A novel mineral separation process: New opportunity for clean coal utilization and soil remediation

Abstract

China currently consumes nearly 4 billion tons of coal annually with 64.7% of China's electricity in 2019 being sourced from coal-firing power plants. There are about 700000 small and medium-sized coal-burning boilers which consume 750 million tons of coal annually in 2017. These boilers are one of the major sources of air pollution and smog in China. The cost for equipping each small and medium-sized boiler with desulfurization and denitrification facilities (such as selective catalytic reduction, SCR) is prohibitively high. Additionally, it is not feasible to convert most of these coal-fired boilers to burn natural gas as the natural gas supply in China equates to about 220 million tons of standard coal units. Therefore, the only viable option for reducing air pollution while retaining energy security is to make the coal cleaner cost effectively prior to combustion. Also the introduction of chemical fertilizers (like ammonium nitrate) stimulated greater yield of crops, but changed the subsurface chemistry of the soil structure, locking up calcium, burning out humus, causing acidic soils and destroying the microorganism/mineral balance. A novel mineral separation technology has been developed. This technology (hereafter called "RevTech minerals separation technology" or "RMS technology") combines milling, separation, particle grading and soil remediation, enhanced by nanotechnology and advanced materials science with an innovative product conditioning system in energy and chemical engineering field. It effectively separates minerals and trace elements from carbonaceous feedstocks, producing high-grade and low-emission fuels, namely clean solid fuel (CSF) and pseudo liquid fuel (PLF), and natural ancient minerals called soil remediation minerals (SRM). The technology mainly involves four process steps: (1) Particles are milled using low-power consumption micronization technology, based on mineralogical characteristics; (2) carbonaceous and mineral particles are separated after specified surface modification and multiphase flow interphase regulation with proprietary reagents; (3) carbonaceous particulate flow is prepared to CSF by de-watering or pumped to PLF preparation unit, while mineral particulate flow is prepared to SRM by de-watering too; (4) the carbonaceous particulate flow is used to produce a high solid concentration PLF via multi-peaking gradation. RMS technology has been well demonstrated in a lab-scale test unit and another industrial scale-up test unit. The dry basis ash content (Ad) of the raw materials is about 55%. In the laboratory scale test unit, Ad of the CSF obtained is reduced to 7.58%, and Ad of the SRM enriched at the bottom is 86.16% using RMS technology process. In the industrial scale-up test unit, Ad of the raw materials is about 50%. Ad of the CSF is reduced to 6.12%, and Ad of SRM is 86.26% using RMS process. The calculation results indicated that when the solid mass fraction of PLF increased from 60% to 70%, the production cost of methanol could be saved by 234 million CNY/a and the CO2 emission could be decreased by 1.35 Mt/a for a 1.8 Mt/a methanol production plant. A 250 kt/a RMS commercial plant is under construction. This project has been evaluated to have good technical and market competitiveness. SRM is used to produce natural mineral fertilizer (NMF) and soil remediation amendment (SRA), offering potential solutions for soil remediation and topsoil restoration. SRM comprises feldspar, kaolinite and chlorite that are important components of healthy soils, at the total content of 50%-85%. The SRM derived products could increase vegetation productivity, strengthen plant & soil carbon sequestration, and achieve carbon neutrality. RMS technology could provide cost-effective clean fuels, and realize the resource utilization of coal-derived solid wastes. It provides a reliable way for the efficient and clean utilization of coal and CO2 emission reduction.