Micro Scale Energy Generation Combined Heat and...

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

qq

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

Thank You for Your Attention !

Dr. Ferenc Lezsovitslezsovits@energia.bme.hu