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Energy and exergy analyses of a biogas driven multigenerational system
Accepted Manuscript Energy and Exergy Analyses of a Biogas Driven Multigenerational System
Eren Sevinchan, Ibrahim Dincer, Haoxiang Lang PII:
S0360-5442(18)32075-9
DOI:
10.1016/j.energy.2018.10.085
Reference:
EGY 13982
To appear in:
Energy
Received Date:
18 April 2018
Accepted Date:
15 October 2018
Please cite this article as: Eren Sevinchan, Ibrahim Dincer, Haoxiang Lang, Energy and Exergy Analyses of a Biogas Driven Multigenerational System, Energy (2018), doi: 10.1016/j.energy. 2018.10.085
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ACCEPTED MANUSCRIPT Energy and Exergy Analyses of a Biogas Driven Multigenerational System Eren Sevinchan, Ibrahim Dincer, Haoxiang Lang Clean Energy Research Laboratory, Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario L1H 7K4, Canada
Abstract In this study, energy and exergy analyses of a biogas driven multigeneration system is conducted for performance assessment and evaluation. In this regard, the multigeneration system with a biomass digestion process is developed for this purpose. Multigeneration system consists of a two-stage biomass digester, an open-type Brayton cycle, an Organic Rankine Cycle (ORC), a single-effect absorption chiller, a heat recovery subsystem, a water separator. This multigeneration system aims to generate electrical power for at least 300 houses, heating power for five greenhouses, cooling power and product water from flue gas for agricultural consumption in greenhouses. The analysis results indicate that the overall energy efficiencies of the proposed system is 72.5% with 1078 kW electrical, 198 kW heating, and 87.54 kW cooling power, and daily around 40 kg water production. However, the maximum exergy efficiency of the multigeneration system is obtained as 30.44%, with 65% of the highest exergy destruction rate in combustion chamber. Keywords: Biogas, multigeneration, Organic Rankine Cycle, energy, exergy, efficiency. 1. INTRODUCTION The energy demand of the world population increases dramatically due to fast-developing technology in recent years. There is no doubt that the impact of these constantly increasing technological developments on our planet is more than ever before. Therefore, clean and effective production of energy has a significant role to supply energy demand of the world by more environmentally friendly methods. Thus, energy production methods, fuels types and clean fuel production processes are important and need to be further investigated. In this case, energy production from biogas is emerged because of its multi-directional consumption. As a renewable energy source, biogas can be produced from various resources, such as animal, agricultural and organic wastes. Meanwhile, digestate that is a product of biogas digestion process is enabled to be used as fertilizer in agriculture. Furthermore, the impact of the biogas on the environment is less than any other fossil fuels, which makes biogas one of the cleanest and most effective energy sources. In conjunction with this, the distribution of renewable energy sources for power generation are presented in Figure 1. Biogas is a gas mixture, which consists of various content of methane, carbon dioxide, nitrogen, oxygen, hydrogen sulfide, water vapor, ammonia and low concentration of hydrocarbons, based on chemical properties of biomass and biogas production method. Out of methane, other gasses are considered as biogas pollutant, which is not wanted in the content of biogas. When CO2 and N2 content increase, the lower heating value (LHV) of biogas, which has the highly significant effect on energy and exergy efficiency of the system, decreases corresponding to biogas pollutant content of biogas. Because of this reason, some biogas upgrading methods have been developed in the literature to remove biogas pollutant content of the gas, which increases LHV of the fuel. Figure 2 demonstrates biogas-upgrading methods where chemical scrubber, membrane, and water scrubber methods have the highest percentage, respectively. 1
ACCEPTED MANUSCRIPT There are some advantages of biogas consumption, which makes it enable to be used in many different application areas. Biogas is a gas that can be produced when it is required and easily to be stored [1]. On the other hand, it can be easily consumed as a fuel for cooking and transportation [2]. Biogas and bio-methane consumption in transportation can decrease greenhouse gas emissions by 60-80% in comparison to gasoline [3]. However, biogas consumption may decrease nitrogen oxide emissions as well [4]. Depending on this high environmentally efficient feature of the biogas, it is expected to increase its consumption in energy generation. In addition, the major part of the energy generation has been suggested to be supplied biogas sources by European Union for the year of 2020. However, the 25% of this biogas production can be produced by wet organic materials [5]. Furthermore, in the agricultural sector of European Union, 1500 million tons of biomass can be digested in anaerobic digesters in a year [6]. Multigeneration energy systems are systems that have more than three useful outputs. These outputs may vary, but they are usually electricity, heating, cooling and another useful output, such as hydrogen, water, ammonia etc. Multigeneration is the most effective system, which takes advantage of waste heat as a heat source for other applications in the system. The applications that utilize waste heat to operate may be district heating, absorption cooling systems or another energy system that produces electrical power, such as Organic Rankine Cycle (ORC). Energy and exergy efficiency of these systems significantly depend on how waste heat is effectively used. In this case, there is no doubt that the energy efficiency of a multigeneration system is expected to be higher than other energy systems, such as co-trigeneration systems. Therefore, effective consumption of waste heat is a significant parameter, which determines the efficiency of the system. In the open literature, there are a lot of different co-tri and multi-generation power plants, which use biogas as main fuel [7β9]. Gazda et al. [10] have developed a biogas-fired trigeneration system, where electricity, cooling and heating generation are supported by a photovoltaic system (PV). According to their results, the energy efficiency increases between almost 37% and 43% based on load ratio from 50% to 100%. Meanwhile, the decrease of greenhouse gasses and energy savings in average have been found as 67.37% and 54.50% respectively [10]. Huicochea et al. [11] have studied a trigeneration system that has a 28 kW micro turbine and a double-effect absorption chiller to supply cooling power for the system. Bruno et al. [12] have studied another biogas driven trigeneration energy system, which consists of a micro gas turbine (MGT) and absorption cooling system with 24.92% net electrical efficiency. Cacua et al. [13] analyzed a trigeneration system that is driven by diesel-biogas dual fuel, where waste heat is consumed for heating air and absorption unit freezer. According to their results, overall energy efficiency of the system is 40% with diesel fuel and 31% with dual fuel. Although biogas is widely used in many energy systems as fuel, biomass is also another option to generate electricity. Ahmadi et al. [14] designed and analyzed biomass-driven multigeneration energy system, where they obtained overall exergy efficiency of the system is 22.20% with the electricity generation of 671 kW. Although biogas can be used as main fuel of an energy generation system, it also can be used in hybrid systems. A hybrid energy system, which consists of biogas, is studied by Su et al. [16] to improve energy performance of a trigeneration system by using additional solar energy system. According to their results, energy efficiency of the system varies between almost 38.5% and 48% corresponding to different power load of the system, where the 2
ACCEPTED MANUSCRIPT maximum 1600.2 kW cooling energy production takes place. However, Coskun et al. [17] were analyzed hydrogen production from biogas based electricity, where they achieved energy efficiency of the overall system between 7.86% and 86.90% depends on three different types of electrolysers. Furthermore, biomass also can be used directly as an energy source in an energy system. The current studies mostly focus on energy analysis of biogas driven co-trigeneration energy systems. However, there is a gap in terms of design and analysis of a biogas energy system with all aspects, such as exergy analysis of biogas production, the environmental impact of the system for the same system. The objective of this study is to design a biogas driven multigeneration energy system and analysis this system from the energetic, exergetic and environmental point of view. This biogas driven multigeneration energy system produces biogas from chicken manure and maize silage, and generates electricity, heating and cooling power. In addition to these three outputs, the water content of the flue gas of the system passes through a water separator to provide water for agricultural usage. Energy and exergy analysis and environmental impact assessment of the system will be examined in detail for each component of the system in this study. 2. SYSTEM DESCRIPTION In this study, biogas driven multigeneration system consists of various subsystems, such as a two-stage biomass digester, Brayton Cycle, single-effect absorption chiller, Organic Rankine Cycle (ORC), greenhouse heating and water separation of flue gas. As a biomass input of the biogas production subsystem, the mixture of chicken manure and maize silage has been considered, with 70000 kg and 30000 daily input respectively. Since biomasses have various chemical content depending on biomass type, individual consideration of these two biomasses is a significant point for energy and exergy analysis of biogas production process. Table 1 shows chemical composition of chicken manure, maize silage, and digestate, which is the product of biogas production process. Figure 3 illustrates the layout of the designed system, where two-stage biogas production has been preferred to enhance the quality of the produced biogas in the system. As a feature of two-stage biomass digestion systems, the first three steps of biogas production, which are hydrolysis, Acidogenesis and Acetogenesis, take place in the first digester; while the last step, methanogenesis, occurs in the second digester. After biomass digestion, biogas passes through a gas pre-heater to improve combustion quality in the combustion chamber. The heated biogas comes to combustion chamber mix with amount of compressed air, which depends on air-fuel ratio of biogas. After the combustion process, exhaust air operates a turbine to demand primary electricity generation of the system. Biomass digester units are heated by the exhausted gas after the turbine process to keep them around 35oC. Single effect absorption chiller takes place after biomass digester heating process. Exhausted air passes through generator of the absorption chiller to supply sufficient energy input to produce cooling power. After that, ORC is operated with exhaust air to generate secondary electrical power generation of the system, which is lower than the electricity production in Brayton Cycle. After the condenser of ORC, super heated n-octane, which is the working fluid of the ORC, is used for gas pre-heater process of the biogas. Greenhouse heating process is after ORC to supply heating power for five greenhouses to keep their temperature 3
ACCEPTED MANUSCRIPT around 29 oC. As a final process, the vapor water content of the exhaust air has been taken by a water separator to produce as high as possible amount of water for agricultural usage. System has been developed to supply electrical energy demand of at least 300 houses, heat 5 greenhouses, and provide cooling power and produce water for agricultural purposes. According to Statistic Canada [20], average of annual energy consumption per house is estimated as 105 GJ. The required electrical energy for 300 houses can be found as π πΈ =
105πΊπ½ Γ 300 βππ’π ππ = 3.59 πΊπ½/πππ¦ 365 πππ¦π Γ 24 βππ’ππ
(1)
The required total electrical energy need of 300 houses is estimated as above, which is 3.59 GJ per day. 3. ENERGY AND EXERGY ANALYSES There are several assumptions in energy and exergy analyses of the multigeneration system, which are shown in Table 2 with some input data of the system. First of all, system is assumed to operate at steady state conditions. In addition, pressure change in the system is neglected except for changes in pumps, valves, and turbines. Furthermore, combustion in the combustion chamber is studied as complete combustion with 80% thermal efficiency. In addition, the model for single-effect absorption chiller is validated with the data from Dincer et al. [21]. 3.1 Energy Analysis Energy analysis is studied for cogeneration heating, cogeneration cooling, trigeneration and multigeneration systems. The net power of the cogeneration heating, cogeneration cooling, and trigeneration systems is defined as (2)
ππππ‘ = ππ,π΅ + ππ,ππ πΆ β πππππ β πππ’πππ
where π is the power and the subscripts eB, eORC, comp, pumps, ws indicate electricity generation of Brayton Cycle, electricity generation of ORC, compressor, pumps and water separator, respectively.
