Open access peer-reviewed chapter

# Micro Gas Turbine Engine: A Review

By Marco Antônio Rosa do Nascimento, Lucilene de Oliveira Rodrigues, Eraldo Cruz dos Santos, Eli Eber Batista Gomes, Fagner Luis Goulart Dias, Elkin Iván Gutiérrez Velásques and Rubén Alexis Miranda Carrillo

Submitted: March 20th 2012Reviewed: October 22nd 2012Published: June 19th 2013

DOI: 10.5772/54444

## 1. Introduction

Microturbines are energy generators whose capacity ranges from 15 to 300 kW. Their basic principle comes from open cycle gas turbines, although they present several typical features, such as: variable speed, high speed operation, compact size, simple operability, easy installation, low maintenance, air bearings, low NOX emissions and usually a recuperator (Hamilton, 2001).

Microturbines came into the automotive market between 1950 and 1970. The first microturbines were based on gas turbine designed to be used in generators of missile launching stations, aircraft and bus engines, among other commercial means of transport. The use of this equipment in the energy market increased between 1980 and 1990, when the demand for distributed generating technologies increased as well (LISS, 1999).

Distributed generation systems may prove more attractive in a competitive market to those seeking to increase reliability and gain independence by self-generating. Manufacturers of gas and liquid-fueled microturbines and advanced turbine systems have bench test results showing that they will either meet or beat current emission goals for nitrogen oxides (NOX) and other pollutants (Hamilton, 2001). Air quality regulation agencies need to account for this technological innovation. Emission control technologies and regulations for distributed generation system are not yet precisely defined. However, control technologies that could reduce emissions from fossil-fueled components of a distributed generation system to levels similar to other traditional fossil-fueled generation equipment are already available.

Combustion processes can result in the formation of significant amounts of nitrogen dioxide (NO2) and carbon monoxide (CO). Some manufacturers of microturbines have developed advanced combustion technologies to minimize the formation of these pollutants. They have assured low emissions levels from microturbines fueled with gaseous and liquid fuels.

## 2. History

In fact, the technology of microturbines is not new, as researches on this subject can be found since 1970, when the automotive industry viewed the possibility of using microturbines to replace traditional reciprocating piston engines. However, for a variety of reasons, microturbines did not achieve great success in the automotive segment. The first generation of microturbines was based on turbines originally designed for commercial applications in generating electricity for airplanes, buses, and other means of commercial transportation.

The interest in the market for stationary power spread in the mid-1980 and accelerated in the 1990s, with its reuse in the automobile market in hybrid vehicles and when demand for distributed generation increased (Liss, 1999). Currently, the operation of hybrid vehicles through a microturbine connected to an electric motor, have received special attention from some of the major car manufacturers such as Ford, and research centers (Barker, 1997).

In 1978, Allison began a project aimed at the development and construction of generating groups for military applications, driven by small gas turbines. The main results obtained during testing of these generators revealed: reduction in fuel consumption of 180 l/h to 60 l/h, compared with previous models, frequency stability of about 1%, noise levels below 90 dB and the possibility of using different fuels (diesel, gasoline, etc.). In 1981, a batch with 200 generators was delivered to the U.S. Army, and since then, more than 2,000 units have been provided to integrate the system of electricity generation for Patriot missile launchers (Patriot Systems) (Scott, 2000).

The deregulation of the electricity market in the United States began in 1978 when the Power Utility Regulatory Policy Act (PURPA) revolutionized the energy market in the United States, breaking the monopoly of the electricity generation sector, enabling the beginning of the expansion of distributed generation. Since then there has been a significant increase in the proportion of independent generation in the country and, according to a projection made in 1999 by the Gas Research Institute (GRI), this in-house production should reach 35% in 2015 (Gri, 1999).

With a new market structure, i.e., with the possibility of attracting small consumers of energy, microturbines began to be the target of intense research. Already in 1980, under the support of the Gas Research Institute, a program entitled Advanced Energy System (AES) was initiated with a view to develop a small gas turbine, with typical features of aviation turbine, rated at 50 kW and equipped with a heat recovery for a system cogeneration. The program was abandoned around 1990 by the Gas Research Institute, on the grounds of problems with the final cost of the product (Watts, 1999). Since then, the Gas Research Institute began to support new projects in partnership with several companies, such as the Northern Research & Engineering Energy Systems, also supporting the first efforts of Capstone Turbine Corporation (still under the name of its precursor, NoMac Energy Systems) (Gri, 1999).

