Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.

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Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies

Modeling chemical and physical processes of wood and biomass pyrolysis

In this review, we summarize the knowledge of the production and properties of charcoal that has been accumulated over the past 38 millenia. The manipulation of pressure, moisture content, and gas flow enables biomass carbonization with fixed-carbon yields that approachor attainthe theoretical limit after reaction times of a few tens of minutes. Much of the heat needed to carbonize the feed is released by vigorous, exothermic secondary reactions that reduce the formation of unwanted tars by augmenting the charcoal yield in a well-designed carbonizer. As a renewable fuel, charcoal has many attractive features:  it contains virtually no sulfur or mercury and is low in nitrogen and ash; it is highly reactive yet easy to store and handle. Carbonized charcoal can be a good adsorbent with a large surface area and a semimetal with an electrical resistivity comparable to that of graphite. Recent advances in knowledge about the production and properties of charcoal presage its expanded use as a renewable fuel, red...

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The Art, Science, and Technology of Charcoal Production†

Roles of water for chemical reactions in high-temperature water

Biomass pyrolysis kinetics: A comparative critical review with relevant agricultural residue case studies

Results from a numerical model for endothermic biomass pyrolysis, which includes both high activation energy kinetics and heat transfer across a boundary layer to the reacting solid particle, are presented. The model accounts for conventional thermocouple thermal lag and unconventional thermal lag due to heat demand by the chemical reaction (which is governed by Arrhenius kinetics). Biomass fusion, first identified quantitatively by Lede and Villermaux, is shown to be a manifestation of severe thermal lag that results from the chemical reaction heat demand. Over the wide range of conditions studied, the true substrate temperature remains almost constant during pyrolysis, as is the case with compounds undergoing fusion or sublimation at constant pressure. A simple algebraic model, whose derivation presupposes the idea that biomass pyrolysis mimics the melting of a block of ice, accurately predicts the maximum value of thermal lag during pyrolysis. Unidentified thermal lag in TGA experiments lowers the valu...

Thermal Lag, Fusion, and the Compensation Effect during Biomass Pyrolysis†

Influence of pressure on the acid-catalyzed rate constant for 1-propanol dehydration in supercritical water

A study of zinc sulfate decomposition at low heating rates

This paper describes the experimental and analytical methods required to study decomposition of zinc sulfate in a simulated solar environment. Experiments were conducted at sample heating rates greater than 2K/s and temperatures in excess of 1400 K in a specially designed thermogravimetric system which employed a 30-kW/sub e//2-kW/sub th/ downward-facing beam, arc-image furnace. The zinc sulfate decomposition took place almost exclusively through the high-temperature ZnSO/sub 4/..beta.. phase under experimental conditions of this study. The kinetic parameters were determined from the thermogravimetric data by using a nonlinear least-squares optimization algorithm. An apparent activation energy, E, between 210 and 250 kJ/mol and an apparent reaction order, n, between 0 and 0.3 were obtained for ..beta..-phase ZnSO/sub 4/ decomposition reaction. The comparison of these results with those from lower temperature and lower heating rate zinc sulfate decomposition tends to suggest a change in reaction mechanism at the high heating rates expected in a concentrated solar environment.

Solar thermal, decomposition kinetics of zinc sulfate at high heating rates

Abstract Background  Radiology is among India's top five speciality choices pursued by meritorious medical graduates. With the advent of the subspecialization degree courses, fellowships, the requirement of senior residency as faculty eligibility criteria, and the lucrative option of private practice, the final-year postgraduates are given opportunities to choose from but with little guidance on what and how to choose. This study aims to analyze the views of the final-year radiology postgraduate residents in India regarding their understanding of how to proceed in their professional life with options available. Materials and Methods  A cross-sectional, questionnaire-based study was conducted online via Google forms distributed via email and social media platforms. The questionnaire was prepared after going through previous literature, video blogs, and media available on the Internet and was further validated for content. Results  About half (48%) of them wished to pursue higher studies in the form of Doctorate of Medicine (DM) degree courses or fellowships. Almost three-quarters of the participants preferred short-term subspecialization via fellowships over 3-year DM courses (28%). Regarding clinical practice, 61.9% preferred to take up senior residency, while slightly over one-third (35.7%) expressed their will to move on to private practice. Conclusion  A relative conundrum was observed in the decision to take up senior residency or private practice or to go for DM but had to pursue a fellowship due to limited choice in topics and seats available in the country for subspecialization.

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Ravi Narayan

Papers

Thermal Lag, Fusion, and the Compensation Effect during Biomass Pyrolysis†

Influence of pressure on the acid-catalyzed rate constant for 1-propanol dehydration in supercritical water

A study of zinc sulfate decomposition at low heating rates

Solar thermal, decomposition kinetics of zinc sulfate at high heating rates

Subspecialization, Senior Residency, or Private Practice: The Dilemma of Final-Year Radiology Postgraduate Residents in India