To improve the structure of energy and Control SO2 pollution
By: Xu Shubi, Senior Engineer, Vice Director of Chongqing Environmental Protection Bureau
Guo Yijun, Master of Science, Division Chief of Chongqing Environmental Protection Bureau
November 2001
1. Preface
Located at the link field between middle and west part of China, upper Yangtze, which links 5 provinces including Sichuan, Shanxi, Hubei, Hunan and Guizhou, Chongqing is the 4th Municipality directly under the jurisdiction of central government established in 1997.
There are 40 districts or counties under the jurisdiction of Chongqing, the City has a land area of 82,000 square kilometers and a population of 30.9109 million by end of 2000 including agricultural population of 24.3020 million and non-agricultural population of 6.6089 million, enabling to be a typical municipality backed up by big city and big countryside.
The main city zone has a constructed land area of 190 km2 and a non-agricultural population of 2.313 million. The total GDP of Chongqing in 2000 was RMB 159 billion Yuan, which is an average of RMB5,157 Yuan per capita.
Since late 70’s to early 90’s of the 20th century, the SO2 and acid rain pollutions appeared to be very critical due to various causes, which seriously restrained the sustainable social and economic development.
With the support of Chinese government and international communities, Chongqing has made continued effort to effectively prevent the SO2 pollution and created a clean and fresh environment for Chongqing’s sustainable social and economic development.
2. Basic Information
2.1 Geographic and Weather Conditions
The main city zone of Chongqing is located at a valley-hill land between Tongle Mountain and Zhongliang Mountain, and is split by Yangtze and Jialing River, it is higher at west side and lower at east side.
Chongqing has a sub-tropical wet monsoon weather, with large humidity, low wind velocity and high countercurrent temperature frequency. Its relative humidity is at about 80%, weak wind frequency over 50%, the average wind velocity of the year is 1.1-1.7 m/s, countercurrent temperature frequency at 60-80%. Therefore, The above geographic and weather conditions are disadvantageous to pollution diffusion.
2.2 Industrial Structure
Chongqing is a comprehensive traditional industrial city and industrial accretion makes up a high proportion of its total economy (Please refer to figure 1).
In 2000 the proportion of accretion of the 3 industries in total economy is respectively 17.8:41.4:40.8. Chongqing’s pillar industries which are made up by automobile, motorcycle, metallurgical and chemical works contribute to large energy consumption.
2.3 Energy Consumption
The coal consumed in 2000 was 20.98 million tons in total, including 15.11 million tons of fuel coal and 5.87 million tons of raw coal. In 1999, coal consumed in main city zone was 4.40 million tons including 2.10 million tons consumed by the Chongqing Power Plant and 2.30 million tons consumed by industries and civilians. The coal consumed in the city is mainly from local source, which is mainly high sulfur and high ash content coal with an average of sulfur content of 3.5%, and an average ash content of 25%.
2.4 Emission of Pollutants
It is estimated, in 2000, Chongqing emitted 839,400 tons of SO2 to the air, in which industrial emission contributed to 664,200 tons and domestic contributed to 175,200 tons, making up respectively 79.1% and 20.9%. In 1999, the SO2 emission to the air from the main city zone was 274,000 tons. The flue gas dust emission of Chongqing to the air every year is 213,500 tons, including industrial emissions 121,800 tons and domestic emissions of 91,700 tons, making up respectively 57% and 43%.
2.5 Pollutions of SO2 and Acid Rain
It can be seen from Figure 2 and 3 that there have been serious air pollution in the main city zone due to many causes. From 1979 to 1996, the average yearly daily SO2 concentration in main city zone exceeded 0.32mg/m3, which is 4.3 times of the standard; the acid rain frequency every year exceeded 60% and the rainfall pH value every year was below 5.0. The anion of acid rain is based mainly on SO42-, which reaches above 80%, and was mainly attributable to SO2 contamination. In 1979, the yearly daily SO2 average concentration in main city zone exceeded 0.56mg/m3, which is 8.3 times of the standard. In 1984, the acid rain rate in main city zone was 100%, every rainfall was an acid rain. In 1989, the rainfall pH value was only 4.07, which is equal to the pH value of citric acid and has seriously corroded building materials and endangered ecologic system. In mid 80’s, the heavy acid rain caused the death of 10,000 Mu of red pines at one side of the Nanshan Mountain (Part of Tongle Mountain), which is close to the main city zone.
