Spray dryer apparatus and method of controlling such apparatus

Abstract

A spray dryer apparatus comprises a spray dryer device (1), a heat pump (14) and a dehumidifier device (24), a primary liquid circuit (20) and a secondary liquid circuit (22). The spray dryer apparatus comprises: a bypass conduit (66) provided in the secondary liquid circuit for bypassing the second heat exchanger (23) and a controllable valve (34) for controlling the flow of secondary liquid into the bypass conduit (66) and to the second heat exchanger (23), respectively; a temperature sensor (35) for measuring the temperature of the secondary liquid in the secondary liquid circuit (22); and a control unit (36) configured to control the controllable valve (34) based on an input from the temperature sensor (35) and to thereby adjust the temperature of the secondary liquid in the secondary circuit (22) to within a predetermined temperature range.

Description

Technical Field

[0001] The present invention relates to a spray dryer device, the spray dryer device comprising:

[0002] a spray dryer device comprising an air inlet and an air outlet as well as an inlet for introducing material to be dried and an outlet for removing material that has been dried in the spray dryer device,

[0003] a heat pump comprising a closed circuit in which a heat transfer medium circulates, wherein the closed circuit comprises a compressor, an expansion valve device, an evaporator and a condenser,

[0004] a dehumidifier device comprising an air inlet and an air outlet and a dehumidifier element for dehumidifying air introduced through the air inlet and removed through the air outlet,

[0005] a primary liquid circuit connected to the closed circuit of the heat pump via heat exchange through a condenser and comprising a first heat exchanger configured for heat exchange between the primary liquid and air to be introduced into the spray dryer device through its inlet, and

[0006] a secondary liquid circuit which is connected to the closed circuit of the heat pump via heat exchange through the evaporator and which comprises a second heat exchanger configured for heat exchange between the secondary liquid and air removed from the spray dryer device via the spray dryer device air outlet.

[0007] The present invention also includes a method of controlling such a spray dryer apparatus. Background Art

[0008] Spray dryer apparatus comprising a spray dryer device and a dehumidifier device connected to a heat pump are known in the prior art. The heat pump is used to provide a hot liquid which is used to heat the air to be introduced into the spray dryer device for the purpose of drying the wet material introduced into the same spray dryer device. The air passing through the spray dryer device will leave the spray dryer device as relatively warm exhaust gas which may have considerable energy.

[0009] The air to be introduced into the spray dryer device is dried in the dehumidifier device before being heated by heat exchange with the hot liquid from the heat pump. The dehumidifier may be of a type that can utilize energy in the exhaust gases from the spray dryer device. For example, the dehumidifier may be of a desiccant type that requires hot air for regenerating its dehumidifier elements. Depending on the temperature of the surrounding atmosphere, the air to be introduced into the dehumidifier device may also need to be heated. Therefore, the hot liquid on the hot side of the heat pump can be used not only to heat the air to be introduced into the spray dryer device, but also to heat the air to be introduced into the dehumidifier device and to heat the air for regenerating the dehumidifier elements of the dehumidifier device.

[0010] The cold side of the heat pump includes a liquid, usually water, which exchanges heat with the heat transfer medium of the heat pump through the evaporator of the heat pump. Depending on the temperature of the surrounding atmosphere, the cold liquid on the cold side of the heat pump can be used to pre-cool the air to be introduced into the dehumidifier device.

[0011] The heat (energy) from the exhaust gases of the spray dryer unit can be used for the purpose of heating the cold liquid on the cold side of the heat pump before returning the cold liquid for further heat exchange via the evaporator.

[0012] The output of the compressor of the heat pump may be controlled for the purpose of controlling the temperature of the liquid on the hot side of the heat pump and hence the temperature of the air to be introduced into the spray dryer apparatus.

[0013] The balance of the plant is crucial for its energy efficiency. Advantageously, only one heat pump is used, and the capacity of the heat pump is as small as possible, but still capable of delivering the heat required for the spray dryer, the heating of the dehumidifier (both for regeneration and for the air to be introduced into the dehumidifier). The balance also includes making the plant able to cope with different ambient air temperatures, for example from minus 20 degrees Celsius up to plus 50 degrees Celsius.

