**4. Conclusions**

In tropical climate countries, the potential of cogeneration (and as such, its calculation) of the industrial sector is dependent on particular climate conditions, consumption behavior, cogeneration schemes, and fuel availability. Tropical countries such as Ecuador do not necessitate indoor heating (an important energy requirement in tempered climate countries), although air conditioning is prominently used. Thus, large cogeneration projects are more suitable in the industrial sector and in places where hot and cold fluids are used (e.g., hospitals, hotels, airports, and shopping malls). This study has shown that the adoption of cogeneration at a large scale promotes environmental, economic, and social benefits to countries by reducing GHG emissions, promoting fuel savings and energy efficiency, and by creating new jobs, respectively. In the case of Ecuador, the potential of cogeneration in the industrial sector (including hospitals, hotels, shopping malls and two airports) is approximately 600 MWel, which is around 7% of the total electricity generation installed capacity in the country. If this cogeneration potential is implemented, the energy efficiency in the Ecuadorian industry could be increased by 35–40%. This potential could save up to 18.6 × 106 L/month of oil-derived fuels, avoiding up to 576,800 tCO2/year, and creating more than 2600 direct jobs. Lack of NG for cogeneration is seen as a problem that needs to be addressed in the future to reduce the cost of electricity generation in cogeneration plants. The use of diesel and gas engines (the main types of prime movers in the conditions of the industry in Ecuador) presents opportunities to easily move from fossil-derived fuels to renewable fuels, i.e., to use biodiesel and biogas in substitution of diesel and NG, respectively. This topic deserves further analysis, especially in identifying options for producing biofuels. Further studies should also address the logistics of integration of cogeneration with other electricity generation sources such as hydropower, or the logistics of biomass for cogeneration, to mention two aspects. Distributed generation through cogeneration offers opportunities to diversify local (small scale) electricity generation to optimize the use of the national grid and offset one of the

problems of the Ecuadorian electricity sector: its high dependency on hydropower that has large seasonal variations due to water flow reductions.

**Author Contributions:** Conceptualization, M.R.P.-S., J.L.E., J.J.-A., P.R.-G. and P.R.; methodology, M.R.P.-S., J.L.E., J.J.-A., F.M.-A., P.A.-R.; validation, M.R.P.-S., J.L.E., J.J.-A., P.A.-R.; data curation, M.R.P.-S., J.L.E. and T.G.-P.; writing—original draft preparation, M.R.P.-S. and J.L.E.; writing—review and editing, M.R.P.-S., J.L.E., J.J.-A., F.M.-A. and T.G.-P.; supervision, J.L.E. and M.R.P.-S.; project administration, J.J.-A.; funding acquisition, J.J.-A., P.R.-G. and P.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the former Ministry of Electricity and Renewable Energy—MEER (currently Ministry of Energy and Natural Non-renewable Resources) and the Corporación Eléctrica del Ecuador—CELEC EP (Contract No. 042-2016).

**Acknowledgments:** To the former Ministry of Electricity and Renewable Energy—MEER (currently Ministry of Energy and Natural Non-renewable Resources) and the Corporación Eléctrica del Ecuador—CELEC EP, institutions that have authorized this publication. Thanks to Stalin Vaca, Diego Suárez, Jaime Alvarado, Ricardo Álvarez, Robinson Machuca, Guillermo Pérez, Tamara Serrano, Rommel Vargas, and Fernanda Orellana for their support in conducting field research; to all the Ecuadorian industrial facilities that contributed information to conduct this study; to the ARCH and the ARCONEL for providing information on energy consumption in Ecuador; to Paul Martinez and Jorge Ortiz (CELEC EP) for their constructive comments on the results of the study; and to Raul Pelaez-Garcia for revising the English in the text.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Appendix A. Schematics of Proposed Cogeneration Systems**

**Figure A1.** Schematic of cogeneration system based on Rankine cycle for companies that can use biomass as fuel (e.g., sugarcane, pulp and paper, oil palm industries) and back pressure steam turbines. Adapted from [18,19,23,28,32,49,51].

