Paddy split-range variable-temperature drying process

Abstract

The invention belongs to the technical field of grain drying, and particularly relates to a rice drying process, in particular to a rice split-range variable-temperature drying process. The rice split-range variable-temperature drying process is carried out in a batch type circulating grain drying machine, and when used for rice with the water content higher than 22%, the rice split-range variable-temperature drying process comprises the following steps that 1, first-process drying is carried out, specifically, harvested rice with the water content higher than 22.00% is subjected to one or more drying-tempering circulation till the water content of the rice is reduced to 22.00 + / -0.50%; (2) second-process drying is conducted, specifically, the rice is subjected to one or more times of drying-tempering circulation till the water content of the rice is reduced to 18.00 + / -0.50%; and (3) third-process drying is conducted, specifically, the rice is subjected to one or more times of drying-tempering circulation till the water content of the rice is reduced to 14.00 + / -0.50%, and the rice is conveyed into a warehouse to be stored. According to the invention, the harvested rice is subjected to split-range variable-temperature drying which is completed by one-time drying, and the process from the process of feeding the unprocessed rice into the machine to the process of discharging the unprocessed rice out of the machine by safe water is completed by one-time drying without temporary storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of grain drying, and particularly relates to a process for drying paddy rice, especially a process for drying paddy rice with variable temperature in different stages. Background Art

[0002] Paddy rice is an important food crop in China. Nearly 60% of the population mainly eats rice. At the same time, paddy rice is widely planted in China. Generally, taking the Qinling Mountains and Huaihe River as the boundary, it is divided into two regions, the north and the south, with more paddy rice planted in the southern region. Due to the different climates and regions in the north and south, the moisture content of paddy rice after harvest will also be different. Paddy rice in the northern region is harvested in the relatively dry autumn, while paddy rice in the southern region is generally harvested in the high-humidity environment in summer and autumn. The difference in the harvesting environment results in a higher moisture content of paddy rice in the southern region. The harvesting period of southern paddy rice is concentrated, and the moisture content of most of it is higher than 22.0%. After harvest, paddy rice is extremely prone to heat and deterioration when stored in a high-temperature and high-humidity state. Excessive moisture content will cause deterioration of the quality of paddy rice during storage. Ensuring the quality safety of paddy rice after harvest and during storage is particularly important for ensuring the quality of grain. Therefore, it is necessary to carry out timely and effective drying treatment on the harvested paddy rice. Generally, it is required to dry the harvested paddy rice to a safe moisture content, that is, the moisture content is reduced to 13.0% - 15.0%.

[0003] In recent years, with the development of paddy rice planting in China, much progress has been made in the research on paddy rice drying. Paddy rice drying technologies include hot air drying, infrared drying, microwave drying, vacuum drying, solar drying, etc. The large-scale production and processing of paddy rice are restricted by various factors such as technology, cost, and site. Hot air drying still occupies the mainstream market. Different from the drying of other grains, paddy rice drying has particularities. For example, paddy rice is thermosensitive and has a large sensitivity to temperature. Excessive temperature during drying will cause a decline in quality. Secondly, paddy rice has special structural characteristics. Paddy rice is a false fruit, and the outer layer of the caryopsis grain is wrapped by the protective husk. The dense outer shell not only protects the caryopsis but also hinders the transfer of internal moisture, increasing the drying difficulty during drying. Generally speaking, the research on paddy rice drying is of great significance to the production and processing of paddy rice.

[0004] During the paddy rice harvesting season, if there is rainy weather, the moisture content of paddy rice at the time of harvesting is relatively high, and the relative humidity of the air is also relatively high. The quality of paddy rice is very easy to deteriorate, and mechanical drying for timely water reduction is highly needed. Machine drying requires high drying efficiency and can save energy as much as possible on the basis of ensuring quality. The drying process flow is paddy rice entering the machine - drying - tempering - drying - tempering... cyclic drying to reach the calibrated moisture content - tempering - leaving the machine. At present, continuous hot air drying is mainly used for paddy rice drying, including constant temperature drying and variable temperature drying in different stages.

