System suitable for energy optimization of a paper mill

Abstract

System (20) suitable for energy optimization of a paper mill (A) including: - a conditioning section (B) configured for cooling the empty air (1) coming from the paper mill (A), - a vacuum generation section (C), e - a cooling section (D), the system (20) being characterized in that - the conditioning section (B) is configured to eliminate the condensable water vapor from the vacuum air (1), to lower the temperature of the vacuum air (1) producing conditioned vacuum air (2) with reduced mass flow and reduced volumetric flow rate compared to the respective mass and volumetric flow rates of the vacuum air (1) and to recover a greater quantity of water from the production process, and by the fact that - the vacuum generation section (C) and the cooling section (D) are equipped with heat recovery systems for the conversion of the thermal energy contained in the fumes and / or exhaust gases into energy available for cooling the aspirated air under vacuum, through the production of chilled water.

Description

Technical field of the invention

[0001] The present invention relates to a system suitable for energy optimization of a paper mill. In particular, the system is suitable for reducing the energy used in the vacuum section for paper production.Background art

[0002] As is known for example from US2004099393, the paper manufacturing process can be divided into the following phases: the wood is debarked and reduced into small pieces, by adding water and additives, thanks to mechanical or chemical processes, the lignin is defibrated thus producing a pulp of cellulose fibers, the fibers are subjected to screening and cleaning and, finally, mixed with water, the dough thus obtained in the dough preparation section is sent onto a porous support (forming cloth) via a system called the headbox. The forming cloth has the ability to quickly drain much of the water present in the fibrous mixture, retaining an extremely moist sheet on the surface. Water permeates through the canvas, while the fibers tend to bond together, the material obtained is sent to the pressing section in order to further reduce the water content.

[0003] Here the wet sheet passes onto a further type of support capable of absorbing humidity from the sheet itself and, thanks to suction boxes connected to a vacuum production and maintenance system, the quantity of water in the sheet is further reduced.

[0004] The main uses of vacuum in a paper making machine are listed below: drainage of the paper sheet, maintenance and control of the path of the sheet of paper through the press section, conditioning of the absorbent support (typically felt) of the presses, maintenance and control of the drainage jet on at least one suction cylinder.

[0005] According to the background art, it is not imaginable to have a paper production machine without a system that creates vacuum and drainage via an absorbent support. This is and still remains the most common way to dehydrate paper in the press section.

[0006] Vacuum levels on a papermaking machine are typically between 5 and 70 kPa, while airflows are very high due to the large open areas found in such machines.

[0007] Obtaining the vacuum, which is created by sucking air through a narrow section, requires an expensive instrument and represents one of the largest electrical consumptions among the different sections with which a "continuous machine" is made, i.e. a paper production machine.

[0008] Currently, to meet the need to improve the efficiency of the machine and reduce operating costs, vacuum level control systems are installed in the different areas of the machine which act as much as possible on the operating point of the vacuum production equipment itself.

[0009] The solutions commonly adopted for the production of vacuum involve the use of liquid ring pumps, fans, turbo blowers and / or dry vacuum pumps. Paper mills often use a combination of these devices.

[0010] Liquid ring pumps require careful water management in terms of temperature, flow rate, consumption and purity.

[0011] Turbo blowers, more efficient than the previous ones, require the removal of anything that could damage the impeller and possibly, in order to maximize energy efficiency, the recovery of thermal energy at the exhaust.

[0012] Subsequently, from the absorbent support, through the pressing section, the sheet passes into the drying section. This section, depending on the type of production, is made up of one or more cylinders kept at temperature thanks to a steam current.

[0013] In the case of paper production tissue (toilet paper, handkerchiefs and absorbent paper) the drying system consists of a single cylinder, called a Yankee, which rotates inside the cavity formed by the drying hoods.

[0014] These hoods are equipment with which the external air is heated to the optimal temperature for drying the processed product.

[0015] The temperature of the drying air is obtained by means of burners or by using fumes coming from a cogeneration system or by a mix of both solutions.

[0016] The dry air and steam-heated cylinder surface then remove residual moisture from the paper. The flow of exhausted and humid air (the fumes) is then sucked in by the hoods themselves and subsequently released into the atmosphere.

[0017] In some cases, before being released into the atmosphere, thermal energy is recovered from the air in order to produce hot water mainly used for the air conditioning of buildings during the winter period.

[0018] In the case of production of non-tissue paper, cardboard and cardboard, the drying system, called dryers, has the purpose of almost completely dehydrating the product by passing it over steam-heated drying cylinders.

