Process Description
Sea Water Pumps
Screened sea water from the sump at battery limits is pumped to the Dissolved Air Flotation Unit (DAF) and the Cooling Water System by Sea Water Pumps P-101A/B. These are electric motor-driven centrifugal pumps. Normally only one pump is in operation. The bearings are cooled with circulating cooling water to preserve their mechanical integrity. Cooling water for the pump bearings is supplied from the A and B cooling water headers and returned back to the cooling water system.
The design flow of sea water to the unit is 503 GPM at a temperature of 56 DEG F. The salinity of sea water is 3.5 weight %. Sea water flow to the DAF is normally 245 GPM and flow to the Cooling Water System is normally 206 GPM. The sea water distribution header normally operates at 40.0 PSIG.
Cooling Sea Water Filters
Sea water from P-101A/B and destined for the Cooling Water System is first filtered in Cooling Sea Water Filters F-101A/B. These are cartridge filters designed to remove any suspended solids from the feed water. The sea water supply to the unit has had debris and large particles removed prior to entering the unit. However, suspended solids remaining in the sea water can easily foul and plug the heat exchangers in the Cooling Water System heat exchangers. Normally, only the “A” filter is in operation.
The turbidity (cloudiness) of the sea water due to suspended solids is indicated by its NTU analysis (Nephelometric Turbidity Unit). The sea water feed normally has a 15.0 NTU. F-101A/B normally reduce the turbidity to 3.5 which is sufficiently low for use in the Cooling System’s heat exchangers.
Flocculators
Prior to entering the Flocculator compartments of the Dissolved Air Flotation Unit, sulfuric acid from Sulfuric Acid Pump P-111 is injected into the feed sea water from Sea Water Feed Pumps P-101A/B to decrease its pH from 7.90 to 6.51. This represents the optimum pH of the sea water to maximize the coalescence efficiency of the flocculant to produce sludge in the DAF Basin. A flocculant is a chemical that promotes coalescence of the suspended solids into larger particles so they can be more easily separated from the sea water. The flocculant used in the DAF process is ferric chloride (FeCl3). It is injected into the feed sea water by Ferric Chloride Pump P-112. The flow rates of the sulfuric acid and the ferric chloride are very small compared to the sea water flow rate. These chemicals are intimately mixed with sea water in In-line Chemical Mixer MX-101 prior to entering the Flocculators.
The Flocculators R-101A/B are chambers within the DAF Basin T-101. The DAF Basin is a large box that provides sufficient residence time for the coalescence of the suspended solid particles. Sea water first flows down along and under the feed baffle of Flocculator R-101A. Agitator AG-113A circulates the sea water and flocculatant mixture within the chamber of R-101A to ensure intimate contacting of the flocculant and the suspended solids. This mixture then passes into the chamber of Flocculator R-101B in the same way. This chamber is agitated by AG-113B. The flocculated sea water from R-101B then flows over its exit baffle and down into the Dissolved Air Flotation Basin’s (T-101) main chamber.
Dissolved Air Flotation Basin
Flocculated sea water from Flocculator R-101B flows into the main chamber of the Dissolved Air Flow Basin T-101 through the channel formed by the baffles separating the two compartments. As the sea water enters, it mixes with an upward flow of recirculated sea water containing saturated air which is distributed along the bottom of the DAF Basin. An angled baffle along the width of the basin forces the sea water to rise up to the top of the basin. As the hydrostatic pressure decreases toward the top, the air is increasingly released and forms small bubbles that rise to the top of the basin. Agglomerated solid particles (sludge) from flocculation have a somewhat lower bulk density than water so they will float up to the top of the basin, assisted by the small, rising air bubbles. The sludge will accumulate and float on top of the water in the basin and the sea water will flow over the angled baffle.
The floating sludge on the top of the basin will then tend to move toward and then over a baffle at the far end of the main DAF Basin chamber and into the Sludge Trough. The movement of the floating sludge toward the trough is greatly assisted by a motor-driven Sludge Scraper outfitted at the top of the main chamber of the DAF Basin (not shown on Schematic #6 for clarity of the instrumentation). The scraper is a slowly rotating belt with rubber scraping blades that skim the sludge along toward the Sludge Trough. Sludge is intermittently removed from the Sludge Trough by DAF Sludge Pumps P-103A/B which are electric motor-driven slurry pumps.
Clarified sea water then flows down and through a set of perforated lateral draw-off pipes near the bottom of the main chamber under the Sludge Trough. Clarified sea water then flows up and over a baffle and into a collection well at the end of the basin assembly. Clarified water is drawn from here by the UF Feed Pumps, P-105A/B to be further filtered in the UF Section.
A portion of the clarified sea water passing through the perforated pipes is circulated back to the main chamber of the DAF Basin by DAF Recycle Pumps P-102A/B. These are electric motor-driven centrifugal pumps. Normally only one pump is in operation. The normal flow of recirculated sea water is 100 GPM. These are electric motor centrifugal pumps. Normally only one pump is in operation. The recirculated sea water then flows into the top of the DAF Air Saturator Tank V-101.
Dissolved Air Flotation Basin
Flocculated sea water from Flocculator R-101B flows into the main chamber of the Dissolved Air Flow Basin T-101 through the channel formed by baffles separating the two compartments. As sea water enters, it mixes with an upward flow of recirculated sea water that contains saturated air which is distributed along the bottom of the DAF Basin. An angled baffle along the width of the basin forces the sea water to rise up to the top of the basin. As the hydrostatic pressure decreases toward the top, air is increasingly released and forms small bubbles that rise to the top of the basin. Agglomerated solid particles (sludge) from flocculation have a somewhat lower bulk density than water so they will float up to the top of the basin, assisted by the small, rising air bubbles. The sludge accumulates and floats on top of the water in the basin and the sea water flows over the angled baffle.
