Drying is the operation of using heat energy to vaporize and remove moisture such as water in wet materials to obtain solid products. Compared with traditional drying methods such as natural drying and electric drying, heat pump drying has the advantages of excellent drying quality, energy saving and environmental protection. Various products dried by air-source heat pumps are gradually welcomed by the drying market and have been widely used in traditional Chinese medicine, food, agricultural products and other fields, and have become a new blue ocean in the industry.

If you want to compete for the air energy heat pump drying market, clear and comprehensive knowledge of heat pump drying is essential. The following 11 questions will explain the knowledge points of heat pump drying.

01

A: Heat pump dryer is a device that uses electricity to drive the fan to absorb heat from the air and drive the compressor to work, so as to obtain four times the heat of the power consumption per kilowatt-hour of electricity. It is an extension product of air energy heat pump. Since 2009, air energy manufacturers have been involved in the research and development of this product.

The heat pump drying system uses a heat pump to provide heat source to heat the wet material, thereby increasing the temperature and dryness of the air and achieving material drying (drying). The air energy high temperature heat pump drying unit uses the reverse Carnot principle to absorb heat from the surrounding environment and transfer it to the heated object (the object with a higher temperature).

02

The heat pump drying system consists of a heat pump main unit, a circulating fan in the drying room, an air duct and a uniform wind plate, a material rack, and a tray.

A. The heat pump main unit is the core part of the main equipment of the entire system, providing the system with heat source and dehumidification functions. Its working principle is consistent with the heat pump main unit in the hot water heating field.

B. Material racks and material trays, that is, devices that carry materials.

C. The internal circulation fan ensures the air flow in the drying room and ensures that the water vapor generated during the material drying process can be taken away in time. If the moisture is not removed in time, the material may become moldy or deteriorate. Common ones include built-in high-temperature and high-humidity axial flow fans, external long-axis axial flow fans, centrifugal fans (which can be installed outside), etc. The most commonly used ones are built-in high-temperature and high-humidity axial flow fans, which are placed indoors. The appearance of the entire system.

D. Electric auxiliary heating is mainly used for rapid heating and emergency response when the equipment fails temporarily, as a backup. Some materials require high temperatures in a short time, or when the heat pump energy efficiency ratio is reduced in low temperature weather, electric heating is required. During the drying process, the temperature requirements of materials at different stages are also different. Some stages require high temperatures. There are two ways to increase the temperature. One is to increase the configuration of the heat pump host, and the other is to use an auxiliary heat source. Currently, most of them use electric heating.

E. The main purpose of the design of the air duct and the uniform air plate is to ensure the uniformity of air flow in the drying room, and to minimize the temperature and humidity differences in various areas of the drying room, thereby improving the uniformity, quality and drying efficiency of the material drying.

F. The drying room warehouse ensures that the entire system operates in a closed space and provides space for material placement.

03

Heat pump drying equipment can be divided into high-efficiency dehumidification heat pump dryer, high-temperature air energy split dryer, and high-temperature air energy integrated drying and dehumidification machine according to different heat sources and moisture removal methods.

The principle of high-efficiency dehumidification heat pump dryer is to use the phase change absorption and release of water to achieve the recycling of heat energy in a closed space in the process of removing moisture from materials. Its advantage is that after removing the moisture from the material, the dry air is left, and the water vapor is discharged through condensed water. The entire drying process does not require heat exchange with the outside air, so it is basically not affected by the ambient temperature, especially in the autumn and winter seasons when the use environment is very low (below 0℃) and there are lower temperature drying requirements (the temperature in the drying room is lower than the ambient temperature). It has advantages in material drying.

Rice noodle high temperature drying project

04

Answer: Advantages of heat pump dryers compared with other types of dryers:

High efficiency and energy saving, low operating costs. The operating cost of heat pump drying is only 30% of that of electric heating dryers, 40% of that of fuel oil dryers, and 60% of that of coal-fired dryers. In addition, heat pump dryers do not need to consume any fuel, which saves the cost of transporting and storing fuel, and the economic benefits are even more obvious.

Safety and environmental protection. The heat pump dryer achieves the purpose of drying by transferring heat from the air to the drying room, so it only consumes the electricity for transporting heat. No other fuel is needed, which means avoiding safety and environmental pollution problems in the transportation and storage of fuel. No pollutants are generated during the operation process.

Good drying effect. Since the heat pump dryer is fully automated, the operating state of the unit can be automatically adjusted according to the set mode, the temperature rise is stable, the temperature is uniform, and the temperature difference fluctuation is small, avoiding the influence of human factors on the drying quality during the operation of the fuel dryer.

High energy utilization efficiency. Heat pumps have a more efficient heating capacity than direct energy supply, which is reflected in its heating energy consumption ratio (COP) is always higher than 1. In the heat pump drying system, in addition to the electrical energy from the compressor, the heat energy of the drying hot air also comes from the heat energy contained in the drying exhaust gas absorbed by the evaporator. Researchers have found that compared with steam drying, it can still save about 40%-70% of energy.

