Micro Scale EnergyGenerationCombined Heat and Power (CHP) systems
Dr. Ferenc Lezsovits
2nd „Green waves”International Autumn Academy
Renewable Energy – Smart Cities Along the Danube
17/11/2013-22/11/2013
Energy demands• Heat:• Domestic:Cooking, Room heating, Hot water
• Industrial:Sterilization. Destillation, Heat treatment, etc. - slightly decreasing
• Cooling & Air conditioning - increasing(most of it electricity driven)
• Electricity - increasing
• Transportation fuel consumption - increasing
General supported development and actions in Europe
• Reduction of energy demands More efficient energy utilization e.g. European Building Directive (EPBD)
• More efficient energy generation and distribution - Co- or tri-, or poly-generation, (parallel heat + electricity + cooling + biofuels)
- Smart grids (Self balanced electricity generation)
• Increasing share of renewables- Biomass - heating, cooling, electricity, fuel- Solar – heating, cooling, PhotoVoltaic (PV)- Hydro, Wind, Tide – electricity- Geothermal - heating, cooling, electricity
• Development of different energy storage facilities
Efficient energy utilisation example Passive house principals
Typical daily electricity demand variation in Hungary
in [MW] on Working days, Saturday, Sunday
Centralized Electricity Generation and Distribution
•An electric utility produces electricity at a power plant and distributes it to consumers through power lines, substations, and transformers.
Typical distributional network loss variation in Hu ngary ~10%in [MW] on Working days, Saturday, Sunday
Micro Scale, Local Electrical Energy Generation, Why?
In order to
• Perform off grid electricity supply- in emergency case or - at remote applications
• Safe distribution network loss
• Adjust generation to local demand variationform Micro-Grid or Smart-Grid
• Reduce fuel consumption
• Reduce CO2 and pollutant emission
Smart Grid– DisributedGeneration
Direct ElectricityGeneration
• Solar Photovoltaic PV
• Wind energy
• Hydro power
n-type semiconductor
p-type semiconductor
+ + + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - -
Physics of Photovoltaic Generation
Depletion Zone
Photovoltaic System
PV Technology Classification
Silicon Crystalline Technology Thin Film Technology
Mono Crystalline PV Cells Amorphous Silicon PV Cells
Multi Crystalline PV Cells Poly Crystalline PV Cells
( Non-Silicon based)
Available Solar Irradiation in Hungary
in June and in December
Application of PV systems
Advantages
• Energy source is freeDrawbacks
• Installation cost is still high
• Sunshine is effected by seasons, weather and day/night time variations
• Storage of electricity is difficult and low efficient
Power Generation from WindPower Generation from Wind
� The power in the wind
“wind” is the movement of air masses:
• caused by pressure differences (due to temperature differences)• influenced by rotation of the earth and terrain features
wind is converted solar energy (1~2 % of solar energy input)
Power extraction per rotor disk area versus wind speed
Typical cP–λ diagrams
for a variety of WT configurations/blades
Variability of winds with height
0
20
40
60
80
100
120
140
0 2 4 6 8 10
Wind Speed (m/s)
Hei
gh
t (m
)
How much energy will be produced by
a given Wind Turbine at a certain site ?
1) use the Wind Turbine Power
Curve
2) combine with wind statistics for
turbine location at hub-height
�Wind Resource Assessment
Application of Wind Power systems
Advantages
• Energy source is freeDrawbacks
• Installation cost is still high
• Wind is not blowing all the time, it is affected by wheather conditions
• Storage of electricity is difficult and low efficient
Hydro Power
PPhydrohydro = = ηηηηηηηηturbineturbine . . ρρρρρρρρwaterwater . g . . g . QQflow flow . . HHdropdrop
Francis turbine
Kaplan turbine
Vertical Pelton turbine
Turbine blades
Banki turbine
Turbine cross section
Application field of different technologies
Application of hydropower systems
Advantages• Energy source is free• Flow can be controlled• Power can be adjusted
to demands• It can be considered as
energy storage facility
Drawbacks• Geographical conditions
determines possibilities• Installation cost is still high• Wheather conditions
determines availablewater flow
• Wintertime freezing could cause problems
Power generation fromheat energy
• According to the 2nd law of Thermodynamics heat power can not be converted totally to mechanical power.
• For power generation a cycle is needed.
• There are different types of cycles available for power generation in theory and some of them are realized in certain engines.
