**2. System description**

As illustrated in **Figure 5**, the configuration consists of four circuits: an ORC cycle circuit represented by the red color, a circuit of the VCC cycle which is in blue, a circuit in purple color of the desalinated seawater, and a red circuit in the heated water. We will couple our facility with a limited renewable energy source which is thermal photovoltaic center, at low temperature (100–130°C). Our approach is to lower the condensing temperature between 10 and 10°C of the ORC cycle so that the delivered work can be increased. So, a cold part produced by VCC will be dedicated to condense the fluid of the ORC cycle. For this, we will integrate an exchanger regenerator1 which is used to condense the ORC fluid by a quantity of cold produced laying vapor phase VCC side.

**Figure 5.** *System of study.*

• **Mode 3**: cogeneration (cold production and electricity power). **Figure 3**

electric power by ORC cycle and cooling capacity by the VCC cycle.

system with a limited renewable energy source.

working fluid as the classic systems.

and biomass.

**4**

**Figure 4.**

*Electrodialysis*

*Tri-generation and desalination mode.*

presents the basic architecture. It receives an external renewable source in the boiler. Through this source, it allows us to have mechanical work at the turbine: this is partially transmitted to the VCC cycle compressor as mode 2. The power provided by the VCC cycle evaporator is partially operated by the condenser ORC cycle. So this operation mode requires a renewable source and offers an

• **Mode 4**: tri-generation and desalination of seawater are illustrated in **Figure 4**. This configuration has four circuits: an ORC cycle circuit that is represented by the red color, a circuit of the VCC cycle in blue, a circuit in purple color of the desalinated seawater, and a red circuit of the heated water. We will couple the

In addition, each installation mode has several configurations depending on the recovery points that will be integrated later, besides its adaptation to any energy source, where we can use biomass, solar, and heat rejects of industry at low temperatures (60–130°C). This system could produce a negative and a positive cold. Although, due to its architecture, it is also characterized by many combinations of selection fluid for the ORC and VCC cycles, it is not necessary to have the same

The main purpose of this presented study is to analyze the performance of a new system that combines the steam compression cycle and the Rankine cycle for trigeneration (electricity, cold, hot) as well as the desalination of water. This system uses a low-temperature heat source such as solar energy, heat from industrial waste,

#### **2.1 Desalinated water circuit description**

First, the seawater is pumped by a pump PMP1 and preheated by the **exchanger 3**. Then, it will be evaporated at constant pressure in the boiler by a solar collector. After having saturated steam, the latter passed the condensation phase using the **regenerator 2** in order to equate the water at a hot temperature which is equal to that of the evaporation. With integrity of exchanger H2, we started the first phase of cooling the salty water and chaffered sanitary water. In the end, for the desalted water to complete this phase of cooling, also we have to warm the water out of the sea, using an exchanger H3.

#### **2.2 Circuit description of heated domestic water**

This is the simplest circuit in our loop. It is enough the sanitary water enters the exchanger H3 to become hot thanks to the quantity of heat provided by the desalted water.

So our system produces electricity due to the mechanical work obtained by the turbine, a refrigeration quantity by the evaporator 1, and de-watered water obtained using two serial transformations (evaporation, condensation) and produces hot water by the exploitation of the hot quantity from the de-watered water.

## **3. The different configurations developed for ORC-VCC combination**

#### **3.1 Configuration A**

The cycle A is the basic configuration. We will combine the two ORC and VCC cycles without any recovery for cogeneration. As shown in **Figure 6**, the only combination is made at the heat exchanger H1 which serves as the condenser of the ORC cycle fluid. This configuration allows having cogeneration with positive or negative cold according to our needs.

almost the same as the temperature of condensation which varies between 10 and 10°C, the idea is to exploit this temperature to make the sub-cooling of the VCC cycle to improve its performance. Cycle B is shown in **Figure 7**, and it is also

*Schematic and T-S diagrams of the configuration A. (a) Schematic of the configuration A, (b) T-S diagrams*

*Performance Analysis of a New Combined Organic Rankine Cycle and Vapor Compression…*

As shown in **Figure 8**, cycle C is used also for cogeneration. Unlike the conventional ORC cycle, which is used only for electricity production at the turbine state, cycle C allows the generation of electricity and cold in the ORC cycle. So, the configuration C is used to produce negative cold, positive cold, and electricity.

