FIELD OF THE INVENTION

[0001] The invention relates to an arrangement for conditioning moist exhaust air and more particularly to an arrangement according to preamble of claim 1. The invention relates also to a method for conditioning moist exhaust air and more particularly to a method according to preamble of claim 13.

BACKGROUND OF THE INVENTION

[0002] In a typical industrial drying process moisture is removed from a product into an air flow creating a moist exhaust air flow. The temperature and the moisture content of the exhaust air flow varies depending on the drying pro cess. Further, the moist exhaust air often contains also unwanted substances such as dust, dirt, odorous vapours and water soluble chemicals.

[0003] After a heat recovery process the moist exhaust air flow is usu ally exhausted to the atmosphere possibly causing emissions. In some areas, even exhausted plumes of a clean water vapour are unacceptable. The visible water va pour plumes can be of concern to the population living close to industrial plants. Further, plume induced fogging and icing rise accident risks and may be dangerous for crops and equipment. Formed fog may react with dust and irritative chemicals, e.g. sulphide compounds, in the surrounding air causing unsafe effects to the health of people in the surroundings.

BRIEF DESCRIPTION OF THE INVENTION

[0004] An object of the present invention is to provide a method and an arrangement so as to solve or at least alleviate the above problems. The objects of the invention are achieved with an arrangement which is characterized by what is stated in claim 1. The objects of the present invention are also achieved with a method which is characterized by what is stated in claim 13. The preferred embod iments of the invention are disclosed in other aspects of the invention.

[0005] The invention is based on the idea of an arrangement for condi tioning moist exhaust air. The arrangement comprises a heat exchanger unit, a washing unit and an air mixing chamber. The heat exchanger unit configured to transfer heat between the moist exhaust air and a supplementary air comprises an inlet and an outlet for the moist exhaust air and an inlet and outlet for the supple mentary air. The outlet for the moist exhaust air is connected to the washing unit configured to clean the moist exhaust air. The washing unit comprises an outlet for the washed moist exhaust air connected to an inlet of the air mixing chamber. The air mixing chamber comprises at least two compartments connected to the inlet of the air mixing chamber, and the compartments comprise inlets connected to the outlet of the supplementary air, and the compartments comprise outlets for the mixture of the washed moist exhaust air and the supplementary air. The arrange ment comprises a control system comprising humidity measuring devices and tem perature measuring devices, and the control system is configured to control a fan configured to pressurize the supplementary air based on measurement results ob tained from the humidity measuring devices and the temperature measuring de- vices located at the outlets of the compartments.

[0006] The invention is based on the idea of a method for conditioning moist exhaust air. The method comprises a heat exchanger unit, a washing unit and an air mixing chamber. A moist exhaust air flow is guided into the heat exchanger unit via an exhaust air inlet and exits via an exhaust air outlet, a supplementary air flow is guided into the heat exchanger unit via a supplementary air inlet and exits via a supplementary air outlet. Heat is transferred between the moist exhaust air flow and the supplementary air flow in the heat exchanger unit. The moist exhaust air flow flows from the outlet into the washing unit cleaning the moist exhaust air. The washed moist exhaust air flow flows from the outlet of the washing unit to an inlet of the air mixing chamber comprising at least two compartments. The washed moist exhaust air flow is divided between the compartments, from the heat ex changer unit exited supplementary air flow is guided to the air mixing chamber and divided between the compartments. In the compartments the washed moist ex haust air flow and the supplementary air flow are mixed, and the mixed washed moist exhaust air flow and the supplementary air flow exit the compartment via a compartment outlet. In the method, a control system comprising humidity meas uring devices and temperature measuring devices controls a fan pressurizing the supplementary air based on measurement results obtained from the humidity measuring devices and the temperature measuring devices located at the outlets of the compartments.

[0007] An advantage of the method and arrangement of the invention is that provides an efficient and a cost-effective dehumidification and cleaning of moist exhaust air.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

Figure 1 shows an arrangement for conditioning moist exhaust air;

Figure 2 shows an arrangement for conditioning moist exhaust air; Figure 3 shows an air mixing chamber.

