The creation of Gothenburg’s district heating system is the city’s biggest environmental project ever. Its foundationswere laid as long ago as the early 1980s. The latest development in the story is the new Rya Combined Heat andPower (CHP) Plant. The plant will meet around 35% of Gothenburg’s district heating demands and 30% of itspower requirements. The CHP plant is a combined cycle plant fired by natural gas. Combining a gas turbine cyclefor power production with a steam turbine cycle for power and heat production results in a plant with a very highlevel of overall efficiency. Thanks to this plant, the city’s heat and power supplies will be secure for a long time tocome. The plant also offers improved reliability, which means that we will be able to maintain supply to keyfunctions in Gothenburg, even in the event of major power failures in the national grid.

badlarsdiagram

Gothenburg’s

most important

environmental project

Photo: Liljewall arkitekter ab

A flexible solution for the future

Göteborg Energi, the municipal energy utility for the cityof Gothenburg, currently produces very little power, con-sidering the large heat basis that can be used for CHP(combined heat and power) production. By means of effi-cient CHP production using natural gas, we can reduceour marginal purchases of power from abroad, which wemake in Sweden throughout the year. The Rya CHPPlant can thus replace other plants in northern Europewhich produce coal-fired condensing power. Such pro-duction is environmentally undesirable in terms of itsemissions of carbon dioxide and acid pollutants. The Ryaplant is also fully in line with the ambitions of theSwedish Parliament and the EU to work for an increasedproportion of CHP plants in energy generation systems.

The construction of the Rya CHP Plant reducesGothenburg’s dependence on external power supplies.Gothenburg has chosen to use natural gas as the primaryfuel, with the option of supplementing it with biogas orsynthetic gas in the future. However, this would requiresome modifications to be made.

The plant can be operated in several different modes,depending on how much power or heat is required.

Well placed in terms of infrastructureIts location in the Rya dock area means that the Rya CHPPlant is well placed in terms of infrastructure. It is situa-ted close to existing district heating and natural gas pipe-line connections.

Its proximity to a stable high-voltage power network inHisingen is also a clear advantage. A lot of work is beingdone to design the connecting systems in an optimal way.The proximity to the river also makes it possible to coolaway surplus heat from the power production processwhich would normally be used in the district heating net-work. Power generation could then take place in so-called‘island mode’, which is an important factor for the securi-ty of the power supply.

This is what Gothenburg’s district heating demand looks like over the year.

The Rya CHP Plant can operate in several different modes, depending on demand.

Variable production costs, öre/kWh

Hydropower

CHP(industrial)

Nuclear power

CHP(districtheating)

Coal condensing power

Electricity generation capacity, TWh/year Total Nordic power consumption Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecDi

stri

ct h

eati

ng, M

W

Oil

Natural gas

Heat pumps

Biofuels

Natural gas, CHP

Rya CHP Plant

Refinery waste heat

Waste incineration

In what sense is coal power “marginal”? When we increase our power generation capacity, using more efficient and less expensive generation from

combined heat and power plants, we reduce imports of the more costly power that is produced in coal condensing plants (on the right of the diagram).

The Rya CHP Plant overlooks the River Göta. Because of the generous use of glass,

the machine hall is on clear view. In the evenings, in particular, the illuminated plant

and silhouetted chimney are a magnificent addition to the Hisingen skyline.

Future heat production in Gothenburg, including the Rya CHP Plant

Waste incineration 29%

Refinery waste heat 26%

Rya CHP Plant 29%

Natural gas in other CHP plants 5%

Biofuels 6%

Heat pumps 4%

Natural gas in hot water boilers

1% approx.

Oil <1%

Photo: Liljewall arkitekter ab

The plant’s environmental impact on Gothenburg itselfwill be very low. When the Rya CHP Plant enters ser-vice, less use will be made of older district heating plantswith poorer environmental profiles. In spite of the in-crease in power production in Gothenburg, emissions ofacid pollutants, sulphur and nitrogen oxides will actual-ly decrease. The plant also blends in well with the exis-ting industrial area and nearby countryside.

