#
Development and Analysis of the Novel Hybridization of a Single-Flash Geothermal Power Plant with Biomass Driven sCO_{2}-Steam Rankine Combined Cycle

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## Abstract

**:**

_{2}-steam Rankine combined cycle, where a solid local biomass source, olive residue, is used as a fuel. The hybrid power plant is modeled using the simulation software EBSILON

^{®}Professional. A topping sCO

_{2}cycle is chosen due to its potential for flexible electricity generation. A synergy between the topping sCO

_{2}and bottoming steam Rankine cycles is achieved by a good temperature match between the coupling heat exchanger, where the waste heat from the topping cycle is utilized in the bottoming cycle. The high-temperature heat addition problem, common in sCO

_{2}cycles, is also eliminated by utilizing the heat in the flue gas in the bottoming cycle. Combined cycle thermal efficiency and a biomass-to-electricity conversion efficiency of 24.9% and 22.4% are achieved, respectively. The corresponding fuel consumption of the hybridized plant is found to be 2.2 kg/s.

_{2}cycle; olive residue; flexibility

## 1. Introduction

_{2}(sCO

_{2}) cycle, as a topping cycle. A sCO

_{2}cycle is chosen for its potential to support flexible electricity generation. The article is structured to allow the method and outcomes to be adapted to other GEPP.

_{2}is used as both heat transmission fluid for geothermal and working fluid for the sCO

_{2}power cycle. Their hybrid system uses geothermal energy as the primary energy source to provide the base-load electricity, and the solar energy is used as a supplement to meet the peak demand whenever possible. Their hybrid plant reaches the maximum thermal efficiency of 22.44% for a CO

_{2}turbine inlet temperature of 600 °C.

_{2}cycle studied in this article is a part-flow type sCO

_{2}cycle. Despite the equivalent or higher thermodynamical efficiencies of sCO

_{2}cycles compared to their steam Rankine counterparts, there has not been a full-scale commercial demonstration of the sCO

_{2}cycles as the studies are limited to laboratory-scale test setups under 1 MW [16,17,18,19]. The underlying reason for sCO

_{2}cycles offering good thermal efficiency is that the compression work of CO

_{2}as a working fluid close to its critical point of 31.1 °C and 7.39 MPa is minimal [20]. However, thermophysical properties of CO

_{2}, such as the isobaric heat capacity in the vicinity of its critical point, exhibit non-linear behavior and result in a pinch-point problem. Utamura [21] demonstrated that a first law efficiency of 45% under maximum operating conditions of 20 MPa and 526.9 °C is achievable for part-flow sCO

_{2}cycles where the pinch-point problem can be avoided. The part-flow configuration helps to confine the likelihood of pinch-point problems to the low-temperature recuperator (LTR) by splitting the rest of the recuperation process to a high-temperature recuperator (HTR). Overall, part-flow sCO

_{2}cycles can offer a more than 5% increase in the thermal efficiency compared to simple recuperated sCO

_{2}cycles, and are the most extensively researched sCO

_{2}cycle in the literature, as they are relatively simple and retain good efficiency [22]. In addition to the pinch-point problem, the sCO

_{2}cycles have another intrinsic problem regarding the heat addition to the cycle. Due to their highly recuperative characteristics, the external heat addition to sCO

_{2}cycles is carried out over a high-temperature interval [23,24,25]. To overcome this limitation, the sCO

_{2}cycles are often combined with bottoming ORC cycles operating at low temperatures [26,27,28,29], or utilized in cascading manner as sCO

_{2}–sCO

_{2}and sCO

_{2}–transcritical carbon dioxide (tCO

_{2}) cycles [23,24,25]. Alternatively, for coal-powered sCO

_{2}cycle designs, advanced boiler and heater designs are introduced to fully exploit the available heat in the flue gas within the cycle, at the cost of obtaining more complex layouts [30,31]. Motivated by the problem of a biomass-powered sCO

_{2}cycle design, Manente and Lazzaretto [32] introduced a novel cascaded sCO

_{2}cycle configuration using woody biomass as a fuel. In their study, two different cascaded sCO

_{2}cycles, namely part-flow–simple-recuperated and simple-recuperated–simple-recuperated, are investigated, along with four different biomass boiler arrangements. Their results showed that part-flow–simple-recuperated cascaded sCO

_{2}cycle design with a counter-current radiative–convective boiler demonstrated the best performance in terms of biomass-to-electricity conversion efficiency, i.e., either 34% or 36%, depending on the presence of an air-preheating unit, for the topping cycle turbine inlet temperature (TIT) of 550 °C.

