Low exergy reactor for decentralized energy utilization

Progress in Nuclear Energy. Vol. 37, No. 1-4, Pp. 405-410. 2000 Q 2000 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0149-1970/00/$ - see front matter

Pergamon www.elsevier.com/locate/pnucene

PII:SO149-1970(00)00079-2

LOW EXERGY REACTOR FOR DECENTRALIZED

YUKITAKA

Research

Laboratory

KATO

for Nuclear Reactors,

Tokyo Institute 0-okayama,

ENERGY UTILIZATION

of Technology,

Meguro-ku,

Tokyo 1528550,

Japan

ABSTRACT A new

conceptual

proposed by

the

and its possibility reactor

environmental

that

water reactors combined

thermal

energy

trend.

energy

Cogeneration energy

supply of the

(LER)’ was

The LER is defined at a temperature

systems

based

on the LER

The enthalpy

was evaluated

system

light

based on the

device and steam turbine

utilization.

systems LER

near

is lower

by the conventional

of the LER was discussed

heat pump, thermoelectric

efficiency

reactor

100°C and 300 “C, which

of the energy generated

for decentralized

those decentralized The

about

The necessity

with absorption

nuclear

qualitatively.

low-exergy

between

technology

were proposed

‘low exergy

was discussed

temperature (LWR).

energy

named

generates

temperature

than the output present

reactor

was

using practical

compared

conventional

LWR system.

decentralized

heating and cooling system. 0 2000 Elsevier

balance

with

Science

data.

that

The LER system was expected to be suitable

of of

for a

Ltd. All

rights reserved. 1. INTRODUCTION Because of recent rapid change in the electricity expected

to be changed

in order to enhance conventional Agency,

drastically

cogeneration

1998).

in the next decades.

energy utilization

systems are installed

Recently

developed

down of the supply area from districts Then, energy generation energy generator.

efficiency

generation

technology,

Cogeneration

and the reduction

systems

the energy supply system is have become

of carbon dioxide

in an area less than about 10 km in diameter

fuel cell and micro-gas to smaller

turbine

technology

areas, that is, buildings

Generally,

(Danish

have enhanced

and residences

Energy the size-

(Lenssen,

1999).

has been no longer special subject, and citizen will be able to own easily a personal

For new nuclear energy systems in future, we would have to consider

supply of non-nuclear

more popular

emission.

systems.

It means that decentralization

key issues for nuclear systems in future. 405

and cogeneration,

such a trend in the

and cost-down

would be

406

Y. Kato Cooling

Cooking

Fig. 1 Energy consumption share at residential and commercial use in Japan in 1997 (Energy

Residential use Commercial use

Data and Modeling

for decalized

commercial

system,

enew

uses in Japan in 1997 (Energy

of 26.0 % in whole national

energy

quality

such as hot water, heating

quality

of electricity

shows a comparison ordinate

Figure

power.

which

Data and Modeling

consumption

of energy

supply scale between

output

of each plant.

is the most developed

country

nuclear reactors is defined by International small reactor defined

by IAEA would

decentralized

system,

supply

energy

accompanied

by heat transfer

a plant like a conventional

scale less than about

because

1 and 2, a reactor

decentralized

cogeneration

smaller

for practical

expensive

0 m

IAEA.

reactor plants.

are operated

Industrial

use.

in

of the

For the discussion is indispensable.

because

these

of The

supplies

are

Larger amount of output from

but thermal

energy distribution

for practical

decentralized

scale for decentralized

in

Then an electrical energy

supply

energy system.

From

(temperature)

output

is suitable

for

REACTOR

in order to meet the requirements

for the decentralized

of

CHP

.

Ornhq CHP plant for 400 people , _........................................................

0 -

100

200

Heat outpur temperature

300

400

500

Ryslinge folk high.__..._........._ school . . . ..___ r...f~~j~s~~~~~~

Fig. 2 Relationship between common energy systems and output scale [I]

600

from a process, T , [‘%I

Fig. 3 Definition of the low exergy reactor, LER 0.1

2

The

practically

The classification

process

cost.

and lower-quality

Figure

A smaller reactor than the ultra

system,

plumbing

energy.

plant

Tomatogleenhpuses _ . . . .. ..__‘“‘iii~~.i;eter~-..._

. .

plants

decentralized

expected

is appropriate

amount

reactor LER is proposed

m Vivorg LargeCHP for 30,000 people

,6

plants and nuclear

of higher cost for the heat transportation.