We will use the heat quantity at low temperature following the pumping step in the ORC cycle in order to produce a positive cold at 18°C for air conditioning. For this reason, we will integrate the H3 exchanger for the heat transfer between the

During this study, we treated the thermodynamic equations as well as the resolution by a calculation program developed by the EES software. Also, this software

allows us to realize the different curves and tables presented in the study.

developed to make cogeneration with a negative cold.

*for ORC cycle, and (c) P-H diagrams for VCC cycle.*

*DOI: http://dx.doi.org/10.5772/intechopen.91871*

**4. Mathematical modeling and validation of the model**

**3.3 Configuration C**

**Figure 6.**

ambient air and the ORC cycle fluid.

**4.1 Thermodynamic modeling**

**7**

The operating principle is described as follows:

First, the ORC cycle fluid enters the boiler in order to heat it up to 100°C by a renewable external source (biomass, industrial and solar thermal discharge, etc.). It suffices that the fluid reaches a saturated vapor phase; it enters a turbine to generate a mechanical work. This phase allows the fluid to pass from the high pressure to the low pressure. After this phase, a condensation phase is necessary to make the fluid in a liquid state. For our application, the condensation is done at low temperature which requires a cold external source. For this, we combined the ORC cycle condenser with the VCC cycle evaporator by integrating a H1 exchanger. For this configuration, after condensation, the fluid goes to the pumping phase.

In addition, the VCC cycle operation is the inverse of those ORC cycle. The VCC fluid is compressed with a mechanical compressor and then condensed at a temperature of 30°C. In this configuration, after this phase, the fluid is released directly by an expansion valve. Then it is evaporated in two phases.

#### **3.2 Configuration B**

For cycle B, we kept the same basic architecture as in cycle A, except that we will integrate an H2 exchanger. This exchanger is mounted just after the pumping phase of the ORC cycle. Seeing that the temperature obtained at the pumping point is

*Performance Analysis of a New Combined Organic Rankine Cycle and Vapor Compression… DOI: http://dx.doi.org/10.5772/intechopen.91871*

#### **Figure 6.**

**2.1 Desalinated water circuit description**

**2.2 Circuit description of heated domestic water**

sea, using an exchanger H3.

**3.1 Configuration A**

pumping phase.

**3.2 Configuration B**

**6**

negative cold according to our needs.

The operating principle is described as follows:

by an expansion valve. Then it is evaporated in two phases.

water.

*Electrodialysis*

First, the seawater is pumped by a pump PMP1 and preheated by the **exchanger 3**. Then, it will be evaporated at constant pressure in the boiler by a solar collector. After having saturated steam, the latter passed the condensation phase using the **regenerator 2** in order to equate the water at a hot temperature which is equal to that of the evaporation. With integrity of exchanger H2, we started the first phase of cooling the salty water and chaffered sanitary water. In the end, for the desalted water to complete this phase of cooling, also we have to warm the water out of the

This is the simplest circuit in our loop. It is enough the sanitary water enters the exchanger H3 to become hot thanks to the quantity of heat provided by the desalted

So our system produces electricity due to the mechanical work obtained by the

**3. The different configurations developed for ORC-VCC combination**

cycles without any recovery for cogeneration. As shown in **Figure 6**, the only combination is made at the heat exchanger H1 which serves as the condenser of the ORC cycle fluid. This configuration allows having cogeneration with positive or

