Rajender Gupta

Progress in carbon dioxide separation and capture: A review

This article reviews the progress made in CO2 separation and capture research and engineering. Various technologies, such as absorption, adsorption, and membrane separation, are thoroughly discussed. New concepts such as chemical-looping combustion and hydrate-based separation are also introduced briefly. Future directions are suggested. Sequestration methods, such as forestation, ocean fertilization and mineral carbonation techniques are also covered. Underground injection and direct ocean dump are not covered.

Kinetic Study and Thermal Decomposition Behavior of Lignite Coal

A thermogravimetric analyzer was employed to investigate the thermal behavior and extract the kinetic parameters of Canadian lignite coal. The pyrolysis experiments were conducted in temperatures ranging from 298 K to 1173 K under inert atmosphere utilizing six different heating rates of 1, 6, 9, 12, 15, and 18 K min−1, respectively. There are different techniques for analyzing the kinetics of solid-state reactions that can generally be classified into two categories: model-fitting and model-free methods. Historically, model-fitting methods are broadly used in solid-state kinetics and show an excellent fit to the experimental data but produce uncertain kinetic parameters especially for nonisothermal conditions. In this work, different model-free techniques such as the Kissinger method and the isoconversional methods of Ozawa, Kissinger-Akahira-Sunose, and Friedman are employed and compared in order to analyze nonisothermal kinetic data and investigate thermal behavior of a lignite coal. Experimental results showed that the activation energy values obtained by the isoconversional methods were in good agreement, but Friedman method was considered to be the best among the model-free methods to evaluate kinetic parameters for solid-state reactions. These results can provide useful information to predict kinetic model of coal pyrolysis and optimization of the process conditions.

Statistical Analysis of Coal Beneficiation Performance in a Continuous Air Dense Medium Fluidized Bed Separator

ABSTRACT In this study, the performance of a continuous air dense medium fluidized bed (ADMFB) separator is investigated for coal beneficiation. The full factorial experimental design method is used to study the effect of superficial air velocity (U), bed length (T), and bed height (H) on the clean-coal ash content, organic material recovery, and overall system separation efficiency. Optimum operating conditions are determined and followed by the effect of feed particle size on separation quality. Statistical analysis of the results revealed that H had no significant effect on product ash content while U and T had negative effects. A reduction in ash content from 19% to 10% was obtained once full bed length was utilized. The increase of all parameters had a negative effect on organic material recovery, while recovery was always above 88%. The only significant mutual interaction was found to be between T and H with even more effectiveness than U on the recovery. Separation efficiency increased by increasing the bed length and reached 20% once full bed length was utilized. The optimum operating condition was determined to be at U = 19.5 cm/s, T = full bed length, and H = 15 cm. It was observed that feeding finer particles deteriorated the beneficiation process.

Bromination of petroleum coke for elemental mercury capture

Activated carbon injection has been proven to be an effective control technology of mercury emission from coal-fired power plants. Petroleum coke is a waste by-product of petroleum refining with large quantities readily available around the world. Due to its high inherent sulfur content, petroleum coke is an attractive raw material for developing mercury capture sorbent, converting a waste material to a value-added product of important environmental applications. In this study, petroleum coke was brominated by chemical-mechanical bromination. The brominated petroleum coke was characterized for thermal stability, mercury capture capacity, and potential mercury and bromine leaching hazards. Bromine loaded on the petroleum coke was found to be stable up to 200°C. Even after treating the brominated petroleum coke for 30min at 600°C, 1/3 bromine remained on the solid. The sorbent from bromination of sulfur-containing petroleum coke was shown to be a promising alternative to commercial brominated activated carbon for capture of elemental mercury from coal combustion flue gases.

A Comparative Study on Lignite Coal Drying by Different Methods

ABSTRACT Abundance of low-rank coal (LRC) and increasing demand for energy provides motivation for upgrading LRC in terms of their high moisture content. Canadian lignite coal (425–1000 µm) was dried at different temperatures using different methods, namely hydrothermal treatment (HT), vacuum drying and hot air drying. These processes resulted in significant reduction (up to 9.65%) in moisture from as-received lignite coal (34%), especially at higher temperatures (300 and 325°C) using HT for 30 minutes. Vacuum drying (70°C) over the period of 7 hours and hot air drying (70°C) for 110 minutes liberated almost the same amount of moisture from the raw coal. Several investigations were conducted on these samples and chars derived from these in conditions similar to a boiler to understand the impact of drying methods. Char samples were prepared by pyrolyzing at 1200°C under inert atmosphere (N2) in a drop tube furnace (DTF). The morphological changes of these char samples were investigated by scanning electron microscopy analysis to see the physiochemical changes that occurred during different treatment processes. Raw and treated coal samples were also analyzed by several analytical techniques including Fourier transform infrared spectroscopy and thermogravimetric analysis (TGA). The present paper also describes the effectiveness of the different processes for upgrading the LRC and how it transforms LRC to a value-added coal that is easily transportable and environmental friendly source of energy.