[0019] The set of drying cylinders is divided into one or more distinct sections, each of which is made up of a certain number of cylinders which are arranged in two overlapping rows.

[0020] The steam enters the cylinders through the pin, which is hollow. The last drying cylinders are kept at decreasing temperature; the last one, then, is cooled with the circulation of water, given that the paper must necessarily come out of the dryers as much as possible in thermal equilibrium with the external environment.

[0021] The dryers are covered by a sheet metal hood, which has the task of conveying the fumes and discharging them into the atmosphere.

[0022] In both cases the steam production system is entrusted to a thermal power plant which can include: a steam generation system using burners, a steam generation system by means of heat recovery (typical of cogeneration systems), or a mix of the two previous solutions.

[0023] For both steam production solutions, the major points of thermal inefficiency consist of: from the exhaust of the fumes respectively of the hoods and dryers into the atmosphere, from the discharge of fumes from the steam generator into the atmosphere. from the returns of hot condensates and / or exhausted steam There is therefore a technical need to improve the energy efficiency of the paper production process, both as regards the creation of the vacuum and as regards the use of the thermal energy currently dissipated. Summary of the invention

[0024] The solution of the technical problems referred to in the previous paragraph is obtained, according to the present invention, by means of a system that allows the energy optimization of a paper mill. In particular, the system is suitable for reducing the energy used in the vacuum section for paper production, through the recovery of thermal energy in other sections of the plant.

[0025] The present invention is particularly suitable for applications in the paper production field where steam and / or hot air is used to dry the paper itself. The developed solution allows you to: reduce the electrical energy used in the vacuum section thanks to one or more heat recovery systems distributed throughout the plant, recover a greater quantity of water from the production process, effectively reducing water consumption per ton of product, increase the "first principle" thermodynamic efficiency of the whole consisting of the thermal power plant and the continuous machine.

[0026] In particular, the innovative solution is the conversion of the thermal energy contained in the fumes and / or exhaust gases which would be dispersed in the chimney of the system into energy available for cooling the air sucked under vacuum, through the production of chilled water. This improves the overall energy efficiency of the paper production process.

[0027] According to one aspect of the present invention, a system is therefore provided for the energy optimization of a paper mill having the characteristics set out in the independent system claim attached to the present description.

[0028] Further preferred and / or particularly advantageous ways of implementing the aforementioned system are described according to the characteristics set out in the attached dependent claims.Brief description of the drawings

[0029] The invention will now be described with reference to the attached drawing, which illustrates a non-limiting example of implementation of the invention, in which: figure 1 schematically illustrates a system for the energy optimization of a paper mill, in a preferred embodiment of the present invention. Detailed description

[0030] In the remainder of this description, it will be indicated by: "paper" a generic product identified as tissue, absorbent paper, paper, cardboard, cardboard and similar and / or similar products, and "continues" the paper production machine.

[0031] With reference to figure 1, the continuum A includes three main sections: the dough forming section A1, the pressing section A2 and the drying section A3.

[0032] Not shown in the figure, as it is of a known type, there is also a thermal and / or thermo-electric power plant for the processing of working fluids and the production of heat and / or electrical energy. The thermal power plant may include a boiler for heating and / or evaporating the working fluids.

[0033] The primary utility flows that power the paper machine and are of interest for the present invention are: electricity 10, water 12, steam 16, air 13 for drying and natural gas 9 (these last two utilities typically for the production of tissue paper).

[0034] The main output flows of interest for the present invention are: exhausted drying air 4, called fumes (typically for tissue production), condensed steam 14 and saturated air 1 in suction to the section for creating the vacuum.

[0035] System 20 for the energy optimization of the paper mill includes a conditioning section B, a vacuum generation section C and a cooling section D.

[0036] The conditioning section B of the saturated air 1 (hereinafter also referred to as vacuum air) allows the volumetric and mass flow rate of the conditioned vacuum air 2 to be reduced for the subsequent vacuum generation section C with consequent reduction in electrical energy 11 consumed in the same section.

[0037] The conditioning section B cools the vacuum air 1 coming from the continuous A through adiabatic cooling (in direct contact with the refrigerant fluid 7) and / or through a battery of heat exchangers B2, installed directly on the air-cooling process.

[0038] The refrigerant fluid 7, with a minimum temperature of up to 10°C, keeps the cooling temperature of the vacuum air 1 constant.

