Sensitive “electronic noses” are giving a soft-drink bottling plant enhanced protection against toxic, explosive and oxygen-depleting gases. The “noses”—sophisticated gas detectors from Minneapolis-based Sensor Electronics—continually monitor critical areas in the plant for dangerous concentrations of chlorine (Cl), ammonia (NH₃) and carbon dioxide (CO₂) .

Along with keeping a beady eye out for unsafe gases, these detectors also keep a watchful eye on themselves. In case of problems anywhere in the system, they immediately spell out what is wrong where.

The plant turns out some 30 million cases of carbonated beverages a year—regular, diet, caffeine-free, flavored and plain versions—plus spring water. To produce this river of beverages, the plant gulps more than a million gallons of water a week—watered that’s filtered, chemically purified using chlorine, chilled to 34 degrees employing ammonia, charged using carbon dioxide, then blended with sugars, flavors and colors. Unfortunately, all three gases are toxic, and one—ammonia— is explosive to boot.

Figure 1. “Electronic Nose” monitors ammonia levels

While even small concentrations of ammonia—as low as 20ppm—are easily detected by the nose, there could be a bigger buildup in say, a storage closet. Inadvertently opening the door could mean throat irritation, external and internal burns, even suffocation.

Chlorine is just as bad. (One form of chlorine is mustard gas.) Worse, chlorine is odorless and colorless, making it a stealthy killer. Like chlorine, carbon dioxide is colorless, odorless, and dangerous. In heavy concentrations it displaces oxygen in the blood, effectively strangling the victim.

To guard the plant, “electronic noses” monitor chlorine levels at gas-distribution
manifolds and closets where chlorine cylinders connect into the system. And ammonia detectors watch over refrigeration compressors and piping networks.

Figure 2. The control room carefully monitors the sensors.

But the plant uses no CO₂ sensors. Instead, it has sensors monitoring oxygen levels at key locations. Because carbon dioxide is heavier than air, it collects at low spots in the plant. There, oxygen sensors stand guard where pipes feed low-pressure CO₂ into the chilled water. If O₂ levels drop, this means CO₂ levels are increasing, and the detector flashes an alarm.

Each of these gas detectors has a “traffic light” that goes from green to red as the gas concentrations change. And these are tailored to the specific gas; the chlorine detector, for example, glows green to 1ppm, yellow at 50 ppm, and red over 50.

For CO₂, the O₂ detector works backward; green with oxygen levels above 19.6%, yellow for O₂ from 19.5 to 16.1%, and red below 16%.

Each detector also shows actual gas levels at that point. Digital readouts from every detector are updated every 5 seconds on a panel in the plant control room.

Panel alarm lights are color coded, and linked to warning horns throughout the plant. Depending on its severity, the detectors can also shut down pumps, close valves, and turn on supply exhaust fans to flood the area with outside air, keeping employees safe from potential gas-related accidents.

By Tom Probst
Sensor Electronics