Horticultural crops are being grown in the Punjab State in about 2.69 lakh hectares area with an annual production of 51.48 lakh tonnes. The fruits and vegetables occupy an area of 70 thousand hectare and 172 thousand hectare respectively with an annual production of 14 lakh Mt of fruits and 36 lakh Mt of vegetables.
The government sees horticulture as a means of agricultural diversification, which not only promotes efficiency in land use, but also creates opportunities for employment –particularly for youth and woman in rural areas. However, the horticultural crops are highly perishable in nature and approximately one-third of these valueable produce goes waste annually during postharvest operations due to lack of adequate postharvest infrastructure and awareness about postharvest handling practices.
Causes of postharvest losses
1- Lack of awareness about post handling practices
2- Gaps in cold chain like poor infrastructure
3-Insufficient cold storage capacity (mostly storages are meant for potatoes). The high humidity and
temperature controlled storage for fruits and vegetables are lacking
Poor transportation and marketing infrastructure etc.
Enough attention has been paid at the pre-harvest stage for boosting up the levels of production by techniques like crop rotation, soil conservation, pest control, fertilizers, irrigation etc. But, post harvest issues have been addressed inadequately. In order to develop suitable handling practices for horticultural produce, it is important to give more focus on creation of postharvest infrastructure, integrated pack houses and cold storages especially for fruits and vegetables.
Status of cold stores in Punjab: In Punjab there are about 550 cold stores having about 19 million ton capacity. Out of which 133 cold stores of 4.53 lakh MT capacity and ripening chambers with 2769 MT capacity are established with the financial assistance from NHM (Details provided by Directorate of Horticulture, Punjab is enclosed in Annexure 1). A good number of cold store owners have established excellent stores with good civil structure, proper design and technology. These stores have efficient refrigeration machinery, proper condensing units, control valve, proper insulation, VFD for electricity management etc. These stores also have sorting and grading lines.
Ripening chambers: All ripening chambers in different districts of Punjab are working satisfactorily and following the ripening technologies as recommended by FSSAI. The bananas are being ripened with ethylene gas. Now some of the entrepreneurs are also ripening papayas with the same technology. The entrepreneurs have understood the importance and usefulness of ethylene based ripening system. This practice will certainly help in checking the use of calcium carbide for ripening of fruits.
Technical details about cold storage infrastructure in Punjab
Types of machinery and technology being used in cold stores:
Cold storage types and infrastructure: There are following types of cold storages being used in Punjab
1-Bunker type cold storage having brick wall with polystyrene insulation. (Older units, not visited personally but had interaction with the owners at the office
of DDH).
2-Fin coil cold storage having brick wall with polystyrene insulation (few also using PUF insulation)
3-Pre-fabricated cold storage (Walk in type, basically for Ripening Chambers).
Civil work: Two types of building are constructed depending on the external environmental temperature and product type. It is double wall having 4 to 6 inch gap between two walls or single wall having 9 inch thickness.
Insulation: The insulating material that was used is Expanded Poly-Styrene (EPS) having a thickness of 4 to 6 inches. A recent development in insulating material is Poly-Urethane Foam (PUF). The later is 4 to 6 times efficient than the former.
Refrigeration system: Two types of refrigeration systems are used depending on product type and cold storage area.
Figure: Interaction with the cold store owners at office of Deputy Director Horticulture…
Ammonia based system: This type of system is mainly installed by Frick India. However, there were systems installed by lesser known players or by local companies also. Some cold store owners have pointed out sale services and spare parts are problems.
Freon/R-22/R 132/R404/R441/ based system: There were few such systems being used for cold storage purposes. Usually the application of this type of technology is limited to Ripening Chambers only. This type of system requires high initial cost and highly skilled operators for smooth operation.
Bunker type vs fin coil technology: Potato cold storages working with ammonia refrigerant traditionally has been using ceiling coils – popularly known as bunker coils as evaporators for cooling the produce and claimed to consume less energy without sacrificing the quality of the stored produce, compared to forced draft air coolers (fin coil units) currently being recommended. The cooling process in Bunker System depends on the network of piping through which liquid ammonia circulates, served with a flooded accumulator and a hand expansion valve at the inlet. The pipe normally used is 32 mm NB, black heavy plain ended steel pipe. Every ton of refrigeration requires approximately 300 ft of pipe, or in layman’s language each bag of 50 kg needs 4.5 inch long 32 NB pipe. For example, the standard practice is to use, for a 1500 ton potato cold storage room, 9000 ft plain pipe with primary surface area of 2943 sq ft and 20 ceiling fans of 75W each with 3 blades, to provide gentle air circulation.