The net electrical power generation of the Brayton cycle is defined as ππ,π΅ = ππππππ,π΅ β πππππ where gen, TB, and comp indicate the generator, turbine of the Brayton Cycle and compressor, respectively. On the other hand, the net electricity generation in the ORC subsystem is defined as ππ,ππ πΆ = ππππππ,ππ πΆ β πππ’ππ
The net electrical energy efficiency of the system is defined as below and verified in multigeneration, trigeneration, cogeneration heating and cooling applications. πππ,ππ =
ππππ‘ πππ
(3)
where πππ indicates total heat input rate of the system, while subscript en,el is electrical energy efficiency.
4
ACCEPTED MANUSCRIPT (4)
πππ = ππππ Γ πΏπ»π
where ππππ is mass flow rate of the biogas and LHV defines lower heating value, which is 17.52 MJ. Cogeneration energy efficiency of heating is defined as πππ,ππβ =
ππππ‘ + πβ
(5)
πππ
where en,coh is heating cogeneration energy efficiency, πβ is heat power that produced for greenhouse heating process, which is defined as (6)
πβ = π26β26 β π27β27 On the other hand, cogeneration energy efficiency for cooling is estimated as ππππ‘ + ππ
πππ,πππ =
(7)
πππ
where en,coc is cooling cogeneration energy efficiency, ππ is cooling power that produced by the system, which is defined as (8)
ππ = π13β13 β π12β12
Trigeneration energy efficiency is also defined as Equation 9, where heating, cooling and electricity generation are products of the system. πππ,π‘ππ =
ππππ‘ + πβ + π
π
(9)
πππ
Net power output of multigeneration is defined as ππππ‘,π, which can be found by Equation 10. ππππ‘,π = ππ,π΅ + ππ,ππ πΆ β πππππ β πππ’πππ β ππ€π
(10)
Finally, multigeneration energy efficiency is indicated as Equation 11, where electricity generation, heating, cooling and water production are products of the system. πππ,ππ’ππ‘π =
ππππ‘,π + πβ + π
π
(11)
πππ
3.2. Exergy Analysis The total exergy rates for each component in the system are calculated by following equation: ππ₯π‘ππ‘ππ = ππ₯ where ππ₯
ππ»
ππ»
+ ππ₯
πΆπ»
(12)
is physical exergy rate per mass flow, which is defined as 2
ππ₯
ππ»
= ππ₯π = βπ β βπ β ππ (π π β π π) +
2
π β π0 2
+ π(π§ β π§0)
(13)
Here, s, V, z, and g indicate enthalpy, entropy, velocity, elevation and gravity, respectively, while j shows state point number, and 0 determines property of surrounding environment. 5
ACCEPTED MANUSCRIPT However, ππ₯ 14 [22]. ππ₯
πΆπ»
determines chemical exergy rate per mass flow, and it can be found by Equation
πΆπ» πΆπ» π = ππ(π₯πππ₯ π + π π0π₯πln (π₯π))
where ππ and ππ₯
πΆπ» π
(14)
are molecular weight and standard chemical exergy value for each state
points, respectively. On the other hand, R and x determine universal gas constant and molar concentration. Furthermore, exergy destruction is another significant value, which indicates the potential work lost due to irreversibility. Exergy destruction for each state point is defined as
( ) π0
πΈπ₯π = βπ 1 β π ππ β π + βπππππ₯π β βπππππ₯π
(15)
π
where T and πΈπ₯π show temperature and exergy destruction rate, respectively. Finally, electrical exergy efficiency of the system can be defined as net power output of the system over chemical exergy of the fuel as Equation 16. πππ₯,ππ =
ππππ‘
(16)
ππ
where ππ is chemical exergy efficiency of the fuel, which is defined as (17)
ππ = πππππΏπ»π
The cogeneration heating exergy efficiency is defined as Equation 18, where electrical and heating power are outputs of the system.
( ( )) π
ππππ‘ + 1 β
πππ₯,ππβ =
π
0
π
βπ
β
(18)
ππ
The cogeneration cooling exergy efficiency is defined as
( ( )) π
ππππ‘ + 1 β
πππ₯,πππ =
π
0
ππ£π
ππ
(19)
ππ
The trigeneration exergy efficiency, which generate electricity, heating and cooling power.
( ( )) ( ( )) π
π
0
0
ππππ‘ + 1 β π πβ + 1 β π π βπ ππ£π
πππ₯,π‘ππ =
π
(20)
ππ
Finally, the exergy efficiency of multigeneration system is defined as
( ( )) ( ( )) π
π
0
0
ππππ‘,π + 1 β π π + 1β π π βπ ππ£
πππ₯,ππ’ππ‘π =
β
ππ
π
(21)
In addition, exergy analysis of biomass digestion process is also studied at steady state conditions. For the chemical exergy analysis of two-stages biomass digester, chemical exergy 6
ACCEPTED MANUSCRIPT rates of organic substances, which are biomass and digestate, during the process are analysed by equation of Song et al. [23]. ππ₯ππ = 362.0083C+1101.841H-86.218O+2.418N+196.701S-21.1A
(22)
where C, H, O, N, S and A determine organic content of the substances, which are carbon, hydrogen, oxygen, nitrogen, sulphur and ash, respectively. This equation is applied for biomass input, biomass substances between two stages, and digestate. However, as a gas content of biogas, chemical exergy rate should be defined for both first and second digester, depending on their products of chemical reactions. The chemical exergy of a gas mixture is defined as π ππ₯πβ = βπ₯πππ₯πβ + π π0βπ₯πln (π₯π)
(23)
4. RESULTS AND DISCUSSION The performance of the system is analysed in five different cases, such as single electricity generation system, cogeneration-heating system, cogeneration-cooling system, trigeneration and multigeneration systems through different parameters for both energetically and exergetically. These parameters are daily biomass input of the system, ambient temperature, and compression ratio. During the thermodynamic analyses, the input data of the system are kept constant at the values that are tabulated in Tables 1 and 2. On the other hand, Table 3 gives the multigeneration system outputs. The greenhouse heating takes place between state point 26 and 27, which requires 198 kW heating power for five greenhouses in ambient temperature of 25β. The net electrical power output is estimated as 1078 kW, which is enough to supply electricity to 326 houses [20]. However, coefficient of performance value of single-effect absorption chiller is defined as 0.68. Thermodynamic properties of each state points are listed in Table 4, where it can be seen that the temperature 4.1. Effect of daily amount of biomass input The daily biomass input of the multigeneration system is defined as 70000 kg chicken manure and 30000 kg maize silage, which makes 100000 kg biomass input in total. There is no doubt that daily amount of biomass input to the biomass digesters has one of the biggest impact on the performance of the system. The increase of the biomass input causes more production of daily biogas. Depending on this change in biogas flow rate, mass flow rate of system increases as well because of air-fuel ratio of the biogas, as long as mass flow rate of the system is not fixed to a specific number or not stored for a further consumption. According to Figure 4, it is clear to see that increase of the daily biomass input goes up from 100000 kg to 150000 kg, while net electrical power output of the system increases between 1000 kW to 1394 kW. On the left side of the graph, increase of the number of houses that can provide from the generated electrical energy in the system is studied corresponding to the net power output of the multigeneration system. As it is discussed before, daily electrical energy need of a house is estimated as 105 GJ in Canada, according to Statistic Canada [20]. Therefore, ratio of electrical power output and daily energy need of a house provides the number of the houses that can access sufficient amount of daily electrical power from the system, which increases from 300 to 420 houses. 4.2. Effect of ambient temperature 7
ACCEPTED MANUSCRIPT The ambient temperature is another parameter that effects performance of the system both energetically and exergetically. When the ambient temperature increases between 288 K and 303 K, ambient air enters the compressor with a high temperature and enthalpy, which also affects the turbine inlet temperature. Depending on this temperature change in the system, net electrical power energy of the system slightly increases from 1048 kW to 1093 kW. The change of the net electrical power output is not a significant difference for the system; however, it has a significant impact on heating power output. In the multigeneration system, heating output of the system is used for space heating of five greenhouses. Since greenhouses should be kept at a specific temperature depending on the best temperature for plants in the greenhouse, heating power output of the multigeneration system decreases when the ambient temperature reaches greenhouse temperature, which is around 29 oC. Therefore, heating power output of the multigeneration system declines from 455 kW to 69.46 kW, while ambient temperature varies between 288 K and 303 K. From energy efficiency point of view, it can be seen that the energy efficiency of cooling cogeneration system and system with only electrical power generation increases from 41.63% to 43.27% and from 38.47% to 40.11%, respectively. The effect of the cooling load and the decrease of the heating power output are main reasons for this energy efficiency variation corresponding to change in ambient temperature. When the amount of required heat that produced by the system for heating applications decrease, the energy efficiency of the system decrease too, which means less energy output from the system and less energy efficiency. This situation can be clearly seen for energy efficiencies of heating cogeneration, trigeneration, and multigeneration. The variation of the ambient temperature has also an impact on exergy efficiency of the system. Figure 5 indicates that exergy efficiency of the system slightly increases around 1% for all systems depending on their useful products, such as heating-cooling cogeneration, trigeneration and multigeneration. However, the effect of the change in ambient temperature on exergy efficiencies comes from the definition of the exergy rate of the heating and cooling power outputs. As it is showed in Equation 17, exergy rate of heat power has linear relation with the ratio of ambient and surface temperature. When ambient temperature increases, exergy rate of heating and cooling power outputs of the system increases too, which is a reason of 1% increment in exergy efficiency of cooling-heating cogeneration, trigeneration and multigeneration systems. 