| Since there are many advantages for the spraying-film evaporation technologies, such as higher evaporation intensity, lower temperature difference required between heat resource and working mass, higher heat-transfer coefficient. This technology has been applied in various fields as desalinization of sea-water, electricity generation by temperature interval of ocean, cooling engineering and chemical engineering and so on. The physical and physic-chemical characteristics of working mass varies significantly in different fields. Scientists world-wide have been making great efforts on heat-transfer mechanism, fundamental theories and specification data for designing and manufacturing of high-efficiency and energy-saving evaporation facilities. The studies on characteristics of black liquor from non-wood fiber chemical pulping process show that such type of black liquor has high content of ash (silicates), pentoses and high viscosity which will influence on the normal evaporation operation, the heat transfer capacity of non wood pulping black liquor is poor and easy to form scales. At present, there are no normal evaporation installations can be operated economically in mill scale. A new type of evaporator was designed and installed by us both in pilot scale and industrial scale. By using of these new designed equipments, high efficiency evaporation technologies, heat transfer efficiencies, mechanism for concentration of non-wood black liquor were investigated, and the mill scale trials were carried out too. It was proved that, due to presenting of effective evaporating space, the new designed horizontal spraying-film evaporator and technology has extremely high evaporating capacity, high heat-transfer coefficient to easy foaming and scaling working mass as non-wood black liquor. The formation of scales on the evaporation tube-bundles was not easy, if some scales formed which was easily to be removed. The mean of evaporation intensity for black liquor ( from wheat straw pulping process ) could reach up to 18~25 kg/m2.h, which was 50% more than the maximum value of reported evaporators in China. This technology has been ranked as the pioneer in the world. Effects of evaporation and heat transfer efficiency of this type of evaporator were compared with different operation specifications (such as liquid spraying rate, heat flux, outlet vapor velocity and solution concentration). The heat transfer performance of horizontal tube spraying—film evaporation with water, straw pulping black liquors of both SFP-AQ process and soda process respectively as actuating medium. Laminar flow math-model was established, forced convective sensible heat transfer of subcooled falling liquor on the horizontal heated tube is studied by using numerical calculation and experiment to investigate the effects of flow conditions and tube diameter. The numerical analysis shows that Nusselt number is governed by the three variables: film Reynolds number, Prantal number and Archimedes number. The calculation adopts a laminar flow math-model and divides the film flow zone into two calculating zones, one is the flow stagnation zone in which the Goertler change method is used, the other is the free film flow zone in which the free flow boundary conditions are changed to the mixed boundary conditions. By the numerical analytical results, a simple theoretical equation is proposed and it agrees well with the experimental data. Besides, selection of defoaming-agent, descaling-agent and period of descaling are explored in the process of concentrating straw pulping black liquor.It would help to prevent the evaporated liquor from scaling on the surface of heat-transferring tube-bundles. The operating time of the system can last longer and the evaporating intensity or efficiency as well as heat transfer coefficient would be enhanced, providing extremely high intensive evaporation for foaming and easy-scaling liquors with specific characteristics, such as higher viscosity and crystallizing.
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