Method for recycling industrial low-temperature waste heat for multi-cycle cooling system
阅读说明：本技术 一种工业低温余热回收用于多周期供冷系统的方法 (Method for recycling industrial low-temperature waste heat for multi-cycle cooling system ) 是由 高为 周宇昊 张海珍 王世朋 阮慧锋 郑梦超 张凌玮 王彧斐 于 2020-01-19 设计创作，主要内容包括：本发明公开了一种工业低温余热回收用于多周期供冷系统的方法,过程如下：从吸收式制冷机组流出的热水经换热器与工业余热换热后,温度升高,再回流至吸收式制冷机组内用于制冷,热水温度降低后流出吸收式制冷机组,经增压泵升压再流入所需要换热的换热器中,在进入换热器前,经过减压阀调节到对应的压力。建立相关数学模型,以制冷的年费用最小化为目标函数,以换热器、增压泵、换热后热水温度等为变量,用户冷量需求在不同季节内是不同的,建立多周期余热回收模型,运用数学规划法得到余热回收设计及各周期下的运行方式。本发明为利用工业低温余热用于多周期制冷的运用、规划和优化提供了合理的建议。(The invention discloses a method for recovering industrial low-temperature waste heat for a multi-period cooling system, which comprises the following steps: the hot water flowing out of the absorption refrigerating unit exchanges heat with industrial waste heat through the heat exchanger, the temperature is raised, the hot water flows back into the absorption refrigerating unit for refrigeration, the hot water flows out of the absorption refrigerating unit after the temperature is lowered, the hot water is boosted through the booster pump and then flows into the heat exchanger needing heat exchange, and the hot water is adjusted to the corresponding pressure through the pressure reducing valve before entering the heat exchanger. Establishing a related mathematical model, taking the annual cost minimization of refrigeration as an objective function, taking a heat exchanger, a booster pump, the temperature of hot water after heat exchange and the like as variables, and taking the cold requirement of a user as different seasons, establishing a multi-period waste heat recovery model, and obtaining waste heat recovery design and an operation mode under each period by applying a mathematical programming method. The invention provides reasonable suggestions for the application, planning and optimization of multi-cycle refrigeration by utilizing industrial low-temperature waste heat.)
1. A method for recycling industrial low-temperature waste heat to be used for a multi-period cooling system is characterized by comprising the following steps: the hot water flowing out of the absorption refrigerating unit exchanges heat with industrial waste heat through the heat exchanger, the temperature is raised, the hot water flows back into the absorption refrigerating unit for refrigeration, the hot water flows out of the absorption refrigerating unit after the temperature is lowered, the hot water is boosted through the booster pump and then flows into the heat exchanger needing heat exchange, and the hot water is adjusted to the corresponding pressure through the pressure reducing valve before entering the heat exchanger.
2. The method for industrial low-temperature waste heat recovery to be used for a multi-cycle cooling system according to claim 1, wherein a relevant mathematical model is established, an objective function is taken as the minimization of the annual cost of refrigeration, the temperature of hot water after heat exchange, a booster pump and the heat exchanger is taken as a variable, the cold requirement of a user is different in different seasons, the multi-cycle waste heat recovery model is established, and a waste heat recovery design and an operation mode under each cycle are obtained by using a mathematical programming method;
in order to realize the gradient recovery of heat, a hierarchical heat exchange network superstructure is adopted to describe the recovery of waste heat, and because the cooling load of a cold trap changes with seasons, related variables are introduced into a set S to be expressed;
Th(i, k, s) is the hot end temperature of the hot stream i in the temperature region k with a period s, Twin(s) is the inlet temperature, T, of the hot water for heat exchange at a period swout(s) is the outlet temperature, T, of the hot water for heat exchange at a period sw(k, s) is the hot end temperature of hot water in the k temperature region at the period s, mw(s) is the mass flow rate of hot water at cycle s, q (i, k, s) is the heat recovered by hot water at temperature zone k from hot stream i at cycle s, and qcu (i, s) is the cold utility load required for hot stream i at cycle s; hot water and waste heat streams meet inlet and outlet temperature constraints;
Th(i,1,s)＝Thin(i) (1)
Tw(1,s)＝Twout(s) (2)
Tw(NT+1,s)＝Twin(s) (3)
in the formula, Th(i,1, s) is the temperature at the warm end of the hot stream i in the first temperature zone, T, at a period sw(1, s) is the temperature of the hot water at the hot end of the first temperature zone at a period s, Tw(NT +1, s) is the temperature of the hot water at the cold end of the last temperature zone for period s.
