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This study presents a numerical investigation of steam gasification of hydrochar derived from fruit wastes. Four fruit wastes, apple chip pomace, grape pomace, rotten apple, and apple juice pomace, were used as feedstocks. Aspen Plus was used to simulate the gasification process. The syngas composition, hydrogen to CO ratio (H2/CO), CO to CO2 ratio (CO/CO2), and heating value (HHV) of the resulting syngas were analyzed. Results show that hydrothermal carbonization (HTC) increases the CO and reduces the CO2 content of the syngas after gasification. Accordingly, H2/CO reduces, and CO/CO2 increases after HTC treatment. Hydrothermal treatment also improves the HHV of the syngas. The obtained HHV of syngas from hydrochar gasification ranged from 10.1 to 15.3 MJ/Nm3 depending on the process parameters. Additionally, effects of process parameters were studied. Increasing the steam to biomass ratio (SBR) leads to a higher H2/CO, enriching the syngas with hydrogen (up to 64.7 vol%). Higher SBR also lowers the CO/CO2 ratio due to the consumption of CO and a rise in CO2. HHV increases with increasing pressure, and hydrochars exhibit more changes in HHV than raw feedstocks. The reaction temperature contributes to an increase in the fraction of CO in the syngas (up to 39.6 vol%). Although hydrogen increased initially with temperature, a slight reduction was observed for the gas at elevated temperatures, reducing the H2/CO ratio and increasing the CO/CO2 ratio.

Plastics are abundant and have a high energy content making their use in energy applications attractive. This article presents a review on plastic waste (PW) management by pyrolysis and gasification, which are two types of thermochemical conversion (TCC) techniques. The conversion of PW and the application of its converted products are important steps toward reducing reliance on fossil fuels, enhancing closed-loop recycling of materials and the circular economy. The review presented herein also focuses on product distribution and yields with emphasis on the energy content and potential integration to energy systems and grids. It is found that pyro-oils have properties similar to conventional fuels such as diesel and can partially substitute for fossil fuels. In fact, the energy content of PW pyro-oils obtained by various researchers range from 41.10−46.16 MJ kg−1 , which is close to the heating values of conventional fuels and thus are potential candidates for fuel applications. Typical treatment post-conversion is also conducted to maintain the quality of the oil produced and the removal of sulfur content to conform with market standards. On the other hand, syngas produced during gasification possesses a lower potential for fuel applications as its energy content may reach values as low as 20 MJ kg−1 in comparison to pyro-oil. However, depending on the process conditions, it is possible to increase the energy content to values of over 40 MJ kg−1 . Additionally, syngas is the building block for many valuable chemicals. With appropriate treatment, the syngas obtained from the gasification of PW can be used in gas engines and can be converted to commercial products such as liquid fuels via the Fischer−Tropsch synthesis. This review also highlights some available commercial-scale plants for the TCC of PW and real-life application of their obtained products. It is noted that the integration of the processes to energy systems is technically and economically feasible. Real-life applications of products obtained from the pyrolysis and gasification of PW in different parts of the world are also discussed. The produced fuels have been used in cooking stoves and burned in a gas turbine, internal combustion engine, and direct injection diesel engine.

The present study investigates the steam gasification of biomass with an in-process CO2 capture. The work is aimed at achieving hydrogen enrichment while reducing the carbon dioxide (CO2) concentra...

With increases in population and industrialization, global energy demand is increasing rapidly and resulting in various environmental challenges related to fossil fuel consumption. These challenges have made it imperative to look for alternative means of environmentally sustainable energy production, such as the thermal degradation of biomass. Biofuels obtained from pyrolysis have the potential to be substituted for fossil fuels, but one of the major barriers to utilization of pyrolysis oil is the presence of oxygenated compounds. An approach to overcome this is to co-pyrolyze the biomass with hydrogen-rich feedstocks such as plastic and tire wastes. Studies have shown that exists a synergistic relationship between plastics/tires and biomass as well as resulting products from co-pyrolysis have higher heating value along with improved bio-oil properties. This paper discusses the current progress on the co-pyrolysis of biomass with waste plastics/tires and their synergistic interactions for high grade fuel production. Co-pyrolysis studies done on pilot-scale have also been discussed in this review.

In recent years, hydrothermal carbonization (HTC) has been introduced as an attractive method for converting biomass into value-added products. The complex reaction chemistry and variable compositi...

