









































11 J Global Clinical Engineering Vol.5 Issue 3: 2023

Received November 28, 2022, accepted December 2, 2022, date of publication February 1, 2023

Application of Molecular Sieve Oxygen Generation Mini-
plant under Harsh Environment

By Jixun Liu1, Chao Qiu2, Jianxiong Zuo2, Xiaomin Lou3

1 Zhejiang Shuren University, China
2 Hangzhou Medoxygen Technology Co., Ltd., China
3 Hangzhou Red Cross Hospital China

ABSTRACT

Pressure Swing Adsorption (PSA) oxygen generation mini-plant is widely used in all various hospitals for its fast, convenient, 
and cost-effective features. However, considering the landscape of global markets, the PSA medical oxygen generation mini-
plant design basis varies from location to location. Therefore, it forces the manufacturer to design and build the PSA oxygen 
generation mini-plant more flexibly to enable its compatibility in different extreme ambient conditions (temperature, humidity, 
pressure, cleanliness) of installation location. For the sake of these concerns, this paper employs the concept of modularity as 
an approach to PSA medical-grade oxygen generation mini-plant design and application and elaborates 10 key components for 
4 modules of PSA medical-grade oxygen generation mini-plant, namely (a) air compressor module; (b) PSA module; (c) oxygen 
compressor module; (d) smart control module. Under this modularized design approach, this paper investigates the technical 
features and the design criticality of modular and key components in fulfilling the expected performance, finally achieving and 
maintaining the overall performance of PSA oxygen generation mini-plant with the selected modules which may be installed 
worldwide. This paper helps to highlight the variability of PSA oxygen generation mini-plants in harsh environments in four 
dimensions (temperature, humidity, pressure, cleanliness) and briefs the methodology of the phase gate model for modular 
approach in oxygen generation mini-plant. It contributes to the literature on this important subject in the modularized design 
method, adsorption technology, air separation process, etc.
Keywords – PSA Oxygen Generation Mini-plant; Harsh Environment; Modularized Design; Process Design; medical-grade 
oxygen .

Copyright © 2021. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY): Creative Commons - Attribu-
tion 4.0 International - CC BY 4.0. The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) 
are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is 
permitted which does not comply with these terms.

INTRODUCTION

Oxygen for industrial purposes is generated through 
several techniques such as cryogenic air separation units, 
and membrane-based or adsorption technology. There-
fore, it is vital for industrial production, environmental 
management of food & and beverage, and healthcare. As 
of 2021, the global annual oxygen turnover has reached 
USD 46.24 billion and will steadily increase.1

Since the first mention of oxygen therapy in the medical 
journal; The Principles of Medicine by Dr. William Osler 
in 1898, the rapid growth of medical oxygen is continu-
ously driven by innovative technology and capital, today 
medical-grade oxygen is an indispensable part of medical 
care in hospital and at home, which the importance and 

http://www.globalce.org
http://globalce.org
http://globalce.org
https://creativecommons.org/licenses/by/4.0/
https://creativecommons.org/licenses/by/4.0/


Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

J Global Clinical Engineering Vol.5 Issue 3: 2023  12

criticality of it have been demonstrated in the context of 
COVID-19. 

Air separation by adsorption to produce oxygen for 
medical-grade applications represents one of several 
important commercialized adsorption processes: adsorp-
tive air separation technologies, nitrogen-selective zeolite 
technologies, and intensification technologies. Further-
more, owing to the development of synthetic molecular 
sieves, the pressure swing adsorption (PSA) technology, 
thus the PSA oxygen generation mini-plant is widely used 
in all various hospitals for its fast, convenient, and cost-
effective features.

In this paper, we have drawn the modularity concept 
and cascaded the PSA oxygen generation mini-plant into 
4 modules. Next, 10 key components (units) are defined 
and elaborated with their respective functionality. Thirdly, 
we discuss how the module approach demonstrates 
flexibility to meet the various ambient conditions with 
its outstanding technical features. Lastly, we introduce 
the phase-gate review to ensure the module approach 
achieves the overall PSA oxygen generation mini-plant 
performance. This paper contributes to the literature on 
the modularized design method, adsorption technology, 
air separation process, etc.

