Thermoeconomic assessment of a novel integrated biomass based power generation system including gas turbine cycle, solid oxide fuel cell and Rankine cycle

https://doi.org/10.1016/j.enconman.2018.01.071Get rights and content

Highlights

  • A novel integrated power plant is investigated and optimized thermoeconomically.

  • This system consists of a gasifier, solid oxide fuel cell, gas turbine and Rankine cycles.

  • The effects of operating parameters on system performance and product cost are investigated.

  • A multi-objective optimization is applied based on the thermoeconomic viewpoint.

Abstract

In this work, a novel combined biomass based power generation system is proposed and investigated. The proposed integrated system consists of a combination of biomass gasifier, solid oxide fuel cell, gas turbine cycle and a Rankine cycle. Three different biomasses are selected: Pine Saw Dust, Municipal Solid Waste and Fowl Manure. A comprehensive thermoeconomic analysis as well as a multi-objective optimization is carried out. The effects of most important operating parameters on thermodynamic performance, unit production cost and total cost rate are investigated for the overall system and components. The operating parameters considered include biomass mass flow rate, compression ratio of air compressor, current density of solid oxide fuel cell and exit temperature of solid oxide fuel cell. The results show that the fuel mass flow rate and current density are the dominant factors affecting the variation of energy and exergy efficiencies as well as unit production cost. Moreover, the best thermodynamic and economic performances are corresponded to the Pine Saw Dust fueled system. Nevertheless, the best environmental performance is related to the Fowl Manure fueled system mainly due to the lowest content of CO2 in flue gas leaving the system to the atmosphere.

Introduction

Environmental problems such as air pollution, global warming, and the reduction of unrenewable energy sources have accelerated the use of new and renewable energy sources, such as geothermal, solar, wind and biomass. Bioenergy is obtained from various biomasses, such as wood waste, agricultural and livestock residues, cereals and vegetable oil. Converting biomass energy into biofuels is performed by biochemical conversion and thermochemical conversion processes [1]. Anaerobic digestion, as biochemical conversion process, is appropriate for moist biomass to produce methane [2]. Thermochemical conversion process such as combustion, gasification and pyrolysis, takes place in a partial oxidizing atmosphere in order to produced syngas [3]. The main advantages of using biomass are utilization any type of biomass in various chemical processes and the product gases can be converted to a variety of fuels. Nevertheless, for thermochemical route, the cleaning of product gas from tar and undesirable contaminants is high costly and due to the high temperatures required is inefficient [4]. Biomass gasification is a high-tech complex process that is used to generate low cost and high efficiency syngas. In order to optimal use of syngas energy the appropriate heat engine systems such as natural gas-based, spark-ignition engine [5], solar-biomass hybrid power system [6] hybrid solar-biomass combined cycle power generation system [7], etc. are required.

In the gasification process, the gas produced during pyrolysis is partially burned, raising the internal temperature and favoring a partial tar decomposition. The gasification process is supposed to occur at ambient pressure using air as gasifying agent [8]. Depending on the kind of biomass, syngas composition will be different and the main factor for selecting biomass, considering the amount of carbon, moisture and oxygen which cause to produce high quality syngas with more methane, hydrogen and steam content that this amounts have significant effect on the bottoming systems performance. So choosing suitable biomass for achieve best operating condition for other bottoming applied systems is necessary. Shabani et al. [9] studied a hydrogen and electricity co-generation plant with rice husk as biofuel where electricity produced using two Rankin cycles. Their main purpose was to eliminate hydrogen combustion for electricity generation and reduce the production of pollutant NOx by the Rankine cycle. Kirsanovs et al. [10] proposed a system to produced thermal energy for heating purposes through the biomass gasification. They used wood chips as biomass and due to the high amount of moisture in this type of biomass downdraft gasifier was employed to reach higher temperature for syngas. The results show that the highest gasifier efficiency was obtained under nominal operating conditions. A model based on a Gibbs free energy reactor is considered by Fernandez-Lopez et al. [11] for The gasification of Fowl Manure in a dual gasifier. They evaluated the effects of using the steam and CO2 as the gasifying agents on the composition, the gasifying/biomass ratio, the gasification temperature and the low heating value (LHV) of the produced syngas. Their results show that the H2 production is higher when steam is used as the gasifying agent and the formation of CO is enhanced when CO2 is considered as gasification agent. To simulate steady state and transient state of gasification process, a mathematical model is developed by Jia et al. [12]. They studied the effects of the equivalence ratio, steam to biomass ratio and mass flow rate of biomass on the steady and transient characteristics of gasifier.

In the recent years, the integration of biomass gasifier with fuel cells is highly mentioned. Fuel cells are the new electrochemical technology that converts the chemical energy from a fuel into electricity through an electrochemical reaction of hydrogen-containing fuel with oxygen or another oxidizing agent [13]. Among different types of fuel cell, the solid oxide fuel cell (SOFC) is chosen due to its benefits [14]. For example, different types of fuels such as biogases, methanol, hydrogen sulfide and hydrocarbons can be used in SOFC. Moreover, high temperature SOFCs could be integrated with thermodynamics cycles such as Brayton, organic Rankine cycle (ORC) and refrigeration systems to rise the overall efficiency [15].

