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New ways in the disposal of Coal Combustion Residuals (CCR)

2/5/2019  | 
Technical Articles
In 2015 the Environmental Protection Agency (EPA) has published a rule that regulates the disposal of coal combustion residuals (CCR) as a solid waste.
CCR consist of: fly ash, bottom ash, boiler slag and flue gas desulfurization material.

Fly ash is a very fine powdery material composed mostly of silica and generated by burning finely ground coal in a boiler; the ash is typically removed from chimneys before it reaches the open air by particle filtration equipment.

Bottom ash instead is a very coarse ash particle, too large and heavy to be brought along the chimneys so it accumulates in the bottom of the boiler. Bottom ash, unlike fly ash, is typically in solid form that must be ground down.

Both Fly and Bottom Ash contain contaminants like mercury, cadmium and arsenic. Without proper management, these contaminants can pollute waterways, ground water, drinking water, and become volatile in the air.

In order to minimize the risk of ash volatility Ash conditioners can be used as an effective pre-treatment system, helping to reduce the amount of ash released into the air prior to final disposal.
Ash conditioners are a key component to ash handling systems; as one of the last steps in the ash handling process, ash conditioners minimize the environmental impact of ash handling and unloading.

Ash Conditioners moisten the dust, this can be obtained by continuously working twin shaft paddle mixer or, even better, a single shaft ploughshare mixer, both necessarily equipped with a water injection device. In between these, exist a variety of alternative systems. The correct consistency of the product is essential not to produce slurry.

Whether for disposal or recycling, the moisture content must be as low as possible in order to keep the energy input and transportation costs low; the moisture content must be kept to the minimum as disposal in landfills and incineration plants is calculated by weight. The general rule is: the lower the moisture content, the lower the weight. Consequently, the mixers used must be absolutely dustproof and operate highly efficiently to guarantee that there will be no air pollution despite the lowest possible moisture content.

Another aspect not to be neglected is the high wear to which the mixing tools are subjected. This is a problem that almost all types of dust have in common once liquid has been added.
For power plants, similar to many other industries, separated dust represents a pure cost.
To solve the problem, various systems have been developed over the years: mixing screw conveyors, twin shaft paddle mixers, pug mills, ploughshare mixers and others. Unfortunately, none of these systems has all the features which are important to the operating authority: high efficiency, low operating costs, modest wear and low purchase price.

WAMGROUP has developed an innovative new equipment that meet all the aforementioned requirements: DUSTFIX.

What is immediately apparent when looking at DUSTFIX is the use of polyurethane-based materials. This gives a high resistance to abrasion as well as an optimum efficiency if compared to other devices, DUSTFIX only needs up to 10/12% of water to be added to stabilize the fly ash prior to transportation compared to 16 to 20% of more traditional systems like pug mills. In addition, the compact design makes the inclusion into existing plants extremely easy which means a lower investment is required.

DUSTFIX has a mixing capacity of up to 47 cubic feet per minute and is suitable for continuous duty applications.

The conditioning chamber is manufactured from a special non-stick abrasion resistant SINT engineering polymer which virtually eliminates the residue inside the chamber; the rotor shaft is made of completely removable modular and individually replaceable mixing tools.

For more information, please visit www.mapmixers.com
 
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