Gasification Gas Research Articles

Graphite-assisted microwave carbon dioxide gasification of wet stalks

In order to realize the low-carbon gasification of the typical wet stalks, the graphite was used as the microwave-absorbing agent and the heat transfer medium in the microwave field, and CO2 was used as the gasification agent to explore the characteristics of microwave CO2 gasification. After mixing the corn stalks, the rice stalks or the wheat stalks with different water contents and the graphite in a mass ratio of 4:1, CO2 was introduced for gasification in a microwave field. Experiments showed that with the increase in the water content, the carbon conversions, the gas yields and the volume fractions of the effective components all increased slowly in the front and rear sections, and increased rapidly in the middle section. When the CO2 flow rate was 0.6 Nm3·kg−1·min−1, the carbon conversions, the gas yields and the volume fractions of the effective components all reached their peaks. It was found that the structure of the three stalks changed from smooth to porous during the intermediate process of the graphite-assisted microwave gasification. The deashed stalks with water content of 60 % was gasified in a microwave field of 700 W for 1.25 min, and the BET specific surface areas of the generated porous carbon reached 2041–2054 m2 g−1, and the volume fractions of the effective components of the gasification gas were more than 95 %. With the prolongation of the gasification time, the carbon conversions increased slowly in the early and late stages, but increased rapidly in the middle stage. The reason was that the large amount of porous carbon generated in the middle stage was the gasifiable strong microwave-absorbing agent, which greatly increased the gasification temperature and accelerated the reaction rates. When the graphite was reused 10 times, the carbon conversions could still reach more than 80 %. The XRD tests were carried out on the graphite used many times to explore its deactivation mechanism. This paper has practical significance for the low-carbon CO2 recycling of stalks biomass, and provides a new way for the preparation of biomass-based porous carbon.

Optimal integration of electrolysis, gasification and reforming for stable hydrogen production

Engineering industries such as petroleum and petrochemicals have strict requirements for the stability of hydrogen supply to ensure the safety and reliability of system operations. However, relying on a single hydrogen production technology is insufficient to meet the requirements of both stable and green hydrogen. This study proposes an integrated hydrogen production system combining water electrolysis, biomass gasification, and natural gas reforming to achieve stable and green hydrogen. To capitalise on the advantages of the individual technologies, the integration among the different hydrogen production methods considers not only energy but also materials. As a by-product of water electrolysis, oxygen can create a pure oxygen atmosphere for biomass gasification and natural gas reforming, thereby considerably improving the energy conversion rate. The heated gases from the biomass gasification transport thermal energy to the natural gas reforming. Stable and maximised hydrogen production can be achieved through optimal coordination of the three hydrogen production technologies and storage devices. Optimisation models are built for each component, and case studies show that the proposed integrated system exhibits energy efficiency of 64.19 %, which is 9.87 % higher than the 54.32 % efficiency of single-energy hydrogen production, and achieves an 67 % carbon emission reduction compared with the existing industrial technology. The integrated system proposed in this study provides a solution for stable hydrogen production under the broad requirement of carbon neutrality, and it will provide valuable guidance for future integrated hydrogen production system development and offer information that is of interest to operators and investors.

Removal of Organic Sulfur Pollutants from Gasification Gases at Intermediate Temperature by Means of a Zinc–Nickel-Oxide Sorbent for Integration in Biofuel Production

