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Cleaner Technology Projects in Denmark 1997

Residual Products from Smoke-Gas Cleansing in Connection with Waste Incineration

Restprodukter fra røggasrensning ved affaldsforbrænding 3
Arbejdsrapport nr. 92, 1997, Miljøstyrelsen

Another aim has been to carry out an evaluation of the common methods’ environmental, technical and economical aspects. Finally the aim has been to recommend which methods are seemingly best suited to Danish conditions. In addition, areas were pointed at that are in need of further research and development.

The completed collection of knowledge has been done through literature reviews, personal contact to a number of companies and individuals both at home and abroad, and through participation in the WASCON 94 conference that constitutes an international forum for the presentation of research results within the treatment and deposition of residual products from waste incineration.

The report starts of in chapter 2 with a short description of the smoke-gas cleansing processes, the actual residual products’ physical and chemical properties and the substance leaching from untreated residual products. This chapter forms the background for the rest of the project.

In chapter 3 an overview of the different disposition possibilities is given together with their mutual connection.

In chapters 4 and 5, a detailed account of the different techniques of treating residual products is given with the aim to reduce substance leaching from them thereby making them more depositive.

In chapter 4 different methods of stabilising and solidifying residual products by means of cement casting, addition of different chemical stabilisation substances and heat treatment, are described and evaluated.

In chapter 5 different treatment methods, which originate from a forced leaching of the residual product’s contents of soluble salts and heavy metals and in the environmentally less problematic salts, are described.

In chapter 6 deposition, including some of the relatively few experiences those are available from full-scale disposition of the residual products.

The report concludes with a summarisation and conclusion of the revised methods’ advantages and disadvantages. Based on the finalised survey, the following recommendations with regards to the future handling of products from smoke-gas products in Denmark, are given:

Due to the insecurity of the technical and economical possibilities of utilising the smoke-gas products it is recommended that the as the first priority treatment and deposition methods must be established, which allow an environmentally safe and sustainable deposition. This must though not hinder at parallel experiment with different types of utilisation, since utilisation is always favourable to deposition.

With regards to the dry/ semi-dry products and fly ask it is recommended that the first step in the treatment is to remove the majority of the apparent soluble salts for example through a aqueous extraction. The removal of the salts will reduce the potential pollution and in many circumstances have a positive effect on the subsequent stabilisation with reference to reducing the potential leaching of trace elements/ heavy metals. This does though naturally count for treatment methods that are intended for substances with a high salt concentration. In many circumstances it is recommendable that residual products from the wet process mixed with fly ash are treated in the same way.

Through the cleansing of the liquid phase for trace elements it must be ensured that the saline, cleaned waste water from the extraction of a residual product is subsequently lead to a marine receiver, or as a second priority, to a waste-water treatment plant.

Methods for the chemical stabilisation of the leached remnants must be developed, which ensure that the latter together with the sludge from the cleansing can be deposited near the coast in correspondence with a strategy based on controlled slippage. If the remnants are to be processed so as to be usable it must be ensured that all secondary residual products can be used or disposed of as previously described. In the light of good international and Danish examination results one should consider to let the stabilisation with phosphor become part of the remnant treatment.

Provided that it is not possible to gain so good a remnant quality as to recommend controlled leaching, it is recommended that use a deposition strategy that corresponds to the collection and treatment of percolate.

In the future with regards to having to avoid removing already deposited dry/semi-dry or wet smoke-gas products from controlled waste disposal sites with percolate collection, experiences with forced in-situ leaching should be gathered. It is recommended that these experiences can also be used in the projection of new residual-products disposal sites.

The environmental and depositive properties of the sludge from the wet process (without mixed-in fly ash) should be examined since the data on this is insufficient. The possibilities of, through treatment, making the sludge more suitable for deposition or use, should be examined.

It is recommended that a protocol is laid down for the testing and evaluation of the environmental quality of processed and unprocessed residual products. In the first part of the test one could carry out a pH statistical leaching where L/S = 100 litres/kg and pH = 4,5,6,7 and 8. Consequently one could carry out a leaching test under more realistic conditions that simulate the long-term scenario conditions (e.g. a column or batch test).

Author/ institution

John Flyvebjerg and Ole Hjelmar, VKI Institute of Water Environment

This report is subsidised by the National Council for Recycling and Cleaner Technology

ISSN no. 0908-9195
ISBN no. 87-7810-912-4

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