# Steam-jet agglomeration of skim-milk powder : influence of the process parameters.

Mathieu Person, Bernard Cuq, Agnès Duri-Bechemilh, Cécile Le Floch-Fouéré, Pierre Schuck, Romain Jeantet

► To cite this version:

Mathieu Person, Bernard Cuq, Agnès Duri-Bechemilh, Cécile Le Floch-Fouéré, Pierre Schuck, et al.. Steam-jet agglomeration of skim-milk powder : influence of the process parameters. .. 8. International Granulation Workshop, Jun 2017, Sheffield, United Kingdom. , 2017. [https://hal.science/hal-01547545](https://hal.science/hal-01547545)

HAL Id: hal-01547545

https://hal.science/hal-01547545

Submitted on 26 Jun 2017

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* Steam-jet agglomeration is used in the dairy industry in order to obtain **instant powders** with improved rehydration.

* Quality control of industrial products remains **experimental** and **empirical** :

* → Steam-jet agglomeration = **black box** process (closed, fast, random collisions).

* → Instant properties = **multi-factorial** causes (structure, composition, physicochemical state).

* Few scientific studies on dairy powders agglomeration and mainly performed with other technologies → **lack of knowledge**.

* → **How can we study and identify the key process parameters that should be controlled?**

Native particles Powder feed rate ($P_{FR}$)

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$$ \frac{S_{FR}}{P_{FR}} = \text{Steam/Powder ratio} $$

Steam Steam flow rate ($S_{FR}$)

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* Two process parameters were studied : the **steam/powder ratio ($R_{S/P}$)** and the **drying time ($t_D$)**. One factorial design was realized in triplicate :

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* **Characterization** of the agglomerates : Circularity, Feret diameter, mechanical strength, water content and wetting time.

* **Statistical analysis** : linear model after standardization of the data.

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## Structure of the pilot plant agglomerates :

* Raw material (left) : Skim-milk powder

* Pilot plant agglomerate (middle) : **porous** structure, **irregular** shape

* Industrial agglomerate (right) : dense structure, spherical shape, regular surface

## Influence of the process parameters :

<table><thead><tr><th></th><th>Circularity</th><th>Feret<br>diameter<br>(mm)</th><th>Mechanical<br>strength<br>(N)</th><th>Water<br>content<br>(g.100 g<sup>-1</sup>)</th><th>Wetting<br>time<br>(s)</th></tr></thead><tbody><tr><td> Steam/Powder<br>ratio</td><td> → </td><td> → → <br> 1 </td><td> → <br> → → → </td><td> → <br> → → → <br> 2 </td><td> → → → <br> → → <br> 3 </td></tr><tr><td> Drying time</td><td> - </td><td> - </td><td> → → <br> → → → <br> 2 </td><td> → → <br> → → → <br> 2 </td><td> → → <br> → → <br> 3 </td></tr><tr><td> Interaction</td><td> - </td><td> - </td><td> - </td><td> - </td><td> → → <br> → → <br> 3 </td></tr></tbody></table>

1. **Steam/Powder ratio** : more liquid bridges comes with more steam available, leading to **larger** agglomerates.

2. **Drying time** : increasing the drying time leads to the formation of **dry** and **brittle** agglomerates.

3. **Interaction** : instant properties mechanisms are **complex** → **difficult** to identify a **key process parameter** to control.

## A steam-jet granulation pilot plant was developed during this study :

* During the agglomeration step, the steam/powder ratio controls the **extent of granulation** in the studied range of values.

* The drying step is crucial for the **storage evolution** to prevent microbial growth, caking or breakage.

* Further studies are needed to understand the **instant properties mechanisms**.

## This pilot plant will allow to study :

* The **agglomeration mechanisms** → hydrotextural diagram (solid volume fraction vs water content).

* The **interactions** between the **raw material** properties, the **process** parameters and the **product** properties.

* The **correlations** between the agglomerates properties to understand the mechanisms of the instant properties (multivariate data analysis).

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