[0005] The invention patent with publication number CN101878813A discloses a method for step-by-step drying of paddy rice, including: 1) the hot air temperature in the first drying section of high-moisture paddy rice is 80°C; 2) the hot air temperature in the second drying section is 62°C; 3) the hot air temperature in the third drying section is 56°C; 4) ventilation and placement of paddy rice in the input temporary storage bin; 5) after several days, the paddy rice in the temporary storage bin is input into the paddy rice dryer again for drying in the drying process of low-moisture paddy rice, which are 58°C, 53°C, and 51°C respectively; 6) the moisture content of the output is less than 14.5%; 7) or perform five cycles of 85°C, 62°C, 56°C, 58°C, and 56°C respectively, store for several days, and then perform hot air drying. This hot air drying process has a high hot air temperature, a slow reduction rate of the internal moisture of paddy rice in the later stage, and a high cracking rate of paddy rice under high-temperature drying.

[0006] The invention patent with publication number CN104351334A discloses a method for step-by-step drying of grains, including: 1) the moisture content of the raw grain > 21%, and the medium temperature is 60 - 70°C; 2) the moisture content of the raw grain < 21%, and the medium temperature is < 60°C; 3) the tempering time is 3 - 5 times the drying time; 4) the moisture content of paddy rice reaches about 18%, store it in the ventilation storage bin, and then dry it to the safe moisture content after the peak purchasing season. The water reduction rate of this drying process is relatively slow, and the drying quality is not shown. Both of the above two drying processes need to be stored and then continue drying, which is time-consuming, laborious, and costly.

[0007] The invention patent with publication number CN111397356A discloses a method for variable-temperature drying of grains, including: at the initial stage of drying, a relatively high drying temperature is not required, but a relatively large air volume is required. When the moisture value drops to a certain extent, a relatively high drying temperature is required, a relatively large air volume is not required, and a relatively long slow-down time is required. This drying method has a low drying temperature first and then a high drying temperature, and the tempering time is not clear.

[0008] In addition to hot air drying, the drying medium for paddy rice drying also has a method combining hot air drying and microwave tempering. For example, the invention patent with publication number CN105532866A discloses a method for microwave tempering drying of rice, and the invention patent with publication number CN110567258A discloses a mobile paddy rice drying equipment based on a microwave-hot air combined drying process. The invention patent with publication number CN107712042A discloses a step-by-step paddy rice drying method, including supercritical fluid treatment and variable-temperature hot air drying treatment steps. The drying machinery of the above combined heat source drying methods requires multiple heat source devices, the dryer is complex and expensive, and the volume space for drying paddy rice needs to be increased.

[0009] At present, the major rice-producing provinces in China have gradually strengthened the basic conditions for timely drying of rice after harvest. By the end of 2023, the mechanized drying coverage rate of rice in Jiangsu Province was close to 90%. How to improve the water removal rate, output, working efficiency, and utilization efficiency of grain dryers while ensuring the drying quality of rice and enhancing the economic benefits of grain dryers is one of the urgent problems to be solved. Summary of the Invention

[0010] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a stepwise variable-temperature drying process for rice.

[0011] The technical solution for the present invention to solve the technical problem is as follows:

[0012] In the first aspect of the present invention, there is provided a stepwise variable-temperature drying process for rice, which is applicable to rice with a moisture content higher than 22%, and is carried out in a batch-circulating grain dryer, including the following steps:

[0013] 1) First-stage drying: The harvested rice with a moisture content higher than 22.00% is subjected to one or more drying-slowing cycles until the moisture content of the rice drops to 22.00 ± 0.50%.

[0014] 2) Second-stage drying: The rice is subjected to one or more drying-slowing cycles until the moisture content of the rice drops to 18.00 ± 0.50%.

[0015] 3) Third-stage drying: The rice is subjected to one or more drying-slowing cycles until the moisture content of the rice drops to 14.00 ± 0.50%, and then it is sent to the warehouse for storage.

[0016] Among them, the first-stage drying adopts hot-air drying, the hot-air temperature is 65.0 ± 1°C, the drying time in each drying-slowing cycle is 12 ± 1 min, and the ratio of the slow-down time to the drying time in each drying-slowing cycle is 6:1 to 4:1.

[0017] The second-stage drying adopts hot-air drying, the hot-air temperature is 55.0 ± 1°C, the drying time in each drying-slowing cycle is 12 ± 1 min, and the ratio of the slow-down time to the drying time in each drying-slowing cycle is 6:1 to 4:1.

[0018] The third-stage drying adopts hot-air drying, the hot-air temperature is 47.0 ± 1°C, the drying time in each drying-slowing cycle is 12 ± 1 min, and the ratio of the slow-down time to the drying time in each drying-slowing cycle is 6:1 to 4:1.

