Experiences with alternative fuels

This week Cemtech hosted a live webinar on best practice for alternative fuels (AF) with renowned speakers from VDZ, FLSmidth and W&P Zement explaining how the cement industry has been developing its AF substitution rates in Europe.

Starting the webinar was Dr Volker Hoenig, managing director of VDZ, which represents the German cement industry, discussed the evolution of AF in Germany. He stressed the most important aspects of using AF were the four core elements of: transparency, quality control, technical expertise and training/education.

While Germany has been one of the leading cement sectors to embrace AF it had a slow beginning burning used tyres in the 1980s, before expanding to contaminated oils a decade later. The waste landfill legislation in 2005 then escalated more widespread use of AF in German cement plants. After introducing animal meal and sewage sludge, the industry reached reached an average fuel substitution rate of 67.5 per cent in 2019.


Transparency
Dr Hoenig said that legislation has played its part in pushing AF development pointing towards the European Industrial Emissions Directive, which sets limits for total dust, NO_X, SO₂ and TOCs amongst other emissions. VDZ carried out pioneering work in evaluating dioxin emissions in 1997, which led to permission being granted for the German cement sector to burn AFs in kilns. But public acceptance was only really gained when VDZ started to collect and publicise plant emission data.


The industry has reacted positively to public concerns and today many of Germany's emission levels are lower than the rest of Europe. Dust levels are restricted to 10mg/m³, NO_x is set at 200mg/m³ and mercury is set at 0.03mg/m³. There are also now 19 SNCR and 15 SCR plants in operation in the German cement sector, as well as two DeCONO_x units and one catalytic bag filter.

The industry is still looking for continual improvements in recognising flame adjustments for AF, the use of thermography and bypass systems for quenching chlorine, sulphur and mercury cycles, as well as researching clinker structure of alite and belite crystals and carrying out bottleneck analysis.

FLSmidth – new requirements for AF
Leading technology solutions and turnkey provider FLSmidth has recently adapted its strategy to better address AF needs, as a response to measures such as the Paris Agreement, and the need to reduce global CO₂ levels. Nour Amrani, FLSmidth’s senior manager of Public Affairs, said that the International Energy Agency recorded that AF only accounted for six per cent of thermal energy use in 2017 and that it would need to reach 17.5 per cent in 2020 and 30 per cent by 2050.

FLSmidth launched its MissionZero sustainability initiative last year to reduce CO₂ levels in the cement sector to zero by 2030. "At the end of last year, we looked into setting up a new sustainability ambition," said Ms Amrani. "FLSmidth has traditionally been a provider of productivity and efficiency solutions, but we decided to go one step further and be more ambitious in what we wanted to achieve in terms of sustainability, focussing mainly on emissions in the cement industry."

FLSmidth recognises the need to deliver solutions, and while 70 per cent of CO₂ emissions can be reduced by the industry with today's technology, FLSmidth believes the extra 30 per cent will only be achieved with external partnered solutions and technology developments that have not yet been created. FLSmidth will implement MissionZero through a three-step process from eliminating fossil fuels, to reducing the clinker factor and finally building the circular economy, carbon capture and sourcing AF raw materials by 2030.

Mads Nielsen, FLSmidth's head of GPLM upgrades – Pyro solution and Alternative Fuels, explained that a simple inexpensive way for companies to start using alternative fuels was with volumetric dosing. Gravimetric dosing will increase the speed and accuracy of substation rates, and storage can be added for more continuous AF extraction.

Mr Nielsen stressed that the inline low NO_x calciner has always been considered the best solution for AF combustion for FLSmidth. "The calciner can meet 80-100 per cent substitution rates with tyre chips below 50mm, while large particles settle at the bottom of the calciner and the large gas presence and low velocities are ideal for AF burning and recirculation with retention times of 30-60 seconds," he stated.

When AF combustion outside of the calciner is required, FLSmidth has the HOTDISC™ which has larger retention times of 2-30 minutes and takes AF directly into the kiln riser. FLSmidth is currently installing a HOTDISC™ in Turkey, as part of a project to raise clinker capacity from 3700 to 5000tpd, which will see 90 per cent AF substitution. In South Korea FLSmidth is also trialling a new HOTDISC™ on the ground version this year at two cement plants. To date, the product has had 29 worldwide sales and Asia has been a popular market for this equipment.

Further optimisation can be made with the use of chlorine bypasses and FLSmidth has been working on by-pass dust washing, which is already well established in the mining industry. The company's burner solutions have also been developed to maximise AF fuel burning and increase flame intensity, while producers are experimenting with different AF dryers and quality control can be stabilised with FLSmidth's PXP/QCX process expert equipment.

W&P Zement – leading the way in AF usage
The final presentation of the webinar looked at one of the elite AF plants in Europe. W&P Zement's Wietersdorf facility (Alpacem group) has recorded impressive 90 per cent AF substitution rates for cement production. 

Wietersdorf's Plant Manager, Florian Salzer, explained that the works started burning tyres in 1987 and moved on to RDF in 1992, before a capacity modernisation project in 2005 saw a new raw mill, kiln, clinker cooler and AF preparation plant installed. This enabled the facility to raise cement capacity to 2200tpd, while further investments for environmental protection amounting to EUR200m have been made at the plant between 2015-20.


Austria's cement industry has an average AF substitution rate of 80 per cent, which is well above the 28.4 per cent European average. This also enables CO₂ levels to be reduced to 539kgCO₂/t well below the world average of 639kgCO₂/t.

In addition, Wietersdorf has a flexible approach to AF management and sources its raw material for AF from not only domestically but also from Italy and Slovenia. SRF, dry and wet sewage sludge can be pneumatically fed to the calciner or pumped directly to the preheater tower, while cardboard fractions, waste wood, paper industry rejects and fibres are also used. Storage for AF includes two 7500m³ halls for calciner and main burner fuels as well as storage for 200t of SRF bales.

The plant operates an ATEC inline calciner with a burning chamber with a 4-5s retention time at over 850˚C. Six weigh feeders can be used for various AF and wet sewage sludge can be pumped, and dry sewage sludge can be conveyed. Approximately 30-40 per cent of AF is prepared on site and 60-70 per cent is delivered ready for use.

AF Equipment includes: a Lindner shredder and classifier to remove glass, stones and heavy rubber; a magnetic separator; second Lindner shredder; storage hall and SRF truck delivery. Last year, Wietersdorf added a new Unitherm MAS 5 35MW main burner and an ATEC Rocket mill. The Rocket mill is important as, "it tears AF material rather than cutting it which increases the surface area," said Mr Salzer. The mill's heavy chains and high air throughput further helps grinding and separation of materials.

Wietersdorf has operated a roadmap of continual improvement:

• 2008: reduced SO₂
• 2011: SNCR NO_x control
• 2015: mercury emission reduction
• 2016: renewal of a baghouse to improve dust collection
• 2017: erection of the regenerative thermal oxidation system to reduce VOCs.

The development of AF doesn't stop at Wietersdorf despite its high achievement record. Mr Salzer believes that 95 per cent AF substitution is possible in the next 12 months at the plant. This can be achieved by partly recalcined AF raw materials (biomass ash), development of binders with low clinker content and by using 25 per cent of its own generated electricity from a hydroelectric power plant.

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