CHEMICAL ENGINEERING TRANSACTIONS VOL. 57, 2017 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Sauro Pierucci, Jiří Jaromír Klemeš, Laura Piazza, Serafim Bakalis Copyright © 2017, AIDIC Servizi S.r.l. ISBN 978-88-95608- 48-8; ISSN 2283-9216 Redesign of Washing Process of Cartridge Case Using a Combination of Acids, Detergents and Anti-tarnish Compounds Martha Roselia Contreras-Valenzuela*, Roy Lopez-Sesenes, Alber E. Duque- Albarez, Viridiana A. Leon-Hernandez, Brenda Trujillo-Sandoval Chemistry Sciences and Engineering College, Autonomous University of Morelos State Av. Universidad 1001 Col. Chamilpa,CP 62209, Cuernavaca Morelos, México marthacv@uaem.mx The current study establishes the conversion from a washing process of cartridge case performed by batch to a continuous process. The materials used during the wash process were a combination of substances such as acids, detergents and anti-tarnishes. Methodologies like Retrofit Design Approach and Hierarchical Decision Procedure by Douglas were combined for: 1) determining input Information, 2) developing diagnosis and identifying improvement proposals, 3) establishing input – output structure of the flowsheet, 4) defining critical variables of the process (CVsP), and 5) designing new units that support the change from batch process to continuous process. The objective of that combination of methodologies was to solve the complex interactions between unknown variables values. The process critical variables identification was made using a method based on analysis of wicked problems. The result of that, determines that pH and temperature were critical for the process and the detergency efficiency and foam density were critical for the quality. A new continuous process was proposed and represented in a Process Diagram Flow. The redesign reduced problems like poor quality generated by lack of standardization, energy losses and ergonomic and safety risks. The results showed the combination of methodologies and the utilization of a method based on analysis of wicked problems instead of using an optimization method for identifying CVPs was effective to provide consistent and viable solution and support for decision-making at implementation phase. 1. Introduction In order that a process guarantees high quality products according with the changes of market forces, it is necessary to improve the process design with update purposes, through an effective evaluation and deep data analysis of its design variables. The improving phase normally consists of incorporate new technology that minimizes production times, guaranties workers’ safety and health, and a high productivity. A well-known methodology called Retrofit is usually applied for redesigning chemical processes, which considers modifications and adaptions of new components, with the objective of minimizing the process changes and maximizing the use of existing equipment and devices. Unfortunately, when a process simultaneously involves numerous design variables, the methodology provides several solution alternatives (Rodríguez, 2005), and many of them are unviable for implement it. Thus, the interactions between design variables are critical. A methodology that reduces the complexity of original models is the Retrofit Design Approach - RDA (Hernández et al., 2011). It consists of three main stages: 1) diagnosis, where the key design variables should be selected, 2) evaluation, where the favourable options that were selected from the diagnosis stage are investigated and 3) optimization, where the optimal values are obtained according with the ranges of parameters required (Lavric, 2013). On the other hand, synthesis activity is complicated because there are many ways to accomplish the same goal. Hence, the Hierarchical Decision Procedure by Douglas (HDP) for conceptual design of chemical processes is a systematic approach for reducing design problem. The HDP applies hierarchy of decisions, using the flowsheet structure at successive levels of detail (Douglas, 1988). At last, the decision-making about implement the redesign was determined when the proposal achieves the DOI: 10.3303/CET1757251 Please cite this article as: Contreras-Valenzuela M.R., Lopez-Sesenes R., Duque-Alvarez A.E., Leon-Hernandez V.A., Trujillo-Sandoval B., 2017, Redesign of washing process of cartridge case using a combination of acids, detergents, and anti-tarnish compounds, Chemical Engineering Transactions, 57, 1501-1506 DOI: 10.3303/CET1757251 1501 objectives, and the cost of investment is viable. Therefore, there is not a single company that invests in a process redesign that has various solution alternatives. In fact, it only needs the most optimal and viable solution for implementing in real conditions, with the less possible cost that guarantees high quality products. The current study, proposes the redesign of a cartridge case