In case fin coil coolers are used, normally 4 air coolers each of 9 to 10 TR capacity are used for each cold room storing 1250-1500 ton potatoes; each cooler has an approximate surface area of 2270 sq ft comprising of 191.5 sq ft bare tube area and 2078.5 sq ft fin area.
Advantage of fin coil evaporators
• They are compact and occupy less space, thus more quantity of product can be stored within the same volume.
• They are factory manufactured with the latest technologies, thus their quality is superior to site-fabricated coils.
• Stainless tube with aluminium fin technology used in modern air coolers prevents rusting due to moisture, which is always present in cold rooms, and makes the coolers much lighter.
• Defrosting is much easier and faster, but more frequent compared to ceiling coils
• Fans can be provided with VFDs to reduce power consumption when the load reduces.
• The installation becomes simpler and chances of moisture dripping on the product are eliminated.
• Product cooling is much faster compared to ceiling coils, which is essential for most products barring a few like potatoes.
• Cost of air cooler vs. ceiling coils is debatable and needs to be analysed on a case to case basis.
Bunker system…
Fin Coil System…
Disadvantages of bunker coil system
• These are generally fabricated at site by lay persons and the refrigerant circuiting is, therefore, not properly designed leading to higher pressure drop in the coil, lower suction pressures, inefficiency in operation of compressor and increasing power consumption.
• Oil accumulates in the coil and is not drained frequently, again leading to lower compressor suction pressure and higher power consumption
• Lower suction pressure leads to frost formation on the coils, reducing its heat transfer capability.
• As the load reduces, suction pressure drops leading to higher power consumption and frost build up. Both these can be prevented if an evaporator pressure regulator is installed to maintain constant evaporating pressure irrespective of load.
Potential energy efficiency measures: The following energy efficiency measures are known as major energy savers for common refrigeration systems and refrigerated spaces.
Premium efficiency motors: Equipment selection should include high efficiency motors for the compressor, condenser fans, evaporator fans and pumps. As an added benefit, these motors require less power and therefore give off less heat than equivalent standard motors, thereby reducing the internal cooling load that the motors contribute to the refrigerated space.
Liquid overfeed evaporators: In overfeed evaporator systems; excess liquid is forced through evaporators, separated from the vapour in a low-pressure receiver. Another benefit of overfeed systems is that the compressors are protected from liquid slugs that might result from fluctuating loads and control malfunction because liquid is separated from the suction gas in the low-pressure receiver.
Evaporator size: Evaporator sizing and selection is based on the maximum cooling load for the system as well as the design Temperature Difference (TD). Increasing the TD increases the capacity of the evaporator. Therefore, the optimal TD minimises both the evaporator fan and compressor power consumption. The evaporator coils should then be sized accordingly.
Purgers: The presence of non-condensable gases in a refrigeration system not only reduces the capacity and efficiency of the system, but leads to unnecessary wear and tear on the compressor. Purgers minimise the negative effects of non-condensable by periodically expelling them at points of accumulation within the system.
Insulation: External loads on refrigeration systems result from heat transmission through the walls, ceiling, and floor. Heat transmission can be reduced through appropriate insulation in the building envelope. Installing tighter insulation can result in substantially lower cooling energy costs. Refrigerant suction lines should always be insulated, so that return gas does not gain unwanted heat from the ambient surroundings. High return gas temperatures decrease system efficiencies and unnecessarily increase refrigeration energy usage.
Poly-styrene insulation…
CO2 / Air exchange system…
High efficiency lighting fixtures and controls: High efficiency lighting in the refrigerated space reduces the facility’s energy consumption, as well as minimising heat gains from the lighting.
Rapid-closing doors: Installing automatic door closers that limit the amount of time the doors are open can minimise energy losses. High-speed cold storage doors allow for rapid entry and exit of the cold storage area while minimising energy loss due to air exchange between the refrigerated space and the outside. Air curtains and plastic strip curtains can also be useful for reducing external loads on the cooling system.
Variable frequency drives: There are several opportunities for using variable frequency drives (VFDs) in refrigeration systems to achieve significant energy savings. VFDs or two speed motor controls can be used effectively on condensers and evaporator fans. VFDs enable more efficient compressor part-load operation over fixed-speed drive alternatives for many screw compressors and other positive displacement machines.
Raising suction pressure: When conditions allow, raising the suction pressure of a refrigeration system can result in overall energy savings. As a rule-of-thumb, compressor capacity increases approximately 2.5% per degree Fahrenheit increase in saturated suction temperature. Therefore, in order to meet the required cooling load and maintain the cooling set point temperature, airflow and/or evaporator surface area must be increased. This is accomplished by increasing the evaporator fan speed or increasing the number of evaporators.
