cogeneration chp (combined heat and power) - …€¢ enclosure: to achieve physical and...

CogenerationCogenerationCHP (combined heat and CHP (combined heat and

power)power)

Gabriel Pita

•Introduction

•Types of cogeneration systems

•Assessment of cogeneration systems

•Energy efficiency opportunities

• Generation of multiple forms of

energy in one system: heat and

power

What’s a Cogeneration/CHP System?

IntroductionIntroduction

power

• Defined by its “prime movers”• Reciprocating engines

• Combustion or gas turbines,

• Steam turbines

• Microturbines

• Fuel cells

When to consider using Combined Heat & Power

(CHP)

CHP should always be considered when:

• designing a new building,

• installing new boiler plant,

• replacing/refurbishing existing plant, • replacing/refurbishing existing plant,

• reviewing electricity supply,

• reviewing standby electrical generation capacity or

plant,

• considering energy efficiency in general.

In a cogeneration system we have to consider the

following elements:

• Primary energy fuel (natural gas, liquid fuel, solid fuel, industrial

waste, biomass, etc.).


• Motor element supplier of mechanical work to the shaft (the gas

turbine, steam turbine, reciprocating engine)

• System to capture the heat energy (conventional boiler, recovery

boiler, dryer, refrigerator cycle absorption ,heat exchanger in

general)

• System to transform the mechanical energy (electric generator,

mechanical drives, etc..)

Components of Combined Heat & Power (CHP)

All CHP schemes consist of a number of core components with variations to

suit the particular application. The fundamental components are:

• Prime mover: an engine to drive the generator

• fuel system

• generator: to produce electricity, which is fed into the building's

power distribution system power distribution system

• heat recovery system: to recover usable heat from the engine

• cooling system: to dissipate heat rejected from the engine that cannot

be recovered

• combustion and ventilation air systems: to supply fresh air to, and

carry exhaust gases away from, the engine,

• control system: to maintain safe and efficient operation

• enclosure: to achieve physical and environmental protection for the

engine and operators, and to reduce noise.

First law of Thermodynamic

The law of conservation of energy

• Heat and work are forms of energy transfer.

• Energy can be neither created nor destroyed.

However, energy can change forms

It is impossible to produce work in the surroundings

Second law of ThermodynamicIt is impossible to produce work in the surroundings

using a cyclic process connected to a single heat

reservoir (Kelvin)

Efficiency Advantage of CHP


P1 €/kWh electric energy ; P2 €/kWh fuel

Cm operating , maintenance and amortization costs /kWh

Energy savings 154-100 = 54

Cost savings 30*P1+56*P2-(100*P2+30*Cm)= 30*(P1-Cm)-44*P2

• Increased efficiency of energy conversion and

use

• Lower emissions, especially CO2

Benefits of Cogeneration / CHP


• Lower emissions, especially CO2

• Ability to use waste materials

• Large cost savings

• Opportunity to decentralize the electricity

generation

• Promoting liberalization in energy markets

Problems associated with cogeneration

Being cogeneration thermodynamically so attractive why their use is not more

widespread ?

The reasons are mainly economic .

1 - If an industry decides to invest in cogeneration is bound to a course of action for

a specified number of years . The project that will finance this project involves a

number of assumptions in the energy needs of the company , fuel prices and


number of assumptions in the energy needs of the company , fuel prices and

availability , interest , maintenance costs , etc ..

2 - Any change in the manufacturing process may result in the need for subsequent

heat or work over a much greater cost than the initial installation.

3 -Any change in the manufacturing process can result in a change in the

proportion of heat / work . With the consequent change in the overall efficiency

of the installation and thus their economic viability .

4 - The need to ensure an emergency system to provide heat and work . This system

is not being heavily used is not able to repay the capital invested .

5 -The problems of noise and pollution may require an extra investment when

regulations are becoming increasingly stringent .

