Study On Energy-Saving Drying Technology By Hot Air And Quality Control Of Garlic Slices

As the largest garlic producer and exporter all over the world,China occupies a decisive position in the international garlic market.Among the export products,dehydrated garlic slices account for a larger proportion.Although hot air drying technology has the advantages of simple process and large capacity,higher energy consumption led to lager production costs due to the lack of systematic research on the control of the hot air drying process.Therefore,the study of energy-saving drying technology by hot air and quality control of garlic slices contributes to the design,optimization and control of the production process.This can save energy and improve the industrial productivity and competitiveness,with a very important practical significance.In this study,the drying processes by constant temperature and multi-stage variable temperature are optimized using garlic from Jinxiang.The main results are as follows:(1)The effects of drying temperature,return air time and loading capacity on the time,?E and energy consumption during the drying process of garlic slices were first studied.As the drying temperature increases,the drying time gradually shortens and the color difference value shows an increasing trend.Furthermore,the unit energy consumption at the end of drying decreases first and then increases.Notably,the energy saving effect is more obvious in the range of 55-65?for the return air treatment.The energy consumption was found to be significant in the range of 55-60?and 65-70?.With the increase of the return air time,the required drying time,the color difference value and the unit energy consumption all show a trend of decreasing first and then increasing.Remarkably,the energy saving effect is obvious when the dry basis moisture is 35-55%,and no evident effect is observed at other moisture levels.The larger loading capacity results in longer drying time and increased color difference value.However,the unit energy consumption at the end of drying shows a trend of decreasing first and then increasing.Obvious energy saving results is found at the loading capacity of 0.8-4.0kg/m~2.(2)According the single-factor experiments,drying temperature is initially determinted as55-70°C,and return air time and loading capacity are identified as 35-55%of dry basis moisture and 0.8-4.0 kg/m~2.Therefore,response surface method is used to optimize the production process of dehydrated garlic slices by hot air.The optimal process conditions are as follows:the drying temperature of 61.10°C,the return air treatment at 45.475%of dry basis moisture,and loading capacity of 2.43 kg/m~2.Under optimal conditions,the allicin content is2.6545 mg/g,the color difference value is 13.1426,and the unit energy consumption is0.353488 kw·h/kg.The verification experiment shows that the actual energy consumption,color difference value and allicin content are basically consistent with the predicted value,indicating that the model fits well and can fully reflect the quality changes of galic slices during the drying process.(3)Following the principle of high temperatures in the early stage and low temperatures in the later stage,the optimal drying conditions obtained by constant temperature drying are used for studying on multi-stage variable temperature drying process.Based on the fitting analysis of four common thin layer drying models,the fitting equations of the four models at different temperatures are obtained.By comparing R~2,?~2 and RMSE of the four equations,it is found that Page model can better predict the pre-and mid-term dehydration process of garlic slices under different temperatures compared with Wang and Singh model,Lewis model and Henderson and Pabis model.In addition,the mathematical relationship between Page model parameters and drying temperature is obtained through regression analysis,with greater than0.99 of fitting degree between drying temperature and parameters.Therefore,the drying temperature can be used to represent the drying model coefficient.It is proved by verification test that Page model can predict the drying process of dehydrated garlic slices.Furthermore,the study on energy consumption shows that variable temperature drying process conditions for the optimal energy-saving are obtained as follows:the first stage of 80?for79.5 min,the second stage of 70?for 36 min,and the third stage of 61?plus return air treatment(dry base moisture content of 45%)to the end point.The total energy consumption is 0.33kw·h/kg,which was 8%more energy-efficient than that of the optimal constant temperature drying process(0.36kw h/kg).