Production of renewable fuels from gasification is based on catalytic processes. Deep desulfurization is required to avoid the poisoning of the catalysts. It means the removal of H2S but also of organic sulfur species. Conventional cleaning consists of a several-step complex approach comprising catalytic hydro-treating followed by H2S removal. In this work, a single-stage process using a zinc and nickel oxide sorbent has been investigated for the removal of organic sulfur species present in syngas. The process is called reactive adsorption and comes from the refinery industry. The challenge investigated by CIEMAT was to prove for the first time that the concept is also valid for syngas. We have studied the process at a lab scale. Thiophene and benzothiophene, two of the main syngas organic sulfur compounds, were selected as target species to remove. The experimental study comprised the analysis of the effect of temperature (250–450 °C), pressure (1–10 bar), space velocity (2000–3500 h−1), tar components (toluene), sulfur species (H2S), and syngas components (H2, CO, and full syngas CO/CO2/CH4/H2). Operating conditions for removal of thiophene and benzothiophene were determined. Increasing pressure and temperature had a positive effect, and full conversion was achieved at 450 °C, 10 bar and 3500 h−1, accompanied by simultaneous hydrogen sulfide capture by the sorbent in accordance with the reactive adsorption desulfurization (RADS) process. Space velocity and hydrogen content in the syngas had little effect on desulfurization. Thiophene conversions from 39% to 75% were obtained when feeding synthetic syngas mimicking different compositions, spanning from air to steam-oxygen-blown gasification. Toluene, as a model tar component present in syngas, did not strongly affect the removal of thiophene and benzothiophene. H2S inhibited their conversion, falling, respectively, to 2% and 69% at 350 °C and 30% and 80% at 400 °C under full syngas blends.

Recent progress of the transition metal-based catalysts in the catalytic biomass gasification: A mini-review

Biomass is regarded as an important renewable resource, which plays a critical role in the development of sustainable energy systems. Biomass can be converted into energy or valuable chemicals by combustion, liquefaction, pyrolysis, and gasification. Among these processes, thermal gasification cracks biomass into light species at high temperatures, which can be applied to biomass with the greatest variety. As the target product of biomass gasification, syngas or H2-rich gas are very important intermediates in the petrochemical industry. However, the troublesome tar produced during gasification could bring a series of problems. Catalytic biomass gasification is a promising strategy to greatly alleviate these issues. The transition metal-based catalysts for catalytic biomass gasification have been studied in the last decades. Various transition metal catalysts for biomass gasification are reviewed in this article, including monometallic and bimetallic Ni-based catalysts, and other Fe-, Co-, and Pt-based catalysts. The performance of these catalysts is evaluated based on applied reaction parameters, the quality of produced syngas, and the performance of tar reduction. The applications of DFT calculation and AI for mechanism studies of biomass gasification have been summarized, and the cause of catalyst deactivation and regeneration of spent catalysts are also discussed. Therefore, the target of this article is to elucidate conventional biomass conversion pathways and review the recent progress on catalyst development in the biomass gasification process.

Experimental Study on Coal Partial Gasification Coproducing Char, Tar, and Gas

Experimental Study on Coal Partial Gasification Coproducing Char, Tar, and Gas

Two-Stage Dry Reforming Process for Biomass Gasification: Product Characteristics and Energy Analysis

The utilization of biomass can not only alleviate the energy crisis but also reduce the pollution of fossil fuels to the environment. Biomass gasification is one of the main utilization methods, which can effectively convert biomass into high-value and wide-use gasification gas. However, this process inevitably produces the by-product tar, which affects the yield of syngas. In order to solve this problem, a two-stage process combining biomass pyrolysis and CO2 catalytic reforming is proposed in this paper, which is used to prepare high calorific value syngas rich in H2 and CO and reduce the by-product tar of biomass gasification while realizing the resource utilization of CO2. The effects of the reforming temperature and CO2/C ratio on the gas yield and calorific value of biomass were investigated by catalytic gasification reforming device, and the system energy consumption was analyzed. With the increase of reforming temperature, the yield of CO increased, and the yield of H2 and the calorific value of gas increased first and then decreased. Increasing the CO2/C ratio within a proper range is beneficial to the formation of syngas. When the reforming temperature is 900 °C and the CO2/C ratio is 1, syngas with a high gas calorific value is obtained, which of is 2.75 MJ/kg is obtained. At this time, the yield of H2 and CO reached the maximums, which were 0.46 Nm3/kg and 0.28 Nm3/kg, respectively. Under these conditions, the total energy consumption of the system is 0.68 MJ/kg, slightly more than 0, and does not require too much external heat.

