Carbon Dioxide Transcritical Power Cycles

• This study analyzes the potential of using low-grade waste heat with a carbon dioxide transcritical power cycle (CDTPC).
• Carbon dioxide (CO2) exhibits better temperature glide match within heat sources at supercritical states compared to alternatives in vapor generation
• The study focuses on optimizing the thermal efficiency of a CDTPC system using a regenerator.
• Mathematical models built with Engineering Equation Solver(EES) software help optimize the chosen cycle.
• Results favor CDTPC with a regenerator.

Dedication

• The thesis study is dedicated to Almighty Allah for providing guidance and strength.
• Appreciation is given to the authors' parents for their inspiration and support.
• Gratitude is extended to brothers, sisters, friends, and classmates for their support.

Certificate

• The thesis, "parametric analysis and optimization of Carbon Dioxide Transcritical Power Cycle," was written by Muhammad Shoaib (18ME67), Zeeshan Ali (18ME28), and Huzaifa Ahmed (18ME29) under the supervision of Prof. Dr. Abdul Fatah Abbasi.

Acknowledgement

• The authors thank Almighty Allah for strength and safety throughout the project.
• Appreciation is extended to the project supervisor, Prof. Dr. Abdul Fatah Abbasi, for encouragement and knowledge.
• Gratitude is expressed to friends and colleagues for their knowledge contribution to improve the thesis.

Abstract

• This research explores the possibility of using low-grade waste heat through carbon dioxide transcritical power cycles (CDTPC).
• CO2 works ideally with better temperature glide match with heat source at supercritical state in vapor generator.
• Thermodynamic parameters were analyzed to calculate energy, work input/output, efficiency, and exergy destruction within the CDTPC.
• Exergy and energy models were mathematically developed with EES software.
• Results were determined with fixed mass flow rates, condensation temperatures, heat sink temperatures, and isentropic efficiencies.

Introduction

• Reducing fossil fuel usage to decrease toxic gases is a global focal point.
• Increased electricity demands lead many nations to consider coal-fired power plants releasing substantial heat and carbon dioxide.
• Diesel engines and nuclear power plants also significantly contribute to environmental pollution.
• Waste Heat Recovery (WHR) extract energy from exhaust gases, converting into useful work.
• CO2 is natural, inexpensive, abundant, and non-toxic.
• CDTPCs can utilize green energy, e.g., from concentrated sunlight or geothermal energy.
• CDTPC has received attention in industry and academia.
• Thesis seeks to increase efficiency of CDTPC using waste heat energy under particular working parameters.

Carbon Dioxide Transcritical Power Cycle

• Transcritical power cycle (TPC) working fluid exists in supercritical and subcritical states within a cycle.
• Working fluid is supercritical at the turbine inlet and subcritical at the condenser and pump outlets.
• Transcritical power cycle (TPC) uses energy from waste heat exhaust gaseous, which converts low-grade waste heat (<150C) and middle-grade waste heat energy (150C to 600C) of the exhaust gaseous for useful work.
• It can use power plants and IC engines geothermal and/or solar energy.
• Carbon dioxide power cycle's working principle resembles a steam turbine.
• Water replaced by CO2, which operates in subcritical and supercritical states.
• Simple transcritical power cycle consists of vapor generator, turbine, condenser and pump.
• Exhaust gas transfers thermal energy to a working medium.
• Working medium transforms between subcritical to supercritical and expands in an expansion device for useful work yield.

Advantages of CO2

• Working fluids impact a cycle's performance in any cycle.
• CO2 is non-toxic/flammable/corrosive/explosive.
• CO2 has high reserves in air.
• CO2 alternatives are more expensive.
• CO2 has strong material compatibility.
• CO2 in supercritical range has high density, potentially using compact expanders.
• CO2 has predictable thermodynamic properties in both subcritical and supercritical conditions.
• CO2 is environmentally friendly.

Problem Statement

• Heat engines and power plants (nuclear/coal) release exhaust gases, leading to global warming and environmental pollution.
• Carbon Dioxide Transcritical Power Cycle (CDTPC) can reduce pollution by using low-grade exhaust energy (greenhouse gases) to produce power. CDTPC can apply sunlight and geothermal sources, decreasing fossil fuel consumption.

Objectives

• Create Carbon dioxide transcritical power cycle thermodynamic model using EES software.
• Parametrically analyze Carbon dioxide transcritical power cycle.
• Optimize performance of Carbon dioxide transcritical power cycle with a regenerator.
• Thermodynamic parameters were analyzed with regeneration and without.
• The first and second laws of thermodynamics were applied with mathematical models into EES software.

Scope of Research

• Research analyzes the performance of waste heat activated CDTPC systems on simple and regenerative models.
• Constant parameters include evaporator temperature and pressure, isentropic efficiency, and condenser temperature.
• Maximum energy efficiencies were observed within independent parameters to determine optimal CDTPC models under given conditions.