CHP Applications

CHP technology exists in a wide variety of energy-intensive

facility types and sizes, including:

•Industrial manufacturers - chemical, refining, ethanol, pulp and

paper, food processing, glass manufacturing


paper, food processing, glass manufacturing

•Institutions - colleges and universities, hospitals, prisons,

military bases

•Commercial buildings - hotels and casinos, airports, high-tech

campuses, large office buildings, nursing homes

•Municipal - district energy systems, wastewater treatment

facilities, K-12 schools

•Residential - multi-family housing, planned communities


30

40

50

60

70

Combined heat and power generation

% of gross electricity generation

1994

1996

1997

1998

2000

0

10

20

2000

2002

2004

2005

2006

2007

2008

2009

2010

2011

Trigeneration or combined cooling, heat and

power (CCHP)

Simultaneous generation of

electricity and useful heating

and cooling from the

combustion of a fuel or a


combustion of a fuel or a

solar heat collector. A plant

producing electricity, heat

and cold is called a

trigeneration


Cogeneration technologies covered by Directive 2004/8/EC

(a) Combined cycle gas turbine with heat recovery

(b) Steam backpressure turbine



(c) Steam condensing extraction turbine

(d) Gas turbine with heat recovery

(e) Internal combustion engine

(f) Microturbines

(g) Stirling engines

(h) Fuel cells

(i) Steam engines

(j) Organic Rankine cycles

(k) Any other type of technology or combination there of falling under the

definition laid down in Article 3(a)

• Steam turbine

• Gas turbine

• Reciprocating engine

• Other classifications:

Type of Cogeneration SystemsType of Cogeneration Systems

• Other classifications:

- Topping cycle

-Bottoming cycle

• Micro combined heat and power

Steam Turbine Cogeneration System

• Widely used in CHP applications

• Oldest prime mover technology


• Capacities: 50 kW to hundreds of MWs

• Thermodynamic cycle is the “Rankin cycle” that uses a

boiler

• Most common types

• Back pressure steam turbine

• Extraction condensing steam turbine

• Steam exits the turbine at a higher pressure that the

atmospheric

Back Pressure Steam Turbine

HP Steam Advantages:

-Simple configuration


Disadvantages:

-Larger steam turbine

-Electrical load and output can

not be matched

Fuel

Boiler Turbine

ProcessCondensate LP

Steam

-Simple configuration

-Low capital cost

-Low need of cooling water

-High total efficiency

• Steam obtained by

extraction from an

intermediate stage

• Remaining steam is

Extraction Condensing Steam

Turbine

Boiler Turbine

HP Steam

Fuel


• Remaining steam is

exhausted

• Relatively high

capital cost, lower

total efficiency

• Control of electrical

power independent of

thermal load

Process

LP Steam

Condensate

Condenser

Fuel

• Operate on thermodynamic “Brayton cycle”

• atmospheric air compressed, heated, expanded

• excess power used to produce power

• Natural gas is most common fuel

Gas Turbine Cogeneration System


• 1MW to 100 MW range

• Rapid developments in recent years

• Two types: open and closed cycle

• Open Brayton cycle:

atmospheric air at

increased pressure to

combustor

Open Cycle Gas Turbine

HRSG

Exhaust

Gases

Condensate

from Process

Steam to

Process• Old/small units: 15:1

New/large units: 30:1


Air

G

Compressor Turbine

Combustor

Fuel

Generator

Process

New/large units: 30:1

• Exhaust gas at 450-

600 oC

• High pressure steam

produced: can drive

steam turbine

• Working fluid circulates

in a closed circuit and

does not cause

corrosion or erosion

Closed Cycle Gas Turbine

Heat Source

Heat Exchanger


corrosion or erosion

• Any fuel, nuclear or

solar energy can be

used

G

Compressor Turbine

Generator

Condensate

from Process

Steam to

Process

• Used as direct mechanical drives

Reciprocating Engine Cogeneration

Systems

• Many advantages:

operation,


operation,

efficiency, fuel

costs

• Used as direct

mechanical drives

• Four sources of

usable waste heat


Combined cycleThe principle is that the exhaust of one heat engine is used as the heat source for

another, thus extracting more useful energy from the heat, increasing the system's

overall efficiency

gas turbine-based trigeneration facility.250 MW combined cycle cogeneration

power facility (85% total efficiency)

Cogeneration systems are normally classified

according to the sequence of energy use and the

adopted operating schemes.

