CN104932449A - Determination method of heat exchanger network heat flux containing non-isothermal phase change fluid - Google Patents

Determination method of heat exchanger network heat flux containing non-isothermal phase change fluid Download PDF

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CN104932449A
CN104932449A CN201510178140.2A CN201510178140A CN104932449A CN 104932449 A CN104932449 A CN 104932449A CN 201510178140 A CN201510178140 A CN 201510178140A CN 104932449 A CN104932449 A CN 104932449A
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蒋宁
徐英杰
李韩伟
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Zhejiang University of Technology ZJUT
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Abstract

一种包含非等温相变流体的换热网络热流量的确定方法，基于流体的实际物性，采用流体实际的温焓物性关系，确定热交换网络内部的可用热量随温度的分布关系，根据非线性物性对局部温区可用热流量的大小和方向的影响，将整个温度区间划分为一系列热流量随温度单调变化的子区间，进而根据各温区累积热流量的大小和方向确定换热网络的热流量。本发明能获得可靠的热流量计算结果。

A method for determining the heat flow rate of a heat exchange network containing a non-isothermal phase change fluid. Based on the actual physical properties of the fluid, the actual temperature-enthalpy physical property relationship of the fluid is used to determine the distribution relationship of the available heat in the heat exchange network with temperature. According to the nonlinear The influence of physical properties on the size and direction of the available heat flow in the local temperature zone, the entire temperature range is divided into a series of sub-ranges in which the heat flow varies monotonically with the temperature, and then the heat exchange network is determined according to the size and direction of the cumulative heat flow in each temperature zone heat flow. The invention can obtain reliable heat flow calculation results.

Description

一种包含非等温相变流体的换热网络热流量的确定方法A Method for Determining the Heat Flow of a Heat Exchange Network Containing a Non-isothermal Phase Change Fluid

技术领域technical field

本发明涉及工业热交换网络的设计领域，尤其是一种包含非等温相变流体的换热网络热流量的确定方法。The invention relates to the design field of an industrial heat exchange network, in particular to a method for determining heat flow of a heat exchange network containing a non-isothermal phase change fluid.

背景技术Background technique

在工业过程中，为了满足工艺的技术需要，一些冷的流体要被加热到工艺条件指定的温度状态，而另外一些热的流体则要被冷却到工艺条件指定的温度状态。通过合理地将这些热、冷流股进行匹配换热，充分利用工业过程内部物流的热量，用热的流体去加热冷的流体，用冷的流体去冷却热的流体，使物流达到指定的温度和相态，通过回收系统内部的热量来减少对外部公用工程的消耗，这就是工业热交换网络(换热网络)的作用。换热网络用于回收系统中可以利用的能量，降低对外部公用工程的需求，是石化、化工、冶金、造纸、水泥、食品、电力等工业系统的一个重要子系统。换热网络回收利用工业系统内部热量的程度直接决定了工业系统的能耗和经济性，对节能减排有着重要影响。In an industrial process, in order to meet the technical requirements of the process, some cold fluids are heated to the temperature state specified by the process conditions, while other hot fluids are cooled to the temperature state specified by the process conditions. By reasonably matching these hot and cold streams for heat exchange, the heat of the internal logistics of the industrial process is fully utilized, and the hot fluid is used to heat the cold fluid, and the cold fluid is used to cool the hot fluid, so that the logistics reaches the specified temperature. And phase state, by recovering the heat inside the system to reduce the consumption of external utilities, this is the role of the industrial heat exchange network (heat exchange network). The heat exchange network is used to recover the energy that can be used in the system and reduce the demand for external public works. It is an important subsystem of petrochemical, chemical, metallurgy, papermaking, cement, food, electric power and other industrial systems. The extent to which the heat exchange network recycles and utilizes the internal heat of the industrial system directly determines the energy consumption and economy of the industrial system, and has an important impact on energy conservation and emission reduction.

在换热网络的设计中，一个重要问题是工业系统内部可以加以回收利用的热量究竟有多少，即如何确定最大热回收潜力。换热网络的最大热回收潜力决定了工业系统的最小能耗需求和节能潜力的大小。In the design of the heat exchange network, an important issue is how much heat can be recycled in the industrial system, that is, how to determine the maximum heat recovery potential. The maximum heat recovery potential of the heat exchange network determines the minimum energy consumption demand and the energy saving potential of the industrial system.

夹点法是换热网络的常用设计方法，该方法以热力学为依据来确定换热网络的最大热回收潜力。夹点法建立在物质比热容为常数这一假设之上，即流体所吸收或释放的热量与其温度变化成正比。石化、化工、气体加工、低温工业等工业过程通常包含诸多蒸馏或精馏、蒸发、冷凝、再沸等操作单元，所涉及的流体常常是多组分混合物，流体的非等温相变过程非常常见。对包含非等温相变的流体的换热网络，其热流量与温度之间的关系呈现出比较显著的非线性特征，此时传统夹点法就无法正确地估计换热网络的热流量，甚至严重误判工业系统的能耗需求。目前在公开文献报道中尚未出现包含非等温相变流体的换热网络热流量的确定方法方面的成果。The pinch method is a common design method for heat exchange networks, which is based on thermodynamics to determine the maximum heat recovery potential of the heat exchange network. The pinch method is based on the assumption that the specific heat capacity of a substance is constant, that is, the heat absorbed or released by a fluid is proportional to its temperature change. Industrial processes such as petrochemical, chemical, gas processing, and low-temperature industries usually include many operating units such as distillation or rectification, evaporation, condensation, and reboiling. The fluids involved are often multi-component mixtures, and the non-isothermal phase transition process of fluids is very common. . For a heat exchange network containing fluids with non-isothermal phase transitions, the relationship between the heat flow and temperature presents a significant nonlinear feature. At this time, the traditional pinch method cannot correctly estimate the heat flow of the heat exchange network, and even Significantly misjudged the energy requirements of industrial systems. At present, there is no achievement in the determination method of the heat flow of the heat exchange network including the non-isothermal phase change fluid in the public literature reports.