[0039] The particulate and condensate produced by cooling are separated from the gaseous stream via a dedicated self-cleaning separator B1. The self-cleaning separator promotes water condensation through a particular geometry and air conveyance.

[0040] The condensed water 8 is sent to the water purification plant, while the vacuum conditioned air 2 is sucked in by a vacuum pump C1.

[0041] The desired degree of vacuum in the continuous A is kept constant and the energy consumption 11 of the vacuum pump C1 is defined by its operating point. Evidently, the energy consumption 11 of the vacuum pump C1 decreases as the inlet volumetric flow rate of the vacuum conditioned air 2 decreases, all other conditions being equal.

[0042] The conditioning section B not only allows the mass flow rate of the vacuum air 1 to be reduced by eliminating the condensable water vapor, but also reduces the volumetric flow rate of the vacuum conditioned air 2 compared to what is typically present in paper mills. According to known technique, in fact, the vacuum air 1 enters directly into the vacuum section C. Furthermore, the conditioning section B allows a greater quantity of water to be recovered from the production process, effectively reducing the consumption of water per ton of product.

[0043] If the vacuum generation section C is made up of liquid ring pumps, the invention allows the feed water 17 to be cooled by inserting at least one heat exchanger G, fed with the cooling fluid 18 produced from the cooling section D.

[0044] If the vacuum generation section C is made up of turbo blowers and / or dry depressors equipped with a heat exchanger C2 for heat recovery at the exhaust 3 of the air from the same vacuum generation section C, the invention allows to recover the thermal energy 16 in the cooling section D.

[0045] The cooling section D is equipped with one or more heat recovery systems, in turn including at least one heat exchanger D1 and an absorption refrigerator D2. The heat recovery systems are used to: heat recovery from the hood fumes 4 (typical for the production of tissue paper), heat recovery from boiler fumes 15, thermal recovery from exhausted steam and / or condensates 14 heat recovery 16 at exhaust C2, of the vacuum generation section C.

[0046] The thermal energy recovered in the form of hot water is converted into refrigerant fluid 7, typically cold water or a glycol water solution, by means of the absorption refrigerator D2 which uses combustion gases to produce chilled water, which is sent to the exchanger of heat on the suction of vacuum pumps.

[0047] The refrigerant fluid 7 is then sent to the conditioning section B of the vacuum air 1, and, if liquid ring vacuum pumps are used, to at least one heat exchanger G used for cooling the feed water 17 for the vacuum pumps.

[0048] The fumes 4 from the hood (typical for the production of tissue paper) and / or the fumes from the boiler 15, i.e. the fumes exiting 5 from the cooling section D are finally released into the atmosphere from the process chimney E of the paper mill.

[0049] The temperature of these chimney fumes is much lower than a conventional system without heat recovery.

[0050] Some operating modes and performances of system 20 for the energy optimization of a paper mill are described below.

[0051] Table 1 shows the operating parameters and performances of a so-called "large" paper machine, i.e. having a daily paper production varying between 65 and 78 tons. Table 1 - "Big" machineINVENTION PARAMETER RIF. UNIT EXISTING Standard Configuration high efficiency Configuration paper productiont / d65-78volumetric flow rate1m3 / min870massive flow1kg / min414pressure1kPa45suction temperature1°C37,4kg H2O / kg dry air10-103pressure3kPa103vacuum group discharge temperature(*)3°C130105100temperature with empty group2°Cn.a.1512chimney temperature5°C17911095absorbed power11kW653542512saved vs existing powern.a.17,0%21,6%condensed water8kg / hn.a.17762110efficiency first principle (**)74,5%85,3%88,5%(*)turbopumps (**) thermal power station + continues

[0052] The table is organized into six columns: the first column shows the reference parameters / monitored performances, the second shows the references present in the attached drawing, the third shows the unit of measurement, the fourth column shows the values of the operating parameters / performances obtained in the case of a continuous system according to the known technique, i.e. in the absence of the system 20, while in the last two columns the values of the same parameters / performances are reported in the presence of the system 20 according to the invention in a standard configuration or in a configuration respectively high efficiency.

[0053] The high efficiency configuration differs from the standard one due to the presence of a higher power absorption refrigerator D2. With the greater usable powers, it is possible to reach, as will be seen, a limit value of 95°C as the flue gas temperature.

