Research progress of spray drying in the processing and utilization of biomass resources

Spray drying technology is widely used in many industrial production fields. This paper summarizes the development of spray drying in the processing and utilization of biomass resources from the aspects of process, mechanism, product quality and energy saving. There are some problems, such as the deterioration of product quality due to high intake air temperature; product sticking in the drying chamber or process tube; low energy efficiency of the system and destruction of active substances in biological products, etc., which need improvement in process and equipment And improve, so it is necessary to conduct more in-depth research on spray drying technology.

Spray drying is a drying process in which a solution, emulsion, suspension and slurry material are processed into a powder, granule, hollow sphere or agglomerated dry product in a single process. The research on spray drying technology began in the early 20th century and has a history of more than 100 years. At first, this technology was mainly used in the manufacture of skim milk powder and applied in the food industry. With the maturity of spray drying technology, its application range has gradually expanded. At present, this technology has been obtained in many industries at home and abroad. Wide range of applications, such as in the food industry for the production of milk powder, whey powder, soy milk powder, egg powder, juice powder, instant coffee, etc. In addition, in other industries such as chemistry, medicine, paper, ceramics, fertilizer, metallurgy Industrial production such as detergents, environmental protection, and biomass active substances are also used. There are a wide range of biomass resources in nature, and extracting beneficial ingredients that have a health-care effect on human health, and making various powdery or granular products that are easy to preserve are important aspects of current development. Spray drying is an essential part of the process of processing and utilizing biomass resources. In the forestry industry, concentrated tannin liquid, disproportionated rosin soap, wood glue, etc. can be completed by atomization drying. The staff used the spray drying process to process the jujube, which not only preserved the nutritional value of the jujube, but also provided a way for the diversification of jujube products. By analyzing the nutrient composition of the fish paste protein fen after spray drying, the data is compared with the quality fishmeal data to find the gap. Although spray drying technology has been greatly developed in terms of depth and breadth in the processing and utilization of biomass resources, it still has its shortcomings, such as the diversity of biomass materials and the differences of various materials, drying. The influence of different quality requirements of the product, the process not only needs to change with the material but also the complexity. Therefore, the research on the spray drying process in the processing and utilization of biomass resources is still an important research content of researchers all over the world. Another example is the spray drying device. The thermal efficiency is between 30% and 70%, so improving the heat utilization rate of spray drying in the processing and utilization of biomass resources is also an important aspect of research. In view of the fact that the in-depth study of spray drying technology CY-8000Y has practical significance for the development and utilization of biomass resources, this paper analyzes and summarizes the development degree of spray drying technology in biomass resources, and at the same time makes the future development trend. Outlook.

1 Study on the mechanism of spray drying in the processing and utilization of biomass resources

1. 1 Study on atomizer performance and atomization mechanism

The atomizer is the core device for atomizing liquid into fine droplets, and its performance directly affects product quality and technical and economic indicators. In production, it is often the case that large particles do not dry out and small particles are already dry. Therefore, the atomizer must meet the production process requirements, not only to ensure the dispersion of the liquid, but also to control the particle size change to a small limit. Theoretically, the relationship formula between atomizer flow rate and atomization angle in spray drying technology is derived. Based on the aerodynamic interference theory, the theoretical formula of the average diameter of droplets after atomization is derived, and their internal relations are found, and relevant experimental data are obtained. authenticating. The staff made a detailed analysis of the causes of centrifugal atomization, and obtained three ways of forming droplets: direct splitting into droplets, filamentous splitting into droplets, and membrane splitting into droplets. Through the comparison and analysis of four kinds of airflow nozzles, such as two-fluid external mixing, two-fluid internal mixing, three-fluid internal mixing and three-fluid internal and external mixing, under different nozzle geometry, liquid-liquid properties and operating conditions, For the application of the nozzle, for example, the two-fluid internal mixing nozzle has a small energy consumption, which is a suitable nozzle for atomization of most low-viscosity materials with water and physical properties close to water; the three-fluid internal mixing nozzle consumes more energy than the two-fluid internal mixing type. Suitable for use in high viscosity materials.

