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 FLXA202 2-wire inductive conductivity analyzer provides concentration reading and realizes to improve substantial maintainability, cost performance and measurement accuracy.
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 | FLXA202-D-BｰD-☐-C5-NN-A-N-LA-☐-NN |
Inductive Conductivity Sensor & Transmitter Installation Diagram
Utilities
| FLXA202 2-wire inductive conductivity analyzer | |
|---|---|
| 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. FLXA202 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
| Concentration (%) | Conductivity (mS/cm) |
|---|---|
| 18 | 293 |
| 24 | 391 |
| 30 | 489 |
Industries
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Chimie
Les usines chimiques s'appuient sur des processus de production continus et discontinus, chacun posant des exigences différentes en matière de système de contrôle. Un processus continu nécessite un système de contrôle robuste et stable qui ne tombera pas en panne et n'entraînera pas l'arrêt d'une ligne de production, alors que dans le cas d'un processus discontinu, l'accent est mis sur un système de contrôle qui permet une grande flexibilité dans les ajustements des formules, des procédures, etc. Les deux types de systèmes doivent être gérés en fonction de l'historique de la qualité du produit et être en mesure d'exécuter des opérations non routinières. Avec son large portefeuille de produits, ses ingénieurs systèmes expérimentés et son réseau mondial de vente et de service, Yokogawa a une solution pour chaque processus d'usine.
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Chimie Fine et de Spéciclité
Yokogawa est depuis longtemps au service des clients du marché de la chimie fine et de spécialité. Avec une solution de dosage leader sur le marché qui offre la meilleure fiabilité et flexibilité de sa catégorie ainsi que des experts industriels qui comprennent les exigences complexes dans la conception d'une solution de dosage, vous pouvez être assuré que dans votre partenariat avec Yokogawa vous aurez un système qui vous permettra de produire des produits qui répondent aux besoins de vos clients à l'avenir tout en maintenant la sécurité et la conformité réglementaire.
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