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Item Development of a real-time operator training simulator for falling film evaporators : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Engineering and Automation at Massey University(Massey University, 1999) Goodwin, ShaneThe Chinese say, "Experience is the only teacher", while an old Western proverb is "Practice makes perfect". In either form, the notion is identical - the more often a task is performed, or a problem confronted, the better it is handled. In the arena of process control involving human operators, the effects of a mistake can be extremely costly to the company. One way to reduce the frequency and severity of mistakes by an operator is to provide training, ideally on a simulation of the process rather than the process itself. This allows the operator to make mistakes and hopefully learn from them, without the company having to lose revenue, lower efficiency, or produce waste product. An operator normally controls a process by changing the settings in a piece of software, which in turn affects the operation of the plant. However, that control software is operating on a machine which is also perfect for modelling and calculating the responses of the process in question. Software to control a process is readily available in a multitude of incarnations and so are packages designed to create models of a process. Used in conjunction, a model-based simulator can be created in order to train operators.Item Investigation of minimum flow conditions for milk products in falling-film evaporators : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology at Institute of Technology and Engineering, Massey University(Massey University, 2001) Paramalingam, ShabesheMultiple-effect evaporators are widely used in dairy industries to concentrate milk, which will be further processed in spray driers to produce powder. Compared to the evaporation stage the drying stage consumes a lot of energy. So, from an energy-saving point of view it is important to remove as much water as possible in the evaporation stage. In producing milk powder about 90% of the water removal takes place in the evaporating stage. The operational conditions must be satisfied within the falling film evaporators in order to have continuous production. One of the constraints to the optimisation of the falling-film evaporator is found to be the minimum peripheral flow (Brenmuhl, 1999). Violation of this constraint could cause fouling due to film break-up within the evaporator tubes. Fouling due to film break-up is a major concern in the operation of falling-film evaporators (Brenmuhl, 1999; Winchester, 2000; Paramalingam et al., 2000). Insufficient flow is found to be the cause of film break-up (Hartley & Murgatroyd, 1964; Chung and Bankoff, 1979; Paramalingam, 1999; Hughes & Bott, 1991). To avoid fouling due to film break-up the flow rate along the tubes should not be less than a minimum flow necessary to sweep off the dry patches. This flow is known as the advancing minimum flow, where the flow can no longer advance to cover a dry area. For the safe operation of falling-film evaporators it is also important to know the minimum flow below which film break-up occurs. This minimum flow is known as the retarding minimum flow, where the flow can no longer support a full film and the film retards leaving a dry area. The purpose of this study is to determine the minimum flows for milk products and for water. To this end two models are used, proposed by Hartley and Murgatroyd (1964) and Hoke and Chen (1992) to predict film break-up and therefore minimum flows.Item Surface modifications to increase dairy production run length : a thesis presented in partial fulfilment of the requirements for the degree of Master of Chemical Engineering at Massey University, [Manawatū], New Zealand.(Massey University, 2013) Runwal, SiddharthFouling is the build-up of undesired deposits on surfaces. In the dairy industry, fouling is mainly seen in heat exchangers where dairy fluid is heated or concentrated. It is one of the primary reasons for restricted run length, causing financial losses from downtime, the use of cleaning chemicals and reduced product quality. Fouling is a complex process and is due to number of factors including the properties of the heat transfer surface. A silica based coating is known to alter the surface properties. This study was carried out to investigate the effect of a silica based coating on fouling by whole milk in a falling film evaporator. Seven independent trials were conducted. In each trial, a control run was carried out followed by a full cleaning of the equipment and then either another control run or a coating run with pasteurized milk from the same batch. There was a six hour interval between the start of the control run and start of the coating run. Since prolonged milk storage may have some effect on fouling rate, control-control runs were carried out to see the effect of prolonged storage. The results obtained from control-control runs were used in analysing the effect of the coating on fouling rate. All coating trials showed consistently lower fouling rate as compared with corresponding control trials. The Pearson’s correlation coefficient of 0.83 showed a strong effect of coating on the fouling rate. Further, a regression analysis gave a p-value of 0.033, indicating that, at the 96.7% level of confidence, coating reduced the fouling rate. The extent of reduction in fouling rate varied from trial to trial. It was estimated that the coating had the potential to increase the run length by a maximum of 34% under the conditions these experiments were carried out.Item Modelling, optimisation and control of a falling-film evaporator : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Production Technology at Institute of Technology and Engineering, Massey University, Palmerston North, New Zealand(Massey University, 2004) Paramalingam, ShabesheFalling-film evaporators in the dairy industry are key process units where most of the water is removed in the production of milk and whey powders. Evaporators of two to eight effects are common in the dairy industry. Mechanical vapour recompression is widely used to increase the energy efficiency of the evaporation process. A Thermal vapour recompression is used to control the final total solids concentration exiting the evaporator at Fonterra-Ingredients, Whareroa. Previous research into the performance of dairy evaporators has focused largely on milk evaporators (Choudhary, 1996; Runyon et al., 1991; Quaak & Gerritsen, 1990; Quaak et al, 1994; Winchester, 2000). The performance of the whey evaporator at whey products was completely different (see Chapter-9) to the performance with milk products (Winchester, 2000). This could be due to the difference in the physical and chemical properties (discussed in Chpter-3).The aim of the current study was to apply mathematical modelling to the optimisation and control of a two-effect thermal vapour recompression evaporator for whey products at Fonterra Ingredients-Whareroa, Fonterra Co-operative Ltd. The purpose of this study is to solve the problems (low throughput, fouling due to film break-up, increased energy consumption and unknown running conditions for each product) currently experienced with the evaporator at whey products. Figure 1.0 illustrates a general whey powder process at Whareroa (see section 2.2). The manufacture of protein ingredients from cheese and casein whey has evolved during the last fifty years into an established part of the world dairy industry (Bylund, 1995). Raw milk is variable in its composition (see Appendix A-3) and most dairy products can be produced in a variety of ways from this milk. Therefore, it is not surprising to find significant variations in reported values for the physical properties of dairy products (Bloore et al., 1981; Snoeren, 1982; Murakami and Okos, 1989; Fernandez-Martin, 1971; Jeurnink and Kruif, 1993, Antonio, 1983; Adam et al., 1994; Middleton, 1996). A major problem in the processing of whey protein ingredients is variation in final product properties (foamability and solubility index) due to factors relating to protein denaturation during processing and to the high variability of raw material composition. These interrelated factors include the source of raw material (whey), cheese manufacturing practices, heat treatment history, protein fractionation procedures and storage conditions (Bloore et al., 1981). The processing of whey powder, types of whey products and their properties are discussed in Chapter 2.Item Heat transfer and fouling in film evaporators with rotating surfaces : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University(Massey University, 1997) Chen, Hong; Chen, HongA study was made on the heat transfer and fouling in thin film evaporators with rotating surfaces. Both theoretical and experimental studies were carried out, in order to gain a better understanding of these evaporators and their design principles, so that this type of evaporator could be effectively used in an on-farm milk evaporation system. By using Nusselt-type assumptions, a theoretical model, which was used to predict the liquid film thickness and heat transfer coefficients on the rotating cone, was developed. The theoretical equations obtained revealed basic relationships between the variables and provided a fundamental knowledge of the liquid flow and heat transfer in the film evaporators with rotating surfaces. The experimental studies on heat transfer were conducted on a Centritherm evaporator, which is available commercially (40° half cone angle), a specially made cone evaporator (10° half cone angle) and a falling film evaporator with a rotating tube. Variables evaluated were the rotating speed, the cone angle, the feed flow rate, the evaporating temperature, the temperature difference between the steam condensing and the liquid evaporating temperatures, and sugar concentration when sugar solution was used. The experimentally measured overall heat transfer coefficients were compared with the theoretical values. It was found that the measured overall heat transfer coefficients increased with increase of the cone rotating speed, and with the rise of the liquid evaporating temperature. The feed flow rate was found to have a more significant effect on the measured overall heat transfer coefficients in the falling film evaporator with a rotating tube than that in the Centritherm and the cone evaporators. The overall heat transfer coefficients decreased with increase of the concentration of sugar solutions, mainly due to the increase of liquid viscosity. It was also found that the measured overall heat transfer coefficients in the Centritherm evaporator increased with an increase in temperature difference up to 30K (for water, 10% sugar solution and skim milk) and then decreased (for water and 10% sugar solution). The formation of bubbles on the evaporating surface at high temperature differences was likely to be cause of this effect. Increase of the cone angle resulted in thinner liquid films and higher heat transfer coefficients. This was reflected in the following experimental results: the measured overall heat transfer coefficients in the falling film evaporator with a rotating tube were slightly lower than those measured in the cone evaporator, but much lower than those obtained in the Centritherm evaporator. The experimental results showed that rotating the tube of a falling film evaporator