Research Journal of Chemical Sciences 
______
______________________________
______
____
 
ISSN 2231
-
606X
 
 
 
Vol. 
2
(
3
), 
58
-
60
, 
March
 
(201
2
)
 
 
Res.J.Chem.Sci.
 
 
 
International Science Congress Association
 
 
 
 
    
58
 
Short Communication
 
Triple Point Behavior of Ammonia under Compression
 
 
Gezerman A.O. and Corbacioglu B.D.
 
Yildiz
 
Technical University, Chemical
-
Metallurgical Faculty, Chemical Engineering Department, Davutpasa,
 
Esenler, Istanbul, TURKEY
 
 
Available online at: 
www.isca.in
 
(Received
 
8
th
 
August 
201
1
, revised
 
18
th
 
November 2011
, accepted
 
3
rd
 
Febru
a
ry 2012
)
 
 
 
Abstract
 
Liquid ammonia has several industrial uses. Based on the end use, ammonia solutions of varying concentration
s 
are used 
commercially. There are several methods to liquefy ammonia. However, the most preferred method for 
liquefying anhydrous 
ammonia is the use of a two stage, two
-
 
cylinder compressor.
 
In this study, we designed a new ammonia compressor based on 
our examination of compressor designs comprising more than one stage and cylinder. Further, our investigation of 
the 
thermodynamic behavior of ammonia at high pressures also influenced our compressor design.
 
 
Key words:
 
Liquefaction, 
o
ne
-
 
stage compressor, 
t
wo
-
 
stage compressor, 
t
riple point
.
 
 
Introduction 
 
Ever since ammonia was 
first studied, its commercial value has 
constantly increased with its industrial demand
1
. Ammonia is 
used in many industrial processes at different stages based on 
the end use. Depending on the nature of the final product, 
ammonia as raw material can be ut
ilized in its liquid or gas 
phase. The storage of liquid ammonia involves extra treatment 
and specialized equipment that increase commercial costs. In 
general, the liquefaction of ammonia involves the use of 
multistage compressors
2
 
and this increases the c
ost of 
liquefaction.
 
 
Material and Methods
 
In order to examine the process of ammonia liquefaction using 
compressors with more stages, it is necessary to study the 
liquefaction process in each stage
3
. The work involved in 
compression in a stage is given by
 
the following expression
4
:
 
 
W = (n/(n 
-
 
1)) × M × R × T × [(p
2
/p
1
)
(n  
-
 
1)/ n
   
-
 
1]
 
W
here
 
W: Compressor power (kW/h)
, 
n: Compressor stage 
number
, 
M:  Quantity of liquefied ammonia (kg/h)
, 
R:   
Liquefaction coefficient of ammonia
, 
T:  Ammonia temperature 
at point of entry into compressor (°C)
, 
p
2
: Compressor output 
pressure
, 
p
1
: Compressor input pressure
 
 
Rewriting this equation for a two
-
 
stage compressor with 100% 
yield, we obtain the following equation:
 
 
W = (2/(2 
-
 
1)) × 2100 × (1.802 × 10
-
5
) ×  (17.9/
0.04)
(2 
-
1 ) / 2 
–
 
1
 
W = 366 kW/h
 
 
It is noteworthy that the design performance of a compressor is 
affected by a variety of factors that influence compressor yield 
under various liquefaction pressures.
 
Results and Discussion
 
In our experiments on the physi
co
-
 
chemical behavior of 
ammonia, we obtained compressibility coefficients for different 
triple points under different pressures; the compressibility 
coefficient in each case described the maximum liquefaction 
tendency of ammonia at each pressure. When the
 
pressure on 
gaseous ammonia was increased beyond a threshold value, 
ammonia showed unsteady behavior at every triple point. Our 
results showed that 0.05% liquid ammonia evaporates for a 
temperature change of 0.5
°C
 
under 20 atm pressure; however, 
the evapo
ration rate reduces to 0.01% for a temperature change 
of 0.5
°C
 
under 13 atm pressure
5
. 
 
 
On the other hand, we determined that at the triple points for 
three different pressure values on the temperature
-
volume graph 
for ammonia, when the slope of the curve
 
along the gaseous 
side of the triple point was parallel to the y axis (figure
-
1), the 
system appeared to show an unsteady equilibrium
6
. 
Consequently, it was difficult to obtain a stable liquid state of 
ammonia under such liquefaction conditions
7
. If a compressor is 
designed on the basis of these values, the increase in the 
number of stages will increase the pressure in the system, which 
will lead to an unstable liquid ammonia state. Hence, increasing 
the number of stages beyond a certain threshol
d is not 
considered viable. 
 
 
Therefore, for the practical design of an ammonia compressor, 
the optimal number of stages is limited to two.
 
