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First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler
Energy Conversion and Management xxx (2015) xxx–xxx
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Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler Goran D. Vucˇkovic´ ⇑, Mirko M. Stojiljkovic´, Mic´a V. Vukic´ University of Niš, Faculty of Mechanical Engineering in Niš, 14 Aleksandra Medvedeva St., Niš, Serbia
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Exergy destruction Advanced exergy analysis Splitting Boiler
a b s t r a c t When complex energy systems are analyzed and when a large number of their components is observed, the destruction of exergy related to a single component is dependent on its own properties, but also on the characteristics of other components. The advanced exergy analysis is useful for providing supplementary information on the interaction between the components. It also exposes the real improvement potential related to each component of a system, but also of a system as a whole. In this paper, an existing complex industrial plant with 33 components and 70 streams is analyzed using the first and second level of exergy destruction splitting for the boiler, as a main plant component from the aspect of destroying the useful work. From the total unavoidable exergy destruction 97.28% comes from the internal irreversibility, 2.72% comes from the irreversibilities of other components, while 95.26% of the unavoidable exergy destruction (186.49 kW) comes from the internal irreversibility, and 4.74% from the external irreversibility. The final result of the advanced exergy analysis for the steam generator is the total value of the avoidable exergy destruction as a real potential that can be avoided. It is 16.19% of the total exergy destruction of the component. That is less than the data obtained in the first decomposition level (186.49 kW) merely due to the existence of mexogenous exergy destruction. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction and background In 2013, the total world fuel consumption was 12,730.4 Mtoe, consisting of: 4185.1 Mtoe of oil (32.9%), 3826.7 Mtoe of coal (30.1%), 3020.4 Mtoe of natural gas (23.7%), 855.8 Mtoe of hydro-electricity (6.7%), 563.2 Mtoe of nuclear energy (4.4%) and 279.3 Mtoe of renewable energy (2.2%) [1]. According to Ref. [2], nearly 45% of global electricity generation originates from coal, about 20% from natural gas and 15% from nuclear energy. Significant amounts of fossil fuels consumption in industry are used for steam generation. Boilers are the components often exploited to convert the chemical energy of fuel to heat necessary for steam and electricity production. That is why the improvements of boilers energy efficiency are very important, even by just a small fraction. The destruction of exergy of a single component of an energy system depends on its own properties, but also on the inefficiencies related to other components of the system it is a part of. The conventional exergy analysis quantifies the irreversibilities related ⇑ Corresponding author. Tel.: +381 63402919. E-mail addresses: [email protected] (G.D. Vucˇkovic´), mirko.stojiljkovic@ masfak.ni.ac.rs (M.M. Stojiljkovic´), [email protected] (M.V. Vukic´).
to a certain component of an energy system. However, it does not provide any information on the origin of the irreversibilities or the potential to avoid them. For that reason, the total exergy destruction can be split into parts in the advanced exergy analysis. In one approach, the total exergy destruction of a component can be separated into the part which can be avoided, therefore called ‘‘avoidable’’, and the part which cannot be avoided, named ‘‘unavoidable’’. According to the other approach, the total exergy destruction of a component is divided into the endogenous and exogenous parts of exergy destruction. In the second level of exergy destruction splitting in the advanced exergy analysis, combining the two previous approaches enhances an exergy analysis and improves the quality of the conclusions [3]. Morosuk and Tsatsaronis [3] suggested the methodology for the calculation of the parts of exergy destruction applying the advanced exergy analysis. This approach is illustrated with an example of a simple gas-turbine system revealing the improvement possibilities and the interactions among the components of the system. Kelly [4] proposed the approach to determine the endogenous part of exergy destruction based on the structural theory. Tsatsaronis and Morosuk [5] showed a detailed exergy analysis of a co-generation concept combining liquefied natural gas (LNG) regasification with power generation. Açikkalp
http://dx.doi.org/10.1016/j.enconman.2015.06.001 0196-8904/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
2
Nomenclature E_ n p Q_ T yD
exergy flow rate (kW) total number of system components pressure (bar) rate of heat transfer (kW) temperature (K) exergy destruction ratio
Greek letters D difference e exergetic efficiency g thermal efficiency Subscripts D destruction F fuel j stream of matter k system component
et al. [6] applied the advanced exergy analysis to an electricity-generating facility using natural gas. They determined the actual potential for system improvements and the relationships between the components. They provided suggestions for increasing system efficiency. The highest exergy destruction rate is found at the combustion chamber because chemical reactions are significant sources of irreversibilities. Morosuk and Tsatsaronis [7] analyzed the improvement potential and the interactions among components in LNG-based cogeneration systems and showed the advantages of the advanced exergy analysis over the conventional one. It is demonstrated that the advanced analysis produces more reliable and detailed results, and leads toward a better understanding of the interactions between components and the possibilities for improvement. In [8], the authors studied the effect of the properties of the working fluids for compression refrigeration machines on the results of advanced exergy analysis. Hepbasli and Keçebasß [9] evaluated exergy destructions of a geothermal district heating system (GDHS) as a real case study using both conventional and advanced exergetic analysis methods to identify the potential for improvement and the interactions among the components. The highest priority for improvement in the advanced exergetic analysis is in the re-injection pump, while it is the heat exchanger in the conventional analysis. Gungor et al. [10] analyzed a gas engine heat pump (GEHP) for food drying processes using both conventional and advanced exergy analyses. For each system component, avoidable and unavoidable exergy destructions, modified exergy efficiency values and modified exergy destruction ratios were determined. Erbay and Hepbasli [11] evaluated the performance of a ground-source heat pump (GSHP) for drying processes in food industry using both conventional and advanced exergy analysis. The results indicate that the most important system component from the design standpoint is the condenser. The inefficiencies within the compressor could particularly be improved by structural improvements of the overall system and the remaining system components. Boilers are certainly among the most important components of industrial energy systems, since they convert fuel energy to heat required for the technological process. However, boilers and combustion chambers are usually the components of energy systems with the highest exergy destruction values caused by exothermic chemical reactions [12]. Mahamud et al. [12] used the exergy analysis of a power plant to identify the areas where the most of the useful energy is lost and
L P tot
loss product overall system
Superscripts AV avoidable EN endogenous EX exogenous max maximal min minimal MX mexogenous r system component (different of k) UN unavoidable 0 saturated liquid 00 saturated vapor ⁄ total values R sum of values
discussed the potential for the improvement of plant energy efficiency. They showed that the boiler of a subcritical power generation plant is the major source of the useful energy lost. Only negligible amounts of useful waste energy could be recovered by implementing a heat recovery system. Wang et al. [13] presented the application of both conventional and advanced exergy analyses to a supercritical coal-fired power plant. Among other things, the results show that the boiler subsystem is proven to have a large amount of exergy destruction caused by the irreversibilities within the remaining components of the overall system. It is also found that the boiler subsystem still has the largest avoidable exergy destruction. However, the enhancement efforts should focus not only on its inherent irreversibilities but also on the inefficiencies within the remaining components. Pal et al. [14] showed the First and the Second Law of Thermodynamics based analysis of the boiler and the turbine that are the components of a coal-fired thermal power plant. Again, the boiler has the highest value of the exergy loss, i.e. the largest related irreversibilities. Petrakopouolu et al. [15] analyzed a combined cycle power plant using both conventional and advanced exergy analyses. The highest exergy destruction is caused by the combustion chamber. Almost 87% of the total exergy destruction within this component results from the operation of the component itself (endogenous exergy destruction) and 68% of the total exergy destruction cannot be avoided (unavoidable exergy destruction). Similar to the results of the conventional analysis, the advanced analysis ranks the improvement priority of the combustion chamber first, followed by the expander and the compressor. Yang et al. [16] presented the comprehensive exergy-based evaluation of a state-of-the-art ultra-supercritical coal-fired power plant. The energy saving potentials for both the overall system and an individual component were found not to be not in accordance their exergy destructions. The boiler subsystem again has the largest exergy destruction. Performance improvement is mainly related to the reduction of the exergy destruction within the boiler. In Ref. [17], the advanced exergy analysis is applied to split the total exergy destruction to the avoidable and unavoidable parts for all the components of a complex industrial energy system. Exergoeconomic evaluation is shown as well. The results of the exergetic and exergoeconomic analysis rank the components according to their improvement potentials, with the goal to
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
