Analysis on the application of ammonia in fishing boat refrigeration system
Release time：2024-08-22click：2
The refrigeration system occupies an important position in fishing boats, especially in large-scale offshore and domestic fishing boats. The performance and effect of the refrigeration device seriously affects the preservation quality of the catch. The freezing processing capacity also determines the production capacity of the fishing boat, which directly affects the economic benefits of the fishing boat.
Refrigerant selection
The refrigeration system of fishing boats is complex, with technical requirements, quality requirements, and safety requirements. higher. The use of different refrigerants corresponds to different regulations and specification requirements. Unreasonable design and use will cause the system to not work properly. In the mild case, it will cause a lot of trouble in daily operation and management, reduce the work efficiency of the system, and in serious cases, it may cause explosions and fires. , leakage of toxic substances, etc., posing a great threat to the safety of fishing vessels and personnel.
01
Requirements related to international conventions/regulations
According to the "Technical Rules for Statutory Inspection of Distant Ocean Fishing Vessels (2019)" and the "Technical Rules for Statutory Inspection of Domestic Ocean Fishing Vessels (2019)", the refrigerants allowed to be used in my country's current technical regulations on ships (hereinafter referred to as the regulations) include:
(1)R717 ammonia (NH3);
(2)R22 Monochlorodifluoromethane (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 approved fishing vessel construction specifications (hereinafter referred to as the specifications) published by the China Maritime Safety Administration in accordance with the prescribed procedures, the refrigerants allowed to be used in the specifications are consistent with the regulations, but the new version of "Steel Ocean-going Fishing Vessels" "Construction Code (2021)" deletes R22 from the permitted refrigerants and adds some environmentally friendly refrigerants, including:
(1) R717: ammonia (NH3);
(2)R134a: Tetrafluoroethane (CH2FCF3);
(3)R404A: R125(44%)+R143a(52% )+R134a(4%) mixture. R125 is pentafluoroethylenealkane (CHF2CF3), R143a is trifluoroethane (CH3CF3), and R134a is tetrafluoroethane (CH2FCF3).
(4) R507A: a mixture of R125 (50%) + 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 monochlorodifluoromethane (CHClF2) belongs to hydrochlorofluorocarbons. Since Freon refrigerants seriously damage the atmospheric ozone layer, it has been completely eliminated internationally. The ban on ozone-depleting substances has gradually restricted the use of hydrochlorofluorocarbon refrigerants, and R22 is about to be phased out globally. Annex VI of the International Convention for the Prevention of Pollution from Ships, "Regulations on the Prevention of Air Pollution from Ships," also imposes greater restrictions on the use of ozone-depleting refrigerants by ocean vessels.
Chapter 5 of Part 15 of the "Technical Rules for Statutory Inspection of Distant Ocean Fishing Vessels" (2019) and the "Technical Rules for Statutory Inspection of Domestic Ocean Fishing Vessels (2019)" have the following requirements:
The use of devices containing ozone-depleting substances (other than hydrochlorofluorocarbons) shall be prohibited under the following circumstances:
(1) On May 19, 2005 For fishing vessels built on or after May 19, 2005; (2) For fishing vessels built before May 19, 2005, the equipment contract delivery date on board is May 19, 2005 or after, or There is no contract delivery date, the date of actual equipment delivery on board is May 19, 2005 or later.
The use of hydrochlorofluorocarbon-containing devices shall be prohibited under the following circumstances:
(1) On or after January 1, 2020 Fishing vessels built;
(2) For fishing vessels built before January 1, 2020, the equipment contract delivery date on board is January 1, 2020 or later, or there is no contract delivery Date, the date of actual equipment delivery on board is January 1, 2020 or later.
Therefore, existing offshore fisheriesIf the refrigeration equipment already installed on ships (400 gross tonnage and above) uses refrigerant R22, it can continue to be used, but it should be ensured that matters related to use, repair, maintenance, and consumption of hydrochlorofluorocarbons (HCFCs) are listed in the "Ozone Depleting Substances" "Record Book" and keep it on board;
For existing offshore fishing vessels and domestic fishing vessels, if the vessel's refrigeration system is charged after natural consumption, January 1, 2020 should be used Stocks of refrigerants that have been produced recently (that is, it is prohibited to continue to purchase refrigerants such as hydrochlorofluorocarbons (HCFCs) produced after January 1, 2020).
