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Alloy Selection for a Cofired Circulating Fluidized Bed Boiler Vortex Finder Application at 880 degrees C in a Complex Mixed Mode Corrosion Environment
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.ORCID-id: 0000-0001-7856-0209
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
2017 (Engelska)Ingår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, nr 11, s. 12857-12866Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

X-ray diffraction and scanning electron microscopy (SEM) were used on a corroded industrial-scale circulating fluidized bed (CFB) boiler vortex finder (VF) 253MA alloy plate material to identify the dominating corrosion products and to enable a qualified selection of candidate alloys for the long-term, full-scale exposure study. Alloys 253MA, 310S, 800H/HT, Alloy DS, and Alloy 600 were chosen, and the alloy plates were exposed to the CFB boiler combustion atmosphere having an average temperature of approximately 880 degrees C, consisting of a moist globally oxidizing gas, burning hydrocarbons, CO2, CO, SO2, HCl, NH3, N-2, alkali species, and erosive particles. The exposure times used in this study were 1750, 8000, 12000, and 16000 operating hours. After exposure, the alloy samples were cut, and cross-sections were dry-polished and analyzed with an SEM-backscatter electron detector (BSD) setup to quantify material loss and penetration depth of the corrosion attack. This work suggests two novel concepts: heavily affected depth (HAD) enabling quantitative evaluation of heavily degraded alloys and remaining serviceable metal thickness (RSMT) enabling the use of long-term corrosion data from one alloy to make rough service life estimations of other alloys exposed for significantly shorter periods. The findings of this work show that there is no simple correlation between the heavily affected depth of the alloy and the nickel, chromium, or iron content. Instead, there seem to be two successful alloy composition principles that work well for this application. Furthermore, the work shows that major improvements can be made in terms of both technical life-span and the cost-effectiveness of the VF application if the most appropriate alloy is selected. In this study, a replacement of the frequently used Alloy 253MA with Alloy 310S doubled the lifespan of full-scale VFs, reducing the average VF maintenance cost to half.

Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2017. Vol. 31, nr 11, s. 12857-12866
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
URN: urn:nbn:se:umu:diva-143614DOI: 10.1021/acs.energyfuels.7b00984ISI: 000416204800136Scopus ID: 2-s2.0-85034573409OAI: oai:DiVA.org:umu-143614DiVA, id: diva2:1170791
Projekt
Bio4Energy
Forskningsfinansiär
Bio4EnergyTillgänglig från: 2018-01-04 Skapad: 2018-01-04 Senast uppdaterad: 2023-03-23Bibliografiskt granskad
Ingår i avhandling
1. Co-firing complex biomass in a CFB boiler: ash transformation, corrosion control and materials selection
Öppna denna publikation i ny flik eller fönster >>Co-firing complex biomass in a CFB boiler: ash transformation, corrosion control and materials selection
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Samförbränning av komplex biomassa i en CFB-panna : askomvandling, korrosion och materialval
Abstract [en]

The effects of greenhouse gas net emissions on global warming, stricter legislation on waste handling, and the pursuit of ever cheaper heat- and power production are all important factors driving the introduction of complex fuels in incineration plants. However - without fundamental knowledge regarding ash transformation, corrosion control, and materials selection – this introduction of potentially economically and environmentally beneficial fuels, might instead cause economic loss and environmentally adverse effects.

The present work is a contribution to the transition from today's CO2 net generating energy conversion system, to a more environmentally friendly and cost-efficient one. This is done using scientific methods to generate knowledge concerning mechanisms of ash transformation, corrosion control, and materials selection, in a co-fired industrial scale circulating fluidized bed (CFB) boiler, using a novel and biomass-based fuel mix, rich in Na, K, Cl, N, S, P, Ca and Si. Fuel fractions, ashes, flue gas, deposits, and construction material samples have been collected and analyzed using various techniques, including scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray Diffraction (XRD). The experimental results have been evaluated and interpreted using chemical equilibrium calculations.

The results of this work include:

1) An analysis of; the failure and preventive maintenance statistics of the industrial scale CFB boiler at hand; the elemental composition of boiler ashes and deposits, the flue gas composition and elemental composition of a multitude of fuel fractions; correlations between boiler design, operational parameters, elemental composition of deposits and boiler availability; a boiler elemental mass balance revealing details regarding deposit buildup mechanisms; properties of the fly ash relevant to flue gas filter design; and findings regarding the nitrogen chemistry of the novel and nitrogen-rich fuel mix.

2) Speciation and description of the overall ash transformation and fireside alloy interaction, enabling the implementation of on-line corrosion control which significantly inhibits superheater and dew-point corrosion in the boiler; and, an equation describing the sulfation potential of the fuel mix, as a result of the direct and indirect interactions between all major ash-forming elements.

3) A literature review relevant for the co-fired CFB cyclone vortex finder alloy selection and corrosion at 880 °C; An alloy selection study including long term exposures of several commercially available alloys identifying materials that are more than twice as cost-efficient as the often used alloy 253MA; a suggestion of novel methods for both systematic comparison of heavily degraded alloys, and for alloy service-life estimations; a detailed analysis of heavily degraded alloys 310S, 800H/HT and 600, identifying the driving corrosion mechanisms of the VF alloy degradation, including aspects of how the alloy internal mass transport and fireside surface interaction develops over time.

The knowledge gained during this project has been used in the improvement work of the Perstorp 50 MWth CFB boiler, improving the boiler availability with 7 %, reducing the overall energy conversion costs with around 1.7 MEUR/year.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University, 2018. s. 106
Nyckelord
ash transformation, process control, equilibrium calculations, boiler availability, failures, alloy selection, alloy degradation, vortex finder (VF), service life estimation, sulfation, chloridation, high temperature corrosion, biomass, waste derived fuels, forest residues, RDF, Biomal, slaughterhouse waste, peat, waste wood, industrial waste water treatment sludge, HAD, RSMT, Alloy 253MA, Alloy 310S, Alloy 800H/HT, Alloy DS, Alloy 600
Nationell ämneskategori
Korrosionsteknik Kemiska processer Tillförlitlighets- och kvalitetsteknik Energiteknik
Identifikatorer
urn:nbn:se:umu:diva-145106 (URN)978-91-7601-855-2 (ISBN)
Disputation
2018-03-16, N460, Naturvetarhuset, Umeå Universitet, Umeå, 13:00 (Svenska)
Opponent
Handledare
Forskningsfinansiär
Bio4EnergyVetenskapsrådet
Tillgänglig från: 2018-02-23 Skapad: 2018-02-21 Senast uppdaterad: 2018-06-09Bibliografiskt granskad

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Hagman, HenrikBoström, Dan

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