enhance the exergy efficiency of the entire system. The results also show that over 92% of the total exergy destruction in the boiler cannot be avoided by applying the available technologies. Ref. [18] further splits the total exergy destruction of each component of the same complex energy system to the exogenous and endogenous parts. The results illustrate that the exergy destruction decrease in a component can be achieved by reducing the irreversibilities of that component, but also by lowering the negative impact of the other components of the system. As seen from the above studies, boilers are the components of energy systems that often have the highest values of exergy destruction. Still – to the best of the authors’ knowledge – no studies on exergy destruction splitting and assessment with the special emphasis on boilers in a complex energy system have appeared in the open literature. This is the main motivation behind performing this work, related to a deeper analysis of the boiler irreversibilities and combinational splitting of exergy destruction (second level) within the advanced exergy analysis. The realistic operational data for the boiler are observed. It is regarded as a part of the energy system with many components. This paper represents an extension of the previous work of the authors summarized in Refs. [17,18] and is related to the same industrial plant as in the previous research. It analyzes a real complex industrial plant for rubber products with an emphasis on the first and second level of exergy destruction splitting on the main component (steam boiler). The plant is, as already described in Refs. [17,18], observed as a system of 33 main components interconnected with 70 matter streams. The inputs to the mathematical model are partly data obtained from the onsite measurements such as operation-related thermodynamic and flow parameters. The mathematical model consists of a large set of nonlinear and linear equations, including the ones required to determine working fluids properties. This problem is solved numerically using the Engineering Equation Solver [19]. Generally, the first and second levels of exergy destruction splitting in advanced exergy analysis have the purpose to provide more useful information related to the improvement potential of energy systems [17]. 2. Process description The detailed energy system and process description is given in Refs. [17,18]. The main purpose of the energy system is the generation of saturated steam at the pressure of 10 bar, production of compressed air at the pressure of 7 bar, and provision of cooling water to the plant. The entire system is divided into 33 main components interconnected with 70 streams of fluids. The scheme of the system, the components and the streams are given in Fig. 1. The most important component from the exergy destruction point of view [18] is the steam boiler (STB). It has three inlet streams: fuel (stream 1), feed water (stream 2) and air (stream 8); electricity inlet; two outlet streams: superheated steam (stream 3) and combustion products (stream 4), as well as heat loss of 2% of the total heating capacity. 3. Methodology
E_ F;tot ¼ E_ P;tot þ E_ L;tot þ E_ D;tot
ð1Þ
It should be noted that the values of exergy loss and destruction might vary with the boundaries, i.e. if the nearby environment is considered as a part of a system – if the boundaries of a system or a component are set where the ambient temperature is equal to the referent environment temperature, exergy loss is equal to zero, E˙L,k = 0. However, the sum of the two should remain the same. Exergetic efficiency is very important for the evaluation of thermodynamic characteristics of energy systems. It was defined by Tsatsaronis in 1993, using the ‘‘Fuel-Product’’ concept as a ratio between the exergy values of the product and the fuel:
E_
E_
E_
!1
ek ¼ _ P;k ¼ _ P;k_ ¼ 1 þ _ D;k EF;k EP;k þ ED;k EP;k
ð2Þ
As defined in Eq. (2), exergetic efficiency represents the part of fuel exergy that remain in the product, while the difference to 100% is the relative part destroyed or lost [24]. Another useful variable for comparison of components is the exergy destruction ratio:
yD;k ¼
E_ D;k E_ F;tot
ð3Þ
representing the contribution of the exergy destruction within the k-th component to the reduction of the overall exergetic efficiency [24]. 3.2. Advanced exergy analysis The advanced exergy analysis suggests, as illustrated in Fig. 2, splitting exergy destruction of each component k of the system into its: – avoidable and unavoidable parts, – endogenous and exogenous parts, in order to obtain detailed and useful information on the potential for overall efficiency improvement [6]. Dividing total exergy destruction, calculated from the exergy balance of the component k, into avoidable and unavoidable parts [3,6] is illustrated in Eq. (4):
_ UN E_ D;k ¼ E_ AV D;k þ ED;k
ð4Þ
The unavoidable exergy destruction of a component cannot be eliminated from the system, even with the application of the best available technologies. It is determined by analyzing the observed component separately from others, i.e. not as a part of the containing system. It should be assumed that this component operates in so called unavoidable conditions, i.e. with the best possible performance, e.g. the highest efficiency and minimal losses. The specific unavoidable exergy destruction is then defined as the ratio between the exergy destruction of the component and the exergy of its product (E˙D,k/E˙P,k)UN. Unavoidable exergy destruction is obtained by multiplying the specific unavoidable exergy destruction and the exergy of the product of the component in real operating conditions [25], as illustrated in Eq. (5):
3.1. Fuel-product concept and exergetic efficiency The fundamentals of exergy analysis are given in Refs. [20–22]. The exergy analysis is entirely based on so-called ‘‘Fuel-Product’’ concept [23]. Both the fuel and the product are expressed in exergy dimensions. The value of exergy destruction for the overall system as well as for a single component can be calculated from the exergy balance using the ‘‘Fuel-Product’’ concept [24], as shown in Eq. (1):
3
E_ D;k _ E_ UN D;k ¼ EP;k E_ P;k
!UN ð5Þ
For the calculation of unavoidable exergy destruction, the decision maker has to use some assumptions on the work conditions of the components, which might – to some extent – rely on the subjective comprehension and predictions related to the future enhancements.
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
27
EA
28
28 27
24
CAS
EP
41
F2
MA 34
EP
ED
ECT
EP
30
31
39 29
38
EA
39
SHW
57 CW 59
37 CP4 C 25 35 W 33 D 36 EP
CP3 32
58 HW
53
29 25
37
42
Energy Supply Sector Factory 1 26
EP
4
54
9
13 10
RV1 12
11
14
RV2 15
6
16
3 SD1 10 bar
SD3 3 bar
SD2 4,5 bar
40
61 TCH
HA
60 IA
HWP
62
17
CG 6 10
3 HO
5
1
PFH 7
CO
STP
49
55
4
EP
STB
SW
63
RW
65
17 44
CP1 EP
RV3 16
FW 23
18
46 19 CP2
22 DEA 20 FWT
36
26
50
FP TEC
56
70
CT1
EP
52 53 S 54 D 55 5 4bar 56
2 EP
64
RV4
8
EA
TSS
10bar 49 S 50 D 51 4
38
45
SB1
42
41
65
66
44
62 CWT 21
Legend CA Compress Air CG Combustion Gasses CO Condensate CP Circulation Pump CT Condensate Tank CW Cold Water EA Environmental Air ED Engineering Department EP Electric Power FW Flash Water FP Factory Products F2 Factory 2 IA Indoor Air HA Hot Air HO Heavy Oil HW Hot Water MA Moist Air PF Primary Fuel RV Reduce Valve RW Return Water SB Steam Branch SD Steam Distributor SW Supply Water WA Waste Air WB Water Branch CAS Compress Air Station COP Condensate Pipeline CWD Cold Water Distributor CWT Chemical Water Treatment DEA Deaerator ECT Evaporative Cooling Tower FWT Feed Water Tank PFH Primary Fuel Heating STB Steam Boiler STP Steam Pipeline SHW Sanitary Hot Water TCH Thermal Comfort Hall TEC Technologic Consumers TSS Thermal Substation HWP Hot Water Pool
43 WB1
59 67
FW
CT2 31
70
COP
CP6 69
68
48 CP5 47
Fig. 1. Complex industrial plant.
the other, r-th component has on exergy destruction of the k-th component. It is important to notice that the sum of all E_ EX;r terms D;k
is lower than the exogenous exergy destruction within the k-th component because of the simultaneous interactions of all (n 1) components. This difference, called the mexogenous exergy destruction is calculated from Ref. [3]:
_ EX E_ MX D;k ¼ ED;k
n X E_ EX;r
ð7Þ
D;k
r¼1 r–k
Fig. 2. Options for splitting the exergy destruction within the component of a system in advanced exergy analysis.
On the other hand, the avoidable part of exergy destruction is a difference between total and unavoidable exergy and represents realistic improvement potential of the energy system or component efficiency. The other approach to exergy destruction splitting is the use of the principles of the advanced exergy analysis to obtain its endogenous and exogenous parts [3]:
_ EN E_ D;k ¼ E_ EX D;k þ ED;k
ð6Þ
where the endogenous part is related to the irreversibilities related to the observed, e.g. the k-th component, which operates realistically, while all other components are presumed to operate ideally and the exogenous part of the exergy destruction is due to the irreversibilities of the remaining components. In addition to that, mexogenous exergy destruction is a consequence of the interconnections of the irreversibilities in all components. Splitting the exogenous exergy destruction of the k-th component, E_ EX;r , shows the effect that the irreversibility within D;k
Combining the two mentioned approaches of splitting the exergy destruction, i.e. expressing total exergy destruction as the sum:
E_ D;k ¼ E_ AV;EN þ E_ AV;EX þ E_ UN;EN þ E_ UN;EX D;k D;k D;k D;k
ð8Þ
enables deeper and more sophisticated exergy analysis and might improve the quality of the derived conclusions [6]. The methodology for splitting the exergy destruction to avoidable and unavoidable parts, as well as endogenous and exogenous parts is presented in detail in Refs. [3,6,7,25]. Another variable related to each component k of an observed system is introduced in Ref. [5] with the purpose to use the results of the advanced exergy analysis to identify priorities for improving components. It is the sum of avoidable endogenous exergy destruction within the k-th component and of all the avoidable exogenous destructions within the other components caused by the k-th component [6]: R _ AV;EN þ E_ AV; D;k ¼ ED;k
n X E_ AV;EX;r D;k
ð9Þ
r¼1 r–k
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
3.3. Real, unavoidable and theoretical operation conditions The real operation conditions (ROC) are realistic currently achievable operation performance data for all the components of the observed energy system, e.g. actual thermodynamic efficiency. The unavoidable operation conditions (UOC) are also realistic operation data, but achievable only in perspective, i.e. in the future. Unavoidable operating conditions are those that cannot be achieved in a foreseeable or near future (e.g. the next decade) with the current trends of technological development. Their choice is arbitrary to some extent and depends on decision makers and their understanding of processes and theoretical backgrounds [13], as well as following current scientific and practical achievements. They are important when formulating the foreseen potential for further improvements of each component and accordingly determining the unavoidable part of the exergy destruction. Establishing UOC for each component requires the forecasts of the development tendencies and achievements for that type of component. Theoretical operation conditions (TOC) of a component cannot be achieved in practice. They are based on the assumption of ideal operation, e.g. with maximal theoretical efficiency. TOC are used to calculate endogenous and exogenous exergy destruction. In Table 1, the summary of the assumptions of real, unavoidable and theoretical operation conditions based on the adopted approach published in Ref. [25] is shown for the important components of the system for this analysis.
