Measurement of Concentration of Supersaturated NaCl Solution in Salt Dissolvers at Electrolysis Plants

Download (246 KB)

Introduction

Control of sodium chloride (NaCl) concentration at a salt dissolver where solid salt is dissolved in water, is highly important because of the electrolysis efficiency. A conventional way of measuring the concentration of supersaturated NaCl solution had been performed by using non-contact type sensors (e.g., γ-ray density meter) since NaCl, impurities, and precipitates are in the solution. In this way, there were disadvantages such as troublesome maintenance and therefore, the radiation control is required for γ-ray density meter. Responding to these backgrounds, the ISC202 inductive conductivity analyzer provides concentration reading and realizes to improve substantial maintainability, cost performance and measurement accuracy.

Caustic Soda Production Process

Caustic Soda Production Process

Expected Benefits

  • Measures NaCl concentration in salt dissolvers
  • Reduces operating costs

Process Overview

In an electrolysis plant, the solid salt is dissolved in water in a salt dissolver to make brine. This brine contains impurities, such as calcium, magnesium or sulfates, that decrease electrolysis efficiency. The brine is purified by removing these impurities before being fed to an electrolyzer, where the purified brine is electrolyzed to produce caustic soda and chlorine. The caustic soda solution produced at the cathode in the electrolyzer is concentrated in a multiple effect evaporator, as a result the concentration is increased from approximately 32% to 48%.

Solution Details

Measurement system

2-wire inductive conductivity system

Sensor ISC40G(J)-GG-T1-☐☐
Flow-through holder ISC40FF(J)-PJ
Transmitter ISC202G-A-E
Dedicated distributor for transmitter PH201G-A☐*B

Inductive Conductivity Sensor & Transmitter Installation Diagram

Inductive Conductivity Sensor & Transmitter Installation Diagram

Utilities

ISC202G inductive conductivity transmitter
Power supply voltage: 17 - 40 V DC (from distributor)
Power consumption: 0.9 VA maximum
PH201G distributor
Power supply:
100 V: 20 to130 V DC/80 to 138 V AC, 47 to 63 Hz
220 V: 120 to 340 V DC/138 to 264 V AC, 47 to 63 Hz
Power consumption: 24 V DC: approx. 200 mA
100 V AC: approx. 7 VA
220 V AC: approx. 11 VA

Notes

Sampling should be done in the supernatant liquid in a salt dissolver. The supernatant liquid is collected in a settling tank and then the supernatant liquid of the tank is transported to a measurement tank where the sensor is installed.

Field Data

1. Process conditions (salt dissolver)

Temperature: Approx. 65°C
Pressure: Atmospheric pressure
Sample: Supersaturated brine
NaCl concentration control range: 200 to 360 g/L
--> 18.1 to 30 wt%*

* Depends on user's actual data of specific gravity.

2. ISC202G setting parameters

Relationship between conductivity and concentration is based
on the linear approximation of S = 16.3x that is obtained by actual measurement using SC72 Personal Conductivity Meter.

  • NaCl temperature compensation table is used
  • Reference temperature setting: 25°C
  • Output setting: Code 04
Output (%) Concentration (%) Conductivity (mS/cm)
0 18 293
50 24 391
100 30 489

Industries

Related Products & Solutions

2-Wire Transmitter/Analyzer FLXA202/21

The FLEXA™ series analyzers are used for continuous on-line measurements in industrial installations. With an option for single or dual sensor measurement, they are the most flexible two-wire analyzer available.

Inductive (Torodial, Electrodeless) Conductivity Sensor ISC40

The model ISC40 sensors are designed for use with the EXA ISC analyzers. This combination exceeds all expectations for conductivity measurement in terms of reliability, accuracy, rangeability and price performance. 

Conductivity Sensors

Conductivity sensors and electrodes are used to measure process conductivity, resistivity, WIFI, demineralizer water, RO water, percent concentration, boiler blowdown and TDS. Various installation options including retractable, flow thru, immersion, and direct insertion. Proper electrode/sensor selection is critical for optimal measurement results.

pH and ORP Analyzers

pH and ORP meters, analyzers and transmitters are used for continuous process monitoring of pH and ORP to ensure water/product quality, monitor effluent discharge, batch neutralization, pulp stock, scrubbers, cooling towers, chemical, water/wastewater treatment and many other applications.

×

Have Questions?

Contact a Yokogawa Expert to learn how we can help you solve your challenges.

Top