Promoting effect of biomass ash additives on high-temperature gasification of petroleum coke: Reactivity and kinetic analysis

The effect of biomass ash (rice straw ash (RSA) and cotton straw ash (CSA)) on the gasification reactivity and the evolution of physicochemical structure of petcoke char was investigated. The catalytic effect of CSA was significantly higher than that of RSA, and the catalytic effect of biomass ash was enhanced at lower gasification temperature and for higher blending ratio of biomass ash. The promoting effect of biomass ash was related to the increase of active AAEM content, the decrease of order degree of carbon structure and the development of surface structure in char gasification after biomass ash addition, which was more significant for CSA, at lower temperature and for higher blending ratio. Moreover, the shrinking core model was suitable for char gasification, and the additions of RSA and CSA reduced the activation energy of petcoke char gasification from 199.84 kJ mol⁻¹ to 159.85 kJ mol⁻¹ and 62.75 kJ mol⁻¹, respectively.     

CO2 gasification of dairy and swine manure: A life cycle assessment approach

CO₂ gasification of three different chars obtained from the pyrolysis of two dairy manure samples and a swine manure sample was evaluated. Dairy samples were firstly pretreated by anaerobic digestion process and swine sample by bio-drying process. Subsequently, manure samples were pyrolyzed between 30 °C and 980 °C obtaining a solid fuel (biochar), which was later gasified using different vol.% CO₂ (15–90%) which was the gasifying agent. Gasification was conducted at 900 °C. Thermal behavior and gasification characteristics were studied by means of the thermogravimetric-mass spectrometric analysis. In this sense, the reactivity of the samples was influenced by the catalytic activity of the mineral matter contained in the remaining biomass ashes. On the other hand, the viability of the manure gasification process vs the traditional use of manure as fertilizer was studied by means of the life cycle assessment (LCA) methodology. Two different scenarios were analyzed: gasification of manure sample before anaerobic digestion (Pre) and gasification of manure after anaerobic digestion (Dig R). According to the results obtained, the gasification of char Pre was the most viable scenario from the economic and environmental viewpoints whereas the gasification of char Dig R was the best energetic option.     

Effect of pore structure on CO2 gasification reactivity of biomass chars under high-temperature pyrolysis

The CO₂ gasification reactivity of pine sawdust chars (PS char) obtained from the different high-temperature pyrolysis is studied based on non-isothermal thermogravimetric method. Results show that the order of gasification reactivity is PS char-1073 > PS char-1273 > PS char-1473. Under the effect of high-temperature pyrolysis, the surface structure of biomass char is gradually destroyed and the pore structure parameters of specific surface area, total pore volume and average pore diameter increase. By means of the N₂ adsorption-desorption isotherms, it is seen that biomass char has more micro- and mesoporous at higher pyrolysis temperature. Besides, the PS char-1073 mostly has rich closed cylinder pores and parallel plate pores, and the PS char-1273 and PS char-1473 have plentiful open cylinder pores and parallel plate pores. An increase of pyrolysis temperature contributes to the development of porosity and improves diffusion path, which promotes the gasification reactivity. But, its effect on the decline of active site hinders the gasification reactivity. What's more, the kinetic model of distributed activation energy model (DAEM) is applied to calculate activation energy and pre-exponential factor with the integral and differential methods. The calculation results of integral method is more accurate and precise because the differential method is more sensitive than integral method for experimental noise. There is a compensation effect in the CO₂ gasification process.     

