Scope and Objectives

1. To develop a cold flow model of dual fluidized bed gasifier unit which can establish an optimum circulation rate and residence time of solid particles in the system. 2. To develop a comprehensive Numerical model which can predict various output parameters such as solid circulation, syngas yield, temperature, species concentration in the syngas. 3. To develop an atmospheric dual fluidized bed gasifier unit which will utilize a different type of carbonaceous feedstock primarily high-ash Indian coal/pet coke to produce Hydrogen-rich syngas. 4. To optimize the gasification efficiency and enhance solid fuel conversion after examining the effects of ash content on the gasifier operation. 5. To develop a pressurized dual fluidized bed gasifier unit which can handle larger solid fuel feed obsoleting bulkier unit. 6. To develop a cutting-edge gas cleaning system which will make syngas directly employable to the IGCC operation.

Deliverables

1. An extensive numerical model to predict important parameters related to gasification such as solid particle circulation, product gas composition, and output. 2. An efficient atmospheric dual fluidized bed gasifier unit with an improved conversion of low grade, high-ash Indian coal into high calorific value syngas. 3. A pressurized dual fluidized bed gasifier unit integrated with an advanced gas cleaning system to deliver syngas, free of impurities, tar usable in high-pressure applications. 4. 2 Ph.D. and 2 MTech thesis, patents and journal publications.

Scientific Output

The hydrodynamic study of a 3D closed loop cold model of an internal circulating dual fluidized bed gasifier (ICDFBG) has been carried out. The cold model of the present ICDFBG system has a fast fluidized bed (riser), the solids separator, a bubbling fluidized bed, and solids recycle valve for solid circulation (loop seal). Both beds are concentrically placed such that the riser is in the core position and the bubbling bed is an annular portion. Solids separator, at the exit of the riser, is designed to separate solid bed materials and coarse ash particles from the gas-solids mixture. Compact design and geometric configuration of this ICDFBG system is the novelty of this study. Different components of ICDFBG are interconnected in such a manner that when gas is injected through different aeration ports, a stable internal loop of solids circulation was established. The effects of geometric configuration and operating parameters on hydrodynamic behavior of the system have been examined. The eulerian-eulerian approach based numerical model incorporating Kinetic Theory of Granular Flows has been developed and validated with reported experimental results. Sensitivity analysis of operating parameters which can potentially influence solids distribution and solids recirculation rate in the ICDFBG is conducted. Investigation showed that the highest pressure region was formed in the bottom of the loop seal when the statistical steady state of solids circulation was reached.The specific design of solids separator allowed the selective disengagement of solids from the gas-solids mixture for the riser superficial gas velocity maintained in the range of .3 m/s to 7 m/s. Particles having a mean diameter of than 300 microns were removed in solids separator from the gas stream up to riser gas superficial velocity of 7 m/s.

Results and outcome till date

1. Exhaustive numerical simulations of hydrodynamics are carried out in order to optimize the solid circulation rate between the combustor and the gasifier. Numerical simulations provided the fair idea about the maximum solid circulation that can be achieved in the system. 2. Based on numerical simulations, few changes are made in the final theoretical design of cold flow dual fluidized bed reactor and are being implemented by the vendor in the actual one. 3. Conceptual design of various components of full reacting atmospheric dual fluidized bed reactor is completed. 4. An OpenFOAM based CFD solver is built. Validation of the solver with experimental data is being performed.

Societal benefit and impact anticipated

Coal is still a major source of energy and is expected to continue to play an important role in the future energy infrastructure in the future as well. Coal resources are abundant compared to oil, but conventional conversion processes cannot compete with natural gas fuels plants, from an environmental point of view. Efficient and clean conversion of coal is required to be competitive with other fossil fuels. Gasification offers the option to use coal with minimal environmental impact by conversion of the coal into Synthetic Natural Gas (SNG), i.e. high-quality methane. During the production of SNG, part of the carbon in the coal is separated from the gas as CO2. When this relatively pure CO2 stream is sequestrated, the CO2 footprint can be reduced to the same level as natural gas. Indian coal resources are of very low quality. Ash concentrations of over 50wt% are not uncommon. This makes these reserves unsuitable for conventional combustion and gasification processes. At the moment, these coals are washed to separate the coal in a (very) high ash fraction and a usable fraction with a lower ash content. By this separation, part of the coal reserves is wasted.

