Industry News
Location:Home > NEWS > Industry News >Cold Storage And Refrigeration Industry
Type：Industry News
Date：2017-10-13 15:50:30
Cold Storage And Refrigeration Industry
India is the largest producer of fruits and second largest producer of vegetables in the world. In spite of that per capita availability of fruits and vegetables is quite low because of post harvest losses which account for about 25% to 30% of production. Besides, quality of a sizable quantity of products also deteriorates by the time it reaches the consumer...
Cooling effect has been known from the origin of human life. But the implementation came into practice later. Jacob Perkins built the first Vapour Compression Refrigeration system (VCR) in the world, which was a closed cycle. The first VCR system which was commercialised and built by James Harrison, a British journalist in 1856 – whose patent was VCR using ether, alcohol, or ammonia. The first gas absorption refrigeration system using gaseous ammonia dissolved in water was developed by Ferdinand Carre of France in 1859. But it was comparatively costlier and not widely used. Cold Storage is a special kind of room, the temperature of which is kept very low with the help of refrigerating machines and precision instruments. One of such a room or cold storage has been shown in figure 1. This is based on the principle of refrigeration and air conditioning. The cold storage is specially designed and built with concrete, stone and cement to prevent the leakage. Its walls, floors and ceilings are insulated with low thermal conductivity materials.
Need of cold storage
India is the largest producer of fruits and second largest producer of vegetables in the world. In spite of that per capita availability of fruits and vegetables is quite low because of post harvest losses that account for about 25 to 30% of production. Besides, quality of a sizable quantity of products also deteriorates by the time it reaches the consumer. This is mainly because of perishable nature of the products, which require a cold chain arrangement to maintain the quality and extend the shelf life if consumption is not meant immediately after harvest. In the absence of a cold storage and related cold chain facilities, the farmers are being forced to sell their products immediately after harvest, which results in glut situations and low price realisation. Cooling of the harvested product controls the rate of quality loss by slowing down the rate of respiration. The cooler the temperature, the slower is the deterioration and longer is the storage life. Some products like beverages taste good when they are cooled. Use of refrigeration is not limited to food items.
Cold storages are essential for extending the shelf life, period of marketing, avoiding glut, reducing transport bottlenecks during peak period of production and maintenance of quality of produce. The development of cold storage industry has therefore an important role to play in reducing the wastages of the perishable commodities and thus providing remunerative prices to the growers. The optimum temperatures for storing some common foods are given in table 1. The desired temperature and humidity levels for different commodities are listed in table 2.
Major challenges faced by cold storages in India
India has a huge potential to produce different kinds of commodities such as potatoes, vegetables, fruits, meat, fish and dairy products. Unfortunately, these cannot be stored in sufficient amount for the use during the unproductive period of a particular commodity due to lack of perseveration at desired temperature and humidity conditions. In other words, India does not have required quantity of cold storages in operational condition. The main problems with these are as follows:
The major issue faced by cold storage facility providers is power supply. Insufficient and irregular power supply causes problem for the operators, and hence disturbs the entire cold chain.
Availability of skilled human resources is a big challenge in Indian cold storage industry.
rising real estate cost is a real barrier for the development of the cold storage facilty. A fully integrated cold storage facility of international standards, with one million cubic feet of storage space will require an area of approximately an acre, which is a huge investment.
Cooling units are not mobile units, so the location of such units becomes a key constraint as there are very few parcels of large land spaces available in India.
The cold storages present in India can cater to single commodity only. Different commodities require different temperature conditions, resulting in poor capacity utilisation and low financial viability.
The Government of India is one of the driving forces in developing the cold-chain industry – and supports private participation through various subsidy schemes and grants. The national policy aims to increase the percentage of food being processed in the country to 25% by 2025.
Types of cold storages
Cold storages can be classified into different categories depending upon the controlling parameters inside the storage room. They are as follows:
Control atmosphere cold storage: Control atmosphere cold storage mainly used for long-term storage of perishable fruits. In this type of cold storage, apart from temperature, concentrations of oxygen, carbon dioxide, ethylene and nitrogen are maintained as per the requirement of the storage materials. These are mainly used for the storage of apples, pears, lemon, litchi, mango and other perishable fruits.
Temperature controlled cold storage: This type of cold storage is mainly used for storage of grains, dry fruits and spices. In this type of storage constant pre-determined temperature is maintained throughout the room.
High humidity cold storage: This type of cold storage is mainly used for storage of fresh vegetables. In this type of storage, constant pre-determined temperature with high humidity is maintained throughout the room. Apart from temperature and humidity, carbon dioxide and air circulations within the products are maintained automatically.
