MICRO TURBINEA Seminar Report

Submitted by

ISHFAQ AHMAD NAJAR

In partial fulfilment for the award of the degree

Of

BACHELOR OF TECHNOLOGY

IN

CHEMICAL ENGINEERING

At

National Institute of Technology

Hazratbal, Srinagar

june 2016

1

CERTIFICATE

Certified that ISHFAQ AHMAD NAJAR (enrollment no-219/12) has presented a seminar on “MICRO TURBINE”in partial fulfilment for the award of degree of Bachelor of technology in Chemical engineering at National Institute of Technology, Srinagar under our supervision and guidance during the academic session Autumn 2016

Seminar Coordinator Head of Department

(Associate professor) Mr TanveerRasool Dr.faisalqayoom

2

Contents

Abstract4

Chapter 1: Literature Review 5

Chapter 2: Micro Turbine6

2.1 Micro Turbine

2.2 Types of Micro turbine7

2.3 Functional

2.4Productive

2.5Characteristics of Micro turbine 8

2.6 TECHNOLOGY DISCRIPTION OF MICROTURBINES

2.6.1Basic Processes

2.6.2 Thermodynamic Heat Cycle 9

2.6.3 Basic Components 10

2.7 Design Characteristics of micro turbines14

2.8 Advantages of Micro turbine15

2.9 Economics of Micro turbines16

2.91Application17

Chapter 3: Conclusion 18

References 19

3

ABSTRACT

Micro turbines are a relatively new type of combustion turbine that produces both heat and electricity on a small scale. Micro turbines offer an efficient and clean solution to direct mechanical drive markets such as compression and air-conditioning. This report focuses on the design and development of a micro turbine driven by compressed nitrogen gas. The availableliterature regarding the design aspects of micro turbine were reviewed in detail. Gas turbine cycle and operation of micro turbine was studied and reported. The turbine blades and nozzleswere designed with the help of Gambit software using a given set of cylindrical coordinates. The turbine has a radial inlet and axial outlet. A proper meshing scheme was used to mesh the turbineand nozzle assembly. CFD analysis was carried out by fluent software to get the velocity vectors using a set of suitable inputs.

Keywords: Gas turbine, turbine blade, nozzle, nitrogen

4

Chapter 1

LITERATURE REVIEW:-

Micro turbine is one of the important components in a micro gas turbine engine. Micro gas Turbine engine is a promising solution to provide high-density power source for micro systems. A micro gas turbine engine consists of a radial inflow turbine, a centrifugal compressor and a combustor. This thesis mainly deals with the design aspects of a micro turbine. Various journals have been published on designing of various types of micro turbines Exhaustive study has been done on these papers and the major points have been highlighted here.

Micro turbines are a relatively new distributed generation technology being used for stationary energy generation applications. They are a type of combustion turbine that produces both heat and electricity on a relatively small scale. Micro turbines offer several potential advantages compared to other technologies for small-scale power generation, including: a small number of moving parts, compact size, lightweight, greater efficiency, lower emissions, lower electricity costs, and opportunities to utilize waste fuels. Waste heat recovery can also be used with these systems to achieve efficiencies greater than 80%.

Because of their small size, relatively low capital costs, expected low operations and maintenance costs, and automatic electronic control, micro turbines are expected to capture a significant share of the distributed generation market. In addition, micro turbines offer an efficient and clean solution to direct mechanical drive markets such as compression and air-condition

Chapter 2

MICRO TURBINE:

2.1 Micro turbine

Micro turbine Overview

Commercially Available-Yes (Limited)

Size Range-25-500 kW

Fuel- Natural gas, hydrogen, propane, diesel

Efficiency- 20-30% (Recuperated)

5

Environmental- Low (<9-50 ppm) NOx

Other Features- Cogeneration (50-80°C water)

Commercial Status- Small volume production,Commercial prototypes now

Fig 2.1 Capstone turbine

Micro turbines are small combustion turbines with outputs of 25 kW to 500 kW. They evolved from automotive and truck turbochargers, auxiliary power units (APUs) for airplanes, and small jet engines. Micro turbines are a relatively new distributed generation technology being used for stationary energy generation applications. They are a type of combustion turbine that produces both heat and electricity on a relatively small scale.

