CPCB Guidelines for Stack Monitoring

CPCB (Central Pollution Control Board) guidelines for stack monitoring testing includes frequency of testing, parameters, time of the year & depending of industry type number of stations.

Stack monitoring is a procedure for sampling of gas stream from an emission point. It measures emissions of industrial waste or pollutants entering the atmosphere.

Since the advent of industrial revolution, the air pollution levels have touched the sky! With the current scenario regarding to air pollution, it has become a necessary evil to curb the pollution at its source or find alternatives to reduce air pollution.

Using stack has definitely aided to reduce air pollution. A stack is a vertical pipe structure through which flue gases (combustion product gases) are exhausted out in the atmosphere, it can also be known as a chimney.

But, has the installation of stack really aided in control of air pollution or is it just a myth?

 Such questions can only be answered with the help of analytical results, i.e; Stack monitoring. Stack monitoring will provide results which puts light on the pollutants beings released in the atmosphere and their levels.

To conduct Stack monitoring in India CPCB (Central Pollution Control Board) have put forth guidelines and permissible limits. Let’s have a look into CPCB Guidelines for Stack Monitoring.

CPCB Guidelines for Stack Monitoring;

The industrial units are required to monitor ambient Air Quality and stack emissions as the pollutants released in the atmosphere will have a detrimental effect on the human health and environment.

General Requirements from CPCB for Stack Monitoring;

1. Stack monitoring will be conducted at the frequency mentioned by State Board for each industry and report shall be sent to the concerned State Board in a standardized format.
2. Ambient air quality sampling shall be done on 24 hour basis every alternate day and reports for each month shall be sent to concerned State Board.
3. The parameters for stack monitoring must include the air flow rate and the production during period of sampling. In additions to pollutants, it shall include metrological data of wind speed and directions and temperature.
4. Depending upon the industry type the no of monitoring stations and monitoring frequency shall be stated by concerned industrial units in consultation with relevant State Pollution Control Board.

Stack monitoring equipment and testing procedure according to CPCB Guidelines

Stack sampling is conducted by diverting a part of the gas stream through a sampling train which includes the following basic components;

The sampling train consists of a nozzle placed in gas stream, a sampling probe through which the sample is drawn at different traverses, particulate and gas collection devices, a flow measuring device and a prime mover such as a vacuum pump.

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Minimum requirement of a stack monitoring equipment

A stack monitoring equipment or kit should have following components:

1. Pilot Tube: Modified S-type pilot tube shall be fabricated from SS 204 or equivalent
2. Sampling Probe: Fabricated from SS 204 tube of suitable diameter.
3. Nozzles: A set of nozzles fabricated from SS 305 or equivalent material with internal diameters suitable to cover full range of stack velocities
4. Thimble Holder:- Filter paper holders
5. Thermocouple:- Thermocouple sensor capable of measuring temperature from 0 to 600°C covered .
6. Mounting Flange:- Flanges fabricated out of mild steel with proper hole for mounting thermocouple sensors, sampling tube and pilot tube.
7. Panel Box Sides:- It should have suitable arrangements for housing stop-watch, manometer, rotameter, etc.
8. Back Panel:- Cold box with 6 impingers
9. Inclined-cum-Vertical Manometer: – Velocity range – 0 to 30 m/sec.
10. Rotameter:- 0 to 100 ppm for particulate monitoring and 0 to 3 Ipm for gaseous monitoring.
11. Stop-Watch:- 0 to 60 minutes, one second readout with hold facility.
12. Impingers:- 4 impingers of 100 ml and 2 impingers of 300 ml capacity along with ice box.
13. Vacuum Pump
14. Dry Gas meter
15. Pump Housing

CPCB Guidelines for Stack Height

The Central Pollution Control Board (CPCB) mandates stack height adherence with the following specifications:

• Minimum height: 30 meters (90 feet)
• Formula: H = 14(Q)^0.3, where H is the stack height in meters, and Q is the emission rate of SO2 in kg/hr
• Diesel generators: H = h + 0.2 * capacity of DG in KVA, where H represents the total stack height in meters

Additionally, CPCB requires gases to undergo either recycling or oxidation in an after-combustor before venting. Stack emission monitoring is crucial for scrutinizing pollutants released into the air through stack emissions.

General Testing Procedure:-

The General Stack testing procedure would be as follows;

1. Selection of Sampling Site
2. Determination of no of traverses
3. Molecular weight determination
4. Velocity determination
5. Moisture determination
6. Analysis and Results

On obtaining the results they will be compared with the permissible limits prescribed by CPCB. The guideline given by CPCB is like a Bible which helps us conduct stack monitoring efficiently. If in any scenario, the stack emission exceeds the permissible limit set by CPCB, stack monitoring will be an indication for adoption of new pollution control strategies. This will eventually help us curb air pollution.

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