Gasification Performance Research Articles

Preparation of pitch semi-coke water slurry and its properties of slurryability and gasification

ABSTRACT A new strategy for the preparation of pitch semi-coke water slurry (p-SCWS) with pitch as raw material and semi-coke powder was proposed. The slurryability and gasification performance of p-SCWS were evaluated by apparent viscosity, stability, FTIR, XRD, and TG/DTG characterization methods. Compared with SCWS, the hydrophilic functional groups of SCWS prepared by coal pitch (CP), modified pitch (MP), and petroleum pitch (PP) increased significantly. p-SCWS and SCWS have similar pseudoplastic rheological properties-shear thinning. p-SCWS exhibits better stability than SCWS, with the lowest WSR at 0% and the highest at 8.49%. The addition of pitch lowered the initial (Ts) and final reaction temperatures (Te) of gasification, increased the activation energy and pre-exponential factor, and enhanced the gasification activity. The Ts and Te of CP-SCWS showed the most significant decrease, reaching 869.95°C and 1010.96°C, respectively, compared to 902.39°C and 1075.60°C for SCWS. The activation energy and pre-exponential factor were highest for PP-SCWS.

Chemical looping gasification of vinegar residue with enhanced LD slag composite Ca-Fe oxygen carrier for syngas production

Biomass chemical looping gasification (BCLG) is an emerging technology that enables waste co-processing into clean energy. A laboratory-scale vertical fixed-bed reactor was used to conduct CLG experiments with vinegar residue (VR) as a biomass fuel, and the effect of enhanced LD slag composite Ca-Fe material as an oxygen carrier (OC) on the production of syngas from BCLG was investigated. This study analyzed the influence of LD slag proportion, kinds of OC, and operational conditions (temperature, oxygen carrier/biomass (OC/B) ratio, and steam/biomass (S/B) ratio) on gasification performance. Results indicate that the syngas yield under the gasification operating conditions at about 850 °C, OC/B = 1, and S/B = 2.5 obtained 1.36 Nm3/kg, the CCE and CGE achieved about 80.82% and 98.16%, respectively, and the H2/CO molar ratio was as high as 2.57. The OCs multi-redox cycle test revealed that after undergoing 10 redox cycles under the conditions mentioned above, the gas yield, CCE, and CGE were reduced to varying extents, but still maintained impressive reactivity. The mechanism analysis showed that the performance degradation of the LD slag composite Ca-Fe OC during the multi-cycle process was related to its agglomeration due to thermal stress and steam. This study provides a new perspective on the synthesis of low-cost OCs and the co-utilization of solid wastes.

Evaluating the role of feedstock composition and component interactions on biomass gasification

Biomass gasification offers a solution to waste concerns while generating clean energy. This study examines the gasification of pine sawdust (PS), used ground coffee (UGC), and wheat straw (WS) under identical conditions. The compositions of the biomass samples are determined, and the gasification of individual components (hemicellulose, cellulose, and lignin) are conducted to understand the process’ dependency on the biomass characteristics. The results suggest cellulose and cellulose-rich biomass (PS) produces more tar and less hydrogen than lignin and lignin-rich biomass (UGC and WS). High lignin and hemicellulose content leave more char. Gasification of PS, UGC, and WS yields 12.7, 15.7, and 17.2 vol% hydrogen, respectively. Additionally, cellulose, hemicellulose, and lignin gasification yield 10.5, 22.1, and 30.4 vol% hydrogen, respectively. Comparing experimental and theoretical values for the three biomass samples reveals significant differences due to component interactions. Thermogravimetry analysis (TGA) indicates significant degradation interactions between hemicellulose-lignin, cellulose-hemicellulose, and cellulose-lignin. It is concluded that high cellulose content biomass shows more predictable results, while high lignin and hemicellulose biomass increases secondary reactions or interactions, exacerbating predictability. These findings assist in estimating gasification performance for better biomass selection.

