The implications of chlorine-associated corrosion on the operation of biomass-fired boilers
TL;DR: In this paper, the potential corrosion problems associated with burning biomass fuels either alone or in blends with coal, for electricity production are discussed, and the most severe corrosion problems in biomass-fired systems are expected to occur due to Cl-rich deposits formed on superheater tubes.
About: This article is published in Progress in Energy and Combustion Science.The article was published on 2000-06-01. It has received 669 citations till now. The article focuses on the topics: Corrosion & Erosion corrosion.
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TL;DR: In this paper, several aspects which are associated with burning biomass in boilers have been investigated such as composition of biomass, estimating the higher heating value of biomass and comparison between biomass and other fuels.
Abstract: Currently, fossil fuels such as oil, coal and natural gas represent the prime energy sources in the world. However, it is anticipated that these sources of energy will deplete within the next 40–50 years. Moreover, the expected environmental damages such as the global warming, acid rain and urban smog due to the production of emissions from these sources have tempted the world to try to reduce carbon emissions by 80% and shift towards utilizing a variety of renewable energy resources (RES) which are less environmentally harmful such as solar, wind, biomass etc. in a sustainable way. Biomass is one of the earliest sources of energy with very specific properties. In this review, several aspects which are associated with burning biomass in boilers have been investigated such as composition of biomass, estimating the higher heating value of biomass, comparison between biomass and other fuels, combustion of biomass, co-firing of biomass and coal, impacts of biomass, economic and social analysis of biomass, transportation of biomass, densification of biomass, problems of biomass and future of biomass. It has been found that utilizing biomass in boilers offers many economical, social and environmental benefits such as financial net saving, conservation of fossil fuel resources, job opportunities creation and CO 2 and NO x emissions reduction. However, care should be taken to other environmental impacts of biomass such as land and water resources, soil erosion, loss of biodiversity and deforestation. Fouling, marketing, low heating value, storage and collections and handling are all associated problems when burning biomass in boilers. The future of biomass in boilers depends upon the development of the markets for fossil fuels and on policy decisions regarding the biomass market.
1,293 citations
TL;DR: In this article, the authors present the major issues concerned with biomass combustion with special reference to the small scale fluidized bed systems (small to pilot scale). Problems have been identified, mechanisms explained and solutions have been indicated.
1,012 citations
TL;DR: In this article, the authors provide a summary of knowledge and research developments concerning these ash-related issues, including alkali-induced slagging, silicate melt induced slagging (ash fusion), agglomeration, corrosion, and ash utilization.
691 citations
TL;DR: In this paper, the authors explore the reasons for and technical challenges associated with co-combustion of biomass and coal in boilers designed for coal (mainly pulverized coal) combustion.
572 citations
TL;DR: In this article, a detailed review on new concepts in biomass gasification is provided, which aim to enable higher process efficiencies, better gas quality and purity, and lower investment costs.
517 citations
References
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15 Nov 1989-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effects of alloying elements on NaCl-induced hot corrosion properties at temperatures below its melting point were examined to investigate the properties of various stainless steels.
Abstract: Various stainless steels were examined to investigate the effects of alloying elements on NaCl-induced hot corrosion properties at temperatures below its melting point. The corrosion rate increases with increasing testing temperature. Austenitic stainless steels exhibit better hot corrosion resistance than ferritic stainless steels. Aluminium is effective in improving the hot corrosion resistance of ferritic stainless steel. Silicon improves the hot corrosion resistance of austenitic stainless steel, and nickel is also effective. Corrosion is increased when Cr 2 O 3 reacts with NaCl to form Na 2 CrO 4 instead of a protective scale. It is considered that austenitic stainless steel with high silicon content forms SiO 2 which is not liable to react with NaCl.
56 citations
TL;DR: In this paper, high-temperature (> 200°C) corrosion of metals and alloys in atmospheres containing Cl2 and/or HCl, which are widely encountered in many industrial environments, is reviewed.