The cycle A is the basic configuration. We will combine the two ORC and VCC

First, the ORC cycle fluid enters the boiler in order to heat it up to 100°C by a renewable external source (biomass, industrial and solar thermal discharge, etc.). It suffices that the fluid reaches a saturated vapor phase; it enters a turbine to generate a mechanical work. This phase allows the fluid to pass from the high pressure to the low pressure. After this phase, a condensation phase is necessary to make the fluid in a liquid state. For our application, the condensation is done at low temperature which requires a cold external source. For this, we combined the ORC cycle condenser with the VCC cycle evaporator by integrating a H1 exchanger. For this configuration, after condensation, the fluid goes to the

In addition, the VCC cycle operation is the inverse of those ORC cycle. The VCC fluid is compressed with a mechanical compressor and then condensed at a temperature of 30°C. In this configuration, after this phase, the fluid is released directly

For cycle B, we kept the same basic architecture as in cycle A, except that we will integrate an H2 exchanger. This exchanger is mounted just after the pumping phase of the ORC cycle. Seeing that the temperature obtained at the pumping point is

turbine, a refrigeration quantity by the evaporator 1, and de-watered water obtained using two serial transformations (evaporation, condensation) and produces hot water by the exploitation of the hot quantity from the de-watered water.

*Schematic and T-S diagrams of the configuration A. (a) Schematic of the configuration A, (b) T-S diagrams for ORC cycle, and (c) P-H diagrams for VCC cycle.*

almost the same as the temperature of condensation which varies between 10 and 10°C, the idea is to exploit this temperature to make the sub-cooling of the VCC cycle to improve its performance. Cycle B is shown in **Figure 7**, and it is also developed to make cogeneration with a negative cold.

#### **3.3 Configuration C**

As shown in **Figure 8**, cycle C is used also for cogeneration. Unlike the conventional ORC cycle, which is used only for electricity production at the turbine state, cycle C allows the generation of electricity and cold in the ORC cycle. So, the configuration C is used to produce negative cold, positive cold, and electricity.

We will use the heat quantity at low temperature following the pumping step in the ORC cycle in order to produce a positive cold at 18°C for air conditioning. For this reason, we will integrate the H3 exchanger for the heat transfer between the ambient air and the ORC cycle fluid.

#### **4. Mathematical modeling and validation of the model**

#### **4.1 Thermodynamic modeling**

During this study, we treated the thermodynamic equations as well as the resolution by a calculation program developed by the EES software. Also, this software allows us to realize the different curves and tables presented in the study.

**Table 1** illustrates the different thermodynamic models used throughout the

*Performance Analysis of a New Combined Organic Rankine Cycle and Vapor Compression…*

The approach followed to validate our model is based on two procedures of the developed model. The ORC and the VCC are validated, respectively, in Sections

The model developed for the ORC is tested with the results by Saleh et al. [29], which is the most appropriate configuration to validate the current model using the

Boiler (1) *Qb* ¼ *m*\_ <sup>1</sup>ð Þ *h*<sup>3</sup> � *h*<sup>2</sup>

Condenser *Qcond* ¼ *m*\_ <sup>1</sup>ð Þ *h*<sup>4</sup> � *h*<sup>1</sup> Thermal efficiency <sup>μ</sup>*orc* <sup>¼</sup> ð Þ *WT*�*Wp*

First evaporator *Qev*<sup>1</sup> ¼ *m*\_ <sup>2</sup>ð Þ *h*<sup>14</sup> � *h*<sup>13</sup> Second evaporator *Qev*<sup>2</sup> ¼ *m*\_ <sup>2</sup>ð Þ *h*<sup>10</sup> � *h*<sup>14</sup>

Net work *Wnet* ¼ *WT* � *Wp* � *WC*

Efficacity (1 and 2) E <sup>¼</sup> *Qev*<sup>1</sup>

*Thermodynamic modeling of different configurations ((1) cycle A; (2) cycle B, and (3) cycle C).*

Overall evaporator *Qev* ¼ *m*\_ <sup>2</sup>ð Þ¼ *h*<sup>10</sup> � *h*<sup>13</sup> *Qev*<sup>1</sup> þ *Qev*<sup>2</sup>