1. 2 Movement and relative motion of airflow and particles during spray drying

The spray drying system is a complex system with multiple inputs and multiple outputs. It takes a long time, has a large loss, and has a high test cost. With the development of computer technology, the complicated process of simulating spray drying has become possible. Combined with the characteristics of spray drying, a model of gas-particle two-phase turbulent flow in simulated spray drying room was established. The computational fluid dynamics was used to simulate the gas-grain two-phase flow of food drying in the dryer. The origin of the sediment particles in the food spray drying was studied, and the suitable conditions for reducing the wall deposition rate were obtained: zui large spray taper 60b and zui a large number of vortex intake 62b. The computational fluid dynamics was used to compare the spray drying properties of maltodextrin in centrifugal atomizer and pressure tube atomizer. The simulation results show that the two atomizers produce very different particle size distribution and atomization pattern. Particle trajectories show different temperatures, flow rates, and drying characteristics, providing the material for a feasibility study to achieve spray drying of multiple biomass materials in a spray drying chamber. Although the application of CFD has become more and more extensive, the model verification of CFD requires more experimental data support, and it is difficult to obtain good test data in the spray drying environment in the processing and utilization of biomass resources, making CFD technology in the spray drying of biomass materials. The application has yet to be further improved.

1. 3 The drying rate of the droplets and the shape of the product

The drying rate of droplets is directly related to the distribution of droplets. Mass production practices have shown that the particle size distribution of biomass powders is affected by the following process parameters: feed concentration, feed rate, temperature, atomization method, drying medium flow, Gas-liquid contact mode and properties of solvents and solutes. The biomass product obtained by spray drying is generally spherical particles, but the improper control of the process parameters often leads to deformation of the particles, such as hollow spheres, hollow rings, ellipsoids or apples. By analyzing the temperature and particle state changes of the biomass material in the whole spray drying stage, the relationship between the glass transition characteristics of the biomass material and the product quality and the drying process parameters was studied, so as to improve the drying rate of the droplets and obtain qualified The shape of the product provides a theoretical basis. For biomass materials, due to the natural and biomass properties of the products, the requirements for the drying process are more stringent. Improper drying processes will directly reduce the quality of the products, such as color, aroma, taste, active active ingredients, etc. Process research continues to present new challenges.

2 Process research on spray drying system in the processing and utilization of biomass resources Spray drying process is a multi-disciplinary system engineering involving heat transfer, mass transfer, fluid mechanics, mechanical engineering, automation technology, etc., in the processing and utilization of biomass resources. The steady state of the process is mainly affected by the following factors: different materials to be processed; different requirements for drying products; significant differences in drying time; physical changes, chemical changes, mass transfer and heat transfer processes during drying vary; The heat input method is different; the control method is different. Many researchers at home and abroad are also researching based on these differences to optimize their processes and improve their efficiency. For example, in the food industry, two-fluid and high-speed rotation of modified edible microcrystalline cellulose solution is carried out according to the solid content of the solution. In the dish spray drying test, the spray drying characteristics of modified edible microcrystalline cellulose were studied, and the optimized spray drying conditions for the economic operation of modified edible microcrystalline cellulose were obtained: hot air inlet temperature 160 ~ 170 e, dry The air temperature of the tower is 85 ~ 92 e, the solid content of the liquid is 12%, the temperature of the liquid is 60 e, the atomization method is two-fluid atomization; the optimal spray drying conditions for obtaining fine powder: hot air inlet temperature 170 e The air temperature of the drying tower is 90 e, the solid content of the liquid is 2%, the temperature of the liquid is 60 e, and the atomization method is a high-speed rotating disc. According to the stability of carotenoid powder, the production process of carotenoid powder was studied. The obtained process conditions were as follows: the solid content of the feed was 15%, the inlet temperature was 135~145 e, and the outlet temperature was 90~100 e. In addition, in the pharmaceutical, paper, feed and other biomass resources processing and utilization industries, there are a lot of researches on spray drying process and optimization of process conditions. Another important direction in the current research on the processing and utilization of biomass resources is microcapsule process research, which is to prepare microcapsule preparations from the active ingredients extracted from biomass resources by spray drying technology. This technology prevents oxidation, hydrolysis and volatilization of active ingredients in the formulation, masks bad odors, improves stability and bioavailability, and reduces irritation, toxicity and side effects. Microcapsule technology is widely used in traditional Chinese medicine, such as slow release, prolonged drug release time to reduce the number of doses; it can also be made into a targeted preparation for targeted action on the affected area. There are two methods for preparing microcapsules by spray drying, namely fluidized bed spray drying and droplet spray drying, wherein droplet spray drying is a commonly used method in the preparation of microcapsules, which is a mixture of a capsule and a capsule directly. A method of dispersing into a droplet by an atomizer and rapidly evaporating and drying in a hot gas stream to form a microcapsule. The spray drying method is suitable for microencapsulation of lipophilic liquid materials, and the stronger the water repellency of the core material, the better the embedding effect. In recent years, many researchers at home and abroad have been engaged in the research of microcapsule technology for the processing and utilization of biomass resources. The effects of emulsion configuration and related spray drying process parameters on the microencapsulation process in the process of preparing microcapsules by spray drying technology are detailed. Explain that the diversity of wall materials and the diversity of nuclear materials, as well as the preparation of emulsions and the diversity of parameters during spray drying, make the process of spray drying to prepare microcapsules quite complicated, and must pay attention to wall materials, nuclear materials, Good influence factors such as feed rate, concentration, temperature and inlet and outlet air temperature can obtain good microcapsule products. The product was stabilized by changing the process parameters by spraying the single crucible with a gum arabic by spray drying technique.

