which decreases the pressure in the boiler (the boiler however remains under negative pressure) if the heat sources remain constant, which requires the compressors to increase their compression ratio up to the operating point and then increase steam production to the desired pressure level. Obviously, the compressors are sized for the maximum point in terms of flow and pressure.

[0048] This self-regulation goes hand in hand with an optimization of the energy consumed by the compressor(s), since the reduction in steam demand leads to an increase in pressure in the boiler (which nevertheless remains under pressure), a lower compression ratio and therefore lower consumption by the compressors.

[0049] The compressors, particularly efficient when they have low compression ratios, can be installed in series if necessary to ensure high compression ratios, in parallel to ensure significant adaptation capacity of the installation, and can be totally or partially bypassed in start-up operations or in continuous operation.

[0050] The working fluid and the compressor(s) are chosen to operate in a temperature and pressure range compatible with putting the boiler under vacuum during all operating phases, taking into account the desired temperature at the injector exchangers. In a particularly advantageous manner, the invention makes it possible to implement this drying installation with water as the boiler's working fluid. Water has the great advantage of being a natural, non-polluting, inexpensive and readily available element, unlike the technical fluids generally used in thermodynamic installations.

[0051] Also very advantageously, the use of water as the working fluid of the boiler, permitted by the invention, also makes it possible to use the water from the drying of the wet product as make-up water for the water / steam network with water treatment such as a softener, osmosis, or demineralization if necessary.

[0052] The invention thus makes it possible in a particularly advantageous manner to respond to environmental challenges both in terms of energy savings (in a highly consuming technical field) and in terms of the neutrality and low danger of the products used. The invention represents an implementation, in the field of energy, of the capacity to create value through sobriety, thanks to the implementation of circularity.

[0053] In order to ensure the start of the boiling operation within the boiler, the installation may include a means capable of initiating the operation of the boiler(s) by supplying heat, which consists of a heat source, i.e. an energy flow in which it is possible to recover additional heat. This additional heat source is located in the boiler, in the inlet drying fluid, in the enclosure itself or in dedicated steam production rooms, and may consist of any means of supplying calories, and in particular resistance or induction technology, a fuel boiler, by at least one electric immersion heater, by at least one exchanger supplied by a heat transfer fluid such as hot water, thermal oil or steam, or by an external heat source available at start-up.

[0054] Furthermore, this additional start-up heat source can also act as a backup means in the event of mechanical, electrical, pneumatic, automation or hydraulic failure on the installation. It can also act as a backup, in the event that the sizing of this system is carried out, for example, to ensure 80% of the dryer's operating cases. Finally, this start-up / backup / backup source can be used as a vector for hybridizing the drying process power supply, in order to also become an electrical shedding capacity for the common electrical network and facilitate the intermittency of electrical sources. This source is therefore a start-up / backup / backup / shedding vector.

[0055] Correspondingly, the installation may also provide a device for creating a vacuum in the boiler in order to allow the boiling operation to start within the latter if necessary, the compressor(s) then taking over to maintain a vacuum in the boiler.

[0056] In order to optimize the drying installation of the invention, the compressor(s) are regulated according to the drying needs defined by the drying kinetics of the different products: the installation allows an adaptation of the condensation temperatures of the steam by variation of the compression ratios of the compressor(s) by variation of the speed of the compressor. The compressor(s) are thus regulated according to at least one parameter representative of the humidity of the wet product to be dried present in the drying enclosure. It is thus possible to obtain an injection of steam at different pressure levels for the same heat injector exchanger, according to the drying needs of the product. This is done by means of measurements allowing an estimation of the drying kinetics in order to avoid overdrying.This regulation thus makes it possible to limit the electrical energy consumption necessary for the operation of the compressor; when the drying temperature requirement is lower, the steam is compressed to lower pressure levels.

[0057] In doing so, electricity consumption is substantially limited by avoiding excessively high and unnecessary pressures. Thus, an online measurement of the humidity of the product or the variation in the temperature of the product to be dried, for example by infrared or using a thermal camera, makes it possible to control the drying kinetics of the product in question and avoid overdrying by defining the appropriate pressure / temperature levels.

[0058] Furthermore, in order to facilitate the operation of the boiler, the installation may also include a heat pump (HP) intended to raise the temperature level obtained by the heat recovery exchanger located on the evacuation circuit, particularly if the pressure at the temperature obtained is not achievable under satisfactory technical conditions, while ensuring that the boiler operates well in depression. In the theoretical ideal, the evaporator of the heat pump is directly positioned in the flow of the extraction fluid, and the condenser in the boiler. The condenser of the heat pump then forms the boiling exchanger of the boiler.

[0059] However, a low temperature recovery loop (LT loop) to supply the heat pump evaporator can advantageously be implemented to take advantage of the calories present on other heat sources in the installation, and which are thus recovered on this LT loop. A water (or glycolated water) loop on the condenser side of the heat pump can also be interesting to facilitate the use of calories and / or the recovery of the latter on the same high temperature recovery loop (HT loop).

[0060] According to a particular configuration of the invention in a closed loop, the intake drying fluid comes from the extraction drying fluid, after drying by means of a heat recovery exchanger then reheating by means of a heat injector exchanger.

[0061] In other words, the installation may provide a closed loop assembly on the drying fluid to allow total or partial recycling of the extraction drying fluid, where appropriate by implementing means for filtering said drying fluid and managing the fatal heat.

[0062] In one embodiment, the drying fluid is air, and the product processed by the drying facility is dried by water extraction. The inlet drying fluid is then relatively dry air, and the extraction drying fluid is moisture-laden air, also called "mists".

[0063] The drying installation according to the invention may further comprise the following additional characteristics, alone or in combination:

[0064] - the installation further comprises a condensate circuit adapted to return to the boiler the condensates resulting from the condensation of the steam in the at least one heat injector exchanger;

[0065] - the installation includes a working fluid top-up device.

[0066] - the working fluid top-up device is adapted to add condensed water from the drying fluid discharge circuit to the condensate circuit;

[0067] - the condensate circuit comprises at least one condensate collector;

[0068] - the working fluid top-up device is arranged in the condensate collector;

[0069] - the condensate collector comprises a device for degassing and / or discharging incondensables; - the heat recovery circuit on which the boiling exchanger is mounted comprises a heat source constituted by the drying fluid discharge circuit, the boiling exchanger being arranged on the drying fluid discharge circuit, or on an intermediate heat transfer loop from the drying fluid discharge circuit;

[0070] - the heat recovery circuit on which the boiling exchanger is mounted comprises at least one exchanger external to the dryer;

[0071] - the heat recovery circuit on which the boiling exchanger is mounted comprises an intermediate heat transfer loop comprising: a heat recovery exchanger arranged on a heat source; and the boiling exchanger;

[0072] - the intermediate heat transfer loop comprises a low temperature recovery loop with a heat recovery exchanger arranged on said heat source, a high temperature recovery loop on which the boiling exchanger is arranged, and a heat pump adapted to raise the temperature of the low temperature recovery loop to reinject the heat into the high temperature recovery loop;

[0073] - the low temperature recovery loop also includes at least one injector exchanger external to the dryer;

[0074] - the high temperature recovery loop also includes at least one injector exchanger external to the dryer;

[0075] - the high temperature recovery loop further comprises at least one heat recovery exchanger external to the dryer;

[0076] - the installation also includes a hot water storage tank in communication with the high temperature recovery loop;

[0077] - said at least one heat injector exchanger is adapted to supply heat to the drying enclosure;

[0078] - said at least one heat injector exchanger is positioned within the drying enclosure; - said at least one heat injector exchanger is positioned within the inlet drying fluid introduction circuit;

