Home >> Industry Knowledge >> Nitrogen Generator (Nitrogen equipment) Absorber Development
Preface
By activated alumina and molecular sieve adsorption bed consisting of double bed smoking
Appendage is a cryogenic air separation plant in France to achieve the heavy air purification materials
To equipment.
With the large-scale air separation plant, molecular sieve adsorption purification increase in volume
Large, horizontal adsorber covers an area of large, evenly distributed airflow is difficult
Shortcomings exposed. In recent years, in order to adapt to the larger molecular sieve adsorber
Type air separation unit development requirements of China is committed to ASU
Vertical double-bed molecular sieve adsorber radial flow of development and research. 2005
Year in July by the China Air Separation Equipment Corporation independently designed, developed legislation
Double-bed radial flow-type molecular sieve adsorber is first applied to Jiangyin Xing Cheng
Special Steel Company 20000m3 / h air separation plants, and be successful. The
Man of domestic self-developed the first vertical double bed radial flow adsorption
The design and debugging situation, and so an introduction.
A principle of adsorption purification
In the double-bed adsorber, the raw material through the activity of the air oxidation of the first
Aluminum adsorption layer, and then through the molecular sieve adsorption layer. As the activated alumina
And molecular sieve moisture contained in the air, carbon dioxide, acetylene and
Other gases such as hydrocarbons can be adsorbed impurities in the adsorption amount of suction
Attached in such areas as speed, and differences in absorption, as well as adsorbent adsorption
Capacity with temperature and pressure changes in changes in 0.6MPa (A),
l8 ℃ conditions, the activated alumina can be used to achieve the air in the water
Sub-adsorption purification, molecular sieve to achieve carbon dioxide in the air, B
Acetylene and other hydrocarbons can be adsorbed adsorption purification; in
0.11MPa (A), 160 ℃ under the conditions of desorption of the adsorption process of miscellaneous
Quality components, to achieve regeneration.
Recycling adsorption bed adsorption difference shown in Figure 1. Curve
Following is an area of the end of adsorption bed adsorption, curve
2 area of the regeneration process following the end of the bed adsorption capacity of the curve
1 and curve 2 the area between the cycle can be used suction
Attached to the amount that the poor adsorption capacity.
In the adsorption phase, water and carbon dioxide in the air
Bed of activated alumina and molecular sieve bed in the content distribution in Figure 2
Shown. Adsorber regeneration cycle of adsorption one shown in Figure 3.
2 Mathematical Model
Vertical double-bed radial flow adsorption Used for linear driving force model for
(LDF) to solve more appropriate. Linear driving force model is applicable to
Arbitrary components and Langmuir adsorption isotherm systems. Linear drive
Model consists of a group of mass balance equations, solid-phase linear driving force mass transfer side
Process, adsorption isotherm equation and the corresponding boundary conditions and initial conditions
Composition.
2.1 Material balance equation
Set the direction of air flow of raw materials is positive, the process of material empty adsorption
Gas accounting for adsorbate components of quality:
A component (H2O)
Where: C is water vapor concentration, mol/cm3; C for dioxin
Dioxide gas concentration, mol / cm. ; D for the diffusion coefficient, cm2 / s;
q for water adsorption capacity, mol / c ~; q carbon dioxide adsorption capacity,
mol / cm. ; T is time, s; V for the gas flow rate, cm / s; X for
Bed thickness, cm; e is porosity.
2.2 Solid-phase linear driving force mass transfer equation
Where: K for the adsorption bed of the water mass transfer coefficient, s. . ; K
For the adsorbent bed of the carbon dioxide mass transfer coefficient, s ~; q for water
Equilibrium adsorption capacity, mol / cm. ; Q for the carbon dioxide equilibrium adsorption
Volume, m0l/cm. .
2.3 Adsorption isotherm equation
In the adsorption equilibrium, the uniform surface of the gas molecules adsorption isotherm
Line Langmuir equation is:
Where: b the Langmuir equilibrium constant for water; b for the two
Carbon dioxide of the Langmuir equilibrium constant.
Where: Ll as active alumina bed thickness, cm; L for the
Molecular sieve bed thickness, cm; P for the desorption pressure, atm; PH
For the adsorption pressure, arm.
2.5 Gas flow rate boundary condition
I: 0 = VoA
--
O
--
VI
- R)
OX I 1
OV J
1 = c,
(5 1 a)
Where:. As the raw material of air flow rate, cm / s.
