microturbine generators - · web viewmicroturbine generators(mtg) are small, high speed power...

Microturbine Generators

1. INTRODUCTION

As energy demands increase and the associated costs increasing with demand, newer

energy alternatives are becoming more important to society and also consumers want an

uninterrupted and economical electric power. Recently, distributed generation (DG) has become

an attractive method of providing electricity to consumers and retailers. In addition, from the

viewpoint of economic feasibility, the costs of installing generators and producing the electricity

can be comparatively inexpensive using the DG method.

One of DG sources is Microturbine Generation systems. Microturbine generator systems

are those generator systems equipped with small combustion turbines approximately the size of a

refrigerator with outputs of 25kW to 500kW.They operate at a high speed generally in the range

of 50,000 to 120,000rpm.Electric power is produced in the range of 1400-4000Hz.They are most

suitable for small to medium-sized commercial and industrial loads. The microturbine provides

input mechanical energy for the generator system which is converted by the generator to

electrical energy. The electrical energy is later converted to normal supply frequency and passed

through the transformer, is delivered to the distribution system and the local load.

Fig 1.Block diagram of a microturbine generator system

The microturbine generators come under the Distributed Energy Resources. Device

category. Those devices enable renewable energies utilization and more efficient utilization of

waste heat in combined heat and power (CHP) applications and lowering emissions. Unlike

Department of Electrical & Electronics Engineering, 1


traditional backup generators, microturbine generators are designed to operate for extended

periods of time and require little maintenance. They can supply customer’s base-load

requirements or can be used for standby, peak shaving and cogeneration applications.

As microturbine generators don’t have reciprocating parts, there is no need of lubricating

and all. Some microturbines even utilize air bearings and air cooling, thereby completely

eliminating the need to change and dispose of hazardous liquid lubricants and coolants. In any

case, microturbines are similar to major power plants, able to run for extended periods at full

power output, and require little scheduled maintenance compared with traditional reciprocating

engine generators of similar size. This makes them ideal for stationary prime power applications.

The combustion process in a microturbine is continuous and clean burning, similar to modern

gas turbine power plants. Microturbine manufacturers have deployed state of the art lean-burn

combustion technology to control emissions without the need for expensive catalytic exhaust

treatment equipment or chemicals.



2. MICROTURBINE GENERATORMicroturbine generators(MTG) are small, high speed power plants that are usually

include the turbine, compressor and power electronics to deliver the power to the grid. These

small power plants typically operate on natural gas. Future units may have the potential to use

lower energy fuels such as gas produced from landfill or digester gas. Microturbine generators

are classified into two types:

Unrecuperated (simple cycle) microturbine generators.

Recuperated microturbine generators.

2.1 UNRECUPERATED MTG

In a simple cycle or unrecuperated systems the 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 MTGs have lower efficiency at around 15%, but also

lower capital costs, higher reliability and more heat available for co-generation applications than

recuperated units.

2.2 RECUPERATED MTG

Recuperated units use a thin sheet-metal heat exchanger that recovers some of the heat

from an exhaust stream (1,200ºF) and transfers it to the incoming air stream, boosting the

temperature of the air stream (around 300ºF) supplied to the combustor. Further exhaust heat

recovery can be used in a co-generation configuration. 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. Depending on the microturbine operating parameters, recuperators

can more than double machine efficiency.



3. TECHNICAL BACKGROUND

The entire microturbine generator system can be divided into three primary sub-systems:

3.1 Mechanical

The mechanical system comprises the turbine, generator, compressor and recuperator.

The compressor-turbine package is the heart of the microturbine generator system. They are

commonly mounted on a single shaft along with the electric generator. Two bearings support the

single shaft. The microturbine generator system produces electrical power via a high speed

generator turning on the single turbo-compressor shaft. 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 1400Hz-4000Hz) be converted to 50Hz for the general

use. They operate at cool, clean, low-vibration, environment and offers 160,000 hours of normal

service.