The serious acid rain problem used to cause great loss to Chongqing’s economy. A survey made by Chongqing Environmental Protection Bureau in association with the Environment & Economic Policy Research Center of the state Environmental Protection Bureau reveals a loss of RMB1.765 billion Yuan resulting from acid rain in 1993, which accounted for 4.42% of Chongqing’s GDP in the same year, much higher than the level of 1.1% of USA.
3. Identification of Solutions to SO2 Contamination
3.1 Difficulties in Effective Control over SO2
3.1.1 Control on SO2 in the early stages
Before the 1990s of 20th century, control over flue gas dust on the main city zone was implemented to have effectively controlled the flue gas dust contamination and black smoke from stacks was basically eliminated. At the same time necessary measures were taken to control SO2 through:
1. To have adjusted reasonably the layout of industries to remove air-contaminated enterprises (workshops) to the outside of main city zone.
2. To have applied advanced technology to more efficient utilization of energy and less consumption of energy.
3. To have developed domestic gasification and reduced the domestic coal use.
4. To have promoted a wide use of briquette and washed coal .
3.1.2 Solution to SO2 with Coal Being Major Fuel
Chongqing established a SO2 Control System in 1994, covering coal wash and screening and distribution yard, methane gas exploration, development of briquette, FGD engineering, coal gasification and boiler renovation. This System, which is estimated to have a total investment of RMB2.4 billion Yuan demonstrates the ideas of controlling SO2 while the coal-majored structure of energy still remains unchanged.
3.1.3 Problems for Using Coal as a Major Fuel
The SO2 Control System requires large investment, which is difficult to have the fund in place and it is also difficult to supervise or monitor the use of washed coal and briquette while coal gasification has a high cost and proceeds slowly. Additionally the effect of this Control System on SO2 removal is rather limited. Suppose that the desulphurized rate of washed coal and that of the briquette is 40%, the raw coal produced locally will be still sulfur coal with a content of 2.1% even after washed or sulfur-fixed. It is impossible for Chongqing which has a bad air condition to diffuse polluted air to lower its SO2 yearly daily average concentration from 0.3mg/m3 to the standard at 0.06mg/m3.
3.2 Solution to SO2 with Improvement to the Structure of Energy
3.2.1 Improvement to Structure of Energy is a necessity of Effective Control over SO2
From 1991 to 1996, Chongqing Environment Scientific Research Institute co-operated with other research institutes including Physics Research Institute of China Academy of Science in the “ Chongqing Air Pollution Controlling Planing Study”, the findings were that middle high, low and ground level mid and small-sized boilers, tea-burners and kitchen stoves all over the areas contributed to the ground SO2, among which the Central District has an SO2 generating rate of 87.9% and is a key area where SO2 needs to be controlled. In 1991, the Central District and the Jiangbei District were determined as SO2 Controlling Demonstration District. The SO2 controlling demonstration through years shows that the large quantity of mid and small-sized boilers, tea-burners and kitchen stove burning coal will not help to reduce SO2 contamination while use of clean energy like natural gas, liquefied petroleum gas, electricity and light diesel must be developed, and fuel coal will be banned gradually.
3.2.2 Feasibility and Scientific Workability of Improvement to the Structure of Energy
Chongqing has rich natural gas resources and sufficient gas reserves. The rich resource created a good condition for an improvement to the structure of energy. The thermal efficiency of fuel gas is higher than that of fuel coal, the thermal efficiency of boiler, tea-burner and kitchen stoves is estimated to be respectively 1.3, 2.4 and 4 times of that of fuel coal. Therefore an improvement to the structure of energy can save energy effectively.
3.2.3 Solution to SO2 with Improvement to Structure of Energy
In 1996, a demonstration promotion of clean energy was implemented in restaurants of the central District and the Jiangbei District, followed by promotions to restaurants in all districts, and as a result the wide application of clean energy reduced SO2 effectively. The average yearly daily SO2 concentration of 1997 was 0.208mg/m3, which was a drop of 35% over that of 1996, this provides a good foundation for the new idea of controlling SO2 by improvement to the structure of energy. In 1997 Japanese Government expressed its support to build 3 Chinese cities inclusive of Chongqing into Environment Protection Demonstrative City by 2005. Chongqing Government attaches great importance to the construction program and has proposed, after repeated review and programming a program based on improvement to the structure of energy while imposing FGD plant on some major pollution sources to control SO2 pollution. This program stipulates clearly that all coal boiler and kitchen stoves under the capacity of 10t/h within the main city zone should be replaced by clean energy.
