# Les procédés d'agglomération par sollicitations mécaniques. Application à la structuration de la semoule de blé dur pour la fabrication du couscous

Bettina Bellocq, Bernard Cuq, Agnès Duri-Bechemilh, Thierry Ruiz

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Bettina Bellocq, Bernard Cuq, Agnès Duri-Bechemilh, Thierry Ruiz. Les procédés d'agglomération par sollicitations mécaniques. Application à la structuration de la semoule de blé dur pour la fabrication du couscous. 16. Congrès de la société française de génie des procédés (SFGP 2017), Jul 2017, Nancy, France. hal-01602787

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<figure><img src="image_1.png" /></figure>
# LES PROCÉDÉS D'AGGLOMÉRATION PAR SOLLICITATIONS MECANIQUES.

## APPLICATION A LA STRUCTURATION DE LA SEMOULE DE BLÉ DUR POUR LA FABRICATION DU COUSCOUS.

### Bettina Bellocq

Under the supervision of:

Pr. Bernard CUQ, Dr. Thierry RUIZ and Dr. Agnès DURI

UMR IATE - INRA Montpellier - France

### 16ème Congrès de la Société Française de Génie des Procédés

Nancy – 12 Juillet 2017

<figure><img src="image_2.png" /></figure>
Plan

<figure><img src="image_3.png" /></figure>

1 INTRODUCTION - WET AGGLOMERATION

2 DURUM WHEAT SEMOLINA AND MIXERS

3 IMPACT OF THE PROCESS

4 HYDROTEXTURAL ANALYSIS

5 CONCLUSION
Plan

<figure><img src="image_4.png" /></figure>

1 INTRODUCTION - WET AGGLOMERATION

2 DURUM WHEAT SEMOLINA AND MIXERS

3 IMPACT OF THE PROCESS

4 HYDROTEXTURAL ANALYSIS

5 CONCLUSION
## 1.1. WET AGGLOMERATION OF FOOD POWDERS

**Agglomeration** is largely used to improve the powders **properties and behaviour**:

- Reduction in dust production.

- Enhancement in flowability.

- Increase in bulk density.

- Reduction in segregation.

During the agglomeration process... ...the **native small particles** are gathered to form **larger assemblies** with specific **porous structures**, called the **agglomerates**.

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

### Agglomerated food powders

- Cocoa beverage powders

- Instant soluble coffee

- Culinary powders

- Flavors powders

- Protein powders

- Infant formulas

- Couscous grains

- Dairy powders

- Milk powders

- Bakery mixes

- Starch
# 1.1. WET AGGLOMERATION OF FOOD POWDERS

Agglomeration is largely used to improve the powders properties and behaviour:

- Reduction in dust production.

- Enhancement in flowability.

- Increase in bulk density.

- Reduction in segregation.

During the agglomeration process... ...the native small particles are gathered to form larger assemblies with specific porous structures, called the agglomerates.

## Agglomerated food powders

- Cocoa beverage powders

- Instant soluble coffee

- Culinary powders

- Flavors powders

- Protein powders

- Infant formulas

### - Couscous grains

- Dairy powders

- Milk powders

- Bakery mixes

- Starch

<figure><img src="image_9.png" /></figure>
## 1.2. WET AGGLOMERATION - PROCESS

During the agglomeration process, a **liquid binder (water) is sprayed** over an **agitated powder bed**.

It generates **attractive interactions** and **links** between the native particles and...

... Promotes the **spatial arrangement of the native particles** with the binder.

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

http://www.cjtech.co.kr/Process%20Principles%20Agglomeration%20Granulation.htm
## 1.2. WET AGGLOMERATION - PROCESS

Different technologies have been used for wet agglomeration processes. They can be classified in two categories according to the type of the mixing energy.

The **pneumatic mixing granulators** (e.g. steam jet, spray drying, or fluid bed) use **air steam to agitate** the particles under low shear conditions.

<figure><img src="image_12.png" /><figcaption>Ex. Fluidized bed</figcaption></figure>

The **mixing granulators** (e.g. mechanical mixer, pan, disk, or drum granulators) use **mechanical system** to agitate the particles.

