Successful Application of Ammonia Refrigeration System in Industrial Field
In the past 30 years, due to the adverse effects on the environment, the use of synthetic refrigerants has been subject to many restrictions. Under this trend, people have turned their attention to ammonia and carbon dioxide, which are harmless to the earth’s ecosystem. Ammonia refrigeration has been in a dominant position in the industrial field for 150 years. Due to its unique refrigeration characteristics and high energy efficiency, ammonia has always been the mainstream refrigerant for large-scale industrial refrigeration. In recent years, with the continuous development of chemistry, materials science, refrigeration technology and manufacturing technology in the industrial field, ammonia has begun to be gradually applied to small refrigeration systems. In the past, these small refrigeration systems mostly used other refrigerants, such as HFCs and HCFC. Ammonia is defined as a toxic and slightly flammable gas. With the development of technology, safety requirements have been implemented for it. International refrigeration safety standards include ASHRAE 15, EN 378 and ISO 5149, and each country has its own rules and regulations on workplace health and safety. In European countries, although there are general safety guidelines, their implementation methods are different in different countries.
1. Design and safety requirements
When planning to design a new ammonia refrigeration system, requirements such as process, safety, and environmental impact must all be taken into consideration. The system must meet the requirements for cooling capacity, temperature and energy efficiency. For large-scale ammonia refrigeration systems, the requirements for safety are much higher than those of non-toxic refrigerants. Before the refrigeration system is built and put into operation, a large number of qualification documents need to be provided. The number and content of the documents required by different national agencies are different, but the basic safety and operational requirements are the same.
2. Safety system design
The first basic requirements for engineers when designing industrial refrigeration systems are:
1) Ensure compliance with all relevant safety regulations and meet all standard requirements.
2) Ensure that the system is highly efficient and can meet the cooling capacity and temperature requirements.
3) Install components and equipment with detection functions in a place that is easy to operate to facilitate system inspection and maintenance.
The second point of system design is the final construction and installation. It is very important for the final design to ensure that all standard requirements are met. The design documents cannot list all the details. Therefore, experienced installers and skilled installation techniques are required to ensure that the system ultimately meets all standard requirements.
In terms of the safe operation of the factory, the operator must fully understand the factory and be able to take corrective measures when rare and unexpected situations occur.
3. Design methods and principles are the key to determining the safety of the entire system
The following operation methods can ensure safe operation, but you need to pay more attention to the parts and accessories of the system. Hot gas defrosting is one of the most important and common standard operations, as shown in Figure 2. This method is fast, reliable, and economical, but requires accurate operation to ensure safety. During the hot gas defrosting process, the main refrigeration circuit is cut off, and the hot gas is injected into the cold evaporator, and some liquid is produced at this time. During the defrosting process, the pressure continues to rise. At this time, the evaporator acts like a condenser, liquefying the gas. After defrosting, the system returns to the normal operation mode, but if the valve is opened too fast, the high-pressure liquid is suddenly pushed out by the evaporator under the impact of a large amount of hot gas, which will cause a “liquid strike” in the pipeline. Liquid shock can cause damage to components and pipes, leading to safety accidents. Therefore, “liquid hammer” must never happen. Liquid level detection, correct valve size and effective control switch are the keys to ensuring the safety and efficiency of the hot gas defrosting program. When analyzing the above defrosting process, there are some easy mistakes that need special attention.
Ammonia is a high-quality natural working fluid with high refrigeration efficiency, but at the same time ammonia is also a toxic gas, so the design and installation location of the system are particularly important.
The construction of a large-scale safety system faces many challenges. Over the years, many methods have been adopted to continuously improve and develop technical standards and guidelines.
Authorities in various countries are increasingly concerned about the risks of ammonia refrigeration. Risk assessment and filing of large-scale refrigeration systems located in densely populated areas has become a mandatory requirement in many countries.
Pay attention to all safety items, evaluate all safety factors one by one, and ensure that best practices are implemented to ensure that the entire system is at a low risk level.
As an alternative, other solutions, such as ammonia/carbon dioxide cascade refrigeration, must also meet the safety requirements of the system.
Post time: Sep-13-2021