Plant and method for drying a material of plant origin

Abstract

A plant (1) for drying a material of plant origin, in particular of the smoking article industry, configured to operate continuously and comprising a drying unit (100) for a material of plant origin, configured to dry a first predetermined amount of material by means of a second predetermined amount of process fluid so as to obtain a third predetermined amount of dried material and a fourth predetermined amount of used process fluid. A plant (1) comprises a discharge line (40) configured to discharge a discharge portion of the fourth predetermined amount of used process fluid from the drying unit (100) towards a cleaning network (50) for the used process fluid. A plant (1) comprises a heat recovery unit (200), configured to promote a heat exchange between said at least one discharge portion and a heat recovery fluid.

Description

[0001] DESCRIPTION

[0002] PLANT AND METHOD FOR DRYING A MATERIAL OF PLANT ORIGIN.

[0003] Technical field

[0004] The present invention relates to a plant and a method for drying a material of plant origin, in particular for the smoking article industry.

[0005] Background art

[0006] In the relevant field of the present invention, systems for drying tobacco are known, based on the use of a process fluid in the gaseous state, typically hot air or a mixture of air and superheated water vapor, allowing the treatment of the tobacco in order to dry it and increase the volume thereof.

[0007] Such drying systems can be configured to operate in an open cycle or in a recirculation cycle.

[0008] According to the first type, the systems are supplied with a predetermined amount of material to be dried, and with a corresponding amount of fresh process fluid. Once the tobacco has been treated and has reached the desired volume, it is separated from the used process fluid: the dried tobacco is conveyed into a respective dedicated collection line while the used process fluid is in turn completely discharged into a respective discharge line for subsequent external treatments.

[0009] According to the second type, once the tobacco has been treated and has reached the desired volume, only a discharge portion of the used process fluid is discharged into the discharge line for subsequent external treatments. The remaining part of this used process fluid is in fact recycled within the system. Therefore, in usual operating cycles, only a part of fresh process fluid is fed into the plant. The discharge of a portion of the used process fluid is necessary to maintain a correct pressure balance in the circuit and to ensure that the system operates efficiently. Indeed, during the operations, part of the moisture content initially present in the material is transferred to the process fluid, increasing the water component thereof and thus increasing the internal pressure of the system. This discharge further allows removing contaminants that can have been generated during the drying process.

[0010] In the relevant field of the present invention, there is a growing need to reduce energy consumption, since tobacco drying plants are known to be characterized by a high energy demand. This need results from the drying process requiring the use of large amounts of energy.

[0011] In the relevant field of the present invention, further difficulties associated with the disposal of the used process fluid remain, which fluid, at the end of the drying cycle, has a significantly high temperature. This not only causes issues related to heat emission control, but also the need to adopt cooling or heat dissipation systems (e.g., cooling towers), which in turn require further energy consumption.

[0012] In such a context, the technical task of the present invention is thus to provide a plant and a method for drying a material of plant origin, in particular of the smoking article industry, which are configured to reduce the overall energy consumption during the drying process, while maintaining an effective drying of the treated material.

[0013] Disclosure of the invention

[0014] It is thus the object of the present invention to provide a plant and a method for drying a material of plant origin, in particular of the smoking article industry, which are capable of improving the overall efficiency of the system while minimizing waste and environmental impact resulting from the process.

[0015] It is a further object of the present invention to provide a plant and a method for drying a material of plant origin, in particular of the smoking article industry, which are capable of optimizing the use of the process fluid.

[0016] The specified technical task and the specified object are substantially achieved by a plant for drying a plant based material, in particular of the smoking article industry, according to the present invention.

[0017] The plant is preferably configured to operate in a continuous cycle.

[0018] The plant comprises a drying unit for drying the aforesaid material of plant origin by means of a process fluid.

[0019] The term "material of plant origin" refers to any substance derived from plants that can be used in the production of smoking articles. This concept is broad and comprises not only tobacco, which is the main material used in the production of cigarettes, cigars, and other smoking articles, but also other plant substances that can be processed and used as alternatives, such as rapeseed, hemp, straw or other varieties, cellulose or cellulose derivatives, aromatic leaves, or others, for example.

[0020] Furthermore, the term “process fluid” refers to a fluid used to implement the drying process. In particular, the process fluid, in use, is in the gaseous state and can be a mixture of air and water vapor, which is used for heating, partially drying and expanding the aforesaid material, or hot air. This process fluid plays a crucial role in transferring thermal energy to the tobacco, causing the evaporation of the internal moisture and the expansion of the plant cells, which is necessary to obtain the desired final product.

[0021] In a first embodiment, the drying unit is in the form of a drying tower and uses a process fluid in the form of vapor or hot air.

[0022] In a second embodiment, the drying unit is in the form of a drying cylinder in which the material to be dried is caused to remain while being brought into contact with hot air and preferably rotated. Such a unit can operate continuously or in batch.

