The implications of chlorine-associated corrosion on the operation of biomass-fired boilers
01 Jun 2000-Progress in Energy and Combustion Science (Pergamon)-Vol. 26, Iss: 3, pp 283-298
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.
Abstract: The design of new biomass-fired power plants with increased steam temperature raises concerns of high-temperature corrosion. The high potassium and chlorine contents in many biomasses are potentially harmful elements with regard to corrosion. This paper condenses the current knowledge of chlorine-induced, high-temperature corrosion and describes the potential corrosion problems associated with burning biomass fuels either alone or in blends with coal, for electricity production. Chlorine may cause accelerated corrosion resulting in increased oxidation, metal wastage, internal attack, void formations, and loose non-adherent scales. The partial pressure of HCl in a biomass-derived flue gas, is not high enough to cause severe gas-phase corrosion attacks, but may provide scale failure and increased sulfidation of water walls in areas where locally reducing conditions occur due to poor combustion and flame impingement. The most severe corrosion problems in biomass-fired systems are expected to occur due to Cl-rich deposits formed on superheater tubes. The presence of alkali chloride salts in deposits may cause accelerated corrosion well below the melting point of the salt. The corrosion can be severe in air but may be further enhanced by SO2 which may cause intra-deposit sulfation of the alkali chlorides liberating HCl or Cl2 gas close to the metal surface. In case the metal surface temperature becomes high enough for molten phases to form in the deposit, the corrosion may be even further enhanced.
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.
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.
Abstract: Due to increasing environmental concerns especially related with the use of fossil fuels, new solutions to limit the greenhouse gas effect are continuously sought. Among the available alternative energy sources, including hydro, solar, wind etc. to mitigate greenhouse emissions, biomass is the only carbon-based sustainable option. On one hand, the versatile nature of biomass enables it to be utilized in all parts of the world, and on the other, this diversity makes biomass a complex and difficult fuel. Especially the high percentages of alkali (potassium) and chlorine, together with high ash content, in some brands of biomass prove to be a major source of concern. However, mechanisms leading to corrosion and high dust emissions problems have been identified and a range of possible solutions is already available. Among the technologies that can be used for biomass combustion, fluidized beds are emerging as the best due to their flexibility and high efficiency. Although agglomeration problems associated with fluidized bed combustors for certain herbaceous biofuels is still a major issue, however, but successful and applicable/implementable solutions have been reported. This review article presents 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. In conclusion, a range of concerns including environmental, economical and technical associated with biomass exist, but none of these issues represent an insurmountable obstacle for this sustainable energy source.
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.
Abstract: Biomass is available from many sources or can be mass-produced. Moreover, biomass has a high energy-generation potential, produces less toxic emissions than some other fuels, is mostly carbon neutrality, and burns easily. Biomass has been widely utilized as a raw material in thermal chemical conversion, replacing coal and oil, including power generation. Biomass firing and co-firing in pulverized coal boilers, fluidized bed boilers, and grate furnaces or stokerfed boilers have been developed around the world because of the worsening environmental problems and developing energy crisis. However, many issues hinder the efficient and clean utilization of biomass in energy applications. They include preparation, firing and co-firing, and ash-related issues during and after combustion. In particular, ash-related issues, including alkali-induced slagging, silicate melt-induced slagging (ash fusion), agglomeration, corrosion, and ash utilization, are among the most challenging problems. The current review provides a summary of knowledge and research developments concerning these ash-related issues. It also gives an in-depth analysis and discussion on the formation mechanisms, urgent requirements, and potential countermeasures including the use of additives, co-firing, leaching, and alloying. Alkali species, particularly alkali chlorides and sulfates, cause alkali-induced slagging during biomass combustion. Thus, the mechanisms of generation, transformation, and sequestration of alkali species and the formation and growth of alkali-induced slagging, formed as an alternating overlapping multi-layered structure, are discussed in detail. For silicate melt-induced slagging (ash fusion), the evolutions of chemical composition of both the elements and minerals in the ash during combustion