4. Results and discussion Table 2 provides the results of exergy analysis at the levels of the components. The values of thermodynamic and other parameters of the streams of matter are not illustrated here for brevity, but can be found in Ref. [18]. Table 2 presents the following quantities at the level of the components: exergy of the fuel (E_ F;k ), exergy of the product (E_ P;k ), exergy destruction (E_ D;k ), specific unavoidable exergy destruction UN (ðE_ D;k =E_ P;k Þ ), avoidable exergy destruction (E_ UN D;k ), unavoidable exergy destruction (E_ AV ), endogenous exergy destruction (E_ EN ), D;k
D;k
exogenous exergy destruction (E_ EX D;k ), the coefficient of total exergy destruction (yD;k ), exergetic efficiency.
5
The same Table presents the following quantities related to the entire plant: exergy of the fuel, exergy of the product, exergy destruction, exergy loss, the coefficient of total exergy destruction, exergetic efficiency. The influence of the technology consumers on the observed energy system is taken into account through the values of process fluids flows that correspond to the operation of the real plant and depend on the quantity of the final products. Exergetic efficiency of the overall energy system of 35.90% implies that the potential exists for total efficiency improvement and costs reduction. Exergy losses are mostly related to the streams of matter, especially exhaust gasses, but also to heat transfer to environment. The loss related to the exhaust gasses is 238.53 kW or 95.20% of total exergy losses. Total exergy losses (250.56 kW) are equal to 10.39% of the fuel exergy delivered to the entire energy system via the stream of matter number 5, while 58.54% of the fuel exergy supplied to the entire system is destroyed in the components of this system. Fig. 3 shows the value of the exergy of fuel, exergy of product and exergy destruction for the components. The steam generator has the greatest impact on reducing the exergetic efficiency of the overall system, given that it destroys 1132.21 kW of exergy, Table 1, Fig. 3. The steam generator has a high potential for increasing efficiency, keeping in mind that the exergy destruction in it amounts to 80.19% of the total exergy destruction in the system. In addition, exergetic efficiency of the steam generator is very low, 48.19%. Fig. 4 shows the current and maximal exergetic efficiency values of the components. It can be observed that the components with very low exergetic efficiency are: TCH (3.40%), SHW (6.46%), TSS (9.97%), PFH (15.96%), Table 1. However, it is important that high values of exergetic efficiency of these components cannot be achieved, i.e. they are respectively 26.64%, 28.47%, 46.46% and 36.96%, because the devices are not capable of utilizing available potential to produce work contained in the chemical exergy of steam. Besides, exergetic efficiency of the steam generator is below 50%, i.e. 48.19%, and can be improved only slightly, up to the maximum of 52.69%, due to imperfections in the combustion process. Fig. 5 illustrates the coefficients of exergy destruction of the components relative to the overall coefficient of exergy destruction related to the overall system. It can be observed that over 80% of total exergy destruction happens in the steam generator, thus it
Table 1 Real, unavoidable and theoretical operation conditions for the most important components of the system. Comp.
ROC
UOC
TOC
STB
g ¼ 90%; Q_ L – 0
g ¼ 98%; Q_ L 0
g ¼ 100%; Q_ L ¼ 0
PFH
DT min > 50 K; Q_ L – 0
DEA
pj ct: T 20 > T 46 ; T 19 > T 23
FWT
pj ct; T j – ct: Q_ L – 0 g ¼ 80% g ¼ 90%
Dp0 ¼ Dp00 0 DT min ¼ 50 K pj ct; T j ct: Q_ L 0 pj ct; T j ct: Q_ L 0 g ¼ 95% g ¼ 98%; T 26 ¼ T 24 T 29 ¼ T 26 2 K p ; T j ct; Q_ L 0
Dp0 ¼ Dp00 ¼ 0 g ¼ 100%; Q_ L ¼ 0 pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 g ¼ 100% g ¼ 100%; Q_ L ¼ 0 T 26 ¼ T 24 ; T 29 ¼ T 26 p ; T j ¼ ct; Q_ L ¼ 0
pj ct; T j ct: Q_ L 0 pj ¼ ct; T j ¼ ct: Q_ L 0 Dp0 ¼ Dp00 0 DT min ¼ 70 K;Q_ L 0 DT min ¼ 70 K Dp0 ¼ Dp00 0 DT min ¼ 60 K;Q_ L 0
pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 Dp0 ¼ Dp00 ¼ 0 g ¼ 100%; Q_ L ¼ 0
CP (1–5) CAS HWP STD & CWD CT (1–2) SHW TCH TSS
pj ; T j – ct; Q_ L – 0 pj ct; T j – ct: Q_ L – 0 pj – ct; T j – ct: Q_ L – 0 DT min > 70 K; Q_ L – 0 DT min > 70 K DT min > 60 K; Q_ L – 0
j
j
g ¼ 100% Dp0 ¼ Dp00 ¼ 0 g ¼ 100%; Q_ L ¼ 0
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
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6
Table 2 Results of conventional and advanced exergy analysis for the most important components of the system. Components
Exergy analysis Conventional
STB PFH DEA FWT STP CAS ECT HWP CT1 CWT SHW TCH TSS CT2 COP Overall system Exergy loss
Advanced
E_ F;k
E_ P;k
E_ D;k
(kW)
(kW)
(kW)
2185.50 2.13 7.24 46.87 626.11 82.70 32.83 120.89 79.61 3.13 15.33 60.92 15.54 4.69 2.90 2582.59 250.56
1053.29 0.34 2.78 33.43 626.11 54.84 4.80 106.20 15.51 3.13 0.99 2.07 1.55 2.90 2.90 920.27
1132.21 1.79 4.46 13.44 0.00 27.86 28.03 14.69 64.10 0.00 14.34 58.85 13.99 1.79 0.00 1411.77
Variables
ðE_ D;k =E_ P;k Þ (–)
E_ UN D;k
E_ AV D;k
E_ EN D;k
E_ EX D;k
yD;k
ek
(kW)
(kW)
(kW)
(kW)
(–)
(%)
0.898 1.706 0.000 0.000 0.000 0.403 0.227 0.000 0.000 0.000 2.512 2.754 1.152 0.000 0.000
945.72 0.58 0.00 0.00 0.00 22.08 1.09 0.04 0.00 0.00 2.49 5.70 1.79 0.00 0.00
186.49 1.21 4.46 13.44 0.00 5.78 26.94 14.65 64.10 0.00 11.85 53.15 12.20 1.79 0.00
1097.63 1.58 4.33 4.24 0.00 27.86 22.75 14.49 63.56 0.00 14.16 58.76 13.96 2.18 0.00
34.58 0.21 0.13 9.20 0.00 0.00 5.28 0.20 0.55 0.00 0.18 0.09 0.03 -0.39 0.00
0.8020 0.0013 0.0032 0.0095 0.0000 0.0197 0.0199 0.0104 0.0454 0.0000 0.0102 0.0417 0.0099 0.0013 0.0000 1.0000
48.19 15.96 38.37 71.32 100.00 66.31 14.62 87.85 19.48 100.00 6.46 3.40 9.97 61.83 100.00 35.90
UN
Exergy of fuel
Exergy of product
Exergy destrucon
Values of exergy [kW]
2,500.00 2,000.00 1,500.00 1,000.00 500.00
STB PFH DEA FWT CP1 CP2 CD1 CD2 CD3 STP CAS CP3 ECT HWP CP4 CWD CT1 CWT CP5 SD4 SD5 SHW TCH TSS CT2 RV3 CP6 COP SB1 WB1
0.00
Components (Acronym) Fig. 3. Exergy of fuel, exergy of product and exergy destruction in components of system.
Curent
Maximal
100.00
Exergec efficiency [%]
90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 STB PFH DEA FWT CP1 CP2 CD1 CD2 CD3 STP CAS CP3 ECT HWP CP4 CWD CT1 CWT CP5 SD4 SD5 SHW TCH TSS CT2 RV3 CP6 COP SB1 WB1
0.00
Component s (Acronym) Fig. 4. Real and maximal exergetic efficiency of the system components.
is obvious that this component influences the overall system efficiency the most. The values of maximal exergetic efficiencies are given in [18]. The ultimate goal of analyses of complex energy systems is the improvement of systems efficiency. Having in mind that current
exergetic efficiency of the system is 35.90%, Table 1, it is important to understand why this value is low. Useful quantities for this purpose are exergy destruction coefficient and exergy loss coefficient. Exergetic efficiency of the overall system and the influence of these coefficients on its value are illustrated in Fig. 6.
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
STB
PFH
DEA
FWT
CP1
CP2
CD1
CD2
CD3
CAS
CP3
ECT
HWP
CP4
CWD
CT1
CWT
CP5
SD4
SD5
SHW
TCH
TSS
CT2
RV3
CP6
COP
SB1
WB1
0.8
0
7
STP
0.9
1
Distribuon of overall coefficient of exergy destrucon Fig. 5. The coefficients of exergy destruction of the components and the overall coefficient of exergy destruction.
