Water is an ever-more precious and increasingly expensive commodity, and demand to reduce the quantities used in industrial processes has never been greater. John Crane Safematic’s commercial manager Jussi Sorvoja examines how today’s advanced seal water monitoring and control equipment can help cut your plant’s water usage and looks at some of the points to consider when choosing the correct meter for your application.

In many modern industrial sectors, the need to cut costs and conserve resources has begun to focus increasing amounts of attention on the water that is used to quench and lubricate the mechanical seals used on pumps and other process machinery. These processes present significant opportunities to save water, and this is especially true of mechanical seals that operate in harsh environments where high temperatures, high pressures and chemically aggressive elements are present. For example, the pulp and paper, and chemical and mining industries are sectors that have traditionally used significant volumes of water to cool mechanical seals operating in their demanding environments. The pulp and paper sector in particular is one that has taken significant steps in this area and is now leading the race to cut water usage, and, by doing so, reduce overall operating costs.

Seal water is used to cool a mechanical seal and lubricate the seal faces. This creates specific water flow requirements depending on the type of seal and its specific operating conditions, and while exceeding these flow requirements does not bring any benefit in terms of improved seal operation and reliability, it does generate extra costs due to increased water consumption. The financial driver to reduce water consumption is powerful enough in itself, but growing concerns for the environment coupled with the need to conserve natural resources such as water – which the pulp and paper industry often takes directly from rivers – are now playing an increasingly important role.

Reducing consumption

The process of examining what can be done to reduce water consumption needs to start with the actual monitoring of the water flow, and this is where the flow meter comes in. The flow meter must be designed to minimize any internal pressure loss during operation; this ensures that there is no danger of the seal overheating due to pressure or flow loss. The unit’s design should also be optimized to prevent the risk of clogging from any foreign bodies present in the water. This can be a significant hazard when water is drawn from natural sources rather from a main supply, which can lead to pressure loss. Fortunately, technologies are improving all the time and the modern breed of seal water systems can monitor the water flow with extremely high degrees of accuracy and reliability, without affecting the pressure but still giving the user a very clear picture of the situation. Many meters incorporate some form of integral flow indicator and pressure gauge, which makes continuous status monitoring easy and provides reassurance that everything is operating as it should.

In addition to monitoring the flow, the meter’s other principal job is to adjust the flow rate and pressure to their optimum levels. By only providing the water that is actually needed, (rather than exceeding this requirement in order to be safe) a good flow meter will significantly reduce water consumption and generate significant savings. But the advantages of proper flow control don’t stop there, and some of today’s better units have also been proven to increase the operational reliability of the pumps whose water supply they control.

By assessing the way the seal is using water and detecting any internal seal leakage, some flow meters can provide valuable information that can help predict a failure of the seal or its packing. (For this reason, it is usually a good idea to make sure that an electronic alarm option is available so that the meter can provide direct warnings to the operator if a failure appears likely.)

Minimizing failure risk

A good flow meter can also help the user determine the likely maximum volume of seal water consumption. This type of information can be equally invaluable to the plant operator in terms of planning maintenance schedules and minimizing the risk of a dramatic seal failure and all the financial penalties that can follow. This ability to promote trouble-free operation of process machinery in all types of conditions is a key hallmark of a good flow meter and can make a significant contribution to helping the end-user to achieve the maximum life-cycle profit on their investment.

Of course, this places a significant demand on the flow meter itself. The unit must be sufficiently robust to withstand the harsh operating environment in which it will be used. Process demands often require that the unit be resistant to such things as chemical attack or corrosion, and the plant operator must be certain that the unit in question is able to meet all the process demands at the specification stage. Harsh environments usually involve significant operating temperatures (anything up to 100oC) so the meter must be able to withstand this. Similarly, pressure requirements are often similarly high, so the ability to handle something like a 60 bar pressure is also useful.

The better monitoring and control units normally offer a compact design optimized to ensure that it is user-friendly. This type of seemingly small design element can assume much greater significance once the unit is in place and operating, so it is important to ensure that the meter you choose offers such features as an integrated check valve that can be used to flush the unit clean during operation. An easily cleaned, glass-fronted display can also make life much easier for the operator when the unit is being used in a dangerous or dirty environment. Similarly, the ability to clean the monitoring and control unit while the equipment it serves is still operating can also prove to be beneficial in terms of process availability and reduced maintenance times.

A comprehensive package

One design is never going to fit every application. The better manufacturers will offer a variety of different units for use with packing or single flush seals, quench seals and double mechanical seals, and this enables them to provide a comprehensive package that includes a flow meter for each application in the customer’s facility. That package should not stop at the products either. The plant operator must be able to access reliable technical support from the unit’s manufacturer. This can pay huge dividends in terms of selecting the correct unit for the job at hand, as well as time saved if problems do occur. Access to technical support must be quick and easy from the customer’s point of view.

Choosing the correct flow meter can also simplify the initial set up of the seal water system. The better meters can be adopted as a standard component of the seal water system, which eliminates the traditional headache of accommodating a variety of different piping compo-nents, valves and couplings. This makes the installation of the system a faster and less complicated task than it might otherwise be and increases the likelihood of achieving an effective and leak-free installation on the first attempt.

The cost savings and efficiency benefits that monitoring and metering equipment can provide are at their greatest when the units in question form part of a genuinely integrated seal support system. When the flow meter has been designed specifically to operate with other equipment such as water filter units there are obvious synergies that come into play, both in terms of installation and operational benefits.

Choosing the correct flow meter for a particular application requires careful thought, liaison with the manufacturer and attention to detail. If you get these stages rights you can help the environment, make a huge difference in your water consumption rates, and boost your bottom line.

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