[0079] - said at least one heat injector exchanger is positioned on an external heat injection circuit;

[0080] - the installation also includes at least one means capable of initiating the operation of the boiler by supplying third-party heat;

[0081] - at least one compressor is regulated according to at least one parameter representative of the humidity of the wet product to be dried;

[0082] - the installation further comprises a device for placing at least one boiler under vacuum;

[0083] - the installation further comprises a steam accumulator downstream of at least one compressor;

[0084] - the at least one compressor comprises a set of compressors arranged in series and / or in parallel;

[0085] - the installation comprises two compressors in series, and it further comprises at least one thermocompressor supplied with steam from the steam coming from the first compressor and the steam coming from the second compressor, so as to supply the at least one heat injector exchanger with steam at an intermediate pressure between the pressures of the steam at the outlet of the first compressor and the second compressor;

[0086] - the installation also includes desuperheaters capable of injecting liquid working fluid into the steam leaving the compressors;

[0087] - the installation comprises a first compression stage consisting of one or more thermocompressors located upstream of at least one compressor;

[0088] - the installation includes a heat exchanger on the drying fluid discharge circuit, suitable for preheating the inlet drying fluid;

[0089] - the installation operates in a closed loop, and in that the inlet drying fluid comes from the extraction drying fluid from the drying enclosure, which is dried by means of the boiling exchanger, then reheated by means of the at least one heat injector exchanger;

[0090] - the installation comprises a plurality of drying chambers, mounted in series, the most upstream chamber receiving the product to be dried having the highest degree of humidity, and the most downstream chamber receiving the product to be dried after transit in the upstream chambers, in which: the inlet drying fluid conveyed into the upstream chamber relative to the direction of progression of the wet product to be dried comes from the drying fluid laden with humidity from the drying chamber mounted immediately downstream of said upstream chamber after reheating by a heat injector exchanger, i being an integer between 1 and n-2, the steam from the at least one boiler and the pressure of which has been increased using a main compressor, is conveyed as a priority into a heat injector exchanger arranged in the drying fluid introduction circuit of the most upstream chamber,part of this steam is subjected to compression at the level of an additional compressor to convey a higher pressure steam to the level of a heat injector exchanger arranged within a circuit for introducing drying fluid into said downstream enclosure with possible supply of new drying fluid for mixing; this compression process towards the downstream enclosure being likely to occur 1, 2, ..., n-2 times, the drying fluid from the enclosure comes from the drying fluid leaving the enclosure, preheated by the hot product to be dried coming from the enclosure, which has cooled in the enclosure by giving up its heat to the drying fluid and possibly by drying the drying fluid by hygroscopicity of the product, and the inlet drying fluid of the enclosure, furthest downstream, consists of dry drying fluid,possibly of vapors dried by the recovery exchanger in the case of closed loop operation on the drying fluid;,

[0091] - the working fluid of the boiler is water;

[0092] - the condensate collector is maintained in a liquid / vapor phase equilibrium, with the vapor part connected to the inlet of said at least one compressor, or to said at least one heat injector exchanger or to a heat recovery exchanger; - the installation comprises a sub-cooler exchanger arranged downstream of the at least one heat injector exchanger, on the condensate circuit, and adapted to preheat the heat injection circuit;

[0093] - the subcooler exchanger is suitable for heating the inlet drying fluid introduction circuit.

[0094] The method according to the invention may further comprise the following additional characteristics, alone or in combination:

[0095] - the step of heating the working fluid of the boiler is carried out with an intermediate heat transfer loop by recovering heat from a heat recovery exchanger arranged on a heat source; and transferring it to the boiling exchanger;

[0096] - the step of heating the working fluid of the boiler is carried out by recovering heat from a heat recovery exchanger arranged on said heat source, with a low temperature recovery loop and a high temperature recovery loop on which the boiling exchanger is arranged; and by increasing the temperature of the high temperature recovery loop relative to the low temperature recovery loop using a heat pump.

[0097] The term "external exchanger" refers to exchangers that can be placed on external industrial equipment from which heat is to be recovered.

[0098] BRIEF DESCRIPTION OF THE FIGURES

[0099] The manner in which the invention can be implemented and the advantages which result therefrom will become more apparent from the following examples of implementation, given for informational and non-limiting purposes, in support of the appended figures.

[0100] Figure 1 is a schematic representation illustrating the basic drying installation of the invention.

[0101] Figure 2 is a variant of Figure 1 incorporating an additional heat injector exchanger integrated into the drying chamber itself.

[0102] Figure 3 is a variant of Figure 2 comprising two heat injector exchangers integrated within the drying chamber. Figure 4 illustrates a more complex installation, for dryers with large evaporative capacity, integrating several (n) drying chambers connected in series, equipped with their respective drying fluid inlet system.

[0103] Figure 5 illustrates a closed-loop drying installation, as described in the last paragraph of the state of the art, implementing the principle of the invention.

[0104] Figure 6 illustrates a variant of Figure 4 in closed-loop mode.

[0105] Figure 7 schematically illustrates a particular embodiment of the invention in which the heat recovery circuit on which the heat recovery exchanger is mounted comprises a heat source constituted by the discharge circuit, the heat recovery exchanger being arranged on an intermediate heat transfer loop from the discharge circuit. This heat recovery circuit implements a low temperature (LT) loop and a high temperature (HT) loop, with a heat pump to raise the temperature levels of the heat source. The evaporator of the heat pump is on the LT loop and is arranged in the discharge circuit, to be heated by the extraction drying fluid. The condenser of the heat pump is on the HT loop and constitutes in this example the heat recovery exchanger, being arranged in the boiler tank.

[0106] Figure 8 illustrates a variant of Figure 3 integrating a first stage of pressure increase achieved by thermocompressors.

[0107] Figure 9 illustrates a variant of Figure 7 with water storage on the HT loop.

[0108] Figure 10 illustrates a variant of Figure 7 with heat recovery from several heat sources on the LV loop.

[0109] Figure 11 illustrates a variant of Figure 3, in which the operation of the dryer with the selected compressors requires the creation of inertia on the steam network to ensure the instabilities of steam consumption of the dryer, ensured by a steam accumulator.

[0110] Figure 12 illustrates a variant of Figure 3 with the use of a thermocompressor to have steam at an intermediate pressure level, between the outlet pressure levels of the two mechanical compressors in the installation.

[0111] Figure 13 illustrates a variant of Figure 3 with injection of water into the superheated steam to desuperheat - return it to the state of saturated steam - said steam downstream of the compressors which superheat the steam, in order to transport the steam at a temperature close to the saturation temperature.

[0112] Figure 14 illustrates a variant of Figure 7 with heat recovery from multiple heat sources on the HT loop.

[0113] Figure 15 illustrates a variant of Figure 7 with a valorization of the heat of the BT and HT loops on the insufflation of drying air.

[0114] Figure 16 illustrates a variant of Figure 3 with heat recovery by exchanger on the extraction drying fluid for preheating of drying fluid;

[0115] Figure 17 illustrates a variant of Figure 3 in which the heat recovery exchanger is mounted on an external heat recovery circuit.

[0116] Figure 18 illustrates a variant of Figure 3 in which a heat injector exchanger makes it possible to use the steam produced by the installation for the benefit of other processes or installations.

[0117] Figure 19 illustrates a variant of Figure 17 in which one or more vents allow the removal of non-condensables.

[0118] Figure 20 illustrates a variant in which the installation comprises a single heat injector exchanger, arranged in the drying enclosure.

