khaled

Reverse Osmosis Desalination Plant in Nuweiba City (Case Study)

Dr. Eng. Ibrahim Khaled El-Sayed

Chairman

1 North & South Sinai Company for Water & Wastewater

North & South Sinai Company for Water and Wastewater

( NSSCWW )

Introduction


Desalination is a process removing dissolved minerals from the

saline water.

Many technologies have been developed for the sea and brackish

water, but the most common and widely used process is the reverse

osmosis (RO).

The RO desalination plant consists of 4 major systems; pre-

treatment system, high pressure pumps, membrane systems, and

post-treatment.

RO membranes are 3 types; spiral wound, hollow fiber & plate and

frame.

The major parameters affecting the RO plant performance are the

feed water temperature, pressure and salinity.

Objectives of the study


This case study is carried out to study :

the influence of main design and operating parameters on

the RO plant performance

the cost analysis of the RO plant

the evaluation of the overall system reliability for long-

term automatic operation for a certain maintenance

procedure

Considered Plant


The considered plant has been constructed at Nuweiba City in

South Sinai, Egypt.

It started the actual production on August 2001.

The required electrical power for the plant is supplied from

the local electrical power network.

The saline water is supplied from 8 beach wells near the coast

of Aqaba Gulf.

The salinity of feed sea water is in the order of 44000 ppm.

The plant consists of 5 units; each has a capacity of 1000

m3/day.

Considered Plant


Experimental Procedures


The plant consists of the following main systems :

1. Intake :

saline water is pumped from the beach wells through the deep well pumps to a PVC header and then to the sand filters (activated carbon filters)

2. Raw water pre-treatment unit :

the water is sterilized to prevent the growth of bacteria and algae

activated carbon (AC) filtration is most effective in removing organic contaminants from saline water. After new design by PX system, the activated carbon increased from 12 filters to 24 filters

the plant is provided with one cartridge filter which ensure that particles larger than 5 microns, carried over from the dual media filters will not enter the membranes This system changed from 1 filter to 5 cartridge filters (1 micron)



3. RO membrane units:

the membrane stainless steel skid consists of 15 vessels; each one

contains 5 elements of membranes of spiral wound type. Total

elements 75 SU820. After using PX system, the total 24 vessels 120

elements TM820-400

4. Post-treatment system :

it consists of chlorinating to allow chlorine residual and pH adjusting

within the acceptable range of 7.5 to 8.5 ppm. This system is suitable

for the new capacity

5. The plant is completely automatically controlled using PLC

and SCADA system

The pressure required to operate Nuweiba RO plant is 60-70 bar.



4- Feed Pump 3- Raw Water Tank 2- Carbon Filter 1- Sand Filter

8- RO Membrane 7- Turbocharger 6- High Pressure Pump 5- Cartridge Filter

11- Chemicals Tank 10- Flushing Pump 9- Aerated Tank



Simply

activated

carbon filters

(Sand Filters)



Cartridge

Filters



Chemical

Pre-treatment



High Pressure

Pump

315 kW



Degasifier



Turbocharger

(before PX)



P X

Pressure Exchanger (PX)


PX is an isobaric energy recovery device that transfers pressure from the

membrane reject stream to a seawater membrane feed stream with

extremely high efficiency :

High Pressure OUT

Low Pressure IN

High Pressure IN

Low Pressure OUT

Pressure Exchanger (PX)




During the normal operation, the following data have been

recorded daily :

1. The pressure before and after each filter, pump,

turbocharger and RO element

2. Temperature before and after each RO element

3. Thermal conductivity before and after each RO element.

Salinity of a stream is calculated from the measured thermal

conductivity

4. The mass flow rate of both the product water and brine



Site experimental work has been carried out on one RO unit of the

plant to study the effect of feed water temperature, pressure and

salinity on the productivity of the unit.

The change in the salinity of feed water was carried out by adding

product water to the feed saline water.

The pressure of the feed water was changed by the pump and by

passing the feed water.

To study the effect of temperature of the feed water, tests are

carried out during different times of the year with different ambient

temperatures.