Comprehensive experimental assessment of biomass steam gasification with different types: correlation and multiple linear regression analysis with feedstock characteristics

In order to reveal the correlation between gasification behavior and products with feedstock characteristics, the steam gasification of 13 biomasses was investigated using a thermogravimetric analyzer and a fixed-bed reactor. Meanwhile, a multiple linear regression was used to construct correlation models. The results showed that cellulose content and crystallinity had the greatest influence on pyrolysis reactivity, which was reflected that the cellulose content was strongly positively correlated with the pyrolysis reactivity (Pmax = 0.77), while the lignin content and cellulose crystallinity were opposite. H/C, O/C ratios and SiO2 content had the greatest influence on gasification stage. O/C were strongly negatively correlated with gasification reactivity (Pmax = −0.81). But correlations of K and Ca contents were much less than that of Si. Husk has the best gasification performance than straw and woody with highest H2 and total gas yield of 28.26 and 68.93 mmol·g−1. H2 concentration and yield were significantly affected by the cellulose crystallinity and the fixed carbon content with positively correlation (P = 0.69–0.85). CH4 and CnHm were also influenced by them, but the trend was opposite to that of H2. Cellulose content, followed by SiO2 content mainly affected CO and CO2 and negatively correlated with CO while positively with CO2.

CO2 Conversion by Oxygen-Enriched Gasification of Wood Chips

With increasing efforts to lower CO2 emissions globally, the demand for carbon-based resources in industries remains on a high level, leading to new technologies being able to provide those essential carbon sources. To the best of our knowledge, we were able to show for the first time the adaption of a readily available gasifier for the gasification of wood chips using only O2 (18.4–23.1 Vol.-%) and CO2 as gasification agents, creating a nitrogen-free product gas. It was found that the setup used was able to convert up to 27.2% of the CO2 from the gasification agent to CO, creating a promising route for the production of renewable carbon sources for future carbon-based applications. Furthermore, no decrease in gasification performance was observed as the cold gas efficiency was at 83.5–95.5% with only minor formation of tar.

Investigations on performance of gasifier engine integration using three different biomasses as feedstocks

The integration of a downdraft gasifier with modified internal combustion engines presents a feasible solution for heat and power production, such as off-grid areas. This study conducted an experimental analysis to evaluate combustion in a modified engine. The morphological characteristics of the agricultural residue used in the gasifier were analyzed using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM), along with an examination of the slagging inorganic constituents. The engine used in the experiments was a modified single-cylinder design paired with a downdraft gasifier. Three types of biomass feedstocks—eucalyptus, corncob, and pearl millet in pellet form —were tested. The performance of the downdraft gasifier was stabilized, and the engine was run independently on each type of producer gas at a constant speed under different loads to determine the optimum load. Cylinder pressure measurements were taken to estimate the heat release rate.The study found that power generation was lower than typical woody biomasses due to the lower calorific value of the producer gas from the tested feedstocks. Additionally, lower cylinder pressures and heat release rates were recorded, along with longer combustion durations. The varying proportions of producer gas affected combustion stability. Among the studied ashes, pearl millet corncob (PMC) exhibited the highest slagging tendency, followed by corncob (CC). Morphological analysis indicated that the eucalyptus residue's increased porosity was caused by the volatiles changing, forming pores and tube-like structures. An aliphatic C–H peak (3000–2500 cm⁻1) is absent from the residue, indicating that the aliphatic structure was disturbed during thermochemical conversion. During the gasification process, the residue's crystallinity reduced as it split down.