[0119] Figure 21 illustrates an implementation with an example of compressors in series and with desuperheating means at the compressor outlet.

[0120] DETAILED DESCRIPTION OF THE INVENTION

[0121] The various figures schematically illustrate different variants of the installation according to the invention. As mentioned in the preamble, this installation can be implemented for all types of dryers (except superheated steam dryers) and needs to be adapted in order to have the capacity to meet the needs of the wet products to be dried.

[0122] The implementation of the present invention coupled with other drying means (infrared, by dielectric losses such as microwaves or high frequencies) is possibly conceivable in order to ensure the best performance of the whole and to meet the drying needs of the products.

[0123] The invention therefore relates to a drying installation using drying fluid, for a wet product comprising a drying enclosure (1) within which the wet product to be dried (2) and the drying fluid ensuring the drying pass, said enclosure comprising at least one introduction circuit (4) for inlet drying fluid, and at least one evacuation circuit (5) for extraction drying fluid, which is the drying fluid loaded with moisture resulting from the exchange of water and energy with the wet product to be dried. The installation comprises:

[0124] - at least one boiler (7) operating with a working fluid, preferably water, configured: to recover heat from one or more heat sources constituted by the extraction drying fluid by means of a heat recovery exchanger (6); and to generate steam using the heat thus recovered, the boiling temperature of the working fluid being adapted by means of the pressure in the boiler (7) to the temperature of the heat source(s), possibly by means of an intermediate heat transfer loop;

[0125] - optionally, at least one means capable of initiating the operation of said heat recovery by supplying third-party heat;

[0126] - at least one compressor (11, 11.1, 11.2, 11.3) capable of increasing the pressure, and therefore the temperature, of the steam generated in said boiler(s) (7), while maintaining a depression in the boiler (7), to achieve said adaptation of the boiling temperature of the working fluid to the temperature of the heat source(s);

[0127] - at least one heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2) capable of condensing the steam from said at least one compressor (11, 11.1, 11.2, 11.3). The heat injector exchanger(s) (12, 12.1, 12.2, 14, 14.1, 14.2) may be positioned inside the drying enclosure (1), and / or on the introduction circuit (to heat the inlet drying fluid upstream of the drying enclosure (1)), and / or on an external circuit to use the heat produced for other equipment or processes.

[0128] In one embodiment, the fluid-based drying installation for drying a wet product according to the invention is characterized in that said at least one boiler (7) operates with a working fluid being water.

[0129] In one embodiment, the wet product is selected from the group consisting of web products, for example paper, cardboard or textile, pasty products, for example sewage sludge, process sludge, paint sludge, concentrated paint, wet cakes, infant flours, potato flakes, yeasts, gelatins or pulps, powdered or granular products, for example zinc oxides, metal oxides, silicon, cocoa, milk powder, instant flours, lactose, pharmaceutical powders, paint powders, detergent powders, pigments, sand, sugar, starch powders, coffee, yeasts, oxides, proteins, wood particles, dyes, wood pellets, wood panel particles, carbon black, potassium chloride, talc, barley, protein pea, sunflower, wheat, corn, legumes,spelt, soybeans, rapeseed, oats, rice, beans, millet, buckwheat, quinoa, flocculants or powdered milk, lump products, e.g. vegetables, cereals, molded objects, ceramics, tiles, foodstuffs, plasterboard, hardwood or softwood, chips, pasta, animal feed, biscuits, bricks, roof tiles, latex mattresses or foams, fibrous products, e.g. wool, cotton, wood fiber, sawdust, paper pulp, herbs and medicinal plants, alfalfa or coconut, flat products, e.g. insulation boards, wood or particleboard, and liquid products, e.g. PVC latex, aqueous solutions, milk or juices.,

[0130] In one embodiment, the temperature of introduction of the drying fluid into the drying chamber is between about 40°C and about 600°C, preferably between about 40°C and about 200°C, preferably between about 40°C and about 150°C, preferably between about 40°C and about 100°C, preferably between about 40°C and about 80°C, preferably between about 40°C and about 60°C.

[0131] All figures share the same legend conventions:

[0132] - the extraction drying fluid (also called “fumes” in this illustrative example) is in dotted lines;

[0133] - the intake drying fluid (also called “intake air” in this illustrative example) is in wide dotted lines;

[0134] - the steam produced by the boiler is in solid, bold lines;

[0135] - Condensates from the water / steam network are in dotted gray;

[0136] - the product to be dried is represented by arrows around the drying enclosure in thin solid lines;

[0137] - the condensed water (23), recovered by condensation on the evacuation circuit, is in fine dotted lines.

[0138] In Figure 1, the drying enclosure (1) is intended to receive a wet product to be dried (2). Thus, the wet product (2) enters the enclosure, undergoes drying in the enclosure (1), and leaves it in dry form (3).

[0139] Within this drying enclosure (1), an inlet drying fluid is introduced via an introduction circuit (4), this inlet drying fluid is hot. After exchange within the drying enclosure resulting from the phenomenon of convection and mass transfer between the hot inlet drying fluid and the wet product to be dried, an extraction drying fluid (which is a fluid with a high moisture content) leaves said enclosure via an evacuation circuit (5). In the case of air drying, which is a preferred embodiment, the extraction drying fluid can be called "vapors".

[0140] The extraction drying fluid emerges at a relatively high temperature and humidity, and part of the heat of the extraction drying fluid is recovered by means of a heat recovery exchanger (6) by recovering energy in the form of sensible heat as well as latent energy from the extraction drying fluid by condensing water, originating from the evaporated product water, which can be recovered (23), this heat being transferred to the working fluid in the boiler (7). This concerns an example of an application in which the heat of the extraction drying fluid is recovered.

[0141] However, the invention makes it possible in a generic manner to recover heat via an intermediate loop to produce steam within the boiler (7) by the heat recovery exchanger (6, 6.2, 27) which it contains, compress this steam and reinject it into heat sinks via injector exchangers (12, 14.1, 14.2). This configuration can be implemented as is, or with an initial temperature increase by heat pump and intermediate loop as described below.

[0142] The heat recovery exchanger (6, 6.2, 27) is mounted on a heat recovery circuit which can be linked to the extraction drying fluid, to the exhaust circuit (5), or to another heat source available in the environment of the drying installation. This heat can thus be recovered directly from the extraction circuit (5), which is the case illustrated in Figure 1 where the extraction circuit passes directly through the heat recovery exchanger (6). This heat can also be recovered from the extraction circuit (5) indirectly, via an intermediate heat transfer loop, with an exchanger recovering the heat in the extraction circuit (5), and bringing it to the boiling exchanger (6.2).In an embodiment more suited to autonomous operation of a dryer in energy recovery, this intermediate loop can be equipped with a heat pump (8) as described below, which is the example of figures 7, 9, 10, 14, and 15.

[0143] The intermediate loop is then composed of:

[0144] - A low-temperature recovery loop, called a low-temperature loop, which allows energy to be recovered from several heat sources using heat recovery exchangers on site. Advantageously, this low-temperature loop can also be used to recover this low-temperature heat using low-temperature heat injectors;

[0145] - A high temperature recovery loop, called the HT loop, which allows energy to be recovered from high temperature heat sources via heat recovery exchangers, to inject this heat into heat sinks via heat injector exchangers, but above all to supply the boiler(s) with energy via a boiling exchanger (6.2) which will work at higher pressure levels than if it were located on the BT loop;

[0146] - A heat pump which allows the LV and HV loops to be thermally connected, to take low temperature heat from an exchanger on the LV loop, and to reinject this heat plus the electrical consumption of the heat pump (the compressor) into the HV loop.

