Dry sorbent injection

Dry Sorbent Injection (DSI) is an air pollution control technology in which a powdered sorbent is injected directly into a contaminated gas stream. The sorbent reacts with pollutants, either by chemically neutralizing them or by adsorbing them onto its surface. After contact with the gas stream, the sorbent is separated from the air and collected for disposal, treatment, or, in some cases, partial reuse.

DSI is a highly versatile technology that can be applied to the removal of acidic gases such as hydrogen chloride (HCl), hydrogen fluoride (HF), and sulfur dioxide (SO₂), as well as a wide range of volatile organic compounds (VOCs). One of its key advantages is its ability to operate at elevated temperatures, often between 100°C and 300°C, without requiring gas cooling. In addition, DSI generates a dry solid waste stream, which is often simpler and less costly to handle than the liquid effluents produced by wet scrubbing systems.

How does dry sorbent injection work?

The choice of sorbent depends on the composition of the gas stream, its temperature and humidity, and the pollutants to be removed. Commonly used sorbents include activated carbon, hydrated lime, sodium bicarbonate, and other alkaline materials.

In a typical DSI system, the sorbent is stored in a dedicated hopper and metered into the process air stream by a dosing system. Injection lances distribute the sorbent into the ductwork using compressed air or nitrogen as a transport medium.

Following injection, the gas stream passes through a section of ducting or a dedicated reaction chamber. This provides sufficient residence time and turbulence for the sorbent particles to mix thoroughly with the gas and react with the target pollutants.

The spent sorbent must subsequently be removed from the gas stream. This is most commonly achieved using a self-cleaning baghouse filter. The collected sorbent accumulates in a hopper beneath the filter and is periodically discharged for disposal or further treatment.

In many installations, the layer of sorbent that forms on the surface of the filter bags, known as the filter cake, contributes significantly to pollutant removal. As the gas passes through this layer, additional contact time is created, allowing further reaction and adsorption to take place before the gas is discharged.

Where do you use a dry sorbent injection system?

DSI is particularly attractive in applications where:

The pollutants consist primarily of acidic gases or VOCs.

Dry sorbent injection is widely used for the removal of HCl, HF, SO₂, and certain organic compounds.

The gas stream is relatively hot.

DSI can often operate effectively at temperatures between 100°C and 300°C, avoiding the need for costly gas cooling systems.

Water addition is undesirable.

Because DSI is a completely dry process, it avoids corrosion risks associated with wet treatment systems and eliminates the generation of wastewater.

Ultra-low outlet concentrations are not required.

While DSI can achieve high removal efficiencies, wet scrubbers or other technologies may be more appropriate when exceptionally low emission limits must be achieved.

The benefits of a dry process outweigh the higher sorbent consumption.

Although operating costs may be higher than those of a wet scrubber due to ongoing sorbent usage, DSI can provide significant advantages in terms of simplicity, reliability, corrosion control, and operation at elevated temperatures.

When to use a DSI vs a wet scrubber?

Wet scrubber

Best choice when maximum removal efficiency is required

Particularly effective for acid gases and highly water-soluble compounds
Can achieve very stringent emission limits
Typically offers lower reagent consumption due to efficient gas-liquid contact
Well suited for moderate-temperature gas streams
Simultaneously removes gases and certain particulate matter
Produces a wastewater stream that must be treated or disposed of
Moisture and acidic conditions can increase corrosion risks if materials are not selected appropriately

DSI

Best choice when a dry, high-temperature process is preferred

Suitable for acid gases and a wide range of VOCs
Effective at elevated temperatures, typically between 100°C and 300°C
Keeps the process stream dry, minimizing corrosion risks
Produces a dry waste product that is often easier to handle and transport than wastewater
Can often be retrofitted into existing installations with minimal modifications
Relatively simple equipment with straightforward operation
Typically requires higher sorbent consumption than a wet scrubber
Usually more suitable for moderate emission limits than for ultra-low outlet concentrations

Frequently asked questions about DSI

Can DSI treat multiple pollutants simultaneously?

Yes.

A single DSI system can often remove several pollutants at the same time. For example, hydrated lime can neutralize acid gases while activated carbon can be injected simultaneously for VOC and odour control.

What happens to the collected sorbent?

The collected material is usually disposed of as industrial waste. Depending on the sorbent used, the pollutants removed, and local regulations, some materials may be suitable for recovery or reuse.

How is the spent sorbent removed from the gas stream?

The sorbent is typically captured using a baghouse filter. The spent sorbent and reaction products are collected in hoppers beneath the filter and discharged for treatment or disposal.

What pollutants can be removed with Dry Sorbent Injection?

DSI is commonly used for acid gases such as hydrochloric acid (HCl), hydrofluoric acid (HF), and sulfur dioxide (SO₂). Activated carbon injection can also be used for VOCs, odorous compounds, and certain trace contaminants.

Which sorbents are commonly used in a DSI system?

The most common sorbents are hydrated lime, sodium bicarbonate, and activated carbon. The choice depends on the pollutants present, the gas temperature, the required removal efficiency, and the operating costs.

Can dry sorbent injection be retrofitted into an existing system?

Yes.
DSI systems can often be integrated into existing ductwork with relatively limited modifications. In many cases, only the sorbent dosing equipment, injection lances, and a suitable particulate removal system need to be added.

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