The temperature of a hot water inlet and a hot water outlet for driving the circulation of the absorption refrigerating unit has an obvious linear relation, and the formula (4) can be obtained through linear fitting;
Twin(s)＝0.426·Twout(s)+52.8 (4)
the hot water and the waste heat stream satisfy heat balance equations (5) - (7);
Fh(i)·(Th(i,k,s)-Th(i,k+1,s))＝q(i,k,s) (6)
in the formula, CpwIs the specific heat capacity of water;
the existence of the heat exchanger is determined by the heat load logic constraint and the heat transfer temperature difference logic constraint;
q(i,k,s)≤zs(i,k,s)·Qh(i) (8)
dt(i,k,s)≤Th(i,k,s)-Tw(k,s)+[1-zs(i,k,s)]· (9)
dt(i,k+1,s)≤Th(i,k+1,s)-Tw(k+1,s)+[1-zs(i,k,s)]· (10)
dt(i,k)≥ΔTmin(11)
wherein zs (i, k, s) is a binary variable determining whether a heat exchanger between a temperature zone k and a hot material flow i exists for hot water under a period s, dt (i, k, s) and dt (i, k +1, s) are heat transfer temperature differences of the hot end and the cold end of the heat exchanger respectively, the upper limit of the heat transfer temperature difference is 250 ℃, and delta T is takenminTo minimize the temperature difference of heat transfer, take the value of Delta Tmin＝10℃；
The load on the cooler of hot stream i at period s is calculated from equation (12);
qcu(i,s)＝Fh(i)·[Th(i,NT+1,s)-Thout(i)](12)
for a heat exchanger with hot water between the temperature zone k and the hot stream i, if the heat exchanger exists for at least one period, the heat exchanger should exist;
z(i,k)≥zs(i,k,s) (13)
wherein z (i, k) is a binary variable that determines whether a heat exchanger of the hot water between temperature zone k and hot stream i is present;
the heat exchange area A required by hot water in the temperature zone k for recovering the heat of the hot material flow i under the period ses(i, k, s) are calculated from equations (14) and (15).
Aes(i,k,s)＝q(i,k,s)·[hw -1+hh(i)-1]/LMTD(i,k,s) (14)
LMTD(i,k,s)＝[dt(i,k,s)·dt(i,k+1,s)·(dt(i,k,s)+dt(i,k+1,s))/2]1/3(15)
In the formula, LMTD (i, k, s) is the logarithmic mean heat transfer temperature difference of the heat exchanger, and in order to reduce the solving difficulty, the calculation adopts a Chen approximate formula; h iswIs the heat transfer coefficient of hot water, hh(i) Is the heat transfer coefficient of the hot stream i;
for a multicycle heat exchange network, area A of the heat exchangere(i, k) taking the maximum value of the area under each period, wherein the maximum value is represented by inequality constraint, and the upper limit value of the maximum value is limited by an objective function;
Ae(i,k)≥Aes(i,k,s) (16)
for a LiBr single-effect refrigerator, under the condition that the electric energy consumed by the unit can be ignored, the relation between the refrigeration load and the input heat in each period is calculated by an expression (17);
Qcd(s)＝COP(s)·[Cp·mw(s)·(Twout(s)-Twin(s))](17)
wherein COP (coefficient of performance)(s) is the coefficient of performance of the absorption refrigeration unit at the period s, and is related to the temperature of hot water entering the absorption refrigeration unit; COP(s) and Twout(s) is not linear, and the piecewise linear fit result is shown in the following formula (18);
3. the method for industrial low-temperature waste heat recovery for a multi-cycle cooling system according to claim 1, wherein the hot water is divided into a plurality of streams in the kth temperature zone to exchange heat with a plurality of waste heat streams, and the pressure drop of each hot water branch is equal in a stable flowing state; however, the distances from the waste heat streams i to the absorption refrigeration unit are unequal, so that the pressure caused by the distances during individual conveying is reducedHead loss Hf,branch(i) Not equal, therefore total head loss H in the kth temperature zonef,total(k, s) should be H for each branchf,branch(i) Is represented by an inequality constraint, the upper limit value of which is limited by an objective function, as shown in equation (19);
Hf,total(k,s)≥zs(i,k,s)·Hf,branch(i) (19)
for Hf,branch(i) A smaller branch, in order to ensure that the hot water flow of the branch is not changed, an additional head loss H is added through a pressure reducing valvef,valve(i, k, s) such that the head loss of the branch is equal to Hf,total(k,s)；
Hf,valve(i,k,s)＝Hf,total(k,s)-Hf,branch(i) (20)。
Technical Field
The invention relates to a method for using industrial low-temperature waste heat recovery for a multi-cycle cooling system, and belongs to a waste heat and waste heat recovery optimization method.