3 Research on the effect of spray drying on product performance in the processing and utilization of biomass resources. The indicators for judging product quality in the spray drying of biomass materials usually include product particle size distribution, residual water content, particle morphology, bulk density, color, Active substance content, resolubility and fluidity. In actual production, it is quite difficult for these indicators to meet the requirements at the same time, and users often only emphasize one or several of them. The factors affecting the performance of these biomass products can be broadly divided into two major parts: equipment and process.

3. 1 Impact of equipment on product performance

In the equipment, the atomizer is mainly used. The atomization of the biomass material directly affects the particle size distribution, which indirectly causes the particle shape to be diversified, the residual water content to increase, the color unevenness, and the active substance content to decrease. , re-solubility and fluidity are all worse, and even cause sticking to the wall, interrupting production. Atomizers are generally classified into centrifugal atomizers, pressure atomizers, and airflow atomizers. Generally, the centrifugal atomized particles are fine, the required power is small, the solid content and viscosity of the material are not required, and the fluctuation of the feed rate has little effect on the droplet size; the droplet atomization generated by the pressure atomizer It is thick and suitable for three types of drying methods: downstream, countercurrent and mixed flow. The airflow atomizer produces uneven particles and consumes a lot of energy. The spray angle of the atomizer was studied with food as the raw material, and it is considered that the zui is 62b, which can make the wall deposition rate tend to decrease. After the accurate calculation of the proposed diameter (ie volume-area diameter), mastering the spray droplet distribution to improve product quality, improve the structure and performance of the sprayer, accurately determine the drying tower diameter and tower height, reduce energy consumption, etc. An important role.

3. 2 Effect of process on product performance

Factors affecting product performance in the process include the choice of excipients, ratio, feed of the mixture, discharge, filtration, and temperature and flow of the inlet and outlet gases. In the spray drying of whey protein, the solubility loss of B-lactoglobulin and A-lactalbumin was studied, showing that the solubility of the two proteins is not affected by the temperature of the low temperature (60~ 80 e) outlet gas. However, it is affected by the temperature of the high temperature (100~120 e) outlet gas, and the solubility of B-lactoglobulin is reduced. The research progress of spray drying in the processing and utilization of biomass resources is more serious than that of A-lactalbumin. Increasing the feed concentration at higher outlet gas temperatures also results in a significant decrease in solubility. The effects of operating conditions (such as operating temperature, feed rate, spray, annular gas rate, etc.) on the quality of mango sauce in spray fluidized bed drying were investigated. Experiments have shown that high production temperatures provide better drying performance and product quality. . In summary, most researchers at home and abroad have conducted experimental research on certain biomass materials, and have not been able to find a general law or trend, and the quality of products is the purpose of drying, therefore, in a variety of It is necessary to further study the spray drying technology in the processing and utilization of biomass resources, especially to study the law of the drying process of biomass resources containing active substances.

