PROCESS ANALYTICS

Flue Gas Desulfurization

In the wet scrubber, the corrosive SO₂ gas from the exhaust flue gases of fossil-fuel power plants or incineration plants is removed. Limestone powder, burnt lime, or calcium hydroxide are used to absorb SO₂. Gypsum, which can be reused in the building materials industry, is the result. Accurate pH measurement is indispensable in this process in order to completely remove the SO₂ and fulfill the official regulations for clean air.

Energy

Key Facts About the Application

Sector

Power plants with flue gas absorbers

Application

3 applications (1. Verifying the pH value in the pre-scrubber, 2. Neutralization, 3. Lime scrubber)

Measuring Parameter

pH

Main Requirements

The measuring loops are corrosive and thick incrustations form.

Measurement in Processes that Build Up Thick Gypsum Layers

Description of application

Application 1:
In the pre-scrubber (stage 1) the hot flue gas is cooled by bringing it into contact with lime slurry. The pH value is only slightly increased (normally between pH 1 and 2 at 80 °C). Here, the pH value must not rise above 2, since only HCl/HF and heavy metals must be precipitated. The SO₂ is not bonded until stage 2. Precise pH control is crucial.

Application 2:
In stage 2, the main scrubber, the pH value is increased by adding more lime. SO₂ is bonded. The addition of lime slurry must be controlled by constant pH measurement. If the pH values are too high, too much lime was added (higher costs) and the gypsum is contaminated by excessive calcium hydroxide. If the pH values are too low, the SO₂ bond is less efficient.

The optimal pH value is between 5.5 and 6.0. Higher values lead to soft, greasy calcium sulfite deposits (soft plugging) and slightly reduced efficiency. Lower pH values lead to thick incrustations that are not easy to remove (formation of hard scale). In general, the pH measuring loop is in the backflow circulation line of the calcium sulfite/gypsum slurry.

Application 3:
The surplus water that remains after the precipitation/thickening of the gypsum must undergo a neutralization process. Sulfuric acid is added to bond the excess lime. Further, thick incrustations and deposits occur at this measuring loop.

All three measuring loops are extremely important for optimal process conditions. The points are corrosive and thick incrustations that necessitate a high maintenance effort are formed. Knick recommends fully automated cleaning and calibration systems for these applications in order to reduce manual effort and increase process reliability

Requirements of the application

The major challenge of this application is to build up thick layers of gypsum in the gas scrubbers.

Why Knick?
Due to its unique ceramic seal, Ceramat is the only fitting that is worth considering here. The deposit remover (pump sock) for Ceramat removes deposits that would otherwise completely clog the system. The unique sensor maintenance system cleans and calibrates the sensors fully automatically and reduces maintenance effort many times over.

Associated Products

SE656 Toroidal Conductivity Sensor | Memosens | Fixed cable | PFA | Resistant to highly oxidizing media

Product number:

SE656N -GEFTW0KM

SE555 pH Sensor | VP | 120 mm | Ex | Sterilizable | For aggressive media

Product number:

SE555X/1-NVPN

Product number:

4400 XC/24V

Associated Industries and Applications

Energy

In power plants, water is used in many processes with completely different requirements: for example, for steam generation, cooling, and flue gas scrubbing.

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Measurement of pH value, redox potential, and conductivity in cooling water, which has to be continuously treated with acid and biocides.

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Since steam generators fulfill application-critical functions and the cost of their downtime or replacement is extremely high, damage caused by wear should be prevented by monitoring water quality.

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Measurement of pH value, dissolved oxygen, and redox potential in various applications during the water treatment process of power plant wastewater.

Reverse Osmosis Systems

Reverse osmosis systems are used for water treatment in a wide range of industrial applications. The main application is industrial saltwater desalination.

Energy Industry Brochure

Overview of specific applications and product solutions in different areas of power plants.

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