Residue Treatment
Fly ash washing
Introduction

If fly ash is collected separately from bottom ash and flue gas cleaning residues, two different methods may be applied to remove or immobilise heavy metals from fly ash:

  • Acid washing

  • Neutral washing

Acidic fly ash washing

Acidic fly ash washing uses acidic scrubber blowdown to wash out the heavy metals from fly ash. Heavy metals can be recovered in the effluent treatment stage and recycled. After that, the fly ash can be landfilled together with the bottom ash.

Neutral fly ash washing

The aim of this process is to transform fly ash into a stable, leach-proof matrix. Neutral, easily soluble salts are extracted in a cascade of stirred vessels. By controlling pH in a slightly alkaline range, soluble heavy metals are precipitated. Washing liquid is separated from the solids by filtration and cleaned in the effluent treatment stage. Dewatered solids are mixed with hydraulic binders to form a solid, stable and leach-resistant matrix when landfilled.

Visual acidic fly ash washing 1

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Further related technologies

Grate Combustion systems

The combustion system is the best-proven thermal waste treatment technology for mixed municipal, industrial or hazardous waste, and the heart of any modern, state-of-the-art Waste to Energy (WtE) plant.

Flue gas treatment

Incinerating waste produces exhaust gases laden with diverse pollutants. Different processes are used to remove these pollutants before the purified flue gas leaves the plant safely through the stack.

Carbon capture

Capturing carbon dioxide (CO₂) from the flue gas produced in hard-to-abate industries and properly storing it (a process called carbon capture and storage or CCS) is a key component of most governments’ net-zero strategies.

Energy recovery

Recovering the energy content of waste is a key component of WtE technology. Since the process is largely renewable and involves only a low level of emissions, it also helps significantly reduce greenhouse gases.

Residue treatment

Thermal waste treatment produces residues which can be either reused or landfilled. The principal components are slags and ashes, consisting mostly of non-combustible waste constituents such as glass, minerals or scrap metals.

EcoFlex™ WtE plant solution

The new pre-engineered EcoFlex™ solution provides a modern waste infrastructure based on proven in-house technologies, allowing a cost-optimised design of single-line Waste to Energy plant construction and operation.