The floating sludge on the top of the basin will move toward and then over a baffle at the far end of the main DAF Basin chamber and into the Sludge Trough. The movement of the floating sludge toward the trough is greatly assisted by a motor driven Sludge Scraper outfitted at the top of the main chamber of the DAF Basin (Not shown on Schematic #6 for clarity of the instrumentation). The scraper is a slow, rotating belt with rubber scraping blades that skim the sludge along toward the Sludge Trough. Sludge is intermittently removed from the Sludge Trough by DAF Sludge Pumps P-103A/B which are electric motor-driven slurry pumps.
Clarified sea water then flows down and through a set of perforated lateral draw-off pipes near the bottom of the main chamber under the Sludge Trough. Clarified sea water then flows up and over a baffle and into a collection well at the end of the basin assembly. Clarified water is drawn from here by the UF Feed Pumps, P-105A/B to be further filtered in the UF Section. A portion of the clarified sea water passing through the perforated pipes is circulated back to the main chamber of the DAF Basin by DAF Recycle Pumps P-102A/B. These are electric motor-driven centrifugal pumps. Normally only one pump is in operation. The normal flow of recirculated sea water is 100 GPM. These are electric motor centrifugal pumps. Normally only one pump is in operation. The recirculated sea water then flows into the top of the DAF Air Saturator Tank V-101.
Compressed air from DAF Air Compressor C-101 is injected into the side of the DAF Air Saturator Tank and distributed into the recycle sea water entering the top of the tank. The injected air flow is relatively small (160 SCF/H) because only enough air to assist in gently lifting sludge to the surface is needed. Internal spargers are used to distribute the air evenly into the water. The DAF Air Compressor is an electric motor driven rotary compressor.
The DAF Saturator Tank V-101 contains a large bed of packing that provides surface area and mixing for the saturation of the injected air into the circulating sea water. The air-saturated water and any unabsorbed air flow out the bottom of the tank and into the bottom of the entrance to the main chamber of the DAF Basin. A set of distribution spargers at the bottom promotes release of air from the circulating sea water as microbubbles which will enhance the lifting of the agglomerated particles from the Flocculators to the surface of the basin to form a floating sludge phase.
UF Feed Pumps
Clarified sea water from the outlet well of DAF Basin T-101 is pumped to the UF Autostrainers F-102A/B by UF Feed Pumps P-105A/B. A small amount of clarified sea water is dumped to the sea for purposes of level control of the DAF Basin’s outlet well. These are electric motor-driven centrifugal pumps. Normally only one pump is in operation. The bearings are cooled with circulating cooling water to preserve their mechanical integrity. Cooling water for the pump bearings is supplied from the A and B cooling water headers and returned back to the cooling water system.
The design flow of sea water to the UF Section is 230 GPM. The normal flow of dumped clarified sea water is 15.0 GPM. The outlet pressure of the UF Feed Pumps is normally 65.0 PSIG.
UF Autostrainers
Clarified sea water from UF Feed Pumps P-105A/B is first strained in UF Autostrainers F-102A/B. These strainers prevent any larger particles (e.g. sludge) that might be present in the clarified sea water from passing on to the downstream ultrafiltration cartridges in the UF Unit. The internal strainer is a large mesh-coated cylinder. Sea water passes through the mesh to remove any of these particles and is collected in the bottom of the strainer vessel and passed on to the UF Units X-101A/B.
The mesh can be periodically cleaned by means of a rotating rubber wiper assembly which will gently dislodge any accumulated solids on the outside of the mesh. A manual purge valve is provided on each autostrainer for the removal of this material from the vessel for disposal. The purge valve is normally only opened when the mesh is being wiped. Normally only the A Autostrainer is in operation.
Ultrafiltration Units
Strained, clarified sea water from the UF Autostrainers F-102A/B flows to the Ultrafiltration Units X-101A/B. These units consists of modular racks of ultrafiltration cartridges that remove very small solid particles from the sea water, so they do not plug the downstream Reverse Osmosis Unit. These smaller particles are continuously removed from the ultrafiltration cartridges. Ultrafiltration cartridges use permeable membranes that have small pores sized such that most of the sea water will pass through the pores while most microscopic solid particles will not. A continuous purge of sea water at the end of the UF cartridges ensures removal of these solid particles that will not pass through the membrane.
The flow rate of sea water to the UF Units is normally 230.0 GPM. The purge flow rate is normally 30.0 GPM. Normally only the A unit is in operation. The pressure drop across the operating UF Unit is normally 19.8 PSI. The outlet of each UF Unit is combined and then sent to the RO Feed Pumps P-201A/B.
Over time, the pores of the UF membranes will tend to plug and capacity of the unit will be reduced resulting in an unacceptable high pressure drop. The UF Units are outfitted with connections to a cleaning system which is shared with the downstream RO Units. The cleaning system allows the UF and RO Units to be flushed, cleaned and sanitized. Because the connections of the UF and RO Units to the cleaning system are permanent, the cleaning system is referred to as a clean-in-place (CIP) system.