4 Spraying in the utilization of biomass resources

Research on energy saving and sticking problems in drying With the global energy shortage and the skyrocketing energy prices, energy conservation and consumption reduction have become the research topics of various countries. In the processing and utilization of biomass resources, spray drying technology itself is a unit operation with high energy consumption. Reducing energy consumption and improving heat utilization are the common goals of researchers in various countries. Through in-depth study of economic analysis and energy-saving technology of spray drying equipment, the main factors affecting the energy consumption of spray drying and the corresponding results are obtained, and the targeted methods to solve the high energy consumption of spray drying are proposed: 1) Adjusting the spray The drying operation parameters can achieve the energy-saving effect, and the drying inlet temperature can be increased, the outlet temperature can be lowered, the original content and temperature of the liquid solution can be appropriately increased, and the relative humidity of the imported ambient air can be reduced; 2) adjusting from the spray drying process to achieve energy saving purposes, After spray drying, exhaust air waste heat recovery, such as heat exchange recovery, concentrated feed liquid, etc., may also be taken to return the partially exhausted air to the dry air inlet section or directly combined drying; 3) from the spray drying equipment itself, strengthen the equipment insulation , heat insulation, reduce unnecessary heat dissipation; 4) For different biomass materials, the above combination is used. Spray drying can achieve the desired energy saving effect in the processing and utilization of biomass resources. The application of the direct-fired hot air device with the linear burner as the core on the spray drying tower focuses on the energy consumption of the linear burner direct-fired hot air device, the steam boiler hot air device and the electric heating hot air device. The data analysis shows that the linear burner direct-fired hot air device has certain advantages in energy saving compared with the conventional hot air device with heat exchanger. In the spray drying of biomass resources, the biomass material has the characteristics of high sugar content and heat sensitivity, which makes the problem of sticking wall a major obstacle to the processing and utilization of biomass resources. In addition to reducing the quality of the product, the sticky wall can also interrupt production and at the same time cause energy waste, which has always been a problem that is difficult to solve in biomass spray drying. Aiming at the sticking phenomenon in the drying of Chinese herbal extracts, the main types of sticking walls and their influencing factors were analyzed, and the method of focusing on the sticky wall was introduced. The structure and process adjustment of the drying tower of traditional Chinese medicine were explained by experiments to solve the extraction of traditional Chinese medicine. The effectiveness of liquid spray drying sticking problems. In a medium spray drying test with a two-fluid atomizer and a height of 1.5 m, the adhesion of skim milk and maltodextrin was compared in the same process conditions: atomizer gas pressure 200 KPa, intake air temperature 230 e, feed rate 1. 6 L / h, spray drying of skim milk and maltodextrin respectively. The results showed that the malt dextrin stick wall was lighter than skim milk, which may be related to the higher glass transition temperature of maltodextrin.

5 Outlook

Although spray drying technology has matured on the surface in the processing and utilization of biomass resources, it is often encountered in industrial applications, mainly due to the limitations of research materials and the differences and complexity of biomass materials. Wait. For the limitations of material types, most of the research occurs in chemical products. For the drying of biomass resources, the drying of high value-added products is less, so the spray drying technology is still used in the processing and utilization of biomass resources. There is a broad space for research and development, and there are several aspects worthy of study: 1) The quality of biomass products obtained by spray drying by the business community and researchers still needs in-depth research, so that products obtained from natural biomass resources are more It retains its original internal biomass activity and also has good solubility. The active ingredients will not deteriorate and will not volatilize during storage. The storage period is limited by the length of time and storage conditions. 2) In-depth study of the influence of process parameters of spray drying technology on various properties of biomass products, and find the corresponding relationship between various process parameters and impact performance, in order to obtain better biomass products. 3) Biomass spray drying process operation is not universal. The limitations of dry materials make the scope of spray drying technology in the processing and utilization of biomass resources need to be further expanded, and more biomass drying products should be developed to meet the special needs of the market. . 4) Compare the spray drying technology with the freeze-drying technology in the processing and utilization of biomass resources, explore the low-temperature or sub-low temperature spray drying technology, find the optimization process for processing heat-sensitive biomass materials, and change the history of freeze-drying heat-sensitive biomass materials. Or combined with other drying technologies, on the basis of ensuring the quality of biomass products, Zui has a large amount of energy saving. In addition, in the harmonious development of man and nature, creating a harmonious society today, in the processing and utilization of biomass resources / green 0 drying technology is also a major direction of spray drying technology research.