I would like to ask if there are any magnesium-based desulfurization projects under development in China? Are any of them currently in construction?

Magnesium-based desulfurization is also a relatively mature desulfurization process that is widely used in Japan; however, its application status in China is not well known. It is known that a power plant in Wuxi uses this technology for boiler desulfurization, and it is already in operation. Are there any others under construction?

Everyone is also welcome to discuss the advantages and disadvantages of magnesium-based desulfurization compared to other processes such as ammonia-based, gypsum-based, and double-alkali methods.

-------------------------------------------------------------------------------- Selection of desulfurization processes for coal-fired power plants 1　Requirements imposed by the desulfurization situation 　At present, coal-based power generation accounts for about 3/4 of China’s total electricity production, and this proportion is not expected to change significantly in the foreseeable future. In the process of converting primary energy in the form of coal into secondary energy in the form of electricity, coal-fired power plants generate pollutants such as exhaust gases, wastewater, ash, and noise. SO2 in these exhaust gases is one of the main pollutants in the atmosphere. 　　According to statistics from the **Environmental Protection Agency**, China emits over 20.9 million tons of SO2 each year, and the losses caused by acid rain exceed 110 billion yuan per year, which means the cost associated with each ton of SO2 emitted is nearly 5,000 yuan. The capacity of coal-fired power plants in our country currently exceeds 150 million kW, and it is estimated that they emit over 6 million tons of SO2 each year. 　　To implement the strategy for the sustainable development of China’s national economy, **environmental protection has been given increasing importance; clear requirements are set out in both the short-term goals and long-term plans for environmental protection, and a number of policies and regulations have been introduced, primarily using economic measures to encourage enterprises to take action to control SO2 emissions. Coal-fired power plants, which are major sources of SO2 emissions, should take the lead in addressing SO2 issues. In response, relevant agencies and departments have accelerated their research and development efforts; some coal-fired power plants have already installed desulfurization equipment, while more are in the process of planning to do so. 2 Overview of Desulfurization Technologies Although desulfurization technologies in China have been developed for over a decade, they have not seen significant progress due to economic reasons. In some developed countries in the West, as well as in Japan and South Korea, desulfurization technologies are highly advanced and come in a wide variety – over 200 different types in total. These technologies can be classified into four main categories: (1) Pre-combustion desulfurization (a process for purifying raw coal, primarily to remove inorganic sulfur) ； (2) Desulfurization during combustion [including fluidized bed combustion (CFB) and in-furnace injection of absorbents, etc.] ； (3) Post-combustion desulfurization (including wet limestone process, semi-dry limestone process, dry limestone process, seawater process, ammonia-alkali process, electron beam irradiation method, and absorbent regeneration, etc.) ； (4) Combined desulfurization (including in-furnace absorbent injection with tail-end wetting and activation methods, and gasification combined cycle, etc.). The most widely used method at present is post-combustion desulfurization, of which the limestone-gypsum process accounts for 70% of the existing desulfurization technologies; other processes are also being increasingly utilized as technology advances. 3 Current Status and Main Technical Characteristics of Desulfurization Technology in China Since the 1980s, China has gradually carried out research on flue gas desulfurization in coal-fired power plants, and has successively installed various desulfurization devices. 3.1 Limestone-gypsum process The first and second phases of the Chongqing Luohuang Power Plant, Taiyuan No.1 Thermal Power Plant, Chongqing Power Plant, Hangzhou Banshan Power Plant, and Shaanxi Hancheng No.2 Power Plant have all adopted this process. 　　The Chongqing Luohuang Power Plant utilizes process technology from the Japanese company Mitsubishi. It has 4 units with a capacity of 360 MW each, with an investment of 730.509 million RMB. The sulfur content in the coal used is 4.02%, the inlet SO2 concentration is around 3500 mg/m3, and the desulfurization efficiency is over 95%. 　　