RO Feed Pumps
Filtered feed water from X-101A/B is pumped to high pressure by RO Feed Pumps P201A/B which are specially designed, high head, electric motor-driven centrifugal pumps. Each pump only operates with its respective RO Unit; P-201A feeds only X201A and P-201B feeds only X-201B. Normally only one RO Feed Pump/RO Unit is in operation. The design flow of sea water to the operating RO Pump/RO Unit is 200 GPM. The discharge pressure of the RO Pump in operation is normally 1,131 PSIG.
The high pressure developed by the RO Pumps generates a lot of force on the pumps’ bearings which can result in excessive temperatures of the bearings. Therefore, the bearings are cooled with circulating cooling water to preserve their mechanical integrity. Cooling water for the pump bearings is supplied from the A and B cooling water headers and returned back to the cooling water system.
Reverse Osmosis Units
High pressure sea water from the RO Feed Pumps P-201A/B is fed to its respective Reverse Osmosis (RO) Unit X-201A/B. Each RO Unit consists of 3 racks of 6 permeable membrane units. Each rack of permeable membranes operate in parallel. Each membrane unit consists of 20-foot long spiral-wound membrane sheets within an 8-inch diameter housing. The spirally wound configuration permits a large cross-sectional area of the membrane sheets to be installed in a relatively small volume.
The membrane sheets are specially fitted on each end of the housing to segregate the feed side from the permeate (purified water) side. A feed manifold routes the sea water to the inlet sides of the membrane units and two outlet manifolds collect the permeate and the brine reject.
A high differential pressure across the RO membrane (1,028 PSI) results in a large osmotic pressure differential of water across the membrane. The membrane is fabricated with material that will mainly permit smaller molecules to diffuse through it. In sea water, the smallest molecule is water. The combination of high membrane cross-sectional area combined with a high differential pressure across the membrane results in commercially economic rates of water diffusion/transport through the membrane. The water produced from reverse osmosis is termed permeate. Most of the non-water molecules remain on the high-pressure side of the membrane, resulting in purification of the sea water.
By design, a large fraction of the feed water flow does not permeate the membrane to keep the impurity concentrations fairly low at the outlet end of the high-pressure side of the membrane. Otherwise, high concentrations of impurities would increase their osmotic pressure and force their way through the membrane. The excess water and impurities (brine) are collected and routed to disposal facilities.
The Reverse Osmosis Unit normally operates at 1,038 PSIG on the sea water (brine) side and at 20 PSIG on the permeate side. The unit normally produces 80 GPM of permeate and about 120 GPM of reject brine is produced.
Over time, the pores of the RO membranes will tend to plug and capacity of the unit will be reduced resulting in decreased permeate production. The RO Units are outfitted with connections to a cleaning system which is shared with the upstream UF Units. The cleaning system allows the UF and RO Units to be flushed, cleaned, and sanitized. Because the connections of the UF and RO Units to the cleaning system are permanent, the cleaning system is referred to as a clean-in-place (CIP) system.
Permeate Tanks & Pumps
The permeate streams from the Reverse Osmosis Units X-201A/B are collected in the Permeate Tank T-201. Permeate is highly corrosive to steel piping and equipment over time because it lacks the minerals naturally found in ordinary surface and well waters as a result of passing through the RO Unit. As a result, its pH is somewhat acidic (in the range of 5.0 to 7.0).
The permeate is pumped from T-201 to the Limestone Filters by Permeate Pumps P202A/B which are electric motor-driven centrifugal pumps. Normally, only one pump is in service. The design flow rate of permeate taken from the tank is the same as the permeate flow rate produced by the RO Unit (80 GPM)
Limestone Filters
Normally, a large portion (63%) of the permeate from the Permeate Pumps flows to one of the Limestone Filters F-231A/B. These filters contain limestone (mainly calcium carbonate with smaller amounts of other natural minerals) in fixed beds. The permeate flows downward through the bed and dissolves some of the limestone in the bed of the filter. This results in neutralization of the acidic permeate and adds minerals to the water. The concentration of the calcium oxide in water is commonly referred to as ‘hardness’. The hardness of the water leaving the Limestone Filter is 140 milligrams per litre (mg/l). After combining with the balance of permeate bypassing the limestone filters the final hardness of the permeate is 90 mg/l which is suitable for potable (drinkable) water standards.
Product Filters
Prior to distribution, water from the Limestone Filter section is filtered in cartridge filter F-240 to remove any solid particles and in activated carbon filter F-241 to remove any trace organic compounds. Either product filter can be bypassed for maintenance. Potable water is sent to users at the battery limits.
Two lines are provided from the outlet of F-241. One is for filling the Expansion Tanks TK-603A/B of the Cooling Water System as needed. Normally there is no flow of potable water to the Expansion Tanks. The second line sends potable water to the Cleaning System for flushing, cleaning and sanitization of the UF and RO Units as needed. Normally, there is no flow of potable water to the Cleaning System.
Cooling Water System
The Reverse Osmosis simulator also includes a Cooling Water System which provides circulating cooling water for protection of the Sea Water Pumps P-101A/B, the UF Feed Pumps P-105A/B and the RO Feed Pumps P-201A/B. Warm cooling water is collected from users via the Cooling Water Return Header. Two elevated Expansion Tanks TK-603A/B are connected to the header to allow for expansion of the water in the system as the density of the water changes with temperature. Water is denser at lower temperatures, so for a given fixed mass of water in the system, the volume of water will be lower, and the expansion tanks will transfer some of its water to the Return Header by gravity. Conversely, when the cooling water becomes hotter it will occupy more volume and water from the Return Header will be pushed up into the tanks as the water expands.
