Volume 03 Issue 09-2023
14
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
ABSTRACT
The research of operational indicators of compressor units shows that undercooling of air in reciprocating
compressors for every 5-6
℃
increases energy consumption for air compression by 1%, and productivity decreases by
8-10%, which leads to tangible economic losses in compressed air production. The existing cooling systems of
compressor units have a number of significant shortcomings due to the peculiarities of their operation, the paper
considers various ways to improve the operation of the cooling system, proposed new technical solutions, the
implementation of which will reduce the energy consumption of compressor units.
KEYWORDS
Compressor, cooling system, temperature, compressed air, heat transfer, cooling tower, intermediate cooler, heat
exchanger, end cooler, productivity, power consumption.
INTRODUCTION
In many industries, pneumatic energy, or compressed
air energy, is widely used in addition to electrical
energy.
The widespread use of compressed air in the mining
industry is due to the fact that pneumatic equipment is
safe, especially in gas and dust hazardous mines where
the use of electricity in underground mining is
dangerous due to sudden gas emissions.Along with
this, pneumatic energy has a number of significant
disadvantages. The main disadvantage of compressed
Research Article
IMPROVEMENT OF COOLING SYSTEM OF MINE RECIPROCATING
COMPRESSOR UNITS
Submission Date:
September 12, 2023,
Accepted Date:
September 17, 2023,
Published Date:
September 22, 2023
Crossref doi:
https://doi.org/10.37547/ajast/Volume03Issue09-04
D.N. Khatamova
Senior Lecturer Of "Mining Engineering" Department, Navoi State Mining And Technological University,
Uzbekistan
E.U. Yuldashev
Assistant Of "Mining Electromechanics" Department, Almalyk Branch Of Tashkent State Technical University
Named After Islam Karimov, Uzbekistan
Journal
Website:
https://theusajournals.
com/index.php/ajast
Copyright:
Original
content from this work
may be used under the
terms of the creative
commons
attributes
4.0 licence.
Volume 03 Issue 09-2023
15
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
air as an energy carrier is its high cost relative to
electricity due to the large amount of electrical energy
consumed by compressors during compressed air
production [1].
Mine compressors are energy-consuming installations,
the specific weight of which in the consumption of
electrical energy by mining enterprises is a significant
share. Considering such a wide application of
pneumatic energy, it is necessary to reduce operating
costs by developing resource-saving technical
solutions in the process of compressed air production
at industrial enterprises.
Efficient operation of a compressor unit depends to a
large extent on cooling. The cooling system of the
compressor unit solves three tasks - it reduces the
energy consumption of the compression process in the
cylinder, eliminates the probability of burning of
lubricating oils and contributes to the improvement of
the operating conditions of the compressor working
units. Violations of the cooling system, as a rule, are
associated with forced stoppage of the compressor
and increased specific power consumption for the
production of compressed air [2].In the majority of
industrial enterprises of Uzbekistan the cooling system
of stationary compressors is made by circulating open
loop scheme. Fig. 1 shows the open circuit cooling
system of a two-stage reciprocating compressor.
Fig.1. Schematic diagram of the open-circuit cooling system of a two-stage reciprocating compressor.
1-air intake, 2-filter, 3-first compressor stage, 4-second compressor stage, 5-intermediate cooler, 6-end cooler, 7-
cooler, 8-pump, 9,10-fans, 11-pipeline of chilled water, 12-pipeline of heated water.
Volume 03 Issue 09-2023
16
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
Analysis of compressor units operation shows that
undercooling of air in intercoolers of reciprocating
compressor for every 5-6
℃
increases energy
consumption for air compression by 1% [3].
The existing cooling systems of compressor machines
have significant disadvantages caused by the
peculiarities of their operation. Water used for cooling
has a high content of salts and various impurities. In
most cases the total water hardness, reaching more
than 20 mg-eq/l, is almost 3 times higher than the
permissible values, which is the main reason for rapid
contamination of heat exchange surfaces. Decrease in
intensity of heat exchange processes, due to the
growth of deposits in the form of scale, contributes to
the reduction of safety and efficiency of compressor
equipment.
Presence of scale layer 0,1 mm thick leads to decrease
of air cooling in the refrigerator by 10-15 %. The scale
layer reduces the heat transfer coefficient by adding
additional thermal resistance [4].
At the outlet of the intermediate cooler, the normal
temperature of compressed air should not exceed the
inlet cooling water temperature by more than 5-10 ºC.
If the temperature difference increases up to 20 ºC, the
power consumption may increase by 14 %, all other
things being equal. Scale on the inner walls of the tubes
sharply reduces heat transfer to the cooling water, Fig.
2 shows the graphical dependence of the heat transfer
coefficient on the thickness of the scale layer [4].
Fig
.2. Variation of heat transfer coefficient as a function of scale layer thickness.