Low emissions mean better air for GothenburgThe flue gases are cleaned in a catalyser (usingSCR/Selective Catalytic Reduction technology), redu-cing the level of nitrogen oxides (NOx) to well under 20mg/MJ, when operating on natural gas. In principle,natural gas fuel produces no sulphur emissions. This,together with the low emissions of nitrogen oxides, therefore represents a major contribution to reduced aci-dification.

Operation on gas means that there is no need to dealwith any ash. Natural gas contains practically no envi-ronmentally hazardous heavy metals, and its combustionis very clean. Because of the high chimney stack, the fluegases do not contribute to the inversion problems thatsometimes affect Gothenburg.

As the gas fuel is supplied by pipeline, no transport isrequired. Removal of nitrogen oxides using SCR techno-logy involves handling ammonia (25% aqueous solu-tion) within the plant and transporting it by lorry. Thishandling is managed in such a way that the safety of personnel is guaranteed and there is no damage to theexternal environment.

The local environmentOut of consideration for groundwater levels, air quality,flora and fauna, an environmental control programmefor the Rya forest will be implemented before and afterthe plant is commissioned.

The rather neglected local area has been cleared ofthe effects of previous activities (e.g., oily soil).

When district heating demand is low, the plant can becooled with water from the River Göta. There will be asmall increase in the water temperature as a result, butonly affecting a very limited part of the river.

No additional noiseOne condition of the Environmental Court permit isthat the noise level 100m from the plant must not exce-ed 50 dB(A). The Rya CHP Plant will not add any extranoise to an already noisy environment. For purposes ofcomparison, a kitchen fan emits between 40 and 63dB(A), and a normal conversation 50 dB(A).

Carbon dioxide emissions in a wider perspectiveEmissions of carbon dioxide will increase in Gothenburgas a consequence of increased power production. Thisincrease will be more than compensated by reduced oper-ating times for coal-based power plants in northernEurope. From a north European perspective, annualemissions of carbon dioxide will fall by around 500,000tonnes.

Huge benefits for the environment – and not just in Gothenburg

Conditions of environmental permit

• 100m high chimney stack

• Max. 20 mg NOx/MJ of fuel input

• Max. 5 ppm ammonia slip

• Cooling water into river:

– max. flow 5 m3/s

– max. 10°C temperature rise in cooling water

The diagram clearly reveals the positive environmental impact of the expansion

of district heating in Gothenburg.

Ener

gy (G

Wh)

Sulphur District heating supplyOwn production of district heat

Emis

sion

s (t

, kt

for

CO2)

Carbon dioxide emissions per kWh produced by the RyaCHP Plant, compared with coal and oil-fired condensingpower plants:

Progress of emissions reduction since 1973

Oil

Coal

Rya CHP, Natural Gas

What is produced at the Rya CHP Plant, and why?

The Rya CHP Plant is one of the largest gas-fired, com-bined cycle plants in Scandinavia.

The plant comprises two cycles, one for gas turbinesand one for steam. Utilising the residual heat in the fluegases from the gas turbine as the driving force in thesteam cycle increases the overall level of efficiency.

This boosts the power output and results in an overallplant efficiency of as much as 92.5%. Siemens is turn-key contractor for the plant which is based on productsusing Siemens' proven technology.

What was the thinking behind our choice?Göteborg Energi wanted to build a plant that couldachieve large-scale, stable and resilient production ofdistrict heat and power. The flexibility of the plant withregard to variations in district heating requirements wasprioritised. The optimisation chosen was expressed interms of an alpha value and an overall efficiency level.

The alpha value is the ratio of the plant’s power out-put to its heat output, i.e. a measure of the energy

generation mix. In a plant optimised for power produc-tion, the alpha value would be around 1.2 and the ove-rall efficiency 88%. The Rya CHP Plant, however, hasbeen optimised to produce as high an overall efficiencyas possible - 92.5% - so the alpha value is a little lowerat 0.9.

The plant is extremely flexible, so it can easily beadjusted to match the load. This stems from two impor-tant factors. The first is the solution of using three gasturbines instead of one single large one. The second isthe supplementary firing capability of the heat recoverysteam generators (boilers). This makes it possible tomaximise power production at any given level of heatproduction.

