The use and profitability of hermetic technologies for grain storage among smallholder farmers in eastern Kenya

Hermetic storage technologies (HSTs) have been disseminated in Sub-Saharan Africa (including Kenya) to reduce grain storage losses among farmers. We carried out a study in three counties in eastern Kenya to assess the use and profitability of HSTs among farmers. Data were collected from 613 farmers using a semi-structured questionnaire and Kobo Toolbox via android tablets. Results showed an increase in use of HSTs among farmers from 53.7% in 2015 to 91.2% in 2017. PICS was the most used hermetic bags by farmers (84%) in 2017. Majority of farmers (73.5%) received training in the use of HSTs from extension agents and agro-dealers. About 40% of respondents purchased additional (one to five) bags after their first experience using them. The quantity of grain produced made up about half of the farmer’s decision to store. The primary reason (87%) farmers used hermetic bags was the need to manage insect pests. Maize and beans were the most produced and most stored crops; but maize was the most stored in HST. Grain price seasonality showed a near doubling effect between the lean and harvest seasons. Estimates of the return on investments (ROI) ranged between 13 and 80% for all crops and maize stored in hermetic bags had the highest ROI. Awareness and trainings are key in increasing adoption and proper use of HSTs.     

阿卡波糖发酵过程的放大研究

研究了阿卡波糖产生菌游动放线菌A-56在30 m3罐上的发酵放大策略。首先通过摇瓶分批补料发酵,考察了补料培养基中麦芽糖和葡萄糖配比对阿卡波糖合成的影响,结果表明,麦芽糖和葡萄糖的配比对阿卡波糖的生物合成具有显著的影响,且麦芽糖和葡萄糖的配比为3∶1最利于阿卡波糖合成;在此基础上,在100 L发酵罐上进一步考察了碳源控制对阿卡波糖发酵的影响,结果表明,补料阶段的发酵液总糖和还原糖浓度分别控制在75～80 g/L和45～50 g/L时,最利于阿卡波糖合成。因此,筛选出总糖和还原糖(麦芽糖和葡萄糖)这两个关键参数作为放大因子,成功地实现了阿卡波糖从100 L罐到30 m3罐的工业化发酵放大,最终(168 h)的阿卡波糖产量达到4 327 mg/L。     

An appraisal of the energy-size reduction relationships for mill scale-up design

In this paper, several well-known energy-size reduction relationships have been analyzed using Kapur’s similarity solution to the integro-differential equation of batch grinding. It has been shown that: (i) relationships proposed in terms of the energy actually utilized for breakage of particles, E, cannot be used to develop a practical energy-size reduction relationship as E is neither measurable nor it is found to be proportional to the measurable net energy input, E_n, (ii) the exponent of the characteristic particle size, $\overline{\mathrm{x}}$, in the relationship between E_n and $\overline{\mathrm{x}}$ is same as the exponent of particle size in the expression for the specific breakage rate function, α, which is not a function of $\overline{\mathrm{x}}$ in the case of ball mills, (iii) α values of 0, 0.5 and 1 cannot be associated with the laws of Kick, Bond and Rittinger, respectively. Based on the results of this analysis, the empirical scale-up models proposed by Bond and Morrell have been modified by replacing the exponents of 80% passing sizes by α. Further investigations have been recommended for resolution of large differences in the energy estimates obtained from these models for materials characterized by grindabilty values less than 1.0 and greater than 3.0?g/rev.     

反胶团法制备ZrO2超细粉末过程的放大模型

使用喷射 -搅拌混合器 ,使油水两相可以快速而且充分接触 ,从而利用反胶团法得到粒度分布均匀的ZrO2 超细粉末 .首先利用模型预测了不同转速和不同相比下两相传质的结果 ,然后用实验验证了模型的准确性 ,建议利用该模型进行放大研究     

Scale Effects on Hydrodynamic and Mass Transfer Characteristics of External Loop Airlift Reactors

Gas hold-up and oxygen transfer have been investigated in two geometrically similar external loop airlift reactors of linear scale ratio of 2. In mass transfer experiments, the sampling location was found to be important as significantly different k_La values can be obtained. The variations of k_La with probe location have been explained in terms of non-uniform hydrodynamic properties and the results obtained have been validated by means of high speed video camera recordings. At higher gas flowrates, the gas hold-up was significantly higher in the large-scale reactor. It was found that in order to maintain the gas hold-up or k_La constant in both the small- and large-scale reactor, the small-scale reactor required 25% and 27% more power input per unit volume of liquid respectively. © 1997 SCI.     

反应器类型对流动影响的数值模拟

在油-氢气体系中使用欧拉-欧拉双流体模型考察了温度703.15 K和压力11 MPa下气升式环流反应器和鼓泡床反应器对气液两相流动的影响. 结果表明,环流反应器中气含率和轴向液速沿导流筒径向存在突增现象,环流反应器中气含率在径向0~0.5和0.75~1时明显大于鼓泡床反应器,在径向0.5~0.75处前者的平均气含率比后者高约6%;环流反应器中上升管内环流液速明显大于鼓泡床反应器,且在下降区有所增强,环流反应器平均轴向液速比鼓泡床反应器高约21%;反应器尺寸较小时环流反应器和鼓泡床反应器的流动特性相差不大,反应器体积放大过程中前者的流动特性优于后者的趋势逐渐明显.     

同向旋转双螺杆挤出机相似放大参数优化深入探讨

采用FEM与正交试验设计相结合的方法,分别将20和72同向旋转双螺杆挤出机作为基准机型和目标机型,选用螺槽深度、螺杆转速和螺杆与机筒间隙作为试验因素,将产量、比能耗、最大剪切应力和平均停留时间作为评价指标,综合分析了不同几何参数对各个指标的影响,得出目标机型最优几何参数水平组合。     

PTT合成放大实验及其纺丝性能研究

在聚对苯二甲酸丙二醇酯(PTT)合成的小试研究基础上,进行了在20 L熔融缩聚反应釜中合成PTT的放大实验,并进行了PTT纺丝实验。结果表明:合成得到的PTT特性黏数为0.89 dL/g,端羧基含量为48μmol/g,3,3-氧基二丙醇质量分数为0.46%,玻璃化转变温度为45℃,熔点为228℃。PTT初步达到纤维级别的要求,在400 m/min的速度下能够顺利纺丝,经过2.5倍拉伸后,纤维线密度为96.7 dtex,断裂强度为1.3 cN/dtex,断裂伸长率为97.35%,模量为2.7 cN/dtex。     

BF3催化1-癸烯制备聚α-烯烃合成润滑油基础油

低黏度聚α-烯烃（PAO）合成技术主要为国外所垄断,国内少有研究报道。为了解决这一技术问题,本文以1-癸烯为原料,在1L高压反应釜中进行聚合实验,考察反应压力、反应温度、引发剂、反应时间对转化率及聚合产物组成分布的影响,并以优化后的工艺条件在200L低黏度PAO中试试验装置上进行中试放大试验。结果表明,在反应压力为0.2MPa、反应温度为20℃、催化剂加入量为850g、引发剂加入量685mL（与1-癸烯质量比为0.5%）、反应时间2h的条件下,转化率大于95%,产品关键组分三聚体和四聚体含量大于80%,反应放热量约为6.3×10⁴kJ。以此条件获得的产品100℃运动黏度4.3mm²/s,黏度指数132,-40℃低温动力黏度2318 mm²/s,倾点-60℃,与国外产品主要性能指标相当。