The Chongqing Power Plant utilizes German process technology, featuring 2 units with a capacity of 200 MW each; the investment amounted to 74.443 million Marks, and the desulfurization efficiency is also over 95%. 　　The main features of this method are: (1) The system is stable and reliable, with high efficiency, generally exceeding 95%, and it is widely used in industrial applications ； (2) High flue gas treatment capacity, strong adaptability to different coal types, and significant advantages for large-capacity units using high-sulfur coal ； (3) The absorbent is inexpensive, readily available, and has a high utilization rate; the calcium-sulfur ratio is generally around 1.03 ； (4) It has no impact on the dust collector, nor on the quality of fly ash ； (5) The by-product is gypsum dihydrate, which is easy to utilize ； (6) High investment, large land area, relatively high water consumption, with minor wastewater discharge ； (7) High quality requirements are imposed on by-products, necessitating high efficiency of dust collectors. 3.2 Spray drying method Both Sichuan Baima Power Plant and Shandong Huangdao Power Plant have chosen this method. 　　Sichuan Baima Power Plant is a medium-sized testing facility designed and built in China. With an investment of 9.5 million RMB, it is capable of handling 70,000 Nm3/h of flue gas; the concentration of SO2 entering the plant is 3,000 mg/m3. When the calcium-to-sulfur ratio is 1.4, the efficiency can exceed 80%. 　　The Huangdao Power Plant in Shandong Province utilizes process technology from Mitsubishi Corporation of Japan, with an investment of 1.6 billion yen; it can handle 300,000 Nm3/h of flue gas, achieving an efficiency of around 70%. 　　The main features of this method are: (1) Lime is generally used as the absorbent, with a moderate utilization rate; the calcium-sulfur ratio is usually around 1.3 to 1.6 ； (2) The system is stable and reliable, with high efficiency, generally exceeding 90% ； (3) High investment, large land area, low water consumption, no wastewater discharge ； (4) It has significant advantages in small and medium-sized units that burn coal with low sulfur content ； (5) The by-product is mostly CaSO3, which is difficult to utilize and remains attached to the fly ash, thereby affecting the comprehensive use of the fly ash ； (6) The dust removal capacity of the dust collector has increased, resulting in easy accumulation of dust on the tower walls and blockages at the bottom of the tower. 3.3 Calcium injection in the furnace with tail humidification activation – Nanjing Xiaguan Power Plant, Zhejiang Qianqing Power Plant, and Liaoning Fushun Power Plant have all adopted this method, utilizing the LIFAC process technology developed by the Finnish company Fortum. 　　Nanjing Xiaguan Power Plant has 2 units with a capacity of 125 MW each; the investment amount was 123.5 million RMB. The total floor area is approximately 600 m2. The sulfur content in the coal used is 0.92%, the flue gas volume per unit is 600,000 Nm3/h, the calcium-sulfur ratio is 2.5, and the efficiency is over 75%. 　　Zhejiang Qianqing Power Plant has 1 unit with a capacity of 125 MW; the investment in this unit was 50 million RMB. The sulfur content in the coal used is between 0.9% and 1.2%, and a desulfurization efficiency of 65% is required. 　　The main features of this method are: (1) simple and flexible process, low investment, small floor area, and low energy consumption ； (2) The absorbent is generally limestone, with a low utilization rate of about 2.5% ； (3) The desulfurization efficiency is moderate, generally ranging from (75–85)% ； (4) It has low water consumption and produces no wastewater, offering significant advantages for use in small and medium-sized coal-fired units with low sulfur content ； (5) Slight impact on the boiler and flue gas treatment system ； (6) The by-products are CaSO3 and CaSO4, which have an impact on the utilization of fly ash. 3.4 Electron beam irradiation method The Chengdu Thermal Power Plant in Sichuan adopted this method, utilizing the process technology from Ebara Corporation of Japan. The unit’s capacity is 90 MW, with an investment of 90 million RMB. It can handle 300,000 Nm3/h of flue gas; the SO2 concentration is 1,800 mg/m3, and the NOX concentration is 400 mg/m3. The desulfurization efficiency is 80%, while the denitrification efficiency is 10%. 　　