From the graph in Fig. 2, it is observed that the heat
transfer coefficient deteriorates as the thickness of
scale layer increases. Exceeding the compressed air
temperature of 150
℃
can lead to spontaneous
combustion
of
carbon-oil
deposits
in
air
communications, which is the cause of detonation
explosions. Analysis of the operation of compressor
units operating at industrial enterprises of Uzbekistan
shows that the temperature of compressed air at the
compressor outlet reaches 170-180
℃
and higher.
Another important factor affecting the efficient
operation of compressor units is air heating in the
suction process, due to the resistance of the suction
0
200
400
600
800
1000
1200
Основной
Основной
Основной
Основной
Основной
Основной
Основной
Основной
Основной
H
ea
t
tr
an
sf
er
c
o
ef
fi
ci
en
t
W
(
m
2
k)
Scale layer thickness, mm.
Volume 03 Issue 09-2023
17
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
path and heat exchange with heated components of
the equipment. Decrease in mass capacity and
compressor volumetric delivery, reduced to normal
atmospheric conditions, is due to the lower density of
heated air, relative to normal atmospheric air.
The influence of air heating on compressor
performance is estimated by its temperature
coefficient, the value of which is tentatively equal to
the ratio of normal atmospheric temperature T0 to the
air temperature T1 in the cylinder at the end of suction
[5]:
𝜆
т
≅
Т
0
Т
1
;
(1)
It should be emphasized that an increase in
atmospheric temperature leads to an increase in T1
temperature and a decrease in the compressor unit
capacity.
In Uzbekistan, during the hot period of the year,
especially from May to September, the air temperature
can reach 40-45
℃
and higher, which leads to
significant heating of the compressor suction air. The
increase in temperature and decrease in air density
contributes to an 8-10% decrease in compressor
performance, resulting in tangible economic losses in
compressed air production [6].
The efficiency of the cooling system of compressor
units also depends on the operation of the cooling
tower. In a circulating chiller water supply system,
cooling water from the compressor enters the cooling
tower for cooling. For the optimal operation of the
compressor, the temperature difference of the cooling
water between the inlet and outlet should not be more
than 15
℃
. The water temperature should not exceed
+25
℃
at the inlet and +40
℃
at the outlet of the cooling
system [7].
Most of the cooling towers in use at compressor
stations were built according to the designs of 70-80s
of the last century, most of them are in unsatisfactory
condition, and the technical solutions incorporated in
the designs of these cooling towers are outdated [8].
As a result, the recycled water is undercooled,
especially in the warm period of the year, which leads
to overconsumption of energy resources and other
negative consequences.
Research conducted on compressor cooling systems
has revealed the following major factors that lead to
reduced plant efficiency. These include:- increased
temperature of atmospheric air at the inlet to the
compressor unit, which leads to increased electrical
energy consumption for compression and reduced
productivity;
-unsatisfactory operation of cooling tower coolers,
especially during the hot period of the year, the cooling
towers currently used in the enterprises do not cope
with the cooling of circulating water, as the water
spray nozzles used in most cooling towers do not
provide the required atomization of water, which leads
to undercooling of circulating water. Frequent
formation of contaminants on heat exchange surfaces,
reduction of heat exchange intensity due to scaling
layer formation on the walls of intermediate and end
coolers.
In order to increase the energy efficiency of
reciprocating compressor units operation, based on
the above-mentioned factors leading to the decrease
of compressor units efficiency, we propose the
following technical solutions.
Artificial cooling of the air at the inlet to the
compressor. It is obvious that lowering the
temperature of the intake air leads to an increase in the
Volume 03 Issue 09-2023
18
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
weight capacity, artificial cooling can always achieve an
increase in capacity.
However, the used special refrigeration units for
artificial cooling of the suction air are quite expensive
and energy-consuming, the use of which is not always
economically feasible.
Therefore, we propose to cool the air before the
compressor with the use of a tubular heat exchanger,
using as a cooler circulating water from the cooling
tower. In this case, the heat exchanger is made in such
a way that it does not create hydraulic resistance to the
movement of the intake air. By cooling the suction air
before the compressor by 5-6
℃
, the compression
energy saving is 1-2%.
Modernization of cooling tower chillers based on
improving the design of water spray nozzles. As
mentioned above, the existing water spray nozzles do
not provide efficient water atomization. Application of
new design of ejection water-splashing nozzles with
swirler allows to intensify heat exchange, thus
improving cooling of circulating cooling water. Figure 3
shows a general view of our proposed ejection spray
nozzle.
Figure 3. General view of the proposed induction water spray nozzle.
1-outer tube, 2-nozzle displacement chamber, 3-air inlet hole, 4-vortex atomizer.
Prevention of scale layer formation on the walls of
intermediate and end coolers. Increasing the efficiency
of compressor unit cooling system operation is
possible due to intensification of heat exchange
between the cooled (compressed air) and cooling
(water) coolants. This is primarily realized by
preventing scale and sludge deposits in the coolers.
