Improving Water Pumping Performance

Pumps and Pumping Stations Form a Vital Component of the UK's Water Distribution Network, Providing the Means by Which Huge Quantities of Water are Transported Across the Country

Pumps and pumping stations form a vital component of the UK's water distribution network, providing the means by which huge quantities of water are transported across the country. In the Thames Water region alone, there are 288 pumping stations supplying an average of 2,600m litres of drinking water every day. These are joined by another 2,530 sewage pumping stations which are used to remove a daily average of 4,400m litres of wastewater.

Each one of these pumping stations uses vast quantities of energy, with 1,286GWh of electricity used to pump and treat water and sewage in 2012/2013*.

Multiply these sorts of figures across the UK and it quickly becomes apparent why the water industry ranks among the top users of energy in the UK.

Not surprisingly, the UK's water companies have set themselves the target of significantly reducing energy consumption, both through internal programmes involving refurbishment and replacement of aging or inefficient equipment, and external programmes aimed at educating the public on reducing their water use.

Furthermore, many water companies are now shifting towards a total expenditure (TOTEX) approach to investment, which focuses on the total life costs of an installation.

How can flowmeters help improve pump efficiency?

When it comes to pumping, there are various ways in which efficiency can be improved, ranging from replacing older units through to installing the latest energy efficient motors and variable speed drives.

The use of flowmeters in clean and waste water pumping applications can also have a significant impact on pump performance. By helping to match pump speed to the flow rate, flowmeters can help operators to save energy through more effective control of the speed of the pump motor.

Using a flowmeter can also provide a useful indication of overall system efficiency, by helping operators to identify whether the flow of water is properly matched to the speed of the pump. For example, if flows are restricted even with the pumps running at full speed, then this may be indicative of a blockage somewhere upstream of the flowmeter.

Furthermore, keeping a record of flowmeter data can help to determine the long-term performance of a pump, with any variations in flow totals being indicative of a potential problem or deterioration.

As well as helping to monitor and optimise pump efficiency, flowmeters can also help to fulfil several other key roles in both clean and waste water applications, including:

• Calculation of distribution system losses - given the energy intensive nature of pumping, it is important to ensure that every last drop of water is accounted for. Measuring the quantities of water being pumped around a network will provide the data needed to help measure distribution losses, enabling leaks to be quantified and pinpointed
• Calculation of bills for water supplied
• In the case of wastewater pumping, to monitor flows of effluent to the environment in order to satisfy any relevant discharge legislation

Up until the emergence of magmeters in the mid-1980s, the most common method of metering in pumping applications was to use orifice or venturi technologies. These techniques deliberately created a pressure drop in the main proportion of the flow, which had an adverse effect on pumping efficiency.

Making the right selection

For the best levels of long-term accuracy and performance in pumping station applications, it is important to choose the right type of flowmeter. Selecting the appropriate flowmeter for the application depends on a number of factors, including the desired accuracy and repeatability and also the characteristics of the installation.

Various types of flowmeters can be used in pumping station applications, with the most commonly employed being mechanical, ultrasonic and electromagnetic flowmeters.

Preferred for their lost cost, mechanical flowmeters have several drawbacks which can affect their performance in pumping applications, particularly when handling effluent flows that may contain high levels of particulate matter. Wear and tear on the moving parts of mechanical meters can have a detrimental impact on their measurement accuracy, resulting in correct flow measurements that can lead to reduced pumping efficiency. Depending on the characteristics of the installation, mechanical meters will only ever be truly accurate within the first few months of operation.

Where ultrasonic flowmeters are concerned, their lack of moving parts immediately presents a more preferable alternative. In particular, developments in clamp-on technology are making ultrasonic flowmeters increasingly attractive, with no requirements to excavate or disturb pipelines. However, they are generally most effective in locations where there is at least 10 pipe diameters of uninterrupted pipe length, in order to minimise the impact of velocity profile distortions that can affect accuracy.

Electromagnetic flowmeters have none of these problems. Compared with other flowmeter types, electromagnetic flowmeters offer greatly enhanced accuracy and repeatability throughout their operational life, with uncertainty of ±0.2 percent reading or better. With no moving parts, they do not suffer from problems with wear and tear and require no upstream strainers to filter sediment. A choice of flow primary linings affords further protection against high sediment flows, with users able to choose from a variety of materials, including ceramic linings for particularly abrasive flows.

Electromagnetic flowmeters are also better at handling distorted flow velocity profiles, greatly reducing the amount of piping required upstream and downstream of the meter.

Source: Process and Control

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Taxonomy

• Technology
• Flowmetering
• Pumps Installation