Methods to produce low temperatures
The various principles and processes involved in the production of low temperatures are dry ice refrigeration, air refrigeration, evaporative cooling, thermoelectric cooling and Vapour Compression Refrigeration (VCR) System. VCR is the most widely used refrigeration system suitable for the production of low temperature needed for cold storages.
Vapour Compression Refrigeration (VCR) System
The VCR works on Clausius statement of second law of thermodynamics. According to Clausius statement one needs to put extra energy in order to transfer heat from low temperature body to high temperature body. This energy is given in the form of compressor work. The main components of a VCR system are compressor, condenser, receiver, expansion valve, evaporator and blower. The schematic diagram of the system in the simplified form has been shown in figure 2.
Compressor compresses vaporised refrigerant to high temperature and pressure to increase its saturation temperature point. The condenser then desuperheat and liquefies the vapour refrigerant. Thus heat is rejected in the condenser from the refrigerant to the atmosphere or circulating water. The condensate from the condenser is collected in the reservoir and allowed to pass though expansion valve where its pressure and temperature decreases. The low pressure liquid refrigerant then passes through the refrigerated space where it gets evaporated by absorbing heat from the air and the air gets cooled. Blower circulates the chilled air to the cold storage where different fruits and vegetables are kept. Refrigerant is the working fluid used in VCR system which absorbs and rejects heat alternatively in the evaporator and condenser respectively. The first refrigerant used was ether. Later on sulphur dioxide, R-12 and R-22 came into picture. Some of the common refrigerants used for modern day refrigeration system are NH3, R134a and R123.
Cooling load calculation
The first step in designing any cold storage or air conditioning system is to correctly calculate the cooling heat i.e., the heat to be removed in unit time. There are several equations and also empirical relations used to evaluate it. Different heat loads are classified and can be calculated using the following equations.
Structural heat leakage load: The cooling load due to the structural heat leakage was determined from heat transferred through the walls, roof and floor. The space heat gain through roof or walls exposed to solar radiation can be determined following ASHRAE hand book as:
The values of different coefficients such as bi, ci and di, and the overall heat transfer coefficients are available in ASHRAE handbook for 42 different representative roof assemblies and 41 different wall assemblies having widely varying components. The actual overall heat transfer coefficient of a roof or a wall is calculated as:
The cooling load due to conduction or space heat gain through cold storage building structure is given as:
The average daily structural heat load can be calculated from the following equation:
Product Load: The product load consists of sensible heat to reduce the temperature of product from the initial value to storage temperature and heat of respiration of the product. The product load on a particular day can be estimated using the following relation:
Infiltration heat gain: The walls, roof and floor of the cold store are considered to be air tight. Outside air infiltration is only limited to opening and closing of the doors during loading period. Based on the above said assumptions, the infiltration heat load can be calculated from the following correlation:
Load due to condensation and freezing of moisture on cooling coil
The moisture that is lost from products like vegetables and that entered with infiltrated air reaches the evaporator coil, condenses and freezes thereon. It can be assumed that half of the condensed moisture is converted into ice. This load can be obtained as:
Load due to fans, lights and human beings: The heat load due to lights and human beings occurred only during the loading time in a day. However, the fans liberate the heat throughout the day due to their continuous operation. The cooling load from lights, fans and human beings are calculated from the relation given in ASHRAE handbook as:
The total cooling load due to all components can be computed from the summation of all the individual components as given by equations (1-8).
Advanced refrigeration technology
Intense research is on for past several decades only targeting to develop refrigeration systems with better operating characteristics, improved energy efficiency and low power consumption. Systems that can run on low grade thermal energy such as cheaply available waste heat from nearby process industries are under intense improvement phase. Researchers and scientists are trying to implement the following refrigeration systems in cold storages.
NH3/CO2 cascade system
In such systems ammonia and carbon dioxide are employed as refrigerants in two different refrigeration cycles. The schematic diagram of such system has been shown in figure 3. Such systems are still in development stage – and newly introduced design instillations are under trial around the globe. The amount of ammonia charge is very low and safety problems are considerably reduced as ammonia circuit is not in direct contact with the cold room. At the other hand, carbon dioxide is harmless for most edibles as it is non-toxic, odorless and non-inflammable. The energy consumption by such a system is less compared to conventionally employed units. These systems are the most promising development for future.
