Process flow and gathering system

Session VI

Elín Hallgrímsdóttir and Lilja Tryggvadóttir

Mannvit Strasbourg, Nov.8, 2012

Presentation overview

• Presentations reviewing different work cycles

• Main concept of the gathering system

• Calculated example showing methods used within geothermal steam gathering system design

Geothermal in Iceland

Process flow

• A review of thermodynamic cycles used in geothermal energy production with emphasis on electricity generation

• Flash steam cycles with single flash and double flash as well as different binary cycles as ORC and Kalina Cycle are introduced and compared

Back Pressure Steam Power Plant

Steam separator

Turbine Generator

G

Production wells Reinjection wells

Phigh

Plow

2 phase flow Vapor

Liquid

Back pressure unit - layout Separator

Machine Hall

Electrical cabinets & Control room

Asphalted area for installation and maintenance purposes

0

100

200

300

400

500

600

700

00,20,40,60,811,2

Turb

ine

Po

we

r [k

J/kg

]

Turbine outlet pressure [bara]

Calculated examples Different turbine outlet pressure

G

Production wells

Geothermal fluid

Steam separator

Turbine

Condenser

Steam Generator

Silencer

Mist eliminator

Water

Condensate

Condensate

Cooling tower

Reinjection wells

Gas Extraction System

Steam Power Plant with Condenser

Steam Power Plant – Double Pressure

G

Production wells

Two phase flow Turbine - generator HP steam

LP steam

Reinjection wells

Condenser Tcw

Cooling system

Steam separator

LP Steam separator

Two phase flow

Svartsengi – the“Octopus”

Steam Power Plant – Double Flash

Production wells Reinjection wells

G

Steam supply system Turbine - generator Primary steam

Secondary steam

Condenser Tcw

Cooling system

G

LP Turbine - generator

Tcw

Cooling system

Steam separator

LP Steam separator

Hellisheiði – low pressure unit

Steam Power Plant w. District Heating

G

Production wells

Steam supply system Turbine - generator Primary steam

Reinjection wells

Condenser

Tcw

Cooling system

Steam separator

District heating system

Freshwater wells

To district heating

District heating plant

25. 02. 2008

Production wells

Two phase flow

Steam separators

Geothermal water

Steam

Well head silencers

Re-injection wells

Pressure

regulation

Geothermal water

emergency exhaust

Turbines

Generators

Mist separators

Cooling

towers

Hot water tank

Cold water pump

Condensers

Heat exchangers

De-aerators

De-aerators

Condensers

Process Flow Diagram

G Tsource

Tdischarge

Phigh

Plow

Condenser

Turbine Generator

Circulation pump

Evaporator

Tcw

Cooling system

Binary Cycles

G Tsource

Tdischarge

Phigh

Plow

Tcw Condenser

Turbine Generator

Circulation pump

Evaporator

Recuperator

Cooling system

Binary Cycles – with Recuperation

Binary Plant Berlin – El Salvador LaGeo

G

Separator

High temp recuperator

Low temp recuperator

Condenser

Evaporator

Turbine Generator

Tsource

Tdischarge

Tcw

Circulation pump

Cooling system

Binary Cycles – Kalina

Húsavik Kalina plant

2 0 02 5 03 0 03 5 04 0 04 5 05 0 05 5 0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

Heat transfer

Tem

pera

ture

0 0 , 2 0 , 4 0 , 6 0 , 8 1

5 0

6 0

7 0

8 0

9 0

1 0 0

1 1 0

1 2 0

Heat Transfer

Te

mp

era

ture

ORC Kalina

G

Tsource

Tdischarge

Cooling system

Binary Cycles – Kalex

Work Cycle Comparison Specific Power

0

2

4

6

8

10

12

80 85 90 95 100 105 110 115 120 125 130

€/W

Inlet Temperature [°C]

Kalina

Kalex

ORC

Work Cycle Cost Comparison

G

G

G

Steam supply system Turbine - generator

Primary binary turbine - generator

Evaporator

Secondary binary turbine - generator

Cooling system

Cooling system

Production wells Reinjection wells

Demonstration of model

• Turboden ORC model: http://www.turboden.eu/en/rankine/rankine-calculator.php

Gathering System

• This session will present an overview of the design process of a geothermal gathering system with emphasis on particularities of the geothermal fluid.

