Zhong Liang, Shao Zengqi, Tang Xingyan, Wang Xiaoxia
(Nanjing Rongdian Food Technology Co., Ltd., Jiangsu Province Instant Tea Powder Engineering Technology Research Center, Nanjing 211300, China)
Abstract: As a kind of high-quality clean fuel, biomass pellet fuel has attracted more and more people's attention. Taking tea residue biomass as raw material and sludge as binder, research on key technology of pellet molding shows that: The preferred preparation technique is that the moisture content of the tea residue is between 13% and 17%; the outlet temperature of the three-return tumble dryer is 85 to 90 ° C; the sludge addition ratio is 5% to 10%; and on this basis, A large-scale (time-production 3t), low-cost tea residue biomass fuel production line has been built, which provides a new way for the comprehensive utilization of tea.
Energy is the material basis for the survival and development of human society. With the rapid development of the world economy and the rapid increase in population, the demand for energy will continue to increase. [1]In addition to the reduction of fossil fuels and the environmental pollution caused by it, it is especially important to find renewable energy. Biomass fuel is gradually being valued because of its renewable and small pollution. [2]Biomass pellet fuel mainly uses agricultural and forestry waste as raw materials, and is converted into granular fuel by special equipment. [3]China is a big country in tea production and consumption. Every year, it produces a lot of tea waste, which pollutes the environment and wastes resources. The comprehensive utilization of waste tea residue has been studied extensively at home and abroad, mainly focusing on the extraction of active ingredients of tea residue. Tea residue adsorbent, tea residue as biological organic fertilizer, animal feed, edible fungus culture material, etc. [4]1. Preparation of biomass pellet fuel with tea residue has rarely been reported.
In this paper, the waste tea residue is used as raw material to study the key technical parameters of the preparation of pelletized fuel with sludge compounding. On this basis, the large-scale tea residue biomass pellet fuel production line is finally completed, which is the treatment of waste tea residue in tea deep processing enterprises. And use to provide a new way.
1 Materials and methods
1.1 sample preparation
Tea residue: The particle size is 2.36~ 4.75mm. It is pressed by a diaphragm type frame filter press to 55%~60%, the pressing pressure is 1.2~1.5Mpa, and the pressing time is 20~30min.
Sludge: Pressed with a diaphragm-type frame filter press to a moisture content of 68% to 73%, a press pressure of 1.2 to 1.5Mpa, and a pressing time of 20 to 30 minutes.
1.2 main instruments and equipment
Diaphragm plate and frame filter press purchased from Jingjin Environmental Protection Co., Ltd., filter filter area 400m 2The thickness of the filter cake is 35~40mm; the three-return tumble dryer is purchased from Jingjiang Wansu Machinery Manufacturing Co., Ltd.; the ring mold machine is purchased from Jiangsu Muyang Group Co., Ltd., the production processing capacity is 1.5t/h, and the power consumption is 55kW/t. , the inner diameter of the ring mold is 420mm; DHG-9003BS electric heating constant temperature blast drying box is purchased from Shanghai Xinmiao Medical Device Manufacturing Co., Ltd.; AL204 electronic balance is purchased from METTLER TOLEDO (Shanghai) Co., Ltd.; SDACM3000 calorimeter is purchased from Changsha Sande Industrial Co., Ltd.
1.3 method
1.3.1 Effect of water content of tea residue on molding
The effect of water content on fuel forming is much studied. Most of the research results tend to be consistent. Considering the research results of various scholars, the moisture content of granulated tea residue is not more than 20% '5', and the water content is 9.5. %, 11.0%, 12.3%, 13.5%, 15.2%, 16.8%, 17.7%, 18.5%, 20.1% of the sample, the moisture content of the granulated tea residue was determined by the molding density and the appearance of the granules.
1.3.2 Three-way tumble dryer drying temperature optimization
According to the results of 1.3.1, adjust the outlet air temperature of the three-return tumble dryer, and set the outlet air temperature to 78 °C, 82 °C, 85 °C, 87 °C, 90 °C, 92 °C, 95 °C, and several gradients. The determination of the moisture of the tea residue makes the water content of the tea residue meet the granulation requirements.
1.3.3 Effect of sludge addition ratio on molding fuel
Add 0%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50% of the sludge separately, mix with the tea residue and use the ring mold particle mechanism to measure the density of the particles and Calorific value, determine the proportion of sludge added.
1.3.4 analysis of industrial components of tea residue biomass pellet fuel and coal
The tea residue biomass pellet fuel and the commercially available coal will be prepared, and the industrial component analysis will be carried out according to relevant industry standards and national standards.
Design of production line for producing 3 tons of tea residue biomass pellet fuel at 1.3.5
On the basis of the previous research, the production line of 3t tea residue biomass pellet fuel is designed according to the amount of tea residue produced by the enterprise.