DETAILED DESCRIPTION OF THE INVENTION

[0009] Figures 1 and 2 show an arrangement 1 for conditioning moist exhaust air 2. The arrangement conditions moist exhaust air 2 and it comprises a heat exchanger unit 3, a washing unit 4 and an air mixing chamber 5. The heat ex- changer unit 3 configured to transfer heat between the moist exhaust air 2 and a supplementary air 6. The heat exchanger unit 3 comprises an inlet 7 and an outlet 8 for the moist exhaust air and an inlet 9 and outlet 10 for the supplementary air. The outlet for the moist exhaust air 8 is connected to the washing unit 4. The wash ing unit 4 is configured to clean the moist exhaust air 2. The washing unit 4 com- prises an outlet 11 for the washed moist exhaust air connected to an inlet of the air mixing chamber 12. The air mixing chamber 5 comprises at least two compart ments 13a-e connected to the inlet of the air mixing chamber 12. The compart ments comprise inlets 14a-e for the supplementary air 6 which are connected to the outlet of the supplementary air 10. The compartments 13a-e comprise outlets 15a-e for the mixture 16a-e of the washed moist exhaust air 2a and the supplemen tary air. The arrangement comprises a control system comprising humidity meas uring devices 17 and temperature measuring devices 18. The control system is con figured to control a fan 19 configured to pressurize the supplementary air 6 based on measurement results obtained from the humidity measuring devices 17 and the temperature measuring devices 18 located at the outlets of the compartments 15a- e.

[0010] The method for conditioning moist exhaust air 2 comprises a heat exchanger unit 3, a washing unit 4 and an air mixing chamber 5. A moist ex haust air 2 flow is guided into the heat exchanger unit 3 via an exhaust air inlet 7 and exits via an exhaust air outlet 8. A supplementary air 6 flow is guided into the heat exchanger unit 3 via a supplementary air inlet 9 and exits via a supplementary air outlet 10 and heat is transferred between the moist exhaust air 2 flow and the supplementary air 6 flow in the heat exchanger unit 3. The moist exhaust air flow flows from the outlet 8 into the washing unit 4 cleaning the moist exhaust air, the washed moist exhaust air 2a flow flows from the outlet of the washing unit 11 to an inlet of the air mixing chamber 12 comprising at least two compartments 13a-e. The washed moist exhaust air 2a flow is divided between the compartments 13a- e, from the heat exchanger unit 3 exited supplementary air flow is guided to the air mixing chamber5 and divided between the compartments 13a-e. In the compart - ments 13a-e the washed moist exhaust air 2a flow and the supplementary air 6 flow are mixed, and the mixture of the washed moist exhaust air flow and the sup plementary air flow 16a-e exit the compartment via a compartment outlet 15a-e. In the method, a control system comprising humidity measuring devices 17 and temperature measuring devices 18 controls a fan 19 pressurizing the supplemen- tary air 6 based on measurement results obtained from the humidity measuring devices 17 and the temperature measuring devices 18 located at the outlets of the compartments 15a-e.

[0011] In Figure 1 the moist exhaust air 2 is guided to a bottom part of the housing containing the heat exchanger unit. The flow guiding may comprise pressurizing the moist exhaust air flow 2 with one or more fans 20.

[0012] The heat exchanger unit 3 comprises two heat exchangers, which are air-to-air heat exchangers. The type is a cross flow heat exchanger, for instance. The supplementary air 6 comprises preferably outdoor air. In the heat exchanger unit 3 the temperature of the moist exhaust air 2 decreases and the tem- perature of the supplementary air 6 increases.

[0013] In Figure 1 the heat exchanger unit 3, the washing unit 4 and the air mixing chamber 5 are contained in a same housing, and arranged one upon the another. The moist exhaust air 2 flow flows upwards in the heat exchanger unit 3, in the washing unit 4 and in the air mixing chamber 5 in vertical direction y.

[0014] The moist exhaust air 2 flows from the heat exchanger unit 3 into the washing unit 4. In the Figures 1-2 shown washing unit 4 is scrubbing the moist exhaust air 2 flow with a washing water. The washing unit 4 comprises a wet scrubber. The wet scrubber is utilized for cleaning and reducing the temperature and the moisture content of a moist exhaust air 2. The scrubber is advantageous in drying the moist exhaust air 2 as it offers large volume for the heat and mass trans fer. The wet scrubber is cost effective as the required heat and mass transfer sur face is considerably lower compared to conventional plate heat exchanger systems or a tube-in-a-shell heat exchanger systems. The scrubber cleans the moist exhaust air 2 by removing unwanted substances from the moist exhaust air 2. Examples of removable substances are dust, dirt, odorous vapours and water soluble chemicals.

