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Sludge minimization and production improvement by changing filtration and reaction techniques in vinyl acetate-ethylene copolymerization
Journal of Cleaner Production 24 (2012) 109e116
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Sludge minimization and production improvement by changing filtration and reaction techniques in vinyl acetate-ethylene copolymerization Atilla Mutlu a, Byeong-Kyu Lee a, *, Chi-Hyeon Lee a, Jong-Yong Kim b a b
Department of Civil and Environmental Engineering, University of Ulsan, Ulsan 680-749, Republic of Korea Air Products Korea Inc., Ulsan 680-150, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 August 2011 Received in revised form 14 November 2011 Accepted 14 November 2011 Available online 27 November 2011
The handling of generated sludge waste during polymer production is one of the main environmental concerns of the polymer industry. An alternative filtration technique was applied to determine the efficiency of different types of filtering media for polymer production. A vibration filter media was replaced with a non-woven fabric filter that was previously used in the refining facility. The purpose of this study is to analyze how much the new filtration affects sludge generation and final production. The application of these alternative filtration techniques have resulted in a significant reduction in the amount of non-recyclable sludge by approximately 77%, while the total amount of polymer production has increased by 41% during the six-year study period. The refining facility saved a total of 617,710 USD/y by changing the filtration system, resulting in an increase in product recovery and a decrease in sludge generation, as well as an improvement in reaction conditions. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: VAE Filtration Vibration filters Sludge Waste minimization
1. Introduction For the last few decades, minimizing of waste and emissions, process optimization and use of sustainable energy at the source have been getting a great deal of attention in major industries (Dursun and Sengul, 2006; García et al., 2008; Dovì et al., 2009; Klemes et al., 2010). In particular, Klemes and Huisingh (2008, 2005) have extensively reported roles, ideas, techniques, and progresses of cleaner production, using process optimization, waste minimization, life cycle assessment (LCA) and renewable energy, for sustainable development (Berlin et al., 2007; Baas, 2008; Bonilla et al., 2010; USEPA, 2010a). A cleaner and healthier environment can be attained with performing innovative and sustainable technologies and management approaches (Wainwright and Cresswell, 2001; Eder, 2003; Hossain et al., 2008; Dovì et al., 2009) and pollution prevention strategies (USEPA, 2010b) including effective environmental management (Khan et al., 2002) and engineering designs for minimizing waste practices (Douglas, 1992; Petek and Glavic, 1996). It is an essential approach for optimizing processes and minimizing the production of wastes at the sites of industrial operations (Peden et al., 1998; Abraham, 2000; LaGrega et al., 2001; Klemes et al., 2010). However, many industries usually focus on
* Corresponding author. Tel.: þ82 52 259 2864; fax: þ82 52 259 2629. E-mail address: [email protected] (B.-K. Lee). 0959-6526/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2011.11.047
treatment and disposal rather than on source reduction. This situation can be explained by the way in which regulations emphasize overall management practices including treatment, disposal, recycling, and source reduction (Wainwright et al., 2002; Azabar et al., 2004; Miller et al., 2008). Thus, it is highly suggested that industries need to be familiar with the current knowledge related to the application of source reduction methods to their production processes (USEPA, 2010b). Despite the different types and amounts of waste generated by different industrial processes, there are common goals that all major industrial operations should consider when waste reduction plans at sources are needed. The management plan for source reduction should be framed toward achieving a main goal of avoiding waste generation (Dangelico and Pontrandolfo, 2010). This goal can be achieved by instituting a variety of processes, including reducing on-site pollutants, minimizing the use of hazardous materials, and process optimization (Warren et al., 1999; Hossain et al., 2008; García et al., 2008). Polymer filtration is a key factor in maintaining quality, and is considered a necessary and important processing step for most polymer production operations (Morland and Baur, 1997; Potthast and Sandmeyer, 1998; Mancini et al., 2010). Polymer filtration may be an expensive process because of the high cost of labor and maintenance. This statement could be considered true at first glance, and may be valid for systems that were improperly designed, resulting in poor quality polymer production. However, the overall cost, a unit of capital per mass of polymer, is usually
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lower when filtration systems undergo comprehensive cost analysis. A detailed cost analysis for a polymer filtration system may include the following criteria: Cost effective filtration including costs of filtration, equipment, replacement, maintenance, and labor; improving yield (how much polymer can be safely transferred through the filtration system and collected); quality of the final product (degradation rates, acceptable polymer losses during filtration); and reducing waste. The on-stream life of a filter is an important factor for filtration systems, and has a great impact on the overall operation cost (Meiss, 1998). Also, it should be stated that improving operating efficiency and controlling polymer production process have become also considerable parameters in polymer production (Ganzeveld et al., 1999; Lucas et al., 2009; Rivas, 2010). In this study, an alternative filtration technique was applied in order to determine the efficiency of different types of filtering media for polymer production. A vibration filter media was replaced with a non-woven fabric filter that was previously used in a refining facility. The aim of implementing the new filter was to reduce the amount of sludge that accumulated during filtration by increasing the filtration ratio of polymer products. The manufacturing process, including the operational cost of the new filter media and waste handling system, was also evaluated. In this article, the results of testing alternative filtration performances for reducing sludge generated from polymer filtration applications are presented in terms of the economic and environmental benefits. 2. Materials and methods 2.1. Study facility description This study was conducted in the vinyl acetate-ethylene (VAE) copolymer production facility located in Ulsan, Korea. The VAE product contains solids in the range of 40e72%, and the solid phase consists of 2e4% dispersing agent and surfactant, such as hydrolyzed polyvinyl-alcohol (Choi et al., 2004). VAE is widely utilized in various applications such as paint, adhesives, coatings, and as an oil processing material (Garret et al., 2000; Robenson and Vratsanos, 2000; Robeson and Berner, 2001; Choi and Lee, 2010). As illustrated in Fig. 1, the VAE polymerization process begins with the addition of the surfactant solution containing the dispersing agent, catalyst, and the reducing agent (ethylene) into the “reactor” of 11.3 m3. The dispersed VAE begins to form a polymer under the high pressure of ethylene (14.1e61.6 kg cm2) with the catalyst (H2O2) and reducing agent. Polymerization is an exothermic reaction that includes vinyl acetate (VA) and ethylene [see Eq. (1)].