Fig 2. Internal view showing the parts of an MTG Block



3.1.1 Generator/Gearbox

The standard Power Works (NREC’s microturbine) package incorporates a single-stage

helical gear set to transfer power from the turbine to the 3600 RPM generator. The low-torque,

highsliding- velocity results in exceptional design-life margins. At the conditions specified for

the PSOFC, the gear and bearing life exceed one million hours.

A commercial 2-pole 3600 RPM induction generator is standard with the Power Works

package, and for a production version of the proposed system would be the probable choice. The

manufacturer predicts a B10 life of 160,000 hours for normal service. The generator has been

conservatively selected and operates in a cool, clean, low-vibration environment. For cold

weather and extended peaking-power operation, a higher power rated generator can be provided.

An optional synchronous generator can also be substituted for grid-isolated operation, as

proposed in connection with the current experimental program.

3.1.2 Combustor

The combustor proposed for the integrated PSOFC package would be a modification of

the standard patented Power Works (NREC’s microturbine) design, originally developed in 1990

in collaboration with SoCal Gas. It has consistently demonstrated NOx levels below 9ppmv, with

exceptionally good turndown stability and proven durability.

Departure from the standard Power Works (NREC’s microturbine) design is needed to

limit combustor pressure loss during unfired operation. Combustor inlet temperature under these

conditions will be in the vicinity of 1600F, whereas the current running condition is around

1200F. The design change needed to accommodate this difference is straightforward, and is

roughly a matter of increasing the effective flow area of the combustor.

3.1.3 Recuperator

Recuperator is a heat exchanger which transfers heat from the exhaust gas to the

discharge air before it enters the combustor to reduce the amount of fuel required to raise the

discharge air temperature to that required by the turbine.



3.1.4 Turbine

There are two kinds of turbines, high speed single shaft turbine and split shaft turbines.

All are small gas turbines.

Fig 3. Isometric view of an MTG

3.2 Electrical

The electrical system includes main control software, inverter and power firmware.

3.2.1 Engine controller

Engine controller is a digital system which controls the entire process of the microturbine

generator. They provide the provision of automated starting and all. And we can set the delay



using this system. They will also locate the fault occurred and perform the safety functions &

speed can be controlled. Engine controller will reduce the power output produced if the engine is

running near its maximum permitted temperature. They also have the ability to interact with the

other parts of the generator control systems.

3.2.2 Power Conditioning System

We know the power output of a microturbine generator will be between the frequency

ranges 1.5-4 kHz. For our usage it must have to be converted to the useable standard mode.

Fig 4. Simplified diagram of a power conditioning system

The power conditioning system converts the unregulated, variable-frequency output of

the generator into a high quality, regulated waveform. The waveform quality surpasses the

general utility standards and is suitable for supplying sensitive equipment. Output voltage and

frequency are adjustable between desirable ranges, allowing the system to be easily configured

for the operation anywhere.

We know that the electrical output from the MTG will have a frequency in the range of

1,400-4,000Hz. The high frequency power from the generator is introduced into an inverter

where it is converted into dc before the inverter followed by it can reconstruct a three-phase

voltage supply at a lower frequency required for the grid connections.



In the figure, we can see that an MTG feeding 3-phase power to a rectifier and the dc is

then fed to a high frequency, a single-phase inverter so that a compact, high frequency

transformer can be used. The secondary of the transformer feeds an ac/ac converter that takes the

single phase, high frequency voltage to produce a 3-phase voltage at a frequency and phase

needed to make a direct connection to the grid.

The circuit has following advantages:

The use of a transformer for robust isolation.

The high frequency inverter permits the use of compact, high frequency transformers.

The use a transformer permits the easy addition of other isolated loads and supplies via

additional windings and taps.

The circuit eliminates the need for static transfer switches.

Ancillary services can be provided with control software changes and additional

hardware.

Adding additional hardware is easier.

3.2.3 Power Controller

They are mostly on-board, pc-based, a processor linked to pc, etc., depending on

constraints and factors such as MTG packaging, desired versatility, type of available features,

and the sophistication/maturity of the system design. A power controller control and co-ordinates

the operation of the power conditioning circuit by ensuring that the functions such as voltage

following, current following, phase matching, harmonic suppression, etc are performed reliably

and at high efficiency.