[0015] In the scrubber of Figure 1 the moist exhaust air 2 flow flows upwards and droplets of a cooling water are injected into the exhaust air flow from a plurality of nozzles 21. The cooling water droplets are flowing downwards in counter flow to the exhaust air 2 flow. The moist exhaust air 2 collides with the cooling water creating a turbulent zone where the air/water interface is continu ously and rapidly renewed. Scrubbing is effectively accomplished by the thorough mixing of the exhaust air 2 and scrubbing cooling water in the scrubber.

[0016] The cleaned, washed moist exhaust air 2a is discharged from the scrubber through one or more exhaust air openings at the top part of the scrubber. A droplet separator 22 is arranged between the washing unit 4 and the air mixing chamber 5 for separating droplets from the washed moist exhaust air 2a.

[0017] In the Figures 1 and 2 the air mixing chamber 5 comprises three separate compartments 13a-c. Depending on the application, the number of com partments may be smaller, e.g. two as shown in Figure 3, or higher, e.g. four. Each compartment 13a-e comprises an inlet for the washed moist exhaust air and an inlet for the supplementary air 14a-e. The washed moist exhaust air 2a flow flow ing from the washing unit 4 into the air mixing chamber 5 is divided between the compartments 13a-e. In the heat exchanger unit 3 heated supplementary air 6 flow is guided to the air mixing chamber 5 and divided between the compartments 13a- e. In the compartments 13a-e the washed moist exhaust air 2a flow and the supple mentary air 6 flow are mixed. Preferably, the mixing ratio of the washed moist ex haust air 2a flow and the supplementary air 6 flow differs in adjacent compart ments 13a-e. This means that the state of the mixed air flow, i.e. the state of the mixture of the washed moist exhaust air flow and the supplementary air flow 16a- e, is different at adjacent compartment outlets 15a-e.

[0018] For instance, the air mixing chamber 5 comprises three com- partmentsl3a-c, and the the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-c at each compartment outlet 15a-c comprises differ ent temperature and/or humidity.

[0019] As an example, a following volume distribution of the washed moist exhaust air 2a flow and the supplementary air 6 flow can be used. The com bined volume flow of the washed moist exhaust air 2a flow and the supplementary air 6 flow into the first compartment 13a comprises 10-30%, the combined volume flow into the second compartment 13b comprises 10-30% and the combined vol ume flow into the third compartment 13c comprises 30-80% of the combined vol ume flows into all the compartments 13a-c. [0020] As an example, a following volume distribution of the compart ments 13a-c can be used. The volume of the first compartment 13a comprises 10- 30%, the volume of the second compartment 13b comprises 10-30% and the vol ume of the third compartment 13c comprises 30-80% of the combined volumes of the compartments 13a-c.

[0021] The arrangement shown in Figures 1-2 comprises a control sys tem comprising humidity measuring devices 17 and temperature measuring de vices 18. The control system is configured to control a fan 19 configured to pres surize the supplementary air 6 based on measurement results obtained from the humidity measuring devices 17 and the temperature measuring devices 18 located at the outlets of the compartments 15a-c.

[0022] The opening of the outlet of the compartment 15a-c can be ad justed to control the volume flow out of the compartment 13a-c.

[0023] The control system may further comprise an outdoor air humid- ity measuring device 17a, an outdoor air temperature measuring device 18a and a computing unit 23. The computing unit 23 determines a relative humidity of a dis charge air based on the measured temperatures and humidities. The discharge air comprises the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e at the outlet of one of the compartments 15a-e and surrounding out- door air. The control system controls the fan 19 configured to pressurize the sup plementary air 6 based on the determined relative humidity of a discharge air.

[0024] The fan 19 pressurizing the supplementary air 6 increases or decreases the supplementary air 6 flow such that the computed relative humidity of the discharge air remains below 98%. This prevents the formation of the plumes of a water vapour when the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e from the one of the compartments 13a-e is dis charged into outdoor air.

[0025] Figure 2 shows an arrangement for conditioning moist exhaust air 2. The reference numbers used in Figure 1 are used for corresponding compo- nents in Figure 2. In the arrangement shown in Figure 2 the placement of some of the components and the flow path of the moist exhaust air 2 flow differs from the arrangement of Figure 1. The description of Figure 1 is otherwise valid and is not repeated.

