RETROFIT AND EXPANSION OF A 10 MGD UF SYSTEM IN GRANBURY, TEXAS. Abstract

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1 RETROFIT AND EXPANSION OF A 10 MGD UF SYSTEM IN GRANBURY, TEXAS Jason D. Nay, WesTech Engineering, Inc., 3665 S West Temple, Salt Lake City, UT jnay@westech-inc.com, Phone: Libbie Linton, PE, WesTech Engineering, Salt Lake City, UT; Alain Richard, Brazos Regional Public Utility Agency, Granbury, TX Joshua Berryhill, PE, Enprotec / Hibbs & Todd, Abilene, TX Dan Dye, PhD, PE, WesTech Engineering, Inc., Salt Lake City, Utah Abstract The Surface Water and Treatment System facility consists of lime-softened clarification, dual media filtration, ultrafiltration membrane filtration, and reverse osmosis (RO) membrane treatment. This system treats water from Lake Granbury in Granbury, Texas, which has elevated levels of chlorides ranging from 50 to 1,400 mg/l. As designed, the system was unable to meet an increase in production demand. Accordingly, efforts were undertaken by the Brazos Regional Public Utility Agency and Enprotec / Hibbs & Todd to evaluate options for retrofit and expansion of the existing system. The SWATS facility UF system is comprised of 5 treatment trains and was originally designed to produce 8 MGD with Hydranautics HydraCAP UF membranes in As a result of excessive fiber breakage and performance challenges, the facility elected to retrofit the system in 2008 to accommodate Norit X-Flow membranes. With the 2008 retrofit, the system was supposed to produce 10.0 MGD. As a result of this retrofit effort in 2008, the 5 treatment trains were fully populated with 80 modules per train, thereby eliminating the possibility of future expansion. The purpose of this project was to expand the SWATS facility to meet increased production demand of 10 MGD, with consideration of potential further future expansion. With this expansion, the intent was to engineer a custom design to allow for reuse of existing support systems to the fullest extent possible, including stainless steel frames, piping, chemical cleaning systems, feed pumps, prestrainers, compressors, valves, and instrumentation. This paper will discuss preliminary design considerations for optimizing reuse of existing equipment and consideration of flow pattern, operations, and physical differences between various modules. As part of this work, pilot testing was performed to both meet regulatory approval requirements for an alternative membrane module and to evaluate UF performance with the aim to eliminate lime softening. Lastly, the execution of the retrofit will be discussed, including final system design, unexpected challenges, coordination of the retrofit process, operational downtime and staging, controls integration, and other site modifications. 1

2 Introduction The Brazos Regional Public Agency (BRPUA) operates a regional water treatment plant in Granbury, TX. The Surface Water Treatment System (SWATS) was originally built in 1988 and consisted of clarification, dual media filtration, and electrodialysis reversal (EDR). In 2001, the plant expanded to include ultrafiltration and reverse osmosis (RO) to produce better effluent. The desalination process was added to address the fluctuating levels in Lake Granbury of 50 to 1,400 mg/l [Berryhill. 2016]. Although the dual media filters are still available for use, the typical treatment process at the plant is currently coagulant addition (Ferric Chloride), lime-softened clarification, recarbonation, UF, and RO as shown in Figure 1. Figure 1. SWATS typical process flow. Four ultrafiltration units were installed in 2001 with HydraCAP membranes along with an RO system. In 2008, the plant expanded by adding a fifth unit and retrofitted the plant to use Norit X- Flow membranes. Approximately one year later, the RO system was also expanded. As the X-Flow membranes approached the end of the useful life, demonstrated by fiber breakage, BRPUA recognized an opportunity to retrofit the existing UF system. Consideration for future expansion and anticipation of the need for additional RO capacity to meet production demands drove BRPUA towards a retrofit. 2