washing process performed by batch, which uses a combination of acids, detergents and anti-tarnish compounds. The design objective was to change the washing process performed by batch for a process that operate continuously. As result a conceptual design was proposed. The existing batch process flowsheet was used as input information, moreover the analysis was made through RDA and HDP. The design critical variables identification was developed based on methodology for resolving wicked problems. Considering the redesign as a wicked problem (Buchanan, 1992), in other words as a problem inaccurately formulated, where the information was confused with conflicted values, from different clients and decision-makers, and the whole system are thoroughly unclear. 2. Problem statement The manufacturing process of rifle bullet casings consists on nine steps, and at the end of each one the product requires to be washed. Thus, the washing is one of the most important process elements during the production of cartridge cases, and it is essential for granted high quality products. The washing process improved in the present work, have been performed by batch and manually handled for a long time (more than 60 years). For carried out the cartridge case washing, the operator mixed different solid components and aqueous solutions such as acid, detergents, and anti-tarnishes. The chemical mixtures were prepared into a barrel of 200L of capacity; the components were slowly added by hand into 180L of water using a plastic bucket and the mix was heating by dipping a pipe with steam. The washing procedure is showed on Table 1. The washing objective is to remove the residues of lubricant, which was used during draw process, as well as clean off the tarnishes over the metallic surface that were generated during manufacturing operation. The workers wore only a coverall and plastic gloves as personal protection equipment to develop the task, and they did not wear protective gas masks, resulting on a exposure to the mixture of acid gases remained on the workstation during the full shift. The company has identified two problems to solve: 1) poor quality of washing caused by non-standardized work method, 2) exposure of the personnel to ergonomic risk, unsafe and unhealthy work conditions. Table 1: Washing procedure Step 1: Solution preparation Barrel 1: mix powdered detergent with water, heat the mixture with steam Barrel 2: mix powdered degreaser with water, heat the mixture with steam Barrel 3: mix acid solution 1 with water. Add the acid slowly using a plastic bucket. Barrel 4: mix acid solution 2 with water and anti-tarnish. Use a plastic bucket. Total batches by mix 4 with equivalent to 800L consumed by shift Step 2: Fill washing tank with a batch of cartridge cases Step 3: Add solutions to washing tank Note 1: The mix temperature and heating time are not determined; the operator heats the mixture by dipping a pipe with steam until the barrel is empty. Note 2: The component proportions have been omitted as request of the company. 3. Hierarchical design methodology based on retrofit for washing process of cartridge case From hierarchical decision procedure (HDP) were only considered two stages: input-output structure of the flowsheet and batch versus continuous, the rest of levels were not considered due they are not necessary for the process. Moreover the requirements analyses for flowsheet conceptualization were developed in base of Turton recommendations (Turton et al, 2009). From the retrofit design approach (RDA), only were considered: diagnosis and evaluation, nevertheless for diagnosing and evaluating the critical process variables (CPVs), the method “Determination Matrix for CPVs” was used (Contreras, 2011). 3.1 Diagnosis 1. Diagnosis about batch operation method 2. Process variables identification from the batch washing process 3.2 Input Output structure of flowsheet 1. Development of Input-output flowsheet for the batch washing process: it includes conceptualization and analysis of the process, process topology, stream information and equipment information as follow: 1502 a. Establish input and output streams b. Determine stream characteristics c. Identify equipment d. Locate auxiliary equipment for power and heat generation 3.3 Evaluation 1. Evaluate the process variables using CPVs – Determination Matrix as follow: a. By experts about the process define which process variables meet the follow requirements: i. Corresponds to Input – Output structure ii. Is independent variable, iii. It affects the production volumes, iv. It impacts on the equipment operation, v. It is present during the whole process vi. It impacts the operation time, the product quality and productivity indices. b. The matrix columns are building by alternatives that represent the variables. c. The rows characterize criteria described above. d. A weight