发明内容Contents of the invention

为了克服现有夹点法不能正确估计包含非等温相变流体的换热网络的热流量的局限性，本发明提供一种基于流体实际物性的、包含非等温相变流体的换热网络热流量的确定方法。In order to overcome the limitation that the existing pinch point method cannot correctly estimate the heat flow of a heat exchange network containing a non-isothermal phase change fluid, the present invention provides a heat flow of a heat exchange network containing a non-isothermal phase change fluid based on the actual physical properties of the fluid method of determination.

本发明解决其技术问题所采用的技术方案是：The technical solution adopted by the present invention to solve its technical problems is:

一种包含非等温相变流体的换热网络热流量的确定方法，所述方法包括以下步骤：A method for determining the heat flow rate of a heat exchange network comprising a non-isothermal phase change fluid, the method comprising the following steps:

1)提取流体的工艺参数和物性数据1) Extract the process parameters and physical property data of the fluid

物流的工艺参数和物性数据包括：组成，流量，进口温度Tin，出口温度Tout，焓和比热容，采用流体实际的温焓物性关系；The process parameters and physical property data of logistics include: composition, flow rate, inlet temperature T in , outlet temperature T out , enthalpy and specific heat capacity, using the actual temperature-enthalpy physical property relationship of the fluid;

2)设置换热网络的最小传热温差ΔTmin 2) Set the minimum heat transfer temperature difference ΔT min of the heat exchange network

3)进行冷、热流体温度修正3) Perform cold and hot fluid temperature correction

将冷流体的温度升高ΔTmin/2，将每股热流体的温度降低ΔTmin/2，从而确保热流体的温度高于冷流体的温度，并满足最小传热温差ΔTmin的要求，冷、热流体温度修正分别参照公式(1)-(2)：Increase the temperature of the cold fluid by ΔT min /2, and decrease the temperature of each hot fluid by ΔT min /2, so as to ensure that the temperature of the hot fluid is higher than the temperature of the cold fluid, and meet the minimum heat transfer temperature difference ΔT min requirement, the cold , thermal fluid temperature correction respectively refer to the formula (1)-(2):

TT CC ,, jj ** == TT CC ,, jj ++ ΔTΔT minmin // 22 -- -- -- (( 11 ))

TT Hh ,, ii ** == TT Hh ,, ii -- ΔTΔT minmin // 22 -- -- -- (( 22 ))

在式(1)-(2)中，ΔTmin为步骤2)指定的最小传热温差；TH,i和TC,j分别为热流股i和冷流股j的实际温度；T* H,i和T* C,j分别为热流股i和冷流股j进行温度修正之后的温度；In formulas (1)-(2), ΔT min is the minimum heat transfer temperature difference specified in step 2); T H,i and T C,j are the actual temperatures of hot stream i and cold stream j respectively; T * H ,i and T * C,j are the temperature after temperature correction of hot stream i and cold stream j respectively;

4)划分原始温度区间4) Divide the original temperature range

以步骤3)中冷、热流体修正之后的进、出口温度为依据，划分温度区间，将所有冷、热流体经步骤3)修正之后的进口温度和出口温度按从高到低的顺序排列，记为：T1、T2、…、TN1、TN1+1，其中N1+1为温度端点的个数，所划分的温区个数为N1，温区编号从1到N1，第k个温区[Tk，Tk+1]以温度范围Tk+1到Tk定义，且Tk＞Tk+1；Based on the corrected inlet and outlet temperatures of the cold and hot fluids in step 3), divide the temperature range, and arrange the inlet and outlet temperatures of all the cold and hot fluids after the correction in step 3) in order from high to low, Recorded as: T 1 , T 2 ,..., T N1 , T N1+1 , where N1+1 is the number of temperature endpoints, the number of divided temperature zones is N1, and the number of temperature zones is from 1 to N1, the kth A temperature zone [T k , T k+1 ] is defined by the temperature range T k+1 to T k , and T k >T k+1 ;

5)计算各温区内的可用热量5) Calculate the available heat in each temperature zone

在步骤4)所划分的每一温度区间，根据热力学第一定律，基于流体真实的温焓关系，计算各个温度区间内可用热量随温度的数值变化关系，参照公式(3)-公式(7)：In each temperature interval divided in step 4), according to the first law of thermodynamics, based on the real temperature-enthalpy relationship of the fluid, the relationship between the available heat in each temperature interval and the numerical change of temperature is calculated, referring to formula (3) - formula (7) :

QQ KK (( TT )) == ΣΣ ii ∈∈ {{ hothot }} kk (( Hh ii (( YY kk hh )) -- Hh ii (( TT hh )) )) -- ΣΣ jj ∈∈ {{ coldcold }} kk (( Hh jj (( TT kk cc )) -- Hh jj (( TT cc )) )) -- -- -- (( 33 ))

TT kk hh == TT kk ++ ΔTΔT minmin // 22 -- -- -- (( 44 ))

TT kk cc == TT kk -- ΔTΔT minmin // 22 -- -- -- (( 55 ))

Th＝T+ΔTmin/2   (6)T h =T+ΔT min /2 (6)

Tc＝T-ΔTmin/2   (7)T c =T-ΔT min /2 (7)

在式(3)-(7)中，Qk(T)为第k个温度区间内的可用热量，可用热量的大小随温度T变化；温度T∈[Tk+1,Tk]；{hot}k代表第k个温度区间内所有的热流股构成的热流体集；{cold}k代表第k个温度区间内所有的冷流股构成的冷流体集；k＝1,2,3,…,N1；流体的焓H为温度和流量的函数；为热流体i在温度处的焓，温度由公式(4)计算；Hi(Th)为热流体i在温度Th处的焓，温度Th由公式(6)计算；为冷流体j在温度处的焓，温度由公式(5)计算；Hj(Tc)为冷流体j在温度Tc处的焓，温度Tc由公式(7)计算；In formulas (3)-(7), Q k (T) is the available heat in the kth temperature interval, and the size of the available heat varies with temperature T; temperature T∈[T k+1 ,T k ]; { hot} k represents the hot fluid set composed of all the hot streams in the kth temperature interval; {cold} k represents the cold fluid set composed of all the cold streams in the kth temperature interval; k=1,2,3, ..., N1; the enthalpy H of the fluid is a function of temperature and flow; is the thermal fluid i at temperature Enthalpy at temperature Calculated by formula (4); H i (T h ) is the enthalpy of thermal fluid i at temperature T h , and temperature T h is calculated by formula (6); is the cold fluid j at temperature Enthalpy at temperature Calculated by formula (5); H j (T c ) is the enthalpy of cold fluid j at temperature T c , and temperature T c is calculated by formula (7);

