ORC與非恒溫熱源換熱匹配對工質篩選及系統(tǒng)性能的影響
發(fā)布時間：2019-06-21 15:30
【摘要】：有機朗肯循環(huán)(ORC)是回收低品位工業(yè)余熱促進節(jié)能減排的重要技術手段,過去十年間大量學者對循環(huán)本身進行研究,取得了豐富的成果。但是目前該技術尚未大范圍推廣,還有若干關鍵問題比如如何減小ORC機組與熱源換熱中的不可逆損失、如何在考慮換熱匹配的影響下選擇合適的工質、如何評價熱源對機組主要部件蒸發(fā)器及膨脹機之間(火用)損分布及匹配的影響等亟待解決。對于低溫非恒溫熱源驅動的動力系統(tǒng),熱源條件及其與循環(huán)的相互作用顯然對系統(tǒng)性能有重要影響。本文的目的正是研究此類熱源對工質篩選及循環(huán)性能的影響。非恒溫熱源驅動的ORC,蒸發(fā)器中的(火用)損情況對機組性能具有重要影響,但是目前換熱過程的匹配程度與不可逆損失之間還沒有明確的量化關系,因此本文嘗試建立兩者間的聯(lián)系,從而為通過控制換熱路徑實現(xiàn)控制不可逆損失提供理論基礎。有機工質的定壓比熱容在臨界區(qū)發(fā)生突變,在質量流量一定時,T-Q圖上的換熱過程線斜率在臨界區(qū)附近有明顯變化,這為利用變比熱控制換熱路徑提供了可能。本文第二章首先通過推導換熱過程積分溫差及無量綱(火用)溫度的表達式建立了換熱路徑與換熱不可逆損失之間的聯(lián)系,證明了積分溫差與不可逆損失之間的擬線性關系,將對不可逆損失的衡量轉化為對積分溫差的衡量。之后提出利用工質比熱變化改善換熱匹配的模型。對于固定兩側流體出入口溫度的換熱器,計算了流體變比熱對換熱積分溫差的影響,提出可使換熱過程不可逆損失最小的比熱組合,對于減小ORC機組與熱源換熱中的不可逆損失有一定指導意義。目前對于亞臨界循環(huán)的最佳工質尚無統(tǒng)一結論,對于熱源的影響及關鍵物性的影響討論不足。本文以增大輸出功及減小積分溫差為目標,為亞臨界及跨臨界循環(huán)建立工質篩選準則。第二章數(shù)學推導時沒有采用實際的工質物性及壓力等參數(shù),而第三、四章根據(jù)熱力學定律建立模型,以REFPROP 9.0數(shù)據(jù)庫中的實際物性為基礎進行熱力學計算。首先研究有機工質在100~300°C熱源條件下,亞臨界飽和蒸汽基本循環(huán)中的表現(xiàn),以輸出功和換熱器面積為篩選指標,同時考慮毒性、可燃性、環(huán)境影響等因素。計算發(fā)現(xiàn),臨界溫度Tc低于熱源入口溫度Tgas,in的工質,不同的Tc對輸出功影響明顯,Tc高于Tgas,in的工質,不同的Tc對輸出功的影響不明顯。能夠提供最大輸出功的工質,是T-S圖上包絡線與熱源線相切或接近相切的工質,其臨界溫度低于熱源入口溫度15~25K。其它物性對循環(huán)熱效率的影響規(guī)律較分散,僅考慮輸出功時臨界溫度可以作為工質篩選準則。第四章利用約束熱源出入口溫度的熱力學模型,計算工質在非恒溫熱源驅動的跨臨界ORC中的表現(xiàn),分析蒸發(fā)器內窄點溫差及工質物性對循環(huán)性能的影響。結果表明,Tc低于煙氣出口溫度的工質,及Tc高于0.88倍煙氣入口溫度的工質,臨界溫度是循環(huán)效率的主要影響因素;Tc在上述范圍之間的工質,干濕性對循環(huán)效率影響顯著,濕工質效率明顯高于干工質。所有循環(huán)中,該臨界溫度范圍內的濕工質熱效率最高。Tc高于0.88倍煙氣入口溫度的工質,窄點溫差可能出現(xiàn)在蒸發(fā)過程中或蒸發(fā)器出口,從熱力性能角度看,窄點出現(xiàn)在蒸發(fā)過程中的循環(huán)明顯優(yōu)于窄點出現(xiàn)在蒸發(fā)器出口的循環(huán)。改變熱源入口及出口溫度不會影響上述結論。以上二至四章主要關注了熱源對蒸發(fā)器的影響,沒有考慮蒸發(fā)器與膨脹機之間的聯(lián)系。熱源影響蒸發(fā)器內的(火用)損,而蒸發(fā)器與膨脹機間又存在(火用)損匹配問題。近期有文獻報道顯示積分溫差會影響膨脹機效率,并由此影響機組整體效率。為了反映熱源對蒸發(fā)器及膨脹機之間(火用)損分布及匹配的影響,提出了將膨脹機效率假設為無量綱積分溫差的函數(shù)的熱力學模型,用數(shù)值模擬的方式復現(xiàn)以R123為工質采用渦旋膨脹機的ORC實驗過程,在給定蒸發(fā)器面積及換熱量、熱源入口溫度等條件下,計算熱力學循環(huán)中的各狀態(tài)點參數(shù)及輸出功、熱效率、(火用)效率等系統(tǒng)性能,并對采用積分溫差決定膨脹機效率的模型及以膨脹機效率為定值的模型結果進行比較,分析了存在使系統(tǒng)性能最佳的無量綱積分溫差的原因,反映出非恒溫熱源與ORC的換熱匹配不僅影響蒸發(fā)器(火用)損,也會影響膨脹機的性能,將膨脹機效率視為無量綱積分溫差的函數(shù)的模型比將其作為定值的模型計算結果更符合實際。
[Abstract]:The organic Rankine cycle (ORC) is an important technical means for recovering low-grade industrial waste heat to promote energy-saving and emission reduction. However, the technology has not been widely promoted at present, and there are several key problems such as how to reduce the irreversible loss of the ORC unit and the heat source heat exchange, and how to select the proper working medium under the influence of the heat exchange matching. How to evaluate the influence of heat source on the distribution and matching of the main component evaporator and expander of the unit. The dynamic system, the heat source condition and the interaction with the circulation of the low-temperature non-constant-temperature heat source obviously have an important influence on the performance of the system. The purpose of this paper is to study the effect of such a heat source on the selection and circulation of the working medium. In the case of the ORC driven by the non-constant temperature heat source, the damage of the (fire) in the evaporator has an important influence on the performance of the unit, but there is no definite quantitative relation between the matching degree of the heat exchange process and the irreversible loss, so this paper attempts to establish the relationship between the two. So as to provide a theoretical basis for controlling the irreversible loss by controlling the heat exchange path. The specific heat capacity of the organic working medium is changed in the critical region, and when the mass flow is constant, the slope of the heat transfer peak line on the T-Q graph is obviously changed near the critical region, which provides a possibility to control the heat exchange path by using the variable heat of the variable heat. In the second chapter, the relationship between the heat transfer path and the irreversible loss of heat transfer is established by deriving the integral temperature difference of the heat transfer process and the dimensionless (exergy) temperature, and the quasi-linear relationship between the integral temperature difference and the irreversible loss is proved. The measurement of the irreversible loss is converted into a measure of the integral temperature difference. And then a model for improving the heat exchange matching by utilizing the specific heat change of the working medium is proposed. The influence of the specific heat of the fluid on the temperature difference of the heat exchange integral is calculated for the