A micro gas turbine engine consists of a radial inflow turbine, a centrifugal compressor and a combustor. The micro turbine is one of the critical components in a micro gas turbine engine, since it is used for outputting power as well as for rotating the compressor. Micro turbines are becoming widespread for distributed power and combined heat and power applications. They are one of the most promising technologies for powering hybrid electric vehicles. They range from hand held units producing less than a kilowatt, to commercial sized systems that produce tens or hundreds of kilowatts.

Part of their success is due to advances in electronics, which allows unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows the generator to be integrated with the turbine shaft, and to double as the starter motor.

6

They accept most commercial fuels, such as gasoline, natural gas, propane, diesel, and kerosene as well as renewable fuels such as E85, biodiesel and biogas.

Most micro turbines are comprised of a compressor, combustor, turbine, alternator, recuperator (a device that captures waste heat to improve the efficiency of the compressor stage), and generator.

2.2 Types of Micro turbine

Micro turbines are classified by the physical arrangement of the component parts: single shaft or two-shaft, simple cycle, or recuperated, inter-cooled, and reheat. The machines generally rotate over 40,000 revolutions per minute. The bearing selection—oil or air—is dependent on usage. A single shaft micro turbine with high rotating speeds of 90,000 to 120,000 revolutions per minute is the more common design, as it is simpler and less expensive to build. Conversely, the split shaft is necessary for machine drive applications, which does not require an inverter to change the frequency of the AC power.

Microturbine generators can also be divided into two general classes:

Unrecuperated (or simple cycle) micro turbines—In a simple cycle, or unrecuperated, turbine, compressed air is mixed with fuel and burned under constant pressure conditions. The resulting hot gas is allowed to expand through a turbine to perform work. Simple cycle micro turbines have lower efficiencies at around 15%, but also lower capital costs, higher reliability, and more heat available for cogeneration applications than recuperated units.

Recuperated micro turbines—Recuperated units use a sheet-metal heat exchanger that recovers some of the heat from an exhaust stream and transfers it to the incoming air stream, boosting the temperature of the air stream supplied to the combustor. Further exhaust heat recovery can be used in a cogeneration configuration. The figures below illustrate a recuperated micro turbine system. The fuel-energy-to-electrical-conversion efficiencies are in the range of 20 to 30%. In addition, recuperated units can produce 30 to 40% fuel savings from preheating.

Cogeneration is an option in many cases as a micro turbine is located at the point-of-power utilization. The combined thermal electrical efficiency of micro turbines in such cogeneration applications can reach as high as 85% depending on the heat process requirements.

7

Micro turbine Efficiency:Configuration EfficiencyUnrecuperated- 15%Recuperated- 20-30%With Heat Recovery- Up to 85%

2.3 Functions:

Provides better power reliability and quality, especially for those in areas where brownouts, surges, etc. are common or utility power is less dependable

Provides power to remote applications where traditional transmission and distribution lines are not an option such as construction sites and offshore facilities

Can be an alternative to diesel generators for on-site power for mission critical functions (e.g., communications centres )

Possesses combined heat and power capabilities Reduces upstream overload of transmission lines Optimizes utilization of existing grid assets—including potential to free up

transmission assets for increased wheeling capacity Improves grid reliability Facilitates faster permitting than transmission line upgrades Can be located on sites with space limitations for the production of power

2.4 Productive:

Provides high-quality power for sensitive applications Responds faster to new power demands—as capacity additions can be made more

quickly Facilitates less capital tied up in unproductive assets—as the modular nature of

micro turbines means capacity additions and reductions can be made in small increments, closely matched with demand, instead of constructing central power plants sized to meet estimated future (rather than current) demand

Stand-by power decreases downtime, enabling employees to resume working Produces less noise than reciprocating engines

2.5 Characteristics of Micro turbine

Some of the primary characteristics for micro turbines include:

Distributed generation—stand-alone, on-site applications remote from power grids

8

Quality power and reliability—reduced frequency variations, voltage transients, surges, dips, or other disruptions

Stand-by power—used in the event of an outage, as a back-up to the electric grid

Peak shaving—the use of micro turbines during times when electric use and demand charges are high

Boost power—boost localized generation capacity and on more remote grids Low-cost energy—the use of micro turbines as base load or primary power that

is less expensive to produce locally than it is to purchase from the electric utility Combined heat and power (cogeneration)—increases the efficiency of

on-site power generation by using the waste heat for existing thermal process.

2.6 TECHNOLOGY DISCRIPTIONOF MICROTURBINES

Basic Processes:

Micro turbines are small gas turbines, most of which feature an internal heat exchanger called a recuperator. In a micro turbine, a radial flow (centrifugal) compressor compresses the inlet air that is then preheated in the recuperator using heat from the turbine exhaust. Next, the heated air from the recuperator mixes with fuel in the combustor and hot combustion gas expands through the expansion and power turbines. The expansion turbine turns the compressor and, in single shaft models, turns the generator as well. Two-shaft models use the compressor drive turbine’s exhaust to power a second turbine that drives the generator. Finally, the recuperator uses the exhaust of the power turbine to preheat the air from the compressor. Single-shaft models generally operate at speeds over 60,000 revolutions per minute (rpm) and generate electrical power of high frequency, and of variable frequency (alternating current --AC). This power is rectified to direct current (DC) and then inverted to 60 hertz (Hz) for U.S. commercial use. In the two-shaft version, the power turbine connects via a gearbox to a generator that produces power at 60 Hz. Some manufacturers offer units producing 50 Hz for use in

countries where 50 Hz is standard, such as in Europe and parts of Asia.

Thermodynamic Heat Cycle

In principle, micro turbines and larger gas turbines operate on the same thermodynamic heat cycle, the Brayton cycle. In this cycle, atmospheric air is compressed, heated at constant Pressure, and then expanded, with the excess power produced by the expander (also called the turbine) consumed by the compressor used to generate electricity. The

9

power produced by an expansion turbine and consumed by a compressor is proportional to the absolute temperature of the gas passing through those devices. Higher expander inlet temperature and pressure ratios result in higher efficiency and specific power. Higher pressure ratios increase efficiency and specific power until an optimum pressure ratio is achieved, beyond which efficiency and specific power decrease. The optimum pressure ratio is considerably lower when a recuperator is used. Consequently, for good power and efficiency, it is advantageous to operate the expansion turbine at the highest practical inlet temperature consistent with economic turbine blade materials and to operate the compressor with inlet air at the lowest temperature possible. The general trend in gas turbine advancement has been toward a combination of higher temperatures and pressures.

However, micro turbine inlet temperatures are generally limited to 1750°F or below to enable the use of relatively inexpensive materials for the turbine wheel and recuperator. For recuperated turbines, the optimum pressure ratio for best efficiency is usually less than 4:1.

Basic Components

Components of Micro turbine:

I. Turbo-Compressor Package:-The basic components of a micro turbine are the compressor, turbine generator, and recuperator Figure 2.2 the heart of the micro turbine is the compressor-turbine package, which is commonly mounted on a single shaft along with the electric generator. Two bearings support the single shaft. The single moving part of the one-shaft design has the potential for reducing maintenance needs and enhancing overall reliability. There are also two-shaft versions, in which the turbine on the first shaft directly drives the compressor while a power turbine on the second shaft drives a gearbox and conventional electrical generator producing 60 Hz power. The two shaft design features more moving parts but does not require complicated power electronics to convert high frequency AC power output to 60 Hz. Moderate to large-size gas turbines

10

use multi-stage axial flow turbines and compressors, in which the gas flows along the axis of the shaft and is compressed and expanded in multiple stages. However, micro turbine turbo machinery is based on single-stage radial flow compressor and turbines. Rotary vane and scroll compression are the most commonly used technology in the micro turbine industry. Second generation gas compressor technologies are in development or being introduced. That may reduce costs and target on-board application Rotary vane compression technology offers a wide range of gaseous fuel flexibility Parasitic loads vary based on type of gas and inlet pressures available, general rule 4 to 6% for natural gas and 10 to 15% for bio gas.