[0023] In a third embodiment, the drying unit is in the form of a drying support of the vibrating type, preferably configured as a porous, mesh, or net support to promote the passage of hot air therethrough, so as to dry the material arranged resting on the drying support.

[0024] In a fourth embodiment, the drying unit is in the form of a linear conveyor, in particular a belt conveyor, a so-called “toaster”, performing a progressive drying of the material arranged resting thereon by means of hot air.

[0025] The drying unit is configured to bring into contact a first predetermined amount of material with a second predetermined amount of process fluid so as to obtain a third predetermined amount of dried material and a fourth predetermined amount of used process fluid.

[0026] The term "used process fluid" means the gaseous fluid which results at the end of the material drying process. This process fluid, depending on the type of process performed, mainly consists of a mixture of water vapor and air or of air, but has a greater fraction of water compared to the fresh process fluid, since it includes the moisture evaporated during the treatment of the material. Furthermore, the used process fluid can contain a variation in pollutants resulting from the degradation of the material, which can include volatile organic compounds and other residual particles. In addition, in the context of a plant operating continuously, the term "amount" should be interpreted as the flow rate, i.e., a measurement of the amount of material or process fluid which passes through a given point of the plant per unit of time. This results in a mass flow rate or volume flow rate depending on the nature of the substance considered. For example, the "amount" can be expressed as mass flow rate (kg / s or kg / h). Therefore, when reference is made to a "predetermined amount", it means a flow rate established at the design or operation stage, which is kept constant or adjusted over time.

[0027] It is apparent that, during operations, the aforesaid amounts are constantly balanced. In particular, the sum of the first predetermined amount and the second predetermined amount is equal to the sum of the third predetermined amount and the fourth predetermined amount.

[0028] The plant comprises a material feeding line configured to feed the aforesaid first predetermined amount of material into the drying unit.

[0029] The plant comprises a process fluid feeding line configured to feed a second predetermined amount of process fluid.

[0030] The plant therefore comprises a collection line configured to discharge the third predetermined amount of dried material from the drying unit. In other words, the collection line is configured to collect the dried material.

[0031] The plant comprises a discharge line configured to discharge at least one discharge portion of the fourth predetermined amount of used process fluid from the drying unit towards a cleaning network for the used process fluid.

[0032] The term “cleaning network” refers to a system, of a technology known in the prior art, intended for purifying the used process fluid or at least one component thereof.

[0033] Furthermore, the term “at least one discharge portion” means that the used process fluid discharge line can discharge the entire fourth predetermined amount of used process fluid from the drying unit or, preferably, it means that the used process fluid discharge line can discharge only a portion of the fourth predetermined amount of used process fluid.

[0034] In other words, according to a first example of implementation, the plant can operate according to a substantially open cycle. The discharge line is configured to discharge all the entire fourth predetermined amount of used process fluid from the drying unit, whereas the feeding line is configured to feed the entire second predetermined amount of fresh process fluid from the outside into the drying unit. In other words, in such an embodiment, the feeding line is a line configured to draw fresh process fluid from the outside and feed it into the feeding unit.

[0035] According to a second, preferred example of implementation, the plant is instead configured to operate according to a recirculation cycle. The discharge line is configured to discharge only a discharge portion of the fourth predetermined amount of used process fluid. The plant comprises a recirculation line, configured to recirculate a part of the fourth predetermined amount of used process fluid from the drying unit to the feeding line, and a make-up line configured to feed a make-up portion of process fluid to the feeding line. Obviously, the make-up line is thus configured to feed only a portion of the second predetermined amount of fresh process fluid from the outside into the drying unit. The recirculation line and the make-up line thus converge into the feeding line: therefore, in such an embodiment, the feeding line is defined by an inner section of the plant. Irrespective of the embodiment adopted, as previously described, during the operating cycles, the aforesaid amounts are constantly balanced.

[0036] Advantageously, according to an aspect of the present invention, the plant comprises a heat recovery unit configured to promote a heat exchange between the at least one discharge portion and a heat recovery fluid.

[0037] The Applicant has hound that recovering part of the thermal energy of the used process fluid, which would otherwise be dissipated, is a considerable advantage in terms of overall energy efficiency. Using a heat recovery unit, the residual energy in the used process fluid can be transferred to a heat recovery fluid allowing it to be used for various purposes, ranging from the heating of other processes to the optimization of the internal operations of the plant. This results in a decrease in the overall energy consumption, while maintaining the effectiveness of the drying process. Such an approach further contributes to reducing the environmental impact of the system, minimizing energy waste and optimizing the use of thermal resources.

[0038] According to an aspect, the thermal energy recovered from the at least one discharge portion of the used process fluid can be at least partially used for preheating the fresh process fluid being fed to the drying unit. In other words, the term “heat recovery fluid” means, in this solution, the process fluid entering in the process fluid feeding line.