In case of leaks or maintenance purges of cooling water from the system, potable water from the Activated Carbon Filter F-241 can be used to fill the Expansion Tanks back to their normal operating levels. When this is needed, corrosion inhibitor should be added from the Corrosion Inhibitor Tanks TK-601A/B. Small motor-driven Corrosion Inhibitor Injection Pumps P-606A/B are used to transfer the corrosion inhibitor from the Corrosion Inhibitor Tanks to the Expansion Tanks.
Four motor-driven, centrifugal Cooling Water Pumps P-602A/B/C/D pump warm cooling water from the Return Header, through the Cooling Water Coolers HX-601A/B/C/D and into the two Cooling Water Supply Headers (A & B). Normally, three pumps P-602A, P-602B and P-602C are in operation. The flow of each pump is normally 24 GPM. The returned, warm cooling water is cooled with filtered sea water from the Cooling Sea Water Filters F-101A/B. The warmed sea water is returned to the sea via a discharge header at battery limit. At design, the cooling water supply temperature is 57.9 DEG F. The cooling water return temperature is 105.3 DEG F.
Cooled water from Cooling Water Supply Header A is routed to pumps P-101A, P105A and P-202A. Cooled water from Cooling Water Supply Header B is routed to pumps P-101B, P-105B and P-201B. All circulated cooling water is returned to the Cooling Water Return Header.
Cleaning System
Overview of the Cleaning System
The Cleaning System is used to flush, clean, and sanitize the UF Units X-101A/B and the RO Units X-201A/B. The system is designed to treat one offline unit at a time.
The Cleaning System consists of:
- Cleaning Tank TK-701
- Cleaning/Flushing Pumps P-701A/B
- Cartridge Filter F-701
- Sulfuric Acid Pump P-702
- Sulfuric Acid Drum D-702
- Caustic Soda Pump P-703
- Caustic Soda Drum D-703
- Sodium Hypochlorite Pump P-704
- Sodium Hypochlorite Drum D-704
- Inline Chemical Mixer MX-701
Sulfuric acid and caustic soda are used to adjust the pH of the circulating cleaning/flushing solution as needed. Sodium hypochlorite is a sanitizing chemical which is injected as needed to kill bacteria in the system.
RO and UF cartridge manufacturers have varying requirements on how to clean their cartridges. Most often the following basic steps are performed:
- Perform a once-through flush of the offline unit with potable water (no return to the Cleaning Tank)
- Perform a finer cleaning by circulation of pH-adjusted potable water (return water to the Cleaning Tank)
- Dump the circulation water, add fresh water, and perform a sanitizing circulation (return water to the Cleaning Tank)
- Dump the sanitizing circulation solution and perform a once-through final flush of the unit to ready it for service (no return to the Cleaning Tank)
Detailed Process Description of the Cleaning System
Potable water from Activated Carbon Filter F-241 is brought into the Cleaning Tank TK-701 via the suction line to the Cleaning/Flushing Pumps P-701A/B. If the pumps are stopped, all the potable water will back-fill the tank. If one of the pumps is running, the pump will preferentially take the potable water flow. Any excess water not used by the operating pump will back-fill the tank.
The working capacity of TK-701 is about 1,000 gallons. The Cleaning Tank is outfitted with an electric heater to raise the temperature of the cleaning solution to the UF/RO cartridge manufacturer’s recommended cleaning temperature.
Cleaning/Flushing Pumps P-701A/B are electric motor-driven centrifugal pumps that normally circulate 30.0 GPM of water through either one of the offline UF or RO Units. Only one pump is normally in service. A dump line is provided for disposal of circulated cleaning water at battery limits.
In circulation mode, no potable water will be added to the Cleaning System and the Cleaning/Flushing Pumps will draw solution exclusively from the Cleaning Tank. In flushing mode, potable water will be added to the pump suction at a flow rate equal to or slightly higher than the pump circulation flow rate so as not to draw any solution from the Cleaning Tank.
Flow from P-701A/B is routed through Cartridge Filter F-701 to remove any solids removed during operation of the system. Flow continues from the Cartridge Filter to the In-line Chemical Mixer MX-701 which intimately mixes circulating water/solution with any of the three injected chemical solutions: sulfuric acid, caustic soda, and sodium hypochlorite. The outlet flow from the mixer is then routed to one of the UF or RO Units as needed for flushing/cleaning.
The three chemical injection pumps P-702, P-7023 and P-704 are electric motor driven, variable frequency drive (VFD) injection pumps.
The flow rate of the circulating water/solution is controlled at the common cleaning solution return line from either the UF or RO Units. Refer to Schematic #9 for the UF Units and Schematic #11 for the RO Units. The cleaning solution is returned back from these units to the Cleaning Tank. A three-way valve HV-702 is used to divert the returned solution to the Cleaning Tank (circulation mode) or to the disposal facilities (flushing mode).
Instrumentation
Sea Water Pumps
The temperature of the sea water feed is indicated on TI-100. The status of the motors of Sea Water Pumps P-101A/B is indicated on switches HS-101A/B. These switches are also used to start/stop the pumps.
Switches FV-109A/B are used to open the cooling water valves to pumps P-101A/B, respectively. The temperature of the pumps’ bearings are indicated on TI-109A/B, respectively. Interlocks I-109A/B will generate trip alarms THH-109A/B if the bearing temperatures become too high. See the “Interlocks” section below for functional details of I-109A and I-109B.
