DESALINATION

Process flow diagram

[image] Shown above PFD (flow of processes diagram) is sufficient to deliver the product with guaranteed quality and quantity. Each constituent process is concisely defined by a simple verb. In fact, each node represents the P&ID piece. Their operational characteristics and the battery limits are given below.

67 generic P&ID symbols are described here.

Intake station

[image] This P&ID shows implementation of seawater coarse filtration and pumping steps. First seawater goes through static bar screen which allows coping with high inrush of jellyfish. Then seawater is filtered in the rotating band screen. Both screens are non-pool-out design but may be isolated with the stop logs to perform necessary inspection and maintenance of submerged parts. The rotating band screen is equipped with the cleaning system and the debris disposal one. The first cleans the screens by high-velocity jets produced in specially designed nozzles. They are fed with seawater taken from the discharge manifold of the main pumps, then additionally filtered and pressurized up to 4 Barg in the auxiliary pumps. The debris disposal system is a set of interconnecting shoots and conveyers (not shown on P&ID). Ancillaries include the pigging system, the chlorination system and the compressed air one. Pigging is a batch process which is started every time the water level in the sump approaches the minimum submergence for the main pumps. The second subsystem is simple and rugged in design as it is used only on rare occasions. The shock-chlorination dosing rates are monitored at the station discharge manifold. The compressed air is fed to the intake head to build the ?bubble? screen that should scare away fish. The last subsystem is the sacrificial-anode protection of the screens and the main pumps against corrosion (not shown on P&ID). The pumping requested turn-down ratio and spare (standby and rotating) capacity are provided with a number of pumps connected in parallel, each pump being driven by the variable speed drive (VSD).

Pretreatment

[image] The selected standard fine filtration process and implementation match the target SDI of 3.5 for output at the high TSS (total suspended solids) of the initial seawater (of up to 40). Polymer and flocculent are admixed to seawater. Then it goes through fast mixing and slow mixing chambers before entering the lamella clarifier - a rack of inclined plates, which cause flocks of suspended solids material to precipitate from water that flows across the plates. The flocks ? sludge - settle at the bottom and are collected and fed by a slow-rotating scraper to the progressive-cavity pump through the sludge outlet located at the clarifier center. Small part of settled sludge is used for seeding; it is extracted just above the scraper and re-circulated to the flocculation chambers. Clear water stream from the lamella is directed to the multi-media filters working at the atmospheric pressure. This type of filter requires periodical backwashing as the build-up of the filtrated material gradually plugs it. The selected backwashing system does not cause any dips in the plant production during its operation. The said system contains an open tank with the submersible low-head pump, and the air scouring system. The tank is continuously filled with the brine rejected from the reverse osmosis process. After backwashing the filter goes through maturing phase during which the filtrated water quality returns to the normal one. This water flow is diverted and fed again to the filters. The filtration quality is periodically checked through water sampling to SDI- monitoring system. Shown on P&ID polymer preparation system is common for the pretreatment and the sludge disposal systems.

High pressure pump

[image] High pressure pump forced oil lubrication system P&ID is an illustration of the equipment manufacturer drawing integration without re-drawing it according to the Crenger graphics standards. This lubrication system serves both the pump and the motor. For higher reliability of this system, one oil pump is coupled to the shaft of the high pressure pump. At power supply interruption this pump continues pumping oil to the bearings till the complete stoppage of the pump set. The system contains minimum amount of instrumentation as it is a major source of failure. To cool the oil, the lubrication system is plugged into a cooling system common for all water-cooled motors.

SWRO

[image] Selected implementation of the seawater reverse osmosis desalination is built round PX300 - energy recovery device brand produced by ERI company. As shown on P&ID SWRO membrane array is fed with 2 streams of seawater. First stream is pressurized in the high pressure booster pump and the high pressure pump connected in train. The second stream is pumped by the low pressure booster pump to ERI where its pressure is further increased through the energy recuperation from the brine reject. Due to the brine pressure being below the one at the SWRO membranes inlet, and inevitable energy losses in ERI, the second stream is additionally pressurized in the ERI booster pump before being fed to SWRO membranes. The high pressure booster pump serves 2 purposes; it accommodates the pressure variation in the SWRO process and, secondly, it boosts the pressure before the high pressure pump to avoid cavitation incipience. To decrease the risk of SWRO membrane fouling via scaling formation, the antiscalant is constantly added to seawater streams. During the intake chlorination, the free chlorine control is engaged, injecting SMBS into seawater if needed. To shave off occasional flares in SDI values (triggered by hydraulic transients in the pretreatment system), after first-stage pressure boosting seawater goes through micron filters of cartridge type. The permeate streams extracted from the membranes front end and the rear one differ in quality generally defined by remained TDS and Br content. By varying the ratio between the permeate streams the front-end quality may be tailored to that of the final product delivered to the client.

