Produktion of lightweight aggregates
By using sludge from local sewage treatment plants as additive in the production of lightweight clinkers, the energy content in the sludge is utilised and the mineral part is a substitution to natural materials.
Purpose: The purpose is to produce lightweight aggregates from coal fly ash and wastewater sludge. Lightweight aggregates are used in building material such as concrete elements, drain sheeting, roofing and insulating flooring, etc. The purpose is both to utilise by-products and to exploit energy resources in coal fly ash and wastwater sludge. Wastewater sludge: The Danish municipalities have difficulties utilising wastewater sludge and thus new fields of application must be found. Coal fly ash: Coal fly ash with a high content of unburned coal is not suitable in concrete elements. Furthermore, a new regulation from the National Agency of Environmental Protection will probably make it even harder to utilise by-products. Procedure: Laboratory and full scale experiments with subsequent material testing are to be carried out. In addition, analyses for handling, logistics, energy balances and emissions will be realised. A market survey and a feasibility study are to be prepared as well. Expected production method for aggregates through utilisation of sludge and ash: De-watered sludge, ash and plastic clay are mixed and led into a rotating kiln in which the organic material in both sludge and ash is burned. This process creates cavity spaces in the material and the compressive strength of the material is obtained
In landfills with fly ash from closed power plants where the technological development did not enable a good burning out in the boilers, the ash contains a lot of unburned carbon. In the production of lightweight clinkers, coal is - to a large extend - used as fuel for drying and sintering of the base material (clay), taking place in the rotary kiln. By adding coal fly ash, both the energy content and the mineral part are utilised, thus replacing digging of natural materials. Laboratory tests with mixtures as well as full-scale tests with sludge and with coal fly ash respectively have been performed. Approx 40 tonnes of sludge and 30 tonnes of coal fly ash were used for the full-scale tests. Addition of coal fly ash gives a heavier and stronger product which could be used as an aggregate in concrete. Replacing the natural aggregate with strong lightweight clinkers gives a concrete with a lower dead load. Adding sewage sludge causes no considerable changes in the volume weight. The flue gas has been examined for the content of Hg. An increased content of Hg has been noted when adding sludge, however, it does not exceed the limit value. Lightweight clinkers used for numerous purposes, have so far been marketed as a 100 per cent natural product. Mixed with sludge the marketing has to be adjusted. There were no insoluble technical problems in connection with the full-scale tests
Key figures
Category
Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Dansk Leca A/S | ||
| Affald Varme Århus |
Contact
Kraftværksvej 53
DK-7000 Fredericia, Denmark
Kofod, Jørgen ; Projektleder: Schmidt, Erik Ravn , 79233333, ep@elsamprojekt.dk
Øvr. Partnere: Dansk Leca A/S; Århus Kommune; A/S Midtkraft Studstrupværket