DESIGN CONCEPT

Adsorption air separation technologies can generate 
oxygen from the ambient air in the range of several ki-
lograms to hundreds of tons of Per Day Oxygen (TPDO, 
normally limited to 300 TPDO) at a purity of 93%±3%. 
Such oxygen purity levels are simply because the heavy 
component (nitrogen) accounts for ~78% of the feed air. 
Other elements, such as argon and moisture, must be pre-
treated or integrated into the separation process. Therefore, 
it is understood that adsorption technology’s basis is the 
adsorbent’s variable absorptive capacity, depending on the 
consumption scale of hospitals and medical institutions 
and the characteristics of their oxygen therapy. Further, 
as a pressure swing cycle is tailored to the characteristics 
of the adsorbent, the final capacity very much relies on 
the temperature, pressure, and other ambient conditions 
such as humility and cleanliness of the feed air.

To fulfill the customer’s requirements flexibly while 
managing balance of quality and costs, a product manage-
ment methodology is introduced to ensure a consistent 
product portfolio across all markets and drive the stan-
dardization and modularization of PSA oxygen genera-
tion mini-plants for medical applications. It combines 
standardization and modularization, such as standardized 
components designed to ensure exchangeability. Mean-
while, the whole mini-plant is organized by combining 
several fixed & adapted modules engineered on a project 
basis to improve its constructability, as it is usually pre-
assembled and skid-mounted. 

The concept of modularity

Modularity is very popular in design and manufacturing, 
and it is widely used in medical devices for its compatible 
assembly and flexible adaption to various applications. 
Modularity generally refers to breaking down complex 
product systems into simpler units called modules that 
may function independently. Specifically, modules are 
self-contained functional units that connect with other 
units, but do not rely on those other units for their own 
stable operation.2

The properties of modularity

The modular approach featured four defined key 
properties. When defined in terms of these properties, 
modularity is not an all-or-nothing feature of designs but 
can be described in degrees.3 
1. Partial decomposability. It refers to the notion that a 

complex system may be partially divided into smaller 
meaningful functional units – modules.4 Depending 
upon the complexity of product systems and the 
necessity of product management, it can be divided 
from 3–5 modules to hundreds of modules with clear 
boundaries called battery limits. 

2. Proper functioning. It signifies that the operation of 
each module in the design is expected to produce the 
intended result. This intended result is an integral part 
of the whole function of the designed complex system. 
For instance, the air compressor module generates 
the compressed air to feed gas into PSA module with 
the proper technical specifications range of pressure, 
temperature, and dew point. 



13 J Global Clinical Engineering Vol.5 Issue 3: 2023

Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

3. Standardized interface. It denotes that modules 
within the design can connect or communicate with 
each other in a structured fashion. Interface manage-
ment systematically controls all communications that 
support a process operation. In the most basic sense, 
this property is similar to the property of children’s 
LEGO building blocks – pieces are designed so that 
one can plug into the next.

4. Information hiding. It is also known as “encapsula-
tion” and refers to keeping the specific operation de-
tails within a module.5 For example, the smart control 
module aims to control the whole product system. 
But its control philosophy, logic, process parameter, 
and value are not disclosed to others unless specified. 

SKETCH OF MOLECULAR SIEVE OXYGEN 
GENERATION MINI-PLANT

PSA oxygen generation mini-plant has been developed 
steadily over the last four decades since Praxair built the 
first small-scale prototype in 1985.6 which turned out from 
early progress driven primarily by large-scale industrial 
application. This development contributes to the on-site 
medical oxygen supply solution that prevails in hospital 
and other medical institutions. To fulfill the more flex-
ibly designated function of the PSA oxygen generation 
mini-plant, the concept of modularity is applied and fixed 
modules and adapted modules were developed. Further, 
to make the modules more stable and minimize the cost, 
the components forming these modules are standardized, 
which could be sourced from off-the-shelf market or in-
house manufactured. 