II. Generator: - The micro turbine produces electrical power either via a high-speed generator turning on the single turbo-compressor shaft or with a separate power turbine driving a gearbox and conventional 3,600 rpm generator. The high-speed generator of the single-shaft design employs a permanent magnet (typically Samarium-Cobalt) alternator, and requires that the high frequency AC output (about 1,600 Hz for a 30 kW machine) be converted to 60 Hz for general use. This power conditioning involves rectifying the high frequency AC to DC, and then inverting the DC to 60 Hz AC. Power conversion comes with an efficiency penalty (approximately five percent).To start-up a single shaft design, the generator acts as a motor turning the turbo-compressor shaft until sufficient rpm is reached to start the combustor. Full start-up requires several minutes. If the system is operating independent of the grid (black starting), a power storage unit (typically a battery UPS) is used to power the generator for start-up.

III. Recuperators:-Recuperators are heat exchangers that use the hot turbine exhaust gas (typically around 1,200ºF) to preheat the compressed air (typically around 300ºF) going into the combustor, thereby reducing the fuel needed to heat the compressed air to turbine inlet temperature. Depending on micro turbine operating parameters, recuperators can more than double machine efficiency. However, since there is increased pressure drop in both the compressed air and turbine exhaust sides of the recuperator, power output typically declines 10 to 15% from that attainable without the recuperator. Recuperators also lower the temperature of the micro turbine exhaust, reducing the micro turbine’s effectiveness in CHP applications.

IV. Air bearings:-They allow the turbine to spin on a thin layer of air, so friction is low and rpm is high. No OIL or oil pump is needed. Air bearings offer simplicity of operation without the cost, reliability concerns, maintenance requirements, or power drain of an oil supply and filtering system. Concern does exist for the reliability of air bearings under

11

numerous and repeated starts due to metal on metal friction during start up, shutdown, and load changes. Reliability depends largely on individual manufacturers' quality control methodology more than on design engineering, and will only be proven after significant experience with substantial numbers of units with long numbers of operating hours and on/off cycles.

V. Power Electronics-The high frequency AC is rectified to DC, inverted back to 60 or 50 Hz AC, and then filtered to reduce harmonic distortion... To allow for transients and voltage spikes, power electronics designs are generally able to handle seven times the nominal voltage. Most micro turbine power electronics are generating three phase electricity. Electronic components also direct all of the operating and start up functions.

Fig 2.2 Basic parts of micro turbine

Micro turbines are very small gas turbines (30 to 400 kilowatts [kW]) that usually have an internal heat-recovery heat exchanger (called a recuperator) to improve electric efficiency. In typical micro turbines, the cycle is similar to that of a conventional gas turbine. It consists of the following processes:

● Inlet air is compressed in a radial (centrifugal) compressor, then

● Preheated in the recuperator using heat from the turbine exhaust.

12

● Heated air from the recuperator is mixed with fuel in the combustor and burned.

The hot combustion gas is then expanded in one or more turbine sections, which produces rotating mechanical power to drive the compressor and the electric generator. The recuperator efficiency is the key to whether a particular micro turbine is economically viable. By comparison, in a conventional gas turbine, the gas flow path is as follows: compressed air from the compressor (more air mass can be ―introduced‖ by inter-cooling) is burned with fuel.

