A cogeneration-district-heating scheme for Leicester city, UK

Energy Vol. IX. No. 6. pp. f&i-69X.

1‘993 Printed in Great Britain. All rights reserved

A COGENERATION-DISTRACT-HEATING

SCHEME FOR LEICESTER CITY, UK

YASURO TAKI $, RAMIZ F. BABUSHAD

+ Research & Development Nishimiyahara l-7-31,

4 Department

of Applied

Cranfield

Department, Yodogawa-ku,

Energy,

Institute

Abstract - The use of cogeneration UK.

private

It has

attracted

sector.

assessment Leicester.

In this

paper,

Several

generating

capacities,

30 November

we

describe

cogeneration

investment

which

are considered.

the financial

The use attractive

of a centralised cogeneration option if environmental costs

for various

COGENERATION or

combined

simultaneous utilisation is used in the national the

cogeneration

ranges

number

individual

countries

(e.g.,

As the area supplied and installation costs

economic

respect

to

was

the

space

may convey

and Sweden).

for

one

third

to

production

of

heating,

shaft

domestic

hot water

hesitancy slow

power

with

hot

water

and

or both

under

wide

and institutional

compared

Nevertheless,

the

and from

with

barriers

that

percentage

in other

rise in the

significant.

rather than a financially profitable business. to which high CO, concentrations in the

environmental

power half

most-

by a cogeneration-DH scheme becomes large, the following apply: (i) the capital of laying the distribution network become dominant, and (ii) the scheme tends

service effect,

world-wide

In the UK, electric

to

conditions.

financially

atmosphere

contributor, results in a large part from burning of fossil fuels. The reduction serious environmental concern. The Earth Summit held in Rio de Janeiro important

performed

and demand

steam,

Due to political

is now

of and

is usually transformed to electricity a heated fluid can be distributed

has been disappointingly

Germany

numbers

HEATING

implies

provide

economics

for the city

to plant

assessment scenarios

DISTRICT

(CHP)

pipelines

systems

and

scheme

plant is found to be the are taken into account.

to consumers.

Denmark,

cogeneration

with

The shaft power (DH) pipelines,

buildings

of cogeneration-DH

of small-scale

to become a public The greenhouse

power

District-heating

and temperatures

in the UK, the growth European

to

energy.

of pressures

and

UK

environment

district-heating differ

WITH

of the heat produced. grid. Via district-heating

plant

industrial-process

heat

OAL,

1992)

A robustness

compare

Cogeneration

Engineering,

MK43

an energy, with

options,

returns

Bedford

with district heating is not a common practice rn significant support from the Government or the

neither

for a proposed

IDEC lzumi Corporation, Osaka 532, Japan of Mechanical

of Technology,

(Received

the

School

DOUGLAS PROBERT +

and

+.*

stations

of the

total

conference, are the largest CO,

emitted.

reflects single Various

increasing

polluter

public

are

the

major

of atmospheric CO, is of in 1992, which was an concern

of the environment,

alternative-energy

about being

resources

for

this

issue.

responsible electricity

generation (e.g., nuclear power, wind turbines and solar energy) have been developed, but at variable or high costs. If used, they would reduce the total rate of CO, produced. Cogeneration-DH is one of the better costs.

’ To whom

practical

means

all correspondence

for achieving

should

energy

conservation

be addressed.

687

and hence

CO,

reduction

at acceptable

YASURO TAKI et al

688

COGENERATION-DH

IN THE UK

First attempts to introduce DH in the UK occurred horticulturist, used pipes to distribute steam for heating

in 1742 a room.’

when Hugh Plat, a lawyer and In 1745, William Cook, conveyed

steam by similar means to heat his home in Manchester. He also attempted to heat a group buildings in this same way from a single source of heat. Cogeneration in the UK started in industry the Singer factory in Clydebank in 1898. One of the earliest cogeneration schemes was installed 191 1 at Bloom was

Street,

followed

The Marshall

Report

A political 1973

Manchester,

by other

schemes

price

that

cogeneration-DH

was

found

steam

in the

to neighbouring

1950s

shops,

offices

and Nottingham

and factories.

in the early

This

197Os.*

(19791

pressure-group

fossil-fuel

to supply in London

of at in

advocating

cogeneration

crisis.

