Geothermal energy

LOW ENTHALPY LOW ENTHALPY APPLICATIONAPPLICATION OF OF

GEOTHERMAL ENERGYGEOTHERMAL ENERGYPART IPART I

Ruggero BertaniRuggero Bertani

Enel – InternationalEnel – International

Rome – ItalyRome – Italy

ruggero.bertani@enel.itruggero.bertani@enel.it

Rome, 2007 10Rome, 2007 10thth May May

Geothermal energy

Contents1° PART1° PART

1. Introduction

2. Geothermal energy basic concepts

3. Electricity generation

4. Binary plants

• Case studies

2° PART

1. Low Enthalpy applications

• Introduction

2. Direct Uses

• SPA

• Heating

• Geothermal Heat Pumps

• Agriculture

• Aquaculture

• Industrial applications

3. Conclusion and case studies

Geothermal energy

Enel 2006 Results

Power plants MW

Hydro (616 pp)18,151

Thermal (53 pp)28,857

Wind (46 pp)591

Geothermal (31 pp)671

Other Renewables (6 pp)46

Nuclear (2 pp) 2,460

Total production (TWh)131,4

Domestic103.9

International27.5

Net installed capacity (MW)50,776

Domestic40,475

International10,301

Electricity Distribution & Sales

Enel distribution (TWh)267.6

Domestic255.0

International12.6

Enel sales (TWh) 159.9

Domestic142.7

International17.2

Customers (millions)32.5

Domestic30.4

International2.1

Netz (km/thousands)1,179.3

Gas Distribution & Sales

Enel Sales (bcm)

4.5Customers (millions)

2.3Gas Pipeline (km/thousand)

31.1

Geothermal energy

Canada 22 MWHydro, biomass

USA 380 MWHydro, wind

Guatemala 69 MW - Hydro

Costa Rica55 MW - Hydro, wind

Chile100 MW - Hydro

Italy 15,358 MW Hydro, geothermal, wind, solar

Spain900 MW

Hydro, wind, cogeneration

Slovakia 2.329 MW

Hydro

Brazil97 MW - HydroPanama

300 MW - Hydro

Over 19.000 MW

of renewable energy

El Salvador

44 MW geo

Geothermal energy

Northern Pool

SouthEastern EU

Central EU +Centrel + Italy

Iberia

NorthAmerica

LatinAmerica

A solid international playerA solid international player

• Growth in all technologies & upstream gas in Europe and Russia

• Growth in Renewables worldwide

• Growth in all technologies & upstream gas in Europe and Russia

• Growth in Renewables worldwide

Geothermal energy

Contents1° PART1° PART

1. Introduction

2. Geothermal energy basic concepts

3. Electricity generation

4. Binary plants

• Case studies

2° PART

1. Low Enthalpy applications

• Introduction

2. Direct Uses

• SPA

• Heating

• Geothermal Heat Pumps

• Agriculture

• Aquaculture

• Industrial applications

3. Conclusion and case studies

Geothermal energy

Geothermal system

Heat source

Depth 5-10 km

T > 600- 700 ° C

Meteoric water

Hot fluid

Production wells

CaprockThickness 500 – 1500 m

Impervious rocks

Utilization of geothermal energy has been limited to areas in which geological conditions permit a carrier (water in the liquid phase or

steam) to 'transfer' the heat from deep hot zones to or near the surface, thus giving rise to geothermal system

ReservoirPorous – fractured

rocksTickness 500 – 1500 m

T = 150 – 300 °C

Reinjection well

Power plant

Steam gathering

system Drilling rig

Geothermal energy

Geothermal systems

Geothermal energy

400oF (200oC)

300oF (150oC)

200oF (95oC)

100oF (40oC)

0oF (-20oC)

Temperature use for direct use applications

Geothermal energy

Utilization of geothermal energy as a

function of the resource

temperature

Geothermal energy

Energy saving & pollution avoidedGEOTHERMAL ENERGY FOR ELECTRICITY GENERATION

56875 GWh in 2004

2%

44%

37%

12% 5% AFRICA

AMERICAS

ASIA

EUROPE

OCEANIA

Electric use

•Energy saving of fuel oil per year 96,6 million barrels or 14, 5 millions tonnes

•Carbon pollution avoided (millions tonnes year) 3 (natural gas) or 13 (oil) or 15 (coal)

