As a kind of high-efficiency energy-saving product, heat pump drying has significant energy-saving effect compared with traditional drying. The dry quality of dry materials is kept better. The unit adopts heat recovery technology and the comprehensive energy efficiency is up to 5.0. It is especially suitable for drying sensitive and volatile products and improves the quality of materials. At the same time, the entire heat pump drying process adopts intelligent control technology, and has built-in various drying process curves, which saves labor costs, saves time and labor. At present, agriculture, food, chemical, ceramics, medicine, mineral processing to pulp and paper, wood processing and textile industry, almost all industries have a dry production process, drying has become a key to improve product quality in the production process. Link, but the drying process is also a high energy process. In the total energy consumption of various industrial sectors in China, the drying energy consumption is 4% (chemical industry) -35% (paper industry). Developed countries, such as the United States, France, the United Kingdom, Japan, etc. About 12% of industrial energy is used for drying. Heat pump drying is a mild, near-natural drying, suitable for most heat-sensitive materials such as agricultural products and medicinal materials. therefore. In the field of drying technology, the application of heat pumps can effectively use energy, protect the environment, reduce the greenhouse effect and prevent the destruction of the ozone layer.

A heat pump is a system that collects a small amount of high-quality energy (mechanical energy, electric energy, etc.) or high-temperature heat energy to collect low-quality heat energy in the air, and uses a condenser to release heat to supply heat. China's GDP has been growing at a rapid rate of more than 8% for many years, but the energy problems that come with it have become more and more serious. With the development of the times and the increasing energy, the efficiency and energy saving for all walks of life. The requirements are also getting higher and higher. Heat pump is an energy-saving technology. It can be used in the drying process to reduce energy consumption, which is of great significance to alleviate the energy shortage in China.

First, the history of dry vegetables in China and existing problems

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%.

Second, 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.

Third, the principle of heat pump drying

The common heat pump drying device adopts a convection drying system, and the gas from the heat pump heats and drys the raw materials in the drying device. Heat pump drying principle

As shown in Figure 1.

Analysis of economic and technical indicators of heat pump drying and traditional drying process

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 (ie heat pump main machine) processes 1t fresh vegetable consumption standard coal 20kg, heat pump 2.75kW, circulating fan power consumption 0.2kW, according to working 4h, its energy consumption is 11.8kW, standard coal The conversion factor is 407g/(kW·h) and the standard coal is 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.