SWRO membrane array

[image] This P&ID shows SWRO membrane arrays arrangement and manifold fittings. As seen every membrane location is described by row, column, and ordinal number inside the pressure vessel. This membrane address is extensively used by the membrane tracking software.

SWRO dosing

[image] This P&ID shows the antiscalant and SMBS daily storage and dosing systems. Such an implementation is safe and simple in maintenance. Batch recharging of the dosing systems is quick and fully automatic. The typical storage system includes an open tank with a spill berm, the group of transfer pumps with 100% reserve capacity, and the strainer installed at the pumps common suction line. The storage system is common for all SWRO units. The dosing system has 50% redundant capacity and a means to check the metering pump calibration (measuring bucket and/or mass-meter).

BWRO membrane array

[image] This P&ID shows BWRO membrane arrays arrangement in a single rack. It is unique in that membrane vessels may be easily added to any pass, and the ratio between the adjacent passes may keep between 2:1 to 3:1.

BWRO

[image] This P&ID shows Brackish Water Reverse Osmosis (BWRO) unit needed to raise the quality of the rear-end permeate produced by SWRO unit, the permeate surge tank, and the water cooling system of the main pumps. BWRO unit consists of the feed pump delivering the rear-end permeate to the first array of the membranes, which brine reject is fed to the second array by the booster pump. Reverse osmosis is conducted at the slightly increased pH-values to maintain the high Boron rejection. The permeate streams collected from the membrane arrays are mixed with the front-end permeate in the permeate tank. The volume of the latter is enough to feed the SWRO membranes during direct osmosis following the plant emergency outage and the SWRO membranes de-pressurization.

Posttreatment

[image] This P&ID describes the remineralization of desalted water in the limestone reactors to make it more stable and less corrosive. The process is controlled by a set of criteria such as alkalinity, hardness, pH and LSI. Only 25-30% of desalted water passes through the limestone reactors. To accelerate the limestone dissolution the CO2 gas is injected into the influent. The mineral-enriched water stream is then discharged to the buffer tank, its volume being selected based on the residence-time criterion. After the buffer tank this constant-flow stream is mixed with untreated desalted water. This mixture pH and/or LSI are checked and corrected by injecting caustic soda (NaOH) or sulfuric acid (H2SO4) before the mixture being discharged to the product tank. Its capacity shall be enough to supply the product water for at least 4 hours - time needed to handle most (over 95%) of the plant anticipated failures. The limestone reactors quantity is selected to minimize the impact of the reactor refilling with limestone on the final product quality as at any conditions the flow rate through any isolated reactor is kept constant to keep down the product turbidity index. As the permeate water used for the reactor backwashing has high content of solids, it is treated by the sludge treatment system.

CIP

[image] CIP system is an auxiliary system used to prolong the membrane life before it being replaced for a new one. Fixed percentage of the membrane replacement is a standard clause in the warranty agreement. The system is used for membrane cleaning off scale deposition and for flushing after the unit emergency shutdown. Cleaning is a batch process that may be sensitive to the solution temperature. So CIP scope additionally includes a water-to-water cooler and a heater. To execute pH-control, CIP system is equipped with continuous and batch dosing subsystems. Before being fed to SWRO membranes the CIP solution is passed through the micron cartridge filter. The CIP interconnecting piping is designed for maximum allowable velocity to cut down the piping volumes to be flushed after each cleaning.

Sludge treatment

[image] Shown on this P&ID system treats 3 effluents to make them suitable for final disposal: the liquid sludge from the lamella clarifier, brine after the multimedia filters backwashing, and permeate after of the limestone reactor backwashing. All the streams are collected in the waste water pool, from which the water is pumped at the constant flow rate to the flocculation chambers before being admitted to the lamella thickener equipped with rotating scraper. After the lamella settler the clean stream is disposed to the brine outfall, while the liquid sludge is pumped to the centrifuge for final dewatering and disposal.

Plant layout

[image] The plant layout provides minimum length of interconnecting piping, clearly defines the project areas, and meets work safety and O&M requirements. All chemical storage tanks have direct access for trucks. Neither SWRO membrane vessel ends nor BWRO ones overlook the maintenance areas which are mostly frequently visited.

© copyright crenger.com

AppStore