The resulting

would

be important

not to be economic

was

Government when

at the then

formed

in 1975

Combined

Heat

oil and gas become

current

(i.e.

1979)

scarce

net unit

as a consequence

and Power

Group

although

prices

of the

concluded

cogeneration-DH

levels

of oil, electricity,

etc. Nevertheless, the report recommended construction of cogeneration-DH demonstration projects and formation of a National Heat Board. However, these recommendations were subsequently rejected by the now-defunct Department of Energy (DOE).* The lack of penetration of cogeneration and DH into the UK market has been due to two major reasons: (i) the abundance of natural gas at low unit prices and (ii) considerable freedom in the choice of fuels

used

The Atkins

by consumers

Report

in comparison

with

that

prevailing

in other

countries.

(1982)

In response proceed with

to the Marshall Report, studies of the viabilities

the DOE appointed of cogeneration-DH

Atkins Report and Tyneside

In 1980 recommended be selected for further

that the cities of Belfast, Glasgow, study. In 1981, the DOE announced

six

plus

Edinburgh,

Leicester

programme.* However, Edinburgh and London of return.

and

the Atkins to develop

Manchester,

would

Report3 in 1982 cogeneration-DH

The subsequent response of the Government 1984, invited bids from local consortia, involving detailed

studies

in up to three

(Northern

Ireland),

the

City

Lead

Edinburgh

Scheme).

Of

the

during

recommended that schemes as these

cities.

and Leicester

rejected

be examined

cities,

However,

(England),

Sheffield,

Act

(1983)

in 1985, and offered

London

that

local electricity

It is logical

distributors

should

allow

and

privately-owned

their excess electricity to the national grid. For potential cogeneration earner is one of the key factors that influences the decision whether Since well

1909,

as that

in this respect first

legislative

generator customers, distribution

in the UK, a private of a third

to:

party.*

and tended support

to suppress from

to meet utilities

the Local

in private with

the

Electricity

generation

Energy Board

Act

of the

DOE, in further

the DOE selected

Belfast

a total

of f 750,000

Newcastle

(i.e.

continued,

in

support.

As

Government

its own

units to export

electricity

possessed

almost

and, hence, (I 983).

This

(LEB) for its own

privately generated electricity to the LEB, and (iii) use of the LEB for its own use or the use of its customers.

The Government speculated that the former Central Electricity in cogeneration and promote the sale of heat in the same way electricity grids and the electricity markets. However, this Act

phase

delayed until the for grants towards

cogeneration

has been allowed

came

next

installers, this potential revenue or not to introduce the scheme.

electricity-supply

investments

for cogeneration

(i) buy electricity

(ii) sell network

generator

Nevertheless,

the

funding be provided for Belfast, cities provided the highest rate

conjunction with the private sector, developing their own schemes without a result, six UK cities attempted to introduce cogeneration-DH schemes.* The Eneray

Atkins and Partners to locations. The interim

Liverpool, London, Sheffield that nine cities, the original

to the Atkins Report was public and private sectors,

of the nine chosen (Scotland)

the consultants W.S. schemes in particular

demand

cogeneration. allows

as

a monopoly the

The private

use or the use of its the

transmission

and

Generating Board (CEGB) would invest as they had developed the nation-wide helped those investors in industrial and

small-scale cogeneration applications. The LEBs did not actively take it into consideration. The CEGB was not willing to build cogeneration plants, even in the lead cities, although the estimated financial return was acceptable according to the CEGB’s normal criteria.

689

scheme

A cogeneration-djstrict-seating

The Lead Cities The progress

achieved

with

respect

to cogeneration-DH

in the three

lead cities as well as the other

three privately-supported cities has been disappointing. Although Belfast City Council was enthusiastic about cogeneration-DH, the limited powers of local government in Northern Ireland inhibited its active promotion. So a consortium was set up excluding Belfast City Council. A study showed that the total capital expenditure would be high before any revenue could be generated. Regardless, the return on any investment

would

be well

worthwhile

over a 20 year period,

should be the lead (and a substantial) investor.4,5 Edinburgh District Council set up a consortium to investigate cogeneration4X-l of-return

system:

it halted progress

on the investments

for financing

of the Belfast

solely by the private

Leicester has established scheme. The cogeneration

to await

further

and Edinburgh

but for success

the financial

the Government

viability

financial

assistance.’

schemes

were

of their proposed

The predicted

not significantly

rates-

attractive

sector.

a consortium and is proceeding with a plan for a city-wide cogeneration-DH plant, originally due to start production in 199 1, has been delayed.