[0147] This heat can also be recovered from any other heat source that one wishes to use, for example the heat recovery circuit can include exchangers on fumes, waste water or process water to be cooled. Figures 10, 14, 17 and 19 illustrate this case in a generic manner: the heat recovery exchanger (27, 32, 40) is thus linked to an external heat source (not shown), other than the evacuation circuit (5).

[0148] This working fluid can be demineralized or softened water. The heat supplied via the heat recovery exchanger (6) will heat the working fluid to the pressure saturation temperature in the boiler. This working fluid in liquid / vapor phase equilibrium in the boiler thus generates steam at the saturation temperature.

[0149] In one embodiment, the working fluid is R718 refrigerant fluid water optionally treated by demineralization, softener, osmosis and mixtures thereof.

[0150] In nominal operation, the at least one compressor (11) maintains a steam supply to the process at the pressure and power level requested by the latter, which generates a depression inside the boiler (7), to promote the production of steam by the boiler (7), and to allow the adaptation of the boiling point, or the pressure and temperature within the boiler according to the quantity of recoverable heat available at the given temperature, in a self-regulated manner. A reduction in the boiler pressure by increasing the steam demand implies an increase in the heat available at the heat recovery exchangers. Conversely, a reduction in the demand for steam flow (10) with constant heat sources implies an increase in the temperature, therefore the pressure of the boiler.

[0151] However, and in order to limit the volume flow rates in the compressors (11), a preliminary temperature rise may be necessary to limit the depression of the boiler. This is the case when the heat recovery exchanger (6, 6.2, 27) is mounted on a heat recovery circuit which is linked to the extraction drying fluid, on the evacuation circuit (5), recovered indirectly, via an intermediate heat transfer loop containing a heat pump (8).

[0152] This temperature increase can be achieved by a heat pump (8) (see figures 7, 9, 10, 14, and 15), taking the heat from the evacuation circuit (5) of the extraction drying fluid, possibly by means of two recovery loops ((25.1) for the BT loop and (25.2) for the HT loop), consisting for example of water or glycolated water, as described previously.

[0153] Cold start of the installation can be facilitated by an additional heat source to initiate the operation of the system. This heat source can be provided for example;

[0154] - by a high-pressure steam boiler which initiates drying by injecting steam into the injector exchangers, and thus launches heat recovery before gradually switching off in favor of recovery;

[0155] - by an energy source in the boiler;

[0156] - by the installation itself which draws calories from recovery exchangers other than those on the dryer extraction drying fluid which can have calories when the dryer is not in operation, which represents an additional advantage of carrying out multi-source recovery.

[0157] Furthermore, still with the same objective of initiating the boiling process of the working fluid within the boiler (7), the pressure may have to be adapted to the temperature of the heat source before starting the main compressors (11). In this regard, the boiler can be connected to a vacuum device (9) (see figure 11), in order to lower the pressure within the boiler during the start-up phases. This device is then stopped. The compressor (11) associated with the heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2) then ensures that the depression in the boiler is maintained during normal operation, with a thermal balance between the supply by the heat recovery exchanger

[0158] (6) and the need for the heat injector exchanger.

[0159] In stabilized operation, the steam produced in the boiler (7) is conveyed (10) to a compressor (11, 11.1, 11.2) intended to increase the pressure, and therefore the temperature of the steam thus generated, according to the well-known laws of thermodynamics.

[0160] This steam, thus compressed, is conveyed superheated or desuperheated to a heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2) allowing the heating of the drying enclosure (1) upstream and / or directly in this enclosure.

[0161] The heat injector exchanger (12, 12.1, 12.2) can be positioned in the introduction circuit (4) to heat the inlet drying fluid upstream of its entry into the drying enclosure (1), as in the examples of figures 1 to 19.

[0162] The heat injector exchanger (14, 14.1, 14.2) can also be positioned directly in the drying chamber (1), as in the examples of figures 2, 3, 7 to 20. In this case the heat injector exchanger (14, 14.1, 14.2) can be heating cylinders, double walls of the drying chamber, screws, pallets and / or steam radiators arranged in the drying chamber (1).

[0163] The heat injector exchanger (32, 39, 40) can be positioned in a process other than the dryer for heating another fluid, allowing the heat recovery on the dryer to lead to the heating of other elements in the industry considered, or to supply heat networks, offices or neighboring industries.

[0164] So, once the boiling starts within the boiler

[0165] (7) carried out, the only significant electrical consumption lies in the power supply of the compressor(s) (11, 11.1, 11.2, 11.3), which are regulated according to the steam requirement of the process. The compressor(s) (11, 11.1, 11.2, 11.3) is associated with the heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2) and possibly with an expansion or purge member (37, 37.1, 37.2) ensuring the maintenance of the depression in the boiler during normal operation.

[0166] The compressed steam feeds the heat injector exchangers (12, 12.1, 12.2, 14, 14.1, 14.2) in which the steam condenses, releasing the latent energy of vaporization to the process at constant temperature.

[0167] The liquid condensates, possibly sub-cooled at high pressure, feed the condensate circuit (13, 16, 19), then lowered to the saturation temperature of the working fluid at low pressure with a possible flash, allowing the heat exchange occurring at the level of the heat recovery exchangers (6, 6.1). The passage from high pressure to low pressure is done by means of a device allowing expansion, which can be a control valve, an expansion valve, an orifice, a trap. It may happen that the condensates are not returned for processes which consume steam injected into the process, or because the condensate return pipes have not been implemented, which should be prohibited to avoid thermal losses.

[0168] Water can be condensed (23) at the level of the evacuation circuit (5), either directly by the heat recovery exchanger (6) as in the example of figures 1 to 6, or by a heat recovery exchanger (6.1), as in the examples of figures 7, 9, 10, 14, 15. In a particularly advantageous example, the working fluid of the boiler (7) is water, and the condensed water (23) is reused in the installation after possible water treatments depending on the case, these treatments being able to be those of pH, Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and particles in particular. This condensed water (23) makes it possible to limit the consumption of industrial water and in fact constitutes an additional advantage of the invention, particularly interesting in a context in which water resources are increasingly under tension.

[0169] Figure 2 illustrates a first variant of the drying installation according to the invention. In this, the drying of the wet product (2) in the drying enclosure (1) occurs not only due to the introduction of the drying fluid, as illustrated in Figure 1, but also by at least one other heat injection exchanger (14) positioned inside the drying enclosure (1).

[0170] For example, this other heat injector exchanger (14) consists of one or more heating cylinders, the heating of which is provided by steam. Optionally, in Figure 2, part of the steam produced by the boiler (7), and the pressure of which is increased by the compressor (11) is conveyed into a heat injector exchanger (14) to be condensed there, then is sub-cooled in another sub-cooler exchanger (15) preheating the inlet drying fluid. Advantageously, the condensate (16) produced in the injector exchanger (14.1, 14.2) joins a condensate sub-cooler exchanger (15), then joins the condensate circuit (13) of the boiler (7).