[0019] Preferably, in the first-stage, second-stage, and third-stage drying, the ratio of the slow-down time to the drying time in each drying-slowing cycle is 5:1.

[0020] In the second aspect of the present invention, a stepwise variable-temperature drying process for paddy is provided, which is applicable to paddy with a moisture content lower than 22% and higher than 18%, and is carried out in a batch-circulating grain dryer, including the following steps:

[0021] 1) Subject the paddy to one or more drying-slowing cycles until the moisture content of the paddy drops to 18.00 ± 0.50%;

[0022] 2) Subject the paddy to one or more drying-slowing cycles until the moisture content of the paddy drops to 14.00 ± 0.50%, and then send it to the warehouse for storage.

[0023] Among them, in the first step of drying, hot-air drying is adopted, the hot-air temperature is 55.0 ± 1 °C, the drying time in each drying-slowing cycle is 12 ± 1 min, and the ratio of the slowing time to the drying time in each drying-slowing cycle is 6:1 to 4:1.

[0024] In the second step of drying, hot-air drying is adopted, the hot-air temperature is 47.0 ± 1 °C, the drying time in each drying-slowing cycle is 12 ± 1 min, and the ratio of the slowing time to the drying time in each drying-slowing cycle is 6:1 to 4:1.

[0025] Preferably, in the first and second steps of drying, the ratio of the slowing time to the drying time in each drying-slowing cycle is 5:1.

[0026] In the third aspect of the present invention, a stepwise variable-temperature drying process for paddy is provided, which is applicable to paddy with a moisture content lower than 18% but higher than 14%, and is carried out in a batch-circulating grain dryer, including the following steps: Subject the paddy to one or more drying-slowing cycles until the moisture content of the paddy drops to 14.00 ± 0.50%, and then send it to the warehouse for storage;

[0027] The paddy drying is carried out by hot-air drying, the hot-air temperature is 47.0 ± 1 °C, the drying time in each drying-slowing cycle is 12 ± 1 min, and the ratio of the slowing time to the drying time in each drying-slowing cycle is 6:1 to 4:1.

[0028] Preferably, the ratio of the slowing time to the drying time in each drying-slowing cycle is 5:1.

[0029] In the present invention, the number of drying - tempering cycles is not fixed and is determined by factors such as the initial moisture content of paddy and the drying temperature. The time of each drying - tempering cycle is determined by the discharge amount of the feeding mechanism per unit time. The drying time is related to the feeding frequency of the feeding wheel and can be selected from 30 Hz, 50 Hz, etc. The volume of the drying section is fixed, and the drying time is calculated based on the feeding frequency and the volume of the drying section. The volume of the tempering section of this model can reach up to 5 times that of the drying section. According to the radar level sensor, the volume of paddy in the upper tempering section is judged, and the tempering time is calculated proportionally.

[0030] The present invention has the following technical effects:

[0031] 1) The present invention adopts a step - variable temperature drying method for one - time drying of harvested paddy. From the time when the raw grain enters the machine for drying to the time when it exits the machine at a safe moisture content, the drying is completed in one - time without the need for a temporary storage drying method. Aiming at the phenomenon that the quality of paddy decreases due to simple hot - air drying, especially high - temperature constant drying, and the problem of long drying time in low - temperature constant drying, the present invention uses initial high - temperature drying to quickly remove the surface moisture of paddy, and later low - temperature drying to avoid the quality decline problem caused by uneven internal moisture loss. The residual heat during the drying of high - moisture paddy is used to reduce the drying temperature of the paddy undergoing the second - stage drying, reducing the loss of the dryer and improving the drying efficiency. The drying efficiency of paddy with the same moisture content is increased by 0.3% / h, enabling the grain dryer to perform drying operations more efficiently after the paddy harvest season, and improving the utilization efficiency and economic benefits of the grain dryer.

[0032] 2) Utilizing the tempering process is beneficial for the balance of moisture and temperature. The adopted moisture - reducing speed is faster than that in the general paddy drying process at the same moisture content, which is beneficial for improving the paddy drying output and economic benefits. In the paddy drying process, the main function of tempering is to make the moisture and temperature inside the paddy grains tend to balance. If it is necessary to make the moisture and temperature inside the grain reach complete balance, it generally takes one hour. Therefore, increasing the ratio of the tempering time to the drying time is beneficial for improving the drying quality and increasing the moisture - reducing rate. However, extending the tempering time will also increase the volume of the dryer and the drying time. The present invention selects the ratio of the tempering time to the drying time with optimized drying quality and drying time according to the volume of the existing mainstream batch - cycle dryer.