[0014] WO2018091049A1 discloses a device similar to the one disclosed above. However, WO2018091049A1 is quite vague about how to control the device and balance the device in a way that achieves favorable efficiency.

[0015] Therefore, the object of the present invention is to propose a spray dryer device which is designed in a manner to promote its stable and efficient operation, which is capable of delivering air of a predetermined temperature to the spray dryer device independently of differences in ambient air temperature, and which spray dryer device does not require an oversized heat pump due to its design. Summary of the invention

[0016] The objects of the invention are achieved by means of the initially defined spray dryer apparatus, which also comprises the following features:

[0017] a bypass conduit provided in the secondary liquid circuit for bypassing the second heat exchanger and a controllable valve for controlling the flow of secondary liquid into the bypass conduit and to the second heat exchanger, respectively,

[0018] a temperature sensor for measuring the temperature of the secondary liquid in the secondary liquid circuit, and

[0019] - a control unit configured to control the controllable valve based on an input from the temperature sensor and configured thereby to adjust the temperature of the secondary liquid in the secondary circuit to within a predetermined temperature range.

[0020] If the temperature of the liquid in the secondary liquid circuit is below a predetermined temperature, the control unit is configured to control the valve so as to increase the flow of the secondary liquid through the second heat exchanger and to reduce the flow through the bypass duct. If the temperature is too high, the control unit is configured to control the valve so as to reduce the flow of the secondary liquid through the second heat exchanger and to increase the flow through the bypass duct. Thus, a stabilization of the spray dryer plant and a stabilization of the preconditions for the operation of the heat pump are achieved. The aim is to obtain a constant set temperature of the secondary liquid at the evaporator. Therefore, the control unit is configured to control the distribution of the secondary liquid to the second heat exchanger and the bypass duct as a response to the measured temperature in the circuit so as to achieve the set temperature value.

[0021] According to an embodiment, the secondary liquid circuit comprises a third heat exchanger configured for heat exchange between the secondary liquid and air introduced into the dehumidifier device through the dehumidifier device air inlet. Preferably, the spray dryer device comprises a temperature sensor for measuring the temperature of the air leaving the third heat exchanger, and the control unit is configured to control the flow of the secondary liquid to and through the third heat exchanger based on input from the temperature sensor so as to control the temperature of the air leaving the third heat exchanger.

[0022] According to an embodiment,

[0023] - the dehumidifier element comprises an air inlet and an air outlet for passing air through a portion of the dehumidifier element to heat the portion of the dehumidifier element, and

[0024] - the primary liquid circuit comprises a fourth heat exchanger configured for heat exchange between the primary liquid and air introduced into the dehumidifier element via said dehumidifier air inlet. According to one embodiment, the dehumidifier is a desiccant dehumidifier and said portion is a portion of the dehumidifier element which is temporarily not used for drying air passing through the dehumidifier. In other words, said heating is used for regeneration of the dehumidifier element.

[0025] The object of the present invention is also achieved by means of a method for controlling a spray dryer device, the spray dryer device comprising:

[0026] a spray dryer device comprising an air inlet and an air outlet, and an inlet for introducing material to be dried and an outlet for removing material already dried in the spray dryer device,

[0027] a heat pump comprising a closed circuit in which a heat transfer medium circulates, wherein the closed circuit comprises a compressor, an expansion valve device, an evaporator and a condenser,

[0028] a dehumidifier device comprising an air inlet and an air outlet, and a dehumidifier element for dehumidifying air introduced through the air inlet and removed through the air outlet,

[0029] a primary liquid circuit connected to the closed circuit of the heat pump via heat exchange through a condenser and comprising a first heat exchanger configured for heat exchange between the primary liquid and air to be introduced into the spray dryer device through the spray dryer device inlet,

[0030] a secondary liquid circuit connected to the closed circuit of the heat pump via heat exchange through the evaporator and comprising a second heat exchanger configured for heat exchange between the secondary liquid and air removed from the spray dryer device via the spray dryer device air outlet, and a bypass conduit provided in the secondary liquid circuit for bypassing the second heat exchanger,

[0031] Wherein, the method comprises the following steps:

[0032] - measuring the temperature of the secondary liquid in the secondary liquid circuit, and

[0033] - controlling the flow of secondary liquid into the bypass conduit and to the second heat exchanger, respectively, based on the measured temperature and thereby regulating the temperature of the secondary liquid in the secondary circuit within a predetermined temperature range.