Out of 100% of the maximal overall exergetic efficiency, 43.66% is destroyed in the steam generator, 10.78% in all other components and 9.66% is due to energy system exergy losses. In Table 2, the results of the first and second level of exergy destruction splitting are shown, obtained within the frame of the advanced exergy analysis for the steam generator. This component is the part of the system correlated to the highest amount of the destructed useful work potential, i.e. has largest value of exergy destruction, as shown in the previous chapter. Within the frame of the first level of splitting, besides the results for unavoidable (E_ UN ) and avoidable exergy destruction D;k
_ EN (E_ AV D;k ), as well as endogenous (ED;k ) and exogenous exergy destruction (E_ EX ), shown in Table 1, this paper also presents the results of D;k
the decomposition of exogenous exergy destruction to the parts originating from the other components (E_ EX;r ) and the mexogenous D;k
exergy destruction (E_ MX D;k ) which is the consequence of the simultaneous influence of other components on the observed component. Thus, the following components are the most significant from the aspect of the influence on exogenous exergy destruction of the steam generator of 34.58 kW:
Heating substation – TSS (3.19 kW or 9.22%), condensate reservoir 2 – CT2 (2.69 kW or 7.78%), hall thermal comfort – TCH (2.51 kW or 7.26%), sanitary hot water preparation - SHW (2.42 kW or 6.94%).
D;k
D;k
) and unavoidable-exogenous unavoidable-endogenous (E_ UN;EN D;k ). Total unavoidable exergy destruction is 945.72 kW and a (E_ UN;EX D;k large part (919.47 kW or 97.28%) comes from the internal irreversibilities, while 25.75 kW (2.72%) is due to the influences of other components. Total avoidable exergy destruction is 186.49 kW and 177.66 kW (95.26%) is from the internal irreversibilities and 8.83 kW (4.74%) from the external irreversibilities. As a final result of the advanced exergy analysis for the steam generator, the total value of avoidable exergy destruction for the component of interest (E_ AV;R ) is presented: 183.33 kW or 16.19% D;k
In addition to that, the results of the additional splitting of external exergy destruction for the steam generator shown in Table 2 suggest that the influence of the components CP1, CP2
Exergec efficiency of the overall system and influence of these coefficient on maximal exegec efficiency [%]
and SD1 on exergy destruction in the steam generator (2.13 kW, 1.79 kW and 1.23 kW) is higher than internal exergy destruction in these components (0.15 kW, 0.01 kW and 0.58 kW) given in Table 3. These data illustrate that efficiency of the mentioned components has a significant impact on exergetic efficiency of the entire energy system [4]. External exergy destruction of the steam generator increases for 3.16 kW due to the simultaneous impact of all the other components (mexogenous exergy destruction), which is 9.14% of total external exergy destruction of this component, i.e. 0.28% of its total exergy destruction. Within the frame of the second level of splitting, the splitting of avoidable/unavoidable exergy destruction is combined with internal/external exergy destruction, i.e. the results are presented for avoidable-endogenous (E_ AV;EN ), avoidable-exogenous (E_ AV;EX ),
of total exergy destruction of the component. This value is somewhat smaller than the value obtained in the first level of splitting (186.49 kW) due to the existence of mexogenous exergy destruction components.
100.00 9.66
90.00 10.78
80.00 Exergy loss rao
70.00 60.00
Exergy destrucon rao of other components
43.66
50.00 35.90 43.66 10.78 9.66
40.00 30.00 20.00
Exergy destrucon rao of STB Exergec efficiency of overall system
35.90
10.00 0.00
Fig. 6. Exergetic efficiency of the entire system and the influence of exergy destruction coefficient and exergy loss coefficient on its value.
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
8
Component
Exergy Analysis Conventional
Advanced (Detailed) First level of exergy destruction splitting
No.
1
k
STB
Second level of exergy destruction splitting
Splitting the Total Exergy Destruction
Splitting the Exogenous part E_ EX D;k
Unavoidable/avoidable
Endogenous/exogenous
Component
E_ D;k
E_ UN D;k
E_ AV D;k
E_ EN D;k
(kW)
(kW)
(kW)
(kW)
(kW)
No.
r
(kW)
(kW)
(kW)
(kW)
(kW)
(kW)
(kW)
1132.21
945.72 (83.53%)
186.49 (16.47%)
1097.63 (96.95%)
34.58 (3.05%)
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 E_ MX
PFH DEA FWT CP1 CP2 SD1 SD2 RV1 SD3 RV2 STP CAS CP3 ECT HWP CP4 CWD CT1 CWT CP5 SD4 SD5 RV4 SHW TCH TSS CT2 RV3 CP6 COP SB1 WB1
1099.29 1098.82 1099.15 1099.76 1099.42 1098.86 1099.13 1097.76 1099.24 1097.76 1097.63 1098.77 1097.63 1099.44 1099.03 1097.63 1097.63 1100.05 1098.31 1097.63 1098.49 1098.65 1097.76 1100.03 1100.14 1100.82 1100.32 1097.63 1097.63 1097.63 1097.63 1097.63
1.66 1.19 1.52 2.13 1.79 1.23 1.50 0.00 1.61 0.00 0.00 1.14 0.00 1.81 1.40 0.00 0.00 2.40 0.68 0.00 0.86 1.02 0.00 2.42 2.51 3.19 2.69 0.00 0.00 0.00 0.00 0.00 3.16
919.97 (97.28%)
25.75 (2.72%)
177.66 (95.26%)
8.83 (4.74%)
183.33 (16.19%)
E_ EN;rþ D;k
Splitting E_ UN D;k E_ EX;r D;k
E_ UN;EN D;k
R E_ AV; D;k
Splitting E_ AV D;k E_ UN;EX D;k
E_ AV;EN D;k
E_ AV;EX D;k
E_ EX D;k
D;k
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
Table 3 Results of first and second level of exergy destruction splitting in advanced exergy analysis.
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
5. Conclusions This paper presents the results of advanced exergy analysis for a real complex industrial plant, with emphasis on the main component (steam boiler) from the energy efficiency point of view. Exergetic efficiency of the overall energy system of 35.90% implies that the potential exists for total efficiency improvement and costs reduction. Exergetic efficiency of the steam generator is 48.19% and can be improved just slightly, up to maximal 52.69%, due to imperfections in the combustion process. Out of 100% of the maximal overall exergetic efficiency, 43.66% is destructed in the steam generator. The next four components are the most significant from the aspect of the influence on external exergy destruction of the steam generator: Thermal substation (9.22%), Condensate tank 2 (7.78%), Thermal comfort of hall (7.26%) and Sanitary hot water preparation (6.94%). Large part (97.28%) of the total unavoidable exergy destruction for Steam boiler comes from the internal irreversibilities, while 2.72% is due to the influences of other components. From the internal irreversibilities os steam boiler comes 95.26% of the total avoidable exergy destruction, and only 4.74% comes from the external irreversibilities. The final result of the advanced exergy analysis for the steam generator is the total value of avoidable exergy destruction, with 183.33 kW or 16.19% of total exergy destruction of the component. For the representative industrial plant, advanced exergy analysis without doubt ranks the improvement priority of the steam generator first. The research results have sufficient accuracy and a high degree of generality, since the selected reference plant consists of components that are encountered in most industrial and process plants, so that the advanced exergy analysis could be successfully applied to any complex thermal process plant and its components. This analysis provides an insight into realistic exergy efficiency improvement potential related to the boiler operation, taking into account the influence of other components as well. It may be used to evaluate possible enhancements of the system, but also to compare different steam generating options – technologies and fuels. Investigating the implications of boiler or fuel switching using the advanced exergy analysis is a possible direction for the future work. References [1] BP statistical review of the world energy
9
[3] Morosuk T, Tsatsaronis G. Advanced exergy analysis for chemically reacting systems-application to a simple open gas-turbine system. Int J Thermodyn 2009;12(3):105–11. [4] Kelly S. Energy systems improvement based on endogenous and exogenous exergy destruction, Ph.D. Thesis, Technischen Universität Berlin, Berlin, Germany; 2008. [5] Tsatsaronis G, Morosuk T. Advanced exergetic analysis of a novel system for generating electricity and vaporizing liquefied natural gas. Energy 2010;35(2): 820–9. [6] Açikkalp E, Aras H, Hepbasli A. Advanced exergy analysis of an electricitygenerating facility using natural gas. Energy Convers Manage 2014;82:146–53. [7] Morosuk T, Tsatsaronis G. Comparative evaluation of LNG – based cogeneration systems using advanced exergetic analysis. Energy 2011;36(6): 3771–8. [8] Morosuk T, Tsatsaronis G. Advanced exergetic evaluation of refrigeration machines using different working fluids. Energy 2009;34(12):2248–58. [9] Hepbasli A, Keçebasß A. A comparative study on conventional and advanced exergetic analyses of geothermal district heating systems based on actual operational data. Energy Build 2013;61:193–201. [10] Gungor A, Erbay Z, Hepbasli A, Gunerhan H. Splitting the exergy destruction into avoidable and unavoidable parts of a gas engine heat pump (GEHP) for food drying processes based on experimental values. Energy Convers Manage 2013;73:309–16. [11] Erbay Z, Hepbasli A. Application of conventional and advanced exergy analyses to evaluate the performance of a ground-source heat pump (GSHP) dryer used in food drying. Energy Convers Manage 2014;78:499–507. [12] Mahamud R, Khan MMK, Rasul MG, Leinster MG. Exergy analysis and efficiency improvement of a coal fired thermal power plant in Queensland. In: Rasul MG, editor. Thermal power plants: advanced applications. Croatia: InTech; 2013. http://dx.doi.org/10.5772/55574 [chapter 1:3-28]. [13] Wang L, Yang Y, Morosuk T, Tsatsaronis G. Advanced thermodynamic analysis and evaluation of a supercritical power plant. Energies 2012;5:1850–63. [14] Pal MK, Kumar A, Chandra H. Energy and exergy analysis of boiler and turbine of coal fired thermal power plant. Int J Eng Res Technol 2013;2(6):1428–39. [15] Petrakopoulou F, Tsatsaronis G, Morosuk T, Carassai A. Conventional and advanced exergetic analyses applied to a combined cycle power plant. Energy 2012;41(1):146–52. [16] Yang Y, Wang L, Dong C, Xu G, Morosuk T, Tsatsaronis G. Comprehensive exergy-based evaluation and parametric study of a coal-fired ultrasupercritical power plant. Appl Energy 2013;112:1087–99. [17] Vucˇkovic´ G, Vukic´ M, Stojiljkovic´ M, Vucˇkovic´ D. Avoidable and unavoidable exergy destruction and exergoeconomic evaluation of the thermal processes in a real industrial plant. Thermal Sci 2012;16(S2):S433–46. [18] Vucˇkovic´ G, Stojiljkovic´ M, Vukic´ M, Stefanovic´ G, Dedeic´ E. Advanced exergy analysis and exergoeconomic performance evaluation of thermal processes in an existing industrial plant. Energy Convers Manage 2014;85:655–62. [19] Engineering Equation Solver.
