Svenska EnergiAskors logga  

Energy ash is an environmentally friendly resource

Environmental issues

In Sweden we have a smart energy system where we take care of all resources. Biofules and waste are used to produce electricity and heat with low impact on the climate. The combustion in Swedish district heating plants is increasing. The remanining ashes can be recycled to a great extent. Every year 1.7 million tons of energy ash is produced in Sweden. The ashes can be recycled in various ways. For example, they can be used to make concrete by replacing the cement with ash or to stabilize  dredged material to construction material when building ports. The ash is also important to reduce the acidification in the forest and to cover old landfills to prevent them from leaking greenhouse gas emissions.

Ash is a useful raw material resource that can be used to replace chemical liming agents and fertilizers in forest and land and to achieve sustainable forestry when bringing fuel from the forests. It is a proven and resource-efficient material with good technical characteristics. Ash may, for example, be used instead of natural fillers in the construction of roads and ports. In roads in the forests, ash is a good material because it is frost resistant.

What is energy ash?
When burning solid fuels, ash is the residue, as a natural part of energy production. When the combustible substance is fired up, what is left is bottom ash or slag to be removed from the boiler bottom and the fly ash that comes with the flue gas. In this pamphlet we are normally talking about none coal ashes.

The bottom ash/slag resembles a mixture of sand and stone. The fly ash separated from the flue gas is reminiscent of cement and also has cement-like properties. Often the flue gas is scrubbed from for example sulphur oxides with lime and other additives. The flue gas cleaning residue is often included in the fly ash.

Ash has previously been seen as a kind of waste to get rid of, but it is more and more realized as a resource that can replace non-renewable natural materials. In Sweden about 1.5 million tons of ash is produced annually and more than 1 million tons of this is utilized. Most of it to cover old domestic landfill.
Ashes have different properties and composition depending on the fuel being fired – for example forest fuels, fuels from agriculture, waste, peat or coal, on the type of boiler in use– for example fluidizing bed, powder boiler, grate fired combustion chamber boiler - how the boiler has been run - part load or full load. This is important to consider when trying tofind suitable uses for ash.

There are various examples of utilizing ash, one is to return ash to the forest. The ashes then will replace the nutrients removed when taking the fuel out of the forest. In drained peat woodland, ash is a fertilizer that increases tree growth. Ashes also can solve the problem of contaminated dredged material when ports are to be rebuilt. When mixed with the ashes, the heavy metals are bound and the dredged materials can be reused as building material in the port. Ash also may substitute crushed rock and gravel and provide some improved properties in the construction of roads and covering of landfills. Some ashes are suitable to mix into cement.





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