Ammonia Absorption Refrigeration Plants (AARP)
At fundamental level, in such a unit, instead of employing a compressor unit NH3 vapours are caused to be absorbed by weak solution (changing it to strong solution), which is then pumped to high pressure side. such systems are designed to run mostly on heat energy and can therefore, very easily operate on thermal energy sources like waste
steam, hot water, superheated water, hot oil, direct heating, engine/gas turbine/furnace exhaust and low pressure steam from steam turbine exhaust.
AARP systems are now also available with 2-stage units. The schematic diagram of AARP refrigeration plant used for cold storage application has been shown in figure 4. Cold storages based on AARP have definitely some advantages. The total electricity requirement reduces substantially. Only small DG set is adequate for auxiliary power needs of cold storage.
The bio-mass and other agro-fuels which are available locally can be used to derive AARP. The operating cost and maintenance cost of the cold storage is very low. The cold storage can store wide range of products at different temperatures due to versatile AARP. Any other simultaneous refrigeration load such as ice plant and milk chiller can also be met with the same plant.
Solar photovoltaic applications
Solar photovoltaic cells directly convert sunlight into electricity. Incorporation of photovoltaic solar cells for generation of electricity for running cold storage appliances (Fig. 5) including compressors is keenly awaited. As the technology available now, monocrystalline cells offer 14 to 20% conversion efficiency, close to these are the poly or multicrystalline cells with 10 to 12% conversion efficiency. Cheaper and better technology can certainly change the very face of cold storage industry. Ecozen recently designed a pioneering and innovative micro-cold storage product that is powered by solar energy. In India alone, 10 million tons of cold storage capacity is required to prevent the over 30% wastage of perishable products. The product primarily designed for the rural segment serves their needs ideally, as it does not depend on grid electricity and after a 2-year breakeven, leads to over 40% increase in their profits. This innovative product can be suitably adapted for local conditions across the world.
Modular cold storage
Modular cold storage is a relatively new concept, and it can be considered as walk-in refrigeration warehouse plant with various standard dimension sizes. The storage capacity of the modular walk in cooler and modular walk in freezer specified or selected according to customer's requirements. One such a modular cold storage has been shown in figure 6.
The storage temperature of the walk-in cold storage room is displayed and controlled by digital thermostat for precise temperature control and temperature adjustment to achieve the utmost energy efficiency and perfect storage of food.
India is the largest producer of fruits and second largest producer of vegetables in the world. In spite of that per capita availability of fruits and vegetables is quite low because of post harvest losses which account for about 25% to 30% of production. Besides, quality of a sizable quantity of products also deteriorates by the time it reaches the consumer...
Cooling effect has been known from the origin of human life. But the implementation came into practice later. Jacob Perkins built the first Vapour Compression Refrigeration system (VCR) in the world, which was a closed cycle. The first VCR system which was commercialised and built by James Harrison, a British journalist in 1856 – whose patent was VCR using ether, alcohol, or ammonia. The first gas absorption refrigeration system using gaseous ammonia dissolved in water was developed by Ferdinand Carre of France in 1859. But it was comparatively costlier and not widely used. Cold Storage is a special kind of room, the temperature of which is kept very low with the help of refrigerating machines and precision instruments. One of such a room or cold storage has been shown in figure 1. This is based on the principle of refrigeration and air conditioning. The cold storage is specially designed and built with concrete, stone and cement to prevent the leakage. Its walls, floors and ceilings are insulated with low thermal conductivity materials.
Need of cold storage
India is the largest producer of fruits and second largest producer of vegetables in the world. In spite of that per capita availability of fruits and vegetables is quite low because of post harvest losses that account for about 25 to 30% of production. Besides, quality of a sizable quantity of products also deteriorates by the time it reaches the consumer. This is mainly because of perishable nature of the products, which require a cold chain arrangement to maintain the quality and extend the shelf life if consumption is not meant immediately after harvest. In the absence of a cold storage and related cold chain facilities, the farmers are being forced to sell their products immediately after harvest, which results in glut situations and low price realisation. Cooling of the harvested product controls the rate of quality loss by slowing down the rate of respiration. The cooler the temperature, the slower is the deterioration and longer is the storage life. Some products like beverages taste good when they are cooled. Use of refrigeration is not limited to food items.
Cold storages are essential for extending the shelf life, period of marketing, avoiding glut, reducing transport bottlenecks during peak period of production and maintenance of quality of produce. The development of cold storage industry has therefore an important role to play in reducing the wastages of the perishable commodities and thus providing remunerative prices to the growers. The optimum temperatures for storing some common foods are given in table 1. The desired temperature and humidity levels for different commodities are listed in table 2.
