THERMOECONOMIC EVALUATION OF A MODIFIED KALINA POWER CYCLE FOR DUAL COOLING APPLICATION

CHAPTER 1: INTRODUCTION

3.2.2     Energy balance for separator 1 (2, 3, 10)                    18

3.2.3     Energy balance for turbine (3, 4)                              18

3.2.7      Energy balance for evaporator 1 (8, 9, 38, 39)         19

3.2.20     Energy balance for pump 2 (22, 23)                                                23

3.3.2    Exergy balance for separator 1 (2, 3, 10)                                           25

3.4.12     Cost balance for condenser 2 (14, 15, 34, 35)                               35

3.4.14     Cost balance for heat exchanger 1 (1, 17, 12, 43)                           35

3.4.15     Cost balance for desorber (44, 43, 24, 25, 18)                                35

3.4.16     Cost balance for condenser 3 (18, 19, 32, 33)                                36

3.4.17     Cost balance for valve 4 (19, 20)                                                   36

3.4.19     Cost balance for absorber (21, 30, 22, 27, 31)                                 36

CHAPTER 4   RESULTS AND DISCUSSION                                         38

4.4    Performance Index of the System at Design Conditions                      42

4.5    Component Analysis of the System                                                         43

4.6    Parametric Analysis of the System at Stated Conditions                       44

4.6.1  Effect of expander inlet pressure on system 

4.6.2  Effect of expander inlet press. on system efficiency and turb 

4.6.3   Effect of expander inlet pressure on kalina evap. cooling 

4.6.5   Effect of expander inlet temperature on turbine output

4.6.6   Effect of expander inlet temperature on ammonia mass 

4.6.7   Effect of expander inlet temperature on kalina energy 

CHAPTER 5: CONCLUSION AND RECOMMENDATIONS             58

                                                                                                                    

4.6   Summary of component exergoeconomic performance index              54

4.7   Life cycle cost analysis                                                                           57 

                                                                                                                    

4.1  Effect of expander inlet pressure on system efficiency and 

4.2   Effect of expander inlet pressure on system efficiency and

                                                                                                                  

4.3  Effect of expander inlet pressure on Kalina evaporator cooling and ammonia mass fract.    48 

                                                                  

4.4  Effect of expander inlet pressure on turbine output                                 49 

                        

4.5  Effect of expander inlet temperature on turbine output and 

                     

4.6  Effect of expander inlet temperature on ammonia mass 

               

4.7  Effect of expander inlet temperature on Kalina energy and 

ṁ                     Mass Flow Rate

W_P                   Pump Work

ϕ                      Maintenance Factor

Ċ                      Cost of Exergy Stream

ĊCI                    Capital Investment Cost

The ever increasing cost of energy and the finite nature of resources have prompted the utilization of low-grade heat sources for power generation. These waste heat sources comprises low-temperature geothermal energy, solar irradiance, and industrial waste. And with recent advancement in technology, there is great interest in designing more efficient, reliable, and cost-effective energy conversion systems which will provide a means of utilization of low temperature heat sources which might not otherwise be used. Kalina and organic Rankine cycles (ORCs) are potentially feasible alternatives proficient in recovering energy efficiently from low-temperature heat sources. The development of ORCs using an organic fluid instead of water as working fluid has been applied in many real applications for recovering geothermal and waste heat for power generation (Badr et al., 1990; Hung et al., 1997; Abam et al., 2017).

When working with a low-temperature heat source, a binary working fluid such as an ammonia–water mixture offers an enhanced thermal performance due to better thermal matching achieved at the evaporator and condenser (Angelino et al., 1998; Ibrahim and Klein, 1996). This cycle configuration was achieved in the early 1980s when Kalina proposed a new family of thermodynamic power cycles using an ammonia/water mixture as the working fluid. (Kalina, 1982; Kalina, 1983; Kalina, 1984). These cycles have been proposed for a variety of applications ranging from bottoming cycles for gas turbines to providing power from lower temperature waste heat sources (Kalina, 1989). 

Performance simulations of Kalina based cycles have included both first and second law models where the concept of exergy have been applied (Cao et al., 2017). The exergy concept provides a more realistic view of all thermodynamic processes. A comprehensive exergy analysis involving the degree of exergy destruction identifies the location, the magnitude and the source of thermodynamic inefficiencies in thermal systems (Saidur and Jamaluddin, 2007). This knowledge is useful in directing the attention of process design researchers and practicing engineers to those components of the system analysed that offer the maximum opportunities for improvement (Dincer, 2007). Exergy analysis usually calculates the thermodynamic performance and the inefficiency of an energy system. In addition, the concepts of exergy in recent times have been applied in analysing the performance of a wide range of thermal systems (Antonio et al., 1993; Abam et al., 2012; Carton, 2000; Sahin, 1995). 