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
Contents lists available at ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler Goran D. Vucˇkovic´ ⇑, Mirko M. Stojiljkovic´, Mic´a V. Vukic´ University of Niš, Faculty of Mechanical Engineering in Niš, 14 Aleksandra Medvedeva St., Niš, Serbia
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Exergy destruction Advanced exergy analysis Splitting Boiler
a b s t r a c t When complex energy systems are analyzed and when a large number of their components is observed, the destruction of exergy related to a single component is dependent on its own properties, but also on the characteristics of other components. The advanced exergy analysis is useful for providing supplementary information on the interaction between the components. It also exposes the real improvement potential related to each component of a system, but also of a system as a whole. In this paper, an existing complex industrial plant with 33 components and 70 streams is analyzed using the first and second level of exergy destruction splitting for the boiler, as a main plant component from the aspect of destroying the useful work. From the total unavoidable exergy destruction 97.28% comes from the internal irreversibility, 2.72% comes from the irreversibilities of other components, while 95.26% of the unavoidable exergy destruction (186.49 kW) comes from the internal irreversibility, and 4.74% from the external irreversibility. The final result of the advanced exergy analysis for the steam generator is the total value of the avoidable exergy destruction as a real potential that can be avoided. It is 16.19% of the total exergy destruction of the component. That is less than the data obtained in the first decomposition level (186.49 kW) merely due to the existence of mexogenous exergy destruction. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction and background In 2013, the total world fuel consumption was 12,730.4 Mtoe, consisting of: 4185.1 Mtoe of oil (32.9%), 3826.7 Mtoe of coal (30.1%), 3020.4 Mtoe of natural gas (23.7%), 855.8 Mtoe of hydro-electricity (6.7%), 563.2 Mtoe of nuclear energy (4.4%) and 279.3 Mtoe of renewable energy (2.2%) [1]. According to Ref. [2], nearly 45% of global electricity generation originates from coal, about 20% from natural gas and 15% from nuclear energy. Significant amounts of fossil fuels consumption in industry are used for steam generation. Boilers are the components often exploited to convert the chemical energy of fuel to heat necessary for steam and electricity production. That is why the improvements of boilers energy efficiency are very important, even by just a small fraction. The destruction of exergy of a single component of an energy system depends on its own properties, but also on the inefficiencies related to other components of the system it is a part of. The conventional exergy analysis quantifies the irreversibilities related ⇑ Corresponding author. Tel.: +381 63402919. E-mail addresses: [email protected] (G.D. Vucˇkovic´), mirko.stojiljkovic@ masfak.ni.ac.rs (M.M. Stojiljkovic´), [email protected] (M.V. Vukic´).
to a certain component of an energy system. However, it does not provide any information on the origin of the irreversibilities or the potential to avoid them. For that reason, the total exergy destruction can be split into parts in the advanced exergy analysis. In one approach, the total exergy destruction of a component can be separated into the part which can be avoided, therefore called ‘‘avoidable’’, and the part which cannot be avoided, named ‘‘unavoidable’’. According to the other approach, the total exergy destruction of a component is divided into the endogenous and exogenous parts of exergy destruction. In the second level of exergy destruction splitting in the advanced exergy analysis, combining the two previous approaches enhances an exergy analysis and improves the quality of the conclusions [3]. Morosuk and Tsatsaronis [3] suggested the methodology for the calculation of the parts of exergy destruction applying the advanced exergy analysis. This approach is illustrated with an example of a simple gas-turbine system revealing the improvement possibilities and the interactions among the components of the system. Kelly [4] proposed the approach to determine the endogenous part of exergy destruction based on the structural theory. Tsatsaronis and Morosuk [5] showed a detailed exergy analysis of a co-generation concept combining liquefied natural gas (LNG) regasification with power generation. Açikkalp
http://dx.doi.org/10.1016/j.enconman.2015.06.001 0196-8904/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
2
Nomenclature E_ n p Q_ T yD
exergy flow rate (kW) total number of system components pressure (bar) rate of heat transfer (kW) temperature (K) exergy destruction ratio
Greek letters D difference e exergetic efficiency g thermal efficiency Subscripts D destruction F fuel j stream of matter k system component
et al. [6] applied the advanced exergy analysis to an electricity-generating facility using natural gas. They determined the actual potential for system improvements and the relationships between the components. They provided suggestions for increasing system efficiency. The highest exergy destruction rate is found at the combustion chamber because chemical reactions are significant sources of irreversibilities. Morosuk and Tsatsaronis [7] analyzed the improvement potential and the interactions among components in LNG-based cogeneration systems and showed the advantages of the advanced exergy analysis over the conventional one. It is demonstrated that the advanced analysis produces more reliable and detailed results, and leads toward a better understanding of the interactions between components and the possibilities for improvement. In [8], the authors studied the effect of the properties of the working fluids for compression refrigeration machines on the results of advanced exergy analysis. Hepbasli and Keçebasß [9] evaluated exergy destructions of a geothermal district heating system (GDHS) as a real case study using both conventional and advanced exergetic analysis methods to identify the potential for improvement and the interactions among the components. The highest priority for improvement in the advanced exergetic analysis is in the re-injection pump, while it is the heat exchanger in the conventional analysis. Gungor et al. [10] analyzed a gas engine heat pump (GEHP) for food drying processes using both conventional and advanced exergy analyses. For each system component, avoidable and unavoidable exergy destructions, modified exergy efficiency values and modified exergy destruction ratios were determined. Erbay and Hepbasli [11] evaluated the performance of a ground-source heat pump (GSHP) for drying processes in food industry using both conventional and advanced exergy analysis. The results indicate that the most important system component from the design standpoint is the condenser. The inefficiencies within the compressor could particularly be improved by structural improvements of the overall system and the remaining system components. Boilers are certainly among the most important components of industrial energy systems, since they convert fuel energy to heat required for the technological process. However, boilers and combustion chambers are usually the components of energy systems with the highest exergy destruction values caused by exothermic chemical reactions [12]. Mahamud et al. [12] used the exergy analysis of a power plant to identify the areas where the most of the useful energy is lost and
L P tot
loss product overall system
Superscripts AV avoidable EN endogenous EX exogenous max maximal min minimal MX mexogenous r system component (different of k) UN unavoidable 0 saturated liquid 00 saturated vapor ⁄ total values R sum of values
discussed the potential for the improvement of plant energy efficiency. They showed that the boiler of a subcritical power generation plant is the major source of the useful energy lost. Only negligible amounts of useful waste energy could be recovered by implementing a heat recovery system. Wang et al. [13] presented the application of both conventional and advanced exergy analyses to a supercritical coal-fired power plant. Among other things, the results show that the boiler subsystem is proven to have a large amount of exergy destruction caused by the irreversibilities within the remaining components of the overall system. It is also found that the boiler subsystem still has the largest avoidable exergy destruction. However, the enhancement efforts should focus not only on its inherent irreversibilities but also on the inefficiencies within the remaining components. Pal et al. [14] showed the First and the Second Law of Thermodynamics based analysis of the boiler and the turbine that are the components of a coal-fired thermal power plant. Again, the boiler has the highest value of the exergy loss, i.e. the largest related irreversibilities. Petrakopouolu et al. [15] analyzed a combined cycle power plant using both conventional and advanced exergy analyses. The highest exergy destruction is caused by the combustion chamber. Almost 87% of the total exergy destruction within this component results from the operation of the component itself (endogenous exergy destruction) and 68% of the total exergy destruction cannot be avoided (unavoidable exergy destruction). Similar to the results of the conventional analysis, the advanced analysis ranks the improvement priority of the combustion chamber first, followed by the expander and the compressor. Yang et al. [16] presented the comprehensive exergy-based evaluation of a state-of-the-art ultra-supercritical coal-fired power plant. The energy saving potentials for both the overall system and an individual component were found not to be not in accordance their exergy destructions. The boiler subsystem again has the largest exergy destruction. Performance improvement is mainly related to the reduction of the exergy destruction within the boiler. In Ref. [17], the advanced exergy analysis is applied to split the total exergy destruction to the avoidable and unavoidable parts for all the components of a complex industrial energy system. Exergoeconomic evaluation is shown as well. The results of the exergetic and exergoeconomic analysis rank the components according to their improvement potentials, with the goal to
