Vegetable dehydration process: air can be used in high temperature drying technology

At present, the main export products of drying equipment in China are vacuum drying equipment, vibration drying equipment, small and medium-sized food, food and agricultural and forestry products drying equipment, with an annual export volume of more than 100 units. The main export areas are Southeast Asia and other developing countries. Has opened the door to the European and American markets. At present, China's dry equipment export products account for less than 5% of domestic dry equipment, experts expect the 12th Five-Year; during the period of export products in the total domestic dry equipment will account for more than 10%.

The heat pump drying technology uses a working medium (such as ammonia, water, etc.) to evaporate under reduced pressure in the evaporator, so that the surface temperature of the evaporator is lower than the indoor air dew point, so that when the air flows through the evaporator, it is cooled and lowered below the dew point. When the excess steam in the air is condensed and precipitated on the surface of the evaporator, the condensed water is poured into the water tray and then drained into the water container by the drain pipe.

First, the basic concept of heat pump drying technology.

The heat pump drying technology uses a working medium (such as ammonia, water, etc.) to evaporate under reduced pressure in the evaporator, so that the surface temperature of the evaporator is lower than the indoor air dew point, so that when the air flows through the evaporator, it is cooled and lowered below the dew point. When the excess steam in the air is condensed and precipitated on the surface of the evaporator, the condensed water is poured into the water tray and then drained into the water container by the drain pipe. After the liquid working medium is heated and vaporized, it is sent to the condenser through the compressor, and the condenser emits a large amount of latent heat of vaporization under high temperature and high pressure. When the air cooled in the evaporator passes through the condenser, the endothermic temperature rises, and is discharged in a dry state, and is mixed with the room air. Thereby reducing the indoor air humidity and achieving the purpose of drying and dehydrating.

Second, the status quo and problems of dehydrated vegetables production.

At present, most of the dehydrated vegetable production adopts the traditional drying method--heating and drying method of the drying room, which has the following problems:

1. The heating temperature is too high. Traditional process drying technology, heating temperature is not easy to control. Generally, the heating temperature is about 75-90 ° C, and the drying process of the dehydrated vegetable requires that the drying temperature should not exceed 65 ° C.

2. Drying time is too long. According to the traditional method, it takes at least 24 hours for each vegetable processed, even if it is occasionally reworked due to poor drying effect and reheating and drying.

3. The energy consumption is large. The traditional drying process has a low thermal efficiency of about 30%-60%. During the drying process, the heat of drying and evaporating water accounts for about 36%, and the loss of exhaust gas accounts for about 58%. The dry material takes away heat and the heat of the dryer. The losses accounted for 2% and 2% respectively, and the thermal efficiency was only 40%.

Third, the advantages of heat pump drying technology in the production of dehydrated vegetables.

Heat pump drying technology is widely used in computer rooms, warehouses, archives, libraries and other industries due to its unique characteristics. Its advantages when applied to dehydrated vegetable production are:

1. The heating temperature is low. The heat pump drying technology production process can be reduced by about 38-52 ° C compared with the conventional drying process, and the heating temperature of the heat pump drying process is about 37 ° C.

2. Short drying time. The heat pump drying and dehydrating vegetable production process takes up to 8 hours, and is generally completed from preheating to product release for 4 hours.

3, good quality. The vegetables produced by the heat pump drying process have good color and stable internal quality.

4. Low energy consumption. Since this process utilizes air circulation, the heating temperature is low, the drying time is short, and the capacity is large. Therefore, the heat pump drying process consumes less energy and is a good energy-saving product.

Fourth, heat pump drying and traditional drying process economic and technical indicators analysis.

The test results show that the economic and technical indicators of the heat pump drying technology process are much better than the traditional drying process, mainly reflected in energy saving, high quality and high efficiency.

1, energy consumption comparison
(1) Heat pump drying process: According to the test results, the heater processes 1t fresh vegetables consumption standard coal 20kg, heat pump 2.75kW, circulating fan power consumption 0.2kW, according to the work 4h, its energy consumption is 11.8kW, standard coal conversion coefficient 407g/(kW ?h), standard coal 4.803kg. The total energy consumption is 20kg 4.803kg = 24.803kg (standard coal).

(2) Traditional drying process: 240kg of standard coal is consumed, 2.4kW of circulating fan is consumed, and the standard coal coefficient is 407g/(kW?h), which is equivalent to 0.977kg of standard coal. The total energy consumption is 240 0.977 = 240.977 kg (standard coal).

(3) Calculate the energy saving rate: (1-24.803/240.977) × 100% = 90%.

2. Quality comparison. The heat pump drying process has stable product quality, good color and no residual substances such as SO2.

3. Comparison of drying efficiency. The heat pump drying process product has qualified moisture content, no rework, and short drying time.

V. Comprehensive evaluation.

The use of heat pump drying equipment not only saves a lot of energy, but also greatly improves work efficiency. The heat pump drying process is used for vegetable dehydration production. It is a technically feasible and economically reasonable energy-saving project. This new technology and new technology are very successful from theory to practice.

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