The total flow from the pumps is indicated on FI-101. The discharge pressure of the Sea Water Pumps P-101A/B is controlled by PIC-101 which adjust the position of control valve PV-101. FIC-102 controls the flow of sea water to the DAF Unit by adjusting the position of control valve FV-102. The PV of controller FIC-102 is used by interlock I-102 (Low Sea Water Flow Interlock). FLL-102 is a switch that indicates the status of the interlock. See the “Interlocks” section below for functional details of I-102.
The flow of sea water to the Cooling Sea Water Filters F-101A/B is indicated on FI-103.
Cooling Sea Water Filters
AI-102 indicates the turbidity (cloudiness) of the water entering the Cooling Sea Water Filters F-101A/B and is measured in NTU (Nephelometric Turbidity Units). An NTU value less than 5 represents a very clear fluid, which is normally produced by the Sea Water Filters. Visually discernible cloudiness starts between an NTU of 10 to 20. Values above 100 are obviously cloudy. AI-103 indicates the turbidity of the sea water leaving the filters.
PDI-101A and PDI-101B indicate the pressure drop across F-101A/B, respectively. Normally only the A filter is in service.
HV-102A and HV-103A are switches to open and close the block valves of filter F101A. HV-102B and HV-103B are switches to open and close the block valves of filter F-101B.
Flocculators
AI-111 indicates the pH of the sea water feed to the In-line Chemical Mixer MX-101. AI-113 indicates the pH of the sea water leaving MX-101.
Switch HS-111 is used to start/stop the motor of Sulfuric Acid Pump P-111. FIC-111 controls the flow rate of sulfuric acid to MX-101 by adjusting the speed of P-111.
Switch HS-112 is used to start/stop the motor of Ferric Chloride Pump P-112. FIC-112 controls the flow rate of ferric chloride to MX-101 by adjusting the speed of P-112.
Low Sea Water Flow Interlock I-102 will stop the flow of sulfuric acid and ferric chloride to MX-101 in the event of very low sea water flow to MX-101. See the “Interlocks” section below for functional details of I-102.
LI-113A indicates the level of sea water in the chamber of Flocculator R-101A. Switch AG-113A is used to start/stop the motor of the agitator for R-101A.
LI-113B indicates the level of sea water in the chamber of Flocculator R-101B. Switch AG-113B is used to start/stop the motor of the agitator for R-101B.
Dissolved Air Flotation
Switch HS-114 is used to start/stop the motor of the Sludge Scraper of the DAF Basin T-101.
LI-114 indicates the level of sea water in the main chamber of T-101. LI-115 indicates the level of sludge in the in the Sludge Trough of T-101. This indication is used by interlock I-103 to automatically start and stop the motors of either of the DAF Sludge Pumps P-103A/B. See the “Interlocks” section below for functional details of I-103. Switches HS-115A/B are used to control the functions of interlock I103.
Switches HS-103A/B are used to manually start/stop the motors of DAF Sludge Pumps P-103A/B.
LIC-116 controls the level of clarified sea water in the collection well at the end of the DAF Basin assembly by adjusting the position of control valve LV-116 which dumps clarified sea water from the discharge of UF Feed Pumps P-105A/B to the sea. AI-116 indicates the turbidity of the clarified sea water drawn from the collection well.
Switches HS-102A/B are used to start/stop the motors of DAF Recycle Pumps P103A/B. FIC-117 controls the flow of DAF recycle sea water by adjusting the position of control valve FV-117. Switch HS-116 is used to start/stop the motor of DAF Air Compressor C-101. FIC-118 controls the flow of air to the DAF Air Saturator Tank by adjusting the position of control valve FV-118.
UF Feed Pumps
The status of the motors of UF Feed Pumps P-105A/B is indicated on switches HS105A/B. These switches are also used to start/stop the pumps.
Switches FV-129A/B are used to open the cooling water valves to pumps P-105A/B, respectively. The temperature of the pumps’ bearings are indicated on TI-129A/B, respectively. Interlocks I-129A/B will generate trip alarms THH-129A/B if the bearing temperatures become too high. See the “Interlocks” section below for functional details of I-129A and I-129B.
The flow from the pumps to the UF Autostrainers F-102A/B is indicated on FI-121. The discharge pressure of the UF Feed Pumps P-105A/B is indicated by PI-121. The temperature of the sea water from P-105A/B is indicated on TI-121. FI-122 indicates the flow of sea water through control valve LV-116 which is controlled by the DAF Basin collection well level controller LIC-116.
UF Autostrainers
Switch HV-125A opens/closes the inlet hand valve HV-125A of UF Autostrainer F102A. Switch MOV-125A opens/closes the main outlet motor-operated valve of F102A. Switch POV-125A opens/closes the pilot-operated purge valve POV-125A.
PDI-125A indicates the pressure drop across F-102A. Switch HS-125A stops/runs the motor of the rotating rubber wiper of F-102A to loosen accumulated material on the filter mesh basket when indicated by high pressure drop. Normally, HV-125A and MOV-125A are open and POV-125A is closed. POV-125A is opened to purge loosened material while the rotating wiper is operating.
UF Autostrainer F-102B is identically instrumented to F-102A. Instrument tags differ by the suffix A or B. Normally, F-102B is on standby service with all its valves closed and its motor stopped.