and existing problems in testing are overviewed. Pseudo-4D phase diagrams of (Ma2O)-MaeO-P2O5-Al2O3 and (Ma2O)-MaeO-SiO2-Al2O3 are proposed as effective tools to predict ash fusion characteristics and the properties of melt-induced slagging. Concerning agglomeration that typically occurs in fluidized bed furnaces, melt-induced and coating-induced agglomeration and coating-forming mechanisms are highlighted. Concerning corrosion, seven corrosion mechanisms associated with Cl2, gaseous, solid/deposited, and molten alkali chlorides, molten alkali sulfates and carbonates, and the sulfation/silication of alkali chlorides are comprehensively reviewed. The effects of alloying, salt state (solid, molten, or gaseous), combustion atmosphere, and temperature are also discussed systematically. For ash utilization, potential approaches to the use of fly ash, bottom ash, and biomass/coal co-fired ash as construction and agricultural materials are explored. Several criteria or evaluation indexes are introduced for alkali-induced slagging and agglomeration, and chemical equilibrium calculation and multicomponent phase diagrams of silicate melt-induced slagging and agglomeration. Meanwhile, remedies, including the use of additives, co-firing, leaching, alloying, and the establishment of regulations, are discussed. It is suggested that considerable attention should be focused on an understanding of the kinetics of alkali chemistry, which is essential for the transformation and sequestration of alkali species. A combination of heterogeneous chemical kinetics and multiphase equilibrium modeling is critical to estimating the speciation, saturation levels, and the presence of melt of the ash-forming matter. Further practical evaluation and improvement of the existing criterion numbers of alkali-induced slagging and agglomeration should be improved. The pseudo-4D phase diagrams of (Ma2O)-MaeO-P2O5-Al2O3 and (Ma2O)-MaeO-SiO2-Al2O3 should be constructed from the data derived from real biomass ashes rather than those of simulated ashes in order to provide the capability to predict the properties of silicate melt-induced slagging. Apart from Cr, research should be conducted to understand the effects of Si, Al, and Co, which exhibit high corrosion resistance, and heavy metals such as Zn and Pb, which may form low-melting chlorides that accelerate corrosion. Regulations, cooperation among biomass-fired power plants and other industries, potential technical research, and logistics should be strengthened to enable the extensive utilization of biomass ash. Finally, alkali-induced slagging, silicate melt-induced slagging, agglomeration, and corrosion occur concurrently, and thus, these issues should be investigated jointly rather than separately.
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.
Abstract: This investigation explores the reasons for and technical challenges associated with co-combustion of biomass and coal in boilers designed for coal (mainly pulverized coal) combustion. Biomass-coal co-combustion represents a near-term, low-risk, low-cost, sustainable, renewable energy option that promises reduction in net CO2 emissions, reduction in SOx and often NOx emissions, and several societal benefits. Technical issues associated with cofiring include fuel supply, handling and storage challenges, potential increases in corrosion, decreases in overall efficiency, ash deposition issues, pollutant emissions, carbon burnout, impacts on ash marketing, impacts on SCR performance, and overall economics. Each of these issues has been investigated and this presentation summarizes the state-of-the-art in each area, both in the US and abroad. The focus is on fireside issues. While each of the issues can be significant, the conclusion is that biomass residues represent possibly the best (cheapest and lowest risk) renewable energy option for many power producers.
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.
Abstract: Gasification is considered as a key technology for the use of biomass. In order to promote this technology in the future, advanced, cost-effective, and highly efficient gasification processes and systems are required. This paper provides a detailed review on new concepts in biomass gasification. Concepts for process integration and combination aim to enable higher process efficiencies, better gas quality and purity, and lower investment costs. The recently developed UNIQUE gasifier which integrates gasification, gas cleaning and conditioning in one reactor unit is an example for a promising process integration. Other interesting concepts combine pyrolysis and gasification or gasification and combustion in single controlled stages. An approach to improve the economic viability and sustainability of the utilization of biomass via gasification is the combined production of more than one product. Polygeneration strategies for the production of multiple energy products from biomass gasification syngas offer high efficiency and flexibility.
22 Apr 1988
08 Jun 2013
TL;DR: In this article, the authors discuss the effect of surface barrier effects on the performance of anode-oxide films on the surface charge of a metal and the role of the metal in Inhibition.