During the planning stage of the Newcastle cogeneration-DH scheme, the predicted rate of return appeared to be sufficient to enable the scheme to be financed solely by the private sector. However, the privatisation of the national electricity-supply industry discouraged proceeding with the scheme. A DH system has been built in part of Sheffield to cogeneration.7 The Electricity This

Act

resulted

regional

customers.

as the fuel: the city is now converting

(1989)

in two

electricity

using refuse

major

electricity

companies

The electricity

generators

(RECs) which

trade

between

(i.e.

National

are responsible

Power

and PowerGen)

for supplying

the major generators

and twelve

the domestic

and the RECs takes

and industrial

place through

an

electricity pool via a competitive pricing system. These arrangements encourage a free market and competition between the electricity generators and suppliers, and hence allow, in theory, fair trade for new private generators and cogeneration users. Joining the electricity-supply business requires obtaining a licence.e However, exemption from the necessity

for having a licence were permitted.’

include:

fi) any generator

who never

The main exemption

provides

more than

10 MW

categories

relating

to cogeneration

or who only provides

more than

10

MW to a single consumer, and (ii) self-generation, where 51% or more of the output of a generating station is provided to a single consumer on the same site as the station. The RECs have a duty to buy any surplus them,

electricity

according

whose

main

business

cogeneration

employers

installations.

However,

second

from exempted

to the Energy Act

category.

generators

1983.

is not electricity including many

Hence,

production.

almost

industrial

these

and also have to offer the usage of their network

As a whole,

these Category

all commercial generators

exemptions

regulations

give privileges

(i) involves

as well

can also be eligible

appear

comparatively

as public

to be encouraging

suppliers,

to

to generators small-scale and industrial

to be considered to prospective

under

the

cogeneration

operations in the industrial, commercial and public sectors. A city-wide cogeneration-DH plant generally cannot usually be categonsed within these exemptions, as a single plant may easily exceed a IO MWe output. If the cogeneration-DH organisation then was other

than

generation

an electricity

company,

which

not be the main purpose

The produced case

forces

Agreement.

would

electricity

the

wide scheme

to try to obtain

the organisation

the National Grid electricity-generation

could

be a problem.

The scheme

would

involve

electricity

of the scheme.

could be sold either through

organisation

Then

there

the pool or to the tocal customers.

pool membership

will face charges

under

the

Pooling

(for using the cogeneratron

and

system)

The former Settlement from either

Company or the local REC as well as experience competition with the major companies.‘“~” Several small-scale cogeneration plants could be linked into a city-

and so then would

not be exempt

from obtaining

CURRENT

a licence.

POLICY

The UK has been fortunate in that it has a wide diversity of energy resources from which it can meet its needs. However, the Government does not have any explicit energy policy other than nominally to allow for market electricity

it is inevitable fuel thrift

E6Y 18:6-F

forces to operate.

power-generators

Major energy suppliers,

are all privatised

that they will act in a partisan

national

benefit

is achieved.

and compete financial-manner

i.e. British Gas plc, the RECs and the major for market

share.

With

the present

and so not ensure that maximum

rules, fossil-

690

YASURO TAKI

et al.