Modules Definition

Considering the definition of modularity and the proper 
functioning above, we have described 4 modules of the 
PSA medical oxygen generation mini-plant, 3 of them are 
mechanical, and 1 module is instrumentation & control 
related. Their functionalities are introduced as follows:
1. Air compressor module. The system compresses 

atmospheric air by a screw-type air compressor to a 
required pressure and cools to ambient temperature 
through refrigerating drier. The condensed moisture 
is drained out automatically from the air receiver 
through an automatic drain valve. As a meaningful 

functional unit, it has clean compressed dry air as feed 
gas at 7–8 bar, with air quality that optimally fits the 
oxygen generator.

2. PSA module. The compressed air at constant pressure 
is passed through filters set and then passed through 
twin tower PSA module packed with special grade 
Zeolite molecular sieves, where compressed air is 
separated to oxygen at the purity of 93%±3% and at 
a pressure range of 4.5–6 bar. In a few cases, it can be 
directly delivered to the downstream user.

3. Oxygen compressor module. The produced oxygen 
is filled in the oxygen buffer tank and then boosted by 
an oxygen compressor to higher pressure. It typically 
has two configurations: (i) it is boosted to 6–8 bar 
to achieve oxygen reservation, then delivered to the 
central pipeline system; (ii) it is additionally pressured 
to 150 bar for filling oxygen cylinders; however, this 
is not allowed in China.

4. Smart control module. The system has a 7” color 
touch screen control panel with an integrated oxygen 
monitor. The touch screen provides a normal user 
interface for the start-up system, monitors/controls 
the operation of the process valves, monitors signals 
coming from the pressure transducers, and provides 
an alarm system when conditions require it, as well 
as a fail-safe shutdown mode. This control panel also 
features diagnostic capabilities and remote monitoring 
of process parameters.

Standardized components

The total 10 key components are standardized in series:

FIGURE 1. Typical PSA Medical Oxygen Generation Mini-plant 



Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

J Global Clinical Engineering Vol.5 Issue 3: 2023  14

• (1-a) Feed air compressor system. The mechani-
cal compressor is the essential component in the 
Generation mini-plant. It gives the compressed air 
at 7–8 bar for air separation. It typically consumes 
more than 90% of the generation mini-plant’s power 
and generates most of the noise and vibration. It is 
either oil-free or oil-injected rotary screw type and 
air-cooled. It should have a built-in oil separator and 
air filter; its controls are suction throttle valve type 
with on-off line control and motor stopper start con-
trol. Normally, the advanced compressor should be 
provided with a soft start or variable speed drive and 
have a digital display indicating failure, LCD display, 
and records at least 24 hours of operational data.

• (1-b) Air dryer. This is a refrigerant-type capacity 
air dry with a dew point of <+3℃ and pre-filters with 
automatic drains. The alternative is a desiccant type 
with auto-regenerating. It removes more than 90% 
of water in compressed air from the compressor to 
protect the molecular sieve and piping.

• (1-c) Air receiver tank. There is at least one set of 
air receiver tanks after the compressor. It is made of 
painted carbon steel with a capacity of at least 1000 
L, depending on the compressor. It is equipped with 
a pressure gauge to indicate the vessel pressure, a 
safety valve, and a level-sensing auto drain valve.

• (1-d) Filter system. A three-stage air filter removes 
the compressed air’s dust, oil, and other impurities. 
The micro and active carbon layers remove oil and 
dust up to < 0.01 mg/m³. The filtration level should 
comply with ISO Standard 8573-1:2010.1.4.1. 

• (2-a) PSA oxygen generator. The duplexed tower 
PSA oxygen generator packed with special Zeolite 
molecular sieve is skid mounted. It produces 93±3% 
oxygen from compressed air with a capacity of 3 
Nm3/h to 60 Nm3/h and usually not less than 4 bar 
outlet pressure. 

• (2-b) medical grade oxygen receiver tank. The 
oxygen is separated through a PSA generator and 
received in an oxygen tank with less than 1000 L 
capacity with a bacterial/sterile filter. The oxygen 
receiver tank should be equipped with a pressure 
sensor. As aforesaid, the oxygen can be supplied to 
the central pipeline system.

