analysis of a biomass-fueled stirling heat · pdf fileanalysis of a biomass-fueled stirling...

Introduction Characteristics System Maximization Inputs/Outputs Reducing emissions

Analysis of a Biomass-fueled Stirling Heat

Engine

James Robinson

April 29, 2008

James Robinson — Analysis of a Biomass-fueled Stirling Heat Engine 1/27


Outline

1 IntroductionObjectivesJustification

2 CharacteristicsTradeoffs

3 System

4 Maximization

5 Inputs/Outputs

6 Reducing emissions



Aim of Study

Objectives

Justify reasons for analysis

Describe Stirling Engine functions and their benefits.

Present a biomass system that incorporates a StirlingEngine

Identify methods for improvement

Define inputs/outputs of the system

Suggest new applications for a Stirling engine thatdecreases emissions/environmental impact



Stirling Engine

Figure: Model Stirling Engine

Justification

Stirling Engines have an elegant design

The environmental impact is potentially very low

The technology needs to be improved

www.steamengine.com.au/stirling/models/baileycraft/index.html



Stirling Engine2.670 Stirling Engine Animation

http://web.mit.edu/2.670/www/spotlight_2005/engine_anim.html 4/28/2008 5:09:06 AM

Figure: Inside of a Stirling Engine

web.mit.edu/2.670/www/spotlight-2005/engine-anim.html



Stirling Engine

Figure: P-V and T-S diagram of a theoretical Stirling engine(Sonntag et.al., 2003)



Stirling Engine

HEATED END COOLED END

1 I-

UISPLACEK PISTON (VERY LUOSE) [TIGHT FIT)

Figure: Inside of a Stirling Engine Steps 1-2 (Ross, 1977)



Stirling Engine

Figure: Inside of a Stirling Engine steps 3-4 (Ross, 1977)



Stirling Engine2.670 Stirling Engine Animation

http://web.mit.edu/2.670/www/spotlight_2005/engine_anim.html 4/28/2008 5:09:06 AM

Figure: Inside of a Stirling Engine

web.mit.edu/2.670/www/spotlight-2005/engine-anim.html



Stirling Engine

Advantages

Heat source external to the engine

Quiet while operating

Rejected heat can be cogenerated-no corrosive exhaust

Disadvantages

Operates at close to limit of materials properties

Temperature affects metallurgical propertiesPressure strains gaskets and seals



Biomass Heated Stirling EngineSystem Diagram

1052 WREC 1998

5. ELECTRICITY PRODUCTION WITH A BIOMASS STIRLING ENGINE

The primary goal of the small scale plant sowed in Fitzure 3 is the grid independent production of electricity from biomass in the capacity range of 5 to 30 kWei The principle arrangement of the components is indicated in Figure 3. The important parts of the small scale power production unit are the biomass combuster, the Stirling engine as showed in Figure 1, the electric generator, the engine cooler circuit with pump, fan and the water/air heat exchanger. Biomass wastes like coffee shells, rice husks, agricultural residues or any kind of wood may be used as a fuel. Adaptations of the biomass combuster to several biofuels for improvements of the combustion process will be necessary. The heater of the Stirling engine is directly heated by the hot flue gas of the combuster. A heat exchanger with smooth surface at the flue gas side for heat recovery is used to preheat the combustion air to some hundred degree centigrade before entering the combuster. The belt driven blower and the cooling water pump (not visible in Figure 3) of the engine cooler are important components for rejecting the heat.

air in 20°C C Cooler

COM Combustor

F Frame

G Generator

HR Heat Recovery

Pel Electric Power

STE Stirling Engine

V Ventilator

biomass

??agricultural waste ??wood ??rice husks ??coffee shells

.

6.

/I/

I21

131 I4

. I I I

. I F

flue gas 760°C

I I F IEF-981014 I

Figure 3: Electricity production from biomass by a Stirling engine

REFERENCES

Sitte, G.: Marktuntersuchungen fir Stirlingmotoren NT Stromerzeugung mit dem Brennstoff Biomasse, diploma thesis at the Technical University Graz, 1998 Podesser, E.; Dermouz, H; Padinger, R.; Wenzel, T.: Entwicklung eines mit Holz betriebenen Stirling- Kleinkrathverkes zur dezentralen Strom- und Wiirmeerzeugung - Phase II, REPORT IEF-B-12/95, JOANNEUM RESEARCH, Institute for Bnergy Research, 1995. Hargreaves, CM.: The Philips StirIing Engine, Elsevi&-Verlag, 1991. Carlsen H.: 40 kW-Stirling engine for solid fuel; Fachbericht beim Stirling-Forum Osnabrtick, 1996.

