Energy saving in the Process Industries

If there is one thing that can be accurately predicted, it is that energy costs are going to go up significantly over the short and medium term. And with energy a major cost in many process industries, managers must take efficiency far more seriously if they are to remain competitive, says Andy Parker-Bates of Parker SSD Drives.

The last couple of years have not been easy for running any sort of business, least of all a process or production operation. But five years from now we may look back on the turn of the decade as biggest move of goalposts in economic history.

Most managers and engineers have been focused on getting through the biggest economic downturn in living memory for the last year or two. It’s been very tempting to put energy efficiency on the back burner in order to deal with the urgent issues of the day.

But few can have remained ignorant of the fact that energy is climbing up the political and business agenda. Collectively, we have finally woken up to the fact that global warming is becoming critical and we have to tackle the root causes. This basically means reducing energy consumption by driving up its cost. But the cost also needs to go up in order to pay for infrastructure renewal and to finance research and development into low- and zero carbon generation technologies.

Any engineer who has opened a technical magazine in the past 20 years has probably read plenty of articles about the advantages of fitting variable speed drives to motors in order to reduce energy consumption. They are very seductive, quoting the fact that energy savings are proportional to the cube of the speed reduction and that financial payback of the capital outlay can be achieved in quick order.

Magazines often carry case studies showing how such and such an organisation has scored a real success with the installation of one or more drives. Others have explained the principles in greater or lesser technical detail. In fact it is difficult to imagine that the technology was not comprehensively picked up 10 or 15 years ago and that processing plants across the globe are now paragons of virtuous efficiency.

The perhaps shocking truth is that of all the motors in industry that would benefit from a variable speed drive, 80 or 90 percent have yet to be fitted with them!

The reasons for this are complex and multi-faceted. In some cases the payback period is believed to be too long to appease the finance department, who don’t want to take the temporary hit on their balance sheet. In other cases, the disruption to production during installation is seen as too much to consider. In yet others, the worry is that they add complexity to control systems and therefore reduce overall reliability. But most of these objections are unfounded and in reality no more than an excuse for the ‘if it ain’t broke, don’t fix it’ inertia that permeates so much of the processing sector.

Over the years all the drive suppliers have tried to stimulate their potential market with creative ideas such as pay-from-your-energy-savings schemes, leasing to avoid capital outlay, free energy surveys, and pilots schemes.

For the last 10 years most national governments in the developed world have followed suit and tried to promote the take up of drives. Various schemes have been tried; all have tried not to compromise business’s international commercial competitiveness by simply increasing energy taxes, but have instead gone for the idea of persuasion.
But with the global warming clock ticking ever closer toward midnight, there is an increasing imperative to reduce energy usage by the greater use of drives. The British government is now trying a programme called the Carbon Reduction Commitment (See boxed insert of details), which is designed to reward energy saving projects and punish those companies that make insufficient effort.

The best energy savings are made on motors simply powering pumps and fans – and they account for the majority of all energy consumed. 

Viewing the British processing sector as a whole, huge amounts of energy could be saved through the comprehensive use of variable speed drives. Most of these would be fitted to pump or fan motors. Cutting overall operating speed of such a motor by a fifth will typically save as much as 50% in energy consumption. Installation will be straightforward and need not disrupt production at all.

Typically mechanical devices are used to control flow, relief valves for pumps/liquids and louvres for fans/air. Replacing these therefore has considerable potential for saving energy. The motors operate at a constant (and high) flow rate, even though peak demand may only be required for a very small proportion of the duty cycle. Additionally such motors tend to be oversized for day-to-day needs, so that they have the capacity to cope with maximum flow scenarios which only happen very occasionally.

In many installations, such as compressed air systems, HVAC and coolant distribution, the conventional design concept is to maintain peak flow throughout the entire system then reduce it to match local demand at individual work stations. Energy wastage is inherent in such as a system design, and can be massive in a process industry environment which often runs 24/7. This reflects straight onto the financial bottom line, and also accelerates wear of machine, equipment and pipework infrastructure. 