Major challenges faced by cold storages in India
India has a huge potential to produce different kinds of commodities such as potatoes, vegetables, fruits, meat, fish and dairy products. Unfortunately, these cannot be stored in sufficient amount for the use during the unproductive period of a particular commodity due to lack of perseveration at desired temperature and humidity conditions. In other words, India does not have required quantity of cold storages in operational condition. The main problems with these are as follows:
The major issue faced by cold storage facility providers is power supply. Insufficient and irregular power supply causes problem for the operators, and hence disturbs the entire cold chain.
Availability of skilled human resources is a big challenge in Indian cold storage industry.
rising real estate cost is a real barrier for the development of the cold storage facilty. A fully integrated cold storage facility of international standards, with one million cubic feet of storage space will require an area of approximately an acre, which is a huge investment.
Cooling units are not mobile units, so the location of such units becomes a key constraint as there are very few parcels of large land spaces available in India.
The cold storages present in India can cater to single commodity only. Different commodities require different temperature conditions, resulting in poor capacity utilisation and low financial viability.
The Government of India is one of the driving forces in developing the cold-chain industry – and supports private participation through various subsidy schemes and grants. The national policy aims to increase the percentage of food being processed in the country to 25% by 2025.
Types of cold storages
Cold storages can be classified into different categories depending upon the controlling parameters inside the storage room. They are as follows:
Control atmosphere cold storage: Control atmosphere cold storage mainly used for long-term storage of perishable fruits. In this type of cold storage, apart from temperature, concentrations of oxygen, carbon dioxide, ethylene and nitrogen are maintained as per the requirement of the storage materials. These are mainly used for the storage of apples, pears, lemon, litchi, mango and other perishable fruits.
Temperature controlled cold storage: This type of cold storage is mainly used for storage of grains, dry fruits and spices. In this type of storage constant pre-determined temperature is maintained throughout the room.
High humidity cold storage: This type of cold storage is mainly used for storage of fresh vegetables. In this type of storage, constant pre-determined temperature with high humidity is maintained throughout the room. Apart from temperature and humidity, carbon dioxide and air circulations within the products are maintained automatically.
Methods to produce low temperatures
The various principles and processes involved in the production of low temperatures are dry ice refrigeration, air refrigeration, evaporative cooling, thermoelectric cooling and Vapour Compression Refrigeration (VCR) System. VCR is the most widely used refrigeration system suitable for the production of low temperature needed for cold storages.
Vapour Compression Refrigeration (VCR) System
The VCR works on Clausius statement of second law of thermodynamics. According to Clausius statement one needs to put extra energy in order to transfer heat from low temperature body to high temperature body. This energy is given in the form of compressor work. The main components of a VCR system are compressor, condenser, receiver, expansion valve, evaporator and blower. The schematic diagram of the system in the simplified form has been shown in figure 2.
Compressor compresses vaporised refrigerant to high temperature and pressure to increase its saturation temperature point. The condenser then desuperheat and liquefies the vapour refrigerant. Thus heat is rejected in the condenser from the refrigerant to the atmosphere or circulating water. The condensate from the condenser is collected in the reservoir and allowed to pass though expansion valve where its pressure and temperature decreases. The low pressure liquid refrigerant then passes through the refrigerated space where it gets evaporated by absorbing heat from the air and the air gets cooled. Blower circulates the chilled air to the cold storage where different fruits and vegetables are kept. Refrigerant is the working fluid used in VCR system which absorbs and rejects heat alternatively in the evaporator and condenser respectively. The first refrigerant used was ether. Later on sulphur dioxide, R-12 and R-22 came into picture. Some of the common refrigerants used for modern day refrigeration system are NH3, R134a and R123.
Cooling load calculation
The first step in designing any cold storage or air conditioning system is to correctly calculate the cooling heat i.e., the heat to be removed in unit time. There are several equations and also empirical relations used to evaluate it. Different heat loads are classified and can be calculated using the following equations.
