Analysis of the application of ammonia in the refrigeration system of fishing boats

2023-12-19

The refrigeration system plays an important role in fishing vessels, especially in long-distance and domestic large-scale fishing vessels. The performance and effectiveness of the refrigeration device seriously affect the preservation quality of the catch, and the refrigeration processing capacity also determines the production capacity of the fishing vessel, directly affecting the economic benefits of the fishing vessel.

Selection of refrigerants

The refrigeration system of fishing boats is complex, with high technical, quality, and safety requirements. The use of different refrigerants corresponds to different regulations and regulatory requirements. Improper design and use can cause the system to malfunction. Mild cases can cause a lot of trouble in daily operation and management, reduce the efficiency of the system, and severe cases may cause explosions, fires, toxic substance leaks, etc., posing a great threat to the safety of fishing boats and personnel.

01

Requirements related to international conventions/regulations

According to the Technical Rules for Statutory Inspection of Oceangoing Fishing Vessels (2019) and the Technical Rules for Statutory Inspection of Domestic Marine Fishing Vessels (2019), the refrigerants allowed to be used in China's current ship technical regulations (hereinafter referred to as the regulations) include:

(1) R717 ammonia (NH3);

(2) R22 Chlorodifluoromethane (CHClF2);

(3) R404A: A mixture of R125 (44%)+R143a (52%)+R134a (4%). R125 is pentafluoroethane (CHF2CF3), R143a is trifluoroethane (CH3CF3), and R134a is tetrafluoroethane (CH2FCF3).

According to the recognized fishing vessel construction standards (hereinafter referred to as the standards) published by the China Maritime Safety Administration in accordance with the prescribed procedures, the refrigerants allowed to be used in the standards are consistent with the regulations. However, in the new version of the "Steel Oceangoing Fishing Vessel Construction Standards (2021)", R22 has been removed from the allowed refrigerants, and some environmentally friendly refrigerants have been added, including:

(1) R717: Ammonia (NH3);

(2) R134a: Tetrafluoroethane (CH2FCF3);

(3) R404A: A mixture of R125 (44%)+R143a (52%)+R134a (4%). R125 is pentafluoroethane (CHF2CF3), R143a is trifluoroethane (CH3CF3), and R134a is tetrafluoroethane (CH2FCF3).

(4) R507A: A mixture of R125 (50%) and R143a (50%). R125 is pentafluoroethane (CHF2CF3), and R143a is trifluoroethane (CH3CF3).

(5) R407C: A mixture of R32 (23%)+R125 (25%)+R134a (52%). R32 is difluoromethane, R125 is pentafluoroethane (CHF2CF3), and R134a is tetrafluoroethane (CH2FCF3).

Among the refrigerants allowed to be used in current regulations, R22 dichlorodifluoromethane (CHClF2) belongs to the category of hydrochlorofluorocarbons. Due to the serious damage of fluorocarbons to the atmospheric ozone layer, ozone depleting substances have been completely banned internationally, and the use of hydrochlorofluorocarbons has gradually been restricted. R22 will face global elimination. Annex VI of the International Convention for the Prevention of Pollution from Ships, "Rules for the Prevention of Air Pollution from Ships," also increases restrictions on the use of ozone depleting refrigerants by marine vessels.

The following requirements are required in Chapter 5 of Chapter 15 of the "Technical Rules for Statutory Inspection of Oceangoing Fishing Vessels" (2019) and "Technical Rules for Statutory Inspection of Domestic Marine Fishing Vessels":

The use of devices containing ozone depleting substances (excluding hydrogenated chlorofluorocarbons) should be prohibited in the following situations:

(1) Fishing vessels built on or after May 19, 2005;

(2) For fishing vessels built before May 19, 2005, the equipment contract delivery date on the vessel is May 19, 2005 or later, or if there is no contract delivery date, the actual equipment delivery date on the vessel is May 19, 2005 or later.

Under the following circumstances, the use of devices containing hydrogenated chlorofluorocarbons should be prohibited:

(1) Fishing vessels built on or after January 1, 2020;

(2) For fishing vessels built before January 1, 2020, the equipment contract delivery date on the vessel is January 1, 2020 or later, or if there is no contract delivery date, the actual equipment delivery date on the vessel is January 1, 2020 or later.

Therefore, the refrigeration equipment already installed on existing ocean going fishing vessels (400 gross tons and above), such as refrigerant R22, can continue to be used, but matters related to use, repair, maintenance, and consumption of hydrochlorofluorocarbons (HCFCs) should be recorded and saved on board the Ozone Depleting Substances Record Book;

For existing ocean going fishing vessels and domestic fishing vessels, if the refrigeration system of the vessel is charged due to natural consumption, the refrigerant inventory already produced before January 1, 2020 should be used (i.e. it is prohibited to continue purchasing refrigerants such as hydrochlorofluorocarbons and HCFCs produced after January 1, 2020).

