OPERATION ANALYSIS OF THE
DEUTERIUM DEPLETED WATER PILOT PLANT
C. Croitoru, Gh. Titescu, I. Saros
National Institute of Researche-Development for Cryogenic and Isotopic Technologies,
ICSI Rm. Valcea Str. Uzinei nr. 4,Tel. 0040-050-732744, Fax 0040-050-732746, Romania
ABSTRACT
The first stage of the pilot plant for the heavy water final concentration has been utilised for
the deuterium depleted water production. Now the installation is fed in bottom of the
second column with water of 144 ppm D/(D+H). The product of the plant, extracted at the
top of first column, must be of 30 ppm D/(D+H), maximum. Simulation of steady state
functioning of this plant has permit to establish the separation capacity in the plant
operation conditions and the internal fluids flow that provides a significant increase of the
plant production. . It also has been analysed the influence of thermal feed state on the plant
performances. On the basis of the unsteady state functioning simulation it has been
established the evolution of plant production concentration in the period of setting in
operation and after the changes of plant operation regimes
Key words: deuterium depleted water, isotopic separation, vacuum distillation,
mathematical model
1. Introduction
Deuterium depleted water is represented by water that has an isotopic concentration of 20-80
ppm D/(D+H), smaller than natural concentration, of 145 ppm D/(D+H). As a result of
investigation’s increasing in isotopic separation domain, NR&DICIT has elaborated and patented a
method and an installation for deuterium depleted water yield. Beginning with 1996 NR&DICIT cooperated with Romanian specialised institutes for biological effects of deuterium depleted water.
The paper presents operation analysis of deuterium depleted water pilot plant.
In our institute deuterium depleted water (DDW) is produced in the first stage of the pilot
plant for heavy water final concentration, by vacuum distillation. Fig. 1 shows installation scheme.
The plant is fed at the bottom of the second column and the product extraction is make at the top of
the first column. Installation production, for the first year of operation, is shown qualitatively and
quantitatively in fig. 2 [1].
The analyse of DDW plant operation is based on simulation models, in order to establish the
optimum values of operating parameters and to evaluate installation behaviour when it is operated in
unsteady states.
2. Methods
The mathematical models used for simulation programs is composed of equation of isotopic
equilibrium, equations for total mass balance and isotopic balance, in steady state, respectively
unsteady state [2,3].

x  1  y 
y  1  x 
(1)
PR
TI
TI
TI
F
PI
F
F
P, XP
TI
TI
PI
LI
PI
LR
R
R
F, XF
W, XW
Fig. 1 Scheme of deuterium depleted water pilot
plant
P
(l/h)
Xp
(ppm)
140
25
P
120
20
100
15
80
Xp
60
10
40
5
20
0
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 2 4 6 8 10 12 14 16 18 20 22 24 26 28 31 2 4 6 8 10 12 14 13 15 17 19 21 23 25 27 29
July
June
November
May
date
Fig. 2 Production of DDW pilot plant
steady state
M
N
m1
n 1
 I m   En  0
(2)
  I m  x I ,m     I n  y I ,n     Er  x E ,r     E s  y E ,s   0
M
N
R
S
m1
n 1
r 1
s1
(3)
unsteady state
M
N
m1
n 1
h
 I m   En   t
(4)

M
m1

N


R


S


I m  x I ,m   I n  y I ,n   E r  x E ,r   E s  y E ,s 
n 1
r 1
s1

 h  x
t
(5)
where:
I, E - feeding, outlet flow rate, kmol/h
x, y - isotopic concentration in liquid, vapour phase, mol fraction D/(D+H)
h - liquid hold-up, kmol/h
The model includes also relations for separation factor and fluids density calculation as a
function of temperature, and relation for isotopic efficiency calculation as a function of vapour
charge [4 ].
We make the assumptions that through distillation columns the temperature is constant and
the vapour hold-up can be neglected. We solved the equation system using numerical methods.
3. Results
Using the program for steady state simulation, we determined, in the operating conditions for
the first year, the plant separation capacity. The calculated values for product, flow rate and
concentration, close to the values realised in installation. In analysed functioning period feeding flow
rate has varied about 8–33 l/h.
Imposing for product concentration value of 25 ppm, we have determined the level whereat
feeding flow rate influence is insignificant. Optimal feeding flow rate is about 40 l/h.
For optimal feeding flow rate we have determined the plant separation capacity, as a function
of extracted product concentration. For extracted product flow rates takes in domain 10-12 l/h the
plant production concentration lies in domain 20-30 ppm. Attempts to extract more products lied to
product depreciation. These situations there is particularly in first period of plant functioning (fig. 2).
At present, in both plant columns, it can assuring maximum of liquid flow rate about 230 l/h.
By simulation we have established that maximum charge supported by columns lie at level 400 l/h,
value whereat package efficiency is 7,8 NTP/m, in comparison with 8,5 NTP/m at 220 l/h. Reflux
doubling have as result production increasing with 67,7 %.
We have determined the influence of the thermal state of feeding, as a function of the feeding
flow rate. The production increases in case of vapour phase feeding comparative with liquid phase
feeding, but it is not significant (<1 %).
The prediction of unsteady state period, at plant start-up or at the modification of operating
parameter, offers effective support in plant operation. With unsteady state simulation program, we
have established that after two days from plant start-up, without feeding and extraction, isotopic
concentration in product extraction zone reaches about 25 ppm.
Establishment of product flow rate at 11,5 l/h assures the obtainment of a concentration of 25
ppm. Simulation results, having at base May operating parameters, recorded in every other hour,
evidence the correctness of mathematical description and liquid hold-up evaluation. Fig. 3 shows
theoretical curve of temporal variation of product concentration and measured values of product flow
rate and concentration.
4. Conclusions
This paper present the analyse of installation operation, based on simulation models, in order
to establish the optimum values of operating parameters and to evaluate the installation behaviour
when is operated in unsteady states.
Using the program drawn up for steady state simulation, we have determined the separation capacity of
the installation, in operating conditions of the first functioning year. The calculated values for product, flow rate
and concentration approach the values realised in installation.
P
Xp
(l/h)
(ppm)
140
Xp theoretic
25
al
120
20
100
P measured
15
80
60
10
40
5
Xp measured
0
20
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
data
Fig. 8 Theoretical curve of temporal variation of product concentration
and measured values of product flow rate and concentration
Having the confirmation that the model describe correct the isotopic separation process in
steady state, we determined the level until which the influence of feeding flow rate is significant, the
separation capacity of the installation as function of product concentration, product variation with the
charge of vapours phase and the influence of feeding thermal state as function of the feeding flow
rate.
Using the simulation program for unsteady state, we established the time of unsteady state at
starting, function of extraction flow rate. The results of simulation, based on operating parameters
registered every two hours, emphasise the accurate mathematical description of isotopic separation
process in unsteady state as well as the correct evaluation of water hold-up from the installation.
5. References
[1] I. Stefanescu, M. Peculea, Gh. Titescu, Procedeu si instalatie pentru producerea apei saracite in
deuteriu, Patent nr. 11422, Romania
[2] C. Croitoru, M. Dumitrescu, G. Isbasescu, Adaptarea si aplicarea modelelor si a programelor de
calcul pentru proiectarea si simularea instalatiilor de distilare izotopica din cadrul C. Ch. Drobeta,
S410/20.09.1988
[3] V. A. Kirillina, Tiajelaia, Teplofizischie cvoistva, 1973
[4] M. Pavelescu, M. Peculea, Schimbul izotopic H2O - H2S. Proprietati termodinamice, Uzina “G”,
Rm. Valcea, 1975