The heat generated during polymerization is recovered by an external heat exchanger. The polymerization process maintained at 80 C is finalized when the amount of vinyl acetate monomer remaining in the reactor is less than 1%. After the reaction, the polymerized product is transferred to the “defoamer? thanks to the pressure of the ethylene (2.069 106 Pa) followed by several consecutive processing stages including filtration, cooling, and pH adjustment. Subsequently, the unreacted ethylene is burnt at the flare stack because of safety issues. However, the heat recovery
Surfactant
Catalysist
Ethylene
Initiating VAM
Reactor
Defoam Tank
Filtering Media
Blender Tank
PostBiocide Treatment
Storage Tank Fig. 1. Stages of the polymerization process in the VAE plant.
after being burnt was not conducted, yet. The last stage of the polymerization process is the transfer of the accumulated VAE product into the “blender tank.” 2.2. Analysis of sludge accumulation and product loss This study analyzed the main problems associated with the polymer production. They were loss of the main product in the sludge that accumulates during the filtration process. Sludge accumulation occurs both in the refining facility and in the reactor during VAE production. The existing filtration system consists of non-woven filters as the primary media, followed by bag filters as the secondary filtering media. The loss of product occurs at this point; some of the product still remains on the primary (nonwoven) filters while the separated solid particles accumulate in the sludge. As the filtering process continues, the amount of accumulated sludge increases, which results in an increase in the amount of VAE product present in the sludge. Because of the ineffective
filtration process, the efficiency of polymer production decreases, while the accumulated sludge containing the final polymer product dramatically increases. 2.3. A new filtration design In order to solve the polymer filtration problems, this study attempted to apply a proper engineering design concept consisting of two individual steps. The first step was replacing the non-woven
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Fig. 2. A body feature and schematic of a vibration filter system.
filtering media with an ultrasonic vibration filtering system in order to ensure a better filtration process. Fig. 2 shows a body feature and schematic of a vibration filter system that was used for this study. High frequency current of 30 kHz by a generator is converted to microwave through a converter. Then the generated microwave vibration is transported to the screen of the vibration filter by resonance action. Viscous products injected into the vibration filter system through the inlet are separated by three-dimensional vibration (with high efficiency) on the twist screen. Products with smaller size than the opening of each deck mesh are passed though the screen, while the larger sizeproducts are vented out through the outlet by centrifugal force. In order to prevent from blocking the mesh opening by products and maximize material separation efficiency in the system operation, the vibration system uses cleaning kits such as slide ring or ball inserted between the mesh and the punched plate (Fig. 2). In particular, the slide ring can minimize frequent cleaning required to remove stagnant materials accumulated on the punched plate with use of ball type cleaning kit (Fig. 3). A vibration filter media (Ildong Industrial Machinery Co., Korea) was installed in the current system. The efficiency of the new filtration system was tested and evaluated its performance results for minimizing generated sludge and increasing final polymer production. A vibration filter specifically designed for a chemical process was compared to the existing filtration system (non-woven filter media). For the testing procedure, the vibration filter media
with a diameter of 1200 mm was selected, and filter screens were used with different sizes in mm (No.: 70, 100, 150, and 200). In the new filtration design (Fig. 4), the filtration rate was set at 0.35 m3 h1 which can be applicable to continuous operation of 4e5 batches (12 Mt/batch). The performance of the new filter system was assessed according to the number of batches and amount of sludge generated during the filtration process. 2.4. Improving the reaction conditions The second design step for engineering approach was related to improving the reaction efficiency using simplified reaction conditions. The polymer production process was also investigated in order to determine ways in which to improve reaction efficiency. The polymer product is an adhesive material, and it may easily remain inside the chamber without any filtration process. This build-up of polymer may not only cause a decrease in reaction efficiency, but it will also increase the amount of sludge, resulting in important production loss. For the purposes of improving reaction conditions, the internal surfaces of the reactor and the heat exchanger were coated to allow the product to easily move through the filtration system without any accumulation inside the reactor. In addition, the standard method of adding the initial surfactant into the reactor was also changed in order to determine if any possible enhancement of reaction conditions could be achieved as a result. The surfactant was partially added into the reactor over the
Fig. 3. Schematic structure of a vibration filter system (left) and a photo of slide ring (right).
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Reactor
Current Non-woven Filtration System
The New Filtration System Using Vibration Filter
Non-woven Filter
Sludge Outlet
Vibration Filter for Testing
to the bagfilter
VAE Product Outlet Pump for Discharging the Final Product
Fig. 4. The new filter design with the existing filtering system.
course of an hour instead of being entirely added immediately at the beginning of the reaction.
second smallest value among the measured flow rates. The smallest amount of sludge, 25 kgpb, was generated when the EP-706 grade VAE was used with a No. 100 size of screen at a flow rate of 1.8 hpb.
3. Results and discussion 3.1. Sludge generation
3.2. Filtration system change
A simple test was carried out to measure the amount of final product lost within the accumulated sludge. In the experiment, a non-woven filter, with dimensions of 50 cm 80 cm, was used as a primary filter and weighed before and after the filtration. The weight of the filter was 9.8 g before filtration was applied in the system. After the filtration process, the weight of the filter was recorded as 262 g, which included a mixture of solid particles, the final product, and the filter itself. This simple test showed that the efficiency of non-woven filter media is considerably low, and a large amount of VAE product was being thrown away as sludge, requiring special treatment as designated waste. This situation may have serious environmental and economic impacts. The existing filtration system not only decreased the amount of final product, but also changed the disposal classification of the generated sludge from general waste to designated waste. In February of 2002, new sets of vibration filter media were installed, and the sludge generation was tested as a function of screen size (mm) and flow rate. For this test, different grades of VAE polymers were utilized. The data obtained from the testing process, including flow rates in hours per batch (hpb) and the amount of generated sludge in kg per batch (kgpb), are presented in Table 1. The highest flow rate of 3.2 hbp occurred using an EP-706 grade of VAE product with a No. 200 size of screen. Generated sludge was measured at 60 kgpb, which was the second highest value throughout the test. The highest amount of sludge, 80 kgpb, was generated when the EP-705R grade VAE and the largest (No. 70) size of screen were used at a flow rate of 1.4 hpb, which was the
Table 2 summarizes the data from the VAE polymer production for six consecutive years. The non-woven filtering system was employed for the first three years (yr 10, yr 20 , and yr 30 ), whereas the vibration filters were installed and tested at the beginning of the fourth year through the sixth year (yr 100, yr 200 , and yr 300 ). During the operation of the non-woven filtration system, the total annual production of the polymer was nearly the same every year. However, sludge generation significantly increased from 300 to 424 Mt/y. For the first three-year (yr 10, yr 20 , and yr 30 ) operation of the non-woven filter system, unit sludge generation and the sludge disposal cost increased every year. The increased amount of them in the third year under the non-woven filtration reached up to by 39.8 and 41.3%, respectively, as compared to those in the first year. Thus, the company paid higher annual costs to dispose of its sludge in spite of similar polymer production. In order to save the
Table 1 Test results after applying the vibration filter. Test number
Screen size (mm)
Grade
Flow rate (h/batch)
Sludge (kg/batch)
1 2 3 4 5 6 7
70 70 100 100 100 200 200
EP-705R EP-705R EP-706K EP-706K EP-706 EP-705 EP-706
1.5 1.4 1.3 1.6 1.8 1.8 3.2
35 80 30 30 25 40 60
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Table 2 Overall production statistics of product and sludge for the years in which different techniques of pollution prevention were applied. Non-woven filter (NWF) Year
yr 10
Application method for waste minimization
Not applied
Type of filtering media Production (Mt) Sludge (Mt) Unit sludge generation (kg waste/Mt product) Sludge disposal cost (as designated waste, USD/y)
NWF 23,500 300 12.8
NWF 23,700 376 15.9
63,000
79,000
a
yr 20
Vibration filter (VF) yr 30
yr 100
yr 200
yr 300
Partial VF filtration
Complete VF filtration
NWF 23,718 424 17.9
NWF þ VF 27,523 391.8 14.2
VF 28,153 229 8.1
Complete VF filtration þ Rxn improvement VFþRxna 33,151 98.5 3.0
89,000
82,000
63,000
39,000
Improvement of Reaction Conditions.
disposal costs of the sludge generated from polymer production, the company began replacing the old non-woven filtration system with the new vibration filtration system from the fourth year (yr 100 ). As a result, the amount of polymer production in the fourth year increased considerably by approximately 3800 Mt/y (16% increase), and the generated sludge associated with production decreased slightly from 424 to 392 Mt/y (7.5% decrease) compared to the third year. Because of the decrease in sludge generation, the unit sludge generation in the fourth year (yr 100 ) decreased by 20.7% as compared to that in the third year (yr 10 ). As a result of the decreased sludge generation, the company was able to save 7.9% of the disposal cost, even with a 16% increase in polymer production. The company continued using the vibration filtration system, and completed the replacement of the old non-woven filtration system in the fifth year (yr 200 ). Even though the production of VAE polymer in the fifth year (yr 200 ) increased even more to 630 Mt/y as compared to that in the fourth year (yr 100 ), the total generation of sludge in the fifth year decreased from 392 to 229 Mt/y, which was a decrease of 41.6%, as compared to that in the fourth year. Therefore, the company was able to reduce the unit sludge generation by 43% in the fifth year, compared to the fourth year. Thus, the resulting disposal cost of generated sludge in the fifth year (yr 200 ) was reduced by 23.2%, compared to that the fourth year (yr 100 ), while the polymer production increased by 2.2%. 3.3. Vibration filter efficiency The non-woven filter media was substituted for the vibration filter media as a primary filtration system, and used with bag filters as a secondary filtration system. Different grades of VAE polymer
products, such as EP-706K and EP-705/706/705R, were used for the filtration process with different size of screens (No. 150/200). Table 3 shows the basic results of generated sludge reduction from the testing procedure. The vibration filters and bag filter screens were compared in terms of their longevity during one cycle. A cycle refers to the active service duration of a filter screen after one use. The vibration filter screens had greater service duration and could be used for 80 batches, while the bag filter screens had lower service duration and could only be used for either 5 or 2 batches using No. 150 or No. 200 size of screens, respectively. The unit generation of waste (97.7 kg of sludge per batch) resulting from the utilization of vibration filters in the fifth year, which had complete replacement by vibration filters, was approximately 54.4% less than the unit value of waste (219 kg of sludge per batch) when using the non-woven filters in the third year. The total reduced amount of generated sludge was then 119.3 kg of waste per batch using vibration filters, with bag filters as a secondary system. This combination of primary (vibration) and secondary (bag) filtering systems also provided a more efficient cycle in terms of the unit generation of waste per batch. There was a need for 6 bag filters to complete one batch for each cycle [1.0 cycle (6 bag filters) per batch)]. However, there was a 68% reduction (0.32 cycles per batch) in the number of cycles required per batch when the combination of vibration filters and bag filters was completely employed. In other words, only two bag filters were needed to complete one production batch due to the improved filtration efficiency conferred by the vibration filters. Although the clogging of raw material at the filtering media is a common problem with vibration filtering applications, a special design for device cleaning, including slider rings or filter balls, may
Table 3 Operation results after changes to the vibration filter. Product grade and filter
Screens (mm)
VAE products
EP-706K EP-705/706/705R other grades
150/200 200
Filter System
Filter screen Bag filter (2nd filtering system)
Bag filter (2nd filtering system) 150 200 150
200 80 batch/1cycle 5 batch/1cycle 150 2 batch/1cycle 200 Sludge Generation
Required Filters per Batch
Non-woven filter application (average amount of designated waste treated in 2001) Vibration filter application-conversion of the production unit (average amount of designated waste treated in 2004) The reduced amount Non-woven filter Vibration filter Saved number of filters
219 kg/batch
99.7 kg/batch
119.3 kg/batch 6 filters (1.00 cycle)/batch 2 filters (0.32 cycle)/batch 4 filters (0.68 cycle)/batch
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Fig. 5. VAE production and sludge variations during the use of two different filter applications.
be utilized to prevent (or reduce) clogging problems and to increase screening efficiency. Recently, slider rings have been considered better substitutions for filter balls among most self-cleaning devices (Brock, 2004). 3.4. Improvement of reaction conditions Even though the total polymer production in the sixth year (yr 300 ) increased by 17.8% compared to that in the fifth year (yr 200 ), the total generation of the sludge associated with the production decreased by 57% (Table 1 and Fig. 5). This reduction in sludge generation was due to a change in the surfactant addition method, reactor cleaning practice, and filter exchange cycle in the sixth year (yr 300 ). The required amount of all the surfactants had been added into the reactor over a period of a few seconds, resulting in lower reactivity. However, beginning in the sixth year, the surfactant was slowly added to the reactor by dropping a small amount of droplets evenly over the course of 1 h. Furthermore, the cleaning cycles of the reactors were shortened in the sixth year. Thus, the reactor was frequently cleaned before the VAE polymer or other solid particles had significantly coated the inside of the reactor’s inner walls. In addition, the exchange cycles of the filters were shortened in the sixth year resulting in a reduced pressure drop in the filtration system. The combined activities of reactivity improvement, frequent reactor cleaning, and filter exchange cycle shortening greatly contributed to reducing the total volume of sludge generation associated with VAE polymer production. Finally, the company was able to increase their production of VAE polymer. Fig. 5 shows variations in the total production of VAE polymer and the total sludge generation associated with production over six consecutive years (yr 10, yr 20 , yr 30 , yr 100, yr 200 , and yr 300 ) using information on the past and current filtration system applications. In the end of the sixth year, total VAE polymer production reached 33,151 Mt/y, which was the highest value for the six-year study period. However, total sludge generation associated with the polymer production was only 98.5 Mt/y, which was the lowest value during the whole study period. This great improvement in the reduction of sludge generation was due to the combination of the complete operation of the vibration filter system among all the filtration systems, as well as a change in the reaction conditions. 3.5. Cost-benefit analysis
filtration benefits, was made based upon the testing results and the investment and installation costs given in Table 4. The annual VAE production in the fifth year was 28,153 Mt/y. Based on the production capacity of a unit batch (12.25 Mt/batch), the total required number of batches was calculated to be 2298 batches per year. Analysis sections (in Table 5) included the fifth-year production data from the production facility, product recovery cost, waste treatment cost, and the reduced cost of changing the filter system. The operation of the vibration filter system can minimize sludge generation resulting in more polymer product recovery, and a reduction in the number of filters that are required. The amount of additionally recovered product after the vibration filter system was applied was approximately 120 kg per batch (in Table 3), and the total annual amount of reduced generated sludge was 275.7 Mt/y. The annual savings resulting from the additional product recovery was calculated to be 275,760 USD/y resulting in the largest savings. Based on the waste treatment cost of 230 USD/Mt, in the fifth year the resulting annual savings on the waste treatment cost accompanied by the complete application of vibration filters instead of non-woven filters was 63,250 USD. The annual cost of non-woven filters, if used, would be 126,000 USD. The annual reduced cost of bag filters (with the use of vibration filters) was 28,000 USD. The annual cost for utilization of vibration filter screens required 5800 USD. Thus, the total annual cost savings obtained from filter use reduction accompanied by the changing of the filtration systems from non-woven filters to vibration filters was 148,200 USD in the fifth year. Thus, the company saved a total of 487,200 USD/y by applying alternative filtration techniques in the fifth year with complete replacement. In addition, in the sixth year, the company greatly minimized its sludge generation and recovered more VAE polymer product by a combination of improving the reaction conditions and adapting the vibration filter system. Given in Table 5, the additional savings obtained through improving reaction conditions in the sixth year was 130,500 USD/y. Finally, by applying new filtration and processing techniques (adapting the vibration filter systems and improving reaction conditions), the VAE polymer production company was able to achieve total benefits of 617,710 USD/y in the sixth year, which includes benefits resulting from the sale of the Table 4 The investment and installation cost of vibration filters. Investment equipment
A set of three vibration filters, including filter media, a holding tank, piping, and valves, were installed, and the total investment costs are presented in Table 4. The overall installation and investment cost was 96,000 USD. An analysis for determining the annual economic efficiency, including a comparison of the old and the new
Vibration filters On/Off valves Control valves Other (shipping, labor, etc.) Total cost
Unit price (USD)
Quantity
Cost (USD)
2000 5000
3 ea 3 ea 3 ea
45,000 6000 15,000 30,000 96,000
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Table 5 Cost-benefit analysis using the vibration filter system. Annual capacity: 28,153 Mt/y Unit batch capacity: 12.25 Mt/batch Total batches requirement: 2298 batch/y Annual Production
Product recovery cost
Reduction of treatment cost of sludge Reduced cost of Filter
Reaction Condition Improvement Annual Total Saved Cost
Amount of generated sludge (the 5th year) Annual usage of drum filter roll (55 batch/roll) Price of drum filter Reduction of 2nd bag filter Price of bag filter Price of product Price of filter screen Annual usage of screen filter (80 batch/1ea) Amount of recovered product/batch Saved cost/batch Annual saved cost Treatment cost of designated waste (the 5th year) Annual reduction of generated waste Annual saved cost of waste treatment Annual saved cost due to change the filter Annual reduced cost of bag filter Annual usage cost for the vibration filter screen Annual saved cost Additional saving by improving reaction conditions Vibration filtration system (the 5th year) (aþbþc) Vibration filtration system and improved reactor condition (the 6th year) (aþbþcþd)
additional recovered product, the decrease in sludge treatment cost, and a decrease in spending for the purchase of required filters. In the future, if the sludge waste is utilized as potential fuel resources for obtaining heat or energy and/or as raw or intermediate materials for making another product, the company can get more benefits. 4. Conclusions Waste minimizing techniques, including changes in filtration media and improvements to reaction conditions, were applied to reduce sludge generation and increase product recovery in VAE polymer production facilities. One of the alternative filtration techniques utilized in this study was the use of vibration filters as a replacement for non-woven fabric filters, which had been previously used in the refining facilities. Furthermore, a change in the method of surfactant addition to the reactors, a shortened reactor cleaning cycle, and the filtration cycle were employed as the new processing approach in this study. The application of the waste minimizing techniques in the production facilities greatly reduced total sludge generation (83% reduction in sludge generation per unit production) resulting in an increase in total production and additional product recovery. As a result, the applied waste minimizing techniques led to the reduction in sludge (waste) disposal cost and the purchase cost of filters required for production, and also yielded cost benefits in terms of the sale of the additional recovered product. The company obtained total cost benefits of 617,710 USD/y by applying these engineering techniques, and the payback period of the new proposed design for the refining facilities (33,151 Mt/y) was about 2 months. References Abraham, M., 2000. Pollution prevention: fundamentals and practice. Book review. J. Hazard. Mater. 77 (1e3), 262e265. Azabar, N., Bayram, A., Filibeli, A., Muezzinoglu, A., Sengul, F., Ozer, A., 2004. A review of waste management options in Olive oil production. Crit. Rev. Environ. Sci. Technol. 34, 209e247. Baas, L., 2008. Cleaner production and industrial ecology: a Dire need for 21st Century manufacturing. In: Misra, K.B. (Ed.), Handbook of Performability Engineering. Springer-Verlag, New York, USA, pp. 139e156.
229 Mt/y 42 Roll 3000 USD 4 filter (0.68 cycle)/batch 3.00 USD 1.00 USD/kg 200 USD 29 ea 120 kg/batch 120 USD/batch 275,760a USD/y 230 USD/Mt 275 Mt 63,250b USD/y 126,000 USD/y 28,000 USD/y 5800 USD/y 148,200c USD/y 130,500d USD/y 487,210 USD/y 617,710 USD/y
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Meiss, T.D., 1998. The design of polymer filtration systems: a general overview. Filt. Separ., 421e426. June. Miller, G., Burke, J., McComas, C., Dick, K., 2008. Advancing pollution prevention and cleaner production-USA’s contribution. J. Clean. Prod. 16, 665e672. Morland, C.D., Baur, E., 1997. Polymer filtration: filter medium selection and element design. Filt. Separ., 931e936. November. Peden, J., Miller, G.D., Burke, E., Case, L., Harris, C., Lindsey, T.C., Merrifield, L., Brown, J., Barnes, L.L., Shen, L.-C., 1998. Pollution Prevention in the Primary Metals Industry: a Manual for Pollution Prevention Technical Assistance Providers (accessed on 11.11.11). Petek, J., Glavic, P., 1996. An integral approach to waste minimization in process industries. Resour. Conserv. Recycl. 17, 169e188. Potthast, P., Sandmeyer, O., 1998. Comparison of metal filter media for polymer melt filtration using the standard multipass and polymer tests. Filt. Separ., 427e432. June. Rivas, B.L., Shkinev, Dzherajan, T.G., Danilova, T.V., Pereira, E.D., Maureira, A., 2010. Online multi-stage membrane filtration of synthetic polydispersed water-
soluble polymers with UV visible absorption as a mode for their detection. J. Chil. Chem. Soc. 55, 53e55. Robeson, L.M., Vratsanos, M.S., 2000. Mechanical characterization of vinyl acetate based emulsion polymer blends. Macromol. Symp. 155, 117e138. Robeson, L.M., Berner, R.A., 2001. Mechanical properties of emulsion polymer blends. J. Polym. Science, Part B. Polym. Phy. 39, 1093e1106. USEPA, 2010a. Pollution Prevention (P2) Basic Information Washington, D.C. (accessed on 11.11.11). USEPA, 2010b. 2010e2014 Pollution Prevention (P2) Program Strategic Plan Washington D.C. (accessed on 11.11.11). Wainwright, P.J., Cresswell, D.J.F., 2001. Synthetic aggregates from combustion ashes using an innovative rotary kiln. Waste Manage. 21, 241e246. Wainwright, P.J., Cresswell, D.J.F., van der Sloot, H.A., 2002. The production of synthetic aggregate from a quarry waste using an innovative style rotary kiln. Waste Manage. Res. 20, 279e289. Warren, K.A., Ortolano, L., Rozelle, S., 1999. Pollution prevention incentives and responses in Chinese firms. Environ. Impact Assess. Rev. 19, 521e540.