<figure><img src="image_13.png" /><figcaption>Ex. Planetary mixer</figcaption></figure>

The variability of the raw materials associated with the differences between different apparatus induce a high degree of complexity in the process.
## 1.3. WET AGGLOMERATION - MECHANISMS

Wet agglomeration process is classically described as a combination of successive mechanisms at different rates :

- Wetting and nucleation.

- Growth and consolidation.

- Breakage, erosion, rupture

The cohesion forces generate interactions between particles, and promote granules growth.

<figure><img src="image_14.png" /></figure>
## 1.3. WET AGGLOMERATION - MECHANISMS

Wet agglomeration process is classically described as a combination of successive mechanisms at different rates :

- Wetting and nucleation.

- Growth and consolidation.

- **Breakage, erosion, rupture**

The **rupture forces** and **shearing** effects, lead to **breakage** and to reduce the granule size.

<figure><img src="image_15.png" /></figure>

The wet agglomeration process is a **balance between growth and breakage**
**1.4. HYDROTEXTURAL APPROACH**

**Hydrotextural approach** is used to
describe agglomeration mechanisms
based on changes in compactness and
diameter of the agglomerates as a
function to the water content.

<figure><img src="image_16.png" /><figcaption>Schema of the hydrotextural diagram (Ruiz et al., 2005)</figcaption></figure>
**1.4. HYDROTEXTURAL APPROACH**

**Hydrotextural approach** is used to
describe agglomeration mechanisms
based on changes in compactness and
diameter of the agglomerates as a
function to the water content.

Hydrotextural diagram is limited by the
**saturation curve** until which
agglomerates are completely filled by
water.

<figure><img src="image_17.png" /><figcaption>Schema of the hydrotextural diagram (Ruiz et al., 2005)</figcaption></figure>
## 1.4. HYDROTEXTURAL APPROACH

Hydrotextural approach is used to describe agglomeration mechanisms based on changes in compactness and diameter of the agglomerates as a function to the water content.

Hydrotextural diagram is limited by the **saturation curve** until which agglomerates are completely filled by water.

<figure><img src="image_18.png" /><figcaption>Schema of the hydrotextural diagram (Ruiz et al., 2005)</figcaption></figure>

Agglomerates were analysed by measuring :

<table><tr><td>Size</td><td>= Median diameter</td></tr><tr><td>Water content</td><td>= Mass of water / Mass of dry product</td></tr><tr><td>Compactness</td><td>= Volume of solid / Total Volume</td></tr><tr><td>Saturation degree</td><td>= Volume of liquid / Volume of void</td></tr></table>
## 1.5. CASE OF THE COUSCOUS GRAINS

- 3 unit operations.

- Polydispersity of the size
  cause a high ratio of out of
  scope (too large >2 mm, or too
  small <1 mm).

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

Agglomeration

Cooking

Drying

Semolina

Water

Mixing and rolling

Sieving

Wet couscous grains

Steam cooking

Cooked couscous grains

Drying

Sieving

Final couscous grains

Dust

Dried
recyclates

Crushing

Too large

Too small
## 1.5. CASE OF THE COUSCOUS GRAINS

- 3 unit operations.

- Polydispersity of the size
  cause a high ratio of out of
  scope (too large >2 mm, or too
  small <1 mm).

- Agglomeration is a key unit operation to control the size of the couscous grains.

<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /></figure>
## 1.6. OBJECTIVES

AGGLOMERATION

ROLLING

COOKING

DRYING

<figure><img src="image_24.png" /><figcaption>Durum wheat semolina</figcaption></figure>

<figure><img src="image_25.png" /><figcaption>Wet agglomerates</figcaption></figure>

<figure><img src="image_26.png" /></figure>

<figure><img src="image_27.png" /><figcaption>Cooked agglomerates</figcaption></figure>

<figure><img src="image_28.png" /></figure>

<figure><img src="image_29.png" /><figcaption>Couscous grains</figcaption></figure>

### Our objectives were:

- To describe the agglomeration by analysing experimental investigations.

- To understand how the process impact the agglomeration.

- To understand how the raw material (diameter and protein) impact the agglomeration.
## 1.6. OBJECTIVES

AGGLOMERATION

ROLLING

COOKING

DRYING

<figure><img src="image_30.png" /><figcaption>Durum wheat semolina</figcaption></figure>

<figure><img src="image_31.png" /><figcaption>Wet agglomerates</figcaption></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /><figcaption>Cooked agglomerates</figcaption></figure>

<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /><figcaption>Couscous grains</figcaption></figure>

### Our objectives were:

* To describe the agglomeration by analysing experimental investigations.