Efficiency well above the normThis plant has been optimised for district heating pro-duction and utilises the energy content of the fuel extre-mely efficiently. These are some of the reasons:

– Combustion takes place in two stages, first in the gasturbines and then in the heat recovery steam generators(boilers). The same combustion air is utilised, whichmeans lower flue gas losses. A smaller quantity of airresults in lower losses.

– There is a high level of heat recovery, i.e. a low levelof heat loss to the environment. This is achieved partlyby making use of heat that would normally be cooledaway. For example, the recovery of heat from the lubri-cating oil system alone results in a 0.5% increase in effi-ciency, or an extra 3 MW produced, enough to heat anadditional 250-300 homes.

– The steam turbine is tailored to the application andis of modern design, with low throttling losses.

– The final cooling of the flue gases occurs in a districtheating economiser, in the final stage of the heat reco-very steam generator. This means that the flue gas tem-perature is reduced as much as possible, thus increasingthe generation of district heat.

• 92.5% electric power and heat

• 5% losses in flue gases

• 0.7% losses in generators

• 0.5% losses through ventilation

• 1.3% other losses, e.g., leakages, hot water

What happens to the 600 MW that we feed into the plant?

Efficiency

is the ratio (expressed in %) between

the total useful output, electric power

+ heat, and the fuel energy input:

Electrical efficiency

Electrical output

Fuel input

Electric power production (261 MW): 43.5%

Losses: 7.5%

Heat production (294 MW): 49%

Alpha value

Electrical output

Heat output= α

When compared with the gas

turbine process, the electrical

efficiency of the steam

turbine process is not as high.

But when the two processes

are combined, a much higher

level of overall efficiency can

be achieved.

Gas turbineprocess

Steam process

Total output

Fuel input

63% losses

Gas turbine

Fuel

Electric power generated

Electrical efficiency 37%

Total efficiency 37%

Boiler

Losses 6%

Fuel

Steam turbine

District heating condenserHeat produced

Electric power generated

Electrical efficiency 35%

Total efficiency 94%

Alpha value 0.59

= η

= ηel

Definitions

1. The gas is supplied by pipeline from Denmark. When it arrives at

the Rya CHP Plant, its pressure, 26-28 bar, is suitable for the gas

turbines with no need for a pressure increase.

2. The air enters via air intakes on the roof of each gas turbine. To

ensure high efficiency and prevent ice formation in the air intakes,

these are furnished with heat exchangers to preheat the air. The air

preheating uses waste heat from the lubricating oil system for the

purposes of good economy and to raise the overall level of plant

efficiency.

3. The gas turbine compressor increases the pressure of the inco-

ming air in 15 stages. The temperature is increased to 400°C.

4. In the combustion chamber, the gas/air mixture is burned using

30 low-NOx burners to form flue gases with a temperature of

1,200°C. At this stage, the flue gases contain 30 mg NOx per MJ

of fired natural gas. The higher the temperature, the higher the

efficiency of the gas turbine process will be. But there are also

disadvantages, including high material temperatures and NOxgeneration, which means that a compromise has to be made.

5. The flue gases expand in the turbine, in two air-cooled stages

and one uncooled stage. This provides the driving force for the tur-

bine shaft, which in turn drives the electrical generator (and the

compressor). The rotor speed is 6,600 rpm. The flue gases exhaus-

ted from the turbine have a temperature of 538°C and contain

around 15% oxygen by weight.

6. The flue gases are fed into the heat recovery steam generator

(boiler), where they are heated to around 1,000°C by means of sup-

plementary firing. As there is 15% oxygen left in the flue gases

exhausted from the gas turbine, no further air needs to be added.

Thanks to the relatively high level of supplementary firing, the Rya

CHP Plant can produce more heat at low cost than other compa-

rable plants.

7. The flue gases that are finally emitted into the environment via

the stack have a temperature of around 70°C. After passing

through the catalyser, the flue gases contain considerably less

than 20 mg NOx/MJ of fired natural gas.