Figure: Biomass-Stirling engine prototype (Podesser, 1999)James Robinson — Analysis of a Biomass-fueled Stirling Heat Engine 11/27


Biomass Heated Stirling EngineSystem Specifications

Table: Specifications for the Biomass-Stirling Engine(Podesser,1999)

WREC 1998 I051

?? The higher weight of Stirling engines operating with air (nitrogen) as working gas is of little significance in stationary applications.

?? The coefficient of performance generaly does not depend on the working gas.

The crank mechanism used in the Stirling engine was that of a series produced engine for a motor cycle. Fieure 1 shows this biomass test Stirling engine. The relatively large dead space of fhe heat exchangers requires, therefore, that the active working space of the entire Stirling engine be adapted accordingly.

3. TECHNICAL PERFORMANCE DATA MEASURED

The tests with the experimental Stirling engine were performed on a testbed configuration with a wood chip furnace. Results were found as showed in Table I:

Table I: Test results with a 3 kW biomass Stirling engine in 1996 /2/ Flue gas temp. 1.000 “C Mean preassure 33 (40) bar Dust content 70 . . . 700 mg/m3N Bore/stroke 14015 1 mm Engine cooler 30 . . . 70 “C Swept piston volume 840 cm3 Cylinder cooler 20 . . . 30 “C Compensator 17 liter Rod seals cooler 20... 30 “C Working speed 600 RPM Thermal input 12,5 kW Idling speed 950 RPM Engine cooler 8,75 kW Efficiency (COP) 0,25 1.. 0,28 - Cylinder coolers 0,52 kW Crankmechanism DUCATI 500 cm3 Rod seals cooler 0,03 kW FlyweeVstarter Austrian Truck Shaft Dower max. 3.2 kW Workine eas air. nitroeen

4. PROCESS CONFIGURATION IN PRICIPLE

Figure 2a shows the configuration of the biomass Stirling engine unit in principle which includes a heat exchanger to preheat the combustion air by heat recovery from the flue gas. This measure makes sense if the relationship between electricity produced (ELP) and the biomass fed (BFin) should be enlarged. The sankey diagram in Figure 2b indicates further that this relationship reaches 0,20. The COP expected for this application will be 0,33. The sankey diagram shows the relationship between the electricity produced and the thermal capacity of the combuster. It is easy to see that the combustor has to have about 50 kWth if an electric power of 10 kWe should be generated. The heat rejected by the engine cooler at temperatures of 60/40 “C will reach about 25 kWth at full load.

Figure 2: Biomass Stirling engine (a) for grid independent electricity production and sankey diagram (b). BB . . . biomass boiler, BFin biofuel input. DH . . . engine cooler (40/60 “C), STE . . . Stirling engine, ELP electric power, HOME heat recovery -heat exchanger, L . . . thermal losses, SHP shaft

power, qSTE COP of the Stirling engine,



Biomass Heated Stirling Engine

System

1 Rated output: 3 kW

2 Combustion of biomass: 12.5 kW

3 Rejected heat, via coolant: 8.75 kW

4 Average pressure ≈ 33 kPa

5 Efficiency 25%



Efficiency

Efficiency verification

ηHE =WHE

QH

=3.2kW

12.5kW= 25.6%



Maximization Methods

Possible Methods for Improvement

Increase temperature of hot side, decrease temperature ofcold side

Maximization requires no addition of heat

Best achieved by effective heat exchange

Coolant can be used but requires pumping work

Regenerator: No heat, no work



Maximization MethodsRegenerator

Figure: Diagram showing the regenerative matrix to increaseefficiency (West, 1986)



Maximization MethodsEfficiency Increase

Figure: Work output increased (1-2‘-3-4-1), heat input remains thesame (a-2‘-3-4-d-a)



Maximization MethodsEfficiency Increase

New Efficiency Calculation

η =W

Q

= 1−52(TH − TC ) + TC ln(Vf

Vi)

52(TH − TC ) + TH ln(Vf

Vi)

= 1−52(1473− 333) + 333ln(840)

52(1473− 333) + 1473ln(840)