Some companies in the United States, England and Sweden have recently introduced in the world market commercial units of microturbines. Among these companies are: AlliedSignal, Elliott Energy Systems, Capstone, Ingersoll-Rand Energy Systems & Power Recuperators WorksTM, Turbec, Browman Power and ABB Distributed Generation & Volvo Aero Corporation.

## 3. State-of-the-art microturbines

### Table 12.

Economical analysis of the peak shaving case

* With peak shaving; ** Without peak shaving

Figure 19 shows payback period in relation to microturbine cost. There is a strong fall on the payback period of the states of SP and RJ, due to a decrease in the microturbine cost.

A few manufactures intend to decrease microturbine costs to about 400 US$/kW until 2005 (Dunn & Flavin, 2000). If the microturbine cost is 400 US$/kW, the payback period will be between 2.5 and 5 years, as shown in Figure 19.

In this case, a microturbine produces electricity to a gas station according to the base load demand, as shows Figure 20. The conditions of this case are in table 13, whereas Table 14 shows the Brazilian regions analyzed in the base load case.

 Model of microturbine Capstone 330 Number of microturbines 1 Life time of microturbines 10 years Net power 27,5 kW Microturbine installed cost 1,538 US$/kW Natural gas consumption (HHV) 6,918 m3/month Average price of natural gas(taxes included) 0.24 - 1.02 R$/m3

### Table 13.

Conditions of the base load case.

 Brazilian States 1st Region São Paulo (SP) and Rio de Janeiro (RJ) 2nd Region Rio Grande do Sul (RS) and Paraná (PR) 3rd Region Rio Grande do Norte (RN) 4th Region Others

### Table 14.

Brazilian regions analyzed in the base load case.

Table 15 displays the economical analysis of the base load case for gas stations. Up to the present moment this kind of business is not feasible, except in the state of Rio Grande do Norte (RN) where payback period can be 3.1 years, once local gas distribution companies have encouraged thermoelectric small scale power generation, according to natural gas price lower than others kind of fuels.

### 8.3. Cogeneration case

In this case, two microturbines and a heat recovery system produced electricity and hot water to buildings in a residential segment, according to the base load demand, as can be seen in Figure 23.

A cogeneration plant can result in substantial savings of energy. However, these systems usually result in greater capital expenditures than non-cogeneration plants. This incremental capital investment for cogeneration must be justified by reduced annual energy costs and reduced payback periods.

A course of action involving minimum capital expenditures can be determined as the conventional case. In this study a low pressure boiler supplying process heat and the purchase of all electric power from utility system is the conventional case. Although the conventional case has the lowest investment cost, it usually has annual operating costs significantly higher than those available with cogeneration alternatives. Table 16 shows the conditions of this case, while Table 17 shows the Brazilian regions analyzed in the base load case.

 System cogeneration model MG2-C1 Number of Capstone microturbines 2 Number of heat recovery systems 1 Life time of microturbines 10 years Power output 54 kW Heat recovery systems (hot water generation) Water pressure 10 bar Water flow 2.22 t/h Inlet water temperature 25 ºC Outlet water temperature 67 ºC Outlet exit gas temperature 93 ºC Net power 53 kW System cogeneration installed cost 1,872 US$/kW Natural gas consumption (HHV) 13,653 m3/day Average price of natural gas (taxes included) 0.24 - 0.90 R$/m3

### Table 16.

Conditions of the cogeneration case.

 Brazilian States 1st Region Rio de Janeiro (RJ) 2nd Region Paraná (PR) 3rd Region Rio Grande do Norte (RN) 4th Region Others

### Table 17.

Brazilian regions analyzed in the cogeneration case.

Table 18 displays the economical analysis of the cogeneration case. Investments costs are lower in the conventional case than in the cogeneration system, and, although the annual cost is higher, savings can be up to US$24,907 per year. The payback period is between 2.8 and 3.8 years and the minimal cost of the electricity generated is 84 US$/MWh.