Structural heat leakage load: The cooling load due to the structural heat leakage was determined from heat transferred through the walls, roof and floor. The space heat gain through roof or walls exposed to solar radiation can be determined following ASHRAE hand book as:
The values of different coefficients such as bi, ci and di, and the overall heat transfer coefficients are available in ASHRAE handbook for 42 different representative roof assemblies and 41 different wall assemblies having widely varying components. The actual overall heat transfer coefficient of a roof or a wall is calculated as:
The cooling load due to conduction or space heat gain through cold storage building structure is given as:
The average daily structural heat load can be calculated from the following equation:
Product Load: The product load consists of sensible heat to reduce the temperature of product from the initial value to storage temperature and heat of respiration of the product. The product load on a particular day can be estimated using the following relation:
Infiltration heat gain: The walls, roof and floor of the cold store are considered to be air tight. Outside air infiltration is only limited to opening and closing of the doors during loading period. Based on the above said assumptions, the infiltration heat load can be calculated from the following correlation:
Load due to condensation and freezing of moisture on cooling coil
The moisture that is lost from products like vegetables and that entered with infiltrated air reaches the evaporator coil, condenses and freezes thereon. It can be assumed that half of the condensed moisture is converted into ice. This load can be obtained as:
Load due to fans, lights and human beings: The heat load due to lights and human beings occurred only during the loading time in a day. However, the fans liberate the heat throughout the day due to their continuous operation. The cooling load from lights, fans and human beings are calculated from the relation given in ASHRAE handbook as:
The total cooling load due to all components can be computed from the summation of all the individual components as given by equations (1-8).
Advanced refrigeration technology
Intense research is on for past several decades only targeting to develop refrigeration systems with better operating characteristics, improved energy efficiency and low power consumption. Systems that can run on low grade thermal energy such as cheaply available waste heat from nearby process industries are under intense improvement phase. Researchers and scientists are trying to implement the following refrigeration systems in cold storages.
NH3/CO2 cascade system
In such systems ammonia and carbon dioxide are employed as refrigerants in two different refrigeration cycles. The schematic diagram of such system has been shown in figure 3. Such systems are still in development stage – and newly introduced design instillations are under trial around the globe. The amount of ammonia charge is very low and safety problems are considerably reduced as ammonia circuit is not in direct contact with the cold room. At the other hand, carbon dioxide is harmless for most edibles as it is non-toxic, odorless and non-inflammable. The energy consumption by such a system is less compared to conventionally employed units. These systems are the most promising development for future.
Ammonia Absorption Refrigeration Plants (AARP)
At fundamental level, in such a unit, instead of employing a compressor unit NH3 vapours are caused to be absorbed by weak solution (changing it to strong solution), which is then pumped to high pressure side. such systems are designed to run mostly on heat energy and can therefore, very easily operate on thermal energy sources like waste
steam, hot water, superheated water, hot oil, direct heating, engine/gas turbine/furnace exhaust and low pressure steam from steam turbine exhaust.
AARP systems are now also available with 2-stage units. The schematic diagram of AARP refrigeration plant used for cold storage application has been shown in figure 4. Cold storages based on AARP have definitely some advantages. The total electricity requirement reduces substantially. Only small DG set is adequate for auxiliary power needs of cold storage.
The bio-mass and other agro-fuels which are available locally can be used to derive AARP. The operating cost and maintenance cost of the cold storage is very low. The cold storage can store wide range of products at different temperatures due to versatile AARP. Any other simultaneous refrigeration load such as ice plant and milk chiller can also be met with the same plant.
Solar photovoltaic applications
Solar photovoltaic cells directly convert sunlight into electricity. Incorporation of photovoltaic solar cells for generation of electricity for running cold storage appliances (Fig. 5) including compressors is keenly awaited. As the technology available now, monocrystalline cells offer 14 to 20% conversion efficiency, close to these are the poly or multicrystalline cells with 10 to 12% conversion efficiency. Cheaper and better technology can certainly change the very face of cold storage industry. Ecozen recently designed a pioneering and innovative micro-cold storage product that is powered by solar energy. In India alone, 10 million tons of cold storage capacity is required to prevent the over 30% wastage of perishable products. The product primarily designed for the rural segment serves their needs ideally, as it does not depend on grid electricity and after a 2-year breakeven, leads to over 40% increase in their profits. This innovative product can be suitably adapted for local conditions across the world.
Modular cold storage
Modular cold storage is a relatively new concept, and it can be considered as walk-in refrigeration warehouse plant with various standard dimension sizes. The storage capacity of the modular walk in cooler and modular walk in freezer specified or selected according to customer's requirements. One such a modular cold storage has been shown in figure 6.
The storage temperature of the walk-in cold storage room is displayed and controlled by digital thermostat for precise temperature control and temperature adjustment to achieve the utmost energy efficiency and perfect storage of food.
1
Copyright © Taizhou Cheng Shunrefrigeration equipment Co., Ltd. All Rights Reserved. Support：tyj1188.com