Techno-economic assessment of high efficient energy production (SOFC-GT) for residential application from natural gas

https://doi.org/10.1016/j.jngse.2014.07.033Get rights and content

Highlights

  • High efficient electrical power and heating generation system from natural gas is introduced.

  • Complete thermodynamic simulation of internal reformer SOFC-GT hybrid cycle is carried out.

  • Sizes of each component are computed based on energy generation-consumption in each climate area.

  • Economic assessment in a specific condition of fuel cost and market price is carried out.

  • The effect of variations in fuel cost and market price on the period of return of considered system was studied.

Abstract

Fuel cells, as alternatives for conventional energy conversion systems, have the prospect for exploiting fossil fuels (especially natural gas) more benignly and efficiently. High temperature Solid Oxide Fuel Cell (SOFC) with the ability of direct natural gas reforming is promised to be the most efficient device for a direct conversion of the fuel chemical energy into the electricity. Its efficiency can be further increased up to 70% when the SOFC is coupled with a Gas Turbine (GT) cycle. To provide the required energy for the household application, a kW range SOFC-GT (11–42.9 kWe) combined cycle is proposed in this article. Complete thermodynamic simulation of a SOFC-GT power system is done. Then a four floor building is introduced for energy consumption section. Each floor has the 100 m2 flat. After calculating the required electrical and thermal load of building, the size of proposed system is determined and the economic evaluation is considered. Four different climatic areas of Iran are selected for this study. The results show that among the selected cities, SOFC-GT is more economic in the hot and wet climate area (Ahvaz). The prime cost of electrical energy per kWh and the period of return is 0.0208 US$ and 8.3494 years respectively in Ahvaz.

Introduction

Nowadays, finding efficient power systems is one of the major concerns, especially with the depletion of fossil fuel sources over time. Energy demands are expected to keep increasing in the future. The energy roadmaps indicate that the world energy consumption is expected to increase approximately 40 percent during 2006–2030 (Energy Information Administration, 2009). The efficiency of conventional thermal plants is usually less than 39% where most of the energy is lost as the waste heat. Therefore, the consideration of an efficient system that can effectively utilize the waste heat is crucial for the improvement of overall plant efficiency. Thus, finding an efficacious system is vital to increase the unit of the produced energy per unit of the consumed fuel (Al-Sulaimana et al., 2010).

Fuel cells have attracted considerable interest during recent years. Among the different types, solid oxide fuel cell (SOFC) technology is very promising because of its high efficiency, less polluting, fuel flexibility and high temperature of the exhaust heat, which can be used for additional electricity generation through cogeneration (Singhal and Kendal, 2003). The most typical hybrid configuration suggested in the literatures is an integrated gas turbine process with the SOFC as the core of the system. The prediction of electrical efficiency for such a system is more than 60 percent (Costamagna et al., 2001). Recently, many researchers have studied SOFC-GT hybrid system from thermodynamic and economic points of view. Table 1 shows a number of these studies and important results of them.

The main goals of this study are as follow.

  • Introduction of an efficient hybrid cycle (SOFC-GT) as an electrical and heating energy supplier for a residential area and in each specific climate area.

  • Sensitivity analyses of fuel cost and market price of the suggested system product is performed to find a solution for the substitution of a traditional power production with an introduced system.

Application of SOFC-GT to supply the electrical and heating demands of a residential area is examined in this article. A four floor building is considered for this purpose and the electrical, heating and cooling load of considered building are calculated for four different climate areas. In the next step, the thermodynamic modeling of SOFC-GT combined heat and power system is considered. Then, by using energy demand of the building, the size of power generation system is calculated. After that, the rate of energy production and consumption in different months of a year at these four points are calculated and the rate of extra energy is determined as well. The economic analysis evaluates the proposed project from the economic point of view in the last part of this study.

Fig. 1 shows the scheme of examined system. The structure of suggested system is based on the industrial sample by Siemens Westinghouse (Siemens) but it is developed by the author to supply the electrical energy-cooling and heating demand of the building. This system consists of solid oxide fuel cell, internal reformer, fuel compressor, air compressor, gas turbine and three heat exchangers. The preheated air and fuel enters the fuel cell and after that, the extra fuel is ignited in the combustor. Then the hot flow gas enters the gas expander for second stage of power generation (first stage is happens in SOFC). To prevent the waste of energy from the gas turbine stack, two heat exchangers (air recuperator and fuel recuperator) are used for pre-heating air and fuel before entering SOFC.

All simulations are carried out by using the Matlab commercial code.

Section snippets

Calculation of cooling and heating energy

As mentioned before, a four floor building is considered in this study. Each floor has the 100 m2 flat.

Fig. 2 shows the scheme of the considered building. Table 2 indicates the characteristics of the considered building.

The heating load of the building is supplied by the generated hot water from SOFC-GT cycle. The heating system of building is central and the circulated water from the floors of building is used as the inlet of water heater. The heat losses in the pipelines are neglected but the

Results of building energy modeling

According to the energy model of the building which is developed before, Table 9 shows the energy consumption in cooling, heating and electrical instruments of each floor. In power consumption calculation, it is assumed that all the electrical instruments are activated in the same time and the power generation system should supply all of them. Also the cooling load in selected cities is prepared by SOFC-GT electrical power (Air condition unit) but for heating load, the required energy is

Conclusion

Simulation and economic assessment of SOFC-GT in household application is subjected in this article. Results of simulation indicate that the maximum power of SOFC-GT power system can be approached in the limiting current density. So, this value is chosen as an operational set point for SOFC-GT power cycle. The cooling, heating and electrical energy consumption of the 100 m2 building are computed and applied for sizing the SOFC-GT power cycle in selected cities. The maximum power consumption

References (22)

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