[0054] In particular, the rows of the table show: the daily paper production (t / d) in continuous A, parameters relating to the vacuum air 1 coming from the continuous air: volumetric flow rate (m3 / min), mass flow rate (kg / min), pressure (kPa), temperature (°C), humidity expressed as the ratio between mass of water and mass of dry air (kg H2O / kg dry air), pressure (kPa) and temperature (°C) at exhaust 3 of the air from the vacuum generation section C, temperature (°C) of the vacuum conditioned air 2, temperature (°C) of the fumes exiting 5 from the cooling section D, power absorbed (kW) by the DC and power saved (%) in the case of using system 20, mass flow rate (kg / h) of condensed water 8, first principle efficiency (%), considering the thermal and continuous power plant together.

[0055] As can be appreciated from Table 1, the use of the system allows: the reduction of approximately 17% of the power absorbed by the DC, with the system 20 in standard configuration, and of over 21% with the system 20 in a high efficiency configuration, a notable drop in the temperature of the fumes exiting 5 from the cooling section D, more marked with system 20 in the high efficiency configuration (up to 95°C), an increase in first principle efficiency of over 10 percentage points (system in standard configuration) or of approximately 14 percentage points (system in high efficiency configuration).

[0056] Table 2 shows the operating parameters and performances of a so-called "small" paper machine, i.e. having a daily paper production varying between 44 and 53 tons.

[0057] The organization of table 2 is identical to that of table 1 to whose description we refer.

[0058] As can be appreciated from table 2, even in the case of a small machine, the use of system 20 allows: the reduction of approximately 17% of the power absorbed by the DC, with system 20 in standard configuration, and of approximately 21% with system 20 in a high efficiency configuration, a notable drop in the temperature of the fumes exiting 5 from the cooling section D, more marked with system 20 in the high efficiency configuration (also in this configuration, up to 95°C), an increase in first principle efficiency of approximately 9 percentage points (system in standard configuration) or approximately 11 percentage points (system in high efficiency configuration). Table 2 - "Small" machine INVENZIONE PARAMETRO RIF. UNITA' ESISTENTE Configurazione standard Configurazione alta efficienza paper productiont / d44-53volumetric flow rate1m3 / min523massive flow1kg / min254pressure1kPa46suction temperature1°C38,0kg H2O / kg dry air10,104pressure3kPa103vacuum group discharge temperature (*)3°C133105100temperature with empty group2°Cn.a.1512chimney temperature5°C16811095absorbed power11kW445370352saved vs existing powern.a.16,9%20,9%condensed water8kg / hn.a.9781150efficiency first principle (**)76,3%85,3%87,6% (*) turbopumps (**) thermal power station + continues

[0059] Although at least one exemplary embodiment has been presented in the summary and detailed description, it must be understood that there are a large number of variations within the scope of the invention. Furthermore, it must be understood that the embodiment or embodiments presented are merely examples, which are not intended to limit in any way the scope of protection of the invention or its application or configurations. Rather, the summary and detailed description provide the skilled technician in the sector with a convenient guide to implement at least one exemplary embodiment, it being clear that numerous variations can be made in the function and assembly of the elements described herein, without departing from the scope of protection of the invention as established by the attached claims.

Examples

Embodiment Construction

[0030]In the remainder of this description, it will be indicated by:

"paper" a generic product identified as tissue, absorbent paper, paper, cardboard, cardboard and similar and / or similar products, and "continues" the paper production machine.

[0031]With reference to figure 1, the continuum A includes three main sections: the dough forming section A1, the pressing section A2 and the drying section A3.

[0032]Not shown in the figure, as it is of a known type, there is also a thermal and / or thermo-electric power plant for the processing of working fluids and the production of heat and / or electrical energy. The thermal power plant may include a boiler for heating and / or evaporating the working fluids.

[0033]The primary utility flows that power the paper machine and are of interest for the present invention are: electricity 10, water 12, steam 16, air 13 for drying and natural gas 9 (these last two utilities typically for the production of tissue paper).

[0034]The main output flows of inte...

Technical field of the invention

[0001] The present invention relates to a system suitable for energy optimization of a paper mill. In particular, the system is suitable for reducing the energy used in the vacuum section for paper production.Background art

[0002] As is known for example from US2004099393, the paper manufacturing process can be divided into the following phases: the wood is debarked and reduced into small pieces, by adding water and additives, thanks to mechanical or chemical processes, the lignin is defibrated thus producing a pulp of cellulose fibers, the fibers are subjected to screening and cleaning and, finally, mixed with water, the dough thus obtained in the dough preparation section is sent onto a porous support (forming cloth) via a system called the headbox. The forming cloth has the ability to quickly drain much of the water present in the fibrous mixture, retaining an extremely moist sheet on the surface. Water permeates through the canvas, while the fibers tend to bond together, the material obtained is sent to the pressing section in order to further reduce the water content.

