A spray dryer arrangement and a method of controlling such an arrangement

A spray dryer arrangement comprising

• a spray dryer device comprising an air inlet and an air outlet and an inlet for introduction of material to be dried and an outlet for removal of material that has been dried in the spray dryer device;
• a heat pump comprising a closed circuit in which a heat transferring medium is circulated, wherein the closed circuit comprises a compressor, an expansion valve device, an evaporator and a condenser;
• a dehumidifier device comprising an air inlet and an air outlet, and a dehumidifier element for dehumidification of air introduced through the air inlet and removed through the air outlet;
• a primary liquid circuit, which is connected to the closed circuit of the heat pump via heat-exchange through the condenser and which comprises a first heat exchanger configured for heat exchange between the primary liquid and air which is to be introduced into the spray drier device through the spray dryer device inlet;
• 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;
• a bypass conduit provided in the secondary liquid circuit for bypassing the second heat exchanger, and a controllable valve for controlling a flow of secondary liquid into the bypass conduit and to the second heat exchanger, respectively;
• a temperature sensor for measuring the temperature of the secondary liquid in the secondary liquid circuit;
• and
• a control unit configured to control the controllable valve on basis of input from the temperature sensor, and configured to thereby regulate the temperature of the secondary liquid in the secondary circuit to be within a predetermined temperature range.

A method of controlling a spray dryer arrangement, the spray dryer arrangement comprising:

• a spray dryer device comprising an air inlet and an air outlet, and an inlet for introduction of material to be dried and an outlet for removal of material that has been dried in the spray dryer device;
• a heat pump comprising a closed circuit in which a heat transferring medium is circulated, wherein the closed circuit comprises a compressor, an expansion valve device, an evaporator and a condenser;
• a dehumidifier device comprising an air inlet and an air outlet, and a dehumidifier element for dehumidification of air introduced through the air inlet and removed through the air outlet;
• a primary liquid circuit, which is connected to the closed circuit of the heat pump via heat-exchange through the condenser and which comprises a first heat exchanger configured for heat exchange between the primary liquid and air which is to be introduced into the spray drier device through the spray dryer device inlet;
• and
• 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, and a bypass conduit provided in the secondary liquid circuit for bypassing the second heat exchanger,
• the method comprising the steps of:
• measuring the temperature of the secondary liquid in the secondary liquid circuit;
• and
• controlling a flow of secondary liquid into the bypass conduit and to the second heat exchanger, respectively, on basis of the measured temperature, and thereby regulating the temperature of the secondary liquid in the secondary circuit to be within a predetermined temperature range.