我国火力发电用水情况预测及节水技术发展分析

第34卷第32期中国电机工程学报V ol.34 No.32 Nov.15, 20142014年11月15日Proceedings of the CSEE ©2014 Chin.Soc.for Elec.Eng. 5717 DOI：10.13334/j.0258-8013.pcsee.2014.32.004 文章编号：0258-8013 (2014) 32-5717-11 中图分类号：TM 46我国火力发电用水情况预测及节水技术发展分析魏高升，邢丽婧，孟洁，杜小泽，杨勇平(电站设备状态监测与控制教育部重点实验室(华北电力大学)，北京市昌平区 102206)Predictive on Water Usage and Analysis on Water Conservation Development inThermal Power Generation of ChinaWEI Gaosheng, XING Lijing, MENG Jie, DU Xiaoze, YANG Yongping(Key Laboratory of Condition Monitoring and Control for Power Plant Equipment (North China Electric Power University), Ministryof Education, Changping District, Beijing 102206, China)ABSTRACT: Based on the state-of-art water consumption investigation in thermal power plants of China, the water usage projects for the next two decades were predicted and analyzed. Through economic development and the electric demand prediction, five feasible power development programs were presented, and the quantitative water consumption analysis was made based on each program. The results show that although the water withdrawal in thermal power generation has a minor increase (about 15%-20%), the water consumption increases at least 2.6 times higher compared with years of 2008 in next two decades if the water usage strategy develops at the current situation. In such situation many development strategies were considered, for example, the renewable energy and nuclear power generation have made great development, the once-through cooling systems in thermal power generation are replaced gradually, and the air cooling systems as well as the large capacity units with high parameters are constructed substantially. In order to solve the above water usage problems, great efforts should be made including accelerating water conservation technologies exploitation and application. Some potential water conservation technologies were also prospected and analyzed.KEY WORDS: water resources; thermal power generation; water-conservation technology; water consumption; forecast摘要：在对我国火力发电用水现状进行调查的基础上，主要预测分析了未来的用水方案。

在对我国经济发展和电力需求进行预测的基础上，提出了5种可行的火力发电发展方案，并针对每种方案的用水情况进行了分析研究。

结果表明，如果没有较大调整，未来20年火力发电的用水量增加率不会很大(增加约15%~20%)，但耗水量增长巨大，将在2008年基金项目：中央高校基本科研业务费专项资金资助项目(13ZD02)。

Project Supported by the Fundamental Research Funds for the Central Universities (13ZD02). 基础上至少增加2.6倍。

在这一预测中，考虑了较多因素，如可再生能源发电和核能发电得到了充分发展，直流冷却火力发电形式逐渐被取缔，空冷技术以及大容量高参数机组得以大量建设。

为了解决火力发电用水问题，未来应加快节水技术的开发和应用，文中同时对一些潜在的节水技术进行了分析和展望。

关键词：水资源；火力发电；节水技术；水耗；预测0 INTRODUCTIONThe total amount of water resources is huge on the earth，but that can be directly used in life and production is rarely. In fact，the total amount of freshwater resources on land accounts for 2.53% of the total amount of the earth water，but most are solid glaciers mainly distributed in the north and south poles. At present，the freshwater resources reserves that is relatively easier to use only accounts for 0.3% of total freshwater，7/100000 of the global total water. With population growth and rapid expansion of industrial and agricultural production，the global freshwater consumption grows fast. From 1900-1975，the world’s agricultural water consumption increased by 7 times，industrial water consumption increased by 20 times. In recent decades，water consumption at an annual rate of 4%-8% continues to increase. In addition，the environmental pollution is increasingly serious，and industrial wastewater and domestic sewage have increased dramatically. In aspect of industry，thermal power industry is a major water user，but also one of the heavy pollution industries. Thus the power sector is highly vulnerable to changes5718 中国电机工程学报第34卷in water resources，especially those that may result from potential climatic changes[1-2]. Therefore，water resources and environmental problems caused by thermal power industry should need to get more attention.In the world，the water using situation in thermal power industry has gained widely attention. For example，the US Department of Energy’s National Energy Technology Laboratory(NETL) is engaging ina research and development program to reduce freshwater withdrawal and consumption from existing and future thermoelectric power generating facilities[3-5]. In addition，various studies have attempted to consolidate published estimates of water use impacts of electricity generating technologies，resulting in a wide range of technologies and values based on different primary sources of literature[6-11].In China，the economy still maintained an annual growth rate of about 10% in recent years. With the rapid development of economy and society，the contradiction of water resources is more and more outstanding and a series of environmental problems is