A cogeneration system can be classified as either a

topping or a bottoming cycle on the basis of the

sequence of energy use


sequence of energy use

• Supplied fuel first produces power

followed by thermal energy

• Thermal energy is a by product

used for process heat or other

• Most popular method of

Topping Cycle


•

cogeneration

• In a topping cycle, the supplied fuel is used to first produce power and then

thermal energy, which is the by-product of the cycle. This is used to satisfy

process heat or other thermal requirements. Topping cycle cogeneration is

widely used and is the most popular method of cogeneration.

• Examples include a combined-cycle topping system; steam turbine topping

system; and gas turbine topping system


Bottoming Cycle

• Primary fuel produces high

temperature thermal energy

• Rejected heat is used to

generate power

• Suitable for manufacturing •

processes

• In a bottoming cycle, the primary fuel produces high temperature thermal

energy and the rejected heat from the process is used to generate power

through a recovery boiler and a turbine generator.

• Bottoming cycles are suitable for manufacturing processes that require heat at

high temperature in furnaces and kilns, and that reject heat at significantly high

temperatures. Typical areas of application include cement, steel, ceramic, gas

and petrochemical industries.

Micro combined heat and power or micro-CHP


A micro-CHP system is a small heat engine (power plant) which provides all the

power for an individual building; heating, ventilation, and air conditioning,

mechanical energy and electric power. It is a smaller-scale version of cogeneration

schemes which have been used with large scale electric power plants.

It is not practical to transport heat long distances, due to heat loss from the

pipes. Since electricity can be transported practically, it is more efficient to generate

the electricity near where the waste heat can be used. So in a "micro-combined

heat and power system" (micro-CHP), small power plants are instead located where

Micro combined heat

and power or micro-CHP


For three decades, these larger CHP systems were more economically justifiable

than micro-CHP, due to the . After the year 2000, micro-CHP has

become cost effective in many markets around the world, due to rising energy

costs. The development of micro-CHP systems has also been facilitated by recent

technological developments of small heat engines. This includes improved

performance and cost-effectiveness of

.

heat and power system" (micro-CHP), small power plants are instead located where

the secondary heat can be used, in individual buildings. Micro-CHP are defined by

the EC as being of less than 50 kW electrical power output.

http://youtu.be/s5S0seVAGY4

Power to Heat ratio of a cogeneration unit


"power to heat ratio" shall mean the ratio between electricity from cogeneration

and useful heat when operating in full cogeneration mode using operational data

of the specific unit;

Assessment of Cogeneration SystemsAssessment of Cogeneration Systems

Total System Efficiency

(Energy Utilisation Factor)



Directive 2004/8/EC of the European Parliament and of the Council of 11

February 2004 on the promotion of cogeneration based on a useful heat

demand in the internal energy market and amending Directive 92/42/EE

Values used for calculation of electricity from cogeneration shall be determined on the basis of the

expected or actual operation of the unit under normal conditions of use. For micro- cogeneration

units the calculation may be based on certified values.

(a) Electricity production from cogeneration shall be considered equal to total annual electricity

production of the unit measured at the outlet of the main generators;

(i) in cogeneration units of types (b), (d), (e), (f), (g) and (h) referred to in Part II with an annual(i) in cogeneration units of types (b), (d), (e), (f), (g) and (h) referred to in Part II with an annual

overall efficiency set by Member States at a level of at least 75 %, and

(ii) in cogeneration units of types (a) and (c) referred to in Part II with an annual overall efficiency

set by Member States at a level of at least 80 %.



