In order to solve the problem of removing small impurities after straw harvest, the raw materials of corn straw with grain size less than 10mm were divided into 9 grain size grades by sample analysis compost trommel screen, and then the thermal characteristics and settlement test were carried out. Through the comparative test of thermal characteristics of corn straw raw materials with different particle sizes, the proportion and influence of dust and other fine particulate matter impurities in raw materials with different particle sizes were analyzed. It was found that the dust mass fraction of materials with particle size of 0.2~0.33 and <0.2mm was more than 50, but the percentage of total mass was only 3.39. Therefore, it is suggested that the best size range of raw material screening is <0.33mm. Optimized and modified screening and impurity removal device, the best working conditions of the technical parameters are: screen length 1000mm, screen diameter 500mm, screen inclination Angle 10%, speed 34r/min, screen mesh aperture 0.33mm. Using the device, screening condition determination test, verification and comparison test and economic analysis, it is found that: the use of the screen after the material pressing block forming, volatile and calorific value has been greatly increased, ash reduced 25.21 greatly reduce the straw material on the key parts of the molding machine caused by wear and slag risk of combustion equipment. After sifting, the economic value of the pressing fuel is increased to 563.5 yuan /, which can increase the income by 6.91. This paper presents a screening technology and auxiliary equipment suitable for the large-scale production of biomass molding fuel in China, which provides technical support for the cleaning process of biomass fuel and provides important parameter basis for the energy utilization of straw.
As a clean renewable energy, crop residues such as straw can be compressed into biomass molding fuel, which can directly replace coal and has great application potential. However, due to more impurities in crop straw raw materials (metal, plastic fabric, dust, soil, fine sand, etc.)-I, affect the quality of biomass molding fuel products.
In the crushed straw, the content of large particle size impurities such as metal and plastic fabric is lower, <0.01, while the content of small particle size impurities such as dust and sand is higher. The composition of the dust is complex, and the fine sand and stone it contains will aggravate the wear of the key parts of the molding equipment. The mixed dust and small particle size materials will directly affect the calorific value and combustion characteristics of the fuel. Therefore, in the straw molding production, should try to remove the small particle size impurities.
The research and application of screening in China are mostly concentrated in coal mine, metallurgy, chemical industry, building materials and other aspects. The few researches used in the field of biomass energy are also concentrated in the process of raw material acquisition and material conveying 123, which cannot solve the problem of removing small and medium impurities in straw after harvest.
Therefore, this paper mainly studies corn straw raw materials with particle size below 10mm. It is intended to study the influence of dust and other fine particles on the quality of corn straw raw materials through the comparative test of thermal characteristics of corn straw raw materials of different sizes, analyze the proportion and influence of impurities in raw materials of different sizes, put forward the best size range of raw materials screening, improve the purity of raw materials, optimize the design of a connected between the crusher and the molding machine impurity removal device. In order to ensure the fuel quality of the molded corn straw, it provides parameters for the energy utilization of the straw.
3.1 Transformation and processing of compost trommel screen through the above test analysis and reference to a large number of literature, on the basis of the previous production of compost trommel screen F transformation and processing. The roller screen is adjustable for length-diameter ratio, dip angle and roller speed, and the aperture is 5mm, which can remove the straw impurities of 5mm particle size.
In the general compost trommel screen screening industry, the dip Angle range is 25, and the application in the straw solid molding of material impurities screening Angle range is far beyond this value.
This is because the content of impurities in straw materials is relatively small, generally less than 3, rarely more than 10. Therefore, the original compost trommel screen processing is: screen cylinder length 1000mm, diameter 500mm, inclination 10, according to the previous screen processing into the aperture of 0.33mm, the motor speed is controlled by the frequency converter, through the chain drive and the roller spindle connected to drive the drum screen rotation, so as to achieve the purpose of removing the particle size of 0.33mm impurities.
3.2 The best working condition of the compost trommel screen determines that the drum screening should be in the cascade movement as far as possible, to avoid centrifugal and sliding movement 1-7, combined with literature and the test found that when the drum speed is 22r/min, the material appears the phenomenon of sliding movement; When the rotating speed of the cylinder is 40r/min, centrifugal movement occurs. Therefore, through the control of the roller speed, with the screening rate as the main index, get the best operating condition of the compost trommel screen.
The test results are shown in Table 5. Through the control of the rotating speed of the compost trommel screen, the test shows that the rotating speed of the compost trommel screen increases from 24r/min to 38r/min, and the screening rate increases first and then decreases. When the rotating speed is 34r/min, the impurity removal effect is the best, and it is determined as the best working condition.
3.3 By comparing the forming rate of straw pressing block and the thermochemical engineering characteristics of the pressing block before and after the screening of raw materials, the impurity removal efficiency of the compost trommel screen was analyzed. Under the optimal parameters of roller screening test, the crushed piles of straw placed in the open air were sampled. 1kg of straw formed by pressing block after installation of screening device and 1kg of straw formed by pressing block without installation of screening device were taken respectively. After drying and mixing evenly, the thermochemical engineering characteristic values were tested.
According to the test analysis of the thermochemical engineering characteristics of the materials before and after screening in Table 6, it can be seen that the molding rate of straw particles before and after screening has little influence, but the ash content of the materials after screening decreases significantly, from 13.21 before screening to 9.88, and the ash content decreases by 25.211.
The ash content is greatly reduced, which reduces the influence of wear on the key parts of the molding machine and slagging on the blockage of the burner. Volatilization and calorific value increased significantly. Volatilization after screening increased by 3.52 and calorific value increased by 11.27 compared with that before screening.