is assigned as criterion value (see Figure 2 and 3). The highest value represents the CPVs. 3.4 Batch vs Continous 1. Batch versus Continuous: a comparison of a batch process design to a continuous process design should be made. 2. Proposal of Redesign 4. Results and Discussion The results from batch process were summarized in the process diagram flow (PDF) showed in Figure 1. Four main pipes represented the input structure; they distributed steam and cool water in an independent way to the barrels and washing tanks. The pipes were identified from 1 to 4: pipes 1 and 3 contain steam; pipes 2 and 4 contain cold water. There were not pipes between barrels and washing tanks, thus the mixtures supply from barrels to washing tanks was carried out by hand. The draining of mixtures from the washing tank to the water treatment plant represented the output structure, and it was identified with number 5. All the equipment was identified and numbered, the services equipment for heating generation was not represented in the PDF due it was located outside of the washing area. Finally all process variables were identified. Figure 1: Process diagram flow of batch process from cartridge case washing Process Diagram Flow from Actual Washing Process of Cartridge Case Process variables Input streams: cool water ,2 ,4 Temperature °C pH Foam ρ kg/m3 Detergency efficiency % liquid ρ kg/m3 χ % Production volume by shift (7.5h) Time of loading cartdrige cases to washing tank in min Manual operate valve Process Time of cartdrige cases unloading from washing tank in min Water Time of mixtures loading in min On-Off Valve Steam Time of mixtures unloading in min Time of mixtures preparation in min Washing time min/batch Input streams: steam 1,3 Output streams: draining of mixtures 5 Barrel 1 Mix detergent and hot water Barrel 2 Mix degreaser and hot water Barrel 3 Mix acid solution 1 and water Barrel 4 Mix acid solution 2 and water Washing tank 1 Washing tank 5Washing tank 4Washing tank 3Washing tank 2 1 2 3 4 5 V1 V3 V2 V4 V9 V5 V10 V6 V11 V12 V7 V13 V8 V14 V18 V21V20V19V17 V16 V15 1503 During the evaluation of batch process variables using CPVs – Determination Matrix (see Figure 2), only seven process variables were selected for to be evaluated: materials pH (detergent, degreaser and acid solutions), temperature of water °C, foam density kg/m3, detergency efficiency %, liquid mixture density kg/m3 and concentration %. The criterion value was assigned by the process experts, in base of production and quality importance. After the analysis and evaluation of batch process, the results were the following: materials pH were the critical process variables, unfortunately the pH value was unknown during the process of redesign, to be specific, it was always unknown not because it cannot be determined, in spite of it was the most important value of the process, simply the company decided to keep it as industrial secret. On the other hand, foam density and detergency efficiency were on second place due to both variables were critical to quality. The diagnosis and Identification of variables for the process redesign was made using the same determination matrix, but in this case the variables were evaluated thinking in a continuous process, see Figure 3. After the analysis and evaluation, the results were the following: again, materials pH were the critical process variables and temperature and flow rate were on second position as common in continuous process. However, foam density and detergency efficiency were on fourth place. That result represented an inconsistency due to high foam density is necessary to guarantees high quality products, but at the same time high foam density represented a system restriction attributable to it could block the stream flow from the water and detergent mixture. Thus, in order to solve that situation, a study about equilibrium point between foam density and detergency was carried out; with the intention of prevent blockages in the streams flow. Figure 2: Critical Variables of Process (CVsP) – Determination Matrix from batch process Figure 3: Critical Variables of Process (CVsP) – Determination Matrix from continuous process The comparison established in section 3.4 batch versus continuous was developed in a table with the same name, an example of the results is shown in Table 2. The first column enclose the draw of one barrel from batch process, the second column describes the features needed for the operation, the third column include a draw of the mixing tank proposed as redesign for the continuous process, finally the fourth column contains an example of the equipment characteristics required by the continuous process. The results about mass and energy balance, sensitivity analysis, process capability, determination of equipment materials, among others are omitted in the present work as request of the