Colpan et al. [16] presented a thermodynamic model for the direct internal reforming SOFC where the syngas form the gasifier has been used as the fuel enters anode. They also investigated the effects of SOFC operating parameters such as fuel utilization ratio, recirculation ratio on the biofuel mass flow rate, inlet temperature of fuel, electrical efficiency, network and cell voltage. They concluded that at higher current densities, by increasing the recirculation ratio, the electrical efficiency and output power of the SOFC decrease. Mortazaei and Rahimi [17] analyzed two different trigeneration systems integrated gasifier and digester based SOFC to produce cooling, heating and power from thermodynamic and environmental points of views. They showed that the energy efficiency of digester based SOFC system is 11.1% higher than gasifier based SOFC system, while the gasifier based SOFC system has higher thermal and cooling capacity due to higher mass flow. Gadsbøll et al. [18] experimentally studied a combined power plant consists of gasification and SOFC to examine the potential of the commercial agent of these two technologies. They showed that by employing a two-stage gasifier an electrical efficiency of 46.4% is achieved. Ebrahimi and Moradpoor [19] presented a new power generation system combining three technologies of SOFC, micro gas turbine and ORC. They investigated the effects of variation of operating parameters include current density, steam to carbon ratio, reformer temperature, fuel utilization factor and minimum and maximum pressure of the ORC on electrical efficiency.

In the present research, a novel biomass fueled power generation system is proposed and a comprehensive thermoeconomically assessment is carried out. The proposed power plant consists of a gasifier, a syngas based SOFC, a syngas based gas turbine cycle (GTC) and a Rankine cycle (RC) to produce electricity. In this system, syngas produced in gasifier at different pressure is fed to the SOFC and combustion chamber of GTC. The required high pressure steam for gasification process is supplied from RC which is run by heat recovery from flue gases exhausted gas turbine. In the literature, to the best of the authors’ knowledge, a comprehensive thermodynamic, economic and environmental impact assessment of an integrated power generation system based on biomass gasification at higher pressure than atmospheric pressure has not been reported. Moreover, three different biomasses are used to discover the effect of employed biomass on the system performance. As it mentioned before, type of biomass plays an important role in biomass-based systems. A parametric investigation is performed to discover the effects of various operational parameters on the overall energy and exergy efficiencies as well as total cost rate and unit production cost of the proposed system. The simulation is performed based on a code developed in the EES software program. The specific objectives of this study are presented as follows:

  • To develop a novel power generation system consisting of a syngas fueled GTC, a syngas fueled SOFC and a RC

  • To conduct energy, exergy, economic and environmental analyses of this integrated power generation system.

  • To evaluate overall energy and exergy efficiency of proposed system.

  • To evaluate total cost rate and unit production cost (electricity) of proposed system.

  • To optimize the performance of the system using a multi-objective optimization technique.

  • To find out the best performance among three most usage biomasses.

Section snippets

System description

Fig. 1 illustrates the schematic of proposed combined power generation system consists of a biomass gasifier, gas turbine cycle, SOFC system and Rankine cycle plant. The proposed power generation system employs biomass as a renewable energy source to produce electricity. Below all subsystems processes are explained in detail.

Thermoeconomic formulations

Thermodynamic and economic assessments are carried out to evaluate the energy and exergy efficiencies as well as total cost rate and unit production cost of the proposed power generation system. The assumptions required for system simulation presented in this work are:

  • Heat loss and pressure drop in the heat exchangers and pipelines are neglected.

  • The steady-state model is developed to analysis all components. Also, potential and kinetic energy effects are negligible.

  • The isentropic efficiency of

Biomass selection

Regarding to the following criteria three different types of biomass were selected:

  • Pine trees grow widely throughout the world and widely used for wood-based products. For this reason, one of the most common waste wood products is Pine Saw Dust. in this study, Pine Saw Dust obtained from Brazil was used [31].

  • For developing countries, the management of Municipal Solid Waste is one of the most important problems. Incineration is of the main categories of dealing with solid waste that can convert

Model validation

The simulation of the proposed cycle is developed using an EES program to analyze the system performance. In order to assess the validity of the present modeling, the existent numerical and experimental results in literature are considered. The model developed in this study for Municipal Solid Waste gasification process is verified by comparing the results of syngas composition with the presented data by Srinivas et al. [23] and Jarungthammachote and Dutta [32]. Table 5 shows the comparison of

Results and discussion

A parametric study of factors influencing the thermoeconomic performance of proposed system is carried out. The followings decision variables are considered for parametric analysis: biomass mass flow rate, compression ratio of air compressor (or gasifier and SOFC working pressure), current density of SOFC and temperature of the SOFC. In the parametric study, when the variation of one factor is investigated, the other factors are kept constant based on the given data in Table 1.

Conclusion

A novel biomass fueled combined electrical power generation is proposed and a comprehensive thermoeconomic analysis of the proposed system are successfully carried out. The proposed integrated system is the combination of a biomass gasifier, a SOFC, a gas turbine cycle and a Rankine cycle. Three different biomasses are selected as fuel. A parametric study and multi-objective optimization are performed to evaluate thermoeconomic performance and optimal value of decision parameters of the overall

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