The release of thermal energy is a by-product from orthodox power-generation plants, and so an electricity generator could possibly make a profit by selling such heat via a DH scheme. However, the former CEGB, and, at present, the National Power and PowerGen have not been involved actively in cogeneration-DH schemes. They have been concerned primarily with electricity production and so have not been cogeneration-DH advocates. Nevertheless, since the decision to privatise the electricity-supply industry, the Enron Corporation completed a feasibility study for the construction of a 1725 MW gas-fired independent cogeneration station at ICI’s Wilton Works, on Teesside. This has now been constructed. The station’s generating capacity is the equivalent of 3% of the current UK total electricity supply, and its proposed natural-gas consumption would represent over 6% of the total gas market. This will be the largest independent power plant to be built in the UK and the largest cogeneration station in the world.‘* In addition, the Corporation of London has given its approval for Citygen (a joint venture between British Gas plc and Utilicom Holdings) to proceed with plans for a cogeneration scheme to serve the City of London. The plant is expected to be completed in three phases: the first with a base load of 20-30 MW, with subsequent phases to bring the capacity up to more than 90 MW.13.14 Several local councils are enthusiastic about cogeneration, and the consequent energy-thrift and CO,emission reduction achievable. Such councils wish to promote cogeneration-DH schemes, however, most of them face difficulties in attracting private investment to initiate such schemes. In addition, they (e.g. Leicester City Council) would prefer not to become involved in supplying electricity to their customers. Selling all the produced electricity via the local REC or directly to the pool was not always an advantageous financial option because of the low unit-price offered. Thus, it could be reasonable to run smaller cogeneration-DH schemes that are exempted from the requirement of obtaining legal licenses. The DH thermal-energy schemes in the city of Leicester are supplying the required heating to several thousand residential flats, maisonettes, and public buildings such as schools, nursery houses, and old persons’ homes. When these DH facilities need full or partial replacements and refurbishment, it is the intention of the Leicester City Council to develop and convert the existing DH facilities to cogenerationDH scheme(s). It is the aim of the present investigation to study a proposed cogeneration-DH scheme for Leicester and to analyse its long-term perspective. An energy, environment and economics assessment model is employed.

ENERGY-ENVIRONMENT-ECONOMICS

(EEE) MODEL

The EEE model15 is a mathematical tool developed to run on a personal computer and designed to predict the feasibilities of cogeneration-DH schemes as well as their contributions (when substituted for existing heating and electricity-producing systems) to global CO, reductions. The operation of the model is divided into three sequential stages (see Fig. 1): (iI simulation of the operation of the components, (ii) an economic account, and (iii) presentation of the economic and environmental results. At all stages of the analysis, the data bases can process several options and various economic conditions without the necessity for inputting data repetition. With this model, the performance of a proposed cogeneration-DH plant has been assessed over a complete life-cycle. The hourly heat-demands with a given monthly heat-demands as well as their time pattern have been predicted for the selected cogeneration-units. Then, the model readily accounts for the imported and exported electricity with respect to the REC. The employed tariffs are regularly updated. According to the given investment and the running schedule, the net cash receipt is calculated for the proposed cogeneration-DH scheme. The net present value (NPV) method is adopted to evaluate the financial returns for the various economic scenarios considered. The amount of CO, emission from the cogeneration-DH system is compared with that equivalent energy output from the conventional boiler and the electricity supply utility. In conjunction with a sensitivity analysis, a robustness assessment of the cogeneration-DH scheme is made: it considers for several options and various scenarios which can affect the economy of the scheme. Economic performances for investments in each of these options are predicted and compared for any selected economic scenario as well as for different tariffs and several demand estimations.

A cogeneration-district-heating

Fig. 1. Schematic

diagram

scheme

of the EEE model.

LEICESTER COGENERATION/DH Since being selected wide cogeneration-DH

691

as one of the lead cities, Leicester scheme. The development started

SCHEME

has continued in 1987 with

its efforts a planned

to introduce DH network

a cityacross

the city and a combined-cycle cogeneration system based on an existing gas-turbine plant, then owned by the CEGB.” At the time this scheme was initiated, the energy-thrift advantage of cogeneration-DH had been recognised. Later, Leicester City Council began to consider this scheme as a more environmentally-friendly

energy

1990, Leicester was chosen campaign for a sustainable sustainable

developments

transport,

waste

environment achieving reducing

within

and pollution,

and energy

supply,

social thrift

in association

as the UK’s ecosystem. the food

constraints

of

and agriculture,

environment.

with

national

a working economy

Cogeneration-DH

simultaneously

the

environment

campaign.

