Milk Powder Plant Research Articles

Techno-Economic Evaluation of a Skimmed Milk Powder Production Process

Milk powder is a highly demanded food that is used in various ways, both in the industrial area and in everyday life. In the present work, an innovative and unprecedented techno-economic evaluation of a technological proposal for a skimmed milk powder production plant with an annual capacity of 700 tons was carried out through the use of the SuperPro Designer® simulator, in order to know its main economic and profitability indicators under the current economic conditions in Cuba. For economic performance evaluation, the total capital investment, unit production cost, internal rate of return (IRR), net present value (NPV) and project payback time (PT) among other indicators, were determined. A sensitivity study was also accomplished, to determine from what value of the fluid milk unit cost the proposed skimmed milk powder plant begins to be unprofitable. A total capital investment of USD 22 744 000, an annual operating cost of USD 9 884 000, a working capital of USD 647 000 and a unit production cost of USD 352.95 per 25 kg bag were obtained. From the techno-economic results obtained, it can be concluded that the evaluated skimmed milk powder production plant is profitable and feasible due to the values of NPV (USD 14 475 000), IRR (18.98 %) and PT (4.46 years) obtained. The proposed production plant becomes unprofitable from a value of the fluid milk unit cost of USD 1.32/L.

Prevalence, characterization, and antibiotic susceptibility of Cronobacter spp. in a milk powder processing environment: The first reported case in Serbia.

Cronobacter spp. are opportunistic foodborne pathogens that most often infect neonates and infants through contaminated powdered infant formula. No reports have been published in Serbia on the prevalence of Cronobacter spp. in powdered milk production environments. Consequently, this study aimed to determine the prevalence, molecular characterization, antimicrobial susceptibility, and biofilm‐forming ability of Cronobacter spp. isolated from a milk powder plant. Hundred samples were collected from the production facility. Fifteen Cronobacter sakazakii strains were isolated and identified, giving a contamination rate of 15%. Using multi‐locus sequence typing, the isolates were divided into five sequence types (STs). Cronobacter sakazakii ST4 (50%), ST1 (16.67%), and ST83 (16.67%) were the dominant STs isolated. A novel sequence type (ST759) was identified and registered in the Cronobacter MLST database. The results of the antibiotic susceptibility testing indicated that C. sakazakii strains were susceptible to piperacillin/tazobactam, ampicillin/sulbactam, and amoxicillin/clavulanate, especially to meropenem and cefotaxime. Most of the ST4 showed moderate‐to‐strong biofilm‐forming ability. The presence of clinically relevant isolates (ST4, ST1, ST83, and ST8) revealed that the production plant is likely a potential concern for public health. Finally, finding new sequence types like the one detected in this study (ST759) underlines evolving genetic changes in C. sakazakii.

High counts of thermophilic spore formers in dairy powders originate from persisting strains in processing lines

During the last decades, thermophilic spore counts became a very important quality parameter for manufacturers with regard to powdered dairy products. Low-spore count powders are highly demanded but challenging to produce when high production volume and long process times are intended. In this study a detailed monitoring of microbial levels in three skim milk powder plants was conducted. Anoxybacillus flavithermus was found to be primarily responsible for increased spore levels with increasing spore numbers being detected after 6–8 h already during initial processing steps. Simultaneously, the species composition shifted from a diverse bulk tank milk microbiota where different Bacillus species represented around 90% of the thermophilic bacteria to a dominance of A. flavithermus in the end product. The analysis of A. flavithermus isolates from different powder batches with RAPD PCR revealed recurring patterns in each of the eight German manufacturers sampled over several months. The high relatedness of isolates exhibiting identical RAPD patterns was exemplified by cgMLST based on whole genome sequences. We assume that A. flavithermus strains persisted in production plants and were not eliminated by cleaning. It is concluded that such persisting strains recurrently recontaminated subsequent powder productions. The data highlight that a targeted optimization of cleaning and disinfection procedures is the most promising measure to effectively reduce thermophilic spore counts in German dairy powders.

