Potatoes refrigerator design and matters needing attention
Potatoes characterized by thin, tender, high water content, easy to collision damage, more diseases, perishable, and its stems are rich in starch, mainly for food, vegetables and feed, but also the raw material light and food industries. Because of its nutrient-rich, good taste, the store often used to adjust the supply of off-season vegetables to enrich people's lives.
A.potato library features
1.storage temperature and humidity
Potatoes are very sensitive to the ambient temperature storage, low temperature frostbite easily degenerate, lose food value; temperature is too easy to germinate to produce toxins. Temperature will have a huge impact on the conversion process inside the potato starch and sugars. Experiments show that at 0 ℃ condition potato inside due to the increased activity of starch hydrolyzing enzymes, starch hydrolysis to sugars faster, respiration rate decrease, so potatoes suitable storage temperature is 3 ~ 10 ℃, according potatoes use their different storage temperatures have the difference (see Table 1). Relative humidity storage environment on postharvest quality potatoes also have an impact, the air is dry fast water evaporation, potato skins to produce shrinkage, the air is moist and easy to sweat, causing a large number of potato rot, its storage suitable relative humidity of 95 to 98% of the between.
Cold storage stack temperature and humidity potatoes recommended
|Use||Storage temperature ℃||Relative humidity φ =%|
|Market needs fresh potatoes||4~7||95～98|
|For processed potatoes||8~10||95～98|
2.potatoes, cooling rate
When using mechanical harvesting potatoes, there are always some skin damage, in order to heal those wounds, immediately after harvest potatoes within the injured into the relatively high temperature and high relative humidity library warehouse stored for 2 to 3 weeks, during this period, due to the formation of a wound periderm, the wound heal. If the newly harvested potatoes immediately cooled to 5 ℃ or lower epidermis is easily frostbite. Therefore, the general requirements to purchase potatoes library temperature is about 25 ℃, into the warehouse within two weeks after it dropped to 18 ℃ from 25 ℃, after falling 1 ℃ every day, and then decreased to the storage temperature required for different commodities. So to calculate and conduct selection of equipment in accordance with potatoes cooling rate cooling consumption of potatoes library computing and machine configuration should be in.
3.potatoes library humidification
Like all living organisms, like potatoes contain water, the potatoes library, there is the body of water and potato requires a balance between the outside air humidity, this balance occurs when the relative humidity of air is called equilibrium moisture value. Equilibrium moisture value of potatoes is 99.3%, at this point, the body of water the potatoes will not emit into the air, so the relative humidity is relatively high potatoes library, in addition to increasing chiller design of heat transfer area, reducing the inside temperature and the outside temperature difference between the evaporation temperature should be calculated in accordance with the appropriate library humidifying device. Selection humidifier should consider avoiding water droplets fall on the potatoes with the air causing rotting potatoes, and to prevent ground water.
4.potatoes library Heating
Usually in September potatoes in storage, depending on the use of potatoes, at its storage temperature between 3 ~ 10 ℃. In the northern winter outdoor temperature is low, generally below -10 ℃, and high temperature storage of potatoes. So in the design of potatoes library, they should breathe heat, the heat emitted when the chiller is not cooling operation, as well as lighting, summarized and compared with the maintenance of the structure of the incoming cold, calculated, if necessary, should be additional heating means (electric heating or steam heating) on the chiller.
5.potato storehouse ventilation
Potatoes during storage to breathe, and release heat, moisture and some harmful gas components, discharge time and a certain amount of evaporation of water, if not the heat, moisture and harmful gas emissions during storage, can make refrigeration temperature, humidity, excessive ripening gas components, so that the storage of potatoes, shortening, and even deterioration, in order to ensure the storage quality of potatoes and potato storehouse temperature and humidity, and when the library CO2 concentrations higher than 1% , you need fresh air ventilation, every 24 hours for an 10 m3 per tonne of potatoes in the fresh air, the library volume coefficient of 0.7, ventilation of 20 times / day, ventilation time 8h / day, every day about 5 working ventilation system hours per cubic meter of air inside the circulation capacity is 80 ~ 100m3 / h.
