Increase of efficiency in phosphate recovery by understanding the interaction of flow and loading processes with modeling and simulation

磷是一种重要的不可替代的营养物质，是重要的农业肥料。工业回收过程在化肥生产中起着重要作用。根据2012年12月《肥料条例》的要求，必须确保以五氧化二磷为基础的肥料的磷酸盐含量至少为10%。目前，许多流程不满足这些要求。P-RoC工艺（通过结晶法从废水中回收磷）是一种很有前途的工艺，其中水相中溶解的磷酸盐与多孔水化硅酸钙（C-S-H）颗粒结合。C-S-H颗粒容易脱水，装载后可直接作为肥料使用。吸收过程发生在搅拌反应器中，是动态的，取决于电流、颗粒的空间分布和磷酸盐浓度等因素。这些因素对过程效率的影响还不完全清楚，反应的动力学也不完全清楚。用数值流动模拟的方法研究考虑动力学过程的反应和过程动力学不仅具有多尺度的特点，而且具有很大的改进潜力。该项目的目的是澄清动态流动和反应过程，特别是它们的相互作用对磷酸盐摄取的影响程度。目的是通过数值研究确定动力学模型方程。这将为脱离经验确定参数的反应动力学计算提供一个基本的和新的见解，并将其直接用于流动模拟，以预测C-S-H颗粒的磷酸盐吸收过程。在计划中的项目中，CSH颗粒纳米级反应过程的反应动力学将通过使用分子动力学方法和孔或颗粒表面合适的势方程建模来捕获。对于物质系统磷酸盐和C-S-H，将使用基于离散元素方法（DEM）的粗粒度模型进行离散化和模拟。得到的反应动力学转化为微观和宏观尺度的流动模拟，并与晶格玻尔兹曼方法（LBM）相结合。通过文献比较以及现有和准备的实验室实验进行了验证。所有的调查都将通过基于LBM和DEM的仿真来完成，并使用开源软件OpenLB。这使得在一个统一的框架内实现水动力学和粗粒度建模，同时确保转移到与反应动力学有关的其他问题。

The essential and non-substitutable nutrient, phosphate, is an important fertilizer in agriculture. Industrial recovery processes play an important role in fertilizer production. A phosphate content of the fertilizer of at least ten percent, based on phosphorus pentoxide, has to be ensured in accordance with the requirements of the Fertilizer Ordinance of December 2012. Currently, many processes do not meet these requirements. The P-RoC process (phosphorus recovery from waste water by crystallization) is a promising one, where dissolved phosphate from the aqueous phase binds to particles of porous calcium silicate hydrate (C-S-H). C-S-H particles are easy to dewater and can be used directly as fertilizers when loaded. The uptake process takes place in a stirred reactor, is dynamic and depends on factors such as currents, spatial distribution of particle and phosphate concentrations. The influence of the factors on the efficiency of the process is not fully understood, nor is the kinetics of the reaction. The investigation of the reaction and process kinetics under consideration of the dynamic processes by means of numerical flow simulation poses a challenge not only because of the multi-scale nature, but also has a great potential to improve the process. The aim of the project is to clear up the extent to which the dynamic flow and reaction processes and in particular their interaction influence the phosphate uptake. The aim is also to determine the model equations of the kinetic by means of numerical investigations. This will provide a fundamental and new insight into a calculation of reaction kinetics detached from empirically determined parameters and their direct use in flow simulation to predict the phosphate uptake process of the C-S-H particles.In the planned project, the reaction kinetics of the nanoscale reaction process at the CSH particles is to be captured by means of modelling using a molecular dynamic approach and suitable potential equations at the pore or particle surface. This will be discretized and simulated using a coarse-grained model, based on a discrete element method (DEM), for the substance system phosphate and C-S-H. The reaction kinetics obtained are transferred to the micro- and macro-scale flow simulations and coupled with the lattice Boltzmann methods (LBM). The validation is carried out by literature comparison as well as existing and prepared laboratory experiments. All investigations will be performed by simulations based on the LBM and the DEM with the open source software OpenLB. This enables the implementation of hydrokinetic and coarse-grained modelling within a uniform framework and at the same time ensures a transfer to other questions in connection with reaction kinetics to be determined.