[0034] According to an embodiment, the method further comprises the following steps:

[0035] - exchanging heat between the secondary liquid and air introduced into the dehumidifier device through the dehumidifier device air inlet.

[0036] According to an embodiment, the method further comprises the following additional steps:

[0037] - passing air through a portion of the dehumidifier element for heating the portion of the dehumidifier element, and,

[0038] - Exchange of heat between the primary liquid and the air that will pass through said portion of the dehumidifier element.

[0039] According to one embodiment, during operation of the disclosed spray dryer apparatus, the flow rate of the primary liquid through the primary loop remains constant and the flow rate of the secondary liquid through the secondary loop remains constant.

[0040] Other features are presented in the detailed description of the embodiments which follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic diagram of a heat pump circuit, a primary liquid circuit and a secondary liquid circuit according to the present invention, indicating the positions where heat exchangers between the primary liquid circuit and the air and between the secondary liquid circuit and the air are arranged, and

[0042] Figure 2 is a schematic diagram of a spray dryer apparatus according to the present invention, which also indicates the positions at which heat exchangers between the primary liquid circuit and the air and between the secondary liquid circuit and the air are arranged in the apparatus.

[0043] Figure 3 is corresponding to Figure 2 Schematic diagram of a second embodiment of a spray dryer apparatus. DETAILED DESCRIPTION

[0044] Figure 1 and Figure 2 An alternative representation of the same spray dryer apparatus is shown, although Figure 1 The heat pump and the liquid circuit are shown more intensively, while Figure 2 The focus is more on showing how the air to be heated or cooled by means of the heat pump flows into and out of the corresponding components of the spray dryer device.

[0045] Reference Figure 1 and Figure 2 , the spray dryer apparatus comprises a spray dryer device 1, which comprises a spray dryer 2 having air inlets 3, 4, 5 and an exhaust gas outlet 6. The spray dryer 2 also comprises an inlet 7 for introducing material to be dried and an outlet 8 for removing material that has been dried in the spray dryer 2. The spray dryer device 2 also comprises a fluidized bed 9 configured to receive the dried material from the outlet 8 of the spray dryer 2. The fluidized bed 9 has air inlets 10, 11, 12 for introducing air for further drying and an outlet 13 for exhaust gas from the fluidized bed 9. The outlet 13 from the fluidized bed 9 is connected to the outlet 6 of the spray dryer 2 so that the exhaust gas from the spray dryer 2 is mixed with the exhaust gas from the fluidized bed 9. A fan 53 is provided downstream of the outlets 6 and 13.

[0046] The spray dryer apparatus further comprises a heat pump 14 comprising a closed circuit 15 in which a heat transfer medium circulates, wherein the closed circuit 15 comprises a compressor 16 , an expansion valve device 17 , an evaporator 18 and a condenser 19 .

[0047] Primary liquid circuit 20 (see in particular Figure 1 ) is connected to a closed loop 15 of a heat pump 14 via heat exchange through a condenser 19. The primary liquid loop 20 comprises first heat exchangers 21a, 21b, 21c, 21d, 21e configured for heat exchange between the primary liquid and air to be introduced into the spray dryer device 1 through the inlets 3, 4, 5 of the spray dryer 2 and the inlets 10, 11, 12 of the fluidized bed 9.

[0048] The secondary liquid circuit 22 is connected to the closed circuit 15 of the heat pump via heat exchange through the evaporator 18, thereby forming the cold side of the heat pump 14. The secondary liquid circuit 22 comprises a second heat exchanger 23 configured for heat exchange between the secondary liquid and the exhaust gas removed from the spray dryer device 1 via the outlet 6 from the spray dryer 2 and the outlet 13 from the fluidized bed 9.

