Is there a best practice alternative fuel production process for the cement industry?

Kuchl, Jun 12, 2016

Refuse Derived Fuels | Alternative fuels

With such a fragmented waste landscape across the globe, is it possible to create a best practice waste to energy process to feed alternative fuel to the cement industry? That was the question that international journal ‘World Cement’ put to Peter Streinik, UNTHA’s Head of Business Unit Waste, a few weeks ago...

“If we were to provide an over-arching statement about the waste to energy landscape globally, it would be safe to say that, generally, there is growing acknowledgement for the role that alternative fuels play in our modern resource agenda. Granted, a ‘reduce and reuse’ philosophy should be prioritised to minimise waste creation and ensure the optimum use of raw materials – and where possible, recycling activities should be pursued thereafter. Yet with ever-depleting fossil fuel stock, comes the need to source an alternative, high quality and robust energy source for the cement industry. Thankfully, waste is increasingly recognised as a renewable resource that can plug that gap."

When the waste to energy market itself is examined in a little more detail however, we see a number of variations from one location to another. What is regarded as a Solid Recovered Fuel (SRF) in one country may be called a Refuse Derived Fuel (RDF) in another. It is also important to note that, generally, a high calorific, homogenous <30mm material is required for a main burner, whereas a 80mm particle would suffice for a calciner. Yet both may be referred to, interchangeably, as an RDF or SRF. The most crucial thing is that, if the cement company’s specification is entirely satisfied, the ‘name’ given to the fuel is largely irrelevant.

The nature of the waste and the wider waste management landscape also presents variants that need to be considered. If we look at the waste industry in Europe, for example, the market is very diverse. Countries like Germany and Denmark have long been harnessing the potential of alternative fuels therefore their waste infrastructure is quite advanced. Investment has been significant and WtE plants are considered something to be proud of; a valued part of the community. These facilities often even have education centres that teach local schoolchildren about the energy generation process and the importance of living a sustainable life.

In Poland on the other hand, the market is in its comparative infancy, yet it is evolving at a rapid pace. The Municipal Cleanliness and Tidiness Act meant that in January 2012, citizens were no longer the legal owners of waste. Municipalities – referred to as local authorities in some countries – were then given 18 months to create a modern waste management system for their district. Some progress was made but still too much Municipal Solid Waste (MSW) was being sent to landfill. New legislation therefore came into place this January 2016, to prohibit this disposal method being used for high calorific (6000kJ/kg) materials.

This goes some way to explaining why PGK EKOM proactively overhauled their waste strategy last year. This forward-thinking public sector company in Nysa, south west Poland, invested heavily in the creation of a state-of-the-art RDF production plant capable of handling 4,000 tonnes of MSW per month.

A global search for the best-fit waste processing technology began in January 2015. Machinery was required to shred pre-sorted MSW that had been collected by local government and separated on a purpose-built sorting line. The brief was to process 12.5 tonnes of waste per hour and produce a 30mm fuel for the main burner of a local cement kiln.

Given the stringent quality specification that had to be achieved, it was deemed that a dual step shredding solution – with a pre and post shredder – would best satisfy the requirements of this plant. The tender criteria prioritised the importance of the machines’ proven robustness, ease of maintenance and operator safety. The energy efficiency of the overall solution was also key – there seemed little point working so hard to manufacture a sustainable fuel if the power consumption of the plant prevented any net environmental gain.

Following a thorough audit of the marketplace PGK selected the UNTHA XR waste pre-shredder with 65kW motor, Ripper cutting concept and screen bars capable of achieving a consistent 215mm particle size. A post (secondary) waste shredder – the UNTHA TR – was also chosen to complete the process, by shredding down to the homogenous 95% <30mm requirement.

The shredders were delivered from Austria in July and were fully installed and commissioned by November. Once fully operational, PGK found the throughput to be higher than expected, with 14 tonnes easily achievable per hour. Low noise levels have also been cited, which protects operator wellbeing and minimises disruption to neighbouring communities. And foreign object protection, a quick change cutting system and an ergonomic design for easy access, has delivered maintenance simplicity to date.

