Gasification performance of olive pomace in updraft and downdraft fixed bed reactors

This study aims to investigate the gasification potential of olive pomace with using different fixed-bed gasifier systems. Olive pomace as a dried form was supplied from a chemical industry plant working on olive oil soap, located in Izmir, Türkiye. After a complete characterization of olive pomace, gasification experiments by using fixed bed reactor systems were done at three different gasifier temperatures as 700, 800 and 900 °C. As a gasification agent, dry air was used with four different flowrates (0.4, 0.2, 0.1, 0.05 L/min) while pure oxygen experiments were carried out with a flow rate of 0.01 L/min. Syngas with H₂ content of 48% and 45% (volumetric) were obtained in updraft and downdraft gasifiers, respectively, by using dried air as a gasifying agent. Heating value of syngas was around 12.4 MJ/Nm³. In the pure oxygen atmosphere, H₂ contents of the syngas were measured as 53% and 39%vol. In the updraft and downdraft gasifiers. This paper presents the research results on the olive pomace gasification study as a part of a large-scale research project and discuss them in the context of hydrogen production from the fixed bed reactors.     

Options for net zero emissions hydrogen from Victorian lignite. Part 1: Gaseous and liquefied hydrogen

This two-part paper investigates the feasibility of producing export quantities (770 t/d) of blue hydrogen meeting international standards, by gasification of Victorian lignite plus carbon capture and storage (CCS). The study involves a detailed Aspen Plus simulation analysis of the entire production process, taking into account fugitive methane emissions during lignite mining. Part 1 focusses on the resources, energy requirements and greenhouse gas emissions associated with production of gaseous and liquefied hydrogen, while Part 2 focusses on production of ammonia as a hydrogen carrier.In this study, the proposed process comprises lignite mining, lignite drying and milling, air separation unit (ASU), dry-feed entrained flow gasification, gas cooling and cleaning, sour water-gas shift reaction, acid gas removal, pressure swing adsorption (PSA) for hydrogen purification, elemental sulphur recovery, CO₂ compression for transport and injection, hydrogen liquefaction, steam and gas turbines to generate all process power, plus an optional post-combustion CO₂ capture step. High grade waste heat is utilised for process heat and power generation. Three alternative process scenarios are investigated as options to reduce resource utilisation and greenhouse gas emissions: replacing the gas turbine with renewable energy from off-site wind turbines, and co-gasification of lignite with either biomass or biochar. In each case, the specific net greenhouse gas intensity is estimated and compared to the EU Taxonomy specification for sustainable hydrogen.This is the first time that a coal-to-hydrogen study has quantified the greenhouse gas emissions across the entire production chain, including upstream fugitive methane emissions. It is found that both gaseous and liquefied hydrogen can be produced from Victorian lignite, along with all necessary electricity, with specific emissions intensity (SEI) of 2.70 kg CO₂-e/kg H₂ and 2.73 kg CO₂-e/kg H₂, respectively. These values conform to the EU Taxonomy limit of 3.0 kg CO₂-e/kg H₂. This result is achieved using a Selexol™ plant for CO₂ capture, operating at 89.5%–91.7% overall capture efficiency. Importantly, the very low fugitive methane emissions associated with Victorian lignite mining is crucial to the low SEI of the process, making this is a critical advantage over the alternative natural gas or black coal processes.This study shows that there are technical options available to further reduce the SEI to meet tightening emissions targets. An additional post-combustion MDEA CO₂ capture unit can be added to increase the capture efficiency to 99.0%–99.2% and reduce the SEI to 0.3 kg CO₂-e/kg H₂. Emissions intensity can be further reduced by utilising renewable energy rather than co-production of electricity on site. Net zero emissions can then be achieved by co-gasification with ≤1.4 dry wt.% biomass, while a higher proportion of biomass would achieve net-negative emissions. Thus, options exist for production of blue hydrogen from Victorian lignite consistent with a ‘net zero by 2050’ target.     

Characterisation of submicron particles produced during oxygen blown entrained flow gasification of biomass

In this paper submicron particles sampled after the quench during 200 kW, 2 bar(a) pressurised, oxygen blown gasification of three biomass fuels, pure stem wood of pine and spruce, bark from spruce and a bark mixture, have been characterised with respect to particle size distribution with a low pressure cascade impactor. The particles were also characterised for morphology and elemental composition by a combination of scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and high resolution transmission electron microscopy/energy dispersive spectroscopy/selected area electron diffraction pattern (HRTEM/EDS/SAED) techniques. The resulting particle concentration in the syngas after the quench varied between 46 and 289 mg/Nm³ consisting of both carbon and easily volatile ash forming element significantly depending on the fuel ash content. Several different types of particles could be identified from classic soot particles to pure metallic zinc particles depending on the individual particle relation of carbon and ash forming elements. The results also indicate that ash forming elements and especially zinc interacts in the soot formation process creating a particle with shape and microstructure significantly different from a classical soot particle.     

