Waste to Energy Analysis

Kuchl, Jul 08, 2015

Analysing the energy efficiency of WtE

The manufacturing of SRF in a single pass is not a new concept. However, with the environmental efficacy of alternative fuel production under seemingly increasing scrutiny, a one-step process is of growing importance, believes Peter Streinik, Head of Business Unit Waste at UNTHA.

There can be no disputing that alternative fuel production is being increasingly acknowledged as a valuable part of the global resource agenda. Whilst it has long been a staple energy source in parts of continental Europe, its value is now being embraced in wider parts of the world too.

In developing countries such as parts of Asia for example, where waste streams are less refined and waste management infrastructures not as established, the role of SRF is coming to the fore. Solutions are even being developed for materials that we would consider a challenge to process for WtE in the West, such as mixed textile and rubber footwear products.

It seems a number of cement producers are taking proactive steps to improve the WtE landscape too. In South East Asia, for instance, we’ve seen a growing number of cement kilns shortening the supply chain by opening their own waste plants. By closing the loop, they are ensuring the security of their input energy materials, safeguarding the specification to which their SRF is produced, and making productive use of resources that may otherwise be dismissed simply as ‘rubbish’.

Whilst SRF specifications are defined in every instance, the globalisation of alternative fuel production does seem to present slightly differing terminologies and opinions as to what constitutes SRF. A 50mm particle size can suffice for some calcinators, for example, with others stipulating a 30mm. Elsewhere, some main burners require 30mm in three dimensions, which could mean an output size as low as 15mm. It all depends on the technology being used. However, with calorific values typically rising as the output size requirement is lowered, the cost of production will also increase.

One thing that remains an increasingly uniform priority worldwide, however, is the need to produce this alternative fuel in the most efficient way possible, without compromising on fuel quality or the safety of operatives. But as the global spotlight shines brighter on SRF, the environmental efficacy of its production seemingly attracts greater scrutiny.

This is perhaps unsurprising. SRF production and usage must reap commercial advantages of course. But to truly commit to and improve our worldwide sustainability agenda, those involved in the market should also consider the energy efficiency of WtE technologies, not just outputs and the bottom line.

If electricity consumption during the production process is excessive for instance, the parasitic load of WtE plants has to be questioned. On the other hand, by designing processes and commissioning technologies that lessen electricity consumption, SRF manufacturers can maximise the net environmental gain of their operations. And organisations with a watchful eye on costs will reap the financial benefits that come with energy savings too.

There are a number of ways to achieve greater energy efficiency within an SRF production plant, and feed-in arrangements seem the obvious starting point. If pre-sorted input materials can be fed into an SRF shredder using just one wheeled loader rather than two pieces of plant such as a grab and shovel, this reduces the amount of diesel – not to mention labour – required to power the kit.

This benefit is magnified if SRF can be manufactured in a single step shredding process, as the cost to procure and run one machine is naturally less than it is to operate both a pre and post shredder.  It is not uncommon for a dual-stage diesel-fuelled SRF production process to run at £25-35/tonne in operating costs alone, for instance.

But replace with electricity powered shredding technology – and better still a single electric-drive machine that can produce SRF without the need for two shredders – and such energy consumption and associated costs are soon eroded.

Water-cooled synchronous motors play a significant role here. In our new waste shredder for example, we’ve implemented an Eco Drive concept that has taken four years to engineer, develop, trial and roll out. This enables our motors to work tirelessly without overheating. The machine can achieve the same tonnage as traditional static shredders, but with 50% less power consumption. When compared with mobile diesel shredders, the power savings can reach up to 220%. This enhances the environmental efficacy of the operation and could equate to electricity savings in excess of £500,000 over the lifetime of the machine.

In terms of the wider plant, by taking advantage of ever-more sophisticated sorting technologies, it is possible to produce a high quality, well-defined fuel, with fewer pieces of equipment. Yes in some instances a simple conveyor, over band magnet and wind shifter may be required, in addition to the shredder and in-feed/out-feed kit. But with experience and innovation, increasingly refined plant designs are possible. Gone are the days of multiple machines and auxiliary equipment, and thus otherwise avoidable energy consumption.

This goes to show that the drive to adopt a more environmentally sound approach to SRF production should not restrict producers with unnecessary ‘red tape’, nor should it erode their margins. On the contrary, more energy efficient considerations should reduce unnecessary financial spend, not to mention the impact on the environment.

It could also be argued that thinking about SRF production from this perspective will futureproof operators from the potential industry developments beyond their control. It must be acknowledged for example that, really, the alternative fuels market is in its infancy at present. As it grows and matures, the regulations that govern it will undoubtedly evolve too. So, as with any business environment, the WtE sector will require increasingly sophisticated methodologies if operators are to thrive commercially, whilst remaining compliant.

Being more environmentally responsible than is perhaps necessary now, will help to ensure greater compliance when WtE production protocol inevitably becomes more stringent.

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