6)判断各个温度区间内是否存在热流方向的转折6) Judging whether there is a turning point in the direction of heat flow in each temperature range

利用步骤5)得到的各个温度区间内可用热量随温度的数值变化关系，寻找各个温区可用热量的极值点，极值点是指可用热量随温度的变化关系发生了改变，从温区1到温区N1，分别找出每个温区内所有的可用热量的极值点；Using the relationship between available heat and temperature in each temperature range obtained in step 5), find the extreme point of available heat in each temperature zone. The extreme point refers to the change in the relationship between available heat and temperature. From temperature zone 1 To the temperature zone N1, find out the extreme points of all available heat in each temperature zone;

7)重新划分温度区间7) Re-divide the temperature range

将步骤4)中所有原始温区的温度端点与步骤6)找到的极值点相对应的温度点合并在一起，按从高温到低温的顺序排列，重新划分温度区间，温区个数记为N2，温度区间端点数为N2+1；Merge the temperature endpoints of all original temperature zones in step 4) with the temperature points corresponding to the extreme points found in step 6), arrange them in the order from high temperature to low temperature, re-divide the temperature range, and record the number of temperature zones as N2, the number of endpoints in the temperature range is N2+1;

8)重新计算每个温度区间的可用热量8) Recalculate the available heat for each temperature interval

在步骤7)新划分的温度区间的基础上，根据公式(3)-公式(7)，重新计算所有温度区间内的可用热量；On the basis of the newly divided temperature intervals in step 7), according to formula (3)-formula (7), recalculate the available heat in all temperature intervals;

9)计算各温区的累积热流量9) Calculate the cumulative heat flow in each temperature zone

在步骤7)所划分的每一温度区间，计算每个温度区间可以传递到下一个温度区间的累积热流量，参照公式(8)：In each temperature interval divided by step 7), calculate the cumulative heat flow that can be transferred from each temperature interval to the next temperature interval, referring to formula (8):

CC kk == CC kk -- 11 ++ ΣΣ ii ∈∈ {{ hothot }} kk (( Hh ii (( TT kk hh )) -- Hh ii (( TT kk ++ 11 hh )) )) -- ΣΣ jj ∈∈ {{ coldcold }} kk (( Hh jj (( TT kk cc )) -- Hh jj (( TT kk ++ 11 cc )) )) -- -- -- (( 88 ))

在公式(8)中，Ck为从第k个温区传递到第k+1个温区的累积热流量；C0＝0；k＝1,2,3,…,N2，根据每个温度区间的累计热流量的正负，可以判断热回收的可能性和热量传递的方向，Ck为正值，则表示从温度区间k传递到第k+1个温区的热流方向为正，即较高温区存在多余的热量可以传递给下一温区加以回收利用；Ck为负值，则表示温区k传递到第k+1个温区的热流方向为负，即该温区需要从外界吸收热量，该温区不存在多余的热量可供下一温区回收利用。In formula (8), C k is the cumulative heat flow transferred from the kth temperature zone to the k+1th temperature zone; C 0 =0; k=1,2,3,...,N2, according to each The positive or negative of the cumulative heat flow in the temperature range can determine the possibility of heat recovery and the direction of heat transfer. If C k is a positive value, it means that the direction of heat flow transferred from the temperature range k to the k+1th temperature zone is positive. That is, the excess heat in the higher temperature zone can be transferred to the next temperature zone for recycling; if C k is negative, it means that the heat flow direction of the temperature zone k transferred to the k+1th temperature zone is negative, that is, the temperature zone needs Heat is absorbed from the outside, and there is no excess heat in this temperature zone for recycling in the next temperature zone.

本发明的技术构思为：基于流体的实际物性，采用流体实际的温焓物性关系，确定热交换网络内部的可用热量随温度的分布关系，根据非线性物性对局部温区可用热流量的大小和方向的影响，将整个温度区间划分为一系列热流量随温度单调变化的子区间，得到各温区累积热流量的大小和方向。The technical idea of the present invention is: based on the actual physical properties of the fluid, using the actual temperature-enthalpy physical property relationship of the fluid to determine the distribution relationship of the available heat in the heat exchange network with temperature, and according to the nonlinear physical properties of the available heat flow in the local temperature zone and According to the influence of direction, the entire temperature range is divided into a series of sub-ranges in which the heat flux changes monotonously with the temperature, and the magnitude and direction of the cumulative heat flux in each temperature zone are obtained.

