Challenges of High-Temperature Concentrated Sulfuric Acid Level Measurement
In industry, level measurement of concentrated sulfuric acid is relatively troublesome, especially under high-temperature working conditions. Taking E+H instruments as an example, 98% concentrated sulfuric acid will produce acid mist at high temperatures, interfering with measurement. This article will analyze the causes of acid mist and give instrument selection recommendations.
Mechanism of Acid Mist Generation
98% concentrated sulfuric acid is a three-component equilibrium liquid phase of sulfuric acid, SO3, and equilibrium moisture. When the temperature reaches about 200°C, the equilibrium partial pressure of SO3 rises sharply and overflows in large quantities from the liquid surface; at the same time, moisture volatilizes, and SO3 reacts with water to generate sulfuric acid vapor. Supersaturated vapor condenses into fine droplets, forming white mist.
In addition, sulfuric acid undergoes thermal decomposition at high temperatures, continuously replenishing SO3 and water vapor, generating acid mist endlessly. The higher the temperature, the faster the decomposition rate and the greater the amount of mist. Therefore, white mist is not caused by volatilization of concentrated sulfuric acid; only concentrated hydrochloric acid and concentrated nitric acid are prone to volatilization.
Impact of Acid Mist on Radar Level Gauges
Concentrated sulfuric acid mist will interfere with radar measurement, mainly in two aspects:
- Microwave signal interference: causes measurement jumps, false levels, wave loss, etc.
- Corrosion hazards: generally does not occur if materials are selected correctly, but attention is needed.
Under 185°C working conditions, moisture boils and vaporizes and reacts with SO3, while sulfuric acid decomposes to generate these two substances, forming gas-phase dualization. Special attention should be paid during selection.
Instrument Selection Key Points
Radar Level Gauge
Prefer high-frequency radar, which has a small beam angle and concentrated energy, reducing acid mist interference. It is recommended to use a lens antenna or horn antenna, and install a purging device to prevent condensation.
Wetted Instruments
When using wetted instruments, the measuring rod cannot be made of pure metal; it must be coated with corrosion-resistant material, such as PTFE, PFA, etc. At the same time, flanges and seals also need to be corrosion-resistant.
| Instrument Type | Advantages | Disadvantages | Applicable Conditions |
|---|---|---|---|
| Radar level gauge | Non-contact, corrosion-resistant | Susceptible to acid mist interference | High temperature, strong corrosion |
| Wetted type (coated) | Strong anti-interference | Requires corrosion-resistant coating | Room temperature to 185°C |
Summary
High-temperature concentrated sulfuric acid level measurement requires comprehensive consideration of acid mist interference and corrosion issues. Radar level gauges should be high-frequency and equipped with purging; wetted instruments must be coated with corrosion-resistant materials. Correct selection can ensure stable and reliable measurement.
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