 RJ PR RN Other States Total Investment* US$23077 23077 23077 23077 Total Investment** US$ 136797 136797 136797 136797 Annual cost* US$/year 128566 110022 90323 98328 Annual cost** US$/year 110337 96655 65416 77534 Annual savings US$/year 18228 13367 24907 20795 Electricity generated US$/MWh 174 146 84 112 Payback Period years 3,3 3,8 2,8 3,1

### Table 18.

Economical analysis of the cogeneration case.

* Conventional; ** Cogeneration

In the cogeneration case, the fuel cost is the most influential component on the return on investment, similar to the base load case. Figure 24 shows fuel costs can represent up to 71% of the cost of the electricity generated.

Figure 25, Figure 26 and Figure 27 show the combined influence of microturbine cost and the average price of natural gas on the return on investment in the states of Rio de Janeiro and Paraná (Figure 25), Rio Grande do Norte (Figure 26) and the other states (Figure 27). Based on the perspective of microturbine manufactures and with natural gas average price of 0.25 R\$/m3, the payback period can be between 1.5 and 3 years.

## 9. Conclusions

The variable speed operation and the electric power conditioner increase part-load efficiency of microturbines as they allow for the improvement of part-load fuel savings, especially increased recuperator effectiveness at lower part-load airflows. The variable speed control improves part-load performance but requires a system able to sense load and optimize speed. According to the results shown in this study, the microturbines efficiency is at its highest when Capstone microturbines are operating over an output range between 12 kW and full load.

Capstone microturbines use clean combustion technology to achieve low emissions. Nitrogen oxides (NOX) and carbon monoxide (CO) emission levels of these machines are lower than 7 ppmv@15%O2 at full load when these microturbines are fueled with natural gas.

Microturbines exhibit low emissions of all classes of pollutants and have environmental benefits as they release fewer emissions compared to other distributed generation technologies, like internal combustion engines. Besides, these units are clean enough to be placed in a community with residential and commercial buildings.

Microturbine generators have shown good perspectives for electricity distributed generation in small scales, once they have high reliability and simple design (high potential for large scale cheap manufacturing).

Although results show microturbines are not feasible to provide energy at peak demand, in this case the microturbines can supply peak demand and improve the level of reliability of the electricity supplying, because they can provide stand-by capabilities should the electric grid fail.

In the base load case this sort of business is feasible just in states of Brazil where natural gas distributing companies have encouraged small thermal power generation by natural gas with lower prices, since the price is the most influential cost component of the electricity generated.

The most feasible investment in microturbines is in the cogeneration case. In this case, economical feasibility is certain in all states of Brazil as cogeneration systems can provide considerable annual savings. Besides, under the perspective of manufacturers, and with the incentive of natural gas distribution companies together with the rise in electricity prices of Brazilian utility companies, investments in microturbines for the next years will be higher than currently.

## Acknowledgments

The authors would like to thank CAPES, FAPEMIG, FAPEPE and CNPq, for their financial support.

chapter PDF
Citations in RIS format
Citations in bibtex format

## More

© 2013 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## How to cite and reference

### Cite this chapter Copy to clipboard

Marco Antônio Rosa do Nascimento, Lucilene de Oliveira Rodrigues, Eraldo Cruz dos Santos, Eli Eber Batista Gomes, Fagner Luis Goulart Dias, Elkin Iván Gutiérrez Velásques and Rubén Alexis Miranda Carrillo (June 19th 2013). Micro Gas Turbine Engine: A Review, Progress in Gas Turbine Performance, Ernesto Benini, IntechOpen, DOI: 10.5772/54444. Available from:

### chapter statistics

28Crossref citations

### Related Content

#### Progress in Gas Turbine Performance

Edited by Ernesto Benini

Next chapter

#### Review of the New Combustion Technologies in Modern Gas Turbines

By M. Khosravy el_Hossaini

#### Advances in Gas Turbine Technology

Edited by Ernesto Benini

First chapter

#### Future Aero Engine Designs: An Evolving Vision

By Konstantinos G. Kyprianidis

We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. We share our knowledge and peer-reveiwed research papers with libraries, scientific and engineering societies, and also work with corporate R&D departments and government entities.