• (3-a) Oxygen booster. The oxygen booster is config-
ured for dynamic oxygen reservation. This has two 
primary purposes: backup to a short-time turndown 
case or adjusting the peak oxygen demand. In this 
scenario, a medical oxygen compressor with an 
aftercooler is required to boost the oxygen pres-
sure back to 8 bar at a similar feed-in temperature. 
After that, the boosted oxygen is connected to the 
high-pressure oxygen receiver with a capacity of 
1000–3000L. 

• (3-b) Cylinder filling station. This component is 
optional and could be added at the client’s request 
and as local regulations allow. The system comprises 
an oil-free oxygen-filling compressor at 150 bar pres-
sure and a filling ramp for cylinders to be connected 
simultaneously. For filling the cylinder, wall-mounted 
racks shall be on the other side of the wall of the PSA 
mini-plant room.

• (4-a) Measurement devices. Several technical 
parameters are measured, such as the process’s 
temperature, pressure, and flow rate. The measure-
ment devices are installed in-field for easy check-
ing. They are also transmitted to the centralized 
control system. Further, there is an integrated and 
continuous oxygen quality monitoring unit with the 
following alarm setting: Carbon monoxide (CO) @ 5 
ppm, Carbon dioxide (CO2) @ 300 ppm, water vapor 
(H2O) @ 67 ppm, Oxygen (O2) @ 90%. 

• (4-b) Smart control system. With the installed sen-
sor and transmitter of in-field measurement devices, 
the process data is automatically collected, recorded, 
and self-diagnosed under configured program em-
bedded with the control philosophy and algorithm. 
Considering the tolerance of normal operation, alarm, 
and trip, as the three safety zones are pre-defined, 
the control system will be automatically triggered 
once the collected data is out of the normal operation 
range to protect against the potential damage of the 
PSA oxygen generation mini-plant. Consequently, 
the oxygen supplies will be shifted to other oxygen 
sources immediately.



15 J Global Clinical Engineering Vol.5 Issue 3: 2023

Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

MATRIX OF DESIGN BASIS COVERING HARSH 
ENVIRONMENT

The performance of the PSA oxygen generation mini-
plant is determined by the adsorption and desorption 
process, which takes place in the duplexed adsorbers. 
The key variables for the adsorption and desorption 
process are multi-component thermodynamics and ki-
netics. Therefore, how to select and optimize those key 
variables are heavily linked to the physical properties 
of the adsorbent particles.6 Moreover, their operating 
environment is even more discrete when exporting them 
to the global market. Therefore, a design basis rooted in 
local operation conditions has to be seriously considered 
to capture these key variables. 

Matrix of Design Basis

The landscape of China from the eastern coast to western 
Tibet is totally different, and the operating condition of 
PSA oxygen Generation mini-plant is remarkably changed. 
Assuming this PSA oxygen Generation mini-plant will be 
installed not only in China but also for global marketing, 
the full range of design basis has to be assured. The ac-
tual operating condition is very complicated, but in this 
paper, we focus on the four main factors: temperature, 
humidity, atmospheric pressure, and cleanliness. While 
optimizing the cost and balancing the design standardiza-
tion, we define that the normal case shall cover 80% of 
application cases and extend to the extreme case in the 
remaining 20%. Ultimately the design basis is specified 
as follows in Table 1. 

Ambient Temperature

In the normal design, the ambient temperature is in 
the range of 20℃±15℃. As the suctioned air as feed gas 

is compressed, the temperature will be increased, and an 
air-cooled aftercooler is installed to ensure the discharged 
compressed air temperature is less than 10℃ rising to the 
original ambient temperature. Further, the air dryer will 
continue to cool down to the pre-defined temperature 
before entering the PSA module. This cooling-down will 
generate cold, dry air for the temperature and minimize 
feed-gas moisture.

