4 CHP Plants for Cities

8/14/2019 4 CHP Plants for Cities

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CHP PLANTS FOR CITIES AND INDUSTRIES BENEFICIAL FORTHE ECONOMY AND THE ENVIRONMENT

Harald Dichtl,Business Development Manager,Siemens Power Generation

Introduction:

China faces a great challenge to secure the electricity supply for a steadily growing economy

and at the same time use environmentally friendly technologies. One way to improve the

environmental efficiency of power generation is the simultaneous production of electric

power and heat (Combined Heat and Power = CHP, synonymous with cogeneration). It is a

prerequisite for CHP plants that there are users for the waste heat, as heat cannot be stored or

transported over distances. In China there are more than 300 cities with a district heating

infrastructure and a daily growing number of industrial facilities with power and heat demand.

Therefore China can benefit substantially from the advantages of CHP plants: fuel saving,

fewer emissions of carbon dioxide and other pollutants.

CHP Technology

CHP plants can be based on different technologies. Each technology has different properties

in terms of fuel, power to heat ratio, electrical efficiency and heat quality.

In the small power range (less than 10 MW) piston engines are the widest spread technology.

In the higher power range (more than 10 MW) steam and combustion turbines are the

dominant technology. Generally the boundary conditions like the availability of fuel (such as

coal, natural gas, waste gases and oil), fuel prices, power and heat demand curve define the

power generation technology.

The standard solution for CHP in China is coal-fired power plants, which use the waste heat

from the steam process. This process is well proven and profits from advanced combustion

and turbine technology.

Siemens AG 2005. All rights reserved.


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If natural gas is available for power generation, the most efficient CHP solution in terms of

environmental efficiency is a combined cycle power plant. This type of power plant is very

flexible in terms of the ratio of power and heat output.

In terms of total efficiency (the sum of electricity and useful heat divided by fuel input) all

cogeneration technologies can reach very high efficiencies of up to 90% and more, provided

the boundary conditions like heat level, return condensate temperature and heat load curve are

appropriate for the respective technology. The following table shows a range of CHP

technologies and their properties.

PRIMEMOVER

FUEL USED SIZERANGE(MWe)

HEAT:POWERRATIO

ELECTRICALGENERATINGEFFICIENCY

TYPICALOVERALLEFFICIENCY

HEAT QUALITY

EXTRACTIONSTEAMTURBINE

ANY FUEL 1 to 300+ 3:1 to8:1+

20 35% UP TO 90% STEAM ATMULTIPLEPRESSURELEVELS

BACKPRESSURESTEAMTURBINE

ANY FUEL 0.5 to500

3:1 to10:1+

20 - 35% UP TO 90% STEAM ATMULTIPLEPRESSURELEVELS

COMBINEDCYCLE GASTURBINE

GASBIOGASGASOILLFOLPGNAPHTHA

3 to 300+ 1:1 to3:1*

35 55% 70 - 90% MEDIUM GRADESTEAMHIGHTEMPERATUREHOT WATER

OPEN CYCLEGASTURBINE

GASBIOGASGASOILHFOLFOLPGNAPHTHA

0.25 to50+

1.5:1 to5:1*

25 42% 65 90% HIGH GRADESTEAMHIGHTEMPERATUREHOT WATER

COMPRESS.IGNITIONENGINE

GASBIOGASGASOILHFOLHONAPHTHA

0.2 to 20 0.5:1 to3:1*

Alfavalue0.9-2

35 45% 65 - 90% LOWPRESSURESTEAMLOW ANDMEDIUMTEMPERATUREHOT WATER

SPARKIGNITIONENGINE

GASBIOGASLHONAPHTHA

0.003 to6

1:1 to 3:1 Alfavalue0.9-2

25 - 43% 70 90% LOW ANDMEDIUMTEMPERATUREHOT WATER

* Highest heat to power ratios for these systems are achieved with supplementary firing.

From this chart it can easily be seen that there is no right or wrong CHP technology, all

technologies cover a market segment which is defined by fuel, size or heat level. One of the

main differentiators for environmental efficiency of a plant is the heat to power ratio. This

ratio describes how much electrical power a plant produces in relation to the heat output. The



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following chart shows in an example, what kind of output can be produced with three typical

CHP plants of different technologies. For the example a fuel input of 100 MW for each plant

was assumed.