[0049] In the embodiment shown, the primary liquid is water and the second liquid is water. In addition, the spray dryer device comprises a dehumidifier device 24, which comprises an air inlet 25 and an air outlet 26 and a dehumidifier element 27 for dehumidifying the air introduced through the air inlet 25 and removed through the air outlet 26. The dry air removed from the outlet 26 of the dehumidifier device 24 after having passed through the dehumidifier element 27 is guided to the corresponding air inlets 3, 4, 5 of the spray dryer 2 and the corresponding air inlets 10, 11, 12 of the fluidized bed 9 via branches 28, 29, 30, 31, 32 of the air guide duct 33. The first heat exchangers 21a to 21e mentioned above are arranged in the branches 28 to 32, one in each branch. In each of the branches 28 to 32, fans 54 to 58 are provided. In two of the branches, branches 29 and 30, electric heaters 59, 60 are provided for supplementary heating of the air flowing in these branches.

[0050] The spray dryer apparatus further comprises a bypass conduit 66 provided in the secondary liquid circuit for bypassing the second heat exchanger and a controllable valve 34 for controlling the flow of secondary liquid into the bypass conduit 66 and to the second heat exchanger 23 respectively.

[0051] The spray dryer device also includes a temperature sensor 35 for measuring the temperature of the secondary liquid in the secondary liquid loop 22 and a control unit 36, the temperature sensor 35 being used to measure the temperature of the secondary liquid in the secondary liquid loop 22, and the control unit 36 ​​being configured to control the controllable valve 34 based on the input from the temperature sensor 35 and configured to thereby adjust the temperature of the secondary liquid in the secondary loop 22 to a predetermined temperature. If the temperature of the liquid in the secondary liquid loop is lower than the predetermined temperature, the flow of the secondary liquid entering the second heat exchanger 23 is increased, and the flow of the secondary liquid entering the bypass duct is reduced. If the temperature is too high, the opposite flow adjustment is performed. Thus, the stability of the spray dryer device and the stability of the preconditions for the operation of the heat pump 14 are achieved. The purpose of controlling the flows through the second heat exchanger 23 and the bypass duct 66, respectively, is to obtain a constant set temperature of the secondary liquid at the evaporator 18.

[0052] It should also be mentioned that during operation of the disclosed spray dryer apparatus, the flow rate of the primary liquid through the primary loop 20 remains constant and the flow rate of the secondary liquid through the secondary loop 22 remains constant.

[0053] Furthermore, the secondary liquid circuit 22 comprises a third heat exchanger 37 configured for heat exchange between the secondary liquid and the air introduced into the dehumidifier device 24 through the dehumidifier device air inlet 25. A control valve 38 is used to control the flow of the secondary liquid to the third heat exchanger 37. A temperature sensor 39 for measuring the temperature of the air flowing toward the dehumidifier element 27 is provided between the third heat exchanger 37 and the dehumidifier element 27. The control unit 36 ​​is connected to the temperature sensor 39 and the control valve 38, and is configured to control the control valve 38 based on an input from the temperature sensor 39 so as to obtain a predetermined temperature of the air guided to the dehumidifier element 27.

[0054] A temperature sensor 49 for measuring the ambient air temperature is also provided. The control unit 36 ​​is configured to control the control valve 38 of the third heat exchanger 37 also based on the input from the ambient air temperature sensor 49. If the temperature sensor 49 indicates that the ambient air temperature is below a predetermined value - which indicates that the environment is cold and therefore dry - the control unit 36 ​​closes the control valve 38 of the third heat exchanger 37 and turns off the active action of the dehumidifier element 27. In this case, this means that the wheel 27 keeps rotating, but the regeneration by heating thereof is turned off.

[0055] The secondary liquid loop 22 further includes a cold water storage tank 40 and a pump 41 .