caused. Currently thermal power generation is the main style in electric power supply in China，and large amounts of water are needed，accounting for about 40% of the national industrial water withdrawal[12]. By the end of 2010，the installed capacity of power generation equipment in China is about 966.4GW，up 10.56% than 2009，and thermal power generation is 709.7GW，accounting for about 73.4% of total capacity[12]. Despite the state encourages renewable energy and nuclear power generation，thermal power generation style will still be in a dominant position fora long times. In addition，the average installed water consumption rate of thermal power generation is higher than the international advanced level of 40% to 50%[13]. Therefore，with the increasingly tense of water resources and the improvement of environmental protection requirements，water resources and environmental problems have become increasingly prominent[13-16]. Active promotion and application of water conservation technology is a strong guarantee for the sustainable development of thermal power generation.In this paper，by economic development and the electric demand prediction，based on the state-of-the art water consumption investigation in thermal power plants of China，the water usage projects for the next two decades are predicted and analyzed. It is expected to provide a reference for the construction of development program and strategy of national electric power industry.1 ELECTRIC POWER DEMANDING ESTIMATIONElectric power and economy are closely related and influence each other. Based on state-of-art economic development and power generation sketch of China，The electricity power generation and electricity consumption in future are predicted in our previous study as shown in Table 1[17].Tab. 1 Electricity consumption prediction in next twodecades in ChinaYearsThe growthrate ofGDP/%The elasticcoefficientThe growth rate ofElectricityconsumption/%Electricityconsumption/(TW⋅h) 201010.40 1.42 14.76 4199.8 2015 8.00 1.20 9.60 6 641.72020 7.00 1.00 7.00 9 315.32030 5.00 0.80 4.00 13 788.9The electricity consumption elastic coefficient is used in this prediction. It is defined as the ratio of the annual average growth rate of electricity consumption and the annual average GDP growth rate. It is an aggregative indicator reflects the relationships between electric power consumption and economy development. In above estimation the elastic coefficient is set to 1.2(2013—2015)，1(2016—2020) and 0.8(2021—2030) respectively. In view of the basic national conditions and policy，that is，full implementation of “well-off society” in 2020，some uncertain factors are ignored in this study，and the GDP growing rate of 8% in 2013—2015，7% in 2016—2020，and 5% in 2020—2030 are supposed respectively. By this trend，the amount of electricity power consumption in 2020 is 2.2 times that in 2010，and 3.3 times in 2030 that in 2010.Thermal power generation is the main style in electric power supply in China，accounting for over第32期魏高升等：我国火力发电用水情况预测及节水技术发展分析 571970% of total electric power accommodation presently.Due to the great pressure came from environmentalprotection and resources，the renewable energy powergeneration style will be encouraged and developedgreatly in near future，and the proportion of renewableenergy power supply will be increased gradually.Nowadays，hydraulic power generation accounts for17.4% of total generation capacity[18]. If no majornatural disasters occur，the proportion of hydraulicpower generation will get a slightly elevation on thebasis of 17.4%. For nuclear power generation，although the development speed has been sloweddown due to the effect of Japan's Fukushima nuclearplant accident recently，the long-range increasing pacewill not be suppressed. According to the planning，theinstalled capacity will reach to 4.94GW in 2015，andgradually increased to 90-95GW in 2020，accountingfor about 4% of total generation capacity. Thecapacity of nuclear power generation is expected toreach 200GW by 2030，accounting for 8.5% of thetotal national generating capacity[19]. Currently，windpower generation has been a great developed electricpower generation style in China. By estimation，theinstalled capacity of wind power unit is expected to upto 150GW by 2020，and 300-500GW by 2030[20].Based on above analysis，the power generation sketchof China in next two decades is predicted as shown inTable 2[17]. The electric power growth task cannot becompleted by renewable energy style can only bedone by thermal power generation. This is the generalpattern to solve the problem of electricity shortage inChina. It is shown that the thermal power generationwill increase significantly in next two decades，and itwill be 