02
Refrigerant application trends
Environment and energy issues are the two major issues facing mankind today, and ozone layer depletion and global warming 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, bringing hydrofluorocarbons into the scope of control and opening up a new era of coordinated response to ozone layer depletion and climate change. Chapter. In 2021, our country officially accepted the "Kigali Amendment" and took effect. According to the requirements of the "Kigali Amendment", our country needs to freeze the production and consumption of hydrofluorocarbons at the baseline level in 2024. From 2029 Begin to phase out HFC production and consumption. Therefore, our country also tends to choose more environmentally friendly refrigerants in fishing vessel refrigeration systems in terms of regulations (Figure 1 and Figure 2).
Figure 1 Comparison of ozone depletion potential (ODP) of refrigerants permitted in regulations and specifications
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Figure 2 Comparison of global warming potential (GWP) of refrigerants permitted in regulations
Through Figure 1 and Figure 2 A comparison of the ozone depleting potential (ODP) and global warming potential (GWP) of several commonly used refrigerants shows that ammonia refrigerant (R717) is the most environmentally friendly and is not destructive to the natural environment.
03
Characteristics of ammonia (R717) refrigerant < /div>
Ammonia is a natural medium-temperature refrigerant because of its excellent thermophysical properties, high refrigeration efficiency and lowDue to its low price and green environmental protection, it is favored by the industrial refrigeration and refrigeration field.
The advantages of ammonia are:
(1) The standard boiling point is low (33.3℃), the critical temperature is high (132.5℃), and it can be used for work Wide range, moderate pressure in normal and ordinary low temperature range;
(2) Large cooling capacity per unit volume, large latent heat of vaporization, small throttling loss, good heat transfer performance, refrigeration system heat pump The circulation performance coefficient is high;
(3) It has strong water absorption, which can prevent "ice blockage" of pipelines;
(4) And lubricating oil Basically insoluble in each other, and lighter than oil, it is easy to drain oil from the system;
(5) Cheap and easy to prepare;
(6) High chemical and thermal stability at normal and low temperatures;
(7) It has a pungent odor and is easily detected once it leaks. When the air contains 20ppm ammonia, the human sense of smell is It can be distinguished and protective measures can be taken in time before reaching dangerous concentrations;
(8) Does not destroy the ozone layer and has no greenhouse effect.
The disadvantages of ammonia are:
(1) Toxic and volatile - harmful to human mucosal tissues (such as eyes, nose, pharynx and lungs, etc.) parts) has a strong irritating effect. When its volume content in the air reaches more than 1,700 ppm, people will be poisoned or even die if they stay in it for 30 minutes. If there is leakage, it will also contaminate food or products;
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(2) Flammable and explosive - when the volume concentration of ammonia in the air reaches 11%~14%, it can ignite (ignition point 651℃), when the volume concentration reaches 15.7%~27.4%, it encounters an open flame May cause explosion.
The safe application of ammonia in refrigeration systems
In view of the friendliness of ammonia to the natural environment, Chinese fishery experts advocate Promote ammonia as a refrigerant in fishing vessel refrigeration systems. "Code for the Construction of Steel Marine Fishing Vessels (2015)" cancels "For fishing vessels in limited navigation areas, if the total capacity of the refrigerated fish holds is less than 500m³, a discharge pipe cooling system with direct ammonia evaporation may be used."The restrictions allow ammonia refrigerant direct evaporative refrigeration to be applied to any tank volume. The scope of application of ammonia refrigerants on fishing vessels has been expanded.
When refrigeration systems are used on ships, safety is the primary consideration. Due to the toxic and explosive properties of ammonia, some fishing vessels are reluctant to use ammonia as a refrigerant. If the characteristics of refrigerants can be correctly understood during design and construction, reasonable and reliable system solutions can be designed, regular maintenance and upkeep can be carried out during ship operation, and relevant operators on board can receive corresponding training and abide by operating procedures, then the use of natural refrigeration such as ammonia can The risk of the agent will be greatly reduced.
The requirements for refrigeration systems in the current "Technical Rules for Statutory Inspection of Distant Ocean Fishing Vessels" (2019) and "Technical Rules for Statutory Inspection of Domestic Ocean Fishing Vessels (2019)" mainly involve the safety control of refrigeration equipment, The cabin's airtight separation, ventilation settings, water spray system, leakage alarm device, fire-fighting equipment, operating procedure guide implementation, etc., the specific ammonia refrigeration compressor room and ammonia leakage monitoring and alarm system respectively pointed to the China Maritime Safety Administration in accordance with regulations The procedure publishes the relevant requirements of the approved (approved) "Code for the Construction of Steel Domestic Ocean Fishing Vessels" and the "Code for the Construction of Steel Domestic Ocean Fishing Vessels".