[0056] The primary liquid circuit 20 comprises a fourth heat exchanger 42 configured for heat exchange between the primary liquid and the air introduced into the dehumidifier element 27 via the dehumidifier air inlet 25. The fourth heat exchanger 42 can be used to heat the air if the ambient temperature sensor indicates that the ambient air temperature is below a predetermined value. In this case, the predetermined value is the same value at which the control unit 36 ​​closes the control valve 38 of the third heat exchanger 37 and deactivates the dehumidifier element 27. The control unit 36 ​​is also configured to control the flow of the primary liquid through the fourth heat exchanger 42 based on input from a temperature sensor 39 disposed between the third heat exchanger 37 and the dehumidifier element 27. In the case where the third heat exchanger 37 is not activated (valve 38 is closed), the temperature of the air flowing through the dehumidifier 24 towards the spray dryer 1 is thus controlled, more precisely raised, by the activation of the fourth heat exchanger 42. In the illustrated embodiment, the third heat exchanger 37 is located downstream of the fourth heat exchanger 42 as seen in the flow direction of air through the third heat exchanger 37 and the fourth heat exchanger 42 .

[0057] The primary liquid circuit further comprises a fifth heat exchanger 47 configured for heat exchange with air for regenerating the dehumidifier element 27. In an exemplary embodiment, the dehumidifier 24 is a desiccant dehumidifier and the dehumidifier element 27 is a wheel carrying a desiccant, wherein the hot air introduced via the air inlet 25 of the dehumidifier device 24 is branched off from the air to be dried and is used instead to regenerate the temporarily inactive part of the wheel. The dehumidifier 24 comprises a pump or fan 48 for pumping air branched off from the dehumidifier element 27 and used to regenerate the dehumidifier element 27. A controllable valve (not shown) for controlling the flow of the primary liquid through the fifth heat exchanger may preferably be provided. An air humidity sensor 51 is provided downstream of the dehumidifier element 27 for the purpose of determining the moisture content of the air that has been dried in the dehumidifier 24. The control unit is configured to control the controllable valve 52, the rotation speed of the wheel 27 and the output of the fan / pump 48 based on input from the air humidity sensor 51. A separate outlet 46 for air that has been used to regenerate the dehumidifier element 27 is provided.

[0058] The primary liquid circuit 20 also includes a warm water storage tank 43 and a pump 44 for storing and pumping the primary liquid in the primary liquid circuit 20 .

[0059] Furthermore, the primary liquid circuit 20 comprises a temperature sensor 45 for measuring the temperature of the primary liquid. The control unit 36 ​​is configured to control the compressor 16 of the heat pump 14 based on an input from the temperature sensor 45.

[0060] exist Figure 1 Other components visible in the figure but not described in further detail here are:

[0061] - temperature sensors 61a to 61e for measuring the temperature of the air downstream of each of the first heat exchangers 21a to 21e; ​​control valves 62a to 62e for controlling the flow of primary liquid through each of the first heat exchangers 21a to 21e based on input from the temperature sensors 61a to 61e;

[0062] a temperature sensor 63 for measuring the temperature of the air downstream of the fifth heat exchanger 47, wherein the controllable valve 52 for controlling the primary liquid flow through the fifth heat exchanger is controlled by the control unit 26 based on input from said temperature sensor.

[0063] Figure 3 The alternative embodiment shown in Figure 1 and Figure 2 The embodiment shown in FIG. 1 differs only in that the compressor 16 comprises a low-pressure compressor 16a and a high-pressure compressor 16b. An intercooler is also provided. Therefore, the control unit 36 ​​is configured to control both the low-pressure compressor 16a and the high-pressure compressor 16b.