2.7 times that of 2010 in 2030.Tab. 2 Power generation sketch in next two decades inChinaYear Hydraulicpower/%Nuclearpower/%Windpowerandothers/%Thermalpower/%Totalgeneratingcapacity/(TW⋅h)Thermalpowercapacity/(TW⋅h)The incrementvalue ofthermal powercapacity than2008 /(TW⋅h)2015 17.70 2.20 2.00 78.10 6 641.7 5 187.2 2 407.9 2020 18.10 4.10 3.10 74.709 315.3 6 958.5 4 179.2 2030 20.00 8.50 4.70 66.8013 788.9 9 211.0 6 431.7 2 THE WATER USAGE PREDICTION IN THERMAL POWER GENERATION2.1 Analysis of Water Usage in Thermal Power PlantThe water used in thermal power generation can be divided into two broad categories：the production water usage and domestic water usage. The former is the main water consumption part，mainly includes the water used in thermodynamic system，cooling system，dust and slag removal system，flue gas desulfurization system and chemical water treatment system etc. There are two important concepts about water consumption in thermal power plant that should be indicated. One is installed water consumption，the other one is water consumption in power generation. Installed water consumption refers to the ratio of total quantity of fresh water used in power plant construction to the installed generation capacity，and for a power plant in running，the concept has no great practical significance. The power generation water consumption refers to the ratio of total quantity of fresh water withdrawal in electric power generation to the total generating capacity. The analyzed water consumption in this paper mainly refers to the water consumption in power generation.The water consumption proportion in various parts of thermal power plant has great relationship with the unit form. In typical wet cooling thermal power plant，the water consumption in cooling system is the largest one，accounting for about 70% of total water usage. Actually，the water consumption in thermal power plant with different cooling style varies greatly. Generally，two types of cooling system are adopted in thermal power plant，wet cooling system and dry cooling system. The wet cooling system is also classified into once-through cooling system and circulated cooling system. The one-through cooling system consumes little water due to the fact that no evaporation，windage and blowdown losses in factory，although amount of water are needed in cooling process. The one-through cooling system is very suitable for application in the areas with vast water sources，e.g. near the big river or coastal area. In5720 中国电机工程学报第34卷coastal area，seawater is used as circulating water orauxiliary cooling water，which can reduce fresh waterconsumption significantly.The cooling water circulates between thecondenser and cooling tower in circulated coolingsystem. This cooling style is suitable for application indry areas，but water consumption is observably largerthan once-through cooling system.The dry cooling system is also called as aircooling system. The freshwater consumption of aircooling system is substantially less than of wetcooling system，but higher than the seawater once-through cooling system. The air cooling system is atypical water conservation technology although with arelative higher fossil fuel consumption. A large numberof units with air cooling system are constructed in threenorthern area of China in last decade in order to savefresh water consumption[21-23].Based on above analysis and refer to thestatistical data in literature[24-26]，the waterconsumption data in thermal power plant withdifferent cooling types are summarized in Table 3.Compared with once-through cooling system andcirculated cooling system, the air cooling system andseawater cooling system have significantly freshwatersaving effect. From the point of view of freshwaterconservation, these two kinds of units should beconstructed widely in future.Tab. 3 Typical value of water consumption andwithdrawal per electrical generating capacity for differentcooling unitCooling typeFreshwaterconsumption perunit capacity/(kg/(kW⋅h))Freshwaterwithdrawal perunit capacity/(kg/(kW⋅h))Freshwater once-through cooling 0.3~1 30~60Seawater once-through cooling 0.24~0.62 0.24~0.62Freshwater circulated cooling 2~8 3~6Air cooling 0.2~0.6 0.2~0.62.2 The Water Usage Prediction in Next Two DecadesAlthough much uncertainty exists in future，whether it is favored or not，the China’s economy will continue to grow at the current situation. Regardless of how to develop the electrical power industry，the installed capacity of thermal power generation will continue to increase. Growing concerns about freshwater availability must be reconciled with growing demand for power in China. In order to give a reasonable prediction for water usage in