(c) Steam condensing extraction turbine

(d) Gas turbine with heat recovery

(e) Internal combustion engine

(f) Microturbines

(g) Stirling engines

(h) Fuel cells

Cogeneration technologies covered by Directive 2004/8/EC

Effective Electric Efficiency

EE

Electricity - 3 0 Units

Heat - 45 Units

Fuel - 100 Units

Effective electric efficiency (ξEE) where (WE) is the net useful power output, (ΣQTH) is

the sum of the net useful thermal outputs, (QFUEL) is the total fuel input, and ∝ equals

the efficiency of the conventional technology that otherwise would be used to

produce the useful thermal energy output if the CHP system did not exist:

For example, if a CHP system is natural gas fired and produces steam, then α

represents the efficiency of a conventional natural gas-fired boiler. Typical a values

for boilers are: 0.8 for natural gas-fired boiler, 0.75 for a biomass-fired boiler, and

0.83 for a coal-fired boiler.

Typical effective electrical efficiencies for combustion turbine-based CHP systems are

in the range of 51 to 69 percent. For reciprocating engine-based CHP systems are in

the range of 69 to 84 percent.

ANNEX III

Methodology for determining the efficiency of the cogeneration process

Values used for calculation of efficiency of cogeneration and primary energy savings

shall be determined on the basis of the expected or actual operation of the unit under

normal conditions of use.

Directive 2004/8/EC of the European Parliament and of the Council of 11

February 2004 on the promotion of cogeneration based on a useful heat

demand in the internal energy market and amending Directive 92/42/EE

(a) High-efficiency cogenerationFor the purpose of this Directive high-efficiency cogeneration shall fulfill the

following criteria:

- cogeneration production from cogeneration units shall provide primary energy

savings calculated according to point (b) of at least 10 % compared with the

references for separate production of heat and electricity,

- production from small scale and micro cogeneration units providing primary energy

savings may qualify as high-efficiency cogeneration.

"micro-cogeneration unit" shall mean a cogeneration unit with a maximum capacity below 50 kWe;

"small scale cogeneration" shall mean cogeneration units with an installed capacity below 1 MWe;

"cogeneration production" shall mean the sum of electricity and mechanical energy and useful heat from cogeneration.

Directive 2004/8/EC

Calculation of primary energy savingsThe amount of primary energy savings provided by cogeneration production defined in accordance

with Annex II shall be calculated on the basis of the following formula:

Where:

• PES is primary energy savings.

• CHP Hη is the heat efficiency of the cogeneration production defined as annual useful heat

output divided by the fuel input used to produce the sum of useful heat output and electricity

from cogeneration.

• Ref Hη is the efficiency reference value for separate heat production.

• CHP Eη is the electrical efficiency of the cogeneration production defined as annual electricity

from cogeneration divided by the fuel input used to produce the sum of useful heat output and

electricity from cogeneration. Where a cogeneration unit generates mechanical energy, the

annual electricity from cogeneration may be increased by an additional element representing the

amount of electricity which is equivalent to that of mechanical energy. This additional element

will not create a right to issue guarantees of origin in accordance with Article 5.

• Ref Eη is the efficiency reference value for separate electricity production.

The efficiency reference, Ref E and Ref Hη , values shall be calculated according to

the following principles:

1. For cogeneration units the comparison with separate electricity production

shall be based on the principle that the same fuel categories are compared.

2. Each cogeneration unit shall be compared with the best available and

The efficiency reference

Directive 2004/8/EC

2. Each cogeneration unit shall be compared with the best available and

economically justifiable technology for separate production of heat and

electricity on the market in the year of construction of the cogeneration unit.

3. The efficiency reference values for cogeneration units older than 10 years of

age shall be fixed on the reference values of units of 10 years of age.