Next steps

1. Experiments on cold flow hydrodynamics of DFB 2. Finalization of the drawings of the hot flow setup and give it for fabrication 3. Procurement of remaining sub-systems for the gasifier (screw feeder, ash disposal and material handling units) 4. Development of the test rig of the hot flow setup

Publications and reports

1. Gupta S., De S., Karmakar M. (2017) Hydrodynamic study of a novel dual fluidized bed gasifier using numerical simulations., Paper ID; IHMTC2017-13-0407. In: Proceedings of the 24th National and 2ndInternational ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2017), December 27-30, 2017, BITS Pilani, Hyderabad, India. 2. Gupta S., Bhaskaran S., De S. (2018) Numerical Modelling of Fluidized Bed Gasification: An Overview. In: De S., Agarwal A., Moholkar V., Thallada B. (eds) Coal and Biomass Gasification. Energy, Environment, and Sustainability. Springer, Singapore. 3.Bhaskaran S., Gupta S., De S. (2018) Dual Fluidized Bed Gasification of Solid Fuels. In: De S., Agarwal A., Moholkar V., Thallada B. (eds) Coal and Biomass Gasification. Energy, Environment, and Sustainability. Springer, Singapore. 4.Loha C., Karmakar M.K., De S., Chatterjee P.K. (2018) Gasifiers: Types, Operational Principles, and Commercial Forms. In: De S., Agarwal A., Moholkar V., Thallada B. (eds) Coal and Biomass Gasification. Energy, Environment, and Sustainability. Springer, Singapore. 5.Karmakar M.K., Loha C., De S., Chatterjee P.K. (2018) Hydrodynamics of Circulating Fluidized Bed Systems. In: De S., Agarwal A., Moholkar V., Thallada B. (eds) Coal and Biomass Gasification. Energy, Environment, and Sustainability. Springer, Singapore. 6.. Gupta S., De S., Karmakar M. (2018), Numerical assessment of different drag models on particle-laden flow in a circulating fluidized bed. In: International Conference on Recent Innovations and Developments in Mechanical Engineering, NIT Meghalaya, Shillong, India, November 8-10, 2018. 7.Gupta S., De S., Karmakar M. (2018) Effects of Drag Models on Hydrodynamics of a Bubbling Fluidized Bed. In Proceedings of the 7th International and 45th National Conference on Fluid Mechanics and Fluid Power (FMFP) December 10-12, 2018, IIT Bombay, Mumbai, India.

Patents

Scholars and Project Staff

Saurabh Gupta Ph.D. scholar Feb 2017 - ongoing Suraj Ms Student (Ongoing) Dec 2017 - ongoing Shikhar BT-MT Student (Ongoing) May 2018 - ongoing Nishant M.Tech student May 2017 - May 2018

Challenges faced

1. Non-availability of first and second year full budget (only 50% of budget came during first two years), is posing major difficulty in terms of planning and execution of such a complex, industrial project. Fabrication cost of gasifiers involve large expenses due to high temperature operation under pressurized condition. Kindly release full budget as soon as possible. 2. Delay in getting required lab-space caused some delay in setting up of the gasifier, which we are trying to make-up 3. Not getting technical manpower with suitable background. Training present set of project staff (research scholars) takes a lot of time.

Other information

COLD FLOW MODEL of the actual gasifier is being constructed. The cold flow model is used to study the fundamental hydrodynamics in circulating fluidized bed gasification reactor. The hydrodynamic behavior of the DFB determines; 1.The temperature difference between the combustor and gasifier riser. Temperature difference between gasifier and combustor depends on solids circulation study. Any deviation from optimum solids circulation rate results in greater temperature difference between the two reactors. 2. Gas exchange between the combustor and gasifier riser. Main advantage of DFBG is that the product gas of gasification is free of N2 and CO2. Therefore, any leakage of flue gas from combustor to gasifier must be averted. 3. The loss of char from the system. Sufficient char should be transport to combustor from gasifier otherwise combustor will not generate sufficient heat to sustain endothermic reactions