thermal power generation in near future，based on the water consumption situation presently， 5 possible development cases are assumed here.Case 1：Maintaining existing pattern — Additional units and the existing units are both proportional to current water usage situation and the cooling pattern.Case 2：Regulatory-driven — All additional units adopt freshwater circulated cooling system，while the existing units are proportional to current water usage situation and the cooling pattern.Case 3：Developing large units — Among the new units，ultra-supercritical units accounts for 30%，supercritical units accounts for 35%，and 35% of additions are subcritical units. All the new units adopt freshwater circulated cooling system. The existing units are proportional to the current water usage situation and the cooling pattern.Case 4：Regulatory-light — The large units are constructed in the same proportion of Case 3，while the cooling types are adjusted. The new units in coastal areas adopt seawater once-through cooling system，accounting for 10% of the additions. 80% of additions use fresh water circulated cooling system，the other 10% of additions use air cooling system. The existing units are proportional to the current water usage situation and the cooling pattern.Case 5：Conversion — The large units are constructed in the same proportion of Case 3. 30% of additions use air cooling system，60% of additions use freshwater circulated cooling system，10% of additions use seawater once-through cooling system. Ten percent of the existing freshwater once-through cooling units are retrofitted with freshwater circulated cooling system every 5 years starting from 2015. The existing units are proportional to current water usage situation and cooling pattern.The water withdrawal and consumption data are calculated based on above five cases as shown in第32期 魏高升等：我国火力发电用水情况预测及节水技术发展分析 5721Fig. 1. The year 2008 was used as a baseline against which to measure projected future water withdrawal and consumption for each case.The results show that as the result of the existence of once-through cooling style ，the water withdrawal of thermal power generation increases. The water withdrawal of case 1 is largest ，and is 1.5-3 times that of other cases. Such a large quantity of water withdrawal make once-through cooling phase out ，especially in arid areas. However ，figure 2(b) shows that the water consumption of case 1 is less than case 2 and case 3. But comparative analysis with the other two programs shows that this can be improved by the application of effective water-saving technologies such as air cooling technology and seawater utilization technology.W a t e r w i t h d r a w a l /(109m 3)2 500 2 000 1 500 1 000 500 (a) Water wi thdrawal predicti onW a t e r w i t h d r a w a l /(109m 3)(b) Water c onsumption prediction400300200100Fig. 1 Water consumption prediction for thermal powergeneration in next two decades in China.In the case 2，all new units adopt fresh water circulating cooling system. Compared with case 1，its water withdrawal decreases a lot ，and is about 40%-60% of the case 1. But water withdrawal of case 2 is also larger than the remaining three cases. The water consumption of case 2 is the largest among the five cases. In the water circulating cooling system ，cooling equipment has two types ：cooling pool and cooling tower ，and both rely mainly on the evaporation of water to reduce water temperature. Moreover ，cooling tower use fans to promote evaporation and cooling water dispersed into air. Therefore water consumption in circulated cooling system is larger. Even though ，the water circulated cooling type has to be adopted broadly in thermal power generation in future due to the fact that less constrains exist in circulated cooling type compared with other cooling type.The water consumption in case 3 is slightly smaller than the value in case 2. In case 3，not only the freshwater circulated cooling type is adopted ，but also the proportions of large units with high parameters are increased greatly. This is also the national policy in the electric power industry development process. Compared with other water conservation measures ，the water consumption decreases minor by employment of large units. However ，application of water-conservation technologies in large units will give significant water conservation effect. As indicated in case 4，the large units are constructed inthe same proportion of Case 3，and 10% of new unitsadopt air cooling system ，and 10% of additions adopt seawater once-through cooling system ，The water conservation effects are widely recognized.In coastal area ，seawater once-through cooling system should be adopted broadly to reduce the