Dry Sorption (XeroSorp)

In Kanadevia Inova’s XeroSorp dry scrubbing process, corrosive acid gases (for example HCl, HF and SO₂) are neutralised with the help of adsorption additives.

The term “xero” is a Greek prefix derived from the word “ξηρός” (xērós), meaning “dry”. As the name suggests, the process does not involve the introduction of any water at all. Instead we use two different adsorption additives for neutralisation: hydrated lime and sodium hydrogen carbonate (commonly known as sodium bicarbonate).

Depending on the additive used for neutralisation we call the process:

• XeroSorp lime (if hydrated lime is used), or
• XeroSorp bicar (if sodium hydrogen carbonate is used).

Semi-Dry Sorption Process (Kanadevia Inova SemiDry)

The Kanadevia Inova SemiDry system involves a semi-dry sorption process employing the principle of the circulating fluidised bed.

Hydrated lime is injected into the fluidised bed reactor to neutralise corrosive acid gases. The temperature in the reactor is key to the sorption process. To achieve the ideal reaction temperature (typically 145°C), water is sprayed into the reactor simultaneously. In addition to regulating the temperature, the water reactivates the recirculated residues, optimising the separation efficiency of the process.

SNCR Process

In the SNCR (selective non-catalytic reduction) process, nitrous oxides (NOx) react with ammonia and are chemically converted into nitrogen (a natural constituent of air) and water vapour.

For efficient denitrification (DeNOx), it is crucial to operate in the right temperature ranges. If the temperature is too high, the ammonia is “burned”. If the temperature is too low, the reaction slows and a large portion of the ammonia reaches the stack unused. The ideal temperature range is to be found in the post-combustion chamber, although there it is subject to fluctuation because of variations in load and fuel. To prevent this, the reducing agent (ammonia water or urea) is injected into the post-combustion chamber at various points.

But even within the optimum temperature range, the NOx separation rate with a conventional SNCR process is limited. Achieving higher NOx removal efficiency requires injecting more ammonia than is consumed. The excess can be removed downstream in a wet scrubbing process. In our patented process, the ammonia is recovered from the effluent and can be re-injected into the post-combustion chamber.

DyNOR^® Dynamic NOx Reduction

The DyNOR^® system developed by Kanadevia Inova’s engineers is an improved SNCR process. It enables nitrogen oxide to be reduced to very low levels with minimal ammonia slip, something that was previously only possible with an SCR process. The non-catalytic DyNOR^® process closes the gap between the costly SCR process and the conventional SNCR process. It is an investment that pays off.

SCR Process

Selective catalytic reduction (SCR) is the most effective DeNOx process. Nitrous oxides (NOx) are converted into nitrogen and water vapour at a catalytic surface, with ammonia water or urea used as a reducing agent.

Using a catalytic converter allows the reduction of nitrous oxides at significantly lower temperatures, and is considerably faster than the SNCR process. DeNOx rates of more than 90% can be achieved. Other advantages of the process are low consumption of ammonia water (almost stoichiometric) and low ammonia slip. If the catalytic surface is sufficiently large, part of the dioxins and furans are destroyed at the same time.

The SCR process is flexible in terms of operating temperature, and can be deployed at various points along the flue gas treatment process chain. On this basis a distinction is made between the following approaches:

Raw gas catalytic converter:

• At the boiler outlet, with upstream electrostatic precipitator
• Operating temperature approx. 260-300°C

Clean gas catalytic converter:

• After prior dust and SO₂separation
• Operating temperature approx. 240-250°C

Low temperature catalytic converter:

• After prior dust and SO₂separation
• Operating temperature approx. 180-190 °C
• Periodic regeneration at approx. 320°C required

Adsorption onto Activated Carbon or Lignite Coke

Both mercury and dioxins/furans can be adsorbed onto activated carbon or lignite coke and then removed from the flue gas.

Depending on the overall flue gas treatment approach, the activated carbon or lignite coke can be introduced and subsequently ejected at different stages of the process:

• In dry sorption (XeroSorp): Introduced into the XeroSorp reactor and removed at the fabric filter (residue discharge)

• In the semi-dry sorption process (Kanadevia Inova SemiDry): Introduced into the SemiDry reactor and removed at the fabric filter (residue discharge)

• In a counterflow process: Injected into the flue gas duct before the fabric filter and removed at the fabric filter (residue discharge)

• In a wet scrubber with a ringjet stage (multi-venturi stage): Injected into the flue gas duct before the wet scrubber, removed at the ringjet stage and finally ejected via the scrubber blowdown
• In a wet scrubber without a ringjet stage (multi-venturi stage): Suspension of activated carbon or lignite coke injected directly into the sump of the packed bed stage; ejected via the scrubber blowdown and removed in a lamella separator