SharpConsultant

Columbia, MD, United States

SharpConsultant

Columbia, MD, United States

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Keiser J.R.,Oak Ridge National Laboratory | Sandy Sharp W.B.A.,SharpConsultant | Singbeil D.L.,FPlnnovations
2013 PEERS Conference, Co-located with the 2013 International Bioenergy and Bioproducts Conference | Year: 2013

Operating superheater tubes of biomass-fired boilers at considerably higher temperatures than can be tolerated by commonly used structural materials could improve boiler efficiency. However, corrosion of the superheater tubes promoted by interaction with the relatively low melting point deposits that accumulate on the tubes becomes a major issue. The objective of this task was to use field exposures to determine if there are materials acceptable for use as superheater tubes that can operate at temperatures at least 100 Celsius degrees above the current maximum superheater temperature. Corrosion probes containing multiple specimens of nine different alloys were exposed for at least 2,000 hours in the superheater area of three biomass boilers where the deposits were determined to be enriched in potassium or chlorine. Similar specimens were also exposed in a boiler co-firing coal and wood. For the probes, specimen temperatures ranged from a low of less than 400°C to temperatures above 600°C for all but one case. Following exposure, a section was taken from each specimen and examined using light microscopy and scanning electron microscopy. Results of the examination of these specimens showed some alloys performed considerably better than others, but the corrosion resistance could not be related to chromium or molybdenum content of the alloys. Copyright © (2013) by the TAPPI Press.


Keiser J.R.,Oak Ridge National Laboratory | Sharp W.B.A.,SharpConsultant | Singbeil D.A.,Pulp and Paper Research Institute of Canada | Frederick L.A.,Pulp and Paper Research Institute of Canada | Clemmons C.,Meadwestvaco Corporation
Tappi Journal | Year: 2013

One method to significantly improve the efficiency of biomass-fired boilers is to increase the temperature and pressure of the steam generated. However, this requires operating the superheater tubes at considerably higher temperatures than can be tolerated by conventional structural materials. The limiting temperature for conventional materials is primarily determined by corrosion of the superheater tubes that is promoted by interaction with the relatively low melting point deposits that accumulate on the tubes. An air-cooled deposit probe was used to collect samples of the deposits that accumulated on tubes in the superheater area of a recovery boiler in a mill processing primarily hardwood. These deposits were found to be enriched in potassium. Subsequently, a corrosion probe containing multiple samples of nine different alloys was exposed for 2000 h in the same location of the superheater area of the same recovery boiler. The temperature of samples in the probe ranged from a low of about 400°C (752°F) to temperatures above 620°C (1148°F), compared to the boiler's estimated maximum tube temperature of 470°C (878°F). Following exposure, sections were taken from each of the 30 samples and examined using light microscopy and scanning electron microscopy. Results of the examination of these samples showed significant differences among the corrosion rates at temperatures 100°C above the current upper superheater tube temperature. A brief comparison is made to data from a parallel laboratory study. Application: This paper provides guidance on the selection of an alternate material for the highest temperature portion of the superheater tubes.


Sharp W.B.A.,SharpConsultant | Jones W.A.,Industrial Construction Consultants
Tappi Journal | Year: 2016

Near-drum thinning affects the fireside surface of recovery boiler generating bank tubes near the surface of the mud drum. Although sophisticated thickness scanning equipment has been developed to rapidly make tens of thousands of thickness measurements in the portion of a tube that is vulnerable to near-drum thinning, methods for using these data to evaluate fitness-for-service have not shown similar advances. Non-destructive testing companies typically use a technician's subjective judgment to identify the "thinnest reliable" thickness measurement on each tube. Some mills decide whether tubes can continue in operation or should be plugged or replaced based on this single thickness measurement. However, finite element analysis of the remaining strength of individual tubes thinned in the near-drum area suggests that it is essentially impossible to identify the weakest tubes from simple empirical rules. In the absence of an industry standard for evaluating these data, different mills could reach different conclusions about the fitness-for-service of a tube from the same data set. This paper reviews the technology for scanning the thickness of generating bank tubes and discusses approaches that have been used to identify the tubes most weakened by near-drum thinning and to evaluate the fitness-for-service of individual tubes. © 2016, TAPPI Press. All rights reserved.


