Pollutants, Effects And Controlling methods of thermal or steam power plant

TABLE OF CONTENTS

1. Pollutants

2. Effect of pollutants

3. Pollution control methods

3.1 Cyclone separator 

3.2 Wet scrubber 

3.3 Electro static precipitator

1. Pollutants

The main pollutants in steam power plants are as follows

• Carbon monoxide (co)
• Carbon dioxide (CO₂)
• Sulphur dioxide (SO₂)
• Nitrous oxides 
• Smoke and dust particles 
• Hydrogen sulphate (H₂S)

2. Effect of pollutants

Co – Co combines with Fe in hemoglobin in blood. It causes less oxygen supplied to body cells, Headache, shortness of breath, dizziness, vomiting.

CO₂ − It causes dizziness, headache, visual disturbances, disease in  the heart and respiratory. Also it affects the cerebral function.

SO₂−It causes asthma, lung cancer, cardiovascular illness, also plant damage.

NO_X  −  It causes pneumonia, lung cancer, oxygen deficiency, irritation of lungs, also reduce the oxygen in body cells. 

3. Pollution control devices for steam power plant

For pollution control, the following devices are used in steam power plant

i.   Cyclone separator 

ii.  Wet scrubber 

iii. Electro static precipitator

• To remove sulphur content, limestone is added with coal during coal preparation.
• Fluidized bed combustion reduces SO₂  and NO_X contents.
• Cyclone separation is used to remove dust particles.
• H₂S is removed by using wet scrubber.
• Fly ash content is removed by using electro static precipitator. 

3.1 Cyclone Separator

• Cyclone separator is used to remove dust particles from flue gases.
• A barrel consists of tangential inlet duct and conical container called cyclone.
• High velocity flue gases carrying dust particles enters into tangential inlet duct and it is passed into conical shell. 
• So air flows in a helical pattern.
• Due to this action whirling motion is created.
• Due to the whirling motion, heaviest dust particles are crushed by the centrifugal force.
• Rotational effects and gravitational force are used to remove the solid particles from flue gases.
• They are collected at the bottom of the collector.
• The cleaned gases goes out at the top of the device.

Advantages of cyclone separator

• Low maintenance.
• Suitable for large particles.

Disadvantages of cyclone separator

• Not suitable for small size particles

3.2 Wet Scrubber

• Wet scrubber is a device which is used to control the air pollution in steam power plants.
• It is operated by passing the fuel gases with a scrubbing liquid.
• The flue gases are passed at the bottom as shown in figure.
• Scrubbing liquid is a mixture of water and lime stone.
• Scrubbing liquid is sprayed through a nozzle from top of the tank.
• Scrubbing liquid wets the dust particles so that the weight of the particle is increased.
• SO₂ and H₂S gases are absorbed by lime stone.
• They are collected at the bottom of the tank due to gravitational force.
• The cleaned gases goes out at the top of the device.

Advantages of wet scrubber

• Less area is sufficient.
• It is suitable for removing fine and coarse dust particles 
• Most suitable to remove SO₂. 

Disadvantages of wet scrubber

• Highly corrosive.
• Disposal of dirty water is a major problem.
• High installation cost.

    

3.3 Electro Static Precipitator

• Electro static precipitator is a device which is used to remove dust particles from flue gases by means of electro static attraction and repulsion.
• It is a high effective filtration device and it can easily remove fine dust particles from flue gases.
• It consist of two electrodes one is emitting plate and another one is collector plate.
• Initially the flue gases are charged by passing them through an electric field and it gets ionized.
• Electro static field exerts the force on the negative charged dust particles.
• The collector plates carries the negative charged dust particles.
• The collected dust particles are removed either by staking or washing the collector plates.

Advantages 

• Suitable for small particles. 
• Low maintenance cost.
• Easy operation. 
• High efficiency.

Disadvantages  

• Operating cost is high 
• More space is required
• High electricity needed 

OUR VIDEO LECTURES

Video 1 - Pollutants, Effects

Video 2 - Controlling methods of thermal or steam power plant