Steam reforming of biomass gasification gas for hydrogen production: From thermodynamic analysis to experimental validation

Biomass gasification produces syngas composed mainly of hydrogen, carbon monoxide, carbon dioxide, methane, water, and higher hydrocarbons, till C4, mainly ethane. The hydrocarbon content can be upgraded into richer hydrogen streams through the steam reforming reaction. This study assessed the steam reforming process at the thermodynamic equilibrium of five streams, with different compositions, from the gasification of three different biomass sources (Lignin, Miscanthus, and Eucalyptus). The simulations were performed on Aspen Plus V12 software using the Gibbs energy minimization method. The influence of the operating conditions on the hydrogen yield was assessed: temperature in the range of 200 to 1100 °C, pressures of 1 to 20 bar, and steam-to‑carbon (S/C) molar ratios from 0 (only dry reforming) to 10. It was observed that operating conditions of 725 to 850 °C, 1 bar, and an S/C ratio of 3 enhanced the streams' hydrogen content and led to nearly complete hydrocarbon conversion (>99%). Regarding hydrogen purity, the stream obtained from the gasification of Lignin and followed by a conditioning phase (stream 5) has the highest hydrogen purity, 52.7%, and an hydrogen yield of 48.7%. In contrast, the stream obtained from the gasification of Lignin without any conditioning (stream 1) led to the greatest increase in hydrogen purity, from 19% to 51.2% and a hydrogen yield of 61.8%. Concerning coke formation, it can be mitigated for S/C molar ratios and temperatures >2 and 700 °C, respectively. Experimental tests with stream 1 were carried out, which show a similar trend to the simulation results, particularly at high temperatures (700–800 °C).

Machine learning approach to predict the biofuel production via biomass gasification and natural gas integrating to develop a low-carbon and environmental-friendly design: Thermodynamic-conceptual assessment

A hybrid energy cycle (HEC) based on biomass gasification can be suggested as an efficient, modern and low-carbon energy power plant. In the current article, a thermodynamic-conceptual design of a HEC based on biomass and solar energies has been developed in order to generate electric power, heat and hydrogen energy. The planned HEC consists of six main units: two electric energy production units, a heat recovery unit (HRU), a hydrogen energy generation cycle based on water electrolysis, a thermal power generation unit (based on LFR field), and a biofuel production unit (based on biomass gasification process). Conceptual analysis is based on the development of energy, exergy and exergoeconomic assessments. Besides that, the reduction rate of pollutant emission through the planned HEC compared to conventional power plants is presented. In the planned HEC, when hydrogen energy is not needed, excess hydrogen is feed into the combustion chamber to improve system performance and reduce the need for natural gas. Accordingly, the rate of polluting gases emitted from the cycle can be mitigated due to the reduction of fossil fuels consumption. Further, based on the machine learning technique (MLT), the level of biofuel produced from the mentioned process is estimated. In this regard, two algorithms (i.e., Support vector machine and Gaussian process regression) have been employed to develop the prediction model. The findings indicated that the considered HEC can produce about 10.2 MW of electricity, 153 kW of thermal power, and 71.8 kmol/h of hydrogen energy. In both training and testing sets, the Support vector machine model exhibits better behavior compared the two Gaussian process regression model. Based on machine learning technique, with increasing gasification pressure, the level of biofuel obtained from the process does not increase significantly.

Distributions of and environmental risks posed by Cr and Zn when co-treating solid waste in different kilns

