In the heart of China’s energy strategy lies a bold vision: to transform coal, a resource long associated with environmental concerns, into a clean and efficient energy source. At the forefront of this endeavor is Zhen Dong, a researcher from the Research Institute of Petroleum Exploration & Development, PetroChina, who has been delving into the intricacies of underground coal pyrolysis. His latest study, published in Meitan xuebao, which translates to Coal Science and Technology, offers a glimpse into the future of coal utilization, promising a paradigm shift in the energy sector.
Dong’s research focuses on the production capacity prediction of U-shaped horizontal wells for in-situ pyrolysis of tar-rich coal. This method, he argues, could be a game-changer in the quest for clean energy. “Underground coal pyrolysis has the advantages of high resource abundance, clean and low-carbon gas products, and low geological risk,” Dong asserts. This process involves heating coal underground to produce tar and gas, which can then be extracted and utilized.
The study, conducted in the Santanghu Basin, involved block coal overburden pyrolysis experiments on two main coal seams. The results are promising. The coal from the Badaowan Formation, for instance, showed a higher tar and coal gas yield compared to the Xishanyao Formation. The experiments revealed that tar production peaks at temperatures between 400−500 ℃, while coal gas production increases rapidly at 300−400 ℃ and slows down beyond 600 ℃. The confining pressure, Dong notes, plays a crucial role in this process. “Confining pressure has a negative effect on reducing the mass transfer capacity of pyrolysis products and a positive effect on improving heat transfer efficiency,” he explains. This balance is critical for optimizing the pyrolysis process.
The research also introduced a productivity prediction method for U-shaped horizontal wells, a development that could significantly enhance the efficiency of coal pyrolysis. The study found that the tar and coal gas productivity follows a distinct pattern: low production in the early stage, rapid production in the middle stage, and stable production in the late stage. Over five years, a single U-type well could potentially produce 1.56×104 tons of tar, 260.21×104 cubic meters of methane, and 201.83×104 cubic meters of hydrogen annually. The energy return rate is estimated to be 2.09, a figure that underscores the economic viability of this technology.
One of the most compelling aspects of this research is its potential to reduce carbon emissions. According to Dong, underground coal pyrolysis can reduce carbon emissions by 97% compared to surface coal combustion. Moreover, the CO2 produced can be absorbed and buried through the semi-coke layer, paving the way for carbon neutrality.
The implications of this research are far-reaching. For the energy sector, it offers a pathway to harness coal’s energy potential while mitigating its environmental impact. For investors, it presents an opportunity to tap into a clean and efficient energy source. For policymakers, it provides a roadmap for achieving the “dual carbon” goals—peaking carbon emissions and achieving carbon neutrality.
As the world grapples with the challenges of climate change and energy security, Dong’s research offers a beacon of hope. It is a testament to the power of innovation and the potential of technology to transform our energy landscape. With further development and implementation, underground coal pyrolysis could indeed become a cornerstone of the clean energy revolution. The study, published in Meitan xuebao, is a significant step in this direction, one that could shape the future of the energy sector.
