*2.1. System Description*

The instant co ffee was dried in an industrial scale spray drying system. Figure 1 illustrates a schematic diagram of the process. The co ffee extract (44% m/m of soluble co ffee) comes from a storage tank that had a temperature of 12 ◦C. A flow rate of 528 kg/h of co ffee extract (stream 2) was pumped by a low-pressure pump (LP) and mixed with 7.4 kg/h of carbon dioxide (stream 1). Then it was pumped by a high-pressure pump (HP) into a heat exchanger unit (HXE) where steam increased its temperature to 32 ◦C. The co ffee extract (stream 6) was sprayed by a nozzle into the drying unit (SD), which is at vacuum pressure. A flow rate of 9922 kg/h of ambient air (stream 7) was heated by the main heat exchanger (MHX) using steam until it reached the temperature of 180 ◦C. A flow rate of 4002 kg/h of ambient air (stream 10) with an absolute humidity of 0.02 kg water/kg dry air was dehumidified to 8 × 10−<sup>3</sup> kg water/kg dry air by a cooler (CHX) and then a fraction of it (stream 11) was heated and distributed in order to maintain a fluidized bed in the bottom of the spray dryer. The dried instant co ffee produced with a humidity of about 3% m/m (stream 23) was then collected on a belt (BT), where two streams of dehumidified air at 85 ◦C (stream 16) and 27 ◦C (stream 20) were used to gradually cool the co ffee and prevent it from agglomerating. Then the instant co ffee (stream 25) was passed through vibratory screen (S) in order to obtain the required particle size. The fraction of instant co ffee with the smallest particle size (stream 28) was recirculated to the process using dried air at 27 ◦C (stream 22) while the biggest particle size of instant co ffee (stream 27) was considered waste. The humidified air (stream 29) that exits the spray dryer was passed through a cyclone separator (FF) to remove solid co ffee particles. These solid particles (stream 32) were recirculated into the process and the humidified air (stream 31) was released to the environment.

**Figure 1.** Process flow diagram of the spray dryer system.

To develop the process modeling, the following assumptions were made:

