THE ART OF RETROFITTING UF/MF SYSTEMS: A COMPARISON OF STRATEGIES, COSTS, AND RESULTS. Abstract

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1 THE ART OF RETROFITTING UF/MF SYSTEMS: A COMPARISON OF STRATEGIES, COSTS, AND RESULTS Daniel J. Dye, PhD, PE, WesTech Engineering, Inc., 3665 S. West Temple Salt Lake City, Utah ddye@westech-inc.com, Ph: Jason D. Nay, WesTech Engineering, Inc., Salt Lake City, Utah Libbie Linton, PE, WesTech Engineering, Inc., Salt Lake City, Utah Abstract As UF/MF membrane modules reach the end of their useful life, end-users have more options than ever before to either purchase direct module replacements or upgrade the system. Recent trends and advancements in membrane materials, configuration, and process design have improved the performance of low pressure membrane systems. With more options for high quality membrane modules available, a systematic process is required in selecting which membrane is the best fit for a specific retrofit application. Considerations such as available footprint, existing physical skid design, process differences, water quality, and flow paths are required while taking into account existing plant controls, ancillary equipment, and installation time. Membrane system retrofits are carried out to address expansion capacity in the existing system framework, technical obsolescence of original equipment, high pricing of proprietary module replacements, or unsatisfactory membrane performance. Although retrofit costs can be significant, ranging from 20-50% of original equipment capital cost, there are often life cycle cost benefits associated with achieving higher production rates and/or decreasing operations costs through reduced fiber breakage and fouling. A comparison of multiple case studies is provided, highlighting projects in Oregon, Alabama, and Texas with system flow rates of 45 GPM, 3 MGD, and 10 MGD. These projects vary in membrane type and complexity of the retrofit process, ranging from reuse of existing equipment with minor plumbing and process changes to complete rack replacement and controls/ancillary equipment upgrades. Factors affecting approach are discussed, such as system layout, footprint constraints, cost, and overall project goals. 1

2 Introduction Ultrafiltration and Microfiltration (UF/MF) membrane fibers and modules have improved substantially over the last years, and several new brands have become available. Each manufacturer touts unique membrane characteristics, hydraulic properties, fiber durability, warranty support, resistance to fouling, and operational flexibility. Despite the rise in quality, the abundance of competitive brands on the market has driven costs down. These factors have caused several water plant owners to consider retrofitting their plant when it comes time to replace part or all of their old modules. Several factors may contribute to the decision to retrofit, including: Technical obsolescence of existing modules Expensive replacement modules and service Flow expansion within the plant, or even within an existing footprint Membrane performance: o Production limitations o Fiber breakages o Excessive chemical cleaning In order to proceed with a retrofit, the economics of course must make sense, and several factors must be taken into consideration. The costs to perform the retrofit (equipment, construction labor, engineering, system downtime) need to be closely scrutinized and compared to the costs of maintaining the existing system. Maintaining an existing system could mean more frequent module replacements with outdated membranes, high operating and maintenance costs, and more frequent downtime for maintenance or replacement. Table 1 includes some very simple figures which an owner used to assist with the decision to retrofit their plant. At this particular plant, they were replacing their original modules every 3-4 years, and expect to only have to replace the new brand every 10 years. This table simply shows the capital costs of the modules and the equipment retrofit, but doesn t include the pinning labor, cleaning chemical costs, or plant downtime associated with the original plant, nor does it include any contractor or engineering fees associated with the retrofit. All of these factors must be taken into consideration, along with Capital costs. These economic analyses are performed during the preliminary design assessment, and several different brands may be evaluated during this step. 2

3 Retrofit Strategies Membrane retrofits fall into three main categories: 1. Direct module replacement 2. Integrating new modules into existing framework, with minimal plumbing and controls changes 3. Major equipment replacement, including membrane module racks and supporting equipment, as needed Direct module replacements are typically the fastest way to retrofit a system, but aren t always in the owner s best-interest. Options 2 and 3 above require a preliminary design assessment performed by an equipment manufacturer and an engineer to determine the feasibility and economics of the retrofit. Assuming the economics work, a comprehensive design process is followed. The following sections describe some key aspects of each of these project phases. Table 1 Example Capital Cost Schedule: Retaining Original Brand vs. Retrofitting YEAR ORIGINAL BRAND RETROFIT OPTION 0 Replace half of $173,560 Change plant over $347,991 existing modules to new brand Replace full set of $345, existing modules Replace half of $172, existing modules Replace full set of $110,000 new modules Total $690,240 $457,991 3

4 Preliminary Assessment & Design The early stages of design typically consist of the following activities: Listing module options, and each brand s impact on the ability to reuse existing components Determining the available footprint and height for the module skid, transition skid (if required), and any other process equipment which may change Assessing the costs of the proposed options, and comparing it to the costs of retaining the existing brand During the preliminary design, the first step is typically creating a short-list of possible module candidates. The list may be based on the owner, Engineer, or equipment manufacturer s preferences based on experience and relationships with module manufacturers. The list could also be based on successful installations or pilot studies in the area which have demonstrated the effectiveness of that particular brand. Table 2 (previously reported in part by [Vickers et al. (2016)]) shows an abbreviated list of several low-pressure hollow-fiber membrane module brands typically seen in municipal drinking water and industrial water treatment plants and some of their key physical and operational features. Most of the brands are converging on a common hydraulic flow path and shape, but there are still several physical operational differences which make each module unique. Table 2 Survey of a variety of low-pressure hollow-fiber MF/UF modules The module selection process includes collecting design projections, warranty terms, and costs from each brand of interest. The module manufacturer s application engineers will assist with the preliminary design, as far as determining suggested design flux and the resulting number of modules installed. Once the number of modules is determined, the equipment manufacturer typically takes the lead on sketching out the full process, determining how to retrofit the module skids, and determining which process equipment can be reused and which must be replaced. 4

5 The hydraulic process for the new modules may be substantially different than the previous modules, which would impact the design of the retrofit skids. In some situations, the feed, filtrate, and backwash waste headers are in such drastically different locations (e.g. Figure 1), that a transition skid is required to redirect the feed, filtrate, or backwash supply piping from top to bottom or to split any of that piping into multiple branches. This transition skid needs to be as compact as possible - since it adds to the overall length of the skid - and the additional fabrication and assembly costs must be integrated into the retrofit pricing. Once the module options are identified, the equipment changes are listed out, and the costs are gathered, the owner can review the total capital costs of the retrofit and compare against maintaining their existing plant. In addition to capital costs, the owner must consider any engineer fees that may be incurred, any costs associated with securing approval from the state, construction costs, and piloting costs if required. Even with all of these factors considered, the economics and benefits of retrofitting the plant frequently work out in the owner s favor. This is also frequently the point where a pilot study would be performed, especially if the performance of different module options needs to be evaluated. The goals of the pilot study would be to confirm the flux rate and other operational set-points for the different module brands, confirm projections on cleaning cycle frequency and chemical consumption, and secure approval from the State if required. If the water is challenging to process, the results of these pilot study can be very important in selecting the proper membrane module. Figure 1 Three different module brands, with drastically different locations for feed, filtrate, backwash supply, backwash waste, drain, and air scour ports (where applicable) 5

6 Detailed Design Process Once the preliminary design phase has been concluded and the Owner has secured funding to retrofit the plant, the detailed design phase begins. This phase involves a coordinated effort between the Engineer and the equipment manufacturer, as every detail of the process is evaluated and redesigned as necessary. The following pieces of equipment must be scrutinized closely, to determine if they are sized appropriately to support the new modules: Module skids (typically replaced, but may just be modified) Feed pump Feed strainer Backwash pump Air compressor or blower Chemical pumps Clean-in-place equipment (heater, CIP pump, supply and return connections, instrumentation) Skid and plant instrumentation PLC and HMI panels, skid control panels, and other SCADA equipment Each component is carefully evaluated and modified/replaced as necessary. Process differences between the different brands may not only mean upsizing the equipment, but also upsizing the interconnecting piping and possibly the power feed to the equipment. Also, the retrofit is an opportune time for the owner to replace outdated or poorly-performing equipment, and make other system or process upgrades in their plant. Most retrofits will also involve an overhaul of the PLC and HMI programs to account for the different process steps for the new brand of modules. Even though the module brands are converging on a similar shape and similar fiber properties, the operational sequences that each brand uses can be fairly different and requires a competent programmer to modify or replace the program to accommodate the new processes. During this phase, the engineer, owner, and equipment manufacturer must communicate very well to ensure a successful retrofit. Minimizing system downtime is critical on these projects, so all details of the retrofit must be carefully thought out and detailed, to minimize errors and surprises. When all factors have been accounted for properly and all equipment and materials are available for the retrofit, the actual retrofit can transpire rapidly. Experience has shown that the retrofit system can be back online within hours of the shutdown. 6

7 Case Study 1: South Coast WTP, Oregon The South Coast WTP, located in southern Oregon, has a compact, packaged, 45-GPM ultrafiltration skid. The UF system is fed from surface water filtered by a granular media filter and supplies drinking water to a small community of homes near the coast. While the plant has produced quality drinking water for the past eight years, the owners were spending too much time pinning fibers, performing aggressive CIPs to clean the membranes in order to maintain filtrate production rates, and were replacing modules too often. These conditions led the owner to search for alternative membranes, and looking for support in retrofitting their plant. This plant was in a small building, with minimal footprint and little overhead space available. The height limitation ruled out several UF module options, as it would have required extensive modifications to the building. After evaluating compact options, the equipment manufacturer and owner decided on the Inge dizzer XL module due to its shorter profile, good performance, and low probability of broken fibers, among other features. The surface area of this module and the design flux required an additional module to meet the system filtrate flow rate. This change required a much higher backwash flow-rate than the existing system, but fortunately it was determined that simply increasing the size of the backwash waste piping would be sufficient to reduce backpressure and allow the pump to operate within the system curve. Because the Inge module doesn t require air-scour and uses a caustic soda and chlorine for cleaning cycles, the existing compressed air system and chemical pumps were sized appropriately and were able to be reused. Existing instrumentation and valves were also reused and relocated as needed. Three valves were added to accommodate the differences in filtration, backwash, and CIP processes between the original and the retrofit modules. A list of reused and retrofit components is shown intable 2. The retrofit was accomplished simply by moving the modules off skid and rebuilding the feed, filtrate, and backwash waste piping between the original skid piping and the new modules, as shown in Figure 1. Valves were added in this piping to accommodate the new processes, but the bulk of the skids valves were reused. The physical rebuild only took one day, and the system was reprogrammed and producing water within 36 hours of the shutdown. The plant has operated well with zero fiber breaks in the first 24 months of operation since the retrofit, and the owners spend significantly less time performing maintenance and cleaning at the plant. 7

8 Table 3 Reused and retrofit components at the South Coast WTP Component Reused Retrofit Packaged Skid Yes, with minor modifications Added process valves and reconfigured the piping Feed Pump Yes - Feed Strainer Yes - Backwash Pump Yes Met head and flow requirements, after reducing back-pressure off-skid PLC & HMI Yes Updated the PLC and HMI programs to control the new modules Skid Local Control Panel Yes Added solenoid valves for the new process valves Chemical Feed Pumps Yes - Compressed air system Yes - Clean-In-Place System Yes Added feed return line and control valve to skid Figure 2 The original system (left) was retrofit by adding three valves, re-arranging the piping and location of pressure transmitters, and modifying the controls system. The retrofit system (right), occupies slightly more floor space, but fit within the available footprint and headspace. 8

9 Case Study 2: High Point WTP, Alabama In 2014, the Northeast Alabama Water District needed to expand the High Point WTP capacity from 2 MGD to 3 MGD, but did not want to add another skid with the same type of modules because of fiber pinning and performance issues. The owner, engineer, and equipment provider all agreed that switching to the Toray HFU module at this plant would be preferable, because of a successful retrofit with the Toray module at the DeKalb-Jackson WTP [Nay et al. (2015)] a nearby water plant with the same feed water. During the preliminary design phase, the equipment manufacturer worked closely with Toray to size the equipment, and worked closely with the Engineer to assess all plant components. The list of reused or retrofit components is shown in Table 4. The third skid was designed to look identical to the first two skids (Figure 3), even though that wasn t the most efficient design for a new plant. This was done so that all three skids matched and operated the same. Table 4 List of major components that were either reused or replaced at the High Point WTP Component Reused Retrofit UF Control Skid Yes, with modifications, including adding transition skid piping between the control and module skids Added process valves and piping connections for gravitydrain and CIP return lines UF Module Skids No Retrofit with new frames, HDPE headers, and PVC piping laterals to connect to the new modules Feed Pump Yes - Feed Strainer Yes - Backwash Pump Yes Oversized, but VFD could accommodate Master PLC Panel & HMI Yes Updated the PLC and HMI programs to control the new modules Skid Local Control Panel Yes Added solenoid valves for the new process valves Chemical Feed Pumps HCL Upsized citric acid and sodium hypochlorite Compressed air system Yes Replaced flow meter and regulators to accommodate higher rate air-scour Clean-In-Place System No This retrofit was also done in a short time period. The first skid was retrofit and filtering water within 24 hours, and the second was filtering water approximately 12 hours later. The full commissioning took a few more days, and the plant has been operating efficiently ever since. 9

10 Original Skid Retrofit Skid Figure 3 The North East WTP (Alabama) retrofit included a transition piping between the control skid and the module rack. This transition piping was required because of the inverse flow paths of the original (top to bottom) and the new (bottom to top) modules. 10

11 Case Study 3: Brazos WTP, Texas The Brazos Regional Public Utility Agency (BRPUA) is currently in the process of retrofitting their 10 MGD Surface Water and Treatment System (SWATS) facility. This is their second retrofit, and they are interested in creating expansion capacity within their existing system footprint by using higher-flux modules. By switching to the Toray HFU module, they were able to operate at high flux and reduce the number of modules installed per skid, which gives them expansion capacity simply by adding more modules at a later date. The retrofit skid, shown in Figure 4, is capable of producing 50% more flow by simply increasing the number of installed UF modules. In this project, the consulting engineer took the lead on the preliminary phase, worked closely with the owner, and consulted with an equipment manufacturer to assess needs and produce a detailed specification for the retrofit. In addition to adding expansion capacity to their plant, the owner took advantage of this opportunity to upgrade their controls system, simplify chemical cleaning procedures, and require modules with reduced fiber breakage rates and better warranty support. The equipment procurement stage took all of these factors into consideration, and included the requirement for the equipment manufacturer to perform a pilot study, ensuring full compliance with the Texas Commission on Environmental Quality requirements. Table 5 shows a summary of the reused and replaced components in this facility. Fabrication of the equipment is underway at the writing of this paper, and results may be published at a future date. Figure 4 This skid at the Brazos SWATS was retrofit by modifying the frame, headers, and headerto-module laterals, but the majority of the system hardware was retained and unchanged. This skid is capable of producing 2 MGD as shown, and will produce 3 MGD by simply adding modules. 11

12 Table 5 List of major components that were either reused or retrofit at the BRPUA SWATS Component Reused Retrofit UF Module Skids Yes Retrofit with new HDPE and SS headers, structural steel supports, air scour piping, and PVC piping laterals to connect to the new modules Feed Pump Yes - Feed Strainer Yes - Backwash Pump Yes - Master PLC Panel & HMI Yes Updated the PLC and HMI programs to control the new modules Skid Local Control Panel Yes Added solenoid valves for the new process valves Chemical Feed Pumps Yes; eliminated sodium - hydroxide pumps Compressed air system Yes Added air scour delivery piping and valves to each skid Clean-In-Place System No Conclusion As UF/MF membrane modules reach the end of their useful life, end-users have more options available to them to either purchase direct module replacements or upgrade the system to accommodate alternative membrane styles. Recent trends and advancements in membrane materials, configuration, and process design have improved the operational range and performance flexibility of low pressure membrane systems. Additionally, there are more high quality membrane modules available in the market than ever before. The concept of open-platform systems is quickly gaining popularity in the industry. The concept skids and systems which are designed to easily accommodate a variety of brands - significantly reduce the retrofit efforts described above. The open-platform concept frees the owner from module technical obsolescence, and improves their ability to secure fair and competitive pricing and service when it is time to replace modules or retrofit. References Nay J, Linton L, and Housley L. Side-by-side UF membrane comparison and retrofit of a 3 MGD system. AWWA AMTA Membrane Technology Conference, March 2-5, 2015, Orlando, FL Vickers J, Zylstra D, and Owens E. West Basin s Universal Membrane System Pressurized PVDF Performance Pilot Program Particulars. AWWA AMTA Membrane Technology Conference, February 1-4, 2016, San Antonio, TX 12