Coal Quality, the Key Factor to Affect Energy Utilization Efficiency and Environmental Emissions in China
Oral Presentation

ABSTRACT

China is rich in coal reserves and is also the largest coal producer and consumer in the world. In China, coal has constituted over 70 percent of the total energy consumption for many years. Some 85 percent of coal production is burned directly, not only because of obsolete coal combustion technology and equipment but also because of coal quality, which causes low energy utilization efficiency and serious air pollution problems. However, on the basis of China's specific energy structure, coal utilization will remain the dominant means of energy usage. High-quality coal and clean coal technology must be the way forward if problems involving energy utilization efficiency and the environmental are to be resolved. This paper describes the status of coal in China's energy structure. Coal quality, coal utilization efficiency, and related environmental issues are also discussed. Coal-fired industrial boilers and coal-fired powerplants, which consume over 75 percent of total coal production and are the largest coal consumers, are discussed as well as the effects of coal quality on the energy utilization efficiency and environmental emissions in China and the solutions.

THE STATUS OF COAL IN CHINA'S ENERGY STRUCTURE

In terms of natural resources, China's coal reserves account for 11 percent, crude oil accounts for 2.4 percent and natural gas accounts for 1.2 percent of total world reserves. Although China accounts for some 20 percent of the total world population, China's own quantity of energy resources per capita is only one half of the world average level and one tenth of the U.S. level.

Of the various world energy resources, coal reserves are the richest in China. The proven national coal reserves have reached 1,022.9 billion metric tons, accounting for 94.3 percent of total proven fossil fuel reserves for the nation. China ranks second in the world. Of China's resources, 70 percent is bituminous coal, 14 percent is lignite, and 14 percent is anthracite. The production and consumption of raw coal were 1.25 and 1.295 billion metric tons, respectively, in 1998, ranking first in the world. Seventy-one percent is bituminous coal, 5.1 percent is lean coal, 19.8 percent is anthracite, and 4.1 percent is lignite.

China's energy structure is quite different from that of other countries. Environmentally cleaner energy, such as hydropower, nuclear energy, petroleum, and natural gas, represents only a small proportion of energy use in China. Table 1 shows that the percentage of coal in world average energy consumption has decreased from 55.6 percent in 1955 to 26.9 percent in 1996, a change in predominant energy from coal to oil and gas. Meanwhile, coal has constituted more than 70 percent of China's total energy production and consumption for many years, as tables 2 and 3 show, and as such is a predominant factor in the primary energy consumption. Along with the fast development of China's economy, the demand for high-quality energy (such as oil and gas) will be increasing, and the demand for coal will be decreasing. It is estimated that coal will account for 64 percent, 60 percent, and 50 percent in 2005, 2010, and 2030, respectively, and coal will be the dominant factor in China's primary energy consumption for many years to come. Today in China, some 75 percent of industrial fuel, 76 percent of electric power, 80 percent of domestic and commercial energy, and 60 percent of chemical raw material are derived from coal.

[SCE, standard coal equivalents]

[SCE, standard coal equivalents]

In China, 85 percent of coal is utilized through direct combustion. Most coals are burned by industrial and utility boilers, as table 4 shows. This structure of coal consumption is quite different from that in developed countries, as table 5 shows. In developed countries, because most coals are used for power generation, it much more efficient, and emission control is easier. In contrast to that in developed countries, coal utilization in China is very dispersed and is mostly used in small-sized industrial and domestic equipment. Therefore, coal quality greatly affects energy efficiency and pollutant emissions.

Table 4. Percentage of total coal consumption by sectors in 1998 in China

(Total coal consumption in 1998 was 1.295 billion metric tons)

[-, no data]

COAL QUALITY IN CHINA

Large, state-owned coal mines account for only about 44 percent of total coal produced in China; the rest is produced by mines owned by local governments and townships. Over 80,000 small coal mines contribute 37 percent of the total coal production, coal being of variable quality. Table 6 shows average sulfur content of coal samples from major coal mines in China. Most Chinese coals have average sulfur contents greater than 1 percent. Table 7 shows that high sulfur coal is concentrated in the middle south, especially southwest of China, such as Sichuan, Guizhou and Guangxi Provinces. Some 20 percent of annual coal production is high sulfur coal (sulfur content higher than 2 percent). Washed coal accounts for only 30 percent of the total coal production and is used mostly for making metallurgical coke, far below the figures of 50 to 100 percent in developed countries. Commodity coal is almost "run-of mine" raw coal. Because it is not selected, size graded, and washed, the ash content averages 26 to 30 percent. These practices cause the quality of commercial coal in China's market to be much lower than that in the international market (table 8). Steam coal is the main feed stock for industrial and utility boilers. Table 9, which gives the distribution of ash and sulfur content for steam coal, shows that China's steam coal has very high ash content and relatively high sulfur content. Because most commodity coal, including steam coal, is used with almost no environmental control measures, serious air pollution problems result. In order to control the ash and sulfur content of steam coal to levels of less than 20 and 1 percent, respectively, over 60 percent of existing steam coal should be washed.

Table 6. Average sulfur content of coal samples from major coal mines
in China (dry basis) (from Mao and others, 2000)

¹This value does not include the coal in the southwest market of China, where the sulfur
content of coals can be as high as 3 to 4 percent.

Coal washing can remove 50 to 80 percent of the ash and 30 to 40 percent of the sulfur from raw coal. Every 100 million metric tons of washed coal used instead of unwashed coal will reduce SO₂ emission by 1.5 million metric tons, whereas the cost of washing coal is only 10 percent of the cost of installing wet scrubber flue gas desulfurization (FGD). The production of total washed coal increased from 260 million metric tons in 1995 to 337 million metric tons by the end of 2000; this latter number accounted for about 30 percent of total coal production. Today, most washed coals are used to make coke for metallurgical applications and for export. Increases in the production of washed coal from 30 percent to 40 to 50 percent are planned over the next 5 years. The intention is that the additional washed coal will be used for industrial boiler application, not coke making.

By the end of 1998, the actual capability of coal washeries was 493 million metric tons. The estimated production of washed coal should reach 30 percent of total coal production by the end of 2000. However, at present in China, the actual production capability of washed coal is greater than the market demand for washed coal. The main barrier to a further increase in the use of washed coal is the price. For example, the average price of raw coal in Beijing is 230 RMB/ton (28 USD/ton), but the price of washed coal is 290 RMB/ton (35 USD/ton), which is 60 RMB (7 USD/ton) higher than that of raw coal. Thus, customers' resistance to paying the higher price is a major problem.

Ash and sulfur content are not the only main characteristics of coal quality. For different coal applications, especially for steam coal, quality parameters become key factors in energy efficiency and environmental emissions. The main characteristics of coal quality include heating value, ash, sulfur, moisture, volatile matter, swelling index, coal particle size distribution, and ash fusion temperature. Therefore, high-quality coal must be produced and prepared through a comprehensive process of selecting and grading as well as by washing.

ENERGY UTILIZATION EFFICIENCY

Some 85 percent of the coal produced in China is consumed through direct combustion, and widespread use of low-quality coal and obsolete coal combustion equipment causes a very low overall thermal efficiency. For example, there are over 460,000 industrial boilers. Most of them are stoke fired and small in size and operate at 60-percent efficiency, consuming over a third of the total coal production every year. In addition, there are about 130,000 coal-fired industrial kilns that operate at only 20 to 30 percent thermal efficiency and hundreds of thousands of domestic stoves that operate at an even lower efficiency. Table 10 compares the structure of coal consumption in China with that in some developed countries. Table 11 compares energy utilization efficiency in China with that in OECD countries.

[-, no data]

Table 11. Comparison of energy utilization efficiency between China
and OECD countries (Huo, 1999)

[gce, grams of standard coal equivalents; -, no data]

EMISSIONS FROM COAL UTILIZATION

Table 6 provides data on the average sulfur content of coal samples from major coal mines in China. The average sulfur content of most kinds of Chinese coals is higher than 1 percent. More than 20 percent of annual coal production is high-sulfur coal (sulfur content >2 percent). Because most coal is used almost without any environmental control measures, serious air pollution problems result. Table 12 lists the emissions of dust and SO₂ from coal utilization. Table 13 gives the ratio of pollutants from coal utilization to the total pollutants in the air.

Table 13 indicates that coal utilization is the main cause of air pollution in China. In 1997, the total emission of SO₂ was 23.46 million tons, ranking first in the world; 90 percent was coming from coal combustion (Zhou, 1999). Acid rain caused by coal combustion has covered over 30 percent of China's total land area. Acid rain damages forest, crops, and the ecology in general and impairs people's health. Acid rain has caused annual 116.2 RMB (14 billion USD) in economic losses, equivalent to about 2 percent of GDP in China (Zhou, 1999). Of total SO₂ emissions, 460,000 coal-fired industrial boilers contribute 36.5 percent, and 212,220 MW coal-fired utility boilers contribute 37.3 percent. These two sectors contributed 73.8 percent of total SO₂ emissions. Therefore, the key to reducing SO₂ emissions in China is to control SO₂ emissions from both industrial and utility boilers.

INDUSTRIAL BOILERS

China's total installed coal-fired industrial boilers of over 460,000 units (~880,000 MW_th) consumed 390 million metric tons of raw coal in 1998. The average boiler efficiency is only 60 percent. SO₂ emissions from industrial boilers and kilns account for over 49 percent of total SO₂ emissions, the largest SO₂ pollution source in China. Although flue gas desulfurization (FGD) is available in principle for reducing SO₂ emissions from industrial boilers, in practice the cost of FGD for industrial boilers is often too high to permit widespread use.

Coal used for industrial boilers in China is always "run-of-mine" raw coal. Because it is not even size graded, much less washed, the ash yield averages 26 percent; values up to 30 percent are common. Fines content (that is, coal size > 3 mm) can reach 60 percent, whereas "lump" coal (>10 mm) is only 15 to 30 percent. The latter values indicate the existence of some very large pieces that must be broken manually, creating even more fines. Making matters worse, coal used for industrial boilers is not selected with regard to its "coking" (that is,  swelling) tendency on heating. Coal that swells excessively can form sticky coke masses on the grate of the boiler; these masses adhere together and prevent the free flow of combustion air. The main properties that impede the efficient burning of raw coal are listed below.

1. Excessive coal fines, together with a poor-quality grate construction, increase the tendency for coal to be lost unburned by sifting between the grate links into the wind box. Unless they are moistened before firing, excessive coal fines can also lead to high carbon losses in fly ash at the boiler exit.

2. Excessive ash and swelling characteristics slow down the rate of coal burning, so that combustion may not be complete at the end of the grate.

3. Variations in coal-size grading cause an imbalance in air flow from the wind box, so part of the firebed receives a wasteful excess of combustion air while other parts are air starved. The starved areas will not complete their combustion by the time burning coal reaches the end of the grate.

Even though Chinese coal-burning equipment shares many physical characteristics with the equipment used in developed countries, the latter is more compact,  mainly because, in order to improve coal burn-out, Chinese engineers utilize a boiler grate area that can have up to twice the thermal rating of an equivalent grate in developed countries and extensive rear refractory arches. Despite the best endeavors of Chinese boiler engineers, low boiler efficiency is still normal, especially for small-sized industrial boilers having capacities smaller than 7MW_th; such boilers make up over 90 percent of national stock boilers.

In contrast, in developed countries, industrial coal is selected with respect to low swelling characteristics and is size graded and washed; these procedures result in over 20 percent higher boiler efficiency and much lower emissions than China's industrial boilers. Therefore, coal quality is a key factor in the efficiency and emissions of industrial boilers. China must learn from international experience to improve coal quality for industrial boilers. Washed coal should be used with ash yield of 10 to 15 percent (as-received basis) and sulfur content of less than 0.8 percent (as-received basis), and its size distribution should be graded into two main products:

1. Washed "singles," being essentially 25 to 10 mm in size and containing only a small percentage of particles smaller than 3 mm. This coal is used to fire small industrial boilers having a capacity of less than 5MW_th.

2. Washed "smalls," being around 13 mm top size and containing around 30 percent particles smaller than 3 mm. This coal is used to fire industrial boilers with moving grates, individually 5 to 50 MW_th.

Because it is not realistic for small-sized industrial boilers to use desulfurization systems, the best way to improve the efficiency and reduce the emissions for industrial boilers is to use selected, washed, and graded coals, which give reliable, clean, reproducible combustion. Equipment can be guaranteed for thermal output and efficiency. Stack emissions are predictable, and environmental regulations are easily achievable.

As mentioned above, the main barrier to a further increase in the use of selected, washed, and graded high-quality coal is the price. The new Air Pollution Law issued on September 1, 2000, is a strong driving force behind the use of high-quality coal for industrial boilers. This law will make it illegal to exceed air emission levels when using coal-fired equipment. The exact details for implementation are still being finalized but will be in effect as follows:

1. Specific emission levels will be set for dust and SO₂, as shown in tables 14 and 15.

   
   
   Table 14. Dust emission limits for industrial coal-fired boilers
   (GWPB3 - China's emission standard)
   
   

   [mg/Nm³, milligram per standard cubic meter]

   Applicable area	Dust emission legislation4 (mg/Nm3)	Dust emission legislation5 (mg/Nm3)
   First area1	100	80
   Second area2	250	200
   Third area3	350	250

   ¹ Forests and scenic areas
   ² Residential, commercial and general industrial areas
   ³ Special industrial area
   ⁴ Boiler in operation before December 31, 2000
   ⁵ Boiler in operation after January 1, 2001

   
   
   Table 15. SO₂ emission levels for coal-fired boilers in all areas of
   China (GWPB - China's emission standard)
   [mg/Nm³, milligram per standard cubic meter]
   
   

   SO2 emission limit1 mg/Nm3	SO2 emission limit2 mg/Nm3
   1200	900

   ¹ Boiler in operation before December 31, 2000.
   ² Boiler in operation after January 1, 2001.

2. The local environmental protection agency will, at each plant, set a limit for the total SO₂ emissions on an annual basis, regardless of the specific levels.

3. Users of each plant will have to pay a dust and SO₂ tax on total production of pollutants each year. The SO₂ tax will vary geographically (for example, Beijing set a tax of 1.7Yuan/kgSO₂ (0.2 USD/kg SO₂)).

4. If coal users exceed either specific or annual pollutant emissions, they will be served notice of the need for improvement. They will then have a fixed period of time in which to deal with the problem. At the end of the period, if the improvements have not been made, users will be fined. Ultimate solutions are closure or relocation.

In order to implement the Air Pollution Law, many local governments make local regulations to restrict the use of low-grade coal. For example, the Beijing City Government has issued a regulation that permits only coals having an ash yield of less than 10 percent and a sulfur content of less than 0.5 percent (as-received basis) to be used in Beijing.

In summary, the key factor to improving coal burning and reducing pollutants emissions for industrial boilers is improving coal quality. China should draw on the experience of developed countries to make Chinese industrial coal compatible with that of developed countries. Initially this compatibility will be achieved by grading industrial raw coal to minimize the fines content. Excess fines will be sent to pulverized coal-fired power stations. Because price is no longer the limiting factor in the coal market, many coal suppliers have started to produce graded coal to meet the market requirement. However, this degree of coal preparation is not likely to be sufficient. Further selection to produce a better quality coal via coal beneficiation to ensure low sulfur, low ash, and low swelling characteristics is the second step to be applied in the near future. Therefore, State policy is to encourage the application of clean coal technology and selected, washed, and graded coal. A specification for graded (though still unwashed) coal supplies has been framed by the authority. The production of washed coal is planned to increase from 30 to 40 to 50 percent over the next 5 years to improve the supply of high-quality coal for industrial boilers.

COAL-FIRED UTILITY BOILERS

The total installed electric power capacity of China was 277,290 MWe by the end of 1998,  212,220 MWe of which was from coal-fired powerplants. This amounted to 76.5 percent of total installed capacity, consuming 527 million metric tons of coal and accounting for 40.7 percent of China's total coal production. The total SO₂ emissions in 1998 in China were 20.91 million tons, 7.8 million tons of which were produced from coal-fired powerplants. Table 16 shows the estimated uncontrolled emissions of SO₂ from total thermal powerplants having a unit capacity of larger than 50MWe in China. Up to now, most thermal powerplants in China have had no sulfur removal system.