heat exchanger which is used for fixing the temperature of the fluid inlet and outlet on both sides, and the specific heat combination which can minimize the irreversible loss of the heat exchange process is proposed, which is of great significance for reducing the irreversible loss in the heat exchange between the ORC unit and the heat source. At present, there is no unified conclusion on the optimal working medium of the subcritical cycle, and the influence of the heat source and the influence of the key physical properties is not enough. In order to increase the output power and reduce the integral temperature difference, the working medium selection criteria are established for subcritical and transcritical cycles. In the second chapter, the parameters such as the physical properties and the pressure of the working medium are not used in the mathematical derivation, and the third and the fourth chapter establish the model according to the law of thermodynamics, and the thermodynamic calculation is carried out based on the actual physical properties in the REFPROP 9.0 database. First, the performance of the organic working medium under the condition of 100-300 擄 C heat source and the basic cycle of the sub-critical saturated steam is studied, and the output work and the heat exchanger area are selected as the screening index, and the factors such as toxicity, flammability and environmental impact are considered. It is found that the critical temperature Tc is lower than that of the heat source inlet temperature Tgas, in, the influence of different Tc on the output work is obvious, Tc is higher than that of Tgas and in, and the effect of different Tc on the output work is not obvious. The working medium capable of providing the maximum output work is a working medium which is tangent to or close to the heat source line on the T-S graph, and the critical temperature of the working medium is lower than that of the heat source inlet temperature of 15 to 25K. The influence of other physical properties on the circulating thermal efficiency is more dispersed, and only the critical temperature of the output power can be used as the working medium screening criterion. In the fourth chapter, by using the thermodynamic model of the temperature of the inlet and outlet of the constrained heat source, the performance of the working medium in the transcritical ORC driven by the non-constant temperature heat source is calculated, and the influence of the temperature difference of the narrow point and the physical properties of the working medium on the circulation performance of the evaporator is analyzed. The results show that Tc is lower than the working medium of the flue gas outlet temperature and the working medium with Tc higher than 0.88 times the inlet temperature of the flue gas, the critical temperature is the main influence factor of the cycle efficiency; the working medium between the above ranges, the dry-wet property has significant influence on the circulation efficiency, and the efficiency of the wet working medium is obviously higher than that of the dry working medium. In all cycles, the thermal efficiency of the wet working medium in the critical temperature range is the highest. A working medium with Tc higher than 0.88 times the inlet temperature of the flue gas, the temperature difference of the narrow point may appear in the evaporation process or the outlet of the evaporator, and the circulation of the narrow point in the evaporation process is obviously better than the circulation of the narrow point in the outlet of the evaporator from the viewpoint of thermal performance. Changing the heat source inlet and outlet temperature does not affect the above conclusion. The above two and four chapters mainly focus on the influence of the heat source on the evaporator, and the relationship between the evaporator and the expander is not taken into account. The heat source affects the (fire) loss in the evaporator, and there is a (fire) loss matching problem between the evaporator and the expander. Recent literature reports show that the integral temperature difference will affect the efficiency of the expander and thus affect the overall efficiency of the unit. In order to reflect the influence of the heat source on the distribution and matching of the loss of heat between the evaporator and the expander, the thermodynamic model of the function of increasing the efficiency of the expander to the dimensionless integral temperature difference is put forward, and the ORC experimental process of using the R123 as the working medium by the numerical