05

According to the state of the material in the drying room, it can be divided into two types: static drying system and dynamic drying system.

Static drying system is the common material entering the drying room in the form of a cart (material rack) tray. The material does not move during the entire drying process (except for the inverted tray and reverse), and the material is loaded and unloaded manually. It is suitable for materials with long drying time, slow water discharge, and small drying volume. Its disadvantage is high labor cost;

Dynamic drying system is the so-called drying line. The material in and out is completed by the lifting device or the discharging device. The material is dried in a dynamic form on the conveyor belt. It is suitable for materials with large drying volume and short drying time. The disadvantage is high investment and large installation location size requirements.

06

For the renovated drying room, attention should be paid to the materials and insulation conditions of the original drying room. Heat pump drying has much higher insulation requirements for the drying room than the traditional method. At present, most drying rooms use polyurethane integral foam board as the insulation layer, and the inner and outer skins are made of color steel, stainless steel or galvanized sheet. The installation is relatively simple and is a lock-type on-site assembly.

Usually 5-10cm insulation board is used. The insulation materials generally use rock wool, polyphenylene, phenolic, and polyurethane materials. At present, the most used and can meet the national standards are polyurethane insulation boards. If the service life or insulation effect of the warehouse material does not meet the requirements of heat pump drying, even if the host is energy-saving, the energy-saving effect of the entire system will not be very good.

Fig drying project in Sihong, Jiangsu

The outer skin of the warehouse board is generally made of color steel, galvanized sheet, and stainless steel according to customer needs. The most commonly used color steel plate, such as 304 food-grade stainless steel, is mostly used for high-demand food processing enterprises. The cost of color steel plate and food-grade stainless steel is quite different, so it is necessary to choose according to the actual situation of the material and the customer.

The specific steps for the transformation and construction of the drying room are: install the bottom plate → install the vertical plate → install the top plate → install the bottom plate reinforcement plate (to facilitate workers to use carts and clean the drying room) → install the main machine → install the circulating fan → install the duct plate or the uniform wind plate → connect the power cord and the drain pipe.

The installation location of the drying room needs to be well ventilated to facilitate the absorption of air heat. The discharge port should be as close to the outer wall as possible to facilitate the installation of the air duct to discharge the humid air to the outside, so as to avoid water vapor staying in the room, affecting the hygiene of the production workshop and the personal safety of the staff. Ordinary drying processing places and high-efficiency dehumidification drying rooms can ignore the exhaust problem.

07

The essence of material drying is to remove the moisture from the material, and the factors that affect the removal of moisture include the temperature in the drying room, wind speed (circulating air volume), surface area, relative humidity (air in the drying room), material's own moisture dissipation rate, and material form.

The main function of temperature is to evaporate the water inside the material. Generally speaking, the higher the temperature, the faster the water will come out. Different materials require different drying temperatures. Another function is to ensure the shape and color of the finished product after the material is dried.

Cured duck drying project

The main function of wind speed is to bring heat to the material and take away the moisture on the surface of the material. Sufficient air volume can ensure the complete circulation of air inside the warehouse, which needs to be designed according to the material characteristics and unit parameters.

Surface area refers to the paving thickness of the material. The larger the surface area of ​​the material in contact with the air, the faster the moisture will be taken away. Relative humidity, the lower the relative humidity of the air in the drying room, the faster the material will be discharged. However, not all materials or different drying stages are suitable for fast water discharge. Some people may think that the thinner the material is placed, the better. In fact, the larger the surface area, the faster the wind flow rate, and the less heat the material absorbs.

The material's own moisture dissipation speed is determined by the material's own characteristics, and it is also one of the important factors affecting the drying time and equipment selection. Generally speaking, fast moisture dissipation is dried in a small amount and in a short time, and slow moisture dissipation is dried by increasing the amount and extending the time; the material forms mainly include strips, blocks, flakes, powder, etc. Generally speaking, the drying efficiency of flake materials is faster, and the drying efficiency of block or rhizome materials is slower. The material form determines the material placement method and the design of the air duct.

08

The design of the drying room air duct plays a vital role in the drying uniformity and drying efficiency. The main thing to do in the drying room air duct is to avoid and reduce the dead corners of heat and air volume as much as possible, and in a simple and economical way, the through-flow and horizontal flow types are generally used in the design of the drying duct.

The so-called through-flow type is a duct structure in which the wind passes through the material from top to bottom or from bottom to top. The through-flow type is widely used in the drying of hanging materials, such as bacon, sausage, pressed duck, and other meat products, as well as noodles, vermicelli, tobacco leaves, etc., which can better maintain their shape when hung.

