FGD System

The FGD system can remove S0₂ or sulfur dioxides from exhaust flue gases by using a wet, semi-dry, and dry process.

Wet Flue Gas Desulphurization System

In many situations, the wet FGD system is the most common in fossil-fuel power plants.

In this process, the flue gases are saturated steam with an absorbent in an aqueous solution. The absorbents used are:

• sodium sulfite
• ammonia

These absorbents can remove about 99% of sulfur dioxide (SO₂) from the flue gas.

Moreover, using limestone slurry or lime is also widely used. This process is called Wet Limestone Scrubbing.

The alkaline-based limestone slurry is used for scrubbing the flue gases. Limestone is also absorbent but not that expensive.

Wet Limestone Scrubbing

1. First, the lime slurry and water will be mixed. But, the limestone or lime is not soluble in water. So, the absorbent will come in the form of:

• powdered form
• aqueous slurry
• dry form

2. Then, the absorbent will be injected through the spray nozzles of the flue gas scrubber. The scrubbers used comes in many types such as:

• Double Contact Flow Scrubber
• Spray Tower Scrubber
• Venturi-Rod Scrubber
• Plate Tower Scrubber
• Packed Bed Scrubber
• Trayed Tower Scrubber

3. After that, the SO₂ or sulfur dioxide will be removed by the spray or droplets of the lime slurry.
4. The sulfur dioxide will then become a wet calcium sulfite.
5. Then, a by-product of that calcium sulfite will be converted into gypsum.

Dry Flue Gas Desulphurization System

There are 2 processes of dry FGD systems such as spray drying system and dry injection system.

These processes work by injecting lime into the flue gas to remove the SO₂ or sulfur dioxide.

Dry Injection System

This system starts by directly injecting the flue gas using these sorbents:

• limestone sorbent
• powdered lime
• dry hydrated lime

The dry sorbent will be injected into one of these 3 locations:

1. the upper part of the steam generator
2. economizer part of the steam generator
3. the ducting among the electrostatic precipitator and the air preheater

And the powdered sorbent will be injected through the lances. So, the powdered sorbent will spread equally through the flow path of the flue gas.

The SO₂ will directly react with the powdered lime. And the wasted sorbent will be removed from the flue gas including the combustion fly ashes.

Spray Drying System

The spray dry system is also called the semi-dry process. They are the 2nd most common FGD system.

The spray drying system has a sulfur dioxide removal rate of less than 90%.

This process can be used for gas with a sulfur level of up to 3.5%.

The spray dry system uses lime slurry as a reagent. The lime slurry is usually atomized.

Then, it will be sprayed into a separate vessel.

The spray dry system is:

• simple
• low investment
• high performance

The FGD system has a lot of advantages and features such as:

• Utility and Energy Saving
• High Reliability and Performance
• Multiple Pollutant Control
• Up to 99% of SO₂ Removal Efficiency
• Flexible Operation Scheme
• Low Space Requirement
• Low Water Consumption
• No Color Plume
• Safe By-Product

We can use the FGD system in different industries such as:

• Petrochemical Industry
• Carbon Black Industry
• Steel Industry
• Thermal Power Plant
• paper Industry
• Chemical Industry
• Cement Industry
• Waste to Energy Plants
• Coking Industry
• Power Plants
• Mineral Ore Processing Plants
• Coal-and-Oil fired Combustion Units
• Utility Boilers
• Industrial Boilers
• Municipal Waste Incinerators
• Medical Waste Incinerators
• Petroleum Refineries
• Lime Kiln Plants
• Metal Smelters
• Sulfuric Acid Plants

The FGD system is very effective.

It can remove sulfur compounds in the range of 50% and 99%.

The highest percent is reached by the wet FGD system. And the lowest percent is by the dry FGD system.