Pembroke RO Plant Visit 9th July 2010

A Walk With a Difference.

Some 20 ramblers turned up for today’s visit to the Pembroke Reverse Osmosis Plant, ably organised by our member Godwin Darmanin. We were lucky enough to be led around the plant by the plant manager himself, engineer Warren Vella. Mr Vella exhibited his deep knowledge of the process during the tour.

We were first given an overview of the whole RO process. Malta’s three RO plants (Pembroke, Cirkewwa and Ghar Lapsi) produce 55% of Malta’s total potable water, with the Pembroke plant producing half of the total RO amount. The three RO plants consume 25% of Malta’s total electricity generation capacity. So no electricity from the power stations means no RO water.

The Pembroke RO plant itself consists of Plant A and a newer Plant B, with each plant having six trains each. The total capacity of both plants is 54,000 cubic meters of water a day.

After the introduction, we went outside to view the large pipe picking up seawater pumped up from around twelve boreholes situated on the foreshore. This is then fed to a sea-water reservoir. This method constitutes the first filtration of the seawater and ensures that the water is free of solid particles, fish, etc.

From this reservoir, the sea water is pumped to the first set of filters.

From here, the water goes to a high pressure pump, driven by a one-megawatt electric motor, where the pressure is raised to 70 bar. This water goes to a set of RO filters, with the outlet producing potable water. The pressure drop across the RO filters is only 2 bar, so the outlet pressure is still at 68 bar. It would be a waste of energy to simply exhaust this water to the sea. So the RO plant employs energy-recovery devices.

In Plant A, the outlet water is conducted to a turbine that drives the 70 bar compressor through a shaft on the other side of the electric motor, thus supplying some of the driving power to the compressor. In this way, energy recovery is around 40%.

In Plant B, energy recovery is through a series of pressure exchangers. This is a more advanced technology. Each pressure exchanger contains only one moving part, and is maintenance free. Moreover, energy recovery is around 80%. So this is obviously a lot more efficient than the older technology.

The outlet from the RO filters consists of potable water of very good quality. After suitable treatment, this water is then pumped to reservoirs, mixed with boreholes water, and eventually finishes up in our households.

All in all, a very interesting tour.

Some photos below.

Two RAM walk leaders

Our tour guide explaining a point

The sea-water reservoir

The first set of filters

Plant A, with turbine energy-recovery systems

Plant B, with pressure exchangers energy-recovery systems

The RO filters

The control room