6.to prevent moisture in the air condenses on the interior walls and ceilings
Composite board envelope potatoes library use, both to be placed in the ambient temperature is high cooling capacity through the building envelope losses. Should also consider the heat loss through the building envelope ambient temperature is low. But also to prevent moisture in the air inside the inner walls and ceilings condensation. In the northern region, when the ambient temperature is very low, due to the storage compartment air temperature is between 3-10 ℃, relative humidity close to 100%, so it is easy indoor water vapor condenses on the interior walls and ceiling, if you do not take treatment measures, resulting in condensation of water droplets potatoes in a large area of potatoes will rot. So the library roof potatoes shall be provided a 10% slope, the condensed water can be discharged.
B.potatoes library type
Most of the world of potatoes for human consumption and processing are not artificial refrigeration storage, but in some cases, such as in tropical climates require long-term storage, the quality has special requirements and higher economic value to the case before refrigeration storage of potatoes. Artificial refrigeration potatoes library has two kinds of practices.
1.bulk potatoes library
This is somewhat similar to cold storage depot. The bottom of the refrigerator cloth ventilation system, air from the bottom of the storage room to go up (see Figure 1). Main air duct conveying air evenly into each manifold through the manifold airflow evenly delivered to the storage chamber floor surface to allow air to flow upward. When outdoor temperature is low by utilizing the mixing valve cooling cycle gas potatoes mixed cold outdoor air and indoor post. Each room features a cold set of automatic control system, set by the operator status value, the control system according to outdoor ambient wet bulb temperature, combined with the use of the indoor environment to determine the refrigeration system or natural ventilation system to control the temperature of the cold room. Units bulk stowing repository relatively large volume can reach 590Kg / m3. So its storage costs are relatively lower than the shelf-type storage containers.
2.box-mounted shelf stacker potatoes Library:
In addition to this cold storage should meet some of the special properties of potatoes stored outside. Form its stowage and cold with a high temperature library general not a big difference. But in practice the refrigeration system cooling consumption calculation aspect ventilation, heating, heating of calculation should be given special attention. Its stowage volume of about 400 ~ 420Kg / m3, with a library for the pileup with shelves, so the unit is less than the amount of bulk potatoes stowed library, the storage costs are relatively higher than the bulk stowed library. However, this type of cold storage when not stored potatoes can be stored for more flexible use of other fruits and vegetables.
C.shelf stacker potatoes library design
Here we are introduced to the design of Tianjin, a library 5000t ten thousand tons of potatoes library. The cold storage of potatoes in addition to the requirements of the Party, it must also be able to store other commodities.
1) Design parameters: outdoor design temperature: 29 ℃ condensing temperature: 38 ℃ evaporation temperature: -7 ℃.
2) storage capacity: Potato library five (including two dual-purpose library), storage temperature 0 ~ 18 ℃, storage capacity in each library as the 1000t, a total capacity of about 5000t. Each daily purchase 200t, stock temperature 25 ℃, after two weeks dropped to 18 ℃, a day after falling 1 ℃, storage temperature until the desired product.
3) Cooling System: The cooling system uses "ammonia" as refrigerants, ammonia pump forced circulation chillers with screw compressors, single-stage compression, the working fluid is cooled, condensing evaporative condensers.
2.cooling consumption calculation and refrigerator selection
Calculated cooling consumption shall be three stages.
1)Each library every day into the 200t potatoes, stock temperature ranging from 25 ℃ for 14 days to 18 ℃.
Calculated in accordance with: the stage machine load Qj = 7 million kcal / h
2)Each day the Treasury from 18 ℃ down 1 ℃ (after 15 days) dropped to 3 ℃.
Calculated in accordance with: the stage machine load Qj = 10 million kcal / h
3)Each of the Treasury dropped after 3 ℃ incubation stage machine since load Qj = 4.8 million kcal / Based on the above results, according to the Treasury each time drawing a stock analysis chart machine load, according to the analysis As a result, the selection performed refrigerator. (See FIG. 2) in accordance with Figure 2 cooling capacity analysis:
a) The first day to 25 days for the purchase stage, up to 26 days to 34 days for 8 days maximum load of the machine, to 450,000 kcal / h (523KW).
b) 5 to 44 days after the entire library of the temperature dropped to 3 ℃, at this time, cold storage insulation in the operational phase of the machine-load of 48 000 kcal / Jian × 5 = 240 000 kcal / h (279KW).
c) Based on the above analysis 1 set JZ2LG16 and JZ2LG12.5 screw refrigeration compressor, its tx = 38 ℃, t0 = 10 ~ -4 ℃ when the cooling capacity of the machine as follows:
JZ2LG16, JZ2LG12.5 different conditions early cold Scale (KW)
|machine type||Evaporation temperature ℃|
4)evaporation temperature of the machine is running according to the daily minimum temperature required 5 warehouse adjusted. Set the machine running the number of units shown in the table load and machine cooling capacity in different conditions to decide.
