Switchable two-stage cascade energy-saving ultralow-temperature refrigeration system for ships
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Solution Overview
Problem
Conventional refrigeration systems face limitations in achieving ultralow temperatures below -25°C due to high pressure ratios and inefficiencies in single-stage compression, leading to increased power consumption and reduced efficiency, and traditional defrosting methods are power-intensive and inadequate.
Innovation Solution
A switchable two-stage and cascade marine energy-saving ultralow-temperature refrigeration system that combines a high-temperature two-stage refrigeration system with a low-temperature cascade system, using variable frequency screw compressors and solenoid valves to regulate evaporating temperatures from -30°C to -80°C, and employs a hot fluorine defrosting system for efficient and safe defrosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage compression refrigeration system is used to simplify the system, then the system complexity is reduced, but the evaporating temperature can only reach -40°C and cannot satisfy ultralow temperature requirements below -25°C
Solution Approach 1:
The refrigeration system is divided into two independent stages: a high-temperature level refrigeration system (using R404A refrigerant for -30°C to -60°C) and a low-temperature level refrigeration system (using R23 refrigerant for -60°C to -80°C). Each stage operates with its own compressor, condenser, and expansion valve, allowing the system to achieve ultralow temperatures while maintaining manageable complexity through modular design.
2Temperature
If a two-stage compression refrigeration system is used to achieve evaporating temperature of -30°C to -60°C, then the temperature range is extended, but the system cannot satisfy requirements for -60°C to -80°C due to refrigerant solidifying point and system pressure ratio limitations
Solution Approach 1:
The system changes the refrigerant parameter by using different refrigerants for different temperature levels: R404A for the high-temperature level and R23 for the low-temperature level. This parameter change allows the system to operate efficiently across a wider temperature range (-30°C to -80°C) without encountering refrigerant solidification issues or excessive pressure ratios.
Solution Approach 2:
The system employs a composite refrigeration architecture combining two different refrigeration cycles (R404A cycle and R23 cycle) that operate in parallel. The high-temperature level system handles -30°C to -60°C while the low-temperature level system handles -60°C to -80°C, creating a composite system that covers the entire ultralow temperature range with optimized performance at each level.
3Temperature
If a cascade refrigeration system is used to achieve evaporating temperature of -50°C to -80°C, then the ultralow temperature requirement is met, but the power consumption increases due to single-stage compression at high pressure ratio
Solution Approach 1:
The high-temperature level refrigeration system is segmented into two compression stages: a low-pressure stage and a high-pressure stage. The low-pressure stage compresses refrigerant from evaporating pressure to intermediate pressure, while the high-pressure stage compresses from intermediate pressure to condensing pressure. This segmentation reduces the pressure ratio of each stage, improving compressor efficiency and reducing power consumption.
Solution Approach 2:
An intercooler is introduced as an intermediary component between the low-pressure stage and high-pressure stage compressors. The intercooler cools the refrigerant vapor discharged from the low-pressure stage before it enters the high-pressure stage, reducing the inlet temperature and pressure ratio of the high-pressure compressor, thereby improving overall system efficiency and reducing power consumption.
4Ease of operation
If traditional electrical heating is used for defrosting the air cooler, then the defrosting function is provided, but the power consumption is large and the defrosting is inadequate
Solution Approach 1:
The system uses the high-temperature refrigerant vapor discharged from the compressor to directly defrost the air cooler evaporator. The hot refrigerant vapor absorbs heat from the frost layer, melting it and draining away. This self-service defrosting method eliminates the need for separate electrical heating elements, significantly reducing defrosting power consumption while improving defrosting effectiveness.
Solution Approach 2:
The system converts the harmful high-temperature refrigerant vapor that would otherwise be wasted into a useful defrosting heat source. By directing this hot vapor through the evaporator during defrosting cycles, the system efficiently melts frost buildup while utilizing energy that would otherwise be discarded, transforming a potential harm (waste heat) into a beneficial defrosting mechanism.
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
The system achieves continuous temperature regulation and significant energy savings while ensuring stable operation and precise temperature control, with improved compressor efficiency and reduced power consumption, and provides a safe and efficient defrosting process.
Implementation Method 1
A switchable two-stage and cascade marine energy-saving ultralow-temperature refrigeration system that combines a high-temperature two-stage refrigeration system with a low-temperature cascade system, using variable frequency screw compressors
Implementation Method 2
An overlapped device of the high-temperature portion and the low-temperature portion is a condensation evaporator which is an evaporator of the high-temperature portion as well as a condenser of the low-temperature portion. In the condensation evaporator, an intermediate temperate refrigerant of the high-temperature portion performs vaporization and heat absorption for condensation of the refrigerant of the low-temperature portion.
Implementation Method 3
using variable frequency screw compressors and solenoid valves to regulate evaporating temperatures from -30°C to -80°C
Implementation Method 4
employs a hot fluorine defrosting system for efficient and safe defrosting
Data Source
Figure 1
AI summary
The present invention discloses a switchable two-stage and cascade marine energy-saving ultralow-temperature refrigeration system which comprises a high-temperature level refrigeration system, a low-temperature level refrigeration system, a hot fluorine defrosting system of a high-temperature level air cooler and a hot fluorine defrosting system of a low-temperature level air cooler. The hot fluorine defrosting system of the high-temperature level air cooler comprises a high-temperature level compressor of which the outlet is divided into two paths through a first oil separator; and the second path is connected with an air suction port of the high-temperature level compressor through a first solenoid valve, the high-temperature level air cooler, a third solenoid valve, a first pressure relief valve, a first gas-liquid separator, a first check valve and a first heat regenerator. The hot fluorine defrosting system of the low-temperature level air cooler comprises a low-temperature level compressor of which the outlet is divided into two paths through a precooler and a second oil separator; and the second path is connected with an air suction port of the low-temperature level compressor through an eighth solenoid valve, the low-temperature level air cooler, a sixth solenoid valve, a second pressure relief valve, a second gas-liquid separator, a third check valve and a second heat regenerator. The present invention has the obvious effects of large refrigeration section, high cooling rate, good energy-saving effect and thorough defrosting.