3.3 Fuel system

Microturbine generator have fuel flexibility and are capable of using alternative fuels

including natural gas, diesel, ethanol, landfill gas and other bio-mass derived liquids & gases.

The microturbine generators are fitted with fuel boosters which reduce the fuel consumption. For

2 kW power, the machine consumes only 25 icfm.



Fig 5. Complete view of an MTG

4. WORKING

Mechanically the microturbine generator is a single shaft gas turbine with the entire

compressor, power turbine and the permanent magnet generator being mounted on the same

shaft. The power turbine drives the generator which produces the electrical power and speed of

rotation of this power turbine is from 50000-120,000 rpm.

During engine operation, air is drawn into the compressor unit through an air filter. The

air filter will filter out unwanted components in the air. The compressor unit will then compress

in taken air and raises its pressure to a heavy value. The high pressure air then is introduced into

a recuperator arrangement where the heat exchanging process takes place. Inside the recuperator,

the exhaust air from the turbine after burning the fuel, possessing a temperature around 650

degrees Celsius will then transfer the heat to the compressed air and thereby increase the

temperature by 200 degree Celsius.



Fig 6. Figure illustrating the working of an MTG

Now, the hot air is passed into the combustion chamber. Simultaneously the fuel which is

also get compressed in a gas compressor is introduced and mixed with high temperature air and

due to this burning of fuel will occur, producing high temperature gas or steam. This gas is then

taken into the power turbine by means of a nozzle. As a result the thermal energy holding by the

gas is used effectively to rotate the turbine to high speed.

Thus the generator which is coupled to the turbine wheel is get rotated and eventually the

electrical power is produced at higher frequencies which is later get regulated.



Fig 7. Working processes



5. MACHINE PERFORMANCE TESTS

Various tests have been performed on a microturbine generator to evaluate its

performance, maintenance requirements and all.

5.1 Endurance Test

In this test program, microturbine generator will be operated as long as practicable at

normal load. Daily operating parameters such as fuel flow, air pressure, temperature, humidity,

power produced, operating temperature and pressure are noted & verified.

5.2 Transient Response

Microturbine generator should be capable to respond adequately to load changes. For the

units that are not capable to operate on isolated bus will operate parallel with system grid.

Changes in the system load will be picked up by the grid and noted by microturbine generator

units. Load changes on these microturbine generator units will be accomplished by manually

setting load using a control system arrangement.

5.3 Noise Measurement

Ambient noise levels will be measured using a handheld noise meter. Each unit will be

operated independently to acquire the noise measurements during operations, it is found that the

microturbine generator have the least noise level as compared to other generator sets and is

around 63 db.

5.4 Emission measurement

The exhaust of the microturbine generator is subjected to emission tests. Additionally, periodic

measurements with available handheld equipment would be made to determine trends and any

condition of degradation that may occur with operating hours.

Microturbine generators have the least NOx emission, which is the main factor behind the

global warming. The amount of NOx emitted is only 7ppm whereas it is too higher for the

conventional generator sets. A microturbine generator will produce only .564 kg of CO2 per kW

of electricity. That’s why we prefer this technology of power production.



5.5 Peak Load Gross and Net

Peak load gross and net measurements will be taken with a BMI meter or equivalent

recorder that measures power. For units without compressors, or compressors that are externally

powered, the net output must be determined by subtracting the external power requirements to

sustain MTG operation. Results of this test will yield performance characteristics such as

efficiency, heat rate, fuel consumption and operating hours. Comparisons will be made to

manufacturer specifications.

6. ECONOMIC ASPECTS

The capital cost for a microturbine generator is estimated as 700-1000 $/kW which

include all the hardware, associated manuals, software and all. 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 costs.

Microturbine manufacturers are targeting a future cost below 650$/kW. This appears to

be feasible if the market expands and sales volume increases.

With fewer moving parts, microturbine 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 microturbine 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.



Table 1

ECONOMICS OF AN MTG

Type of cost Cost(in dollars)

Capital cost $700-$1000/kW

Operational & maintenance cost $.005-$.016/kW

7. CHARACTERISTICS OF AN MTG

7.1 Aesthetics

Improves sightlines and views with off-the-grid systems, which eliminate the need for

overhead power lines.