* To understand how **the process** impact the agglomeration.

* To understand how the raw material (diameter and protein) impact the agglomeration.
Plan

<figure><img src="image_36.png" /></figure>

1 INTRODUCTION - WET AGGLOMERATION

2 DURUM WHEAT SEMOLINA AND MIXERS

3 IMPACT OF THE PROCESS

4 HYDROTEXTURAL ANALYSIS

5 CONCLUSION
## 2.1. RAW MATERIAL

### Wheat powder (durum wheat semolina)

- Large particles ($d_{50}$ = 287 µm) with distribution of diameters.

- Dense native particles (not porous).

Biochemical composition : **starch** (85%), **proteins** (12%), **fibres** (2%), and **lipids** (1%).

- Components are **partly soluble**.

<figure><img src="image_37.png" /><figcaption>Durum wheat semolina</figcaption></figure>

<table><thead><tr><th>Characteristics</th><th>Values</th><th>Method</th></tr></thead><tbody><tr><td>Water content (%)</td><td>16.4 (± 0.5)</td><td>Method 44-15A AACC</td></tr><tr><td>Protein content (%)</td><td>12.4 (± 0.4)</td><td>Method 050 (AFNOR)</td></tr><tr><td>Particle size mediam diameter (µm)</td><td>287 (± 8)</td><td>Laser granulometry</td></tr><tr><td>Particle size span (-)</td><td>1.56 (± 0.17)</td><td>Laser granulometry</td></tr><tr><td>True density (g/cm³)</td><td>1.478 (± 0.005)</td><td>Helium pycnometry</td></tr><tr><td>Plastic limit (%)</td><td>59 (± 1)</td><td>Atterberg tests</td></tr><tr><td>Liquid limit (%)</td><td>76 (± 2)</td><td>Atterberg tests</td></tr></tbody></table>
## 2.2. MECHANICAL MIXERS

<figure><img src="image_38.png" /><figcaption>Planetary mixer</figcaption></figure>

<figure><img src="image_39.png" /><figcaption>Horizontal mixer</figcaption></figure>

<figure><img src="image_40.png" /><figcaption>Vertical mixer</figcaption></figure>

<table><thead><tr><td>Mixers</td><td>Speed (rpm)</td><td>Froude number (-)</td><td>Water content (-)</td><td>Mixing time (min)</td></tr></thead><tbody><tr><td>Planetary</td><td>70 - 180</td><td>0.03 - 0.16</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr><tr><td>Horizontal</td><td>114 - 228</td><td>0.02 - 0.05</td><td>0.39 - 0.42 - 0.49</td><td>0 - 5 - 15</td></tr><tr><td>Vertical</td><td>80 - 200</td><td>0.03 - 0.17</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr></tbody></table>
## 2.2. MECHANICAL MIXERS

<figure><img src="image_41.png" /><figcaption>Planetary mixer</figcaption></figure>

<figure><img src="image_42.png" /><figcaption>Horizontal mixer</figcaption></figure>

<figure><img src="image_43.png" /><figcaption>Vertical mixer</figcaption></figure>

<table><thead><tr><td>Mixers</td><td>Speed (rpm)</td><td>Froude number (-)</td><td>Water content (-)</td><td>Mixing time (min)</td></tr></thead><tbody><tr><td>Planetary</td><td>70 - 180</td><td>0.03 - 0.16</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr><tr><td>Horizontal</td><td>114 - 228</td><td>0.02 - 0.05</td><td>0.39 - 0.42 - 0.49</td><td>0 - 5 - 15</td></tr><tr><td>Vertical</td><td>80 - 200</td><td>0.03 - 0.17</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr></tbody></table>
## 2.2. MECHANICAL MIXERS

<figure><img src="image_44.png" /><figcaption>Planetary mixer</figcaption></figure>

<figure><img src="image_45.png" /><figcaption>Horizontal mixer</figcaption></figure>

<figure><img src="image_46.png" /><figcaption>Vertical mixer</figcaption></figure>