There are two sources for the extremely high ambient 
temperature. One is the high ambient temperature origi-
nating from hot summer land, a common understanding. 
However, another source actually comes from the air 
compressor. The heat radiation leads to heat accumula-
tion, thus, high temperature. Therefore, ventilating fan 
and pipe duct shall be connected to the compressor’s 
terminal to remove discharged hot air to minimize the 
negative compact on the ambient temperature of feed 
gas. In addition, an air conditioner shall be added for the 
area with the highest ambient temperature over 35℃.

However, heat preservation is required in cold areas 
in winter to maintain indoor temperatures above 5℃. 
Therefore, the discharged air of high temperature could 
somehow be utilized to warm the feed gas to meet the 
minimum requirement of 5℃. Therefore, in case of the 
gap to the normal range of 5–35℃ is still extant after all 
heat balance and recycle measures, then a heater as an 
auxiliary facility shall be added and switched on in case 
the indoor temperature of the mini-plant house is lower 
than 5℃. 

Ambient Humidity

In the normal design, the relative air humidity ranges 
from 60±20%. The air that leaves a compressor reaches 
100% humidity as the air is compressed and has a higher 
temperature. Unfortunately, the compressed air also con-
tains limited oil (unless you use an oil-free compressor) 
and solid particles. Together, they form an abrasive, often 
acidic, oily sludge. Without air treatment, this murky mix 
will enter the PSA module, harming the molecular sieve 
adsorbents, corroding pipework, damaging pneumatic 
tools, and potentially compromising oxygen products.

The air treatment typically includes three parts. Firstly, 
the condensate shall be drained out by the steam traps. 

TABLE 1. Matrix of Design Basis 

Ambient 
Condition Temperature Humidity Pressure Cleanliness

Normal 5–35 ℃ 40–80% 0.09–0.1 MPa ≤10 mg/m3

Extreme 
high 55 ℃ 95% (Not 

applicable) 400 mg/m3

Extreme 
low −30 ℃ (Be better) 0.059 MPa (Be better)



Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

J Global Clinical Engineering Vol.5 Issue 3: 2023  16

Although an automatic trap is usually mounted, in some 
cases, a manual trap also makes sense, depending on 
the amount of condensate. In addition, a humidity sen-
sor is recommended to install to capture the failure of 
condensation prevention. Secondly, as a partial air dryer, 
the saturated air with 100% humidity is cooled down to 
dewpoint; thus, the moisture in the compressed air is 
removed. 

As aforesaid, there are two types of air dryers. One is a 
refrigerant type with a pressure dewpoint of <3℃ (100% 
relative humidity at 20℃), and another is a desiccant 
type with auto regenerating. In the normal case, both are 
suitable. However, if the ambient humidity is high, the 
refrigerant type is strongly recommended to ensure its 
higher reliability. Further, to meet the high humidity, the 
sufficient design margin of the air dryer shall be consid-
ered. For instance, 130–150% of the calculated capacity 
shall be configured.

Atmosphere Pressure

When addressing the pressure, it refers to the plateau 
area where the atmospheric pressure is less than 0.1 
MPa. In the normal design, the mini-plant is assumed to 
be installed at an elevation no more than 1000 meters, 
which equals its atmosphere pressure in the range of 
0.09-0.1 MPa. Therefore, when the atmospheric pressure 
decreases by 0.01MPa, the compression ratio of the air 
compressor will increase by 6~8%, and the compression 
energy consumption will increase accordingly. In addition, 
the reduction of atmospheric pressure will reduce the 
displacement of the air compressor, and the correspond-
ing oxygen production will also be reduced.

To maintain the feed-air to the PSA module at the 
optimum pressure, the logical thinking is to enlarge the 
compressor’s power to compensate for the insufficient 
pressure from the atmosphere. Adjustment to the atmo-
spheric pressure by selecting the suitable compressor 
model is possible, while it should keep in mind that each 
compressor has a maximum compression ratio that cannot 
be exceeded. Further, for the compressor and its auxiliary 
equipment, in practice, it will have a significant impact 
on power consumption and air consumption. Meanwhile, 
changes due to altitude will also affect the rated power 
provided by the motor and internal combustion engine.