The outlet pressure of sea water from F-102A/B is indicated on PI-125. The flow of sea water to the Ultrafiltration Units X-101A/B is indicated on FI-125.
Ultrafiltration Units
Switch HV-127A opens/closes the sea water inlet hand valve HV-127A of UF Autostrainer Unit X-101A. Switch HV-128A opens/closes the sea water outlet valve HV-128A from X-101A. Hand controller HIC-129A adjusts the position of concentrate control valve HV-129A. Switch HV-711A opens/closes the cleaning solution supply valve HV 711A. Switch HV-712A opens/closes the cleaning solution outlet valve HV712A.
In normal operation, the sea water inlet and outlet valves HV-127A and HV-128A are open and the concentrate control valve HV-129 is open 30% while the cleaning solution valves HV-711A and HV-712A are closed.
Ultrafiltration Units
Ultrafiltration Unit X-101B is identically instrumented to X-101A. Instrument tags differ by the suffix A or B.
Normally, X-101B is normally in cleaning mode (circulation from/to Cleaning Tank TK-701 with potable water). In this situation, the two sea water valves HV-127B and HV-128B are closed and the concentrate control valve HV-129B is fully closed (0% open). The cleaning solution valves HV-711B and HV-712B are open to allow circulation of cleaning water through the cartridges of X-101B.
The cleaning lines from X-101A and X-101B are combined and pass-through control valve FV-712. FIC-712 controls the cleaning solution circulation flow through the UF Unit being cleaned.
The combined flow of sea water from the Ultrafiltration Units to the RO Feed Pumps P-102A/B is indicated on FI-128.
RO Feed Pumps
The status of the motor of RO Feed Pumps P-201A is indicated on switch HS-201A. This switch is also used to start/stop the pump.
Switch FV-129A is used to open the cooling water valves to pump P-201A. The temperature of the pump’s bearings are indicated on TI-209A. Interlock I-209A/B will generate trip alarm THH-209A if the bearing temperature becomes too high. See the “Interlocks” section below for functional details of I-209A (and I-209B).
PI-201A indicates the suction pressure of P-201A. PI-202A indicates the discharge pressure. The differential pressure across the pump is calculated by the difference of these two pressure indications and is indicated on PDI-203A. TI-201A indicates the discharge temperature of P-201A.
Switch MOV-201A opens/closes the discharge motor-operated valve MOV-201A.
Pump differential pressure indication PDI-203A is used as a trip sensor to protect the pump from low flow conditions. See the “Interlocks” section below for functional details of I-201A (and I-201B).
RO Pump P-201B is identically instrumented to P-201A. Instrument tags differ by the suffix A or B. Normally only P-201A is in operation.
The motors of the RO Pumps will also be stopped by interlock I-221 in case of high level in the Permeate Tank T-201. See the “Interlocks” section below for functional details of I-221.
Reverse Osmosis Units
The sea water flow to the Reverse Osmosis Unit X-201A is controlled by FIC-210A by adjusting the position of control valve FV-210A. PI-210A indicates the inlet pressure of sea water to X-201A. PI-211A indicates the outlet pressure of permeate from X201A. The pressure differential across RO membranes is calculated from these two pressure indications and is indicated on PDI-210A.
The pressure of the reject brine is controlled by PIC-212A by adjusting the position of control valve PV-212A. The flow of reject brine is indicated on FI-212A.
The flow rate of permeate produce by X-201A is indicated on FI-211A. Hand controller HIC-211A adjusts the position of permeate control valve HV-211A. Normally this valve is 100% open. Closing it will increase the back pressure of permeate against the RO membrane which will cause a reduction in permeate production.
Switch HV-721A opens/closes the cleaning solution supply valve HV-712A of X-201A. Switch HV-722A opens/closes the cleaning solution outlet valve HV-722A. In normal operation, the cleaning valves are closed.
RO Unit X-201B is identically instrumented to X-201A. Instrument tags differ by the suffix A or B. Normally, X-201B is completely isolated. In this situation the sea water feed control valve FV-210B, the brine control valve PV-212B, the permeate control valve HV-211B and the cleaning solution valves HV-721B and HV-712B are all fully
closed.
The cleaning lines from X-201A and X-201B are combined and pass-through control valve FV-722. FIC-722 controls the cleaning solution circulation flow through the RO Unit being cleaned.
Permeate Tank & Pumps
TI-220 indicates the temperature of the combined permeate flowing from the RO Units X-201A/B to Permeate Tank T-201. The water level in Permeate Tank T-201 is indicated on LI-220, LAH-221 and LAL-222. All three indications are based on independent level transmitters and level taps. LAH-221 and LAL-222 are connected to interlocks I-221 and I-222 which are activated in case of high or low level, respectively, in T-201 (see the “Interlocks” section below for functional details of I221 and I-222).
AI-220 indicates the conductivity of the permeate in siemens per meter (S/M) units. A high value indicates a probable leak in the operating RO Unit. Its normal value is 0.020 S/M.
The status of the Permeate Pumps P-202A/B is indicated on switches HS-202A/B which are used to start/stop the pumps. The discharge pressure of Permeate Pumps P-202A/B is indicated on PI-221. The flow rate of permeate to the Limestone Filters is indicated on FI-221.
Limestone Filters
The flow of permeate to the Limestone Filters F-231A/B is controlled by FIC-231 by adjusting the position of control valve FV-231. Switches MOV-231A and MOV-232A control the motor-operated valves at the inlet and outlet of F-231A. Switches MOV231B and MOV-232B control the motor-operated valves at the inlet and outlet of F231B. Normally F-231A is in service and F-231B is on standby (isolated with MOV231B and MOV-232B closed).
PDI-231A/B indicate the pressure drop across F-231A/B, respectively.
The Limestone Filter bypass flow is controlled by PIC-231 which keeps the pressure at the outlet of the Limestone Filters steady by adjusting the position of control valve PV-231. In case both Limestone Filters are out of service or if there is an upset of the flow to the Limestone Filters then PIC-231 will automatically open control valve PV-231 to ensure adequate flow to the downstream product filters.
The mineral content (hardness) of the mineralized water to the product filters is indicated on AI-231 in mg/l.
Product Filters
PDI-240 and PDI-241 indicate the pressure drop across the Cartridge Filter F-240 and the Activated Carbon Filter F-241, respectively.
Switch HV-240A opens/close the inlet block valve of Cartridge Filter F-240. Switch HV-241 opens/closes the inlet block valve of Activated Carbon Filter F-241. Switch HV-240B opens/closes the bypass valve of F-240. Switch HV-241B opens/close the bypass valve of F-241.
FIC-242 controls the flow rate of potable water to the users by adjusting the position of control valve FV-242. The temperature of the potable water is indicated on TI-242.
The flow of potable water to the Expansion Tanks of the Cooling Water System is indicated on FI-243. Normally there is no flow to the Expansion Tanks. In case there is flow, FI-243 will alarm to alert the operator that potable water is being used within the unit.
The flow of potable water to the Cleaning System is indicated on FI-244. Normally there is no flow to the Cleaning System. In case there is flow, FI-244 will alarm to alert the operator that potable water is being used within the unit.
Cooling Water System
Corrosion Inhibitor System
LI-620A/B indicate the levels of Corrosion Inhibitor Tanks TK-601A/B, respectively. Switches AG-620A/B control the motors of the agitators on these tanks. Agitation ensures the corrosion inhibitor is uniformly mixed within the tank. The motors of Corrosion Inhibitor Pumps P-606A/B are controlled by switches HS-606A/B, respectively. If the Corrosion Inhibitor Tanks need to be refilled, switches HS-601AF and HS-601BF are used to add more corrosion inhibitor to the respective tank. Normally, no corrosion inhibitor is being added to the Expansion Tanks, TK-603A/B. Corrosion inhibitor normally needs to be added when potable water is being added to the Expansion Tanks or as maintenance needs dictate.
Expansion Tanks
LI-631A/B indicate the level of cooling water in Expansion Tanks TK-603A/B, respectively. Potable water is added to the tanks by switches LV-631A/B, respectively, in case the tank levels become unacceptably low. This can happen in the case of a maintenance purge or leak in the Cooling Water System. Note that as the temperatures in the system change, the levels of water in the Expansion Tanks will rise and fall accordingly but should stabilize as temperatures stabilize.
Cooling Water Circulation
The motors of the Cooling Water Pumps P-602A/B/C/D are controlled by switches HS-602A/B/C/D, respectively. Normally the A, B and C pumps are in operation. The inlet temperatures to Cooling Water Coolers HX-601A/B/C/D are indicated on TI602A/B/C/D, respectively. The corresponding outlet temperatures are indicated on TI-603A/B/C/D. The pressures of the Cooling Water Supply Headers A/B are indicated on PI-603A/B, respectively.
The cooling sea water supply block valves HV-601A/B/C/D are opened/closed by switches HV-601A/B/C/D, respectively. If a Cooling Water Cooler is out of service, its respective cooling sea water block valve should be closed to avoid unnecessary energy consumption by the Sea Water Feed Pumps P-101A/B.
Cleaning System
Cleaning Tank
LI-701 indicates the level of water/cleaning solution in Cleaning Tank TK-701. Switch AG-701 starts/stops the motor of the agitator for TK-701. TIC-701 controls the temperature of the contents of the tank by turning on and off the tanks electric heater as needed when the controller is in automatic mode. When the controller is placed into manual mode, the heater is off. Switch TS-701 indicates the tank heater’s operating status.
Switch HV-702 controls the position of three-way valve HV-702 on the solution return line. When circulating water/solution through a unit, the valve should be placed in the TANK position. When water/solution is being used for flushing on a once-through basis, the valve should be placed in the DUMP position.
FIC-705 controls the flow of permeate from the Activated Carbon Filter F-241 by adjusting the position of control valve FV-705.
Cleaning/Flushing Pumps
Switches HS-701A/B start/stop the motors of Cleaning/Flushing Pumps P-701A/B, respectively. AI-701 indicates the pH of water/solution flowing from P-701A/B. HIC701 controls the position of dump valve HV-701.
Cartridge Filter
The flow through Cartridge Filter F-701 is indicated on FI-701. The PV of FI-701 is also used by Low Cleaning Flow Interlock I-701 to prevent chemical injection at low circulation flow rates (see the “Interlocks” section below for functional details of I701). The status of the interlock is indicated on switch FLL-701.
The pressure drop across the filter is indicated on PDI-701.
Chemical Mixing
AI-702 indicates the pH of the solution leaving In-line Chemical Mixer MX-701.
