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Augsburg, Germany

Heuss-Assbichler S.,Ludwig Maximilians University of Munich | Magel G.,CheMin GmbH | Fehr K.T.,Ludwig Maximilians University of Munich
Waste Management | Year: 2010

Long-term hydrogen generation was observed in a Bavarian mono-landfill for municipal solid waste incineration (MSWI) residues. Hydration reactions of non-noble metals, especially aluminum, predominantly produce hydrogen at alkaline reaction conditions. Microscopic investigations show that aluminum metal may occur in different forms: as larger single grains, as small particles embedded in a vitrified matrix or less frequently in blowholes together with metallic silica.Four types of corrosion texture were observed, indicating different reaction mechanisms: aluminum hydroxide rims caused by hydration reactions at alkaline reaction conditions (reaction type 1) and multiphase rims with ettringite and hydrocalumite due to the reaction of aluminum hydroxide with sulfate and chloride ions which are solved in the pore water (reaction type 2). Galvanic corrosion textures due to the electric potential difference between aluminum and embedded intermetallic Fe- or Cu-rich exsolution phases lead to two further corrosion textures: Strong hydration effects of aluminum except a border of aluminum remnant directly beside the Fe- or Cu-rich segregations were only observed in fresh samples (reaction type 3). The reaction type 4 shows a network of Al-hydroxide veins occurring along the embedded intermetallic Fe- or Cu-rich exsolution segregation pattern within the metallic aluminum grain. Metal particles enclosed in vitrified particles offers the potential for future corrosion processes.The occurrence of corrosion types 1, 2 and 3 in fresh bottom ashes indicates that these reaction mechanisms predominate during the first reaction period in the presence of chlorine in an alkaline solution. Corrosion type 4, however, was additionally observed in aged samples. Here aluminum acts as sacrificed anode implying electrochemical reaction due to electrolytic pore water. Chloride in the system keeps the reaction alive as Al-hydroxide is solved which normally builds a protection shield around the aluminum metal particles.Due to field observations and experimental results we have reasonable indications that after an initial strong formation of hydrogen the reaction time for hydrogen production in the landfill is lengthened for several decades by the presence of chloride in the alkaline pore water. © 2010 Elsevier Ltd. Source

Grahl S.,TU Dresden | Beckmann M.,TU Dresden | Magel G.,CheMin GmbH | Spiegel W.,CheMin GmbH
International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors 2010 | Year: 2010

The combustion of biomass and heat-recoverable waste products often leads to corrosive deposits at the evaporator finned tube walls, which subsequently cause material damage, greater exhaust gas losses or unacceptably high material stress. For prevention the deposits are being cleaned regularly, largely mechanical, during the plant shutdowns. To reduce the maintenance and service efforts and thus increase the economic efficiency, plant shutdowns for cleaning and removal of corrosion damages should be minimized. Due to the obstruction of heat extraction caused by deposits as well as the large temperature gradient between the finned tube panel surface and the exhaust gas on one side and the appearance of a deposit material with corrosive, temperature-dependent properties on the other side, there exists a qualitative relationship between formation and structure of deposits and the heat flux hitting the evaporator wall. The latter can therefore be used to characterize deposits at finned tube walls of steam generators as well as to determine the point in time of cleaning and to assess the corrosion potential of the deposit. For this purpose a method was developed that can use the Fourier transform of the heat flux signal to determine the temperature-dependent material properties of the deposits. Currently, the change of heat flux density of a finned tube wall with deposits compared to the clean state is experimentally demonstrated and a further development takes place by means of signal processing to derive information about the deposit situation in practical application. The results are discussed in the following paper. Source

Schmidl W.,CheMin GmbH | Herzog T.,CheMin GmbH | Magel G.,CheMin GmbH | Muller W.,CheMin GmbH | Spiegel W.,CheMin GmbH
VGB PowerTech | Year: 2011

Corrosion by chlorine at high temperatures and corrosion by salt melts sometimes cause severe risk and loss of operational availability in waste- and biomass-fired power plants [1]. This corrosion very often affects the superheater. Wear rates of up to 1 mm per 1000 hours can occur on unprotected carbon steel tubes, caused by a combination of locally occurring heat flux, flue gas composition and fouling. Due to high maintenance needs, several approaches to anti-corrosion coating have been developed. Nickel-based alloys such as alloy 625 are chosen to be applied as cladding or by thermal spraying. Operation periods have been considerably increased by these methods. But still there are some shortcomings in corrosion protection due to application and/or material. This article depicts some experiences with corrosion inhibiting applications, gathered by the authors during quality control on application or examination of damage. On the whole, the efficacy of both application forms, thermal spray and cladding, can be assumed. Especially local corrosion protection of discrete parts of a superheater can be a good alternative to complete white" or black" solutions. Source

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