【作者】 林振娴；

【导师】 杨勇平；

【作者基本信息】 华北电力大学（北京） ， 制冷及低温工程， 2011， 博士

【摘要】 改革开放以来,随着我国城市化水平的提高和居民生活条件的不断改善,我国热电联产事业得到了迅速的发展,然而对这一体系的研究尚不够完善。2008年我国热电联产的装机容量比2007年增加8.71%,但供热量反而比2007年减少3.83%；2009年热电联产的装机容量比2008年增加24.87%,年供热量仅增加3.4%,这说明一些供热机组的供热能力并未发挥出来。“节能减排,科学发展”是当前我国经济发展过程中的一项重要举措,热电联产不但是国内外公认的有效节能措施,也是改善城市环境质量的重要手段,更是低碳经济发展的必由之路,为此对热电联产进行深入研究提出新的目标。本文首先将传统的热电厂总热效率公式进行改进,将公式中的分子表示为热电联产机组纯凝工况运行时的发电量、抽汽工况运行时的供热量和由于供热而损失的发电量3部分组成。该公式不但将热电联产机组在非供热期和供热期的两种运行情况同时反映出来,并且还指出了提高供热机组总热效率的3个途径,明确了供热机组与纯凝机组的区别。供热机组的先进性应体现在提高机组的供热能力,并且在机组提供相同供热量的情况下,机组能够多发电。热电联产的研究应是对冷源领域的科学研究。将供热机组、热网加热器、供热热网系统、热用户和室外环境组成的总能系统建立为热电联产系统,分析各子系统的自身特性和与其它子系统之间的耦合机理,对热电联产系统进行全工况研究,由此针对不同容量的供热机组提出不同的运行方案。以热网加热器为热电联产系统联合特性研究的切入点,考虑热网加热器内换热管壁厚对其传热性能的影响,根据传热学的基本理论,对换热管的内、外侧壁温进行迭代计算,准确计算热网加热器的传热系数K。建立热网加热器的数学模型,得到不同回水温度下,热网加热器供热抽汽量与饱和蒸汽压力的性能曲线；再结合热网系统性能得到热网加热器性能曲线,即随着热负荷的增加,热网加热器所需的抽汽流量和抽汽压力也随之提高。将热网加热器性能和汽轮机低压缸性能联合得到热电联产系统联合特性,即汽轮机中压缸排汽压力呈“V”字型变化,供热机组的无节流工况(中压缸排汽压力、低压缸进汽压力和热网加热器抽汽压力都相等)为机组运行时中压缸排汽压力的最低点；并根据无节流工况特点提出最佳冷凝热网加热器——使热电联产系统的无节流工况的压力达到中压缸允许的最低排汽压力时的热网加热器,并对其具体的计算方法进行详细介绍。热电联产系统联合特性的提出,为热电联产系统中能量的合理匹配及系统优化指明了方向。开展供热机组的变工况功率计算,准确计算出不同供热参数下,机组的发电功率,也就是可计算出机组由于对外供热抽汽而减少的发电功率的量化,并将热电联产系统联合特性与供热机组的变工况特性结合,编制热电联产系统变工况计算程序。已知室外温度的变化,可求得热网的供、回水温度,热负荷的需求,热网加热器的主要参数以及汽轮机的各段参数,并提供该工况下汽轮机的热平衡图。为热电联产冷源领域研究能够实现节能增效提供可靠的数据依据。根据能量梯级利用原理和热电联产联合特性提出供热系统运行的新模式——供热系统串联布置的方案。在应用过程中对该方案进行优化,提出非对称式串联供热布置方式,即两台供热机组串联布置,分段加热热网水,并采取增加高温段热网加热器换热面积的方法降低供热抽汽压力,减小供热抽汽对机组发电量的影响。以200MW供热机组为例,非对称式串联供热布置方式比传统并联布置方式,在额定工况下,机组可增加发电功率约1万kW。并针对目前我国300MW供热机组中低压分缸压力过高的问题,将溴化锂吸收式热泵应用于该机组的供热过程中,回收机组排入凝汽器的余热,两台机组采用串联布置的供热模式,提高机组的供热能力和发电功率。更多还原