One reason why it is possible to reduce the flue gas temperatu-

re to such a low level without unwanted side-effects, such as cor-

rosion, is that the plant operates on a clean fuel. Another reason is

that the district heating network can be utilised to remove the

heat from the flue gases. It is therefore economically possible to

reduce the temperature of the flue gases substantially and extract

much of their energy content. This is the main reason why the plant

can achieve an efficiency level as high as 92.5%.

Steam Process8. The water in the steam process is pumped up to the right press-

ure, around 100 bar, by the feedwater pump.

9. In the heat recovery steam generator, the water is heated in

several stages in two economisers (1 and 2). It is heated by means

of the flue gases from the gas turbines, which flow in the opposite

direction to the water.

10. Steam is separated from water in the steam dome. The water

that has not yet become steam is fed down via faller pipes to the

bottom of the steam generator to be re-circulated in the evapora-

tion tubes via a self-circulation system.

11. The steam is superheated to 540°C in three superheaters.

12. The superheated steam from the three heat recovery steam

generators is fed to the steam turbine.

13. In the steam turbine, the steam impacts the turbine’s blades at

a speed of around 700 km/h. The blades convert this speed into

mechanical energy in over 20 stages and thus drive the turbine

rotor. The steam turbine rotor in turn drives the electrical genera-

tor.

14. The steam that flows out of the steam turbine is condensed in

the two heat condensers and the heat is fed to the district heating

system. The advantage of having two condensers, rather than one,

is that it is possible to let half the steam continue to expand in a

further stage of the steam turbine.

As the Rya CHP Plant is optimised for district heating, with a

relatively large proportion of supplementary firing, there is a high

level of heat production at low cost.

15. The steam has now passed into the water phase, i.e. it is con-

densate.

How does production take place?

600MW

3x44 MW power

Natural gas

Air

2

4

5

1

3

150,000 t

16. The condensate is cleaned and degassed and finally returns

via the feedwater pump to start a new cycle via the heat re-

covery steam generator.

17. For increased flexibility, there is a dump condenser that is

used for heat production in the event of operating problems

preventing steam from being passed through the steam turbi-

ne. The dump condenser is also used when the plant is being

started up.

18. Distribution pumps for the district heating network.

Natural gas input: 600 MW

Total electric power output: 261 MW

Total heat output: 294 MW

Electric power production: 1250 GWh/yr (approx.)

Heat production: 1450 GWh/yr

Efficiency η=92,5%

Electrical efficiency ηel=43,5%

Alpha value α=0,9

294 MW heat75-110˚C

137 MWpower

40-60˚C

9

15

13

14 17

11

10

168

7

6

12

18

Superheater 3 Superheater 2 Superheater 1

Steam dome

Steam generator SCR catalyser Economiser 2 Economiser 1 District

heat

30 M

W lo

sses

Some technical data

What does the plant

look like?

Gas turbine and

electrical generator

Heat recovery steam

generator

Steam turbine and electrical generator

Condensers

Electric power

District heat

Air

Cleaned flue gas

Automation, remote control, operation and maintenance

The Rya CHP Plant is built to be monitored remotely, aunique situation, considering the size of the plant. Theoverall operations monitoring system for the whole ofGothenburg’s district heating is located at the operationsmanagement centre in Sävenäs, which is manned 24h/day. At the Rya CHP Plant, there is a local control sys-tem for the combined cycle plant, which is also control-led remotely from Sävenäs.

A service and spare parts agreement has been signedwith the plant supplier, which means that Siemens isresponsible for maintenance of the gas and steam turbi-nes and the control and auxiliary systems.

Siemens is also available to provide assistance on site,as well as telephone support.

The supply includes training for the operating andmaintenance staff. The training leads to certification forthe operating personnel. Personnel from GöteborgEnergi participate in the final phase of the plant’s testperiod and commissioning.

Control and monitoring systemThe plant’s control and monitoring system is based on astandard system, with three operator stations. The sys-tem is integrated into the overall Sävenäs system, whichcollects information on the conditions in Gothenburg.On the basis of this information, decisions can be maderegarding the operation of the Rya CHP Plant. Data isalso stored for use in generating forecasts and simula-tions. The database is distributed and redundant. Thereis also a separate, independent process safety system,which automatically takes action when events occurthat have an impact on safety.