[0026] In Figure 2 shown arrangement, the heat exchanger unit 3 and the washing unit 4 are contained in a same housing, and the air mixing chamber 5 is arranged side by side in horizontal direction x. [0027] In Figure 2, the heat exchanger unit 3 is divided into two parts. The moist exhaust air 2 flow enters the first heat exchanger part 3a of the heat ex changer unit 3 and flows upwards y through the first heat exchanger part 3a into the washing unit 4. In the washing unit 4 the moist exhaust air 2 flow is cleaned and it moves horizontally x towards the second heat exchanger part 3b of the heat exchanger unit 3. In the second heat exchanger part 3b of the heat exchanger unit 3 the washed moist exhaust air 2a flows downwards.

[0028] The washed moist exhaust air 2a flows then substantially hori zontally towards the bottom part of the air mixing chamber 5. The washed moist exhaust air 2a flows enters the bottom part of the air mixing chamber 5 and starts to flow upwards. A droplet separator 22 is arranged between the bottom part of the air mixing chamber 5 and the compartments 13a-c for separating droplets from the washed moist exhaust air 2a.

[0029] The arrangement of the compartments and the control system corresponds the ones shown in Figure 1.

[0030] Figure 3 shows an air mixing chamber 5. The air mixing cham ber 5 is applicable to the embodiments shown in Figures 1 and 2. The washed moist exhaust air 2a flow is guided to the bottom part of the air mixing chamber 5. In Figure 3 the washed moist exhaust air 2a flows into the air mixing chamber 5 in horizontal direction, but the air mixing chamber 5 can be arranged on the top of the air washing unit 4 as shown in Figure 1. The air mixing chamber 5 comprises two compartments 13d-e. Each compartment 13d-e comprises an inlet for the washed moist exhaust air 2a and for the supplementary airl4 d-e. The washed moist exhaust air 2a flow flowing from the washing unit 4 into the air mixing cham- ber 5 is divided between the two compartments 13d-e. In the heat exchanger unit 3 heated supplementary air 6 flow is guided to the air mixing chamber 5 via inlets 14d-e and divided between the two compartments 13d-e.

[0031] In the compartments the washed moist exhaust air 2a flow and the supplementary air 6 flow are mixed. The mixing ratio of the washed moist ex- haust air 2a flow and the supplementary air 6 flow differs in adjacent compart ments 13d-e. This means that the state of the mixed air flow, i.e. the state of the mixture of the washed moist exhaust air flow and the supplementary air flow 16d- e, is different at adjacent compartment outlets 15d-e.

[0032] The mixture of the washed moist exhaust air flow and the sup- plementary air flowl6d-e from the compartments 13d-e is arranged to be distrib utable at the outlets 15d-e into two separate air flows such that the mixture 16d-e from both compartments 13d-e can be discharged into outdoor air. Thus, 0-100% of the mixture of the washed moist exhaust air flow and the supplementary air flow 16d-e exiting a compartment 13d-e can be discharged into outdoor air.

[0033] In an embodiment, the moist exhaust air 2 is process air from a drying process. In the drying process moisture is removed from a product into a hot air flow creating a moist exhaust air flow. The drying process is preferably con tinuous energy intensive drying process where the moist exhaust air flow may comprise 80-200 grams of water vapour per kg of air, for instance, where the tem perature of the moist exhaust air comprises 48°C-85°C. Examples of continuous energy intensive drying processes are drying of paper, pulp, wood, lumber or waste sludge.

[0034] In an embodiment, the arrangement is connected to a dryer hood system of a paper or pulp machine, wherein the dryer hood system comprises a dryer hood arranged above paper or pulp machine in a production hall, the pro- duction hall comprises an inlet for a building supply air, the dryer hood comprising a hood supply air inlet and an hood exhaust air outlet, wherein the hood exhaust air outlet is connected to the inlet of the moist exhaust air 7 in the heat exchanger unit 3, and the hood supply air inlet is connected to one of the outlets of the com partments 15a-e of the air mixing chamber 5, and another of the outlets of the com- partments 15a-e of the air mixing chamber 5 is connected to the inlet for a building supply air of the production hall. Preferably, the mixture of the washed moist ex haust air flow and the supplementary air flow 16a-e from the compartment 13a-e connected to the hood supply air inlet comprises more water vapour per kg of air than the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e from the compartment 13a-e connected to the inlet for a building supply air of the production hall.

[0035] Further, in the arrangement connected to a dryer hood system of a paper or pulp machine the air mixing chamber can comprise a third compart ment 13a-e, and from the outlet of the third compartment 15a-e of the air mixing chamber 5 the mixture of the washed moist exhaust air flow and the supplemen tary air flow 16a-e is discharged into outdoor air.