Gasification of waste biomass chars by carbon dioxide via thermogravimetry. Part I: Effect of mineral matter

A series of carbon dioxide gasification tests of waste biomass chars were performed in a thermogravimetric analysis system, at non-isothermal heating conditions. The effects of the inorganic constituents of the fuels on thermal conversion characteristics were examined. Reaction rates were determined by developing a power law model.The bulk of char gasification process occurred between 800 and 950 °C. Maximum reaction rate and conversion were exhibited by waste paper char, due to its higher surface area.Inherent alkaline and alkaline earth carbonates and sulphates acted as catalysts, by increasing the reactivity of the fuels in carbon dioxide and causing their degradation to start at lower temperatures (60-75 °C).The kinetic model fitted the experimental results accurately. Activation energy values and reaction order ranged from 180 to 370 kJ/mol and 0.4 to 0.6, respectively, among the chars, indicating a chemically controlled process.     

Gasification of heavy fuel oils: A thermochemical equilibrium approach

Combustion of heavy fuel oils is a major source of production of particulate emissions and ash, as well as considerable volumes of SO_x and NO_x. Gasification is a technologically advanced and environmentally friendly process of disposing heavy fuel oils by converting them into clean combustible gas products. Thermochemical equilibrium modeling is the basis of an original numerical method implemented in this study to predict the performance of a heavy fuel oil gasifier. The model combines both the chemical and thermodynamic equilibriums of the global gasification reaction in order to predict the final syngas species distribution. Having obtained the composition of the produced syngas, various characteristics of the gasification process can be determined; they include the H₂:CO ratio, process temperature, and heating value of the produced syngas, as well as the cold gas efficiency and carbon conversion efficiency of the process. The influence of the equivalence ratio, oxygen enrichment (the amount of oxygen available in the gasification agent), and pressure on the gasification characteristics is analyzed. The results of simulations are compared with reported experimental measurements through which the numerical model is validated. The detailed investigation performed in the course of this study reveals that the heavy oil gasification is a feasible process that can be utilized to generate a syngas for various industrial applications.     

Heißgasfiltration im Synthesegas aus Biomasse

During thermochemical conversion of biological material in a fluidized bed reactor the nutrients are remaining as dust in the product gas. Hot gas filtration represents a possibility to recover these minerals. The characteristics of this gas add up new technical tasks. The following article gives an account of long lasting experience of operation and optimization in a pilot plant.     

Kinetics of tire derived fuel (TDF) char oxidation and accompanying changes in surface area

The oxidation behavior of tire-derived fuel (TDF) char has recently been studied by several groups. In the present study, TDF char oxidation has been examined between 670 and 825 K, at oxygen partial pressures ranging from 2 to 19.8 kPa. The order of reaction with respect to oxygen varied with burnoff, and was in the range 0.72-0.86. The activation energy of reaction ranged with burnoff from 138 to 150 kJ/mol. The reaction rate does not correlate well with BET surface area, but did correlate well with the surface area in pores ranging in size from 1.2 to roughly 7 nm in width. Pores smaller than 1.2 nm exist in the char, but appear not to be used or developed by the oxidation reaction. Results for chars that have been acid washed to remove some inorganic matter show lowered reactivity, and a distinctly different pattern of pore development with burnoff. This is, in turn, reflected in a very different pattern of reactivity change with burnoff for such materials.     

Conversion of brown coal in supercritical water without and with addition of oxygen at continuous supply of coal-water slurry

A study of conversion of organic matter of brown coal in supercritical water (SCW) at 30 MPa, 400−760 °C and continuous supply of coal-water slurry (CWS) into a tubular reactor is presented. It was found that 48−63% (depending on the SCW temperature) of coal organic matter (COM) is ejected from CWS coal particles as liquid and gaseous products when they move through the reactor. We termed this stage of SCW conversion as dynamic conversion (DC) of coal. It turns out that the particles which underwent the DC stage did not aggregate in the reactor during static conversion (SC) within a coal layer due to continuous pumping through this layer. The experimental data on the composition of DC and SC products, degree of coal conversion, and the data on the degree of combustion of carbon in the presence of oxygen are given.     

Modeling of an oxygen-staged membrane wall gasifier: effects of secondary oxygen

A new type of entrained flow gasifier with membrane wall and two-stage oxygen supply is being developed in China. The fraction of the secondary oxygen in total oxygen (FSO) is an important parameter for this kind of gasifier. A dynamic reduced order model (ROM) based on a reactor network model (RNM) is developed for this gasifier, which is used to investigate the effects of FSO on the slag layer thickness profile on the wall and explore the potential of FSO in dynamic slag control. The ROM adopts a flexible RNM blocking method, which varies with FSO to account for the influence of FSO on the flow pattern in the gasifier. Available industrial data was used to validate the model and a detailed sensitivity analysis for the calculation of slag layer thickness was performed. Static analyses show that FSO has a marked effect on the slag thickness distribution and higher FSO leads to lower heat loss through the wall. Finally, a slag control system, which introduced FSO as an auxiliary regulator, is proposed. Dynamic simulation shows that the new control system offers an improved performance in slag control and can broaden the regulating range of operating temperature.     

Reaction kinetics of the combined pyrolysis and steam-gasification of carbonaceous waste materials

Synthesis gas production by steam-gasification of carbonaceous waste materials with high volatile contents (e.g., sewage and industrial sludge, fluff, and scrap tire powder) is kinetically examined. A multiple pseudo-component first-order reaction model is formulated to describe the rates of the combined pyrolysis and gasification processes. Arrhenius-type kinetic parameters are determined by dynamic thermogravimetric experimental runs conducted in the temperature range 473-1476 K.