<table><thead><tr><td>Mixers</td><td>Speed (rpm)</td><td>Froude number (-)</td><td>Water content (-)</td><td>Mixing time (min)</td></tr></thead><tbody><tr><td>Planetary</td><td>70 - 180</td><td>0.03 - 0.16</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr><tr><td>Horizontal</td><td>114 - 228</td><td>0.02 - 0.05</td><td>0.39 - 0.42 - 0.49</td><td>0 - 5 - 15</td></tr><tr><td>Vertical</td><td>80 - 200</td><td>0.03 - 0.17</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr></tbody></table>

<figure><img src="image_47.png" /></figure>
## 2.2. MECHANICAL MIXERS

<figure><img src="image_48.png" /><figcaption>Planetary mixer</figcaption></figure>

<figure><img src="image_49.png" /><figcaption>Horizontal mixer</figcaption></figure>

<figure><img src="image_50.png" /><figcaption>Vertical mixer</figcaption></figure>

<table><thead><tr><td>Mixers</td><td>Speed (rpm)</td><td>Froude number (-)</td><td>Water content (-)</td><td>Mixing time (min)</td></tr></thead><tbody><tr><td>Planetary</td><td>70 - 180</td><td>0.03 - 0.16</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr><tr><td>Horizontal</td><td>114 - 228</td><td>0.02 - 0.05</td><td>0.39 - 0.42 - 0.49</td><td>0 - 5 - 15</td></tr><tr><td>Vertical</td><td>80 - 200</td><td>0.03 - 0.17</td><td>0.33 - 0.38 - 0.45</td><td>0 - 5 - 15</td></tr></tbody></table>
## 2.3. WET GRANULATION PROCESS

<figure><img src="image_51.png" /></figure>

Stage 1 - Mixing

Stage 2 - Water addition and agglomeration

<figure><img src="image_52.png" /></figure>

Power consumption by the mixer arm during the process.

<figure><img src="image_53.png" /></figure>

Water added manually or using a water **spraying nozzle** with a **constant flow rate** (2 g/sec).

<figure><img src="image_54.png" /></figure>

<figure><img src="image_55.png" /></figure>

Final mass close to 50% of the capacity of the mixer.
**2.4. AGGLOMERATES CHARACTERISTICS**

To **describe the agglomeration mechanisms** and the product characteristics, we evaluated the **size distribution** and the **agglomerates characteristics on each sieve**.

<figure><img src="image_56.png" /></figure>

**Size distribution** by sieving: d50, span, yield per sieves.

**Distribution of water content** by weighing after oven drying at 105°C for 24h.

**Distribution of compactness** hydrostatic balance (Precisa serie 321 LX 120+ density kit).
Plan

<figure><img src="image_57.png" /></figure>

1 INTRODUCTION - WET AGGLOMERATION

2 DURUM WHEAT SEMOLINA AND MIXERS

3 IMPACT OF THE PROCESS

4 HYDROTEXTURAL ANALYSIS

5 CONCLUSION
**3.1. DESCRIPTION OF THE GRANULATION**

**Large dispersion** in size was observed. Specific shape and hydrotextural characteristics allow distinguishing **5 types of structures** according to their diameter:

- **Small** (0.3 – 0.5 mm) = native particles of semolina

- **Fragments** (0.5 – 0.6 mm) = mechanical erosion of larger structures

- **Nuclei** (0.6 – 1.0 mm) = primary association of semolina particles

- **Agglomerates** (1.0 – 2.0 mm) = association of fragments and/or nuclei

- **Dough pieces** (>2.0 mm) = association of agglomerates which passes the percolation state

<figure><img src="image_58.png" /></figure>
**3.1. DESCRIPTION OF THE GRANULATION**

Agglomeration growth of semolina
to produce couscous grains leads to:

- Increasing water content

- Decreasing compactness

according to an **increase in the median diameter** of the structures.

Evolution of the size distribution of the
agglomerated structures with water
content and compactness shows:

(i) A continuous growth process associated with the expansion of their internal structure.

(ii) A fragmentation of the dough pieces.

<figure><img src="image_59.png" /></figure>

<figure><img src="image_60.png" /></figure>
**3.2. IMPACT OF THE WATER CONTENT**

**Polydispersity** of the size. **5 structures** with specific characteristics of size, compactness and water content.

<figure><img src="image_61.png" /></figure>

An increase of the water content lead to an increase of the median diameter of the population in the mixer after the granulation.
## 3.2. IMPACT OF THE WATER CONTENT

An increase of the water content **increase the mean water content** of each structure after the granulation.