increased the overall heat transfer coefficient but the increase obtained was very dependent on feed flow rate, and was not sufficient to justify the use of this evaporator in the industry. With the Centritherm evaporator, good agreement between theoretical and experimental overall heat transfer coefficients as a function of the cone rotating speed was obtained by using water. The theoretical model, however, does not adequately describe the whole evaporation process at conditions other than those assumed in the model, which are: laminar liquid film flow, and heat transfer by conduction through the liquid film. It is suggested that waves existing in the liquid film at high Reynolds numbers, and bubble formation on the heating surface at high temperature difference, are the major reasons for the discrepancy between theoretical and experimental results. For the fouling study, the Centritherm evaporator was mainly employed, and three liquid systems: reconstituted skim milk, reconstituted whey solutions and sweet cheese whey solution, were selected. It was found that no fouling was detected after 6 hours' operation in the Centritherm evaporator when reconstituted skim milk and reconstituted whey solutions were used. This indicates that the aggregated whey proteins, which are formed in the manufacture of skim milk powder and whey powder, are less active in inducing fouling. For this reason, only the sweet cheese whey solution was used in further studies. It was confirmed that fouling is strongly linked with the liquid evaporating temperature and the temperature difference between steam condensing and liquid evaporating temperatures. In general, the higher the evaporating temperature and the temperature difference, the faster the deposition rate and the greater the fouling on the surface. It was found that 72% Bovine Serum Albumins (BSA) denatured after running the evaporator, at a evaporating temperature of 70°C and a temperature difference of 20K, for 6 hours. Though the content of BSA in whey solution is small, the denatured BSA could be easily attached to the surface. By association with other depositable materials existing in the whey solution, the thin layer of deposit could reduce the heat transfer coefficients significantly. This was attributed to the lower thermal conductivity of the deposited layer. Fouling was also found to be a function of the liquid velocity. This effect was more significant at lower evaporation temperatures. Increasing the rotating velocity would delay the formation of an initial layer and reduce the rate of fouling. It was also found that there was an induction period in the fouling curves when the evaporating temperature was 60°C. The induction period was reduced when new whey solutions were introduced into the evaporator. It proved the fact that depositable materials are much more easily adsorbed on fouled or unclean surfaces than on clean surfaces. The increase of fouling rate when new whey solutions were introduced suggested that the concentration of activated molecules in the solutions strongly affected the fouling process. A possible mechanism of whey fouling on the rotating surface was proposed. During this study, an attempt was made to develop a new type of evaporator in which a vapour compressor would be integrated with the rotating surface. This was unsuccessful due to the failure of compressing the vapour. Concerning the on-farm evaporation system, which requires an evaporator with high efficiency, compact, and minimum heat load to milk, it is suggested that a rotating surface evaporator with the top cone angle close to 90° (like a disk evaporator) would be optimum and worth to explore.Item Model based analysis of the operation and control of falling film evaporators : a thesis presented for the degree of Doctor of Philosophy in Technology and Engineering, Massey University, Palmerston North, New Zealand(Massey University, 2000) Winchester, JamesFalling film evaporators are commonly used in the New Zealand dairy industry for the production of milk powders. Milk powder is not susceptible to bacterial damage and it is easy to transport, whereas milk itself has neither of these characteristics. As a result milk powders are an ideal export product for the New Zealand Dairy industry. However, despite their large amount of industrial use, there is a shortage of knowledge on the design, operation and control of falling film evaporators. The work discussed in this thesis was initiated with the aim of improving this situation. The aims of this work are split into three broad areas. Develop Model A first principles model for the Evaporator A plant at Kiwi Co-op Dairies will be developed from the Laws of Thermodynamics. The model is dynamic and includes the evaporator preheat sections. We will concentrate on developing the model for the subsequent analysis of the Evaporator A plant. Specifically, a steady state model will be developed for the optimisation/operation studies and a linear dynamic model for the controllability studies. Optimisation Studies Using the steady state model the operation/optimisation of the Evaporator A plant will be investigated. There are some simple aspects of the evaporator and preheat sections that will be discussed. However, an important aspect will be the evaporator operational optimisation with respect to energy costs, fouling, throughput and milk powder quality. Controllability Studies Using the dynamic model we will investigate the control of the evaporator plant. The dynamic model derived from first principles will be linearised to produce a linear constant coefficient dynamic model. This can be analysed using the standard traditional and some advanced control methods. Specifically we will be interested in disturbance rejection.