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
enhance the exergy efficiency of the entire system. The results also show that over 92% of the total exergy destruction in the boiler cannot be avoided by applying the available technologies. Ref. [18] further splits the total exergy destruction of each component of the same complex energy system to the exogenous and endogenous parts. The results illustrate that the exergy destruction decrease in a component can be achieved by reducing the irreversibilities of that component, but also by lowering the negative impact of the other components of the system. As seen from the above studies, boilers are the components of energy systems that often have the highest values of exergy destruction. Still – to the best of the authors’ knowledge – no studies on exergy destruction splitting and assessment with the special emphasis on boilers in a complex energy system have appeared in the open literature. This is the main motivation behind performing this work, related to a deeper analysis of the boiler irreversibilities and combinational splitting of exergy destruction (second level) within the advanced exergy analysis. The realistic operational data for the boiler are observed. It is regarded as a part of the energy system with many components. This paper represents an extension of the previous work of the authors summarized in Refs. [17,18] and is related to the same industrial plant as in the previous research. It analyzes a real complex industrial plant for rubber products with an emphasis on the first and second level of exergy destruction splitting on the main component (steam boiler). The plant is, as already described in Refs. [17,18], observed as a system of 33 main components interconnected with 70 matter streams. The inputs to the mathematical model are partly data obtained from the onsite measurements such as operation-related thermodynamic and flow parameters. The mathematical model consists of a large set of nonlinear and linear equations, including the ones required to determine working fluids properties. This problem is solved numerically using the Engineering Equation Solver [19]. Generally, the first and second levels of exergy destruction splitting in advanced exergy analysis have the purpose to provide more useful information related to the improvement potential of energy systems [17]. 2. Process description The detailed energy system and process description is given in Refs. [17,18]. The main purpose of the energy system is the generation of saturated steam at the pressure of 10 bar, production of compressed air at the pressure of 7 bar, and provision of cooling water to the plant. The entire system is divided into 33 main components interconnected with 70 streams of fluids. The scheme of the system, the components and the streams are given in Fig. 1. The most important component from the exergy destruction point of view [18] is the steam boiler (STB). It has three inlet streams: fuel (stream 1), feed water (stream 2) and air (stream 8); electricity inlet; two outlet streams: superheated steam (stream 3) and combustion products (stream 4), as well as heat loss of 2% of the total heating capacity. 3. Methodology
E_ F;tot ¼ E_ P;tot þ E_ L;tot þ E_ D;tot
ð1Þ
It should be noted that the values of exergy loss and destruction might vary with the boundaries, i.e. if the nearby environment is considered as a part of a system – if the boundaries of a system or a component are set where the ambient temperature is equal to the referent environment temperature, exergy loss is equal to zero, E˙L,k = 0. However, the sum of the two should remain the same. Exergetic efficiency is very important for the evaluation of thermodynamic characteristics of energy systems. It was defined by Tsatsaronis in 1993, using the ‘‘Fuel-Product’’ concept as a ratio between the exergy values of the product and the fuel:
E_
E_
E_
!1
ek ¼ _ P;k ¼ _ P;k_ ¼ 1 þ _ D;k EF;k EP;k þ ED;k EP;k
ð2Þ
As defined in Eq. (2), exergetic efficiency represents the part of fuel exergy that remain in the product, while the difference to 100% is the relative part destroyed or lost [24]. Another useful variable for comparison of components is the exergy destruction ratio:
yD;k ¼
E_ D;k E_ F;tot
ð3Þ
representing the contribution of the exergy destruction within the k-th component to the reduction of the overall exergetic efficiency [24]. 3.2. Advanced exergy analysis The advanced exergy analysis suggests, as illustrated in Fig. 2, splitting exergy destruction of each component k of the system into its: – avoidable and unavoidable parts, – endogenous and exogenous parts, in order to obtain detailed and useful information on the potential for overall efficiency improvement [6]. Dividing total exergy destruction, calculated from the exergy balance of the component k, into avoidable and unavoidable parts [3,6] is illustrated in Eq. (4):
_ UN E_ D;k ¼ E_ AV D;k þ ED;k
ð4Þ
The unavoidable exergy destruction of a component cannot be eliminated from the system, even with the application of the best available technologies. It is determined by analyzing the observed component separately from others, i.e. not as a part of the containing system. It should be assumed that this component operates in so called unavoidable conditions, i.e. with the best possible performance, e.g. the highest efficiency and minimal losses. The specific unavoidable exergy destruction is then defined as the ratio between the exergy destruction of the component and the exergy of its product (E˙D,k/E˙P,k)UN. Unavoidable exergy destruction is obtained by multiplying the specific unavoidable exergy destruction and the exergy of the product of the component in real operating conditions [25], as illustrated in Eq. (5):
3.1. Fuel-product concept and exergetic efficiency The fundamentals of exergy analysis are given in Refs. [20–22]. The exergy analysis is entirely based on so-called ‘‘Fuel-Product’’ concept [23]. Both the fuel and the product are expressed in exergy dimensions. The value of exergy destruction for the overall system as well as for a single component can be calculated from the exergy balance using the ‘‘Fuel-Product’’ concept [24], as shown in Eq. (1):
3
E_ D;k _ E_ UN D;k ¼ EP;k E_ P;k
!UN ð5Þ
For the calculation of unavoidable exergy destruction, the decision maker has to use some assumptions on the work conditions of the components, which might – to some extent – rely on the subjective comprehension and predictions related to the future enhancements.
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
27
EA
28
28 27
24
CAS
EP
41
F2
MA 34
EP
ED
ECT
EP
30
31
39 29
38
EA
39
SHW
57 CW 59
37 CP4 C 25 35 W 33 D 36 EP
CP3 32
58 HW
53
29 25
37
42
Energy Supply Sector Factory 1 26
EP
4
54
9
13 10
RV1 12
11
14
RV2 15
6
16
3 SD1 10 bar
SD3 3 bar
SD2 4,5 bar
40
61 TCH
HA
60 IA
HWP
62
17
CG 6 10
3 HO
5
1
PFH 7
CO
STP
49
55
4
EP
STB
SW
63
RW
65
17 44
CP1 EP
RV3 16
FW 23
18
46 19 CP2
22 DEA 20 FWT
36
26
50
FP TEC
56
70
CT1
EP
52 53 S 54 D 55 5 4bar 56
2 EP
64
RV4
8
EA
TSS
10bar 49 S 50 D 51 4
38
45
SB1
42
41
65
66
44
62 CWT 21
Legend CA Compress Air CG Combustion Gasses CO Condensate CP Circulation Pump CT Condensate Tank CW Cold Water EA Environmental Air ED Engineering Department EP Electric Power FW Flash Water FP Factory Products F2 Factory 2 IA Indoor Air HA Hot Air HO Heavy Oil HW Hot Water MA Moist Air PF Primary Fuel RV Reduce Valve RW Return Water SB Steam Branch SD Steam Distributor SW Supply Water WA Waste Air WB Water Branch CAS Compress Air Station COP Condensate Pipeline CWD Cold Water Distributor CWT Chemical Water Treatment DEA Deaerator ECT Evaporative Cooling Tower FWT Feed Water Tank PFH Primary Fuel Heating STB Steam Boiler STP Steam Pipeline SHW Sanitary Hot Water TCH Thermal Comfort Hall TEC Technologic Consumers TSS Thermal Substation HWP Hot Water Pool
43 WB1
59 67
FW
CT2 31
70
COP
CP6 69
68
48 CP5 47
Fig. 1. Complex industrial plant.
the other, r-th component has on exergy destruction of the k-th component. It is important to notice that the sum of all E_ EX;r terms D;k
is lower than the exogenous exergy destruction within the k-th component because of the simultaneous interactions of all (n 1) components. This difference, called the mexogenous exergy destruction is calculated from Ref. [3]:
_ EX E_ MX D;k ¼ ED;k
n X E_ EX;r
ð7Þ
D;k
r¼1 r–k
Fig. 2. Options for splitting the exergy destruction within the component of a system in advanced exergy analysis.