Background
In 2018, China, as a major industrial product producing country, has total social energy consumption of about 46.4 hundred million tons of standard coal, wherein the industrial energy consumption accounts for about 70 percent of the total social energy consumption. Due to the limitation of energy requirement of the process, the industrial production process has a large amount of medium-low temperature industrial waste heat, wherein the total amount of waste heat available for town heat supply in northern areas is about equal to 1 hundred million tons of standard coal. Meanwhile, a large amount of fossil fuel is combusted to generate high-quality energy so as to meet the energy demand of urban buildings. If industrial low-temperature waste heat can be effectively utilized in urban heating and cooling, the consumption of fossil fuels and the emission of greenhouse gases can be reduced, and the utilization efficiency of energy sources is improved. There have been some current studies on integrating low temperature waste heat into district heating systems, however, there are few studies on combining low temperature waste heat recovery with district cooling; second, most studies do not take into account seasonal fluctuations in user demand.
Meanwhile, the air conditioner in the extremely hot period in summer in China has high power load demand, the phenomenon of switching off and power limiting still exists in partial areas, and the power supply quality cannot be guaranteed. At present, the electric load of the air conditioner becomes one of the main reasons for the continuous increase of the peak load and the peak-valley difference of the power grid in winter and summer. In commercial buildings, the air conditioning consumes up to 30-60% of the total energy. The power consumption mode causes great increase of load pressure of a power grid in summer and difficult peak regulation, and seriously threatens the safety and stability of the operation of the power grid. In recent years, regional cooling techniques have been considered and developed that use energy stations to concentrate cooling and deliver the cooling to surrounding users. The refrigeration mode of the central cooling equipment can be divided into compression refrigeration and absorption refrigeration, and compared with the compression refrigeration mainly driven by electricity, the absorption refrigeration can drive the operation of the refrigeration cycle by utilizing low-temperature waste heat resources, so that the utilization efficiency of energy is improved, and the absorption refrigeration technology has stronger attraction in regional cold supply.
The invention aims to provide the heat required by the absorption refrigerator by recovering the industrial low-temperature waste heat so as to meet the cold quantity requirement of users. The main work is to establish a relevant mathematical model, minimize the annual cost of refrigeration as an objective function, and determine the waste heat recovery scheme under the known refrigeration requirement by using a mathematical programming method. The demand of the building for cooling capacity is changed with seasons, so that a multi-period description is added into the model, and system operation optimization under different periods is considered.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a method for recovering industrial low-temperature waste heat for a multi-cycle cooling system.
The technical scheme adopted by the invention for solving the problems is as follows: a method for recycling industrial low-temperature waste heat to be used for a multi-period cooling system is characterized by comprising the following steps: the hot water flowing out of the absorption refrigerating unit exchanges heat with industrial waste heat through the heat exchanger, the temperature is raised, the hot water flows back into the absorption refrigerating unit for refrigeration, the hot water flows out of the absorption refrigerating unit after the temperature is lowered, the hot water is boosted through the booster pump and then flows into the heat exchanger needing heat exchange, and the hot water is adjusted to the corresponding pressure through the pressure reducing valve before entering the heat exchanger.