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Sludge minimization and production improvement by changing filtration and reaction techniques in vinyl acetate-ethylene copolymerization Atilla Mutlu a, Byeong-Kyu Lee a, *, Chi-Hyeon Lee a, Jong-Yong Kim b a b
Department of Civil and Environmental Engineering, University of Ulsan, Ulsan 680-749, Republic of Korea Air Products Korea Inc., Ulsan 680-150, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 August 2011 Received in revised form 14 November 2011 Accepted 14 November 2011 Available online 27 November 2011
The handling of generated sludge waste during polymer production is one of the main environmental concerns of the polymer industry. An alternative filtration technique was applied to determine the efficiency of different types of filtering media for polymer production. A vibration filter media was replaced with a non-woven fabric filter that was previously used in the refining facility. The purpose of this study is to analyze how much the new filtration affects sludge generation and final production. The application of these alternative filtration techniques have resulted in a significant reduction in the amount of non-recyclable sludge by approximately 77%, while the total amount of polymer production has increased by 41% during the six-year study period. The refining facility saved a total of 617,710 USD/y by changing the filtration system, resulting in an increase in product recovery and a decrease in sludge generation, as well as an improvement in reaction conditions. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: VAE Filtration Vibration filters Sludge Waste minimization
1. Introduction For the last few decades, minimizing of waste and emissions, process optimization and use of sustainable energy at the source have been getting a great deal of attention in major industries (Dursun and Sengul, 2006; García et al., 2008; Dovì et al., 2009; Klemes et al., 2010). In particular, Klemes and Huisingh (2008, 2005) have extensively reported roles, ideas, techniques, and progresses of cleaner production, using process optimization, waste minimization, life cycle assessment (LCA) and renewable energy, for sustainable development (Berlin et al., 2007; Baas, 2008; Bonilla et al., 2010; USEPA, 2010a). A cleaner and healthier environment can be attained with performing innovative and sustainable technologies and management approaches (Wainwright and Cresswell, 2001; Eder, 2003; Hossain et al., 2008; Dovì et al., 2009) and pollution prevention strategies (USEPA, 2010b) including effective environmental management (Khan et al., 2002) and engineering designs for minimizing waste practices (Douglas, 1992; Petek and Glavic, 1996). It is an essential approach for optimizing processes and minimizing the production of wastes at the sites of industrial operations (Peden et al., 1998; Abraham, 2000; LaGrega et al., 2001; Klemes et al., 2010). However, many industries usually focus on
* Corresponding author. Tel.: þ82 52 259 2864; fax: þ82 52 259 2629. E-mail address: [email protected] (B.-K. Lee). 0959-6526/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jclepro.2011.11.047
treatment and disposal rather than on source reduction. This situation can be explained by the way in which regulations emphasize overall management practices including treatment, disposal, recycling, and source reduction (Wainwright et al., 2002; Azabar et al., 2004; Miller et al., 2008). Thus, it is highly suggested that industries need to be familiar with the current knowledge related to the application of source reduction methods to their production processes (USEPA, 2010b). Despite the different types and amounts of waste generated by different industrial processes, there are common goals that all major industrial operations should consider when waste reduction plans at sources are needed. The management plan for source reduction should be framed toward achieving a main goal of avoiding waste generation (Dangelico and Pontrandolfo, 2010). This goal can be achieved by instituting a variety of processes, including reducing on-site pollutants, minimizing the use of hazardous materials, and process optimization (Warren et al., 1999; Hossain et al., 2008; García et al., 2008). Polymer filtration is a key factor in maintaining quality, and is considered a necessary and important processing step for most polymer production operations (Morland and Baur, 1997; Potthast and Sandmeyer, 1998; Mancini et al., 2010). Polymer filtration may be an expensive process because of the high cost of labor and maintenance. This statement could be considered true at first glance, and may be valid for systems that were improperly designed, resulting in poor quality polymer production. However, the overall cost, a unit of capital per mass of polymer, is usually
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lower when filtration systems undergo comprehensive cost analysis. A detailed cost analysis for a polymer filtration system may include the following criteria: Cost effective filtration including costs of filtration, equipment, replacement, maintenance, and labor; improving yield (how much polymer can be safely transferred through the filtration system and collected); quality of the final product (degradation rates, acceptable polymer losses during filtration); and reducing waste. The on-stream life of a filter is an important factor for filtration systems, and has a great impact on the overall operation cost (Meiss, 1998). Also, it should be stated that improving operating efficiency and controlling polymer production process have become also considerable parameters in polymer production (Ganzeveld et al., 1999; Lucas et al., 2009; Rivas, 2010). In this study, an alternative filtration technique was applied in order to determine the efficiency of different types of filtering media for polymer production. A vibration filter media was replaced with a non-woven fabric filter that was previously used in a refining facility. The aim of implementing the new filter was to reduce the amount of sludge that accumulated during filtration by increasing the filtration ratio of polymer products. The manufacturing process, including the operational cost of the new filter media and waste handling system, was also evaluated. In this article, the results of testing alternative filtration performances for reducing sludge generated from polymer filtration applications are presented in terms of the economic and environmental benefits. 2. Materials and methods 2.1. Study facility description This study was conducted in the vinyl acetate-ethylene (VAE) copolymer production facility located in Ulsan, Korea. The VAE product contains solids in the range of 40e72%, and the solid phase consists of 2e4% dispersing agent and surfactant, such as hydrolyzed polyvinyl-alcohol (Choi et al., 2004). VAE is widely utilized in various applications such as paint, adhesives, coatings, and as an oil processing material (Garret et al., 2000; Robenson and Vratsanos, 2000; Robeson and Berner, 2001; Choi and Lee, 2010). As illustrated in Fig. 1, the VAE polymerization process begins with the addition of the surfactant solution containing the dispersing agent, catalyst, and the reducing agent (ethylene) into the “reactor” of 11.3 m3. The dispersed VAE begins to form a polymer under the high pressure of ethylene (14.1e61.6 kg cm2) with the catalyst (H2O2) and reducing agent. Polymerization is an exothermic reaction that includes vinyl acetate (VA) and ethylene [see Eq. (1)].
