Gasification provides a promising pathway for transforming waste materials into valuable products, such as fuels and chemicals. This study investigates the steam co-gasification of low-density polyethylene (LDPE) and compressed thickener underflow, representative of coal refuse (CR), in a drop tube reactor. The effects of feed blend ratio (0-100 wt% LDPE) and temperature (800-1000 degrees C) on syngas composition, tar formation, and process efficiency are examined. The high volatility of LDPE makes it more reactive than CR but also promotes the formation of 2-7 ring aromatic tars. Increasing temperature improves carbon conversion efficiency (CCE), cold gas efficiency (CGE), and syngas yield, although the lower heating value (LHV) of syngas decreases. Hydrogen is the dominant gas product, reaching 59 vol% with the H2/CO molar ratio ranging from 2.27 to 4.74. Synergistic effects from alkali and alkali earth metals (AAEMs), particularly K and Ca, in CR ash enhance syngas yield by catalyzing char gasification and tar cracking. Hematite (Fe2O3) and ash from sub-bituminous/bituminous coals are explored as tar reforming catalysts. Fe2O3 achieves 100 % tar reforming efficiency, while coal ash, with a lower Fe2O3 content (15 wt%), is less effective at cracking polycyclic aromatic hydrocarbons, particularly naphthalene. These findings demonstrate the flexibility of co-gasification, allowing precise tuning of syngas characteristics for specific downstream applications. Further optimization of waste-derived catalysts could enhance the economic viability of gasification in waste-to-energy processes.

Pyrolysis is a promising technology for converting plastic waste into valuable raw materials while offering a potential solution to the global plastic pollution crisis. In this study, the thermal pyrolysis of high-density polyethylene (HDPE) is investigated in a drop tube reactor under nearly isothermal conditions. The impact of reaction temperature and gas/volatile residence time on carbon conversion and product distribution is examined across a range of 500 -900 degrees C and 3.6 -32.2 s, respectively. Non-condensable gas products detected by online mass spectrometry are H 2 , CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 6 , and C 3 H 8 . At elevated temperatures and prolonged residence time, H 2 yield reaches as high as 8.6 wt% of the initial HDPE mass due to intensified cracking reactions of C 2 -C 3 hydrocarbons and long-chain aliphatic compounds. Consequently, pyrolysis tars consist mainly of polycyclic aromatic hydrocarbons (PAHs) with 5 -7 rings, accompanied by visible coke deposition within the reactor. HDPE decomposition to volatiles is an endothermic process and it is complete at a temperature between 492 degrees C and 525 degrees C, depending on the heating rate employed, from non-isothermal thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) measurements. The thermal degradation of HDPE pellets follows the twodimensional nucleation growth model for conversion levels up to 0.8 with an apparent activation energy of 259 -270 kJ/mol and a pre-exponential factor of 4.83 x 10 17 -1.37 x 10 19 min- 1 , determined from various isoconversional methods such as Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink, along with Criado 's master plots. These findings provide valuable insights into optimizing process parameters and refining reactor design for pyrolysis, which can be integrated with gasification and reforming processes to enhance hydrogen production on a larger scale.

Compared with a pulverized coal power plant, the integrated gasification combined cycle (IGCC) has several advantages, including, among others better environmental performance and low CO2 capture cost. Hot/warm CO2 removal from syngas has also been a subject of research due to its potentially higher thermal efficiency. In this study, we proposed a generic adsorption based hot/warm CO2 removal process for IGCC power plants. Through analyses of the proposed generic process we have demonstrated that higher temperature of the hot/warm CO2 removal process will results in larger heat of adsorption, which in turns may increase energy consumption of the process. Under most of the operating temperature range, hot/warm CO2 removal process will lead to more electricity loss compared to the baseline Selexol process. However, if the adsorption step takes place at a temperature close to or higher than the highest steam temperature in steam cycle, our analysis indicates that the process may lead to minimal electricity loss. The study also provided some other insights into the pathways for hot/warm CO2 removal process to improve its energy performance through process and sorbent designs.

It has been reported that among the various geologic storage options, deep saline aquifers have the largest estimated capacity for CO2 storage. Obtaining knowledge of possible artificially geochemically induced changes to the permeability and porosity of host CO2 storage deposits will enable us to gain insight on long-term reservoir behavior under CO2 storage conditions. An experimental study of the interaction of CO2/brine/rock on saline formations was conducted in a static system under CO2 storage conditions. Chemical interactions in the Cedar Keys-Lawson Formation carbonate during exposure to CO2 and brine under sequestration conditions were studied. Samples were exposed to the simulated in-situ reaction conditions for one and six months. The samples were exposed to a model brine at 55 °C and CO2 pressure of 23.8 MPa (3,500 psig). Computed tomography (CT), x-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive x-ray spectroscopy (EDS), brine composition, core porosity, and core permeability analyses were conducted prior to and after the exposure experiments. Preliminary permeability measurements obtained from the core samples showed changes after they were exposed to CO2-saturated brine for one and six months. This observation suggests that mineral dissolution and mineral precipitation could occur in the host deposit altering its characteristics for CO2 storage over time. The 3D images of the pore space clearly illustrate the degree of dissolution that occurred during exposure. It is noted that the dissolution that occurred during the six-month exposure could have enhanced the connectivity between voids. This may contribute the increase of permeability after the CO2/brine exposure. In addition, the primary minerals comprising the core are dolomite and gypsum. Both minerals could dissolve in the CO2/brine environment resulting in the increase of permeability after the six-month exposure.