本发明利用局部温区可用热量的极值点将温区分割为一系列热流量随温度单调变化的子区间，这样可以客观地反映出流体非线性温焓物性对热交换网络设计的影响。当流体的比热容是定值时，各温度区间内可用热量随温度的变化单调地增加或者减少；而在流体非线性温焓物性关系的影响下，各温度区间内可用热量随温度的变化情况有可能出现反转态势，即存在极值点，极值点是指可用热量随温度的变化关系发生改变的状态点，可用热量随温度的变化可能出现先增加再减小、或者先减小再增大两种不同情况，反映出在非线性温焓物性的影响下换热网络中可回收利用的热流量的大小和方向随温度的两种不同分布情况。极大值点对应于可用热量随温度的降低呈现先增大后减小的分界点；极小值点对应于可用热量随温度的降低呈现先减小后增大的分界点。当出现极大值点时，在高于极大值点的温区，存在多余的热量可供较低温区回收利用，可以进行系统内部的热量回收；当出现极小值点时，在高于极小值点的温区，需要从外界吸收热量才能满足该温区的热量需求，该温区无法向低温区提供多余的热量，不能进行系统内部的热量回收利用。所以极大值和极小值两种情况将带来不同的可用热量和累积热量随温度的分布关系，必须加以区分和单独处理。The invention utilizes the extremum point of available heat in the local temperature zone to divide the temperature zone into a series of sub-intervals in which the heat flow varies monotonously with the temperature, which can objectively reflect the influence of the fluid nonlinear temperature-enthalpy physical property on the design of the heat exchange network. When the specific heat capacity of the fluid is a constant value, the available heat in each temperature interval increases or decreases monotonously with the change of temperature; and under the influence of the nonlinear temperature-enthalpy physical property relationship of the fluid, the available heat in each temperature interval varies with temperature as follows: There may be a reversal trend, that is, there is an extreme point. The extreme point refers to the state point where the relationship between the available heat and the temperature changes. The available heat may increase first and then decrease, or first decrease and then increase. There are two different situations, which reflect the two different distributions of the size and direction of the recyclable heat flow in the heat exchange network with temperature under the influence of nonlinear temperature and enthalpy properties. The maximum value point corresponds to the boundary point where the available heat increases first and then decreases with the decrease of temperature; the minimum value point corresponds to the boundary point where the available heat decreases first and then increases with the decrease of temperature. When the maximum value point appears, in the temperature zone higher than the maximum value point, there is excess heat that can be recycled in the lower temperature zone, and the heat recovery inside the system can be carried out; when the minimum value point appears, in the temperature zone higher than The temperature zone at the minimum point needs to absorb heat from the outside to meet the heat demand of this temperature zone. This temperature zone cannot provide excess heat to the low temperature zone, and cannot perform heat recovery and utilization within the system. Therefore, the two situations of maximum value and minimum value will bring different distribution relations of available heat and accumulated heat with temperature, which must be distinguished and dealt with separately.

本发明的有益效果为：1、该方法基于流体的实际物性，采用流体实际的温焓物性关系确定可用热量随温度的分布，相比传统方法，可以获得可靠的热流量计算结果；2、该方法根据非线性物性对局部温区可用热流量的大小和方向的影响，将整个温度区间划分为一系列热流量随温度单调变化的子区间，而传统方法无法确定非线性对热量集成的影响。The beneficial effects of the present invention are: 1. Based on the actual physical properties of the fluid, the method uses the actual temperature-enthalpy physical property relationship of the fluid to determine the distribution of available heat with temperature. Compared with the traditional method, reliable heat flow calculation results can be obtained; 2. The method According to the influence of nonlinear physical properties on the size and direction of the available heat flow in the local temperature zone, the entire temperature range is divided into a series of sub-ranges in which the heat flow varies monotonously with temperature, and the traditional method cannot determine the influence of nonlinearity on heat integration.

附图说明Description of drawings

图1是局部温区可用热量随温度的变化关系图。Figure 1 is a graph showing the variation of available heat with temperature in a local temperature zone.

图2是基于流体实际物性从高温区到低温区的累积热流量图。Figure 2 is a diagram of the cumulative heat flow from the high temperature region to the low temperature region based on the actual physical properties of the fluid.

图3是基于定比热容从高温区到低温区的累积热流量图。Fig. 3 is a graph of cumulative heat flow from a high temperature region to a low temperature region based on constant specific heat capacity.

具体实施方式Detailed ways

下面结合附图对本发明作进一步描述。The present invention will be further described below in conjunction with the accompanying drawings.

参照图1～图3，一种包含非等温相变流体的换热网络热流量的确定方法，包括以下步骤：Referring to Figures 1 to 3, a method for determining the heat flow of a heat exchange network including a non-isothermal phase change fluid includes the following steps:

1)提取流体的工艺参数和物性数据1) Extract the process parameters and physical property data of the fluid

物流的工艺参数和物性数据包括：组成，流量，进口温度Tin(初始温度)，出口温度Tout(指定的目标温度)，焓和比热容。所述方法基于流体的实际物性，采用流体实际的温焓物性关系，而不是假设物质的比热容为常数。The process parameters and physical data of the stream include: composition, flow rate, inlet temperature T in (initial temperature), outlet temperature T out (specified target temperature), enthalpy and specific heat capacity. The method is based on the actual physical properties of the fluid, and adopts the actual temperature-enthalpy physical property relationship of the fluid instead of assuming that the specific heat capacity of the substance is constant.

2)设置换热网络的最小传热温差ΔTmin 2) Set the minimum heat transfer temperature difference ΔT min of the heat exchange network

设定换热网络的最小传热温差ΔTmin。ΔTmin是传热的推动力，是保证冷、热流体之间进行换热的必要条件。Set the minimum heat transfer temperature difference ΔT min of the heat exchange network. ΔT min is the driving force of heat transfer and a necessary condition to ensure heat exchange between cold and hot fluids.

3)进行冷、热流体温度修正3) Perform cold and hot fluid temperature correction

热流体如果要把热量传递给冷流体，为了保证传热的进行，则热流体的温度要高于冷流体的温度，其温差应不低于步骤2)设定的最小传热温差要求。对冷、热流体的温度进行修正，将冷流体的温度升高ΔTmin/2，将每股热流体的温度降低ΔTmin/2，从而确保热流体的温度高于冷流体的温度，并满足最小传热温差ΔTmin的要求。冷、热流体温度修正分别参照公式(1)-(2)：If the hot fluid transfers heat to the cold fluid, in order to ensure the heat transfer, the temperature of the hot fluid should be higher than that of the cold fluid, and the temperature difference should not be lower than the minimum heat transfer temperature difference requirement set in step 2). Correct the temperature of the cold and hot fluids, increase the temperature of the cold fluid by ΔT min /2, and decrease the temperature of each hot fluid by ΔT min /2, so as to ensure that the temperature of the hot fluid is higher than the temperature of the cold fluid, and satisfy Minimum heat transfer temperature difference ΔT min requirements. Refer to formulas (1)-(2) for temperature correction of cold and hot fluids respectively:

TT CC ,, jj ** == TT CC ,, jj ++ ΔTΔT minmin // 22 -- -- -- (( 11 ))

TT Hh ,, ii ** == TT Hh ,, ii -- ΔTΔT minmin // 22 -- -- -- (( 22 ))

在式(1)-(2)中，ΔTmin为步骤2)指定的最小传热温差；TH,i和TC,j分别为热流股i和冷流股j的实际温度；T* H,i和T* C,j分别为热流股i和冷流股j进行温度修正之后的温度。In formulas (1)-(2), ΔT min is the minimum heat transfer temperature difference specified in step 2); T H,i and T C,j are the actual temperatures of hot stream i and cold stream j respectively; T * H ,i and T * C,j are the temperatures of hot stream i and cold stream j after temperature correction, respectively.