Sustainable Energy Production From Biomass: A Case Study On Tasmanian Blue Gum Eucalyptus Gasification

The global transition to renewable energy sources is a crucial response to the urgent need to reduce global warming and its negative environment consequences. One feasible approach within this paradigm is to generate steam from syngas produced by biomass gasification. Background: Gasification is a thermochemical process that transforms organic materials into combustible gas mixtures, provides a sustainable and renewable way to generate energy, chemicals and fuels. This technology helps to minimize greenhouse gas emissions and reliance on fossil fuels. Materials and methods: In this experiment, Tasmanian blue gum eucalyptus sawdust is used to generate pellets which will subsequently be processed into syngas using downdraft gasifier. The experiment investigates the effect of increasing air velocities specifically 10, 15, 20 and 25 M/sec as a gasifying agent to the gasification process. Results: The air velocity is measured at 10, 15, 20 and 25 m/s resulting in the time taken of 2280, 1860, 1560 and 1380 with efficiency increases of 41.11, 47.73, 49.62 and 54.67, respectively. This implies that optimizing air velocity is crucial for improving the overall performance of biomass gasification. The proximate and ultimate results of pellet are some better compared to the raw eucalyptus by researcher Filomena Pinto [16]. The efficiency is slightly high compared with the researcher R. Ravi Kumar [25]. The generated syngas may eventually replace the fossil fuel LPG for domestic purposes. Conclusion: The time taken for the gasification decreases with the increase of air velocity up to 25m/s. As the result the efficiency increases.

Waste-to-Energy technologies for municipal solid waste management: Bibliometric review, life cycle assessment, and energy potential case study

Inadequate municipal solid waste (MSW) management threatens public health and the environment. The waste-to-energy (WtE) route allows the production of electricity, heat, and other valuable chemical products. WtE consists of incineration, gasification, pyrolysis, and some emerging technologies. This study applies the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to conduct a bibliometric analysis of WtE technologies for MSW management research. Scopus-indexed articles were examined between 1971 and 2023. Four periods were determined and analyzed in terms of their most significant results. In addition, the most pertinent journals, Waste Management, Chemosphere, and Waste Management & Research, were ranked first, second, and third, respectively. Moreover, the top contributor countries are one in America (the United States), three in Asia (China, Japan, and India), and five in Europe (Spain, Italy, Germany, Sweden, and the United Kingdom). Throughout a Life Cycle Assessment (LCA) case study, the environmental performance of gasification and incineration as relevant technologies for treating MSW were contrasted. Gasification excelled in seven environmental parameters, suggesting that developing strategies for MSW gasification on a commercial scale should prioritize this aspect. Finally, the energy potential was assessed, which provided valuable information on the societal benefits of WtE technologies in various sectors, such as education, health, and electromobility. Under their respective contexts, stakeholders should enhance MSW sorting policies, pretreatment methods, and emerging valorization options. Increasing global interest in WtE requires a social, environmental, and economic evaluation before implementation.

Evaluation of the chemical looping gasification characteristics of kitchen waste using CuFe2O4 and NiFe2O4 as oxygen carriers

Chemical looping gasification (CLG) technology is promising for renewable energy, efficiently transforming biomass into high-quality syngas with minimal tar and pollutants. In this study, we examined the CLG characteristics of soy protein (SP), a model compound present in kitchen waste (KW), using two different oxygen carriers (OCs): Cu-Fe and Ni-Fe. The study revealed that enhancing the carbon conversion ratio (ηc) could be effectively achieved by increasing the oxygen equivalent coefficient (α) and the steam content. Consequently, the optimal gasification performance was attained when the Cu-Fe and Ni-Fe OCs were operated at the α values of 0.3 and 0.4, and steam contents of 30% and 40%, respectively. After ten cycles of chemical looping, both OCs retained their robust oxidation activity, ensuring that the ηc remained consistent throughout the ten cycles. Under optimized experimental conditions, the CLG characteristics of KW were successfully determined. Notably, the ηc of KW was substantially enhanced, doubling in comparison to previous levels. The Cu-Fe OC emerged as a more suitable candidate for the CLG of KW due to its lower cost and non-toxic nature. This study provides important theoretical support and practical insights for the harmless treatment and resource utilization of KW.

