Copyright © 2006 Rithmware Technologies Inc. All rights reserved.

Example 4 – Combined Dryer and Heater

 

Problem

 

Material is known as follows

 

Type: solid particles

Feed moisture content = 0.03 kg/kg wet basis.

Feed temperature = 20 oC.

Product moisture content = 0.002 kg/kg wet basis.

Product temperature = 50 oC

Specific heat of the absolute dry material = 1.26 kJ/kg.oC.

Mass flow rate wet basis = 2000 kg/hr

 

Drying air has the following conditions:

 

Pressure at heater inlet = 104 kPa

Temperature at heater inlet = 20 oC

Absolute Humidity at heater inlet = 0.009 kg/kg dry air

Temperature at heater outlet = 90 oC

Pressure drop of air in heater = 0.8 kPa

Pressure drop of air in dryer = 1.2 kPa

 

Calculate the required mass flow rate of the drying air, the thermal energy to heat the air as well as the outlet humidity of the drying air from the dryer.

 

Solution Steps:

 

1.      Materials | New Material Settings. Select “Generic Drying Material” and click “Set” button to set this material as the drying material of the to-be-created new flowsheet if you have already created the Generic Drying Material in the material catalog. Otherwise, create the Generic Drying Material and then go to New Material Settings to set it.

2.      Create a new flowsheet by clicking the first icon  in the toolbar or clicking File | New.

3.      Create a heater on the flowsheet.

4.      Delete the outlet gas stream of the heater by selecting the stream, right clicking mouse and hitting the “Delete” in the pop-up menu. 

5.      Create a solid dryer.

6.      Connect the dryer’s gas inlet with the heater outlet port (the center of area on the right side of the heater’s icon)..

7.      Double click the heater’s icon to bring up the heater’s editor.

8.      Input in “Gas 1” column 104 kPa in the Pressure field, 20oC in the Dry-bulb Temperature field and 0.009 kg/kg in the Absolute Humidity field.

9.      Input in “Gas 2” column 90oC in the Dry-bulb Temperature field.

10.  Input in Pressure Drop field of the Heater group box 0.8 kPa.

11.  Double click the dryer icon to bring up the dryer’s editor.

12.  Input in “Mat 1” column 2000 kg/hr in the Mass Flow Rate (wet basis) field, 20oC in the Dry-bulb Temperature field and 0.03 in the Moisture Content (wet basis) field.

13.  Input in “Mat 2” column 50oC in the Dry-bulb Temperature field and 0.002 in the Moisture Content (wet basis) field.

14.  Input “Gas 3” column 48 oC in the Dry-bulb Temperature field.

15.  Input in “Gas Pressure Drop” field of the Dryer group box 1.2 kPa.

16.  After the enter key of last input is hit, both the dryer and the heater are solved and all the calculated variable values are displayed as shown in Figure 4a and 4b.

 

 

Figure 4a

 

 

Figure 4b

 

Alternative Solution Steps:

 

1.      Following the above solution steps 1 through 6. 

2.      Go to Edit | Flowsheet Data to bring up the global editor

3.      Input the known values in the gas and material streams’ columns of Gas 1, Gas 2, Gas 3, Mat 1, Mat 2. Input the pressure drop values for the heater and dryer in the Heater 1 and Dryer 1 in the global editor.

4.      After the enter key of last input is hit, both the dryer and the heater are solved and all the calculated variable values are displayed as shown in Figure 4c.

 

 

Figure 4c

 

Tip:

 

If the Heating Duty of the Heater (Heater 1) is known as 98.961 kJ/s (the same unit as kW) rather than the Temperature of the heater outlet (90 oC), you can delete the heater’s outlet temperature and then input 98.96 in the Heating Duty field of the heater. You will get the same results for the solved heater and dryer.