η = 59.7%

*Temperatures in KelvinDerived with Wes Bliven



Combustion of Biomass

Assumptions

Biomass consists of 3 main molecules in woody plants:Cellulose, hemicellulose and lignin

Complete combustion

All carbon emitted as CO2

Example

C6H10O5 +1

2C5H8O4 +

1

2C10H12O3 + 14.25O2 + 49.31N2

→ 13.5CO2 + 10H2O + 49.31N2

• For every unit of biomass (774 g), 594 g of CO2 areproduced



Combustion of BiomassCO2 Emissions

Using a typical Heat of Combustion for biomass 20kJg

(Levine,

1991):

Example

CO2 emissions = η × mCO2

mR× 1 g

20 kJ R× 3600 kJ

1 kWh

= (0.256)(594 g

774 g)(

1 g

20 kJ)R(

3600 kJ

1 kWh)

CO2 emissions = 33.15g

kWh



Combustion of BiomassAvoided CO2 Emissions

GREENHOUSE GASES l'-Y^lDED by RENET-.'.YES (includes avoided fossil fueled generation GHG emissions)

GEOTHERMAL SOUR (gas assist)

NUCLEAR

Figure: CO2 equivalent offset by use of bio-fuels (CA DOE, 2007)

• Converting 3400 lbmCO2

MWhto 1.54× 10−3 g

kWh

• Avoided CO2 during combustion is negligible.• Must be higher accounting for life-cycle of live plant



Modifications to Biomass Flume

Possibilities

Long, heat resistant pipes allow particulates to settle.

Cloth fiber filters enhance catchment of particulates

Electrostatic precipitators

Figure: Electrostatic precipitatorhttp://www.bbc.co.uk/schools/gcsebitesize/physics/images/ph-elect28.gif



deduced. The thermal output of the engine can be measured com-bining precise temperature and flow measurements of the coolingwater to a calorimetric measurement.

Insolation Data MeasurementThe exact measurement of the direct normal insolation is cru-

cial for the whole measurement series. It is obtained from anactinometric station placed on top of the Odeillo big solar furnacea few hundred meters away from the dish/Stirling system. Thesolar part of the station is equipped with three sensors, a normalincident pyrheliometer �EPPLEY� to measure the direct normalinsolation �I� and two CM6 �Kipp & Zonen� pyranometers in or-der to obtain the global horizontal �G� and diffuse horizontal �D�insolation. The sensors are periodically calibrated at the laborato-ries of Carpantras, which is part of the Météo-France network andin possession of an absolute radiometer on the international radio-metric scale. The measurement uncertainties are about 1.5% forthe pyrheliometer and 3.5% for the pyranometers �1�.

Flux-Mapping SystemA flux measuring system for dish/Stirling systems developed by

DLR was used to map the flux distributions close to the focalplane. It consists basically of a Lambertian target placed in thebeam path, a charge coupled device �CCD� camera, and a com-puter that controls target positioning and image acquisition. Thetarget is made up of a water-cooled aluminum plate with aplasma-sprayed alumina coating, which is close to ideal diffusereflection properties. A Peltier-cooled slow-scan CCD camera ismounted in the central hole of the concentrator taking pictures ofthe illuminated target. The acquired images are automatically pro-cessed and evaluated in the image analysis program OPTIMAS®.Image calibration is achieved by calculating the total reflectedpower coming from the dish and relating it to the integrated grayvalues measured on the target in the focal plane. This calibrationmethod assumes that the target in the focal plane intercepts all thesunlight reflected by the dish. Simulations for the given case

proved that spillage is almost negligible being less than 1% evenfor bad sunshapes. Error analysis resulted in a calibration uncer-tainty of ±2.5% and local measurement uncertainties of −2.5% to+8.5% for this measurement system �2,3�.

Cooling Power Measurement SystemTo precisely measure the power evacuated by the cooling sys-

tem, the change of coolant enthalpy between water inlet and outletwas determined, and the mass flow was measured. A mixingchamber was connected to the outlet and a temperature sensorplaced at the outlet of this chamber to guarantee a homogeneoustemperature in the outlet stream. At the motor inlet, a proper mix-ing was assumed due to the short distance between the circulationpump and the motor inlet. Thus, the sensor was simply placed inthe center of the inlet water tube.