[0003] Here the wet sheet passes onto a further type of support capable of absorbing humidity from the sheet itself and, thanks to suction boxes connected to a vacuum production and maintenance system, the quantity of water in the sheet is further reduced.

[0004] The main uses of vacuum in a paper making machine are listed below: drainage of the paper sheet, maintenance and control of the path of the sheet of paper through the press section, conditioning of the absorbent support (typically felt) of the presses, maintenance and control of the drainage jet on at least one suction cylinder.

[0005] According to the background art, it is not imaginable to have a paper production machine without a system that creates vacuum and drainage via an absorbent support. This is and still remains the most common way to dehydrate paper in the press section.

[0006] Vacuum levels on a papermaking machine are typically between 5 and 70 kPa, while airflows are very high due to the large open areas found in such machines.

[0007] Obtaining the vacuum, which is created by sucking air through a narrow section, requires an expensive instrument and represents one of the largest electrical consumptions among the different sections with which a "continuous machine" is made, i.e. a paper production machine.

[0008] Currently, to meet the need to improve the efficiency of the machine and reduce operating costs, vacuum level control systems are installed in the different areas of the machine which act as much as possible on the operating point of the vacuum production equipment itself.

[0009] The solutions commonly adopted for the production of vacuum involve the use of liquid ring pumps, fans, turbo blowers and / or dry vacuum pumps. Paper mills often use a combination of these devices.

[0010] Liquid ring pumps require careful water management in terms of temperature, flow rate, consumption and purity.

[0011] Turbo blowers, more efficient than the previous ones, require the removal of anything that could damage the impeller and possibly, in order to maximize energy efficiency, the recovery of thermal energy at the exhaust.

[0012] Subsequently, from the absorbent support, through the pressing section, the sheet passes into the drying section. This section, depending on the type of production, is made up of one or more cylinders kept at temperature thanks to a steam current.

[0013] In the case of paper production tissue (toilet paper, handkerchiefs and absorbent paper) the drying system consists of a single cylinder, called a Yankee, which rotates inside the cavity formed by the drying hoods.

[0014] These hoods are equipment with which the external air is heated to the optimal temperature for drying the processed product.

[0015] The temperature of the drying air is obtained by means of burners or by using fumes coming from a cogeneration system or by a mix of both solutions.

[0016] The dry air and steam-heated cylinder surface then remove residual moisture from the paper. The flow of exhausted and humid air (the fumes) is then sucked in by the hoods themselves and subsequently released into the atmosphere.

[0017] In some cases, before being released into the atmosphere, thermal energy is recovered from the air in order to produce hot water mainly used for the air conditioning of buildings during the winter period.

[0018] In the case of production of non-tissue paper, cardboard and cardboard, the drying system, called dryers, has the purpose of almost completely dehydrating the product by passing it over steam-heated drying cylinders.

[0019] The set of drying cylinders is divided into one or more distinct sections, each of which is made up of a certain number of cylinders which are arranged in two overlapping rows.

[0020] The steam enters the cylinders through the pin, which is hollow. The last drying cylinders are kept at decreasing temperature; the last one, then, is cooled with the circulation of water, given that the paper must necessarily come out of the dryers as much as possible in thermal equilibrium with the external environment.

[0021] The dryers are covered by a sheet metal hood, which has the task of conveying the fumes and discharging them into the atmosphere.

[0022] In both cases the steam production system is entrusted to a thermal power plant which can include: a steam generation system using burners, a steam generation system by means of heat recovery (typical of cogeneration systems), or a mix of the two previous solutions.

[0023] For both steam production solutions, the major points of thermal inefficiency consist of: from the exhaust of the fumes respectively of the hoods and dryers into the atmosphere, from the discharge of fumes from the steam generator into the atmosphere. from the returns of hot condensates and / or exhausted steam There is therefore a technical need to improve the energy efficiency of the paper production process, both as regards the creation of the vacuum and as regards the use of the thermal energy currently dissipated. Summary of the invention

[0024] The solution of the technical problems referred to in the previous paragraph is obtained, according to the present invention, by means of a system that allows the energy optimization of a paper mill. In particular, the system is suitable for reducing the energy used in the vacuum section for paper production, through the recovery of thermal energy in other sections of the plant.