Total energy saving of fuel oil per year over 220 million barrels

Total carbon pollution avoided per year over 29 (oil) million tonnes

GEOTHERMAL ENERGY FOR DIRECT USE OF HEAT

72632 GWh

1%32%

21%

44%

2% AFRICA

AMERICAS

ASIA

EUROPE

OCEANIA

Direct uses

•Energy saving of fuel oil per year123,4 million barrels or 18,5 millions tonnes

•Carbon pollution avoided (millions tonnes year) 4 (natural gas) or 16 (oil) or 18 (coal)

Geothermal energy

Contents1° PART1° PART

1. Introduction

2. Geothermal energy basic concepts

3. Electricity generation

4. Binary plants

• Case studies

2° PART

1. Low Enthalpy applications

• Introduction

2. Direct Uses

• SPA

• Heating

• Geothermal Heat Pumps

• Agriculture

• Aquaculture

• Industrial applications

3. Conclusion and case studies

Geothermal energy

Geothermal system

Geothermal energy

Japan

535 MW

Russia 79

MW

Philippines 1970

MW

Indonesia 992 MW

New Zealand 472 MW

USA 2687 MW

Costa Rica

163 MWKenya 129 MW

Iceland421 MW

Italy 811 MW Turkey

38 MW

Portugal 23 MW

Ethiopia 7 MW

France 15 MW

China 28 MW

Mexico 953 MW

Australia 0,2 MW

Austria 1 MW

Germany 8 MW

El Salvador204 MW

Guatemala

53 MWNicaragua

87 MW

PapuaNew

Guinea 56 MW

Thailand

0,3 MW

GEOTHERMAL ELECTRICIT WORLDWIDE TOTAL INSTALLED CAPACITY 9,7 GW

Geothermal energy

Contents1° PART1° PART

1. Introduction

2. Geothermal energy basic concepts

3. Electricity generation

4. Binary plants

• Case studies

2° PART

1. Low Enthalpy applications

• Introduction

2. Direct Uses

• SPA

• Heating

• Geothermal Heat Pumps

• Agriculture

• Aquaculture

• Industrial applications

3. Conclusion and case studies

Geothermal energy

Generating electricity from low-to-medium temperature geothermal fluids and from the waste hot waters coming from the separators in

water - dominated geothermal fields has made considerable progress since improvements were made in binary fluid technology.

The binary plants utilize a secondary working fluid, usually an organic fluid

that has a low boiling point and high vapour pressure at low temperatures when compared to steam.

The secondary fluid is operated through a conventional Rankine cycle: the geothermal fluid yields heat to the secondary fluid through heat exchangers, in which this fluid is heated and vaporizes; the vapour

produced drives a normal axial flow turbine, is then cooled and condensed, and the cycle begins again.

Geothermal energy

By selecting suitable secondary fluids, binary systems can be designed to utilize geothermal fluids in the temperature range 85-

175°C.

The upper limit depends on the thermal stability of the organic binary fluid, and the lower limit on technical-economic factors: below this temperature the size of the heat exchangers required would render

the project uneconomical.

Apart from low-to-medium temperature geothermal fluids and waste fluids, binary systems can also be utilized where flashing of the geothermal fluids should preferably be avoided (for example, to

prevent well sealing).

In this case, downhole pumps can be used to keep the fluids in a pressurized liquid state, and the energy can be extracted from

the circulating fluid by means of binary units.

Geothermal energy

Geothermal energy

After long trial and error, binary plant technology is emerging as a very cost-effective and reliable means of converting into electricity the energy available from water-dominated geothermal fields (below

175°C).

A new binary cycle system has been developed recently, called the Kalina cycle.

The Kalina cycle uses an ammonia-water mixture as the working fluid and takes advantage of regenerative heating.

The ammonia-water mixture has a low boiling point, so that the excess heat coming from the turbine’s exhaust can be used to vaporize a substantial portion of the working fluid.

This plant is estimated to be up to 40% more efficient than existing geothermal binary power plants.