As production continues, an eco-drive concept with water-cooled synchronous motors will ensure the shredders work tirelessly without overheating. This energy conscious design feature will also minimise electricity consumption, enabling a return on investment to be achieved in five years’ time.

In light of the rigorous tender process required for this public sector plant, many people would consider the design and technology of this facility as a best practice Waste to Energy model that could be replicated elsewhere. And to a certain extent this would work. However, when recapping on one of the aforementioned points, about the diverse nature of the waste landscape globally, a ‘one size fits all’ mentality is not always ideal.

In South East Asia for instance, we see huge market fragmentation. Singapore was the first country to declare waste a national resource, and Thailand has since followed suit as a result of a pro-environment Government defining the country’s energy policy and waste issues making the national news. Yet in developing economies such as Vietnam, there is much more work to be done.

Here there is no waste collection system, meaning MSW is incredibly mixed, with organic content as high as 60%, moisture typically 70% and construction and demolition waste often present. Without any careful pre-separation of materials, producing a specification-driven fuel is therefore no mean feat. That’s not to say the value of Waste to Energy has not been acknowledged, but it is definitely an emerging market at present.

Global cement giant LafargeHolcim, however, is actively pursuing a worldwide ‘green manufacturing’ strategy to reduce CO2 emissions, improve energy efficiency, reduce non-renewable fossil fuel use and lower the clinker factor in finished cement. The use of waste as an alternative fuel in Vietnam fulfils this brief entirely.

Here, LafargeHolcim is shredding a prevalent yet notoriously difficult material to process – footwear production ‘waste’. Comprising a mixture of tough materials – rubber, textiles, plastics, metals, sponge, reinforcements, and more – this waste requires a very robust shredding solution.

An XR3000C waste shredder has therefore been extensively configured, re-engineered and trialled until it was perfectly suited to this demanding application. The cutting concept was refined and two 113kW motors installed to provide sufficient, yet energy efficient, power.

Designed for maximum efficiencies, the result is a single step shredding solution with only one machine, rather than a pre and post shredding operation. Complete with discharge conveyor, over band magnet and control room, the entire plant was fully pre-fabricated and pre-assembled in Salzburg, for acceptance testing by the client, LafargeHolcim Vietnam, and its Swiss technical support group. A 95%<80mm SRF specification was exceeded, with 97% of materials consistently achieving the required particle size, consistently high (15-20GJ/t) calorific value and 10 tonnes per hour throughputs. The continuous rotor speed also proved the system’s uptime robustness.

For heightened safety, the equipment was manufactured with an anti-explosive Atex-specification coating, and intelligent in-built fire suppression technology. Carefully positioned UV, infrared, heat and spark detectors on the inlet hopper and conveyor can sense if a fire is likely to start. In the event of a significant temperature increase, extinguishing nozzles, positioned in the same place as the sensors and thus pointing directly at the fire risk, will automatically spray water onto the targeted area. If the risk is within the shredder, the materials can be cooled and/or the fire put out before anything is discharged from the machine. If the problem is on the conveyor, the nozzles prevent hot, glowing fractions from entering the pile of output material, where a fire could otherwise break out.

To make the 10,000km journey to LafargeHolcim’s Hon Chong plant in Vietnam’s capital Ho Chi Minh City, all equipment was carefully packed for cost-effective sea freight shipping. Two 40ft containers held the shredder, conveyors, FE-separator and support frames, whilst a third 20ft container housed the control cabinet room. A special sea freight transport package was not required. A carefully planned installation plan meant a team of UNTHA technicians was on site in Vietnam when the equipment arrived. The installation began the next day, the commissioning phase was underway only four days later, and 11 days thereafter, the final acceptance test took place.

Whilst simple to operate, by design, the XR was installed with full operator and maintenance training. Should LafargeHolcim’s fuel specification change, the shredder’s indexable cutters and interchangeable screens can be alternated to achieve an even more precise shred.

The two alternative fuel production facilities highlighted here are vastly different. But it could equally be argued that both companies have achieved a best-in-class process for their given waste to energy scenarios. It is therefore unfair to suggest that there can be a uniform approach to RDF or SRF production around the world. To close the waste gap and secure a high quality feedstock for the cement industry, it is far more important to concentrate on devising a solution tailored to the input materials and output specification required.


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