External Cleanliness

Cleanliness is very crucial for the oxygen industry. There 
is a significant issue regarding internal surface cleanliness 
resulting from machine and equipment, process-compatible 
coatings, and, more important, the grave consequence of 
molecular sieve pulverization. This is a profound issue 
that can be addressed in another special edition. In this 
paper, we only concentrate on external cleanliness, which 
is affected by the external environment, such as the oil, 
grease, particles, and liquid moisture in the feed air. 

Therefore, it is heavily linked to two portions: (1) the 
inlet self-protected dust filter by the compressor. It is 
designed to remove dust and other physical impurities 
from the ambient air before it is further compressed in 
the air compressor; (2) the three-level filtration system 
for compressed air. Untreated compressed air can be 
contaminated by dust, water, and oil. This makes filtra-
tion a crucial component in the air compressor module. 
Depending on the external cleanliness, a series of filtra-
tion solutions are needed to protect the air-proceeded 
equipment and the final oxygen products. For instance, 
wrapped media for wet particles, pleated media for solid 
particles, macro-structured activated carbon for oil vapors, 
cyclone for moisture, etc.

DISCUSSION

The adsorption and desorption processes within the 
duplexed adsorbers are affected by pressure and pressure 
drop, heat and mass transfer, temperature gradients, and 
airflow velocity of the feed gas. These elements jointly 
determine the dense packing of the adsorbents and their 
fluidization for achieving optimum oxygen production. 
Taken individually, many of these elements may seem to 
be conceptually straightforward. However, integrating 
them to achieve a high-performance process concerning 
high oxygen purity, high oxygen productivity, and low 
power consumption at a competitive cost is not trivial.

Modular approach

The modular approach is widely used for complex 
product systems, including process plants. However, how 
to define the modular boundaries, the input and output 



17 J Global Clinical Engineering Vol.5 Issue 3: 2023

Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

of the modules, and their coordination interface become 
more important. 

Before applying and executing a project, a phase gate 
review is recommended to ensure the standardized 
components are properly selected and maintained in due 
time. Specifically, the phase aligns with the project’s time 
frame, and the gate has a strictly defined project quality. 
For example, for successfully applying modules for PSA 
oxygen generation mini-plant, we recommend splitting 
them into the following phases: conceptual design, basic 
engineering, and detailed engineering. For the gate review, 
the gate requirement is specified in advance in Table 2.

Temperature

Ambient temperature is a key parameter influencing 
the performance of oxygen generation mini-plant. The 
ambient temperature will have three impacts on the 
mini-plant’s performance, finally determining its uptime 

in the harshest conditions and its build-up cost. Firstly, 
each compressor has an ideal operational range, reflecting 
the operation temperature, pressure, and flow rate. Thus, 
the model selection shall be fixed during the conceptual 
design, and the deviation from the optimal operating tem-
perature will decrease the compressor efficiency. When 
the ambient temperature rises, the discharge flowrate of 
the air compressor will decrease, which means that the 
shaft power will increase. The record shows that the shaft 
power increases by about 1% for every 3℃ increment in 
ambient temperature.

 Secondly, increasing the ambient temperature will also 
increase the exhaust temperature of the air compressor, 
which requires more refrigeration capacity to compen-
sate for the cooling loss, ultimately leading to increased 
energy consumption. Furthermore, the higher ambient 
temperature will also decrease the efficiency of the air 
dryer by 10% for every 5℃ and leads to a higher dew point 
of compressed air, which will have a grave consequence 
of molecular sieve pulverization. Therefore, the high 
ambient temperature needs more heat exchange by the 
pre-cooler or aftercooler of the air compressor. Therefore, 
it is calculated and additionally configured. Alternatively, 
a higher-capacity of air dryer is also possible.

Thirdly, the low ambient temperature will decrease 
adsorption efficiency and oxygen purity in northern 
winters, especially in extremely low-temperature con-
ditions. Further, in the winterization, the electrical and 
instrumentation parts, including in-field measurement 
devices, could be blocked or malfunction, and the safety 
of the mini-plant could be destroyed.

