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Liquid Flows and Chemical Flow Meters for Corrosive Acid Batching Infrastructure

Quick Answer

Quick Answer: For corrosive chemical acid batching, select a flow meter with PTFE or PFA liner and Hastelloy C or tantalum electrodes. Electromagnetic flowmeters cover most acid batch lines from DN10 to DN300. Coriolis mass flowmeters are better for small batch accuracy below 100 kg/h. Silver Instruments supplies both types with 4-20 mA HART output.

Silver Automation Instruments has supplied acid batching meters to chemical plants in Vietnam, Indonesia, Thailand and Saudi Arabia. The common failure is not the flow sensor body. The failure is the liner and electrode material. A general purpose water meter fails because the rubber liner swells and the stainless steel electrodes pit. Batch accuracy drifts. The process adds too much acid or too little. The specification must start with chemical compatibility.

Which flow meter works best for corrosive acid batching?

An electromagnetic flowmeter is the first choice for most acid batching lines. It has no moving parts and the pressure drop is low. Most acid solutions in batching have conductivity above 200 µS/cm. This is enough for a stable signal. The wetted liner must be PTFE or PFA. The electrodes must be Hastelloy C-276, tantalum or platinum. Silver Instruments AMF series electromagnetic flowmeters can be built with PTFE liner and Hastelloy C electrodes. The line size covers DN10 to DN300. Accuracy is plus or minus 0.5 percent of reading for flow velocity above 0.3 m/s. This works well for hydrochloric acid, sulfuric acid and sodium hydroxide.

For small batch dosing under 100 kg/h, a Coriolis mass flowmeter is a better fit. The SCF series from Silver Instruments measures mass directly. It handles DN3 to DN50 with plus or minus 0.2 percent accuracy. Use it for expensive additives, acid catalysts or exothermic mixing where mass ratio matters. A paint manufacturer in Vietnam replaced a positive displacement meter with an SCF Coriolis meter on a sulfuric acid catalyst line. The batch weight error dropped from 1.8 percent to less than 0.3 percent.

What materials are safe for acid batching?

PTFE and PFA liners handle most acids at temperatures up to 120 Celsius. Electrode material selection depends on the acid type. Hastelloy C-276 works for hydrochloric acid and sulfuric acid in many concentrations. Tantalum is better for concentrated sulfuric acid at higher temperatures. Platinum works for nitric acid and mixed acids. Grounding rings should match the electrode material. If the pipe is non metallic, use grounding rings. Do not use 316L stainless steel electrodes in hydrochloric acid. They will pit and the meter will drift within weeks.

Installation rules for acid batch lines

Install the meter on the discharge side of the batch pump. Keep the measuring tube full at all times. For vertical pipes, flow should move upward. This prevents air pockets and empty pipe errors. Air elimination is critical in acid batch dosing. One bubble in a 20 kg acid batch changes the final pH. In practice, most engineers skip this part. They focus on chemical compatibility but ignore air binding. The batch controller then overshoots and the product is off spec. Use an air release valve upstream if the acid line has frequent pump starts.

Most acid batch systems run at 2 to 6 bar and 25 to 80 Celsius. Silver Instruments meters are rated for 16 bar and 120 Celsius as standard. For ATEX Zone 1 or Zone 2 areas, order the meter with the required certification. Tell us the zone classification when you send the inquiry.

Signal wiring and batching controller outputs

Use a screened cable for 4-20 mA HART signal. Keep the signal cable away from the pump variable frequency drive cable. Variable frequency drives are noisy in acid batching panels. A 4-20 mA HART signal plus a pulse output c