PROCESS ANALYTICS

Flue gas desulfurization

To remove the corrosive SO₂-gas from fossil fuel or waste power plant off gas, a wet scrubber process is used. Limestone, quicklime or calcium hydroxide is used to absorb the SO₂ by forming gypsum which can be reused in building materials. Critical in this process is an accurate pH measurement to ensure complete removal of SO₂ to meet government standards for clean air.

Energy

Keyfacts Application

Sector

Power plants with flue gas scrubber units

Application

3 Applications:

Check pH in pre-scrubber
Neutralization
Lime Scrubber

Measured Parameter

pH

Key Requirements

The Locations of the measurement points are corrosive and heavy incrustations are formed.

Measuring in processes that build up thick layers of gypsum

Application Description

Application 1:

In the pre-scrubber (1st stage) the hot flue gas is cooled by injecting milk of lime. The pH value is only slightly increased (typically between pH 1–2 at 80 °C). Here, the pH must not rise above 2 because only HCl / HF and heavy metals are to be precipitated but SO₂ binding is to occur at the second stage. Accurate pH control is essential.

Application 2:

In the second stage, the main scrubber, the pH is increased by further addition of lime. SO₂ is bound. Here, the lime milk addition must be controlled by continuous pH measurement. When the pH values are too high, too much lime has been added (increased costs) and the gypsum is polluted by excess calcium hydroxide. When the pH values are too low, the binding of SO₂ is less efficient.

The optimum lies between pH 5.5 and 6.0. Higher values lead to soft and greasy calcium sulfite coatings (soft plugging) at slightly reduced efficiency. Lower pH values cause heavy incrustations which are difficult to remove (hard scale formation). Generally, the pH measuring point lies in the backflow circulation line of the calcium sulfite / gypsum sludge.

Application 3:

The excess water remaining after precipitation / thickening of the gypsum must be subjected to a neutralization procedure. For that purpose, sulfuric acid is added to bind the excess lime. Also, at this measuring point, there are heavy incrustations and deposits.

All 3 measuring points are extremely important to run the process in optimal condition. The locations are corrosive and heavy incrustations are formed, resulting in high maintenance. Knick recommends fully automated cleaning and calibration systems for these applications to reduce manual labor and increase process safety.

Requirements of Application

The immense challenge of this application is building up thick layers of gypsum in the gas scrubber units.

Why Knick ?
Ceramat is the only fitting which can be used due to the unique ceramic sealing. Deposit remover (“Pump Sock”) for Ceramat can remove deposits, which would otherwise clog the system completely. The unique Sensor Maintenance System cleans and calibrates the sensor fully automatically and reduces the maintenance efforts tremendously.

Matching 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

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