Configuration optimization of a biomass chemical looping gasification (CLG) system combined with CO2 absorption

Biomass chemical looping gasification (CLG) combined with CO2 absorption in a dual circulating fluidized bed (DCFB) has emerged as an advanced technology for clean and efficient biomass utilization, yet the reactor design for achieving higher gasification performance and the in-depth understanding of physical-thermal-chemical characteristics is still lacking. This study presents an optimized design aimed at enhancing hydrogen production and carbon reduction in the biomass CLG process with a DCFB reactor by employing the multiphase particle-in-cell (MP-PIC) method integrated with thermochemical sub-models. The proposed reactor is comprehensively compared with the original reactor from the experimental setup in terms of particle mixing, heat transfer, and gasification behaviors. The results indicate that compared to the original setups, the proposed CLG system demonstrates: (i) an improved gas-solid mixing, as evidenced by the particle mixing index rising from 0.23 to 0.34; (ii) an enhanced particle heat transfer coefficient, which boosts heat and mass transfer process; (iii) a 10.11 % increase in H2 concentration alongside a 23.71 % decrease in CO2 concentration; (iv) a particle distribution characterized by higher concentration at the bottom and lower concentration at the top, along with intensified particle back-mixing. The pressure drop inside the combustor is higher than that in the gasifier. A smaller absorbent mean particle diameter and lower-positioned biomass feeding port contribute to the improvement of the CLG performance.

Performance analysis of a pilot gasification system of biomass with stepwise intake of air-steam considering waste heat utilization

Although the fixed-bed gasifier is widely used because of their simple structure, easy operation, and strong adaptability to biomass type, its economy is weakened by their low bioenergy conversion ability and heat utilization efficiency. Therefore, a novel biomass gasifier with stepwise intake of air–steam is proposed, which also innovatively integrates the concept of multi-stage utilization of waste heat generated during the gasification process into its design. And a pilot system comprising the novel biomass gasifier with a biomass consumption of 30 kg/h has been built. A series of continuous air-steam gasification experiments on pine wood particles shown that, the high-temperature steam in the reduction zone enhanced the ring opening of aromatic hydrocarbons, decarboxylation, dehydroxylation, and the conversion of long-chain to short-chain hydrocarbons, thus increasing the yield of small-molecule gases. The steam reforming reaction played an active role in increasing the hydrogen content, the gasification gas's production and low calorific value. And the relationship among the reaction rates on the surface of char should be VC + H2O＞VC+2H2O＞VC + CO2＞VC+2H2. The minimum input temperature of steam was 350 °C, otherwise more char would be consumed in the oxidation zone to provide heat. The proposed steam-air gasification system achieved optimal performance with an air-to-steam mass ratio (A/S) of approximately 8, a steam temperature of 400 °C, and an air-to-biomass mass ratio (A/B) of 1.2. The average gas production could reach 2.67 m3/kg, with the average low calorific value of 5.1 MJ/m3. The average hydrogen content could reach 20 %, with the average H2/CO ratio of 2. The average effective gasification efficiency could reach 69.72 %. Compared with air gasification, the proposed air-steam gasification was equivalent to the use of 1 kWh of electricity to produce 2.4 kWh of electricity. Combining market research, the price of steam produced by the proposed system was approximately 70 CNY/t less than when using natural gas. This study aims to provide a technical reference for improving the performance of biomass gasification in practical applications.

Regulation mechanism of phenol on intermediates during supercritical water gasification of coal

Supercritical water (SCW) gasification technology can enable the efficient utilization of coal by converting it to hydrogen-rich gas. However, poly-cyclic aromatic hydrocarbons and heavy components, which are intermediates of supercritical water gasification, tend to generate char, hindering the complete gasification of coal. In this work, phenol is recycled to enhance the gasification process and reduce the formation of these intermediates during SCWG, and the regulation mechanism is investigated. The results demonstrate that both gas yield and gasification efficiency increase with the presence of phenol, reaching approximately 98.5% at 750 °C, concentration of 2%with the effect of phenol, which is 27% higher than that in the coal-water system. Organics removal rate reaches about 98% with the addition of phenol. Phenol can enhance the gasification performance by facilitating the conversion of heavy components to lightweight components. The transient reactivity of coal in the poly-condensation stage is increased by about 50 times with the presence of phenol. The regulation mechanism of phenol in the poly-condensation stage during coal gasification involves the decomposition of SCW forming hydroxyl radicals, which replaces the substituents on the benzene ring, facilitating the dissociation of benzene ring into small molecules that are prone to polymerize. The interacting force between phenol and multi-rings disrupts the conjugate structure, aiding in the decomposition of polycyclic organics into small molecules.