Available fuels
State of matter Fossil Renewable
• Solid Coal Biomass: black, brown, lignite wood, cane, grass, etc.
energy plants & waste materials
• Liquid Crude Oil Biomass:Petrol, kerosene, Vegetable oil & bio-dieselDiesel oil, Fuel oil Bio-ethanol
• Gaseous Natural gas Bio-gas
Digester gas,
pyrolysis-gas from gasification
Carnot cycle• 1 – 2 process is isentropic
compression needs work to be fed (win)
• 2 – 3 process is isothermal heat feeding (qin)
• 3 – 4 process is isentropic expansion work is generated (wout)
• 4 – 1 process is isothermal heat-removal (qout)
=−=−=−=in
out
in
outin
in
inoutC q
q1
q
q
wwη2
1
122
121 1)(
)(1
T
T
SST
SST −=−−−
CoCo--GenerationGeneration parallel parallel heatheat and and electricityelectricity generationgeneration
Rankine steam-cycle the most traditional one
Simple Rankine cycle - - theoretical and ___ realefficiency variation with maximal pressure
at 30ºC (red) and at 120ºC (blue) cond. temp.
20 40 60 80 100 120 140 160 180 200
10
20
30
40
50
p
[%]
[bar]
Cogeneration with Rankine cycle
Backpressure steam turbine
A CHP system using a backpressure steam turbine consists of: a boiler, the turbine, a heat exchanger and a pump
• Heat supply driven operation
• The total efficiency of a backpressure steam turbine CHP system is the highest.
• When an efficient boiler is used, the overall thermal efficiency of the system can reach 90%.
�Extraction - condensing steam turbine
• More flexible operation, higher electricity generation share • These turbines have higher power to heat ratio in comparison to backpressure
case • Overall thermal efficiency< that of backpressure turbine system (exhaust heat
cannot be utilized - normally lost in the cooling water circuit).
Rankine cycle based coneneration system
Application of Rankine cycle based cogeneration operated with water/steam
Any combustible, even waste materialsApplicable fuels
Only in large or medium size systems where steam is inevitable necessary
Application
Pressure increase brings parallel higher initial and operational cost
Profitability
Depending on fuel CO, NOx, SO2, particulate, can be kept at low level
Pollutant emission
~90% nearly equal with boiler efficiency
Possible overall efficiency
65% - 88%Possible efficiency of heat utilization
2% - 25% depending mainly on pressure drop level
Efficiency of electricity generation
Properties ORC mediavs. Steam
Commonly usedORC working fluidsand cycle efficiency variations
Application ranges of different fluids in case of radial inflow turbine application
Organic Rankine Cycle (ORC)
Advanced ORC process based cogeneration
Energy flow chart of the ORC process
ORC plant
ORC processwhole module fixed in a container
Application of ORC system based cogeneration
Any combustible, even waste materialsApplicable fuels
Small and medium power rate systems (Prefabricated systems available nowadays in the range of 200 kWe – 2 MWe)
Application
Temperature increase brings parallel higher initial and operational cost
Profitability
Depending on fuel CO, NOx, SO2, particulate, can be kept at low level
Pollutant emission
75% - 85% Possible overall efficiency
65% - 75%Possible efficiency of heat utilization
10% - 20% depending on input and output temperature levels
Efficiency of electricity generation
Geothermal energyGeothermal energy utilisationutilisation
Geothermal energy generation with ORC system
Geothermal energy generation with ORC system
Application of geothermal energy generation with ORC system
None!Applicable fuels
In medium sized heating systemsApplication
Drilling of wells is very expensive.
Re-injection of geothermal water needs a lot of pumping work.
Profitability
None!Pollutant emission
30% - 50% Possible overall efficiency
20% - 40%Possible efficiency of heat utilization
8% - 12% depending on temperature levels, min. 80ºC temperature difference is necessary
Efficiency of electricity generation
� Cogeneration with Internal Combustion Engines (ICEs)• IC engines:
� are mostly used in low and medium power CHP units;
� have higher electrical efficiency compared to other prime movers, but the thermal energy produced is not easily used (due to its lower temperatures it is dispersed between exhaust gases and engine cooling systems).
• IC engines can be: spark ignition (Otto-cycle) or compression ignition (Diesel-cycle)
Schematic diagram of cogeneration with an internal combustion engine
�Advantages (relative to other CHP technologies):
� low start-up and operating costs;
� reliable onsite and clean energy;
� ease of maintenance;
�wide service infrastructure.
Operation principal of the 4 stroke
engine
Efficiency variation of Otto and Diesel cycle
Real cycles
Otto Diesel
Complex cogeneration system with IC engine
Energy flow diagram of the gas engine
Application of IC engine based cogeneration
Only liquid or gaseous clean fuel can be applied, it is very sensitive to fuel quality because of periodical short time combustion
Applicable fuels
Small and medium sized systems.Application
Fast start up can be performed, can be applied as emergency electricity supply system.
Frequent maintenance is necessary.