4)划分原始温度区间4) Divide the original temperature range

以步骤3)中冷、热流体修正之后的进、出口温度为依据，划分温度区间。将所有冷、热流体经步骤3)修正之后的进口温度和出口温度按从高到低的顺序排列，记为：T1、T2、…、TN1、TN1+1，其中N1+1为温度端点的个数，所划分的温区个数为N1，温区编号从1到N1。例如，第k个温区[Tk，Tk+1]以温度范围Tk+1到Tk定义，且Tk＞Tk+1。Based on the corrected inlet and outlet temperatures of the intermediate cooling and heating fluids in step 3), the temperature ranges are divided. Arrange the inlet and outlet temperatures of all cold and hot fluids corrected in step 3) in descending order, recorded as: T 1 , T 2 , ..., T N1 , T N1+1 , where N1+1 is the number of temperature endpoints, the number of divided temperature zones is N1, and the temperature zone numbers are from 1 to N1. For example, the kth temperature zone [T k , T k+1 ] is defined by the temperature range T k+1 to T k , and T k >T k+1 .

5)计算各温区内的可用热量5) Calculate the available heat in each temperature zone

在步骤4)所划分的每一温度区间，根据热力学第一定律，基于流体真实的温焓关系，计算各个温度区间内可用热量随温度的数值变化关系，参照公式(3)-公式(7)：In each temperature interval divided in step 4), according to the first law of thermodynamics, based on the real temperature-enthalpy relationship of the fluid, the relationship between the available heat in each temperature interval and the numerical change of temperature is calculated, referring to formula (3) - formula (7) :

QQ KK (( TT )) == ΣΣ ii ∈∈ {{ hothot }} kk (( Hh ii (( YY kk hh )) -- Hh ii (( TT hh )) )) -- ΣΣ jj ∈∈ {{ coldcold }} kk (( Hh jj (( TT kk cc )) -- Hh jj (( TT cc )) )) -- -- -- (( 33 ))

TT kk hh == TT kk ++ ΔTΔT minmin // 22 -- -- -- (( 44 ))

TT kk cc == TT kk -- ΔTΔT minmin // 22 -- -- -- (( 55 ))

Th＝T+ΔTmin/2   (6)T h =T+ΔT min /2 (6)

Tc＝T-ΔTmin/2   (7)T c =T-ΔT min /2 (7)

在式(3)-(7)中，Qk(T)为第k个温度区间内的可用热量，可用热量的大小随温度T变化；温度T∈[Tk+1,Tk]；{hot}k代表第k个温度区间内所有的热流股构成的热流体集；{cold}k代表第k个温度区间内所有的冷流股构成的冷流体集；k＝1,2,3,…,N1；流体的焓H为温度和流量的函数；为热流体i在温度处的焓，温度由公式(4)计算；Hi(Th)为热流体i在温度Th处的焓，温度Th由公式(6)计算；为冷流体j在温度处的焓，温度由公式(5)计算；Hj(Tc)为冷流体j在温度Tc处的焓，温度Tc由公式(7)计算。In formulas (3)-(7), Q k (T) is the available heat in the kth temperature interval, and the size of the available heat varies with temperature T; temperature T∈[T k+1 ,T k ]; { hot} k represents the hot fluid set composed of all the hot streams in the kth temperature interval; {cold} k represents the cold fluid set composed of all the cold streams in the kth temperature interval; k=1,2,3, ..., N1; the enthalpy H of the fluid is a function of temperature and flow; is the thermal fluid i at temperature Enthalpy at temperature Calculated by formula (4); H i (T h ) is the enthalpy of thermal fluid i at temperature T h , and temperature T h is calculated by formula (6); is the cold fluid j at temperature Enthalpy at temperature Calculated by formula (5); H j (T c ) is the enthalpy of cold fluid j at temperature T c , and temperature T c is calculated by formula (7).

各温度区间内可用热量随温度的变化情况反映出换热网络中可回收利用的热流量的大小、方向、及其随温度的分布情况。The change of available heat with temperature in each temperature range reflects the magnitude, direction, and distribution of the recyclable heat flow in the heat exchange network with temperature.

6)判断各个温度区间内是否存在热流方向的转折6) Judging whether there is a turning point in the direction of heat flow in each temperature range

利用步骤5)得到的各个温度区间内可用热量随温度的数值变化关系，寻找各个温区可用热量的极值点。极值点是指可用热量随温度的变化关系发生改变的转折点。从温区1到温区N1，分别找出每个温区内所有的可用热量的极值点。Using the numerical change relationship of available heat in each temperature range obtained in step 5) with temperature, find the extremum point of available heat in each temperature range. The extreme point refers to the turning point where the relationship between available heat and temperature changes. From temperature zone 1 to temperature zone N1, find out the extreme points of all available heat in each temperature zone.

7)重新划分温度区间7) Re-divide the temperature range

将步骤4)中所有原始温区的温度端点与步骤6)找到的极值点相对应的温度点合并在一起，按从高温到低温的顺序排列，重新划分温度区间，温区个数记为N2，温度区间端点数为N2+1，此时的温度区间的个数跟步骤4)的原始温区相比可能会有所增加。但如果步骤6)未发现任何极值点，则温区数目保持不变。Merge the temperature endpoints of all original temperature zones in step 4) with the temperature points corresponding to the extreme points found in step 6), arrange them in the order from high temperature to low temperature, re-divide the temperature range, and record the number of temperature zones as N2, the number of endpoints of the temperature range is N2+1, and the number of temperature ranges at this time may increase compared with the original temperature range in step 4). But if no extreme point is found in step 6), the number of temperature zones remains unchanged.

8)重新计算每个温度区间的可用热量8) Recalculate the available heat for each temperature interval

在步骤7)新划分的温度区间的基础上，根据公式(3)-公式(7)，重新计算所有温度区间内的可用热量。On the basis of the newly divided temperature intervals in step 7), according to formula (3)-formula (7), recalculate the available heat in all temperature intervals.

