Monitoring and control for CA / DCA storage

Optimize your CA / DCA storage with intelligent sensors

Do you want to optimize the quality of your fruit and vegetable storage and ensure that your products stay fresh for longer? Our smart sensors for monitoring and controlling the atmosphere in CA / DCA storage facilities ensure that your produce is stored under optimal conditions. With our sensors, you can ensure that the air composition, temperature and humidity in the warehouse are always in perfect balance to maximize the shelf life and quality of your products. Our sensors are easy to use and can be integrated into almost any CA / DCA storage system

Application example: Freshly harvested apples thanks to a controlled atmosphere

Controlled atmosphere (CA) storage is a widely used technique for the long-term storage of freshly harvested fruit and vegetables. In the past, CA storage was the most important method for the long-term storage of apples. Through a biological process called respiration, apples absorb oxygen and produce carbon dioxide, water and heat.

Controlled atmosphere storage is a completely natural process that minimizes the effects of respiration by controlling the environmental conditions for the stored fruit. CA storage makes it possible to buy crisp, juicy apples all year round. Many apple varieties can be kept for a remarkable 9-12 months in CA storage, as opposed to only 2-3 months when stored in the refrigerator.

• +

    Show more

  The optimum environmental conditions are crucial

  To preserve apples effectively, the storage atmosphere must have a controlled level of humidity, oxygen (O2), carbon dioxide (CO2) and temperature. The key to CA storage is the range for O2 and CO2 concentrations, both of which must be maintained between 0.5 and 2.5%. The exact optimal concentrations vary depending on the apple variety (e.g. Golden Delicious apples require different conditions than Jonagold apples, etc.). The relative humidity is kept in the range of 90 to 95%. A high relative humidity slows down water loss and extends the shelf life of the product, but too high a humidity promotes bacterial growth. The temperature in the storage container is kept at around 1 °C, the lowest possible temperature before the fabric is damaged.

  Carefully thought-out process

  The typical process of CA storage begins with filling a storage chamber with apples. Some chambers are large enough to hold up to 400 tons of apples. Then the cooling system is activated to reach the target temperature of 1 °C. During cooling, the windows or other chamber openings are left open to prevent possible collapse due to pressure fluctuations. When the desired storage temperature is reached, the chamber is sealed airtight with a CA door.
  After sealing, a nitrogen generator is started to reduce the O2 concentration in the chamber from 21% (as in normal air) to around 3%.
  
  

  Once this level is reached, the fruit will continue to reduce the O2 concentration through the respiration process. Should the O2 concentration ever drop to zero, the apples would suffer undesirable and irreversible fermentation reactions in the fruit. If the O2 level falls below the safe concentration, outside air is supplied to the chamber to raise the O2 concentration back to the intended level.

  The apples not only produce CO2, but also the gas ethylene, which accelerates ripening. An increased CO2 content stops ethylene production and thus drastically slows down the ripening process of the apples. However, if the CO2 concentration is too high, it can end the life of the apple by affecting its appearance, taste and nutritional value. To keep the CO2 level at the desired level, the excess CO2 must be removed from the air in the chamber. Gas analyzers are used to monitor and control the addition and removal of O2 and the reduction of CO2 throughout the storage period. Because of their role in controlling the desired gas concentrations in the chambers, these analyzers are critical to the operation of the entire system.

  

  From lime bags to more sophisticated methods

  Years ago, storage chamber operators used hydrated lime to control CO2 in fruit storage. Bags of lime were loaded onto pallets and brought into the store, which absorbed all the CO2 given off by the apples, eventually leaving the store with no CO2. Lime (calcium oxide, CaO) absorbs CO2 and then reacts to form calcium carbonate (limestone, CaCO3). Once all the lime was converted to calcium carbonate, the operator was forced to manually ventilate the room or purge with nitrogen to control CO2 levels. Nitrogen generators require large, powerful air compressors that can be costly to run continuously. A carbon dioxide scrubber is a more efficient and cost-effective means of removing and controlling CO2 in a fruit storage facility. CO2 scrubbers not only remove CO2, but also some volatile organic carbons (VOCs) and ethylene, allowing for optimal fruit storage.

  Really smart CO2 scrubbers

  Storage Control Systems, Inc. is a company that specializes in gas analyzers, nitrogen generators and CO2 scrubbers for CA storage systems. The company has been in the industry for over 25 years, making it one of the longest established CA companies in the world. SCS supplies a unique CO2 scrubber, the Series II Smart Scrubber. This scrubber consists of two cylindrical beds containing activated carbon. Activated carbon is a porous adsorbent, which means that the carbon dioxide molecules are attracted to the surface of the activated carbon and stick to it. The activated carbon gradually becomes saturated, so it is necessary to regularly flush the beds with fresh air to remove the CO2. The device is programmed to adsorb on one bed and purge with fresh air on the other to allow continuous cleaning. The Series II Smart Scrubber is also programmed with a "DeOx" cycle to minimize oxygen recirculation into the CA room. The Series II scrubber uses a programmable logic controller (PLC) with a color touchscreen interface to perform its control and sequencing functions. The PLC user interface allows for easy programming of CO2 concentrations, resulting in highly effective storage regimes for fresh fruit.

  The Vaisala CARBOCAP^® Carbon Dioxide Probe GMP251 is used to monitor CO2 output from the beds, controlling the switching of the process from washing to regeneration or vice versa at the most efficient time. The GMP251 is also used to take a snapshot of the CO2 coming out of the room at the start of the cycle. This information is stored in the PLC, which uses the readings to determine the optimum set points for cleaning and regeneration. The Vaisala carbon dioxide sensor is extremely stable, highly reliable, requires no routine calibration and is capable of measuring gas concentrations over several months with an accuracy of <0.5%. This is critical for successful long-term storage of fruit and requires minimal maintenance by the operator.

  

  The article was originally published in Vaisala News 175/2007 (Penny Hickey, Application Engineer, Vaisala, Woburn, MA, USA).

Vaisala Indigo transmitter with two freely selectable sensors for humidity, temperature and CO2 measurement in CA / DCA storage rooms

Transmitter and multiple sensor options

Real-time monitoring of air composition and temperature
Our system continuously monitors the air composition and temperature in your warehouse and provides you with real-time information about the condition of your products. This allows you to react quickly to deviations, take action and ensure that your goods stay fresh for longer.

Alerts in the event of deviations from the preset values
If defined values are exceeded or not reached, you are immediately alerted by email or text message. This allows you to act quickly to prevent potential damage to your products.

Simple integration into existing storage processes
Our sensors are easy to install and can be easily integrated into almost any CA / DCA storage system. This allows you to benefit from the advantages of precise control of the storage atmosphere in a short space of time.

Learn more about the product