[0039] With reference to the embodiment in which the plant operates according to an open cycle, the heat recovery fluid is thus the entire second predetermined amount of process fluid. With reference instead to the embodiment in which the plant operates according to a recirculation cycle, the heat recovery fluid is instead the process fluid flowing into, or towards, the make-up line. In other words, the heat recovery fluid is only the make-up portion of the second predetermined amount of process fluid.

[0040] Irrespective of the embodiment, the recovered thermal energy can be used to heat and promote a liquid / gas phase change of the process fluid, so as to obtain saturated water vapor or hot air to be fed to the drying unit.

[0041] Advantageously, the use of the thermal energy recovered from the used process fluid for the preheating, and possibly the phase change, of the process fluid entering in the process fluid feeding line offers significant advantages in terms of energy efficiency and reduction in operating costs. By providing heat to the process fluid entering in the process fluid feeding line, the energy demand to bring the fluid to the desired operating temperature and / or to the desired operating state is reduced, thus decreasing the primary energy input required by the system. This not only increases the overall efficiency of the process, but also allows reducing the consumption of fuels or other energy sources, resulting in the reduction in operating costs. Furthermore, the recovery of the thermal energy from the used fluid contributes to reducing the dispersion of heat to the environment, thus improving the thermal balance and the sustainability of the plant.

[0042] According to an aspect, the thermal energy recovered from the used process fluid can be directly used for predefined purposes or after conversion to optimize the use thereof. In other words, the thermal energy recovered from the used process fluid can be directly transferred to the heat recovery fluid, or intermediate steps of transferring and / or transforming the recovered thermal energy can be included before transfer to the heat recovery fluid. For example, according to the second methodology, the heat recovery unit can comprise a closed heat transfer circuit in which a recirculating carrier fluid flows: the heat recovery unit is thus configured to promote a first heat exchange between the at least one discharge portion of the used process fluid and the recirculating carrier fluid and a second heat exchange between the recirculating carrier fluid and the heat recovery fluid. The nature and functionality of the recirculating carrier fluid will be clarified in detail below in the present description.

[0043] Advantageously, therefore, as is known in the relevant field of the present invention, the temperature of the used fluid is relatively high, which gives the recovered energy an excellent quality. This allows fully utilizing the thermal potential, thus ensuring a high efficiency in the energy transfer and usage. Advantageously, the use of high-quality thermal energy allows improving the overall energy efficiency of the system, reducing the primary energy demand and thus the operating costs. The possibility of transforming the recovered energy for a more effective use offers greater flexibility in operations, allowing the system to be adapted to the various operating needs. Furthermore, this approach contributes to minimizing heat losses and improving the environmental sustainability of the plant, promoting a more responsible management of energy resources.

[0044] Hereinafter, for explanation and thus not limiting purposes, three possible embodiments of the plant according to the present invention will now be described, with particular attention to the structure of the heat recovery unit. Such examples of implementation of the heat recovery unit can be implemented indifferently for a drying plant operating in an open cycle as well as for a drying plant operating in a recirculation cycle.

[0045] Furthermore, for simplicity of exposition, the examples of implementation now described relate to the embodiments in which the heat recovery fluid is the process fluid entering in the process fluid feeding line.

[0046] According to a first example of implementation, the heat recovery unit comprises a heat exchanger, configured to transfer the thermal energy directly from the at least one discharge portion of the used process fluid to the process fluid entering in the process fluid feeding line. Structurally, the heat exchanger is configured to receive the aforesaid discharge line, which is configured to cause the at least one discharge portion of the used process fluid to flow through the heat exchanger. In addition, the heat exchanger is configured to receive the aforesaid feeding line or the make-up line for fresh process fluid, which is configured to cause the fresh process fluid entering in the drying unit to flow through the heat exchanger. The at least one discharge portion of the used process fluid transfers heat directly to the process fluid entering in the drying unit. Advantageously, such an embodiment is very simple and potentially very cost-effective.

[0047] According to a second example of implementation, the heat recovery unit comprises the aforesaid closed heat transfer circuit in which a recirculating carrier fluid flows: the heat recovery unit is configured to promote a first heat exchange between the at least one discharge portion and the recirculating carrier fluid, and a second heat exchange between the recirculating carrier fluid and the heat recovery fluid.

[0048] In particular, the closed heat transfer circuit can be configured to operate by means of a refrigeration cycle, preferably as a heat pump (operating, for example, with two stage vapor compression or with an inverted Stirling cycle). In this case, the recirculating carrier fluid is a coolant suitable for use with phase changes.

[0049] The term “coolant” means a substance that absorbs and releases heat by means of state changes (e.g., from liquid to gas and vice versa) within the aforesaid refrigeration cycle. Specifically, in the case of a heat pump, the coolant transfers heat from the used process fluid to the process fluid entering in the drying unit. The coolant is selected based on the respective heat transfer properties and the capacity to change state at specific temperatures and pressures.