In

Environment (i.e. ‘Green’) City and started planning its own The aim of its campaign is to permit only realistic and

with

city.

is deemed

contributing

Its

concerns

and work,

to satisfy

to

built

involve

environment,

be a prospective

the environmental

energy, natural means

mission

of

(e.g. by

CO, emissions).

The Site The present case study Matthew’s and St. Mark’s

refers to three council-owned estates, at which the Leicester

The three

during

sites

maisonettes The newly

installed

A proposal operation present

investigation Enerav

heat

loads

estates,

Some

were

respectively

and early

plants

of the DH facilities with

future

1970s.

They

are equipped

pipelines

of these

supply includes than

are comprised

with

either

of 2142

gas or coal-fired

hot water

at up to 120

individual

variable-volume

can be linked

rather

the St. Peter’s, St. operating DH plants. and

boilers.

“C. and dual-fuel

to the cogeneration-DH

existing

flats

scheme.

The

resources.“-”

Demands

the beginning

about

February was surprisingly for the same period were 3).

distribution

is concerned

from

1960s

The DH plants

refurbishment

and Electricitv years

the

buildings.

preinsulated

for the

For the three Mark’s

built

of the boilers.

Thermal

base

were

and 13 public

housing sites, namely, City Council is currently

4 MW,

3.5

of 1987 MW

to the end of 1989,

and

(see Fig. 2). The prime

2 MW movers

for the were

St.

the estimated Peter’s,

chosen

St.

to satisfy

average Matthew’s these

monthly and St.

base loads.

warm in each of the three years considered. The monthly electricity evaluated according to the case study for a high-rise block of flats?

demands (see Fig.

YASURO TAKI et al.

692

m

St.Peter’s

&

1 -I StMark’s

StMatthew’s

I

1

I

1 Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Ott

Nov

Dee

Month Fig. 2. Monthly

thermal-energy

demands

based

on average

consumptions.

I I m

St.Peter’s

u

St.Matthew’s

rl

St.Mark’s

1

3000

u

s

__I

1500 1000 500 0

Jan

Feb

Mar

Apr

May

Jun

Jui

Aug

Sep

Ott

Nov

Dee

Month Fig. 3. Estimated

Heat

monthly

electricity

demands.

Charoinq

Currently,

the Leicester

the charging for each

rates

dwelling.

depend This

City

Council

imposes

on the floor-areas leads

to an average

a fixed

unit-heat

of the dwellings, annual

heating

charge

for its DH supplies.

Although

the average

is calculated

as f8.501week

bill of over

f400

is considerably

which

higher than the average annual heating bill (about f200) for other DH schemes in the UK. Nevertheless, according to the fixed rate and the average heat demand from the DH schemes in Leicester, the equivalent average unit price is deduced to be about 1.8 pence/kWh (the gas price is about 1 to 1.5 pence/kWh), which is lower than the average unit rate (about 2.5 pence/kWh) employed in other DH schemes. This contradiction suggests that the rate of heat demand/wastage in Leicester is significantly higher than for the other schemes. Unfortunately an incentive to reduce the

A cogeneration-district-heating

heat

wastage

home

by customers

consumptions.

but these

were

heat meters energy (i.e.

Such

built

before

bills

provided

as the

of energy

the 1973

energy

financial

charges

card

in advance

do not

crisis.

To overcome

for the heat

with

this problem,

consumption.

reflect

other

individual

individual

DH schemes, card-operated

for the amounts of consumed system, a customer has to

This

system

is incorporated

in this

economic growth and the subsequent increases in unit fuel prices suggest that the unit rate should be about 3 pence/kWh. However, in order to avoid a significant increase in the heat

of the

proposed

residents,

a reasonable

cogeneration-DH

Electricity

unit

rate

of about

2.5

pence/kWh

is employed

in the

currently

schemes.