Kinetics of CO2 gasification of biomass char in granulated blast furnace slag

The CO₂ gasification reactions of biomass char in granulated BFS (blast furnace slag) were isothermally investigated using a thermogravimetric analyzer with the temperature ranging from 1173 K to 1323 K. The effects of temperature, biomass type and granulated BFS on the kinetic characterizations of CO₂ gasification of biomass char were illuminated. The kinetic mechanism models and parameters were obtained through a novel two-step calculation method. The results indicated that the CO₂ gasification reactivity of biomass char as conversion and gasification index increased with the increase of temperature and it could be promoted through granulated BFS. The CO₂ gasification reactivity of CS (cornstalk) char with lower alkali index was lower than that of PS (peanut shell) char. The A₄ model (Avrami-Erofeev (m = 4) model) and A₃ model (Avrami-Erofeev (m = 3) model) were demonstrated as the best appropriate models for CO₂ gasification of CS char and PS char, respectively. The gasification activation energy of CS char ranging from 155.08 to 160.48 kJ/mol was higher than that of PS char whether with or without granulated BFS. Granulated BFS could decrease the activation energy of CO₂ gasification of char at any biomass type.     

Gasification of woody biomass under high heating rate conditions in pure CO2: Experiments and modelling

The present paper focuses on the gasification of thin wood particles in pure CO₂ at 850 °C under high heating rate conditions (similar to fluidized bed gasifiers). The aim is to assess the potential use of CO₂ as gasifying medium and to learn more about its effects on the pyrolysis as well as on the char gasification stages. Experimental and numerical modelling results provide answers on the unfolding of the whole CO₂ biomass pyro-gasification process. It was found that despite the CO₂ is present inside the particle during the pyrolysis stage, it has no noticeable impacts neither on the reaction rate nor on the char yield due to the relatively low temperature inside the particle. The CO₂ char gasification is the rate limiting step of the global pyro-gasification reaction as its duration is near to 95% of the entire biomass conversion time.     

Integrated drying and gasification of wet microalgae biomass to produce H2 rich syngas – A thermodynamic approach by considering in-situ energy supply

A novel integrated drying and gasification of microalgae wet biomass process, involving a chemical-looping combustion (CLC) option to supply energy, is developed using Aspen Plus. The integrated gasification system consists of four primary units, including (i) a wet biomass drying unit, (ii) the gasification system, (iii) the CLC section, and (iv) the gas purification process. The model shows a good accuracy (relative error < 10%) in predicting the product compositions as compared to the experimental results under consistent operating conditions. The performance of the integrated gasification system is evaluated using Spirulina microalgae at various moisture contents (0–45 wt%). The effect of gasifying agents O₂/steam and the fraction of the produced char used in the CLC section on the gasification performance is also evaluated. The tar is successfully reformed into syngas in the pyrolysis stage by adjusting the O₂ flow rate. The C (char) to CLC provides to a positive effect on the syngas composition, particularly for gasification of wet biomass, but brings an adverse impact on the yield of the syngas product. The integration of the CLC process and CO₂ absorber in the gasification system provides high-quality syngas by removing CO₂. The separated pure CO₂ can be used as a feedstock for other chemical industries.     

Hydrogen production from autothermal CO2 gasification of cellulose in a fixed-bed reactor: Influence of thermal compensation from CaO carbonation

Biomass gasification is a promising technology to produce renewable syngas used for energy and chemical applications. However, biomass gasification has challenges of low process energy efficiency, low syngas production with low H₂/CO ratio and the sintering of biomass ash which limit the deployment of the technology. This work investigated the influence of in-situ generated heat from CaO–CO₂ on cellulose CO₂ gasification using a fixed bed reactor, thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR) and differential scanning calorimetry (DSC). Experimental results indicate an approximate 20 °C temperature difference in the fix-bed reactor between cellulose CO₂ gasification with the energy compensation of CaO carbonation (denoted auto-thermal biomass gasification) and conventional CO₂ gasification of cellulose after the power of external furnaces were turned off. Around 5 times H₂/CO molar ratio is obtained after switching off the power in the auto-thermal biomass gasification compared with conventional gasification. The gas yield enhances significantly from 0.29 g g^?1 cellulose to 0.56 g g^?1 cellulose when CaO/cellulose mass ratio increases from 0 to 5. Furthermore, the TGA-FTIR results demonstrate the feasibility of adopting energy compensation of CaO carbonation to reduce the gasification temperature. DSC analysis also proves that the released heat from the CaO–CO₂ reaction reduces the required energy for cellulose degradation.     

