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Haseen Siddiqui

Name: Haseen Siddiqui

Email Address: haseen011@gmail.com

Roll number: 154020015

Department: Chemical Engineering

Programme: Ph.D.

Year of study: 5

Name of Supervisor:  Prof. Sanjay Mahajani, Department of Chemical Engineering

Topic of Research: Experimental and Modeling Study of Downdraft Gasification for High Ash Content Feedstock

Description of research work: 

Depleting conventional energy resources and their adverse impact on the environment stimulate the need for alternate renewable and clean resources. Biomass can be a potential renewable alternate owing to broad abundance and high energy content. Gasification converts biomass into a synthesis gas that can be subsequently used for electricity, fuel and chemical productions. The chemical and physical properties of biomass have huge variations depending on its type and geographical conditions that make the gasification process biomass specific. Such limitations deteriorate gasification performance and make the process expensive.

The idea of my work is to come up with a user friendly and efficient gasifier that can accommodate a wide range of biomass, irrespective of its physical and chemical properties. The feedstock taken for the study is garden-waste that incorporates biomass ranging from forest waste, agro-waste, tree leaves and twigs. These biomasses show good variation in terms of their calorific value, ash content, proximate and ultimate analysis, cellulose, hemicellulose and lignin content. 
The experiments were performed using commercial TERI gasifier and the major issues were observed with the biomass having high ash content. The ash present in the biomass melted at high temperature and agglomerated causing the complete shutdown of the process. The agglomeration of ash is called clinker formation. This drastically lowers down the gas quality and cause huge loss of accessories. 

To solve this operational issue, operating parameters viz. air flow rate, air distribution ratio and grate rotation period were varied. Based on the results of this parametric study, a revamped design of gasifier was proposed that drastically reduce the clinker formation from 4% of feed to 0.08% feed.  To make the process more efficient, work on rigorous kinetic modelling is going on. Particle level modelling study has been completed and that will be extended for completer reactor scale modelling.

1. How your work will help solve the present problem of clean energy?

The work is based on the technology of Gasification which is very efficient in extracting the energy from biomass viz. agro-waste, garden waste. It converts the dry biomass waste into useful producer gas (H2 + CO) which subsequently can be used for electricity generation, chemical and fertilizer production. It is a carbon-neutral process in the sense that there is no extra release of CO2 during the process. SOx and NOx emissions are also significantly low. Apart from that, it also helps in overcoming the global waste generation problem. 

The objective of my work is to explore the thermal application of producer gas as cooking gas at a community scale. The producer gas normally has lower heating value in the range of 3 – 5 MJ/Nm3 in case of air as gasifying agent which can be enhanced to 17 – 20 MJ/Nm3 with the employment of steam as a gasifying agent. Therefore, our goal is to come up with a user-friendly, efficient process and gasifier that can accommodate a wide variety of biomass. This will help in replacing conventional cookstoves in rural areas as well as in dealing with the problem of open burning of agro-waste. This will thus give a huge share in protecting the health and environment. 

2. Any quantitative analysis of benefits?

With our parametric study experiments, we have revamped the design of commercially available gasifier that led to enhancement in the gas quality. The lower heating value of syngas has got increased to 5 MJ/Nm3. The major advantage with the modified design is the smooth operation of process with wide variety of biomass ranging from low ash content to high ash content biomass. The clinker formation which causes hindrance in the conventional process, is now reduced significantly from 4 % w/w of feed to 0.08 % w/w of feed, in the proposed design. A unit has been set up in an ashram school in the Dharani village, Amravati, Maharashtra and the response has been encouraging. 

3. What is the yield in your process?

The yield of the process is measured in terms of cold gas efficiency and flame stability time. The cold gas efficiency of the process has got increased to 62.61% from 51.40 % in the proposed design.  The flame was observed to remain stable for 130 min in proposed design which was earlier only 85 min. 

4. What is the future direction?

A complete rigorous mathematical model is being developed for a downdraft gasifier and it will be eventually validated with the help of experimental data. The model considers reaction kinetics, transport limitations, clinker formation kinetics and non-ideal gas flow patterns.  The experimentally validated model will be used further for rational design equipment and control strategies for the smooth operation.