ð Þ *h*2*s*�*h*<sup>1</sup> ƞ*pump*

*Qb*

*COPVCC* <sup>¼</sup> *Qev*1þ*Qev*<sup>2</sup> ð Þ *Wcomp*

(3) E <sup>¼</sup> *Qev*<sup>1</sup>þ*Qhx*<sup>3</sup> *Wnet*

*R*<sup>2</sup> ¼ *m*1*=m*<sup>4</sup> *R*<sup>3</sup> ¼ *m*2*=m*<sup>4</sup> *R*<sup>4</sup> ¼ *m*3*=m*<sup>4</sup>

(1 and 2) *COPs* <sup>¼</sup> ð Þ *Qev*1þ*Wnet*

*Wnet*

Exchanger 1 *Qhx*<sup>1</sup> ¼ *Qev*<sup>2</sup> ¼ *Qcond*

*Qexh*<sup>3</sup> ¼ *m*\_ <sup>1</sup>ð Þ¼ *h*<sup>5</sup> � *h*<sup>4</sup> *m*\_ <sup>3</sup>ð Þ *h*<sup>18</sup> � *h*<sup>17</sup> *Qexh*<sup>4</sup> ¼ *m*\_ <sup>3</sup>ð Þ¼ *h*<sup>19</sup> � *h*<sup>18</sup> *m*\_ <sup>4</sup>ð Þ *h*<sup>22</sup> � *h*<sup>21</sup> *Qexh*<sup>5</sup> ¼ *m*\_ <sup>3</sup>ð Þ¼ *h*<sup>20</sup> � *h*<sup>19</sup> *m*\_ <sup>3</sup>ð Þ *h*<sup>15</sup> � *h*<sup>14</sup>

(3) *COPs* <sup>¼</sup> *Qev*1þ*Wnet*þ*Qhx*<sup>3</sup>

*Qb*

Exchanger 2 *Qhx*<sup>2</sup> ¼ *m*\_ <sup>1</sup>ð Þ¼ *h*<sup>5</sup> � *h*<sup>2</sup> *m*\_ <sup>2</sup>ð Þ *h*<sup>12</sup> � *h*<sup>15</sup> Exchanger 3 *Qhx*<sup>2</sup> ¼ *m*\_ <sup>1</sup>ð Þ¼ *h*<sup>5</sup> � *h*<sup>2</sup> *m*\_ <sup>2</sup>ð Þ *h*<sup>16</sup> � *h*<sup>17</sup>

*Qb*

ð Þ *h*11*s*�*h*<sup>10</sup> ƞ*comp*

(2) *Qb* ¼ *m*\_ <sup>1</sup>ð Þ *h*<sup>3</sup> � *h*<sup>5</sup> (3) *Qb* ¼ *m*\_ <sup>1</sup>ð Þ *h*<sup>3</sup> � *h*<sup>6</sup>

work and the different configurations for cogeneration mode.

ORC Turbine *WT* ¼ *m*\_ <sup>1</sup>ð Þ *h*<sup>3</sup> � *h*4*<sup>s</sup> :*ƞ*exp*

VCC Compressor *WC* <sup>¼</sup> *<sup>m</sup>*\_ <sup>2</sup>

Coefficient of performance

the system

Exchangers for cogeneration

Exchangers for trigeneration

Mass ratio *R*<sup>1</sup> ¼ *m*3*=m*<sup>4</sup>

Overall performance of

Pump *Wp* <sup>¼</sup> *<sup>m</sup>*\_ <sup>1</sup>

**4.2 Validation of the model**

*DOI: http://dx.doi.org/10.5772/intechopen.91871*

4.2.1 and 4.2.2.