**Figure A2.** Schematic of a cogeneration system using gas engines for the oil palm industry.

**Figure A3.** Schematic of a proposed trigeneration system using gas engines or diesel engines for the beverage industry, dairy industry, and food industry.

**Figure A4.** Schematic of a proposed trigeneration system using gas engines or diesel engines for service industries (e.g., hotels, hospitals). Adapted from [46].

**Figure A5.** Schematic of a proposed bottom cogeneration system used in cement industry. HRSG—heat recovery steam generator (adapted from [55,101]).

#### **Appendix B. Main Equations Used for the Computation of Cogeneration Systems (Units Are Presented in Brackets)**

(a) Cogeneration plant efficiency (CHPeff)

> CHPeff = (power output + useful heat recovered)/energy in fuel

(b) Energy in fuel (Qfuel)

```
Qfuel = mfuel*LHVfuel [kW]
```
mfuel—fuel rate [kg/s]

LHVfuel—fuel lower heating value [kJ/kg]

(c) Energy in steam (Qsteam)

> Qsteam = msteam\*(hsteam − hwater) [kW]

> > msteam—flow rate (production) of steam [kg/s]

hsteam—enthalpy of steam at the boiler exit [kJ/kg]

hwater—enthalpy of water at the entrance of boiler [kJ/kg]

(d) Efficiency of boiler [ηboiler]

> ηboiler = Qsteam/Qfuel

(e) Energy in combustion gases (Qcgas) that is used, for instance, in a heat recovery steam generator (HRSG)

Qcgas = mcgas\*(hhotgas − hcoldgas) [kW]

> mcgas—flow rate of combustion gases [kg/s] (e.g., gases from gas engine)

hhotgas—enthalpy of combustion gases at the entrance of heat recovery unit [kJ/kg]

holdgas—enthalpy of combustion gases after passing through the heat recovery equipment [kJ/kg]

(f) Electric energy efficiency of prime movers (motors) (ηEE)

ηEE = Welec/Qfuel

> Welec—electric power (useful energy output) [kW]

(g) Heat recovery unit (HRU) efficiency (ηHRU) for water heating

ηHRU = QHRUactual/QHRUtheor

QHRUactual—actual heat transfer rate [kJ/s]

> QHRUtheor—maximum possible heat transfer rate [kJ/s]

> > QHRUactual = mwaterHRU \* (hwaterHRUent − hwaterHRUexit)

> > > mwaterHRU—water flow rate in the HRU [kg/s]

hwaterHRUexit—enthalpy of water at the entrance of the HRU [kJ/kg]

hwaterHRUent—enthalpy of water at the exit of the HRU [kJ/kg]

(h) Heat recovery steam generator efficiency (ηHRSG) (for steam production)

ηHRSG = QHRSGactual/QHRSGtheor

QHRSGactual—actual heat transfer rate [kJ/s]

> QHRSGheor—maximum possible heat transfer rate [kJ/s]

> > QHRSGactual = msteamHRSG \* (hsteamHRSGent − hwaterHRSGexit)

mwaterHRU—steam (or water) flow rate in the HRSG [kg/s]

hwaterHRUexit—enthalpy of water at the entrance of the HRSG [kJ/kg]

hsteamHRUent—enthalpy of steam at the exit of the HRSG [kJ/kg]

(i) Efficiency of absorption chiller (COPAchill)

> COPAchill = Qevap/Qin

> > Qevap—rate at which water is cooled by the evaporator [kJ/s]

Qin—heat input (rate of heat loss from exhaust gas or steam that are used by the absorption unit) [kJ/s]

(j) Electricity produced by steam turbine-generator (Egen) [kWh/month]

Egen = Qsteam\*ηturb\*ηgen\*Toper\*pf [kWh/month]

> ηturb—steam turbine efficiency

<sup>η</sup>gen—generator efficiency

Toper—time generator operates [h/month]

(k) Present worth (present value) (Ct) of C monetary units

Ct = <sup>C</sup>/(1+i)t;

> i—discount rate; t—number of time periods

(l) Net present value (NPV)

> NPV = (C1+C2+C3+ ... + Cn)

> > C1, C2, C3, ... , Cn – Present worth of anticipated cash flows
