pH Measurement in Flue Gas Desulfurization Systems That Use Magnesium Hydroxide Slurry

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Introduction

Flue Gas Desulfurization Process
Flue Gas Desulfurization Process

In flue gas desulfurization systems that use magnesium hydroxide (Mg(OH)2) slurry, the consumption of the desulfurization agent (Mg(OH)2) is controlled by using online pH analyzers. A great concern in the pH measurement is heavy staining of the pH electrodes by the Mg(OH)2 slurry. To ensure accurate measurement, frequent cleaning of the electrodes with an acid is required, adding to both maintenance workload and cost.

The EXA AUTO CLEAN chemical cleaning system automates the acid cleaning process, which not only saves both time and expense but also ensures precise pH measurement over long periods.

Expected Benefits

  • Improves the efficiency of a flue gas desulfurization system with Mg(OH)2 slurry
  • Ensures stable, continuous pH measurement
  • Reduces operating costs
  • Eliminates manual cleaning

Process Overview

In the flue gas desulfurization system, Mg(OH)2 is used as the absorbent to remove sulfur dioxide (SO2) from the flue gas.

Absorption reaction 1: Mg(OH)2 + SO2 ->MgSO3 + H2O
Absorption reaction 2: MgSO3 + SO2 + H2O -> Mg(HSO3)2

After absorbing SO2, the solution undergoes pH adjustment, oxidation, and filtration for detoxification before discharge.

pH adjustment: Mg(HSO3)2 + Mg(OH)2 -> 2MgSO3 + 2H2O
Oxidation: MgSO3 + 1/2O2 -> MgSO4

Solution Details

Measurement System & Operation Outline

Measurement System & Operation Outline

Field Data

When performing pH measurement in a flue gas desulfurization system with Mg(OH)2 slurry, the electrodes tend to become heavily stained by the slurry. The cleaning of the electrodes and the reduction of maintenance time and cost are key points to consider when selecting a pH analyzer for the system.

  pH System with Chemical Cleaning General pH Analyzer
Cleaning "Automatic acid cleaning: 2 or 3 times/day, user programmable Manual acid cleaning: approx. monthly" "Manual acid cleaning: once/day"
Calibration Manual calibration: weekly "Manual 2-point calibration: weekly"
Other maintenance Replenishment of chemical tank: approx. every 2 months -

Acid cleaning is done with a 4% hydrochloric acid solution.

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