01
Gas detection and alarm settings< br />
Gas detection is mainly aimed at toxicity, not deflagration, because toxicity alarms and corresponding safety controls have been activated before the fire alarm.
Table 1 Requirements for ammonia (R717) refrigeration system detectors in approved fishing vessel construction regulations
GBZ 1-2010 "Hygienic Standards for Design of Industrial Enterprises" stipulates that the poison alarm value should be at least an alarm value and a high alarm value based on the toxicity of toxic gases and the actual situation on site. The forecast value is 1/2 of MAC or PC-STEL; the alarm value is the maximum allowable concentration (MAC) or PC-STEL; the high alarm value should comprehensively consider various factors such as toxic gas toxicity, operator conditions, accident consequences, and process equipment. Set later. GBZ2.1 2019 "Occupational Exposure Limits for Hazardous Factors in the Workplace - Chemical Hazardous Factors" stipulates the allowable concentration of ammonia for short-term exposure (PC-STEL), that is, the allowable concentration within 15 minutes is 30mg/m³ (39.5ppm). Therefore, it is recommended that the level 1 alarm value in the ammonia refrigeration device alarm system of fishing boats in my country should not exceed 39.5ppm.
02
Emergency requirements for gas leaks
Workplaces where toxic substances may exist or be produced should be equipped with on-site first aid supplies, ventilation devices, water spray equipment, emergency evacuation channels, emergency releases, and protective signs based on the physical and chemical properties and hazard characteristics of toxic substances.
Table 2 Emergency requirements for ammonia (R717) leakage in approved fishing vessel construction regulations
Domestic fishing vessels At present, emergency and protection requirements are only put forward for the refrigeration machine room, but there are no corresponding requirements for quick-frozen processing rooms and refrigerated fish tanks where people often process fish products. In fact, these places are at high risk of ammonia refrigerant leakage. For each region, the corresponding emergency requirements also need to be clarified.
According to the emergency response requirements for leaks in the current industry standard HG/T 4686-2014 "Methods for Treatment and Disposal of Liquid Ammonia Leakage", when a small leakage occurs, on-site ventilation should be provided; when a large leakage occurs, Use water sources or fire hoses to build a water curtain wall, spray mist water containing hydrochloric acid to neutralize, dilute and dissolve, and then exhaust or forcefully ventilate. Therefore, ventilation devices should also be installed in refrigerated fish holds and quick-frozen processing rooms, and ventilation standards should be clarified.
Because ammonia has a very high affinity with water, at 0°C and 1.3 bar, 1L of water can absorb approximately 560L of ammonia vapor. Once ammonia gas leaks, the water spray system or water curtain plays an important role. Therefore, in addition to the refrigerator room, a water spray system should be installed on the fishing boat. It should also be installed in all areas including the refrigerated fish hold and quick-frozen processing room. Provide water curtains in areas that may be involved in ammonia leaks.
03
Filling of ammonia refrigerant
In addition to the requirements for the storage space of backup refrigerant, the current regulations and specifications do not involve refrigerant refilling. When using backup refrigerant for filling, ammonia leakage prevention technology and measures must also be focused on. In addition to constructing and operating the refrigeration system in accordance with current regulations and specifications, leak prevention technology, personal protection and safety procedures should also be considered:
(1) Filling pipeline, filling Reasonable installation of leakage collection devices at joints and other parts;
(2)In view of the toxicity of ammonia refrigerant, equip filling personnel with personal protective equipment and decontamination facilities;
(3) Formulate refrigerant filling procedures and guidelines for the refrigeration system and post them at the filling station .
The refrigeration system of fishing boats is crucial to the storage and transportation of catches. In the process of using ammonia refrigerant, we must not only have a sense of awe and prevent human abuse, but also establish confidence in its correct and reasonable use. We must not "demonize" ammonia and give up eating it because of choking. Fishing vessels should apply for various inspections in accordance with laws and regulations and hold valid fishing vessel certificates. Crew members should follow the requirements of the refrigeration system equipment manufacturer for regular maintenance and upkeep to ensure the safe and reliable operation of the refrigeration system, especially the refrigeration compressor unit.
References:
[1] Alexander Cohr PACHAI, Qi Xiaoxia, Xi Ye, Xu Xiaojiao. Safety design and maintenance analysis of ammonia refrigeration system [J ]. Refrigeration Technology. 2014, 6
[2] Huang Jian. Analysis of ammonia concentration alarm limit in ship ammonia refrigeration engine room [J]. China Water Transport, 2021(10):42- 44
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