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    CFD analysis of the downdraft gasifier using species-transport and discrete phase model
    (Elsevier, 2022-11) Sheth, Pratik N.
    In the present study, a 2-D axisymmetric steady-state computational fluid dynamics (CFD) model has been developed for biomass gasification in a fixed bed Imbert downdraft gasifier. A discrete phase model (DPM) based on the Euler-Lagrangian approach with species transport is applied to the gasifier having the capacity of ≈ 5 kW. The use of DPM for the particle-continuous phase interaction leads to capture more realistic gasification phenomena. The proposed model is an effort to carry forward the CFD technique by implementing an alternative chemical kinetic scheme to study the various gasification parameters. The model is validated at different values of equivalence ratios (0.19–0.33) for producer gas composition and found to be in better agreement with the experimental values reported in the literature. The standard estimated error for the present model is 6.64, 7.55, 2.92, and 5.28 % for carbon monoxide, hydrogen, methane, and carbon dioxide, respectively. Moreover, the calculated standard deviation is 0.44 only. The biomass feed and airflow rates vary from 3.43 to 5.82 kg/h and 2.41–8.02 Nm3/h, respectively. It has been found that an equivalence ratio in the range of 0.25 to 0.30 is the most appropriate condition in the present operating range of the gasifier. The proposed scheme allows accurate prediction under various operating conditions, which may enable the designer to optimise the operating conditions. The model predictions would help to design the process integration of gasification with any existing commercial energy-producing unit based on conventional fuels. Hence, it deliberates significant contribution and value addition in the current literature for the CFD modelling of biomass gasification. The present study not only helps to improve the overall performance of the gasifier but also provides the profiles of essential design variables across the length of the gasifier.
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    Tar cracking enhancement by air sparger installation in the combustion zone of the downdraft gasifier
    (Elsevier, 2022-11) Sheth, Pratik N.
    In the present article, experimental studies are performed on Imbert downdraft gasifier using two different air distribution systems (two-nozzle and air-sparger) for the combustion zone. A novel air distribution system (air-sparger) is designed to supply uniform air across the combustion zone for achieving uniform temperature and enhancing the tar cracking. The effect of operating parameters (Equivalence ratio, temperature, air flow rate, and biomass consumption) on the tar cracking and producer gas compositions are investigated. Tar is measured in the producer gas before and after the gas cleaning units using a stack monitoring system. The experiments are performed by varying the airflow rate between 3 and 7 Nm3 h−1, and the equivalence ratio varies from 0.24 to 0.38. The operating parameters and air-sparger have significantly influenced the zone's temperature, producer gas composition, and the tar content in the producer gas. The maximum temperature of the combustion zone and reduction zone increases from 764 to 975 °C and 467 to 760 °C respectively with the air-sparger compared to the two-nozzle conventional air distribution system at the airflow rate of 7 Nm3 h−1. The lower heating value of the producer gas and the cold gas efficiency of the gasifier increased from 4.28 to 4.37 MJ Nm−3 and 48.55–55.05%, respectively, with the air-sparger. The incorporation of air-sparger reduces tar in producer gas from 23.95 to 0.97 g Nm−3 before gas cleaning unit at the airflow rate of 7 Nm3 h−1. Air-sparger has shown the adequate potential to enhance tar cracking and improve the overall gasifier performance.
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    Co-processing of petcoke and producer gas obtained from RDF gasification in a white cement plant: A techno-economic analysis
    (Elsevier, 2023-02) Sheth, Pratik N.
    White cement production, unlike grey cement, depends entirely on ashless conventional fuels (oil, petcoke) to meet its thermal energy requirement. The primary barrier to utilizing any solid alternative fuel in white cement is the impact on whiteness due to ash content. The study is focused on establishing producer gas from refuse-derived fuel (RDF) gasification as an alternative fuel in clinker production in an Indian white cement plant with a 15% thermal substitution rate (TSR). A stoichiometric calciner model has been developed to predict calciner outlet parameters considering co-firing of petcoke and producer gas, where producer gas has a high heating value (HHV) of 3.95 MJ/Nm3 and gas yield of 2.36 Nm3/kg RDF. The model predicted the decrease in calciner outlet temperature by 2.6% at 15% TSR with 8.49% CO2 mitigation potential by replacing conventional fuel. It is concluded that RDF gasification is viable for white cement plants considering an IRR of 13.57% and discounted payback period of six years and two months for a 10-year gasifier operation. The study will facilitate the utilization of the RDF in white cement plants, reducing their manufacturing cost and dependence on fossil fuels.