[0025] The present invention is particularly suitable for applications in the paper production field where steam and / or hot air is used to dry the paper itself. The developed solution allows you to: reduce the electrical energy used in the vacuum section thanks to one or more heat recovery systems distributed throughout the plant, recover a greater quantity of water from the production process, effectively reducing water consumption per ton of product, increase the "first principle" thermodynamic efficiency of the whole consisting of the thermal power plant and the continuous machine.

[0026] In particular, the innovative solution is the conversion of the thermal energy contained in the fumes and / or exhaust gases which would be dispersed in the chimney of the system into energy available for cooling the air sucked under vacuum, through the production of chilled water. This improves the overall energy efficiency of the paper production process.

[0027] According to one aspect of the present invention, a system is therefore provided for the energy optimization of a paper mill having the characteristics set out in the independent system claim attached to the present description.

[0028] Further preferred and / or particularly advantageous ways of implementing the aforementioned system are described according to the characteristics set out in the attached dependent claims.Brief description of the drawings

[0029] The invention will now be described with reference to the attached drawing, which illustrates a non-limiting example of implementation of the invention, in which: figure 1 schematically illustrates a system for the energy optimization of a paper mill, in a preferred embodiment of the present invention. Detailed description

[0030] In the remainder of this description, it will be indicated by: "paper" a generic product identified as tissue, absorbent paper, paper, cardboard, cardboard and similar and / or similar products, and "continues" the paper production machine.

[0031] With reference to figure 1, the continuum A includes three main sections: the dough forming section A1, the pressing section A2 and the drying section A3.

[0032] Not shown in the figure, as it is of a known type, there is also a thermal and / or thermo-electric power plant for the processing of working fluids and the production of heat and / or electrical energy. The thermal power plant may include a boiler for heating and / or evaporating the working fluids.

[0033] The primary utility flows that power the paper machine and are of interest for the present invention are: electricity 10, water 12, steam 16, air 13 for drying and natural gas 9 (these last two utilities typically for the production of tissue paper).

[0034] The main output flows of interest for the present invention are: exhausted drying air 4, called fumes (typically for tissue production), condensed steam 14 and saturated air 1 in suction to the section for creating the vacuum.

[0035] System 20 for the energy optimization of the paper mill includes a conditioning section B, a vacuum generation section C and a cooling section D.

[0036] The conditioning section B of the saturated air 1 (hereinafter also referred to as vacuum air) allows the volumetric and mass flow rate of the conditioned vacuum air 2 to be reduced for the subsequent vacuum generation section C with consequent reduction in electrical energy 11 consumed in the same section.

[0037] The conditioning section B cools the vacuum air 1 coming from the continuous A through adiabatic cooling (in direct contact with the refrigerant fluid 7) and / or through a battery of heat exchangers B2, installed directly on the air-cooling process.

[0038] The refrigerant fluid 7, with a minimum temperature of up to 10°C, keeps the cooling temperature of the vacuum air 1 constant.

[0039] The particulate and condensate produced by cooling are separated from the gaseous stream via a dedicated self-cleaning separator B1. The self-cleaning separator promotes water condensation through a particular geometry and air conveyance.

[0040] The condensed water 8 is sent to the water purification plant, while the vacuum conditioned air 2 is sucked in by a vacuum pump C1.

[0041] The desired degree of vacuum in the continuous A is kept constant and the energy consumption 11 of the vacuum pump C1 is defined by its operating point. Evidently, the energy consumption 11 of the vacuum pump C1 decreases as the inlet volumetric flow rate of the vacuum conditioned air 2 decreases, all other conditions being equal.

[0042] The conditioning section B not only allows the mass flow rate of the vacuum air 1 to be reduced by eliminating the condensable water vapor, but also reduces the volumetric flow rate of the vacuum conditioned air 2 compared to what is typically present in paper mills. According to known technique, in fact, the vacuum air 1 enters directly into the vacuum section C. Furthermore, the conditioning section B allows a greater quantity of water to be recovered from the production process, effectively reducing the consumption of water per ton of product.

[0043] If the vacuum generation section C is made up of liquid ring pumps, the invention allows the feed water 17 to be cooled by inserting at least one heat exchanger G, fed with the cooling fluid 18 produced from the cooling section D.

[0044] If the vacuum generation section C is made up of turbo blowers and / or dry depressors equipped with a heat exchanger C2 for heat recovery at the exhaust 3 of the air from the same vacuum generation section C, the invention allows to recover the thermal energy 16 in the cooling section D.