Improving the energy efficiency of cyclone dust collectors

Our study, aimed at assessing the impact exerted by the inclusion to a low-efficiency cyclone of an additional "bypass" pipe connecting the cyclone's inlet branch pipe and the exhaust pipe, has been established the mechanisms to improve the energy efficiency and the process of purifying air from dust. It has been proven that the increase in the degree of purification is explained by a decrease in the radial flow rate under the exhaust pipe of the cyclone. The decrease in hydraulic resistance is due to a decrease in the flow rate along the inlet branch pipe when the air is fed separately to the body through the inlet branch pipe and the "bypass" pipe. Our experimental study has confirmed that when the cyclone design is supplemented with a "bypass" pipe in the most dangerous area of the cyclone in terms of dust release (under the exhaust pipe), the radial rate of the gas flow that negatively affects purification is reduced. This leads to an increase in the overall degree of purification from dust. The result of analytical calculations and computer simulation by the SolidWorks-2009 software were experimentally confirmed when investigating the effectiveness of dust capture from powdered skimmed milk in an industrial cyclone (a 630-mm diameter) with a "bypass" pipe. Such a cyclone is installed in the system of pneumatical transportation at the spray dryer "CT-500" at Ichnya Milk Powder and Butter Plant (Ukraine). Specifically, it has been established that the removal of dust is reduced almost twice, hydraulic resistance ‒ by 15 %, and the energy efficiency of the cyclone with a "bypass" pipe increases by 2.43 times.Thus, there is a reason to argue about the possibility of significant energy efficiency improvement of the cyclone with a "bypass" pipe.This makes it possible to assess the energy efficiency of the cyclone in the early stages of design

Predictive modelling of instant whole milk powder functional performance across three industrial plants

The efficient production of instant whole milk powders with stringent functional requirements is the economic goal for large-scale milk powder plants. However, the physical predictors of functional properties are not sufficiently characterised to ensure quality at the time of manufacture, and given high production rates, the time delays for testing can lead to significant amounts of devalued product if functional tests are subsequently failed. This work combines big-data collection and alignment with multivariate methods on a re-sampled, balanced data set to provide a real-time proxy measurement. A unique dataset was constructed to compare three large-scale plants of different designs, overcoming significant challenges in alignment of disparate data sources, across six years of production. Models were clearly able to differentiate plant and process changes, and by appropriate weighting of the unusual results, were able to predict functional test results, especially the production of off-spec product. These models can be used in real-time to significantly lower the likelihood of producing powder that will fail customer functional tests, and therefore substantially reduce cost of quality failure.

Modelling of a milk powder falling film evaporator for predicting process trends and comparison of energy consumption

In this study, two commonly used types of milk powder evaporators: a conventional five-effect falling-film evaporator without mechanical vapour recompression (MVR), and a three-effect evaporator with MVR were modelled in a commercial process simulator. The objectives were to predict the process variable trends (temperature profile along the tube side and the shell side of the evaporator) and to compare energy consumption for the two types of evaporators. Heat-recovery processes were integrated into the model so that energy consumption could be compared for the two processes. The size of the evaporator required was also estimated so that so that operating and capital costs could be assessed. The model prediction results were validated using industrial data from a local milk powder plant. The developed model successfully predicted temperature profiles similar to industrial evaporator. Furthermore, energy comparison between two types of evaporators was consistent with a known fact that a three-effect falling-film evaporator with MVR could consume 60% less energy than a conventional five-effect evaporator. These developed models in a commercial process simulator are novel in the dairy industry and can be used for simulating heat-recovery integrated evaporation processes but they still remain sufficiently generic and flexible to be applied to other production processes.

Process and utility systems integration and optimisation for ultra-low energy milk powder production

This study applies a Total Site Heat Integration approach in conjunction with a detailed process and utility model, to develop an innovative ultra-low energy milk powder plant design. The basis for the analysis is a state-of-the-art modern milk powder plant that requires 5265 MJ/tp of fuel and 210.5 kWh/tp (58.5 MJe/tp) of electricity. The model of the modern milk powder plant was validated against industrial data and changes to process and/or utility systems are targeted and implemented into the model to understand the impacts on thermal and electrical demands and emissions. Results show that seven significant changes are beneficial: (1) pre-concentration of milk to 30% using reverse osmosis, (2) a two-stage intermediate concentrate (30%) homogenisation to enable high solids (60%) spray drying, (3) an ultra-low energy Mechanical Vapour Recompression evaporator system, (4) spray dryer exhaust heat recovery, (5) condensing economiser for the boiler, (6) upgrade and integration of chiller condenser heat with hot water utility systems, and (7) recycling of air in the building ventilation system. These changes are estimated to reduce thermal energy use by 51.5%, electricity use by 19.0%, and emissions by 48.6% compared to a modern milk powder plant.