[0050] The closed heat transfer circuit can comprise an evaporator to perform a heat transfer from the discharge portion of the used process fluid, and a condenser to perform a heat transfer to the fresh process fluid entering in the drying unit: structurally, the heat recovery unit comprises a first heat exchanger, configured to transfer thermal energy from the discharge line to the evaporator of the closed heat transfer circuit, so that the thermal energy is transferred from the used process fluid to the coolant, and a second heat exchanger, configured to transfer thermal energy from the coolant in the condenser of the closed heat transfer circuit to the process fluid at the inlet of the drying unit.

[0051] Advantageously, such an embodiment is structurally more complex than the preceding one, but more efficient in the recovery of thermal energy.

[0052] According to a particularly advantageous third example of implementation, the heat recovery unit comprises the aforesaid closed heat transfer circuit in which a recirculating carrier fluid flows, according to the explanation given for the second example of implementation, and further provides for operating the aforesaid first heat exchange using a water circuit. In other words, the heat recovery unit is configured to promote a first heat exchange between the at least one discharge portion and the recirculating carrier fluid, and a second heat exchange between the recirculating carrier fluid and the heat recovery fluid, in which such a first heat exchange is carried out by means of a closed water circuit. Such a water circuit is thus operatively interposed between the discharge line of the used process fluid and the closed heat transfer circuit.

[0053] To this end, the heat recovery unit comprises a first exchanger configured to receive the aforesaid discharge line, which is configured to cause the at least one discharge portion of the used process fluid to flow through the heat exchanger, and to receive the water circuit, so that the used process fluid transfers thermal energy to the water circuit.

[0054] The heat recovery unit comprises a second heat exchanger configured to transfer thermal energy from the water of the water circuit to the evaporator of the closed heat transfer circuit, so as to be transferred to the coolant.

[0055] The heat recovery unit comprises a third heat exchanger configured to transfer thermal energy from the coolant in the condenser of the closed heat transfer circuit to the process fluid entering in the drying unit.

[0056] Advantageously, despite having a relatively complex structure, such an embodiment offers several technical and operating advantages. The high heat recovery efficiency thereof allows significantly reducing the overall energy consumption of the plant, thus optimizing the process heat balance. This results in a decrease in the energy required to heat the process fluid entering in the drying unit, contributing not only to limiting the operating costs, but also to reducing the pollutant emissions and the environmental impact associated with the energy cycle.

[0057] According to an aspect, in the (second and third) embodiments in which the closed heat transfer circuit configured to operate by means of a refrigeration cycle is provided, in particular as a heat pump, the plant can be configured to operate at full capacity solely using the energy introduced by the same closed heat transfer circuit. In other words, the closed heat transfer circuit is configured to provide the heat required to operate the plant at full capacity. At a practical level, the closed heat transfer circuit is capable of providing the process fluid with sufficient heat to reach an operating state by means of the energy supplied by the refrigeration cycle, and in particular by the heat pump, making the installation of a boiler or a dedicated auxiliary vapor generator unnecessary, resulting in a benefit in terms of reduction of the initial investment. Furthermore, in such a configuration, under usual operating conditions, the heat pump recovers the thermal energy from the used process fluid and converts it into vapor or hot air to be fed to the drying chamber, making the presence of a dedicated boiler or a boiler room for producing vapor unnecessary and thus reducing the initial investment in auxiliary equipment. However, it must be expected that, in the start-up step, the closed heat transfer circuit will not be capable of immediately providing the required heat.

[0058] To this end, the plant can comprise an auxiliary heating system, integrated into or connected to the drying unit, and configured to provide at least partially heat to the process fluid during the start-up of the plant.

[0059] According to a first embodiment of the auxiliary heating system, such an auxiliary heating system comprises an electrical resistor and / or a burner installed or connected to the closed heat transfer circuit, or in an intermediate circuit, such as the water circuit. Such a system is dimensioned to provide the minimum heat required for the heat pump to be capable of producing a sufficient amount of heat for the start-up of the plant.

[0060] In a second embodiment, implementable in synergy with the first one, the preheating step is optimized by the injection, exclusively during preheating, of a combination of vapor produced by the heat pump and atomized liquid water introduced into the drying chamber by means of atomizing nozzles. The injected liquid water vaporizes utilizing the heat supplied by the burner or the inner boiler, and by adiabatically mixing with the injected, slightly superheated vapor. This solution allows reducing the instantaneous amount of vapor that the closed heat transfer circuit must provide in the initial step, allowing the heat pump to operate at reduced capacity during preheating, and thus to limit the power required from the electrical integration resistor.

[0061] According to an aspect, irrespective of the specific embodiment, the drying plant is configured to operate in synergy with the energy systems connected to the drying plant. In fact, the drying unit can produce a greater amount of waste heat than the heat demand of the drying process itself. Therefore, the heat recovery unit can be configured to allocate the excess thermal energy to other heat utilities of the industrial plant or to district heating systems.