Isothermal and non-isothermal kinetic study on CO2 gasification of torrefied forest residues

CO₂ gasification of torrefied forest residues (birch and spruce branches) was investigated by means of a thermogravimetric analyser operated non-isothermally (400–1273 K) and isothermally (1123 K) under the kinetic regime, followed by kinetic analyses assuming different models. For the non-isothermal gasification, the distributed activation energy model (DAEM) with four or five pseudo-components was assumed. It is found that the severity level of torrefaction had great influences on gasification behaviour as well as devolatilization step. The activation energy of non-isothermal gasification step of three samples varied in the range of 260–290 kJ/mol. The char reactivity decreased with increased torrefaction temperature. For the isothermal gasification, the random pore model (RPM), shrinking core model (SCM), and homogeneous model (HM) were tested. The result has confirmed the trend of decrease in char reactivity with increased torrefaction temperature observed from the non-isothermal gasification. However, different trends in char reactivity due to different wood types were observed by the two methods of gasification.     

Steam gasification of energy crops of high cultivation potential in Poland to hydrogen-rich gas

In the paper energy crops of considerable cultivation potential in Poland, namely: Salix viminalis, Helianthus tuberosus, Sida hermaphrodita, Spartina pectinata, Andropogon gerardi and Miscanthus X giganteus were tested in terms of steam gasification reactivity of biomass chars, as well as yields and composition of product gas in steam gasification and lime-enhanced steam gasification in a laboratory scale fixed bed reactor at 650 °, 700 ° and 800 °C.The highest value of reactivity for 50% of carbon conversion, R₅₀, was observed for Sida hermaphrodita, regardless the process temperature.Application of CaO for in-situ CO₂ capture in steam gasification of biomass chars resulted in hydrogen content increase at 650 °C to the levels comparable with the ones reached at 800 °C without carbonation reaction. Also hydrogen and total gas yields increased in tests of lime-enhanced gasification.     

Fuel conversion characteristics of black liquor and pyrolysis oil mixtures: Efficient gasification with inherent catalyst

Alkali metals inherent in black liquor (BL) have strong catalytic activity during gasification. A catalytic co-gasification process based on BL with pyrolysis oil (PO) has the potential to be a part of efficient and fuel-flexible biofuel production systems. The objective of the paper is to investigate how adding PO into BL alters fuel conversion under gasification conditions. First, the conversion times of single fuel droplet were observed in a flat flame burner under different conditions. Fuel conversion times of PO/BL mixtures were significantly lower than PO and comparable to BL. Initial droplet size (300–1500 μm) was the main variable affecting devolatilization, indicating control by external heat transfer. Char oxidation was affected by droplet size and the surrounding gas composition. Then, the intrinsic reactivity of char gasification was measured in an isothermal thermogravimetric analyser at T = 993–1133 K under the flow of CO₂–N₂ mixtures. All the BL-based samples (100% BL, 20% PO/80% BL, and 30% PO/70% BL on mass basis) showed very high char conversion. Conversion rate of char gasification for PO/BL mixtures was comparable to that of pure BL although the fraction of alkali metal in char decreased because of mixing. The reactivities of BL and BL/PO chars were higher than the literature values for solid biomass and coal chars by several orders of magnitude. The combined results suggest that fuel mixtures containing up to 30% of PO on mass basis may be feasible in existing BL gasification technology.     