[0033] 3) The method of the present invention has a shorter drying time and better drying quality in stepwise drying than in constant-temperature drying. As can be seen from Table 2, the reduction range of the moisture content of paddy rice in stepwise drying is higher than that in constant-temperature drying, and its drying efficiency is higher. As can be seen from Table 3, in the entire drying process from the start of hot air drying to the completion of ventilation after reaching the safe moisture content, the stepwise variable-temperature drying time is on average 10 h less than the constant-temperature drying time (the initial moisture content of the test paddy rice is above 31.4%). As can be seen from Table 5, for the Nanjing 9108 variety, the head rice yield of paddy rice in stepwise drying increased by 4.37% compared with that in constant-temperature drying, and the ratio increased by 5.5%; the head rice rate of paddy rice increased by 4.39%, and the ratio increased by 6.5%. For the Nanjing 46 variety, the head rice yield of paddy rice in stepwise drying increased by 1.86% compared with that in constant-temperature drying, and the ratio increased by 2.3%; the head rice rate of paddy rice increased by 2.94%, and the ratio increased by 4.2%. It can be seen that the rice yield and drying quality of paddy rice in stepwise drying are better than those in constant-temperature drying. From Figure 2 It can be seen that for the Nanjing 9108 variety, the cracking rate of paddy rice in stepwise drying decreased by 20.50% compared with that in constant-temperature drying. For the Nanjing 46 variety, the cracking rate of paddy rice in stepwise drying decreased by 7.15% compared with that in constant-temperature drying. It can be seen that the appearance quality of rice in stepwise drying is better than that in constant-temperature drying. From Figure 3 It can be seen that for the Nanjing 9108 variety, the ratio of fatty acid value of paddy rice in stepwise drying decreased by 46.15% compared with that in constant-temperature drying. For the Nanjing 46 variety, the ratio of fatty acid value of paddy rice in stepwise drying decreased by 38.46% compared with that in constant-temperature drying. It can be seen that the eating quality of rice in stepwise drying is better than that in constant-temperature drying. Description of the Drawings

[0034] Figure 1 shows the influence of the drying temperature and drying time in the first stage on the head rice rate of paddy rice.

[0035] Figure 2 shows the cracking rates of Nanjing 9108 and Nanjing 46 paddy rice under different drying processes.

[0036] Figure 3 shows the fatty acid value contents of Nanjing 9108 and Nanjing 46 paddy rice under different drying processes. Detailed Embodiments

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0038] The present invention provides a rice drying process with variable temperature in different stages. The overall drying process of rice is divided into three stages, and different drying temperatures are adopted in different moisture content ranges for stage-by-stage drying. First, single-factor experiments and response surface experiments are carried out in the laboratory to obtain the optimized rice drying process, and then the drying process is applied and verified on a batch-circulating grain dryer. During the optimization process, rice samples with moisture contents of 26.00±0.50%, 22.00±0.50%, and 18.00±0.50% are selected for thin-layer drying experiments, and the rice with different moisture contents is subjected to stage-by-stage drying in different hot air drying stages. For high-moisture rice (moisture content > 22.00±0.50%), drying is first carried out at a high hot air temperature (65.0±1°C) in stage I. After the moisture content ≤ 22.00±0.50%, drying at different temperatures (55.0±1°C) is carried out in stage II. After the rice moisture content ≤ 18.00±0.50%, drying at different temperatures (47.0±1°C) is carried out in stage III. When the rice moisture content ≤ 14.00±0.50%, the drying ends. Four variables, namely the drying temperature and drying time in stage I, stage II, and stage III, are selected, and the head rice rate, whole milled rice rate, and increased cracking rate of the rice are used as response values. The optimized drying process is applied to a 15-ton batch-circulating grain dryer for grain drying.

[0039] Example 1

[0040] Turn on the power supply of the forced air drying oven. First, adjust the temperature parameter setting button, and then turn on the blower and the heating key until the air volume and temperature in the drying oven are stable.

