中英文翻译-能源与环境工程

Power from coal with responsibility

The technology to capture and store carbon pollution safely and effectively

is developing fast. But without effective preparations now, vital opportunities will

be lost, says Jon Gibbins.

The world faces an enormous challenge to produce the energy we need without

damaging the lives of our children and grandchildren. Capturing the carbon dioxide

produced from combustion of fossil fuels such as coal, oil and gas

before

it gets into

the atmosphere and placing it instead in secure storage deep underground is a key to

meeting our responsibilities. Welcome to the world of Carbon Capture and Storage, or

CCS.

Carbon

dioxide

can

be

captured

from

all

types

of

modern

power

plants,

conventional

steam

boilers

and

integrated

gasifier

combined

cycle

plants

that

are

planned for future construction. 'Post- combustion' systems wash carbon dioxide out of

waste

combustion

gases

before

they

go

to

the

plant's

chimney

with

a

continuously-recycled solvent. State- of-the-art designs are a significant improvement

over the small capture units that have been used for half a century to produce carbon

dioxide for carbonated drinks, dry ice, fire extinguishers and other industrial uses.

In gasification-based power plants with 'pre-combustion' capture the coal gas is

reacted

with

steam

to

make

hydrogen,

which

can

be

burnt

in

a

gas

turbine

to

raise

electricity

without

producing

carbon

dioxide.

New

power

plants

of

either

type

are

expected to have similar costs and performance with capture. In the longer term other

types of capture system may be tried out to see if they can give better performance.

Perhaps the best know of these is oxyfuel combustion; pure oxygen is produced and

used to burn the coal, giving nearly pure CO

2

with little additional processing. But

there are also a lot of ways in which the current post- combustion and pre-combustion

systems can be improved. So, as with all other new technologies, there are plenty of

opportunities for industries to compete to produce better products and for users to take

advantage of a competitive market with multiple suppliers.

There

is

a

catch:

capturing

carbon

dioxide

costs

money.

With

current

designs

about

25%

extra

fuel

has

to

be

burnt

and

additional

equipment

must

be

purchased.

This adds between 30 and 40% to the cost of electricity. This may seem like a lot, but

dividing

the

extra

cost

by

the

amount

of

carbon

dioxide

that

is

not

emitted

to

atmosphere has been estimated to give 'abatement costs' of 25-

30 ? per tonne of CO

2

(250-300 yuan or US$$30-38), a price already reached last winter in the EU Emissions

Trading Scheme

(ETS).

Although

carbon prices

are now lower, in

the ETS

and the

international

Clean

Development

Mechanism

(CDM),

it

does

show

that

financing

CCS

in

China

could

be

quite

an

effective

way

to

offset

emissions

elsewhere

in

the

world,

especially

as

technology

improves

and

capture

costs

go

down.

The

key

is

reaching

international

agreement

to

pursue

sustained

and

significant

emission

reductions.

Another way to finance CCS, at least at first, is through 'enhanced oil recovery'

(EOR). Carbon dioxide, compressed to a liquid, can be placed underground in old oil

and gas wells. In oil wells, the carbon dioxide can help to wash out oil that is stuck in

the

pores

of

the

rock

and

cannot

be

released

by

other

means.

Current

prices

in

the

USA for carbon dioxide for EOR are around $$20/tonne CO

2

. Petrochina and CNOOC

are

currently

examining

similar

EOR

schemes

in

China.

But,

while

old

oil

and

gas

reservoirs

offer

proven

leak-tight

storage

and

EOR

can

give

an

extra

source

of

revenue,

most

of

the

potential

storage

capacity

for

carbon

dioxide

in

China

(and

globally)

is

in

deep

layers

of

porous

rock

a

kilometre

or

more

underground

that

contain only salty water, known as saline aquifers. One of these, under the North Sea,

has already been used successfully to store a million tonnes of CO

2

a year from the

Norwegian Sleipner gas platform, and requires only a single injection pipe.

While

we

are

waiting

for

the

necessary

political

progress

on

climate

change

mitigation to make CCS a marketable service, Western governments have offered to

work with China to find out how much carbon dioxide can be stored underground in

China

and

where

the

best

storage

sites

might

be

and

also

to

build

the

first

CO

2

capture

plants

in

China.

Preliminary

results

from

an

Australian

storage

capacity

project are shown in Figure 1; this work will be continuing with a team of Chinese

and international geologists. While it held the EU Presidency in 2005 the UK set up

the

UK- EU-China

Near-Zero

Emissions

Coal

(NZEC)

project,

which

is

planned

to

lead

to

a

jointly- designed

and

constructed

power

plant

with

carbon

capture

and

storage

starting

operation

by

2014.

There

are

also

other

CCS-related

research

and

capacity-building

projects

with

the

EU

and,

under

bilateral

agreements,

with

individual countries and the number of these is set to increase significantly.

Figure

1:

Large

sources

of

carbon

dioxide

in

China

and

regions

for

prospective deep geological storage in China

China

can

also

follow

Western

developments

by

seeing

that

new

power

plants

are built to be 'capture-ready'. This means that a few simple and inexpensive changes

(principally space in the right places and access to carbon dioxide storage sites) are

included

at

the

design

stage

so

that

capture

equipment

can

be

added

without

prohibitive costs in the future. Utility companies building power plants in Europe and

the USA are already doing this in their domestic markets to make sure they can use

CCS to avoid large cost penalties for CO

2

emissions in the future.

Another

energy-related

development

that

prepares

for

CCS

is

introducing

new

ways

to

use

'decarbonised'

energy,

electricity

and

hydrogen.

Even

when

the

carbon

dioxide produced in the production process is captured, making synthetic gasoline or

diesel

fuel

from

coal

still

results

in

half

of

the

coal

carbon

being

emitted

to

atmosphere.

In

contrast,

using

electricity

made

from

coal

with

CCS

in

an

electric

vehicle or a new plug-in hybrid vehicle or using hydrogen made from coal, releases