Fault diagnosis of an industrial plant using a Monte Carlo analysis coupled with systematic troubleshooting

Efficiently troubleshooting a fortification issue at an industrial milk powder plant is a complex undertaking given the myriad of possible causes. Multiple causes, even when simple, are not easy to diagnose, however every single cause needs to be addressed in order to consistently meet product quality specifications. This paper uses statistical modelling in the form of Monte Carlo simulations to investigate the probable causes for unexpected excessive product variation. This approach alone, refines but does not completely solve, the production issues, so a systematic approach was required to definitively solve other root causes. This two-step fault diagnosis approach ensured that all of the differing causes proposed by plant personnel could be addressed, and sound recommendations for good manufacturing operations could be made and adopted.

The significance of powder breakdown during conveying within industrial milk powder plants

Instant whole milk powder is designed to rapidly dissolve in water, which depends on the particle size distribution (PSD). The fragile powder exiting the dryer is conveyed for packing which breaks down the particles, worsening the dissolution properties. This work investigated the effect of conveying on the final functional properties using two industrial plants with differing transport systems; a pneumatic system and bucket elevator. It was expected that the plant with the bucket elevator consistently produced powder with superior dissolution due to lower breakdown during transport. This was evaluated using the change in PSD. It was found that the plant with the bucket elevator had at least as large a change in the median particle size as the plant with the pneumatic transport system, contrary to the expectation. However, the plant with the bucket elevator had an initially larger particle size, and so the percentage of fine particles that negatively impact dissolution, remained low post transport. When quantified using the change in bulk density, having an initially low bulk density compensated for large increases in bulk density during conveying and powder with lower bulk density pre-transport showed better wettability post transport. Thus in order to produce powder with the desired functionalities the focus should be on improving the initial agglomeration and generating larger particles and lower bulk density pre-transport, as opposed to optimising the powder transport.

Prevalence and characterization of Staphylococcus aureus isolated from goat milk powder processing plants

Staphylococcus aureus is a major concern for the food processing industry because of its virulence factors. The aim of this study was to determine the prevalence of S. aureus strains in goat milk powder processing plants, and to characterize these strains by antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) and PCR. PCR detected genes encoding staphylococcal enterotoxin (sea to set), staphylococcal enterotoxin-like (selj to selv), toxic-shock syndrome toxin-1 (tst), exfoliative toxin (eta and etb), Paton-Valentine Leukocidin (pvl), and methicillin resistance (mecA). A total of 910 samples including 62 raw goat milk samples from a milking station and 848 samples from seven different sampling sites in four goat milk powder plants were collected. Out of 910 samples, 95 (10.4%) samples, including 34 (54.8%) of 62 milking station samples and 61 (7.2%) of 848 milk powder processing plant samples, were positive for S. aureus. 63.2% of 95 isolates contained one or more virulence genes. The five most predominant virulence genes were pvl (29.5%), sec (23.2%), ser (16.8%), tst (14.7%), and seb (12.6%). 90.5% of strains were resistant to at least one antibiotic. Resistance was most frequently observed to trimethoprim/sulfamethoxazole (89.5%), erythromycin (30.5%), tetracycline (22.1%), ampicillin (16.8%), chloramphenicol (15.8%), and rifampicin (9.5%). A total of 44 PFGE patterns were generated among all the isolates. PFGE demonstrated that some isolates with the same PFGE patterns came from different goat milk powder processing stages. Our findings indicate that S. aureus has spread among different goat milk powder producing locations. In addition, cross-contamination of S. aureus exists in goat milk powder processing stages. The presence of S. aureus strains in goat milk powder processing stages poses a potential threat to public health.

A derivative based method for cost optimal area allocation in heat exchanger networks

This paper presents a novel Cost Derivative Method (CDM) for finding the optimal area allocation for a defined Heat Exchanger Network (HEN) structure and stream data to achieve minimum total cost. Using the Pinch Design Method (PDM) to determine the HEN structure, the approach attempts to add, remove and shift area to exchangers where economic benefits are returned. From the derivation of the method, it is found that the slope of the ɛ-NTU relationship for the specific heat exchanger type, in combination with the difference in exchanger inlet temperatures and the overall heat transfer coefficient, are critical to calculating the extra overall duty each incremental area element returns. The approach is able to account for differences in film coefficients, heat exchanger types, flow arrangements, exchanger cost functions, and utility pricing. Incorporated into the method is the newly defined “heat duty flow-on” factor, θ, which evaluates downstream effects on utility use and cost that are caused by changing the area of one exchanger. To illustrate the method, the CDM is illustrated by application to a simple distillation process and a milk powder plant case study. After applying the new CDM, the total annual cost was reduced by 7.1% for the distillation problem and 5.8% for the milk powder plant. For the distillation process, the CDM solution was found to give a comparable minimum total area and cost to four recently published programming HEN synthesis solutions for the same problem without requiring the increased network complexity through multiple stream splits. The CDM has significant potential and is expected to improve with further development.