Metering

As the total electricity-production capacity does not exceed cogeneration-DH scheme is exempted from obtaining a license. can be traded

with

the Regional

national grid can be either line’s capacity and length. The

made

use has been experienced

need to be installed in each home. While a customer pays in the form of electricity, or natural gas) in the orthodox

purchase a magnetic investigation. Recent for heat

is not inefficiency

693

scheme

REC provides

whereas

Electricity

tariff

i.e. East Midlands

via a 11 or a 33 kV line. The capital

guaranteed

a day-rate

Company,

10 MW for the Leicester system, the Nevertheless, the generated electricity

‘top-up’

of only about

and

‘back-up’

2 pencelkwh

cost

plc. Physical

(about

electricity

105f)

supplies

is paid for electricity

connection

to the

is dependent

on the

at about

exported

5 pence/kWh,

to the national

Therefore, only the surplus electricity which is not consumed at the sites will be exported. The conventional metering, undertaken by the RECs, is one of the most labour-dependent electricity-supply industry. A more sophisticated system for metering incurring communications

between

the supplier

and the customer

is needed:

e.g. signalling

grid.

jobs in the two-way

via the mains

(as in

the USA) or a cellular network of static receivers (as already exists in the UK). Remote, error-free meter reading is thus a practical option. The ultimate purpose of these communication devices would be to set the customer free to choose and charge the electricity supplier at will. However, at present, the RECs are not enthusiastic to invest in such communication systems because the perceived benefit IS insufficient for electricity suppliers as a result of such investments. Also, standardisation is no yet lacking

for such

A simple electricity flat).

systems

and cheap (as well

schemes

back

The

can

at the

cogeneration-DH

via hot water,

at a design

to be employed, maintain.

the

This

an instant

of flats

can be achieved

(e.g. a meter

photograph

panel

of the

panel,

in the

near

to be employed

are responsible

electricity

for

have

temperature

for such

during

by installing

at the entrance

and future

the

to each

the

readings

for

cogeneration-DH

can

be

schemes.

production an imported

The

4)

will

comprise

two

The cogenerated

gas

turbines

at 70 “C. The pre-insulated because

last

meter

meters

imbalance,

is less than

the

decade for

they

(i) measuring

and the supply

the

network

and

heat will be supplied,

the

and the consumed

network.

Fig.

“C and returned

heat

The electricity

at the plant,

signifies

(see

and heat demands.

of 120

popular

a card-operated

charging.

electricity

Leicester

the electricity

become

computerised value

Louistical

depots

will

financial

cogeneration negative

for a block in one place

is likely

local councils

to fulfil

have

Each dwelling

via

meters

take This

plant

boilers

generated

procedure

Scheme

supplementary

appropriate

then

office.

in the UK, where

The Proposed

effective.”

as gas and water)

A meter-reader

interpreted

to be fully

meter-reading

are easy consumed belong

pipelines,

to install heat,

and

and (ii)

to the REC. The

electricity

at the sites

if

between the two values (i.e. the is bought by the company, whereas a

positive,

demand)

will be checked

by the REC

electricity.

Analysis

is applied and their

aim is to achieve costs for a given

commonly locations

to distribution in a physical

systems: distribution

it is helptul system.

when

the optimal trade-off between the total warehousing demand. For the present investigation, an analogous

with respect to the cogeneration-DH energy respectively.

plant

costs

deciding

Warehousing

and the distribution

upon

is a typical

the

number

application:

of the

costs and the total delivery procedure may be employed costs

of electricity

and thermal

YASURO TAKI et al.

694

L~___~~_~~~_~~_~~__~. Cogeneration plant

Fig. 4. The proposed

Gen = Generator GT = Gas turbine cogeneration-DH

scheme for the city of Leicester.

