China’s coal and coal-fired industrial boilers

Thread Content

Coal and Coal-Fired Industrial Boilers in China Mao Jianxiong Tsinghua University, Beijing, China Yang Qijuan China Power Engineering Society, Beijing, China Mark C. Freeman U.S. Department of Energy, **Energy Technology Laboratory Jean Y. Ku U.S. **Renewable Energy Laboratory Abstract: Coal is China’s primary energy source, accounting for 95% of the country’s total fossil fuel reserves. Coal accounts for over 60% of the primary energy consumption structure. The energy structure based on coal causes severe air pollution; over 85% of the country’s CO2 emissions, more than 90% of SO2 emissions, and over 70% of dust emissions stem from the use of coal. Keywords: coal, industrial boilers fueled by coal, efficiency, emissions. In 2000, China had 504,000 industrial boilers, with a total evaporation capacity of 1.2 million steam tons. Industrial boilers are the second-largest coal users in the country, consuming around 400 million tons of coal each year. Most coal-fired industrial boilers are characterized by low capacity, low efficiency, and high emissions. Each year, these boilers emit 750 million tons of CO2, 6.3 million tons of SO2, and 6 million tons of dust. This article will introduce a balanced discussion on (1) the role of coal in China’s primary energy structure ； (2) Coal-fired industry: Boilers are China’s second-largest coal user ； (3) The main reasons for the low efficiency and high emissions of industrial boilers using coal in China ； (4) The main approaches to solving the problems of coal-fired industrial boilers in China ； (5) Conclusion. 1 The role of coal in China’s energy structure: Coal accounts for 95% of China’s fossil fuel reserves, ranking it third in the world in terms of coal reserves. China’s proven reserve of coal is 557 billion tons, with 5,345 coal mining areas identified. The current actual reserves amount to 1,003.26 billion tons, while the guaranteed reserves are 409.5 billion tons. It accounts for one-third of the world’s proven reserves. Although China has abundant daily resources, its per capita coal reserves amount to only 55% of the world’s average per capita reserves. As shown in Table 1, in terms of the structure of primary energy consumption, China differs from most other countries; coal has always been China’s main source of energy, and this status will remain unchanged for many years to come. This position of coal can also be seen from China’s energy production and consumption figures for the year 2000 in Table 2. From the perspective of the energy consumption structure, China differs significantly from developing countries. As can be seen in Table 3, in many developing countries, coal is primarily used for power generation. In China, although thermal power generation is the largest consumer of coal, it is also used in other sectors; industrial boilers represent the second-largest consumer of coal, with their annual consumption accounting for almost one-third of the country’s total coal production, as shown in Table 4. In short, coal holds a very important position in China’s energy structure: over 65% of the country’s energy consumption, 75% of industrial fuel needs, 80% of electricity production, 80% of energy used for domestic and commercial purposes, and 60% of the raw materials used in the chemical industry come from coal. Estimates suggest that in 2005, 2010, and 2030, coal will still account for 64%, 60%, and 55% of China’s energy mix respectively; in other words, for nearly 30 years to come, coal will remain China’s primary source of energy. Table 1: World energy consumption structure in 2000 ** Energy consumption (Mtep): Oil (%) – Natural gas (%) – Coal (%) – Nuclear energy (%) – Hydropower (%) United States: 3235.1, 39.4, 25.8, 24.8, 9.0, 1.0 Russia: 887.3, 19.9, 54.6, 17.8, 5.4, 2.3 Germany: 470.6, 39.3, 21.7, 25.1, 13.3, 0.6 United Kingdom: 323.0, 34.3, 38.1, 16.7, 10.6, 0.3 Canada: 331.1, 35.8, 30.2, 12.6, 8.1, 13.3 Spain: 179.9, 55.6, 12.0, 17.2, 12.7, 2.5 Australia: 151.4, 36.5, 18.0, 44.1, –1.3 China: 1075.3, 30.1, 3.0, 63.8, 0.6, 2.5 World: 12503.4, 40.0, 24.7, 25.0, 7.6, 2.6 Table 2: China’s energy production and consumption in 2000 Item: Raw coal, Crude oil, Natural gas, Hydropower Share of total national energy production (%): 70.3, 17.25, 3.2, 8.9 Share of total national energy consumption (%): 66.1, 23.4, 2.7, 7.8% Table 3: Comparison of energy consumption structures between China and some developed countries (2000) ** Electricity (%) – Coking and gasification (%) – Industrial boilers (%) – Domestic use (%) China: 40.7, 12.53, 37.1, 6.9 United States: 87.0, 3.8, 8.5, 0.7 United Kingdom: 75.3, 9.8, 9.7, 5.2 Australia: 75.3, 14.7, 2.5, 3.5 Canada: 96.6, –, –, – 294 Table 4: China’s coal consumption structure in 2003 Item: Used for power generation (%) – Used for coking and gasification (%) – For industrial boilers (%) – Export and other uses (%) Consumption of raw coal (million tons): 630, 220, 400, 130 Share of total coal consumption (%): 47, 16, 29, 8 The use of coal causes severe air pollution problems. Table 5 shows the pollutants emitted as a result of coal use. Figure 1 illustrates the areas in China designated as acid rain and sulfur dioxide control zones by the Chinese Environmental Protection Agency. As can be seen from the figure, the area of China where rainfall has a pH value of less than 5.6 accounts for 40% of the country’s total land area. Almost all large cities are located in the two control zones, and the economically developed coastal regions of East China, Central China, South China, and Southwest China are all within these two control zones. Table 5: Pollutants emitted in China due to coal utilization
Pollutants: CO2, SO2, dust
Total amount of pollutants emitted from coal utilization: 2.8 billion tons, 22.7 million tons, 12.3 million tons
Share of these pollutants in China’s total pollutant emissions: 85%, 90%, 70%
Source: State Power Corp.