4. Comprehensive Solution to SO2 Contamination
4.1 Improvement to the Structure of Energy and Reduction of Fuel Coal
4.1.1 To Fully Develop Domestic Gasification
Chongqing has speeded up its reworks of natural gas pipeline to enable citizens to use natural gas as much as possible and further reduce use of fuel coal. At present the utilization rate of gas of in main city zone of Chongqing has reached 90%.
4.1.2 Use of Cleaner Energy in Catering Trade
From 1996 to 2000, all stoves in the catering trade in city proper, central towns of each district/county and tourist spots changed to use cleaner energy including natural gas, electric power, light diesel and petroleum liquefied gas, and coal burning is prohibited. This task was organized by district/county government and financed by owners of restaurant business. Since 1996 a total of 39,250 kitchen stoves in restaurant business of the whole city were changed to cleaner energy, involving an investment of close to RMB 40 million Yuan. This reduces 582,300 tons of coal burning annually, resulting in production of less 32,000 tons of SO2 and 15,000 tons of flue gas dust, and also reduces discharge of coal slag of 146,000 tons annually.
4.1.3 Cleaner Energy to be Applied to Mid and Small-Sized Boiler and Tea-Burner
In order to fundamentally improve the structure of energy to effectively control air pollution, and also according to the Sino-Japanese Co-operative Program in Construction of Environmental Demonstrative Cities, Chongqing Government made a decision in January 2000 to carry out the Cleaner Energy Program within 1 and a half of year, which aims to replace all coal boiler under the capacity of 10t/h, tea-burner, and kitchen stoves within the main city zone by clean energy and to prohibit the use of coal by end June 2001.
This task was organized by district government for implementation under the leadership of the municipal government, the concerned departments of municipal government played a part in this task. The task was financed by the owners, and the municipal government and the district government gave a financial subsidy of RMB 40,000 Yuan for each 1t/h while Chongqing Natural Gas Corporation was responsible for the financing of reworks of gas pipeline. According to a preliminary estimation, a total investment of about RMB 380 million Yuan was made in this task including municipal and district financial subsidy of roughly RMB 80 million Yuan (Municipal government gave a subsidy of RMB67 million Yuan, district government gave RMB 13 million Yuan).
The scope of the Cleaner Energy Program is aimed to cover an area of 600km2 (the constructed land area is 190km2), including 9 districts and 2 development zones where 5 million people live. There are 2,653 smoke coal boilers and tea-burners within this scope area, including 1,153 boilers below the capacity of 10t/h units (inclusive of 10t/h) and 1,500 tea burners. By the end of 2000 all tea-burners were replaced, among them 299 units were replaced by cleaner energy (150 units switched to natural gas, 105 units switched to electric power and 44 units switched to light diesel), and 1,201 units were closed down and replaced by separate electric water heaters or cookers. By the end of June 2001 all boilers were replaced, among them 646 units were replaced by cleaner energy (495 units switched to natural gas, 82 units switched to light diesel, 69 units switched to electric power), and 507 coal-burning boilers closed down (including reduced boiler units as a result of plant removal, technical renovation and the consideration that the thermal efficiency of gas is higher than that of coal. According to a preliminary estimation, the main city zone, after implementation of the Cleaner Energy Program reduces 1.36 million tons of coal burning annually, which is equivalent to 60% of total coal consumption of the main city zone excluding coal consumptions by power plant, resulting in production of less 76,000 tons of SO2 and 35,000 tons of flue gas dust annually, and also reduces discharge of coal slag of 340,000 tons.
4.2 Construction of FGD Plant for Major Air Pollution Source
4.2.1 Construction of FGD Plant for Coal-Fired Power Station
Phase One Project of Huaneng Luohuang Power Plant (25km away from down town of Chongqing), which consists of 2 X 360 MW coal-fired units was completed in 1992, and as required an investment of RMB 230 million Yuan (8.13% of the total project investment) was made in construction of corresponding flue gas desulphurization (FGD) units, the first large-size limestone – gypsum in China. The FGD units were supplied by MHI and the desulphurizing rate reaches 95%. Upon the completion of the Phase Two Project of this power plant which consists of another 2 X 360 MW coal-fired units in 2000, similarly RMB358 million Yuan (9.07% of the total project investment) was made in construction of the corresponding limestone-gypsum FGD plant which has a desulphurizing rate of over 80% where the absorber which is the key equipment was still supplied by MHI while rest of equipment was manufactured in China. The 4 FGD units of Huaneng Luohuang Power Plant can reduce discharge of 110,000 tons of SO2 annually.