Selecting the Right Level Switch for Fumed Silica Measurement

Fumed silica is a crucial nano-scale inorganic chemical material known for its low density, fine particles, large surface area, strong adhesion, and high moisture absorption. These properties make it useful in enhancing strength, increasing viscosity, and providing thixotropic and extinction effects. It is widely used in agriculture, pesticides, medicine, food, cosmetics, and silicone rubber industries. For instance, fumed silica is mixed with fertilizer to improve the fluidity of powdery fertilizer, facilitating its transportation and storage and preventing agglomeration due to moisture. Accurate level measurement in fumed silica storage tanks is essential to avoid environmental pollution and material waste. Let’s explore the production process, challenges, and the selection of appropriate level switches for fumed silica.

1. Fumed Silica Production Process Flow

Fumed silica is produced through the gas phase hydrolysis of methyltrichlorosilane at high temperatures in an oxygen-hydrogen flame. The process flow is shown in Figure 1.

In the production process, level switches are required in storage tanks to monitor and control the level of fumed silica, preventing material overflow and ensuring environmental protection.

2. Challenges in Fumed Silica Level Measurement

Level measurement for fumed silica is challenging due to several factors:

• Fumed silica is stored in tall vertical silos (approximately 10 meters).
• It has a very low density (0.01-0.03 g/cm³) and a low dielectric constant.
• To prevent material compaction and adjust the pH value by controlling the chloride ions attached to the fumed silica surface, nitrogen gas is filled from the bottom of the silo, causing rolling and waving of the material and creating airborne “dust” in the silo.

Reliable level measurement is crucial to meet environmental protection and safety standards and to prevent overfill. Therefore, selecting the right level switch for fumed silica is vital.

3. Selecting the Right Level Switch for Fumed Silica

Commonly used level switches include rotary paddle switches, capacitive level switches, RF admittance level switches, and vibrating level switches (including vibrating rod and fork level switches).

• Rotary Paddle Switch: Not suitable for fumed silica due to its low density, which prevents the motor from stopping and triggering the micro switch.
• Capacitive and RF Admittance Level Switches: These switches detect changes in capacitance between the probe and the vessel as the material level changes. However, the low dielectric constant of fumed silica makes these switches ineffective.

The ideal solution for measuring ultra-low density powdery solids like fumed silica is the Fork Level Switch. The measuring principle of the fork level switch is based on detecting the harmonic resonance state of the fork bodies, driven by piezoelectric ceramics, and is independent of the dielectric constant of the material. When precisely adjusted for complete harmonic resonance, the fork level switch achieves maximum sensitivity, making it suitable for ultra-low density measurements.

Jiwei Fork-11 Level Switch

The Jiwei Fork-11 Level Switch features a wider and thinner fork body compared to similar products, and it is finely tuned for complete resonance. Its sensitivity can be pre-adjusted based on the density of the material, with a minimum measurable density as low as 0.008 g/cm³. The Fork-11 has been successfully applied in numerous fumed silica level measurement projects.

Customer Concerns: Some customers worry about measurement accuracy when large amounts of fumed silica adhere to the highly sensitive fork bodies. However, the Fork-11’s resonance is pre-adjusted for high redundancy against material buildup, ensuring reliable performance as long as no “scar” forms on the fork bodies. In severe conditions, where strong adhesive materials may continuously attach and form scars, a nitrogen purge device is recommended to clean the fork bodies before filling the material, preventing heavy buildup.

Jiwei specializes in designing and manufacturing level meters for industrial automation. We tackle challenges and provide professional solutions for various level measurement problems. Our level meters, recognized for their high reliability and cost-effectiveness, compete with global brands and are well-regarded by customers for their performance in complex applications.