4.3. Effect of compression ratio The compression ratio, which is denoted as rp, is a ratio of the absolute stage discharge and suction pressure. The compression ratio of the compressor is defined as 3 at the beginning of the analysis, and then it increased from 3 to 8 to see the effect of the ratio on performance of the system. Thus, the net electrical power output of the system increases from 1078 kW to 1704 kW depending on the compression ratio in Figure 6. On the other hand, energy efficiency of the system increases to because of this change in net electrical power output of the system. Since trigeneration and multigeneration systems have more useful outputs than other systems, their ratio of useful output and the heat input of the system is higher than cogeneration. Therefore, their energy efficiency are higher than other three system types. It can be seen that the energy efficiency of the trigeneration system is higher than multigeneration system because of the additional work input of the multigeneration 8
ACCEPTED MANUSCRIPT system. Multigeneration system has more useful output than other systems but its required energy is higher than others, which keeps its energy efficiency lower than other systems. However, the maximum energy efficiency, which is 69.34%, can be seen for trigeneration system when the compression ratio is 8, while the system with only electricity generation has the lowest energy efficiency, 39.56%, with compression ratio of 3. From exergy efficiency point of view, Figure 7 shows the variation of exergy efficiencies corresponding to change in compression ratio. There is no doubt that exergy efficiency of the system increases because of the increase of the compression ratio from 3 to 8. Depending on the compression ratio, pressure and temperature of compressed air varies. High compression ratio means the inlet air with higher temperature and pressure, which increases the performance of the system. This situation can be clearly seen in Figure 7, where the exergy efficiency and the net electrical power output of the system increase. As it is discussed before, the exergy efficiency of the trigeneration is higher than the multigeneration system because of the additional electrical work input of the water separator. The exergy efficiency of the multigeneration system increases between 30.44% and 48.23%, while total electrical energy that generated by the multigeneration system varies from 1078 kW to 1704 kW. 4.4. Effect of mass flow rate of the system The mass flow rate of the system can be defined based on biogas production of the system, since biogas has an air-fuel ratio that determine the mass flow rate. In this analysis, the mass flow rate of the biogas is changed to see the change in mass flow rate of the system and its effects on cogeneration heating, cogeneration cooling, electricity generation, trigeneration and multigeneration efficiencies. In this analysis, the mass flow rate of the biogas increases from 0.18 kg/s to 2.1 kg/s, which causes to increase of the mass flow rate of the system between 3.86 kg/s and 5.78 kg/s. Figure 8 indicates that energy efficiency of the multigeneration system decreases from 50.03% to 48.89%, because of the decrease of the net power output of the system, which changes between 1099 kW and 1068 kW. On the other hand, energy efficiency of the trigeneration concept of the same system again decreases from 50.65% to 49.51%. It can be seen that the variation of the energy efficiency is not a huge change in the system. To illustrate that, even cogeneration cooling and heating concepts have only around 1% difference corresponding to mass flow rate change of the system. Furthermore, the lowest energy efficiency can be seen in the system that has only electricity generation, which goes down from 40.33% to 39.19%. On the other hand, energy efficiency of the trigeneration concept of the same system again decreases from 50.65% to 49.51%. It can be seen that the variation of the energy efficiency is not a huge change in the system. To illustrate that, even cogeneration cooling and heating concepts have only around 1% difference corresponding to mass flow rate change of the system. Furthermore, the lowest energy efficiency can be seen in the system that has only electricity generation, which goes down from 40.33% to 39.19%. 4.5. Effect of the mass flow rate of the single-effect absorption chiller The effect of the mass flow rate of the single-effect absorption chiller on coefficient of performance (COP) of the chiller, energy and exergy efficiencies of the multigeneration system have been analyzed. The mass flow rate of the solution has been varied, and the mass flow rate of the working fluid of the chiller is changed. The mass flow rate of the working fluid has a 9
ACCEPTED MANUSCRIPT significant role on performance of the single-effect absorption chiller. Since it affects the amount of heat that can be absorbed from the cooled space, investigation of the mass flow rate is a good way to see the effect of the mass flow rate of the chiller on overall system. The COP value of the multigeneration system has been found as 0.68 in the assumed conditions of the multigeneration system. However, it varies from 0.68 to 0.79 depending on the change of the mass flow rate of the cooling system. This COP change indicates that the cooling power of the system increases by the upward change in mass flow rate of the single effect absorption chiller. Furthermore, this situation has an effect on energy and exergy efficiencies of the multigeneration system. Since the cooling power of the system increases by the change in mass flow rate of the working fluid of the cooling system, the overall energy and exergy efficiencies of the multigeneration system increases corresponding to this change in mass flow rate. The energy efficiency of the multigeneration system increases from 50.03% to 54.13%, while the exergy efficiency of the system changes between 30.09% and 31.13%. In addition, Figure 10 shows the exergy destruction of different components in the system, which have the highest rate. In this case, the exergy destruction of the combustion chamber is the highest rate with 1137 kW, while first biomass digester has an exergy destruction rate of 243.6 kW. All the components that have been showed in Figure 10 are components that have such processes which require a huge amount of heat input or output with large rate of losses. 5. CONCLUSIONS Energy and exergy analyses of a biogas-driven multigeneration system are conducted in this study. Performance of the system is studied under variation of different parameters, such as ambient temperature, daily biomass input and compression ratio, from both energy and exergy point of view. The main concluding points of this study are listed as follow: ο·
ο·
ο· ο·
ο·
Multigeneration system is enable to produce 1078 kW electrical, 198 kW heating, 87.54 kW cooling power, and daily almost 40 kg water for greenhouses at 25β temperature and 101.34 kPa pressure. There is no doubt that the energy and exergy efficiencies of the system increases when it produces more useful output. It can be seen in the parametric analyses, energy and exergy efficiency of the multigeneration system are always higher than other cogeneration and single generation figurations of the system, which are 72.5 % and 30.44% respectively. The maximum electrical power energy efficiency is 40.11%, maximum cooling energy efficiency is 62.18%, and maximum heating energy efficiency is 65.35%. The generated electrical energy in the system is a sufficient power to supply electricity for around 300 houses daily, according to the statistics. In this case, storage of the additional electricity generation would be a solution for more efficient consuming of the electricity. Furthermore, depending on the daily biomass input of the system, the amount of biogas that produced additional would be stored for further usage. The combustion chamber of the Brayton Cycle has the highest exergy destruction rate with 65%. The other components with high exergy destruction rate are evaporator of the ORC and biomass digesters, with 9.2% and 14.3% exergy destruction rates, respectively.