The cost characteristics of cogeneration-DH plant can be similar to those of a conventional power plant because there are a lot of common engineering-features between the two. The distribution costs of heat can be qualitatively similar to those of electricity supplies, as DH pipes are characterised by their high capital and low operational costs as well as long lives (i.e. about 25 to 30 years). However, laying a pipeline for the transportation of thermal energy often needs large-scale civil-engineering excavations and is usually more expensive than constructing an electric transmission line for conveying the same amount of energy. In addition, DH pipes would have to be laid, whereas the transmission of electricity can take advantage of the existing national grid. Because the present technologies do not allow much flexibility in the transportation and delivery of heat, it is not financially viable to build a nation-wide heat-distribution network analogous to the existing electricity-supply network. However, many more high heat-demand per square kilometre city-wide schemes are likely in the future. If cogeneration-DH plants are to be centralised, then they will need larger and more complex networks which will inevitably lead to higher constructional costs. On the other hand, it is expected that economies of scale will also apply for the cogeneration plants in a similar way, The optimal number and sizing of the cogeneration plants for supplying a given heat demand can be obtained by summing the two cost functions, namely, the total lifetime transmission costs and the total lifetime plant costs and determining under what conditions a maximum occurs. The three generating sites are remote from each other. Options involving different numbers of plants as well as different engine sizes were considered (see Fig. 5 and Table 1). The Decentralised Option (i.e. three separate plants) involves an independent plant on each site. The demands of the St. Matthew’s and St. Mark’s estates are merged in the intermediate Option (i.e. two plants only). In the Centralised Option, a single large plant supplies the three sites. For the latter two, Large-Scale and Small-Scale engine-sizes were employed. The total length of the pipe networks are about 2.7 km and 1 .2 km for the Centraked Options and the Intermediate Options respectively. Performance

Analvsis

(i) Scenario Analysis: The Large-scale Centralised Option involved the highest capital investment (about flOm), while the other four options each amounted to about f8m. The various annual economic growth indices were categorised into those for unit fuel price, public electricity unit price, local electricity unit price, unit heat charge, maintenance as well as labour cost per kWh supplied, and tax. Initially, all economic indices were rated as identical (i.e. at 8% per year), as a base scenario, and then relative changes of the cumulative NPV profits were deduced while each index was altered by 2% at a time.

A

st.Patafs n C_

S.PWS

JIL

695

scheme

cogeneration-district-heating

n-

Cogeneratlon plant

NewSWS

St.Matthdr

AIL

a-

Coganafation plant

St.Mark’s

St.Mark’s

St.Matio

lllL

n +-

cogeneratlonplanant DECENTRALISED SYSTEM

INTERMEDIATE SYSTEMS

Fig. 5. Design options

CENTRALISED SYSTEMS

of the proposed cogeneration-DH

Table 1. The proposed

scheme.

options.

The change of such an economic index either improved or reduced the attractiveness of the financial investment. The most influential factor was the fuel price index. A change in the heat charge index also affected the economics of all options significantly, as the heat charge provides the major income of the scheme. On the other hand, the tax charge index did not influence the economics significantly. If the discount rate remains the same (i.e. at 8%), altering the economic index did not affect considerably the order of the options with respect to the cumulative NPV profits. Other cases were considered whereby the heat and electricity demands were altered, while the economic scenario remained unchanged. For instance, the heat demand was anticipated to be lower when a unit-rate charge, via a card-operated heat meter, was introduced. Such a reduced heat demand imposed a negative scenario upon the economics of all the options. The smaller-scale engines were also seen to be the better options. (ii) Robustness Measurement: Several scenarios implied disadvantageous economic environments for financial investments in the cogeneration-DH scheme, e.g. high unit fuel price, low unit electricity charge to local customers, low unit heat charge, high maintenance cost, and high tax rate. The concept of economic robustness promotes the selection of a scheme which is economically stable during financially-disadvantageous periods. This policy also meets the aims of the cogeneration-DH scheme, i.e. serving the public and reducing global CO, emissions. Thus, the advantageous economic scenarios were neglected and only the critical scenarios were assessed for robustness.

696

YASURO TAKI et al.

The rank of the options selected scenarios. of the option being

for the investments

The robustness within a certain

measurement of the economic robustness For each of the selected scheme durations, discount rates, i.e. at 2%, 8%, were not significant, the options

Table

were

obtained

according

to the preceding

analysis

of an option can be defined in terms of the quantitative rank among all the options for the proposed scenarios.

of the

possibility A numerical

based on this definition is shown in Table 2 for each option. i.e. 15 and 25 years, three ranks were considered for three

and 14%. Where the differentials of the NPVs could be considered to be of the same rank.

2. The economic

robustness

(a) Myears

of each

for any two

options

the

scheme

of the options.

duration

(b) Z&years duration

The

Small-scale

durations economic sensitive stable

Centralised

or discount rates scenario involving to changes

return

in such

in some

(iii) CO,

Emissions:

options.