In addition to the safety system, the monitoring systemcontains an entry control and burglar alarm system thatincludes camera surveillance.

Monitoring takes place in the automated safety sys-tem. In addition, manual inspection rounds are carriedout by security personnel at least once every 24 hours.An accredited inspection body must ensure that thesafety equipment and alarm management function satis-factorily.

Electrical systemThe power from the generators is supplied via the trans-formers to high-voltage switchgear, rated 130 kV, fortransmission to Gothenburg's power network. Theswitchgear is gas-insulated and highly compact. Com-pared with conventional switchgear, gas-insulatedswitchgear is more operationally reliable in Gothen-burg’s marine climate. Circuit couplers on the transfor-mers make power production less vulnerable to externalvoltage variations.

District heating systemThe return water from the district heating network is fedby means of return pumps to the heat condensers, whereheat from the steam cycle is transferred to the districtheating network. The water is fed back out to the districtheating network by means of feed pumps that maintaina differential pressure between the feed and return linesin the district heating network.

There is also a system for pressurising the district hea-ting network. The pressure is regulated by water beingfed into or drained out of the district heating system.

It was a technical challenge to keep the roof as free as possible of

technical equipment and to make the fans harmonise with the building.

Particular attention was paid to the lightning conductors, as well as

to the integration of the existing cistern foundation in the body of

the building.

Siemens SGT-800 gas turbine just before delivery

from the workshop in Sweden.

Natural gas

Photo: Liljewall arkitekter ab

Gas turbine

Gas turbines

The Siemens SGT-800 gas turbine is technically advan-ced, reliable and designed using the latest, proven tech-nologies. It is highly suited to operation in combinedheat and power plants, where low life-cycle costs, envi-ronmental performance and reliability are critical fac-tors. The SGT-800 can be found operating in many dif-ferent applications throughout the world.

The maintenance costs for this turbine are low. Onereason for this is that the machine is modular in designand constructed with a relatively low number of compo-nents. Another is the service concept. Cables, pipes andconnections are grouped in an auxiliary systems moduleon one side of the machine, allowing very good access forinspection and any work that is required. These are thekey factors that together permit long service intervalsand low maintenance costs.

Although the machine only has one shaft, it is optimi-sed to exhaust into a heat recovery steam generator. Theelectrical generator is driven from the ‘cold’ end of thegas turbine, rather than the ‘hot’ end, where the exhaustduct is located. This allows a straight connection to bemade to the heat recovery steam generator, thus redu-cing losses and raising the efficiency level.

The SGT-800 is fitted with low-NOx burners for ope-ration on both oil and natural gas.

How the gas turbine works

On its way into the turbine, air is filtered so that it is as clean as possible. Then the

air is compressed in the 15 compressor stages, exceeding the speed of sound at the

very first stage. After the combustion chamber, the exhaust gases are expanded in

3 turbine stages. Two-thirds of the power developed in the turbine drives the gas

turbine compressor, and the remaining third drives the generator, which is joined to

the compressor inlet at the machine’s ‘cold’ end. The generator is of 4-pole design

and is connected to the gas turbine via a parallel reducing gearbox. The heat recovery

steam generator (boiler) is located at the ‘hot’ end, next to the gas turbine exhaust.

Siemens SGT-800 gas turbine Air intake Compressor

Some technical data

The blades in the first stage have a single-crystal structure.

They have been precision cast and annealed.

The compressor rotor consists of discs that are welded together into a

robust unit. Electron beam welding provides a homogeneous weld, free

of filler material.

Combustion takes place in 30 third-generation DLE burners. DLE – Dry, Low Emissions

– is a relatively new technology that offers very low emissions, around 30 mg NOx /MJ

of fuel when operating on gas.