Gaseous products expand through the turbine section (where more power can be extracted by reheating the gaseous products). Exhaust gases can provide waste heat recovery or cogeneration potential, as those gases may produce steam to drive a steam turbine, may be led into a greenhouse system, or may optimize thermal efficiency by some other means. Without waste heat recovery or cogeneration of some sort, a gas turbine is said to operate in ―simple cycle‖ mode. With the addition of a boiler (to get steam from waste heat recovery) and a steam turbine, the gas turbine package is said to operate as a ―combined cycle.‖ However, most micro turbines, to be financially viable, have a recuperator (to recover waste heat). This is not quite a simple cycle, but the micro turbine can be said to operate ―solo‖ in power-only applications. Frequently, micro turbines are used to extract heat as a product. This then would be called combined heat and power (CHP) applications. In single-shaft micro turbines, a single expansion turbine turns both the compressor and the generator. Two-shaft models use one turbine to drive the compressor and a second turbine to drive the generator, with exhaust from the compressor turbine powering thegenerator turbine. The power turbine’s exhaust is then used in the recuperator to preheat the air from the compressor.

The basic components of a micro turbine are the compressor, turbine, generator, and recuperator (Figure 1.2). The heart of the micro turbine is the compressor-turbine package, which is most commonly mounted on a single shaft along with the electric generator. The single shaft is supported by two (or more) high-speed bearings. Because single-shaft turbines have only one moving shaft, they have the potential for lower maintenance and higher reliability than turbines with two or more shafts. There are also two-shaft versions of the micro turbine, in which the turbine on the first shaft only drives the compressor while a second power turbine on a second shaft drives a gearbox and conventional electric generator producing 60 or 50 Hz of power. Moderate- to large-sized gas turbines use multistage axial flow compressors and turbines, in which the gas flows parallel to the axis of the shaft and then is compressed and expanded in multiple stages. Most current micro turbines are based on single-stage radial flow compressors and either single- or double-stage turbines.

13

Fig. 2.3Micro turbine based combined heat and power system

Fig2.4 Micro turbine Construction

Design Characteristics of micro turbines

Thermal output: Micro turbines produce thermal output at temperatures in the 400 to 600°F range, suitable for supplying a variety of building thermal needs.

14

Fuel flexibility: -Micro turbines can operate using a number of different fuels:

Sour gases (high sulfur, low Btu content), and liquid fuels such

As gasoline, kerosene, natural gas and diesel fuel/heating OIL.

Life: - Design life is estimated to be in the 40,000 to 80,000 hour range.

Size range: -Micro turbines available and under development are sized

From 25 to 350 KW

Emissions: -Low inlet temperatures and high fuel-to-air ratios result in NOx

Emissions of less than 10 parts per million (ppm) when

Running on natural gas

Modularity: - Units may be connected in parallel to serve larger loads and

Provide power reliability

Dimensions: -About 12 cubic feet.

2.8 Advantages

Micro turbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operates without oil, coolants or other hazardous materials. Micro turbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust, whereas the waste heat of reciprocating engines is split between its exhaust and cooling system. However, reciprocating engine generators are quicker to respond to changes in output power requirement and are usually slightly more efficient, although the efficiency of micro turbines is increasing. Micro turbines also lose more efficiency at low power levels than reciprocating engines.

Micro turbines offer several potential advantages compared to other technologies for small-scale power generation, including: a small number of moving parts, compact size, lightweight, greater efficiency, lower emissions, lower electricity costs, and opportunities to utilize waste fuels.

Waste heat recovery can also be used with these systems to achieve efficiencies greater than 80%. Because of their small size, relatively low capital costs, expected low operations and

15

Maintenance costs, and automatic electronic control, micro turbines are expected to capture a significant share of the distributed generation market. In addition, micro turbines offer an efficient and clean solution to direct mechanical drive markets such as compression and air conditioning.

Micro turbines offer many potential advantages for distributed power generation. Selected strengths and weaknesses of micro turbine technology are listed in the following table from the California Distributed Energy Resources Guide on Micro turbines.

Micro turbines:-

Strengths Weaknesses Small number of moving parts, Low fuel to electricity efficiencies Compact size Loss of power output and efficiency with higher ambient

temperatures and elevation Lightweight Good efficiencies in cogeneration Low emissions Can utilize waste fuels Long maintenance intervals No vibrations Less noise than reciprocating engines Strengthens energy security

2.9 Economics of Micro turbines

Micro turbine capital costs range from $700-$1,100/kW. These costs include all hardware, associated manuals, software, and initial training. Adding heat recovery increases the cost by $75-$350/kW. Installation costs vary significantly by location but generally add 30-50% to the total installed cost.