The main features of this method are: (1) it is capable of efficiently removing both SO2 and NOX from flue gas simultaneously, with a desulfurization rate of over 90% and a denitrification rate of over 80% ； (2) The process is simple and flexible, requires low water consumption, and produces no wastewater ； (3) High investment, large land area, and high energy consumption ； (4) The by-products are sulfuric acid AN and *AO acid AN, which are agricultural fertilizers of high value ； (5) A certain amount of ammonia water is required; the by-products have poor market prospects, and operating costs are high. 3.5 Seawater desulfurization method The Shenzhen West Power Plant adopted this method. Apply the process technology of Norwegian ABB. The unit capacity is 300 MW, with an investment of 196.47 million RMB. It can handle 1.22 million Nm3/h of flue gas, the sulfur content in the coal is 0.63%, and the desulfurization rate is 90%. 　　The main features of this law are: (1) There must be sufficient marine water resources near power plants ； (2) Simple process with low operation and maintenance costs ； (3) High investment, large land area, large volume of flue gas to be treated, and high desulfurization efficiency ； (4) No other additives are required; waste emissions that do not need land treatment ； (5) Saving freshwater ； (6) The sulfur content in the coal used in power plants should not be too high; around 1% is appropriate. A high dust removal efficiency is required, otherwise it will cause pollution to the ocean. 3.6 Charged dry injection method The Dezhou Thermal Power Plant in Shandong, Lanzhou Thermal Power Plant, and the Second Thermal Power Plant of Hangzhou Iron and Steel Group adopted this method. 　　The Dezhou Thermal Power Plant in Shandong Province uses the process technology of the American company Alcan Environmental Resources to treat flue gas at a rate equivalent to that of a boiler with an exhaust volume of 75 t/h; the calcium-sulfur ratio is 1.4, the desulfurization efficiency is 70%, and the investment amount is 2 million RMB. 　　The main features of this method are: (1) simple process, low investment, small floor area, low operating costs, and moderate desulfurization efficiency ； (2) The absorbent is generally dry powdered slaked lime, with a moderate utilization rate of 1.2%–1.5% ； (3) It increases the dust removal capacity of the dust collector, which has an impact on the flue gas system and the utilization of fly ash. 3.7 New Ammonia Flue Gas Desulfurization Process (NADS process) This process is a key scientific and technological research project undertaken by East China University of Science and Technology during the **“Ninth Five-Year Plan” period. With the cooperation of Neijiang Power Plant in Sichuan and Sichuan Yinshan Chemical Group Co., Ltd., an intermediate test with a flue gas flow rate of 100,000 Nm3/h was completed in August 1999; in September 1999, it passed the evaluation of the results and the special acceptance conducted by the relevant authorities. Currently, plans are in place to conduct industrial-scale tests for 20–30 MW units in Beijing. 　　The main features of this method are: (1) It uses synthetic ammonia as an absorbent to produce the valuable intermediate ammonium sulfite; by combining it with chemical plants, valuable chemical products can be manufactured, resulting in high economic benefits. It represents a new type of process technology suitable for China’s national conditions ； (2) Low investment, small land footprint, low energy consumption, and high efficiency, generally exceeding 90% ； (3) By-products need to have a market; otherwise, operating costs will also be high ； (4) There is currently a lack of records of industrial application. 　　The desulfurization process technologies used domestically mentioned above are all relatively mature, widely applied, and hold promising prospects for further development. The main parameter values of these are listed in Table 1 for comparison. Table 1 Comparison Table of Key Parameter Indicators Method Indicator Investment Land Area Required Desulfurizing Agent Calcium-Sulfur Ratio Desulfurization Efficiency /% Operating Cost Flue Gas Volume Treated Availability of By-products Limestone-Gypsum Method 1 1 Limestone 1.03 >95 High Large Good Spray Drying Method 2/3 2/3 Slaked Lime 1.3–1.6 >85 Relatively High Medium Poor Calcium Injection Inside the Furnace with Tail Wetting and Activation 1/2 1/3 Limestone 2.5 75–85 Relatively Low Medium Poor Electron Beam Irradiation Method 4/5 1 Ammonia Water — >90 High Medium Good Seawater Desulfurization Method 4/5 3/2 Seawater — >90 Relatively High Large — Charged Dry Spraying Method 1/4 1/4 Slaked Lime 1.2–1.5 >75 Low Small Poor NADS Method 1/4 1/4 Ammonia Water — >90 Low Large Good 4 Factors to Consider When Selecting a Desulfurization Process 4.1 Local Natural Resources and Social Environment The selection of a desulfurization process should take into account the local natural resources and social environment. The absorbents required for the desulfurization process are readily available locally; they possess abundant natural resources, large reserves, high production volumes, and good quality (such as limestone, lime, seawater, ammonia water, etc.), which meets the needs of desulfurization and helps reduce operating costs. The by-products generated are easy to handle; those with good usability (in the absence of local natural resources) have high demand in society (such as gypsum, high-quality fly ash, agricultural fertilizers, chemical raw materials, etc.), which helps to increase economic income and reduce overall operating costs. 　　