 
The other aspect of our study focused on the number of 
cylinders used in the compressor stages. The initial pressur
e 
required to compress ammonia from its gas phase to its liquid 
phase is less than 1 atm, and this leads to a liquefaction problem 
that is independent of the stage number. Consequently, the 
optimal number of cylinders for compression should maximize 
Research Journal of Chemical Sciences 
______
_
_
_______________________________
______________
_
____
 
ISSN 2231
-
606X
 
 
Vol. 
2
(
3
), 
58
-
60
, 
March 
(201
2
)
 
  
Res.J.Chem.Sci
 
International Science Congress Association
 
 
59
 
the st
able point of liquid ammonia at the triple point for each 
corresponding pressure
8
. 
 
 
For example, a 10 atm outlet pressure obtained at the first stage 
of compression corresponds to a temperature of 90
°C
9
. 
Therefore, increasing the number of cylinders in th
is stage 
increases the temperature of compressed ammonia, and 
consequently, the outlet pressure also increases. If the stage 
number is increased areas of low pressure and high pressure are 
formed. Therefore, increasing the number of compressing 
cylinders i
n each stage ensures a wider compressor design range 
for the various triple points obtained under different pressure 
values.
 
 
For a compressor designed on the basis of the above discussion, 
the evaporation of ammonia occurs at 10
°C
, while condensation 
at 3
5
°C
. These values are valid only for a single compressing 
stage. For high
-
 
pressure compressors, the storage of ammonia 
in the liquid phase can be achieved over a wider temperature 
range. For example, in a multistage compressor, at the high
-
 
pressure stage
, the evaporation temperature of ammonia is 10 
°C
, while its condensation temperature is 35
°C
. For the low
-
 
pressure stage, evaporation occurs at 
-
 
35
°C
, while 
condensation occurs at 
-
10
°C
. Consequently, double
-
 
stage 
ammonia compressors can function over 
a wider temperature 
range
10
. Therefore, it is easier to maintain and transport 
ammonia in its liquefied phase than in its gaseous phase.
 
 
Conclusion
 
In our study, we determined that the liquefaction of gaseous 
ammonia can be optimally achieved by compressors that have 
two stages. According to our calculations and experimental 
observations, the compressor design for optimal condensation 
and evaporation 
values is directly related to the maximum 
pressure value and the physico
-
 
chemical behavior of ammonia 
at the triple point for this pressure. Further, the physico
-
 
chemical behavior of ammonia during liquefaction is unstable 
under such conditions.
 
Referenc
es
 
1.
 
Yurtseven H.
 
and Karacali H.,
 
Temperature and 
Pressure Dependence of Molar Volume in Solid Phases 
of Ammonia near the Melting Point, 
 
J. Mol. Liq
.
,
 
142, 
(1
-
3
)
, 88
-
94
 
(2008)
 
 
2.
 
Savas S. and Yalcin E., Tek ve Cift Kademeli 
Amonyakli SoÄŸutma Sistemlerinde Daha Basit 
Donanim Imkanlari, 
Tesisat Mühendisliği Dergisi
, 
94
, 
5
-
16 
(2006)
 
 
3.
 
Bartholomeus T.M.C., 
Two Stage Piston Compressors 
with Individual Cylinder Connection, Online 
: 
http://www.grasso.nl/en
-
us/News
-
and
-
Media/technical
-
articles
-
Grasso/Pages/two
-
Stagepistoncompressors.aspx
 
4.
 
Kucuksahin F., Teknik Formuller, 
Beta
, (
1)
, 192
 
(1989)
 
5.
 
Haar L., Thermodynamic Properties of Ammonia as an 
Ideal Gas, 
J. Res. N. Res. N. Bureau
 
St. A. Phys. 
Chem.
, 
72A
, 2 
(1968)
 
6.
 
 
Harrison R.H. and Kobe K.A., Thermodynamic 
Properties of Ammonia, 
Chem. Eng. Progress
, 
49
, 
351
(1953)
 
7.
 
Haar L. and Gallagher J.S.,Thermodynamic Properties 
of Ammonia, 
J. Phys. Chem. Ref. Data
, 
7(3),
 
(1978)
 
8
.
 
Kirshen
baum I. and Harold C., The Differences in the 
Vapor Pressures, Heats of Vaporization, and Triple 
Points of Nitrogen (14) and Nitrogen (15) and of 
Ammonia and Trideuteroammonia, 
J. Chem. Phys
., 
10
, 
706
-
709 
(1942)
 
9.
 
Yurtseven H. and Salihoglu
 
S., Critical Behavior of 
Ammonia near the Melting Point, 
Chin. J. Phys.,
 
40
,
 
4
 
(2002)
 
10.
 
Glasser L., 
Equations of State and Phase Diagrams of 
Ammonia
, 
J. Chem. Educ.
, 
86
, 1457 
(2009)
 
 
 
Research Journal of Chemical Sciences 
______
_
_
_______________________________
______________
_
____
 
ISSN 2231
-
606X
 
 
Vol. 
2
(
3
), 
58
-
60
, 
March 
(201
2
)
 
  
Res.J.Chem.Sci
 
International Science Congress Association
 
 
60
 
 
 
Figure
-
1
 
Physico
-
chemical behavior of ammonia 
at different pressures
 
<end>