3 The Decision to Retrofit BRPUA along with their engineer, Enprotec / Hibbs & Todd Inc. (eht), performed an initial review to establish whether it was better to replace the existing system or retrofit the existing UF units. During this review (previously presented in part by [Berryhill. 2016]) the following questions were addressed: Question: Should the UF modules be replaced 1:1 with same type of membranes? o Response: No. This would provide limited capacity to meet current and future facility water production demands. Question: Should the UF system be completely replaced with a new one? o Response: No. The existing units, instrumentation, and support systems still have remaining life, and full replacement would be overkill. Question: Should the existing UF units be retrofitted with new membrane modules? o Response: Yes. Using a module with higher surface area will allow the plant to meet current capacity with less modules, but would also allow for additional capacity of the UF system in the future by installing more modules while maintaining the same footprint. In this case scenario, the responses were in favor of retrofitting the existing UF units with new membranes; this may not be the result in other applications. An economical approach should be taken to evaluate capital and operational cost as well as an evaluation of other factors such as technological advancements, expansion requirements, and existing membrane performance to decide which approach is the best fit for replacing UF membranes. Criteria for Retrofit If a decision is made to proceed with a retrofit design, the first decision that needs to be made is which membrane module to select. The module selection criteria may include design projections, replacement costs, and available warranties. After which, there are many items that must be assessed and a criteria must be established to demonstrate what needs to be reused, modified, added, or replaced. Criteria may be based on plant preference, economical constraints, and/or future needs. Items to be reviewed may include, but are not limited to: Module rack frames Piping Electrical panels and control system Instrumentation Valves 3

4 Ancillary equipment such as: o Compressors o Clean-in-place units o Chemical dosing pumps In the case of the SWATS UF retrofit, the items in Table 1 were evaluated based on the criteria described above. Decisions were made by the customer, engineer, and equipment manufacturer as to which items could be reused and others that needed to be retrofit or replaced. Table 1. List of major components evaluated for reuse or retrofit at the SWATS facility. Component Reused Retrofit Module Racks Yes, with modifications Elevate overhead piping. New structural steel module supports, air scour piping, PVC laterals to connect modules to main headers. Main Headers Yes, with one replacement New HDPE backwash waste header. Elevate filtrate header to accommodate site glasses and isolation valves. Feed Pumps Yes - Feed Strainers Yes - Backwash Pumps Yes - Master Control Panel Yes New, upgraded PLC and HMI. New controls program. Skid Local Control Panel Yes Add solenoid valves for the new process valves. Replace local PLC with remote I/O communications card. Chemical Feed Pumps Yes; eliminated sodium hydroxide pumps Replaced sodium hypochlorite pumps with the project Compressed air system Yes Added air scour delivery piping and valves to each skid Clean-In-Place System Yes - Once the preliminary engineering was completed, the SWATS retrofit followed a four-step process as described below. 4

5 The Retrofit Process Step 1 Pilot The purpose of the pilot was to confirm that the selected UF module, Toray HFU-2020N, would be able to operate at the design conditions for the full scale plant and to meet state piloting requirements. The pilot study was completed in two phases and included an RO pilot to imitate the full-scale membrane system and the effects of the UF on the RO performance based on variations of the membrane pretreatment. Phase 1 was designed to specifically evaluate the performance of the UF membrane and its ability to operate at the selected design flux and other operational parameters. Phase 2 was used to test different pre-treatment schemes, including different coagulants, to optimize both UF and RO performance. During Phase 1 of the study, the pilot operated at a normalized flux of 60.3 gfd. Table 2 provides additional summarized results of the UF pilot. Table 2. Summary of UF pilot results during phase 1 of piloting. Parameter Membrane Module Toray HFU-2020N Flux at Design Temperature (20 C) 60.3 gfd Production Cycle Time 34 minutes Backwash Flow Rate 1.1 times time production flow rate Average TMP 11.0 psi Average Recovery 97% Maintenance Clean Frequency 2 times per week MC chemical solution Sodium Hypochlorite 250 ppm Fiber Breakage No breakage observed during piloting With results of the pilot confirming the projections, the next step in the retrofit process was to complete the detailed engineering and retrofit design. Step 2 Engineering and Design To start this step in the retrofit process, the first task to complete was to reverse engineer the filtration units (Figure 2) to generate a 3D CAD model. To develop the model, available drawings were used, but the majority of the dimensions came from field measurement and verification. A key consideration for all retrofits is that the drawings may not, and often do not, represent the actual installed equipment. 5