## 2. Novel Hybrid Geothermal–Biomass Power Plant Scheme

_{2}cycle, to be operated at a higher temperature than the existing geothermal cycle, can be used as a topping cycle. The part-flow sCO

_{2}cycle can reject its waste heat through its cooler to preheat the condensate of the existing geothermal cycle. A novel biomass heater-boiler designed for this unique application can supply high-temperature heat from biomass combustion through radiative heat transfer to drive the part-flow sCO

_{2}topping cycle, and bring the preheated geothermal condensate to a certain steam quality. The medium-temperature heat of the flue gas is transferred to this steam-water mixture by means of convective heat transfer to create dry steam. This 100% biomass-energy-derived dry steam can be fed to the steam turbine of an existing GEPP operating under capacity due to a reduction in its mass flow. Moreover, when appropriate, the existing unused cooling component capacity of GEPP can be used to condensate the biomass derived steam exhaust for better utilization. Such a novel hybridization scheme offers several advantages. First, the rejected heat of the topping sCO

_{2}cycle is not lost, but instead used to supply heat for an additional dry steam. Second, sCO

_{2}cycles are either utilized in a cascaded manner [23,24,25,32] or combined with ORC bottoming cycles operating at low temperatures [26,27,28,29] due to their high-temperature heat requirement. Since the medium temperature heat of the flue gas is used for the creation of additional dry steam, the need to use an additional bottoming ORC or sCO

_{2}cycle is eliminated. As a result, the existing GEPP can be brought to full capacity to allow for better Capex utilization. Note that only the unused flow capacity of steam turbine and, if possible, an existing cooling system is used for such a hybridization scenario, while operational steam turbine inlet conditions, i.e., pressure and temperature, remain unchanged. In this sense, hybridization is possible without modifying the components of the existing GEPP.

#### 2.1. Application of Proposed Novel Hybridization Scheme to KZD-1 GEPP

#### 2.1.1. Existing Conditions of KZD-1 GEPP

^{−1}and the average steam mass flow rate of 33.34 kg s

^{−1}reported by Gökçen et al. in 2004 [34]. Moreover, the steam turbine of KZD-1 seems to have been worn out over its active years, considering its current calculated isentropic efficiency of 30% and reported isentropic efficiencies of 71.2% and 71.5% in the literature [33,34]. In order to better represent single-flash GEPPs and make the hybridization efforts meaningful, within the context of this article, the isentropic efficiency of the steam turbine is assumed to be 80%, in line with the typical isentropic efficiencies of geothermal steam turbines suggested by DiPippo [33].

^{−1}; it then passed through the steam turbine and the exhaust steam was condensed through the direct contact (DC) steam condenser. The condensed steam was then pumped to the wet cooling tower (WCT), where it was used as a cooling water and ultimately evaporated. The WCT used no make-up water, since the geothermal condensate was used as cooling water.

#### 2.1.2. Biomass Fuel Source

^{−1}, which is in good agreement with the calculated HHV for the OR samples used in this article. The ultimate analysis and heating values of the biomass fuel were used as inputs to simulation software EBSILON

^{®}Professional where the hybrid power plant is modeled.

#### 2.1.3. Model Development

^{®}Professional software for the application of the proposed novel hybridization scheme to KZD-1 GEPP. The thermodynamic concepts of the associated model are highlighted in Figure 2. The proposed hybrid scheme consists of the following three cycles:

- BTC: Biomass combustion driven sCO
_{2}Topping Cycle; - BBC: Bottoming Biomass combustion and topping cycle waste, heat-driven steam Rankine Cycle;
- EGC: Existing open-loop steam Rankine cycle, driven by geothermal energy (EGC).

