CO₂ storage-cavern construction and storage method based on functional backfill

The target of emission peak and carbon neutrality is not only a major strategic decision influencing a community with a shared future for mankind, but also a bellwether to promote the transformation and upgrading of the coal industry for high-quality development. As a provider of high-carbon fossil energy, the problems, such as bulk solid waste storage, formation of large goaf and high carbon emission caused by coal production and consumption, are the key issues to restrict the sustainable exploitation and utilization of coal, and the green and healthy development of coal industry. Based on the principle of "turning harm into benefit" and “arriving where it comes from”, the concept of CO₂ storage-cavern construction and storage based on functional backfill was proposed to seek the organic combination of efficient resource recovery, large-scale solid waste disposal, goaf reuse and the CO₂ storage. Anovel approach of CO₂ sequestration was explored, which includesfunctional backfill materials preparation, functional cemented paste backfill(CPB) and construction of CO₂ storage-cavern, physical-chemistry CO₂storage, CO₂ storage safety and environmental risk assessment. The specific work included the following four aspects.(1) The modification technology of magnesium slag was innovated, and the new modified magnesium slag based mineral cementing materials and functional CPB materials for CO₂ storage had been developed.(2) The short-and long-wall CPB pillarless mining method was put forward to preliminarily build the CO₂ storage space which meets the stability requirements. The CO₂ storage-cavern which meets the airtightness requirement was further constructed based on functional backfill. In addition, the structure, parameters and working model of the CO₂ storage-cavern were discussed.(3) The physical-chemical approach of CO₂ storage was proposed. The physical storage can be divided into shallow to middle deep low-pressure CO₂ storage, and deep supercritical CO₂ storage according to different mining depths. The chemical mechanism of CO₂ storage based alkaline solid waste was revealed.(4) The evaluation index system of functional filling CO₂ storage was sorted out, and the evaluation method of safety and environmental performance of CO₂ storage was given. The proposal of CO₂ storge technology with functional backfill provides a new idea for the CO₂ sequestration. Based on sequestration materials, filling storage, storage mechanism and evaluation, a theoretical and technical concept of using solid waste filling technology to realize the CO₂ storage in mines has been developed.