This study investigates the calcination and carbonation reaction kinetics of eggshell. Nonisothermal (dynamic) thermogravimetry using multiple heating rates was conducted to study the calcination process. On the other hand, isothermal conditions were applied to report on the carbonation process in a carbon dioxide (CO2) atmosphere. Several model-based and isoconversional kinetic methods were used to evaluate the calcination kinetic parameters. The methods include the Friedman, Coats and Redfern, modified Coats and Redfern, Kissinger, Flynn–Wall–Ozawa, and Kissinger–Akahira–Sunose methods. Furthermore, an analytical solution method was developed to evaluate the kinetic parameters and to predict the experimental conversion. The carbonation reaction was modeled with a modified form of the shrinking core model. Both the rapid surface reaction-controlled and the slow diffusion-limited stages of carbonation were analyzed. The results showed that the kinetic parameters obtained with the various methods are in go...

Two of the methods for converting biomass to fuel are hydrothermal carbonization (HTC) and anaerobic digestion (AD). This study is aimed at designing and analyzing two scenarios for bioenergy production from undervalued biomass (sawdust). In one of the scenarios (direct combustion or DC), raw biomass is burned in a combustor to provide the heat that is required by the Rankine cycle to generate electricity. In the other scenario (HTC-AD), the raw biomass first undergoes HTC treatment. While the solid product (hydrochar) is used to produce power by a Rankine cycle, the liquid by-product undergoes an AD process. This results in fuel gas production and it can be used in a Brayton cycle to generate more power. Energy and mass balance analysis of both scenarios were developed for each unit process by using Engineering Equation Solver (EES). The required data were obtained experimentally or from the literature. The performances of the proposed systems were evaluated, and a sensitivity analysis was presented to help in finding the best operational conditions.

This work presents a numerical investigation into CO2 valorization via the gasification of poplar wood. It is aimed at determining an optimum gasification condition for enhancing the production of syngas with a flexible H2 to CO molar ratio (H2/CO), which is essential in many petrochemical processes. The research is performed by simulation in ASPEN Plus, where steam and CO2 are fed as co-gasifying agents. The equilibrium concentrations of the product gas are obtained, and the H2/CO as well as the heating value of the resulting syngas are quantified. It is found that the inclusion of CO2 as a co-gasifying agent promotes CO evolution through the Boudouard reaction. However, it reduces H2 concentration, and consequently decreases the H2/CO. Furthermore, the effects of some process parameters have been studied in this work. It is observed that H2/CO reduces with a rise in temperature, increases with increasing CO2 to biomass ratio (CBR), and shows no significant change with pressure. Results further show that methanol synthesis from syngas can be achieved at temperatures close to 660 °C, while oxo-synthesis requires a higher temperature. A CBR of around 0.6 in the present work would be an optimum value for Fischer-Tropsch synthesis to achieve a H2/CO of 2:1, but the CBR should be lower for processes requiring a lower H2/CO like acetic acid formation and oxo-synthesis.

This article reviews current developments in metal-based sorbents for carbon capture with emphasis on calcium oxide. A broad overview of carbon dioxide capture with metals in various forms including oxides, hydroxides, carbonates and zirconates is presented. Based on the findings from comparative assessments of these sorbents, CaO appears to be the best solid sorbent for CO2 capture at high temperatures, and its numerous advantages are discussed in this work. For this reason, a detailed review has been conducted for calcium oxide, which works as a sorbent at temperatures up to 700 °C through carbonation, and desorbs CO2 above 700 °C by calcination of CaCO3 at atmospheric pressure. A review of studies on kinetics modelling of CO2 capture with CaO-based sorbents is also included in this work. Decay in activity caused by sintering and attrition is identified as the greatest challenge with CaO-based sorbents. This work also focuses on the available techniques for enhancing performance and cyclic stability. Reactivation of the sorbents by hydration and reduction in decay rate by doping with inert supports and synthetic sorbents are reviewed. Additionally, the use of biomass resources (waste animal shells) as competitive sources of CaCO3 is discussed in this work. The review concludes with recommendations for future studies in carbon capture and sequestration.