The

CO,

Option

conditions.

scenarios The

be replaced

as a result

to be financially

involve

attractive

amount

the Small-scale

relatively

of CO,

low

for

various

emission

from

of introducing

the domestic

Intermediate

Option can provide

a

heat demands. is shown

from other than a cogeneration-DH

scheme) is the sum of CO, emissions would

seen

However,

which

annual

emission

was

considered. The Large-scale Centralised Option can be competitive in an a long-duration scheme as well as a low discount-rate and, therefore, is

boilers

in Fig.

6 for

all the

scheme (or CO, emission and conventional

the cogeneration-DH

scheme.

Although

vary slightly, the amount of CO, emissions were reduced by between 40 and 50% by the introduction of one of the considered cogeneration-DH systems.

power

considered

from a DH stations

that

the contributions for any option

case

CONCLUSIONS The popularity of cogeneration schemes in the UK has increased, especially as a result of implementation of the Energy Act (1983) which endowed cogeneration generators with the right to connect the system to the local supplier’s grid and the right to receive a tariff on a fair financial basis. This was

not altered

by the Electricity

Act

(1989)

which

enforced

the privatisation

of electricity

A cogeneration-district-heating

With

m

697

scheme

E

cogeneration

Without

cogeneration

SYSTEM

Decentralised

Large

Centralised

Small Centralised

Large Intermediate

Small intermediate

IO Rate

Fig. 6. Annual

generation

and of the supply

can be issued

10

industry.

these

did not induce

with

Exemptions

for all privately-owned

either

50

(thousand

and without

from

cogeneration

40

30

emission

CO, emissions

stimulated potential cogeneration users Energy supplies in the UK during the However,

20

of carbon-dioxide

60 per year)

cogeneration.

obtaining

systems

tonnes

a generation

of capacities

and/or

less than

a supply

10 MWe.

license This has

in the industrial and the commercial sectors. 198Os, have been controlled superficially by market

the private

sector

or the local councils

to support

forces.

cogeneration-

DH schemes. In addition, global concerns such as energy thrift and environmental pollution have not been considered to be priorities. Political misjudgment, bureaucratic inertia and institutional resistance to change have ensued, leading to excessive procrastination and thereby inhibiting progress. All these constraints could be alleviated through wise Government decisions about the aims of the UK energy policy. Cogeneration with DH should be an important part of any environmental campaign in the UK. An energy, proposed emissions of the

environment

reduction

prime

influential

scheme

achieved

movers

factors

were

possible

economic

and

gas

price

was

employed

Leicester, unit

of plant

heat

economic

numbers indices

NPV profits

scenarios

In

particular,

the

of a

the

as well were

CO,-

as sizes the

most

of the options.

as well

only the critical ones were selected Options were ranked higher for financial

Options.

the viability

as to evaluate

charge

the cumulative

advantageous

to study

as well

options

and

used to predict

hazards,

Decentralised

for

Five different

Unit

scenarios

model

proposed

by the scheme.

were not considered, and In general, the Centralised

Intermediate

computer

recently

considered.

in the economic

So as to avoid conditions assessment. the

and economics

cogeneration-DH

as demand

for the robustness returns than any of

performance

of

the

Small-scale

Centralised Option was the best. The Large-scale Centralised Option was more sensitive to changes in the discount rate and scheme duration, and so would not be recommended. In addition, the sizing of the prime movers is also an influential factor for the economy of a cogeneration-DH scheme. A smaller size prime mover provides a more robust financial return, especially if a reduction in energy demand

is anticipated.

implementation Lower

CO,

and power the “dirty

emissions

plants.

economic

were

depression for all options degradation

and waste

heat produced

- The authors

are grateful

for providing

information

should

not

be regarded

as a restraint

on

the

scheme.

predicted

Less environmental

electricity”

Acknowledgement particular

Any

of a cogeneration-DH

for this

compared

is the virtue by conventional

to the

project.

Leicester

with

the use of conventional

of cogeneration power

City

with

boilers

DH if it replaces

stations.

Council

and

to

Paul

Fleming

in

YASURO TAKI et al.

698

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