What Are Scrubbers in a Controlled Atmosphere Cold Storage?

 

In controlled atmosphere cold storage, a device known as a scrubber is used to remove certain gases from the air within the storage chamber. Scrubbers help prevent overripening and spoilage of fruits and vegetables while maintaining conducive conditions for preserving their quality. It can be understood as a gas filtration system inside the refrigeration system.

The most common gas that this device works to remove from the air is CO2. This is why it is sometimes also referred to as a CO2 scrubber.

When a fruit (such as an apple) respires, like humans, it also intakes O2 and releases CO2, which can deteriorate its quality if the concentration is too high. This metabolic activity of the stored products keeps changing the composition of the gas mixture in the storage rooms, making it essential to remove excess carbon dioxide.

However, how much CO2 will be removed depends on factors like product (apple or mango), the dimensions of the storage area and the atmospheric conditions of storage.

Scrubbers can be classified according to the:

• absorbent material used: Ca(OH)2, NaOH, H2O, zeolites, activated charcoals
• mode of absorption (i.e. chemical or physical), or
• mode of air passage through the absorbing agent.

Activated charcoal is the most popular choice for use in scrubbers these days. The desired CO2 level is maintained using the scrubber (in combination with activated charcoal) once the scrubbing requirement for the connected storage cells are known.

Usually, the scrubber follows two activity cycles:

• Adsorption cycle (Scrub cycle) : This cycle focuses on removing CO2.
• Regeneration cycle (Purge cycle): This cycle involves cleaning or regenerating the active carbon filter.

Composition of Scrubber Unit & Working Process

An activated carbon filter chamber, a low-pressure ventilator, an air-transport system, a control unit, and a buffer system make up the scrubber unit.

The device works by trapping CO2 in a special way and releasing it when it comes into contact with air, even at room temperature. In an activated carbon scrubber, the scrubber contains a bed of activated carbon. Air with CO2 is passed through the carbon bed, where the carbon grabs the CO2. This process cleans the air, allowing the purified air to be released back into the room.

To enable constant monitoring of the status of the carbon beds, scrubbers employ modern electronic PLC control and a panel mounted CO2 Analyzer. This careful monitoring of CO2 levels allows scrubbers to switch cycles only when required. In turn, this helps ensure maximum efficiency with minimum cycles.

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