Carbon emissions from in-situ pyrolysis of tar-rich coal based on full life cycle analysis method

Abstract

The control of carbon emissions has already become a great social strategic problem in China which must be solved at present and in the future. It is imperative to carry out safe, efficient, and low-carbon utilizations in the coal industry under the target of achieving carbon emission peak. Tar-rich coal is abundant in western China. It is mostly combusted for power generation, which results in the wastage of valuable resources and serious environmental pollution. The in-situ pyrolysis process of tar-rich coal provides a new method for generating oil from coal. This method is to produce oil without mining coal while alleviating damage and pollution to geological formations. Compared with traditional coal mining methods, it can reduce the size of goaf section and minimize the damage to rock structure. As a new coal-to-oil route, the in-situ pyrolysis of oil-rich coal is still at an initial stage for research, for which there are still few carbon emission evaluations from the perspective of the full life cycle analysis. Based on the carbon emission accounting method widely adopted, the life cycle analysis (LCA) is employed to analyze the carbon dioxide emission in the whole process of an in-situ tar-rich coal pyrolysis project, including coal seam modification, in-situ heating, product processing, product transportation and terminal consumption. A lateral comparison of greenhouse gas inventory with indirect coal liquefaction and direct coal liquefaction is also carried out. At the same time, the greenhouse gas emission from the in-situ pyrolysis of tar-rich coal is analyzed systematically. The results show that it is necessary to adopt low-carbon energy in the development of in-situ pyrolysis of oil-rich coal. With power grid as the energy source, the LCA carbon emission of in-situ pyrolysis is about 2.234 5 t CO2 for each tonne of coal treated, while with wind power as the energy source, merely 0.608 6 t CO2. The in-situ pyrolysis of tar-rich coal has an obvious advantage in carbon emission reduction over indirect or direct coal liquefaction process. To reduce carbon emissions effectively, several mitigation measures need to be combined, including promoting energy efficiency, optimizing heat sources, and increasing the proportion of clean energy.

Keywords

• in-situ pyrolysis
• life cycle analysis
• carbon emissions
• tar-rich coal
• emission peak