_{2}cycle used for hybridization (BTC) was adapted from the work of Utamura [21]. The characteristics of the optimized BTC are presented in Table 2. The turbine inlet condition is fixed at 550 °C and 20 MPa to be parallel with the part-flow sCO

_{2}cycles designs in the literature [32,39,40,41,42,43]. The heat rejection from BTC was transferred the BBC through the cooler. Heat input to BTC was achieved by means of radiative heat transfer from the biomass heater-boiler (BHB).

#### 2.1.4. Energy Analysis

^{®}Professional software and its EbsBoiler module. The design conditions and characteristics of the components are presented in Table 2. Due to the novelty of the proposed hybrid configuration, the well-known energetic performance parameters are slightly different from their standalone definitions and are defined as follows.

#### 2.1.5. Model Verification

_{2}cycles are modeled in EBSILON

^{®}Professional using the design parameters supplied by Utamura [21] and Mecheri and Moullec [31]. T-s diagrams of the verification models are verified against the T-s diagrams supplied by Utamura [21] and Mecheri and Moullec [31] in Figure 5. The calculated first law efficiencies of 44.6% and 39% for the verification models of these two respective studies are in line with their reported values of 45% and 39%.

^{®}Professional for the different cases presented in the study of Manente and Lazzaretto [32]. The verification results are presented in Table 3 for 1 kg s

^{−1}woody biomass fuel used in their work. Note that the effective temperature of radiation (TEF) and the heat loss in the radiative section is assumed to be 1000 °C and 5%, respectively, throughout this article, to be consistent with Manente and Lazzaretto [32].

#### 2.1.6. Optimization of Input Parameters

_{2}cycle design for waste heat recovery systems, Manente and Fortuna [47] state that one of the main novelties in the recent literature on hybrid plant layouts is the sharing of some equipment to reduce the number of components. The efforts in this article aim to use the existing infrastructure of the KZD-1 GEPP to the fullest extent through sharing the existing steam turbine of KZD-1 with EGC and BBC. Concurrently, hybridization scenarios where the design operating conditions of the existing KZD-1 GEPP are changed by means of an increased steam turbine inlet temperature or the generation of superheat steam through biomass combustion are avoided, as power plant operators are generally not willing to make changes to their design conditions. In this sense, the hybridization exploits the excess steam turbine capacity resulting from the degradation in mass flow of the geothermal steam over the years by using the dry steam derived from biomass combustion in BBC to partially return the steam turbine to its design operating conditions. The mass flow rate of this additional biomass-derived dry steam is equal to the mass flow rate of the BBC working fluid, water.

^{−1}in equal 5 kg s

^{−1}increments, while BBC mass flow rate is varied from 6 to 18 kg s

^{−1}in even 2 kg s

^{−1}increments. The reason BTC flow rate is included in this parametric analysis: BTC is thermally coupled to the BBC. The input parameters of these two cycles are held constant and equal to the values in Table 2, except for part-flow ratio, ψ, and turbine expansion ratio, φ, of BTC. The base inputs for ψ and φ are taken as 2.51 and 0.68, respectively, as suggested by Utamura [21], and are optimized after the mass flow rates are determined.

^{−1}and minimum flow rate of BBC at 6 kg s

^{−1}. The underlying reason for this result is the increase in the main compressor (MC) inlet temperature (State 1) of BTC. The increase in MC inlet temperature is directly proportional to BTC flow rate while being inversely proportional to BBC flow rate for a fixed effectiveness value of the BTC cooler, since the working fluid of BBC acts as a heat rejection medium for BTC. Note that the reason for utilizing CO

_{2}as a working fluid in a closed-loop power cycle is to exploit the thermophysical properties of CO

_{2}requiring minimum compression work in the vicinity of its critical temperature of 31.1 °C [48]. Therefore, the efficiency drops as the MC inlet temperature increases. This behavior is also prominent in Figure 6a, where topping cycle efficiency severely drops to 25%. Second, the BCC thermal efficiency exhibits another minima for the minimum flow rate of BTC at 20 kg s

^{−1}and maximum flow rate of BBC at 18 kg s

^{−1}. Note that the BTC thermal efficiency reaches a maximum for this flow rate pair in Figure 6a, whereas BBC thermal efficiency is independent of the flow rates, owing to its fixed intensive thermodynamic properties defined by the KZD-1 steam turbine inlet temperature and constant ambient temperature. The underlying theory leading to this minima in BCC for this flow rate pair is the increase in the power generation share of BBC, which has a lower thermal efficiency compared to BTC.