Rational design of enhanced oxygen deficiency-enriched NiFe2O4 embedded in silica matrix as oxygen carriers for high-quality syngas production via biomass chemical looping gasification (BCLG)

Biomass chemical looping gasification has attracted wide attention in syngas production. However, the major obstacle is deactivation of oxygen carriers (OCs) caused by sintering, leading to low gasification efficiency. Developing sintering-resistant oxygen carriers is crucial for enhancing the competitiveness of BCLG. This study proposes an effective strategy of embedding NiFe2O4 in silica matrix (NFSM) to fabricate highly dispersed OCs. The gasification performance and cycling stability of OCs for BCLG are systematically researched in a fixed-bed reactor. Based on the characterization analysis, NiFe2O4 is successfully incorporated into the silica matrix. The well-dispersed active components in OCs create more oxygen vacancies and metal adsorption sites, resulting in higher redox activity. Experimental results verify that the optimal parameters for achieving the highest syngas yield (1254 mL/g) and biomass gasification efficiency (68 %) are 0.6 OCs/B, a temperature of 850 °C, and a water injection rate of 0.3 mL/min. After 10 redox cycles, NFSM demonstrates superior redox activity and excellent cycle stability, maintaining its gasification performance and microstructural integrity throughout all chemical looping gasification processes. The silica matrix-supported NiFe2O4 can be a promising candidate for BCLG. This work provides a novel approach to develop and design future OCs of BCLG for alleviating sintering and deactivation phenomena.

Impact of geometric variables on the functionality of downdraft biomass gasifiers across diverse dimensions

This study offers an extensive examination of the fundamental design parameters that influence the performance of biomass downdraft gasifiers. The impact of design parameters such as reactor dimensions, throat diameter, length of converging and diverging section and ratio of maximum to minimum diameter (dmax/dmin) were analysed using FORTRAN code, which was initially developed for 4 kW Imbert gasifier. Simulation results highlight that the optimal range of hearth loads for gasifier operation is influenced by both the gasifier’s size and the particle size of the feedstock. Increasing gasifier size from 20 mm to 100 mm throat diameter, while maintaining the same superficial air velocity (SAV), escalates hearth load and superficial velocity due to heightened biomass consumption, leading to higher hearth temperature and improved gas calorific value. Similar trends are observed across varying SAV values (0.35 m/s to 1.8 m/s), suggesting a need for lower SAV values in larger gasifiers, possibly with larger particle sizes. Additionally, altering the length of the converging and diverging sections impacts gas quality, with deviations from recommended values affecting ignition and overall performance, while dmax/dmin variations show no significant impact.

Investigation of biochars derived from waste lignocellulosic biomass and insulation electric cables: A comprehensive TGA and Macro-TGA analysis

This study investigates the thermochemical decomposition and gasification performance of biochars produced from blends of waste lignocellulosic biomass and waste insulation electrical cables at varying temperatures. Characterization tests revealed changes, particularly in ash content (27.5 %–34 %) and elemental composition, with nitrogen content increasing notably in biochar samples compared to the original feedstock. Van Krevelen diagrams demonstrated a reduction in O/C and H/C ratios with increasing production temperature, resembling fossil fuels more closely. The thermogravimetric and the derived thermogravimetric profiles illustrated distinct degradation stages influenced by heating rates and production temperature. Macro-TGA tests provided insights into biomass residue behavior under gasification conditions, indicating higher reaction rates at elevated temperatures. Syngas analysis highlighted the impact of temperature and equivalence ratio on syngas composition, with higher temperatures favoring hydrogen-rich gas production. The observed trends in cold gas efficiency (42.61 %–50.40 %) and carbon conversion efficiency (45.83 %–50.40 %) underscore the significance of temperature control in maximizing gasification performance. Biochars produced at higher temperatures demonstrated superior gasification performance, suggesting potential for optimizing biochar production processes to enhance energy recovery and waste valorization.