NOMENCLATURE 10
ACCEPTED MANUSCRIPT ππ₯ πΈπ₯ g h LHV π M MGT π ORC P π R rp s T v π wt. % x z
Exergy per unit mass, kJ/kg Exergy rate, kW Gravity, m/s2 Enthalpy per unit mass, kJ/kg Lower heating value, kJ/kg Mass flow rate, kg/s Molecular weight, kg/mol Micro gas turbine Molar flow rate, mol/s Organic Rankine Cycle Pressure, kPa Heat rate, W Universal gas constant, J/mol.K Compression ratio Entropy per unit mass, kJ/kg.K Temperature, K Velocity, m/s2 Work, W Wet basis Molar concentration Elevation, m
Greek letters π
Efficiency
Subscripts 0 abs bio c coc coh comp con d d.b. e,B el en eva ex f gen h hp in multi net net, m OM
Ambient conditions Absorber Biogas Cooling Cogeneration-Cooling Cogeneration-heating Compressor Condenser Destruction Dry basis Electricity generation-Brayton Cycle Electricity generation Energy Evaporator Exergy Fuel Generator Heating Heat process Inlet Multigeneration Net Net-Multigeneration system Organic matter 11
ACCEPTED MANUSCRIPT tri ws
Trigeneration Water separator
Superscripts CH PH
Chemical Physical
REFERENCES [1]
Panwar NL, Kaushik SC, Kothari S. Role of renewable energy sources in environmental protection: A review. Renewable Sustain Energy Rev 2011;15:1513β24. [2] Berglund M, BΓΆrjesson P. Assessment of energy performance in the life-cycle of biogas production. Biomass and Bioenergy 2006;30:254β66. [3] Sahota S, Shah G, Ghosh P, Kapoor R, Sengupta S, Singh P, et al. Review of trends in biogas upgradation technologies and future perspectives. Bioresource Technolgy Reports 2018. [4] Rasi S, LΓ€ntelΓ€ J, Rintala J. Trace compounds affecting biogas energy utilisation - A review. Energy Conversation Management 2011;52:3369β75. [5] Holm-Nielsen JB, Al Seadi T, Oleskowicz-Popiel P. The future of anaerobic digestion and biogas utilization. Bioresource Technolgy 2009;100:5478β84. [6] Weiland P. Biogas production: Current state and perspectives. Applied Microbiology Biotechnolgy 2010;85:849β60. [7] Li H, Zhang X, Liu L, Zeng R, Zhang G. Exergy and environmental assessments of a novel trigeneration system taking biomass and solar energy as co-feeds. Applied Thermal Engineering 2016;104:697β706. [8] Su B, Han W, Jin H. Proposal and assessment of a novel integrated CCHP system with biogas steam reforming using solar energy. Applied Energy 2017;206:1β11. [9] Leonzio G. An innovative trigeneration system using biogas as renewable energy. Chinese Journal of Chemical Engineering 2018. [10] Gazda W, Stanek W. Energy and environmental assessment of integrated biogas trigeneration and photovoltaic plant as more sustainable industrial system. Applied Energy 2016;169:138β49. [11] Huicochea A, Rivera W, GutiΓ©rrez-Urueta G, Bruno JC, Coronas A. Thermodynamic analysis of a trigeneration system consisting of a micro gas turbine and a double effect absorption chiller. Applied Thermal Engineering 2011;31:3347β53. [12] Bruno JC, Ortega-LΓ³pez V, Coronas A. Integration of absorption cooling systems into micro gas turbine trigeneration systems using biogas: Case study of a sewage treatment plant. Applied Energy 2009;86:837β47. [13] Cacua K, Olmos-Villalba L, Herrera B, Gallego A. Experimental evaluation of a dieselbiogas dual fuel engine operated on micro-trigeneration system for power, drying and cooling. Applied Thermal Engineering 2016;100:762β7. [14] Ahmadi P, Dincer I, Rosen MA. Development and assessment of an integrated biomassbased multi-generation energy system. Energy 2013;56:155β66. [15] Angelidaki I, Treu L, Tsapekos P, Luo G, Campanaro S, Wenzel H, et al. Biogas upgrading and utilization: Current status and perspectives. Biotechnolgy Advance 2018;36:452β66. [16] Bosheng S, Zefeng W, Wei H, Hongguang J. Using solar energy to improve the energy performance of trigeneration systems for sewage treatment plants. Energy 2017;142:873β9. [17] Coskun C, Akyuz E, Oktay Z, Dincer I. Energy analysis of hydrogen production using 12
ACCEPTED MANUSCRIPT
[18] [19] [20] [21] [22] [23]
biogas-based electricity. International Journal of Hydrogen Energy 2011;36:11418β24. Fantozzi F, Buratti C. Biogas production from different substrates in an experimental Continuously Stirred Tank Reactor anaerobic digester. Bioresource Technolgy 2009;100:5783β9. Pfeifer J, Obernberger I. Technological Evaluation of an agricultural biogas chp plant as well as definition of guiding values for the improved design and operation. 15th Eur. Biomass Conf. Exhib., Berlin: 2007. Statistics Canada. Households and the Environment: Energy Use. Ottawa: 2011. Al-Sulaiman FA, Dincer I, Hamdullahpur F. Energy and exergy analyses of a biomass trigeneration system using an organic Rankine cycle. Energy 2012;45:975β85. Dincer I, Rosen MA. Exergy: Energy, Environment and Sustainable Development. 2nd ed. Elsevier; 2013. Song G, Xiao J, Zhao H, Shen L. A unified correlation for estimating specific chemical exergy of solid and liquid fuels. Energy 2012;40:164β73.
13
ACCEPTED MANUSCRIPT
Figure 1. Distribution of renewable energy sources for power generation in years (data from Ref. [1]).
Figure 2. Distribution of current technologies for biogas up grading methods (data from Ref. [15]).
ACCEPTED MANUSCRIPT
Manure Tank
1
Mixer
Agricultural Waste Tank
2
Process Line Biogas Line Water Line
4
Digester with Gas Holder
3
Digester
Digestate Storage Tank
32
31
33
34
Gas pre-heater Combustion Chamber
Generator Electrical Power
30 35 36
5
29
7 8 Generator
Greenhouse
37
Turbine
Compressor
38
Electrical Power
Water Separator
39 9
6
10 Heat Recovery
11 12 14
13
Condenser
Generator
15 25
26
24
27
23
28
16 Refrigerant Expansion Valve
Solution Pump
17
18
Solution Expansion Valve
20
Evaporator
19
Solution Heat Exchanger
Absorber
21 22
Figure 3. The layout of biogas driven multigeneration system.
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Figure 4. Effect of daily amount of biomass on net power output and corresponding number of houses.
Figure 5. Effect of ambient temperature on energy and exergy efficiencies, net electrical power and heating power output.
ACCEPTED MANUSCRIPT
Figure 6. Effect of compression ratio on energy efficiency and net electrical power output.
Figure 7. Effect of compression ratio on exergy efficiency and net electrical power output.
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Figure 8. Effect of mass flow rate of the system on energy efficiencies and net power output.
Figure 9. Effect of the mass flow rate of the single-effect absorption chiller on COP, energy and exergy efficiencies of the multigeneration system.
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Figure 10. Exergy destruction of different components in the system.
ACCEPTED MANUSCRIPT HIGHLIGHTS ο· ο· ο· ο·
The overall energy efficiencies of the proposed system is 72.5%. The maximum exergy efficiency of the multigeneration system is obtained as 30.44%. Combustion chamber has the highest exergy destruction rate with 65%. 1078 kW electrical, 198 kW heating and 87.54 kW cooling power are obtained.
ACCEPTED MANUSCRIPT Table 1. Chemical composition of substrates and digestate. Definition
Poultry litter [18]
Maize Silage [19]
Digestate [19]
C [wt%kg d.b.]
37.50
33.71
35.34
H [wt%kg d.b.]
5.5
4.47
4.53
N [wt%kg d.b.]
4.7
11.16
5.35
O [wt%kg d.b.]
29.4
16.86
24.36
A [wt%kg d.b.]
21
33.80
30.38
Table 2. Input data of multigeneration system Brayton Cycle Mass flow rate (kg/s) 3.256 Generator efficiency (%) 90 Compression ratio 3 Turbine inlet pressure (kPa) 304 Combustion Chamber efficiency (%) 80 Organic Rankine Cycle Mass flow rate (kg/s) 3 ORC pump efficiency (%) 80 ORC turbine efficiency (%) 80 ORC generator efficiency (%) 90 Single-effect Absorption Chiller 75 βπππ (kW/K) βπππ (kW/K)
80
βπππ (kW/K)
70
βππ£π (kW/K)
95
Two-Stages Digester Temperature of the first digester (β) 38 Temperature of the second digester (β) 35 Heating load (kW) 66 Gas yield (Nm3/kgdb) 0.73 Greenhouse Length (m) 20 Height (m) 5 Width (m) 10 Temperature (β) 30 Number of greenhouses 5 Table 3. Output data of the system. Definition Output Net electrical power output (kW) 1078 Heating power (kW) 198 COP 0.68 Water Production (kg/day) 39.55
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Table 4. Thermodynamic properties of each state points.
