Gas purification techniques

Selective non Catalytic reduction (SNCR)

At the injection of urea, (NH₂)CO, urea is thermally cracked firstly on high temperature with the forming of NH₃ that afterwards further reacts with NO_x according to the above response diagram.
The most important response parameters are: 

• Temperature

• Molar proportion NH₃/NO_x

• Residents

An alternative of this process is Desonox-process. The Desonox process are combined process for sulphur - and nitrogen disposal from industrial gases. Final products arises as concentrated sulphur acid and nitrogen gas. The industrial gases becomes dedust in a high temperature E-filter. Afterwards the industrial gases pass through a nitrogen disposal step based on zeolite where ammonia is injected. Hereafter follows a catalytic SO₂ oxidation unit. The in series set steps concentrated sulphuric acid condenses
(approx. 70 %) at a temperature of 120 °C. This puts high demands to the used material. In the in series set scrubber the rest quantity sulphuric acid is removed.
The advantages of the SNCR are:

• Under optimum conditions a good reduction of NO_x

• Relatively simple installation

• Low investment costs

• Low energy usage

• Small spatial occupation

The disadvantages are:

• Require high temperatures

• The optimum response temperature lies in a narrow range

• Outside the optimum area ammonia becomes emitted or gets an increase
  of the NO_x emissions there.

• The continuation part of the industrial-gas clean-up system can be charged
  with ammonium.

Selective catalytic reduction is not applied at combustion installations in following sectors:

• Detritus combustion

• Energy call centre

• Metallurgy

• Glass construction and horticulture
  

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