Unlike industrial boilers, utility pulverized coal-fired boilers have much higher efficiencies, and most of them have been equipped with electrostatic precipitators to control dust emissions. Therefore, sulfur content is the only property of coal quality to affect SO₂ emissions. State policy requires that all powerplants burning coals with sulfur contents higher than 1 percent must have emissions of SO₂ that are less than 1200mg/m³N, and FGD systems must be installed on these powerplants before 2010. Table 17 shows the distribution of sulfur content in coals used for powerplants having a unit capacity large than 6 MWe in China. As table 17 shows, low-sulfur coal (sulfur content <1 percent) used for coal-fired powerplants accounted for 56 percent. Medium- and high-sulfur coal (sulfur >1 percent) accounted for 43.6 percent. Low-sulfur coals are mostly used as industrial raw material, so it is not realistic to supply all coal-fired powerplants with low-sulfur coal, even though low- sulfur coal will be used as much as possible. According to an estimation made by the State Economic and Trade Commission (SETC), which is in charge of localization and dissemination of FGD in China, there are at least 44,000 MWe coal-fired powerplants that should be equipped with FGD systems before 2010. The SETC has made a plan for installing FGD systems in coal-fired powerplants before 2010 (table 18).

Therefore, according to China's environmental protection laws and regulations, there will be a large FGD market in China. The market demand for FGD systems will be 17,000 MWe of installed capacity by 2005 and 44,000 MWe by 2010. For such a large market, the ultimate goal is to localize the manufacture of FGD equipment. So far, China has no experience in or technology for supplying a complete set of FGD systems. Therefore, ways to foster the utilization of FGD equipment for coal-fired powerplants and the use of foreign FGD technologies must be achieved through international cooperation. These joint ventures (co-production and combined technology transfers) and trade to introduce foreign equipment and technology to China should create the capability to localize the manufacture and supply of over 95 percent of FGD equipment by 2010.

CONCLUSIONS

1. China is the largest producer and consumer of coal in the world. Coal constitutes around 70 percent of the nation's total primary energy consumption, a situation that has led to low energy utilization and serious air pollution problems. Today, clean energy (such as oil, natural gas, and hydro and nuclear power) accounts for only about 30 percent of total energy consumption. It is unrealistic to assume that the energy structure can be changed from coal (the dominant energy) to clean energy in a short period. Therefore, on the basis of China's special energy structure, coal will remain the dominant form of energy. High-quality coal and clean coal technology must become the standard if energy utilization efficiency is to be improved and environmental problems are to be resolved.

2. Low-quality coal has been a main cause of low energy utilization efficiency and high pollutant emissions in China. During the period when the demand for coal was greater than the supply, coal users did not have the option of selecting coal quality from the market. Along with the rapid development of China's economy and the reformation of its economic structure, the supply of coal has grown to exceed the demand. Coal production and consumption are decreasing, especially because the implementation of the new air pollution law has forced coal users to use more high-quality coal. All of these factors will bring about changes in coal production and supply systems and provide the market with more high-quality coal.

3. For different coal applications, especially for industrial and utility coal-fired boilers, the quality of steam coal is the key factor in energy efficiency and environmental emissions. The main characteristics of coal quality include heating value, ash, sulfur, moisture, volatile matter, swelling index, coal particle-size distribution and ash fusion temperature; therefore, high-quality coal must be produced and prepared through a comprehensive selecting, washing, and grading. This direction is the most favorable one for China to take to improve its energy efficiency and reduce the pollutant emissions caused by coal utilization.

SELECTED BIBLIOGRAPHY

China Statistics Press, 1998a, China energy statistics year book (1991-1996), 1st ed.

_________, 1998b, China industrial economy statistics year book (1998), 1st ed.

_________, 1998c, International statistics year book, 1998, 1st ed.

_________, 2000, China economic statistics year book (1952-1998), 1st ed.

Department of Communications and Energy, 1997, Energy report of China: State Planning Commission of P.R. China: China, Price Publishing House.

Huo, Yaqin, 1999, Current status of China's energy and the countermeasures of its sustainable utilization: China's Energy, no. 2.

Mao, Jianxiong, Mao, Jianquan, and Zhao, Shuming, 2000, Clean combustion of coal, 2d ed.: Science Press.

Ning, Mingdong, 1999, Clean utilization of coal and the strategy of development for clean coal technology: China's Energy, no. 2.

State Environmental Protection Administration, 1997, Program of determination of acid rain control zone and SO₂ control zone in China.

State Environmental Protection Administration, 1997, Emissions standard of air pollutants for coal-fired boiler.

Zhang, Huimin, and Fan, Di, 1997, The status and development trend of flue gas desulfurization technology for coal-fired boilers in China: Proceedings of the First International Conference on Clean Coal Technology.

Zhou, Fengqi, 1999, The challenges that China's energy industry is faced with: China's Energy, no. 12.