^{−1}and 12 kg s

^{−1}is selected for BTC and BBC, respectively. The mass flow rate of the total steam feeding the KZD-1 steam turbine increases from 19.45 kg s

^{−1}to 31.45 kg s

^{−1}with the addition of the biomass-derived dry steam and brings KZD-1 turbine close to its operation conditions in 2004 [34].

## 3. Results and Discussion

_{2}cycle with the same turbine inlet temperature (TIT) of 550 °C, as in this article, is reported to be around 46.5% in the literature [22]. In this work, it is expected that the efficiency of topping the sCO

_{2}cycles will be penalized slightly to maximize the performance of the combined cycle. However, the efficiency penalty of more than 5% exceeds this expectation. For example, the part-flow sCO

_{2}topping cycle in the study of Manente and Lazzaretto [32] has 44.2% thermal efficiency for the same maximum turbine inlet conditions as given in this article. The underlying theory leading to an overly penalized BTC efficiency in this article is the deviation from optimum compressor inlet conditions at State 1. The sCO

_{2}cycles take advantage of the minimal compression work of the working fluid CO

_{2}in the vicinity of its critical temperature of 31.8 °C. Note that the temperature of State 1 in this paper is 42.9 °C, which causes the T-s diagram of the topping cycle to shift slightly right of the saturation curve of CO

_{2}and ultimately decreases the cycle efficiency by about 5% compared to results in the literature. The reason for the deviation from the optimum CO

_{2}compression inlet temperature is that the rejected heat of BTC is recovered in BCC using the coupling heat exchanger, cooler. As the flowrate of the BBC increases, the temperature of the CO

_{2}at the hot side outlet of cooler (State 1) increases under a fixed effectiveness value of the cooler. Although this process penalizes the efficiency of BTC by around 5%, it allows for the utilization of 5 MW thermal heat in the bottoming cycle. In fact, the scale of the topping cycle should be kept as small as possible to use the existing steam turbine of KZD-1 by BBC to the fullest extent. Therefore, the efficiency drop in BTC is diluted in the combined cycle due to the utilization of a significant portion of the biomass-derived heat in BCC, as shown in Figure 11. As a comparison, the net power distribution in the work of Manente and Lazzaretto [32] favors the topping cycle by 90% (topping) to 10% (bottoming), while the bottoming cycle is favored in this article by 61% (bottoming) to 39% (topping).

_{2}and steam Rankine cycles are utilized in a cascaded manner, as in this article, to allow for a comparison of BCC thermal efficiency. However, Jiang et al. reported a hybrid solar thermal–EGS power plant using CO

_{2}as a working fluid as reaching 21.93% and 22.44%, respectively, for TITs of 500 °C and 600 °C, which is in relatively good agreement with the found BCC efficiency [15]. On the other hand, Manente and Lazzaretto reported their biomass-to-electricity conversion efficiency as 34.3% for their combined cycle [32]. Despite their topping cycle being a part-flow sCO

_{2}cycle with the same turbine inlet conditions as in this article, it should be noted that their bottoming cycle is a simple recuperated sCO

_{2}cycle with a TIT of 313.9 °C, while the TIT of the bottoming steam Rankine cycle in this article is restricted by the operational TIT of KZD-1 GEPP at 146.9 °C. Therefore, a lower biomass-to-electricity conversion efficiency is expected in this article, compared to their 34.3% conversion efficiency.

_{2}cycles. Thus, heating below a certain temperature, i.e., 400 °C in this article, cannot be utilized in the topping sCO

_{2}cycle without changing its layout or adding additional heat exchangers. In order to overcome this problem, sCO

_{2}cycles are generally utilized in the literature in a cascaded manner, as mentioned in Section 1 and Section 2. Since a flue gas heat below 400 °C is utilized in BBC through the convective section of BHB, the problem of having a complex sCO

_{2}cycle layout or adding another sCO

_{2}cycle as a bottoming cycle is resolved. Finally, UA values (commonly known as conductance and expressed in units of kW K

^{−1}) for each heat exchanger are supplied as a preliminary economic indicator. It is assumed that the equipment cost scale is within the UA value; recuperators appear to be the heat exchanger units requiring most of the investment costs [44,47].