Geothermal energy

BOTTOM CYCLE BINARY PLANT• In many cases, additional generating capacity may be obtained in a cost-

effective manner by repowering existing geothermal power plant utilizing otherwise untapped geothermal energy, without additional wells;

• For cost effective power generation, the extraction of heat from geothermal fluid must be maximized;

• Often this repowering also provides concomitants environmental benefits, since it conserves energy while reducing environmental hazardous waste;

• These plant retrofit additions can be designed at any stage of the life of each generation facility, they are modular and can be realized in different steps;

• The typical cost is two million USD for MW and the timing for the realization of the entire phases of the project can be very short (one year);

• Approximately 150 MW are installed worldwide.

LOW TEMPERATURE BINARY PLANT• In many cases where it is present a low temperature resource, binary plant

technology is the only one feasible for electricity generation from geothermal fluid;• There are about 600 MW of binary plants installed worldwide.

Geothermal energy

• The utilization of geothermal energy for the electricity production reached the value of 9,000 MW in 24 countries;

• The economics of electricity production is influenced by the drilling costs and resource development;

• The productivity of electricity per well is a function of reservoir fluid thermodynamic characteristics (phase and temperature);

• The higher the energy content of the reservoir fluid, the lesser is the number of required wells and as a consequence the reservoir CAPEX quota is reduced:

Utilization of low temperature resource can be achieved only

with binary plant.

Binary plant can be an efficient way for recovery the energy content of the reservoir fluid after its primary utilization in standard flash plant,

achieving a better energy efficiency of the overall system.

Geothermal energy

Steam Dominated

Water Dominated

Reservoir fluid

Energy Content

Utilization

High Enthalpy

Low Enthalpy

Electricity Productio

n

Direct uses of

the Heat

BINARY PLANT

BOTTOM CYCLE BINARY PLANT

Geothermal energy

OPTIMIZATION• Bottoming cycle technique is widely used

worldwide, as shown in the attached table;• This electricity is produced using the waste water

from the separated brine: it can be considered as an un-expensive and rich of value by-product of the primary flash power plant.

LOW TEMPERATURE• For temperature below 150°C, the conventional

flash is not able to reach satisfactory efficiency: at this temperature, only 10% of steam can be produced at about 1 bar of separation pressure; the steam will have a very low efficiency, due to its low pressure and temperature, for producing 20 MW it will be necessary to mine up to 3,000 t/h of fluid (to be compared with 500 t/h from 300°C liquid reservoir);

• The UNIQUE way to exploit the geothermal energy for producing electricity is the use of a binary plant on the pressurized fluid, which will be handled through a closed loop from production and reinjection.

• It is a zero emission cycle. The total installed capacity of such binary plants is about 600 MW worldwide.

Country PlantCapacit

y (MW)

IcelandSvartseneg

i8

MexicoLos

Azufres3

New Zealand

Kawerau 6

New Zealand

Mokai 27

New Zealand

Rotokawa 13

New Zealand

Wairakei 14

NicaraguaMomotom

bo7

Philippines Mak-Ban 16

Philippines Tongonang 19

PhilippinesMahandon

g19

Philippines Mahiaio 5

Philippines Malitbog 12

TOTAL 150

BINARY PLANTS FOR OPTIMIZATION

Geothermal energy

Typical Flash plant from high enthalpy Liquid Reservoir

~turbine generatorGas extractor

Non condensable gas

condenser

Discarded water

separatorTwo phase mixture

from reservoir

Liquid phase for the reinjection

at 170°C

Steam and non condensable gas

chimney

Cooling tower

Cold reinjection (20°)

Average value for 20 MW plant (Res. Temp. 300°C)•Fluid extraction 470 t/h•Steam in 140 t/h Fluid (30% of the fluid)•Flash: temperature 170°C and pressure 8 bar•Gas out 4 t/h•Cold Reinjection 40 t/h•Hot reinjection 330 t/h•Cooling tower evaporation 96 t/h (75% of steam)

The hot reinjection fluid at 170°C is approximately 2-3 times the steam fraction, accordingly to the initial fluid temperature; this energy can be utilized using a BOTTOM CYCLE BINARY PLANT

Geothermal energy

In El Salvador, our local partner LaGeo installed a new bottom cycle

binary plant at the existing old power station of Berlin (2x28 MW,

completed in 1999), using the separated water from four wells; it is

utilized in two heat exchanger for boiling an organic fluid (Isopentane), which has a low temperature boiling point; the isopentane steam expands

into a 9,5 Gross MW turbine, generating 7,8 MW net of electricity, without any

additional expenditure from the reservoir development, and

achieving a better utilization of the overall energy content of the

geothermal fluid.