Further, a related mathematical model is established, the annual cost of refrigeration is minimized to serve as a target function, the temperature of the heat exchanger, the booster pump, the hot water after heat exchange and the like are taken as variables, the cold quantity requirements of users are different in different seasons, a multi-cycle waste heat recovery model is established, and a waste heat recovery design and an operation mode under each cycle are obtained by applying a mathematical programming method;
in order to realize the gradient recovery of heat, a hierarchical heat exchange network superstructure is adopted to describe the recovery of waste heat, and because the cooling load of a cold trap changes with seasons, a set S is required to be introduced to represent relevant variables;
Th(i, k, s) is the hot end temperature of the hot stream i in the temperature region k with a period s, Twin(s) is the inlet temperature, T, of the hot water for heat exchange at a period swout(s) is the outlet temperature, T, of the hot water for heat exchange at a period sw(k, s) is the hot end temperature of hot water in the k temperature region at the period s, mw(s) is the mass flow rate of hot water at cycle s, q (i, k, s) is the heat recovered by hot water at temperature zone k from hot stream i at cycle s, and qcu (i, s) is the cold utility load required for hot stream i at cycle s; hot water and waste heat streams need to meet inlet and outlet temperature constraints;
Th(i,1,s)＝Thin(i) (1)
Tw(1,s)＝Twout(s) (2)
Tw(NT+1,s)＝Twin(s) (3)
in the formula, Th(i,1, s) is the temperature at the warm end of the hot stream i in the first temperature zone, T, at a period sw(1, s) is the temperature of the hot water at the hot end of the first temperature zone at a period s, Tw(NT +1, s) is the temperature of the hot water at the cold end of the last temperature zone for period s.
The temperature of a hot water inlet and a hot water outlet for driving the circulation of the absorption refrigerating unit has an obvious linear relation, and the formula (4) can be obtained through linear fitting;
Twin(s)＝0.426·Twout(s)+52.8 (4)
the hot water and the waste heat stream satisfy heat balance equations (5) - (7);
Fh(i)·(Th(i,k,s)-Th(i,k+1,s))＝q(i,k,s) (6)
in the formula, CpwIs the specific heat capacity of water;
the presence or absence of a heat exchanger can be determined by thermal load logical constraints and heat transfer temperature difference logical constraints;
q(i,k,s)≤zs(i,k,s)·Qh(i) (8)
dt(i,k,s)≤Th(i,k,s)-Tw(k,s)+[1-zs(i,k,s)]· (9)
dt(i,k+1,s)≤Th(i,k+1,s)-Tw(k+1,s)+[1-zs(i,k,s)]· (10)
dt(i,k)≥ΔTmin(11)
wherein zs (i, k, s) is a binary variable determining whether a heat exchanger between a temperature zone k and a hot material flow i exists for hot water under a period s, dt (i, k, s) and dt (i, k +1, s) are heat transfer temperature differences of the hot end and the cold end of the heat exchanger respectively, the upper limit of the heat transfer temperature difference is 250 ℃, and delta T is takenminTo minimize the temperature difference of heat transfer, take the value of Delta Tmin＝10℃；
The load on the cooler of hot stream i at period s is calculated from equation (12);
qcu(i,s)＝Fh(i)·[Th(i,NT+1,s)-Thout(i)](12)
for a heat exchanger with hot water between the temperature zone k and the hot stream i, if the heat exchanger exists for at least one period, the heat exchanger should exist;
z(i,k)≥zs(i,k,s) (13)
wherein z (i, k) is a binary variable that determines whether a heat exchanger of the hot water between temperature zone k and hot stream i is present;
the heat exchange area A required by hot water in the temperature zone k for recovering the heat of the hot material flow i under the period ses(i, k, s) are calculated from equations (14) and (15).
