Procedure for Estimation of Air Pollutant Emissions from Stacks in Steel Works

At Tata Steel, the emissions from point sources (stacks) are monitored using TMT Analyser for gaseous pollutants (SO2, NOx, etc.) and the stack monitoring kit for Particulate Matter (PM). The sampling rate for PM monitoring is decided based on isokinetic conditions. The stacks in Steel Works are constructed using two types of configuration i.e. cylindrical (tubular) and conical (inverted cone). The smaller diameter/short height stacks are cylindrical and large diameters and tall stacks are conical.

Actual measurement and that generally determine the flow of waste gases in cylindrical stacks in conical ones, by calculations based on carbon input and excess air volumes supplied in the combustion furnace. These volumes are used in the estimation of total PM emissions based on actual measurement of PM using stack-monitoring kits. Gaseous pollutant concentrations measured using TMT Analyser are likewise used in estimation of total gaseous pollution load for cylindrical as well as conical stacks.

These calculations are done every month using software developed in-house. The summary of stacks where actual measurement of waste gases is carried out and that of the ones where calculated values of waste gas volume are used is presented below:

1. Sinter Plants (4 Stacks)
2. Finishing Mills (4 Stacks)
3. Slag Granulation Plant (2 Nos.)
4. Fume/Dust Extraction System at Blast Furnaces & L D Shops (7 Nos.)
5. Coke Quenching Tower & CGC Car in Coke Ovens
6. Lime Kilns (5 Nos.)

1. Blast Furnace Stove Stacks (7 Nos.)
2. Battery under firing stack (6 Nos.)
3. Boiler Stacks in Power Houses (15 Stacks)

The basis for calculation of waste gas volume is;

• Blast Furnace (BF) Gas (10% excess air, multiplying factor –1.62)
• Coke Oven (CO) Gas (20% excess air, multiplying factor – 5.74)
• L D Gas (10% excess air, multiplying factor – 2.16)
• Coal (Boilers) (75% excess air, multiplying factor – 10.1)
• Waste Gas Volume (Nm3/hr) = Coal consumption (t/hr)x10.1x103 +
          BF gas consumption (Million Nm3/hr)x1.62x106 +
          CO gas consumption (Million Nm3/hr)x5.74x106 +
          LD gas consumption (Million Nm3/hr)x2.16x106

Only PM values are estimated for these gases. SO2, NOx and other gaseous pollutants are not estimated as the average concentrations are not available from any source (internationally published data). The PM values are estimated based on the following parameters.

• Crude BF Gas Bleeding – 10 gms/Nm3
• Clean BF Gas Bleeding – Actual mg/Nm3
• LD Gas Bleeding – 10 mg/Nm3
• CO Gas Bleeding – 2 mg/Nm3

Quantity of BF and CO gas bled to atmosphere is continuously recorded and LD gas bleeding is estimated based on total LD gas made minus LD gas recovered.

Note: Data samples from every point source are taken twice every year as per the emission-monitoring plan. Hence, monthly emission load is calculated based on the most recent previous data sample test results. As a consequence, in the early parts of a FY, the monthly load estimates are based on test sample results of the preceding reporting period.