Dry sorbent injection (DSI) has become a widely used method for acid gas control in waste incineration, biomass combustion, cement, and industrial boilers. Simple, flexible, and water-free, DSI systems neutralise harmful gases like SO₂, HCl, and HF before they exit the stack.
But for DSI to be effective, the filtration system downstream must be capable of capturing not just fly ash and PM2.5, but also the spent sorbent and reaction products. Ceramic filters provide an ideal match — offering high efficiency, compatibility with sorbents like sodium bicarbonate and lime, and long-term performance at high temperatures.
What Dry Sorbent Injection Captures
DSI works by injecting powdered sorbents into the flue gas stream. These typically include:
- Sodium bicarbonate — effective for HCl, SO₂, HF
- Hydrated lime (Ca(OH)₂) — common in cement and EfW
- Trona — used in some large-scale utilities
These compounds react with acid gases to form salts such as sodium chloride or calcium sulphate. The process also produces fine particulate, unreacted sorbent, and ash — all of which must be removed before the gas exits the stack.
Because sorbents are injected as fine powders, the filtration system must handle high dust loads, variable particle sizes, and occasional stickiness or hygroscopic behaviour. Many fabric filters struggle to keep up, especially at elevated temperatures.
Why Filter Selection Matters
The wrong filtration system can undermine the performance of a well-designed DSI setup. Problems include:
- Poor PM2.5 capture — allowing sorbent or reaction dust to escape
- Filter blinding — when sorbent cakes and clogs fabric filters
- Low temperature tolerance — requiring upstream gas cooling
- Short media life — particularly with abrasive or alkaline dust
For engineers designing new systems or retrofits, pairing DSI with a filtration technology that matches the gas temperature, dust chemistry, and expected sorbent usage is essential to achieving compliance and minimising OPEX.
Ceramic Filters and Sorbent Injection: A Perfect Match
Ceramic filters provide dry, surface-based filtration that excels in DSI applications. Glosfume ceramic elements capture PM2.5 and finer, and are chemically resistant to acidic, alkaline, or abrasive dust streams.
Key benefits include:
- Temperature tolerance up to 1000°C — no need to quench gas
- Non-combustible — safe with carbon-rich or reactive sorbents
- Pulse-jet cleaning — keeps elements clean even with sticky sorbent dust
- Dry operation — no water, sludge, or liquid waste
- Long filter life — often exceeding 2–3 years
This makes ceramic filters well suited for EfW, biomass, and chemical plants using DSI for SO₂ and HCl control. Systems are also scalable and modular for different flow rates — from small kilns to full-scale boiler stacks.
Case Study: Energy-from-Waste Retrofit with DSI
An energy-from-waste plant in Northern Europe faced tightening emission limits for SO₂ and HCl. The existing bag filter system could not handle increased sorbent use without clogging or overheating. The plant processed 10,000 m³/h of gas at 850°C with sodium bicarbonate injection upstream.
Glosfume installed a ceramic filtration system featuring:
- 96 ceramic elements in a vertical housing
- Automated pulse jet cleaning with DP control
- Dust hopper and sealed bin for sorbent collection
- Optional catalytic polishing module downstream
The retrofit enabled:
- Dust emissions < 1 mg/m³
- HCl emissions < 5 mg/m³ without quenching
- Filter life over 24 months with minimal maintenance
- Safe handling of spent bicarbonate without wet scrubber waste
The plant met IED compliance standards and avoided costly cooling or fabric upgrades.
Design Considerations for DSI-Compatible Filters
To ensure successful DSI operation with ceramic filters, engineers should consider:
- Injection point location: Ensure full mixing and reaction time before filtration
- Sorbent type: Sodium bicarbonate is most compatible with high-temp ceramic media
- Dust discharge: Spent sorbent may require lined bins or dedicated handling systems
- Pulse air supply: Compressed air must be clean and dry to maintain performance
- Monitoring: Include pressure drop, temperature, and emissions sampling ports
For multi-pollutant streams, ceramic filters can also be combined with catalytic media to reduce VOCs or NOx, enabling even higher overall efficiency.
Dry sorbent injection is a powerful tool for acid gas control — but it must be paired with the right filtration media to perform reliably and cleanly. Ceramic filters offer unmatched compatibility with DSI systems, handling heat, reactivity, and fine dust without clogging, degradation, or water use.
For plant operators and designers seeking simple, low-maintenance emission control, specifying ceramic filtration alongside sorbent injection offers a proven path to long-term compliance and efficiency.