Literature Review

• Chen, Yang, and Per Lundqvist analyzed transcritical power cycles in Environmental Equation Solver(EES) using refrigerant CO2.
• IHX is not as efficient due to the changes exhibited by the special heat from the critical point exponentiality.
• Farzaneh-Gord and Mahmood investigated CO2 transcritical power cycles by IC engine exhaust gas. Temperature, pressure, gas coolant rate examined as useful work of 18 kW was attained.
• Chen, Tang, and Platellet compared CO2 transcritical power cycle to ORC with R123. CDTPC resulted in higher output than ORC with R123 operate under identical low-grade waste heat.
• Chuang Wu, Xiao-jiang Yan, multi-stage system better than basic when heat source has higher thermal energy.
• Abdullah A. Al Zahrania researched thermodynamic insights when building transcritical carbon dioxide power cycles (CSP). T-CO2 is integrated w/ absorption refrigeration systems (ARS) to enhance cycle efficiency. Integrated CSP systems saw thermal efficiency of 34% was achieved on T-CO2 power cycles.
• Young-Min, Kook-Young found a 5 degree Celsius increase in coolant temp, in between 20-50 degree C range, resulted drop in thermal efficiency/heat recovery cycle.
• Maoqing Li/Yiping Dai researched thermo-economic analysis with ORC operated by low-temperature geothermal source.
• Xiaoya Li, Hua Tian study w/ heavy-duty truck engine exhaust integrated to GT-SUITE software.
• Salli Li, Yiping Dai, The Kalina exhibited greater net power output as opposite exergy efficiency CDTPC.
• Guangdai Huang, investigation on axial turbine expander w/ 4.5kW capacity on turbine 10,555 rpm was 14,685 rpm adjusted via resistance load.
• Fredy Velez, José Segovia, the carbon dioxide transcritical power, analyzed by pressure until resultant work was zero and exergy cycle was compared.
• Lisheng Pan, Bo Li analyzed CO2 transcritical power cycle using rolling piston expander. Power generation/ thermal efficiency/operational measured
• Dongpeng Zhao, Ruikai Zhao, the modified cycle displayed a higher energy efficiencies when flue was introduced.
• Youcal Liang studied cooling based on supercritical CO2 power.
• Man-Hoe Kim proposed system using CO2 combined w/ waste heat recovering carbon dioxides. Efficiency, theoretical calculation, and efficient conversion

Methodology

• Section analyzes processes in the Carbon dioxide transcritical power cycle (CDTPC).

Basic CDTPC

• 1-2 non-isentropic expansive device,
• 2-3 constant pressure heat rejection in condenser,
• 3-4 non-isentropic compression in pump,
• 4-1 constant pressure heat addition in vapor generator.

CDTPC with Regenerator

• 1-2 non isentropic expansion expansive device,
• 2-3 constant pressure heat rejection from hot fluid to cold fluid in regenerator,
• 3-4 constant pressure heat rejection in condenser,
• 4-5 non isentropic compression in pump,
• 5-6 constant pressure heat addition to cold fluid from hot fluid in regenerator,
• 6-1 constant pressure heat addition in vapor generator.

Thermodynamic Analysis of Carbon Dioxide Transcritical Power Cycle

• Assumptions include steady state/negligible system pipe heat loss and saturated liquid working mediums post condenser,
• Pressure drop is considered zero,
• Turbine isentropic assumed to compensate non-ideal expansion with EES software.

Mathematical Model

• Mathematical model based both exergy / energy analysis developed for Transcritical Dioxide Power Cylces (CDTPC).

Energy Analysis of CDTPC

• Energy analysis of carbon dioxide transcritical power happens with work-input measuring thermodynamics 1st laws.
• For basic CDTPC power is generated with turbine using power output (kW), which WTur is mass flow,isothermal temp, and turbine efficiency.
• Realeased heat from Q is cooling from Condenser within a cycle (mass liquid rates * specific heat capacity).
• Generated heat comes from the vapor(Q in) where heat rates come from processing gas (mass liquid rates * difference thermal constant pressure).
• Net power output (WTur-Wp), measured via turbine and pump. Then thermal efficiency can be derived.

CDTPC With Regenerator

• Energy formulas similar, apart from all the components are used when fully measured, utilizing the regenerator.
• AT reg (Temperature after regeration + before condensor) = temp of working fluid, after pump.
• Other factors such as work output and thermal efficency are identical given.

Exergy analysis of CDTPC

• Thermodynamics are used to determine exergy efficiency and destruction in each component.
• Potential exergies/physical exergies have zero Kinetic
• The equations use the constants To and Po, also referred as dead reference states.

Additional information from the formulas above

• M is mass flow, h is enthalpy, and s is entropy.
• Mass flow rate of exhaust gas.
• Enthalpy of exhaust gas.
• Exergy State:

Methodology

• Constant parametric values help calculate the cycle performance of carbon dioxide within specified values.
• Basic figures analyzed within EES, then imported to MS Excel.

Constant Parametric Variables

• Vapor Generator pressure -10 and 30 Mpa
• Isentropic Efficiency of pump/expander will be 80%
• Condenser/Environment temperature is 15/10
• Mass exhaust / Cooling temp flowrate is 1
• The constant parametric temperatures of exhaust will be 130 to 210

Working Fluid Analysis

• Carbon dioxide (CO2) is chosen as working fluid, otherwise known as R744.
• Global (Greenhouse) Warming Potential is amount of heat absorbed, where ozone (ODP) measured degradation. Also safety analysis is economic condition.
• BOiling @ -78 degree Celsisu, 31.1 for critical, and 73.8 bar critical pressure.
• Rating A1 is non-flammable material @ -57 degree celsius.