Visits of recycling facilities for incinerator bottom ash

Michael Stoll:
"Today I am proud to introduce Singapore’s first metal recovery plant for incinerator bottom ash. This milestone marks a pivotal step within Singapore’s long-term strategy to ensure a full recovery for residues from solid waste incineration. This facility is the first of its kind in Asia. It is a result of a successful collaboration of the NEA of Singapore and REMEX."

Venkat Patnaik:
"The moment the contract was awarded to us in 2014, we were faced with two challenges: Space constraints on 1.2 hectares and a tight timeline. The goal was to create a highly efficient plant by maximising the resources available to us. We began construction in October 2014 and within eight months we have exactly achieved what we want. The metal recovery process reduces more than ten percent of the volume of the bottom ash that is sent to landfill, effectively extending its life."

Speaker:
At the REMEX 1.4 hectares purpose built facility, incinerator bottom as or IBA is received daily at our ash receiving hall where it is stored and dried. Then fed into the input feeder for processing.

Once at the first station, the bar sizer screens the fresh IBA and removes any material bigger than 150 mm. And the excavator’s magnetic attachment eliminates all bulky ferrous material.

Back on a conveyer belt, fractions of ferrous metals are separated into metal bays by overbelt electro-magnets. Then at the flip-flow, IBA is sieved into various granular fractions and channelled onto the equipment.

On reaching the advanced recovery, a high-speed rotor isolates the lighter material onto a conveyor which transports it to the discharge hoppers. While the heavier fractions are channelled for the flip-flow for sieving and then to the eddy-current separators for separations.

At the eddy-current separators, non-ferrous material is separated from the IBA as it passes over a high-speeding rotating magnet below the conveyor where out of a total of eight eddy-currents, three are arranged in a cascading configuration for efficient recovery of small and non-ferrous metals.

At the last station, the manual hand-picking station, a team handpicks stainless steel and any remaining ferrous and non-ferrous material to ensure most of the metals are recovered.

Finally, the processed IBA is transported to the discharge hoppers that automatically load the ash-tipping trucks for transfer to the Tuas Marine Transfer Station.

And the recovered metals are loaded into containers for delivery to customers around the world.

Processing more than 600,000 tonnes of IBA a year, recovering up to 90% of ferrous and non-ferrous metals, REMEX helps reduce landfilling rate. And REMEX metal-free IBA can be treated for various applications, making possible zero IBA to the landfill.

REMEX Minerals – your partner in working for the future.

In the Netherlands, REMEX owns one of the biggest plants in Europe for the processing of incinerator bottom ash stemming from energy-from-waste plants. On an area of about 45 ha, the company’s subsidiary HEROS is responsible for the operation of the facility.

Incinerator bottom ash or IBA is first treated in the main processing unit where minerals are separated from metals and organic impurities before entering an extended installation which includes, among other technical processes, numerous additional eddy-current separators and screening processes. The remaining ash forms the base material for the additional hydro-mechanical treatment.

Washing incinerator bottom ash mainly serves to improve the environmental characteristics of IBA. The plant that we see here at the HEROS location has been especially designed to fulfil the requirements of the Dutch Green Deal. It is optimised to meet the mineral specifications of the Dutch market and focuses on the production of hydro-cleaned bottom ash of the fraction size 0 to 14 mm.

The washing of IBA at the Sluiskil plant consists of a two-step process with the aim to produce a purified material in the form of sustainable secondary aggregates. An added benefit of the process is the additional recovery of valuable heavy metals.

At the centre of the hydro-mechanical technology are two washing drums arranged in sequence. The incinerator bottom ash is cleaned with water intensively in these large drums, releasing sludge and organic material from the sand and gravel fraction. The sludge is later landfilled and the organic matter returned to the incineration plant.

After leaving the washing drum, the coarse material bigger than 2 mm is separated from the sand using sieving technology. The fractions are sprayed with water via various drainage screens to remove as many contaminants as possible.

Following this, the fraction smaller 0.063 mm is separated from the sand by means of a cyclone. The remaining sludge is passed on to the sedimentation tank for further treatment and water recycling; it is later disposed of as sludge cake.

The screened and washed material sized 2 to 14 mm is also being drained. Together with the fine ash fraction, the material is then stored before it is ready for the second hydro-mechanical treatment process.

After leaving the second washing drum and screening process, the material sized 2 to 14 mm is passed on to an extra technology called jig. The coarse IBA – which still contains valuable heavy non-ferrous metals – is swirled around in water by a pulsating waterflow. The metals sink faster than the ash and collect at the bottom of the jig from which they are discharged through an adjustable weir. The remaining mineral fraction is passed on to the mixing drum. Here, it is merged in a fixed ratio with the grain size of up to 2 mm. The final result is hydro-cleaned IBA granulate 0 to 14 mm.

Water required in the operation of the plant is collected at all stages during the process. It passes through several water clarification installations, including a sedimentation tank with flocculant as clarifying agent. After physical and chemical treatment, the cleansed water is returned to the production process - thus reducing fresh water consumption to a minimum.

The metals recovered during the washing process include copper, zinc, lead, stainless steel and small amounts of gold and silver - valuable non-ferrous metals which are sold to smelting and metal processing companies. Using recycled metals such as these in metal production means a lower carbon footprint, reducing the emission of greenhouse gases in metal production.

As for the final minerals, the washed material quality enables the full reuse of incinerator bottom ash in high-end applications. Our group of companies markets these aggregates under the brand name GRANOVA. A strict quality control process makes sure that all required environmental and structural standards are met.

The main applications for IBA with hydro-cleaned qualities are:

• Road construction,
• Earthworks,
• Asphalt production and
• Concrete products

As part of ongoing research projects the use of IBA in applications such as bricks, ceramics or cement is under development.