[0041] Conduct the following tests:

[0042] Single-factor experimental design: Analyze the hot air temperature in the first stage, the hot air temperature in the second stage, and the hot air temperature in the third stage during the paddy drying process as variables to obtain optimal drying process parameters for the next experiment. The details are as follows: The single-factor experiment selects the following four factors: the drying temperature in the first stage, the drying temperature in the second stage, the drying temperature in the third stage, and the drying time. Weigh 100.0 ± 0.2 g of paddy samples with an initial wet basis moisture content of 26 ± 0.10% after removing impurities, spread them evenly in a stainless-steel tray to a thickness of 15 mm, and place them in preheated different drying ovens for drying. The average ambient temperature around the drying oven is about 20°C, and the relative ambient humidity is about 55%. The different drying temperatures in the first stage are 75.0 ± 1°C, 70.0 ± 1°C, 65.0 ± 1°C, 60.0 ± 1°C, and 55.0 ± 1°C. When the paddy moisture content drops to 22.0 ± 0.1%, start the second-stage drying, and the different drying temperatures are 65.0 ± 1°C, 60.0 ± 1°C, 55.0 ± 1°C, 50.0 ± 1°C, and 45.0 ± 1°C. When the paddy moisture content drops to 18.0 ± 0.1%, start the third-stage drying, and the different drying temperatures are 53.0 ± 1°C, 50.0 ± 1°C, 47.0 ± 1°C, 43.0 ± 1°C, and 40.0 ± 1°C. Start timing for drying, sample according to the single-factor drying time (the different drying times are 12 min, 14 min, 16 min, 18 min, and 20 min). When sampling, weigh the mass of the paddy samples and measure the moisture content, and calculate the moisture reduction rate in combination with the drying time. Simulate the tempering grain temperature during the operation of the batch cyclic dryer and the tempering process in the dryer (the length ratio of the drying section to the tempering section is 1:5), temper the paddy samples in an incubator at 40°C, and the tempering time varies with the drying time (corresponding to different drying times, the tempering times are 60 min, 70 min, 80 min, 90 min, and 100 min). Stop drying until the moisture content drops to 14.0 ± 0.10%. After each stage of drying, detect the moisture content of the grains, change the drying temperature according to the different moisture contents, and continue the drying and tempering cycle of the grains.

[0043] Response surface optimization design: According to the Box-Behnken design principle, combined with the control of drying duration in actual production, on the basis of the single-factor experiment, taking the drying temperatures (°C) in the I stage, II stage, and III stage and the drying time (h) as variables, select the optimization intervals of the 4 factors as shown in Table 1. Taking the head rice rate (%) of the paddy after drying and the total drying duration (h) as response values, combined with the grain feeding wheel speed of the dryer, according to the Box-Behnken design principle, use Design-Expert 13 to conduct a response surface experiment design with four factors and three levels, and comprehensively obtain the optimal scheme for the variable-temperature drying process of paddy in stages.

[0044] 3) Grain storage: After the grain fully meets the moisture content requirements, store the grain in the drying equipment.

[0045] Test results: During the drying process, the head rice rate of paddy rice shows a downward trend with the increase of drying temperature and drying time. For example, the experimental results of the drying temperature and drying time in the first stage and the head rice rate are as Figure 1 shown. In this stage, the maximum drying temperature of paddy rice should not exceed 70 °C (at this time, the head rice rate of paddy rice is 66.43%). The optimized interval results of the four factors are shown in Table 1. The drying temperature in the first stage is 55 - 65 °C, the drying temperature in the second stage is 45 - 55 °C, the drying temperature in the third stage is 40 - 47 °C, and the drying time is 12 - 16 min.

[0046] Table 1 Factor level table for response surface experiment design

[0047]

[0048] Comprehensive evaluation function model constructed through response surface experiment:

[0049] Y = 70.00 + 1.45X1 + 0.90X2 - 0.50X3 - 0.12X1 2 - 0.21X2 2 - 0.05X3 2 + 0.31X1X2 - 0.15X1X3

[0050] + 0.22X2X3. The Y value is the head rice rate. The regression equation of the Y value has P < 0.0001 and R2 > 0.95, and the lack - of - fit term is not significant. The results show that the data fitting effect is good and the response surface analysis results are credible. Under the condition of ensuring drying efficiency, the optimal variable - temperature drying scheme in stages is as follows: the drying temperature in the first stage is 65 ± 1 °C; the drying temperature in the second stage is 55 ± 1 °C; the drying temperature in the third stage is 47 ± 1 °C; the drying time is 12 ± 1 min. Conditioning time: The ratio of conditioning time to drying time can be 5:1 or 5:1 - 4:1.