【Abstract】 Since the reform and opening-up, the cogeneration utilities in China has been rapidly developed with the increase of urbanization and the continuous improvement of living conditions. However, the study on this system is still imperfect. Comparing to those in 2007, the installed capacity of the combined heat and power in 2008 increased by 8.71%, while the heat supply decreased by 3.83%; and in 2009 the installed capacity of the combined heat and power increased by 24.87%, while the heat supply increased by only 3.83%, compared to those in 2008. These indicated that the heating ability of some heating units is not in full play. "Energy conservation and pollution reduction, Science development" is an important measure for China’s economic development at present. Combined heat and power is not only an effective energy-saving measure recognized at home and abroad, but also is an important method to improve the urban environmental quality. Moreover, it is the only way to develop the low-carbon economy. These proposed new goals for the further study of the combined heat and power.In this paper, traditional overall thermal efficiency formula of the power plant is improved. The numerator is composed of 3 parts, which are power generation at condensing runtime of the units, heat load during the heat-supply and the loss of generation produced by the heat-supply. The improved formula demonstrates the running conditions of the combined heat and power units during both the heating period and the off-heating period; it also provides three methods for improving the fuel utilization factors of the heating units; and the difference between the heating units and the condensing units can be definite according to the formula. The advance of the heating units should not only be demonstrated in increasing the heating ability of the heating units but also in generating as much as possible when the heating load is not changed. The research direction of the combined heat and power is the cold source. The total energy system, which is composed by the heating units, the heat exchanger for heating network, the heating network system, the heat users and the outdoor environment, is established as the combined heat and power system. The characteristics of the subsystems and the coupling mechanism between them are analyzed and the full conditions of the CHP are researched. Therefore, different running schemes are proposed for the heating unites with different capacities.The cut-in point of the combining characteristic research of the CHP system is the hot water heater for heating network. The heat transfer coefficient K can be computed accurately by means of the iterative computations for the wall temperature of the heat exchanger tubes according to the basic theory of heat transfer and the influence of the wall thickness on the heat transfer performance of heat exchanger tubes in the hot water heater for heating network. The performance curve under different backwater temperatures can be obtained by establishing the mathematical model of the hot water heater for heating network, which is denoted by the amount of heating extraction and the saturated vapor pressure. Combined with the thermal-system performance of the heating network, performance curve of the hot water heater for heating network can be obtained. The flow and the pressure of the extraction steam needed by the hot water heater for heating network are increasing with the increase of the heat load. The combined performance curve of the CHP system can be obtained by combining the performance of the hot water heater for heating network with that of the low pressure casing, the "V" style variation occurs in the variation process of intermediate pressure casing exhaust pressure, it is obtained that equilibrium without throttling of heating units is the minimum exhaust pressure of intermediate pressure casing when the units are operating (the back pressure of intermediate pressure casing is equal to inlet pressure of the low pressure casing and equal to the extraction pressure of the hot water heater for heating network); The optimum cooling source hot water heater for heating network, which makes the pressure of the CHP system under the condition without throttling reach the minimum pressure allowed by the intermediate casing, is proposed according to the performance of equilibrium without throttling; and then its calculation method is introduced detailedly. The combined performance of CHP is proposed, which points out the development direction for the energy reasonable match and the system optimization of the CHP system.The off-design equilibrium performance calculation of the heating units is developed to calculate the electricity production of the units under the different heating conditions, that quantizes the loss of generated output caused by the extraction steam of units for external heat-supply; and then the off-design calculation of the CHP system is programmed through combining the combined performance of the CHP system and the off-design performance of the heating units. Provided with the variation of the outdoor temperature, the supply and return water temperature of the heating network, the heat load demand, the main parameters of the hot water heater for heating network and the parameters of each section of the turbine can be obtained accurately and the heat balance chart of the turbine is provided under the operating equilibrium. It provides the reliable data criterion to achieve the aim of energy saving and efficiency improvement for the cooling source field of the CHP.The new operating models of the heating system that are series arrangement of heating system are proposed according to the theory of stepwise use of energy and combined performance of the CHP. The asymmetric series arrangement of heating system is proposed by optimizing the scheme in the application process; two heating units are in parallel arrangement; the heating network water is sectionalized heated, and at the same time, the heat exchange area of the hot water heater for heating network at high-temperature section are increased and the extraction pressure of the heating units are decreased, so the influence of the heating extraction on the electricity production of the units is decreased. Take the 200MW heating units for example; the generating power of the heating units in asymmetric series arrangement can increase about 10,000 kW more than that in the traditional parallel arrangement under the rated condition. At present, in our country, the pressure used to distinguish the intermediate pressure casing and low pressure casing is too high for the 300MW heating units, the lithium bromide absorption pumps are used in the heating-supply process of the units to recover the waste heat discharged into the condenser by units. The new heating model that two units are in series arrangement can increase the heat efficiency and the heating capacity of the units.更多还原