Singbeil D.L.,FPlnnovations | Frederick L.,FPlnnovations | Keiser J.R.,Oak Ridge National Laboratory | Sandy Sharp W.B.A.,SharpConsultant
2013 PEERS Conference, Co-located with the 2013 International Bioenergy and Bioproducts Conference | Year: 2013

A laboratory-based program was designed to evaluate candidate alloys for superheaters operating at temperatures substantially higher than currently used in practice for biomass and chemical recovery boilers. However, the data is also applicable to superheaters operating in very corrosive conditions at lower temperatures. Alloys are ranked according to their performance in simulated environments. Copyright © (2013) by the TAPPI Press.


Sharp W.B.A.,SharpConsultant | Singbeil D.L.,Pulp and Paper Research Institute of Canada | Keiser Jr. J.R.,Oak Ridge National Laboratory
NACE - International Corrosion Conference Series | Year: 2012

About 90% of the world's bioenergy is produced by burning renewable biomass fuels. Low-cost biomass fuels such as agricultural wastes typically contain more alkali metals and chlorine than conventional fuels. Although the efficiency of a boiler's steam cycle can be increased by raising its maximum steam temperature, alkali metals and chlorine released in biofuel boilers cause accelerated corrosion and fouling at high superheater steam temperatures. Most alloys that resist high temperature corrosion protect themselves with a surface layer of Cr 2O 3. However, this Cr 2O 3 can be fluxed away by reactions that form alkali chromates or volatilized as chromic acid. This paper reviews recent research on superheater corrosion mechanisms and superheater alloy performance in biomass boilers firing black liquor, biomass fuels, blends of biomass with fossil fuels and municipal waste.


Sharp W.B.A.S.,SharpConsultant | Kiefer L.A.,BlueWave Microbics
Tappi Journal | Year: 2015

This introduction to microbiologically influenced corrosion (MIC) describes how bacteria can cause MIC where inadequate disinfection of mill water or white water allows biofilms to grow on metal surfaces. Although planktonic bacteria (that float in solution) rarely cause corrosion, sessile bacteria (that adhere to surfaces) can produce corrosive chemicals or promote under-deposit corrosion. The diagnosis of MIC requires knowledge not only of corrosion processes, but also of microbiology, water treatment, and plant operations. Although the presence of bacteria does not prove that the corrosion was caused by MIC, factors such as the presence in the corroded area of bacteria that can cause MIC, of chemical indicators of MIC, of features of the corrosion damage that are characteristic of MIC, and recent operational changes that could have enhanced the activity of microorganisms can combine to provide compelling evidence. Because of the complexity of mill water environments, test data must be reviewed with care because of the possibility that other components of the water could have interfered with the analytical results. Application: Although MIC is one of the most difficult types of corrosion to diagnose, the characteristic features and tests described in this paper can help identify it as the cause of corrosion damage in cooling water or white water systems.


Sharp W.B.A.,SharpConsultant | Jones W.A.,Industrial Construction Consultants Inc.
PEERS Conference 2015: Sustainable Solutions for Our Future | Year: 2015

Near-drum thinning affects recovery boiler generating bank tubes near the surface of the mud drum. Although sophisticated thickness scanning equipment has been developed to make tens of thousands of thickness measurements in the portion of a tube vulnerable to near-drum thinning, methods for using these data to evaluate fitness-for-service have not shown similar advances. Non-destructive testing companies typically use a technician's subjective judgment, to identify the "thinnest reliable" thickness measurement on each tube. Some mills decide whether tubes can continue in operation or should be plugged or replaced based on this single thickness measurement. However, rigorous Finite Element Analysis of the remaining strength of individual tubes thinned in the near-drum area suggests that it is essentially impossible to identify the weakest tubes from simple empirical rules. In the absence of an industry standard for evaluating these data, different mills could reach different conclusions about the fitness-for-service of a tube from the same data set. This paper will review the technology for scanning the thickness of generating bank tubes and discuss approaches that have been used to identify the tubes most weakened by near-drum thinning and evaluate the fitness-for service of individual tubes. We hope that this may form the basis for discussions to develop industry guidelines or a new Technical Information Paper to provide guidance to boiler operators, testing companies and insurance companies about how to interpret near-drum thinning data.