[0051] Example 2: Use a 15 - ton batch - type circulating grain dryer to dry paddy rice

[0052] Drying object: After the paddy rice matured in the field is harvested by a harvester and transported to the drying plant by truck, record the different varieties of the harvested paddy rice (Nanjing 46, Nanjing 9108). After preliminary cleaning of sundries, the fresh paddy rice is lifted into the drying bin through the feeding pipeline of the dryer, record the initial moisture content of the paddy rice, and classify the paddy rice to be dried into high - moisture paddy rice (≥26%) and medium - moisture paddy rice (26% - 22%).

[0053] Drying method:

[0054] The stepwise temperature-variable drying process obtained in Example 1 was applied to a batch-circulating grain dryer (5HXJ). Before grain drying, its initial moisture content was measured. Different drying processes were adopted for paddy rice in different moisture content ranges. For paddy rice with high moisture content (≥26%) and medium moisture content (26% - 22%), three-step and two-step drying processes were respectively carried out for drying. During the paddy rice drying test, the average ambient atmospheric temperature in the dryer workshop was about 15.0 °C, and the relative humidity was about 57.00%. The specific drying process flow for paddy rice with a moisture content of ≥26.0 ± 0.50% is as follows.

[0055] For the first-step drying of the batch-circulating grain dryer, the hot air temperature was 65.0 ± 1 °C, and the time for one cycle (12.5 min of hot air drying and 62.5 min of tempering) was 75 minutes, until the moisture content of the paddy rice decreased to 22.0 ± 0.50%, and then the total drying time of this step was recorded.

[0056] For the second-step drying of the batch-circulating grain dryer, the hot air temperature was 55 ± 1 °C, and the time for one cycle was 75 minutes (12.5 min of hot air drying and 60 min of tempering), until the moisture content of the paddy rice decreased to 18.0 ± 0.50%, and then the total drying time of this step was recorded.

[0057] For the third-step drying of the batch-circulating grain dryer, the hot air temperature was 47.0 ± 1 °C, and the time for one cycle was 75 minutes (12.5 min of hot air drying and 60 min of tempering), until the moisture content of the paddy rice decreased to 15.0 ± 0.50%, and then the total drying time of this step was recorded.

[0058] After completing the drying process flow for paddy rice with lower moisture content, after ventilation and cooling, the moisture content of the paddy rice when leaving the machine was 14.00 ± 0.50%, and then the paddy rice left the machine.

[0059] Control test: Constant temperature drying

[0060] After the field-ripened paddy rice was harvested and transported to the drying plant, different varieties of the harvested paddy rice (Nanjing 46, Nanjing 9108) were recorded. After preliminary cleaning of sundries, the fresh paddy rice was lifted into the drying bin through the feeding pipeline of the dryer, and the initial moisture content of the paddy rice was recorded. Drying was carried out on a batch-circulating grain dryer (5HXJ), and hot air drying at 50 ± 1 °C was adopted throughout the process until the moisture content of the paddy rice decreased to 15.0 ± 0.50%, and then the total drying time was recorded. After ventilation and cooling, when the moisture content of the paddy rice was 14.00 ± 0.50%, the paddy rice left the machine.

[0061] After drying, the effects on the head rice rate (%), whole milled rice rate (%), chalky rice rate (%), and fatty acid value at different levels were analyzed.

[0062] Net paddy is paddy after removing impurities and brown rice outside the paddy.

[0063] Husked rice rate: It is determined by referring to the method of GB / T 5495-2008: the mass fraction of the husked rice (where the mass of incomplete grains is calculated by halving) after dehulling the net paddy sample in the sample.

[0064] Head rice rate: It is determined by referring to the method of GB / T 21719-2008: Head rice refers to the grains that reach three-fourths or more of the average length of the complete grains when the net paddy is dehulled into brown rice and the brown rice is milled into rice with a processing accuracy of the third grade of the national standard (GB 1354) by an experimental rice mill. And the head rice rate is the mass fraction of head rice in the net paddy sample.