Abstract: 1 Techniques for the Measurement of Electrode Processes at Temperatures Above 100 C.- Experimental Techniques.- Pressure Vessels and Liners.- Insulation and Sealing of Electrode Leads.- Metallized Ceramic Seals.- Compression Seals.- Line Seals.- Reference Electrodes.- High-Temperature Reference Electrodes.- External Reference Electrodes.- Application of High-Temperature Electrochemical Techniques.- Corrosion Studies.- Nonferrous Alloys.- Ferrous Materials.- Measurement of emf.- Measurement of pH.- Conductance Measurements.- Electrodeposition and Electrolysis.- Polarography.- Fuel Cells.- Acknowledgments.- References.- 2 Surface- and Environment-Sensitive Mechanical Behavior.- The Nature of Crystal Surfaces.- Clean Surfaces.- Surface Structure.- Chemical Segregation at Free Surfaces.- Space-Charge Effects.- Summary.- Environmental Effects on Crystalline Solids with Clean Surfaces.- Metals.- Clean Metals in Electrolytes.- Adsorption of Surface-Active Species.- Gaseous Environments and Vacuum Effects.- Nonmetals.- Solvent Environments (Joffe Effect).- Effects of Surface-Active Species.- Effects of Solid Surface Films.- Nonmetals.- Metals.- Mechanism of Surface Barrier Effects.- Elastic Theory.- Atomistic Nature of the Film-Substrate Interface.- Concluding Remarks.- Acknowledgments.- References.- 3 Mechanism and Phenomenology of Organic Inhibitors.- Mechanisms of the Action of Organic Inhibitors.- Adsorption.- Influence of Structural Parameters on Adsorption and Inhibition.- Action of Reduction, Polymerization, or Reaction Products.- Steric Effects.- Action of the Organic Cations.- The Role of the Metal in Inhibition.- Surface Charge of the Metal.- Cold Working.- Surface State.- Surface Treatments.- Purity of the Metal.- Hydrogen Penetration.- Methods of Studying Inhibitors.- Corrosion Rate Measurements.- Electrochemical Methods.- Radiochemical Methods.- IR and UV Spectroscopic Methods.- Mass Spectrometry and NMR Methods.- Other Methods.- Determination of Inhibitor Behavior vs Hydrogen Penetration.- Organic Inhibitors in Various Aggressive Environments.- Atmospheric Corrosion Inhibitors.- Inhibitors in the Steam Zone of Industrial Installations.- Inhibitors in Aqueous Solutions.- Inhibitors in Acid Solutions.- Inhibitors in Alkaline Solutions.- Inhibitors in a Nonaqueous Environment.- Summary.- References.- 4 Anodic Oxidation of Aluminum.- Short History.- Anodizing Processes of Current Importance and Interest.- Outline of Anodic Oxidation of Aluminum.- Scope of Anodizing Electrolytes and Their Characteristics.- Sulfuric Acid.- Oxalic Acid.- Chromic Acid.- Sulfamic Acid.- Phosphoric Acid.- Bright Anodizing.- Hard Anodizing.- Integral Color Anodizing.- Coloring by Dyestuffs and Pigments.- Special Anodizing Processes.- Anodizing in Molten Salts.- Anodizing in a Nonaqueous Solvent System.- Continuous and High-Current Anodizing.- Sealing.- Mechanism of Anodic Oxidation.- Stability and Corrosion of Aluminum (Pourbaix Diagram).- Classification of Anodic Films on Metal.- Chemical Composition of Anodic Oxide Films.- Barrier Film.- Duplex Film.- Theory of Dyeing Anodic Films.- Sealing Mechanism.- Properties of Anodic Oxide Films on Aluminum.- Corrosion Problems in Anodized Aluminum.- Acknowledgment.- References.
TL;DR: In this article, it was shown that the evaporation of FeCl2(g) and its outward diffusion through the scale is the rate controlling step of the active oxidation of a low alloy steel at 500°C and high alloy steels at 600 and 700°C.
