Method for cooling a solid and system for carrying out the method
The present disclosure relates to a method and a device for cooling a solid, in particular a hygroscopic bulk material, in a more energy-efficient manner. For this purpose, an air flow is, if needed, cooled and/or dehumidified and/or subsequently heated in order to reduce the relative humidity of the air flow. The cooling air flow conditioned in this manner is then used in a contact device for cooling the solid, and a heated exhaust air flow is drawn from the contact device. According to the invention, a part of the exhaust air flow is mixed with the air flow in order to pre-heat the air flow and thus reduce the relative humidity of the air flow. In addition, a second part of the exhaust air flow can be mixed with feed air and used in a separate second contact device in order to pre-cool the solid.
1. A method for cooling a solid, in particular a hygroscopic bulk material, comprising:
passing the solid through a contact device;
injecting a cooling airflow into the contact device to cool the solid within the contact device and generate a heated exhaust air flow;
splitting the heated exhaust air flow into a first recycled partial exhaust air flow and a second partial heated exhaust air flow; and
mixing the first recycled partial exhaust air flow into the cooling air flow, to preheat the cooling air flow.
2. The method of claim 1 , wherein the cooling airflow is at least one of cooled, dehumidified, or reheated prior to said mixing step.
3. The method of claim 1 , further comprising:
prior to said mixing step, cooling the cooling airflow, by indirect heat exchange with a refrigerant, to a temperature below the dew point; and
separating condensate from the cooled cooling airflow.
4. The method of claim 1 , further comprising:
prior to said mixing step, cooling the cooling airflow, by indirect heat exchange with a refrigerant, to a temperature above the dew point.
5. The method of claim 1 , further comprising:
prior to said mixing step, heating the cooling air flow in a heating device by a heat transfer medium.
6. The method of claim 1 , wherein the contact device is one of a fluidized bed cooler or a drum cooler.
7. The method of claim 1 , wherein the cooling air flow is a conditioned cooling air flow having a relative humidity that remains below a critical limit value at which water passes, by exchange of heat and material, into the solid to be cooled.
8. The method of claim 1 , further comprising cooling the solid in at least a first cooling stage and a second cooling stage connected in series.
9. The method of claim 8 , further comprising:
conveying the solid to the first cooling stage;
in the first cooling stage, precooling the solid by heat exchange whereby the solid is contacted with a mixture of fresh air and the second partial heated exhaust airflow that is drawn from the second cooling stage;
conveying the solid to the second cooling stage; and
in the second cooling stage, further cooling the solid to a desired final temperature by heat exchange, whereby the solid is contacted with the cooling air flow, wherein the cooling airflow has been preconditioned.
10. The method of claim 9 , wherein a quantity of fresh air supplied to the first cooling stage is substantially equal to a quantity of the first recycled partial exhaust air flow that is mixed into the cooling airflow.
11. A system for cooling a solid, in particular a hygroscopic bulk material, comprising:
a contact device configured to cool the solid by heat exchange, whereby the solid is contacted with preconditioned cooling air within said contact device; and
an air recycling device in gaseous communication with said contact device and configured to recycle a partial flow of cooling air that is drawn from the contact device and has been heated in said contact device by exchange of heat with the solid.
12. The system of claim 11 , further comprising:
a preconditioning device configured to at least one of cool or dehumidify the cooling air prior to the cooling air entering the contact device as preconditioned cooling air; and
a heating device configured to heat the cooling air prior to the cooling air entering the contact device as preconditioned cooling air.
13. The system of claim 11 , wherein said contact device comprises:
a first contact device configured to precool the solid by heat exchange, whereby the solid is contacted with air within said contact device;
a second contact device in communication with said first contact device and configured to cool the solid by heat exchange to a final desired temperature, whereby the solid that has been precooled in the first contact device can be contacted with the preconditioned cooling air.
14. The system of claim 13 , wherein said air recycling device is in gaseous communication with said second contact device and configured to recycle a first partial flow of cooling air that is drawn from said second contact device and has been heated in said second contact device by exchange of heat with the solid.
15. The system of claim 14 , further comprising a mixing device in gaseous communication with said second contact device and configured to mix intake air with a second partial flow of the heated cooling air that is drawn from said second contact device, and supply the mixed cooling air to said first contact device to be used to precool the solid.