Sharp W.B.A.,SharpConsultant | Frederick W.J.,Table Mountain Consulting | Keiser J.R.,Oak Ridge National Laboratory | Singbeil D.L.,FPInnovalions
Tappi Journal | Year: 2014

The efficiencies of biomass-fueled power plants are much lower than those of coal-fueled plants because they restrict their exit steam temperatures to inhibit fireside corrosion of superheater tubes. However, restricting the temperature of a given mass of steam produced by a biomass boiler decreases the amount of power that can be generated from this steam in the turbine generator. This paper examines the relationship between the temperature of superheated steam produced by a boiler and the quantity of power that it can generate. The thermodynamic basis for this relationship is presented, and the value of the additional power that could be generated by operating with higher superheated steam temperatures is estimated. Calculations are presented for five plants that produce both steam and power. Two are powered by black liquor recovery boilers and three by wood-fired boilers. Steam generation parameters for these plants were supplied by industrial partners. Calculations using thermodynamics-based plant simulation software show that the value of the increased power that could be generated in these units by increasing superheated steam temperatures 100°C above current operating conditions ranges between US$2,410,000 and US$11,180,000 per year. The costs and benefits of achieving higher superheated steam conditions in an individual boiler depend on local plant conditions and the price of power. However, the magnitude of the increased power that can be generated by increasing superheated steam temperatures is so great that it appears to justify the cost of corrosion-mitigation methods such as installing corrosion-resistant materials costing far more than current superheater alloys; redesigning biomassfueled boilers to remove the superheater from the flue gas path: or adding chemicals to remove corrosive constituents from the flue gas. The most economic pathways to higher steam temperatures will very likely involve combinations of these methods. Particularly attractive approaches include installing more corrosion-resistant alloys in the hottest superheater locations, and relocating the superheater from the flue gas path to an externally-fired location or to the loop seal of a circulating fluidized bed boiler. Application: The value of additional power that could be generated by raising biomass boiler steam temperatures by 100 Celsius degrees appears to justify substantial expenditures to avoid superheater corrosion at the higher temperature, including the use of much more expensive corrosion-resistant alloys or substantial design and operational changes, particularly if the high temperature superheaters were designed for rapid replacement.


Keiser J.R.,Oak Ridge National Laboratory | Sharp W.B.A.,SharpConsultant | Singbeil D.L.,Pulp and Paper Research Institute of Canada
Tappi Journal | Year: 2014

Operating superheater tubes of biomass-fired boilers at considerably higher temperatures than can be tolerated by commonly used structural materials could improve boiler efficiency. However, corrosion of the superheater tubes promoted by interaction with the relatively low melting point deposits that accumulate on the tubes becomes a major issue. The objective of this study was to use field exposures to determine if there are materials acceptable for use as superheater tubes that can operate at temperatures at least 100 Celsius degrees above the current maximum superheater temperature. Corrosion probes containing multiple specimens of nine different alloys were exposed for at least 2000 h in the superheater area of three biomass boilers where the deposits were determined to be enriched in potassium or chlorine. Similar specimens were also exposed in a boiler co-firing coal and wood. For the probes, specimen temperatures ranged from a low of less than 400°C to temperatures above 600°C for all but one case. Following exposure, a section was taken from each specimen and examined using light microscopy and scanning electron microscopy. Results of the examination of these specimens showed some alloys performed considerably better than others, but the corrosion resistance could not be related to chromium or molybdenum content of the alloys. Application: The results of this study provide guidance on the selection of superheater tube alloys for applications where it is desired to operate in hostile environment at temperatures as much as 100 Celsius degrees higher than normally used in that environment.


Sharp W.B.A.,SharpConsultant | Singbeil D.L.,Pulp and Paper Research Institute of Canada | Keiser J.R.,Oak Ridge National Laboratory
2011 TAPPI PEERS Conference | Year: 2011

The steam temperature of biofuel boilers is limited by high temperature corrosion of superheater alloys in the ash deposit/flue gas environment. Advanced European biomass boilers combine design modifications, process changes and corrosion-resistant alloys to achieve substantially higher steam temperatures and efficiencies than U.S. biomass boilers. This review of design modifications and process changes is part of a US DOE-funded study of opportunities to increase heat recovery from renewable fuels. The role of advanced alloys in increasing superheater temperatures will be reviewed in a subsequent paper. Design modifications to reduce superheater corrosion include adding an "empty pass" between the furnace and the superheater, installing cool tubes to trap low melting temperature chlorine deposits ahead of the superheater, heating the final superheater in the recirculated fludizing medium of a CFB boiler, operating with a slagging superheater, designing superheaters for quick replacement, raising the superheater temperature above the dew point of the most corrosive deposits and installing an external superheater fired by a less-corrosive fuel. Process changes include diluting corrosive biomaterials with less-corrosive fuels, adding high sulfur fuels to convert alkali chlorides to lower melting temperature sulfates before they reach the superheater, washing chlorides out of agricultural residues and adding chemicals that convert alkali chlorides to aluminosilicates.

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