In order to dispose solid waste reasonably and provide reference data for solid waste co-treatment in industrial kilns, coal chemical products were co-treated in a pulverized coal furnace and refuse-derived fuel was co-treated in a gasifier-coupled pulverized coal furnace system. The distribution and environmental risks of Cr and Zn in different kilns were compared and analyzed. The Cr and Zn distributions in the solid products from the pulverized coal furnace tests were similar. Fly ash contained > 80% of the Cr and Zn. In the gasifier, cyclone dust and gasification gas contained only ∼ 60% of the Cr and Zn, and gasification slag contained > 40% of the Cr and Zn. The gasification gas contained ∼ 33% of the Cr and Zn volatilized. The pulverized coal furnace temperature was > 1,500 °C. Most of the Cr and Zn volatilized and then condensed, so became enriched in the fly ash. The gasifier temperature was ∼ 750 °C, so less volatilization occurred and Cr and Zn became enriched in the gasification slag. The Cr and Zn concentrations in leachates of the solid products were lower than the limits of “GB 5085.3–2007”. However, the Cr and Zn concentrations in the gasification slag and cyclone dust leachates were close to the limits and tens to hundreds of times higher than the concentrations in the pulverized coal furnace fly ash and slag leachates. The low temperatures and low-oxygen environments of gasifiers are not conducive to heavy metals being stable in the solid products, and the environmental risks posed by heavy metals in the solid products are high. The risks to the environment are less serious for co-treating solid waste in pulverized coal furnaces than gasifiers.

K2CO3-catalyzed gasification of coal of different ranks in supercritical water for hydrogen production: A general kinetic model with good coal adaptability

Supercritical water gasification (SCWG) of coal provides a new solution for the green transformation and upgrading of traditional coal industry. Considering the good coal adaptability of SCWG and the excellent catalytic performance of K2CO3, a new kinetic model was developed in this work for predicting the catalytic gasification characteristics of coal of different ranks in supercritical water (SCW). In this model, various ranks of coal are characterized by the combination of three types of primary coal in different proportions, and the proportions can be obtained based on elemental analysis data and matrix computation. The SCWG of various ranks of coal can be considered as a combination of reactions of three types of primary coal in SCW. The model contains a total of 18 reactions, and various intermediates are represented by phenol and a high-carbon hydrocarbon. K2CO3-catalyzed SCWG experimental data of three different coal samples obtained in an improved quartz tube reactor system were used for the determination of model kinetic parameters. Then the experimental results of catalytic SCWG of other coal samples were used for the model validation, and it was found that the model can effectively predict the variations of gaseous products within an acceptable error. Afterward, the model was used to predict carbon gasification efficiency and gas compositions for coal of different ranks and to analyze carbon distribution and reaction rates for specific coal. The proposed kinetic model fits well with the good coal adaptability of SCWG technology, and it has great significance for the promotion of SCWG technology.

Decision analysis for plastic waste gasification considering energy, exergy, and environmental criteria using TOPSIS and grey relational analysis

Plastic waste is becoming of increasing interest in gasification research because the gasification of plastic waste not only produces a valuable hydrogen-rich syngas but also can help reduce environmental problems caused by these materials. Most studies in the field of plastic waste gasification have only focused on evaluating effects of process parameters and optimizing the process by considering input variables. The present study explores the comparative performance analysis of a wide range of prevalent plastic waste types utilizing multi-criteria decision-making techniques. This study uses the “technique for order preference by similarity to ideal solution” (TOPSIS) and grey relational analysis (GRA) and presents a thorough sensitivity analysis. Low-density polyethylene results in maximum lower heating value of syngas and has a desirable performance from cold gas and exergy efficiencies viewpoints in air gasification. The findings of TOPSIS and GRA techniques show that low-density polyethylene as plastic waste exhibits the best performance in an air gasification process and the results of the sensitivity analysis confirm this. However, the decision making in steam gasification was challenging where TOPSIS and GRA techniques introduced high-density polyethylene and low-density polyethylene as the best candidates, respectively. Again, the findings of the sensitivity analysis confirmed the result. High-density polyethylene exhibits the best performance in steam gasification according to sensitivity analysis via the TOPSIS technique while low-density polyethylene ranked first according to sensitivity analysis of GRA. The findings can contribute to a better understanding of the selection of plastic waste feedstock for air and steam gasification by considering energy, exergy, and environmental factors.

