The system produces coal gas in two stages.
The UPSTAGE GAS is produced when the coal in the gasifier upstage is dried and preheated making the volatile matter in the coal to evaporate into coal gas. This gas has a temperature of around 100-120 ｰC.
The DOWN STAGE GAS is made by a mixture of steam and air, which goes through red-hot fixed burning bed. The oxygen content in the air and steam react with the carbon in the fuel; generating the producer gas
Reaction of steam and carbon is endothermic reaction:
C + H2O= CO + H2
When oxygen and carbon react, and then heat output:
2C + O2 =2CO ; C + O2 = CO2 ; CO + H2O = CO2 + H2
In the reducing zone, quick reaction is occurred when the temperature is below 1200 Celsius degree
CO2 + C = 2CO and H2O + C=H2 + CO
When the coal gas goes through the reducing zone, flammable gas content raises rapidly, carbon dioxide and steam content decrease. Across the reducing zone, this part of coal gas is withdrawn through a series of vent in the gasifier walls and taken out through its outlet. Its temperature is around 300-400 Celsius degree and container dust and ash particles.
The upstage gas is passed into electric detarrer which is a specially designed ESP (Electro Static Precipitator) to remove tar. Tar come from the bottom of electric detarrer is sent to the tar tank.
The down stage coal gas is passed by cyclone separator to remove dust particles that it may contain.
Both these gases are then mixed in a pipeline mixer and then this clean gas of average temperature of 200 C , and calorific value of 1350 Kcal / Nm3 is transmitted to the user point.
|COAL GAS PARAMETERS
||>1350 Kcal / Nm3
||~ 0.4 Kpa or 40 ・50 mmwc
||> 150 ｰ C
||< 0.2 g / Nm3
||> 1.2 g / Nm3
||in vapour form
||NON STOP AVALIABLITY OF SYSTEM
||~ 180 ・300 days
||PIPELINE DISTANCE FROM USAGE
||~ 150 - 160 m
COAL GAS OUTPUT *1(Nm3/hr)
3500 – 4500
5000 – 6250
6000 – 7000
6750 – 7800
HEAT OUTPUT ( M cal/hr)
4.8 – 6.0
6.7 – 8.5
8.1 – 9.4
9.1 – 10.5
ENERGY OUTPUT ( Kw/h )
5480 – 6970
7780 – 9870
9400 – 10900
10580 – 12250
B GRADE COAL (5500 Kcal/Kg)
• Best suited for the Indian Bituminous Coal of high VM and high ash which are easily available and are economically more viable than.
• High gasification rate per kg of coal % at about average 3.3 Nm3 / kg which is higher than single stage gasifiers by around 7- 10 %.
• High calorific value of the mixed coal gas at about 1450 Kcal / Nm3 which is higher than single stage gasifiers by around 10 ・15 %.
• High thermal efficiency of the complete system when measured as GCV of Coal Gas / Coal at around 71 - 76% which is higher than single stage gasifiers by around 10 ・15 %.
• Clean coal gas after detarring and the clogging in the gas transmission pipelines is almost nil.
• Longer distance to which the gas can be transmitted increases to double to about 160 m.
• Low shutdown for the pipeline and equipment cleaning with the frequency of shutdown is 1/3 as compared to single stage Gasifier because of cleaner gas quality.
• High return due to the sale of tar recovered from the electric Detarrer. A minimum of 5 ・8% of coal is recovered as tar which could be sold for Rs. 25 - 28 per kg.
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