Two phase flow

Steam separators

Geothermal

water

Steam

Re-injection wells

Pressure

relief Production wells

Turbines

Generators

Mist separators

Cooling

towers

Condensers

Steam Supply - Preliminary P&ID

emergency exhaust

Nesjavellir Power Plant

Separation

station

Steam vent

station

Steam

pipelines

Two phase

flow

Power

Plant

Production

Well

Cooling towers

Gathering system- Design

• Design standards

• Standards i.e. Pressure directive 97/23/EC

• Pressure selection • Chemical constraints

• Power generation

• Productivity curves

0

200

400

600

800

1000

1200

1400

1.00 10.00 100.00

SiO

2(m

g/k

g)

Pressure (bar-a)

quartz solubility (F&P82)

amorphous silica solubility (F77)

330 °C

300 °C

270 °C

240 °C

Chemical constraints

• Scaling

• Corrosivity

• Radioactivity

Mitigation:

• Pressure control / closed loop system

• „cleaning“ of the steam

• Inhibitors

h = 1600 kJ/kg

h = 1800 kJ/kg

h = 2000 kJ/kg

h = 2200 kJ/kg

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10 12 14 16 18 20

Turb

ine

po

we

r [k

J/kg

]

Separator pressure [bara]

Assumptions: Total turbine efficiency: 0,8

Power generation

Typical productivity curves

Well Pump – Low Enthalpy

• Type

• Submersible pump

• Line shaft pump

• Selection and operation

• Depth

• Temperature

• Scaling

• Bubble point

Gathering System– Design load

• Constant load – Weight – Pressure

• Variable load (depending on location) – Wind load – Snow load – Earthquake

• Frictional load – Thermal expansion – Friction

Gathering System - Pipelines

• Pipe laying

• Under ground

• Above ground

• Material selection

• Pipe size

• Pressure/temperature

Steam Supply System – Pipelines

300

400

500

600

700

800

900

1000

0 20 40 60 80 100 120 140 160

Pip

e d

iam

ete

r [m

m]

Flow [kg/s]

7 bar-a

20 bar-a

Gathering system – route selection

• Public safety

• Environmental impact

• Restriction on land

• Cost efficiency

Steam pipelines

Steam Supply - Layout

• Central separation station

• Satellite separation stations

• Individual separators

Central Satellite Individual

Power plant layout

Steam Supply - Separators

• Cyclone separators

• Gravity separators

• Efficiency

• Steam separator and moisture separator should together achieve 99,99 % bw. liquid removal or better

Calculated example

• The presenter will go through a calculated example to show methods used for basic engineering within steam gathering system design. The example taken will be connected to the special conditions encountered in geothermal energy.

Example • Example for 1200 kJ/kg well enthalpy

– 40-50°C condensing temperature

– Back pressure

• Objective

– Maximize the power production

• Assumptions

– We know the reservoir enthalpy

– We know the condenser temperature

– Separation pressure does not influence the well flow

Example, condensing unit

Example, condensing unit

• The maximum power will be 12,4 MW

– Entalpy = 1200 kJ/kg

– Condensing pressure 0,075 bara / temperature 40°C

– Separation pressure 6 bara

– Flow 100 kg/s

• What if we selected backpressure instead?

Example, back pressure

Example, back pressure

• The maximum power will be 6,4 MW

– Entalpy = 1200 kJ/kg

– Separation pressure 12 bara

– Flow 100 kg/s

Example

• Optimum separation pressure is 6 bara, is that ok?

• Saturation temperature for 1200 kJ/kg is 273°C

0

200

400

600

800

1000

1200

1400

1.00 10.00 100.00

SiO

2(m

g/k

g)

Pressure (bar-a)

quartz solubility (F&P82)

amorphous silica solubility (F77)

330 °C

300 °C

270 °C

240 °C

Thank You! VISIT GEOELEC.EU