## 4. Conclusions

_{2}topping and steam Rankine bottoming cycles where locally sourced olive residue is used as a biomass fuel source. While a topping sCO

_{2}cycle is specifically chosen due to its potential for flexible electricity generation, as a first step to develop this novel hybridization scheme, only the steady-state design conditions of hybridization are modeled in this work. The proposed working fluid mass flow rates for topping and bottoming cycles, i.e., 45 kg s

^{−1}and 12 kg s

^{−1}, respectively, can represent the nominal case. For off-design scenarios, these flow rates can be downscaled proportionally by controlling the combusted biomass fuel flow, such that the intensive thermodynamic properties remain close to their design values. Although a decrease in both thermal efficiency and power generation can occur for off-design calculations, the scenarios for hourly fluctuations or seasonal variations can be investigated in future work.

^{−1}to 31.45 s

^{−1}and brings the steam turbine closer to its operating conditions reported in 2004 [34]. Then, 3.4 MWe and 5.3 MWe additional net powers are generated through the topping and bottoming cycles, with 40.1% and 16.9% thermal efficiencies, respectively. The combined cycle composed of the combination of topping and bottoming cycle has a thermal efficiency of 24.9% and net power generation of 8.7 MWe. Biomass to electricity conversion efficiency is calculated as 22.4% for a fuel consumption rate of 2.2 kg s

^{−1}. Despite the penalties in terms of topping cycle thermal efficiency and biomass-to-electricity conversion efficiency compared to the literature, the motivation in the hybridization scenario in this article is using the existing infrastructure of KZD-1 GEPP to the fullest extent by keeping the topping cycle and additional investments costs as small as possible while retaining the maximum possible efficiency. In this context, the goal of sharing existing components in hybrid power plant layouts is arguably achieved [47]. Moreover, the high-temperature heat addition problem of sCO

_{2}cycles is resolved by utilizing a flue gas heat under 400 °C in the bottoming cycle. Consequently, the need to add a bottoming sCO

_{2}cycle or have a complex sCO

_{2}cycle layout is avoided.

_{2}cycle, a biomass heater boiler, and a dry cooling system. Although reliable cost correlation parameters of conventional systems, such as boilers or dry cooling systems, are present in the literature for economic analysis, the equipment costs of next-generation sCO

_{2}power cycles that have not been commercialized yet remain unknown. As a rough estimation, Wright et al. consider the cost of all heat exchangers in the sCO

_{2}cycle (recuperators, primary heat exchangers, preheaters, etc.) as about 50% of the total system costs [52]. Even if a complete economic analysis is not incorporated in this article, UA values of the heat exchangers are supplied in Figure 12 as an economic indicator, and sCO

_{2}recuperators seem to be the components that would account for most of the additional investment costs of such a hybridization.

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations/Nomenclature

b2e | biomass to electricity |

BBC | biomass bottoming cycle |

BCC | biomass combined cycle |

BHB | biomass heater boiler |

BTC | biomass topping cycle |

CSP | concentrated solar power |

DC | direct contact |

DSG | direct steam generation |

EGS | enhanced geothermal system |

GEPP | geothermal electric power plant |

HHV | higher heating value |

HP | lower heating value |

HTR | High-temperature recuperator |

KZD-1 | Kızıldere-1 |

KZD-2 | Kızıldere-2 |

LCOE | levelized cost of electricity |

LHV | lower heating value |

LP | low pressure |

LTR | Low-temperature recuperator |

MC | main compressor |

NGC | non-condensable gas |

OR | olive residue |

ORC | organic Rankine cycle |

PTC | parabolic trough collector |

PV | photovoltaic |

RC | recompressor |

sCO_{2} | supercritical CO_{2} |

TAF | adiabatic flame temperature |

tCO_{2} | transcritical CO_{2} |

TEF | effective temperature of radiation |

TIT | turbine inlet temperature |

WCT | wet cooling tower |

WHR | waste heat recovery |

λ | excess air ratio |

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**Figure 6.**Results of parametric analysis conducted on the flow rates of BTC and BBC. (

