Division 1.5.3 SOx emissions

United Kingdom

	Technique	Description
a	Absorbent addition	Absorbent is either added to the raw materials (e.g. hydrated lime addition) or injected into the gas stream (e.g. hydrated or slaked lime (Ca(OH)₂), quicklime (CaO), activated fly ash with a high CaO content or sodium bicarbonate (NaHCO₃)). Hydrated lime can be charged into the raw mill together with the raw material constituents or directly added to the kiln feed. The addition of hydrated lime offers the advantage that the calcium-bearing additive forms reaction products that can be directly incorporated into the clinker-burning process. Absorbent injection into the gas stream can be applied in a dry or wet form (semi-dry scrubbing). The absorbent is injected into the flue-gas path at temperatures close to the water dew point, which results in more favourable conditions for SO₂ capture. In cement kiln systems, this temperature range is usually reached in the area between the raw mill and the dust collector
b	Wet scrubber	The wet scrubber is the most commonly used technique for flue-gas desulphurisation in coal-fired power plants. For cement manufacturing processes, the wet process for reducing SO₂ emissions is an established technique. Wet scrubbing is based on the following chemical reaction: ${SO}_{2} {+ ½ O}_{2} {+ 2 H}_{2} {O + CaCO}_{3} {←→ CaSO}_{4} {· 2 H}_{2} {O + CO}_{2}$ SO_x are absorbed by a liquid/slurry which is sprayed in a spray tower. The absorbent is generally calcium carbonate. Wet scrubbing systems provide the highest removal efficiencies for soluble acid gases of all flue-gas desulphurisation (FGD) methods with the lowest excess stoichiometric factors and the lowest solid waste production rate. The technique requires certain amounts of water with a consequent need for waste water treatment

Technique

Description

Absorbent addition

Absorbent is either added to the raw materials (e.g. hydrated lime addition) or injected into the gas stream (e.g. hydrated or slaked lime (Ca(OH)₂), quicklime (CaO), activated fly ash with a high CaO content or sodium bicarbonate (NaHCO₃)).

Hydrated lime can be charged into the raw mill together with the raw material constituents or directly added to the kiln feed. The addition of hydrated lime offers the advantage that the calcium-bearing additive forms reaction products that can be directly incorporated into the clinker-burning process.

Absorbent injection into the gas stream can be applied in a dry or wet form (semi-dry scrubbing). The absorbent is injected into the flue-gas path at temperatures close to the water dew point, which results in more favourable conditions for SO₂ capture. In cement kiln systems, this temperature range is usually reached in the area between the raw mill and the dust collector

Wet scrubber

The wet scrubber is the most commonly used technique for flue-gas desulphurisation in coal-fired power plants. For cement manufacturing processes, the wet process for reducing SO₂ emissions is an established technique. Wet scrubbing is based on the following chemical reaction:

{SO}_{2} {+ ½ O}_{2} {+ 2 H}_{2} {O + CaCO}_{3} {←→ CaSO}_{4} {· 2 H}_{2} {O + CO}_{2}

SO_x are absorbed by a liquid/slurry which is sprayed in a spray tower. The absorbent is generally calcium carbonate. Wet scrubbing systems provide the highest removal efficiencies for soluble acid gases of all flue-gas desulphurisation (FGD) methods with the lowest excess stoichiometric factors and the lowest solid waste production rate. The technique requires certain amounts of water with a consequent need for waste water treatment