The present work provides numerical investigations of oxygen permeation, hydrogen generation through water splitting using an oxygen transport membrane and oxy-combustion of syngas. The work involves two models; one for hydrogen generation and oxygen permeation from water splitting, and the other for syngas reaction kinetics. Considering steam dissociation reaction and oxygen permeation process, the hydrogen generation model is developed from oxygen permeation model using user defined function (UDF) that enable the transfer of oxygen across the membrane. The codes were written in C++, then compiled and hooked to the ANSYS Fluent 15.0 software. The investigations revealed that, due to combustion, the syngas reactive flow results in higher oxygen permeation and hydrogen generation rates than the non-reactive case. Effects of various influential parameters such as fuel composition, membrane thickness, operating temperature, sweep gas flow rate and CO 2 circulation are investigated in the present study. It was realized that increase in sweep flow rate and inlet temperature results in enhanced oxygen permeation and hydrogen generation rates. Whereas, increase in CO/H 2 ratio, membrane thickness and CO 2 circulation reduces the amounts of hydrogen and oxygen generated.

This chapter presents plastic waste treatment by chemical recycling techniques that convert plastic waste into fuel and other valuable products. The status, challenges, competitive technologies, and opportunities for further research in plastic waste gasification are explored in the chapter. Pyrolysis and plasma gasification are identified as the competitive technologies to gasification. The chapter also discusses different types of reactor for plastic waste gasification and pyrolysis, and operating conditions affecting their performances in laboratory, pilot, and industrial scales. The operating parameters that are common to the discussed chemical plastic recycling processes are temperature, pressure, type of feedstock, and catalysts. Currently, there are several reactor types available for conversion of plastics. However, the commercialization of the thermo-chemical conversion processes is still in progress and much investigation is required to design more robust systems. The use of heterogeneous catalysts in pyrolysis is a promising technique because they can be optimized to increase the yield of desired products and at lower temperatures. Catalysts are also used in copyrolysis of plastic wastes and biomass to produce certain desired products. Product distribution in terms of gas, char, tar, and oil from various investigators is presented in this chapter. Another interesting aspect covered in the chapter is cogasification of plastic waste with biomass and/or coal.

Hydrothermal carbonization (HTC) is a useful method to convert wet biomass to value-added products. Fruit waste generated in juice industries is a huge source of moist feedstock for such conversion to produce hydrochar. This paper deals with four types of fruit wastes as feedstocks for HTC; namely, rotten apple (RA), apple chip pomace (ACP), apple juice pomace (AJP), and grape pomace (GP). The operating conditions for HTC processing were 190 °C, 225 °C, and 260 °C for 15 min. For all samples, higher heating value and fixed carbon increased, while volatile matter and oxygen content decreased after HTC. Except for ACP, the ash content of all samples increased after 225 °C. For RA, AJP, and GP, the possible explanation for increased ash content above 225 °C is that the hydrochar increases in porosity after 230 °C. It was observed that an increase in HTC temperature resulted in an increase in the mass yield for RA and GP, which is in contrast with increasing HTC temperature for lignocellulose biomass. Other characterization tests like thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) also showed that the HTC process can be successfully used to convert fruit wastes into valuable products.

A horizontal cross flow air heated humidifier is designed for three modes of heating. It is tested to investigate its performance in terms of its ability to effectively humidify air. The system investigated in this study has both the humidifier and the heater(s) integrated in one unit. Special low pressure-drop nozzles are used to spray water such that they provide a fine mist, thus they break a liquid to tiny droplets to increase the surface area for better heat and mass transfer between the hot air and sprayed water. Several attempts to improve system performance are made. For example, the effect of adding packing material to further increase heat and mass transfer surface area is attempted. Another attempt is by having an inter-stage heating such that a heating coil (basically a heat exchanger where hot water is circulated in a closed loop) is placed after a first-stage sprayer to heat the air again such that its ability to absorb more moisture increases as it is passed through a second-stage sprayer. A mist eliminator is placed at the exit of the humidifier to make sure water droplets are not allowed to leave the humidifier with the exit humid air stream. Performance parameters used in the analysis include the temperature and humidity of the exit air stream in addition to the humidifier effectiveness that is considered one of the crucial parameters in designing a HDH desalination system. A comparison between different modification to the humidifier are made to select the mode that results in the closest exit air stream to saturation condition and the highest humidifier effectiveness. Adding the packing material showed insignificant improvement to the humidifier performance. On the other hand, the inter-stage heating is believed to be effective in increasing the unit effectiveness.Copyright © 2015 by ASME