The heat generated during polymerization is recovered by an external heat exchanger. The polymerization process maintained at 80 C is finalized when the amount of vinyl acetate monomer remaining in the reactor is less than 1%. After the reaction, the polymerized product is transferred to the “defoamer? thanks to the pressure of the ethylene (2.069 106 Pa) followed by several consecutive processing stages including filtration, cooling, and pH adjustment. Subsequently, the unreacted ethylene is burnt at the flare stack because of safety issues. However, the heat recovery
Surfactant
Catalysist
Ethylene
Initiating VAM
Reactor
Defoam Tank
Filtering Media
Blender Tank
PostBiocide Treatment
Storage Tank Fig. 1. Stages of the polymerization process in the VAE plant.
after being burnt was not conducted, yet. The last stage of the polymerization process is the transfer of the accumulated VAE product into the “blender tank.” 2.2. Analysis of sludge accumulation and product loss This study analyzed the main problems associated with the polymer production. They were loss of the main product in the sludge that accumulates during the filtration process. Sludge accumulation occurs both in the refining facility and in the reactor during VAE production. The existing filtration system consists of non-woven filters as the primary media, followed by bag filters as the secondary filtering media. The loss of product occurs at this point; some of the product still remains on the primary (nonwoven) filters while the separated solid particles accumulate in the sludge. As the filtering process continues, the amount of accumulated sludge increases, which results in an increase in the amount of VAE product present in the sludge. Because of the ineffective
filtration process, the efficiency of polymer production decreases, while the accumulated sludge containing the final polymer product dramatically increases. 2.3. A new filtration design In order to solve the polymer filtration problems, this study attempted to apply a proper engineering design concept consisting of two individual steps. The first step was replacing the non-woven
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Fig. 2. A body feature and schematic of a vibration filter system.
filtering media with an ultrasonic vibration filtering system in order to ensure a better filtration process. Fig. 2 shows a body feature and schematic of a vibration filter system that was used for this study. High frequency current of 30 kHz by a generator is converted to microwave through a converter. Then the generated microwave vibration is transported to the screen of the vibration filter by resonance action. Viscous products injected into the vibration filter system through the inlet are separated by three-dimensional vibration (with high efficiency) on the twist screen. Products with smaller size than the opening of each deck mesh are passed though the screen, while the larger sizeproducts are vented out through the outlet by centrifugal force. In order to prevent from blocking the mesh opening by products and maximize material separation efficiency in the system operation, the vibration system uses cleaning kits such as slide ring or ball inserted between the mesh and the punched plate (Fig. 2). In particular, the slide ring can minimize frequent cleaning required to remove stagnant materials accumulated on the punched plate with use of ball type cleaning kit (Fig. 3). A vibration filter media (Ildong Industrial Machinery Co., Korea) was installed in the current system. The efficiency of the new filtration system was tested and evaluated its performance results for minimizing generated sludge and increasing final polymer production. A vibration filter specifically designed for a chemical process was compared to the existing filtration system (non-woven filter media). For the testing procedure, the vibration filter media
with a diameter of 1200 mm was selected, and filter screens were used with different sizes in mm (No.: 70, 100, 150, and 200). In the new filtration design (Fig. 4), the filtration rate was set at 0.35 m3 h1 which can be applicable to continuous operation of 4e5 batches (12 Mt/batch). The performance of the new filter system was assessed according to the number of batches and amount of sludge generated during the filtration process. 2.4. Improving the reaction conditions The second design step for engineering approach was related to improving the reaction efficiency using simplified reaction conditions. The polymer production process was also investigated in order to determine ways in which to improve reaction efficiency. The polymer product is an adhesive material, and it may easily remain inside the chamber without any filtration process. This build-up of polymer may not only cause a decrease in reaction efficiency, but it will also increase the amount of sludge, resulting in important production loss. For the purposes of improving reaction conditions, the internal surfaces of the reactor and the heat exchanger were coated to allow the product to easily move through the filtration system without any accumulation inside the reactor. In addition, the standard method of adding the initial surfactant into the reactor was also changed in order to determine if any possible enhancement of reaction conditions could be achieved as a result. The surfactant was partially added into the reactor over the
Fig. 3. Schematic structure of a vibration filter system (left) and a photo of slide ring (right).
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Reactor
Current Non-woven Filtration System
The New Filtration System Using Vibration Filter
Non-woven Filter
Sludge Outlet
Vibration Filter for Testing
to the bagfilter
VAE Product Outlet Pump for Discharging the Final Product
Fig. 4. The new filter design with the existing filtering system.
course of an hour instead of being entirely added immediately at the beginning of the reaction.
second smallest value among the measured flow rates. The smallest amount of sludge, 25 kgpb, was generated when the EP-706 grade VAE was used with a No. 100 size of screen at a flow rate of 1.8 hpb.