Micro turbine manufacturers are targeting a future cost below $650/kW. This appears to be feasible if the market expands and sales volumes increase. With fewer moving parts, micro turbine vendors hope the units can provide higher reliability than conventional reciprocating generating technologies. Manufacturers expect that initial units will require more unexpected visits, but as the products mature, a once-a-year maintenance schedule should suffice. Most manufacturers are targeting maintenance intervals of 5,000-8,000 hours.Maintenance costs for micro turbine units are still based on forecasts with minimal real-life situations. Estimates range from $0.005-$0.016 per kWh, which would be

comparable to that for small reciprocating engine systems.

Micro turbine Cost:

16

Capital Cost- $700-$1,100/kW

O&M Cost- $0.005-0.016/kW

Maintenance Interval- 5,000-8,000 hrs.

2.10 Applications

Micro turbines can be used for stand-by power, power quality and reliability, peak shaving, and cogeneration applications. In addition, because micro turbines are being developed to utilize a variety of fuels, they are being used for resource recovery and landfill gas applications. Micro turbines are well suited for small commercial building establishments such as: restaurants, hotels/motels, small offices, retail stores, and many others.

The variety of energy consumers that are already using micro turbines is large and growing fast. For example:

A McDonald's restaurant in Chicago, Illinois, gets most of its electricity from a natural-gas-powered micro turbine, cutting $1,500 off its total monthly power bill. More

Landfill gas-fired micro turbines installed at the Jamacha Landfill in Spring Valley, California supply power on-site and back to the grid.

A textile mill ensures continuous operation by getting its power from micro turbines.

The development of micro turbine technology for transportation applications is also in progress. Automotive companies are interested in micro turbines as a lightweight and efficient fossil-fuel-based energy source for hybrid electric vehicles, especially buses.

Other ongoing developments to improve micro turbine design, lower costs, and increase performance in order to produce a competitive distributed generation product include heat recovery/cogeneration, fuel flexibility, and hybrid systems (e.g., fuel cell/micro turbine, flywheel/micro turbine).

Chapter 3

17

CONCLUSION

The drawbacks of centralized power generation and shortage of power leading to concept of Distributed generation (DG).DG tends to several advantages and concept of DG is more feasible. Micro turbine is the application of DG .The history of IC engine. Shows several year research works for today’s better result. Therefore micro turbine is tomorrow’s world. Micro turbine can use low grade of fuel very effectively like waste gases, sour gases etc.

Thus micro turbine gives chance of low fuel cost and less emission. The dimensions of micro turbine comparatively small by which it can be installed at field where power is consumed. It has few efficiency problems. Due to chemical recuperation the thermal efficiency increases sharply. Micro turbine is also effective in CHP operation .It is having problem of Starting time and that’s why it fails as standby power generator compared to IC engines. In India the micro turbine is quite useful. The power shortage effect can be solved using micro turbine, using fuels like biogas, etc. But in India the technology is still underdevelopment so the present seminar is an honest attempt to introduce micro turbine technology in India for solving the problem of power generation in future.

18

REFERENCES

1] Experimental and simulation analysis of micro turbines- by S. M. Flockhart and R. S.Dhariwal

2] A micro turbine device with enhanced micro air bearings-by X. C. Shan, Q. D. Zhang , Y. F. Sun and R. Maed

3] http://www.wbdg.org/resources/microturbines.php{

4] Engineringcorner.blogspot.in

5] Experimental simulation on the integration of solid oxide fuel cell and micro-turbine generation system-by Wei-Hsiang Lai , Chi-An Hsiao , Chien-Hsiung Lee , Yau-PinChyoub, Yu-Ching Tsai

6] Analytical and Experimental Studies on Turbo expander‖ - Ghosh, P and Sarangi, IIT Kharagpur (2002)

19