Profitability
Depending on fuel, CO, SO2, NOx generally the highest comparing with other methods
Pollutant emission
80% - 90% Possible overall efficiency
40% - 50%Possible efficiency of heat utilization
30% - 50%Efficiency of electricity generation
Externally Fired Stirling engine
Stirling cycle
Operation of Stirling engines
Stirling engine for biomass firing
Example for Stirling engine installation
Application of Stirling engine based cogeneration
Any even soild fuel can be applied.Applicable fuels
In small and medium scale systemsApplication
Few available application, system is under development.
Profitability
Depending on the fuel, CO, SO2, particulate, NOxPollutant emission
70% - 80% Possible overall efficiency
40% - 50%Possible efficiency of heat utilization
~ 30% Efficiency of electricity generation
� Cogeneration with gas turbine
⇒Two main categories of gas turbines:
• aero-derivative turbines (modified versions of the original aircraft turbines):
� Main characteristics: low specific weight, low fuel consumption, high reliability.
� Advantages: high levels of efficiency, compact design, easy access for maintenance.
� Disadvantages: relatively high specific investment cost, high quality fuel, alowering in output and efficiency after a long period of operation.
• industrial gas turbines (robust units for stationary duty and continuous operation)
Operational flow chart of a micro gasturbine based cogeneration system
Micro gasturbine based cogeneration system
Application of gasturbine based cogenerationOnly liquid or gaseous clean fuel can be applied,
but less sensitive to fuel quality than IC engines because of continuous combustion
Applicable fuels
In medium sized energy supply systems.Application
Fast start up can be performed, can be applied as emergency electricity supply system.
Less maintenance demand comparing with IC engines.
Profitability
Depending on fuel, CO, SO2,NOx generally more than in case of firing in boilers
Pollutant emission
75% - 85% Possible overall efficiency
47% - 55%Possible efficiency of heat utilization
28% - 38%Efficiency of electricity generation
Externally fired gasturbine (EGT)
Externally fired gasturbine (EGT) cycle
Application of EGT based systemsIt can be operated even with solid fuels.
(This is the main aim of applications.)
Applicable fuels
In small and medium sized systems.Application
Hot air heat-exchanger is critical part.
Has to be proofed to high temperature.
Sensitive to pollutions and deposits.
Profitability
Depending on the fuel, CO, SO2, particulate, NOxPollutant emission
~ 80% Possible overall efficiency
45% - 55%Possible efficiency of heat utilization
25% - 35%Efficiency of electricity generation
� Cogeneration with combined cycle
• CHP with combined cycle = Combination of different CHP types:
� The gas turbine - steam turbine combination is the most common one!
• Supplementary firing can increase the flexibility of the system, but in case of application reduce electrical efficiency.
Combined cycle principals
Efficiency of combined cycle:
in
.steamGT
tot
Q
PP +=η
Efficiency of gasturbine:
in
.GT
GT
Q
P=η
Efficiency of steam cycle: ε
η⋅
=transfer
.steam
steam
Q
P
Where input heat to the steam cycle: letminstea
.
transfer
.
QQ =⋅ε
Total efficiency of combined cycle
( )GTin
.
GTin
.
transfer
.
1QPQQ η−=−=
( )GTin
.
transfer
.
letminstea
.
1QQQ ηεε −⋅=⋅=
Psteam= ( )GTin
.
steamletminstea
.
steam 1QQ ηεηη −⋅⋅=⋅
( )in
.GTin
.
steamGTtot
Q
1QP ηεηη −⋅⋅+=
⋅−+= εηε
ηηηη steam
GT
steamGTtot 1
Examples:
8,0
3,0
3,0
GT
steam
==
=
εηη
47,0tot =η
9,0
38,0
35,0
GT
steam
==
=
εηη
ηtot = 0.575
Expected development of power generation
Application of combined cycles
Only liquid or gaseous clean fuel can be applied,
but less sensitive to fuel quality than IC engines because of continuous combustion
Applicable fuels
In large scale systems principally for electricity generation
Application
Complex but efficient system with high initial costProfitability
Depending on fuel, CO, SO2,NOx generally more than in case of firing in boilers
Pollutant emission
50% - 90% Possible overall efficiency
0% - 40%Possible efficiency of heat utilization
50% - 60%Efficiency of electricity generation
Summary of biomass conversion technologies
Schematic diagram of a wet biogas system
Dry Biogas Fermentation
System
Dry Biogas Fermentation System
Gasifier example with auxiliary systems
Electrical efficiency increase possibilities of IGCC systems
Application of IGCC systems
Solid fuels, coal or biomass Applicable fuels
In large scale systems principally for electricity generation
Application
Very complex but efficient system with very high initial cost
Profitability
Depending on the fuel, CO, SO2, particulate, NOxPollutant emission
50% - 85% Possible overall efficiency
0% - 40%Possible efficiency of heat utilization
45% - 55%Efficiency of electricity generation
Fuel cell
Operation principal of fuel cells:
Fuel cell operationprincipal
�Fuel cells
• They generate electricity by electro-chemical reaction directly from the fuel based on the oxidation of H2
• A typical single cell delivers up to 1 V.