The sensors used were high precision PT100 1/10 DIN B ac-cording IEC751 with an accuracy of ±0.013 K. Their signal wasmeasured with an ICP DAS model I-7033 in four wire configura-tion with an accuracy of 0.1%. An additional calibration was con-ducted by adjusting their temperature difference signal to zerowith the water pump switched on and the engine in stow position.A noise of 0.05°C under static conditions was measured.

An electromagnetic flowmeter was selected to determine themass flow of the coolant. This device is able to measure the flowof conductive liquids regardless of their composition with veryhigh precision. The flowmeter was installed according to themanufacturer’s specifications and its inner diameter is the same asthe main rectilinear return pipe in order to be in unruliness state.The low liquid temperature and the expansion vessel in the cool-ing circuit prevent appearance of bubbles.

The Siemens Sitran MAG 3100 with a maximum flow rate of5000 l /h and the electronic evaluation unit �MAG 6000� has aspecified precision of ±0.5%. The calibration report indicates amaximum error of ±0.17% from 25% to 91% of the full scaleflow.

The measurements were taken in winter with negative outsidetemperatures. The cooling mixture used is a standard automotive-type ELAN FLUID D with full protection down to −26°C. Sincethe exact composition was not known, a sample was taken andanalyzed by the French Laboratoire National d’Essais. The mea-sured heat capacity as function of the temperature had an unex-pected high uncertainty of ±4%. The mean density was deter-mined to be 1060 kg /m3.

Electric Power Measurement SystemMeasurements of the electric power output of the generator and

the consumption of the individual components were performedusing a WEIGEL DUW 2.0 power transducer together with therecommended transformers �30 /1� for the current measurementinputs. With a true three-phase conversion of the current and volt-age inputs, this device guarantees an absolute correct result of themeasurements within the accuracy class of ±0.5%. Since thetransducer was placed at the output of the Stirling engine’s electriccircuit and therefore measures the net output, the constant con-

Fig. 1 The CNRS EuroDish System

Fig. 2 Energy flow in a dish/Stirling system

011013-2 / Vol. 130, FEBRUARY 2008 Transactions of the ASME

Downloaded 16 Apr 2008 to 137.150.173.106. Redistribution subject to ASME license or copyright; see http://www.asme.org/terms/Terms_Use.cfm

Figure: 10 kW Stirling-Dish assembly (Reinalter et. al., 2008)

• Only outputs are 18.53 kW waste heat and 10.85 kW network.• Overall efficiency is 39.4%. Stirling engine efficiency is34.3%.



Conclusion

Figure: Southern California Edison 150 kW model of a potential825 MW system

http://www.edison.com/pressroom/pr.asp?id=5885



Conclusions

Conclusions

The biomass fired Stirling engine can run constantly givenfuels supply

Efficiency can be increased from 25% to a maximum of59% if a regenerator is used

Major downfall of biomass-fired Stirling engine is the dustand emissions

Improvements to the heat source can make the use ofStirling Engines more viable



References

1 Podesser, Erich (1999). “Electricity production in rural villages with a biomass Stirling engine.“ RenewableEnergy, 16, 1049-1052

2 Edison, Int’l, Inc. (2008) “Bettering Energy Efficiency and Power Sources - Solar Energy Project,“http://www.sce.com/PowerandEnvironment/BetteringEnergyEfficiencyPowerSources/SolarProject/about.htmaccessed: 3/01/08

3 Levine, J.S. (1991) Global Biomass Burning: Atmospheric, Climatic, and Biospheric Implications, MITPress

4 Reinalter, W., Ulmer, S., Heller, P., Rauch, T., Gineste, J.M., Ferriere, A., and Nepveu, F. (2008)”Detailed Performance Analysis of a 10 kW Dish/Stirling System.” Journal of Solar Energy Engineering,130. pp: 011013-1 - 011013-6 (Purchased ASME)

5 Ross, Andy (1977) Stirling Cycle Engines, Imperial Litho/Graphics

6 Sonntag, R.E., Borgnakke, C and Van Wylen, G.J. (2003)

7 West, C.D., (1986) Principles and Applications of Stirling Engines, Van Norstrand Reinhold Co., Inc., NewYork, NY.



END

Questions?

Figure: Large 25 kW Stirling engine built by Stirling Energy

Typeset in LATEX


analysis of a biomass-fueled stirling heat · pdf fileanalysis of a biomass-fueled stirling...

Documents