Understanding Micro Turbine for Electric Power Generation

The technology of micro turbine is not new, the research on this technology can be found since 1970 by the automotive industry.The prefix “micro” is generally used to express “small” and the word turbine can be defined as an energy generator which converts the flow of a fluid (steam, water, hot gases or air) into a mechanical motion for producing electricity.

The basic principle of micro turbine originates from the gas turbines though it exhibits a number of typical features such as compactness of size, ease of installation, variable speed, low maintenance, air bearing capacity, etc. In India, the Cummins power generation is the leading manufacturing company of diesel-fuel power systems. It provides complete power solutions for almost all sectors – a few of such significant sectors include reality, hospitality, food processing, construction, pharma and infrastructure.

The first generation of micro turbines were based on the turbines originally designed for commercial applications in generating electricity for buses,airplanes, These turbines are fit for many applications wherein electricity is required, such as stationary power generators, hybrid electric vehicles and weak grids. By considering a few examples these microturbines can be classified into different types. They include steam micro turbines, hydro micro turbines and aero derivative turbines.

Micro Turbine For Electric Power Generation

There are different energy resources that can be used to make electric power generation. These resources can be divided into two categories:renewable and nonrenewable. The non-renewable resources include oil, coal, nuclear power and natural gas, which are used in many power plants. These resources took millions of years to form. Renewable resources mainly include wood, sunshine, biomass, geothermal and wind power generator, etc.

Micro turbines are relatively a new type of burning turbines that produces both electricity and heat on a small scale. These turbines offer a clean solution to direct mechanical drive markets such as compression and air-conditioning.

Microturbines are classified into different types, based on the physical arrangements of their parts, such as single shaft or two shafts, recuperated, simple cycle, reheat and inter cooled. These machines generally rotate over 40,000 RPM. And, in such machines, the selection of bearings depends on the usage. A single-shaft microturbine rotates at a speed range of 90,000 to 120,000 RPM. The single-shaft microturbine is simple,easy and expensive to build.

The major characteristics of microturbines include distributed generation, reliabile and quality power, peak shaving, standby power, low energy cost, power boost, combined power and heat. Micro turbines are advantageous as they have compact systems, free moving parts, low emissions, low maintenance and low investment costs, etc. The disadvantages of micro turbines include low fuel to electricity efficiencies, higher operating RPM and higher ambient temperatures with efficiency.

Micro Turbine System

This article focuses on the design and development of a micro turbine driven bycompressed nitrogen gas. The available literature about the design aspects of micro turbine was described in detail. The turbine blades and nozzles were designed with the help of “Gambit” software using a given set of cylindrical coordinates.

Micro turbines are small power generators that burn liquid and gas fuels to create high-speed rotation that turns an electrical generator on. The basic components of a microturbine are, recuperator, fuel compressor, generator, turbine, compressor and Combustor. The heart of the microturbine is the compressor, which is mounted on a single shaft along with the generator. The single shaft is supported by two bearings. As this type of turbines has only one moving shaft, it is highly reliabile and has low maintenance than other shafts.

The recuperator is an internal heat exchanger. In a micro turbine, a compressor compresses the inlet air, then the air is preheated in the recuperator using the exhaust. After that, the heated air from the recuperator mixes with the fuel in the combustor and the hot combustion gas expands through the power turbines.

In single shaft models, the turbine turns the compressor as well as the generator. Two shaft models use the compressor to power a second turbine, which drives the generator.  The waste heat, which is generated from the turbine, is used to heat building space, produce hot water, drive absorption cooling and to supply thermal energy to industrial process.

Micro Turbine Design:

Cummins power generation is a microturbine manufacturer, that uses a different recuperator which has made separate tradeoffs between cost and performance. The exploded view of micro turbine is shown below. A Laval turbine is chosen for construction and assembling of the microturbine due to its simple construction. The parts of the microturbine include pneumatic connector, Ring, Nozzle Disc, Bearing, Turbine, Outlet disc, Circlip and Housing.

When compressed air penetrates  through the pneumatic connector, it expands over the stationary nozzle wherein it is redirected in a tangential direction to the rotor. After the air has passed the rotor blades, it leaves the device through the outlet disc. Turning the pneumatic connector in the housing pushes the nozzle disc against the shoulder in the housing. The router is supported by two ball bearings: one is mounted in the nozzle and the other one is mounted in the outlet disc. The outlet disc is locked by a circlip in the housing.

The diameter of the turbine rotor is 10mm and the diameter of the housing is 15mm and is 25mm long. All parts of the microturbine are made with stainless steel except circlip and pneumatic connector.

Turbine Test Bench:

Turbine  test bench is used to measure the characteristics of the microturbine that is connected to a generator by a spring that acts as a flexible coupling. The controller of the generator is mounted on four leaf springs (two leaf springs are noticeable). At the center line of the generator, each pair has a virtual intersection point. A total of four strain tests is mounted on the two right leaf springs and results in a full bridge motion sensor.

At the same time, this test bench setup allows measuring the electrical and mechanical characteristics. In the previous tests, the electrical characteristics were measured with this setup while the mechanical characteristics were measured by an acceleration test. But this new setup measures the mechanical characteristics accurately.

Advantages:

Micro turbines offer many advantages compared to other technologies for small scale power generation, including greater efficiency, light weight, compact size, the small number of moving parts, lower emissions and lower electricity costs, etc. In addition, these systems offer a clean and efficient solution for mechanical drive markets such a air conditioning and compression.

Applications:

Microturbines can be used for power quality, peak shaving, reliability standby power and cogeneration applications. These systems are well suited for commercial building establishments such as retail stores, small offices, hotels, restaurants and so on.

Thus, Cummins power generation is the leading manufacturing company for microturbines .To design a turbine nozzle and blades, a suitable design can be chosen from the available methods.This article gives an extensive literature review to study about the micro turbine and its applications. For more information regarding this article, please give your suggestions, feedback in the comments section below.

Photo Credits:

• Micro turbine by fastmail
• Recuperated Microturbine by wbdg
• Micro Turbine System by enertwin
• Micro Turbine Design by kuleuven
• Applications of Microturbine by wbdg