气化飞灰精准分离及资源化利用

Precise separation and resource utilization of coal gasification fly ash

煤炭气化技术在中国经济发展中发挥着极其重要的作用,但气化过程中,部分未反应的炭及细渣会由合成气带出,产生大量的气化飞灰,引发固体废弃物的处理及资源化利用问题。由喷淋收集得到的飞灰,经初步絮凝脱水后,水分含量在55%～60%,其余为残炭和玻璃体的混合固体颗粒。为实现气化飞灰的资源化利用,必须对气化飞灰的结构特征、持水特性以及水与固体颗粒之间的相互作用进行深入研究,寻求气化飞灰科学高效的分离及资源化利用技术。笔者论述了气化飞灰脱水脱炭的意义,分析了飞灰持水特性及水分脱除技术,重点阐述了飞灰综合利用方案,并对气化飞灰精准分离及资源化利用方向进行展望。课题组前期试验表明,飞灰基沸石具有较高的表面积、独特的孔隙特征和优异的离子交换能力,可用于土壤、废水等中重金属的去除,以及作为吸附剂用于土壤中污染物的固定。飞灰的化学组成成分与黏土相似。传统陶瓷原料资源储量日益减少,国内外研究表明,飞灰制备陶瓷地砖可行。利用飞灰代替传统陶瓷中石英,在一定烧结温度下,通过抗折强度、吸水率、收缩率、失重率等变化研究对试样陶瓷性能的影响,说明添加飞灰的陶瓷性能优于传统陶瓷。通过泡沫浮选法分离气化飞灰固体颗粒,分别得到纯度较高的气化飞灰残炭和玻璃体,以分离后的残炭作为催化石墨化的碳源,在高温热处理过程中加入催化剂,对其进行催化石墨化处理,以探索气化飞灰制备石墨化材料的可行性,残余炭在较高温度和适量的催化剂条件下,得到了与商用石墨的性能相似的有序石墨化材料。气化飞灰和电厂粉煤灰都具有较高的硅铝含量,这使得气化飞灰成为沸石分子筛等多孔材料的潜在重要来源,而制备沸石也是飞灰回收利用中效益最高的途径,这项工艺不仅减轻了灰渣废料带来的环境负担,更应用于催化、分离、吸附等方面。未来应深入研究飞灰中水的赋存形态及其与飞灰颗粒的相互作用机制,同时构建灰-水作用界面模型,在此基础上寻求飞灰脱水新技术,进一步降低飞灰含水量。研究能耗低、效率高、污染少的残炭-玻璃体分选技术,降低分选产品的杂质含量。研究分选后残炭和玻璃体资源化利用新领域,最大限度发挥气化飞灰的价值。

Coal gasification technology plays an extremely important role in China’s economic development.But it will generate a large amount of fly ash which is consisted of unreacted pulverized coal and slag brought by synthesis gas.After preliminary flocculation,the moisture content of fly ash collected by spraying is 55%-60%,and the rest of the ash is mixture of residual carbon and glass particles.It is necessary to have a better understanding of the structural characteristics,water holding properties and the interaction between water and solid particles of fly ash so that the ash can be fully utilized.In this paper,the significance of dehydration and decarburization,the characteristics of water holding capacity,the technology of water removal and the scheme of comprehensive utilization of fly ash were discussed in order to seek the scientific separation and resource utilization technology of fly ash.At last,prospects for precise separation and resource utilization of coal gasification fly ash was forecasted.Previous experiments show that fly ash-based zeolite has high surface area,unique pore characteristics and excellent ion exchange ability,which can be used to remove heavy metals in soil and wastewater,and as adsorbent to fix pollutants in soil.The chemical composition of fly ash is similar to clay.The reserves of traditional ceramic raw materials are decreasing day by day.Some studies at home and abroad have confirmed that it is feasible to prepare ceramic floor tiles with fly ash.Foreign scholars used fly ash to replace quartz in traditional ceramics.At a certain sintering temperature,the effects of fly ash on the properties of sample ceramics were studied through the changes of flexural strength,water absorption,shrinkage,weight loss rate and so on.It was concluded that the properties of ceramics with fly ash were better than those of traditional ceramics.The gasification fly ash particles were separated by foam flotation method,and the carbon and vitreous of gasification fly ash were obtained respectively.The separated carbon residue was used as the carbon source for catalytic graphitization.The catalyst was then treated by adding graphitization in the process of high temperature heat treatment,so as to explore the feasibility of preparing the graphitized material by gasification fly ash.Ordered graphitization materials with similar properties to commercial graphite were obtained under catalytic conditions.Gasification fly ash and power plant fly ash both have high content of silicon and aluminium,which makes gasified fly ash a potential important source of porous materials such as zeolite molecular sieves.The preparation of zeolite is also the most efficient way to recycle fly ash.This process not only reduces the environmental burden of ash waste,but also applies to catalysis,separation and adsorption.In the future,the occurrence of water in fly ash and its interaction mechanism with fly ash particles should be studied in depth.At the same time,the interface model of ash-water interaction should be constructed.On this basis,new technology of fly ash dewatering should be sought to further reduce the water content of fly ash.The carbon-vitreous separation technology with low energy consumption,high efficiency and less pollution should be studied to reduce the impurity content of the separation products,and new fields of resource utilization of sorted charcoal and vitreous body should be studied to maximize the value of gasified fly ash.