1.4 Analysis method
1.4.1 Determination of moisture content
The sample is baked in a constant temperature drying oven at 105±5°C for 4~8h, and then weighed after cooling. Repeated baking for 1~2h to be weighed after cooling, until the difference between the two weighings is less than the sample one.
1.4.2 Determination of molding density
Reference Cai Wenbi [5]Forming density determination method, the formed tea residue biomass pellet fuel is naturally air-dried at room temperature, and the length, diameter and quality of the formed fuel are respectively measured by a vernier caliper and an electronic balance, and the biomass pellet fuel is calculated according to the following formula. Density.
1.4.3 Determination of calorific value
According to the method specified in GB/T 213-2008 "Calculation method of calorific value of coal", '6', the average value of high calorific value and low calorific value is calculated.
1.4.4 Analysis method of coal industry composition
Determination of moisture, ash, volatile matter and fixed carbon of coal according to GB/T 212-2008 "Industrial Analysis Method of Coal"[7]Determination of the method specified in the method, total sulfur according to GB/T 214-2007 "Method for determination of total sulfur in coal"[8]The method specified in the determination.
1.4.5 Biomass forming fuel industrial composition analysis method
Test method for moisture, ash and volatile matter of tea residue biomass pellet fuel with reference to biomass solid molding fuel [9]The method specified in the method, fixed carbon and total sulfur refer to GB/T 212-2008 '7' and GB/T 214-2007 respectively[8]The method specified in the determination.
2 results and analysis
2.1 Influence of water content of tea residue on molding
The moisture content of the material has a relatively large influence on the compression molding effect of biomass, which is a very important factor in the process of biomass molding. [10]If the moisture content is too low, the lignin can not be fully converted, the bonding effect is greatly reduced, and the compressive strength between the particles is enhanced. Not only the molding is difficult, but also excessive compression energy is generated; the moisture content is too high, and the heating process is generated. The steam can not be discharged from the center hole of the molding fuel. The light will cause the fuel to crack, the surface is very rough, and the heavy one will produce a popping sound. At the same time, the high moisture content may also cause the heat conduction rate between the biomass particles to be greatly reduced. [11]It can be seen from Table 1 that when the moisture content of the tea residue is less than 13%, the molding density is small, the surface of the molding fuel is rough, and there are some cracks, and the molding effect is general; when the moisture content of the tea residue is higher than 17% or higher, the surface of the molded fuel has Crack, with the increase of water content, the poorer the forming effect, the worse the fracture resistance of the forming fuel, and the brittleness. When the moisture content of the tea residue is 15%~17%, the surface of the molding fuel is smooth, the density is large, and the forming effect The best. Considering that the water content control in the actual production process is difficult, it is not so strict, so the water content of the granulated tea residue can be between 13% and 17%. The test results are in line with the standard NY/T 1878-2010.[12]Basic performance requirements for technical conditions of biomass solid molding fuel.
2.2 Three-way tumble dryer drying temperature optimization
It can be seen from the results in Table 1 that the water content of the granulated tea residue is 13% to 17%, and the water content of the tea residue after pressing is generally about 55%. The return tumble dryer further dries the pressed tea residue. When drying, the drum frequency is fixed, that is, the drying time is the same, 15min, and the drying temperature is optimized under this condition. As can be seen from Fig. 1, the roller When the outlet temperature of the dryer is 85~90°C, the moisture content of the tea slag is 13%~17%, which can meet the requirements of granulation moisture content. Therefore, the outlet temperature of the three-return tumble dryer in production is 85. ~ 90 ° C.
2.3 Effect of sludge addition ratio on molding fuel
Figure 2 reflects the variation of the density and calorific value of the tea slag pellets when different ratios of sludge are added under other conditions. As can be seen from Figure 2, as the sludge addition ratio increases, the pellet fuel density increases first. Basically, it tends to be stable. When the sludge addition ratio reaches 20%, the density of the pellet fuel does not change much. This may be because the proper amount of sludge can fill the gap between the tea residue particles and increase the adhesion between the tea residue particles. 5', which is more conducive to the formation of tea residue. When the sludge addition ratio reaches 20%, it is enough to fill the particle gap. Continued addition of sludge has little effect on the filling of the gap between the tea residue particles and the adhesion between the particles. It is one of the important performance indicators of pellet fuel, which directly reflects the combustion quality of fuel.[13].
As can be seen from the figure, a small amount of sludge contributes to the combustion of the particulate fuel, probably because the sludge has a lower ignition point and can quickly start the combustion of the tea pellet fuel. [5]However, with the increase of sludge addition ratio, the calorific value of pellet fuel decreases significantly. Combined with fuel density and calorific value, the sludge addition ratio is 5%~10%.
