Introduction to Dry Sorbent Injection System for Acid Gas and SOx Control in Industrial Flue Gas

A dry sorbent injection (DSI) system for acid gas and SOx control in industrial flue gas is an advanced, cost-effective air pollution control technology that directly injects powdered alkaline materials into the flue gas stream to neutralize harmful acidic gases. Widely adopted in power plants, cement kilns, waste-to-energy incinerators, and industrial boilers, this technology offers a low-capex, flexible solution for reducing sulfur dioxide (SO₂), hydrogen chloride (HCl), and hydrogen fluoride (HF) emissions. The dry sorbent injection system for acid gas and SOx control in industrial flue gas is ideal for retrofitting existing plants, where space constraints or cost prevent installation of larger wet scrubbing systems.

Working Principle of Dry Sorbent Injection System for Acid Gas and SOx Control in Industrial Flue Gas

The core mechanism of the dry sorbent injection system for acid gas and SOx control in industrial flue gas involves the dispersion of a finely powdered sorbent—typically hydrated lime (Ca(OH)₂), sodium bicarbonate (NaHCO₃), or trona—into a hot flue gas stream. The sorbent reacts chemically with acid gases:

• SO₂ + Ca(OH)₂ → CaSO₃ + H₂O

• HCl + NaHCO₃ → NaCl + CO₂ + H₂O

These reactions form solid salts that are captured downstream using bag filters or electrostatic precipitators (ESP). Because the reaction occurs in the gas phase without any water usage, the system is termed “dry,” and it eliminates the need for wastewater treatment, making it an environmentally friendly and space-efficient solution.

System Components of Dry Sorbent Injection System for Acid Gas and SOx Control in Industrial Flue Gas

A complete dry sorbent injection system includes:

• Sorbent Storage Silo: Holds hydrated lime, sodium bicarbonate, or trona in powder form

• Sorbent Feeder: A volumetric or gravimetric dosing system controls injection rate

• Pneumatic Conveying System: Transfers the sorbent into the flue gas duct using compressed air or blowers

• Injection Lance or Nozzle Array: Ensures uniform dispersion and mixing with flue gas

• Reaction Zone: Typically located upstream of the particulate control device

• Particulate Collection Unit: Baghouse or ESP to capture reacted sorbent and byproducts

• Instrumentation and Controls: pH sensors, SOx analyzers, flow meters, and temperature controls

Materials are selected to withstand high temperatures (150–450°C) and abrasive particles.

Applications of Dry Sorbent Injection System for Acid Gas and SOx Control in Industrial Flue Gas

The dry sorbent injection system is suitable for a variety of emission-intensive industrial processes:

• Coal and Biomass-Fired Power Plants: Retrofitting older plants with SO₂ and HCl control without major structural changes

• Waste-to-Energy Incinerators: For controlling acid gases released from mixed waste combustion

• Cement and Lime Kilns: To neutralize SOx and chlorine-containing gases

• Glass and Ceramics Industries: High-temperature furnaces generating acidic fumes

• Steel Reheating Furnaces and Sinter Plants: For acid gas and fluoride removal

• Chemical Manufacturing Units: Controlling emissions from process vents and dryers

Performance Metrics and Design Parameters

A well-designed dry sorbent injection system for acid gas and SOx control in industrial flue gas typically delivers:

• SO₂ Removal Efficiency: 50–90% depending on sorbent type and dosage

• HCl and HF Removal: 90–99% in waste incineration and halogenated gas streams

• Injection Rate: 1–5 kg of sorbent per kg of SO₂ (stoichiometric ratio varies)

• Temperature Range: Optimal at 150–400°C

• Particulate Carryover: Controlled with downstream filtration (≥99.9% capture with bag filters)

• Reaction Time: Typically 1–2 seconds in the duct section

Advantages of Dry Sorbent Injection System for Acid Gas and SOx Control in Industrial Flue Gas

There are several benefits of using this system, particularly in retrofit and cost-sensitive scenarios:

• Low Capital Investment: No scrubber tower or wastewater treatment required

• Fast Installation: Ideal for plants needing quick compliance upgrades

• Minimal Space Requirement: Compact layout with flexible duct placement

• Zero Liquid Discharge: No water use or wastewater generation

• Modular and Scalable: Can be expanded or combined with existing control devices

• Multi-Gas Control: Effective against SO₂, HCl, HF, and other acid gases

Limitations and Mitigation Strategies

Though effective, the dry sorbent injection system has some limitations:

• Higher Sorbent Consumption: Compared to wet scrubbing, more reagent is typically required

• Residual Ash Volume: Reacted and unreacted sorbents increase fly ash generation

• Reactivity Sensitivity: Sodium-based sorbents perform better at lower temperatures; lime-based require higher contact time

• Bag Filter Dependence: System efficiency relies on high-performing particulate collection

These issues can be managed through proper sorbent selection, injection optimization, and high-efficiency dust collection units.

Regulatory Compliance Enabled by DSI Systems

DSI systems help industries meet global air emission standards, such as:

• US EPA MATS Rule: Requires reduction of SO₂, HCl, and heavy metal emissions

• EU IED Directive: Prescribes strict SOx and acid gas limits in incineration and combustion

• India CPCB Guidelines: SO₂ limits vary from 100–600 mg/Nm³ depending on fuel and industry

The DSI system is recognized as a viable Best Available Technology (BAT) for SOx and acid gas control in plants lacking wet scrubber infrastructure.

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Conclusion: Why Dry Sorbent Injection System for Acid Gas and SOx Control in Industrial Flue Gas Is a Smart Retrofit Solution

For industries seeking fast, flexible, and cost-effective compliance with SOx and acid gas emission norms, the dry sorbent injection system for acid gas and SOx control in industrial flue gas offers a powerful solution. Its dry operation, minimal footprint, high efficiency, and adaptability to existing infrastructure make it ideal for both new installations and retrofits. As regulatory pressure increases and industries seek sustainable options without large capital outlays, DSI systems are proving to be one of the most practical and scalable emission control technologies available.