simulation is repeated. in that condition of a given evaporator area and heat exchange rate, a heat source inlet temperature and the like, the parameters of each state point in the thermodynamic cycle and the system performance such as output work, thermal efficiency, exergy efficiency and the like are calculated, The model for determining the efficiency of the expander and the model result of the expander efficiency are compared, and the reason of the non-dimensional integral temperature difference which is the best performance of the system is analyzed, and the heat exchange matching between the non-constant temperature heat source and the ORC not only influences the damage of the evaporator (fire), The performance of the expander is also affected, and the model ratio of the expansion machine efficiency as a function of the dimensionless integral temperature difference is more practical than the model calculation result of the fixed value.
【學位授予單位】：華北電力大學(北京)
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TK115
本文編號：2504181
[Abstract]:The organic Rankine cycle (ORC) is an important technical means for recovering low-grade industrial waste heat to promote energy-saving and emission reduction. However, the technology has not been widely promoted at present, and there are several key problems such as how to reduce the irreversible loss of the ORC unit and the heat source heat exchange, and how to select the proper working medium under the influence of the heat exchange matching. How to evaluate the influence of heat source on the distribution and matching of the main component evaporator and expander of the unit. The dynamic system, the heat source condition and the interaction with the circulation of the low-temperature non-constant-temperature heat source obviously have an important influence on the performance of the system. The purpose of this paper is to study the effect of such a heat source on the selection and circulation of the working medium. In the case of the ORC driven by the non-constant temperature heat source, the damage of the (fire) in the evaporator has an important influence on the performance of the unit, but there is no definite quantitative relation between the matching degree of the heat exchange process and the irreversible loss, so this paper attempts to establish the relationship between the two. So as to provide a theoretical basis for controlling the irreversible loss by controlling the heat exchange path. The specific heat capacity of the organic working medium is changed in the critical region, and when the mass flow is constant, the slope of the heat transfer peak line on the T-Q graph is obviously changed near the critical region, which provides a possibility to control the heat exchange path by using the variable heat of the variable heat. In the second chapter, the relationship between the heat transfer path and the irreversible loss of heat transfer is established by deriving the integral temperature difference of the heat transfer process and the dimensionless (exergy) temperature, and the quasi-linear relationship between the integral temperature difference and the irreversible loss is proved. The measurement of the irreversible loss is converted into a measure of the integral temperature difference. And then a model for improving the heat exchange matching by utilizing the specific heat change of the working medium is proposed. The influence of the specific heat of the fluid on the temperature difference of the heat exchange integral is calculated for the heat exchanger which is used for fixing the temperature of the fluid inlet and outlet on both sides, and the specific heat combination which can minimize the irreversible loss of the heat exchange process is proposed, which is of great significance for reducing the irreversible loss in the heat exchange between the ORC unit and the heat source. At present, there is no unified conclusion on the optimal working medium of the subcritical cycle, and the influence of the heat source and the influence of the key physical properties is not enough. In order to increase the output power and reduce the integral temperature difference, the working medium selection criteria are established for subcritical and transcritical cycles. In the second chapter, the parameters such as the physical properties and the pressure of the working medium are not used in the mathematical derivation, and the third and the fourth chapter establish the model according to the law of thermodynamics, and the thermodynamic calculation is carried out based on the actual physical properties in the REFPROP 