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            Calcium is sprayed in the furnace

         

 

The in-furnace calcium injection desulfurization process in flue gas desulfurization (FGD) is a common dry desulfurization technology, which is mainly used for the control of sulfur dioxide (SO) emissions from coal-fired boilers and industrial kilns. Its core principle is to desulfurize by spraying calcium-based absorbents (usually limestone or slaked lime) into the furnace or flue, reacting with SOin the flue gas to form calcium sulfate.


Process principle


Main chemical reactions:

n Limestone (CaCO) pyrolysis: decomposes into calcium oxide (CaO) and carbon dioxide (CO) at high temperatures.

 

CaCO₃→CaO+CO

CaCO₃→CaO+CO


n SO₂ absorption: CaO reacts with SO₂ in flue gas to form calcium sulfate (CaSO).

 

CaO+SO½O₂→CaSO

CaO+SO½O₂→CaSO


n If slaked lime (Ca(OH)₂ is sprayed, it reacts directly with SO:

 

Ca(OH)+SO₂→CaSO+HO

Ca(OH)+SO₂→CaSO+HO

 

(Subsequent oxidation to produce CaSO).

 Process flow


In-Furnace Injection

l Injection location: Spray powdered limestone (CaCO) or slaked lime (Ca(OH)) in the boiler combustion area (8001200°C) or tail flue (500600°C).


l Reaction temperature: High temperature is conducive to limestone decomposition, but too high temperature (>1200°C) will lead to CaO sintering and reduce activity.



Key influencing factors

l Calcium-sulfur ratio (Ca/S): Typically maintained at 23 (molar ratio), higher Ca/S increases desulfurization efficiency but increases absorbent consumption.

 

l Reaction temperature: The optimal temperature is 800950°C (inside the furnace) or 500600°C (flue).

 

l Absorbent particle size: The finer the particles, the larger the specific surface area, and the higher the reaction efficiency (generally requires a particle size of < 20μm).

 

l Flue gas residence time: Extending the reaction time can improve the SO₂ absorption rate.


Advantages


l Simple equipment: no need for complex wet systems, low investment and operating costs.

 

l No wastewater generation: The dry process avoids wastewater treatment problems.

 

l Wide applicability: It can be used to retrofit existing boilers, especially for low-sulfur coal (<2% sulfur content).


The calcium injection desulfurization process in the furnace is an economical and practical dry desulfurization technology, which is suitable for small and medium-sized boilers or low-sulfur coal scenarios, but it needs to be combined with auxiliary measures such as humidification and activation according to specific needs. For high-sulfur coal or strict emission standards, wet or other efficient desulfurization processes still need to be considered.

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