**a**) BTC thermal efficiency,${\mathsf{\eta}}_{\mathrm{btc}}$; (

**b**) BTC net power output,${\dot{\mathrm{W}}}_{\mathrm{net},\mathrm{btc}}$; (

**c**) BCC thermal efficiency,${\mathsf{\eta}}_{\mathrm{bcc}}$.

**Figure 7.**Optimization of part-flow ratio: (

**a**) Variations in BTC and BCC thermal efficiencies with changing part-flow ratio; (

**b**) Variations in the heat duties and pinch point of the recuperators with changing part-flow ratio.

**Figure 8.**Optimization of turbine expansion ratio: (

**a**) Variations in thermal efficiencies of BCC and BTC with changing turbine expansion ratio; (

**b**) Variations in the heat duties and pinch point of the recuperators with changing turbine expansion ratio.

**Figure 9.**Heat transfer distribution and the flue gas temperature leaving the radiative section of the BHB (State 21) with varying intermediate steam quality.

**Figure 10.**T-s diagrams of the thermodynamic cycles used in hybridization of KZD-1 GEPP: (

**a**) BTC; (

**b**) BBC.

**Figure 11.**Heat and power distribution between the cycles: (

**a**) Allocation of biomass energy; (

**b**) Net power distribution.

**Figure 12.**Q-T diagram of the heat exchangers. (

**a**) Cooler; (

**b**) Recuperators; (

**c**) Radiative-convective counter-current heater-boiler (BHB) with assumed TEF = 1000 °C.

Parameter | |
---|---|

Proximate analysis (wt.%, dry basis) | |

Volatile matter | 83.9 |

Fixed Carbon ^{a} | 14.2 |

Ash | 1.9 |

Moisture content (wt.%, as received) | |

Moisture | 7.5 |

Ultimate analysis (wt.%, dry ash free) | |

C | 51.5 |

H | 6.2 |

N | 0.7 |

S | - |

O ^{a} | 41.6 |

Calorific value | |

Higher heating value (dry basis) ^{b} (MJ kg^{−1}) | 20.5 |

Lower heating value (wet basis) ^{c} (MJ kg^{−1}) | 17.5 |

Input | Value | Unit | Description | Source/Comment |
---|---|---|---|---|

BTC | ||||

η_{comp} | 90 | % | Isentropic efficiency of the compressors | [21,32] |

η_{turb} | 93 | % | Isentropic efficiency of the turbine | [21,31,44] |

T_{turb} | 550 | °C | Turbine inlet temperature | [22,32,42,45] |

P_{turb} | 20 | MPa | Turbine inlet pressure | [21] |

φ | 3 | - | Expansion ratio of the CO_{2} turbine, P_{5}/P_{6} | Optimized parameter [21]. |

ψ | 0.75 | - | Part-flow ratio, ṁ_{1}/ṁ_{8} | Optimized parameter [21]. |

ε_{recup} | 96 | % | Effectiveness of the recuperators | [21,39,46] |

ε_{cooler} | 80 | % | Effectiveness of the cooler | [21,46] |

ΔP_{hot,recup} | 0.03 | MPa | Pressure drop at hot side of recuperators | [21,47] |

ΔP_{cold,recup} | 0.22 | MPa | Pressure drop at cold side of recuperators | [21,47] |

ΔP_{hot,cooler} | 0.6 | MPa | Pressure drop at hot side of cooler | [21,47] |

ΔP_{cold,cooler} | 0.1 | MPa | Pressure drop at cold side of cooler | [21,47] |

ΔP_{bhb,co2} | 0.24 | MPa | Pressure drop for CO_{2} inside BHB | [21,47] |

BBC | ||||

η_{turb,bot} | 80 | % | Isentropic efficiency of the steam turbine | Assumption. See Section 2.1.1 |

η_{pump} | 80 | % | Isentropic efficiency of the pumps | Generic value. |

η_{air comp} | 90 | % | Isentropic efficiency of the air compressor | Generic value. |