Gasification reactivity and synergistic effect of conventional and microwave pyrolysis derived algae chars in CO2 atmosphere

This research focuses on the isothermal and non-isothermal CO₂ gasification of an algal (Chlorella) char prepared via two different thermal processing systems, i.e. conventional and microwave-assisted pyrolysis. It was found that chars prepared via microwave irradiation showed higher CO₂ gasification reactivity than that of chars prepared via the conventional method. Meanwhile, the activation energy of microwave char was found to be 127.89 kJ/mol, which was 46.3 kJ/mol lower than that of conventional char, indicating improved reactivity of microwave char. The systematic characterisation of both conventional and microwave chars shows that the higher reactivity of microwave char could be attributed to its large BET surface area, low crystalline index and high active sites. In addition, it was found that microwave heating contributed to high reactivity of chars through generating large amount of primary char, the formation of hot spot and high specific surface area and pore volume. Results of co-gasification under isothermal conditions revealed the existence of greater synergistic effects between coal char and microwave algae char than those of coal char and conventional algae char. Furthermore, based on the relative Rs (average gasification rate), a novel index proposed to quantify the interactions in co-gasification process, Australian coal char/microwave assisted char blend experienced 10% higher interactions compared to Australian coal char/conventional assisted char blend.     

Integrated catalytic adsorption (ICA) steam gasification system for enhanced hydrogen production using palm kernel shell

This paper investigates the integrated catalytic adsorption (ICA) steam gasification of palm kernel shell for hydrogen rich gas production using pilot scale fluidized bed gasifier under atmospheric condition. The effect of temperature (600–750 °C) and steam to biomass ratio (1.5–2.5 wt/wt) on hydrogen (H₂) yield, product gas composition, gas yield, char yield, gasification and carbon conversion efficiency, and lower heating values are studied. The results show that H₂ hydrogen composition of 82.11 vol% is achieved at temperature of 675 °C, and negligible carbon dioxide (CO₂) composition is observed at 600 °C and 675 °C at a constant steam to biomass ratio of 2.0 wt/wt. In addition, maximum H₂ yield of 150 g/kg biomass is observed at 750 °C and at steam to biomass ratio of 2.0 wt/wt. A good heating value of product gas which is 14.37 MJ/Nm³ is obtained at 600 °C and steam to biomass ratio of 2.0 wt/wt. Temperature and steam to biomass ratio both enhanced H₂ yield but temperature is the most influential factor. Utilization of adsorbent and catalyst produced higher H₂ composition, yield and gas heating values as demonstrated by biomass catalytic steam gasification and steam gasification with in situ CO₂ adsorbent.     

Kinetics and mechanism of CO2 gasification of coal catalyzed by Na2CO3, FeCO3 and Na2CO3–FeCO3

The purpose is to develop a mild catalytic CO₂-gasification technology that can promote CO₂ utilization and reduce cost in air separation systems with improving system efficiency and obtaining desirable gaseous products. In this study, the influence of Na, Fe and their composite catalysts on the structure and gasification reactivity of chars derived from pyrolysis of Powder River Basin (PRB) coal was investigated. The results showed that a strong positive synergistic effect between Na and Fe catalyst in the gasification process was observed, the catalytic activity of the added catalysts was in order of: 4% Na > 3% Na–1%Fe > 2% Na-2% Fe > 1% Na-3% Fe > 1% Na-2% Fe > 4% Fe > raw coal. The catalysts inhibited the growth of the aromatic ring structure and enriched the generation of O-containing functional groups. Compared to Fe, the Na-based catalyst could easily diffuse into inner pores of coal char, forming C–O–Na structure and thus increasing the gasification reactivity of chars. In addition, due to the formation of inert material between SiO₂ and Na, the catalytic activity of Na catalysts was significantly decrease at the late stage of char conversion. Comparatively, the Fe-based catalysts showed better stability life. Moreover, it was found that the activation energy for CO₂-gasification of PRB coal can be decreased by 50% due to the addition of Na catalyst.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Identifying the roles of MFe2O4 (M=Cu,Ba, Ni,and Co) in the chemical looping reforming of char,pyrolysis gas and tar resulting from biomass pyrolysis