3.the evaporation pressure control
Potato library daily purchase volume of 200t, have five full days into a library, the library before and after the purchase time 5 about 25 days. Its storage temperature difference of about 10 ℃. According to the characteristics of the potatoes cool, each library every day required storage temperature is different, in order to ensure that the temperature difference between the air temperature within each warehouse between the evaporation temperature of not too much, while ensuring that each warehouse during the purchase of different storage temperature requirements. PM3 installation of the main valve solenoid constant pressure in the return pipe each library, according to the library every day to control the value of the temperature difference constant pressure regulating solenoid main valve, this approach not only ensures the Treasury different temperature requirements, and ensures the library between temperature and evaporation temperature of a relatively stable small temperature difference, so that the relative humidity within the library is relatively stable.
4. humidification amount is calculated
Each library with 10 F = 165㎡ ceiling mounted cooling fan, each fan flow Q = 17400m3 / h, storage temperature 3 ℃, evaporation temperature t0 = -4 ℃, Δt = 7 ℃.
Chiller cooling capacity Q0 = 165 × 10 × 7 = 1150 kcal / hour.
The cooler air inlet temperature difference:
Cooler inlet air temperature of 3.5 ℃ outlet temperature = 3.5 ℃ -2.1 ℃ = 1.4 ℃
Charles i-d map: cooler inlet air temperature = 3.5 ℃ = 90% i1 = 4.3 kcal / Kg d1 = 5.8g / Kg
Cooler air temperature = 1.4 ℃ i2 = 3.5 kcal / Kg d2 = 5.2g / Kg
the amount of dehumidification cooler:
Where: D- humidification capacity [Kg / h];
d- air moisture content [g / Kg];
L- air flow [m3 / h];
r- air density [g / m3];
10 hours a day by the chiller:
Working 20 hours a day by the humidifier:
Each is equipped with seven SLB-9.0 centrifugal humidifier, humidification amount.
5.winter heating calculation
According to owner required: inside temperature between 0 ~ 18 ℃ adjustable, Tianjin winter minimum temperature considered for -23 ℃.
Cold winter maintenance of the structure passed as: -16KW
Cooling fan motor heat is: 20KW
Ventilation generates heat as: -17KW
The amount of heat required to:
Each chiller installed 1.5KW electric heater,
Ventilation potatoes library is necessary to consider the amount of circulating air inside to meet the requirements, taking also into account the chiller outlet temperature is not too low to affect the storage quality of potatoes.
Potatoes in the following 0 ℃, activity increased internal potato starch hydrolyzing enzymes, starch hydrolysis to sugars faster, respiration rate decrease, so chiller outlet temperature should be higher than 0 ℃. Through the above calculation: When the air volume Q = 174000m3 / h Δt = 2.1 ℃, the cooler the air temperature was 1.4 ℃.
The air inside the circulation volume: each library storage capacity of 1000t, requires air circulation amount per tonne 80 ~ 100m3 / h, the 1000 × 100 = 100000m3 / h≤174000m3 / h
The new wind added: 49 × 13 × 6.5 × 0.7 = 2898 m3
20 air changes per day: 2898m3 × 20 times / day = 57967m3 / day
Ventilators 5 working hours per day:
Total ventilation: 11593m3 / h × 5 Jian = 57967m3 / h
When considering storage temperature lower than room temperature 2 ℃, it can be used for the energy supply or new fans to the heating section of the library
2 typhoon with an amount of 30000m3 / h of ventilation with axial fan to do, in order to complement the new uniform wind, in the design of the layout of the new air supply system, the ventilation duct to the fresh air will be organized each chiller suction outlet. Exhaust organized also used mechanical ventilation.
The cold officially put into operation last year, after a winter of running stable inside temperature, relative humidity can be controlled at about 95% decay rate of 2 to 3%. Praised by users and foreign experts.