Abstract: Thermogravimetric studies have been conducted on the oxidation of a low alloy steel at 500°C and high alloy steels at 600 and 700°C in which either NaCl or a fly ash (from a waste incineration plant) was deposited on the scale of the steels after 24 h pre-oxidation. The chlorides in the deposits react with the scale under formation of chlorine which enters the scale and causes accelerated oxidation, by the formation of FeCl2(s) at the scale/metal interface, evaporation of FeCl2(g) and its oxidation to Fe2O3 at the scale surface; chlorine partially returning into the scale. This leads to a porous unprotective scale and active oxidation, catalysed by chlorine. By variation of several parameters it was shown that the evaporation of FeCl2(g) and its outward diffusion through the scale is the rate controlling step of the active oxidation. The presence of SO2 in the atmosphere causes a minor increase of active corrosion by the sulfation of chlorides and the generation of chlorine. The presence of HCl in the atmosphere causes a transformation of sulfates in the deposits into chlorides, which induce enhanced active oxidation. In the presence of balanced concentrations of HCl and SO2 in the atmosphere, however, the corrosion is limited.
TL;DR: The role of grain boundaries in corrosion product scales as short-circuit transport paths for the outward diffusion of metal and the inward ingress of oxygen, sulfur and carbon needs to be clarified.
Abstract: At high temperatures, particularly in response to the unique environments associated with the conversion or combustion of fossil fuels, further fundamental studies of alloy reactions with mixed gaseous oxidants are required. Thermodynamic, phase equilibria and diffusion data are lacking in part, and isotope and tracer studies have not been forthcoming. Corrosive thin films of salts and slags on the hardware of gas turbines, heat exchangers, fuel cells and batteries cause an accelerated “hot corrosion”. Thin film electrochemical studies for simple salts and alloys, and supporting thermodynamic studies (solubilities of solids and gases in salts), are required to understand the corrosion mechanism. The effects of several trace gaseous impurities (particularly chlorine) both on the growth and damaging of protective oxide scales and on the degradation of alloy mechanical properties should be studied. High resolution in situ scanning electron microscopy studies could prove fruitful in clarifying uncertain scale growth mechanisms. New protective coating compositions must be found for specific corrosive environments, and more reliable but less expensive coating methods are required. Factors critical to the adhesion of oxide scales (e.g. α-Al2O3 and Cr2O3) on alloys, and the effects of trace alloying elements or dispersed second phases on scale adherence, deserve further attention. The effect on gas-alloy attack of solid deposits, either reactive or relatively inert, should be examined. Electrochemical studies should be made of alloy corrosion in deep salt melts or slags, where the gaseous environment is remote from the alloy surface. The role of grain boundaries in corrosion product scales as short-circuit transport paths for the outward diffusion of metal and the inward ingress of oxygen, sulfur and carbon needs to be clarified. Erosion-corrosion interactions should be studied, with attempts to define the types of coatings that are most resistant to such conditions. Particularly in solar applications, the role of thermal cycling and cyclic stressing on high temperature scaling (corrosion fatigue) needs to be studied. New methods for the monitoring of the concentrations of corrosive components, particularly sulfur and chlorine, in gaseous and fused salt environments require development. The influences of temperature gradients and heat fluxes on material compatibility, redistribution of chemical components and properties of corrosion product layers need further study. High temperature corrosion-resistant alloys excluding the strategic metals chromium and cobalt need to be developed.
TL;DR: In this article, a 10 MW wheat straw fired stoker boiler used for combined power and heat production was investigated, and the results of the practical measurements showed that the plant experiences major problems with deposits on the heat transfer surfaces.
Abstract: Deposition and corrosion measurements were conducted at a 10 MW wheat straw fired stoker boiler used for combined power and heat production. The plant experiences major problems with deposits on the heat transfer surfaces, and test probes have shown enhanced corrosion due to selective corrosion for metal temperatures above 520°C. Deposition measurements carried out at a position equal to the secondary superheater showed deposits rich in potassium and chlorine and to a lesser extent in silicon, calcium, and sulfur. Potassium and chlorine make up 40–80 wt.% of the deposits. Mechanisms of deposit formation and selective corrosion are discussed based on the results of the practical measurements.