9)计算各温区的累积热流量9) Calculate the cumulative heat flow of each temperature zone

在步骤7)所划分的每一温度区间，计算每个温度区间可以传递到下一个温度区间的累积热流量，参照公式(8)：In each temperature interval divided by step 7), calculate the cumulative heat flow that can be transferred from each temperature interval to the next temperature interval, referring to formula (8):

CC kk == CC kk -- 11 ++ ΣΣ ii ∈∈ {{ hothot }} kk (( Hh ii (( TT kk hh )) -- Hh ii (( TT kk ++ 11 hh )) )) -- ΣΣ jj ∈∈ {{ coldcold }} kk (( Hh jj (( TT kk cc )) -- Hh jj (( TT kk ++ 11 cc )) )) -- -- -- (( 88 ))

在公式(8)中，Ck为从第k个温区传递到第k+1个温区的累积热流量；C0＝0；k＝1,2,3,…,N2。根据每个温度区间的累计热流量的正负，可以判断热回收的可能性和热量传递的方向。Ck为正值，则表示从温度区间k传递到第k+1个温区的热流方向为正，即较高温区存在多余的热量可以传递给下一温区加以回收利用；Ck为负值，则表示温区k传递到第k+1个温区的热流方向为负，即该温区需要从外界吸收热量，该温区不存在多余的热量可供下一温区回收利用。In formula (8), C k is the cumulative heat flow transferred from the kth temperature zone to the k+1th temperature zone; C 0 =0; k=1,2,3,...,N2. According to the positive and negative of the cumulative heat flow in each temperature range, the possibility of heat recovery and the direction of heat transfer can be judged. If C k is positive, it means that the direction of heat flow from the temperature range k to the k+1th temperature zone is positive, that is, there is excess heat in the higher temperature zone that can be transferred to the next temperature zone for recycling; C k is negative value, it means that the direction of heat flow transferred from temperature zone k to the k+1th temperature zone is negative, that is, this temperature zone needs to absorb heat from the outside, and there is no excess heat in this temperature zone for recycling in the next temperature zone.

本实施例中，具体步骤如下：In this embodiment, the specific steps are as follows:

第一步，提取物流数据。本实施例采用的物流数据，如表1所示。The first step is to extract logistics data. The logistics data used in this embodiment are shown in Table 1.

第二步，设置换热网络的最小传热温差ΔTmin。在本案例中，取换热网络最小传热温差ΔTmin＝10℃。The second step is to set the minimum heat transfer temperature difference ΔT min of the heat exchange network. In this case, the minimum heat transfer temperature difference ΔT min of the heat exchange network is assumed to be 10°C.

第三步，进行冷、热流体温度修正。根据最小传热温差ΔTmin的要求，参照公式(1)-(2)对冷、热流体的温度进行修正，修正结果见表2。The third step is to correct the temperature of cold and hot fluids. According to the requirements of the minimum heat transfer temperature difference ΔT min , the temperature of the cold and hot fluids is corrected with reference to formulas (1)-(2). The correction results are shown in Table 2.

第四步，划分原始温度区间。根据步骤3)中冷、热流体修正之后的进、出口温度，按从高温到低温的顺序划分为5个温度区间：165℃-145℃温区，145℃-140℃温区，140℃-85℃温区，85℃-55℃温区，55℃-25℃温区。The fourth step is to divide the original temperature range. According to step 3) the corrected inlet and outlet temperatures of the intercooler and hot fluid are divided into five temperature ranges in the order from high temperature to low temperature: 165°C-145°C temperature zone, 145°C-140°C temperature zone, 140°C- 85°C temperature zone, 85°C-55°C temperature zone, 55°C-25°C temperature zone.

第五步，计算各温区内的可用热量。对步骤4)所划分的每一温度区间，基于流体真实的温焓关系，参照公式(3)-公式(7)，计算各个温度区间内可用热量随温度的数值变化关系。以140℃-85℃温区为例，图1给出了140℃-85℃温区可用热量随温度的变化关系图。The fifth step is to calculate the available heat in each temperature zone. For each temperature interval divided by step 4), based on the real temperature-enthalpy relationship of the fluid, refer to formula (3)-formula (7), and calculate the relationship between the available heat and the temperature in each temperature interval. Taking the 140°C-85°C temperature zone as an example, Figure 1 shows the relationship between the available heat and the temperature in the 140°C-85°C temperature zone.

第六步，判断各个温度区间内是否存在热流方向的转折。在本实施例中，140℃-85℃温区和55℃-25℃温区，这两个温区的热流受到了非线性流体的影响，分别出现了可用热量的极值点，这2个极值点对应的温度分别为126.1℃和27.79℃。以140℃-85℃温区为例，图1给出了140℃-85℃温区可用热量随温度的变化关系图，在140℃-126.1℃范围内，可用热量随温度的下降逐渐增加；而在126.1℃-85℃范围内，可用热量随温度的下降逐渐减少；126.1℃为极值点。The sixth step is to determine whether there is a turning point in the direction of heat flow in each temperature range. In this example, the temperature zone of 140°C-85°C and the temperature zone of 55°C-25°C, the heat flow in these two temperature zones is affected by the nonlinear fluid, and the extreme points of available heat appear respectively. The temperatures corresponding to the extreme points are 126.1°C and 27.79°C, respectively. Taking the 140°C-85°C temperature zone as an example, Figure 1 shows the relationship between the available heat and the temperature in the 140°C-85°C temperature zone. In the range of 140°C-126.1°C, the available heat gradually increases with the temperature drop; In the range of 126.1°C-85°C, the available heat gradually decreases with the decrease of temperature; 126.1°C is the extreme point.

第七步，重新划分温度区间。将步骤4)中所有原始温区的温度端点与步骤6)找到的极值点相对应的温度点合并在一起，按从高温到低温的顺序重新划分为7个温度区间：165℃-145℃温区，145℃-140℃温区，140℃-126.1℃温区，126.1℃-85℃温区，85℃-55℃温区，55℃-27.79℃温区，27.79℃-25℃温区。The seventh step is to redefine the temperature range. Combine the temperature endpoints of all original temperature zones in step 4) and the temperature points corresponding to the extreme points found in step 6), and re-divide them into 7 temperature ranges in the order from high temperature to low temperature: 165°C-145°C Temperature zone, 145°C-140°C temperature zone, 140°C-126.1°C temperature zone, 126.1°C-85°C temperature zone, 85°C-55°C temperature zone, 55°C-27.79°C temperature zone, 27.79°C-25°C temperature zone .