02

The application trend of refrigerants

Environmental and energy issues are the two major issues facing humanity today, while ozone depletion and global climate change are the two major environmental issues of concern to the world. In October 2016, the 28th Conference of the Parties to the Montreal Protocol adopted the Kigali Amendment by consensus, which included hydrofluorocarbons in its control scope and opened a new chapter in collaborative efforts to address ozone depletion and climate change. In 2021, China officially accepted the Kigali Amendment and came into effect. According to the requirements of the Kigali Amendment, China needs to freeze the production and consumption of hydrofluorocarbons at baseline levels in 2024, and gradually reduce their production and consumption starting from 2029. Therefore, China also tends to choose more environmentally friendly refrigerants for the refrigeration system of fishing vessels in the formulation of regulations (Figure 1 and Figure 2).

Comparison of ozone depletion potential (ODP) values of refrigerants permitted in regulatory specifications in Figure 1

Comparison of Global Warming Potential (GWP) of Permissible Refrigerants in Regulatory Specifications in Figure 2

By comparing the ozone depletion potential (ODP) and global warming potential (GWP) of several commonly used refrigerants in Figures 1 and 2, it can be concluded that ammonia refrigerant (R717) is the most environmentally friendly and has no destructive effect on the natural environment.

03

Characteristics of ammonia (R717) refrigerant

Ammonia is a natural medium temperature refrigerant, favored by the industrial refrigeration industry due to its excellent thermal and physical properties, high refrigeration efficiency, low price, and green environmental protection.

The advantages of ammonia include:

(1) The standard boiling point is low (33.3 ℃), the critical temperature is high (132.5 ℃), and the working range is wide. The pressure is moderate within the normal temperature and low temperature range;

(2) The refrigeration capacity per unit volume is large, the latent heat of vaporization is high, the throttling loss is small, the heat transfer performance is good, and the cycle performance coefficient of the refrigeration system heat pump is high;

(3) Strong water absorption, able to prevent pipeline "ice blockage";

(4) It is basically immiscible with lubricating oil and lighter than oil, making it easier for the system to drain oil;

(5) Cheap price and easy production;

(6) High chemical and thermal stability at room temperature and low temperature;

(7) There is an irritating odor that can be easily detected once leaked. When there is 20ppm ammonia in the air, the human sense of smell can distinguish it, and protective measures can be taken in a timely manner before reaching a dangerous concentration;

(8) No damage to the ozone layer, no greenhouse effect.

The disadvantages of ammonia include:

(1) Toxic and volatile - it has a strong irritant effect on human mucosal tissues (such as the eyes, nose, pharynx, and lungs). When its volume content in the air reaches 1700 ppm or more, staying in it for 30 minutes can cause poisoning or even death. If there is a leak, it can also contaminate food or products;

(2) Flammable and explosive - ammonia can ignite when its volume concentration in the air reaches 11%~14% (ignition point 651 ℃), and when its volume concentration reaches 15.7%~27.4%, it can cause an explosion when exposed to an open flame.

Safe application of ammonia in refrigeration systems

Given the friendliness of ammonia to the natural environment, Chinese fishery experts advocate promoting ammonia as a refrigerant in the refrigeration system of fishing vessels. The Construction Specification for Steel Ocean Fishing Boats (2015) cancels the requirement that for fishing vessels with limited navigation areas, the total refrigerated fish tank capacity should be less than 500m ³ The limitation of using a direct ammonia evaporation exhaust pipe cooling system allows for the direct evaporation refrigeration of ammonia refrigerant to be applied to any tank capacity. Expanded the applicability of ammonia refrigerants on fishing vessels.

When refrigeration systems are applied on ships, safety is the primary consideration. Due to the toxic and explosive properties of ammonia, some fishing boats are unwilling to use ammonia as a refrigerant. If the characteristics of refrigerants can be correctly understood during design and construction, a reasonable and reliable system scheme can be designed, regular maintenance and upkeep can be carried out during ship operation, and relevant operators on board can receive corresponding training and comply with operating procedures, then the danger of using natural refrigerants such as ammonia will be greatly reduced.

