Spray dryer is one of the popular drying equipment in the industry at present, with a wide range of applications. It can be said that it is a dryer for processing solutions, suspensions, or mud like materials. The drying effect of the spray dryer is also very good and efficient. Its products are in the form of uniform particles, which does not need to increase the crushing process. At present, the market share of spray dryer in chemical industry, light industry and food industry is very high.
At present, with the improvement of living standards, the quality and quality requirements begin to increase. If you want to develop for a long time, you should discuss the advantages and disadvantages of spray dryer technology in detail, and answer the questions in essence.
1、 Advantages of spray dryer:
1. Due to the large surface area/volume ratio of the droplet group, the drying time of the spray dryer is very short (usually 15-30 seconds, sometimes only a few seconds). The spray dryer does not need strict filtering equipment, and if there is no fibrous liquid in the feed liquid, the feed liquid channel will not be blocked basically. It can adapt to high viscosity liquid (compared with pressure spray drying). Due to the easy adjustment of the speed of the atomizer, it is relatively easy to air produce product particle size, and the particle size distribution is also narrow.
2. The spray dryer has large production capacity and high product quality. The amount of spray per hour can reach several hundred tons, which is one of the larger capacity of the dryer. Although the inlet temperature of the drying medium can reach several hundred degrees Celsius, the material temperature does not exceed the wet bulb temperature of the air during most of the whole drying process. Therefore, spray drying is particularly suitable for drying heat sensitive materials (such as food, drugs, biological products and dyes).
3. The spray dryer is easy to adjust, and the operating conditions can be changed in a large range to control the product quality indicators, such as particle size distribution, moisture content, biological activity, solubility, color, aroma, taste, etc. When adjusting the processing capacity, it is not necessary to change the working state of the atomizer, and the same product can be obtained for the feed rate.
4. The spray dryer simplifies the process flow. The operation process of evaporation, crystallization, filtration and crushing can be completed in one step by spray drying. Due to the fact that the mist generated by the centrifugal atomizer is basically on the same horizontal plane, the droplets move along the radial and tangential composite directions, with almost no axial initial velocity, so the diameter of the dryer is relatively large. The diameter and length are relatively small, allowing for maximum utilization of the space in the drying room.
2、 Disadvantages of spray dryer:
1. When the inlet temperature of the drying medium is lower than 150 ℃, the volumetric heat transfer coefficient of the dryer of the spray dryer is low, and the volume of the equipment used is large. In addition, the heat utilization rate of low-temperature operation is low, and the consumption of drying medium is large, so the power consumption is also high. The machining accuracy of the dispersed disc is required to be high, and it should have good dynamic balance performance. If the balance state is poor, the spindle and bearings are easily damaged;
2. For the production of fine powder products, separation equipment is required to avoid product loss and environmental pollution. The bulk density of the product is lower in the spray dryer.
3. The contact mode between fog droplets and gas is basically in a parallel flow form, and the dispersion plate cannot be placed vertically;
In order to meet market needs and improve product solubility, blending, and packaging performance. Some spray drying equipment adds granulation equipment, but it will increase the heat denaturation of products and the loss of aromatic substances. spray drying equipment effectively solves the integration problem of drying tower, separation chamber and cooling chamber. In the falling rate drying stage of spray drying, the temperature of powder increases with the decrease of water content. Taking dairy products as an example, when the temperature of the dry air at the bottom of the drying tower is 90-100 ℃, the temperature of the powder is around 60 ℃. To prevent thermal denaturation, it is hoped to cool down quickly at the end of drying. For this reason, MD type spray dryer is equipped with a flow cooling chamber at the lower part of the drying tower. This system has micro powder separated by cyclone, which is transported to the flow cooling chamber at the lower part of the separation chamber with air, cooled to about 30 ℃ with the powder separated by gravity in the separation chamber, and then discharged. The result has a good control effect on thermal denaturation.
Spray drying equipment has fast drying speed and good product performance
After spray, the feed liquid is atomized into dispersed particles, and the surface area is greatly increased. After contacting with hot air, the drying process can be completed in a very short time. Under normal circumstances, 95% to 98% of water can be evaporated within 1-3 seconds at 100-150 ℃. Due to the instantaneous completion of the drying process, the particles of the finished product can basically maintain a spherical shape similar to the liquid droplets, thus having good dispersibility, excellent washability, and high solubility.