2. LOW EXERGY

‘jb 2

to low-exergy

Those cogeneration

100 MWtherma,is generally

having

corresponds

energy system.

A conceptual

.o .&

with low with high

larger area for consumption,

plant, and an area having a few km of diameter Figs.

Demand

to the heat transportation

loss and, especially,

the larger area is not economical output

for the energy

the scale of decentralized

reactor requires

and

Both uses occupy the share

in the field of cogeneration.

be required

restricts

1999).

share for residential

100°C is larger than that for the energy

Atomic Energy Agency,

the consideration

of heat and cold energy

Center,

(1.5 lx 10’6kJ/year). below

The energy with low quality

shows the electric

Denmark,

1 shows an energy consumption

and cooling

Center)

100

50 Energy consumption share [%]

0

use.

Decentralized

energy

utilization

407

Case 1

Case 2

Case 3

Fig. 4 Proposed systems for decentralized co- and tri-generation based on LER

The

LER

temperature

is defined around

conventional maximum

light

water

possible

temperature,

by the reactor 100 to 300°C. reactors

thermal

which

produces

low-exergy

Figure 3 shows the maximum (LWR)

efficiency

and fast breeder

(the thermal

environmental

The bold

cycle),

of LER and

line

shows

the

vc [-I, for heat output (1)

and 77, indicates

The reactor that produces output

reactor developments

the exergy range

and commercial

maximum

is not efficient

for power

uses as mentioned

generation,

in the following

The lower temperature benefits

and also (4) higher

reliability

for heating

and

The effort for nuclear

output for power generation

with higher

with high efficiency,

however,

for the reactor design such as (1) simpler design, (2) safety and (3) lower-cost, for operation,

(5) material

in the design, (7) easy maintenance

cost and simple design.

efficiency.

as LER in this paper.

but enough

sections.

output is not suitable for power generation

temperature,

power generation

output than the LWR is defined

in the past was oriented to higher temperature

brings simultaneously new-technology

of a reactor and the environmental

and also the theoretical

lower exergy (temperature)

temperature

at residential

efficiency.

(FBR).

of a Camot

near

efficiency

)/T,

where T, [K] and T,, [K] mean the heat output temperature respectively,

cooling

reactors

efficiency

energy

thermal

which is defined as

t7, = (r, -T,,,

The LER’s

thermal possible

endurance

enhancement,

and (8) easier mass production

Then, the LER would have a possibility

(6) no requirement

for

of plant induced by low-

for the promotion

of the nuclear

energy

utilization.

3. DECENTRALIZED The LER is expected system, machines.

because

LER output

As mentioned

COGENERATION

to be suitable temperature

in the Introduction,

uses is for heating and cooling below 100°C. with conventional

heat transformation

for thermal

agrees

SYSTEM energy

BASED ON LER

source

with the operation

for a decentralized

condition

a major part of energy demands The production

cogeneration

of common

at residential

cogeneration

and commercial

of heat and cold energy below 100°C by LER

system would have practical

possibility.

Three types of cogeneration

Y. Kato

408

systems based on the LER are proposed

in Fig. 4.

In Case 1, the LER is combined

pump and a heater to produce

cold and warm heats.

coolant

state.

water at vapor/liquid

device and the absorption and warm heats. generation.

In Case 2, the LER’s

systems

are driven

cascade. . . Q

instead

thermally

Thermal

specifications

of those cogeneration

output

heat is consumed

fundamentally,

device

and utilize

LER’s

The specifications

by

electricity,

is introduced thermal

of these cases is estimated

in Fig. 4.

heat

at a thermoelectric

system generating

of the thermoelectric

performance

components

with an absorption

output from the LER is transferred

That is a tri-generation

heat pump and heater.