[0045] The cooling section D is equipped with one or more heat recovery systems, in turn including at least one heat exchanger D1 and an absorption refrigerator D2. The heat recovery systems are used to: heat recovery from the hood fumes 4 (typical for the production of tissue paper), heat recovery from boiler fumes 15, thermal recovery from exhausted steam and / or condensates 14 heat recovery 16 at exhaust C2, of the vacuum generation section C.

[0046] The thermal energy recovered in the form of hot water is converted into refrigerant fluid 7, typically cold water or a glycol water solution, by means of the absorption refrigerator D2 which uses combustion gases to produce chilled water, which is sent to the exchanger of heat on the suction of vacuum pumps.

[0047] The refrigerant fluid 7 is then sent to the conditioning section B of the vacuum air 1, and, if liquid ring vacuum pumps are used, to at least one heat exchanger G used for cooling the feed water 17 for the vacuum pumps.

[0048] The fumes 4 from the hood (typical for the production of tissue paper) and / or the fumes from the boiler 15, i.e. the fumes exiting 5 from the cooling section D are finally released into the atmosphere from the process chimney E of the paper mill.

[0049] The temperature of these chimney fumes is much lower than a conventional system without heat recovery.

[0050] Some operating modes and performances of system 20 for the energy optimization of a paper mill are described below.

[0051] Table 1 shows the operating parameters and performances of a so-called "large" paper machine, i.e. having a daily paper production varying between 65 and 78 tons. Table 1 - "Big" machineINVENTION PARAMETER RIF. UNIT EXISTING Standard Configuration high efficiency Configuration paper productiont / d65-78volumetric flow rate1m3 / min870massive flow1kg / min414pressure1kPa45suction temperature1°C37,4kg H2O / kg dry air10-103pressure3kPa103vacuum group discharge temperature(*)3°C130105100temperature with empty group2°Cn.a.1512chimney temperature5°C17911095absorbed power11kW653542512saved vs existing powern.a.17,0%21,6%condensed water8kg / hn.a.17762110efficiency first principle (**)74,5%85,3%88,5%(*)turbopumps (**) thermal power station + continues

[0052] The table is organized into six columns: the first column shows the reference parameters / monitored performances, the second shows the references present in the attached drawing, the third shows the unit of measurement, the fourth column shows the values of the operating parameters / performances obtained in the case of a continuous system according to the known technique, i.e. in the absence of the system 20, while in the last two columns the values of the same parameters / performances are reported in the presence of the system 20 according to the invention in a standard configuration or in a configuration respectively high efficiency.

[0053] The high efficiency configuration differs from the standard one due to the presence of a higher power absorption refrigerator D2. With the greater usable powers, it is possible to reach, as will be seen, a limit value of 95°C as the flue gas temperature.

[0054] In particular, the rows of the table show: the daily paper production (t / d) in continuous A, parameters relating to the vacuum air 1 coming from the continuous air: volumetric flow rate (m3 / min), mass flow rate (kg / min), pressure (kPa), temperature (°C), humidity expressed as the ratio between mass of water and mass of dry air (kg H2O / kg dry air), pressure (kPa) and temperature (°C) at exhaust 3 of the air from the vacuum generation section C, temperature (°C) of the vacuum conditioned air 2, temperature (°C) of the fumes exiting 5 from the cooling section D, power absorbed (kW) by the DC and power saved (%) in the case of using system 20, mass flow rate (kg / h) of condensed water 8, first principle efficiency (%), considering the thermal and continuous power plant together.

[0055] As can be appreciated from Table 1, the use of the system allows: the reduction of approximately 17% of the power absorbed by the DC, with the system 20 in standard configuration, and of over 21% with the system 20 in a high efficiency configuration, a notable drop in the temperature of the fumes exiting 5 from the cooling section D, more marked with system 20 in the high efficiency configuration (up to 95°C), an increase in first principle efficiency of over 10 percentage points (system in standard configuration) or of approximately 14 percentage points (system in high efficiency configuration).

[0056] Table 2 shows the operating parameters and performances of a so-called "small" paper machine, i.e. having a daily paper production varying between 44 and 53 tons.

[0057] The organization of table 2 is identical to that of table 1 to whose description we refer.