Aes(i,k,s)＝q(i,k,s)·[hw -1+hh(i)-1]/LMTD(i,k,s) (14)
LMTD(i,k,s)＝[dt(i,k,s)·dt(i,k+1,s)·(dt(i,k,s)+dt(i,k+1,s))/2]1/3(15)
In the formula, LMTD (i, k, s) is the logarithmic mean heat transfer temperature difference of the heat exchanger, and in order to reduce the solving difficulty, the calculation adopts a Chen approximate formula; h iswIs the heat transfer coefficient of hot water, hh(i) Is the heat transfer coefficient of the hot stream i;
for a multicycle heat exchange network, area A of the heat exchangere(i, k) taking the maximum value of the area under each period, wherein the maximum value is represented by inequality constraint, and the upper limit value of the maximum value is limited by an objective function;
Ae(i,k)≥Aes(i,k,s) (16)
for the LiBr single-effect absorption refrigerator, under the condition that the electric energy consumed by the unit can be ignored, the relation between the refrigeration load and the input heat in each period is calculated by an equation (17);
Qcd(s)＝COP(s)·[Cp·mw(s)·(Twout(s)-Twin(s))](17)
where COP(s) is the Coefficient of performance (Coefficient of performance) of the absorption refrigeration unit at the period s, which is related to the temperature of the hot water entering the absorption refrigeration unit (i.e., T)wout(s)) related; COP(s) and Twout(s) is not linear, and the piecewise linear fit result is shown in the following formula (18);
furthermore, the hot water is divided into a plurality of strands in the kth temperature zone to exchange heat with a plurality of waste heat streams, and the pressure drop of each hot water branch is equal under the stable flowing state; however, the distances from the waste heat streams i to the absorption refrigerating unit are unequal, so that the head loss H caused by the distances during independent conveyingf,branch(i) Not equal, therefore total head loss H in the kth temperature zonef,total(k, s) should be H for each branchf,branch(i) Is represented by an inequality constraint, the upper limit value of which is limited by an objective function, as shown in equation (19);
Hf,total(k,s)≥zs(i,k,s)·Hf,branch(i) (19)
for Hf,branch(i) A smaller branch, in order to ensure that the hot water flow of the branch is not changed, an additional head loss H is added through a pressure reducing valvef,valve(i, k, s) such that the head loss of the branch is equal to Hf,total(k,s)；
Hf,valve(i,k,s)＝Hf,total(k,s)-Hf,branch(i) (20)
Compared with the prior art, the invention has the following advantages and effects: the absorption refrigerating unit is driven to refrigerate by recycling industrial low-temperature waste heat, and the absorption refrigerating unit has considerable application prospect in the large environment of developing regional cooling. And solving the MINLP model to obtain a waste heat recovery scheme under each period. When the refrigeration capacity is reduced, the number of streams participating in heat recovery is reduced and some heat exchangers can be shut down. On the premise of meeting the heat demand, the hot water preferentially recovers the heat of the waste heat stream close to the absorption refrigerating unit, so that the pump cost is reduced, and the annual cost of a factory is minimized. Therefore, the invention can save energy and simultaneously can minimize project operation cost and total investment.
Drawings
Fig. 1 is a schematic flow chart of industrial low-temperature waste heat recovery for cooling in the embodiment of the invention.
Fig. 2 is a block diagram of a multi-cycle waste heat recovery system in an embodiment of the present invention.
FIG. 3 is a schematic diagram of a hierarchical superstructure of a heat exchange network in an embodiment of the invention.
Fig. 4 is a diagram of a spring/autumn waste heat recovery scheme in an embodiment of the invention.
FIG. 5 is a diagram of a summer waste heat recovery scheme in an embodiment of the invention.
Fig. 6 is a diagram of a winter waste heat recovery scheme in an embodiment of the invention.
In the figure: the system comprises a heat exchanger 1, a booster pump 2, an absorption refrigerating unit 3, industrial waste heat 4 and a pressure reducing valve 5.
Detailed Description
The present invention will be described in further detail below by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting the present invention.
As shown in fig. 1, in this embodiment, a method for recovering industrial low-temperature waste heat for a multi-cycle cooling system includes the following processes: hot water flowing out of the absorption refrigerating unit 3 exchanges heat with industrial waste heat 4 through the heat exchanger 1, the temperature is raised, the hot water flows back into the absorption refrigerating unit 3 for refrigeration, the hot water flows out of the absorption refrigerating unit 3 after the temperature is lowered, the hot water is boosted through the booster pump 2 and then flows into the heat exchanger 1 needing heat exchange, and the hot water is adjusted to corresponding pressure through the pressure reducing valve 5 before entering the heat exchanger 1.