Calcium looping-enhanced biomass gasification for methanol production: Integrating methane dry reforming and carbon utilization

Developing integrated CO2 capture and utilization (ICCU) is an attractive strategy that aims to reduce CO2 emissions while realizing the potential benefits of CO2. This paper investigates the techno-environmental-economic performance of biomass gasification to methanol (BtM) based on calcium looping (CaL) coupled with dry reforming of methane (DRM) and CaL coupled with reverse Boudouard reaction (RB). The results indicate that BtM systems based on CaL-DRM (BtM:CaL-DRM) and CaL-RB (BtM:CaL-RB) achieve CO2 capture and utilization, and enable efficient methanol synthesis. Compared to BtM:CaL-DRM, BtM:CaL-RB demonstrates higher exergy efficiency and lower global warming potential (GWP). The exergy efficiency of BtM:CaL-RB reaches 71.60 %. In terms of economic viability, BtM:CaL-DRM demonstrates more promising economic feasibility. The BtM systems reaches breakeven when the methanol selling price ranges from 440.8 $/ton to 529 $/ton. This study provides valuable insights into exploring novel ICCU systems.

Gasification performance of wet hydrochar from co-hydrothermal carbonization of high-moisture sludge and fungus bran

Rational utilization of waste biomass is an important renewable energy alternative to address environmental issues caused by fossil fuels and climate change. Hydrothermal carbonization can improve the quality of municipal sewage sludge (SS) fuel by reducing water content, removing chlorine, and increasing energy density. This paper proposes an in-situ steam gasification method for syngas production. The influences of original water vapor content of hydrochar (0–30 %); hydrothermal conditions including severity factor (SF), fungus–bran mixing ratio (FBMR), and the proportion of citric acid mixed promoting agent (CAPA); and gasification temperature (700–900°C) on the composition of syngas. The effects of pure hydrochar gasification and mixed gasification on syngas composition were examined. Response surface methodology was used to optimize and maximize the higher heating value (HHV) of syngas. In addition, life cycle assessment was used to evaluate the environmental impact of the wet hydrochar gasification process. The vapor atmosphere generated automatically by heating wet hydrochar promoted steam reforming and water-gas shift reactions, driving them towards hydrogen production. Excess steam consumed a large amount of energy, leading to decreased reactor temperature, which in turn reduced gasification reaction activity and production of various gas components. As the SF increased, the syngas yield tended to decrease and the gasification reaction index decreased. Conversely, as the FBMR increased, the contents of all syngas components increased, along with the gasification reaction index. Additionally, as the gasification temperature increased, the HHV of the syngas increased. The quality of the syngas produced by mixed gasification was significantly better than that produced by pure hydrochar gasification. Compared to the syngas from the gasification of dry SS hydrochar, the HHV of the syngas from wet SS hydrochar increased by 4.4 %. At optimal conditions of SF 0.1, FBMR 20 %, and CAPA 20 %, the HHV of the syngas from wet hydrochar gasification increased by 28.1 %. Under these optimal conditions generated the highest quality syngas; at a gasification temperature of 900℃, the environmental impact was minimal. The lower quality of syngas and economic costs of drying hydrochar are considered disadvantages of traditional dry hydrochar gasification. However, the high-quality syngas produced from wet hydrochar in this study addressed these issues, laying a solid foundation for future industrial scale applications.

Effect of Low-Rank and High-Rank Coal Blend Characteristics on the Gasification Performance in Fixed Bed Reactor.