[0036] In an embodiment, the arrangement is connected to a dryer hood system of a paper or pulp machine, wherein the dryer hood system comprises a dryer hood arranged above paper or pulp machine in a production hall. The pro- duction hall comprises an inlet for a building supply air, the dryer hood comprising a hood supply air inlet and a hood exhaust air outlet, wherein the hood exhaust air outlet is connected to the inlet of the moist exhaust air 7 in the heat exchanger unit 3. The mixing chamber 5 comprises two separate compartments 13d-e. The hood supply air inlet is connected to the outlet of the first compartment 15d, and the outlet of the second compartment 15e is connected to the inlet for a building supply air of the production hall. At least part of the mixture of the washed moist exhaust air flow and the supplementary air flow 16d-e at the outlets of the first and second compartments 15d-e is dischargeable into outdoor air. Preferably, the mixture of the washed moist exhaust air flow and the supplementary air flow 16d from the first compartment 13d comprises more water vapour per kg of air than the mixture of the washed moist exhaust air flow and the supplementary air flow 16e from the second compartment 13e.

[0037] Further, as an example, a following volume distribution of the washed moist exhaust air 2a flow and the supplementary air 6 flow can be used. The combined volume flow of the washed moist exhaust air 2a flow and the sup- plementary air 6 flow into the first compartment 13d comprises 30-80% and the combined volume flow into the second compartment 13e comprises 10-30% of the combined volume flows into all the compartments 13d-e.

[0038] In an embodiment, in the method a dryer hood system is drying a sheet like material in a paper or pulp machine, wherein the dryer hood system comprises a dryer hood arranged above the paper or pulp machine in a production hall, a building supply air is provided to the production hall via an inlet, a hood supply air is guided to the dryer hood via an inlet and a hood exhaust air is guided away from the dryer hood via an outlet, wherein the hood exhaust air is guided to the inlet of the moist exhaust air 7 in the heat exchanger unit 3, and from one of the outlets of the compartments 15a-e of the air mixing chamber 5 the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e is guided to the hood supply air inlet, and from another of the outlets of the compartments 15a-e of the air mixing chamber 5 the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e is guided to the inlet for a building supply air of the production hall.

[0039] Further, in the method where a dryer hood system is drying a sheet like material in a paper or pulp machine the air mixing chamber can comprise a third compartment 13a-e, and through the outlet of the third compartment 15a- e of the air mixing chamber 5 the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e is discharged into outdoor air. [0040] In an embodiment, in the method a dryer hood system is drying a sheet like material in a paper or pulp machine, wherein the dryer hood system comprises a dryer hood arranged above the paper or pulp machine in a production hall, a building supply air is provided to the production hall via an inlet, a hood supply air is guided to the dryer hood via an inlet and a hood exhaust air is guided away from the dryer hood via an outlet, wherein the hood exhaust air is guided to the inlet of the moist exhaust air 7 in the heat exchanger unit3. The mixing chamber 5 comprises two separate compartments 13a-e, and from the outlet of the first compartment 15a-e the mixture of the washed moist exhaust air flow and the sup- plementary air flow 16a-e is guided to the hood supply air inlet, and from the outlet of the second compartment 15a-e of the air mixing chamber 5 the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e is guided to the inlet for a building supply air of the production hall. At least part of the mixture of the washed moist exhaust air flow and the supplementary air flow 16a-e at the outlets of the first and second compartments 15a-e is dischargeable into outdoor air.

[0041] It will be obvious to a person skilled in the art that, as the tech nology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

[0042] Parts list: 1 an arrangement; 2 moist exhaust air, 2a washed moist exhaust air; 3 a heat exchanger unit; 3a, b a heat exchanger part; 4 a washing unit; 5 an air mixing chamber; 6 a supplementary air; 7 an inlet for the moist ex haust air; 8 an outlet for the moist exhaust air; 9 an inlet for the supplementary air; 10 an outlet for the supplementary air; 11 an outlet of a washing unit; 12 an inlet of an air mixing chamber; 13a-e a compartment; 14a-e an inlet of a compartment for supplementary air; 15a-e an outlet of a compartment; 16a-e a mixture; 17, 17a a humidity measuring device; 18, 18a a temperature measuring device; 19 a sup plementary air fan; 20 a moist exhaust air fan; 21 a nozzle; 22 a droplet separator; 23 a computing unit; x horizontal direction; y vertical direction.