7.2 Cost-Effective

Enables cost savings by reducing the peak demand at a facility, therefore lowering

demand charges.

7.3 Functional

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 centers).

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.

7.4 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

microturbines 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.

7.5 Secure/Safe

Strengthens energy security.

Stand-by power provides quick recovery after an event.

7.6 Sustainable

Produces the lowest emission of any noncatalyzed fossil fuel combustion system.

Has a small footprint, minimizing site disturbance.

Reduces or defers infrastructure (line and substation) upgrades.

For recuperated microturbine, possesses higher energy conversion efficiencies than

central generation.

Enables more effective energy and load management.



8. ADVANTAGES AND DISADVANTAGES

7.1 Advantages

MTG has small number of moving parts, therefore maintenance is comparably less.

It has compact size.

Most of the parts are light weight.

Good efficiency.

Low emission & less noise and vibration than reciprocating systems.

Can utilize waste fuels.

Strengthens energy security.

Cheap and easy installation.

Wide range of benefits in terms of operational and fuel flexibility, service

performance and maintainability.

7.2 Disadvantages

Low power output & efficiency with higher ambient temperatures

Time-variable electrical and thermal demand distorts MTG’s energy balance

sometimes leading to larger fuel requirement.

9. APPLICATIONS



Microturbines can be used for stand-by power, power quality and reliability, peak

shaving, and cogeneration applications. In addition, because microturbines are being developed

to utilize a variety of fuels, they are being used for resource recovery and landfill gas

applications. Microturbines are well suited for small commercial building establishments such

as: restaurants, hotels/motels, small offices, retail stores, and many others.

1. MTG’s are excellent power generators for use in combined heat and power (CHP) systems.

Their low maintenance and clean exhaust make them a reliable choice for base load CHP

applications. Integrating hot water heat recovery into the microturbine package has proven cost

effective, and a growing number of commercial installations are saving money using this

technology. Not only do microturbines provide this cost saving performance day in and day out,

but their value is further increased when the cost for traditional backup generation is eliminated.

By considering the CHP system installed in Radisson Hotel in Santa- Maria, California,

we can examine effectiveness of MTG based systems.

Two C60-ICHP systems are installed at the Radisson Hotel in Santa Maria, California. In

this application, the hot water output is used for several different purposes. One use is for

domestic hot water for the hotel guests. This thermal load is highest in the morning, and then

increases again later in the day. A second use is for laundry service. This is highest during the

working day. The third use is for building heat. This load is seasonal and steady during the day

when outside temperatures are low.

The two C60-ICHP systems are set to operate in parallel with the electric grid, and

Electric Priority mode is used. In this CHP mode, the electric power output for each microturbine

is set at the desired level. For this Radisson hotel with 188 rooms, electric power is normally set

for maximum from each microturbine during the day. This is below the building’s peak electric

demand, and power does not flow back into the electric utility grid. While the microturbines

work to maintain their programmed electrical outputs, the exhaust diverters automatically adjust

to accommodate the changing thermal requirements of the hotel. This example shows how the

flexible control capabilities of the C60-ICHP allow simple integration with a building with

changing thermal requirements.


http://www.wbdg.org/design/office.php


The two C60-ICHP systems are set to operate 24 hours per day. The operating scheme

was selected to match the thermal requirements of the hotel, provide the maximum electric

energy, and reduce time-of-use demand charges from the local electric utility. This results in

maximum financial benefit to the hotel, and helps to offload the utility when power is needed

most by other customers. Powerhouse Energy supplied the ICHP systems to the hotel and

managed the installation, system start-up and continuous operation.

ICHP application qualified for the state’s PUC Self- Generation Incentive Program rebate

of 30% on the total installed cost. The expected energy savings are very good, with a calculated

average savings of about $5,528 a month or $66,336 per year. This savings to the hotel is net of

natural gas, projected lifecycle maintenance costs, and project financing. Total installed cost was

$185,000. The operating availability of the ICHP systems, including start up, commissioning,

and service response time has been better than 95% to date.