T_{turb,bot} | 146.9 | °C | Turbine inlet temperature | Operational KZD-1 data. |

P_{turb} | 0.438 | MPa | Turbine inlet pressure | Operational KZD-1 data. |

ΔP_{bhb,water} | 0.01 | MPa | Pressure drop for water inside BHB | Generic value. |

BHB | ||||

λ | 1.5 | - | Excess air ratio | [32] |

TEF | 1000 | °C | Effective temperature of radiation | [32] |

Rad. loss | 5 | % | Heat loss in the radiative section of BHB | [32] |

ε_{air preheater} | 80 | % | Effectiveness of the air preheater | [46] |

T_{air,in} | 20 | °C | Air inlet temperature to air preheater | [32] |

**Table 3.**BHB verification results based on the model of Manente and Lazzaretto [32].

Inputs | Outputs | ||||||
---|---|---|---|---|---|---|---|

λ | T_{air} (°C) | T_{flue gas} (°C) | m_{flue gas} (kg s^{−1}) | X_{CO2} | X_{H2O} | X_{N2} | X_{O2} |

Manente and Lazzaretto [32] | |||||||

1.5 | 20 | 1405 | 8.225 | 0.1826 | 0.0754 | 0.6738 | 0.0682 |

100 | 1457 | ||||||

2.37 | 20 | 1000 | 12.41 | 0.1211 | 0.0499 | 0.7053 | 0.1237 |

2.56 | 100 | 1000 | 13.33 | 0.1127 | 0.0465 | 0.7095 | 0.1313 |

Verification model | |||||||

1.5 | 20 | 1407 | 8.273 | 0.1820 | 0.0749 | 0.6752 | 0.0679 |

100 | 1458.6 | ||||||

2.37 | 20 | 999.9 | 12.49 | 0.1230 | 0.0496 | 0.7065 | 0.1209 |

2.56 | 100 | 1000.7 | 13.41 | 0.1125 | 0.0462 | 0.7107 | 0.1306 |

Error: (Verif. Model—Ref.)/Ref. | |||||||

0.1% | 0.6% | –0.3% | –0.7% | 0.2% | –0.4% | ||

0.1% | |||||||

0.0% | 0.6% | 1.6% | –0.6% | 0.2% | –2.3% | ||

0.1% | 0.6% | –0.2% | –0.6% | 0.2% | –0.5% |

Cycle | ṁ kg s ^{−1} | η_{th}% | Ẇ_{net}MWe |
---|---|---|---|

Topping part-flow sCO_{2} (BTC)Bottoming steam Rankine (BBC) | 45 | 40.1 | 3.4 |

12 | 16.9 | 5.3 | |

Combined (BCC) | - | 24.9 | 8.7 |

η_{bhb} | ṁ_{fuel} (kg s^{−1}) | ṁ_{flue gas} (kg s^{−1}) | TAF (°C) | T_{21} (°C) | X_{CO2} | X_{H2O} | X_{N2} | X_{O2} |
---|---|---|---|---|---|---|---|---|

0.90 | 2.2 | 21.5 | 1623 | 890.6 | 0.1775 | 0.0623 | 0.6909 | 0.0693 |

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**MDPI and ACS Style**

Mutlu, B.; Baker, D.; Kazanç, F.
Development and Analysis of the Novel Hybridization of a Single-Flash Geothermal Power Plant with Biomass Driven sCO_{2}-Steam Rankine Combined Cycle. *Entropy* **2021**, *23*, 766.
https://doi.org/10.3390/e23060766

**AMA Style**

Mutlu B, Baker D, Kazanç F.
Development and Analysis of the Novel Hybridization of a Single-Flash Geothermal Power Plant with Biomass Driven sCO_{2}-Steam Rankine Combined Cycle. *Entropy*. 2021; 23(6):766.
https://doi.org/10.3390/e23060766

**Chicago/Turabian Style**

Mutlu, Balkan, Derek Baker, and Feyza Kazanç.
2021. "Development and Analysis of the Novel Hybridization of a Single-Flash Geothermal Power Plant with Biomass Driven sCO_{2}-Steam Rankine Combined Cycle" *Entropy* 23, no. 6: 766.
https://doi.org/10.3390/e23060766