Taking the Datong area as an example, it is rich in limestone resources, which are of high quality and yield, yet it lacks natural gypsum resources, leading to high demand from society. According to investigations, there are over a dozen cement plants of various sizes in the Datong area alone. The Datong Cement Plant alone produces 1.5 million tons of cement per year, requiring about 60,000 tons of gypsum, which is purchased from Taiyuan at a price of around 100 yuan per ton ； The annual production of limestone powder is 50,000 tons, with a selling price of around 25 yuan per ton. If a 200 MW unit at Datong No. 2 Power Plant is equipped with a limestone-gypsum desulfurization system with a desulfurization efficiency of 95%, it is calculated that approximately 15,600 tons of limestone are required per year, and about 30,000 tons of gypsum are produced annually. The annual economic benefit, calculated as the revenue from selling the by-products minus the cost of purchasing the absorbent, is: 30,000 tons × 100 yuan/ton – 15,600 tons × 25 yuan/ton = 2.61 million yuan, which helps to reduce the operating costs of the desulfurization system effectively. The effect will be even more significant if two units share one desulfurization unit. 4.2 Sulfur content in coal and unit capacity The sulfur content in coal and the capacity of the units directly determine the amounts of SO2 and flue gases generated. To maintain the same air quality, power plants that use coal with high sulfur content or have large unit capacities should consider using desulfurization systems that are stable in operation, offer high absorber utilization rates, are efficient, and have a large capacity for treating flue gas ； Power plants with low sulfur content in coal or small unit capacities should consider choosing desulfurization devices that are simple in design, require less investment, have low energy consumption, offer flexible operation, and provide moderate efficiency. For example, in the case of the aforementioned Datong No. 2 Power Plant, although the limestone-gypsum desulfurization process seems suitable from the perspective of local natural resources and the social environment, given the low sulfur content in its coal (about 1%) and the small capacity of its generating units, it is necessary to conduct a thorough comparison to determine whether this method is appropriate. 4.3 Conditions of existing power plants Due to lower environmental protection requirements in the past, most of the coal-fired power plants built in China were not designed with regard to the site conditions and requirements for desulfurization facilities, which has become a constraint in selecting desulfurization processes. Therefore, when selecting a desulfurization process, it is necessary to take into comprehensive consideration factors such as the available space in the existing power plant, the layout of the process systems, as well as the lifespan of the units and the equipment in the flue gas system. 4.4 Environmental, geographical location, and environmental protection requirements In many Western countries**, when determining the desulfurization efficiency, factors such as the terrain, topography, wind direction, and wind speed of the location where the power plant is situated also need to be taken into consideration. Environmental protection requirements vary across different regions of our country; areas with low elevations, located near large cities and with dense populations have relatively higher environmental protection standards, while areas with high elevations, in remote locations and with sparse populations have relatively lower such standards. In areas with lower environmental regulations, a desulfurization process with lower efficiency can be considered; in areas with stricter environmental requirements, a more efficient desulfurization process should be chosen. At the same time, processes that can also remove NOX should be preferred, as once a large amount of SO2 in the atmosphere has been removed, NOX becomes the main target for control. 