Biomass chemical looping gasification (BCLG), which employs oxygen carriers (OCs) as the gasification agent, is drawing more attention for its low cost and environmental friendliness. However, the complex products of biomass pyrolysis and the reactions between OCs and the pyrolysis products constrain its development. In this study, MFe₂O₄ (M = Cu, Ba, Ni and Co) ferrites synthesized via the sol-gel method were investigated as OCs in BCLG for hydrogen-rich syngas production. The properties of the as-prepared and spent OCs were characterized by X-ray diffraction (XRD), H₂-temperature programmed reduction (TPR), scanning electron microscopy (SEM), and automatic surface area porosimetry (BET). The three-phase products (char, pyrolysis gas and toluene) derived from biomass pyrolysis were employed as the reactants to investigate the reactivity of the ferrites. Then, BCLG experiments using biomass were conducted on the four ferrites to further determine their performance. The characterization results suggested that the four ferrites are all attractive for the chemical looping process, exhibiting good oxygen transferability and wide distributions of metal cations because of their metal synergistic effects in the spine structure. Reactions with pyrolysis gas and biomass char indicated that BaFe₂O₄ has a higher reactivity via a solid-solid reaction but a lower reactivity with pyrolysis gas, which make it very favorable for the production of hydrogen-rich syngas. Furthermore, BaFe₂O₄ showed excellent performance for toluene catalytic cracking with small amounts of carbon deposition. The synergetic effects between Ba and Fe metals considerably enhanced selective oxidation to produce 26.72% more H₂ than CoFe₂O₄ and 13.79% more H₂ than NiFe₂O₄ and CuFe₂O₄ for biomass gasification. The hydrogen yield produced by BaFe₂O₄ with the assistance of steam for biomass gasification can reach 41.8 mol/kg of biomass.     

Impacts of char structure evolution and inherent alkali and alkaline earth metallic species catalysis on reactivity during the coal char gasification with CO2/H2O

In this work, we studied the effects of char structural evolution and alkali and alkaline earth metallic species (AAEMs) catalysis on the reactivity during the char gasification with CO₂, H₂O, and their mixture. The gasified chars with different carbon conversion levels were prepared, and their physicochemical structures were characterized via nitrogen adsorption and FT‐Raman techniques. The concentrations of AAEMs in different modes were obtained by the sequential chemical extraction method. The reactivities of the raw and gasified chars were analyzed by the thermogravimetric analysis. The gasification atmospheres had varied effects on the physicochemical structure of coal char. The gasified char obtained in the CO₂ atmosphere had a lower aromatic condensation degree compared with that obtained in the H₂O atmosphere, irrespective of the temperature. The impact of the atmospheres on the specific surface area of the char varied with the temperature because H₂O and CO₂ have different routes of development of pore structure with coal char. A large specific surface area facilitates the exposure and dispersion of more AAEMs on the surface of the channel, which is conducive to their contact with the gasification agent to play the catalytic role. Thus, the reactivity of the gasified char is well correlated with its specific surface area at different gasification temperatures. In the absence of AAEMs, the chemical structure of coal char becomes the dominant factor affecting the reactivity.     

Experimental study on the key factors affecting the gasification performance between different biomass: Compare citrus peel with pine sawdust

This work aims to reveal the advantages of citrus peel gasification and investigate the key factors affecting gasification performance. The gasification performance of citrus peel and pine sawdust are compared in a fixed bed reactor, and the reactivity and properties of biochar were investigated. The results showed that the H₂ yield and carbon conversion efficiency of citrus peel gasification were 34.35 mol/kg_biomass and 66.30%, respectively, which were higher than those of pine sawdust. Due to the high reactivity of citrus peel char, it only takes 100 min for the citrus peel to complete the gasification reaction, which is significantly faster than pine sawdust. Although the specific surface area of citrus peel char is lower than that of pine sawdust char, both the low degree of graphitization and the high catalytic index (2426.96) are favorable for the conversion of char, which ultimately lead to the high reactivity of citrus peel char.     

