to be functionally and operationally efficient in the

high level location within the mechanical annexe, but a

production of electricity.

low level position either in the annexe or turbine hall

can be used provided acceptable pump suction condi­

6.3.4

Mechanical annexe

tions can be maintained.

The layout of the feedheating plant for the CEGB’s

Many

CEGB

stations

have

an

annexe

between

the

Littlebrook

D 3

x

660 MW

oil-fired

station

is

shown

in

Fig

2.28

and

Fig

2.29

shows

the

equivalent

for a

turbine

hall

and

the

boiler

house. This annexe

is

used

proposed 2 x 350 MW station.

mainly to accommodate some elements of the feed­

heating system, particularly the de-aerator, which on

CEGB stations has traditionally been located at high

'

7.2 Condenser and auxiliary plant

level to ensure an adequate suction head for the boiler

feed pumps. The annexe is also used to accommodate

The CEGB has experience of pannier and integral

various water storage tanks associated either with the

condenser

arrangements

but

recent

stations

have

feed make-up system

or

auxiliary

cooling

water

adopted

the

more

conventional

underslung

arrange­

systems.

ment where the condenser itself is located directly

Although traditionally termed a mechanical annexe,

beneath the turbine LP cylinders.

the central location within the station makes it suitable

The condenser is essentially an integral part of the

for the location of several other facilities, and it is

turbine but the layout engineer needs to consider the

common practice to locate switchrooms in

the

annexe

construction

and

maintenance

activities

together with

at

various

floor

levels

housing

both

unit

and

station

the

disposition

of auxiliary equipment. The major

switchboards.

space and access requirement is

for

tube

withdrawal

and insertion. Construction practice may allow delivery

6.3.5

Boiler house enclosure

of

full-tubed

condensers, and

due

consideration of

this

fact needs to be made in the station design, but provi­

CEGB

practice is to adopt totally-enclosed boiler

sion still requires to be made lor possible tube replace­

houses for stations within the UK. A small number of

ment during the life of the station. With a transverse

units

were

built some

years

ago

utilising

external

turbine arrangement this is often possible by utilising

boilers with only a roof canopy, as is common practice

loading bays or laydown areas located between units,

with many overseas utilities, but service experience has

but for longitudinal turbine layouts, removal sections of

clearly demonstrated that such a practice is ill-advisable

the building cladding or a separate local enclosure may

to UK weather conditions.

be required to give adequate access,

as indicated

on

Fig 2.30.

.7 Turbine-generator systems

An acceptable cooling water pipework or culvert

routing to the condenser inlet and outlet waterboxes

7.1

Feedheating plant

needs to be established. The design and routing in the

immediate vicinity of the condenser is influenced by the

The

feedheating

plant

forms

an

integral

part

of

the

need

to

ensure

a

good

water

distribution

between

condenser

flow

paths

and

a

uniform

flow

through

the

generating

process

by

raising

the

temperature

and

condenser

inlet

and outlet

isolating

valves which

on

pressure of

the

condensate

returning

from

the

turbine

CEGB

stations

are

typically

of

the

butterfly

type.

to

the

boiler

and,

if

necessary,

accepting

make-up

Elsewhere

within the

turbine

hall

it

is

generally

neces­

supplies from the reserve feedwater system. .

sary to

avoid the

foundations

of

the

main

building

The

plant

is

essentially

a

number

of

pumps

and.

columns, turbine

block, heavy auxiliary

plant items and

heaters

arranged

in

series

and

which

are

linked

by a

areas of

high superimposed

floor

loadings

such

as

lay-

pipework system. The

location

of

each

of

the

com­

ponents in

the system is required

to

follow logical

and

down areas.

The

dimensions

of

the

cooling

water

conduits

arc

defined sequence, and it is important in terms of the

established by optimisation studies with the level below

overall system economics and hydraulic performance,

for each element to be correctly located in relation to

the station basement being determined by reference to

the other and to the turbine in particular.----------------

the hydraulic gradient and acceptable civil construction

The

feedheating system diagram, Fig 2.27, shows

techniques. Since the foundation system for the station

that the system has numerous interfaces and pipework

is very site specific, the overall integration of the

connections to the turbine, and to minimise the overall

conduits into the civil engineering design needs to be

cost and system losses, the CEGB practice is to locate

resolved on a site-by-site basis.

the main elements of the system in logical groups

The main auxiliary plant associated with the con­

around the turbine. The de-aerator and its associated

densers is air extraction equipment for the steamside

storage tank however need to be positioned to provide

and, depending on the system hydraulic conditions, for

water with a suitable suction head for the boiler feed

the waterside also. Steamside air extraction plant

pumps. Traditional CEGB practice has been to adopt a

usually consists of a number of vacuum maintaining

88