# POWER 

# NID TM 

# FLUE GAS DESULPHURIZATION SYSTEM FOR THE POWER INDUSTRY

# NID TM 

# Flue Gas Desulphurization System
The NID TM 

## system is a Dry Flue Gas Desulphurization (DFGD) process that is based on the reaction between
SO 2 

## and Ca(OH) 2 

## in humid conditions. The humidified mixture of hydrated lime and reaction product is injected into the NID system absorber and cools the inlet flue gas by evaporation. The cooled flue gas then flows to the dust collector, preferably a Fabric Filter (FF) or an Electrostatic Precipitator (ESP), where the particles in the flue gas are removed and recycled back through the NID FGD system.

Alstom has over 100 NID system installations covering applications in power generation, iron and steel and waste-to-energy. The NID system is the innovative result of Alstom’s many years of experience in dry and semi-dry FGD systems and other dry flue gas cleaning processes.



# Fabric Filter

The use of a fabric filter offers a distinct advantage in dry FGD systems. The cooled, humid flue gas provides excellent filtration and reaction conditions, resulting in the following advantages:

•	 very low particulate emissions; and •	 additional gas absorption (SO 2 , HCl, SO 3 , HF, Hg) in the dust cake. 

# Absorber

The moistened fine powder recycle provides instantaneous flue gas cooling and humidification. The NID system absorber is integrated into the fabric filter inlet duct, minimizing the system footprint. The reaction and drying times within the NID FGD system are less than two seconds.

DUST H 2 O

REAGENT The heart of the NID system is the patented mixer/humidifier. The equilibrium
moisture content in the ash received from the fabric filter is increased a few percent by the addition of water. The mixer uniformly distributes the water and lime into the entire recycle product stream from the fabric filter prior to injection into the flue gas.

The humidified solids in the mixer continue to behave as a free-flowing powder, without clumping, enabling even distribution of the moist powder into the flue gas for SO 2 absorption. The blending of the lime, water, and recycle product is done externally of the flue gas. This ensures a homogeneous mixture prior to injection back into the flue gas stream. 

# Mixer/Humidifier

MIXER SCHEMATIC

# Compact Design/Small Footprint

The combined size of the NID system mixer and absorber is less than 20% of a conventional spray dryer or fluidized bed reactor. This allows the complete FGD process to fit within the footprint of the fabric filter. The NID FGD system is the most suitable technology for retrofit purposes. Many existing precipitator support structures have been converted into NID systems.

•	 Low investment cost
•	 Low maintenance due to few components
•	 Low power consumption •	 Compact reactor design housed under the

particle collector •	 Low reactive reagent can be used •	 High SO 2 removal efficiency •	 Water, fly ash, reagent are blended outside

the flue gas.
•	 Not limited by coal sulphur content •	 High efficiencies for HAP’s and SO 3 over conventional WFGD. •	 High SO 2 efficiency, 90 to 98% with lime

stoichiometries on par with conventional

spray dryer absorber (SDA) DFGD. 

### ADVANTAGES OF THE NID SYSTEM RECIRCULATION CONCEPT TC

SO 2 WATER END PRODUCT

FLUE GAS

HYDRATOR HUMIDIFIER

REAGENT FABRIC FILTER 

# Reagent/Recirculation Concept

Hydrated Lime (Ca(OH) 2 ), quick lime (CaO) or alkaline ashes can be used

as reagents. CaO is dry slaked to Ca(OH) 2 in the system, which is the real reaction partner to SO 2 . Since the recirculated material has a solid content of 95% or greater, very high recirculation rates are attained. Recirculation rates of 30 to 50 times or higher, ensure high lime utilization.

•	 lightweight aggregate;

• acid mine drainage control; •	 mine backfilling; •	 disposal cell sealing layers; or •	 road beds 

# End Product

The typical end product is a dry powder consisting of a pozzolanic mixture of fly ash, calcium sulfite/sulfate, -hydroxide, -carbonate, -chloride, etc. These products may be disposed of in a landfill, but may also be used in the following applications: 

# End Product Handling

A mechanical transport system or conventional dense-phase pneumatic conveying system can be utilized, due to the low water content in the end product. The end product is stored in a silo similar to the storage of conventional semi-dry end products. Fabric Filter

Absorber

NIDTM SYSTEM 3D ILLUSTRATIONABSORBER

RECIRCULATIONPWS/BPROB/NIDFGD08/eng/ECS/07.08/US/6583©Alstom2008. Alstom, the Alstom logo and any alternative version thereof are trademarks and service marks of Alstom. The other names mentioned, registered or not, are the property of their respective companies. 

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