Direct mining includes open pit mining and underground mining. Open-pit mining is suitable for mining shallow-buried deposits with low cost and high safety factor. Fushun in Liaoning and Maoming in Guangdong are typical examples. There are two underground mining methods: vertical shaft mining and horizontal roadway mining, which are suitable for deep-buried deposits. Direct mining is a relatively primitive mining method, which has great limitations and serious damage to the ecological environment, mainly in three aspects:
First, the ecology and water quality are seriously damaged. Whether it is open-pit mining or underground mining, it is necessary to lower the groundwater level below the horizon containing oil shale. To exploit 1 m3 oil shale, it is generally necessary to extract 25m3 groundwater. Mining water greatly increases the sulfate content in surface water and groundwater. In Brazil, oil shale mining has long destroyed the ecological balance and the stability of water level and water quality in the mining area and its vicinity.
Second, the ash pollution is serious. The oil shale obtained by direct mining is used to refine shale oil or directly burn, resulting in a large amount of ash. If it is not recycled, it will not only cause air pollution, but also occupy a lot of land, in which metal elements and trace elements infiltrate into underground water bodies, endangering people's production and life.
Third, direct mining covers a large area, and once reclaimed, it cannot be completely restored.
Underground transformation process
Underground conversion process (ICP) is a patented technology for exploiting unconventional resources such as oil shale, which is developed by Shell Company with huge investment, and it is especially beneficial for developing deep oil shale. The basic principle of ICP mining oil shale is to heat and crack the underground oil shale seam to convert it into high-quality oil or natural gas, and then extract oil and natural gas respectively through relevant channels; These high-quality oil (gas) can be collected and processed on the ground to produce naphtha, kerosene and other refined oil. The outstanding advantages of this technology are: improving the efficiency of resource development and utilization; Reduce the damage to the ecological environment in the process of mining, that is, less land occupation, no tailings and waste, no air pollution and less groundwater pollution, and minimize the generation of harmful by-products. Although the technology has not been fully commercialized, key technical problems such as technology and equipment have been solved, and commercial demonstrations have been conducted in Colorado, USA and Alberta, Canada. According to the development cost of a barrel of crude oil in May 2005, the traditional dry distillation technology is $20/barrel, and the production cost of ICP technology is 12 $/barrel. The cost of ICP technology is lower than that of traditional dry distillation technology, and it can be profitable when the oil price is higher than $25/barrel. China Jilin Province is rich in oil shale resources, but most of them are buried under plain farmland or deep underground. Jilin Bureau of Geology and Mineral Exploration and Development and Shell Exploration Co., Ltd. signed a cooperation framework agreement on February 8, 2004. According to Shell's research and development of ICP technology in North America and the investigation of oil shale resources in Jilin Province, the joint venture company is expected to start commercial demonstration of ICP technology in 2006 and start full commercial operation after 20 10.
After nearly two centuries of development, the oil shale mining method has gained many successful experiences and is constantly improving. Mature mining technology is a powerful guarantee for the rise of oil shale industry. Fushun dry distillation process is mainly used in China, and most other processes are in the experimental stage. The overall technical level is low, which is related to the support of mountain companies and local governments in the industry, the research cycle and the small scale. In 2007, the National Development and Reform Commission issued the Guiding Catalogue of Industrial Structure Adjustment (2007), indicating that in the next few years, it will vigorously support the development of unconventional energy sources such as oil shale and oil sands in terms of credit and taxation, and industrial technology development is expected to break through.
With the progress of technology and the enhancement of environmental awareness, oil shale resources have developed from simple energy utilization to comprehensive utilization, which greatly improves the utilization rate of resources, reduces costs, reduces environmental pollution, and provides a guarantee for the sustainable utilization of resources. After oil shale ore is mined, it is first used as energy, that is, dry distillation and refining, and as fuel. The shale oil after dry distillation can be sold as fuel oil, and light diesel oil can also be produced by hydrofining and non-hydrofining methods to improve the added value of shale oil, and the refined heavy oil can be used as fuel. As a fuel, oil shale is mainly used for power generation, that is, it is directly used as boiler fuel or gas fuel produced by low-temperature dry distillation, and can also be used for heating and long-distance transportation. Ash and waste gas produced by dry distillation and direct combustion have different uses. Ash can be used for filling minerals, making cement or ceramsite, making bricks, etc. At present, there are many technologies to successfully utilize shale waste residue. Waste gas can be used as steam generated by fuel combustion for production and life, and can also be recycled to provide heat source for oil shale dry distillation.
The utilization of oil shale mainly focuses on refining shale oil and generating electricity, so the development of dry distillation process and combustion boiler directly affects the use effect. The requirements of reducing cost, paying attention to environmental protection and making full use of resources have promoted the innovation of oil shale utilization technology, which is mainly manifested in the improvement of dry distillation process and combustion boiler.
Dry distillation technology
At present, many countries in the world have studied the dry distillation of oil shale, and some of them have formed industrial production scale. The producer furnaces in China, Russia and Estonia and the LR furnace in Germany have small capacity, low oil yield and advanced technology, but less investment, which are suitable for small shale refineries. Estonian Kiviter furnace and American TOSCO-II furnace have large capacity and medium investment, which are suitable for medium-sized oil shale refineries. Galoter in Estonia, Petrosix in Brazil and Alberta-Taciuk in Australia have large capacity, high oil yield and high investment, which are suitable for large and medium-sized oil shale refineries.
Gasification technology of oil shale suspension combustion
As a fuel for power generation, oil shale has experienced a long research and development process, from oil shale suspension combustion and gasification to oil shale fluidized bed combustion and then to oil shale circulating fluidized bed combustion. Technology continues to improve, efficiency continues to improve, and pollution continues to decrease.
The former Soviet Union directly burned oil shale to generate electricity. In 1950s and 1970s, three power plants were established in Estonia and the Baltic Sea, with a total installed capacity of 24 15MW and a boiler output of 65-320 tons/hour. However, there are many problems: the actual output of the boiler is reduced, the furnace is coking, the heating surface is corroded at high temperature, and the tail heating area is blocked by ash; The emission of SO2 and NOX is large, which seriously pollutes the environment; The coal pulverizing system has high power consumption, high boiler maintenance cost and uneconomical operation; The reliability of the unit is poor, and it is often forced to stop for a long time.
Oil shale fluidized bed combustion technology
The former Soviet Union first developed the oil shale fluidized bed boiler, and in 1980s, Estonia and Baltic Power Station reformed the boiler. Oil shale fluidized bed boilers have also been applied in Maoming, Guangdong and Fushun, Liaoning. Its outstanding advantages are that the possibility of coking in the boiler is reduced, there is NO serious ash accumulation on the convection heating surface, the content of NO and NO2 in the flue gas is low, a large amount of sulfur can be absorbed during combustion, and the actual output power of the boiler is increased, and the fly ash will not stick to the superheater and economizer tube bundles of the boiler, and the thermal efficiency of the boiler is above 70%. Practice has proved that oil shale fluidized bed combustion power generation is technically feasible, but the efficiency is low and the economic benefit is poor.
Oil shale circulating fluidized bed combustion technology
Circulating fluidized bed combustion technology effectively improves the utilization rate of oil shale and the thermal efficiency of boiler, and reduces the emission of pollution gas. It is the most favorable combustion mode for oil shale power generation, with good adaptability of coal, low combustion temperature, wide combustion screening particles, extremely low emission of SO2, NO and NO2, and boiler efficiency above 80%. These outstanding advantages have injected new vitality and brought new opportunities for oil shale energy utilization and oil shale combustion power generation technology. China, Israel and other countries have gained successful experience in energy utilization research of oil shale circulating fluidized bed combustion power generation. 1989, the first semi-commercial demonstration power station of circulating fluidized bed combustion of oil shale was built in Israel, using a 50t/h circulating fluidized bed boiler of Ahlstrom Company in Finland. In 1990s, Israel built a commercial power plant burning oil shale with a 230t/h circulating fluidized bed boiler. 1996 Huadian oil shale demonstration thermal power plant in Jilin Province adopted three 65t/h low-rate circulating bed oil shale power plant boilers manufactured by Northeast Electric Power Research Institute, which realized long-term stable operation.
The application technology of oil shale has made great progress and made great contributions to the economic development of many countries. However, the main uses of oil shale in different countries are quite different. Estonia is mainly used for power generation and shale oil extraction. In recent 40 years, 99% of its electricity production mainly depends on oil shale, Brazil is mainly used as transportation fuel, Germany is mainly used to manufacture cement and building materials, China and Australia are mainly used to extract shale oil and use it as fuel, and Russia and Israel are mainly used to generate electricity.