Abstract: High-temperature (> 200° C) corrosion of metals and alloys in atmospheres containing Cl2 and/or HCl, which are widely encountered in many industrial environments, is reviewed Topics include high-temperature corrosion mechanism and kinetics, thermodynamic considerations, and effects of gaseous components in the atmosphere (oxygen, air, water vapour, sulphur dioxide, and nitrogen) on the corrosion
49 citations
Journal Article•
TL;DR: In this article, the authors found that the highest corrosion rates were observed in the tertiary superheater region, that is, in the hottest tube section, and that the history of the growth of corrosion scale was found more precisely under the tube ties than elsewhere.
Abstract: Severe corrosion problems were encountered in a bubbling-fluidised-bed (BFB) boiler burning chlorine-containing fuels. The highest corrosion rates were observed in the tertiary superheater region-that is, in the hottest tube section. The steam outlet temperature of the boiler was 530 °C, corresponding to highest metal temperatures of 560-580 °C. Maximum measured corrosion rate exceeded 10 mm/year. The original material of the superheater tubes was chromium steel CrMoV 12 1 (grade X20) according to DIN 17175. Corroded tertiary superheater tubes were studied with a scanning electron microscope (SEM) and energy-dispersive X-ray (EDXA) and microspot analysis. All the corroded tubes showed a layered structure in the corrosion scale. High chlorine concentrations were always found in the corrosion front-the interface between the metal surface and the scale. The corrosion front was followed by an iron-deficient/chromium-rich layer, which in some cases could be used for measuring the thickness of the corroded area. A third layer, consisting of almost pure iron oxide, was found to form on the original tube surface, but below the layer of ash deposit. Melting of the deposits appeared not to be responsible for the high corrosion rates observed, since the original tube outlines could be traced in the corroded samples. Chlorine, on the other hand, seems to have played a crucial role in the corrosion process. The presence of chlorides at the metal/scale interface seems to have enhanced oxidation of the alloy dramatically. Chlorine penetrates into the metal through grain boundaries, and accelerates the corrosion by destroying individual grains. Iron diffuses towards the metal surface and is subsequently oxidised to iron oxides. The main source of chlorine in the corrosion reactions is apparently the sulphation of alkali chlorides occurring in the deposits of fly-ash on the tubes. However, sulphur and alkalis were not found to participate directly in the corrosion reactions. The morphology of corrosion scale is similar to that observed in high-temperature oxidation. In this case, however, chlorine seems to act as a catalyst, enhancing the diffusion of iron at low temperatures. The history of the growth of corrosion scale was found to be preserved more precisely under the tube ties than elsewhere; therefore samples from those regions were used to study the causes of corrosion.
49 citations
01 Mar 1996
TL;DR: The major findings of the Alkali Deposits Investigation, a collaborative effort to understand the causes of unmanageable ash deposits in biomass-fired electric power boilers, were discussed in this article.
Abstract: This report documents the major findings of the Alkali Deposits Investigation, a collaborative effort to understand the causes of unmanageable ash deposits in biomass-fired electric power boilers. Volume 1 of this report provide an overview of the project, with selected highlights. This volume provides more detail and discussion of the data and implications. This document includes six sections. The first, the introduction, provides the motivation, context, and focus for the investigation. The remaining sections discuss fuel properties, bench-scale combustion tests, a framework for considering ash deposition processes, pilot-scale tests of biomass fuels, and field tests in commercially operating biomass power generation stations. Detailed chemical analyses of eleven biomass fuels representing a broad cross-section of commercially available fuels reveal their properties that relate to ash deposition tendencies. The fuels fall into three broad categories: (1) straws and grasses (herbaceous materials); (2) pits, shells, hulls and other agricultural byproducts of a generally ligneous nature; and (3) woods and waste fuels of commercial interest. This report presents a systematic and reasonably detailed analysis of fuel property, operating condition, and boiler design issues that dictate ash deposit formation and property development. The span of investigations from bench-top experiments to commercial operation and observations including both practical illustrations and theoretical background provide a self-consistent and reasonably robust basis to understand the qualitative nature of ash deposit formation in biomass boilers. While there remain many quantitative details to be pursued, this project encapsulates essentially all of the conceptual aspects of the issue. It provides a basis for understanding and potentially resolving the technical and environmental issues associated with ash deposition during biomass combustion. 81 refs., 124 figs., 76 tabs.