A conventional exergy analysis recognizes the highest exergy destruction within the system components or the process that cause the high exergy destruction. This facilitates the efficiency improvement of a system’s components by reducing the exergy destruction rates within it (Kelly et al., 2009). Nevertheless, the conventional exergy methods are not appropriate in revealing the interactions which exists among the system components or to estimate the real potential for improvement. With no consideration of the interactions in the components, optimization strategies can be mistaken, especially when application is made on complex systems with a large number of mutually affected components. The knowledge of these components’ interactions and the ability of the improvement for each important component are imperative to improve the overall system (Morosuk and Tsatsaronis, 2009). Consequently, understanding the root of the rate of exergy being destroyed in a component’s process is imperative. The theory of splitting the exergy destruction helps to further understand the exergy destruction values from an exergy analysis and hence improves the accuracy of the analysis. It assists in the improvement of energy-related systems. Performance of this process can only be achieved through an advanced exergy analysis method (Morosuk and Tsatsaronis, 2009). Interactions within components determine the exogenous exergy destruction while operating inefficiencies within the component determine the endogenous exergy destruction. Additionally, part of the overall irreversibilities which exists due to physical, technological and economic constraints and cannot be avoided is termed unavoidable exergy destruction. On the other hand, irreversibilities that can be prevented through design improvements form the avoidable exergy destruction. The exogenous and endogenous parts can further be split into avoidable and unavoidable parts facilitating the understanding of component interconnections and the estimation of the potential for improvement (Petrakopoulou et al., 2012). 

Many studies have been conducted on simultaneous cooling and power system using the Kalina cycle which is based on ammonia–water as working fluid. Goswami (1998) proposed a new combined cooling and power system to produce both power and refrigeration output simultaneously with only one heat source using ammonia–water as the working fluid. The proposed system replaced an ammonia–water turbine for a condenser and a valve in ammonia–water absorption refrigeration cycle, achieving a novel combination of a Rankine cycle and an absorption refrigeration cycle. Goswami and Xu (1999) as well as Xu et al. (2000) modified the proposed combined system by adding a super heater between the condenser/rectifier and turbine to increase the turbine inlet temperature and produce more power output. Padilla et al. (2010) examined the effects of boiler pressures, ammonia concentrations, isentropic turbine efficiencies and heat source temperature on the net output, quantity of cooling and effective efficiencies of the Goswami cycle. The results showed that the turbine performance had significant effect on the net output and cooling outputs of the Goswami cycle. Kim et al. (2013) investigated the effects of numerous key parameters on the performance of the Goswami cycle. The results showed that with an increase in turbine inlet pressure, there is a decrease in the system net output, while the specific cooling capacity, total utilization work and thermal efficiency of the system had a maximal value respectively. Also, in addition to these modifications on the basic Kalina cycle, Hasan et al. (2003), Vidal et al. (2006) and Fontalvo et al. (2013) all employed the exergy analysis method to evaluate the exergy destructions in the Goswami cycle.

Accordingly, this research aims at contributing to knowledge by presenting the thermodynamic and thermoeconomic analysis of a modified Kalina power cycle for dual cooling application. A very detailed consideration of this analysis using exergy methods and cost estimations will facilitate the theoretical development of this power plant.

Many studies have been conducted on simultaneous cooling and power systems using the Kalina cycle which is based on ammonia–water as working fluid. Wang et al. (2016) proposed a new combined cooling and power system using ammonia–water mixture to utilizing low grade heat sources, such as industrial waste heat, solar energy and geothermal energy in order to achieve both power and cooling supply for users. The proposed system combines a Kalina cycle and an ammonia–water absorption refrigeration cycle, in which the ammonia–water turbine exhaust was delivered to a separator to extract purer ammonia vapour. In its description, the purer ammonia vapour enters an evaporator to generate refrigeration output after being condensed and throttled. 

 With such higher energy conversion cycles being developed, the utilization of a single heat source for multiple generation in bottoming cycle became necessary. This problem is attempted with the configuration of a Kalina based system for power generation and dual cooling application. The thermodynamics, thermoeconomics, and optimization of this arrangement is imperative in determining optimal sizing and choice of operating variables.

The aim of this study is to make a thermodynamic and thermoeconomic evaluation of a modified Kalina power cycle for dual cooling application. The specific objectives include to:

The scope of this research work covers the following:

Various studies on simultaneous cooling and power generation system using the Kalina cycle which is based on ammonia–water as working fluid are in open literature. Exergy models have been developed and applied in these systems for simulations and thermoeconomic evaluations. For the particular Kalina based structure which features power production and multiple cooling applications, its configuration is not yet in open literature. The research is justified by the development of modified Kalina cycle for power generation and dual cooling application. A very detailed thermodynamic modeling and simulation relating exergy and thermoeconomic implication of this system justify this research since none of such exist in the open literature domain.