[0171] Figure 3 illustrates a variant of the installation of Figure 2. In this, two heat injector exchangers (14.1) and (14.2) are shown, positioned within the drying enclosure (1). Part of the steam from the compressor (11.1), introduced at the first of these heat injector exchangers (14.1), is diverted and sent to another compressor (11.2), supplying the second heat injector exchanger (14.2). The compressor (11.2) is intended to further increase the pressure (and therefore the temperature) of the steam, compared to that supplying the first exchanger (14.1). Indeed, in the example described, this second heat injector exchanger (14.2) is located downstream of the first heat injector exchanger (14.1 ) in the direction of the product flow on purpose, due to the effective progression of the wet product within the enclosure, configuration in which a higher heat source in terms of temperature is required downstream for the purpose of optimizing the drying process. The condensates from the injector exchangers (14.1 ) and (14.2) are returned to a condensate collector (19) which is part of the condensate circuit (13, 16, 19), then sub-cooled in a sub-cooler exchanger (15) preheating the inlet drying fluid before being returned to the condensate circuit (13, 16, 19) of the boiler (7). The condensate collector (19) may be maintained in liquid / vapor phase equilibrium, with the vapor portion connected to the inlet of said at least one compressor (11, 11.1, 11.2, 11.3), or to said at least one heat injector exchanger (14.1) or to a heat recovery exchanger (6.1).

[0172] This condensate collector can thus produce a vapor flash of the incoming condensates, that is to say that the pressure in this collector is lower than the vaporization pressure at the temperature of the condensates entering the collector. The latter therefore undergo a partial transformation into vapor phase called flash. The reason for the low pressure in said collector may be that the vapor phase is connected to the inlet of a vapor compressor, or to a heat exchanger which draws calories to inject them into an injector exchanger or recover them by a recuperator exchanger, thus acting as a thermal vacuum pump. This condensate collector can also receive a liquid / vapor mixture whose vapor phase is valued as described above.

[0173] Figure 4 illustrates yet another embodiment of the invention. In this, the drying chamber is in fact subdivided into a number of chambers (1.1) to (1.n), connected in series with each other, each of said chambers being supplied with hot drying fluid, as previously described.

[0174] However, in this embodiment, the evacuation of the extraction drying fluid, that is to say in this case the drying fluid with the highest moisture content, only occurs at the level of the most upstream enclosure (1.1). For an integer i between 1 and n-2, the enclosure (1.i) is supplied with drying fluid (4.i) originating from the heat and water exchange with the product to be dried from the enclosure immediately downstream (1.i+1), and possibly by additional inlet drying fluid (20.i). This drying fluid undergoes a temperature increase by means of heat injector exchangers (12.i), themselves supplied with steam. The heat injector exchanger (12.1) of the introduction circuit (4.1) of the most upstream enclosure (1.1) is supplied with steam originating from the compressor (11.1). Heat injector exchangers (12.i) downstream introduction circuits are supplied with steam taken from the upstream circuit, and undergoing a rise in pressure (and therefore temperature) by means of compressors (11. i). In fact, the further the wet product to be dried progresses within the enclosures, the hotter and drier the drying fluid is. The most downstream enclosure (1.n) is supplied with fresh air (4.n), i.e. ambient air and the preceding enclosure (1.n-1) is supplied with low humidity air heated by the product passing through the enclosure (1.n); product which cools on contact with the fresh and dry air and possibly absorbs moisture from the air depending on its hygroscopic capacities and its dry matter content.

[0175] It should be noted that the configuration presented in Figure 4 could also include additional heat injector exchangers (14.i) in order to improve the supply of calories to the drying chambers, as presented in Figure 3.

[0176] Figure 5 illustrates the adaptation of the invention to a closed loop drying installation on the drying fluid. In this configuration, the heat recovery exchanger (6) is installed on the discharge circuit (5) to dry them by discharging the water from the product (23). The dried extraction drying fluid is recirculated to the heat injector exchanger (12) in order to generate hot inlet drying fluid (4) to supply the drying enclosure (1).

[0177] This configuration potentially involves excess heat depending on drying temperature regimes, compressor performance, product heat capacity and system losses. This excess heat, called waste heat, can be recovered in an excess heat exchanger (21) so that the condensates can be redirected to the boiler (7).

[0178] This configuration is particularly interesting in terms of the water evaporated from the product, which is thus recovered 100%, as well as the absence of discharges in the form of extraction drying fluid, but only in liquid form.

[0179] Figure 6 illustrates an application equivalent to the operation of Figure 4 with closed loop recirculation of the drying fluid to reuse the extraction drying fluid dried in the heat recovery exchanger (6) to be redirected to the drying fluid inlet (4.n) of the downstream enclosure (1.n).

[0180] Figure 7 illustrates a variant of the invention integrating means for raising the temperature and pressure of the working fluid in the boiler (7). These means consist of a heat pump (8). The latter makes it possible to raise the temperature level of the energy recovered from the extraction drying fluid by means of a heat recovery exchanger (6.1) on the extraction drying fluid circuit (5), supplying the evaporator of the heat pump consisting here of the boiling exchanger (6.2) in the boiler (7), by means of a BT recovery loop (25.1).

[0181] This BT recovery loop is a loop of water, glycolated water or thermal fluid, allowing the heat from the exchanger (6.1) to be conveyed to the heat pump for a temperature increase, then a supply to the boiling exchanger (6.2). This loop also has the capacity to recover heat from other exchangers (40) placed on heat sources (as in the example of figure 10) as well as possibly supplying injector exchangers (34) intended to heat the intake drying fluid (as in the example of figure 15).

[0182] Note that this solution makes it easier to arrange using a standard technological brick produced in large series (heat pump) and facilitating implementation. However, it would be possible to install a compressor and an expansion valve between the exchangers (6.1) and (6.2) with another working fluid, whose saturation temperatures at the recovery temperature in the exchanger (6.1) and at the saturation temperature of the working fluid in the secondary of the heat recovery exchanger (6.2) in the boiler are adapted. This configuration has the important advantage of facilitating an approach:

[0183] - multi-exchangers to recover the heat available from several sources at the level of the LV loop and to be able to reinject the low temperature heat;

[0184] - multi-exchangers to take advantage of the heat at the required temperature levels on the HT loop as well as possibly recovering heat on this same HT loop if the temperature levels of the sources are adequate, as shown in figures 10, 14 and 15.

[0185] Furthermore, this configuration is particularly suitable when the steam pressure inside the boiler (7) at the saturation temperature of the working fluid corresponding to the recovery temperature is not achievable under satisfactory conditions. Thus, the heat pump (8) can directly supply the boiler (7) via its condenser, or via a High Temperature heat recovery loop, called the HT loop (25.2).

[0186] Like the LV loop, this HT recovery loop is a loop of water, glycolated water or thermal fluid, allowing the heat from the heat pump condenser to be conveyed to the boiler (7) and possibly to the exchangers (34). This loop has the advantage of being able to act as a heat sink, as shown in Figure 14, with high temperature heat sources which can supply it directly via exchangers (32).

[0187] An advantageous characteristic of the invention lies in the ability to improve its performance at reduced loads: the compressor(s) (11, 11.1, 11.2, 11.3) are regulated according to the drying needs defined by the drying kinetics of the products entering the drying chamber, and the online measurements of parameters such as humidity, while maintaining a depression inside the boiler (7). The incoming humidity of said products can for example vary according to the seasons, or the recipes, implying a necessary online adaptation of the dryer to the drying need; which the invention allows by consuming less per unit of evaporated water when the drying installation is at low load by reducing the compression ratios of the steam compressors, and therefore their consumption per unit of evaporated water.

[0188] Typically, the invention makes it possible to optimize the drying performance when the tonnage of evaporated water is lower than the sizing value of the dryer, which is very frequently the case in real life by initial oversizing and operation on various products of which the sized product is the most humid. Thus, a regulated pressure increase of the steam from the boiler (7) via the compressors (11, 11.1, 11.2, 11.3) allows:

[0189] - to reduce the temperatures of the drying fluid when the latter does not require too high a temperature;

[0190] - to reduce the temperature in the means of additional heat supply by injector exchangers; - to obtain reduced energy consumption when drying needs are lower, since the steam pressures are lower, generating electricity consumption of the compressors which is also lower.