4. The efficiency reference values for separate electricity production and heat

production shall reflect the climatic differences between Member States.

primary energy savings

Electricity - 3 0 UnitsElectricity - 3 0 Units

Heat - 45 Units

Fuel - 100 Units Natural Gas

Cogeneration with Diesel EngineElectricity 40 u

Heat 40 u



work

Diesel

cogeneration

Heat

40.2u

Electricity

40 u

100u

Work

�=40%

Heat 60u

Heat recovering

�=67%

Power to Heat ratio of a

cogeneration unit

primary energy savings

Cogeneration with Diesel Engine

Diesel

cogeneration

Electricity

40 u

100u

Work

�=40% Total System Efficiency


Cogeneration with Diesel EngineElectricity 40 u

Heat 80 u

cogeneration

Heat

40.2u

Heat 60u

Heat recovering

�=67%

Power to Heat ratio of a

cogeneration unit

Heat

39.8u

boiler

�=82%

48.5 uprimary energy savings

400

500

600

Av

era

ge

he

ati

ng

de

ma

nd

(k

W)

Base heat load sizing strategy for CHP plant

CHP Boilers

0

100

200

300

Jan Feb Mar April May June July Aug Sept Oct Nov Dec.

Av

era

ge

he

ati

ng

de

ma

nd

(k

W)

The CHP unit is sized to meet the base heating load. The CHP unit can run all the year around.

The payback period on the initial capital investments is short

Load patterns

Assessment of Cogeneration SystemsAssessment of Cogeneration Systems

EIA: The Energy Information Administration. U.S. Department of Energy

CHP plant sizing strategies

Necessary energy data

•Monthly electricity and heat energy consumption data in kWh

•Base and peak load demands (in kW) for both electricity and heat

•The operational characteristics of a particular application

•Unit cost data for electricity and gas (oil)

•Monthly electricity and heat energy consumption data in kWh


•Base and peak load demands (in kW) for both electricity and heat

40

60

80

100

120

140

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era

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ctri

c d

em

an

d

(kW

)

40

60

80

100

120

140

Av

era

ge

ele

ctri

c d

em

an

d

(kW

)

CHP Grid

Base electric load sizing strategy for CHP plant


0

100

200

300

400

500

600

Av

era

ge

he

ati

ng

de

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nd

(kW

)

0

20

1 2 3 4 5 6 7 8 9 10 11 12

Av

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ctri

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d

0

100

200

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600


Av

era

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(kW

)

CHP Boilers

0

20

40


Av

era

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ctri

c d

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d

Base heat load sizing strategy for CHP plant

The Economics of CHP

Factors that dominate the economic viability of CHP

•The capital cost of the installation

•The potential number of operating hours per year•The potential number of operating hours per year

•The relative costs of “bought in” electricity and gas (or fuel oil)

•The heat to power ratio of a particular CHP plant

•The difference in maintenance costs between a CHP scheme and a conventional scheme

•The cost of having mains electricity as backup system in case of breakdown or maintenance

An existing building has an average electrical demand of 80 kWe and an average

combined heating and hot water demand of 180 kW. The average annual load

factor for the building is 0.75 . The heating and hot water demand is currently

served b two gas fired boilers and mains electricity is bought in. It is proposed to

install a micro–CHP plant which will run on gas and have a heat to power ratio of

1.7:1. The existing boilers will supplement the heat output from CHP unit . If the

initial cost of CHP installation is 90,000.00 € , determine the simple payback period.

Payback= Capital cost /Annual cost saving

Data:

Efficiency of existing boilers = 70%

CHP unit electric power output = 80kWe

CHP unit gas power input = 286kW

Unit cost of gas = 0.06€/kWh

Unit cost of electricity = 0.15€/kWh

Existing plant maintenance cost = 1,200 € per year

CHP scheme maintenance cost = 6,000€ per year


•The capital cost of the installation

load factor 0.75 heat/work 1.7 cost of CHP installation 90000€

Nº hours per year 6570hr € elec 0.06

€ gas 0.01

0

tradicional elec 31536 CHP gas 18790 payback 4.35

gas 16894 boiler 4130

mant 1200 mant 6000mant 1200 mant 6000

total 49630€/year total 28920€/year

savings 20710€/year



€ gas 0.01

0



mant 1200 mant 6000



•The potential number of operating hours per year




€ gas 0.01

0



mant 1200 mant 6000





€ gas 0.01

0



mant 1200 mant 6000




•The relative costs of “bought in” electricity



€ gas 0.01

0



mant 1200 mant 6000




€ gas 0.01

0



mant 1200 mant 6000





•The relative costs of “bought in” gas



€ gas 0.01

0



mant 1200 mant 6000




€ gas 0.011

0



mant 1200 mant 6000




•The heat to power ratio of a particular CHP plant




€ gas 0.01

0



mant 1200 mant 6000





€ gas 0.01

0



mant 1200 mant 6000



•The difference in maintenance costs between a CHP scheme and a

conventional scheme




€ gas 0.01

0



mant 1200 mant 6000


•The cost of having mains electricity as backup system in case of

breakdown or maintenance



€ gas 0.01

0



mant 1200 mant 6600




Cogeneration systems usually considers the investment = the additional capital to

build the cogeneration unit

Annual return (cost savings) the difference between the operating costs of the

traditional system and the costs of the cogeneration system

Payback= Capital cost /Annual cost saving

A refrigeration ton is approximately equivalent to 12,000 BTU/h or 3,517 W.

One therm is equal to about 105.5 megajoulesmegajoules, 25,200 kilocalories or 29.3 kilowatt-hours.

Cost calculations

Total installed system cost $2,581982

Projected annual electric savings - $1,280,123

Generator operating costs $631,792

(including fuel and maintenance )

Net annual cash flow from savings $648,331

Payback period 3.98 years

Advantages and disadvantages of the method.

a) It is simple to apply and favors projects with short payback times, which reduces the

uncertainties to calculate the energy savings for long periods in the future. The effect of

change in technology and changes in fuel prices is also reduced.

b) has the drawback not take account of cash flows (savings) generated after recovered

the capital invested, which makes it inadvisable in the evaluation of long-term projects.the capital invested, which makes it inadvisable in the evaluation of long-term projects.

c) gives no indication of the rate of return on invested capital.

rate of return on investment = (average annual savings) / cost of capital

d) Does not take into account the timing of the return. Does not distinguish whether the

return on investment is done more in the first year or more in the last years, or equally

over the years of payback time.

The NPV criterion is defined by:

t - year

N - number of years of remaining life

i - the discount rate (the rate of return that could be earned on an investment in

the financial markets with similar risk.); the opportunity cost of capital

Rt - the net cash flow i.e. cash inflow – cash outflow, at time t

NPV - Net Present Value

Rt - the net cash flow i.e. cash inflow – cash outflow, at time t

.

If... It means... Then...

NPV > 0 the investment would add value to the firm the project may be accepted

NPV < 0the investment would subtract value from the

firmthe project should be rejected

NPV = 0the investment would neither gain nor lose

value for the firm

We should be indifferent in the decision

whether to accept or reject the project. This

project adds no monetary value. Decision

should be based on other criteria, e.g.,

strategic positioning or other factors not

explicitly included in the calculation.

The IRR of an investment is the discount rate at which the net present value of

costs (negative cash flows) of the investment equals the net present value of

the benefits (positive cash flows) of the investment.

Internal Rate of Return (IRR )

=0

i=IRR

• Prices change over time. One month you're paying x €/kWh, the next month you're

paying y €/kWh. Unfortunately y is usually greater than x, as energy prices typically rise

over time.

• Electricity costs can depend on the time of the day, the day of the week, and the time

of the year. Energy suppliers/utilities come up with complicated tariffs to define these

rules. Just like prices, tariff structures can also change over time.

Electricity costs

rules. Just like prices, tariff structures can also change over time.

• Electricity costs can also depend on the maximum demand, or peak load, across a

period. For example, given half-hourly data for a month, the peak load or maximum

demand could be defined as the half-hour period that had the highest average kW. The

higher the peak load, the higher the peak-load charge (or maximum-demand charge).

• Electricity tariffs often charge different rates depending on how many kWh you use.

For example, the first 100 kWh might cost x €/kWh, the next might cost y €/kWh.

• There are often standing charges - regular fixed fees that aren't related to how much

energy you use.

cogeneration chp (combined heat and power) - …€¢ enclosure: to achieve physical and...

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