Figure 1: Acid rain and sulfur dioxide in China (control areas)
2. Coal-fired industrial boilers: China’s second-largest user of coal. In 2000, there were 504,000 industrial boilers installed in China, with a total capacity equivalent to 1.26 million steam tons. Of these, industrial boilers that use coal account for 85%, consuming about 400 million tons of coal per year, which is roughly one-third of the country’s total coal production. Although the number of industrial boilers in China is huge, the capacity of each individual boiler is quite small; boilers with a capacity of less than 10 t/h account for over 66% of the total number of industrial boilers. Compared to the boiler efficiency of 85% that corresponds to international advanced levels, the design efficiency of most industrial boilers in China is 70–75%, while their actual average operating efficiency is only 65–70%, which is 10–20 percentage points lower than the international advanced level. Low efficiency also means high emissions; annually, the coal-fired industrial boilers in China emit 6 million tons of dust, 6.3 million tons of SOx, and 750 million tons of CO2, accounting for 50%, 30%, and 25% of the country’s total emissions respectively. China has a total of 706 boiler manufacturing plants with different grades, averaging 24 per province. Among them, there are 27 boiler plants of Class A, 189 of Class B, and a total of 490 of Classes C and D. Class A boiler plants are qualified to manufacture power station boilers. The total manufacturing capacity of Chinese industrial boiler factories is 150,000 steam tons per year, while the actual number of industrial boilers produced each year is 30,000–35,000 units, which corresponds to 72,000–80,000 steam tons. In other words, the manufacturing capacity of industrial boilers in our country is currently twice the actual market demand, which results in highly competitive conditions in the industrial boiler market. Table 6 provides a comparison of fuel consumption for industrial boilers in China. As can be seen from the table, past data, current conditions, and future projections all indicate that, unlike in developed countries, coal will remain the primary fuel for industrial boilers for a long time to come. Therefore, if the problems of low efficiency and high emissions associated with industrial boilers in China are not addressed fundamentally, this will have serious implications for the sustainable development of the country from both economic and environmental perspectives. Table 6: Fuel consumption of industrial boilers in China
Year | Fuel | Consumption
----|------|------------
1998 | Coal | 300 million tons
| Oil | 1.75 million tons
| Natural gas | 3.5 million cubic meters
Percentage of total human fuel consumption in terms of heat value: 98%, 5%, 8%
2000 | Coal | 400 million tons
| Oil | 5 million tons
| Natural gas | 5.7 million cubic meters
Percentage of total human fuel consumption in terms of heat value: 96.9%, 1.2%, 1.9%
2010 | Coal | 460 million tons
| Oil | 6 million tons
| Natural gas | 32 million cubic meters
Percentage of total human fuel consumption in terms of heat value: 89.3%, 2%, 8.7%

3. Main reasons for the low efficiency and high emissions of coal-fired industrial boilers in China
As shown in Table 7, among various types of coal-fired industrial boilers in China, chain grate boilers account for 57.87% of the total. Therefore, they are the most common and representative type of coal-fired industrial boiler in China. Thus, analyzing the main reasons for the low efficiency and high emissions of industrial boilers in China, and finding ways to address the issues associated with chain grate boilers, is key to solving these problems. Table 7 Share of industrial boilers with different combustion equipment in the total thermal power of industrial boilers. Type of combustion equipment: Fixed-bed, chain grate, reciprocating grate, bubbling bed, circulating bed, waste heat boiler, fuel/gas furnace, others. Share of total thermal power (%): 2.45, 57.87, 6.92, 1.20, 1.31, 3.54, 12.21, 14.7. The requirements for complete and efficient combustion of coal in chain grate boilers are: rapid ignition of coal particles ； l No air leakage, no slag formation, and no coal leakage ； The air is evenly distributed ； 296 l, no slag formation or coal leakage ； l Low excess air coefficient and low flue gas temperature. According to the above requirements, the key factors affecting the performance of chain grate boilers are: (1) the design and structure of the chain grate boiler. A considerable number of industrial boiler manufacturers in China lack the capability for research and development as well as independent design; as a result, they often use outdated design drawings. Instead of membrane walls, heavy-type wall structures are used, which leads to high air leakage into the furnace. Additionally, the unreasonable design of the grate results in uneven fuel distribution and leakage of fine coal particles. All these factors contribute to a high excess air coefficient, high mechanical incomplete combustion losses, and high flue gas loss. (2) Quality of coal used in industrial boilers In China, the coal used in industrial boilers is basically raw coal extracted directly from coal mines, without