• The fuel cell generates heat also, which can be utilized.
• Electrical efficiency can reach 40-70% depending on cell type.
• End product is pure water
Polymer Electrolyte Membrane (PEM) Fuel Cells• Polymer electrolyte membrane (PEM) fuel cells—
also called proton exchange membrane fuel cells—deliver high power density and offer the advantages of low weight and volume, compared to other fuel cells. PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum catalyst. They need only hydrogen, oxygen from the air, and water to operate and do not require corrosive fluids like some fuel cells. They are typically fueled with pure hydrogen supplied from storage tanks or onboard reformers.
• Polymer electrolyte membrane fuel cells operate at relatively low temperatures, around 80°C. Low temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, it requires that a noble-metal catalyst (typically platinum) be used to separate the hydrogen's electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to CO poisoning, making it necessary to employ an additional reactor to reduce CO in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This also adds cost. Developers are currently exploring platinum/ruthenium catalysts that are more resistant to CO.
Advantages and benefits of Fuel Cells for
Combined Heat & Power Applications• Distributed generation of heat and power– this can lead
to considerable long term cost savings • Effective use of heat at the point of use– increasing
overall system efficiency • Continuous stack efficiency across variable loads• Reduced frequency of maintenance and routine
shutdowns• Security of supply– the grid is not relied upon and can be
used as backup • Negligible NOx, SOx and particulates means fuel cells
can be installed almost anywhere– e.g. next to playgrounds and on rooftops
• Very low noise and vibrations reduces the need for sound proofing and insulation- saving money
• Fuel Diversity – including natural gas, waste water treatment gas, bio gas and syngas
Problems with fuel-cell application
• H2 is used as fuel can be derived from natural gas, propane or coal, but these are fossil fuels
• Or it can be gained from biomass,• Or through electrolysis from wind or solar
energy• So hydrogen is not an original energy
resource, only an energy storage medium • Further problem is that Hydrogen storage
and supply can not be handled with existing fuel supply systems, new supply system has to be developed.
Residential applicationpossibility of fuel cell
Fuel cell application based on natural gas
Example for residential fuel cell based energy supply center
• Net electrical power output: 2 kWe
• Net electrical efficiency: 28% - 32%
• Net thermal power output:5 kWth
• Overall efficiency:76% - 85%
Application of fuel cell based cogeneration
Basically Hydrogen.Hydrogen can be gained from different resources.
Applicable fuels
In small and medium scale systems.Application
Few available application, systems are under further development.
Available systems are expensive.
Profitability
None, only H2O and CO2Pollutant emission
75% - 85% Possible overall efficiency
45% - 55%Possible efficiency of heat utilization
~ 30% - 60% Efficiency of electricity generation
� Tri-generation systems
CHCP-Combined Heat, Cooling & Power production:
• For space cooling of buildings in the residential, commercial or industrial sector.
• Heat-driven district cooling, requiring heat mainly in summer, can help to balance the seasonal demands for cogenerated heat.
• This increases the overall efficiency of the system.
Tri-generation with absorption chiller
• The absorption refrigerator is a refrigerator that utilizes a heat source to provide the energy needed to drive the cooling system.
• Absorption refrigerators are a popular alternative to regular vapor-compression refrigerators where electricity is unreliable, costly, or unavailable, where noise from the compressor is problematic, or where surplus heat is available (e.g. from turbine exhausts or industrial processes).
Comparison of vapor compression and
absorption chillers
1 kW1 kWCooling capacity
0,25 - 0,33 kWe1,3 – 1,7 kWthInput power
Mechanical power, generally electricity
Heat energyEnergy input
3 – 40,6 – 0,8Coefficient of performance (COP)
Vapor compression cooling
Absorption cooling
System fitting to demand variation
• Efficient cogeneration can be reached when overall efficiency for the season is high enough.
• That is why necessary to utilize as much heat as possible.
• The best method is to adjust system operation to heat demand variation.
• Electricity generation has to be only a useful „byproduct”.
• Electricity generation by any means would lead to waste of energy
• Last but not least, profitability has to be taken into account.
Heating and air-conditioning demand variation over a year in Europe
Load-duration curve of the heating season in temperate climatic zone
Cogeneration system example with ORC
Annual operation of the previous CHP system