In summary, besides the process engineering calcula-
tion and modules matching as a basis, additional measures 
should be tailored to the local conditions of hot/cold are 
assumed. For instance, the air conditioner, ventilating fan 
and/or electric heater shall be installed indoors to reduce 
ambient temperature deviation. In addition, of course, 
the manual assistance to keep the door of the mini-plant 
house full-open, half-open, and full-close (if still possible 
to guarantee its safety) is helpful to maintain the normal 
range of 5–35℃ and save power.

TABLE 2. Phase Gate Review for Modular Approach in Oxygen 
Generation Mini-Plant

Phase Gate Typical Gate Requirement

Conceptual 
Design CD

• Process topology defined
• Utility consumption estimated
• Process and environmental safety concepts 

prepared
• Process flow diagram released for basic 

engineering

Basic 
Engineering BE

• P&ID released for mini-plant design
• Plot plan completed
• Mechanical datasheet/inquiry spec completed
• Mechanical tie-in data, installation dimension, 

and weights fixed
• Basic requirements for operation and 

automation completed

Detailed 
Engineering DE

• P&ID released for construction and 
commissioning

• Electrical and instrumentation materials 
ordered

• Equipment foundation completed
• Isometrics drawing completed
• Factory acceptance test (FAT) for key 

equipment completed



Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

J Global Clinical Engineering Vol.5 Issue 3: 2023  18

Humidity

As aforesaid, the murky mix caused by high humility 
could harm the downstream units by grinding, corrosion, 
and polluting the process air. Secondly, it also could influ-
ence electric insulation seriously. Thirdly, it will increase 
power consumption, leading to a high-pressure drop 
resulting from a block by water vapor or moisture. Last 
but not least, high humidity will increase the operating 
load of the air filter at the compressor inlet and increase 
the replacement cycle.

Although the air that leaves a compressor reaches 
100% humidity, the remaining humidity in compressed 
air turns into water as the air cools while it moves through 
the system. Because water causes corrosion and dam-
age, proper drains function must be installed, whether 
automatic, electronic, or manual, to keep downstream 
equipment working optimally.

One of the most important issues is that the compres-
sor shall be equipped with an aftercooler. It cools the 
air, turning up to 70% of the humidity into water, which 
is immediately drained. However, production facilities 
with extremely high ambient temperatures might need 
additional cooling, meaning double capacity or add-on 
aftercoolers in parallel, preventing excess moisture from 
entering the downstream equipment. 

Pressure

When addressing the pressure, it often refers to the 
plateau area. There are two related two issues. One is the 
atmospheric pressure in a plain area or plateau area. In 
the plateau area, lots of atmosphere pressure-related fac-
tors shall be considered. For instance, is a specific mass 
flow or volume flow required? Can the compression ratio, 
absolute pressure, or gauge pressure be measured? Is the 
temperature of compressed air significant? But of course, 
the most crucial factor is that the suction pressure of feed 
air varies with the altitude. For example, a compressor 
with a compression ratio of 8.0 at sea level will increase 
to 11.1 at 3000 meters above sea level.

Furthermore, the atmospheric pressure also depends 
on the weather. For a specific place, seasonal temperature 
changes can also affect the pressure value by up to 5%. 
By the way, high altitude locations always lead to low 
atmospheric pressure and temperature, which shall be 
considered in advance. For the details, please refers to 
the section on “temperature.”

Another issue is the process pressure inside the mini-
plant, precisely the working pressure of the adsorption and 
desorption process, which is jointly determined by atmo-
sphere pressure, compressed air, and the pressure drop in 
the process. There are two main adsorption technologies 
for air separation by adsorption: PSA and Temperature 
Swing Adsorption (TSA). PSA methods require electric-
ity to be supplied to the compressor or vacuum pump, 
while the TSA method involves heating the adsorption 
bed during the regeneration stage. Here is just a short 
discussion on PSA pressure setting. For Pressure ratio 
(PH/PL) is determined from the pressures at the end of 
the feed step (PH) and at the end of the desorption step 
(PL). These end pressures establish the boundaries for 
the N2 and O2 working capacities. Selecting PH, PL and 
PH/PL is a compromise between O2 recovery and energy 
consumption, all within the constraints of the available 
compression equipment.7 

Cleanliness

Filtration is essential, so the diversified filter types offer 
a range of purity grades to meet the specific requirements 
for removing the smallest contaminants, including bac-
teria and viruses. However, three negative impacts shall 
be considered when selecting the suitable solution for 
every application: the pressure drop, the contamination, 
and the cost of spare parts for filter elements. 

