Go with the flow01 April 2006

Energy efficiency is near the top of every industry's list of business priorities, especially given its impact on the cost of operations and product margins. In addition to conventional means of gaining productivity improvements, in many processes advances in technology can, and do, contribute significantly to the overall operational cost reductions and benefits.

Among the challenges faced in manufacturing and process-driven industries is how businesses can avoid wasted energy and, in particular, those process industries that are dependent on the reliability and accuracy of level and flow measurements. In the past, this may often have relied on operations and technical staff checking gauges manually, recording levels and flows, and making any adjustments. This has required analysis of the product itself at some stage in the process, feeding back the results to operational staff. They then make adjustments to bring the product or process back to the desired status.

Take the relatively simple example of pumps. All processes rely on these to trigger increases or decreases in flow, but are equally dependent on the equipment that is monitoring the position of the valve, whether it is open or closed, or the status of the actuating mechanisms. Similarly, the measurement of the flow of fluids, reagents, mixtures and gases requires efficient and accurate monitoring, if the desired reductions in waste are to be achieved.

The types of processes that use flowmeters may be continuous, or batch oriented. They may be time driven, placed at the start of a reactive, ageing or conditioning process, before triggering a subsequent action. Such operational processes use different types of meter, linked to sensors and device control mechanisms, feeding status information back to control rooms. Here, the status and positions of valves, pump operations and flows are identified through alarms that reduce performance and ultimately waste energy in the manufacture of the end product.

Accurate measurement of the flow of material through the various manufacturing stages is vital to reduce energy waste within, or by, the process. However, in many industries, processes are controlled and monitored in terms of the mass of the raw materials, reagents and products, rather than their volume.

The modern flowmeter needs to be able not only to monitor fluid flows, but also provide diagnostic and status information about itself and, through the use of a common set of electronic components, sensors and housings, provide a relatively simple installation. Connectivity between the installed monitoring device and the plant management systems uses a range of interfaces, from wired to wireless, and builds on known and proven communications techniques.

Of the four examples of flowmeters detailed in the box item on p20, the electromagnetic and ultrasonic devices may be described as 'non-invasive' and perhaps easier to provide as a retrofitting or initial installation solution. The vortex and Coriolis design of meter require insertion in the path of the flow for the measurements to be taken.

In many industries, but especially food and drink, the blending and mixing operations that deliver the end product are dependent on accurate and reliable mass flow measurements. Prior to the development of the coriolis mass flowmeter, the measurements were achieved by calculation and not direct measurement, by using flow rate, pipe dimensions and density of the fluid being monitored. There is clearly room for error in an approach that is dependent on two key measurements, whilst at the same time offering limited scope for cost savings, minimising waste or offering unattended operations. The direct measurement of mass flow rate must be based on acceleration of the fluid and measurement of the resultant force - the Coriolis effect.
Of course, not all developments have been centred on the meters themselves; other techniques of deriving process efficiencies, cost and energy savings are based on the combination of metering, communications and analysis tools. At the meters themselves, performance improvements have been achieved by applying innovative electronics, in combination with Digital Signal Processing (DSP). DSP technology and devices are common to everything from mobile phones to modems, data communications equipment and multimedia PCs, and provide a near de-facto standard approach to process control.

Capturing the data recorded by devices such as flowmeters is actually only the starting point to realising operational and financial benefits, and today a range of software tools provide the solutions to the next essential stages of reporting, analysis and initiating actions that enable the reductions in energy use and costs to be achieved.

A typical example of available software tools comes from Emerson Process Management. The AMS Suite is made up of applications running on a PC platform to provide operational information in real time. The 'real time optimiser' component uses the web browser to view asset information such as alerts, motor and pump performance trends or faults across the factory network. Similarly, 'intelligent device manager' allows communication with the flowmeter or other device through existing control networks, or open systems-based communications networks.

So, with all of this technology around, the combination of intelligent and accurate mass flow meters, coupled with use of open, standard communications networks is making the job of monitoring the process efficiencies simpler. Not only can the use of the latest designs of flow meter lead to energy savings, but also can lead to lower plant upgrade costs. For example, in the US, a leading fruit producer has almost halved the number of mass flow meters installed during a plant upgrade by installing Krohne's Optimass Coriolis flow meter.

