Emissions of Oxides of Nitrogen From Coal

Oxides of nitrogen (NOx) are (?) nitrous oxide (N^O), (ii) nitric oxide (NO), and (ш) nitrogen dioxide is mostly formed by oxidation of the NO, which is discharged in combustion products. About 90% is the form of NO. NO is formed by two mechanisms: (/) oxidation of atmospheric nitrogen, known NO’ and (if) oxidation of nitrogen that is chemically bound within the fuel, known as ‘chemical NO’ of NOx varies widely with boiler conditions. NOx emissions are generally functions of flame temperature excess air, per centage of boiler load, nitrogen content in the coal, and rate of gas cooling. In pulverised coal flames, about 30 - 35% of nitrogen in coal gets converted into NO and remaining nitrogen in the converted into molecular nitrogen. The actual mechanism, whereby atmospheric nitrogen is oxidized through a complex chain of reactions initiated by oxygen atoms. We can however calculate equilit concentrations of NO, using the following reaction:

This is lumped reaction. Generally accepted principle reactions are:

The concentration of nitric oxide (NO) is given by

Where X is the species concentration and К 10.1 is a equilibrium constant and depends upon the gas. Appendix-В gives the equations to compute equilibrium constant for NO reaction.

Concentration values X for O0 N-,, CO„ S02, and NO for the Chandrapur coal, as calculated by method, are given in Table 1.29. The value of the equilibrium constant K10.1 computed at 1700 К is

Table 1.29: Species concentrations in flue gas for the sample coal

Species concentrations (PPM) in the combustion products for the Chandrapur coal are given in Table 1.30 below:

Table 1.30: Species concentrations in parts per million (ppm)

Excess Air%

co2

so2

NO

0

167148

1512

0

5

158754

1436

730

10

151213

1368

1006

15

144356

1306

1202

20

138094

1249

1357

25

132352

1197

1484

30

127069

1149

1591

Carbonaceous Material and Black Carbon

Incomplete and/or inefficient combustion processes of fossil fuel generate carbonaceous aerosols carbonaceous (soot) aerosols are of two types, namely organic carbon (OC) and black carbon (BC) types have different properties in the atmosphere. OC is a reactive species and has scattering pro solar spectrum while the BC, on the other hand, is non reactive in the atmosphere but has highly properties in the solar spectrum. In the thermal power plants, most of the soot carbon emitted form of BC because of the higher temperatures of combustion in the furnaces. When the soot is analysis ranges from CSH to CpH. The importance of BC in the radioactive balance of Earth is grad understood.

The soot carbon from the combustion of coal in the Indian thermal power plants has been calculate basis of prevalent combustion characteristics. It is assumed that approximately, 10% of the coal converted into the bottom ash and about 2% of the carbon forms the soot that may emit with fly ash. Electrostatic Precipitators (ESPs) used in the thermal power plants in India, remove about 99% fly ash from the stack. 1% of generated fly ash, which contains 2% soot carbon is emitted into the atmosphere. These soot part micronic in size. Similar assumption has been used for calculation of soot carbon from lignite thermal power plants in India (viz. Kutch and Neyvelli power plants).

Suspended Particulate Matter

The fly ash in the form of Suspended Particulate Matter (SPM) is a major pollutant from coal burning power plants in India. SPM has been calculated on the basis of the ash contents of the coal. It is assume the ash in the coal goes out through the stack as fly ash after the combustion. Electrostatic precipitator working on 99% efficiency rate allows only 1% of the formed fly ash to emit as SPM.

Coal Reserves

Coal is the primary fuel for energy in India, followed by petroleum, and natural gas. India is third largest producer of coal in the world. According to Geological Survey of India’s estimates, coal reserves billion tones as on January 1, 2000. The state-wise distribution of coal reserves and coal types (geological formation) are as follows:

Table 1.31: Coal reserves (Million tones) in India

State

Proved3

Indicated4

Inferred5

Total

Coal Type

AndhraPradesh

7346

3312

2,929

13,587

Gondwan

Arunachal

31

11

48

90

Tertiary

Assam

259

27

34

320

Tertiary

Jharkhand

34,794

28,692

5,642

69,128

Gondwan

Jammu & Kashmir

90,000

Lignite

Chhatisgarh

13,010

22,148

8,334

43,430

Gondwan

Maharashtra

4,149

1,323

1,605

7,077

Gondwan

Meghalaya

118

41

301

459

Tertiary

Nagaland

4

1

15

20

Tertiary

Orissa

11,140

22,755

16,554

50,449

Tertiary

Uttar Pradesh

766

296

0

1,062

Gondwan

West Bengal

10,799

10,894

4,236

25,909

Gondwan

Furnace oil

526576

Kilo Ltrs.

Light Diesel

317832

Kilo Ltrs.

LSHS/HHS7

1519756

Kilo Ltrs.

Lignite

165.57

Million tones

Natural Gas

13797

Million Cubic meters

High Speed Diesel

120138

Kilo Ltrs.

Naptha

100199

Kilo Ltrs.

Diesel oil

207270

Kilo Ltrs.

 
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