Today, water hardness softening is achieved
chemically. Chemical method of scale prevention is
effective, however, it requires constant expenses,
pollutes the environment and harms the health of
service personnel. Prevention of scale formation is
possible due to electromagnetic treatment of
circulating cooling water [9].
Volume 03 Issue 09-2023
19
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
We have developed in laboratory conditions the
installation
for electromagnetic treatment of
circulating water. In order to determine the
effectiveness of the developed installation of
electromagnetic treatment of circulating water, we
conducted experimental tests. Schematic view of the
experimental unit is shown in Figure 4.
Fig. 4. Schematic view of the experimental setup when testing the device for electromagnetic water treatment.
1-capacity with electric heater, 2-temperature regulator, 3-circulation pump, 4-device for electromagnetic water
treatment, 5-point of water temperature measurement, 6-valve, 7-metal pipe, 8-capacity with water.
Experimental work was carried out in two stages, the
first stage of experimental research was carried out
without the use of the device for electromagnetic
water treatment. The second stage with application of
the device for electromagnetic water treatment.
Duration of experimental work for each cycle was 48
hours, average water hardness 25 mg-eq/l.
The main objective of the experimental work was to
establish the dependence of scale layer formation on
the surface of the metal pipe on the temperature of the
circulating water, with the use of a device for
electromagnetic water treatment and without its use.
The performed experimental tests allowed to
obtain the dependence of scale formation on the metal
surface on the temperature of circulating water with
and without the use of a device for electromagnetic
water treatment, the graphical dependence is
presented in Fig. 5.
Volume 03 Issue 09-2023
20
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
Fig.5. Graphical dependence of scale thickness formation on the temperature of circulating water.
1-without application of the device for electromagnetic water treatment, 2- with application of the device for
electromagnetic water treatment.
From the graph in Fig.5 it is observed that electromagnetic treatment of circulating water, contributes to the reduction
of scale formation on metal surfaces on average by 70-80%.
Fig.6 shows a microscopic photograph of the wall of the metal pipe after the completion of experimental
work. The analysis of microscopic photos shows that the application of electromagnetic treatment reduces the
formation of scale layer on the walls of the metal pipe.
а)
b)
Figure 6. Microscopic photograph of a metal pipe wall.
a) operation of the pipe without using the electromagnetic water treatment device, b) using the electromagnetic
water treatment device.
From Figure 6 it is observed that the scale layer on the wall of the metal pipe, shown in Figure 6a is much thicker,
relative to the one shown in Figure 6b. This makes it possible to conclude that the use of the device for
0.005
0.01
0.015
0.02
0.025
0.03
0.035
Основной Основной Основной Основной Основной Основной Основной
Scal
e
lay
er
t
hi
ck
nes
s,
(m
m
)
Cooling water temperature t (0C)
1
2
Volume 03 Issue 09-2023
21
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
electromagnetic treatment of water, contributes to reducing the formation of scale on the surfaces of heat
exchangers.
Figure 7 shows a schematic view of the cooling system of a two-stage reciprocating compressor after modernization.
Fig.7. Schematic diagram of the open-circuit cooling system of a two-stage reciprocating compressor after
modernization.
1-Air intake, 2-Filter, 3-Air cooler before the
compressor,4-First compressor stage, 5-Intermediate
cooler, 6-Second compressor stage, 7-End cooler, 8-
Cooler, 9-New design of water atomizer, 10 and 11-Fans,
12-Pump, 13-Electromagnetic water treatment device,
14-Chilled water pipeline, 15-Heated water pipeline.
Application of our proposed technical solutions to
improve the efficiency of compressor units, based on
the improvement of the cooling system can increase
productivity and reduce the specific cost of electrical
energy of the compressor for the production of
compressed air. But in this case changes will be made
in the current scheme of the cooling system (Fig. 7).
Realization of our proposed technical solution,
provides the following changes in the current scheme
of the cooling system of compressor units:
-
between the filter and the first stage of the
compressor will be installed air cooling chamber in
the form of a heat exchanger, cooling medium will
be cooled water from the cooling tower;
-
the cooling tower water spray nozzles will be
replaced with a new design of ejection water spray
nozzle;
-
an electromagnetic water treatment device will be
installed on the chilled water pipeline exiting the
cooling tower.
Volume 03 Issue 09-2023
22
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
03
ISSUE
09
Pages:
14-22
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
(2023:
7.063
)
OCLC
–
1121105677
Publisher:
Oscar Publishing Services
Servi
From
analytical
studies
revealed
that
the
implementation of our proposed technical solutions at
compressor plants of mining enterprises contribute to
reducing energy costs of air compression process in
the cylinder on average by 4-5%, to increase
compressor performance to 8%, depending on
operating conditions. And also to exclude emergency
situations and to increase operational indicators of
working units of the compressor, due to which the cost
price of compressed air production will be reduced.
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