In Case 3, a steam turbine

Those

The thermal

cold

for trioutput

in

using conventional

of those components

are

defined as follows. (1) Absorption

heat pump

An absorption

heat pump (Ab) of a double effect steam absorption

media

is employed

indicates results

efficiency (SANYO

employed,

from inlet-water Co., Ltd.,

operation

(heat transformation

A value of coefftcient

mode),

of performance

of the heat pump, is taken from practical

1997).

The COP for the cooling,

(COP,

absorption

COP+

as working a chilled [-I), which heat pump’s

=~Wco,JWg,of 1.20 is

Wcoo, [kW] and W, [kW] mean a cold heat output from Ab and a recovered heat at a Under the heating operation (using a single effect absorption heat pump of Ab, respectively.

where

regenerator

heating operation, generated

operation),

from inlet-water at 20°C. The COP at the [kW] indicates a warm heat output where W,,,,,

warm water at 70°C is produced

COP,,,=I W,,,(IW,,

of 1.70 is employed,

from Ab.

(2) Thermoelectric

device

The Bi,Te, thermoelectric

device using (Bi,Sb),Te,

for the estimate

temperature maximum

the cooling

at 12°C.

of heat transformation Electric

under heat amplifier

adopted

Under

for the estimate.

water at 5°C is produced

chiller type using LiBr-water

because

the working

for p-type element temperature

range around 200°C with high thermoelectric thermoelectric

wcle =L= ma* 77 wr

transformation

r, - Td,h T

efficiency,

and Bi,(Se,Te),

of the device

transformation

r,r,,,,,[-I, is expressed

for n-type element

covers

efficiency

the LER

(Nishida,

is

operation

1996).

The

by,

M-l

(2)

A4 + Td,hIT,

M=JE

(3)

In which a figure of merit, Z [K-l], of 2.3~10.~ is employed

for the device material,

Wd,e[kW] and Td,h[K] depict the heat output rate and output temperature from the device, and the cooling side temperature

where W, [kW], T, [K],

from the LER, the electric output The generation efficiency of

on the device, respectively.

the device r,r,,,, is used for the estimate. (3) Steam turbine A Rankine

cycle steam turbine having an isentropic

efficiency

of 85% is employed.

4. RESULTS AND DISCUSSION Results for the thermal performance estimate of the thermal performance at 200°C (TJ as a representative.

of the proposed

systems

are shown in Figure 5.

It is presumed

in the

for the cases l-3 that the thermal output from the LER is 100 kW,, (W,) Figure 5(a) shows the operation

temperature

range in each process and

Fig. 5(b) shows the enthalpy balance in each case. (1) Case 1:

The thermal

output

of 200°C from LER is consumed

by the absorption

heat pump

(Ab)

Decentralized

energy

Case 2

409

utilization

Case 3

Ab: Absorption heat pump Ht: Heater TE: Themx&ctric device ST: Steam turbine

I A

B

C

Fig. 5 Enthalpy balance of LER cogeneration

systems: A: enthalpy balance of the each case operation, B

and C: generated cold and warm heat by absorption heat pump, D: consumed enthalpy by the heat pump, E: generated

warm heat by a heater, F: generated

electricity

device, G: generated

by the thermoelectric

electricity by the steam turbine, H generated electricity by a steam turbine, J and K generated cold and warm heat by a compression

heat pump driven by the electricity of H.

between

200°C and 95°C and by the heater (Ht) between

reheated

to 200°C in the LER.

exhausted

from the regenerator

The temperature

of Ab, adapts for practical

warm water temperature

for general

comprises

of a consumed

three columns

the cooling

operation

The temperature (2) Case 2:

purpose

(B), and a generated enthalpy

operation.

in residential

enthalpy

The exhausted

(A), a generated

uses.

The enthalpy

as

balance

cold heat output at 5°C by Ab in operation

(0.

Parts of D (96 kW) and E (4.2 kW) in the column

by Ab and the thermal output from Ht, respectively.

