Reduction of CO2-emissions by production of highly reactive belite cement

目前的项目旨在在水泥工业中使用的传统回转窑中生产高活性的白来石多晶，以使生产低二氧化碳排放的水泥成为可能。水泥工业的二氧化碳排放量占人为二氧化碳排放量的5-7%。减少二氧化碳排放的最重要的策略是用水泥熟料替代波特兰水泥熟料。0.8 t CO2/t水泥通过补充胶凝材料如矿渣、粉煤灰、石灰石等产品，具有更低的CO2足迹。此外，未稀释熟料的二氧化碳排放量可以通过将其主要成分alite （72 wt.-% CaO）替换为belite （63 wt.-% CaO）来减少。白橄榄石的反应性通常较低，显著提高该相的反应性是当前研究计划的核心目标。白橄榄石可以以不同的多晶态存在，这些多晶态具有相同的化学成分，但晶体结构不同。众所周知，硅酸盐水泥熟料中通常存在白石的β -多晶，其反应活性相对较低。α -家族高温多晶具有较高的反应活性，并且这些多晶可以通过添加外来元素来稳定。最近的研究表明，也存在其他多态性。其中一种被标记为x，另一种形式的贝利特是一种无定形材料。令人惊讶的是，这两种形式的白石比传统上已知的多晶石更具反应性。3天后反应度可达90%以上，甚至高于alite。这两种形式的白橄榄石的生产目前是基于一个两步的过程，包括一个高压灭菌器，以防止生产高活性的多晶与现有技术。本提案的工作方案旨在利用现有技术以一步生产工艺取代两步生产工艺。这将通过将高活性白石的合成知识从高压釜工艺转移到高温工艺（600-1000°C）来实现。第一个工作包是一个相当广泛的经验研究，其中一些参数，如温度，掺杂元素的类型和浓度将被修改，以了解这些参数对单个多晶形成的影响。这一实证研究将得到对工作包2中多晶的热力学性质（焓、熵、热容）分析的支持。这些数据可用于预测生产高反应性x-多晶型的条件，以替代工作包1中的经验调查。这两个工作包的结果将用于在工作包3的小型回转窑中生产高活性贝利石材料。用这种方法生产的水泥的质量也将在本工作包中进行测试。

The present project aims at the production of highly reactive belite polymorphs in the traditional rotary kilns used in the cement industry to enable manufacturing of cements with low CO2 emissions. The cement industry is responsible for 5-7% of anthropogenic Ccarbon dioxide emissions. The most important strategy to reduce the CO2-emissions is the replacement of Portland cement clinker with approx. 0.8 t CO2/t cement by supplementary cementitious materials such as slag, fly ash, limestone and other products with a much lower CO2 footprint. Additionally, the CO2-emissions for the undiluted clinker can be reduced by replacing its main component alite (72 wt.-% CaO) by belite (63 wt.-% CaO). The reactivity of belite is usually relatively low and it is the core target of the current research proposal to significantly increase the reactivity of this phase. Belite can exist in different polymorphs that have an identical chemical composition but a different crystallographic structure. It is well known that the beta-polymorph of belite is usually present in Portland cement clinker which as a relatively low reactivity. It is also established that the alpha-family of high temperature polymorphs has a higher reactivity and these polymorphs can be stabilized by the addition of foreign elements. Recent investigations have shown that also other polymorphs exist. One of these was labeled x and the other form of belite is an amorphous material. Surprisingly, these two forms of belite are much more reactive than the traditionally known polymorphs. The degree of reaction can exceed 90% after 3 days and is thus even higher than for alite. The production of these two forms of belite is currently based on a 2-step process involving an autoclave which prevents the production of highly reactive polymorphs with existing technology. The work program of the present proposal was designed to replace the 2-step production process by a 1-step production process using the existing technology. This will be achieved by transferring the knowledge of the synthesis of highly reactive belite from the autoclave process to the high temperature process (600-1000°C). The first work package is a rather extensive empiric study where a number of parameters such as temperature, type and concentration of doping elements will be modified to learn about the effect of these parameters on the formation of the individual polymorphs. This empiric study will be supported by the analysis of the thermodynamic properties (enthalpy, entropy, heat capacity) of the polymorphs in work package 2. These data can be used to predict the conditions for the production of the highly reactive x-polymorph alternatively to the empiric investigations in work package 1. The results of both work packages will be used for the production of the highly reactive belite material in small rotary kilns in work package 3. The quality of the cements produced in this way will also be tested in this work package.