Jiangmen Helmet Factory Drying Project

The advection type refers to the wind duct structure form in which the wind passes through the material and the pallet surface evenly from the horizontal direction. The advection type is mainly used for flat materials, such as flakes, blocks, flowers, fine particles and other materials. Common ones are: bergamot slices, banana slices, apple slices, mushrooms, chrysanthemums, roses, starch, etc. The advection type is the most widely used and suitable for most types of items. The wind blows evenly and parallelly from the surface of each layer of the items. In theory, the effect is the best, and the shelf pallet has the best versatility.

Generally speaking, the air outlet of the host is relatively small. If the air volume is not enough, a fan can be added at the front end. In order to make the air volume of each area not much different, a uniform wind plate can be added to the air outlet to make a return zone to increase the heat dissipation area.

09

Drying materials are generally loaded through material trays and then placed on drying racks. They can be divided into the following types:

A. Fixed type is to install the material tray support frame directly inside the warehouse. When in use, the tray is directly placed into the warehouse. This type of material rack is mainly suitable for small warehouses and integrated drying rooms. The drying capacity is generally within 200 kilograms.

B. Mobile material rack. Mobile shelves are generally in the form of carts. The material rack and wheeled carts are fixed together. It is mainly suitable for large and medium-sized drying rooms. The drying capacity is generally large. It requires that the material laying should be convenient and multiple people can operate at the same time. When in use, the materials are placed on the workbench, and the materials are placed on the cart. After the materials are placed, they are pushed into the drying room together. Meat material racks and commonly used mobile material racks are basically universal. When using, you only need to add bamboo sticks or stainless steel rectangular tubes.

C. The main feature of the mesh disk is good air permeability. It is widely used in horizontal and through-flow air ducts. The size of the mesh is mainly selected according to the size of the material. The materials can generally be stainless steel wire mesh, galvanized steel wire mesh, wire mesh, plastic mesh, and bamboo and wood products. It is mainly used for block, sheet, and root materials, such as: bergamot slices, fig tea slices, bamboo shoots, fungi, flowers, etc.

D. The scope of use of the punching disk is also quite wide. The main feature is that the material is easy to clean after adhesion. It is mostly used in horizontal flow air ducts. The size of the punching hole is also made according to the characteristics of the material itself. The materials are generally stainless steel plates and galvanized plates. It is mainly used for fig dried fruit, mulberry dried fruit, etc., which are easy to evaporate sugar and produce adhesion.

E. Material frames are rarely used in drying. Regardless of whether they are used in through-flow or horizontal flow ducts, their air permeability is relatively poor. Therefore, material frames are used as drying trays mainly for materials such as walnuts and peanuts that have good air permeability, low water content, slow water output, low drying temperature, long drying time, and large drying volume.

10

When designing the warehouse and selecting the unit, it is necessary to understand the characteristics of the material. Generally, the reverse method is used, that is, the trays and material racks are planned and designed according to the amount of material to be dried and the discharge requirements, and then the warehouse design and host configuration are carried out according to the required position of the material rack.

The host configuration should be selected according to the moisture content of the material, the speed of water discharge, and the required drying time. For example, I can calculate the size of the drying room based on how much space is needed for 1,000 kilograms of material, and the configuration of the host depends on how much water needs to be removed.

Shandong Pingyin Rose Drying Project

For example, if it is 1000 jin, then calculate according to the required temperature of the material and the speed of water discharge of the material itself. For example, if the water discharge is slow, it takes 25 hours and the customer also took about 25 hours before, and the temperature is 50℃, then it is very simple to use 1000/25=40 jin. According to the equipment, a 6P machine has a dehumidification capacity of 21KG per hour, which can completely handle it. If the water discharge is very fast, it can be completed in 10 hours, and this material cannot be covered, then use 1000/10=100 jin, then you have to increase the configuration and use 12P, with a dehumidification capacity of 50KG per hour.

11

Heat pump drying has a wide range. Most of the items that were previously dried by the sun, burning wood, or using electricity can be replaced by heat pump drying equipment to achieve the goals of energy saving, safety, environmental protection, and improved production efficiency. The maximum drying temperature of the air energy heat pump dryer is 85 degrees, so anything less than or equal to 85 degrees can be used. The main items or projects that can be dried by heat pumps are roughly listed as follows:

Seafood, tobacco drying, pitaya flowers, raisins, lychees, longans, mountain slag, red dates, walnuts, wolfberries, monk fruit, nuts, cured meats, Chinese medicinal materials, tortoise jelly powder, noodles, dried persimmons, tea, chrysanthemums, ganoderma lucidum, honeysuckle, mushrooms, cordyceps flowers, dried vegetables, bean curd, star anise, food constant temperature, wood, furniture, feed, silkworm cocoons, rubber, coal slime, mineral sand, urban sludge, biofertilizer, leather, printing, fabric printing, fireworks beads, paper tubes, mosquito coils, laundry supplies, crop products, low-temperature baking paint, hardware and plastic accessories drying and other special industries. As an efficient and energy-saving product, it has significant energy-saving effects compared with traditional drying equipment, and the quality of the dried materials is higher.