pH Measurement in Flue Gas Desulfurization Systems

Industry	: Chemical, Power
Product	: pH/ORP Analyzer

Introduction

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

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

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

Utilities
Power supply:		100 V AC, 50/60 Hz
Power consumption:		approx. 60 VA
Air source: pressure:		300 to 950 kPa
	Maximum consumption:	approx. 20 L/min
Chemical cleaning solution consumption:		approx. 100 mL
	Tank effective capacity:	approx. 17 L

Notes
-	An organic solvent cannot be used for cleaning.
-	Deterioration of materials in chemical solution piping and air piping When the system is installed in a location where it is exposed to direct sunlight, the polyethylene resin piping will last approximately one year. (It is recommended that fluoro resin piping be used.)