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    Aspen plus simulation of an inline calciner for white cement production with a fuel mix of petcoke and producer gas
    (Elsevier, 2023-11) Sheth, Pratik N.
    The white cement industry is facing the challenge of alternative fuel utilization replacing conventional fuel due to the impact of alternative fuel ash on the whiteness of clinker. On the other hand, municipal solid waste (MSW) disposal is a huge waste management problem worldwide. The present article focuses on utilizing MSW-based refuse derived fuel (RDF) as an alternative fuel in white cement. The ash-free producer gas derived via RDF gasification is proposed to overcome the challenge of direct RDF utilization. Aspen plus-based producer gas co-processing model for a calciner has been developed, considering 100% petcoke firing as the baseline scenario. The co-processing of producer gas further augmented the model to achieve a 15–20% thermal substitution rate (TSR). The developed model is validated using the actual plant data. The model results at 15% TSR predicted that the calciner outlet temperature will get reduced by 19 °C, with a 5.3% rise in calciner exit gas volume, which is manageable. CO2 mitigation potential at 15% TSR is estimated to be 11.33% of the baseline scenario. The TSR contribution of producer gas sensible heat at 593 °C is 2.7%, whereas the petcoke enters the system at 60 °C with negligible sensible heat.
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    Improving the properties of producer gas using high temperature gasification of rice husk in a pilot scale fluidized bed gasifier (FBG)
    (Elsevier, 2019-01) Pandey, Jay
    Biomass gasification is a well-studied thermo-chemical conversion route for the generating producer gas, a renewable energy carrier, for thermal and power applications as well as for bio-fuel production. High energy efficiency and clean gaseous fuel with low tar and suspended particulate matters (SPM) contents are some of the major challenges with biomass gasification. Herein, we report non-catalytic high temperature (720–855 °C) gasification of rice husk using fluidized bed gasifier (FBG). Producer gas mainly comprising of CO and H2 exhibited good higher heating value (HHV) and lower heating value (LHV) of 3.6 and 3.2 MJ/Nm3 respectively. Our experimental observations revealed that 790 °C is the optimum temperature for rice husk gasification with high carbon conversion efficiency (91.6%), thermal efficiency (75%) and high gas yield 2.7 m3/kg. High temperature gasification also resulted into reduced tar + SPM content (0.33 g/Nm3). Rice husk derived producer gas with good heating value and low tar + SPM content can be used as replacement of conventional fossil fuels for thermal applications in many processing industries.
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    Experimental studies on producer gas generation from wood waste in a downdraft biomass gasifier
    (Elsiever, 2009-06) Sheth, P.N.
    A process of conversion of solid carbonaceous fuel into combustible gas by partial combustion is known as gasification. The resulting gas, known as producer gas, is more versatile in its use than the original solid biomass. In the present study, a downdraft biomass gasifier is used to carry out the gasification experiments with the waste generated while making furniture in the carpentry section of the institute’s workshop. Dalbergia sisoo, generally known as sesame wood or rose wood is mainly used in the furniture and wastage of the same is used as a biomass material in the present gasification studies. The effects of air flow rate and moisture content on biomass consumption rate and quality of the producer gas generated are studied by performing experiments. The performance of the biomass gasifier system is evaluated in terms of equivalence ratio, producer gas composition, calorific value of the producer gas, gas production rate, zone temperatures and cold gas efficiency. Material balance is carried out to examine the reliability of the results generated. The experimental results are compared with those reported in the literature.
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    Process simulation of hydrogen rich gas production from producer gas using HTS catalysis
    (Elsiever, 2019-04-15) Sheth, P.N.
    In the present article, ASPEN Plus is used to develop a process model of the hydrogen-rich gas production through cleaning and catalytic conditioning of producer gas. The process includes producer gas cleaning using venturi scrubber and sand bed filter followed by compression of the gas to 0.6 MPa using compressor. The clean producer gas along with steam undergoes high temperature water gas shift reaction to produce hydrogen-rich gas. The power law kinetic model for commercial HTS catalysts reported in the literature is used in the model. Experimental results from our previous study and those reported in the literature are used to validate the developed model for the compositions of CO & H2 in the product gas. The validated model is further simulated to study the effects of parameters such as reactor temperature, catalyst bed length and steam to CO ratio on the product gas composition. The optimum operating conditions for maximizing CO conversion are found and reported. The maximum H2 composition and CO conversion predicted by the model are 27.029% 97.5479% respectively and the corresponding operating conditions are reactor; temperature of 350 °C, S/CO of 8 and GHSV 1000 h−1.