[0062] It is further noted that, in the examples of implementation described above related to the embodiments in which the heat recovery fluid is the process fluid entering in the process fluid feeding line, it is possible to expect that a portion of residual thermal energy of the used process fluid can be further utilized to transfer thermal energy to a heat recovery fluid configured to transfer heat to utilities outside the plant, as it will be more apparent in the detailed description.

[0063] Furthermore, according to the present invention, the thermal energy recovered from the used process fluid can be entirely directed to a heat recovery fluid configured to transfer the thermal energy to a utility outside the plant, as it will be more apparent in the detailed description.

[0064] The specified technical task and the specified object are substantially further achieved by a method for drying a plant based material, in particular of the smoking article industry, according to the present invention, in particular practicable with the aforesaid plant.

[0065] Further features and advantages of the present invention will become more apparent from the illustrative, and thus non limiting, description of an embodiment of a plant for drying a material of plant origin, in particular of the smoking article industry, according to the invention.

[0066] Brief description of drawings

[0067] Such a description will be given below with reference to the accompanying drawings, provided merely for indicative and thus non-limiting purposes:

[0068] - Figure 1 shows a diagrammatic view of a first embodiment of a plant for drying a plant based material, in particular of the smoking article industry, according to the present invention;

[0069] - Figure 2 shows a diagrammatic view of a second embodiment of a plant for drying a plant based material, in particular of the smoking article industry, according to the present invention;

[0070] - Figure 3 shows a diagrammatic view of a third embodiment of a plant for drying a plant based material, in particular of the smoking article industry, according to the present invention;

[0071] - Figure 4 shows a diagrammatic view of a fourth embodiment of a plant for drying a plant based material, in particular of the smoking article industry, according to the present invention. Detailed description of preferred embodiments of the invention

[0072] With reference to the accompanying Figures, a drying plant for drying a material of plant origin, in particular of the smoking article industry, is indicated by reference numeral 1 . The present invention also relates to a method for drying a material of plant origin, in particular of the smoking article industry, practicable by means of the aforesaid plant 1 .

[0073] As it can be seen in the accompanying Figures, the plant 1 comprises a drying unit 100 for a material of plant origin, configured to dry a first predetermined amount of material by means of a second predetermined amount of process fluid so as to obtain a third predetermined amount of dried material and a fourth predetermined amount of used process fluid.

[0074] The plant 1 comprises a material feeding line 10 configured to feed said first predetermined amount of material into the drying unit 100, a process fluid feeding line 20 configured to feed a second predetermined amount of process fluid, a collection line 30 configured to discharge the third predetermined amount of dried material from the drying unit 100, and a discharge line 40 configured to discharge a discharge portion of the fourth predetermined amount of used process fluid from the drying unit towards a cleaning network 50 for the used process fluid.

[0075] More specifically, the process fluid feeding line 20 has a branching section 21 , in which the process fluid feeding line 20 splits into a first branch 22, configured to feed the process fluid to a drying chamber 101 , and a second branch 23, configured to feed the process fluid to a connection section 24 with the material feeding line 10, in which the process fluid is used as a material transport means in order to supply the drying chamber 101. In particular, the branch 23 comprises a blower device 23a for increasing the pressure and the flow rate of the process fluid. The connection section 24 is instead of the Venturi type, configured to increase the speed of the process flow.

[0076] In the drying chamber 101 , the process of drying the first predetermined amount of material by means of the second predetermined amount of process fluid occurs, thus obtaining the third predetermined amount of dried material and the fourth predetermined amount of used process fluid. The third predetermined amount of dried material and the fourth predetermined amount of used process fluid are discharged from the drying chamber by means of a discharge branch 101 a and are fed to a separation device 102, arranged downstream of the drying chamber 101 . The separation device 102 is configured to separate the third predetermined amount of dried material from the fourth predetermined amount of used process fluid: in particular, the third predetermined amount of dried material is conveyed into the collection line 30 while the fourth predetermined amount of used process fluid is conveyed into an outlet branch 102a. The outlet branch 102a has a branching section 102b, in which the outlet branch 102b splits into the discharge line 40, configured to discharge the aforesaid discharge portion of the fourth predetermined amount of used process fluid from the drying unit towards the cleaning network 50, and into a recirculation line 60, configured to recirculate the remaining part of the fourth predetermined amount of used process fluid from the drying unit 101 towards the process fluid feeding line 20. The discharge line 40 can comprise a filter 210 to partially clean the used process fluid.

[0077] In particular, a discharge portion of the used process fluid between 3% and 8% of the fourth amount of the used process fluid is conveyed into the discharge line 40.

[0078] The process fluid feeding line 20 comprises a connection section 25 in which the recirculation line 60 and a make-up line 70, configured to feed a make-up portion of process fluid to the process fluid feeding line 20, converge.

[0079] In particular, a recirculation portion of the used process fluid between 92% and 97% of the second amount of the process fluid is conveyed into the recirculation line 60.