Combustor wall

Flame

Mixing tube Cone Main injector, liquid fuel

Combustor cover

Gas or liquid fuel<

Pilot fuel

Air from compressor

Main injector, gas fuel

Low-NOx burner

• Nominal output: 45 MW/turbine

• Efficiency: 37%

• Air compressor: 15-stage, axial

• Pressure ratio: 19:1, at 130 kg/s gas flow

• Exhaust gas temperature: 538°C

• Turbine speed: 6,608 rpm

• Gas pressure required: 27 bar(a)

Combustion chamber Turbine Exhaust gas duct

Siemens SST-900 steam turbine

The Siemens SST-900 steam turbine, in its district heating(DH) version, is designed to be tailored to meet customerrequirements. Each turbine has a modular construction oftried and tested components, all of which contribute to a veryhigh level of reliability.

The turbine casing is symmetrical, horizontally split andbuilt to provide a high degree of thermo-flexibility. The smalldimensions of the hot parts mean that the SST-900 DH cantolerate short start-up times and rapid load changes. The bla-des of the SST-900 DH are of impulse type with 21 turbinestages in succession. These state-of-the-art blades ensurehigh efficiency. The turbine is one of the most compact onthe market, with a very small installation footprint.

The Siemens SST-900 DH is a flexible, efficient steam tur-bine that can cope with the wide load range required by theRya CHP Plant’s three separate lines of gas turbines and heatrecovery steam generators. The simplicity of the design andlow maintenance costs also translate into high availabilityand operational reliability. The turbine is connected to aseparate 2-pole electrical generator and supplies 137 MW ofpower.

The district heating water is heated in two heat conden-sers, which results in a higher efficiency than if the entire tem-perature increase were produced in just one heat condenser.

Steam turbine

Steam turbine

Electrical generator

Turbine casing

Inlet

Outlet

Some technical data

Nominal output: 137 MW

Steam pressure: 100 bar(a)

Steam temperature: 540ºC

Steam extraction to feedwater tank:

3 bar(a), approx.

Turbine speed: 3,000 rpm

How the steam turbine works

The steam, which comes from the heat recovery steam

generators (boilers), expands and is fed at high speed

through the turbine’s blading system. As it expands, the

steam is diverted by a series of moving blades that are

fixed to the rotor. The diversion provides the turbine shaft

with rotational force, and the shaft, in turn, drives the

electrical generator. Between the moving blades are fixed

guide vanes whose task is to divert the steam back again.

The three heat recovery steam generators (HRSGs) –or boilers – are horizontal and self-circulating. The fluegas flow is therefore horizontal, with suspended verticaltubes. The HRSG is of simple design, with low mainte-nance costs. The HRSGs produce high-pressure steamwith a temperature of 540°C, at a pressure of 100 bar.Each HRSG consists of five prefabricated modules forsimpler assembly. It is connected via bellows to the gasturbine silencer. Each HRSG is designed to fire 200MW of natural gas together with a gas turbine.

On account of the high degree of supplementaryfiring with natural gas, the ducts around the HRSGsuperheaters are fitted with water-cooled, tubed, mem-brane walls with external insulation. The high level ofsupplementary firing produces a large flow of steam,thus allowing a large output of energy.

After the supplementary firing, the duct widens to itsfull cross-sectional area. This widening is unusuallysteep, producing a considerably shorter HRSG thatrequires less space as a consequence. If the widening istoo steep, uneven temperature distribution can arise inthe cross-section of the HRSG, leading to a distortedheat load in the steam generator. This has been obvia-ted with a perforated diffuser plate, which distributesthe flue gases more evenly over the entire cross-sectio-nal area of the duct.

Boiler

Heat recovery steam generators

The economiser, which is divided into two stages, is right at the back of the

HRSG to make optimal use of the heat in the flue gases.

The superheating also provides advantages during the expansion in the

turbine. The steam remains dry (i.e. without water droplets), which reduces

turbine blade erosion.

Superheater module

for the Rya CHP Plant.

Heat recovery steam generator for

the Rya plant during construction.

Why the heat recovery steam generator is efficient

Flue gas cleaning using SCR technologySelective Catalytic Reduction (SCR) technology is currently the most effective com-

mercial method for reducing nitrogen oxides (NOx). The catalyser in the Rya CHP Plant

is dimensioned for around 70% NOx reduction. Nitrogen oxides are reduced by mixing

the flue gases with vaporised ammonia (NH3). The nitrogen oxides react with the

ammonia to form harmless, naturally occurring nitrogen (N2) and water vapour (H2O).