3. Results and discussion 3.1. Sludge generation
3.2. Filtration system change
A simple test was carried out to measure the amount of final product lost within the accumulated sludge. In the experiment, a non-woven filter, with dimensions of 50 cm 80 cm, was used as a primary filter and weighed before and after the filtration. The weight of the filter was 9.8 g before filtration was applied in the system. After the filtration process, the weight of the filter was recorded as 262 g, which included a mixture of solid particles, the final product, and the filter itself. This simple test showed that the efficiency of non-woven filter media is considerably low, and a large amount of VAE product was being thrown away as sludge, requiring special treatment as designated waste. This situation may have serious environmental and economic impacts. The existing filtration system not only decreased the amount of final product, but also changed the disposal classification of the generated sludge from general waste to designated waste. In February of 2002, new sets of vibration filter media were installed, and the sludge generation was tested as a function of screen size (mm) and flow rate. For this test, different grades of VAE polymers were utilized. The data obtained from the testing process, including flow rates in hours per batch (hpb) and the amount of generated sludge in kg per batch (kgpb), are presented in Table 1. The highest flow rate of 3.2 hbp occurred using an EP-706 grade of VAE product with a No. 200 size of screen. Generated sludge was measured at 60 kgpb, which was the second highest value throughout the test. The highest amount of sludge, 80 kgpb, was generated when the EP-705R grade VAE and the largest (No. 70) size of screen were used at a flow rate of 1.4 hpb, which was the
Table 2 summarizes the data from the VAE polymer production for six consecutive years. The non-woven filtering system was employed for the first three years (yr 10, yr 20 , and yr 30 ), whereas the vibration filters were installed and tested at the beginning of the fourth year through the sixth year (yr 100, yr 200 , and yr 300 ). During the operation of the non-woven filtration system, the total annual production of the polymer was nearly the same every year. However, sludge generation significantly increased from 300 to 424 Mt/y. For the first three-year (yr 10, yr 20 , and yr 30 ) operation of the non-woven filter system, unit sludge generation and the sludge disposal cost increased every year. The increased amount of them in the third year under the non-woven filtration reached up to by 39.8 and 41.3%, respectively, as compared to those in the first year. Thus, the company paid higher annual costs to dispose of its sludge in spite of similar polymer production. In order to save the
Table 1 Test results after applying the vibration filter. Test number
Screen size (mm)
Grade
Flow rate (h/batch)
Sludge (kg/batch)
1 2 3 4 5 6 7
70 70 100 100 100 200 200
EP-705R EP-705R EP-706K EP-706K EP-706 EP-705 EP-706
1.5 1.4 1.3 1.6 1.8 1.8 3.2
35 80 30 30 25 40 60
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Table 2 Overall production statistics of product and sludge for the years in which different techniques of pollution prevention were applied. Non-woven filter (NWF) Year
yr 10
Application method for waste minimization
Not applied
Type of filtering media Production (Mt) Sludge (Mt) Unit sludge generation (kg waste/Mt product) Sludge disposal cost (as designated waste, USD/y)
NWF 23,500 300 12.8
NWF 23,700 376 15.9
63,000
79,000
a
yr 20
Vibration filter (VF) yr 30
yr 100
yr 200
yr 300
Partial VF filtration
Complete VF filtration
NWF 23,718 424 17.9
NWF þ VF 27,523 391.8 14.2
VF 28,153 229 8.1
Complete VF filtration þ Rxn improvement VFþRxna 33,151 98.5 3.0
89,000
82,000
63,000
39,000
Improvement of Reaction Conditions.
disposal costs of the sludge generated from polymer production, the company began replacing the old non-woven filtration system with the new vibration filtration system from the fourth year (yr 100 ). As a result, the amount of polymer production in the fourth year increased considerably by approximately 3800 Mt/y (16% increase), and the generated sludge associated with production decreased slightly from 424 to 392 Mt/y (7.5% decrease) compared to the third year. Because of the decrease in sludge generation, the unit sludge generation in the fourth year (yr 100 ) decreased by 20.7% as compared to that in the third year (yr 10 ). As a result of the decreased sludge generation, the company was able to save 7.9% of the disposal cost, even with a 16% increase in polymer production. The company continued using the vibration filtration system, and completed the replacement of the old non-woven filtration system in the fifth year (yr 200 ). Even though the production of VAE polymer in the fifth year (yr 200 ) increased even more to 630 Mt/y as compared to that in the fourth year (yr 100 ), the total generation of sludge in the fifth year decreased from 392 to 229 Mt/y, which was a decrease of 41.6%, as compared to that in the fourth year. Therefore, the company was able to reduce the unit sludge generation by 43% in the fifth year, compared to the fourth year. Thus, the resulting disposal cost of generated sludge in the fifth year (yr 200 ) was reduced by 23.2%, compared to that the fourth year (yr 100 ), while the polymer production increased by 2.2%. 3.3. Vibration filter efficiency The non-woven filter media was substituted for the vibration filter media as a primary filtration system, and used with bag filters as a secondary filtration system. Different grades of VAE polymer
products, such as EP-706K and EP-705/706/705R, were used for the filtration process with different size of screens (No. 150/200). Table 3 shows the basic results of generated sludge reduction from the testing procedure. The vibration filters and bag filter screens were compared in terms of their longevity during one cycle. A cycle refers to the active service duration of a filter screen after one use. The vibration filter screens had greater service duration and could be used for 80 batches, while the bag filter screens had lower service duration and could only be used for either 5 or 2 batches using No. 150 or No. 200 size of screens, respectively. The unit generation of waste (97.7 kg of sludge per batch) resulting from the utilization of vibration filters in the fifth year, which had complete replacement by vibration filters, was approximately 54.4% less than the unit value of waste (219 kg of sludge per batch) when using the non-woven filters in the third year. The total reduced amount of generated sludge was then 119.3 kg of waste per batch using vibration filters, with bag filters as a secondary system. This combination of primary (vibration) and secondary (bag) filtering systems also provided a more efficient cycle in terms of the unit generation of waste per batch. There was a need for 6 bag filters to complete one batch for each cycle [1.0 cycle (6 bag filters) per batch)]. However, there was a 68% reduction (0.32 cycles per batch) in the number of cycles required per batch when the combination of vibration filters and bag filters was completely employed. In other words, only two bag filters were needed to complete one production batch due to the improved filtration efficiency conferred by the vibration filters. Although the clogging of raw material at the filtering media is a common problem with vibration filtering applications, a special design for device cleaning, including slider rings or filter balls, may
Table 3 Operation results after changes to the vibration filter. Product grade and filter
Screens (mm)
VAE products
EP-706K EP-705/706/705R other grades
150/200 200
Filter System
Filter screen Bag filter (2nd filtering system)
Bag filter (2nd filtering system) 150 200 150
200 80 batch/1cycle 5 batch/1cycle 150 2 batch/1cycle 200 Sludge Generation
Required Filters per Batch
Non-woven filter application (average amount of designated waste treated in 2001) Vibration filter application-conversion of the production unit (average amount of designated waste treated in 2004) The reduced amount Non-woven filter Vibration filter Saved number of filters
219 kg/batch
99.7 kg/batch
119.3 kg/batch 6 filters (1.00 cycle)/batch 2 filters (0.32 cycle)/batch 4 filters (0.68 cycle)/batch
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Fig. 5. VAE production and sludge variations during the use of two different filter applications.
