"Water, water, everywhere, nor any drop to drink"
Quote from the poem "The Rime of the Ancient Mariner" by Samuel Taylor Coleridge
The poem was written between 1797 to 1799 and the quote refers to a time when the Ancient Mariner was stuck in the middle of a sea. For a long time it has been a popular saying in colloquial English, but its relevance has never been more important than now. Climate change and poor water resource management is leading to water shortages in even the most developed countries. For example Houston and Sydney are using more water than they can replenish. Southern Europe is becoming drier as a result of climate change and further north Alpine glaciers – a significant source of water – are shrinking.
Increased water conservation and water use efficiency remain the most cost effective priority for supplying water. However a vital process in a number of countries to boost their supply of potable water is that of desalination, which removes excess salt and other minerals from sea water. Large-scale desalination typically requires large amounts of energy as well as specialized, expensive infrastructure, making it very costly compared to the use of fresh water from rivers or groundwater. The large energy reserves of many Middle Eastern countries, along with their relative water scarcity, have led to extensive construction of desalination in this region. Saudi Arabia's desalination plants account for about 24% of total world capacity.
Watson-Marlow Bredel has a long history of supplying pumps to conventional water and waste treatment plants around the globe. Our pumps are used in the metering and dosing of difficult to handle products in treatment process, which are used to remove suspended particles, minerals, contaminants, maintain the ph of the water, disinfect etc. Our pumps have no valves, seals or glands which mean they do not clog, leak, vapour lock or damaged when pumping these abrasive and corrosive chemicals. Similar metering and dosing applications are found in the desalination process.
The first stage in the process is pre-treatment of the raw seawater, which changes the consistency of the water and is similar to the filtration in a water treatment plant. Next the filtered water is pumped through microfilters before it is pushed through the reverse membrane filters, at pressures around 65psi. This removes the salt from the seawater. The water from the reverse osmosis stage is clean, safe and pleasant to drink. Typically around 50% of the feedwater becomes product water the other 50% is returned to the sea. A post-treatment stage of the product water, involves adding some minerals, such as calcium and alkalinity, to improve the taste and stability of the soft processed water. A similar treatment stage is used for soft dam waters as this prevents corrosion in the distribution system. In keeping with other treatment methods, chlorine is also added for cleansing and maintenance of the distribution system.
Watson-Marlow in desalination
Israel has a number of desalination plants which provide about one third of the country's annual demand of 2 billion cubic metres of fresh water and one of the most recent at Palmachim, 30 miles south of Tel Aviv, was designed from the outset with Watson-Marlow peristaltic pumps specified for a range of metering applications. Bepex our long standing distributor Israeli worked closely with Via Maris, the plant operators, to specify and install the pumps required for this 30 million cubic metre per year plant, sufficient to supply 300,000 people. A total of 30 pumps are installed at the plant, which was commissioned in 2007. Its control system is based on the Profibus DP communication protocol which is used to operate sensors and actuators (pumps) from a centralised control centre. The timing of the requirement coincided with Leroy Somer introduction of the Profibus option for their Varmeca 20 drive unit. As a result, 30 off 521VI/R2C pumps with Profibus modules were installed at Palmachim. However we then discovered that Profibus set up was not as straightforward as the RS232 and RS485 serial data signals we were familiar with on our cased pumps.
During the commissioning process Bepex worked intensively with Via Maris to initiate communications between the pumps and the control system. Falmouth and Leroy Somer UK were new to Profibus systems and how the Varmeca Profibus module should be configured, which meant that limited assistance could be given to the Israelis. However with local support from a soft ware engineering company, the pumps were seen on the system and could be controlled. However another problem occurred when Leroy Somer suddenly stopped production of the Varmeca 20 drive unit and somewhat later introduced the Varmeca 30 with a Profibus module. Via Maris needed more pumps and then we discovered that the Varmeca 30 module could not simply be dropped into to replace the Varmeca 20 Profibus without a new generic station description (GSD) file and a new configuration set up. Again Via Maris and Bepex were faced with the headache of setting up a Varmeca Profibus pump. Eventually the software company made it work!
The moral of the tale is that customers and distributors expect us to guide them in how to configure and set up our pumps. We have always been able to do this, but with increasingly sophisticated communication systems, it presents us with a greater challenge. However with the excellent support that Bepex has given to Via Maris, we will take orders later this year for more metering pumps as the Palmachim plant expands to triple its output capacity to 90 million cubic metres per year. The new pumps will be standard fixed speed pumps, with the inverters with Profibus modules housed in the environmentally conditioned control centre.