Decarbonising the iron and steel industries: Production of carbon-negative direct reduced iron by using biosyngas

Bioenergy with carbon capture and storage (CCS) in iron and steel production offers significant potential for CO2 emission reduction and may even result in carbon-negative steel. With a strong ambition to reach net-zero emissions, some countries, such as Sweden, have recently proposed measures to incentivise bioenergy with CCS (BECCS), which opens a window of opportunities to enable the production of carbon-negative steel. One of the main potential applications of this route is to decarbonise the iron reduction processes that account for 85 % of the total CO2 emission in the iron and steel plants. In this study, gasification is proposed to convert biomass into biosyngas to reduce iron ore directly. Different cases of integrating the biomass gasifier, Direct Reduced Iron (DRI) shaft furnace, and CCS are evaluated through process simulation work. Based on the result of the work, the proposed biosyngas DRI route has comparable energy demand compared to other DRI routes, such as the well-established coal gasification and natural gas DRI route. The proposed process can also capture 0.65–1.13 t of CO2 per t DRI depending on the integration scenarios, which indicates a promising route to achieving carbon-negative steel production.

Impact of CO2 atmosphere on coal pyrolysis in indirectly heated fixed bed with internals

To clarify how CO2 affects pyrolysis characteristics in reactor with internals, pyrolysis of Yulin coal under N2 (inert) and CO2 (active) atmospheres is performed in fixed-bed reactors for two kinds of pyrolysis, i.e., with and without internals.CO2 exhibits different impact on tar yield for two types of pyrolysis, i.e., raising tar yield for pyrolysis in reactor without internals but lowering tar yield for that with internals. Tar yield pyrolysis under CO2 atmosphere is 6.31 wt% with internals, which is still higher 15.97% than that without internals at 1000 °C. In addition, CO2 atmosphere can produce more CO, high BET surface area char and high-quality of tar with more light tar (<C10), but less char, H2 and CH4 for both types of pyrolysis. The different impact of CO2 may be ascribed to the various flow routes for two kinds of reactors, and the extent of CO2-inclusive reactions, such as CO2-char gasification and reverse water gas shift (RWGS), is weakened by the adoption of internals due to occurring at lower temperatures and shorter residence time.

A review on global warming potential, challenges and opportunities of renewable hydrogen production technologies

This review compares global warming potential of renewable hydrogen production technologies including wind- and solar PV-powered water electrolysis, biomass gasification and biogas reforming based on 64 hydrogen production cases compiled from the literature. Unlike many previous studies, this review discusses the cases from various countries, while selecting the production technologies that have potential of commercialisation. Among the four reviewed technologies, wind electrolysis performed the best in global warming impacts (1.29 kg CO2 eq/kg H2), whereas biogas reforming technology performed the worst (3.61 kg CO2 eq/kg H2). Key factors that contributed to most of the impacts were found to be materials used for construction of wind- and solar- electricity generation system for both wind- and solar PV-powered electrolysis, and energy consumption during gasification processes for biomass gasification, while methane leakage during biogas production had the highest contribution to the impacts of biogas reforming cases. On average, the renewable hydrogen cases demonstrated 68–92% lower global warming potential when compared to conventional coal gasification and natural gas steam methane reforming systems. Increasing demand for renewable hydrogen and possibility of hydrogen being integrated into existing natural gas networks highlight the important role of renewable hydrogen production in the future.

Optimization and analysis of a hydrogen liquefaction process integrated with the liquefied natural gas gasification and organic Rankine cycle

Combination of the hydrogen pre-cooling and liquefied natural gas gasification processes is forward-looking in the hydrogen liquefaction industry. To enhance the cold energy utilization, a hydrogen liquefaction process integrated in conjunction with a liquefied natural gas gasification process assisted by an organic Rankine cycle is designed. Furthermore, a simplified refrigeration system incorporating a dual-pressure Joule-Brayton cycle is developed to provide efficient cryo-cooling for the hydrogen. A binary mixture consisting of ethylene and propane is preferred as the working fluid for the organic Rankine cycle when liquefied natural gas gasification pressure is 30 bar, which results in 2.2% and 15.5% improvement in the liquefied natural gas cold energy utilization compared to the organic Rankine cycle with the pure refrigeration as the working fluid and the hydrogen pre-cooling process without the organic Rankine cycle, respectively. In the proposed cryo-cooling process using two Joule-Brayton cascade cycles, the utilization rate of the input exergy reaches 48.84%. The exergy loss generated in the compressors and coolers accounts for approximately 66.2% of the total exergy loss. Therefore, they are regarded as the priority targets for improving the hydrogen liquefaction system. After the optimization of the proposed process using the genetic algorithm, optimal results are obtained with a specific energy consumption of 6.59 kWh/kgH2 and an exergy efficiency of 47.0%.