The energy efficient alternative is the use of one or more variable speed drives. In, say, a compressed air system, typically a single drive would be used in the compressor house to provide exact load matching to the constantly changing demand. In more complicated systems, such as those in a refinery or food factory, multiple drives would be used to provide local control.
Applying the principles….
The details of energy saving vary from installation to installation and are highly dependent upon the proportions of the duty cycle that require full (or near-full) power and zero (or near-zero) power. But some fundamental principles apply. For instance a pump running at 80% speed uses only half the energy compared to one running at full speed. This can be integrated over time to show the energy savings across the duty cycle. The simple truth is that in most processing plants far too many pumps and fans run continuously at full speed, with the output regulated by vanes or valves which have no effect whatsoever on reducing energy usage.

Translating this into a typical industrial application, a single 75kW motor running continuously will waste £15,000 worth of energy every year. And this can be multiplied by the number of uncontrolled motors across the plant. It is not difficult to envisage energy and energy bill savings of 20-25 percent across a plant.

The retrofitting of drives in variable flow applications across the British processing industries could yield total energy savings of gigawatt proportions. This would have two benefits: for the individual companies, there would be big cost savings that would help ensure commercial competitiveness; more altruistically there would be a significant reduction in carbon production and therefore reduced global warming.

As noted earlier, the vast majority of motors in industry remain uncontrolled. This is also true of other sectors where motor use is common, such as HVAC. However, other sectors have been reaping the benefits of drives for many years; these include lifts and escalators, cranes and winches and the water industry.  It has been estimated that no more than one in seven motors used in UK applications are controlled by an AC drive. There is a significant margin of error here, the figure may be one in 10 or 12, but this does not alter the basic truths that global warming could be significantly reduced and that motor operators can cut their energy bills on an on-going basis.

There are many arguments made to the effect that the capital investment required to install drives is so high that payback is not viable, but in most cases the cost is not as high as it first appears. For instance, production need not be disrupted at all and there are consequential savings in having to fit and maintain mechanical valves and vanes. There are also additional benefits in improved product quality, reduced waste and scrappage, reduced wear and tear on field equipment, etc.

So much for the theory, but how can this be applied practically, perhaps in the face of a skeptical finance director? One way may be to calculate the running costs of the largest uncontrolled pump or fan on site over a six or 12 month period, then recalculate it, assuming a drive has been fitted, and adjust the result for installation costs.
Accounting for change…..
A few years ago, many accountants would not be interested in listening to such proposals, but the financial environment is changing. Energy costs are projected to rise markedly over the coming years. Additionally, definitions of commercial competitiveness are changing; the days when low cost production regions produced low quality products are drawing to an end.

A more sophisticated approach would be to commission a partial or full energy audit. This is a measured review of all or major energy consuming equipment within the processing plant.


Options for reducing this can then be coolly reviewed. This may include changing the lighting technology, shutting down machinery when it is not used (say over the weekend), controlling refrigeration levels; in a plant environment the options for improving motor control with variable speed drives is likely to be extremely attractive.  

It is relatively easy to understand the saving potential of drives in greenfield and new build situations. Retrofitting drives to uncontrolled motors or to replace less sophisticated controls can also be attractive. Then there is a third class of proposal to consider; replacing existing drives with newer models – the justification is the same, compare the running costs before and after the upgrade. (There is also the improving technology argument that is often used when directors want to renew their company cars!)

The latest generation of drives is 5-10 percent more efficient than their predecessors. Work that through on a medium sized drive in a hard working duty cycle and it is fairly easy to identify savings of £500-£1,500 a year. On top of this, the new drive will provide technical advances that can improve plant uptime and control as well as providing more data, etc. The new drive is also likely to be 25 percent smaller than its predecessor, freeing up valuable floor space and reducing cooling requirements. 

A few short years ago non-technical managers were likely to dismiss the energy saving claims related to drives as the exaggerations of over-eager control engineers. But that is no longer the case. The pressure is on to reduce energy consumption and the government is finding ways to encourage new thinking as it strives to reach its international carbon reduction commitments.

Parker Hannifin Ltd
Warwixk
Warickshire

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