[0065] Chalky rice rate: 24 hours after the drying is completed, the husked rice rate of the paddy is detected. Randomly select 100 whole grains of brown rice, identify them with a magnifying glass, and pick out the grains with cracks. The number of grains obtained is the percentage of cracked grains.

[0066] Fatty acid value: It is determined by referring to the method of GB / T 15684-2015: Take 50.0 g of rice flour, sieve it with a sieve with a pore size of 0.1 mm, weigh 5.0 g of the sample, place it in a centrifuge tube, add 30 ml of ethanol, place it in a shaker for 1 h, transfer 20 ml of the supernatant to a conical flask, add 5 drops of phenolphthalein solution, titrate with KOH ethanol solution until it turns light pink and lasts for 30 s, and record the titration value. Set up a blank test and replace the above 20 ml of supernatant with ethanol. Calculate the fatty acid value A k .

[0067]

[0068] In the formula:

[0069] c —— Concentration of KOH ethanol standard solution, unit is mole per liter (mol / L);

[0070] m —— Mass of the sample, unit is gram (g);

[0071] V1 —— Volume of KOH ethanol standard solution used for determining the sample, unit is milliliter (mL); V0 —— Volume of KOH ethanol standard solution used for the blank test, unit is milliliter (mL) ω —— Moisture content of the sample, %;

[0072] 8415 —— Constant expressed in KOH, that is, 56.1×1.5×100.

[0073] The determination result is accurate to milligram (mg).

[0074] To avoid the influence of storage duration on paddy, all indicators are determined within one week. The results are shown in Table 2 - Table 5.Figures 2 - 3 as shown

[0075] Table 2 Time taken for each process of on-site stepwise drying of different varieties of paddy rice in 2022

[0076]

[0077] Table 3 Comparison of total time taken for on-site constant temperature drying and stepwise drying of different varieties of paddy rice in 2022

[0078]

[0079] Table 4 Time taken for each process and total time of on-site stepwise drying of Nanjing 46 paddy rice in 2023

[0080]

[0081]

[0082] Table 5 Head rice rate and whole milled rice rate of on-site constant temperature drying and stepwise drying of different varieties of paddy rice in 2022

[0083]

[0084] It can be seen from Table 2 - Table 3 that taking the sample of Nanjing 9108 paddy rice with high moisture content in the current year as an example, the results of stepwise drying show that the reduction rate of paddy rice moisture content in the first process is 2.22% - 2.75% per hour, and the reduction rate of moisture content in the second process is 0.82% per hour. The reduction rate of paddy rice moisture content throughout the constant temperature drying process is 0.48% - 0.50% per hour. The reduction rate of paddy rice moisture content in stepwise drying is higher than that in constant temperature drying, and its drying efficiency is higher. The time taken for stepwise drying of paddy rice is less than the total time of constant temperature drying.

[0085] It can be seen from Table 4 that taking the sample of Nanjing 46 paddy rice with relatively high moisture content in the following year as an example, the results of stepwise drying show that the reduction rate of paddy rice moisture content in the first process is 1.49% - 1.84% per hour, the reduction rate of moisture content in the second process is 0.58% - 0.62% per hour, and the reduction rate of moisture content in the third process is 0.64% - 0.74% per hour. The reduction rate of paddy rice moisture content throughout the constant temperature drying process is 0.63 - 0.69% per hour. The reduction rate of paddy rice moisture content in stepwise drying is higher than that in constant temperature drying, and its drying efficiency is higher than that of constant temperature drying. Compared with the paddy rice with high moisture content in Table 2 - 3, it can be seen that the initial moisture content is higher, and the advantage of drying efficiency of stepwise drying is more significant.

[0086] As can be seen from Table 5, for the Nanjing 9108 variety, the brown rice yield of stepwise drying is 4.37% higher than that of constant temperature drying, and the ratio is increased by 5.5%; the head rice yield of paddy is increased by 4.39%, and the ratio is increased by 6.5%. For the Nanjing 46 variety, the brown rice yield of stepwise drying is 1.86% higher than that of constant temperature drying, and the ratio is increased by 2.3%; the head rice yield of paddy is increased by 2.94%, and the ratio is increased by 4.2%. It can be seen that the rice yield and drying quality of stepwise drying are better than those of constant temperature drying.

[0087] From Figure 2 As can be seen, for the Nanjing 9108 variety, the cracking rate of paddy by stepwise drying is 20.50% lower than that by constant temperature drying. For the Nanjing 46 variety, the cracking rate of paddy by stepwise drying is 7.15% lower than that by constant temperature drying. It can be seen that the appearance quality of rice by stepwise drying is better.