be utilized to prevent (or reduce) clogging problems and to increase screening efficiency. Recently, slider rings have been considered better substitutions for filter balls among most self-cleaning devices (Brock, 2004). 3.4. Improvement of reaction conditions Even though the total polymer production in the sixth year (yr 300 ) increased by 17.8% compared to that in the fifth year (yr 200 ), the total generation of the sludge associated with the production decreased by 57% (Table 1 and Fig. 5). This reduction in sludge generation was due to a change in the surfactant addition method, reactor cleaning practice, and filter exchange cycle in the sixth year (yr 300 ). The required amount of all the surfactants had been added into the reactor over a period of a few seconds, resulting in lower reactivity. However, beginning in the sixth year, the surfactant was slowly added to the reactor by dropping a small amount of droplets evenly over the course of 1 h. Furthermore, the cleaning cycles of the reactors were shortened in the sixth year. Thus, the reactor was frequently cleaned before the VAE polymer or other solid particles had significantly coated the inside of the reactor’s inner walls. In addition, the exchange cycles of the filters were shortened in the sixth year resulting in a reduced pressure drop in the filtration system. The combined activities of reactivity improvement, frequent reactor cleaning, and filter exchange cycle shortening greatly contributed to reducing the total volume of sludge generation associated with VAE polymer production. Finally, the company was able to increase their production of VAE polymer. Fig. 5 shows variations in the total production of VAE polymer and the total sludge generation associated with production over six consecutive years (yr 10, yr 20 , yr 30 , yr 100, yr 200 , and yr 300 ) using information on the past and current filtration system applications. In the end of the sixth year, total VAE polymer production reached 33,151 Mt/y, which was the highest value for the six-year study period. However, total sludge generation associated with the polymer production was only 98.5 Mt/y, which was the lowest value during the whole study period. This great improvement in the reduction of sludge generation was due to the combination of the complete operation of the vibration filter system among all the filtration systems, as well as a change in the reaction conditions. 3.5. Cost-benefit analysis
filtration benefits, was made based upon the testing results and the investment and installation costs given in Table 4. The annual VAE production in the fifth year was 28,153 Mt/y. Based on the production capacity of a unit batch (12.25 Mt/batch), the total required number of batches was calculated to be 2298 batches per year. Analysis sections (in Table 5) included the fifth-year production data from the production facility, product recovery cost, waste treatment cost, and the reduced cost of changing the filter system. The operation of the vibration filter system can minimize sludge generation resulting in more polymer product recovery, and a reduction in the number of filters that are required. The amount of additionally recovered product after the vibration filter system was applied was approximately 120 kg per batch (in Table 3), and the total annual amount of reduced generated sludge was 275.7 Mt/y. The annual savings resulting from the additional product recovery was calculated to be 275,760 USD/y resulting in the largest savings. Based on the waste treatment cost of 230 USD/Mt, in the fifth year the resulting annual savings on the waste treatment cost accompanied by the complete application of vibration filters instead of non-woven filters was 63,250 USD. The annual cost of non-woven filters, if used, would be 126,000 USD. The annual reduced cost of bag filters (with the use of vibration filters) was 28,000 USD. The annual cost for utilization of vibration filter screens required 5800 USD. Thus, the total annual cost savings obtained from filter use reduction accompanied by the changing of the filtration systems from non-woven filters to vibration filters was 148,200 USD in the fifth year. Thus, the company saved a total of 487,200 USD/y by applying alternative filtration techniques in the fifth year with complete replacement. In addition, in the sixth year, the company greatly minimized its sludge generation and recovered more VAE polymer product by a combination of improving the reaction conditions and adapting the vibration filter system. Given in Table 5, the additional savings obtained through improving reaction conditions in the sixth year was 130,500 USD/y. Finally, by applying new filtration and processing techniques (adapting the vibration filter systems and improving reaction conditions), the VAE polymer production company was able to achieve total benefits of 617,710 USD/y in the sixth year, which includes benefits resulting from the sale of the Table 4 The investment and installation cost of vibration filters. Investment equipment
A set of three vibration filters, including filter media, a holding tank, piping, and valves, were installed, and the total investment costs are presented in Table 4. The overall installation and investment cost was 96,000 USD. An analysis for determining the annual economic efficiency, including a comparison of the old and the new
Vibration filters On/Off valves Control valves Other (shipping, labor, etc.) Total cost
Unit price (USD)
Quantity
Cost (USD)
2000 5000
3 ea 3 ea 3 ea
45,000 6000 15,000 30,000 96,000
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Table 5 Cost-benefit analysis using the vibration filter system. Annual capacity: 28,153 Mt/y Unit batch capacity: 12.25 Mt/batch Total batches requirement: 2298 batch/y Annual Production
Product recovery cost
Reduction of treatment cost of sludge Reduced cost of Filter
Reaction Condition Improvement Annual Total Saved Cost
Amount of generated sludge (the 5th year) Annual usage of drum filter roll (55 batch/roll) Price of drum filter Reduction of 2nd bag filter Price of bag filter Price of product Price of filter screen Annual usage of screen filter (80 batch/1ea) Amount of recovered product/batch Saved cost/batch Annual saved cost Treatment cost of designated waste (the 5th year) Annual reduction of generated waste Annual saved cost of waste treatment Annual saved cost due to change the filter Annual reduced cost of bag filter Annual usage cost for the vibration filter screen Annual saved cost Additional saving by improving reaction conditions Vibration filtration system (the 5th year) (aþbþc) Vibration filtration system and improved reactor condition (the 6th year) (aþbþcþd)
additional recovered product, the decrease in sludge treatment cost, and a decrease in spending for the purchase of required filters. In the future, if the sludge waste is utilized as potential fuel resources for obtaining heat or energy and/or as raw or intermediate materials for making another product, the company can get more benefits. 4. Conclusions Waste minimizing techniques, including changes in filtration media and improvements to reaction conditions, were applied to reduce sludge generation and increase product recovery in VAE polymer production facilities. One of the alternative filtration techniques utilized in this study was the use of vibration filters as a replacement for non-woven fabric filters, which had been previously used in the refining facilities. Furthermore, a change in the method of surfactant addition to the reactors, a shortened reactor cleaning cycle, and the filtration cycle were employed as the new processing approach in this study. The application of the waste minimizing techniques in the production facilities greatly reduced total sludge generation (83% reduction in sludge generation per unit production) resulting in an increase in total production and additional product recovery. As a result, the applied waste minimizing techniques led to the reduction in sludge (waste) disposal cost and the purchase cost of filters required for production, and also yielded cost benefits in terms of the sale of the additional recovered product. The company obtained total cost benefits of 617,710 USD/y by applying these engineering techniques, and the payback period of the new proposed design for the refining facilities (33,151 Mt/y) was about 2 months. References Abraham, M., 2000. Pollution prevention: fundamentals and practice. Book review. J. Hazard. Mater. 77 (1e3), 262e265. Azabar, N., Bayram, A., Filibeli, A., Muezzinoglu, A., Sengul, F., Ozer, A., 2004. A review of waste management options in Olive oil production. Crit. Rev. Environ. Sci. Technol. 34, 209e247. Baas, L., 2008. Cleaner production and industrial ecology: a Dire need for 21st Century manufacturing. In: Misra, K.B. (Ed.), Handbook of Performability Engineering. Springer-Verlag, New York, USA, pp. 139e156.
229 Mt/y 42 Roll 3000 USD 4 filter (0.68 cycle)/batch 3.00 USD 1.00 USD/kg 200 USD 29 ea 120 kg/batch 120 USD/batch 275,760a USD/y 230 USD/Mt 275 Mt 63,250b USD/y 126,000 USD/y 28,000 USD/y 5800 USD/y 148,200c USD/y 130,500d USD/y 487,210 USD/y 617,710 USD/y
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