Coal gasification technology efficiently converts coal into power, chemicals, fertilizers, and fuels by decomposing it into synthesis gas (syngas) using steam and oxygen at high temperatures and pressures. Key applications include power generation, fertilizer production, methanol synthesis, and hydrogen production, with specific focus on the selection of suitable coal and essential gas cleaning processes. Different gasification techniques, such as fixed bed, moving bed, fluid bed, and entrained-flow gasifiers, vary in operational efficiency and suitability for different coal types.

2. Coal Gasification Technology
• Coal gasification technology efficiently converts coal into:
Power, chemicals, fertilizers, and fuels.
• Clean technology that decomposes coal into components
using steam and oxygen at high pressure and temperature.
• Produces synthesis gas (syngas): a mixture of carbon
monoxide (CO) and hydrogen (H₂).
• Utilized for methanol production as an alternative energy
source.

3. Major Applications of Coal
Gasification
• Power generation
• Fertilizer production
• Methanol synthesis
• Hydrogen production
• Hydrocarbon production
Coal gasification is the only direct route to produce hydrogen
from coal.

4. Process Overview
• Reaction:
• Stages of the process:
1. Pre-treatment of Coal
2. Gasification
3. Gas Cleaning
4. Gas Beneficiation

5. Reactions in Coal Gasification

7. Selection of Suitable Coal for
Gasification
• Critical properties to choose appropriate coal at the initial
stage based on :
• Sulfur content
• Fixed carbon
• Oxygen levels
• Ash and volatile content
Sub-bituminous coal: Lowest sulfur content compared to lignite
and bituminous coal.

8. Gas Cleaning & Acid Gas Removal
• Removal of acid gases (H₂S, CO₂) is crucial for syngas
preparation.
• Low sulfur content in coal minimizes unwanted products like
H₂S and CO2.
Methanol Production
• Syngas ideally has a 1:2 CO to H₂ ratio.

9. Coal Preparation
Pre-treatment step:
• Coal is dried and crushed/pulverized for fluid or entrained
bed gasifiers.
• Moisture removal by drying is essential.
• Caking coals may require partial oxidation for easier gasifier
operation.
• For fixed bed gasifiers, briquetting of fine coal particles is
necessary.

10. Gasification
• Reactor Charging: Pre-treated coal is fed into the gasification reactor.
• Reactions: Coal reacts with oxygen (or air) and steam.
• Operates at 800–1900°C and up to 10 MPa pressure.
• Gas Content: When coal is burned with less than a stoichiometric
quantity of air, with or without steam, the product is a low-heat-
content gas, which after purification can be used as fuel gas.
• Using oxygen instead of air yields a medium-heat-content gas.
• Shift Conversion: Some of CO must be reacted with steam by shift
conversion to get additional hydrogen
• Ash Removal: Ashes are removed as molten slag or in dry form.

11. Purification of Product Gas
Gas Composition: Contains CO, CO₂, H₂, CH₄, organic vapors,
and H₂S.
If air is used, nitrogen is also present.
Impurities: Particulates like coal dust, ash, and tar aerosols.
Purification Steps:
• Gas Quenching: Removes tar and oil.
• Acid Gas Removal: Uses solvent treatment technology to
absorb acid gases (e.g., H₂S, COS, CO₂).
• Methanol can be used as a solvent for absorption.

12. Different Gasification Techniques
1. Fixed Bed Gasifier
2. Moving Bed Gasifier
3. Fluid Bed Gasifier
4. Entrained-Flow Gasifiers

13. Moving Bed Gasifier
• Coal bed moves downwards counter-currently with air.
• Lowest oxygen consumption.
• Operates at low temperatures, leading to:
• Slower reaction rates.
• Increased maintenance costs.

14. Fluid Bed Gasifier
• Provides good mixing and has low overall cost.
• Carbon conversion rate is lower due to:
• Some carbon loss with ash.
• Suitable for low-rank coals like lignite as opposed to sub-
bituminous.

15. Entrained-Flow Gasifier
• Fine coal particles react with steam and oxygen co-
currently.
• Operates at high temperatures, leading to:
• High carbon conversion (~99%).
• Destruction of tar and oil, yielding pure syngas.
• High oxygen demand and sensitivity to high ash content.