2.4 Analysis of industrial composition of coal and tea residue biomass pellet fuel
Table 2 shows the industrial composition analysis of tea residue biomass pellet fuel and commercially available coal. It can be seen from Table 2 that the tea residue biomass pellet fuel has higher volatile matter, much higher than coal, and its ignition performance and combustion performance are better than coal. , belonging to highly active fuel [14]The carbon content is 19.75%, much lower than coal, which makes its calorific value lower than that of coal. [15]The prepared tea residue biomass pellet fuel meets the requirements of the industry standard NY/T 1878-2010 for the basic performance requirements of biomass solid forming fuels. [12], harmful components (sulphur and ash, etc.) are much lower than coal, burning NO X, SO 2The emission is much lower than that of coal, the combustion characteristics are obviously improved, and the utilization efficiency is significantly improved. It can be seen that the tea residue biomass pellet fuel has high quality, clean and high efficiency, and is an ideal fuel for replacing coal.
Design of 3 tons of tea residue biomass pellet fuel production line at 2.5 hours
Figure 3 is a plan layout of the workshop for producing 3 tons of tea residue biomass pellet fuel production line. It mainly includes computer control center, tea residue pressing system, tea residue drying system and granulation system. The main equipments include:
Diaphragm plate and frame filter press: The filter filter area is 400m 2Plate and frame machine, the theoretical thickness of the filter chamber is 35~40mm, and the effective volume is about 7m. 3The slag is about 4.2t per frame. The pressing conditions are: pressure 1.2~ 1.5Mpa, time 20~ 30min, water content of tea residue after pressing is 55%~60%, sludge moisture content is 68%~ 73%.
1.5~ 2t/h tea residue drying line: including water curtain dust pump, cyclone II, induced draft fan II, lift, screw discharge machine, cyclone fan I, kiln tail fan I, induced draft fan I Feeding spiral, feed screw, blower I, II. Drying conditions are: outlet air temperature 85~ 90 °C, drying time 15min, drying water slag moisture content 13%~ 17%.
A set of 3t tea slag granule production line equipment: one granulation speed is greater than or equal to 1.5t / h, the ring mold granule diameter is 8mm, the ring mold inner diameter is 420mm, the ring mold speed is 336r / min. The ratio is 5%~10%, and the granulator squeezes the mixture into Φ10~12mm cylindrical particles (see Figure 4). The particle density is ≥1g/cm. 3, water content ≤ 13%, ash ≤ 6%, low calorific value ≥16.9MJ / kg, breaking rate ≤ 5%, powdering rate ≤ 12%.
3 Discussion
In this paper, the waste tea residue is used as raw material to study the key technical parameters of the preparation of pelletized fuel with sludge. The main parameters are: the moisture content of tea residue is between 13% and 17%; the outlet of three-return tumble dryer The temperature is 85~90°C; the sludge addition ratio is 5%~10%, and on this basis, the large-scale tea residue biomass pellet fuel production line is finally completed, which provides a new treatment for the treatment and utilization of waste tea residue in tea deep processing enterprises. Route.
As a kind of agricultural resource with wide source and low cost, tea residue is in line with the sustainable development viewpoint. It promotes the comprehensive utilization of tea residue and extends the industrial chain to improve the economic and social benefits of China's tea industry. [4]4. Realizing the recycling of resources and energy saving and emission reduction of tea deep processing enterprises is an inevitable trend of the development of the whole industry.
Biomass energy is a renewable and clean energy source that can effectively alleviate the deteriorating environmental pollution and shortcomings of energy. It is considered to be one of the major new energy sources in the future, with significant social and economic benefits. [13, 16]In view of the current incomplete use of waste tea in the deep processing of tea, resulting in environmental pollution and waste of resources, the tea slag is innovated by dewatering with a frame and frame filter press, and then further dehydrated and dried by a tumble dryer and treated with wastewater. The sludge in the process is prepared into a tea residue biomass pellet fuel. At the same time, the large-scale production process and equipment of the tea residue biomass pellet fuel are systematically studied, and a 3t tea residue biomass pellet fuel production line is created to realize the tea residue biomass. Large-scale production and low-cost production of pellet fuel, for in-depth processing and utilization of tea deep processing enterprises [17]The prepared tea residue biomass pellet fuel is incinerated by biomass boiler to generate heat, which provides heat source for tea extraction process, can solve wet tea residue waste, reduce solid waste tea residue, waste sludge transportation and disposal cost, and make tea The slag is fully utilized, and it can replace the large amount of coal, effectively reduce energy consumption, and improve the energy utilization structure of the plant.
The tea residue biomass pellet fuel belongs to biomass energy, and the harmful substance content is only about 1/10 of that of coal, which can reduce air pollution. According to statistics, for enterprises that produce 0.5t instant tea powder, biomass fuel is used instead of coal. Can reduce SO by year 2Discharge 33t/a, reduce NO XThe emission is 29t/a, and the burnt ash can be used as a fertilizer to return to the tea plantation to achieve resource recycling and energy conservation (see Figure 5).
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