State Point
π‘π’ (kJβkg)
π¦π’ (kgβs) P (kPa) T (K)
ππ±π’ (kJ/kg)
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 34 35 36 37 38
10.85 21.11 298.2 338 1168 895.4 2644 104.2 875.2 2618 104.2 263.1 144 144 104.2 21.1 2510 104.2 263.1 67.3 67.3 128.3 244.5 168.5 168.5 835.9 708.4 623.6 104.2 2688 198.8 157.5 161.3 432.7 368.8
0.1896 0.1896 3.067 3.067 3.256 3.256 0.57 0.57 3.256 0.037 0.55 0.55 0.037 0.037 1.056 1.056 0.037 0.94 0.94 0.117 0.117 0.117 0.1 0.1 0.1 3.256 3 3 4.55 4.55 3 3 3 3.256 3.256
1722 1722 0 96.39 573.2 266 2194 0.59 252.8 78.27 0.49 253.1 0.508 -6 0.49 85.95 -176 0.49 2531 11.1 11.1 71.81 117.3 41.64 41.6 227.7 209.5 112 0.49 2214 20.32 15.65 18.84 23.32 7.185
101.3 303.9 101.3 304 304 101.3 37 37 101.3 5.4 37 37 5.4 0.87 37 37 0.87 37 37 0.87 5.4 5.4 5.4 5.4 0.87 101.3 2000 37.5 37 37 37.5 37.5 2000 101.3 101.3
304.5 313 298 337.8 1106 866.1 353 298 847.8 336.5 298 336 307.5 278.2 298 278.16 278.2 298 336 303.4 303.4 332.2 365 321.9 329 812.3 549 432.3 298 365 365 365 365.9 431 368
ACCEPTED MANUSCRIPT 39
374
3.256
101.3
373.1
8.207
Eren Sevinchan, Ibrahim Dincer, Haoxiang Lang PII:
S0360-5442(18)32075-9
DOI:
10.1016/j.energy.2018.10.085
Reference:
EGY 13982
To appear in:
Energy
Received Date:
18 April 2018
Accepted Date:
15 October 2018
Please cite this article as: Eren Sevinchan, Ibrahim Dincer, Haoxiang Lang, Energy and Exergy Analyses of a Biogas Driven Multigenerational System, Energy (2018), doi: 10.1016/j.energy. 2018.10.085
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Energy and Exergy Analyses of a Biogas Driven Multigenerational System Eren Sevinchan, Ibrahim Dincer, Haoxiang Lang Clean Energy Research Laboratory, Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario L1H 7K4, Canada
Abstract In this study, energy and exergy analyses of a biogas driven multigeneration system is conducted for performance assessment and evaluation. In this regard, the multigeneration system with a biomass digestion process is developed for this purpose. Multigeneration system consists of a two-stage biomass digester, an open-type Brayton cycle, an Organic Rankine Cycle (ORC), a single-effect absorption chiller, a heat recovery subsystem, a water separator. This multigeneration system aims to generate electrical power for at least 300 houses, heating power for five greenhouses, cooling power and product water from flue gas for agricultural consumption in greenhouses. The analysis results indicate that the overall energy efficiencies of the proposed system is 72.5% with 1078 kW electrical, 198 kW heating, and 87.54 kW cooling power, and daily around 40 kg water production. However, the maximum exergy efficiency of the multigeneration system is obtained as 30.44%, with 65% of the highest exergy destruction rate in combustion chamber. Keywords: Biogas, multigeneration, Organic Rankine Cycle, energy, exergy, efficiency. 1. INTRODUCTION The energy demand of the world population increases dramatically due to fast-developing technology in recent years. There is no doubt that the impact of these constantly increasing technological developments on our planet is more than ever before. Therefore, clean and effective production of energy has a significant role to supply energy demand of the world by more environmentally friendly methods. Thus, energy production methods, fuels types and clean fuel production processes are important and need to be further investigated. In this case, energy production from biogas is emerged because of its multi-directional consumption. As a renewable energy source, biogas can be produced from various resources, such as animal, agricultural and organic wastes. Meanwhile, digestate that is a product of biogas digestion process is enabled to be used as fertilizer in agriculture. Furthermore, the impact of the biogas on the environment is less than any other fossil fuels, which makes biogas one of the cleanest and most effective energy sources. In conjunction with this, the distribution of renewable energy sources for power generation are presented in Figure 1. Biogas is a gas mixture, which consists of various content of methane, carbon dioxide, nitrogen, oxygen, hydrogen sulfide, water vapor, ammonia and low concentration of hydrocarbons, based on chemical properties of biomass and biogas production method. Out of methane, other gasses are considered as biogas pollutant, which is not wanted in the content of biogas. When CO2 and N2 content increase, the lower heating value (LHV) of biogas, which has the highly significant effect on energy and exergy efficiency of the system, decreases corresponding to biogas pollutant content of biogas. Because of this reason, some biogas upgrading methods have been developed in the literature to remove biogas pollutant content of the gas, which increases LHV of the fuel. Figure 2 demonstrates biogas-upgrading methods where chemical scrubber, membrane, and water scrubber methods have the highest percentage, respectively. 1
ACCEPTED MANUSCRIPT There are some advantages of biogas consumption, which makes it enable to be used in many different application areas. Biogas is a gas that can be produced when it is required and easily to be stored [1]. On the other hand, it can be easily consumed as a fuel for cooking and transportation [2]. Biogas and bio-methane consumption in transportation can decrease greenhouse gas emissions by 60-80% in comparison to gasoline [3]. However, biogas consumption may decrease nitrogen oxide emissions as well [4]. Depending on this high environmentally efficient feature of the biogas, it is expected to increase its consumption in energy generation. In addition, the major part of the energy generation has been suggested to be supplied biogas sources by European Union for the year of 2020. However, the 25% of this biogas production can be produced by wet organic materials [5]. Furthermore, in the agricultural sector of European Union, 1500 million tons of biomass can be digested in anaerobic digesters in a year [6]. Multigeneration energy systems are systems that have more than three useful outputs. These outputs may vary, but they are usually electricity, heating, cooling and another useful output, such as hydrogen, water, ammonia etc. Multigeneration is the most effective system, which takes advantage of waste heat as a heat source for other applications in the system. The applications that utilize waste heat to operate may be district heating, absorption cooling systems or another energy system that produces electrical power, such as Organic Rankine Cycle (ORC). Energy and exergy efficiency of these systems significantly depend on how waste heat is effectively used. In this case, there is no doubt that the energy efficiency of a multigeneration system is expected to be higher than other energy systems, such as co-trigeneration systems. Therefore, effective consumption of waste heat is a significant parameter, which determines the efficiency of the system. In the open literature, there are a lot of different co-tri and multi-generation power plants, which use biogas as main fuel [7β9]. Gazda et al. [10] have developed a biogas-fired trigeneration system, where electricity, cooling and heating generation are supported by a photovoltaic system (PV). According to their results, the energy efficiency increases between almost 37% and 43% based on load ratio from 50% to 100%. Meanwhile, the decrease of greenhouse gasses and energy savings in average have been found as 67.37% and 54.50% respectively [10]. Huicochea et al. [11] have studied a trigeneration system that has a 28 kW micro turbine and a double-effect absorption chiller to supply cooling power for the system. Bruno et al. [12] have studied another biogas driven trigeneration energy system, which consists of a micro gas turbine (MGT) and absorption cooling system with 24.92% net electrical efficiency. Cacua et al. [13] analyzed a trigeneration system that is driven by diesel-biogas dual fuel, where waste heat is consumed for heating air and absorption unit freezer. According to their results, overall energy efficiency of the system is 40% with diesel fuel and 31% with dual fuel. Although biogas is widely used in many energy systems as fuel, biomass is also another option to generate electricity. Ahmadi et al. [14] designed and analyzed biomass-driven multigeneration energy system, where they obtained overall exergy efficiency of the system is 22.20% with the electricity generation of 671 kW. Although biogas can be used as main fuel of an energy generation system, it also can be used in hybrid systems. A hybrid energy system, which consists of biogas, is studied by Su et al. [16] to improve energy performance of a trigeneration system by using additional solar energy system. According to their results, energy efficiency of the system varies between almost 38.5% and 48% corresponding to different power load of the system, where the 2
ACCEPTED MANUSCRIPT maximum 1600.2 kW cooling energy production takes place. However, Coskun et al. [17] were analyzed hydrogen production from biogas based electricity, where they achieved energy efficiency of the overall system between 7.86% and 86.90% depends on three different types of electrolysers. Furthermore, biomass also can be used directly as an energy source in an energy system. The current studies mostly focus on energy analysis of biogas driven co-trigeneration energy systems. However, there is a gap in terms of design and analysis of a biogas energy system with all aspects, such as exergy analysis of biogas production, the environmental impact of the system for the same system. The objective of this study is to design a biogas driven multigeneration energy system and analysis this system from the energetic, exergetic and environmental point of view. This biogas driven multigeneration energy system produces biogas from chicken manure and maize silage, and generates electricity, heating and cooling power. In addition to these three outputs, the water content of the flue gas of the system passes through a water separator to provide water for agricultural usage. Energy and exergy analysis and environmental impact assessment of the system will be examined in detail for each component of the system in this study. 2. SYSTEM DESCRIPTION In this study, biogas driven multigeneration system consists of various subsystems, such as a two-stage biomass digester, Brayton Cycle, single-effect absorption chiller, Organic Rankine Cycle (ORC), greenhouse heating and water separation of flue gas. As a biomass input of the biogas production subsystem, the mixture of chicken manure and maize silage has been considered, with 70000 kg and 30000 daily input respectively. Since biomasses have various chemical content depending on biomass type, individual consideration of these two biomasses is a significant point for energy and exergy analysis of biogas production process. Table 1 shows chemical composition of chicken manure, maize silage, and digestate, which is the product of biogas production process. Figure 3 illustrates the layout of the designed system, where two-stage biogas production has been preferred to enhance the quality of the produced biogas in the system. As a feature of two-stage biomass digestion systems, the first three steps of biogas production, which are hydrolysis, Acidogenesis and Acetogenesis, take place in the first digester; while the last step, methanogenesis, occurs in the second digester. After biomass digestion, biogas passes through a gas pre-heater to improve combustion quality in the combustion chamber. The heated biogas comes to combustion chamber mix with amount of compressed air, which depends on air-fuel ratio of biogas. After the combustion process, exhaust air operates a turbine to demand primary electricity generation of the system. Biomass digester units are heated by the exhausted gas after the turbine process to keep them around 35oC. Single effect absorption chiller takes place after biomass digester heating process. Exhausted air passes through generator of the absorption chiller to supply sufficient energy input to produce cooling power. After that, ORC is operated with exhaust air to generate secondary electrical power generation of the system, which is lower than the electricity production in Brayton Cycle. After the condenser of ORC, super heated n-octane, which is the working fluid of the ORC, is used for gas pre-heater process of the biogas. Greenhouse heating process is after ORC to supply heating power for five greenhouses to keep their temperature 3
ACCEPTED MANUSCRIPT around 29 oC. As a final process, the vapor water content of the exhaust air has been taken by a water separator to produce as high as possible amount of water for agricultural usage. System has been developed to supply electrical energy demand of at least 300 houses, heat 5 greenhouses, and provide cooling power and produce water for agricultural purposes. According to Statistic Canada [20], average of annual energy consumption per house is estimated as 105 GJ. The required electrical energy for 300 houses can be found as π πΈ =
105πΊπ½ Γ 300 βππ’π ππ = 3.59 πΊπ½/πππ¦ 365 πππ¦π Γ 24 βππ’ππ
(1)
The required total electrical energy need of 300 houses is estimated as above, which is 3.59 GJ per day. 3. ENERGY AND EXERGY ANALYSES There are several assumptions in energy and exergy analyses of the multigeneration system, which are shown in Table 2 with some input data of the system. First of all, system is assumed to operate at steady state conditions. In addition, pressure change in the system is neglected except for changes in pumps, valves, and turbines. Furthermore, combustion in the combustion chamber is studied as complete combustion with 80% thermal efficiency. In addition, the model for single-effect absorption chiller is validated with the data from Dincer et al. [21]. 3.1 Energy Analysis Energy analysis is studied for cogeneration heating, cogeneration cooling, trigeneration and multigeneration systems. The net power of the cogeneration heating, cogeneration cooling, and trigeneration systems is defined as (2)
ππππ‘ = ππ,π΅ + ππ,ππ πΆ β πππππ β πππ’πππ
where π is the power and the subscripts eB, eORC, comp, pumps, ws indicate electricity generation of Brayton Cycle, electricity generation of ORC, compressor, pumps and water separator, respectively.