In the heavy industrial zone, the inlet filter has to be 
reinforced, which leads to a pressure drop rising and in-
creases the motor’s load; otherwise, too many impurities in 
the air will increase the purification load of the molecular 
sieve adsorber and filters. If the purified air fails to meet 
the expectation, it will also affect the production efficiency 
of the PSA system and the production quality of oxygen.



19 J Global Clinical Engineering Vol.5 Issue 3: 2023

Liu, Qiu, Zuo, Lou: Application of Molecular Sieve Oxygen Generation Mini-plant under Harsh Environment

CONCLUSION

This paper introduces the PSA oxygen generation mini-
plant, a small-scale complex product system widely used 
in various hospitals, which was neglected in innovation. It 
addresses how to design and build the PSA oxygen genera-
tion mini-plant more flexibly to enable its compatibility 
in different extreme ambient conditions (temperature, 
humidity, pressure, cleanliness) of installation location. 

Specifically, this paper employs the concept of modu-
larity and elaborates 10 key components for 4 modules 
of PSA medical oxygen generation mini-plant, namely 
(a) air compressor module; (b) PSA module; (c) oxygen 
compressor module; (d) smart control module. Under this 
modularized design approach, this paper further investi-
gates the technical features and the design criticality of 
modular and key components in fulfilling the expected 
performance, finally achieving and maintaining the overall 
performance of PSA oxygen generation mini-plant with 
the selected module installed worldwide. 

This paper helps to illuminate the variability of PSA 
oxygen generation mini-plants in a harsh environment 
in four dimensions (temperature, humidity, pressure, 
cleanliness) and briefs the methodology of the phase 
gate model for modular approach in oxygen generation 
mini-plant. Furthermore, it contributes to the literature 
on modular design methods, adsorption technology, air 
separation process, etc.

RECOMMENDATIONS

PSA oxygen Generation mini-plant has been widely 
used in all-levels of hospitals and medical institutions. 
To overcome the harsh environment, a new product de-
velopment process has been established and optimized 

via S/M/P (standardization/modularization/platform) 
approaches to ensure product portfolio management 
and successful application with the selective serialized 
& standardized components.

ACKNOWLEDGEMENTS

We acknowledged this research work to the National 
Institute of Hospital Administration, NHC, China, for their 
funding to the project of Intelligent Energy Saving Solu-
tion for Medical Gas System [GYZ2022HQ45].

REFERENCES
1. Global Info Research. Chemical & Material Market 

Research Report 2022-01-04. Available at: www.
globalinforesearch.com.cn/reports/142044/oxygen

2. Chorpita BF, Daleiden EL, Weisz JR. Modularity in the 
design and application of therapeutic interventions. 
Appl Prevent Psychol 2005:11.3:141–56.

3. Mikkola JH, Gassmann O. Managing modularity of 
product architectures: toward an integrated theory. 
IEEE Transact Engineer Manage 2003;50(2):204–18.

4. Simon HA. The sciences of the artificial 3rd ed. MIT 
Press: Cambridge; 1996.

5. Parnas DL. On the criteria to be used in decomposing 
systems into modules. In: Pioneers and their contri-
butions to software engineering. Springer: Berlin, 
Heidelberg; 1972. 479-498.

6. Ackley MW. Medical oxygen concentrators: a review 
of progress in air separation technology. Adsorption 
2019;25(8):1437–74.

7. Smolarek J, et al. Radial bed vaccum/pressure swing 
adsorber vessel. U.S. Patent No 5,759,242; 1998.

http://www.globalinforesearch.com.cn/reports/142044/oxygen
http://www.globalinforesearch.com.cn/reports/142044/oxygen