第八步，重新计算每个温度区间的可用热量。在步骤7)新划分的温度区间的基础上，根据公式(3)-公式(7)，重新计算所有温度区间内的可用热量，计算结果如表3所示。Step eight, recalculate the available heat for each temperature range. On the basis of the newly divided temperature intervals in step 7), the available heat in all temperature intervals is recalculated according to formula (3)-formula (7), and the calculation results are shown in Table 3.

第九步，计算各温区的累积热流量。在步骤7)所划分的每一温度区间，参照公式(8)，计算每个温度区间可以传递到下一个温度区间的累积热流量，计算结果如表3所示。图2给出了基于流体实际物性从高温区到低温区的累积热流量图。The ninth step is to calculate the cumulative heat flow of each temperature zone. For each temperature interval divided in step 7), refer to formula (8) to calculate the cumulative heat flow that can be transferred from each temperature interval to the next temperature interval. The calculation results are shown in Table 3. Figure 2 shows the cumulative heat flow diagram from the high temperature region to the low temperature region based on the actual physical properties of the fluid.

表1Table 1

表2Table 2

表3table 3

传统夹点法假设所有流体的比热容为常数，作为对比，图3给出了采用传统方法得到的从高温区到低温区的累积热流量的分布情况。在传统方法的计算过程中，由于未考虑流体的非线性温焓关系对局部温度区间内的可用热量和累积热流量的改变作用，错误地估计了换热网络的热流量。The traditional pinch method assumes that the specific heat capacity of all fluids is constant. As a comparison, Figure 3 shows the distribution of the cumulative heat flow from the high temperature area to the low temperature area obtained by the traditional method. In the calculation process of the traditional method, the heat flow of the heat exchange network is wrongly estimated because the nonlinear temperature-enthalpy relationship of the fluid does not consider the change of the available heat and the cumulative heat flow in the local temperature range.

上述实施例用来解释说明本发明，而不是对本发明进行限制，在本发明的精神和权利要求的保护范围内，对本发明做出的任何修改和改变，都落入本发明的保护范围。The above-mentioned embodiments are used to illustrate the present invention, rather than to limit the present invention. Within the spirit of the present invention and the protection scope of the claims, any modification and change made to the present invention will fall into the protection scope of the present invention.

Claims (1)

