To identify the microwave drying characteristics of corn, microwave drying tests were conducted on corn. By taking the moisture content, drying rate, and drying temperature as indices, this research revealed the effects of different microwave powers and loads on the microwave drying characteristics of corn. Moreover, energy consumption and quality of dried corn were analysed under different drying conditions. The results demonstrate that microwave drying has significant energy-saving effects. The energy consumption by microwave drying is less than 0.3 times that used by electrothermal drying under the same load. Both microwave power and load exert significant influences on drying characteristics. Higher microwave power results in a greater average drying rate, wherein shorter periods of time are required to reach the maximum drying rate and higher temperatures of the corn. However, the load shows the opposite tendency. The smaller the load, the higher the temperature of the corn in the early stage of drying. However, as drying continues, the temperature curve changes significantly, and the temperature rises with the increase in load in the later stage of drying. In consideration of energy consumption and dried quality, the load of corn should be increased as appropriate, and the microwave intensity should be limited to no higher than 0.7 W/g in the experiment.
The emission characteristics of pollution gases produced via the combustion of food waste were studied through a laboratory-scale electrically heated tube furnace. The results showed that the pollution gases generated from the combustion of food waste were CO, H2 and NOx. Each emission curve of CO had a peak. When the combustion temperature rose from 400 °C to 1000 °C, the peak first increased (from 400 °C to 700 °C) and then decreased (from 800 °C to 1000 °C). However, the burnout time shortened with the increase in temperature. Therefore, food waste should be combusted at a higher temperature than 700 °C from the perspective of reducing CO emissions. The emissions of H2 were similar to those of CO. In other words, if CO emissions increased, H2 emissions also increased in the same temperature range. Some NOx emission curves had two peaks (the combustion of cooked rice at 1000 °C; the combustion of vegetable leaves in the temperature range of 600 °C to 1000 °C). The higher the combustion temperature, the higher the second NOx emission peak. NOx emissions from the combustion of cooked rice were greater in the temperature range of 400 °C to 500 °C, whereas for vegetable leaves, that temperature range was from 600 °C to 700 °C. Hence, from the viewpoint of reducing pollution gases, food waste should be combusted at a higher temperature than 700 °C.
Fast-growing grass is a biomass material with characteristics such as high temperature and drought resistance; rapid growth and development; and repeated germination and cutting. Therefore, it is a popular biomass fuel. It is required that the pollutants produced during the biomass combustion process are appropriately controlled. For this purpose, our study analyses the influence of combustion temperature and calcium oxide (CaO) on the nitrogen oxides (NOx) and carbon monoxide (CO) emission characteristics of fast-growing grass combustion using the biomass combustion flue gas analysis and testing platform. The results of our analysis revealed that CaO additive can simultaneously reduce the peak and total NOx emissions at 750 °C. Particularly, 5% CaO demonstrated a significant control effect on the NOx emission from the fast-growing grass combustion process, with a peak and total emissions reduction of 47.05% and 56.81%, respectively. In addition, with an increase in temperature, the CO emission curve attains a second peak higher than the first peak, and the peak and total emissions show a decreasing trend.
Fast-growing grass, as a popular renewable energy, is low in sulfur content, so NOx is the major pollutant during its combustion. To study the emission characteristics of NOx and obtain the data of controlling NOx emission, the effects of combustion temperature as well as the additive type and mass fraction were investigated on the emission characteristics of NOx from the combustion of fast-growing grass. Results revealed that the first peak for NOx emission from this combustion gradually increases with an increase in temperature. Moreover, the additives were found to dramatically impact the amount of NOx emission and its representative peak. The optimal additives and their optimal mass fractions were determined at various specific temperatures to reduce NOx emission. At combustion temperatures of 600, 700, 750, 800, and 850°C, the optimal conditions to limit NOx emissions were 5% SiO2, 3% Al2O3, 3% Ca(OH)2, 15% Al2O3, and 3% SiO2 (or 3% Al2O3), respectively; the corresponding emission peaks decreased by 43.59, 44.21, 47.99, 24.18, and 30.60% (or 31.51%), with denitration rates of 63.28, 50.34, 57.44, 27.05, and 27.34% (or 27.28%), respectively.
Monitoring marine primary productivity (PP) is crucial for understanding changes in the marine ecosystem. Based on satellite data and the vertically generalized production model (VGPM), this study investigated the spatiotemporal distribution and long-term trend of PP in the Yellow and Bohai Seas (YBSs) from 2003 to 2020. By using the calibrated satellite data and optimized parameterization scheme, the accuracy of the PP results in the YBSs was significantly improved compared to online PP products. The annual mean PP in the YBSs from 2003 to 2020 was 523.8 mgC/(m2·d), with significant seasonal and interannual differences. Seasonally, PP in the Yellow Sea and the Bohai Sea exhibited bimodal (two peaks in May and October) and unimodal (one peak in June) variation, respectively. The magnitude of mean PP in the YBSs was ranked as spring > summer > autumn > winter, with spring PP (~1000 mgC/(m2·d)) contributing more than 40% of the annual PP. The annual mean PP in the YBSs showed an overall decrease from 2003 to 2020, with a decrease rate of 5–6 mgC/(m2·d)/y. The interannual variation of the PP was mainly related to the variability of the chlorophyll-a concentration and was essentially inverse to the phases of the Pacific Decadal Oscillation and the El Niño-Southern Oscillation.
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