A nanoporous carbon sorbent was synthesized, functionalized with magnesium oxide (MgO), and demonstrated to be a high-performance CO2 capture adsorbent. Taking advantage of a low cost and scalable preparation method, the unique design of the sorbent fosters strong interactions between the metals and acid moieties in the porous carbon media. The high surface area (2130 m2/g) and nanopores (1-2 nm) of the porous carbon enable a high concentration and uniform distribution of metal oxide throughout the sorbent. CO2 uptake capacity of the sorbent at 400 ppm CO2 was 0.12 mmol CO2/g sorbent, which is two orders of magnitude higher than that of the unfunctionalized porous carbon. The CO2 adsorption performance of the MgO functionalized nanoporous carbon at a low partial pressure of CO2 compares favourably with reported CO2 uptake of Mg oxide functionalized porous carbons as well as porous and non-porous metal oxides.

In this work,we investigated leaching of lanthanide and yttrium(REY)from a Central Appalachian coal and its ashes obtained at 550-950℃with the main purpose of understanding the impact of ashing temperature on REY leachability in water,ammonium sulfate,and hydrochloric acid.It is found that the coal contains a negligible amount of water-soluble REY,less than 1％ion-exchangeable REY,and about 28％of HCl-soluble REY.Ashing leads to dramatic changes in REY leachability in both ammonium sulfate and hydrochloric acid solutions,which is believed to be related to transformation and redistribution of organically-associated REY in coal during the ashing process.Ashing temperature significantly affects REY leaching from coal ashes;higher ashing temperature results in lower REY leachability in both so-lutions.Clay minerals may play a significant role in changing the leachability of REY after ashing.In addition,the results also suggest that the organic matter in the coal is relatively enriched in heavy REY.

Thermal stresses may be induced in a hot dry rock when a cold fluid is injected in the well. To study this problem, we look at the thermoelastic response of a hot rock that is suddenly cooled. The cooling is assumed to be either at a constant temperature or at a constant heat flux per unit depth. Our approach is to nondimensionalize the equations and perform a parametric study and look at the temperature distribution and the induced-thermal stresses. The results indicate that depending on the extent of cooling and the cooling time, thermal stresses can be induced. Numerical simulations on sandstone, with an initial uniform temperature of 473K, are also carried out. The results show that if the cooling is due to the surface temperature maintained at 463K (10 degrees C lower than the initial temperature of the hot rock), thermal stresses that are larger than the rock tensile strength could be induced. When the cooling is due to a constant surface heat flux, this temperature can be reached after about 777days of cooling with a minimum value of a heat flux of -20W/m.

This present work reports on the heat losses associated with the upward flow of hot air, water, and CO2 in a production well. The heat losses considered here are the frictional heat loss, the gravitational heat loss, the Joule-Thomson effect, and the conduction heat loss to the surrounding rock formation. These heat losses were characterized using the mass flow rate, the operation time as variable parameters while the surrounding formation was assumed to have constant properties with a linear geothermal gradient. The results show that, the frictional heat loss was small while the influences of the others depended on the flow conditions and the operation time. For water, the Joule-Thomson effect was a heating effect and its magnitude was comparable to that due to the gravitational effect. The conduction heat loss was dominant for all situations. For air as well as CO2, the Joule-Thomson effects were the cooling effects. For low mass flow rates, the conduction heat loss was the dominant heat loss during the initial stages of the operation and the combined heat losses due to the gravitational and the Joule-Thomson effects became dominant during the later times. For high mass flow rates, throughout the operation life time, the gravitational and the Joule-Thomson effects were the dominant heat losses that control the temperature of air and CO2 in the production well. Published by Elsevier Ltd.

Chemical-looping with oxygen uncoupling (CLOU) is considered a promising technology to burn solid fuels with improved CO2 capture and has the potential to improve fuel conversion and reaction rates. Cu-based oxygen carriers (Cu-OC) are often used in solid fuel CLOU. This study focused on investigating Cu-OC derived from a natural mineral for solid fuel CLOU because of their potentially lower cost compared to synthetic OCs. Reactivity and recyclability of a natural ore-derived Cu-OC on coal char (Powder River Basin sub-bituminous coal) were studied at 900 °C in Ar and air using TGA-QMS and fixed-bed reactor-QMS for five cycles. Cu-OC was prepared by simply heating chalcopyrite in air. Chalcopyrite is one of the principle copper sulfide ores and one of the primary ores for copper. The prepared Cu-OC had primarily CuO and CuFe2O4 (CuOFe2O3) as active compounds based on XRD analysis and an oxygen capacity 3.3% from oxygen uncoupling. The carbon conversion efficiency Xc was 0.94 for reduction at a ratio of Cu-OC to char ϕ = 75 and the product gas was primarily CO2 with trace O2. The reactivities and the rates were similar for five redox cycles. These results indicate that the natural ore-derived material with low cost has potential as a competitive oxygen carrier in solid fuel CLOU based on its reactivity in this study.