company. During the redesign of the washing process the principal and auxiliary equipment, requirements of services about steam, water, electricity and air, piping and instrumentation were determined in order to reach the automation of the operation through Programmable Logic Controller (PLC). The automation allowed to standardize the process and eliminated the hazards and risks conditions, increasing the process productivity. Part of the redesign is showed in the Figure 4. Criteria pH Tin °C Flow rate kg/s Foam ρ kg/m3 Detergency efficiency % liquid ρ kg/m 3 χ % Criterion value pH Tin °C Flow rate kg/s Foam ρ kg/m3 Detergency efficiency % liquid ρ kg/m3 χ % Corresponds to Input – Output structure x x x 2 2 2 0 0 0 2 0 It is independent variable x x 1 1 1 0 0 0 0 0 It affects the production volumes x x x x 3 3 0 0 3 3 3 0 It impacts on the equipment operation x 4 4 0 0 0 0 0 0 It is present during the whole process x x x x x 1 1 1 0 1 1 1 0 It Impacts the operation time x x x x 4 4 4 0 4 4 0 0 It impacts productivity indices x x x 4 4 0 0 4 4 0 0 19 8 0 12 12 6 0 X EVALUATION Critical Variables of Process (CVsP) - Determination Matrix Alternatives Results Chart - Results Table selected critical variable Criteria pH Tin °C Flow rate kg/s Foam ρ kg/m3 Detergency efficiency % liquid ρ kg/m 3 χ % Criterion value pH Tin °C Flow rate kg/s Foam ρ kg/m3 Detergency efficiency % liquid ρ kg/m3 χ % Corresponds to Input – Output structure x x x x x 2 2 2 2 0 0 2 2 It is independent variable x x x x x 1 1 1 1 1 1 0 0 It affects the production volumes x x x x x x x 3 3 3 3 3 3 3 2 It impacts on the equipment operation x x x 4 4 4 4 0 0 0 0 It is present during the whole process x x x x x x x 1 1 1 1 1 1 1 2 It Impacts the operation time x x x x 4 4 4 4 0 0 4 0 It impacts productivity indices x x x x 4 4 0 0 4 4 0 2 19 15 15 9 9 10 8 X EVALUATION Critical Variables of Process (CVsP) - Determination Matrix Alternatives Results Chart - Results Table selected critical variable 1504 Table 2: Batch versus Continuous Batch process Continuous process Equipment Description Equipment Description Drum 1 Operation: Mixing detergent and hot water Plastic drum 200L of capacity 2 pipelines of stainless steel SS316 1”diameter. 2 manual operate valve Stream 1 for cold water Stream 2 for steam Temperature unknown pH unknown Density unknown Mixing tank 1 Operation: Mixing detergent and hot water. Stainless steel SS316 tank mixer of 2m height per 0.8m diameter 5 pipelines of stainless steel SS316 1.5”diameter. 2 manual operate valve 2 on-off valves Stream 1 detergent Stream 2 cold water Stream 3 steam input service Stream 4 steam output service Stream 5 mix of detergent and hot water Tin 85°C pH known Density known Figure 4: Partial Process diagram flow of continuous process from cartridge case washing. 2 1 Drum 1 Mix detergent and hot water M Mixing tank 1 V25 V26 V34 2 1 3 4 5 Process Water Steam Anti-tarnish - Solution acid 2 - Steam - Water Socucion acid 1 - Steam - Water Degraser - Water Detergent - Water On-Off Valve Manual operate valve Butterfly valve Diaphragm pump Three way valve Centrifugal pump Angle valve Flow Controler Check valve Flow indicator Butterfly valve Powdered Detergent Desengrasante V1 T2 V2 Mixing tank 4 M Ne utralizer ta nk FC3 V18 V19 Acid Solution 2 BN3 V16 V15 Ne utralizer ta nk FC2 V13 V14 Anti-tarnish BN2 V11 V10 Ne utralizer ta nk FC1 V8 V9 Ne utralizer ta nk Mixing tank 3 M Ne utralizer ta nk Acid Solution 1 BN1 V6 V5 M Mixing tank 1 FI1 FI2 FI3 FI4 FI20FI14 FI8FI2 FI17 FI18 FI16FI15 Jabón T1 V4 V3 M Mixing tank 2 Powdered Degreaser C h a in C o n v e y o r V20 V21 V22 V23 V7 V12 V17 V24 V25 V28 V29 V30 V27 V26 V32 V31 V33 V34 V35 V36 V37 V38 V39 V40 V41 V42 V43 V44 V45 V46 V47 V48 V49 V50 V51 V52 V53 V68 V69 V70 V74 V73 V71 V72 B1 B2 B3 B4 C h a in C o n v e y o r FC1 FI1 Washing tank 1505 5. Conclusions The hierarchical design methodology based on Retrofit for Washing Process of Cartridge Case allowed the conversion from a washing process of cartridge case performed by batch to a continuous process. During the definition of critical variables of the process (CPVs), the results from the evaluation established that the materials pH were the critical variables of process, nevertheless was unknown during the process performance, therefore, was found an inconsistency that was resolved with the redesign. The detergency efficiency and foam density were defined as critical for the quality. Finally, the Process Diagram Flow proposed was effective to provide consistent and viable solution to standardization and risk elimination proportioning support to the decision-making done by the company. Acknowledgments All the company personnel and students by their support during the develop of the present work. Reference Buchanan R., 1992, Wicked Problems in Design Thinking. 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