Container Refrigeration Air Control for O2 and CO2 Balance
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Solution Overview
Problem
Existing container refrigeration systems face challenges in maintaining a high carbon dioxide concentration while lowering oxygen levels, as introduced carbon dioxide is often released during nitrogen-enriched air supply, leading to decreased carbon dioxide concentrations and reduced freshness of plants.
Innovation Solution
An inside air control system with a controller that prioritizes carbon dioxide concentration, stopping nitrogen-enriched air supply when carbon dioxide levels drop below target and restarting when they increase, ensuring oxygen levels are lowered to target while maintaining carbon dioxide levels, using a gas supply device to produce nitrogen-enriched air with a higher nitrogen and lower oxygen concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nitrogen-enriched air is supplied into the container to lower oxygen concentration, then the oxygen concentration is reduced and plant freshness is improved, but the carbon dioxide concentration decreases due to air displacement, worsening the freshness maintenance
Solution Approach 1:
The controller continuously monitors both oxygen and carbon dioxide concentrations inside the container and dynamically adjusts the nitrogen-enriched air supply rate. When carbon dioxide concentration drops below a target level during nitrogen supply, the controller reduces or pauses the supply temporarily, allowing carbon dioxide levels to recover from plant respiration, then resumes supply when levels are sufficient. This closed-loop feedback control prevents carbon dioxide loss while maintaining oxygen reduction.
Solution Approach 2:
The system transitions from static, fixed-rate nitrogen supply to dynamic, variable-rate supply based on real-time gas composition monitoring. The supply rate is continuously adjusted according to the measured oxygen and carbon dioxide levels, enabling the system to adapt to changing conditions inside the container and maintain both gas concentrations within target ranges throughout the transportation process.
2Quantity of substance
If carbon dioxide is introduced into the container to increase carbon dioxide concentration, then plant freshness is improved, but the oxygen concentration increases, causing breathing problems in plants
Solution Approach 1:
The controller uses real-time monitoring of both oxygen and carbon dioxide concentrations to determine when carbon dioxide supplementation is needed. When carbon dioxide levels drop below target (indicating excessive nitrogen supply or high plant respiration), the controller pauses nitrogen supply to allow natural carbon dioxide accumulation from plant respiration, then resumes nitrogen supply when carbon dioxide levels are sufficient, thereby maintaining the proper gas balance without direct carbon dioxide injection.
Solution Approach 2:
The system leverages the natural respiration process of the plants themselves to generate and maintain carbon dioxide levels. By strategically pausing nitrogen-enriched air supply at appropriate moments, the system allows plant respiration to naturally replenish carbon dioxide in the container atmosphere, eliminating the need for external carbon dioxide injection while maintaining beneficial gas concentrations.
3Quantity of substance
If continuous nitrogen-enriched air supply is performed to maintain low oxygen concentration, then plant breathing is controlled, but carbon dioxide concentration continuously decreases, reducing plant freshness
Solution Approach 1:
The system implements periodic pulsing of the nitrogen-enriched air supply rather than continuous supply. The controller operates the supply in cycles: supplying nitrogen-enriched air for a predetermined period to reduce oxygen levels, then pausing supply for a predetermined period to allow carbon dioxide levels to recover through plant respiration and natural container atmosphere equilibrium. This periodic on-off cycling maintains both oxygen and carbon dioxide concentrations within target ranges throughout the transportation process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively maintains target oxygen and carbon dioxide concentrations, preventing significant decreases in carbon dioxide levels during nitrogen-enriched air supply, thereby keeping plants fresh by ensuring optimal gas composition.
Implementation Method 1
an adsorbent adsorbing a nitrogen component in the air when pressurized is used to produce nitrogen-enriched air having a higher nitrogen concentration and a lower oxygen concentration than the air
Implementation Method 2
a carbon dioxide concentration detector that detects a carbon dioxide concentration of the inside air
Data Source
AI summary
A CA system includes a gas supply device which performs a gas supply operation of supplying nitrogen-enriched air into a container, and a controller which performs the gas supply operation so that the inside air has a desired composition. The controller performs carbon dioxide priority control in which the controller performs the gas supply operation if an oxygen concentration of the inside air is equal to or higher than a ceiling concentration higher than a target oxygen concentration, stops the gas supply operation if a carbon dioxide concentration of the inside air is lowered to a critical concentration lower than a target carbon dioxide concentration, and restarts the gas supply operation if the carbon dioxide concentration of the inside air has reached a restart concentration higher than the target carbon dioxide concentration through breathing of the plants.