The cost for this unit is 16,5 MUSD, with a very positive

return of the investment

Total utilized geothermal fluid 1,000 t/h at 180°C; isopentane

flow rate 700 t/h, working between 160°C and 44°CC;

wet cooling tower; GE turbine, ABB generator; Mexican heat Exchanger; Enex (ICELAND) design and EPC contractor.

Geothermal energy

Heat Exchanger

Turbine

Power Plant Housing

Geothermal energy

Chena Hot Springs is located approximately 100 km northeast of Fairbanks, Alaska, in the interior of the state. In August 2006 a low temperature power plant was commissioned to provide power for the isolated resort. The 200 kW plant, a binary or organic Rankine cycle unit built by United Technology Corporation, is the first geothermal power plant in Alaska, and uses the lowest temperature geothermal resource in the world at 74°C for power generation.

The secondary fluid in the plant is R-134a, which has a lower boiling point than water and is heated by geothermal water at 32 l/s through a heat exchanger at 74°C. Cooling water from a shallow well or infiltration gallery is around 4°C, providing a large temperature difference which improves the efficiency of the system. As the resort is isolated from the electric grid, it has used diesel generators in the past, costing around 30 cents/kWh with a daily average cost of $1,000. The new power plant will provide electricity at 7 cents/kWh, a major saving for the resort. Maintenance is estimated to be $50,000 per year.

The total unit cost around $1,300 per installed kW. Plans are to add another 200 kW unit, and then shortly to reach one MW.

Geothermal energy

TURKEY: Salavatli geothermal field is located in one of the most promising geothermal regions, namely on the northern flank of Menderes graben.

The Salavatli-Sultanhisar geothermal system was delimited after a resistivity survey. Two wells were drilled in 1987 and 1988 to 1500m and 962m, and temperatures of 170°C were

recorded. In the past two years, two more wells were also drilled to the depths 1300m and 1430m

for reinjection and stand by production, and both have struck similar temperatures.

The geothermal fluid contains an average of 1% of CO2 by weight, which is similar to that of other geothermal fields in the region.

An air cooled binary power plant with 7 MWe gross power is being installed.

Specific consumption of plant is 500 t/h of water at 156°C, discharged at 76°C, producing 8 MW in winter and 5,3 MW in summer; 600 kW parasitic load of fan cooling.

Geothermal energy

USA: Enel has finalized the acquisition of four geothermal field in USA; these reservoirs should be exploited through binary plants. The relevant data are collected in the attached table.

As working fluid has been selected the isobutane, for achieving better performances in such range of temperatures.

The use of isobutane will requires higher operating pressure which could result in slight increase in equipment cost, and it implies an increase of risks concerning safety aspects due to higher operating pressures

(near supercritical conditions) and its higher volatility respect to isopentane.

All plants will be air cooled, while the Cove Fort units I and II will be water cooled, due to availability of water source.

FieldTemperature

°C

InjectionTemperatur

e°C

Flow Ratet/h

GrossCapacity

MW

Efficient

Capacity

MW

Still Water II NEVADA

154 79 3,200 49 31

Salt Wells NEVADA

135 77 2,000 21 13

Cove Fort IUTAH

152 77 1,500 25 19

Cove Fort IIUTAH

152 77 2,700 44 33

Surprise Valley

CALIFORNIA165 85 2,700 46 32

TOTAL 185 128

Geothermal energy

The most abundant geothermal resource in the world is given by hot pressurized water.

Whereas in the dry steam reservoir (Larderello-Italy, The Geyser-USA) the exploited energy of the fluid can be fully utilized, in all the other

situation the majority of the thermal energy from the extracted fluid is lost, being reinjected at high temperature and practically not-used and wasted.

The binary plants on the reinjection stream could be a very effective way of producing cheap energy, because

there will not be any additional mining costs associated with this extra production

The binary plants technology represents an unique way of producing geothermal electricity for medium/low temperature geothermal system,

Increasing the overall exploitable potential worldwide

CONCLUSIONCONCLUSION

Geothermal energy

Thanks for your attention

For any further information please contact me at the following e-mail address:

ruggero.bertani@enel.it