Condenser criteria: Evaporative condensers are the preferred approach for rejecting heat from industrial and large commercial refrigeration systems. Evaporative condensers can operate at lower head pressures than air cooled condensers because ambient wet bulb temperature is utilised for cooling the condensing coils. Compressor operating efficiency is therefore benefitting from a reduction in head pressure.
Moderately oversized condensers: Moderately oversized condensers are typically an effective energy efficiency option. The larger condensers lower the saturated condensing temperature, reducing the work required from the compressors. The reduction in compressor demand because of the oversized condenser may allow for the selection of smaller compressors. Potentially, additional savings can be realised as a result of this measure by operating a smaller compressor at near full load as opposed to a larger compressor at part load.
Compressor type: Once the appropriate compressor size is determined, compressor type(s) should be selected in light of the variability in loads at the facility. For facilities with significant throughput and new products frequently entering the refrigerated space, the initial pull-down load can be significantly higher than the normal load required in maintaining refrigerated conditions, resulting in high variations in load. At full-load capacity, screw compressors generally perform better than reciprocating compressors. However, reciprocating compressors unload more linearly than screw compressors, and therefore can perform better in systems with highly variable loads.
Figure: Electrical panel and conditions for safe packaging…
Ammonia based refrigeration system – working safely
When used as a refrigerant, pure ammonia gas is compressed to form pure liquid ammonia. Unlike ammonia compounds, pure ammonia, in both gas and liquid forms, is a toxic substance that presents a number of hazards. If proper precautions are not taken while working with or around pure ammonia, serious injury or even death can result. In order to prevent injury, basic safety gadgets/gears/masks needs to be used.
Ammonia: Pure ammonia comes in two forms: gas and liquid. Ammonia gas is colourless and has a suffocating, pungent, penetrating odour. It is also much lighter than air. If ammonia gas escapes from a refrigeration system or a storage container, it tends to collect in high areas or ceilings. Ammonia gas is very irritating to the eyes, nose, and respiratory system, which makes it easy to detect low concentrations in the air. Depending on the concentration, ammonia can cause coughing, chest pain, breathing difficulty, bronchopneumonia, pulmonary edema, and death from bronchial spasm. Ammonia is a severe eye irritant; it can penetrate the eye quickly, causing permanent blindness. Contact with the skin or eyes can cause severe and potentially fatal burns.
Employers must have specific procedures to cover concerns such as:
• Response to an alarm signal.
• Leak control.
• First aid response.
• Dispersal of leaked ammonia inside the plant.Response to an alarm signal.
Figure: Ammonia detector and protective gear that must be available to workers in an ammonia based refrigeration plant…
Control: Engineering and administrative controls are the first line of defence against exposure to ammonia. Proper building design and ventilation are important engineering considerations. Monitoring/alarm systems are also essential in preventing ammonia exposure. Personal protective equipment is the last line of defense.
• Machine rooms must have two or more exit doors to ensure accessible escape routes.
• Emergency controls to shut down the ammonia compressor must be located outside the machine room.
Ventilation: Cold storage rooms must have a door that opens easily from the inside. These rooms must also have a means of alerting other workers if a person is unable to exit the room. The machine room must have an independent mechanical ventilation system. Ventilation fans must have a control switch on a separate circuit located outside the machine room. All ventilating fans must provide at least 15 air changes per hour, and must have switches outside the machine room even when an inside switch is installed. Store ammonia cylinders and containers in a cool, dry, and relatively isolated area, protected from weather and extreme temperatures. If cylinders and containers are stored outside, shield them from direct sunlight.
Emergency equipment: Emergency equipment includes eye wash and shower facilities and first aid kits. Workers must have immediate access to each of these items and must know how to use them in case of emergency.
Eye wash and shower facilities: Workers must have immediate access to an appropriate first aid kit at each ammonia location. The facilities should have a supply of lukewarm water – not running cold water.
Personal protective equipment: Controlling exposure requires strict attention to ammonia exposure limits. Appropriate respiratory, eye, and skin protection are essential.
Eye protection: Eye contact with liquid ammonia for even a short period can cause permanent disability such as blindness. Flushing must begin within 10 seconds.
Notes
• Do not attempt to neutralise the ammonia with other chemicals.
• Do not apply oils, ointments, or medications to the eyes.
Because eye irritation from exposure to ammonia gas normally does not occur until concentrations reach about 70 ppm, eye protection is not mandatory under normal working conditions (in other words, below 25 ppm). All respirators must provide full face protection or be used with effective eye protection.
Skin protection: Skin contact with ammonia can result in severe – even fatal – burns. Workers who are controlling any liquid ammonia leak must have access to full-body protective suits. This equipment must also be available to workers exposed to airborne ammonia concentrations above 300 ppm for more than a few minutes, which causes immediate irritation of moist body areas. (Ammonia reacts instantly with moisture.)
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