On the other hand, the avoidable part of exergy destruction is a difference between total and unavoidable exergy and represents realistic improvement potential of the energy system or component efficiency. The other approach to exergy destruction splitting is the use of the principles of the advanced exergy analysis to obtain its endogenous and exogenous parts [3]:
_ EN E_ D;k ¼ E_ EX D;k þ ED;k
ð6Þ
where the endogenous part is related to the irreversibilities related to the observed, e.g. the k-th component, which operates realistically, while all other components are presumed to operate ideally and the exogenous part of the exergy destruction is due to the irreversibilities of the remaining components. In addition to that, mexogenous exergy destruction is a consequence of the interconnections of the irreversibilities in all components. Splitting the exogenous exergy destruction of the k-th component, E_ EX;r , shows the effect that the irreversibility within D;k
Combining the two mentioned approaches of splitting the exergy destruction, i.e. expressing total exergy destruction as the sum:
E_ D;k ¼ E_ AV;EN þ E_ AV;EX þ E_ UN;EN þ E_ UN;EX D;k D;k D;k D;k
ð8Þ
enables deeper and more sophisticated exergy analysis and might improve the quality of the derived conclusions [6]. The methodology for splitting the exergy destruction to avoidable and unavoidable parts, as well as endogenous and exogenous parts is presented in detail in Refs. [3,6,7,25]. Another variable related to each component k of an observed system is introduced in Ref. [5] with the purpose to use the results of the advanced exergy analysis to identify priorities for improving components. It is the sum of avoidable endogenous exergy destruction within the k-th component and of all the avoidable exogenous destructions within the other components caused by the k-th component [6]: R _ AV;EN þ E_ AV; D;k ¼ ED;k
n X E_ AV;EX;r D;k
ð9Þ
r¼1 r–k
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G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
3.3. Real, unavoidable and theoretical operation conditions The real operation conditions (ROC) are realistic currently achievable operation performance data for all the components of the observed energy system, e.g. actual thermodynamic efficiency. The unavoidable operation conditions (UOC) are also realistic operation data, but achievable only in perspective, i.e. in the future. Unavoidable operating conditions are those that cannot be achieved in a foreseeable or near future (e.g. the next decade) with the current trends of technological development. Their choice is arbitrary to some extent and depends on decision makers and their understanding of processes and theoretical backgrounds [13], as well as following current scientific and practical achievements. They are important when formulating the foreseen potential for further improvements of each component and accordingly determining the unavoidable part of the exergy destruction. Establishing UOC for each component requires the forecasts of the development tendencies and achievements for that type of component. Theoretical operation conditions (TOC) of a component cannot be achieved in practice. They are based on the assumption of ideal operation, e.g. with maximal theoretical efficiency. TOC are used to calculate endogenous and exogenous exergy destruction. In Table 1, the summary of the assumptions of real, unavoidable and theoretical operation conditions based on the adopted approach published in Ref. [25] is shown for the important components of the system for this analysis.
4. Results and discussion Table 2 provides the results of exergy analysis at the levels of the components. The values of thermodynamic and other parameters of the streams of matter are not illustrated here for brevity, but can be found in Ref. [18]. Table 2 presents the following quantities at the level of the components: exergy of the fuel (E_ F;k ), exergy of the product (E_ P;k ), exergy destruction (E_ D;k ), specific unavoidable exergy destruction UN (ðE_ D;k =E_ P;k Þ ), avoidable exergy destruction (E_ UN D;k ), unavoidable exergy destruction (E_ AV ), endogenous exergy destruction (E_ EN ), D;k
D;k
exogenous exergy destruction (E_ EX D;k ), the coefficient of total exergy destruction (yD;k ), exergetic efficiency.
5
The same Table presents the following quantities related to the entire plant: exergy of the fuel, exergy of the product, exergy destruction, exergy loss, the coefficient of total exergy destruction, exergetic efficiency. The influence of the technology consumers on the observed energy system is taken into account through the values of process fluids flows that correspond to the operation of the real plant and depend on the quantity of the final products. Exergetic efficiency of the overall energy system of 35.90% implies that the potential exists for total efficiency improvement and costs reduction. Exergy losses are mostly related to the streams of matter, especially exhaust gasses, but also to heat transfer to environment. The loss related to the exhaust gasses is 238.53 kW or 95.20% of total exergy losses. Total exergy losses (250.56 kW) are equal to 10.39% of the fuel exergy delivered to the entire energy system via the stream of matter number 5, while 58.54% of the fuel exergy supplied to the entire system is destroyed in the components of this system. Fig. 3 shows the value of the exergy of fuel, exergy of product and exergy destruction for the components. The steam generator has the greatest impact on reducing the exergetic efficiency of the overall system, given that it destroys 1132.21 kW of exergy, Table 1, Fig. 3. The steam generator has a high potential for increasing efficiency, keeping in mind that the exergy destruction in it amounts to 80.19% of the total exergy destruction in the system. In addition, exergetic efficiency of the steam generator is very low, 48.19%. Fig. 4 shows the current and maximal exergetic efficiency values of the components. It can be observed that the components with very low exergetic efficiency are: TCH (3.40%), SHW (6.46%), TSS (9.97%), PFH (15.96%), Table 1. However, it is important that high values of exergetic efficiency of these components cannot be achieved, i.e. they are respectively 26.64%, 28.47%, 46.46% and 36.96%, because the devices are not capable of utilizing available potential to produce work contained in the chemical exergy of steam. Besides, exergetic efficiency of the steam generator is below 50%, i.e. 48.19%, and can be improved only slightly, up to the maximum of 52.69%, due to imperfections in the combustion process. Fig. 5 illustrates the coefficients of exergy destruction of the components relative to the overall coefficient of exergy destruction related to the overall system. It can be observed that over 80% of total exergy destruction happens in the steam generator, thus it
Table 1 Real, unavoidable and theoretical operation conditions for the most important components of the system. Comp.
ROC
UOC
TOC
STB
g ¼ 90%; Q_ L – 0
g ¼ 98%; Q_ L 0
g ¼ 100%; Q_ L ¼ 0
PFH
DT min > 50 K; Q_ L – 0
DEA
pj ct: T 20 > T 46 ; T 19 > T 23
FWT
pj ct; T j – ct: Q_ L – 0 g ¼ 80% g ¼ 90%
Dp0 ¼ Dp00 0 DT min ¼ 50 K pj ct; T j ct: Q_ L 0 pj ct; T j ct: Q_ L 0 g ¼ 95% g ¼ 98%; T 26 ¼ T 24 T 29 ¼ T 26 2 K p ; T j ct; Q_ L 0
Dp0 ¼ Dp00 ¼ 0 g ¼ 100%; Q_ L ¼ 0 pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 g ¼ 100% g ¼ 100%; Q_ L ¼ 0 T 26 ¼ T 24 ; T 29 ¼ T 26 p ; T j ¼ ct; Q_ L ¼ 0
pj ct; T j ct: Q_ L 0 pj ¼ ct; T j ¼ ct: Q_ L 0 Dp0 ¼ Dp00 0 DT min ¼ 70 K;Q_ L 0 DT min ¼ 70 K Dp0 ¼ Dp00 0 DT min ¼ 60 K;Q_ L 0
pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 pj ¼ ct; T j ¼ ct: Q_ L ¼ 0 Dp0 ¼ Dp00 ¼ 0 g ¼ 100%; Q_ L ¼ 0
CP (1–5) CAS HWP STD & CWD CT (1–2) SHW TCH TSS
pj ; T j – ct; Q_ L – 0 pj ct; T j – ct: Q_ L – 0 pj – ct; T j – ct: Q_ L – 0 DT min > 70 K; Q_ L – 0 DT min > 70 K DT min > 60 K; Q_ L – 0
j
j
g ¼ 100% Dp0 ¼ Dp00 ¼ 0 g ¼ 100%; Q_ L ¼ 0
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G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
6
Table 2 Results of conventional and advanced exergy analysis for the most important components of the system. Components
Exergy analysis Conventional
STB PFH DEA FWT STP CAS ECT HWP CT1 CWT SHW TCH TSS CT2 COP Overall system Exergy loss
Advanced
E_ F;k
E_ P;k
E_ D;k
(kW)
(kW)
(kW)
2185.50 2.13 7.24 46.87 626.11 82.70 32.83 120.89 79.61 3.13 15.33 60.92 15.54 4.69 2.90 2582.59 250.56
1053.29 0.34 2.78 33.43 626.11 54.84 4.80 106.20 15.51 3.13 0.99 2.07 1.55 2.90 2.90 920.27
1132.21 1.79 4.46 13.44 0.00 27.86 28.03 14.69 64.10 0.00 14.34 58.85 13.99 1.79 0.00 1411.77
Variables
ðE_ D;k =E_ P;k Þ (–)
E_ UN D;k
E_ AV D;k
E_ EN D;k
E_ EX D;k
yD;k
ek
(kW)
(kW)
(kW)
(kW)
(–)
(%)
0.898 1.706 0.000 0.000 0.000 0.403 0.227 0.000 0.000 0.000 2.512 2.754 1.152 0.000 0.000
945.72 0.58 0.00 0.00 0.00 22.08 1.09 0.04 0.00 0.00 2.49 5.70 1.79 0.00 0.00
186.49 1.21 4.46 13.44 0.00 5.78 26.94 14.65 64.10 0.00 11.85 53.15 12.20 1.79 0.00
1097.63 1.58 4.33 4.24 0.00 27.86 22.75 14.49 63.56 0.00 14.16 58.76 13.96 2.18 0.00
34.58 0.21 0.13 9.20 0.00 0.00 5.28 0.20 0.55 0.00 0.18 0.09 0.03 -0.39 0.00
0.8020 0.0013 0.0032 0.0095 0.0000 0.0197 0.0199 0.0104 0.0454 0.0000 0.0102 0.0417 0.0099 0.0013 0.0000 1.0000
48.19 15.96 38.37 71.32 100.00 66.31 14.62 87.85 19.48 100.00 6.46 3.40 9.97 61.83 100.00 35.90
UN
Exergy of fuel
Exergy of product
Exergy destrucon
Values of exergy [kW]
2,500.00 2,000.00 1,500.00 1,000.00 500.00
STB PFH DEA FWT CP1 CP2 CD1 CD2 CD3 STP CAS CP3 ECT HWP CP4 CWD CT1 CWT CP5 SD4 SD5 SHW TCH TSS CT2 RV3 CP6 COP SB1 WB1
0.00
Components (Acronym) Fig. 3. Exergy of fuel, exergy of product and exergy destruction in components of system.