The results are measured by the same instrumentation attached to

the RO desalination plant.

Results & Discussion


Effect of feed water pressure on the productivity

The productivity increases from 7.2 to 124.8 % corresponding to an increase in the feed pressure from 41.37 to 72.4 bar respectively



Effect of feed water temperature on the productivity

The productivity increases from 74.4 to 112.8% corresponding to an increase in the feed temperature from 10 to 32C respectively



Effect of feed water pressure on the product water salinity

The product salinity decreases from 1500 to 300 ppm corresponding to an increase in the feed pressure from 41.37 to 72.4 bar respectively



Effect of feed water salinity on the productivity

The plant productivity decreases from 120 to 100.8% as the feed water salinity increases from 15000 to 45000 ppm respectively



Effect of feed water salinity on the product water salinity

The salinity of feed water increases from 67 to 350 ppm corresponding to an increase in the feed water salinity from 15000 to 45000 ppm respectively

Economical Analysis


1. Power Consumption Cost

Power Cost (Without PX) = 7.8 * 0.22 = 1.716 LE/m3

Power Cost (Using PX) = 3.2 * 0.22 = 0.704 LE/m3

Pump Without PX With PX

kW kWh/m3 kW kWh/m3

Sea Water Pump 18 0.432 18 0.432

Filter Pump 18 0.432 18 0.432

Additive Pump 1 0.024 1 0.024

Product Pump 3 0.072 3 0.072

RO H.P. Pump 285 6.84 84.85 2.036

Circulation Pump - - 8.5 0.204

Total 7.80 3.20

Economical Analysis


2. Chemical Requirements Cost

Chemical Cost = 0.52 LE/m3

Item gr/m3 Cost (LE/m3)

Ca O Cl (Pre + Post) 20 0.03

H Cl (30%) 100 0.08

Anti Scalant 10 0.25

Na O H 80 0.04

Others --- 0.12

Total --- 0.52

Economical Analysis


3. Maintenance & Repairs Cost

Maintenance & Repairs Cost = 0.24 LE/m3

Operation Name Cost (LE/m3)

Cartridge filter 0.03

Pumps and motors 0.08

Controls and electrical, etc. 0.05

Instrument, etc. 0.03

Miscellaneous 0.05

Total 0.24

Economical Analysis


4. Capital Cost

Capital Cost = 5500000/3350000 = 1.642 LE/m3

Without PX

Capital Cost = 5,500,000 LE/Unit

Unit = 1000 m3/day

Working Days = 335 days/year

Expected Life Time = 10 years

Using PX

Capital Cost = 5,500,000 LE/Unit

Design Modify = 1,500,000 LE

Unit = 2000 m3/day

Working Days = 335 days/year

Expected Life Time = 10 years

Capital Cost = 7000000/6700000 = 1.045 LE/m3

Economical Analysis


Total Cost per One Cubic Meter

Total Cost without PX = 4.892 LE/m3

Total Cost using PX = 3.283 LE/m3

5. Labour & Administration Cost

Labor & Administration Cost = 0.50 LE/m3

6. Cost of Wells & Plant Civil Work

Civil Work Cost = 0.274 LE/m3

By using PX, the total cost decreased by 33%.

Conclusions


The following conclusions are obtained based on 5-year

operation :

1. The RO system is found to be sensitive to the variation in the

feed water temperature, pressure and salinity :

Higher feed water temperature increases the plant productivity

Increasing the feed water pressure increases the plant

productivity but decreases the permeate salinity

Higher feed water salinity reports lower productivity and higher

product water salinity

Conclusions


The following conclusions are obtained based on 5-year

operation :

2. The cost analysis of the RO plant (without PX) reveals that

the major factors affecting the product water cost are the

power consumption cost (35%) and capital cost (33.6%) while

the chemical treatment represents 10% of the total cost

3. The cost analysis of the RO plant (using PX) reveals that the

major factors affecting the product water cost are the power

consumption cost (21.5%) and capital cost (31.8%) while the

chemical treatment represents 16% of the total cost

THANK YOU


khaled

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