Research · Clean energy

Gasification of high-ash coal and biomass

India has abundant high-ash coal and agricultural residues that are hard to burn cleanly. We design and run fluidized bed gasifiers that turn these feedstocks into syngas, and back the hardware with CFD of the gas–solid flow. See also pyrolysis of refinery oily sludge.

Background: pilot-scale bubbling fluidized bed gasifier, 100 kg/h

Gasification of high-ash Indian coal

A pilot-scale bubbling fluidized bed gasifier, designed and built in-house, for sub-bituminous coal with more than 45% ash.

Pilot-scale bubbling fluidized bed gasifier with insulated reactor and steel support frame
Pilot-scale gasifier, 100 kg/h
Schematic of the gasifier with screw feeder, lock hopper, steam superheater, air preheater, cyclone, filter, scrubber and gas chromatograph
Layout: coal feed, air and steam supply, cyclone and gas sampling

Coal is fed by a screw conveyor into a 300 mm bed fluidized with preheated air, or air and superheated steam. Syngas leaves through a cyclone, filter and scrubber to a gas chromatograph, with thermocouples and pressure taps along the reactor.

Ash content
> 45%
Operation
Autothermal, air and air–steam
Cold gas eff.
48% (max)
Carbon conv.
85% (max)
Syngas HHV
3 MJ/Nm³ (air–steam)
Steam/coal
0.19 – 0.28 keeps the bed at 800 – 900 °C

Even with low-alkali ash, agglomerates formed at local hot spots when the fluidization number was low, which sets a practical limit on operation.

Gupta & De, Energy 244 (2022) 122868 · First prize, Coal India Hackathon 2024

Effect of air and steam

Top row: air gasification at increasing equivalence ratio φ. Bottom row: air–steam gasification at increasing steam-to-coal ratio ψ. Columns show syngas composition, heating value with bed temperature, and carbon conversion with cold gas efficiency.

Syngas mole fractions of CO, CO2, H2 and CH4 against equivalence ratio
Syngas composition vs φ
Syngas higher heating value and bed temperature against equivalence ratio
HHV and bed temperature vs φ
Carbon conversion and cold gas efficiency against equivalence ratio
Carbon conversion and cold gas efficiency vs φ
Syngas mole fractions against steam to coal ratio
Syngas composition vs ψ
Syngas heating value and bed temperature against steam to coal ratio
HHV and bed temperature vs ψ
Carbon conversion and cold gas efficiency against steam to coal ratio
Carbon conversion and cold gas efficiency vs ψ

Dual fluidized bed gasification

Separating gasification from combustion gives a nitrogen-free, medium-calorific-value syngas.

The dual fluidized bed gasifier rig with riser, cyclone and seals inside the lab
Dual fluidized bed gasifier at IIT Kanpur

In a dual fluidized bed, a bubbling bed gasifies the fuel with steam while a riser burns the leftover char and reheats the bed material. Loop and pot seals pass hot solids between the two without mixing their gases.

Cold-flow experiments and CFD of the rig studied solids circulation, and the segregation of sand and high-ash coal. The rig now gasifies agricultural residues, with municipal solid waste, a pressurized reactor and hot gas cleanup over Ni-based catalysts next.

CFD of gas–solid flow

The experiments are paired with simulations: full-loop LES of a pilot-scale circulating fluidized bed to test drag and subgrid models, Euler–Euler studies of the dual bed, and LES with the multiphase particle-in-cell (MP-PIC) method for rice husk gasification in a bubbling bed.

IMPRINT project with CSIR-CMERI · Gupta & De, Powder Technol. 2021; Adv. Powder Technol. 2021; Chem. Eng. Sci. 2022; Renew. Energy 2021

Publications

  • 2022S. Gupta, S. De. An experimental investigation of high-ash coal gasification in a pilot-scale bubbling fluidized bed reactor. Energy 244, 122868.Publisher ↗
  • 2022S. Gupta, S. De, C. Loha, M. Karmakar. Effects of drag and subgrid-scale turbulence modeling on gas–solid hydrodynamics of a pilot-scale circulating fluidized bed. Chemical Engineering Science 248, 117093.Publisher ↗
  • 2021S. Gupta, S. De. Investigation of hydrodynamics and segregation characteristics in a dual fluidized bed using the binary mixture of sand and high-ash coal. Advanced Powder Technology 32(8), 2690–2702.Publisher ↗
  • 2021S. Gupta, S. De. Investigation of cold flow hydrodynamics in a dual fluidized bed for gasification of high-ash coal. Powder Technology 384, 564.Publisher ↗
  • 2021S. Gupta, S. Choudhary, S. Kumar, S. De. Large eddy simulation of biomass gasification in a bubbling fluidized bed based on the multiphase particle-in-cell method. Renewable Energy 163, 1455–1466.Publisher ↗
  • 2021S. Gupta, S. De. Numerical investigation of cold flow hydrodynamics in an internally circulating dual fluidized bed for coal gasification. Particulate Science and Technology 39(4), 401–414.Publisher ↗
  • 2017S. Gupta, S. De, M. Karmakar. Hydrodynamic study of a novel dual fluidized bed gasifier using numerical simulations. IHMTC-2017, BITS Pilani Hyderabad.Publisher ↗
  • 2018S. Gupta, S. Bhaskaran, S. De. CFD modelling of fluidized bed gasification: An overview. In Coal and Biomass Gasification, Springer.Publisher ↗
  • 2018S. Bhaskaran, S. Gupta, S. De. Dual fluidized bed gasification of solid fuels. In Coal and Biomass Gasification, Springer.Publisher ↗
  • 2018C. Loha, M. K. Karmakar, S. De, P. K. Chatterjee. Gasifiers: Types, operational principles, and commercial forms. In Coal and Biomass Gasification, Springer.Publisher ↗
  • 2018M. K. Karmakar, C. Loha, S. De, P. K. Chatterjee. Hydrodynamics of circulating fluidized bed systems. In Coal and Biomass Gasification, Springer.Publisher ↗

All publications →

Funding

  • IMPRINT (MHRD, Ministry of Coal)Pressurized dual fluidized bed gasifier for high-ash Indian coal, with CSIR-CMERI, 2017 – 2020

People

  • Dr. Saurabh GuptaHydrodynamics and high-ash coal gasification in fluidized beds (PhD 2021)
  • Ajay PawarFluidized bed gasification of biomass and high-ash coal
  • AdwaithNumerical simulation of a dual fluidized bed

Collaborators

  • CSIR-CMERI, DurgapurDr. Malay Karmakar, Dr. Chanchal Loha