[0088] From Figure 3 As can be seen, for the Nanjing 9108 variety, the ratio of fatty acid value of paddy by stepwise drying is 46.15% lower than that by constant temperature drying. For the Nanjing 46 variety, the ratio of fatty acid value of paddy by stepwise drying is 38.46% lower than that by constant temperature drying. It can be seen that the eating quality of rice by stepwise drying is better.

[0089] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent transformation made by using the content of the specification of the present invention, directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A rice step-variable temperature drying process, applicable to rice with a moisture content higher than 22%, is carried out in a batch-circulating grain dryer, and is characterized in that, It includes the following steps: 1) Primary drying: The harvested paddy with a moisture content higher than 22.00% is subjected to one or more drying - tempering cycles until the moisture content of the paddy drops to 22.00 ± 0.50%; 2) Secondary drying: The paddy is subjected to one or more drying - tempering cycles until the moisture content of the paddy drops to 18.00 ± 0.50%; 3) Tertiary drying: The paddy is subjected to one or more drying - tempering cycles until the moisture content of the paddy drops to 14.00 ± 0.50%, and then it is sent to the warehouse for storage; Among them, in the primary drying, hot - air drying is adopted, the hot - air temperature is 65.0 ± 1°C, the drying time in each drying - tempering cycle is 12 ± 1 min, and the ratio of the tempering time to the drying time in each drying - tempering cycle is 6:1 to 4:1; In the secondary drying, hot - air drying is adopted, the hot - air temperature is 55.0 ± 1°C, the drying time in each drying - tempering cycle is 12 ± 1 min, and the ratio of the tempering time to the drying time in each drying - tempering cycle is 6:1 to 4:1; In the tertiary drying, hot - air drying is adopted, the hot - air temperature is 47.0 ± 1°C, the drying time in each drying - tempering cycle is 12 ± 1 min, and the ratio of the tempering time to the drying time in each drying - tempering cycle is 6:1 to 4:

1.

2. The paddy rice stepwise temperature-variable drying process according to claim 1, wherein, In the primary, secondary, and tertiary drying, the ratio of the tempering time to the drying time in each drying - tempering cycle is 5:

1.

3. A rice drying process with variable temperature in different stages, applicable to rice with a moisture content lower than 22% and higher than 18%, and carried out in a batch-circulating grain dryer, characterized in that, It includes the following steps: 1) The paddy is subjected to one or more drying - tempering cycles until the moisture content of the paddy drops to 18.00 ± 0.50%; 2) The paddy is subjected to one or more drying - tempering cycles until the moisture content of the paddy drops to 14.00 ± 0.50%, and then it is sent to the warehouse for storage; Among them, in the 1st step of drying, hot - air drying is adopted, the hot - air temperature is 55.0 ± 1°C, the drying time in each drying - tempering cycle is 12 ± 1 min, and the ratio of the tempering time to the drying time in each drying - tempering cycle is 6:1 to 4:1; In the 2nd step of drying, hot - air drying is adopted, the hot - air temperature is 47.0 ± 1°C, the drying time in each drying - tempering cycle is 12 ± 1 min, and the ratio of the tempering time to the drying time in each drying - tempering cycle is 6:1 to 4:

1.

4. The paddy rice stepwise variable temperature drying process according to claim 3, characterized in that, In the first and second steps of drying, the ratio of the tempering time to the drying time in each drying - tempering cycle is 5:

1.

5. A variable temperature drying process for paddy rice, applicable to paddy rice with a moisture content lower than 18% but higher than 14%, and carried out in a batch circulating grain dryer, is characterized in that, It includes the following steps: The paddy is subjected to one or more drying - tempering cycles until the moisture content of the paddy drops to 14.00 ± 0.50%, and then it is sent to the warehouse for storage; For the drying of the paddy, hot - air drying is adopted, the hot - air temperature is 47.0 ± 1°C, the drying time in each drying - tempering cycle is 12 ± 1 min, and the ratio of the tempering time to the drying time in each drying - tempering cycle is 6:1 to 4:

1.

6. The paddy rice stepwise variable temperature drying process according to claim 5, wherein, The ratio of the tempering time to the drying time in each drying - tempering cycle is 5:1.

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