The net electrical power generation of the Brayton cycle is defined as ππ,π΅ = ππππππ,π΅ β πππππ where gen, TB, and comp indicate the generator, turbine of the Brayton Cycle and compressor, respectively. On the other hand, the net electricity generation in the ORC subsystem is defined as ππ,ππ πΆ = ππππππ,ππ πΆ β πππ’ππ
The net electrical energy efficiency of the system is defined as below and verified in multigeneration, trigeneration, cogeneration heating and cooling applications. πππ,ππ =
ππππ‘ πππ
(3)
where πππ indicates total heat input rate of the system, while subscript en,el is electrical energy efficiency.
4
ACCEPTED MANUSCRIPT (4)
πππ = ππππ Γ πΏπ»π
where ππππ is mass flow rate of the biogas and LHV defines lower heating value, which is 17.52 MJ. Cogeneration energy efficiency of heating is defined as πππ,ππβ =
ππππ‘ + πβ
(5)
πππ
where en,coh is heating cogeneration energy efficiency, πβ is heat power that produced for greenhouse heating process, which is defined as (6)
πβ = π26β26 β π27β27 On the other hand, cogeneration energy efficiency for cooling is estimated as ππππ‘ + ππ
πππ,πππ =
(7)
πππ
where en,coc is cooling cogeneration energy efficiency, ππ is cooling power that produced by the system, which is defined as (8)
ππ = π13β13 β π12β12
Trigeneration energy efficiency is also defined as Equation 9, where heating, cooling and electricity generation are products of the system. πππ,π‘ππ =
ππππ‘ + πβ + π
π
(9)
πππ
Net power output of multigeneration is defined as ππππ‘,π, which can be found by Equation 10. ππππ‘,π = ππ,π΅ + ππ,ππ πΆ β πππππ β πππ’πππ β ππ€π
(10)
Finally, multigeneration energy efficiency is indicated as Equation 11, where electricity generation, heating, cooling and water production are products of the system. πππ,ππ’ππ‘π =
ππππ‘,π + πβ + π
π
(11)
πππ
3.2. Exergy Analysis The total exergy rates for each component in the system are calculated by following equation: ππ₯π‘ππ‘ππ = ππ₯ where ππ₯
ππ»
ππ»
+ ππ₯
πΆπ»
(12)
is physical exergy rate per mass flow, which is defined as 2
ππ₯
ππ»
= ππ₯π = βπ β βπ β ππ (π π β π π) +
2
π β π0 2
+ π(π§ β π§0)
(13)
Here, s, V, z, and g indicate enthalpy, entropy, velocity, elevation and gravity, respectively, while j shows state point number, and 0 determines property of surrounding environment. 5
ACCEPTED MANUSCRIPT However, ππ₯ 14 [22]. ππ₯
πΆπ»
determines chemical exergy rate per mass flow, and it can be found by Equation
πΆπ» πΆπ» π = ππ(π₯πππ₯ π + π π0π₯πln (π₯π))
where ππ and ππ₯
πΆπ» π
(14)
are molecular weight and standard chemical exergy value for each state
points, respectively. On the other hand, R and x determine universal gas constant and molar concentration. Furthermore, exergy destruction is another significant value, which indicates the potential work lost due to irreversibility. Exergy destruction for each state point is defined as
( ) π0
πΈπ₯π = βπ 1 β π ππ β π + βπππππ₯π β βπππππ₯π
(15)
π
where T and πΈπ₯π show temperature and exergy destruction rate, respectively. Finally, electrical exergy efficiency of the system can be defined as net power output of the system over chemical exergy of the fuel as Equation 16. πππ₯,ππ =
ππππ‘
(16)
ππ
where ππ is chemical exergy efficiency of the fuel, which is defined as (17)
ππ = πππππΏπ»π
The cogeneration heating exergy efficiency is defined as Equation 18, where electrical and heating power are outputs of the system.
( ( )) π
ππππ‘ + 1 β
πππ₯,ππβ =
π
0
π
βπ
β
(18)
ππ
The cogeneration cooling exergy efficiency is defined as
( ( )) π
ππππ‘ + 1 β
πππ₯,πππ =
π
0
ππ£π
ππ
(19)
ππ
The trigeneration exergy efficiency, which generate electricity, heating and cooling power.
( ( )) ( ( )) π
π
0
0
ππππ‘ + 1 β π πβ + 1 β π π βπ ππ£π
πππ₯,π‘ππ =
π
(20)
ππ
Finally, the exergy efficiency of multigeneration system is defined as
( ( )) ( ( )) π
π
0
0
ππππ‘,π + 1 β π π + 1β π π βπ ππ£
πππ₯,ππ’ππ‘π =
β
ππ
π
(21)
In addition, exergy analysis of biomass digestion process is also studied at steady state conditions. For the chemical exergy analysis of two-stages biomass digester, chemical exergy 6
ACCEPTED MANUSCRIPT rates of organic substances, which are biomass and digestate, during the process are analysed by equation of Song et al. [23]. ππ₯ππ = 362.0083C+1101.841H-86.218O+2.418N+196.701S-21.1A
(22)
where C, H, O, N, S and A determine organic content of the substances, which are carbon, hydrogen, oxygen, nitrogen, sulphur and ash, respectively. This equation is applied for biomass input, biomass substances between two stages, and digestate. However, as a gas content of biogas, chemical exergy rate should be defined for both first and second digester, depending on their products of chemical reactions. The chemical exergy of a gas mixture is defined as π ππ₯πβ = βπ₯πππ₯πβ + π π0βπ₯πln (π₯π)
(23)
4. RESULTS AND DISCUSSION The performance of the system is analysed in five different cases, such as single electricity generation system, cogeneration-heating system, cogeneration-cooling system, trigeneration and multigeneration systems through different parameters for both energetically and exergetically. These parameters are daily biomass input of the system, ambient temperature, and compression ratio. During the thermodynamic analyses, the input data of the system are kept constant at the values that are tabulated in Tables 1 and 2. On the other hand, Table 3 gives the multigeneration system outputs. The greenhouse heating takes place between state point 26 and 27, which requires 198 kW heating power for five greenhouses in ambient temperature of 25β. The net electrical power output is estimated as 1078 kW, which is enough to supply electricity to 326 houses [20]. However, coefficient of performance value of single-effect absorption chiller is defined as 0.68. Thermodynamic properties of each state points are listed in Table 4, where it can be seen that the temperature 4.1. Effect of daily amount of biomass input The daily biomass input of the multigeneration system is defined as 70000 kg chicken manure and 30000 kg maize silage, which makes 100000 kg biomass input in total. There is no doubt that daily amount of biomass input to the biomass digesters has one of the biggest impact on the performance of the system. The increase of the biomass input causes more production of daily biogas. Depending on this change in biogas flow rate, mass flow rate of system increases as well because of air-fuel ratio of the biogas, as long as mass flow rate of the system is not fixed to a specific number or not stored for a further consumption. According to Figure 4, it is clear to see that increase of the daily biomass input goes up from 100000 kg to 150000 kg, while net electrical power output of the system increases between 1000 kW to 1394 kW. On the left side of the graph, increase of the number of houses that can provide from the generated electrical energy in the system is studied corresponding to the net power output of the multigeneration system. As it is discussed before, daily electrical energy need of a house is estimated as 105 GJ in Canada, according to Statistic Canada [20]. Therefore, ratio of electrical power output and daily energy need of a house provides the number of the houses that can access sufficient amount of daily electrical power from the system, which increases from 300 to 420 houses. 4.2. Effect of ambient temperature 7
ACCEPTED MANUSCRIPT The ambient temperature is another parameter that effects performance of the system both energetically and exergetically. When the ambient temperature increases between 288 K and 303 K, ambient air enters the compressor with a high temperature and enthalpy, which also affects the turbine inlet temperature. Depending on this temperature change in the system, net electrical power energy of the system slightly increases from 1048 kW to 1093 kW. The change of the net electrical power output is not a significant difference for the system; however, it has a significant impact on heating power output. In the multigeneration system, heating output of the system is used for space heating of five greenhouses. Since greenhouses should be kept at a specific temperature depending on the best temperature for plants in the greenhouse, heating power output of the multigeneration system decreases when the ambient temperature reaches greenhouse temperature, which is around 29 oC. Therefore, heating power output of the multigeneration system declines from 455 kW to 69.46 kW, while ambient temperature varies between 288 K and 303 K. From energy efficiency point of view, it can be seen that the energy efficiency of cooling cogeneration system and system with only electrical power generation increases from 41.63% to 43.27% and from 38.47% to 40.11%, respectively. The effect of the cooling load and the decrease of the heating power output are main reasons for this energy efficiency variation corresponding to change in ambient temperature. When the amount of required heat that produced by the system for heating applications decrease, the energy efficiency of the system decrease too, which means less energy output from the system and less energy efficiency. This situation can be clearly seen for energy efficiencies of heating cogeneration, trigeneration, and multigeneration. The variation of the ambient temperature has also an impact on exergy efficiency of the system. Figure 5 indicates that exergy efficiency of the system slightly increases around 1% for all systems depending on their useful products, such as heating-cooling cogeneration, trigeneration and multigeneration. However, the effect of the change in ambient temperature on exergy efficiencies comes from the definition of the exergy rate of the heating and cooling power outputs. As it is showed in Equation 17, exergy rate of heat power has linear relation with the ratio of ambient and surface temperature. When ambient temperature increases, exergy rate of heating and cooling power outputs of the system increases too, which is a reason of 1% increment in exergy efficiency of cooling-heating cogeneration, trigeneration and multigeneration systems. 