atw 2018-04v6

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atw Vol. 63 (2018) | Issue 4 ı April

by m 9 = m 2 – m 4 , and the temperature

of No. 12 can be calculated by using

Equation (2). Finally, m 10 was also

obtained by using Equation (2). Like

the existing IHX loop, in the bypass

mode-added IHX loop, correction

efficiency and pumping power in

accordance with mass flow were

considered, and pumping power used

the above Equation (4). For the

simulation for this, thermodynamic

system analysis software, EES, was

used, in the same way with the

existing IHX loop model obtained

before, and the flow of helium gas

and fluid was analyzed.

3 Result

Table 1 shows the result of physical

value at each point by simulating the

existing IHX loop EES [5]. Physical

value of each point was assumed in

accordance with reference [8], [9]

literature, and the assumed values

were colored.

The temperature of helium fluid

that leaves from the first heat exchanger

after producing the hydrogen

decreases to 846 °C from 910 °C, and

the temperature of helium fluid that

leaves from the second steam generator

is 614.8 °C, and the temperature

of helium fluid that leaves from the

last heat exchanger is 450 °C. The

temperature of helium fluid decreases

steadily, but because the fluid flowing

each steam generator and heat

exchanger is different, efficient electricity

can be produced by using each

characteristics. The existing IHX

Loop’s m 5 and m 8 are in inverse

proportion, as more mass flow moves

toward high efficiency, the amount of

overall electricity output increases.

Although the efficiency of heat

conversion cycle connected to each

steam generator may be influenced by

various causes, but in the present

study, correction factor presumed

about high temperature was used, so

the detailed design for this part would

be needed.

If heat conversion cycle connected

to each steam generator should be

operated simultaneously by a specific

objective, considering the inverse proportion

relationship between m 5 and

m 8 , the output must be distributed.

Besides, the exit temperature at the

tube part of steam generator 2 is in

inverse proportion with the exit

temperature at the shell part. This will

eventually influence on the exit

temperature of the tube part of the

heat exchanger 3. When operating

heat conversion cycle connected to

each steam generator, it is necessary

to find balanced point on the temperature

between steam generators.

In the steam generator 2 and heat

exchanger 3, exit temperature and

mass flow are in inverse proportion.

This is because if high exit enthalpy is

maintained in order to deliver the

same heat energy, less mass flow is

needed, and if a large amount of mass

flow is needed, exit enthalpy should

be maintained low. Maximum output

would be in the parabolic form as exit

enthalpy and temperature change, so

if maximum output is needed, proper

exit temperature must be selected. Or

in case there is a requirement for exit

temperature, it is possible that output

would be determined according to

that.

Table 2 shows the physical value at

each point where IHX loop added by

bypass mode is simulated with EES.

No. Fluid Temperature

(°C)

| | Tab. 1.

IHX loop Simulation Result.

In the case of IHX loop to which

bypass mode was added, the helium

fluid that passed through the first

hydrogen-producing heat exchanger

is 910 °C~ 846 °C, which is the same

as the existing IHX loop, but here by

reheating high-temperature helium

fluid, the temperature increases to

860 °C. The temperature of the helium

fluid that passed through the second

steam generator is 614.8 °C, which

is the same as that of helium fluid

that passed through the second evaporator.

However, since the temperature at

the entrance reheated, and returned,

the amount of electricity output produced

increases. When helium fluid

enters the third heat exchanger, it is

reheated from 614.8 °C to 620 °C, the

temperature of helium fluid is 450 °C,

and the amount of electricity output

Pressure

(kPa)

| | Tab. 2.

Result of IHX Loop to which Bypass Mode was added.

Enthalpy

(kJ/kg)

Mass flow

(kg/hr)

1 Helium 910.0 4000 6,161.00 527,662

2 Water 193.0 18,000 828.70 49,839

3 Water 585.0 16,500 3,528.00 49,839

4 Helium 846.0 4,000 5,829.00 527,662

5 Water 260.2 20,790 1,134.00 208,359

6 Water 836.0 16,475 4,174.00 208,359

7 Helium 614.8 4,000 4,628.00 527,662

8 CO 2 203.5 19,760 96.59 902,043

9 CO 2 604.8 19,290 597.00 902,043

10 Helium 450.0 4,000 3,773.00 527,662

No. Fluid Temperature

(°C)

Pressure

(kPa)

Enthalpy

(kJ/kg)

Mass flow

(kg/hr)

1 Helium 910.0 4,000 6,161.00 527,662

2 Helium 910.0 4,000 6,161.00 122,749

3 Helium 910.0 4,000 6,161.00 404,913

4 Helium 910.0 4,000 6,161.00 113,375

5 Water 195.0 18,000 837.50 50,000

6 Water 585.0 16,500 3,528.00 50,000

7 Helium 846.0 4,000 5,829.00 404,913

8 Helium 860.0 4,000 5,901.00 518,288

9 Helium 910.0 4,000 6,161.00 9,374

10 Water 260.2 20,790 1,134.00 214,580

11 Water 850.0 16,475 4,209.00 214,580

12 Helium 614.8 4,000 4,628.00 518,288

13 Helium 620.0 4,000 4,655.00 527,662

14 SCO 2 203.5 19,760 96.59 918,581

15 SCO 2 610.0 19,290 603.50 918,581

16 Helium 450.0 4,000 3,773.00 527,662

OPERATION AND NEW BUILD 233

Operation and New Build

Heat Balance Analysis for Energy Conversion Systems of VHTR ı SangIL Lee, YeonJae Yoo, Deok Hoon Kye, Gyunyoung Heo, Eojin Jeon and Soyoung Park

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