2. Another example of CHP system is Capstone microturbine installation at Inns of America in

Carlsbad, California, was completed in August 2002 by California Power Partners (Calpwr). It

included a Capstone C60 with fuel gas booster and separate hot water heat recovery module. As

for the Radisson, this microCHP system provides both thermal and electric base load for this

hotel. Energy savings were estimated at 40%. This lowered the daily per room energy cost by

$4.00 – a significant portion of the hotel’s profit margin.

While this installation is saving the hotel owner money every day, there is a unique

attribute that provided even more value than anyone envisioned when the decision to purchase

this system was made. The hotel owner decided to purchase Capstone’s dual mode version

microturbine, with the capability to provide power even when the electric utility is not available.

The logic was to avoid the cost of a traditional backup generator, thereby improving the

economics of this project. Such traditional diesel backup generators are designed and permitted

to operate only for short periods of time in case of a utility outage. But microturbines certified by

the California Air Resources Board can operate continuously without the need for local air

permits.



In October of 2003, Southern California was ravaged by multiple wildfires that lasted

days and crippled the state with huge property and personal losses. Carlsbad, where the hotel is

located, and the nearby San Diego region were especially hard hit. Power lines were shut down,

and many homes and businesses.

During this time, the Inns of America lights remained on, powered by the Capstone

60kW microturbine. In support of the local community, the Inns donated a number of rooms for

people who, and the Inns of America became an emergency base of operations for several

groups. The result for the hotel was increased business and a strengthened relationship with the

community – things that were never directly considered in their original decision to install a

microCHP system.

3. McDonald's restaurant in Chicago, Illinois, gets most of its electricity from a natural-gas-

powered microturbine, cutting $1,500 off its total monthly power bill.

4. The Chesapeake Building on the University of Maryland campus, College Park, Maryland has

a cooling, heating, and power (CHP) system consisting of microturbines, chiller, and stack that

uses waste heat to cool and heat the building, significantly increasing system efficiency.

Fig 8. Chesapeake Building CHP system, University of Maryland

10. CONCLUSION

Thus this new scheme of power generation is having ample importance in the present era

where we are paying a great attention and care for environment friendly power generations. The


http://www.sustainablefacility.com/Articles/Feature_Article/205d94b4ece38010VgnVCM100000f932a8c0____


power generation using a microturbine is becoming popular in North America, Europe because

of its ecofriendly nature along with descent power delivery on considering both efficiency and

economics.

MTG’s continue to find economic application in a growing market.

Integration of hot water heat recovery, absorption chilling, and backup power functions makes

for simple solutions that save money and increase power reliability, with the added social

benefits of clean emissions, reduced greenhouse gas production, and more efficient use of our

limited natural resources. The development of microturbine technology for transportation

applications is also in progress. Automotive companies are interested in microturbines as a

lightweight and efficient fossil-fuel-based energy source for hybrid electric vehicles, especially

buses.

Other ongoing developments to improve microturbine generator 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/microturbine,

flywheel/microturbine).

Manufacturers are moving toward packaging MTGs with integrated heat recovery

equipment to lower both the cost of installation and operation. Moreover, this is a clean source of

electrical power.

A variety of energy consumers that are already using MTG due to its high reliability &

low operating cost, neglecting its high initial cost.

Undoubtedly this technology will conquer the energy sector in the near future, on

considering the present environmental scenario.

11. REFERENCES

1. D.K.Nicholas & Kevin.P.Loving, ASSESSMENT OF MICROTURBINE GENERATORS, IEEE 2003.


http://www.wbdg.org/resources/fuelcell.php


2. Amer Al- Hinai & Ali Feliachi, Dynamic Model of Microturbine Used As a Distributed Generator, West Virginia University, 2006

3. Stephanle.L.Hamilton, MICROTURBINE GENERATOR PROGRAMME, Hawaii Intnl. Conference on System Sciences, 2000.

4. Microturbine Power Conversion Technology, R.H.Staunton & B.Ozpineci.

5. Capstonemicroturbine.com


microturbine generators - · web viewmicroturbine generators(mtg) are small, high speed power...

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