[0080] The drying unit 100 thus comprises a furnace 103, arranged downstream of the connection section 25 and configured to heat the process fluid, so as to make it suitable for being fed to the drying chamber 101 .

[0081] The process fluid exiting from the furnace 103 has a temperature between 190°C and 230°C.

[0082] The process fluid exiting from the furnace 103 has a pressure between 0.01 bar and 0.04 bar.

[0083] The plant 1 further comprises a heat recovery unit 200 configured to promote a heat exchange between the at least one discharge portion of the used process fluid and a heat recovery fluid.

[0084] Preferably, the used process fluid has a discharge temperature between 120°C and 220°C, even more preferably equal to 160°C.

[0085] Figure 1 shows a first embodiment of the heat recovery unit 200.

[0086] In such an embodiment, the heat recovery unit 200 comprises a closed heat transfer circuit 201 in which a recirculating carrier fluid flows: the heat recovery unit 200 is configured to promote a first heat exchange “Q1 ” between the at least one discharge portion of the used process fluid and the recirculating carrier fluid, and a second heat exchange “Q2” between the recirculating carrier fluid and the heat recovery fluid.

[0087] As it can be seen in the accompanying Figures, the first heat exchange “Q1 ” is carried out by using a water circuit 202, which is interposed between the closed heat transfer circuit 201 and the discharge line 40.

[0088] As for the closed heat transfer circuit 201 , it is configured to operate by means of a refrigeration cycle, in particular as a heat pump. The recirculating carrier fluid is a coolant suitable for being used with phase changes.

[0089] Specifically, the closed heat transfer circuit 201 comprises an evaporator 201 a to perform a heat transfer from the discharge portion, and a condenser 201 b to perform a heat transfer to the make-up portion.

[0090] Structurally, therefore, the heat recovery unit 200 comprises a first heat exchanger 203 configured to receive the aforesaid discharge line 40, which is configured to cause the at least one discharge portion of the used process fluid to flow through the heat exchanger 203, and to receive the water circuit 202, so that the used process fluid exchanges thermal energy with the water circuit 202. Functionally, a preliminary heat exchange “Q0” between the used process fluid and the water of the water circuit occurs in the first heat exchanger 203.

[0091] Preferably, the water of the water circuit 202 enters in the first heat exchanger 203 at a temperature between 50°C and 90°C, preferably at a temperature equal to 85°C.

[0092] Preferably, the water of the water circuit 202 exits from the first heat exchanger 203 at a temperature between 90°C and 110°C, preferably at a temperature equal to 100°C.

[0093] In other words, the water of the water circuit has a minimum cyclic temperature between 50°C and 90°C, preferably at a temperature equal to 85°C, and a maximum cyclic temperature between 90°C and 110°C, preferably at a temperature equal to 100°C.

[0094] The heat recovery unit 200 comprises a second heat exchanger 204 (which can coincide with the evaporator 201 a) configured to transfer thermal energy from the water of the water circuit 202 to the evaporator 201a of the closed heat transfer circuit 201 , so as to be released to the coolant. At a functional level, the aforesaid first exchange “Q1 ” between the water of the water circuit and the recirculating carrier fluid occurs in the second heat exchanger 204.

[0095] The heat recovery unit 200 comprises a third heat exchanger 205 (which can coincide with the condenser 201 b) configured to transfer thermal energy from the coolant passing through the condenser 201 b of the closed heat transfer circuit 201 to the process fluid entering in the drying unit and passing through the make-up line 70. At a functional level, the aforesaid second exchange “Q2” between the recirculating carrier fluid and the process fluid flowing in the make-up line 70 occurs in the third heat exchanger 205.

[0096] Preferably, the process fluid entering in the third heat exchanger 205 enters at ambient temperature. Preferably, the process fluid entering in the third heat exchanger 205 enters at a temperature between 10°C and 40°C, even more preferably at a temperature equal to 20°C.

[0097] Preferably, in the solution involving drying by means of a process fluid mainly consisting of vapor, in addition to a temperature increase, the process fluid passing in the make-up line 70 undergoes a liquid / gas phase change so as to enter in the process fluid feeding line 20 under saturated vapor conditions.

[0098] Figure 2 shows a second embodiment of the heat recovery unit 200.

[0099] Such an embodiment of the heat recovery unit 200 differs from the previous one in that it does not comprise the aforesaid water circuit interposed between the discharge line 40 and the closed heat transfer circuit 201 .

[0100] In such an embodiment, the heat recovery unit 200 comprises the closed heat transfer circuit 201 , having a structure similar to that shown above, in which the recirculating carrier fluid flows: the heat recovery unit 200 is configured to promote a first heat exchange “Q1 ” between the at least one discharge portion of the used process fluid and the recirculating carrier fluid, and a second heat exchange “Q2” between the recirculating carrier fluid and the heat recovery fluid.