4.3. Effect of compression ratio The compression ratio, which is denoted as rp, is a ratio of the absolute stage discharge and suction pressure. The compression ratio of the compressor is defined as 3 at the beginning of the analysis, and then it increased from 3 to 8 to see the effect of the ratio on performance of the system. Thus, the net electrical power output of the system increases from 1078 kW to 1704 kW depending on the compression ratio in Figure 6. On the other hand, energy efficiency of the system increases to because of this change in net electrical power output of the system. Since trigeneration and multigeneration systems have more useful outputs than other systems, their ratio of useful output and the heat input of the system is higher than cogeneration. Therefore, their energy efficiency are higher than other three system types. It can be seen that the energy efficiency of the trigeneration system is higher than multigeneration system because of the additional work input of the multigeneration 8
ACCEPTED MANUSCRIPT system. Multigeneration system has more useful output than other systems but its required energy is higher than others, which keeps its energy efficiency lower than other systems. However, the maximum energy efficiency, which is 69.34%, can be seen for trigeneration system when the compression ratio is 8, while the system with only electricity generation has the lowest energy efficiency, 39.56%, with compression ratio of 3. From exergy efficiency point of view, Figure 7 shows the variation of exergy efficiencies corresponding to change in compression ratio. There is no doubt that exergy efficiency of the system increases because of the increase of the compression ratio from 3 to 8. Depending on the compression ratio, pressure and temperature of compressed air varies. High compression ratio means the inlet air with higher temperature and pressure, which increases the performance of the system. This situation can be clearly seen in Figure 7, where the exergy efficiency and the net electrical power output of the system increase. As it is discussed before, the exergy efficiency of the trigeneration is higher than the multigeneration system because of the additional electrical work input of the water separator. The exergy efficiency of the multigeneration system increases between 30.44% and 48.23%, while total electrical energy that generated by the multigeneration system varies from 1078 kW to 1704 kW. 4.4. Effect of mass flow rate of the system The mass flow rate of the system can be defined based on biogas production of the system, since biogas has an air-fuel ratio that determine the mass flow rate. In this analysis, the mass flow rate of the biogas is changed to see the change in mass flow rate of the system and its effects on cogeneration heating, cogeneration cooling, electricity generation, trigeneration and multigeneration efficiencies. In this analysis, the mass flow rate of the biogas increases from 0.18 kg/s to 2.1 kg/s, which causes to increase of the mass flow rate of the system between 3.86 kg/s and 5.78 kg/s. Figure 8 indicates that energy efficiency of the multigeneration system decreases from 50.03% to 48.89%, because of the decrease of the net power output of the system, which changes between 1099 kW and 1068 kW. On the other hand, energy efficiency of the trigeneration concept of the same system again decreases from 50.65% to 49.51%. It can be seen that the variation of the energy efficiency is not a huge change in the system. To illustrate that, even cogeneration cooling and heating concepts have only around 1% difference corresponding to mass flow rate change of the system. Furthermore, the lowest energy efficiency can be seen in the system that has only electricity generation, which goes down from 40.33% to 39.19%. On the other hand, energy efficiency of the trigeneration concept of the same system again decreases from 50.65% to 49.51%. It can be seen that the variation of the energy efficiency is not a huge change in the system. To illustrate that, even cogeneration cooling and heating concepts have only around 1% difference corresponding to mass flow rate change of the system. Furthermore, the lowest energy efficiency can be seen in the system that has only electricity generation, which goes down from 40.33% to 39.19%. 4.5. Effect of the mass flow rate of the single-effect absorption chiller The effect of the mass flow rate of the single-effect absorption chiller on coefficient of performance (COP) of the chiller, energy and exergy efficiencies of the multigeneration system have been analyzed. The mass flow rate of the solution has been varied, and the mass flow rate of the working fluid of the chiller is changed. The mass flow rate of the working fluid has a 9
ACCEPTED MANUSCRIPT significant role on performance of the single-effect absorption chiller. Since it affects the amount of heat that can be absorbed from the cooled space, investigation of the mass flow rate is a good way to see the effect of the mass flow rate of the chiller on overall system. The COP value of the multigeneration system has been found as 0.68 in the assumed conditions of the multigeneration system. However, it varies from 0.68 to 0.79 depending on the change of the mass flow rate of the cooling system. This COP change indicates that the cooling power of the system increases by the upward change in mass flow rate of the single effect absorption chiller. Furthermore, this situation has an effect on energy and exergy efficiencies of the multigeneration system. Since the cooling power of the system increases by the change in mass flow rate of the working fluid of the cooling system, the overall energy and exergy efficiencies of the multigeneration system increases corresponding to this change in mass flow rate. The energy efficiency of the multigeneration system increases from 50.03% to 54.13%, while the exergy efficiency of the system changes between 30.09% and 31.13%. In addition, Figure 10 shows the exergy destruction of different components in the system, which have the highest rate. In this case, the exergy destruction of the combustion chamber is the highest rate with 1137 kW, while first biomass digester has an exergy destruction rate of 243.6 kW. All the components that have been showed in Figure 10 are components that have such processes which require a huge amount of heat input or output with large rate of losses. 5. CONCLUSIONS Energy and exergy analyses of a biogas-driven multigeneration system are conducted in this study. Performance of the system is studied under variation of different parameters, such as ambient temperature, daily biomass input and compression ratio, from both energy and exergy point of view. The main concluding points of this study are listed as follow: ο·
ο·
ο· ο·
ο·
Multigeneration system is enable to produce 1078 kW electrical, 198 kW heating, 87.54 kW cooling power, and daily almost 40 kg water for greenhouses at 25β temperature and 101.34 kPa pressure. There is no doubt that the energy and exergy efficiencies of the system increases when it produces more useful output. It can be seen in the parametric analyses, energy and exergy efficiency of the multigeneration system are always higher than other cogeneration and single generation figurations of the system, which are 72.5 % and 30.44% respectively. The maximum electrical power energy efficiency is 40.11%, maximum cooling energy efficiency is 62.18%, and maximum heating energy efficiency is 65.35%. The generated electrical energy in the system is a sufficient power to supply electricity for around 300 houses daily, according to the statistics. In this case, storage of the additional electricity generation would be a solution for more efficient consuming of the electricity. Furthermore, depending on the daily biomass input of the system, the amount of biogas that produced additional would be stored for further usage. The combustion chamber of the Brayton Cycle has the highest exergy destruction rate with 65%. The other components with high exergy destruction rate are evaporator of the ORC and biomass digesters, with 9.2% and 14.3% exergy destruction rates, respectively.
