Songklanakarin J. Si. Tehnol. 33 (4), 431-440, Jul. - Aug. 2011 http://www.sjst.psu.a.th Original Artile Minimization of water and hemial usage in the leaning in plae proess of a milk pasteurization plant Sathit Niamsuwan 1, Paisan Kittisupakorn 1 * and Iqbal M. Mujtaba 2 1 Department of Chemial Engineering, Faulty of Engineering, Chulalongkorn University, Pathum Wan, Bangkok, 10330 Thailand. 2 Shool of Engineering, Design and Tehnology, University of Bradford, Bradford, West Yorkshire, BD7 1DP, United Kingdom. Reeived 1 Deember 2010; Aepted 1 August 2011 Abstrat Cleaning in plae (CIP) is a method of leaning inner surfaes of piping, vessel, equipment, and assoiated fitting with disassembly. Although, the CIP proesses have been studied ontinually to improve effiieny for hemial and water onsumption, the real onventional plant operations of this proess still have been onsidered as a large amount of onsumption. The objetives of this work are to study proess behaviors and to find out the optimal draining ratio of the CIP leaning hemials in a pasteurized milk plant. To ahieve these, mathematial models of the CIP proess have been developed and validated by the atual proess data. With these models, simulation study has been arried out to desribe the dynami behaviors of the proess with respet to the onentrations and ontaminations in CIP leaning hemials. The optimization problem has been formulated and solved using written programs based on MATLAB appliation program. Keywords: leaning in plae, pasteurized milk, mathematial model, optimal draining ratio, alkali and aid leaning 1. Introdution At the present, food and beverage produtions have been stritly ontrolled in many issues from onsumer and purhaser-proteting agenies. One of the most important issues, whih affets produt image, onerns about trading ontats and relates to a legal obligation is the leanliness of produts. To ahieve the ontrols of leanliness, the key step is not only measurements and separations of the undesired ontaminants in input raw materials, but also leanup of the residual raw materials whih should be properly onsidered. The hardness of the residual lean up is respet to many fators, with raw material properties being the main fators. * Corresponding author. Email address: paisan.k@hula.a.th In this paper, a leaning proess in a pasteurized milk plant where ow milk is a raw material has been studied. Milk, a whitish liquid ontaining proteins, fats, latose, vitamins, and minerals, is one of the raw materials diffiult to be leaned. Owing to this liquid property, milk has a higher ability to ontat with operating surfaes than any solid foods. Milk leads to a thin film of milk oating on old surfaes and burnt ruds adhering to hot surfaes. Sine it is more fertilized with many nutrients than other liquid raw material, miroorganisms an inrease more rapidly in the residuals. Consequently, the leaning systems in a dairy proess have to have a high performane in the elimination of all residual ontaminations. CIP, a ommon type of leaning proesses in most dairy plants, has been applied to lean raw materials and produt residues in vessels, pipe lines, and equipment. The CIP provides reliable, fast, eonomi and effiient leaning without dismantling the equipment. Moreover, the CIP
432 S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 proess has been developed ontinuously for more hemial and water saving, more omfortable operation, and more leaning effiieny. The reovery of spent CIP hemials is a main approah presented in several literatures. The membrane operation, suh as mirofiltration, ultrafiltration, nanofiltration and others are well performed to regenerate the austi leaning solution from the CIP proess in the dairy industry (Henk 1995; Dresh et al., 1999; Mietton-Peuhot 2000; Dresh et al., 2001; Ge san-guiziou et al., 2002). In addition, the development of the CIP proess has beome an approah to improve the onsumption effiieny. The leaning agent ontaining enzyme gives a good performane for removing the milk residue remained in the heated surfae (Grabhoff, 2002). In an automati CIP system, real-time turbidity and alium sensors have been developed and integrated in the ondutivity monitoring tool (Van Asselt et al., 2002) for improving the leaning identifiation. These lead to saving of leaning agents. However, from the evaluation of hemial and water onsumption in twenty Thai dairy plants, whih were sampled, the average onsumption in a CIP proess is about 10-15% and 50-60% of the total onsumption in