Life Cycle Sustainability Assessment of Electricity Generation from Municipal Solid Waste in Nigeria: A Prospective Study

Globally, rising population and rapid urbanisation have resulted in the dual issues of increased electricity demand and waste generation. These exacerbate diverse global problems, ranging from irregular electricity supply and inadequate waste management systems to water/air/soil pollution, climate change, etc. Waste-to-Energy (WtE) approaches have been proposed and developed to address simultaneously these two issues through energy recovery from waste. However, the variety of available waste materials and different WtE technologies make the choice of an appropriate technology challenging for decision-makers. The evaluation of the different WtE technologies in terms of their sustainability could provide a solid comparative base for strategic decision making in the power and waste management domains. This paper presents research conducted using a multidimensional Life Cycle Sustainability Assessment (LCSA) approach to estimate and compare the environmental, economic, and social impacts associated with the generation of electricity from Municipal Solid Waste (MSW) in two major cities, Lagos and Abuja, in Nigeria. These cities provide case studies in a developing world context to explore how their similarities and differences may influence the LCSA impacts for four WtE systems (Anaerobic Digestion, Incineration, Gasification, and Landfill Gas to Energy), and this is the first research of its kind. An LCSA ranking and scoring system and a muti-attribute value theory (MAVT) multi-criteria decision analysis (MCDA) were employed to evaluate the overall sustainability of the prospective use of WtE over a 20-year timeframe. The results from both approaches indicated that the adoption of WtE offered sustainability benefits for both cities, marginally more so for Lagos than Abuja. It was concluded that, for optimal benefits to be achieved, it is vital for decision-makers to think about the various trade-offs revealed by this type of analysis and the varying priorities of relevant stakeholders.

Experimental study on alkali catalytic gasification of oily sludge in supercritical water with a continuous reactor

Realizing the harmless resource utilization of oily sludge is urgent for petroleum industry and of great significance for environmental management. The treatment of oily sludge was investigated using supercritical water gasification (SCWG) with a continuous fluidized bed reactor. The effect of operating parameters on gasification efficiency and gas yield without catalyst was tested, and then the influences of catalyst type (K2CO3 and Na2CO3) and concentrations (1–8 wt%) were systematically studied. The results indicated that a medium mass flow ratio and low feedstock concentration were beneficial for gas production. Alkali catalyst improved carbon gasification efficiency (CE) prominently, and Na2CO3 showed better performance due to its better stability. A maximum CE of 95.87% was achieved when 5 wt% Na2CO3 was added at 650 °C, 23 MPa with 5 wt% oily sludge concentration. Besides, according to XRD patterns of solid residues, Na2CO3 was more stable than K2CO3 during SCWG. SEM-EDX results also revealed that more K was migrated into solid residues than Na. The analysis of pore structure demonstrated that alkali catalyst promoted the evolution of pore structure, resulting in higher specific surface areas and total pore volumes. Na2CO3 has a more substantial destructive effect on solid matrix, causing the matrix structure to collapse and inhibiting pore structure development. The FTIR spectra of solid products exhibited a lower content of carbohydrates and aromatic structures than the initial oily sludge. NH4–N results demonstrated that SCWG was a potential green treatment process for oily sludge. This work can not only give an insight into the reaction mechanism of alkali catalytic gasification of oily sludge, but also help to guide the optimal design of reactor and the regulation of operating parameters.