The combination of communications and the latest generation of high-tech flowmeters can drive overall improvements in process efficiencies and lead to significant benefits.

Emerson Process Management has used Micro Motion Coriolis technology to enable Italian company Euroelettra Sistemi to design a skid-mounted blending system for ceramic slip and colouring materials. Compared to the traditional approach of mixing and maintaining mass quantities, this has led to a 30% improvement in production quality, as seen by Euroelettra's customers. Using the technology and measurement accuracy of the Micro Motion Coriolis flowmeter from Emerson, Euroelettra Sistemi can now consistently monitor and control both the density and flow rate of the components being blended.

Conventional production of coloured ceramics involved preparation and blending over a number of days of the base suspension, or slip, and the colour, in quantities of tens of tonnes at a time, in ball mills and agitation tanks. Once the process was complete, the wasted deposits on the tank walls needed extensive cleaning prior to the next batch. Using this flowmeter, the company was able to deliver in this skid-based system:
- Major savings in production space, since mixing tanks are not required when the blending is done, only at the time of use.
- Electricity and water consumption is reduced due to elimination of the requirement for continuous agitation and significantly reduced cleaning.
- Production repeatability and consistency have reached an unheard of level of 90%, compared to a maximum of 70% previously, this owing to the close control over the colour mixing.

In this example, diagnostic information from the core processor of the flowmeter, using a Modbus connection, enables the blending system to identify any build-up of material within the flowmeter's measuring tube. This ability to signal when cleaning is required has increased equipment availability by around 50% and improved overall efficiency, with a reduction of production rejects of more than 90%, compared to previous trials.

Getting the measure
That said, not every measurement tool uses the coriolis effect, and one of the most interesting examples of how today's technology can deliver improved production efficiency and energy savings uses an electromagnetic meter.

A world-leading ingredients manufacturer has installed Krohne's electromagnetic flowmeters to measure more precisely the volume of effluent discharged from its plant, so it can control water utility costs more accurately. Companies can lose tens of thousands of pounds a year through inaccurate measurement of trade effluent that is pumped into sewers and charged for by utility companies.

This manufacturer has a production plant operating 24 hours per day, 365 days per year, with effluent discharges that can average 33,000 cubic metres per month. These flows were previously measured ultrasonically, in conjunction with a classic flume. However, such arrangements do not give a direct measure of flow, which can result in a +/- 3-5% error in reading, equating to a difference of 1,500 cubic metres per month.
The ingredients manufacturer has now installed two electromagnetic flowmeters from Krohne, which improve measurement accuracy significantly. The instruments are accurate to +/- 0.3%, equating to just 11 cubic metres per month.

The flowmeters are installed in-line with the effluent discharge feeds and consist of a primary head installed in the pipeline itself, and a signal converter, to transmit the measurement readings of the effluent discharged.

"Using these flowmeters has improved significantly how accurately this company measures trade effluent," said Chris Ringer of Krohne. "Previously, it used ultrasonic level but, given the volume of effluent that was generated and their low accuracy, the company could have been paying utility bills that are substantially different from the actual volume of effluent generated - and they would have never known that."

Flowmeters in use today
Electromagnetic flowmeters - using the effect described in Faraday's laws of electromagnetic induction, a magnetic field is generated between coils placed on either side of the flow to be measured, while electrodes, at 90 degrees to the flow, are used to measure the induced current.

Coriolis Mass flowmeters - these are based on the Coriolis effect, produced where a fluid or gas is subjected to an oscillation perpendicular to its direction of movement. If the measuring pipe is driven with a constant torque, the Coriolis force produces either a braking torque or an accelerating torque (dependent on the flow direction) that is directly proportional to the mass flow rate.

Ultrasonic flowmeters - compared with the Coriolis effect, a much more straightforward idea. In essence, the time delay is measured between sensors that simultaneously send and receive the ultrasound signal, and are mounted on the pipe where the fluid flow is to be measured. Some more recent innovations use three signals to provide a 3D picture of the flow through the pipe.

Vortex flowmeters - based on the phenomenon known as the Kármán vortex street, where vortices are formed alternately on either side of a flat object in the measuring tube as fluid flows past. This vortex shedding down each side of the object is directly proportional to the volume flowing past the measurement point. As in all meters, the measurement is converted into a digital signal and relayed back to the monitoring tools.

SOE

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