[0058] As can be appreciated from table 2, even in the case of a small machine, the use of system 20 allows: the reduction of approximately 17% of the power absorbed by the DC, with system 20 in standard configuration, and of approximately 21% with system 20 in a high efficiency configuration, a notable drop in the temperature of the fumes exiting 5 from the cooling section D, more marked with system 20 in the high efficiency configuration (also in this configuration, up to 95°C), an increase in first principle efficiency of approximately 9 percentage points (system in standard configuration) or approximately 11 percentage points (system in high efficiency configuration). Table 2 - "Small" machine INVENZIONE PARAMETRO RIF. UNITA' ESISTENTE Configurazione standard Configurazione alta efficienza paper productiont / d44-53volumetric flow rate1m3 / min523massive flow1kg / min254pressure1kPa46suction temperature1°C38,0kg H2O / kg dry air10,104pressure3kPa103vacuum group discharge temperature (*)3°C133105100temperature with empty group2°Cn.a.1512chimney temperature5°C16811095absorbed power11kW445370352saved vs existing powern.a.16,9%20,9%condensed water8kg / hn.a.9781150efficiency first principle (**)76,3%85,3%87,6% (*) turbopumps (**) thermal power station + continues

[0059] Although at least one exemplary embodiment has been presented in the summary and detailed description, it must be understood that there are a large number of variations within the scope of the invention. Furthermore, it must be understood that the embodiment or embodiments presented are merely examples, which are not intended to limit in any way the scope of protection of the invention or its application or configurations. Rather, the summary and detailed description provide the skilled technician in the sector with a convenient guide to implement at least one exemplary embodiment, it being clear that numerous variations can be made in the function and assembly of the elements described herein, without departing from the scope of protection of the invention as established by the attached claims.

Examples

Embodiment Construction

[0030]In the remainder of this description, it will be indicated by:

"paper" a generic product identified as tissue, absorbent paper, paper, cardboard, cardboard and similar and / or similar products, and "continues" the paper production machine.

[0031]With reference to figure 1, the continuum A includes three main sections: the dough forming section A1, the pressing section A2 and the drying section A3.

[0032]Not shown in the figure, as it is of a known type, there is also a thermal and / or thermo-electric power plant for the processing of working fluids and the production of heat and / or electrical energy. The thermal power plant may include a boiler for heating and / or evaporating the working fluids.

[0033]The primary utility flows that power the paper machine and are of interest for the present invention are: electricity 10, water 12, steam 16, air 13 for drying and natural gas 9 (these last two utilities typically for the production of tissue paper).

[0034]The main output flows of inte...

Claims

1. System (20) suitable for energy optimization of a paper mill (A) including: - a conditioning section (B) configured for cooling the vacuum air (1) coming from the paper mill (A), - a vacuum generation section (C), e - a cooling section (D), the system (20) being characterized in that - the conditioning section (B) is configured to eliminate the condensable water vapor from the vacuum air (1), to lower the temperature of the vacuum air (1) producing conditioned vacuum air (2) with reduced mass flow and reduced volumetric flow rate compared to the respective mass and volumetric flow rates of the vacuum air (1) and to recover a greater quantity of water from the production process, and by the fact that - the vacuum generation section (C) and the cooling section (D) are equipped with heat recovery systems, the heat recovery systems being characterized by being for the conversion of the thermal energy contained in the fumes and / or exhaust gases into energy available for cooling the aspirated air under vacuum, through the production of chilled water.

2. System (20) according to claim 1, wherein the conditioning section (B) is configured to perform an adiabatic cooling of the vacuum air (1) by means of a refrigerant fluid (7).

3. System (20) according to claim 1 or 2, wherein the conditioning section (B) comprises a battery of heat exchangers (B2) installed directly on the air-cooling process.

4. System (20) according to any of the preceding claims, wherein the conditioning section (B) comprises a self-cleaning separator (B1).

5. System (20) according to any of the preceding claims, wherein the vacuum generation section (C) comprises at least one vacuum pump (C1).

6. System (20) according to claim 5, wherein the at least one vacuum pump (C1) is a liquid ring pump and the vacuum generation section (C) comprises at least one heat exchanger (G) supplied with a cooling fluid (18) from the cooling section (D) for cooling the feed water (17) of the at least one liquid ring pump.

7. System (20) according to claim 5, wherein the at least one vacuum pump (C1) is a dry turbocharger and / or depressor and the heat recovery system of the vacuum generation section (C) comprises a heat exchanger (C2).

8. System (20) according to any of the preceding claims, wherein the heat recovery system of the cooling section (D) comprises at least one heat exchanger (D1) and an absorption refrigerator (D2) which uses combustion gases to produce chilled water, which is sent to the heat exchanger (G) on the suction of the vacuum pumps (C1).

Images