Switch HS-702 is used to start/stop the motor of Sulfuric Acid Pump P-702. FIC-702 controls the flow rate of sulfuric acid to MX-701 by adjusting the speed of P-702. Switch HS-703 is used to start/stop the motor of Caustic Soda Pump P-703. FIC-703 controls the flow rate of caustic soda to MX-701 by adjusting the speed of P-703. Switch HS-704 is used to start/stop the motor of Sodium Hypochlorite Pump P-704. FIC-704 controls the flow rate of sodium hypochlorite to MX-701 by adjusting the speed of P-704.
Interlock I-102
Interlock I-102 prevents chemical injection to the DAF Unit in case the sea water feed flow to the DAF Unit is lower than 20 GPM. In this case, switch FLL-102 will indicate LO-LO and an alarm will be generated.
I-102 will stop the Sulfuric Acid Pump P-111 and the Ferric Chloride Pump P-112 (Maintained stop). I-102 will also lock related flow controllers FIC-111 and FIC-112 into manual mode with an output of 0%.
I-102 will automatically reset when the trip condition has cleared. However, the affected pumps must be manually started after the interlock resets.
Interlock I-103
Interlock I-103 automatically starts and stops one of the DAF Sludge Pumps P103A/B based on the level of the Sludge Trough of the DAF Unit as indicated on LI115.
The logic of I-103 is active when HS-115A is placed in the AUTO position. The pump (A or B) to be auto-started/auto-stopped is selected by switch HS-115B.
When LI-115 exceeds 70% the selected pump’s hand switch (HS-103A or HS-103B) will be set to the RUN position. When LI-115 is less than 30% the selected pump’s hand switch will be set to the STOP position.
Note: the selected pump’s hand switch can still be operated manually when LI-115 is less than 70% and LI-115 is greater than 30%. The unselected pump can be operated independently at any sludge level.
Interlocks I-109A/B
Interlocks I-109A/B protect the Sea Water Pumps P-101A/B from mechanical damage in case their respective cooling water valve FV-109A/B is closed or if a high-high bearing temperature is detected (TI-109A/B exceeds 200 DEG F). In this case, switch THH-109A/B will indicate HI-HI and an alarm will be generated.
I-109A/B will stop the corresponding Sea Water Pump P-101A or P-101B (maintained stop). I-109A/B will automatically reset when the trip conditions have cleared. However, the affected Sea Water Pump P-101A/B must be manually started after the interlock resets.
Interlocks I-129A/B
Interlocks I-129A/B protect the UF Feed Pumps P-105A/B from mechanical damage in case their respective cooling water valve FV-129A/B is closed or if a high-high bearing temperature is detected (TI-129A/B exceeds 200 DEG F). In this case, switch THH-129A/B will indicate HI-HI and an alarm will be generated.
I-129A/B will stop the corresponding UF Feed Pump P-105A or P-105B (maintained stop). I-129A/B will automatically reset when the trip conditions have cleared. However, the affected UF Feed Pump P-105A/B must be manually started after the interlock resets.
Interlocks I-201A/B
Interlocks I-201A/B protect the RO Feed Pumps P-201A/B from mechanical damage in case their respective pressure differentials become too high (PDI-203A/B continuously exceeds 1,115 PSI for more than 30 seconds). In this case, switch PDH-203A/B will indicate HI-HI and an alarm will be generated.
I-201A/B will stop the corresponding RO Feed Pump P-201A or P-201B (maintained stop). I-201A/B will automatically reset when the trip conditions have cleared. However, the affected RO Feed Pump P-201A/B must be manually started after the interlock resets.
Interlocks I-209A/B
Interlocks I-209A/B protect the RO Feed Pumps P-201A/B from mechanical damage in case their respective cooling water valve FV-209A/B is closed or if a high-high bearing temperature is detected (TI-209A/B exceeds 200 DEG F). In this case, switch THH-209A/B will indicate HI-HI and an alarm will be generated.
I-209A/B will stop the corresponding RO Feed Pump P-201A or P-201B (maintained stop).
I-209A/B will automatically reset when the trip conditions have cleared. However, the affected RO Feed Pump P-201A/B must be manually started after the interlock resets.
Interlock I-221
Interlock I-221 protects the Permeate Tank T-201 from being overfilled. I-221 is activated when LAH-221 is more than 90%. I-221 will remain active anytime LAH221 is more than 90%. In this case, switch XA-221 will indicate TRIP and an alarm will be generated.
I-221 will stop the RO Feed Pumps P-201A/B (maintained stop).
I-221 will automatically reset when LAH-221 indicates lower than 90%. However, the affected RO Feed Pump P-201A/B must be manually started after the interlock resets.
Interlock I-222
Interlock I-222 protects the Permeate Pumps P-202A/B from cavitation due to low level in Permeate Tank T-201. I-222 is activated when LAL-222 is less than 10%. I222 will remain active anytime LAL-120 is less than 10%. In this case, switch XA-222 will indicate TRIP and an alarm will be generated.
I-222 will stop the Permeate Pumps P-202A/B (maintained stop).
I-222 will automatically reset when LAL-222 indicates higher than 10%. However, the affected Permeate Pump P-202A/B must be manually started after the interlock resets.
Interlock I-701
Interlock I-701 prevents chemical injection to the Cleaning System in case the circulating flow rate is lower than 5.0 GPM.
I-701 will stop the Sulfuric Acid Pump P-702, the Caustic Soda Pump P-703 and the Sodium Hypochlorite Pump P-704 (maintained stop). I-701 will also lock related flow controllers FIC-702, FIC-703 and FIC-704 into manual mode with an output of 0%.
I-701 will automatically reset when the trip condition has cleared. However, the affected pumps must be manually started after the interlock resets.