The diagram shows theextent to which heat istransferred from the hotflue gas to the water in thesteam cycle in particularparts of the heat recoverysteam generator.

Layout of heat recovery steam generator

Flue gas

Ammonia injection (NH3)

Catalyst

Cleanedflue gas

55

85

61,6

274

321321

350

420

401

421

542

321

997

927

839

770

668

9070

Tem

pera

ture

(°C

)

0

100

200

300

400

500

600

700

800

900

1000

0 2010 30 40 50 60 70 80 90 100 1 1 0 120 130 140 150

Hot flue gas from gas turbine

Diffuser plate for flue gas

Burner for supplementary firing

Steam dome

Sile

ncer

Inle

t du

ct

Wat

er-c

oole

d m

embr

ane

wal

l

Supe

rhea

ter

Stea

m g

ener

ator

SCR

unit

Econ

omis

er

Dist

rict

-hea

ting

ec

onom

iser

Exha

ust

gas

duct

Cool

ed fl

ue g

as t

o ch

imne

y

Heat transfer (MW) Flue gas temperature

Steam temperature

Stea

m g

ener

ator

Superheater Economiser

Dist

rict

-hea

ting

eco

nom

iser

Steam generator

Operational reliability

The Rya CHP Plant has a load range that is 20-100% of max-imum heat production. The balance between power and heatproduction may be varied within certain limits. For example,power production may increase independently of districtheating production or the plant may only produce power byutilising the additional district heating cooler connected tothe river. The plant can also be started up when there is noaccess to an external power supply.

High flexibility in relation to the load range not only meansan ability to adapt to varying heat loads and outdoor tempe-ratures. It also ensures secure power and heat production forGothenburg, even under difficult circumstances.

Different operating modesNormal operation includes several different load situations.Here, disturbance-related operating situations are also inclu-ded:• Island operation makes it possible to produce electricityfor parts of the power grid in Gothenburg without having tobe connected to the national grid. This is conditional on theplant having its own equipment to maintain the voltage andadjust the frequency to 50 Hz.• House turbine operation means that the plant can supplyitself and run idle without supplying power or district hea-ting, independently of any external power supply.• If the external power supply fails, there is an emergencydiesel generator, which means that the plant can still be star-ted up without the external supply.

A more secure power supplyGothenburg’s power grid is divided into around 25 sections.This sectioning allows the network to be restored after apower cut, and also enables island operation.

When the Rya CHP Plant is in operation and there is apower cut, the plant enters house turbine operation and runsidle. The plant then enters island operation and begins tosupply power.

To restart power supplies to a dead network, or distributepower during a long-term power cut, a rotating schedule isapplied to the sections.

When the plant is not in operation, for example, duringthe summer, and a power cut occurs, the plant can be startedup with the emergency diesel generator and then enter houseturbine operation. As the plant has three parallel lines, thebasic conditions for secure operation are multiplied.

A more secure heat supplyThe Rya CHP Plant and the Rosenlund, Angered andSävenäs plants all have equipment to pressuriseGothenburg’s district heating network, which is necessary forthe district heating distribution network to function.

The district heating network is divided into four zones:eastern, western, central and northern. In the event of ope-rating disturbances in one or more of the zones, they can beclosed off to ensure delivery to the others. The western zonepreviously did not have satisfactory pressurisation of its ownand therefore could not be operated separately. However, if itis necessary to close down the district heating network in therest of Gothenburg, it is now possible to continue to deliverin the west using the Rya CHP Plant.

Production plants for electric power and/or heat in Gothenburg.

The plants are distributed across the city in order to increase the

security of supply.

Brown shading: existing district heating network

Orange shading: planned extensions

Angered heat plant

Renova waste incinerationSävenäs plant

Riskulla plant

Shell refinery

Preem refinery

Rya CHP PlantRya heat and heat pump plants

Högsbo CHP Plant

Rosenlund CHP Plant