Gasification reactivity of biomass chars with CO2

In this study, carbon conversion was calculated from the data obtained with a real-time gas analyzer. In a lab-scale furnace, each biomass sample was pyrolyzed in a nitrogen environment and became biomass char. For preparation of the char, the furnace was electrically heated over 40 min up to the wall temperature of 850 °C, and maintained at the same temperature over 17 min. The furnace was again heated over 3 min to a temperature higher than 850 °C and then CO₂ was injected. The biomass char was then gasified with CO₂ under isothermal conditions. The reactivity of biomass char was investigated at various temperatures and CO₂ concentrations. The VRM (volume reaction model), SCM (shrinking core model), and RPM (random pore model) were used to interpret the experimental data. For each model, the activation energy (E) and pre-exponential factor (A) of the biomass char-CO₂ reaction were determined from gas-analysis data by using the Arrhenius equation. For the RPM, the apparent reaction order was determined. According to this study, it was found that the experimental data agreed better with the RPM than with the other two models. Through BET analyses, it was found that the structural parameter (ψ) of the surface area for the RPM was obtained as 4.22.     

Reactivity investigation on chemical looping gasification of biomass char using nickel ferrite oxygen carrier

Chemical looping gasification (CLG) involves the use of an oxygen carrier (OC) which transfers oxygen from air to solid fuel to convert the fuel into synthesis gas, and the traditional gasifying agents such as oxygen-enriched air or high temperature steam are avoided. In order to improve the reactivity of OC with biomass char, facilitating biomass high-efficiency conversion, a compound Fe/Ni bimetallic oxide (NiFe₂O₄) was used as an OC in the present work. Effect of OC content and oxygen sources on char gasification were firstly investigated through a TG reactor. When the OC content in mixture sample attains 65 wt.%, the sample shows the maximum weight loss rate at relatively low temperature, indicating that it is very favorable for the redox reactions between OC and biomass char. The NiFe₂O₄ OC exhibits a good performance for char gasification, which is obvious higher than that of individual Fe₂O₃ OC and mechanically mixed Fe₂O₃ + NiO OC due to the Fe/Ni synergistic effect in unique spinel structure. According to the TGA experimental results, effect of the steam content and cyclic numbers on char gasification were investigated in a fixed bed reactor. Either too low steam content or too high steam content doesn't facilitate the char gasification. And suitable steam content of 56.33% is determined with maximum carbon conversion of 88.12% and synthesis gas yield of 2.58 L/g char. The reactivity of NiFe₂O₄ OC particles shows a downtrend within 20 cycles (～64 h) due to the formation of Fe₂O₃ phase, which is derived from the iron element divorced from the Fe/Ni spinel structure. Secondly, the sintering of OC particles and ash deposit on the surface are also the reasons for the deactivation of NiFe₂O₄ OC. However, the carbon conversion and synthesis gas yield at the 20th cycle are still higher than those of the blank experiment. It indicates that the reactivity of NiFe₂O₄ OC can be maintained at a relatively long time and NiFe₂O₄ material can be used as a good OC candidate for char gasification in the long time running.     

Inhibition of steam gasification of biomass char by hydrogen and tar

The influence of hydrogen and tar on the reaction rate of woody biomass char in steam gasification was investigated by varying the concentrations in a rapid-heating thermobalance reactor. It was observed that the steam gasification of biomass char can be separated into two periods. Compared with the first period, in the second period (in which the relative mass of remaining char is smaller than 0.4) the gasification rate is increased. These effects are probably due to inherent potassium catalyst. Higher hydrogen partial pressure greatly inhibits the gasification of biomass char in the first and second periods. By calculating the first-order rate constants of char gasification in the first and second periods, we found that the hydrogen inhibition on biomass char gasification is caused by the reverse oxygen exchange reaction in the first period. In the second period, dissociative hydrogen adsorption on the char is the major inhibition reaction. The influence of levoglucosan, a major tar component derived from cellulose, was also examined. We found that not only hydrogen but also vapor-phase levoglucosan and its pyrolysates inhibited the steam gasification of woody biomass char. By mixing levoglucosan with woody biomass sample, the pyrolysis of char proceeds slightly more rapidly than with woody biomass alone, and gas evolution rates of H₂ and CO₂ are larger in steam gasification.