Coal gasification is the most demanding technology, increasing day by day for synthesis gas and chemical production in a clean environment. Coal is a primary source of energy or fuel. India has a high preservation of high-ash coal. Employment of this coal for gasification is tough due to its abrasive nature. Coal blending is an effective way to utilize such coal and to control the gasification performance. The present study focuses on using high-ash, low-rank Indian coal with high-rank imported coal in a suitable blend. The blending effect on raw gas yield (kg/kg of coal) and heating value (kcal/Nm3) was studied for coal blends-CH1 (20:80), CH2 (30:70), CH3 (40:60), CH4 (50:50), and CH5 (60:40) of RC (raw Indian coal) with RH (raw high-rank imported coal). Also, the gasification characteristics of the WC (washed Indian coal) were studied similarly. It may be seen that the raw gas yield with blends of raw coal and the rank of imported coal is 1.11 to 1.46 (ton/ton of coal), whereas in washed Indian coal, it is 0.95 (ton/ton of coal). A slight change was observed in the heating value of raw gas, and its average value in the blended CH1 to CH5 coal is 2860 kcal/Nm3, whereas in WC, it is 2956 kcal/Nm3. The maximum utilization of raw coal in the blend for gasification can be 60%, which is economical and 0.55 times more effective than WC gasification.

A comparative assessment of sewage sludge valorization via anaerobic digestion and supercritical water gasification: A techno-economic case study in Norway

This study compared the performance of supercritical water gasification (SCWG) to conventional anaerobic digestion (AD) for treating sewage sludge from a wastewater treatment plant (WWTP). Based on plant data from a WWTP in Norway, kinetic-based process models have been developed in Aspen Plus® to investigate the energy and economic feasibility of AD and SCWG for sewage sludge (SS) treatment. The findings showed that low ambient temperatures significantly reduced the energy efficiency of the AD, while their effect on the SCWG process was negligible. At the average ambient temperature of 7 °C and SS concentration of 7 wt%, AD and SCWG achieved thermal energy self-sufficiency (TES) of 0.76 and 0.63, respectively. Under these conditions, the AD and SCWG had energy conversion efficiencies (η) of 25.8% and 46.6%, respectively. However, increasing the SS content in the SCWG to 15 wt% improved the TES to 1.22 and η to 73.2%, making it a more attractive alternative to the AD.At 7 wt% SS concentration, the AD and SCWG processes required an investment cost of $ 4.08 million and $ 6.83 million, respectively. Under the study assumptions, neither AD nor SCWG proved profitable, revealing negative net present values (NPV) and operating costs of $0.96 million and $0.92 million, respectively.

Optimization of hydrogen-rich syngas from coal and sewage sludge co-gasification in supercritical water

Supercritical water gasification (SCWG) of coal and biomass waste complies with the structure of energy consumption and the targets for carbon peaking and carbon neutrality. In this work, the optimal blending ratio and thermochemical transformation characteristics of coal and sewage sludge (SS) co-gasification were explored experimentally at various temperatures (500–660 °C), residence time (0–40 min), feedstock concentrations (5–15 %), and catalyst utilization. The demethylation and dehydroxylation of intermediate products (aliphatic compounds, monocyclic aromatic hydrocarbons (MAHs)) improve the gasification performance under favorable experiment conditions (high temperature, long residence time, low feedstock concentration, and addition of catalysts). The optimal gasification results are an H2 yield of 38.36 mol/Kg and a 118.81 % increase of CGE (cold gas efficiency) in K2CO3-catalyzed gasification compared to the absence of the catalyst. Subsequently, the co-gasification mechanism of coal and SS was determined by the analysis of the three-phase product. Ultimately, a regression model was first established to obtain the practical optimization mechanism and yield prediction of hydrogen-rich syngas through response surface plots and regression equations. As verified in multiple experiments under varying situations, the regression model’s fitting accuracy yields an average relative error of 5.53 %.