Department of Chemical Engineering
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Item 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.Item 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.Item 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.Item 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.