Carbon dioxide capture under postcombustion conditions using amine-functionalized SBA-15: Kinetics and multicyclic performance

ABSTRACT In this work, ordered mesoporous SBA-15 was synthesized and functionalized by polyethyleneimine (PEI). The morphological properties were characterized by N2 adsorption/desorption, field–emission scanning electron microscopy (FE-SEM), high–resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy methods. The carbon dioxide (CO2) uptake on the sorbents, kinetics of CO2 adsorption/desorption and long-term multicycle stability of PEI-impregnated sorbent were measured. An optimal amine loading of 50 wt.% showed a CO2 adsorption capacity ~3.09 mmol g−1 using 10% pre-humidified CO2 at 75°C. The presence of moisture in flue gas showed a promoting effect in CO2 sorption capacity. The temperature swing adsorption/desorption cycles showed excellent multicycle stability over 60 cycles during 65 h of operations under humid CO2.

Metal oxide nanoparticle-modified graphene oxide for removal of elemental mercury

ABSTRACT Mercury is an extremely toxic element that is primarily released by anthropogenic activities and natural sources. Controlling Hg emissions, especially from coal combustion flue gas, is of practical importance in protecting the environment and preventing human health risks. In the present work, three metal oxides (MnO2, CuO, and ZnO) were loaded on graphene oxide (GO) sorbents (designated as MnO2-GO, CuO-GO, and ZnO-GO). All three adsorbents were successfully synthesized and were well characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that the metal oxide nanoparticles (NPs) successfully decorated the GO. The elemental Hg adsorption capabilities of the three sorbents were subsequently evaluated using an in-house built setup for cold vapour atomic fluorescence spectrophotometry (CVAFS) with argon as the carrier gas for mercury detection. The testing temperature ranged from 50°C to 200°C at intervals of 50°C. MnO2-GO showed an excel lent Hg0 adsorption capacity via chemisorption from 50 to 150°C and a mercury removal efficiency as high as 85% at 200°C, indicating that the MnO2-NP-modified GO is applicable for enhancing gas-phase elemental mercury removal. However, neither CuO-GO nor ZnO-GO performed well. This work provides useful insights into the development of novel sorbent materials for the elemental mercury removal from flue gases. GRAPHICAL ABSTRACT

Silica-Silver Nanocomposites as Regenerable Sorbents for Hg0 Removal from Flue Gases

Silica-silver nanocomposites (Ag-SBA-15) are a novel class of multifunctional materials with potential applications as sorbents, catalysts, sensors, and disinfectants. In this work, an innovative yet simple and robust method of depositing silver nanoparticles on a mesoporous silica (SBA-15) was developed. The synthesized Ag-SBA-15 was found to achieve a complete capture of Hg0 at temperatures up to 200 °C. Silver nanoparticles on the SBA-15 were shown to be the critical active sites for the capture of Hg0 by the Ag-Hg0 amalgamation mechanism. An Hg0 capture capacity as high as 13.2 mg·g-1 was achieved by Ag(10)-SBA-15, which is much higher than that achievable by existing Ag-based sorbents and comparable with that achieved by commercial activated carbon. Even after exposure to more complex simulated flue gas flow for 1 h, the Ag(10)-SBA-15 could still achieve an Hg0 removal efficiency as high as 91.6% with a Hg0 capture capacity of 457.3 μg·g-1. More importantly, the spent sorbent could be effectively regenerated and reused without noticeable performance degradation over five cycles. The excellent Hg0 removal efficiency combined with a simple synthesis procedure, strong tolerance to complex flue gas environment, great thermal stability, and outstanding regeneration capability make the Ag-SBA-15 a promising sorbent for practical applications to Hg0 capture from coal-fired flue gases.

Arsenic Emissions and Speciations in High-temperature Treatment of a Typical High Arsenic Coal

A series of experiments on release behaviors of arsenic in thermal treatment, e.g., pyrolysis, combustion, and gasification, of a typical high arsenic coal were conducted in a laboratory-scale drop tube furnace. Mineralogy of the coal and ashes was characterized by X-ray diffraction and field emission scanning electron microscope with energy dispersive X-ray spectrometer. Distributions and speciations of arsenic in the coal and ashes were determined by using the inductively coupled plasma mass spectrometry and time-of-flight secondary ion mass spectrometry. The results indicated that quartz and pyrite in coal would transformed into mullite and hematite. The decompositions of pyrite are followed by the unreacted coal modal and controlled by the surface sulfur vapor pressure, and pyrite would be transformed to Fe or Fe2O3 finally. Bleeding ration of arsenic in air combustion, CO2 gasification, and N2 pyrolysis is 85, 65, and 45 %, respectively, at 1300 °C. Arsenic is obviously enriched in the fine particles of size around 0.1–0.2 μm both in coal combustion and gasification. The arsenic species of arsenic in fine particles generated from coal gasification is As2O5, As, AsO, Ca3(AsO4)2.

Effect of initial coal particle size on coal liquefaction conversion

In coal liquefaction process initial coal particle size can be considered as one of the important process parameters. In this work, particles of coal are prepared by pulverisation and separation into different particle size ranges below 45 to 1,000 µm. Since conventional batch autoclave is not suitable for short contact time experiments, as the time required for the autoclave to reach the reaction temperature can be substantial, the liquefaction runs were investigated with a rapid injection reactor designed specifically for investigating the effect of initial particle size on liquefaction conversion. A Canadian coal was examined in a tubular bomb reactor in presence of tetralin at 400°C for a short reaction time (5 min) with pressure of 6 MPa under nitrogen atmosphere. The results indicated that total conversion obtained during the liquefaction changed according to the different particle size, and optimum particle size (150-212 µm) was detected for the liquefaction condition. [Received: November 27, 2014; Accepted: August 22, 2015]