Reduce wall sticking and coke powder, improve product quality
Severe wall sticking phenomenon
The main performance is that there are adhesive wet powder everywhere in the drying room of spray drying equipment. The reason is that the feed volume is too large to fully evaporate; Insufficient heating of drying chamber before spray; When starting spray, the blanking flow is adjusted too much; The added liquid is unstable. To address the different causes of the aforementioned issues, the following measures can be taken in sequence: appropriately reducing the amount of feed; Appropriately increase the inlet and outlet temperatures of hot air; At the beginning of spray, the flow should be small, gradually increased, and adjusted to an appropriate time; Check if the pipeline is blocked, adjust the solid content of the material, and ensure the fluidity of the material liquid.
Spray dryer, centrifugal spray dryer and multi nozzle spray dryer are three typical spray equipment. The spray direction of centrifugal spray and multi nozzle spray is horizontal or vertical (axis direction). In the horizontal direction, in order to make good contact between the hot air and liquid droplets, improve drying efficiency, and allow the hot air to form vortices, it is easy to produce adhesion phenomenon. The attached and deposited materials will cause thermal denaturation and cleaning difficulties. When the speed of the hot air is along the axis of the drying tower, the hot air flow line often deviates as a whole, and the hot air cannot mix well with the material liquid, resulting in low efficiency and partial adhesion.
The moisture content of the product is too high
The exhaust temperature is the main factor affecting the moisture content of the finished product, so the reason for the high moisture content of the product is generally due to the low exhaust temperature. The exhaust temperature can be adjusted by the feed rate. Therefore, the corresponding measure is to appropriately reduce the feeding amount to increase the exhaust temperature.
Low product purity and excessive impurities
There are several possible reasons for this situation: (1) poor air filtration effect; (2) Mixing accumulated powder into the finished product; (3) Low purity of raw materials; (4) The equipment is not thoroughly cleaned. The remedial measures that can be taken include: checking whether the filter material in the air filter is evenly laid, whether the filter has been used for too long, and if so, replacing it immediately; Check the situation of coke powder at the hot air inlet and overcome eddy currents; Filter the material liquid before spraying; Clean the equipment again.
The product powder particles are too fine, causing serious powder loss and low product yield
Product particles that are too fine can affect their solubility and blending performance. The reason is that the solid content is too low or the feed amount is too small. The remedial measures are to increase the solid content of the feed liquid, increase the feed rate, and increase the inlet air temperature. Excessive powder loss greatly affects the yield of finished products, and the general reason is the poor separation effect of the cyclone separator. If this situation occurs, check whether the cyclone separator is deformed due to knocking or collision; Improve the airtightness of the inlet and outlet of the cyclone separator, and check if there is any blockage of accumulated material on its inner wall and discharge outlet. Of course, the separation efficiency is also related to the specific gravity and particle size of the powder. For certain materials, a second level of dust removal can be added as needed.
The rotating speed of the centrifugal nozzle of spray drying equipment is too low, and the evaporation capacity is too low
The main issue is that the centrifugal nozzle component has malfunctioned, so it is necessary to stop using the nozzle and inspect the internal components of the nozzle. The reason may be: a decrease in the air volume of the entire system; The inlet temperature of hot air is too low; The equipment has air leakage and cold air enters the drying room. The remedial measure is to check whether the speed of the centrifuge is normal; Check if the position of the centrifuge control valve is correct; Check if the air filter and air heater pipes are blocked; Check if the grid voltage is normal; Check if the electric heater is working properly; Check if the connections of each component of the equipment are sealed.
There is noise or vibration during the operation of the centrifugal nozzle
Mainly due to improper cleaning and maintenance of the nozzle, residual substances may be attached to the spray disc or the spindle may bend and deform, which may also be due to poor dynamic balance of the centrifugal disc. Solution: Check whether there is any residual substance in the spray tray, and clean it in time if there is any; If abnormalities are found in the spindle, it is necessary to replace or readjust the dynamic balance of the centrifugal disc.