Curent
Maximal
100.00
Exergec efficiency [%]
90.00 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 STB PFH DEA FWT CP1 CP2 CD1 CD2 CD3 STP CAS CP3 ECT HWP CP4 CWD CT1 CWT CP5 SD4 SD5 SHW TCH TSS CT2 RV3 CP6 COP SB1 WB1
0.00
Component s (Acronym) Fig. 4. Real and maximal exergetic efficiency of the system components.
is obvious that this component influences the overall system efficiency the most. The values of maximal exergetic efficiencies are given in [18]. The ultimate goal of analyses of complex energy systems is the improvement of systems efficiency. Having in mind that current
exergetic efficiency of the system is 35.90%, Table 1, it is important to understand why this value is low. Useful quantities for this purpose are exergy destruction coefficient and exergy loss coefficient. Exergetic efficiency of the overall system and the influence of these coefficients on its value are illustrated in Fig. 6.
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G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
STB
PFH
DEA
FWT
CP1
CP2
CD1
CD2
CD3
CAS
CP3
ECT
HWP
CP4
CWD
CT1
CWT
CP5
SD4
SD5
SHW
TCH
TSS
CT2
RV3
CP6
COP
SB1
WB1
0.8
0
7
STP
0.9
1
Distribuon of overall coefficient of exergy destrucon Fig. 5. The coefficients of exergy destruction of the components and the overall coefficient of exergy destruction.
Out of 100% of the maximal overall exergetic efficiency, 43.66% is destroyed in the steam generator, 10.78% in all other components and 9.66% is due to energy system exergy losses. In Table 2, the results of the first and second level of exergy destruction splitting are shown, obtained within the frame of the advanced exergy analysis for the steam generator. This component is the part of the system correlated to the highest amount of the destructed useful work potential, i.e. has largest value of exergy destruction, as shown in the previous chapter. Within the frame of the first level of splitting, besides the results for unavoidable (E_ UN ) and avoidable exergy destruction D;k
_ EN (E_ AV D;k ), as well as endogenous (ED;k ) and exogenous exergy destruction (E_ EX ), shown in Table 1, this paper also presents the results of D;k
the decomposition of exogenous exergy destruction to the parts originating from the other components (E_ EX;r ) and the mexogenous D;k
exergy destruction (E_ MX D;k ) which is the consequence of the simultaneous influence of other components on the observed component. Thus, the following components are the most significant from the aspect of the influence on exogenous exergy destruction of the steam generator of 34.58 kW:
Heating substation – TSS (3.19 kW or 9.22%), condensate reservoir 2 – CT2 (2.69 kW or 7.78%), hall thermal comfort – TCH (2.51 kW or 7.26%), sanitary hot water preparation - SHW (2.42 kW or 6.94%).
D;k
D;k
) and unavoidable-exogenous unavoidable-endogenous (E_ UN;EN D;k ). Total unavoidable exergy destruction is 945.72 kW and a (E_ UN;EX D;k large part (919.47 kW or 97.28%) comes from the internal irreversibilities, while 25.75 kW (2.72%) is due to the influences of other components. Total avoidable exergy destruction is 186.49 kW and 177.66 kW (95.26%) is from the internal irreversibilities and 8.83 kW (4.74%) from the external irreversibilities. As a final result of the advanced exergy analysis for the steam generator, the total value of avoidable exergy destruction for the component of interest (E_ AV;R ) is presented: 183.33 kW or 16.19% D;k
In addition to that, the results of the additional splitting of external exergy destruction for the steam generator shown in Table 2 suggest that the influence of the components CP1, CP2
Exergec efficiency of the overall system and influence of these coefficient on maximal exegec efficiency [%]
and SD1 on exergy destruction in the steam generator (2.13 kW, 1.79 kW and 1.23 kW) is higher than internal exergy destruction in these components (0.15 kW, 0.01 kW and 0.58 kW) given in Table 3. These data illustrate that efficiency of the mentioned components has a significant impact on exergetic efficiency of the entire energy system [4]. External exergy destruction of the steam generator increases for 3.16 kW due to the simultaneous impact of all the other components (mexogenous exergy destruction), which is 9.14% of total external exergy destruction of this component, i.e. 0.28% of its total exergy destruction. Within the frame of the second level of splitting, the splitting of avoidable/unavoidable exergy destruction is combined with internal/external exergy destruction, i.e. the results are presented for avoidable-endogenous (E_ AV;EN ), avoidable-exogenous (E_ AV;EX ),
of total exergy destruction of the component. This value is somewhat smaller than the value obtained in the first level of splitting (186.49 kW) due to the existence of mexogenous exergy destruction components.
100.00 9.66
90.00 10.78
80.00 Exergy loss rao
70.00 60.00
Exergy destrucon rao of other components
43.66
50.00 35.90 43.66 10.78 9.66
40.00 30.00 20.00
Exergy destrucon rao of STB Exergec efficiency of overall system
35.90
10.00 0.00
Fig. 6. Exergetic efficiency of the entire system and the influence of exergy destruction coefficient and exergy loss coefficient on its value.
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8
Component
Exergy Analysis Conventional
Advanced (Detailed) First level of exergy destruction splitting
No.
1
k
STB
Second level of exergy destruction splitting
Splitting the Total Exergy Destruction
Splitting the Exogenous part E_ EX D;k
Unavoidable/avoidable
Endogenous/exogenous
Component
E_ D;k
E_ UN D;k
E_ AV D;k
E_ EN D;k
(kW)
(kW)
(kW)
(kW)
(kW)
No.
r
(kW)
(kW)
(kW)
(kW)
(kW)
(kW)
(kW)
1132.21
945.72 (83.53%)
186.49 (16.47%)
1097.63 (96.95%)
34.58 (3.05%)
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 E_ MX
PFH DEA FWT CP1 CP2 SD1 SD2 RV1 SD3 RV2 STP CAS CP3 ECT HWP CP4 CWD CT1 CWT CP5 SD4 SD5 RV4 SHW TCH TSS CT2 RV3 CP6 COP SB1 WB1
1099.29 1098.82 1099.15 1099.76 1099.42 1098.86 1099.13 1097.76 1099.24 1097.76 1097.63 1098.77 1097.63 1099.44 1099.03 1097.63 1097.63 1100.05 1098.31 1097.63 1098.49 1098.65 1097.76 1100.03 1100.14 1100.82 1100.32 1097.63 1097.63 1097.63 1097.63 1097.63
1.66 1.19 1.52 2.13 1.79 1.23 1.50 0.00 1.61 0.00 0.00 1.14 0.00 1.81 1.40 0.00 0.00 2.40 0.68 0.00 0.86 1.02 0.00 2.42 2.51 3.19 2.69 0.00 0.00 0.00 0.00 0.00 3.16
919.97 (97.28%)
25.75 (2.72%)
177.66 (95.26%)
8.83 (4.74%)
183.33 (16.19%)
E_ EN;rþ D;k
Splitting E_ UN D;k E_ EX;r D;k
E_ UN;EN D;k
R E_ AV; D;k
Splitting E_ AV D;k E_ UN;EX D;k
E_ AV;EN D;k
E_ AV;EX D;k
E_ EX D;k
D;k
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001
Table 3 Results of first and second level of exergy destruction splitting in advanced exergy analysis.
G.D. Vucˇkovic´ et al. / Energy Conversion and Management xxx (2015) xxx–xxx
5. Conclusions This paper presents the results of advanced exergy analysis for a real complex industrial plant, with emphasis on the main component (steam boiler) from the energy efficiency point of view. Exergetic efficiency of the overall energy system of 35.90% implies that the potential exists for total efficiency improvement and costs reduction. Exergetic efficiency of the steam generator is 48.19% and can be improved just slightly, up to maximal 52.69%, due to imperfections in the combustion process. Out of 100% of the maximal overall exergetic efficiency, 43.66% is destructed in the steam generator. The next four components are the most significant from the aspect of the influence on external exergy destruction of the steam generator: Thermal substation (9.22%), Condensate tank 2 (7.78%), Thermal comfort of hall (7.26%) and Sanitary hot water preparation (6.94%). Large part (97.28%) of the total unavoidable exergy destruction for Steam boiler comes from the internal irreversibilities, while 2.72% is due to the influences of other components. From the internal irreversibilities os steam boiler comes 95.26% of the total avoidable exergy destruction, and only 4.74% comes from the external irreversibilities. The final result of the advanced exergy analysis for the steam generator is the total value of avoidable exergy destruction, with 183.33 kW or 16.19% of total exergy destruction of the component. For the representative industrial plant, advanced exergy analysis without doubt ranks the improvement priority of the steam generator first. The research results have sufficient accuracy and a high degree of generality, since the selected reference plant consists of components that are encountered in most industrial and process plants, so that the advanced exergy analysis could be successfully applied to any complex thermal process plant and its components. This analysis provides an insight into realistic exergy efficiency improvement potential related to the boiler operation, taking into account the influence of other components as well. It may be used to evaluate possible enhancements of the system, but also to compare different steam generating options – technologies and fuels. Investigating the implications of boiler or fuel switching using the advanced exergy analysis is a possible direction for the future work. References [1] BP statistical review of the world energy
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Please cite this article in press as: Vucˇkovic´ GD et al. First and second level of exergy destruction splitting in advanced exergy analysis for an existing boiler. Energy Convers Manage (2015), http://dx.doi.org/10.1016/j.enconman.2015.06.001