fresh water consumption. The fresh water consumption in seawater cooling units is less than 40% of the value in freshwater circulated cooling units. For example ，the Yuhuan thermal power plant located in ChinaSouth-East coastal area of Zhejiang province has four100MW ultra supercritical units with seawater cooling system. The water consumption per generating capacity is only 0.45 kg/(kW ⋅h)[25]. The air cooling system is widely adopted in the past decades in the Three North area of China. Air cooling system does not consume water due to the fact that the steam is cooled by cold air[21-23，26]. Large-scale power plants using air cooling technology can save more than 75% of fresh water compared to those plants with conventional wet cooling technique. For example ，the5722 中国电机工程学报第34卷Togtoh thermal power plant in Inner Mongolia of China is a 600MW subcritical coal-fired unit with direct air cooled system. The fresh water withdrawal is only about 0.15m3/(s⋅GW)[27]，the water conservation effect is predominant. While，it should be indicated that the air cooling units cannot be constructed unlimitedly due to the fact the greater air pollution will occur.On the basis of case 4，the proportion of air cooling system is increased，and the existing freshwater once-through cooling units are retrofitted with freshwater circulated cooling system gradually. This is also expected to be the most likely scenario. As we know，air cooling can distinctly reduce the water consumption，and the circulated cooling increases water consumption. While，this conversion can lead to the water withdrawal reduced obviously，and fresh water usage distribution more reasonable over the country. The results show that the water consumption will present great increase even in case 5，it is at least 2.6 times higher compared with years of 2008 in 2030. It should be noticed that the water withdrawal will be reduced in 2030 due to the fact that the one-through cooling units are gradually eliminated.2.3 Freshwater Conservation in Thermal Power Generation NextAccording to the above prediction and analysis，no matter which case is followed in future，the water usage growth in thermal power generation is still large even if the cooling form is adjusted. Therefore，strengthening the study and application of water conservation technology in thermal power generation is urgent for the protection of fresh water resource and for the healthy development of power industry in China. Then，what can we do next to reduce the freshwater usage in thermal power generation? We believe that the following aspects can at least be strengthened presently.Firstly，the water-conservation reform based on available technology in existing thermal power plant should be strengthened in future. As mentioned above，there is a big difference among the existing thermal power plants in water withdrawal and water consumption. For example，the average water consumption rate of power plants with dry ash removal system is 1.97 kg/(kW⋅h) in circulated cooling unit，while that of plants with hydraulic ash removal system is 2.54 kg/(kW⋅h). If wastewater recycling rate in power plants get 50% or more，the average water consumption rate can be lowered to 1.64 kg/(kW⋅h) for the unit，while a large number of units have a relative higher water consumption more than 2.5 kg/(kW⋅h). Concentration ratio also affects water consumption rate greatly. For example，when the concentration ratio is 4 or more，the average water consumption rate can be lowered to 1.84 kg/(kW⋅h) for circulated cooling unit. The average water consumption rate is about 2.53 kg/(kW⋅h) when concentration ratio is between 3 and 4，and will be increased to 3.19 kg/(kW⋅h) when the concentration ration is 3 or less. According to the actual situation，increasing the concentration ratio of circulated cooling water and reducing the loss of sewage water are two major water-conservation methods in the existing thermal power plant currently.Secondly，Reclaimed water reuse is an effective means of water-conservation method，which should be popularized，especially in the plant near big city. The quality of reclaimed water is between tap water and sewage[28-29]. Urban sewage(including rainwater) and domestic sewage can reach a certain quality standard after the processing. Then these kinds of water can be used repeatedly within a certain scope but undrinkable. Reclaimed water reuse has achieved remarkable succeed nowadays in some thermal power plant in China[30]. For example，the city sewage was used firstly in Huaneng Beijing thermal power plant with annual water conservation up to 1.2×107 t/a[24]. Industrial sewage and domestic sewage were used in Heze power plant with water conservation