The thermal output at 200°C from the LER is used by the thermoelectric by the TE.

of the water

70°C is suitable

warm heat output at 70°C by Ab in the heating

200°C and 16O”C, and by the Ab between output generated

heat at 70°C is

temperature

The temperature

and commercial

balance

5°C is proper for a room space cooling.

A show the consumed

95°C and 70°C.

95”C, which is a condensing

The temperature

160°C is high enough for the operation

two columns

show cooling and heating output generated

(3) Case 3:

Output between

device (TE) between

A part of F (1.6 kW) shows the electricity

160°C and 95°C.

of the Ab.

The other

by the Ab.

200°C and 160°C from the LER is used by the steam turbine (ST), and between

160°C and 95°C by the Ab. (4) Case 4: the comparison

This case utilizes

lOOkW,, output at 300°C generated

of LER and LWR performances.

warm heat generated

from a compression

steam turbine using the LWR (Egawa,

Columns

by common

of J (136 kW) and K (170 kW) depicts cold and

heat pump driven by an electricity

1998).

light water reactor (LWR) for generated

The cold and warm heat conditions

(H, 34 kW) from a

are the same condition

of

Ab. In Case 1, the cooling Ab.

output of 115 kW at 5°C and heating

The heat pump utilizes well the LER output.

output of 163 kW at 70°C are generated

Electricity

consumption

of the absorption

by the

heat pump is

410

Y. Kato

less than 1% of whole thermal input. Then, in Case 2, the system could be operated independently without electricity supply from outside. In case 3 the electricity output (W,,=6.9 kW) is small since only steam pressure change is used for power generating. When the LER output from 200°C to 95°C is consumed fully by the ST, the electricity of 20 kW, is generated. Then the electricity generation by the LER is required for further discussion because the generation efficiency is obviously smaller than LWR’s in Case 4 (34 kW). On the other hand, cooling or heating outputs of Cases 1 or 2 is almost comparable with one of Case 4, because the absorption heat pump has generally high heat transformation efficiency compared with a compression heat pump. A fundamental thermal performance of a thermal process is defined by the ideal thermal efftciency, r,rc,proceu, defined by Eq. (1). Then, a thermodynamic validity of the LER can be depicted as follows, (4) where CL,, and CL, [price/kW] are the energy production costs per unit output of the LER and LWR system, respectively. If CL, of an LER system satisfies Eq. 4, the LER system could have economical validity as a rational energy system.

5. CONCLUSIONS A combined-cogeneration system based on LER and LWR is proposed from the estimate. LER system is suitable for thermal energy supply, which are major energy demands at residential and commercial uses. Since common LWR is superior to LER for electricity supply, then an LER and LWR combinedcogeneration system has a possibility for one of future energy systems. The combined system supplies cold and warm heat by LER at a decentralized energy network and electricity by large centralized network of LWR. LER is realized by using fission products (Sato, 1976) and some advanced small LWR reactor designs. When the LER output is mainly utilized by an absorption heat pump, above 90°C of LER’s output temperature is available. When an LER system. satisfies the condition defined as Eq. 4, the LER system will have rational validity. Acknowledgement The author greatly thanks to Mitsubishi Heavy Industry Ltd., Sanyo Electric Co., LTD., Tokyo Electric Power Company, Tokyo Gas Co., Ltd. and Dr. Tom Obara for their useful advice. References Danish Energy Agency (1998), Combined Heat and Power in Denmark. Egawa K. (1998), DHC Systems Utilizing Computer Heat, Swage Heat and Sea Water. Energy and Resources 19,504. The Energy Data and Modeling Center (1999), 1999 Handbook of Energy & Economic Static in Japan, The Energy Conservation Center, Tokyo Lenssen N. (1999), The Current Situation of Micro-cogeneration in the United States, Proceedings of Cogeneration Symposium ‘99, p. 339, Tokyo, October. Nishida A. (1996), Evaluation of Thermoelectric Properties and High Performances in Improvement Program for Thermoelectric Materials, Material Japan 35,943 SANYO Electric Co., Ltd. (1997), Absorption Heat Pumps, No. 9711ASlB Sato 0. (1976), Utilization of Fission Produced Radioisotopes, Seisan-ken@ 28, 11