*4.2.1 ORC validation*

Overall performance of

ORC-VCC

**Table 1.**

**9**

#### **Figure 7.**

*Schematic and T-S diagrams of the configuration B. (a) Schematic of the configuration B, (b) T-S diagrams for ORC cycle, and (c) P-H diagrams for VCC cycle.*

#### **Figure 8.**

*Schematic and T-S diagrams of the configuration C system. (a) Schematic of the configuration C, (b) T-S diagrams for ORC cycle, and (c) P-H diagrams for VCC cycle.*

*Performance Analysis of a New Combined Organic Rankine Cycle and Vapor Compression… DOI: http://dx.doi.org/10.5772/intechopen.91871*

**Table 1** illustrates the different thermodynamic models used throughout the work and the different configurations for cogeneration mode.

### **4.2 Validation of the model**

The approach followed to validate our model is based on two procedures of the developed model. The ORC and the VCC are validated, respectively, in Sections 4.2.1 and 4.2.2.

#### *4.2.1 ORC validation*

The model developed for the ORC is tested with the results by Saleh et al. [29], which is the most appropriate configuration to validate the current model using the


**Table 1.**

*Thermodynamic modeling of different configurations ((1) cycle A; (2) cycle B, and (3) cycle C).*

**Figure 7.**

*Electrodialysis*

**Figure 8.**

**8**

*ORC cycle, and (c) P-H diagrams for VCC cycle.*

*Schematic and T-S diagrams of the configuration B. (a) Schematic of the configuration B, (b) T-S diagrams for*

*Schematic and T-S diagrams of the configuration C system. (a) Schematic of the configuration C, (b) T-S*

*diagrams for ORC cycle, and (c) P-H diagrams for VCC cycle.*


**5. Selection of the working fluid**

*DOI: http://dx.doi.org/10.5772/intechopen.91871*

is isentropic like R600 and R600a.

than 0.95 of steam rate.

**Figure 9.**

**11**

*The three classes on a T-S diagram.*

The choice of the working fluid for an ORC or VCC cycle is an important criterion to improve the cycle performances. Generally, there are three families of organic fluids. **Figure 9** shows these three classes on a T-S diagram. The distinction between these different types essentially depends on the slope between the saturation temperature and the isentropic variation (ΔT/Δs). If a negative slope is said, the fluid is wet, such as H2O, NH3, and R134a. For a positive slope, we speak of a dry fluid such as benzene and pentane. In cases where the slope is infinite, it is said that this fluid

*Performance Analysis of a New Combined Organic Rankine Cycle and Vapor Compression…*

For the ORC cycle is to have fluid hot admits a weak latent heat in the evaporator, in order to minimize the quantity received by the boiler. Thus, a low latent heat in the condenser minimizes the amount of cold delivered by the VCC cycle. In addition, we are looking for a fluid with a positive slope to avoid vapor having less

We guarantee the elimination of the oxidation effect in the turbine especially that we will make it lower concerning the condensation temperature to 10°C. Based on these criteria and conditions mentioned above, it is necessary to choose a dry or isentropic ORC cycle fluid. We choose the n-hexane; the chemical formula is C6H14. The thermophysical characteristics of this fluid are presented in **Table 4**. The R600 is selected as a working fluid for the VCC cycle. It is a hydrocarbon of formula C4H10 crude which is found in the gas status under normal conditions of temperature and pressure. The physical characteristics of this fluid are presented in **Table 4**. Furthermore, our choice is toward the use of n-hexane for the ORC cycle. This choice is essentially due to the steam rate which is equal to 1 even when the condensation temperature is lowered to a low degree. This allows us to have a margin of confidence and turbine safety (avoid the effect of oxidation). During our

study, we chose the R600 as a working fluid for the VCC cycle. This fluid is characterized by its robustness in the market, so it is used in recent years in several

researches. In addition, we find that the environmental damage is minimal.

set some parameters and define their limits. For example, the network and

To reassure the efficiency and rentability of the system, it is necessary that we

**6. System settings and boundary conditions**

#### **Table 2.**

*Validation results for ORC cycle.*

similar working applied fluid. The comparative results are illustrated in **Table 2**. These results show a small deviation of 2.09% concerning the thermal efficiency. It is worthy to notice that certain changes in the developed model are made for an appropriate comparison. Specifically, the condensation temperature was 40°C and the isentropic efficiency at 85%.
