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The technology of seawater desalination by reverse osmosis



 The original seawater is served directly from the waters of the sea at a depth of 1.5 m by pump H0 and is collected in the intermediate tank.

Immediately in front of container dosing of sodium hypochlorite in an amount of up to 10 mg / l occurs to disinfect and prevent fouling of pipelines and tanks. The dosage of sodium hypochlorite is made from solution-supply tank, dosing pump proportionally to the chlorine sensor readings.

  From the container the pump delivers the raw water to the pre-filter FP1. Pre-filter is necessary to remove the original water from suspended particles larger than 200 mkm. Removal of particles larger than specified size is necessary to prevent them from falling directly into the hollow fiber that helps to prevent damage and possible blockage. It is designed as a disc filter with a rating of 200 mkm filtration. Disks are put on a hollow cylinder. They are color coded with their micron size and are collected into bags depending on the requirements to the quality of filtering. A filtering unit has a spring for compressing discs and a hydraulic cylinder disposed within the piston which is used to switch the filter from the filtration mode to the rinsing mode and back. Switching modes is done in a fully automatic mode.

Taking into consideration the nature of the source water - water intake goes directly from the open sea with a depth of 1.5 m, it is advisable to use the stage of pre-coagulation.

Coagulation is the main technological methods for the removal of the source water of colloidal particles. Basic mechanisms of coagulation:

Firstly, the destabilization of colloidal dispersions as a result of neutralization of the surface charge of the colloidal particles (decrease x - potential), which contributes to their convergence and consolidation (the mutual repulsion due to the same charge colloid decreases) with the possibility of settling and filtration efficiency.

The second mechanism, the mechanism of adsorption of colloidal particles on the developed surface of the coagulant (usually iron hydroxide (III) and aluminum) flakes followed by separation of the parts of coagulant.

The optimal dose of coagulant is determined during the test of coagulation, coagulation unit looks in the following way:

Two solution-expendable containers are cylindrical plastic tanks with charging port, electromechanical agitator and gauges. In these containers there is a daily dissolution of coagulant and its further dosing into water stream with dosing pumps. Dosage goes in proportion to the flow of water from a water meter with pulse output.

Then the water is supplied by the pump to the ultrafiltration module consisting of parallel, vertically set, ultrafiltration hollow fiber elements.

Filtering takes place in a dead end mode with the source of all raw water to the entire installation ultrafiltration. Reverse flowed flush is conducted periodically; frequency of washes is every 25-30 minutes, 60 seconds duration.

One unit consists of ultrafiltration elements with a common pump supplying raw water. Reverse flowed washing of ultrafiltration settings is conducted by the unit of reverse flowed washing. Washing unit includes a pump, tank for washing water storage and dosing units: sodium hypochlorite (consists of a pump - dispenser and flow container), the dosage of sulfuric acid (consists of a pump - dispenser and expenditure capacity, which is proportional to the dosage of the pH sensor).

Ultrafiltration module operates in the following modes:

1. Operating mode - a dead-end filtration.

Duration of the mode between reverse flowed washes: 25-30 minutes.

During operation the raw water pump is supplied to the hollow fiber elements. The filtrate is directed into the intermediate container. The module is equipped with electromagnetic and manual valves for the organization of the process and switching different modes.

2. Reverse flowed mode.

Every 25-30 minutes of continuous operation reverse flowed mode starts. Washing is carried out with a pump from the tank storage filtrate. During flushing the concentration of sodium hypochlorite, 20 mg / l can be dosed into water stream with the help of the metering pump. Flush itself consists of several sub-steps:

2.1. Mode of co-flowed washing.

2.2. Mode of reverse flowed washing up.

2.3. Mode of reverse flowed wash down.

Duration of each mode can be programmed, thereby optimizing the washings operation.

After all modes of reverse-flowed washing plant goes into operation mode.

3. Mode of chemically enhanced cleaning.

In the ultrafiltration unit there is a mode of chemically enhanced washing: acid dosing pump discharge line washing, pH = 2.5, pH control with sensor.

Washing are performed with an interval of 12 - 168 hours, and the best modes are selected in the process of commissioning and subsequent operation of the equipment.

Chemically enhanced flushing consists of several sub-steps:

3.1. Mode co-flowed washing.

3.2. Mode reverse flowed washing up.

In this mode the dosage of an appropriate chemical reagent is done.

3.3. Mode reverse flowed wash down.

In this mode the dosage of an appropriate chemical reagent is done.

3.4. Soaking mode.

The duration of the mode - 30-600 seconds (programmable interval).

3.5. Mode of co-flowed washing.

3.6. Mode of reverse flowed washing up.

3.7. Mode of reverse flowed washing down.

Duration of each mode can be programmed, thereby optimizing the washings operation.

After all modes of reverse-flowed washing plant goes into operation mode.

Plants operate in fully automatic mode, while the unit operates happening control the following parameters:

1. Control of pressure on the pressure lines of pumps.

2. Control of turbidity in the raw water line and the UF control devices turbidity.

3. Control of "dry run" pumps.

4. Control of costs: raw water, filtrate, and the flow on the line of reverse-flowed washing.

5. Control of pressure of raw water at the entrance to the installation on the pressure sensor.

7. Control of pressure in the process of reverse-flowed washing by pressure sensor.

8. Control of water level in the containers.

9. Control of water temperature.