This paper presents the three center design implemented in the South Israel (Ashkelon) seawater reverse osmosis (SWRO) desalination facility with guaranteed production capability of 100 Mm3/year. The facility design is based on the concept of a Three-Center Design: a pumping center, a membrane center and an energy recovery center.
The BOOT 100 Million m3/year Ashkelon Desalination Plant is comprised of two identical plant facilities - North and South – which started operation in the middle and at the end of 2005 respectively.
The plants are based on the concept of a Three-Center Design: a pumping center, a membrane center and an energy recovery center. A pumping center comprised of 3+1 large High-Pressure (HP) pumps, 5.5 MW each, supplies seawater to all 16 RO banks, 105 pressure vessels in each, via a common feed ring. An energy recovery center, made up of 40 DWEER, collects pressurized brine from all 16 RO banks, transfers the energy to the seawater and pumps it to the same common feed ring. The scheme of the Three-Center Design is presented in the attached diagram.
The Three-Center Design is flexible and efficient in operation. The 16 RO banks can operate with one, two, three or four high pressure pumps and demonstrate a wide range of productivity. In each operation mode pumps demonstrate high efficiency, close to 90%. The start of the first HP pump against the RO banks is smooth; and the pressure can be increased as slowly as required. The procedure on pump hook UN and UP is fast and simple.
All RO banks demonstrate equal productivity, recovery, and feed flow distribution.
Decreasing the number of pumps in operation with all RO banks on-line allows a significant reduction in specific power consumption, which is important during the winter period when the client requires less water.
Stopping one RO train does not cause a reduction in water production, as the other banks can compensate production with increased pressure. The process of RO bank stoppage is fast and simple. Each RO train can be unhooked individually, depressurized, flushed, cleaned, drained, filled, pressurized and hooked up.
The ER Center is made up of forty DWEER, divided into 9+1 subsystems of four DWEERs each. The ER subsystem can be UN and UP hooked independently. Stoppage of one or two ER subsystems does not affect water production or recovery, due to the fact that each subsystem can increase its capacity within a few seconds by a faster changing of cycles and increasing circulation pump flow via a frequency converter. The cost of such flexibility is larger pressure loss in the DWEER.
Due to the ER system’s high efficiency, 96%, it is cost effective to run intake, pretreatment and ER at full capacity, independent of actual production. Decrease of recovery results in a decrease of average osmotic pressure in the membranes and reduces power consumption.
The great flexibility of the system and the ability to change production capacity in next to no time, together with features of lowered specific power consumption per m3 of product during partial production, with all RO banks in operation, is critically important. This feature allows following hourly changes in energy cost by producing more water at night when the energy cost is low and reducing production during peak hours when the energy cost is high.
This flexibility, in cases of payment for maximum demand, allows maintaining actual power consumption very near to maximum demand and, by this, significant savings in energy expenses.
The actual operation of the cascade boron removal system shows flexibility and simplicity in operation, high availability, and independent operation between the different parts. The required Boron level was easy to reach in every stage of the Cascade. The stages of Cascade operate in a safe middle position, far from process limiting conditions.
The commissioning procedure was simple and fast. All technological parameters such as power consumption, reagent consumption, product TDS, B ion, Cl ion, Ca ion, LSI and turbidity were exactly reached at first start. This smooth commissioning procedure was possible due to the comprehensive mathematical modeling system performed on the entire desalination plant during the design stage. This modeling system includes both global level and local models. These models reflect, without exception, all chemical and technological features of the desalination plant.
The thousand piece technological puzzle formed a complete picture, with no mistakes – no small achievement in a desalination plant the size of the Ashkelon project.