Claims

1. A spray dryer device comprising: - a spray dryer device (1) comprising an air inlet (3, 4, 5, 10, 11, 12) and an air outlet (6, 13), as well as an inlet (7) for introducing material to be dried and an outlet (8) for removing material already dried in the spray dryer device (1), a heat pump (14), said heat pump (14) comprising a closed circuit (15) in which a heat transfer medium circulates, wherein said closed circuit (15) comprises a compressor (16), an expansion valve device (17), an evaporator (18) and a condenser (19), - a dehumidifier device (24) comprising an air inlet (25) and an air outlet (26), and a dehumidifier element (27) for dehumidifying air introduced through the air inlet (25) and removed through the air outlet (26), a primary liquid circuit (20) connected to the closed circuit (15) of the heat pump (14) via heat exchange through the condenser (19), and comprising a first heat exchanger (21) configured for heat exchange between primary liquid and air to be introduced into the spray dryer device (1) through a spray dryer device inlet (3, 4, 5, 10, 11, 12), a secondary liquid circuit (22) connected to the closed circuit (15) of the heat pump (14) via heat exchange through the evaporator (18), and comprising a second heat exchanger (23) configured for heat exchange between secondary liquid and air removed from the spray dryer device (1) via a spray dryer device air outlet (6, 13), The spray dryer device is characterized in that the spray dryer device comprises: a bypass conduit (66) provided in the secondary liquid circuit for bypassing the second heat exchanger, and a controllable valve (34) for controlling the flow of secondary liquid into the bypass conduit (66) and to the second heat exchanger (23), respectively, - a temperature sensor (35) for measuring the temperature of the secondary liquid in the secondary liquid circuit (22), and - a control unit (36) configured to control the controllable valve (34) based on an input from the temperature sensor (35) and configured to thereby adjust the temperature of the secondary liquid in the secondary circuit (22) to within a predetermined temperature range.

2. The spray dryer apparatus according to claim 1, wherein The secondary liquid circuit (22) includes a third heat exchanger (37) configured for heat exchange between secondary liquid and air introduced into the dehumidifier device (24) through a dehumidifier device air inlet (25).

3. The spray dryer apparatus according to claim 1 or 2, wherein: - the dehumidifier element (27) comprises an air inlet (25) and an air outlet (46) for passing air through a portion of the dehumidifier element (27) to heat a portion of the dehumidifier element (27), and wherein The primary liquid circuit (20) comprises a fourth heat exchanger (42) configured for heat exchange between primary liquid and air introduced into the dehumidifier element (27) via the dehumidifier air inlet (25).

4. A method for controlling a spray dryer device, the spray dryer device comprising: - a spray dryer device (1) comprising an air inlet (3, 4, 5, 10, 11, 12) and an air outlet (6, 13), as well as an inlet (7) for introducing material to be dried and an outlet (8) for removing material already dried in the spray dryer device (1), a heat pump (14), said heat pump (14) comprising a closed circuit (15) in which a heat transfer medium circulates, wherein said closed circuit (15) comprises a compressor (16), an expansion valve device (17), an evaporator (18) and a condenser (19), - a dehumidifier device (24) comprising an air inlet (25) and an air outlet (26), and a dehumidifier element (27) for dehumidifying air introduced through the air inlet (25) and removed through the air outlet (26), a primary liquid circuit (20) connected to the closed circuit (15) of the heat pump (14) via heat exchange through the condenser (19), and comprising a first heat exchanger (21) configured for heat exchange between primary liquid and air to be introduced into the spray dryer device (1) through a spray dryer device inlet (3, 4, 5, 10, 11, 12), a secondary liquid circuit (22) connected to the closed circuit (15) of the heat pump (14) via heat exchange through the evaporator (18), and comprising a second heat exchanger (23) configured for heat exchange between a secondary liquid and air removed from the spray dryer device (1) via a spray dryer device air outlet (6, 13), and a bypass conduit (66) arranged in the secondary liquid circuit for bypassing the second heat exchanger (23), The method is characterized in that the method comprises the following steps: - measuring the temperature of the secondary liquid in the secondary liquid circuit (22), and - controlling the flow of secondary liquid into the bypass conduit (66) and to the second heat exchanger (23), respectively, based on the measured temperature and thereby regulating the temperature of the secondary liquid in the secondary circuit (22) within a predetermined temperature range.

5. The method according to claim 4, comprising the steps of: - exchanging heat between the secondary liquid and the air introduced into the dehumidifier device (24) through the dehumidifier device air inlet (25).

6. The method according to claim 4 or 5, comprising the following additional steps: - passing air through a portion of the dehumidifier element (27) for heating a portion of the dehumidifier element (27), and, - Exchanging heat between a primary liquid and the air that will pass through said portion of said dehumidifier element (27).

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