[0191] This management of the compressor(s) can be carried out by online measurement of the humidity of the product or by variation of temperature of the wet product to be dried at different points for example. This temperature measurement can be carried out by any means of measurement and acquisition, for example infrared measurement or by means of thermal cameras with image processing, integrated into the drying chamber, depending on the dryer configurations and technologies adapted to the temperatures, humidity and potential fouling, possibly with a presence outside the drying chamber with a window if the technologies allow it.

[0192] Figure 8 illustrates the installation according to the invention equipped with a first compression stage, in this case consisting of four thermocompressors (24), located upstream of the compressors (11.1, 11.2), which make it possible to compress the very low pressure steam coming from the boiler, to a few tens of millibars absolute, therefore to high mass volumes, in potentially satisfactory installation conditions. In this example, the thermocompressors use higher pressure steam, coming from compression by the compressor (11.1), to compress the steam coming from the boiler (7), from the outlet of the first thermocompressor, the second thermocompressor, then the third thermocompressor.It should be noted that this configuration currently involves technical challenges with water as a refrigerant, given the significant volume flow rates that this represents, the size that this can represent and above all the current low performance of thermocompressors on the market.

[0193] This configuration nevertheless has the advantage of reducing the space requirements for mechanical compressors that must operate with high volume flow rates for these low pressure levels. Static thermocompressor-type compressors limit space requirements, with elongated designs that can be positioned lengthwise along the boiler, or in a vertical orientation if ceiling heights allow for indoor installation.

[0194] This figure also represents expansion, purge or calibrated orifice type organs (37, 37.1, 37.2) which are accessory organs making it possible to ensure the separation between vapor phase and liquid phase in the vapor / condensate network linked to the boiler (7) and which contribute to maintaining a depression in the boiler (7).

[0195] Figure 8 includes a means for degassing the make-up water and / or discharging the incondensables (35) from the steam, making it possible to extract the air which may have infiltrated into the steam circuits of the installation or present in the make-up water at low temperature. This means for discharging the incondensables may be a vent, an air vent, or any other means making it possible to ensure said function. Also shown in this diagram is the water make-up (36) which makes it possible to compensate for any losses in the water / steam circuit linked to sealing defects, opening of the safety valves, by means of degassing, to the possible use of steam from the direct circuit or to the failure to connect certain purge lines.

[0196] The initial vacuum device, if necessary, and the vent(s) are used as strictly necessary in order to also use the make-up water injection device as little as possible. Indeed, the reality of water / steam installations in industry leads to having circuits that are not completely sealed, which implies non-condensables and a potential need to evacuate the non-condensables. Figure 19 illustrates an example of management of non-condensables (35) by a vent on a steam collector (29). In addition, there are certain losses of working fluid linked to dry seals, poorly tightened flanges or passage to the valves for example. Finally, certain steam requirements require the use of steam injection, leading to a lack of condensate returns in the water / steam cycle.These 3 reasons combined imply the need to install a water make-up as described, with degassing and preliminary water treatment according to the industrial water qualities of the sites, the make-up water flow rates and the recommendations of the equipment suppliers. Figure 9 illustrates yet another variant of the installation of the invention. In this one, a heat storage in the form of a hot water tank (26) is implemented on the HV loop (25.2). This heat storage allows a charge during the periods when energy is available on the LV loop (25.1) and the heat pump (8) has the necessary power to provide the energy for the drying process and the loading of the water storage. The tank (26) discharges via a set of valves and pumps, when the power on the LV loop (25.1) is no longer sufficient to supply the injector exchangers.This allows the system to be resilient during those phases where the coupling between heat recovery and heat use is not ensured. In other words, the heat storage thus achieved ensures continuity of heat supply to the installation, including during short-term interruptions in the supply of calories to the recovery exchangers.

[0197] Figure 10 illustrates a variant of Figure 7 in which additional exchangers (40) are installed on the LV loop (25.1) in order to supplement the energy input of the heat recovery exchanger (6.1) on the extraction drying fluid, and thus facilitate the reuse of waste heat in industry by means of the invention described here. The additional exchangers (40) are connected in series, in parallel or in series-parallel as in Figure 10, depending on the temperature, simultaneity, power levels and the priority defined on each of these heat sources that it is desired to exploit.

[0198] These additional exchangers (40) are capable of recovering energy from any heat source at sufficient temperatures presenting a technical and economic interest. These additional exchangers can also be heat injector exchangers making it possible to recover the energy from the LV loop at low temperature, without the need for electrical consumption.

[0199] Figure 11 illustrates a variant of Figure 3, integrating a steam accumulator (28) which is a reservoir with a liquid / steam phase equilibrium at the pressure in which the steam is injected into this steam accumulator (28). The latter makes it possible to smooth out the peaks in demand of the injector exchangers implemented by loading and unloading said accumulator which tends to: - drop in pressure, therefore vaporize part of the water contained, when the process requires a lot of steam therefore destocking the accumulator;

[0200] - increase the pressure, and therefore the temperature, when the process requires less steam, therefore store the accumulator.

[0201] The inertial function performed by this steam accumulator (28) can prove advantageous, in order to avoid starting / stopping the compressors (11.1 and 11.2), which are mechanical components, and which could become problematic in the process for reasons of mechanical fatigue, inertia of the machines and longevity of the installations.

[0202] Figure 12 illustrates a variant of Figure 3 in which a thermocompressor (30) makes it possible to mix steam from a first compressor (11.1) and steam from a second compressor (11.2) in order to supply the heat injector exchanger (14.1) with steam at an intermediate pressure between the pressures of the steam collector (29) and the steam at the outlet of the second compressor (11.2). This thermocompressor makes it possible to optimize the energy consumption relating to the pressure increase by providing the desired pressure to the consumer.

[0203] Figure 13 illustrates a variant of Figure 3 in which the steam, superheated by the non-isentropic compression at the compressor (11.1), is desuperheated at the outlet of the latter by injection of working fluid (water in this example) by desuperheaters (31.1 and 31.2), in particular if this desuperheating is not provided by the compressors (11.1 and 11.2) in the design of the latter, which is sometimes the case to limit the temperatures reached in the compressors. The desuperheaters (31.1, 31.2) are supplied with working fluid by the condensate circuit (16) and the condensate flow rate is regulated by a control valve (41) arranged on the condensate circuit, or a pump on speed variation. The control of the valve (41), or the pump, makes it possible to divert a portion of the condensate circuit (13, 16, 19) towards the desuperheater(s) (31.1, 31.2, 31.3), by limiting the fluid returning to the boiler (7).

[0204] Figure 14 illustrates a variant of Figure 7 in which additional exchangers (32), mounted on external heat sources that are to be recovered, are installed on the HT loop (25.2) in order to supplement the energy supply from the condenser of the heat pump (8), and thus facilitate the reuse of high-temperature waste heat in industry by means of the innovation described in the present invention. The additional exchangers (32) are connected in series, in parallel or in series-parallel as in Figure 14, depending on the temperature, power, simultaneity and priority levels defined on each of these sources. These exchangers can also be injector exchangers to recover energy at the temperature level of the HT loop.

[0205] Figure 15 illustrates a variant of Figure 7 in which exchangers (33, 34) are integrated into the BT (33) and HT (34) loops in order to allow the recovery of low-temperature calories from the inlet drying fluid (4).

[0206] Figure 16 illustrates a variant of Figure 3 in which a heat exchanger (38) is positioned on the discharge circuit (5), upstream of the heat recovery exchanger (6) in order to preheat the inlet drying fluid (4).