[0101] Structurally, therefore, the heat recovery unit 200 comprises a first heat exchanger 203 configured to promote the first heat exchange “Q1 ” directly between the used process fluid that flows in the discharge line 40 and the recirculating carrier fluid in the closed heat transfer circuit 201 , and a second heat exchanger 204 configured to promote the second exchange “Q2” between the recirculating carrier fluid and the process fluid that flows in the make-up line 70.

[0102] A variant of implementation, not shown, of the embodiments in Figure 1 and Figure 2 will now be described below. In such an embodiment, downstream of the first heat exchanger 203 (which is configured to promote a transfer of thermal energy from the used process fluid, which flows through the discharge line 40, to the water circuit 202 (Figure 1 ) or to the closed heat transfer circuit 201 (Figure 2)) there can be provided a further accessory heat exchanger, arranged downstream of the aforesaid first heat exchanger 203 and configured to promote a transfer of residual thermal energy of the used process fluid which flows in the discharge line 40 towards a separate line, which is adapted to receive and dispense the recovered excess thermal energy towards utilities outside the drying unit.

[0103] In other words, in such an embodiment, not shown, the used process fluid exiting from the exchanger 203, still containing an amount of waste heat in the form of latent heat of condensation, will be sent to a second exchanger to transfer heat to a service fluid.

[0104] Figure 3 shows a variant of implementation of the solution in Figure 1 , in which the heat recovery fluid is not reintegrated into the process fluid feeding line but is a recirculating fluid suitable for transferring heat to other units other than the drying unit 100. Therefore, in this case, the heat recovery fluid circulates in a line 80 separate from the make-up line 70 or from the process fluid feeding line 20.

[0105] The term “separate line 80” means a dedicated heat line, distinct from the make-up line 70 and the feeding line 20, configured to receive and dispense the excess thermal energy recovered by the heat recovery unit 200 towards utilities outside the drying unit 100 (e.g., district heating networks, auxiliary industrial utilities, preheating of process water, or civil services).

[0106] Figure 4 shows the same variant in Figure 3 but applied to the solution in Figure 2.

[0107] An embodiment, not shown, will now be described below, which also relates to the transfer of heat to a separate line 80 (such as the embodiments in Figures 3 and 4, for example) but has some differences from the latter. According to such an alternative embodiment, a controllable hydraulic take-off is provided downstream of the first heat exchanger 203 and / or the water circuit 202 (if present), which diverts a portion of the circulation water between the first heat exchanger 203 and the closed heat transfer circuit 201. Such a secondary flow is adjusted by means of distribution members (diverter valves and / or proportional valves) and variable flow rate pumps, and is directed to a dedicated exchanger connected to line 80, in which the heat transfer to the heat transfer fluid required by the external utilities occurs.

[0108] The present invention achieves the intended objects, eliminating the drawbacks highlighted in the prior art.

[0109] In particular, note that the plant 1 as described and / or claimed (and specifically the heat recovery unit 200) allows significantly reducing the energy consumption of the drying process of the material of plant origin, thus optimizing the use of the process fluid and minimizing energy losses. Such a result is achieved by virtue of an efficient recovery of the residual energy of the used process fluid, which further allows preheating the fresh process fluid being fed to the drying unit.

[0110] Also note that the plant 1 , as described and / or claimed, allows reducing the need for cooling and heat dissipation, thus improving the overall energy efficiency and ensuring greater control of emissions.

Claims

CLAIMS1. A plant (1 ) for drying a material of plant origin, in particular of the smoking article industry, configured to operate continuously and comprising:- a drying unit (100) for a material of plant origin, configured to dry a first predetermined amount of material by means of a second predetermined amount of process fluid so as to obtain a third predetermined amount of dried material and a fourth predetermined amount of used process fluid;- a material feeding line (10), configured to feed said first predetermined amount of material into said drying unit (100);- a process fluid feeding line (20), configured to feed a second predetermined amount of process fluid;- a collection line (30), configured to discharge said third predetermined amount of dried material from said drying unit (100),- a discharge line (40), configured to discharge a discharge portion of said fourth predetermined amount of used process fluid from said drying unit (100); characterized in that it comprises a heat recovery unit (200), configured to promote a heat exchange between said at least one discharge portion and a heat recovery fluid.

2. A plant (1 ) according to claim 1 , wherein said heat recovery fluid is the process fluid entering in the process fluid feeding line (20).

3. A plant (1 ) according to claim 1 , wherein said heat recovery fluid is a recirculating fluid suitable for transferring heat to other units other than the drying unit (100), in particular flowing in a line (80) separate from said process fluid feeding line (20).

4. A plant (1 ) according to any one of the preceding claims, wherein said heat recovery unit (200) comprises a closed heat transfer circuit (201 ) in which a recirculating carrier fluid flows, said heat recovery unit (200) is configured to promote a first heat exchange (Q1 ) between said at least one discharge portion and said recirculating carrier fluid, and a secondheat exchange (Q2) between said recirculating carrier fluid and said heat recovery fluid.