1.一种包含非等温相变流体的换热网络热流量的确定方法，其特征在于：所述方法包括以下步骤：1. A method for determining heat flow in a heat exchange network comprising a non-isothermal phase change fluid, characterized in that: the method comprises the following steps: 1)提取流体的工艺参数和物性数据1) Extract the process parameters and physical property data of the fluid 物流的工艺参数和物性数据包括：组成，流量，进口温度Tin，出口温度Tout，焓和比热容，采用流体实际的温焓物性关系；The process parameters and physical property data of logistics include: composition, flow rate, inlet temperature T in , outlet temperature T out , enthalpy and specific heat capacity, using the actual temperature-enthalpy physical property relationship of the fluid; 2)设置换热网络的最小传热温差ΔTmin 2) Set the minimum heat transfer temperature difference ΔT min of the heat exchange network 3)进行冷、热流体温度修正3) Perform cold and hot fluid temperature correction 将冷流体的温度升高ΔTmin/2，将每股热流体的温度降低ΔTmin/2，从而确保热流体的温度高于冷流体的温度，并满足最小传热温差ΔTmin的要求，冷、热流体温度修正分别参照公式(1)-(2)：Increase the temperature of the cold fluid by ΔT min /2, and decrease the temperature of each hot fluid by ΔT min /2, so as to ensure that the temperature of the hot fluid is higher than the temperature of the cold fluid, and meet the minimum heat transfer temperature difference ΔT min requirement, the cold , thermal fluid temperature correction respectively refer to the formula (1)-(2): TT CC ,, jj ** == TT CC ,, jj ++ ΔΔ TT minmin // 22 -- -- -- (( 11 )) TT Hh ,, ii ** == TT Hh ,, ii -- ΔΔ TT minmin // 22 -- -- -- (( 22 )) 在式(1)-(2)中，ΔTmin为步骤2)指定的最小传热温差；TH,i和TC,j分别为热流股i和冷流股j的实际温度；T* H,i和T* C,j分别为热流股i和冷流股j进行温度修正之后的温度；In formulas (1)-(2), ΔT min is the minimum heat transfer temperature difference specified in step 2); T H,i and T C,j are the actual temperatures of hot stream i and cold stream j respectively; T * H ,i and T * C,j are the temperature after temperature correction of hot stream i and cold stream j respectively; 4)划分原始温度区间4) Divide the original temperature range 以步骤3)中冷、热流体修正之后的进、出口温度为依据，划分温度区间，将所有冷、热流体经步骤3)修正之后的进口温度和出口温度按从高到低的顺序排列，记为：T1、T2、…、TN1、TN1+1，其中N1+1为温度端点的个数，所划分的温区个数为N1，温区编号从1到N1，第k个温区[Tk，Tk+1]以温度范围Tk+1到Tk定义，且Tk＞Tk+1；Based on the corrected inlet and outlet temperatures of the cold and hot fluids in step 3), divide the temperature range, and arrange the inlet and outlet temperatures of all the cold and hot fluids after the correction in step 3) in order from high to low, Recorded as: T 1 , T 2 ,..., T N1 , T N1+1 , where N1+1 is the number of temperature endpoints, the number of divided temperature zones is N1, and the number of temperature zones is from 1 to N1, the kth A temperature zone [T k , T k+1 ] is defined by the temperature range T k+1 to T k , and T k >T k+1 ; 5)计算各温区内的可用热量5) Calculate the available heat in each temperature zone 在步骤4)所划分的每一温度区间，根据热力学第一定律，基于流体真实的温焓关系，计算各个温度区间内可用热量随温度的数值变化关系，参照公式(3)-公式(7)：In each temperature interval divided by step 4), according to the first law of thermodynamics, based on the real temperature-enthalpy relationship of the fluid, the relationship between the available heat in each temperature interval and the numerical change of temperature is calculated, referring to formula (3) - formula (7) : QQ kk (( TT )) == ΣΣ ii ∈∈ {{ hothot }} kk (( Hh ii (( TT kk hh )) -- Hh ii (( TT hh )) )) -- ΣΣ jj ∈∈ {{ coldcold }} kk (( Hh jj (( TT kk cc )) -- Hh jj (( TT cc )) )) -- -- -- (( 33 )) TT kk hh == TT kk ++ ΔΔ TT minmin // 22 -- -- -- (( 44 )) TT kk cc == TT kk -- ΔΔ TT minmin // 22 -- -- -- (( 55 )) Th＝T+ΔTmin/2          (6)T h =T+ΔT min /2 (6) Tc＝T-ΔTmin/2          (7)T c =T-ΔT min /2 (7) 在式(3)-(7)中，Qk(T)为第k个温度区间内的可用热量，可用热量的大小随温度T变化；温度T∈[Tk+1,Tk]；{hot}k代表第k个温度区间内所有的热流股构成的热流体集；{cold}k代表第k个温度区间内所有的冷流股构成的冷流体集；k＝1,2,3,…,N1；流体的焓H为温度和流量的函数；为热流体i在温度处的焓，温度由公式(4)计算；Hi(Th)为热流体i在温度Th处的焓，温度Th由公式(6)计算；为冷流体j在温度处的焓，温度由公式(5)计算；Hj(Tc)为冷流体j在温度Tc处的焓，温度Tc由公式(7)计算；In formulas (3)-(7), Q k (T) is the available heat in the kth temperature interval, and the size of the available heat varies with temperature T; temperature T∈[T k+1 ,T k ]; { hot} k represents the hot fluid set composed of all the hot streams in the kth temperature interval; {cold} k represents the cold fluid set composed of all the cold streams in the kth temperature interval; k=1,2,3, ..., N1; the enthalpy H of the fluid is a function of temperature and flow; is the thermal fluid i at temperature Enthalpy at temperature Calculated by formula (4); H i (T h ) is the enthalpy of thermal fluid i at temperature T h , and temperature T h is calculated by formula (6); is the cold fluid j at temperature Enthalpy at temperature Calculated by formula (5); H j (T c ) is the enthalpy of cold fluid j at temperature T c , and temperature T c is calculated by formula (7); 6)判断各个温度区间内是否存在热流方向的转折6) Judging whether there is a turning point in the direction of heat flow in each temperature range 利用步骤5)得到的各个温度区间内可用热量随温度的数值变化关系，寻找各个温区可用热量的极值点，极值点是指可用热量随温度的变化关系发生了改变，从温区1到温区N1，分别找出每个温区内所有的可用热量的极值点；Using the relationship between available heat and temperature in each temperature range obtained in step 5), find the extreme point of available heat in each temperature zone. The extreme point refers to the change in the relationship between available heat and temperature. From temperature zone 1 To the temperature zone N1, find out the extreme points of all available heat in each temperature zone; 7)重新划分温度区间7) Re-divide the temperature range 将步骤4)中所有原始温区的温度端点与步骤6)找到的极值点相对应的温度点合并在一起，按从高温到低温的顺序排列，重新划分温度区间，温区个数记为N2，温度区间端点数为N2+1；Merge the temperature endpoints of all original temperature zones in step 4) with the temperature points corresponding to the extreme points found in step 6), arrange them in the order from high temperature to low temperature, re-divide the temperature range, and record the number of temperature zones as N2, the number of endpoints in the temperature range is N2+1; 8)重新计算每个温度区间的可用热量8) Recalculate the available heat for each temperature interval 在步骤7)新划分的温度区间的基础上，根据公式(3)-公式(7)，重新计算所有温度区间内的可用热量；On the basis of the newly divided temperature intervals in step 7), according to formula (3)-formula (7), recalculate the available heat in all temperature intervals; 9)计算各温区的累积热流量9) Calculate the cumulative heat flow in each temperature zone 在步骤7)所划分的每一温度区间，计算每个温度区间可以传递到下一个温度区间的累积热流量，参照公式(8)：In each temperature interval divided by step 7), calculate the cumulative heat flow that can be transferred from each temperature interval to the next temperature interval, referring to formula (8): CC kk == CC kk -- 11 ++ ΣΣ ii ∈∈ {{ hothot }} kk (( Hh ii (( TT kk hh )) -- Hh ii (( TT kk ++ 11 hh )) )) -- ΣΣ jj ∈∈ {{ coldcold }} kk (( Hh jj (( TT kk cc )) -- Hh jj (( TT kk ++ 11 cc )) )) -- -- -- (( 88 )) 在公式(8)中，Ck为从第k个温区传递到第k+1个温区的累积热流量；C0＝0；k＝1,2,3,…,N2，根据每个温度区间的累计热流量的正负，可以判断热回收的可能性和热量传递的方向，Ck为正值，则表示从温度区间k传递到第k+1个温区的热流方向为正，即较高温区存在多余的热量可以传递给下一温区加以回收利用；Ck为负值，则表示温区k传递到第k+1个温区的热流方向为负，即该温区需要从外界吸收热量，该温区不存在多余的热量可供下一温区回收利用。In formula (8), C k is the cumulative heat flow transferred from the kth temperature zone to the k+1th temperature zone; C 0 =0; k=1,2,3,...,N2, according to each The positive or negative of the cumulative heat flow in the temperature range can determine the possibility of heat recovery and the direction of heat transfer. If C k is a positive value, it means that the direction of heat flow transferred from the temperature range k to the k+1th temperature zone is positive. That is, the excess heat in the higher temperature zone can be transferred to the next temperature zone for recycling; if C k is negative, it means that the heat flow direction of the temperature zone k transferred to the k+1th temperature zone is negative, that is, the temperature zone needs Heat is absorbed from the outside, and there is no excess heat in this temperature zone for recycling in the next temperature zone.
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