Technology

Contact Information

Global NMI Locations

Nalco.com

Nalco Mobotec Global
1601 W. Diehl Rd.
Naperville, IL 60563
USA

E-Mail us at:
nalcomobotec@nalco.com

Dry Sorbent Injection

Dry Sorbent Desulfurization Systems

Dry sorbent desulfurization systems are used to remove sulfur dioxide (SO2) from flue gas at fossil fuel-fired electric generating stations. In a dry sorbent injection system, a powdered alkaline sorbent is injected into the boiler or into flue gas ahead of a particulate collector. SO2 reacts with the dry sorbent, and the dry reaction products are collected, along with fly ash, in the particulate collector—which is either a fabric filter (baghouse) or electrostatic precipitator (ESP). Fly ash containing SO2 reaction products and unused sorbent can be suitable for use as feedstock to cement plants or for stabilization of earthen structures.

Since desulfurization is all-dry, no water is consumed, and no waste water is produced. The flue gas is not cooled nor saturated with water, so reheating of desulfurized flue gas is not required. No gas-sorbent contacting vessel is required to be installed.

Furnace Sorbent Injection

Furnace sorbent injection using the ROFA® system is one type of dry sorbent desulfurization system that is available from Nalco Mobotec. In furnace sorbent injection, a calcium-based dry sorbent, including limestone (CaCO₃) or hydrated lime (Ca(OH)₂ ), is injected into the upper portion of a coal-fired boiler where combustion gas temperature is optimal for SO₂ capture. SO₂ reacts rapidly with the calcium-based sorbent to form stable calcium sulfate solid.

Where higher SO₂ removal efficiency is required, special sorbents designed by Nalco Mobotec are used in place of normal limestone or lime. Calcium sulfate and unused sorbent are carried by the gas through the boiler backpass air preheater and are removed from flue gas, along with fly ash in the particulate collector. The particulate collector is preferably a fabric filter (baghouse), but an ESP is suitable with modification.

Fly ash from furnace sorbent injection can be suitable for use a feedstock to a cement plant or for stabilization of earthen structures.

Nalco Mobotec’s furnace sorbent injection (FSI) system is most effectively applied in combination with Nalco Mobotec’s ROFA/Rotamix systems, which provides highly efficient mixing of the sorbent and flue gas at the optimum gas temperature for SO₂ capture. Efficient mixing allows sorbent to react with the maximum possible amount of SO₂, which minimizes the amount of sorbent required.

Post-Furnace Sorbent Injection

Post-furnace sorbent injection is another type of dry sorbent desulfurization system available from Nalco Mobotec. In post-furnace injection, a sodium-based dry alkaline sorbent, including powdered sodium bicarbonate (NaHCO3) or sodium sesquicarbonate (NaHCO₃•Na₂CO₃•2H₂O), is injected into the flue gas ductwork immediately after a coal-fired boiler or after an air preheater and ahead of a particulate collector. Sodium sulfate, other dry reaction products, and unused sorbent are carried by the gas and removed from flue gas, along with fly ash in the particulate collector. Where the particulate collector is a fabric filter (baghouse), substantial additional SO₂ capture occurs as flue gas passes through fly ash and sorbent collected on the filter surface.

The primary advantages of FSI and post-FSI sorbent injection using the ROFA/Rotamix systems, compared with typical desulfurization systems, are very low installed equipment cost due to few processing steps, no water consumption, no waste water treatment, and no reheating of flue gas. Dry sorbent injection systems are very easy to retrofit to existing power plants. Power consumption is low—less than 0.5% of generating capacity when applied with the ROFA/Rotamix systems.

ROFA/Rotamix FSI and post-FSI systems are most applicable to generating units 500 MW or smaller, which burn low-sulfur coals (less than 1.5% sulfur) and have a fabric filter (baghouse) for particulate collection. It can be applied to some units with cold-side electrostatic precipitators (ESP) where a fly ash conditioning system is installed ahead of the ESP.

Comparison of Dry Sorbent Injection (DSI) with Wet FGD

	Wet FGD	Dry Sorbent Injection
Capital Cost	$200-400/kW	$40-50/kW
Coal Sulfur Content for Best Application	>2%	<1.5%
SO₂ Reduction Efficiency	95-98%	50-80%
Power Consumption, % of electric generation	1.0 - 2.5%	0.1 - 0.5%
Byproducts	Gypsum solid or MgSO₄ solution for use or disposal	Collected with fly ash
Alkaline Reagent or Sorbent Consumption, kg/kg SO₂ in flue gas	^~2	^~3-7
Water consumption, m³/hr/MW	0.2-0.3	None
Wastewater treatment required?	Yes	No
Flue gas reheating required?	Yes	No
Ease of retrofit to existing power station	Very difficult	Easy

Typical Nalco Mobotec DSI system includes the latest in sorbent feeding and transport technology. The storage silo system is fitted with independent feed hoppers, various types of feed equipment, and a bin vent filtration system. This system includes several equipment advancements to ensure consistent sorbent flow-ability and accurate sorbent injection rates.

Typical DSI conveying blower building configurations consist of an enclosed building which houses the conveying blowers used to transport sorbent from the storage silo into the duct. The typical DSI setup will have transport air conditioning and redundant conveying blowers.

Typical Nalco Mobotec DSI system consists of a sorbent storage silo with a sorbent feeding system, conveying blower system, transport air conditioning system, and optional mill for sorbent fineness control.