[0207] Figure 17 illustrates a variant of Figure 3 in which the heat recovery exchanger (27), arranged in the boiler (7), is mounted on an external heat recovery circuit (not shown), rather than on the evacuation circuit (5). This heat recovery circuit can be linked to any heat that it is desired to recover.

[0208] Figure 18 illustrates a variant of Figure 3, which includes an additional injector exchanger (39) subject to the same conditions as the heat injector exchangers (12, 14.1, 14.2) and making it possible to use the steam produced by the installation for the benefit of other processes or installations, such as heating of premises, etc.

[0209] Figure 19 illustrates a variant of Figure 17 in which one or more vents allow the removal of incondensables (35). In this example these vents are placed on a steam collector (29).

[0210] Figure 20 illustrates a variant in which the installation comprises a single heat injector exchanger (14), arranged in the drying enclosure (1). Figure 21, in the same way as Figure 13, illustrates a variant in which the steam, superheated by the compressors (11.1, 11.2, 11.3) (there are three compressors in series in this illustrative example), is desuperheated at the outlet of the compressors, by injection of working fluid (water in this example) by desuperheaters (31.1, 31.2, 31.3). The desuperheaters (31.1, 31.2, 31.3) are supplied with working fluid by the condensate circuit.

[0211] In this particularly advantageous example, the water flow rate is regulated by a regulating element arranged between the desuperheater(s) (31.1, 31.2, 31.3) and the boiler 7. This regulating element is for example a valve (see for example the valve illustrated on the condensate circuit 13 in figure 21, or the valve 41 in figure 21) arranged on the condensate circuit (13, 16, 19), or a pump, and makes it possible to divert a portion of the condensate circuit (13, 16, 19) towards the desuperheater(s) (31.1, 31.2, 31.3).

[0212] The installation according to the invention constitutes an essential advance compared to those known from the prior art. It has a certain number of advantages, among which we can cite:

[0213] - a very significant increase in the energy performance of drying without degrading the quality of drying, making it possible to move towards the Minimum Exergy Requirement through the electrification of dryers, making it possible to divide energy consumption by a factor of 2 to more than 10;

[0214] - the extremely significant decarbonization potential of this arrangement, particularly in countries where electricity is already low-carbon but ultimately in all countries of the world;

[0215] - complete recovery (closed loop) or a large part of the water extracted from the products to be dried, making it possible to improve the water efficiency of drying operations;

[0216] - the implementation of a limited number of components, and making it possible to limit the lengths of heat transport networks with a process largely self-powered by equipment present at the installation level;

[0217] - the implementation of technological building blocks that are now perfectly mastered and implemented to achieve this objective, with mature technologies; - the use of a potential working fluid that is water, already present as an energy vector in industry (therefore reassuring), facilitating filling in the event of a leak and non-polluting The limitation of the entropy created, because the object of the innovation is to recycle energy, without burning energy that is stored in the Earth's subsoil as a fossil fuel. Fossil fuel whose combustion increases the energy injected into our atmosphere which must be limited in these times of global warming;

[0218] - The hybridization of the drying process with continuous operation by this innovation and punctually by the means of start-up / backup / emergency / load shedding, in order to relieve the electricity network during periods of tension on the latter's supply. This load shedding capacity is, and will become, a significant advantage in the years to come with the increase in electricity from intermittent sources.

[0219] The installation thus allows substantial gains compared to known installations of the prior art, particularly in terms of energy consumption and therefore greenhouse gas emissions, and water consumption.

Claims

CLAIMS 1. Installation for drying a wet product using drying fluid, comprising a drying enclosure (1) within which the wet product to be dried (2) and the drying fluid ensuring the drying pass, said enclosure comprising at least one introduction circuit (4) for the inlet drying fluid, and at least one evacuation circuit (5) for the drying fluid resulting from the exchange of water and energy with the wet product to be dried, characterized in that the installation comprises: • at least one boiler (7) operating with a working fluid adapted to produce steam in a steam circuit (10), and comprising: ° a tank containing the working fluid in a liquid / vapor phase equilibrium at a pressure lower than atmospheric pressure in nominal operation, connected to the steam circuit (10); ° a boiling exchanger (6, 6.2, 27) adapted to heat the working fluid of the boiler (7), mounted on a heat recovery circuit and arranged in said tank; • at least one compressor (11, 11.1, 11.2, 11.3) arranged on the steam circuit, capable of increasing the pressure, and therefore the temperature, of the steam circulating in the steam circuit (10), and adapted to maintain the boiler tank under vacuum; • at least one heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2) capable of condensing the steam from said at least one compressor (11), and of ensuring a heat transfer to a heat injection circuit.

2. Installation for drying by drying fluid of a wet product according to claim 1, characterized in that it further comprises a condensate circuit (13, 16, 19) adapted to return to the boiler (7) the condensates resulting from the condensation of the steam in the at least one heat injector exchanger (12, 14).

3. Fluid drying installation for drying a wet product according to one of the preceding claims, characterized in that it comprises a working fluid top-up device.

4. Fluid drying installation for drying a wet product according to claim 3 when it depends on claim 2, characterized in that the working fluid top-up device is adapted to add condensed water (23) from the drying fluid discharge circuit (5) to the condensate circuit (13, 16, 19).

5. Installation for drying a wet product using a drying fluid according to one of claims 2 to 4, characterized in that the condensate circuit (13, 16, 19) comprises at least one condensate collector (19).

6. Fluid drying installation for drying a wet product according to claim 5 when it depends on one of claims 3 or 4, characterized in that the working fluid top-up device is arranged in the condensate collector (19).

7. Installation for drying a wet product using a drying fluid according to one of claims 5 or 6, characterized in that the condensate collector (19) comprises a device (35) for degassing and / or discharging incondensables.

8. Fluid drying installation for drying a wet product according to any one of the preceding claims, characterized in that the heat recovery circuit on which the boiling exchanger (6, 6.2) is mounted comprises a heat source constituted by the drying fluid discharge circuit (5), the boiling exchanger (6.2) being arranged on the drying fluid discharge circuit (5), or on an intermediate heat transfer loop from the drying fluid discharge circuit (5).

9. Fluid drying installation for drying a wet product according to any one of the preceding claims, characterized in that the heat recovery circuit on which the boiling exchanger (6, 6.2) is mounted comprises at least one exchanger external to the dryer.

10. Fluid drying installation for drying a wet product according to any one of the preceding claims, characterized in that the heat recovery circuit on which the boiling exchanger (6, 6.2) is mounted comprises an intermediate heat transfer loop comprising: a heat recovery exchanger (6.1) arranged on a heat source; and the boiling exchanger (6.2).

11. Fluid drying installation for drying a wet product according to claim 10, characterized in that the intermediate heat transfer loop comprises a low temperature recovery loop (25.1) with a heat recovery exchanger (6.1) arranged on said heat source, a high temperature recovery loop (25.2) on which the boiling exchanger (6.2) is arranged, and a heat pump (8) adapted to raise the temperature of the low temperature recovery loop (25.1) to reinject the heat into the high temperature recovery loop (25.2).

12. Installation for drying by drying fluid of a wet product according to claim 10 or 11, characterized in that the low temperature recovery loop (25.1) further comprises at least one injector exchanger (27) external to the dryer.

13. Installation for drying by means of a drying fluid for a wet product according to claim 11 or 12, characterized in that the high temperature recovery loop (25.2) further comprises at least one injector exchanger (32) external to the dryer.

