Stainless steels for wet conditions in municipal incineration and combustion plants

1 Objectives of the Project Deposited municipal waste constitutes a considerable threat to the immediate environment. On the other hand the waste can be regarded as a renewable energy source if it is incinerated in special power plants. Incineration has thus the advantages of both reducing the problem with leaching from deposits and producing power. The flue gas must be cleaned before emission, but in addition, the flue gas may, after being scrubbed, be cooled to temperatures below the dew point of its water content. By utilising the heat of condensation, the thermal efficiency of the plant can then be improved by as much as 20-30%. The main objectives of the project are: • To characterise the corrosion environment in different parts of the wet cleaning systems in waste incineration plants and by corrosion testing to define application ranges of stainless steels in these environments. Through quantification of the influence of factors determining the corrosivity, e.g. by chemical analyses of condensates, knowledge will be added to the field of dew point corrosion • To enable the use of stainless steels in different parts of the cleaning systems in question by application of the knowledge generated. 2 Comparison of initially planned activities and discussion In this section the actual performed activities have been compared to Annex I to the contract. A copy of the Annex I is provided under the same name to this report. 2.1 Task 1. Coverage of new experience and development in wet cleaning systems, in particular in waste incineration plants, that may arise during the project time The coverage was performed by the partners and through consultation with plant managers and manufacturers of equipment and materials. The coverage comprised: a) Corrosion problems experienced and measures taken b) Constructional development and variants including spray towers, quenchers, scrubbers, gas coolers, condensers, re-heaters, stacks, spray water systems etc. c) Materials used d) Composition of flue gases including oxygen content In summary, Task 1 was performed successfully and fulfilled as initially planned. 2.2 Task 2. Dew point studies a) Coverage of new information that may be available during the project time A constant close contact with plant owners throughout the project period ensured that the information on dew point conditions and related problems was kept up-to-date. b) Condensation conditions Several experiments where performed to analyse dew point conditions in several plants. c) Condensate composition Condensate samples where collected from all plants involved in the project and analysed. In summary, Task 2 was performed successfully and fulfilled as initially planned. 2.3 Task 3. Laboratory corrosion testing The materials to be used for specimens in all tests in the project were subjected to a screening test as to their relative corrosion resistance. Extensive corrosion testing was performed in synthetic condensates of the same compositions as those analysed in Task 2c. a) Screening test All materials in plates and tubes that were to be used for specimens in the project (Table 1, Annex I) were subjected to a Critical Pitting Temperature test (CPT) according to ASTM G-150.