Establishing a related mathematical model, taking the annual cost minimization of refrigeration as an objective function, taking the temperature of hot water after heat exchange and the like of a heat exchanger 1, a booster pump 2 and a heat exchanger as variables, and taking the cold quantity requirements of users to be different in different seasons, establishing a multi-period waste heat recovery model, and obtaining waste heat recovery design and an operation mode under each period by applying a mathematical programming method;
in order to realize the gradient recovery of heat, a hierarchical heat exchange network superstructure is adopted to describe the recovery of waste heat, and because the cooling load of a cold trap changes with seasons, a set S is required to be introduced to represent relevant variables;
Th(i, k, s) is the hot end temperature of the hot stream i in the temperature region k with a period s, Twin(s) is the inlet temperature, T, of the hot water for heat exchange at a period swout(s) is the outlet temperature, T, of the hot water for heat exchange at a period sw(k, s) is the hot end temperature of hot water in the k temperature region at the period s, mw(s) is the mass flow rate of hot water at cycle s, q (i, k, s) is the heat recovered by hot water at temperature zone k from hot stream i at cycle s, and qcu (i, s) is the cold utility load required for hot stream i at cycle s; hot water and waste heat streams need to meet inlet and outlet temperature constraints;
Th(i,1,s)＝Thin(i) (1)
Tw(1,s)＝Twout(s) (2)
Tw(NT+1,s)＝Twin(s) (3)
in the formula, Th(i,1, s) is the temperature at the warm end of the hot stream i in the first temperature zone, T, at a period sw(1, s) is the temperature of the hot water at the hot end of the first temperature zone at a period s, Tw(NT +1, s) is the temperature of the hot water at the cold end of the last temperature zone for period s.
The temperature of a hot water inlet and a hot water outlet for driving the circulation of the absorption refrigerating unit 3 has an obvious linear relation, and the formula (4) can be obtained through linear fitting;
Twin(s)＝0.426·Twout(s)+52.8 (4)
the hot water and the waste heat stream satisfy heat balance equations (5) - (7);
Fh(i)·(Th(i,k,s)-Th(i,k+1,s))＝q(i,k,s) (6)
in the formula, CpwIs the specific heat capacity of water;
the presence or absence of the heat exchanger 1 can be determined by the thermal load logical constraint and the heat transfer temperature difference logical constraint;
q(i,k,s)≤zs(i,k,s)·Qh(i) (8)
dt(i,k,s)≤Th(i,k,s)-Tw(k,s)+[1-zs(i,k,s)]· (9)
dt(i,k+1,s)≤Th(i,k+1,s)-Tw(k+1,s)+[1-zs(i,k,s)]· (10)
dt(i,k)≥ΔTmin(11)
wherein zs (i, k, s) is a binary variable determining whether hot water exists in the heat exchanger 1 between the temperature zone k and the hot material flow i under the period s, dt (i, k, s) and dt (i, k +1, s) are respectively heat transfer temperature differences of the hot end and the cold end of the heat exchanger 1, the upper limit of the heat transfer temperature difference is 250 ℃, and delta T is takenminTo minimize the temperature difference of heat transfer, take the value of Delta Tmin＝10℃；
The load on the cooler of hot stream i at period s is calculated from equation (12);
qcu(i,s)＝Fh(i)·[Th(i,NT+1,s)-Thout(i)](12)
for a heat exchanger 1 in which hot water is between a temperature zone k and a hot stream i, if the heat exchanger 1 exists for at least one period, the heat exchanger 1 should exist;
z(i,k)≥zs(i,k,s) (13)
wherein z (i, k) is a binary variable determining the presence of hot water in the heat exchanger 1 between the temperature zone k and the hot stream i;
the heat exchange area A required by hot water in the temperature zone k for recovering the heat of the hot material flow i under the period ses(i, k, s) are calculated from equations (14) and (15).