4.5 Treatment and Utilization of By-products All desulfurization units generate sulfur-containing by-products. In desulfurization units using limestone and lime, the by-products are generally a solid mixture composed of CaSO3, CaSO4, excess absorbent, and some fly ash; their usability is low, and factors such as secondary pollution, storage space, and costs must be taken into consideration when making a choice. The desulfurization process with better availability of by-products should be selected based on the local industrial structure, in order to avoid increased overall operating costs due to difficulties in selling these by-products. 4.6 The existing comprehensive utilization should not be affected. Markets for the existing use of fly ash in power plants have developed around the world. The comprehensive utilization rate of fly ash in our country is also gradually increasing; high-quality fly ash not only prevents secondary environmental pollution but also generates significant economic benefits. In some large cities in our country, there is still a demand for fly ash that exceeds the supply, so when selecting desulfurization processes, efforts should be made to avoid any impact on this supply. 4.7 Impact on Boilers and Existing Flue Gas Systems Some desulfurization processes may affect boiler combustion, tube wear and slag formation, air preheater wear and blockage, soot accumulation and corrosion in flues, dust collector efficiency and corrosion, induced draft fan load and corrosion, as well as chimney corrosion; these factors should be taken into consideration when making a selection. 4.8 Unit Operation Characteristics To facilitate the adjustment of grid load balance, countries classify units into units that provide base load and units used for peak shaving. For units with base load capacity, due to their large size and stable operation, a desulfurization process that ensures system stability and reliability as well as high efficiency should be considered when making a selection. Due to their smaller capacity and frequent start-stop operations, peak-shaving units should be equipped with a desulfurization process that features a simple system, flexible operation, and moderate efficiency. 4.9 Initial Investment and Annual Operating Costs As with other technologies, when selecting a desulfurization process, it is also necessary to make a balanced comparison between the initial investment and the annual operating costs. The initial investment and annual operating costs of various desulfurization units vary greatly. It is important to conduct a careful analysis and comparison taking into account these factors as well as the available funds, as this is a crucial aspect for the economic operation of desulfurization units. 4.10 Application of New Processes Countries around the world are constantly exploring, researching, and developing new high-tech processes that require low investment and operating costs, and that enable the conversion of waste into valuable resources. Methods such as electron beam irradiation, NADS method, and biological desulfurization are all high-tech processes that can turn waste into resources, effectively reduce operating costs, and even generate economic benefits; they represent the future direction for the development of desulfurization technologies. 5 Summary At present, China’s economy is relatively underdeveloped; it is in a developing stage. It is not possible to simply copy the desulfurization models and methods used in developed Western countries; instead, it is necessary to build on their advanced technologies and experiences, while taking into account China’s national conditions, geographical resources, social environment, and the existing capabilities of enterprises. Adjustments must be made according to local circumstances, and thorough evaluations and comparisons should be conducted from various perspectives. While protecting the environment, minimize the increase in power generation costs to ensure the economic viability of the enterprise.

Why can developed countries such as Japan, South Korea, Taiwan, Australia, and the United States import magnesium oxide from China for desulfurization purposes, while there is little use of magnesium-based desulfurization methods in China itself? It’s clear that China’s approaches to atmospheric desulfurization in terms of environmental protection are something that the whole world finds confusing! There are no experts in environmental protection!

You know, we have the largest magnesium resources in the world – there are even more in the southwest and northwest regions