up to 1.7×106 t/a[31]. However，the recycled sewage usage in thermal power plant is very few over the country presently. In addition，the rainwater in rainy season can also be considered to be collected and reused.Thirdly, construction and expanding of integrated gasification combined cycle(IGCC) unit should be reinforced in future. IGCC technology is an advanced第32期魏高升等：我国火力发电用水情况预测及节水技术发展分析 5723power system combining the coal gasification technology with the efficient gas-steam combined cycle technology. Although the initial investment of IGCC unit is relative large，the electric generating efficiency is obviously increased，and the water conservation effect is evident. The typical IGCC unit is typically composed of two parts：one is the gasification of coal and gas purification，and the otheris gas-steam combined cycle power generation. The steam cycle part of the IGCC plants accounts for about 1/3 of the total generating capacity. Thus the water consumption in IGCC power generating units is reduced greatly, only about 1/3-1/2 of water usage compared with the conventional coal-fired power generating unit[32-33]. If the existing water conservation technologies are used in IGCC plants，the water conservation effect will be more significant. For example，using coal-water slurry gasifier in IGCC power plant，waste water can be recycled for the production of coal-water slurry，which can achieve zero discharge of wastewater[34].In addition above technologies，the hybrid wet-dry cooling systems are ignored for a long time in China. In hybrid cooling systems，both wet and dry components are included，and they can be used separately or simultaneously for water conservation. By hybrid cooling，20 to 80% reduction in water usage compared to all wet recirculated system can be achieved[35], and the seasonal water shortage problem can be solved expectedly.Evaporative condensing technology can be considered an emerging technology that expected to be used in thermal power generation in future. Air cooling and water cooling are combined together in evaporative condenser, and evaporation is the mainly heat dissipating mean to take away the condensation heat of steam turbine. In recent years，evaporative condensing technology has received wide attention from scholars all over the world[36-45]. Numerous data shows that evaporative condenser has a significant advantage in water conservation and energy conservation. Water consumption of evaporative condenser is about 5%~10% of general wet cooling system[40]. Evaporative condenser circulating pump power is about 50% of wet tower cooling system，and fan power consumption is only 50%~80% of wet tower cooling system[41]. Recently，a new plate type evaporative condenser is proposed by Xu et al[46]. It mainly consists of heat exchanger plate，water recycling system and fans. Evaporative condensing technology has been widely used in refrigeration industry and chemical industry，but seldom used in thermal power generation. Only a few small plants abroad adopted this cooling technology[36-47]. Actively promotion of research and application of evaporative condensing technology in thermal power generation will achieve great effect on water conservation and energy conservation. It is indicated that evaporative condenser has potential to become a new generation of water-conservation condensing technology in thermal power generation in research reports by California Department of Energy[48].The boiler fuel gas water recovery and usage is a kind of technology in exploitation over the world. The main components of fossil fuel are hydrocarbons. Water is the main combustion product in thermal power generation. For the coal-fired power plants, water vapor exits with the flue gases at a volume percentage 12%~16%. The goals of this flue gas water recovery project are to develop technology for recovering water from combustion flue gases to reduce the net water requirements of power plants burning fossil fuels and to perform an engineering evaluation to determine how such technology can be integrated into various power-generating systems，including steam turbine and combined-cycle plants. To achieve this technique, Levy et al.[49] designed a pilot-scale water recovery system for boiler flue gas based on multiple condensing heat exchangers，and the results show that the flue gas can be cooled to below 40℃, and water capture efficiencies are 10-35% by using both makeup water and combustion air as cooling source. But this technology needs additional condensed water treatment for water reusing, which is a very costly process. Meanwhile, the conventional heat exchanger needs a large heat transfer area when condensing low-temperature flue。