2.6 Initial conditions
Adsorption of the beginning:
C (X, 0) = 0, q (, 0) = 01,,
C (X, 0) = 0, q (, 0) = 0 J
Adsorption saturation:
C (X, 0) = C o, q (X, 0) = q s1
C (X, 0) = C o, qB (X, 0) = qBs J
(6 1 b)
Where: c poop water as raw materials in the air component concentration, mol / c ~;
c arsenic as a raw material component of the concentration of carbon dioxide in the air, mol/cm3.
3 Structural Design
Double-bed radial flow absorber structure shown in Figure 4. TUBE
By the three-layer grid network and the center tube component, using suspension structure. Activity
Alumina installed in the middle of the outer grid network and the mezzanine between the grid networks,
Zeolite installed in the middle of grid network and the mezzanine between the inner grid networks,
Center barrel set flow splitter, so that the radial air through the adsorption bed
Gas flow rate along the absorber height of axial uniform distribution, the center tube outer wall of the
Filter double as powder filter.
In the adsorption process, raw materials into the air from the bottom of the adsorber, after
Fairing weeks wizard flow, first in the outer layer of activated alumina adsorbent bed adsorption
Removal of moisture from re-entering the inner molecular sieve adsorbent bed adsorption removal B
Acetylene, carbon dioxide and other hydrocarbons can be adsorbed, and then by the
Center tube from the top of the outflow. The advantages of double beds: the outer activity of
Alumina raw materials in the air the full absorption of water, making molecular sieve is not
Absorbed water; into the molecular sieve moisture the air does not improve the molecular
Sieve adsorption capacity of carbon dioxide, thus prolonging the life of molecular sieve.
In the regeneration process, the regeneration of nitrogen pollution into the top tube from the center
Income, the diversion in the flow divider, the regeneration of nitrogen pollution along the axis are
Uniform distribution in the annular adsorbent bed, so that even desorption desorption adsorption bed. At
Adsorbed phase of adhesion of the outer cylinder at the center of the molecular sieve dust screen, in the
Regeneration phase is cleaning removed dust from the bottom of the discharge port.
Figure 4 Schematic diagram of absorber
Center tube flow divider design of radial flow adsorber to the customs
Important. Absorber along the direction of radial flow velocity field a high degree of consistency,
Decided to flow along the axial direction in the adsorber consistency. Velocity distribution
Adsorption layer allows the upper and lower pressure line, and air penetration through the suction
Layer attached to the speed of airflow is consistent, so that absorption edge of the bed axial ministries
Sub-adsorption rate and adsorption amount of uniform, their adsorption saturation time
The same.
Center tube flow distributor design key is to accurately calculate the flow channel
Pressure drop. According to the given flow and pressure drop, calculate flow channel foot
Inch, is not part of the complex fluid mechanics problems.
The absorber design uses 8 x 12 mesh molecular sieve, from the mass transfer rate
Rate point of view, the smaller the particle size, transfer efficiency curve slope of the larger mass transfer
Zone is shorter. Faster adsorption rate. The small size of molecular sieve can not only reduce
Small bed volume, but also its adsorption bed to shorten the length of the mass transfer zone, which
For the radial flow adsorber it is very advantageous.
4 Commissioning
Jiangyin Xing Cheng Special Steel Company 20000m ~ / h air separation plant installed
Into after the purging process of carrying out the tower and found that molecular sieve purification system
Integration of renewable and low peak temperature of the cold winds down from the peak time than the cold wind
Long, the original set adsorber regeneration cycle does not completely renewable, 2
Carbon dioxide analyzer display: air export carbon dioxide absorber
Gradually increased. Thus, in 2005, June 25 to June 27
On the molecular sieve purification system, a preliminary debugging. Debugging can be divided into
Four stages.
Phase I: the user to an air separation plant bare the process of cold
Carried out. Because users fear will lead people to carbon dioxide and water tower,
Impact of bare cold to bare the cold is not the whole volume of adsorber during the run. Empty
Air precooling system bypass DN200mm throttle open, into the adsorber
The air is about 50000m3 / h, gradually increasing to the late
70000m. / H or so, into the absorber of the air temperature is 17 ℃ Left
Right, the resistance of air through the adsorber is 1.5 ~ 2.2kPa, and then angry
Pressure of 12kPa, a temperature of 32 ℃ or so, regeneration time is set to
Pressure relief 8min, heating 44min, cold blowing 121min, Pressure 14min.
