CASE Coal Gasifiers: Types and Usages

The technology of Coal Gasification is to combust the Coal in a controlled oxygen environment. The resultant is the generation of Coal Gas whose primary constituent is CO instead of CO2. Coal gas is used extensively to replace high value fuels for thermal applications. This Gas can also be used to make fertilizers and Chemicals. The gasifiers listed below are primarily used for thermal applications.

Coal Gas Contains Following Gases

CO

H2

CH4

N2

CO2

Depending on the type of gasifier, the percentage of these Gases Changes. So does the Calorific values.

 Checklist for Gasifier Model and Technology Selection:

CASE Coal Gasifier are of various types. Different types of Gasifiers are used for different Applications depending on the following:

Type of Application:

• ·       Gasifier Automation Required:
• ·       Quantity of Gas Required:
• ·       Gas Calorific Value Desired:
• ·       Pressure at Burner Point Desired:
• ·       Distance of user point from the Gasifier:
• ·       Burner level Automation:
• ·       Quality of Coal:
• ·       Granularity of Coal:
• ·       Economic Constraints:

On the basis of the above information provided by the user, the gasification technologist at CASE selects the optimum technology and type of gasifier suitable to meet the users’ demand.

CASE Hot Gasifier:

This is the Basic type of Gasifier. This Gasifier Converts Coal into coal gas and the Gas output temperature is over 450° C and the pressure is about 150mmWC.

The gas composition is as follows. CO 20-25%, H₂ 15-18%, CH₄ 2-4%, N₂ 45-50%. The VM in the coal stays in gaseous form which burns with the gas at the user point. These gasifiers need to be close to the user point. Here Burner level automation is not possible; However, Gasifier operations can be fully automatic. The calorific value of gas without Considering VM is 1250Kcal/Nm³. Considering TAR caloric value being part of Coal Gas in gaseous form, the overall calorific value of the gas can be over and above 1800Kcal/Nm³.

The positive of this technology is low capex and Opex. There is no Tar or Phenol water generated in this technology. The technology is a hot favorite of Steel Rolling mills, Galvanizing Plants, Annealing lines etc.

The cons for this technology are that burner level automation is not possible and these gasifiers need to be installed very close to the user point.

This technology requires Lump coal of size 15mm – 50mm. These gasifiers can be designed for a wide range of coals varying from high grade Anthracite coals to low grade bituminous coals having high ash coal. The Coal quantity required per NM3 of Coal Gas generated depends on the Quality of coal.

 CASE Cold Pyrolysis Gasifier:

These Gasifiers are one generation above Hot Gasifiers. In this technology, Gasifier gas can be scrubbed of the TAR and Clean cold Gas can be boosted to any pressure as per user’s requirements. The phenol water is 100% recirculated back into the system. The Gas composition is almost same as in Hot Gasifier except high CH₄ (4-6%) which results in Calorific value to be over 1400 Kcal/Nm³.

These Gasifiers are fully automatic and are preferably used where burner level Automation is desired like in Automatic Steel Furnaces, Pellet Plants, Glass Plants, Aluminum Calciners etc.

The Negatives of this technology is that if the Gas required is over 35000Nm³/hr, Battery of gasifiers are required resulting in increasing costs on man power and Opex.

Just like hot gasifiers, the gas quantity generated in these gasifiers are similarly dependent on the quality of coal used for gasification. Likewise, coal used in these gasifiers is also of wide variety varying from low ash like “Anthracite” or high ash like “Indian F Grade coal”.

Circulating Fluidized Bed Gasifiers:

These Gasifiers are the third-generation gasifiers where coal fines of 0mm-10mm size can be used for gasification. These Gasifiers have Fluidized Bed where Coal fines, Steam and Air are pumped from the bottom to the top. The gas comes out from the top which needs to be filtered and can be compressed to any pressure depending on the user requirements. In this  technology there is no generation of Tar or Phenols.

The calorific value of gas is about 1300Kcal/Nm3 and can be increased to about 1800Kcal/Nm3 by adding oxygen in the air which is used as gasifying agent.

These gasifiers involve a higher capex but they are low in opex as compared to the other two variants explained above.

The coal used in these gasifiers can be fines below size of 10mm but the ash content needs to be less than 25%. This technology is well established now and many installations are available to vouch for the technology. This technology can generate 60000Nm³/Hr gas in single cell. This is a boon where gas requirement is in high quantities.

 CASE Entrained Flow Coal Gasifiers:

These gasifiers are Fourth-Generation Coal Gasifiers where the technology is better than Circulating bed coal gasifiers. In this technology, High ash coal can be used of size less than 100 microns.

The Gas is filtered and used by the user. The pressure of gas coming out of the gasifier can be plus 80 KPA. In this technology 100% Oxygen can be used instead of air as gasifying agent by which calorific value of plus 2400Kcal/Nm³ can be achieved in the gas. This is a boon where the thermal process requires higher Calorimetric temperatures.

These gasifiers are down draft in contrast to all the above three cousins. In these gasifiers the temperature is maintained over Ash fusion temperature of coal used. The majority ash comes out in liquid form from the bottom.

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