In Yunnan Province, which holds the second-largest reserve of lignite in China—over 17 billion tons—the potential for economic growth and industrial development remains untapped due to lignite’s inherent challenges, such as high moisture content, low calorific value, high volatile matter, and poor thermal stability. Despite these limitations, Yunnan’s Science and Technology Department has spearheaded efforts to harness its lignite resources through the formation of a multi-sectoral coal chemical industry strategic innovation alliance. This initiative has led to the launch of the "Efficient Conversion of Yunnan Lignite: Resource Utilization Engineering Technology Development Demonstration" project, with a total investment of 445.27 million yuan. Supported by 16 million yuan from provincial science and technology funds, the project comprises six key topics aimed at overcoming critical bottlenecks in lignite utilization.
One of the focal points of the project is the advancement of innovative technologies for lignite gasification, a crucial step toward maximizing resource utilization. Researchers have successfully developed large-scale fixed-bed crushing liquid slagging lignite gasifiers capable of processing 1,200 tons of lignite daily. These gasifiers can efficiently convert lignite with moisture levels below 40% into clean fuel product gas, achieving a combustible gas content of 80% and a cold gas efficiency of 85%. The resulting liquid slag has an ash residue carbon content of ≤0.2%, enabling downstream deep processing of valuable by-products. Additionally, this project has pioneered the use of carbon dioxide as a pressurizing agent in gasifiers, marking a significant advancement in China's coal processing technology.
Another breakthrough lies in the direct liquefaction of lignite, particularly focusing on the supercritical water method. Yunnan lignite, exemplified by that from Zhaotong, is notably high in moisture and low in calorific value, making its utilization challenging. Through the "Key Technology for Direct Liquefaction of Supercritical Water with High-Humidity Low-Rank Lignite" project, researchers have constructed a pilot plant with a daily production capacity of two tons and developed a daily processing line capable of handling 100 tons of lignite. This effort has resulted in proprietary core technologies, forming a comprehensive technical system that places the overall technology at an international leading level. The carbon conversion rate exceeds 80%, while the coal utilization rate surpasses 85%, significantly boosting the value-added potential of lignite.
In parallel, efforts have been made to transform lignite into oil-based products, addressing the nation's urgent need for oil alternatives. By developing a one-step process for converting methanol into naphtha and a reactor capable of handling 250,000 tons of methanol annually, the project has established a demonstration unit for synthesizing crude gasoline. This unit also produces 168,000 tons of refined gasoline and 1.3 million tons of mesitylene per year. Further advancements in molecular sieve catalysts allow for the production of clean fuels like liquefied petroleum gas (LPG) and heavy fuel oil, with mesitylene extracted from heavy fuel oil reaching a purity of 99%.
Addressing another critical challenge, the project has tackled the issue of gasification wastewater (gas water), a complex organic wastewater stream. Through the development of key technologies for recovering and treating ammonia and phenolic substances, as well as the refinement of crude phenol, the project has achieved near-zero emissions and significant energy savings. This has not only reduced operational costs but also enhanced the quality of recycled products, ensuring sustainable resource utilization.
Finally, the exploration of clean coal technologies, such as the coal cryogenic retorting method, offers a simpler, cost-effective approach to lignite conversion. With the development of rapid gasification equipment and the establishment of a 50,000-ton lignite processing pilot line, Yunnan has taken strides toward realizing the full potential of its lignite resources.
By the end of 2014, the project aims to complete ten domestic industrial demonstration and pilot production lines, including lignite gasification facilities, with an annual lignite processing capacity exceeding 500,000 tons. This endeavor not only positions Yunnan’s lignite industry at an internationally advanced and domestically leading level but also promises substantial economic returns, with projected annual sales revenue of 2.484 billion yuan and total profits of 300 million yuan. Ultimately, this project seeks to transform Yunnan into a province renowned for both its lignite production and its innovative resource utilization capabilities.
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