PG I5 Presentation06.06.2005 Power Generation 12PG I5BD

Industrial Applications

Typical Power and Heat Output of CHP Power Plant Concepts

0

20

40

60

80

100

120

SteamTurbine

GT Cogen CC Cogen

M W

LossesHeat

El. Power

All fuel s Gas/Oil Gas/Oil

With the same heat input, GT and CC power plants yield more electric power

The appropriate heat to power ratio for a specific application is defined by the demand profile for heat and

power. Demand profiles are characterized by a full load demand and daily or seasonal load variations.

Therefore it is necessary to choose carefully the right plant type and specifications with regard to the load

profile.

With the same total efficiency, the plant with the lower heat to power ratio has the better

environmental efficiency due to the higher exergy value of electricity compared to heat. The benefit of CHP plants can be seen if the CO2 emission of a CHP plant is compared to the

separate generation of electricity and heat by means of the best available technology. If

natural gas is available, the best available technology for power generation is a large-scale

combined cycle power plant with a net efficiency of 57.5%. The best available technology for

heat generation is a gas fired boiler with 90% efficiency. In order to produce the same amount

of electricity and heat, a typical modern Combined Cycle CHP plant (50% electrical

efficiency and 85% total efficiency) uses 20% less fuel and consequently emits 20% less CO2



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than separate power and heat generation plants. In this example it is assumed that the plant

operates at full power and heat load for 8000 hours per year.

CCPP BoilerTotal Separate

Generation CCPP CHPel. Power MW 70 70 70Heat MW 50 50 50Fuel Input MW 122 56 177 140GHG emissions t/a 194783 88889 283671 224000

It has to be mentioned that these favorable results can only be reached if the heat load is

constant enough to reach a high number of annual full load hours for heat delivery. If the heat

load is not as constant as in the previous example, the advantage will be smaller. But with a

heat load of more than 3000 full load hours per year, a CHP plant provides lower fuel

consumption and CO2 emissions than separate generation.

The standard solution for CHP in China is coal fired power plants, which use the waste heat

from the steam process. This process is well proven and profits from advanced combustion

and turbine technology. The heat to power ratio of this plant type is relatively high, i.e. most

of the fuel input is converted into heat. With urban and industrial development, the power

demand rises much faster than the heat demand, which means the heat to power ratio of the

CHP plants should be lower to guarantee a constant heat load for the plant.

One possibility to modify coal fired plants for higher efficiency and more electricity

production is a so-called repowering, the addition of a gas turbine with heat recovery boiler

and the use of the heat in the existing steam process. Of course this requires the availability of

natural gas on site.

In the following, this paper will focus on Combined Cycle Power Plants, which are, in terms

of environmental efficiency, the favorable solution in the larger (> 20 MW) power scale.



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Fig. 4, Combined Heat and Power Process with a Combined Cycle Power Plant

Siemens offers turnkey solutions for combined cycle power plants in all power ranges. If used

as a CHP plant, combined cycle power plants can generate heat levels from 50 up to 500 deg

C, with a high flexibility of power and heat generation.



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Fig. 4, Siemens Industrial Combined Cycle Plant Portfolio

Application examples

In October 2003, Gteborg Energi and Siemens Power Generation Industrial Applications

signed a contract regarding the construction of a new cogeneration power plant of the

combined-cycle SCC-800 at Rya, Gothenburg. The assignment pertains to a cogeneration

power plant with three SGT-800 lines, plus the capability to add another line in the future.

According to the project schedule, the power plant will be ready for test operations during

November 2006. Behind the decision to build this plant is an increasing demand for bothelectricity and district heating in Gothenburg.



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Fig.5, Combined Cycle Power Plant at Rya, Gothenburg

In 2003, Siemens Power Generation Industrial Applications received the order for a turnkey

modernization of a combined heat and power station for the Erlangen municipality

(Stadtwerke Erlangen) in the south of Germany. The SCC-400 (20 MW el) combined cycle

power plant will be used as an extension of an existing coal fired district heating plant. The

power and heat demand profile requires high plant operational flexibility. During the summer

period only a minimum heat output is required (


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In China the savings of CO2 emissions can be converted into financial benefit if the project

complies to the rules of the CDM (Clean Development Mechanism), one of the instruments of

the Kyoto Protocol. A certified CDM project produces so called CERs (Certified Emission

Reductions) which can be traded on a global basis, for example in the European Emissions

Trading System. CHP projects are usually very suitable for this mechanism. In any case it is

very important that every project needs to be evaluated individually for applicability for

CDM. If certified, a considerable income stream for a CHP plant can come from reduced

emissions, amounting to as much as 10% of the electricity sales.


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4 CHP Plants for Cities