ANS:C - gasified

Gasification is a thermochemical process that converts carbonaceous materials, such as coal, biomass, or waste, into a mixture of gases known as synthesis gas or syngas. This process typically involves subjecting the solid or liquid feedstock to high temperatures and controlled amounts of oxygen, steam, or a combination of both in a gasifier reactor. Here's an explanation of gasification:

1. Feedstock Preparation: The feedstock, which can be low-grade coal in this case, is prepared for gasification. This may involve crushing, drying, and sometimes preprocessing to remove impurities or increase its reactivity.
2. Gasifier Reactor: The prepared feedstock is introduced into a gasifier reactor, where it undergoes several thermochemical reactions under controlled conditions of temperature, pressure, and residence time. The gasifier reactor can be of various types, including fixed-bed, fluidized-bed, or entrained-flow gasifiers.
3. Gasification Reactions: Inside the gasifier reactor, several reactions occur:
   • Pyrolysis: At high temperatures in the absence of oxygen (or in limited oxygen supply), the feedstock undergoes thermal decomposition, producing volatile gases, tar, and char.
   • Gasification: The volatile gases and char react with oxygen (or steam) to produce syngas. This involves several reactions, including:
     • Combustion reactions: Conversion of a portion of the carbon in the feedstock into carbon dioxide (CO2) and heat.
     • Reduction reactions: Conversion of carbon dioxide (CO2) and water (H2O) into carbon monoxide (CO) and hydrogen (H2) through reactions such as the water-gas shift reaction.
     • Methanation: Formation of methane (CH4) from carbon monoxide (CO) and hydrogen (H2) under certain conditions.
   • Ash and slag formation: Inorganic components of the feedstock form ash, which may melt and form slag. These byproducts are typically removed from the gasifier.
4. Syngas Production: The main product of gasification is syngas, which is a mixture of gases including hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and trace amounts of other gases. The composition of syngas depends on factors such as the feedstock, gasification conditions, and gasifier type.
5. Syngas Cleanup: The syngas may undergo cleanup processes to remove impurities such as sulfur compounds, particulates, and trace contaminants, depending on the intended use of the syngas.
6. Utilization: The syngas produced through gasification can be used as a fuel for power generation, as a feedstock for chemical synthesis processes (such as ammonia production), or as a source of hydrogen for various industrial applications.

Gasification offers several advantages, including the ability to convert a wide range of feedstocks into useful gases, higher energy efficiency compared to direct combustion, and potential for carbon capture and utilization or storage (CCUS). It is a versatile and efficient process for converting carbonaceous materials into valuable products while minimizing environmental impacts.