any washing, screening, or blending. The ash content in the coal burned in industrial boilers is often as high as 26% to 30% ； The fine powder in coal, that is, the portion with particle sizes of less than 3 mm, can even account for up to 60% ； An excessively high expansion index reflects the cohesiveness of coal during heating. Stratified burners, and in particular chain grate burners, have certain requirements regarding the properties of coal and its particle size distribution. If the coal contains too much fine particles, and if the grate structure is not adequate, the coal can leak through the gaps in the grate into the air chamber ； Too fine coal dust can also be carried out of the furnace by the flue gases before it burns completely, resulting in a high carbon content in the fly ash ； Excessively high ash content and expansion index reduce the burning rate of coal, resulting in the fuel layer not being completely burned by the time the chain reaches its end ； The cohesiveness of coal and the uneven distribution of coal particles cause the air coming from the bellows to be distributed unevenly as it passes through the fuel layer; some areas suffer from a lack of oxygen while other areas have an excess of air. Coal layers with insufficient oxygen lead to incomplete combustion and losses. It is actually very difficult to implement either in-situ desulfurization or flue gas desulfurization in chain grate boilers. However, it is hard to control the sulfur content in raw coal that has not been washed; due to the lack of desulfurization measures, the sulfur dioxide emissions from the vast majority of coal-fired industrial boilers exceed the established emission standards. Using raw coal with high ash content also places higher demands on dust removal equipment; the water film dust collectors that are widely used today often fail to meet the requirements for dust emission standards. (3) Management and operation of boiler rooms: Many industrial boiler rooms in China lack proper measurement and monitoring instruments and equipment, and are not well managed. Most of the personnel responsible for operating the boilers are seasonal workers who lack the necessary and adequate training. Under such circumstances, even if the design of the boilers themselves and issues related to coal quality are resolved, the boilers will still not be able to achieve their intended performance unless the problems related to management standards and the competence of the operators are addressed. 5 Ways to Improve the Efficiency and Emissions of Coal-Fired Industrial Boilers (1) Improving the design and structure of industrial boilers 1) Introducing advanced foreign designs and structures for industrial boilers through international cooperation. GEF project: The Global Environment Facility provided China with $32 million; this funding was used to introduce advanced foreign technologies in order to help Chinese industrial boiler manufacturers improve the design and structure of their boilers, thereby enhancing efficiency and reducing emissions. GEF projects are supervised by the World Bank, with the former **Economic and Trade Commission responsible for their implementation. Nine boiler manufacturers and nine auxiliary equipment manufacturers participated in the GEF project, introducing a total of 9 advanced foreign-made coal-fired industrial boilers, 5 advanced auxiliary equipment types, and 2 control systems. The GEF project was completed at the end of June 2003. All the demonstration boilers of the introduced projects have passed the performance evaluation tests. Table 7 provides an overview of all GEF sub-projects, while Figure 2 shows images of some boilers introduced under the GEF. 297 Table 7 Sub-projects of GEF projects Sub-projects of GEF projects • SZL 1-6t/h quick-installation water tube boiler, imported from German company Babcock Borsig Power ； • DZL improved version – 1-6 t/h water/fire tube quick-install boiler, imported from John Thompson Africa Co. in South Africa ； • 6-20t/h assembled angle-tube steam boilers, imported from Danish company Volund ； • 0.7-14MW corner tube quick-install/assemble hot water boilers, imported from Danish company Volund ； • 4-20t/h quick-install/assemble extended furnace fire-tube/water-tube boilers, imported from Bay Gmbh in Germany ； • 7-70MW hot water boilers, imported from Danish company Volund ； • 35~100t/h CPC fine-grained low-speed circulating fluidized bed boilers, introduced from the American company Combustion Power Co (CPC) ； • JTA chain grate steam boilers with coal injection, with a capacity of 10–100 t/h, imported from South African company John Thompson Africa (JTA) Co ； • Differential fluidized bed boilers for burning high-sulfur coal with a capacity of 6–20 t/h, imported from Bay Gmbh in Germany ； • Ashtray ； Bag filter ； Multi-tube cyclone tube ； Cross-beam grate ； Control systems, etc., are imported from the United States, Germany, and Japan. Figure 2 shows the results of performance testing on some advanced coal-fired industrial boilers imported from abroad, which are part of the GEF project’s demonstration boilers: Boiler efficiency = 80–85% (10–15% higher than the average actual operating efficiency of existing industrial boilers); Dust emission levels