Experimental analysis of spray drying in a process intensified counter flow dryer

Figures & data

Figure 1. Scheme of the Particle Droplet Image Analysis test-rig.^[53]

Table 1. Overview of the conditions for droplet size measurements.

Nozzle type	Operating pressure range (bar)	Liquid composition (w/w)		Density (kg/m^3)	Viscosity (mPa-s)
		Water	Glycerin
Hollow cone pressure nozzle, 15° spray angle	10, 20, 30	100	0	1000	1
		51	47	1118	5
		27	73	1189	30

Figure 2. Schematic diagram of the experimental facility (T - temperature indicator; P - pressure indicator).

Figure 3. The counter-current spray dryer (a) and its schematic representation (b) (+ signs indicate thermocouple positions).

Table 2. Overview of the process conditions for the experimental tests, W-water, SM- skim milk.

Exp #	Feed	Nozzle orifice (mm)	Tin (°C)	Tout (°C)	Texh (°C)	Airflow (kg/h)	Feed flow (kg/h)	Feed pressure (bar)	Droplet SMD (µm)
1	W	0.5	266 ± 2	105 ± 5	112 ± 1	481	21	55 ± 1	40
2	W	0.5	307 ± 2	140 ± 3	132 ± 1	481	21	55 ± 1	40
3	W	0.5	359 ± 4	185 ± 5	163 ± 4	481	21	55 ± 1	40
4	W	0.5	360 ± 2	187 ± 3	164 ± 2	481	21	55 ± 1	40
5	W	0.5	360 ± 1	184 ± 3	163 ± 2	386	21	55 ± 1	40
6	W	0.5	360 ± 1	166 ± 3	147 ± 3	300	21	55 ± 1	40
7	W	0.5	361 ± 1	188 ± 2	186 ± 3	481	17	36 ± 1	49
8	W	0.5	361 ± 1	186 ± 5	176 ± 1	481	19	45 ± 1	44
9	W	0.5	361 ± 1	186 ± 2	165 ± 1	481	21	55 ± 1	40
10	W	0.5	361 ± 1	184 ± 2	162 ± 1	481	23	60 ± 1	37
11	W	0.6	353 ± 1	179 ± 1	157 ± 1	386	23	31 ± 1	60
12	W	0.6	352 ± 2	174 ± 2	149 ± 1	386	25	36 ± 1	56
13	W	0.6	349 ± 1	167 ± 1	143 ± 1	386	27	41 ± 1	51
14	W	0.6	343 ± 2	161 ± 2	138 ± 1	386	28	47 ± 1	44
15	SM	0.5	253 ± 5	140 ± 2	119 ± 1	481	18	36 ± 4	48
16	SM	0.6	237 ± 3	132 ± 1	117 ± 1	481	21	25 ± 1	77

Table 3. Droplet size distribution and particle velocities for different nozzle orifices and viscosities at atomization pressure of 30 bar, Vp- Particle average velocity.

	Dv10 (µm)			Dv90 (µm)			Dv50 (µm)			D32 (µm)			Vp (m/s)
Viscosity (mPa-s)	1	5	30	1	5	30	1	5	30	1	5	30	1	5	30
Nozzle 1 (0.5 mm)	32	32	53	100	106	285	60	64	130	52	54	100	43	36	44
Nozzle 2 (0.6 mm)	35	42	48	134	162	638	73	87	152	61	73	104	48	44	30
Nozzle 3 (0.7 mm)	38	45	58	149	189	471	79	97	145	66	79	112	47	46	38

Figure 4. SMD as a function of liquid pressure and viscosity for different orifice diameter nozzles.

Figure 5. Initial droplet size distribution for the viscosity of 1 mPa.s (a), 5 mPa.s (b), and 30 mPa.s (c) for the different nozzle orifice diameters, at an atomization pressure of 30 bar.

Figure 6. Example droplet images from nozzle 1 for 1 mPa.s (a) 5 mPa.s (b) and 30 mPa.s (c), at an atomization pressure of 30 bar. (Image “a” and “b” are taken at 2 cm while image “c” is taken at 4 cm from the nozzle tip).

Figure 7. Particle average droplet velocity as a function of liquid pressure and viscosity for different orifice diameter nozzles.

Figure 8. Droplet velocities as a function of droplet diameters (atomization pressure of 30 bar and liquid viscosity of 30 mPa.s for nozzle 1).

Figure 9. Temperature profiles along the dryer length (0 cm is at the top of the dryer) for radial thermocouples (a) and axial multipoint thermocouple (b), at different air inlet temperature; (air mass flow rate 481 kg/h, feed rate 21 kg/h, droplet SMD 40 µm).

Figure 10. Temperature profiles along the dryer length (0 cm is at the top of the dryer) for radial thermocouples (a) and axial multipoint thermocouple (b), at different air mass flowrate; (air inlet temperature ≈360 °C, feed rate 21 kg/h, droplet SMD 40 µm).

Figure 11. Temperature profiles along the dryer length (0 cm is at the top of the dryer) for radial thermocouples (a) and axial multipoint thermocouple (b) at different spray feed rates and droplet size for nozzle 1; (air inlet temperature ≈360 °C, air mass flow rate 481 kg/h).

Figure 12. Temperature profiles along the dryer length (0 cm is at the top of the dryer) for radial thermocouples (a) and axial multipoint thermocouple (b) at different spray feed rates and droplet size for nozzle 2; (air inlet temperature ≈360 °C, air mass flow rate 386 kg/h).

Figure 13. Temperature data for the Experiments: 1, 15, and 16; (air inlet temperature ≈260 °C, air mass flow rate 481 kg/hr, feed rate ≈21 kg/h).

Figure 14. Temperature data for the Experiments: 1, 15, and 16 along the dryer length (0 cm is at the top of the dryer) for radial thermocouples (a) and axial multipoint thermocouple (b); (air inlet temperature ≈260 °C, air mass flow rate 481 kg/hr, feed rate ≈21 kg/h).

Figure 15. Deposition pattern in the dryer: (top) results for nozzle 1, (bottom) results for nozzle 2, (left) top-down view from the inside of the dryer, (middle) zoom of the top section with thermocouples, (right) top wall of the dryer with visible viewpoints and exhaust chimney.

Table 4. Powder particle size distribution and moisture content.

Nozzle	Dv90 (µm)	Dv50 (µm)	D32 (µm)	Moisture content (wt.%)
Nozzle 1	292	29	21	6.88
Nozzle 2	102	25	19	7.04
Ref.	150	74	56	4.01

Figure 16. SEM images of recovered powder samples at different magnifications, top row: nozzle 1, bottom row: nozzle 2.

Meijer, R. Atomization of Viscous Newtonian Fluids Using Pressure Swirl Atomizers: An experimental approach using Particle/Droplet Image Analysis for the quantification of spray characteristics [Unpublished master's thesis]. University of Twente, the Netherlands, 2019.

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