<figure><img src="image_62.png" /></figure>

An increase of the water content **decrease the mean compactness** content of each structure after the granulation.

<figure><img src="image_63.png" /></figure>
## 3.3. IMPACT OF THE MIXING SPEED

<figure><img src="image_64.png" /></figure>

- The ratio of the 5 structures is different → An increase of the speed leads to an **increase of the breakage and erosion mechanisms**.

- No impact of the speed in the water content and the compactness of each structure.

<figure><img src="image_65.png" /></figure>
## 3.4. IMPACT OF THE MIXERS

<figure><img src="image_66.png" /></figure>

<figure><img src="image_67.png" /></figure>

- The ratio of the 5 structures is different → More breakage and erosion mechanisms in the planetary mixer.

<figure><img src="image_68.png" /></figure>

- The mixers do not have an impact on the water content and the compactness of each structure.
Plan

<figure><img src="image_69.png" /></figure>

1 INTRODUCTION - WET AGGLOMERATION

2 DURUM WHEAT SEMOLINA AND MIXERS

3 IMPACT OF THE PROCESS

4 HYDROTEXTURAL ANALYSIS

5 CONCLUSION
**4.1. DATA ANALYSIS**

<figure><img src="image_70.png" /></figure>
**4.1. DATA ANALYSIS**

Analysis of the **mean values**
of water content and
compactness.

<figure><img src="image_71.png" /></figure>
**4.1. DATA ANALYSIS**

Analysis of the **mean values**
of water content and
compactness.

Analysis of the **heterogeneity**
of water content and
compactness around their
mean values.

<figure><img src="image_72.png" /></figure>
## 4.1. DATA ANALYSIS

<figure><img src="image_73.png" /></figure>

Analysis of the **mean values** of water content and compactness.

Analysis of the **heterogeneity** of water content and compactness around their mean values.

**Global heterogeneity**

$$W_G = (W_{max} - W_{min})/W_{moy}$$
## 4.1. DATA ANALYSIS

<figure><img src="image_74.png" /></figure>

Analysis of the **mean values** of water content and compactness.

Analysis of the **heterogeneity** of water content and compactness around their mean values.

**Global heterogeneity**

$$W_G = (W_{max} - W_{min})/W_{moy}$$

**Local heterogeneity**

$$W_L = (W - W_{moy})/W_{moy}$$
**4.2. MEAN VALUES ANALYSIS**

We have represented on the diagram **the mean values** of water content and **compactness** of the structures **for all the process conditions**.

<figure><img src="image_75.png" /></figure>

The process conditions **do not change the hydrotextural properties** of the structures: they are **all saturated by water**.
**4.3. LOCAL HETEROGENEITY ANALYSIS**

**The fluctuations** of the **water content** and the **compactness** are **correlated** around their respective mean values **for all the process conditions.**

<figure><img src="image_76.png" /></figure>

The growth of the agglomerates respects an **association by same sizes and hydro-textural categories.**
Plan

<figure><img src="image_77.png" /></figure>

1 INTRODUCTION - WET AGGLOMERATION

2 DURUM WHEAT SEMOLINA AND MIXERS

3 IMPACT OF THE PROCESS

4 HYDROTEXTURAL ANALYSIS

5 CONCLUSION
* **5 structures** in the mixer after the granulation.

* Continuous growth process is associated with the **expansion of the internal structure**.

* The **process** (water content, speed and mixers) has a **significant influence on the yield** of the agglomeration, but...

* ... **does not have an influence on the agglomerates properties** (water content and compactness) as a function to their size.

* **Fluctuations** of the water content and the compactness are correlated around their respective mean values → **association by same sizes and hydro-textural categories.**

<figure><img src="image_78.png" /></figure>
QUESTIONS ?

Bettina Bellocq

Under the supervision of:

Pr. Bernard CUQ, Dr. Thierry RUIZ and Dr. Agnès DURI

UMR IATE - INRA Montpellier - France

16ème Congrès de la Société Française de Génie des Procédés

Nancy – 12 Juillet 2017

<figure><img src="image_79.png" /></figure>