9.0 database. First, the performance of the organic working medium under the condition of 100-300 擄 C heat source and the basic cycle of the sub-critical saturated steam is studied, and the output work and the heat exchanger area are selected as the screening index, and the factors such as toxicity, flammability and environmental impact are considered. It is found that the critical temperature Tc is lower than that of the heat source inlet temperature Tgas, in, the influence of different Tc on the output work is obvious, Tc is higher than that of Tgas and in, and the effect of different Tc on the output work is not obvious. The working medium capable of providing the maximum output work is a working medium which is tangent to or close to the heat source line on the T-S graph, and the critical temperature of the working medium is lower than that of the heat source inlet temperature of 15 to 25K. The influence of other physical properties on the circulating thermal efficiency is more dispersed, and only the critical temperature of the output power can be used as the working medium screening criterion. In the fourth chapter, by using the thermodynamic model of the temperature of the inlet and outlet of the constrained heat source, the performance of the working medium in the transcritical ORC driven by the non-constant temperature heat source is calculated, and the influence of the temperature difference of the narrow point and the physical properties of the working medium on the circulation performance of the evaporator is analyzed. The results show that Tc is lower than the working medium of the flue gas outlet temperature and the working medium with Tc higher than 0.88 times the inlet temperature of the flue gas, the critical temperature is the main influence factor of the cycle efficiency; the working medium between the above ranges, the dry-wet property has significant influence on the circulation efficiency, and the efficiency of the wet working medium is obviously higher than that of the dry working medium. In all cycles, the thermal efficiency of the wet working medium in the critical temperature range is the highest. A working medium with Tc higher than 0.88 times the inlet temperature of the flue gas, the temperature difference of the narrow point may appear in the evaporation process or the outlet of the evaporator, and the circulation of the narrow point in the evaporation process is obviously better than the circulation of the narrow point in the outlet of the evaporator from the viewpoint of thermal performance. Changing the heat source inlet and outlet temperature does not affect the above conclusion. The above two and four chapters mainly focus on the influence of the heat source on the evaporator, and the relationship between the evaporator and the expander is not taken into account. The heat source affects the (fire) loss in the evaporator, and there is a (fire) loss matching problem between the evaporator and the expander. Recent literature reports show that the integral temperature difference will affect the efficiency of the expander and thus affect the overall efficiency of the unit. In order to reflect the influence of the heat source on the distribution and matching of the loss of heat between the evaporator and the expander, the thermodynamic model of the function of increasing the efficiency of the expander to the dimensionless integral temperature difference is put forward, and the ORC experimental process of using the R123 as the working medium by the numerical simulation is repeated. in that condition of a given evaporator area and heat exchange rate, a heat source inlet temperature and the like, the parameters of each state point in the thermodynamic cycle and the system performance such as output work, thermal efficiency, exergy efficiency and the like are calculated, The model for determining the efficiency of the expander and the model result of the expander efficiency are compared, and the reason of the non-dimensional integral temperature difference which is the best performance of the system is analyzed, and the heat exchange matching between the non-constant temperature heat source and the ORC not only influences the damage of the evaporator (fire), The performance of the expander is also affected, and the model ratio of the expansion machine efficiency as a function of the dimensionless integral temperature difference is more practical than the model calculation result of the fixed value.
【學位授予單位】：華北電力大學(北京)
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TK115
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