Aes(i,k,s)＝q(i,k,s)·[hw -1+hh(i)-1]/LMTD(i,k,s) (14)
LMTD(i,k,s)＝[dt(i,k,s)·dt(i,k+1,s)·(dt(i,k,s)+dt(i,k+1,s))/2]1/3(15)
In the formula, LMTD (i, k, s) is the logarithmic mean heat transfer temperature difference of the heat exchanger 1, and in order to reduce the solving difficulty, the calculation adopts a Chen approximate formula; h iswIs the heat transfer coefficient of hot water, hh(i) Is the heat transfer coefficient of the hot stream i;
area A of Heat exchanger 1 for a multicycle Heat exchange networke(i, k) taking the maximum value of the area under each period, wherein the maximum value is represented by inequality constraint, and the upper limit value of the maximum value is limited by an objective function;
Ae(i,k)≥Aes(i,k,s) (16)
for the LiBr single-effect absorption refrigerator, under the condition that the electric energy consumed by the unit can be ignored, the relation between the refrigeration load and the input heat in each period is calculated by an equation (17);
Qcd(s)＝COP(s)·[Cp·mw(s)·(Twout(s)-Twin(s))](17)
where cop(s) is the Coefficient of performance (coeffient of performance) of the absorption refrigeration unit 3 at the period s, which is related to the temperature of the hot water entering the absorption refrigeration unit 3 (i.e., T; (T))wout(s)) related; COP(s) and Twout(s) is not linear, and the piecewise linear fit result is shown in the following formula (18);
the hot water is divided into a plurality of strands in the kth temperature zone to be mixed with a plurality of waste heat streamsPerforming heat exchange, wherein the pressure drop of each hot water branch is equal under the stable flowing state; however, the distances from the waste heat streams i to the absorption refrigerating unit 3 are unequal, so that the head loss H caused by the distances during the independent conveying processf,branch(i) Not equal, therefore total head loss H in the kth temperature zonef,total(k, s) should be H for each branchf,branch(i) Is represented by an inequality constraint, the upper limit value of which is limited by an objective function, as shown in equation (19);
Hf,total(k,s)≥zs(i,k,s)·Hf,branch(i) (19)
for Hf,branch(i) A smaller branch, in order to ensure that the hot water flow of the branch is not changed, an additional head loss H is added through the pressure reducing valve 5f,valve(i, k, s) such that the head loss of the branch is equal to Hf,total(k,s)；
Hf,valve(i,k,s)＝Hf,total(k,s)-Hf,branch(i) (20)
Based on the mixed integer nonlinear programming (MINLP) model, the required refrigeration requirement for each period of a certain hospital is known as shown in table 2. The data relating to the waste heat stream of the plant are shown in table 1.
Table 1 residual heat stream data
TABLE 2 refrigerating capacity data sheet
The values of the relevant parameters involved in each equation are as follows: cpw＝4.2kJ·kg-1·℃-1，hw＝1.8kW·m-2·℃-1，hh(i)＝2.0kW·m-2·℃-1，g＝9.81N/kg，Af＝0.264，α＝11000$，β＝150$·m-2，γ＝1。a＝8600，b＝7310，c＝0.2，uce＝0.1$·kWh-1，η＝0.7。
The TAC' and the cost are shown in the table 3, and the waste heat recovery scheme under each period is shown in the figures 4-6.
TABLE 3 data sheet of the results of the solution
From the above, on the premise of meeting the heat demand, the hot water should preferentially recover the heat of the waste heat stream close to the refrigerating unit, so that the pump cost is reduced, and the annual cost of the energy station is minimized. The result of economic evaluation shows that the energy station undertakes the cooling task of the hospital, although the cost of a refrigerator, a heat exchanger, a pump and the like needs to be invested, the selling of the cooling capacity also brings certain income for the energy station. Therefore, the industrial low-temperature waste heat is recycled for absorption refrigeration, so that the energy-saving and environment-friendly refrigeration system not only can save energy, but also brings certain economic benefit for the energy station.
Those not described in detail in this specification are well within the skill of the art.
Although the present invention has been described with reference to the above embodiments, it should be understood that the scope of the present invention is not limited thereto, and that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention.