Untersuchungen zum thermischen Recycling von Fraktionen aus dem Deponierückbau

• Investigations of the thermal recycling of fractions from landfill reclamation

Rotheut, Martin; Quicker, Peter (Thesis advisor); Flamme, Sabine (Thesis advisor)

Düren : Shaker Verlag (2022)
Book, Dissertation / PhD Thesis

In: Schriftenreihe zur Aufbereitung und Veredlung 81
Page(s)/Article-Nr.: 261 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2022

Abstract

The increasing demand for raw materials and the limited primary resources are becoming increasingly relevant for the recovery of resources from municipal waste landfills. In the future, the occurrence of environmental hazards, the recovery of land and landfill volume as well as the reduction of aftercare costs may require the dismantling of municipal solid waste landfills. In order to achieve an advanced recovery of resources during the landfill reclamation, both mechanical and thermal steps are required to treat the excavated material. The key question in this thesis was to clarify whether thermal recycling of high-calorific value fractions from landfill sites in conventional, state-of-the-art recycling plants is possible and practical for the implementation of enhanced landfill mining (ELFM). For this purpose, a solution methodology was developed, which comprised a combination of theoretical and computational investigations and experimental investigations based on them. The literature study showed that some studies on the composition of excavated material from municipal solid waste landfills have already been carried out nationally and internationally, but that there is little knowledge about the fuel properties of such materials. The state of knowledge on the use of fractions from municipal solid waste landfills in conventional plants for energy recovery is limited to a few studies that have been carried out several decades ago. On the basis of the findings from the literature study, unprepared excavation material, coarse-grained RDF with a low processing depth, various fine-grained RDF with a high processing depth and a wood fraction were selected for carrying out the experimental investigations. Material from different storage periods was obtained in three excavation campaigns from the municipal solid waste landfill Pohlsche Heide in Hille. The selected fractions were made from the excavated material in various mechanical treatment plants. Taking into account the inhomogeneity of the fractions to be examined, a suitable sampling and analysis concept for starting material characterization was developed. The subsequent characterization of the starting material has mostly resulted in problematic fuel properties. The fuel properties of the coarse-grained RDF fractions lead to a limitation of the possible uses in RDF power plants. Use of the largely processed RDF fractions in cement and power plants is also restricted by their fuel properties. The possible uses of the examined light fraction were limited by its high chlorine content. A combustion calculation was carried out with the determined fuel parameters and initial knowledge about the exhaust gas composition was obtained. On the basis of the results of the material characterization and the combustion calculation, combustion trials on a pilot-plant-scale and in a large-scale were planned. A sampling and analysis concept was developed to evaluate the combustion products from the trials. The pilot plant trials in three conceptually different firing systems (grate, fluidised and trough firing) have confirmed that the RDF, mixed plastic and fluff fractions had problematic fuel properties. The light fraction used and the waste wood fraction have proven to be comparatively homogeneous fuels. The large-scale experimental combustion of the coarse-grained RDF was carried out in an waste-to-energy (WtE) plant, a conventional RDF power plant with grate firing and an Energos RDF power plant. In addition, unprepared excavation material was used on a trial basis in the WtE plant. The fine-grained fluff fraction was used in a cement plant with a rotary kiln. The mono-combustion of the RDF has led to operational problems in both the WtE plant and the Energos RDF power plant, such as fluctuations in steam production and blockages in the area of fuel supply. In the experiments with coarse-grained RDF, significant increases in the concentration of SO2 and HCl in the raw gas as well as in some cases greatly increased additive consumption were found. The mono-combustion in the Energos RDF power plant could not be realized over a longer period. However, an RDF treated more extensive was successfully burned over a period of 14 days. The use of untreated excavation material in the incineration plant has led to a breakdown of stable combustion despite the addition of fresh waste in a ratio of 1: 3. During the combustion trials of the extensively processed fluff fraction in the cement plant, the fuel supply was blocked and build-up coatings in the preheater tower. In the product characterization were found remarkably high Fe and non-ferrous metal proportions in the slags from the RDF incineration at the level of ordinary slags from WtE plants. The investigated levels of trace elements in the slag mainly comply with the classification values according to LAGA M20 category Z2. The use of the fluff fraction in the cement plant had no negative impact on the quality of the clinker, but the upper limits of the Cl contents in the bypass dust and in the hot meal were exceeded. From the experimental investigations it was concluded that the direct use of untreated excavation material is not recommended. A aimed and effective mechanical processing of the excavated material was assessed as essential for the use of materials in plants for energetic utilisation. By transferring the results to large-scale applications, the new requirements for plants for energetic utilisation resulting from the use of RDF from landfill material were defined. Suitable technical and operational solution proposals were developed for this. The overall assessment showed that WtE plants and RDF power plants with grate firing can be used for the recycling of coarse-grained RDF from landfill material, taking into account the solutions proposed. A large part of the metal inventory can be recovered through RDF and slag processing. The use of largely processed RDF fractions in suitable cement plants also represents a recycling option. The thermal recycling of RDF fractions from landfill material in the above-mentioned plants was rated as an important component in realizing an ELFM. Further research is required to investigate the long-term effects of the use of materials on the plant technology of recycling plants.

Institutions

• Division of Mineral Resources and Raw Materials Engineering [510000]
• Unit of Technology of Fuels [512220]