Integrating heat recovery from milk powder spray dryer exhausts in the dairy industry

Heat recovery from milk powder spray dryer exhausts has proven challenging due to both economic and thermodynamic constraints. Integrating the dryer with the rest of the process (e.g. evaporation stages) can increase the viability of exhaust recovery. Several potential integration schemes for a milk powder plant have been investigated. Indirect heat transfer via a coupled loop between the spray dryer exhaust and various heat sinks were modelled and the practical heat recovery potential was determined. Hot utility use was reduced by as much as 21% if suitable heat sinks are selected. Due to high particle loading and operating temperatures in the particle sticky regime, powder deposition in the exhaust heat exchanger is perhaps the greatest obstacle for implementing heat recovery schemes on spray dryers. Adequate cleaning systems are needed to ensure continuous dyer operation.

The challenge of integrating non-continuous processes – milk powder plant case study

The integration of non-continuous processes such as a milk powder plant presents a challenge for existing process integration techniques. Current techniques are generally based on steady and continuous operation which for some industries is not the case. Milk production varies considerably during the year as dairy cows in New Zealand are grazed on pasture. In this paper the potential for indirect heat transfer between the several plants using a heat recovery loop and stratified tank at a typical New Zealand dairy factory is investigated. The maximum amount of heat recovery is calculated for a range of recirculation loop temperatures. The maximum amount of heat recovery can be increased considerably if the temperature of the hot fluid in the recirculation loop is varied depending on which condition the site is operating under.

Integration of solar thermal for improved energy efficiency in low-temperature-pinch industrial processes

Solar thermal systems have the potential to provide renewable industrial process heat and are especially suited for low pinch temperature processes such as those in the food, beverage, and textile sectors. When correctly integrated within an industrial process, they can provide significant progress towards both increased energy efficiency and reduction in emissions. However, the integration of renewable solar energy into industrial processes presents a challenge for existing process integration techniques due to the non-continuous nature of the supply. A thorough pinch analysis study of the industrial process, taking in to account non-continuous operating rates, should be performed to evaluate the utility demand profile. Solar collector efficiency data under variable climatic conditions should also be collected for the specific site. A systematic method of combining this information leads to improved design and an optimal operating strategy. This approach has been applied to a New Zealand milk powder plant and benefits of several integration strategies, including mass integration, are investigated. The appropriate placement of the solar heat is analogous to the placement of a hot utility source and an energy penalty will be incurred when the solar thermal system provides heat below the pinch temperature.

Design of baghouses for fines collection in milk powder plants

The design of pulse-jet baghouses for fines collection has been investigated. Firstly, the key design parameters and recommended values for these baghouse are presented, showing a large variation among sources. A procedure for determining the optimal combination of these parameters has been developed that differs from those found in previous literature by including a hitherto ignored area outside the bag bundle. More specifically, a comparison was made among the recommended air to cloth ratios from four published design guidelines, for the case of milk powder collection. Even here, large variation was found. Finally, a comparison between our industrial experience and these guideline values shows that at least for the dairy industry, the guideline of Lőffler et al. [F. Lőffler, H. Dietrich, W. Flatt, Dust Collection with Bag Filters and Envelope Filters, Wiley, 1988] is the best compromise between high capital costs and operational difficulties.

Fines Loadings in Milk Powder Plants with Washable Baghouses

Washable baghouses are increasingly used to filter the small size fractions of milk powder, known as fines, which become entrained with spray dryer outlet air streams in milk powder plants. Surprisingly, very little is known about the quantity of powder that becomes fines, an important parameter for both the control of agglomeration rates and washable bag-house design. A convenient method is reported here that gives estimates of the fines fraction (the ratio of fines flow to total powder flow), using powder size distributions of samples from around the plant. This method was checked against isokinetic sampling using a thimble filter to independently determine powder flow rates. Results showed that that the fines fractions ranged from 49 ± 8% to 86 ± 2% depending on the powder type and plant operating conditions. These values are much greater than what was traditional thought (10–20%). Also, as part of this study results were compared with those from an online optical scintillation instrument. It was concluded that the newly developed particle size distribution method is a simple and reliable way to estimate spray dryer fines fractions, yet is sensitive enough to detect changes in operating conditions.

Experimental Results Contributed to Early Detection of Smouldering Milk Powder as an Integrated Part of Maintaining Spray Drying Plant Safety

Smoldering milk powder lumps deposited on dryer walls or falling through the hot air could potentially start a fire or even an explosion in milk powder dryers. Explosive behavior is more frequently experienced in the modern industry, where high production throughputs are desired. It has been known that powder at such a state emits carbon monoxide (CO). The work reported in this article is the study of the characteristics of CO generation during the incomplete combustion of milk powders. The powders used in the study were whole milk and skim milk. Samples placed in a reactor were heated using air at 300°C. The exhaust air of the reactor was continuously measured for CO concentration using a highly sensitive CO analyzer. Temperatures were monitored, and the smoke produced during the combustion of whole milk powder was collected and analyzed using gas-chromatography mass-spectroscopy (GC-MS). Whole milk powder was found to produce significantly higher amounts of CO than skim milk powder. Hydrocarbons, alcohols, and carboxylic acids were tentatively identified during the GC-MS analyses. Results from the study are definitely useful in optimizing the use of an early fire detection system in milk powder plants.

Effect of preheating and other process parameters on whey protein reactions during skim milk powder manufacture

Skim milk powder was manufactured in a milk powder plant using different preheating temperatures, concentrate heating temperatures and spray drying temperatures. Varying the preheating conditions from 70 °C for 52 s to 120 °C for 52 s had a marked effect on the denaturation of β-lactoglobulin A, β-lactoglobulin B, α-lactalbumin, bovine serum albumin (BSA), and immunoglobulin G. In contrast, varying concentrate heating temperature (65–74 °C) and inlet/outlet air dryer temperature (200/101 °C–160/89 °C) had a minimal effect on whey protein denaturation. Most of the whey protein denaturation and association with the casein micelle occurred in the preheating section of the powder plant. Aggregation of β-lactoglobulin (β-lg) and BSA predominantly involved disulphide bonds. Although, greater than 90% of the β-lg and BSA was denatured after preheating at 120 °C for 52 s, the extent of association with the casein micelle was lower, 50% for β-lg and 75% for BSA.

PERFORMANCE ANALYSIS of the MILK CONCENTRATING SYSTEM FROM A BRAZILIAN MILK POWDER PLANT

ABSTRACTThe steady‐state operation of the concentrating system from an industrial milk powder plant was studied using a simulation approach. This system is composed of two tubular preheaters, a plate pasteurizer, a thermocompressor and four climbing‐falling‐film plate evaporators operating in a multiple‐effect arrangement. Its simulation was performed using the ASPEN Plus shell, into which calculation routines previously developed by the authors had to be introduced in order to enable the calculation of the plate units. For the thermocompressor, a simulation code based on the solution of a design equation and the overall mass and energy balances was formulated and then introduced into ASPEN. In the validation step, simulation results were compared with operating data of the industrial plant, and a good agreement was verified. A sensitivity analysis of the concentrating system was then performed, considering two different operating variables, namely the milk inlet temperature and the motive steam pressure in the thermocompressor.

Thermophile Survival in Milk Fouling and on Stainless Steel During Cleaning

Surface attached thermophiles in milk powder plants that survive cleaning after a manufacturing run can recontaminate the plant, thus reducing the subsequent run time. This study compares thermophile survival in a milk foulant with the survival on stainless steel during an incomplete cleaning process. Multilayered milk fouling deposits were produced on stainless steel surfaces to simulate samples obtained from poorly cleaned areas of industrial milk powder plants. The process involved alternate cycles of surface inoculation and fouling in a pilot plant heat exchanger. Un-fouled stainless steel surfaces were subject to the same bacterial inoculation procedure as the fouled surfaces but without fouling development. Surfaces were cleaned in hot caustic (2%, 65°C) providing no agitation for durations up to 20 min. The cleaning conditions simulated the very low flow velocities found in hard-to-reach areas of milk powder plants. Impedance microbiology was used to assess microbial activity and confocal laser scanning microscopy was used to determine whether thermophiles remained at the surface. After 15 min of cleaning thermophile activity was detected on the fouled surfaces at a level of 105cfu cm−2 but no activity was detected on the un-fouled stainless steel after this time. Microscopy showed that biofilm still remained on the un-fouled stainless steel surfaces after 15 min of cleaning indicating that the cells were killed rather than removed. This suggests that milk fouling layers can provide thermophiles with greater protection from cleaning than a biofilm provides. Therefore it is important to target hard-to-clean areas in milk powder plants and ensure all fouling is removed to reduce the chance of recontamination in subsequent runs.