SELECTED ASPECTS OF SELF-HEATING BEHAVIOUR OF FAT CONTAINING FOOD POWDERS

• Main Author: SHUIB, ANIS SUHAILA
• Format: Thesis
• Language: English
• Published: Universiti Teknologi Petronas 2001
• Subjects: QD Chemistry
• Online Access: http://utpedia.utp.edu.my/id/eprint/6815/1/2001%20Master-Selected%20Aspects%20Of%20Self-Heating%20Behavior%20Of%20Fat%20Containing%20Food%20Powders.pdf; http://utpedia.utp.edu.my/id/eprint/6815/

The self-heating of milk powder deposit in drying devices has been identified as having the potential to cause a serious thermal hazard. The consequences of self-heating can result in disruption to equipment and installation, lost production time, degradation of product quality and that of the prime importance, ie. the danger to life. The preventive and protective measures have been designed and implemented in most dairy plants. In order to aid such efforts, the process conditions which could lead fires have been further investigated. The thermal kinetics of the dairy powders have been studied previously by some researchers but a number of related issues still require more in-depth study. A series of mathematical models simulating the self-heating behaviour of reactive materials have been developed and modified over time but experimental validation is not substantial. This project presents a study evaluating the thermal ignition kinetics of whole milk powder. It is an extension of a previous work in which a novel measurement procedure and a numerical simulation model were proposed (Chong, 1997). In this work, several new aspects has been addressed and experimental validations made. In particular, a much larger sample size was used, so that the effect of heat accumulated inside the sample was more pronounced to make the measurements more accurate. Previously, two reaction regime for whole milk powder were identified in the temperature range of 125°C to 160°C. However, the relationship drawn was not 100% convincing. The number of points plotted at low temperature range were perhaps insufficient to illustrate a definitive trend. In the current work, a similar test was conducted at ambient temperatures ranging from ll6°C (a much lower ambient temperature) to 150°C. The experimental data from this work were plotted together with the previous results which prove the reaction regime discovered by Chong(l997). Hence, the existence of at least two reaction mechanisms during self-heating of whole milk powder have been validated . The experimental conditions employed in this were then simulated using a numerical simulation programme. The experimental results recorded were compared with the simulation data. Some modifications were made to the program, based on the recent available information. The model was able to predict the self-heating behaviour of the milk powder in a larger sample size. From the sensitivity analysis, a more reliable thermal conductivity of milk powders was identified. Hence, the model produced more precise results compared with the experimental data. Further simulations were made on the effect of initial sample temperature and initial water content on the self-heating behaviour. In addition, the measurement techniques and activation energy of various composition of milk powder have been reported previously but the underlying reactions have still been less explained. Fat oxidation of milk powder has been claimed to be a major reaction triggering ignition. For this reason, a set of experiments was carried out to study the effect of fat content on self-ignition propensity. It was found that a large amount of fat can inhibit thermal runaway reaction. However, the presence of small fat component could also enhance the exothermicity. Therefore, a critical fat content in which self ignition may be more easily initiated has been suggested.