During this period found that the regeneration process of outlet absorption peak temperature is low,
Regeneration is incomplete. To re-adjust the set pressure relief 8min, heating
60min, cold blowing 100min, Pressure 12min, by increasing the absorber
Another angry population, the average temperature, making the cold wind to reach peak temperature
103 ℃, and the cold winds down from the peak time, carbon dioxide
Analysis of the instrument display absorber of carbon dioxide levels remained low in the air exit,
Regeneration in good condition.
The second stage: bare the cold to last until June 27 at 3:00 am,
Bare cold effect basically reach. Pre-venting valve for Booster not open,
Increase the absorber of the scheme the amount of air can not be achieved. Calculated,
68000m. / H air-handling capacity of 300min amount equivalent to the whole
105000m. / H air-handling capacity of 194min. With on-site operations
Personnel coordination, to extend the working hours of a single adsorber to 300min (plus
3min and the switching valve in parallel movement time, the actual run of about
308min), exports of carbon dioxide adsorber is going on the air
Lower absorption in good condition. At the same time another regeneration time for stress-relief
8min, heating 70min, cold blowing 210min, Pressure 12min, cold wind
A peak temperature of 113 ℃, regeneration in good condition.
Phase III: June 27 8:00 am, after adjustments
Period of 190min, the pressure relief 8min, heating 70min, cold wind
100min, Pressure 12min, the adsorption of the adsorbed 300min device into the
OK regeneration, another began to adsorption. To 27 at about 9:40,
Close air precooling system bypass DN200mm throttle, adsorber
Start to run the whole amount. At this point the air into the adsorber temperature reaches 23 ℃
Or so, adjusted to the cooling tower gas and air into the adsorber temperature by
Step down to 21.5 ℃, is no longer reduced. Is increasing the amount of air
Meanwhile, another adsorber heating has ended, started blowing cold,
Angry pressure from 12kPa and then fell to 7 9kPa, a reduction of the cold
Inflatable volume, and then angry, out of adsorber peak temperature of the cold winds 84 ℃,
Blowing the end of the cold temperature of 42 ℃. Started to increase the amount of air in the same time,
Analyzer display absorber of carbon dioxide content of air exports have experienced substantial
Fluctuations, but then stabilized until the end of the period of work.
Phase IV: Since the last cycle of regeneration is not ideal, again
Adjust the regeneration cycle to 200min, the pressure relief 8min, heating
74min, cold blowing 106min, Pressure 12min, when the gas was still blowing cold bias
Small, regeneration is still not satisfactory, the peak temperature of the cold winds 85 ℃,
Blowing the end of the cold temperature of 42 ℃. Around 1:00 in the afternoon, DCS system
Commission shows levels of carbon dioxide adsorber air exports upward trend appears
Potential, until 5:00 pm Parking. Parking before the half-re -
Health cycle has to maximize the cold blowing pressure to 11kPa or so, by
In the large adsorption capacity, regeneration effect is not very good.
Through the four stages of debugging and found that adsorber in the adsorption process
Work is good, but there are some problems regeneration process. By recycling
Process heating, cold-blow re-accounting and velocity field of renewable nitrogen pollution sub -
Analysis of the final decision to partially modify the absorber center tube flow splitter.
July 27, 2005, air separation plant to re-drive. Center
Tube flow divider by the partial modification, the original adsorber regeneration process
Problem has been resolved, adsorber reached the design requirements.
In 105000m. / H the whole volume of air into the adsorber adsorption purification
Conditions, the absorption of carbon dioxide content of the air outlet stabilized at 0.3
X 10 below, regeneration time set as follows: pressure relief 8min, heating
74min, cold blowing 92min, Pressure 15min. During the cold wind of renewable pollution
Nitrogen export peak temperature 103 ℃, the cold wind at the end nitrogen recycled sewage
Outlet temperature of 38 ℃, adsorber regeneration good effect.
In order to adsorber in the switching process does not cause pressure on the tower
Is too large fluctuations, are pressing to change the time 15min, than the original set
12min extended 3min, and through the valve by the time controller V1210
Control of pre-opening and pressure tracking adjustment, so that pressure fluctuations on the value of control tower
Within the allowable range. The double-bed radial flow adsorber in the switching process
The last column in the pressure fluctuation has little effect ASU argon condition than
More stable.
Running results show that: The Chinese Air Separation Equipment Corporation developed vertical
Double-bed radial flow adsorber is a success. Domestic Vertical Double Bed Trail
To the flow adsorber is bound in a large air separation plants to play a unique supporting
Advantage of widespread use.