Oxygen Monitor for Closed-Loop Dryers

Quick answer

A dryer oxygen monitor confirms inerting before heating and throughout the cycle. ACCURRA-S reads 0 to 25 % or ppm oxygen and ACCURRA-Hz covers classified areas. Warm, humid, solvent-laden gas needs cooling and filtration before the analyser.

Updated 2 November 2026 · Figures from Sarvesh datasheets

The measurement and why it matters

Closed-loop dryers, tube bundle dryers and spray dryers remove solvents from pharmaceutical and chemical products. Solvent vapour, fine powder and hot surfaces sit together, so the atmosphere is purged with nitrogen before heating and kept inert during drying. A measured oxygen figure is the start permissive, and a continuing check.

ACCURRA-S 3030 and 3130 read percent oxygen from 0 to 25 percent, and 3015 reads trace oxygen to 1000 ppm. Where the area is classified, ACCURRA-Hz covers the requirement. Alarm relays tie into the dryer interlock, and stored calibration and alarm history supports GMP audits.

Solvent-laden gas is wet. Send the solvent type, concentration, temperature and dew point so the sample can be conditioned correctly.

Models and ranges

Model	Measures	Range	Sensor and notes
3030 / 3130	Oxygen percent	0 to 25 %	ACCURRA-S
3015	Oxygen trace	0 to 1000 ppm	ACCURRA-S
ACCURRA-Hz	Oxygen, hazardous area	As required	Certified enclosure

Process notes

Spray dryers

A spray dryer atomises a liquid feed into a hot gas stream so it dries into fine powder. When the feed carries solvent, the dryer runs as a closed loop: nitrogen circulates, a condenser recovers solvent, and the gas returns to the heater. Oxygen is kept low so the solvent vapour and powder cannot ignite.

The gas in the loop is warm, humid and carries fine particles, so the sample system matters. A probe filter with blowback keeps powder out, and a cooler and fine filter dry the gas before it reaches the cell. The oxygen reading then supports an interlock and a record for each batch.

Dryer inerting

Closed-loop dryers, tube bundle dryers and nutsche filter dryers remove solvents from pharmaceutical intermediates. Wet cake and solvent vapour sit with hot surfaces, so the atmosphere is purged with nitrogen before heating and kept inert during drying.

Oxygen measurement gives the permissive to start heating and a continuing check while the cycle runs. Calibration and alarm history stored in the analyser help demonstrate control during audits. The sample is often saturated with solvent, so a coalescing filter protects the cell.

When you specify an analyser for a dryer, list the solvents, the dryer temperature, the pressure or vacuum in the dryer and the zone classification. Vacuum dryers need the sample pump to pull against low pressure, and ACCURRA-S offers an internal sample pump for low-pressure samples. Alarms and outputs are configurable to match your batch procedure.

Sampling and installation

Solvent-laden gas is wet. Send solvent type, concentration, temperature and dew point.
Place the probe after the cyclone or bag filter where the gas is cleaner.
Cool and dry the sample before the analyser, and protect it with a coalescing filter.
Vacuum dryers need the sample drawn against low pressure; ask about the optional internal sample pump.

ACCURRA-S sample specification: non-corrosive, non-toxic, non-flammable, non-condensing and dry, free from entrained oil; sample pressure 2 to 10 psig, regulated externally; flow about 1 LPM; dust below 3 micron. Where your sample differs, we design conditioning around it.

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Application data sheet

The same pre-order design inputs our engineers design from, online. Fill in what you know, leave the rest. Your draft saves as you go, and you can print or send it when ready.

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What the data sheet asks for

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The gases to measure, the range, and the accuracy you need
Background gases and their typical composition
Sample temperature, pressure and dew point at the tapping point
Dust level, and whether the gas carries tar, oil or condensable vapour
Process connection and, for ducts, the duct diameter
Where the sample vents to, and at what pressure
Area classification of the tapping point and of the analyser location, and the IP protection needed
Distance between the tapping point and the analyser
Outputs you need: 4-20 mA, dual range, relays, Modbus RTU
Calibration approach, calibration gas available, and whether blowback is required
Utilities at site: power supply, instrument air, nitrogen, steam and cooling water, and the ambient temperature range
Solvent type and concentration, dryer pressure or vacuum, and area classification