48 citations
01 Mar 1999
TL;DR: In this paper, the authors describe the fate of potassium, chlorine, and sulfur in regard to deposition and corrosion problems in straw-fired boilers, showing that straw may form massive deposits in the convective pass of the boiler.
Abstract: (21/01/2019) Deposition and High-Temperature Corrosion in Biomass-Fired Boilers This thesis describes the fate of potassium, chlorine, and sulfur in regard to deposition and corrosion problems in strawfired boilers. Full-scale deposition studies at Rudkøbing CHP, Kyndby Power Station and Masnedø CHP revealed that straw may form massive deposits in the convective pass of the boiler. Straw deposits consist of a white layer of potassium salts extending the whole circumference of the tube and an ellipse-shaped deposit on the windward side of the probe. The white layer is powdery and very easy to brush off. The main deposit on the windward side of the probe can be quite hard and difficult to remove and consist of impacted fly ash particles and large amounts of condensable salts which form a matrix which bonds the fly ash particles together. The fly ash particles in the deposit are dominated by potassium silicates and potassium-calcium-silicates.The deposition of potassium salts during straw combustion was studied in Sandia's Multifuel Combustor. A layer of condensed potassium salts was found on the side of the deposition probes. The layer had a very characteristic dendritic structure which was made up of small individual particles. Vapor deposition phenomena were investigated with a newly developed condensation probe. SEM analyses revealed that the vapor deposits consisted of individual angular particles of primarily KCl (1-2 μm) and a sponge-like matrix of submicron particles consisting primarily of K2SO4, which may represent vapor condensate agglomerates. Potassium deposits mainly as potassium chloride in straw-fired boilers. If large amounts of sulfur are present in the system, the composition of the condensed potassium salts changes in favor of more potassium sulfate. This phenomenon was observed when straw was co-fired with oil at the Kyndby Power Station and when adding 500 ppmv SO2(g) to straw-combustion under high-temperature combustion conditions in the pilot-scale experiments at Sandia National Laboratories. The potassium sulfate found in these probe deposits are mainly believed to originate from deposition of gaseous potassium sulfate. This is based on a slow sulfation of KCl in the solid phase and that K2SO4 was deposited as clusters of K2SO4 aerosol particles which indicate the formation of gaseous potassium sulfate. With time the deposited potassium chloride may sulfate to form potassium sulfate due to thermodynamically driving forces, but potassium sulfate has only been detected in insignificant amounts in mature deposits in straw-fired boilers formed over months of operation.The corrosion of superheater tubes is closely connected to the material which are deposited on the surface and deposits containing potassium chloride can cause severe hightemperature corrosion at elevated metal temperatures. Lab-scale corrosion experiments, where metal test elements were covered with synthetic potassium salts and real deposits and exposed to a simulated flue gas containing HCl(g) and SO2(g), provided information about the corrosion rate and corrosion mechanisms of boiler steel under conditions similar to straw-fired boilers. A characteristic layer of potassium sulfate and iron oxide was found adjacent to the metal oxide layers on all the metal test elements covered with a deposit containing KCl. The layer had a characteristic structure with iron oxide threads in the dense potassium sulfate matrix. The same characteristic feature was found in the inner deposit layer from the deposits collected at Rudkøbing and Masnedø CHPs. In the probe deposits at Rudkøbing and Masnedø CHPs, KCl was found in the inner deposit layer whereas K2SO4 was the component in the mature deposits at Masnedø CHP. The density and morphology of these layers indicate that they have been molten. This was taken as evidence of a reaction between the deposit and the metal tube.A corrosion mechanism for chlorine corrosion is suggested. The mechanism is based on gaseous chlorine attack where iron and chromium in the metal react with gaseous chlorine forming volatile metal chlorides. The high partial pressure of chlorine close to the metal is believed to be caused by a rapid sulfation of KCl to K2SO4 in a melt formed adjacent to the metal surface. This mechanism can explain the shift in corrosion behavior with temperature which has been observed in full-scale corrosion tests.
47 citations