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Publication Title | An Economical Evaluation of the Water/Steam Injection in a CHP Microturbine Cycle

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Jestr Journal of Engineering Science and Technology Review 5 (2) (2012) 20-25 Research Article

An Economical Evaluation of the Water/Steam Injection in a CHP Microturbine Cycle D. N. Loujendi*, K. A. Sani, A. A. Tofigh, A. Majidian and H. J. Jouybari

Dpt of Mechanical Engineering, Islamic Azad University, Takestan Branch, Takestan, Iran.

Received 14 January 2012; Accepted 20 August 2012 ___________________________________________________________________________________________


In this paper we study the economical evaluation of injecting the water/steam into the micro gas turbine (MT) cycle witch operate in combined heat and powercycle. Heat and electricity cogeneration is a way for optimizing energy consumption. Cogeneration power plants produce both electric and thermal from one energy source. These systems could work by different movers but one of the most important and applied prime movers are Microturbine. Microturbines are small electricity generators which their producted electric power is 25-350 kW and their efficiency is almost 18% that can reach to 30% approximately by use of recuperator in their cycle. By water/steam injection into the MT cycle, the power will be enhanced and its efficiency will be changed too.

The fundamental aim of this study is economic evaluation of outfit the MT cycle to water/steam injection system. Here after the presentation of cogeneration systems, there are explanations of Microturbines and a thermodynamic analysis has been shown. Then the experimental and simulation results of water and steam injection to the different points in the cycle were compared. At last the economic evaluation of these cases and the energy production cost of any system were evaluated by Matlab codes. However injection increase the produced power, but according to the energy and set prices, the injection to the system is not economical. Non-injected system have the least payback (6 year) and its energy production cost is 0.043 $/kWh. But between the injection cases, water injection into the combustor is preferable choice that has 7.1 year as capital payback period, the least energy production cost (0.054 $/kWh) and (-89.8 $) disadvantage (decrease in net incomes) respect to Dry in compare to other case of injection.

Keywords: Economical evaluation, Cogeneration, Microturbine, Water and steam injection. __________________________________________________________________________________________

1. Introduction

Electricity and heat cogeneration systems are those which generate both electricity (axial power) and thermal energy by using energy from one prime source. Thermal power is obtained through regenerating the thermal losses existing in the exhaust hot gasses and it is used as hot water or steam in different sections of the industrial, commercial and residential buildings. Cogeneration was presented in Europe and America in the last 1880s so that about 58 percent of the total generated power was produced as cogeneration in America at the first decade of 1900s. With the notable increase in the fuel cost at the year 1974 and following that the emergence of a crisis to the energy, these systems which have higher energy efficiency, were taken into consideration more. The efficiency of the current conventional systems in localized way is about 27 to 55 percent that the most efficiency of it is belong to the combined cycle power plants while the energy efficiency of cogeneration systems even reaches to 80 percent. The most important components of the cogeneration power plants are their prime movers from which the most useable ones are reciprocating engines, gas turbines, steam turbines and fuel cells. Microturbines are also placed at the gas turbines class. The main difference

between movers involves their type of used fuel, combustion process, total efficiency, the amount and temperature Degree of exhaust energy. In [5] energy consumption and pollutant propagation of CHP systems was compared with conventional systems and 12.1% saving in prime energy was reported. In [6] 2.6% decrease in annual energy costs due to use of CHP system was reported.[7,8] was reported economic advantage of micro CHP in residential and commercial buildings. In [9,10] the results related to the evaluation of different kinds of movers have been reported. In [15] a MT was examined from different viewpoint domestic and industrial customer and the result was achieved that using the MT for exclusive use is superior to buying electricity from network. In [11] a CHP MT was evaluated under four different plans and it is also evaluated its using by heat pomp or using only for a residential building at Tehran and the use of this MT for electric load generation and a portion of thermal loud was known as the most optimum. Reference [12,16] also report an example of economic evaluation of CHP system. In one study recently an economic evaluation of a 500 kW MT which was used for a hospital of 250 bedsteads in order to provide thermal and electric load that as a result of it, the capital payback period was computed about 9.5 year. The economic evaluation has been also reported by Capstone company related to the use of a 30 kW MT for 200 commercial consumers and recuperated and non-recuperated Microturbines have been compared from an economic viewpoint. In reference [17] it


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ISSN: 1791-2377 © 2012 Kavala Institute of Technology. All rights reserved.

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