Prospective Life Cycle Costing of Electricity Generation from Municipal Solid Waste in Nigeria

Waste management and electricity supply have always been among the main challenges faced by developing countries. So far, the use of waste to energy (WtE) is one strategy that could simultaneously address these two challenges. However, the use of such technologies requires detailed studies to ensure their sustainability. In this paper, the potential of WtE in two cities in Nigeria (Abuja and Lagos) using anaerobic digestion (AD), incineration, gasification and landfill gas to energy (LFGTE), is presented with the aim of evaluating their economic viability using life cycle costing (LCC) as an analytical tool. This economic feasibility analysis includes LCC, levelised cost of electricity (LCOE), net present value (NPV), internal rate of return (IRR) and payback period. A sensitivity analysis was conducted to investigate the influence of several parameters on the economic viability of the selected technologies for the two cities. The economic assessment revealed that all the WtE systems were feasible and viable in both cities except for LFGTE in Abuja where the NPV was negative (−USD 105.42/t), and the IRR was 4.17%. Overall, incineration for both cities proved to be the most favourable economic option based on its positive LCC (Lagos USD 214.1/t Abuja USD 232.76/t), lowest LCOE (Lagos USD 0.046/t Abuja USD 0.062/t), lowest payback period (Lagos 1.6 years Abuja 2.2 years) and the highest IRR (Lagos 62.8% Abuja 45.3%). The results of the sensitivity analysis also indicated that variation in parameters such as the capital cost and discount rate have significant effects on the LCC. This paper provides information for potential investors and policy makers to enhance optimal investment in WtE technologies in Nigeria.

Experimental study on condensation flow patterns and heat transfer characteristics of non-azeotropic and immiscible binary mixed vapors

The condensation phenomenon of non-azeotropic and immiscible mixed vapors always occurs in the waste heat recovery process of biomass gasification gas. During the condensation process, the immiscible condensation products, such as tar and water, have a different flow pattern from the pure working fluid, which can affect the waste heat recovery efficiency and the service life of the heat exchanger. However, the relationship between the flow pattern of immiscible condensates and condensation heat transfer is not clear at present. In this paper, water and cyclohexane were used as non-azeotropic and immiscible working fluids. The effects of different mixed vapors mass ratios, cooling water inlet temperatures, and vapor mass flow rates on the condensation heat transfer characteristics of the binary mixed vapors on the vertical wall were studied. And the condensate flow patterns were combined for analysis and discussion. The experimental results showed that the condensation on the wall surface of the mixed vapors presented a film-drop flow pattern comparing with the filmwise condensation of water vapor or cyclohexane vapor. The film-drop flow pattern was manifested as that the cyclohexane condensate was attached on the condensation wall in the form of liquid film, and the water condensate was attached on the cyclohexane film in the form of droplets. And the flow of water droplets on the cyclohexane liquid film can enhance the condensation heat transfer of the mixed vapors. In addition, different from water vapor and cyclohexane vapor, the heat transfer coefficient of the mixed vapors decreased with the increase of the cooling water inlet temperature, which was related to the film-drop condensation flow pattern.

Selection of Waste to Energy Technologies for Municipal Solid Waste Management—Towards Achieving Sustainable Development Goals

The Sustainable Development Goals (SDGs) play an essential role, emphasizing responsible resource use, production, and consumption, including waste management. In addition, SDG 3, 7, 11, 12, and 13 are directly/indirectly related to waste management. This study aims to determine a suitable waste-to-energy (WtE) technology in Chittagong City, Bangladesh, focusing on cleaner technology. Anaerobic digestion, gasification, incineration, and landfill gas (LFG) recovery were considered as possible alternatives. Technical, economic, environmental, and social issues have been considered as necessary criteria for evaluation. An analytical hierarchy process was applied to rank these technologies based on stakeholders’ perceptions. The study found that anaerobic digestion (AD) ranked first, receiving 38% of overall weight. The second preferred technology is LFG (27%). Gasification and incineration stood at third and fourth, respectively (21% and 14%). According to a sensitivity study, the decision is only sensitive to the economy. LFG will become the most favoured solution for WtE conversion if the economy prioritizes more than 38%. Subsequently, this study’s findings will help achieve Bangladesh’s SDG agenda.