5. A plant (1 ) according to claim 4, wherein said closed heat transfer circuit (201 ) is configured to operate by means of a refrigerating cycle, in particular as a heat pump, said recirculating carrier fluid being a coolant suitable for being used with phase changes.

6. A plant (1 ) according to claim 5, wherein said closed heat transfer circuit (201 ) comprises an evaporator (201 a) to perform a heat transfer from the at least one discharge portion, and a condenser (201 b) to perform a heat transfer to the heat recovery fluid.

7. A plant (1 ) according to any one of claims 4 to 6, wherein said heat recovery unit (200) is further configured to perform said first heat exchange (Q1 ) using a water circuit (202).

8. A plant (1 ) according to any one of claims 4 to 7, wherein said first and second heat exchanges (Q1 , Q2) are performed by means of two heat exchangers (203, 204, 205), preferably separate from each other, respectively.

9. A plant (1 ) according to any one of the preceding claims, further comprising a recirculation line (60), configured to recirculate a part of said fourth predetermined amount of used process fluid from said drying unit (100) to the process fluid feeding line (20), and a make-up line (70) configured to feed a make-up portion of process fluid to the process fluid feeding line (20).

10. A plant (1 ) according to claim 9 when dependent on claim 2, wherein said heat recovery fluid is the process fluid flowing into, or towards, the make-up line (70).11 . A plant (1 ) according to any one of claims 4 to 6, wherein said closed heat transfer circuit (201 ) is dimensioned and configured to provide, under usual operating conditions, the total heat required to bring the process fluid to the desired operating state for drying in the drying unit (100), preferably without a further dedicated auxiliary heat source.

12. A plant (1 ) according to claim 11 , comprising an auxiliary heating system, integrated in or connected to the drying unit (100) or to the closed heat transfer circuit (201 ), configured to provide at least partially the heat to the process fluid in a start-up step of the plant (1 ).

13. A method for drying a material of plant origin, in particular of the smoking article industry, in particular practicable by means of a drying plant (1 ) according to any one of the preceding claims; said method comprising the cyclic steps of:- feeding a first predetermined amount of material into said drying unit (100) by means of a material feeding line (10);- feeding a second amount of process fluid into said drying unit (100) by means of a process fluid feeding line (20);- drying said first predetermined amount of material of plant origin by means of said second predetermined amount of process fluid thus obtaining a third predetermined amount of dried material and a fourth predetermined amount of used process fluid, said step of drying being carried out by means of said drying unit (100);- collecting said third predetermined amount of dried material from the drying unit (100) by means of a collection line (30) for the dried material;- discharging at least one portion of said fourth predetermined amount of used process fluid from said drying unit (100) by means of a discharge line (40); characterized in that it comprises a step of recovering thermal energy from the at least one discharge portion of the used process fluid by means of heat transfer from said at least one discharge portion to a heat recovery fluid.

14. A method according to claim 13, wherein said heat recovery fluid is the process fluid entering in the process fluid feeding line (20).

15. A method according to claim 13 or 14, wherein in said step of recovering thermal energy, a first heat exchange (Q1 ) from the at least one discharge portion to a recirculating carrier fluid flowing in a closedheat transfer circuit (201 ) is carried out, and then a second heat exchange (Q2) from the recirculating carrier fluid to said heat recovery fluid is carried out.

16. A method according to claim 15, wherein said closed heat transfer circuit (201 ) operates by means of a refrigeration cycle, in particular as a heat pump; said circulating carrier fluid being a coolant suitable for being used with phase change.

17. A method according to claim 15 or 16, wherein the recirculation carrier fluid is evaporated to carry out a heat transfer from the discharge portion, and wherein the recirculation carrier fluid is condensed to carry out a heat transfer to the heat recovery fluid.

18. A method according to any one of the preceding claims 15 to 17, wherein said first heat exchange is carried out by interposition of a water circuit.

19. A method according to any one of the preceding claims 15 to 18, wherein said first and second heat exchanges are performed by means of a first and a second heat exchanger, preferably separate from each other, respectively.

20. A method according to any one of the preceding claims 13 to 19, comprises a step of recirculating a part of said fourth predetermined amount of used process fluid from said drying unit (100) to the process fluid feeding line (20) by means of a recirculation line (60), and a step of making up a make-up portion of process fluid to the process fluid feeding line (20) by means of a make-up line (70).21 . A method according to claim 20 when dependent on claim 14, wherein said heat recovery fluid is the process fluid flowing into, or towards, the make-up line (70).

22. A method according to any one of claims 13 to 17, wherein, under usual operating conditions, the total heat required to bring the process fluid to the operating state is provided by the closed heat transfer circuit (201 ), preferably without a further dedicated auxiliary heat source.

23. A method according to claim 22, characterized in that it comprises a step of providing, during a start-up of the plant (1 ), an auxiliary heat input to the process fluid, such an auxiliary heat input being interrupted once the usual operating conditions are reached.

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