6 Figure 2. Photo of the existing UF racks the Brazos SWATS facility. Design began once the model was developed. For this project, design included new module supports, backwash waste header, and lateral connections to allow the new modules to fit into the existing module rack. Structural calculations were completed on the new module supports to verify the modified design would support the additional weight. Additionally, new control valves and air scour piping had to be integrated as part of the air system. Figure 3 represents the 3D CAD model developed from the retrofitted module rack. 6

7 Figure 3. This 3D CAD model is a representation of the UF rack after the retrofit is completed at the Brazos SWATS facility. Note that unit is capable of producing 2 MGD as shown, but has the ability to produce 3 MGD simply by adding modules. Electrical engineering and controls development are a part of this step. Some of the decisions made for this particular retrofit were to reuse the existing electrical panels, upgrade the master PLC, convert local PLCs to remote I/O adapters in order to communicate with the master PLC, and add an I/O card to accommodate the addition of position feedback from each of the process control valves. Programming development for this type of application in itself is a two-step process. Step one includes reverse engineering of the existing controls program so the new controls program will communicate with plant SCADA systems and control all of the ancillary equipment and instrumentation. Step 2 is developing the new control logic and HMI interfaces to operate and control the new membranes. Typically, the controls are developed around a controls narrative that clearly defines each of the process sequences, operator inputs, warnings, and alarms. This entire programming process needs to be scrutinized and tested thoroughly to mitigate any down time issues during the execution of the retrofit. Step 3 Fabrication, Planning, and Staging Once the engineering and design is complete and approved by the all the project s stakeholders, the next steps are to fabricate the required retrofit elements and stage the materials/tools needed to execute the retrofit process. There is typically a lot of planning and coordination that is required. Communication during this step is critical. It is requisite that the following items should be discussed: 7

8 Plant downtime limitations Retrofit schedule and contingency plans Contractors understanding of modification and schedule requirements Disinfection requirements and time constraints Controls integration and SCADA impacts Coordination with other contractors and vendors Once all preparations are complete, the next step in the retrofit process is the execution and making the project a success. Step 4 Execution If steps 1-3 are completed thoroughly, the execution step should go smoothly as risk and uncertainty were mitigated up front and contingency plans are set in place. During this step, the schedule and plan developed should be followed so all parties involved remain on the same page through the actual retrofit. The plan may include: mechanical and electrical contract work, membranes installation, controls integration, and start up and commissioning. Conclusion There are many factors that go into deciding whether or not a retrofit is the best option for a plant where the membranes are nearing the end of their useful life. Other potential options for retrofitting membranes may include direct membrane module replacement or upgrading to an entirely new system. For the BRPUA SWATS facility, the best choice was to retrofit due to the fact that the existing filtration units and support equipment have several years of serviceable life remaining. The retrofit will allow the existing UF system designed for 10 MGD to produce up to 15 MGD, by simply reusing the existing module racks and adding modules to help meet future demand on their distribution system. The retrofit process at SWATS is being executed by this four-step process: 1) pilot, 2) engineering and design, fabrication, planning, and staging, and 4) execution. The pilot testing, engineering, and design have been completed on the project thus far. The project is currently in stage three, with stage four anticipated to be completed in March of References Berryhill, J. Don t Panic, The SWATS Guide to a Membrane Filtration System Open Platform Retrofit. Texas Water,