the dairy plant, respetively (DIW, 2007). In addition, from the data olletion in real operations, qualities of waste solutions from CIP proesses at eah time are varied and the optimization in leaning operations has been rarely onsidered. This leads to no leaning standards resulting in ineffetive leaning. As mentioned above, this work presents an optimization approah of a irulation of a CIP proess to ahieve hemial and water saving with respet to given leaning standards. This work firstly studies the proess behavior and an optimization approah to find out an optimal draining ratio for the hemial leaning steps of the CIP proess in a dairy plant. Furthermore, mathematial models have been developed and validated by real plant data to represent the proess behavior and to speify optimization onstraints. 2. Proess Overview The main purpose of the CIP proess is to remove all visible or non-visible dirt and bateria from vessels and piping systems by water and hemial solutions in the food and beverage industry that are always being obliged to maintain high hygieni standards after the end of a run. To ensure the leanliness of an operating system properly, it is neessary that there are a number of steps for leaning in the CIP proess as following. Even though some details of leaning maybe differ in eah plant, the main steps of CIP proess are quite similar. Five steps of CIP proess an be explained onsequently. In the first leaning step, pre-rinsing with water removes the gross amounts of milk residues. Seondly, a hot alkali solution, whih is typially 0.5-1.5% austi soda (NaOH) at 75 C, is used as a detergent solution in irulative leaning (Bylund, 1995). In this step, the residual milk remaining from the first step is eliminated. Next, lean water is employed to remove all remaining hemial solution and milk residues in the alkali leaning step. After that, a hot aid solution, whih is generally 0.5-1% nitri (HNO 3 ) at 68-70 C, is arried out for neutralizing any alkali residues and removing any mineral soil presented in aid leaning step (Bylund, 1995). Lastly, the post-rinsing step by water removes the still remaining soils and hemial residues. On aount of the main objetive of hemial usage redution in CIP proess by the optimization approah, both alkali and aid leaning steps have been espeially taken into aount. 3. Proess Model The alkali and aid leaning steps are ontinuous irulative leaning proesses. The typial diagram of this system is shown in Figure 2. The system onsists of the CIP solution tank and the proess equipment: pasteurized milk storage tanks and filling mahines. To desribe the dynami behavior profile of onentration and ontamination in leaning solution (alkali and aid) at the CIP tanks and relevant proess equipment, mathematial models have been developed using the priniple of mass onservation (Kittisupakorn Figure 1. Cleaning steps of the CIP proess in dairy plants. Figure 2. Alkali and aid-irulated leaning proess.
S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 433 et al., 2007; Thitiyasook et al., 2007; Kittisupakorn, 2008; Chuensakul et al., 2008) and the basis of the ompartment model (Levenspiel, 1999). The assumptions made in the development of the mathematial models are onstant density and given fixed flow rate of leaning solutions (alkali and aid). The overall mass and omponent balanes in the form of the ompartment model on the CIP tank and the proess equipment are given as. dv Fi Fo (1) dt dc dt d dt 1 C C Fi i o (2) V 1 Fi i o (3) V dve Fo Fi (4) dt dce Fi C o C i dt Ve (5) d e Fi o i dt Ve (6) C C C 1 C (7) e o i 1 (8) e o i Beause of non-reative proess and moderately large amount of flow rate ompared with tank volume, a ompartment model is good enough to represent the dynami behavior of the proess. It an be simulated by solving Equation 1 to 8. In the simulation, the initial onditions and proess parameters are obtained by observing data and operating ondition in a real plant. To study the leaning operations, a medium pasteurizing milk plant of whih produt was whole pasteurized milk of natural flavor was visited in Thailand. A deentralized CIP proess, whih obligated the leanliness of three pasteurized milk storage tanks and seven filling mahines with total leaned surfaes of about 1,200 m 2 was investigated. After the end of the pre-rinsing step and the rinsing step, the hemial leaning steps with alkali and aid are arried out, respetively. The alkali leaning is performed two times per day. By this is meant that leaning is arried out