14. Installation for drying by means of a drying fluid of a wet product according to one of claims 11 to 13, characterized in that the loop of high temperature recovery (25.2) further comprises at least one external heat recovery exchanger (32) to the dryer.

15. Installation for drying by drying fluid of a wet product according to one of claims 11 to 14, characterized in that it further comprises a hot water storage tank (26) in communication with the high temperature recovery loop.

16. Installation for drying by means of a drying fluid for a wet product according to any one of the preceding claims, characterized in that said at least one heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2) is adapted to supply heat to the drying enclosure.

17. Installation for drying by means of a drying fluid for a wet product according to claim 16, characterized in that said at least one heat injector exchanger (14, 14.1, 14.2) is positioned within the drying enclosure (1).

18. Drying installation using drying fluid for a wet product according to one of claims 16 or 17, characterized in that said at least one heat injector exchanger (12, 12.1, 12.2) is positioned within the introduction circuit (4) of the inlet drying fluid.

19. Installation for drying by drying fluid of a wet product according to one of the preceding claims, characterized in that said at least one heat injector exchanger (12, 12.1, 12.2) is positioned on an external heat injection circuit.

20. Installation for drying by drying fluid of a wet product according to any one of the preceding claims, characterized in that it further comprises at least one means capable of initiating the operation of the boiler (7) by supplying third-party heat.

21. Installation for drying by means of a drying fluid for a wet product according to any one of the preceding claims, characterized in that the at least one compressor (11) is regulated as a function of at least one parameter representative of the humidity of the wet product to be dried.

22. Installation for drying by drying fluid of a wet product according to any one of the preceding claims, characterized in that it further comprises a vacuum member (9) of at least one boiler (7).

23. Installation for drying by drying fluid of a wet product according to any one of the preceding claims, characterized in that it further comprises a steam accumulator (28) downstream of the at least one compressor (11).

24. Fluid drying installation for drying a wet product according to any one of the preceding claims, characterized in that the at least one compressor comprises a set of compressors arranged in series and / or in parallel.

25. Fluid drying installation for drying a wet product according to claim 24, characterized in that it comprises two compressors (11.1, 11.2) in series, and in that it further comprises at least one thermocompressor (30) supplied with steam from the steam coming from the first compressor (11.1) and the steam coming from the second compressor (11.2), so as to supply the at least one heat injector exchanger (14.1) with steam at an intermediate pressure between the pressures of the steam at the outlet of the first compressor (11.1) and the second compressor (11.2).

26. Installation for drying by means of a drying fluid for a wet product according to any one of the preceding claims, characterized in that it further comprises desuperheaters (31.1, 31.2) capable of injecting liquid working fluid into the steam leaving the compressors (11, 11.1, 11.2, 11.3).

27. Installation for drying by drying fluid of a wet product according to any one of the preceding claims, characterized in that it comprises a first compression stage consisting of one or more thermocompressors (24) located upstream of the at least one compressor (11, 11.1, 11.2).

28. Installation for drying a wet product using drying fluid according to one of the preceding claims, characterized in that it comprises a heat exchanger (38) on the drying fluid discharge circuit (5), suitable for preheating the inlet drying fluid.

29. Drying installation using drying fluid for a wet product according to any one of the preceding claims, characterized in that it operates in a closed loop, and in that the inlet drying fluid comes from the extraction drying fluid from the drying enclosure (1), which is dried by means of the boiling exchanger (6), then reheated by means of the at least one heat injector exchanger (12).

30. Installation for drying a wet product using a drying fluid according to one of claims 1 to 29, comprising a plurality of drying enclosures (1.1, 1.2, ..., 1.n), mounted in series, the most upstream enclosure (1.1) receiving the product to be dried having the highest degree of humidity, and the most downstream enclosure (1.n) receiving the product to be dried (2) after transit through the upstream enclosures, in which: • the inlet drying fluid (4.i) conveyed within the enclosure (1.i) upstream relative to the direction of progression of the wet product to be dried comes from the drying fluid loaded with moisture (4.i+1) from the drying enclosure (1.i+1) mounted immediately downstream of said upstream enclosure after reheating by a heat injector exchanger (12.i), i being an integer between 1 and n-2, • the steam from at least one boiler and the pressure (and therefore the temperature) of which has been increased using a main compressor (11.1), is conveyed as a priority to a heat injector exchanger provided in the drying fluid introduction circuit of the most upstream enclosure (1.1), • part of this steam is subjected to compression at the level of an additional compressor (11.2) to convey a higher pressure steam to the level of a heat injector exchanger (12.1) arranged within a circuit for introducing drying fluid into said downstream enclosure with possible supply of new drying fluid for mixing (20.1); this compression process towards the downstream enclosure being capable of occurring 1, 2, ..., n-2 times, • the drying fluid of the enclosure (1 .n-1) comes from the drying fluid leaving the enclosure (1.n), preheated by the hot product to be dried coming from the enclosure (1.n-1), which has cooled in the enclosure (1.n) by giving up its heat to the drying fluid and possibly by drying the drying fluid (4. n-1) by hygroscopicity of the product, • and the inlet drying fluid of the enclosure (1.n), furthest downstream, consists of dry drying fluid, possibly vapors dried by the recovery exchanger (6) in the case of closed loop operation on the drying fluid.

31. Fluid drying installation for drying a wet product according to any one of the preceding claims, characterized in that the working fluid of the boiler (7) is water.

32. Fluid drying installation for drying a wet product according to one of claims 5 to 7, characterized in that the condensate collector (19) is maintained in a liquid / vapor phase equilibrium, with the vapor part connected to the inlet of said at least one compressor (11, 11.1, 11.2, 11.3), or to said at least one heat injector exchanger (14.1) or to a heat recovery exchanger (6.1).

33. Installation for drying by means of a drying fluid for a wet product according to any one of claims 2 to 32, characterized in that it comprises a sub-cooler exchanger (15) arranged downstream of the at least one heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2), on the condensate circuit, and adapted to preheat the heat injection circuit.

34. Drying installation using a drying fluid for a wet product according to claim 33, characterized in that the sub-cooler exchanger (15) is adapted to heat the introduction circuit (4) of the inlet drying fluid.

35. Method for heating a fluid to be heated, characterized in that it comprises the following steps: - heating the working fluid of a boiler (7) which comprises a tank containing this working fluid in a liquid / vapor phase equilibrium at a pressure lower than atmospheric pressure, and producing steam in a steam circuit (10), thanks to a boiling exchanger (6, 6.2, 27) mounted on a heat recovery circuit and arranged in said tank; - increasing the pressure, and therefore the temperature, of the steam circulating in the steam circuit (10), and maintaining a depression in the boiler tank (7) using at least one compressor (11, 11.1, 11.2, 11.3) arranged on the steam circuit (10); - condensing the steam from said at least one compressor (11, 11.1, 11.2, 11.3), and ensuring the heating of said fluid to be heated, using at least one heat injector exchanger (12, 12.1, 12.2, 14, 14.1, 14.2).

36. Method according to claim 35, characterized in that the step of heating the working fluid of the boiler (7) is carried out with an intermediate heat transfer loop by recovering heat from a heat recovery exchanger (6.1) arranged on a heat source; and transferring it to the boiling exchanger (6.2).

37. Method according to claim 36, characterized in that the step of heating the working fluid of the boiler (7) is carried out by recovering heat from a heat recovery exchanger (6.1) arranged on said heat source, with a low temperature recovery loop (25.1) and a high temperature recovery loop on which the boiling exchanger (6.2) is arranged; and by increasing the temperature of the high temperature recovery loop (25.2) relative to the low temperature recovery loop (25.1) using a heat pump (8).

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