NOMENCLATURE 10
ACCEPTED MANUSCRIPT ππ₯ πΈπ₯ g h LHV π M MGT π ORC P π R rp s T v π wt. % x z
Exergy per unit mass, kJ/kg Exergy rate, kW Gravity, m/s2 Enthalpy per unit mass, kJ/kg Lower heating value, kJ/kg Mass flow rate, kg/s Molecular weight, kg/mol Micro gas turbine Molar flow rate, mol/s Organic Rankine Cycle Pressure, kPa Heat rate, W Universal gas constant, J/mol.K Compression ratio Entropy per unit mass, kJ/kg.K Temperature, K Velocity, m/s2 Work, W Wet basis Molar concentration Elevation, m
Greek letters π
Efficiency
Subscripts 0 abs bio c coc coh comp con d d.b. e,B el en eva ex f gen h hp in multi net net, m OM
Ambient conditions Absorber Biogas Cooling Cogeneration-Cooling Cogeneration-heating Compressor Condenser Destruction Dry basis Electricity generation-Brayton Cycle Electricity generation Energy Evaporator Exergy Fuel Generator Heating Heat process Inlet Multigeneration Net Net-Multigeneration system Organic matter 11
ACCEPTED MANUSCRIPT tri ws
Trigeneration Water separator
Superscripts CH PH
Chemical Physical
REFERENCES [1]
Panwar NL, Kaushik SC, Kothari S. Role of renewable energy sources in environmental protection: A review. Renewable Sustain Energy Rev 2011;15:1513β24. [2] Berglund M, BΓΆrjesson P. Assessment of energy performance in the life-cycle of biogas production. Biomass and Bioenergy 2006;30:254β66. [3] Sahota S, Shah G, Ghosh P, Kapoor R, Sengupta S, Singh P, et al. Review of trends in biogas upgradation technologies and future perspectives. Bioresource Technolgy Reports 2018. [4] Rasi S, LΓ€ntelΓ€ J, Rintala J. Trace compounds affecting biogas energy utilisation - A review. Energy Conversation Management 2011;52:3369β75. [5] Holm-Nielsen JB, Al Seadi T, Oleskowicz-Popiel P. The future of anaerobic digestion and biogas utilization. Bioresource Technolgy 2009;100:5478β84. [6] Weiland P. Biogas production: Current state and perspectives. Applied Microbiology Biotechnolgy 2010;85:849β60. [7] Li H, Zhang X, Liu L, Zeng R, Zhang G. Exergy and environmental assessments of a novel trigeneration system taking biomass and solar energy as co-feeds. Applied Thermal Engineering 2016;104:697β706. [8] Su B, Han W, Jin H. Proposal and assessment of a novel integrated CCHP system with biogas steam reforming using solar energy. Applied Energy 2017;206:1β11. [9] Leonzio G. An innovative trigeneration system using biogas as renewable energy. Chinese Journal of Chemical Engineering 2018. [10] Gazda W, Stanek W. Energy and environmental assessment of integrated biogas trigeneration and photovoltaic plant as more sustainable industrial system. Applied Energy 2016;169:138β49. [11] Huicochea A, Rivera W, GutiΓ©rrez-Urueta G, Bruno JC, Coronas A. Thermodynamic analysis of a trigeneration system consisting of a micro gas turbine and a double effect absorption chiller. Applied Thermal Engineering 2011;31:3347β53. [12] Bruno JC, Ortega-LΓ³pez V, Coronas A. Integration of absorption cooling systems into micro gas turbine trigeneration systems using biogas: Case study of a sewage treatment plant. Applied Energy 2009;86:837β47. [13] Cacua K, Olmos-Villalba L, Herrera B, Gallego A. Experimental evaluation of a dieselbiogas dual fuel engine operated on micro-trigeneration system for power, drying and cooling. Applied Thermal Engineering 2016;100:762β7. [14] Ahmadi P, Dincer I, Rosen MA. Development and assessment of an integrated biomassbased multi-generation energy system. Energy 2013;56:155β66. [15] Angelidaki I, Treu L, Tsapekos P, Luo G, Campanaro S, Wenzel H, et al. Biogas upgrading and utilization: Current status and perspectives. Biotechnolgy Advance 2018;36:452β66. [16] Bosheng S, Zefeng W, Wei H, Hongguang J. Using solar energy to improve the energy performance of trigeneration systems for sewage treatment plants. Energy 2017;142:873β9. [17] Coskun C, Akyuz E, Oktay Z, Dincer I. Energy analysis of hydrogen production using 12
ACCEPTED MANUSCRIPT
[18] [19] [20] [21] [22] [23]
biogas-based electricity. International Journal of Hydrogen Energy 2011;36:11418β24. Fantozzi F, Buratti C. Biogas production from different substrates in an experimental Continuously Stirred Tank Reactor anaerobic digester. Bioresource Technolgy 2009;100:5783β9. Pfeifer J, Obernberger I. Technological Evaluation of an agricultural biogas chp plant as well as definition of guiding values for the improved design and operation. 15th Eur. Biomass Conf. Exhib., Berlin: 2007. Statistics Canada. Households and the Environment: Energy Use. Ottawa: 2011. Al-Sulaiman FA, Dincer I, Hamdullahpur F. Energy and exergy analyses of a biomass trigeneration system using an organic Rankine cycle. Energy 2012;45:975β85. Dincer I, Rosen MA. Exergy: Energy, Environment and Sustainable Development. 2nd ed. Elsevier; 2013. Song G, Xiao J, Zhao H, Shen L. A unified correlation for estimating specific chemical exergy of solid and liquid fuels. Energy 2012;40:164β73.
13
ACCEPTED MANUSCRIPT
Figure 1. Distribution of renewable energy sources for power generation in years (data from Ref. [1]).
Figure 2. Distribution of current technologies for biogas up grading methods (data from Ref. [15]).
ACCEPTED MANUSCRIPT
Manure Tank
1
Mixer
Agricultural Waste Tank
2
Process Line Biogas Line Water Line
4
Digester with Gas Holder
3
Digester
Digestate Storage Tank
32
31
33
34
Gas pre-heater Combustion Chamber
Generator Electrical Power
30 35 36
5
29
7 8 Generator
Greenhouse
37
Turbine
Compressor
38
Electrical Power
Water Separator
39 9
6
10 Heat Recovery
11 12 14
13
Condenser
Generator
15 25
26
24
27
23
28
16 Refrigerant Expansion Valve
Solution Pump
17
18
Solution Expansion Valve
20
Evaporator
19
Solution Heat Exchanger
Absorber
21 22
Figure 3. The layout of biogas driven multigeneration system.
ACCEPTED MANUSCRIPT
Figure 4. Effect of daily amount of biomass on net power output and corresponding number of houses.
Figure 5. Effect of ambient temperature on energy and exergy efficiencies, net electrical power and heating power output.
ACCEPTED MANUSCRIPT
Figure 6. Effect of compression ratio on energy efficiency and net electrical power output.
Figure 7. Effect of compression ratio on exergy efficiency and net electrical power output.
ACCEPTED MANUSCRIPT
Figure 8. Effect of mass flow rate of the system on energy efficiencies and net power output.
Figure 9. Effect of the mass flow rate of the single-effect absorption chiller on COP, energy and exergy efficiencies of the multigeneration system.
ACCEPTED MANUSCRIPT
Figure 10. Exergy destruction of different components in the system.
ACCEPTED MANUSCRIPT HIGHLIGHTS ο· ο· ο· ο·
The overall energy efficiencies of the proposed system is 72.5%. The maximum exergy efficiency of the multigeneration system is obtained as 30.44%. Combustion chamber has the highest exergy destruction rate with 65%. 1078 kW electrical, 198 kW heating and 87.54 kW cooling power are obtained.
ACCEPTED MANUSCRIPT Table 1. Chemical composition of substrates and digestate. Definition
Poultry litter [18]
Maize Silage [19]
Digestate [19]
C [wt%kg d.b.]
37.50
33.71
35.34
H [wt%kg d.b.]
5.5
4.47
4.53
N [wt%kg d.b.]
4.7
11.16
5.35
O [wt%kg d.b.]
29.4
16.86
24.36
A [wt%kg d.b.]
21
33.80
30.38
Table 2. Input data of multigeneration system Brayton Cycle Mass flow rate (kg/s) 3.256 Generator efficiency (%) 90 Compression ratio 3 Turbine inlet pressure (kPa) 304 Combustion Chamber efficiency (%) 80 Organic Rankine Cycle Mass flow rate (kg/s) 3 ORC pump efficiency (%) 80 ORC turbine efficiency (%) 80 ORC generator efficiency (%) 90 Single-effect Absorption Chiller 75 βπππ (kW/K) βπππ (kW/K)
80
βπππ (kW/K)
70
βππ£π (kW/K)
95
Two-Stages Digester Temperature of the first digester (β) 38 Temperature of the second digester (β) 35 Heating load (kW) 66 Gas yield (Nm3/kgdb) 0.73 Greenhouse Length (m) 20 Height (m) 5 Width (m) 10 Temperature (β) 30 Number of greenhouses 5 Table 3. Output data of the system. Definition Output Net electrical power output (kW) 1078 Heating power (kW) 198 COP 0.68 Water Production (kg/day) 39.55
ACCEPTED MANUSCRIPT
Table 4. Thermodynamic properties of each state points.
State Point
π‘π’ (kJβkg)
π¦π’ (kgβs) P (kPa) T (K)
ππ±π’ (kJ/kg)
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 34 35 36 37 38
10.85 21.11 298.2 338 1168 895.4 2644 104.2 875.2 2618 104.2 263.1 144 144 104.2 21.1 2510 104.2 263.1 67.3 67.3 128.3 244.5 168.5 168.5 835.9 708.4 623.6 104.2 2688 198.8 157.5 161.3 432.7 368.8
0.1896 0.1896 3.067 3.067 3.256 3.256 0.57 0.57 3.256 0.037 0.55 0.55 0.037 0.037 1.056 1.056 0.037 0.94 0.94 0.117 0.117 0.117 0.1 0.1 0.1 3.256 3 3 4.55 4.55 3 3 3 3.256 3.256
1722 1722 0 96.39 573.2 266 2194 0.59 252.8 78.27 0.49 253.1 0.508 -6 0.49 85.95 -176 0.49 2531 11.1 11.1 71.81 117.3 41.64 41.6 227.7 209.5 112 0.49 2214 20.32 15.65 18.84 23.32 7.185
101.3 303.9 101.3 304 304 101.3 37 37 101.3 5.4 37 37 5.4 0.87 37 37 0.87 37 37 0.87 5.4 5.4 5.4 5.4 0.87 101.3 2000 37.5 37 37 37.5 37.5 2000 101.3 101.3
304.5 313 298 337.8 1106 866.1 353 298 847.8 336.5 298 336 307.5 278.2 298 278.16 278.2 298 336 303.4 303.4 332.2 365 321.9 329 812.3 549 432.3 298 365 365 365 365.9 431 368
ACCEPTED MANUSCRIPT 39
374
3.256
101.3
373.1
8.207