one a day at the pasteurized milk storage tanks and the filling mahines after the end of the prodution. Meanwhile, the aid leaning is arried out three times per day. The first time is arried out at the filling mahines before the start of the prodution. The last two times of aid leaning are employed at the pasteurized milk storage tanks and the filling mahines at the end of prodution. Referring to onventional plant operations, NaOH and HNO 3 are usually used as the alkali and aid solutions. The leaning period is set as 10 minutes/time and both inlet and outlet flow rates are speified to 200 liter/min and 100 liter/min equally for the leaning of pasteurized milk storage tanks and filling mahines. The operating and initial onditions are given in Table 1. During a leaning yle, the hemial onentrations derease to the aeptable minimum values whereas the ontaminations inrease to the aeptable maximum values. To maintain the quality, the leaning solutions are taken sampling to find the onentration by laboratory analysis after that the fresh hemials are manually added to reset the onentration to the initial value of 1.69%. This pratie is performed every the end of last step of CIP proess. After the leaning solutions used for a week (6 days of operation), both leaning solutions were totally drained out. To ahieve aurate models, the mathematial models have been validated by atual observation data, gathered and analyzed in a laboratory, regarding onentration and ontaminations. The titration methods with either 0.1 mol/dm 3 sodium hydroxide or hydrohlori aid have also been arried Table 1. Initial ondition and proess parameter values. Parameters Min-Max Average Initial hemial onentration of solution at CIP tank (%) 1-2 1.69 Initial hemial onentration of proess equipment (%) - 0 Initial volume of solution at CIP tank (liter) - 500 Initial volume of proess equipment (liter) - 156 Initial ontamination of inlet flow at CIP tank (%) 0-0.001 0 Initial ontamination of alkali solution at proess equipment (gram/liter) 3.13-3.51 3.27 Initial ontamination of aid solution at proess equipment (gram/liter) 0.62-0.84 0.73 Inlet flow rate at pasteurized milk storage tank in proess equipment (liter/min) 198-202 200 Inlet flow rate at filling mahine in proess equipment (liter/min) 98.9-101 100 Outlet flow rate at pasteurized milk storage tank in proess equipment (liter/min) 199-201 200 Outlet flow rate at filling mahine in proess equipment (liter/min) 99.4-102 100
434 S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 out to find the onentration of alkali or aid, respetively. The ontamination of solution onsideration is solid residues and bateria. The determination of solid residues is easily made by evaporation and drying methods. For the bateria, as in the atual operation, the leaning solution is always heated to a temperature of over 75 C, the bateria ontaminant in the leaning solution is negligible. Figure 3 and 4 show validation of dynami behavior profiles of onentration and ontamination. It an be seen that with =0 and =0 the ompartment model represents the model of a ontinuous stirred-tank reator (CSTR) under the assumption of a well-mixed ondition. This model provides inadequately aurate dynami behavior profiles of onentration and ontamination as shown in a dashed line while the mathematial model based on the onept of the ompartment model satisfatorily gives a good predition as seen in the solid line. The parameters of the ompartment models ( and ) in the proess model are obtained by the validated result as given in Table 2. 4. Optimal Draining Ratio To ahieve the hemial and water saving, a onventional plant operation, whih total volume of hemials is disharged, has been replaed by optimal volume of drainage obtained by the optimization method. The objetive funtion is formulated to minimize alkali and aid onsumptions in any time periods (Kittisupakorn, 2007). In this work, the monthly onsumed hemials have been taken into aount. The draining ratio is a deision variable. The optimizations have been proessing under proess model onstraints and limitations of maximum ontaminants and minimum onentrations. D Subjet to 24 t n 1 1 1 1 Min V nj j C D V nj C nj (9) Proess models: (1) to (8) (10) C ( t 0, j,2 j,...,24 j) C (11) ( t 6 j,7 j,8 j,...,24 j) (1 D) (12) 0 D 1 (13) C t C (14) min t (15) max t f Figure 3. Model validation by the ompartment model for onentration and ontamination of alkali during 1 yle. Top: At pasteurized milk storage tanks. Bottom: At filling mahines.
S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 435 Figure 4. Model validation by the ompartment model for onentration and ontamination of aid during 1 yle. Top: At pasteurized milk storage tanks, Bottom: At filling mahines. Table 2. Parameters for ompartment model. Area Type Pasteurized milk storage tanks Alkali 0.78 0.13 Aid 0.70 0.05 Filling mahines Alkali 0.37 0.41 Aid 0.44 0.10 The numbers of leaning yle in a month have been defined as 48 and 72 times for alkali and aid onsequently. An optimal draining ratio defined as a ratio of the optimal amount of leaning solution (alkali or aid) drainage to the gross volume of leaning solution has been determined with respet to aeptable minimum onentration and maximum ontamination in the leaning solution. The minimum onentration (%) and maximum ontamination (%) of new operation are similar to those of onventional plant operation, beause both values are speified to ahieve a minimum use of leaning hemials. 5. Results and Disussions Figure 5 shows the onentration and ontamination profile as well as draining ratio of alkali solution for a onventional plant operation. It an be seen that the onentration of alkali solution is initially at 1.69% and dereases to about 1%. After that the alkali is added to reset the solution onentration at the initial value of 1.69%. This pratie is arried out every seond leaning time. The middle graph shows that the ontamination in the alkali solution goes to 3.03%. To remove this ontamination, the total alkali solution
436 S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 Figure 5. Conentration and ontamination of alkali leaning and draining ratio for the onventional plant operation. Figure 6. Conentration and ontamination of alkali leaning when applying the new operation with 4.34% optimal draining ratio. is drained out and the fresh alkali solution is subsequently filled in at leaning time of 12, 24, and 36 as shown in the bottom graph. In the new operation, the total volume of drainage has been replaed by some volume of hemial solution drainage based on an optimal draining ratio. This leads to the partial ontaminant remaining in the solution but its ontaminant an be ontrolled below the aeptable maximum value. The dynami behavior profiles of onentration and ontamination based on the optimal draining ratio have been shown in Figure 6. At the bottom graph, the optimization finds out the optimal drainage ratio of 4.34%. It means that the volume of alkali is drained at 21.7 liters. The alkali solution is drained at 12, 14, 16,, 46 leaning time (every seond leaning time
S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 437 after one week). The top and middle graphs show that the drainage volume with optimal ratio an be ontrolled the ontaminant profile flutuating around 2.92-3.03% and the onentration profile is almost similar to that of the onventional plant operation. In the ase of aid solution for the onventional plant operation, the dynami behavior profiles of onentration, ontamination and draining ratio are shown in Figure 7. In the top graph, the initial aid onentration of 1.69% gradually dereases to 0.8%. Then, the onentration is adjusted to the initial onentration alike the ase of alkali. This is performed every third leaning time. The middle graph shows that the ontaminant in the solution ontinually inreases owing to spending the solution. Until the ontamination reahes to 0.54%, the spent solution must be replaed by the fresh aid solution in order to remove all the ontaminant. This pratie is employed at 18, 36, and 48 leaning times as shown in the bottom graph. Figure 8 shows the dynami profile of onentration and ontamination as well as draining ratio for the new operation. It an be seen that the optimization determines the optimal draining ratio of 1.70%. This means that the volume of aid is drained at 8.50 liters. In addition, the aid solution is drained at 18, 21, 24,, 69 leaning time (every third leaning time) as shown in the bottom graph. This leads to the onentration profile being similar to the ase of onventional plant operation and the ontamination profile flutuating around 0.42-0.54%. For the new operation of both aid and alkali leaning ases, the volume drainage based on the optimization result leads to redue hemial and water onsumptions. The saving of alkali and aid onsumptions are obtained based on the optimization of the problem statement (Equation 9 to 15) and the water onsumption savings of both ases (Q) are gained by the simply alulation as follows: 3 24 Q V 6nj V 0 DoptV nj 1 n 0 n6 onventional plant operation new operation (16) The benefits of the new operation are given in Table 3. Compared to the onventional plant operation, the optimal draining ratios of 4.34% an provide a saving of 10.39% alkali and 55.49% water in the alkali leaning step. Meanwhile, a 1.70% draining ratio an give the saving of 8.82% aid and 67.36% water for the aid leaning step. In addition, the new operations for alkali and aid leaning have been proved in the pilot sale CIP plant before real implementation as shown in Figure 9. The pilot plant has been test-run to prove the profiles of onentrations and ontamination as shown in Figure 10. It an be seen that the experimental data are almost idential to predited data beause the proess models have been fully adjusted to provide best representation of the real plant before arrying out any optimization. The new operation based on the optimal draining ratio is remarkably appliable at the hemial leaning step of the deentralized CIP proess in the food and beverage Figure 7. Conentration and ontamination of aid leaning and draining ratio for the onventional plant operation.
438 S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 Figure 8. Conentration and ontamination of aid leaning when applying the new operation with 1.70% optimal draining ratio. Table 3. Comparison of operation results of onventional plant and new operations. Results Conventional New operation plant operation Case I: Alkali leaning step Alkali onsumption (liters/month) 153.84 137.8 Water onsumption (liters/month) 2,000 890.6 Minimum onentration (%) 0.98 0.98 Maximum ontamination (%) 3.03 3.03 Case II: Aid leaning step Aid onsumption (liters/month) 188.18 171.6 Water onsumption (liters/month) 2,000 653 Minimum onentration (%) 0.80 0.80 Maximum ontamination (%) 0.54 0.54 industry. This is beause the drainage is determined based on the optimal draining ratio, whih diretly affets to the ontaminant in the hemial solution. In addition, the pilot sale plant has been used to guarantee the leaning effiieny before real implementation. However, a monitoring program should be inluded to ensure food safety. 6. Conlusion CIP has been arried out to lean raw milk and residues in vessels, pipe lines, and equipments in a dairy proess. Referring to the observation in a real plant, the onventional plant operation gives high onsumption for water and leaning agent. Consequently, this paper has proposed the appliation of an optimization approah to find out the optimal draining volume for alkali and aid leaning steps in CIP proess leading to an improvement in the onsumption effiieny. The drainage volume based on the optimal draining ratio of 4.34% and 1.70% for alkali and aid, respetively, respets to the aeptable minimum onentration and maximum ontamination and gives the onsumption saving for the leaning agents, alkali of 10.39%, aid of 8.82%, and water of 61.41%.
S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 439 Figure 9. Pilot sale CIP plant. Figure 10. Conentration and ontamination profile of alkali and aid leaning at pilot sale CIP plant. Left: Alkali leaning, Right: Aid leaning. Aknowledgements The authors would like to thank Thailand Researh Fund (TRF) under The Royal Golden Jubilee Ph.D. Program for finanial support and Sarakhamkaset Co., Ltd. for providing relevant information for this researh. Appendix: Nomenlature C Ce Ci Cs Cf Chemial onentration of solution in CIP tank (% weight by volume) Chemial onentration at proess equipment (% weight by volume) Chemial onentration of inlet flow at CIP tank (% weight by volume) Initial hemial onentration in CIP tank at any leaning yle (% weight by volume) Final hemial onentration in CIP tank at any leaning yle (% weight by volume) Cmin Co Ct D D F F j Q t V i o opt i s Minimum aeptable onentration (% weight by volume) Chemial onentration of outlet flow at CIP tank (% weight by volume) Target onentration for hemials adding (% weight by volume) Draining ratio (% of solution volume in CIP tank) Optimal draining ratio (% of solution volume in CIP tank) Inlet flow rate of solution (liter/min) Outlet flow rate solution (liter/min) Cleaning time in a day for eah type of hemial (time) Water onsumption saving in a month (ubi meter) Cleaning time (time) Solution volume in CIP tank (liter) Contamination in solution of inlet flow at CIP tank (gram/liter) Contamination in solution at CIP tank (gram/liter) Initial ontamination in CIP tank at any leaning yle (gram/liter)
440 S. Niamsuwan et al. / Songklanakarin J. Si. Tehnol. 33 (4), 431-440, 2011 e f max o Referenes Contamination of proess equipment (gram/liter) Final ontamination in CIP tank at any leaning yle (gram/liter) Maximum aeptable ontamination (gram/liter) Contamination in solution of outlet flow at CIP tank (gram/liter) Density of solution (kilogram/ubi meter) Ratio of the bypass stream affeted from the size of flow rate Ratio of the bypass stream affeted from imperfet dissolution of ontamination Bylund, G. 1995. Dairy Proessing Handbook, Tetra Pak Proessing Systems, Sweden, pp. 406-407. Chuensakul, J. and Kittisupakorn, P. 2008. Devise of the reuse system of hromium plating solution and rinse water in hromium plating proess. Proeeding of the International Multi Conferene of Engineers and Computer Sientists, Hong Kong, China, Marh 19-21, 2008, 1660-1664. Department of Industrial Works (DIW)-Bureau of Water Tehnology and Industrial Pollution Management, 2007. Cleaner Tehnology Code of Pratie; Dairy Industry, Department of Industrial Works, Bangkok, Thailand, pp. 11. Dresh, M., Daufin, G. and Chaufer, B. 1999. Membrane proesses for the reovery of dairy leaning-in-plae solutions. Lait. 79, 245 259. Dresh, M., Daufin, G. and Chaufer, B. 2001. Integrated membrane regeneration proess for dairy leaningin-plae. Separation and Purifiation Tehnology. 22-23, 181-191. G esan-guiziou, G., Boyaval, E. and Daufin, G. 2002. Nanofiltration for the reovery of austi leaning-in-plae solutions: robustness towards large variations of omposition. Journal of Dairy Researh. 69, 633-643. Grabhoff, A. 2002. Enzymati leaning of milk pasteurizers. Trans IChemE Part C. 80, 247-252. Henk, M. 1995. Reyling of used austi leaning solutions in the dairy industry by rossflow filtration. Bulletin of the International Dairy Federation. 9504, 175-183. Kittisupakorn, P. 2008. Model Based Control for Chemial Proesses, Chula Press, Bangkok, Thailand, pp. 12-17. Kittisupakorn, P. and Siriburanon, B. 2007. Devise of a leaning in plae (CIP) with irulation proess in a pasteurized milk tank. Proeeding of the International MultiConferene of Engineers and Computer Sientists, Hong Kong, China, Marh 21-23, 2007, 1547-1642. Levenspiel, O. 1999. Chemial Reation Engineering, John Wiley & Sons In., United States of Ameria, pp. 283-293. Mietton-Peuhot, M., Condat-Ouillon, C. and Courtois T. 2000. Regeneration of soda solutions issued from leaningin-plae by ross-flow mirofiltration. Entropie. 226, 44-53. Thitiyasook, P., Kittisupakorn, P., Niamsuwan, S. and Konakom, K. 2007. Modeling and optimization of a rinsing proess in a reyled plasti plant. Computer Aided Chemial Engineering. 24, 545-550. Van Asselt, A.J., Houwelingen, G.V. and Te Giffel, M.C. 2002. Monitoring System for Improving Cleaning Effiieny of Cleaning-In-Plae Proesses in Dairy Environments. Trans IChemE Part C. 80 (4), 276-280.