The requirements for refrigeration systems in the current Technical Rules for Statutory Inspection of Oceangoing Fishing Vessels (2019) and the Technical Rules for Statutory Inspection of Domestic Marine Fishing Vessels (2019) mainly involve safety control of refrigeration equipment, airtight separation of compartments, ventilation settings, water sprinkler systems, leakage alarm devices, firefighting equipment, implementation of operating procedure guidelines, and specific ammonia refrigeration compressor rooms and ammonia leakage monitoring The alarm system points to the relevant requirements of the "Code for Construction of Steel Oceangoing Fishing Vessels" and "Code for Construction of Steel Domestic Marine Fishing Vessels" published and recognized by the China Maritime Safety Administration according to the prescribed procedures.

01

Gas detection and alarm settings

Gas detection is mainly aimed at toxicity rather than explosiveness, as toxicity alarms and corresponding safety controls have been activated before the fire alarm.

Table 1 Requirements for ammonia (R717) refrigeration system detectors in recognized fishing vessel construction specifications

According to GBZ 1-2010 "Hygiene Standards for Industrial Enterprise Design", the alarm value of toxic substances should be set at least based on the toxicity of toxic gases and the actual situation on site, with alarm values and high alarm values. The predicted value is 1/2 of MAC or PC-STEL; The alarm value is the maximum allowable concentration (MAC) or PC-STEL; High alarm values should be set after considering various factors such as toxic gas toxicity, operator conditions, accident consequences, and process equipment. GBZ2.1 2019 "Occupational Exposure Limits for Hazardous Factors in the Workplace" specifies the allowable concentration of short-term exposure to ammonia (PC-STEL), which is 30mg/m within 15 minutes ³ (39.5ppm). Therefore, it is recommended that the first level alarm value in the ammonia refrigeration device alarm system of Chinese fishing vessels should not exceed 39.5ppm.

02

Emergency requirements for gas leakage

Workplaces that may contain or produce toxic substances should be equipped with on-site first aid supplies based on the physical and chemical characteristics and hazard characteristics of the toxic substances. Ventilation devices, water sprinkler equipment, emergency evacuation channels, emergency release, and protective signs should be installed.

Table 2 Emergency requirements for ammonia (R717) leakage in recognized fishing vessel construction specifications

At present, domestic fishing vessels only have various emergency and protection requirements for refrigeration rooms, but there are no corresponding requirements for quick freezing processing rooms and refrigerated fish cabins that are frequently used for fish product processing. In reality, these areas are high-risk areas for ammonia refrigerant leakage, and the corresponding emergency requirements also need to be clarified.

According to the emergency response requirements of the current industry standard HG/T 4686-2014 "Handling and Disposal Methods for Liquid Ammonia Leakage", in the event of a small amount of leakage, on-site ventilation should be carried out; When a large amount of leakage occurs, a water curtain wall should be established using a water source or fire water gun, sprayed with hydrochloric acid mist water, diluted, dissolved, and then drained or strongly ventilated. Therefore, ventilation devices should also be installed in refrigerated fish compartments and quick freezing processing rooms to clarify ventilation standards.

Due to the high affinity between ammonia and water, 1L of water can absorb approximately 560L of ammonia vapor at 0 ℃ and 1.3 bar. Once ammonia gas leakage occurs, the water spray system or water curtain plays an important role. Therefore, in addition to the refrigeration room, a water spray system should be installed on fishing boats, and water curtains should also be installed in all areas that may be involved in ammonia leakage, including refrigerated fish compartments and quick freezing processing rooms.

03

Filling of ammonia refrigerant

At present, apart from the requirements for the storage space of backup refrigerants, the regulations do not involve refrigerant refilling. When using backup refrigerant for filling, the anti leakage technology and measures of ammonia must also be given special attention. In addition to constructing and operating refrigeration systems in accordance with current regulations, considerations should also be given to leak prevention technology, personal protection, and safety procedures:

(1) Reasonably set up leakage collection devices in the filling pipeline, filling joints, and other parts;

(2) Provide personal protective equipment and disinfection facilities for refueling personnel to address the toxicity of ammonia refrigerants;

(3) Develop refrigerant filling procedures and guidelines for the refrigeration system, and post them at the filling point.

The refrigeration system of fishing boats is crucial for the storage and transportation of fish catch. In the process of using ammonia refrigerant, it is necessary to have a sense of awe, prevent human abuse, and establish confidence in correct and reasonable utilization. Ammonia should not be "demonized" and should not be consumed due to choking. Fishing vessels should apply for various inspections in accordance with regulations and specifications, hold valid fishing vessel certificates, and crew members should regularly maintain and upkeep the refrigeration system equipment in accordance with the requirements of the manufacturer to ensure the safe and reliable operation of the refrigeration system, especially the refrigeration compressor unit.

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