CN107479375A - Regulate and control the method for step pressurised seawater desalination system Element Flux balance degree - Google Patents
Regulate and control the method for step pressurised seawater desalination system Element Flux balance degree Download PDFInfo
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- 230000004907 flux Effects 0.000 title claims abstract description 134
- 239000013535 sea water Substances 0.000 title claims abstract description 45
- 238000010612 desalination reaction Methods 0.000 title claims abstract description 44
- 238000000034 method Methods 0.000 title claims abstract description 29
- 238000005520 cutting process Methods 0.000 claims abstract description 75
- 238000009826 distribution Methods 0.000 claims abstract description 24
- 238000006243 chemical reaction Methods 0.000 claims abstract description 13
- 238000001223 reverse osmosis Methods 0.000 claims abstract description 9
- 230000033228 biological regulation Effects 0.000 claims abstract description 8
- 239000012528 membrane Substances 0.000 claims description 61
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 31
- 150000003839 salts Chemical class 0.000 claims description 13
- 230000008569 process Effects 0.000 claims description 10
- 238000005119 centrifugation Methods 0.000 claims description 5
- 230000003204 osmotic effect Effects 0.000 claims description 4
- 238000004364 calculation method Methods 0.000 claims description 3
- 230000035699 permeability Effects 0.000 claims description 3
- 230000010287 polarization Effects 0.000 claims description 3
- 238000009738 saturating Methods 0.000 claims description 3
- 230000000694 effects Effects 0.000 abstract description 2
- 238000005457 optimization Methods 0.000 abstract 1
- 239000013505 freshwater Substances 0.000 description 5
- 238000001764 infiltration Methods 0.000 description 5
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- JEGUKCSWCFPDGT-UHFFFAOYSA-N h2o hydrate Chemical compound O.O JEGUKCSWCFPDGT-UHFFFAOYSA-N 0.000 description 1
- 239000008239 natural water Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B13/00—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/08—Seawater, e.g. for desalination
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- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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Abstract
The present invention provides a kind of method of regulation and control step pressurised seawater desalination system Element Flux balance degree, it is on the basis of step pressurised seawater desalination system structure, for the impeller outer diameter of step booster pump, by the cutting output for calculating the step impeller of pump external diameter at different operating conditions, different pressurization positions, with centrifugal pump motor frequency conversion auxiliary adjustment, reach the linear distribution of system element flux and Element Flux slope is controllable.Effect of the present invention is to reach to regulate and control the purpose of each Element Flux by the way of the step boosting centrifugal pump impeller outer diameter cutting in system and motor frequency modulation.Can effectively solve that step pressurised seawater desalination system flux is unbalance and the uncontrollable problem of Element Flux balance degree using the present invention, be advantageous to reverse osmosis seawater desalination system flux isostatic optimization study, facilitation is played in the development to reverse osmosis seawater desalination system.
Description
Technical field
The present invention relates to field of seawater desalination, the side of regulation and control step pressurised seawater desalination system Element Flux balance degree
Method.
Background technology
Water resource occupies critical role as irreplaceable natural resources in economic development and people's lives.China
It is a serious water shortage country, and a large amount of industry, rural sewage are discharged into natural water, cause huge environmental problem,
So that the supply and demand of water resource is more nervous.Desalination technology is directed to solving the problems, such as shortage of fresh water.In recent years, counter-infiltration
Embrane method as a kind of main desalination technology because its engineering stability reliably with cost is cheap is widely used.
But counter-infiltration system has serious flux unbalance, it is counter-infiltration system along each film of flow to study carefully its main cause
Element water inlet salinity gradually increases, osmotic pressure increase, causes the pure driving directly proportional to aquifer yield to press rapid decrease so as to lean on
Proximal end element aquifer yield reduces.Its secondary cause is due to existing along stroke pressure loss i.e. along journey pressure drop along flow so that film
Element intake pressure gradually reduces so that membrane component aquifer yield gradually reduces.The unbalance of flux system also leads to produce water saliferous
Amount rises, and influences whole system producing water water quality.Because water inlet salt content is low, the rate of recovery is high in bitter system, frequently with segmentation
The method of operation, generally two-part structure.Counter-infiltration is in bitter processing system frequently with section-between boosting, fresh water back pressure etc.
Flux isostatic technological balance system segment flux.
Section-between boosting mode is intersegmental with pump supercharging two, and the intake pressure for improving second segment produces water so as to increase its
Amount.So that two sections of section flux ratio reduces, flux is more balanced.Fresh water back pressure flux isostatic technique is to produce water in system first section
Increase counterbalance valve at pipe, appropriateness adjusts back pressure valve aperture to increase production water resistance.When increase system production water resistance, back pressure valve
Both sides pressure difference is lost with constituting additional-energy by the product of flow.Therefore pressure pump needs to increase pressure to export more
Energy, so that the increase of second segment intake pressure improves its aquifer yield, has reached the purpose of flux isostatic.Section-between boosting with
Fresh water back pressure flux isostatic technique is only capable of the section flux ratio between regulator control system, can not regulate and control flux ratio between each membrane component.And
Because the feedwater salt content of seawater desalination system is very high, system yield is again low, therefore system flow is shorter and is not segmented, and does not adopt typically
With section-between boosting or water back pressure isoflux equilibrium technique is produced, therefore the flux isostatic degree of reverse osmosis seawater desalination system is very poor.
Step pressurization is a kind of new technology balanced for Element Flux newly proposed in recent years, is mainly used in counter-infiltration
Seawater desalination system.In step pressurised seawater desalination system, membranous system feedwater is provided by a high-pressure pump 4, and membrane stack is by multiple 1
Dress putamina 1 is formed, and is connected with pipeline 2 between every putamina in membrane stack, is pressurized by the impellers at different levels 8 of step centrifugal pump 5.Water inlet
Enter membrane component from putamina watering port 3 after supercharging, its concentrated water outflows back to step centrifugal pump 5 from concentrated water port 6 and entered again
Row supercharging enters next membrane component by pipeline.Impellers at different levels are serially connected in step centrifugal pump casing, and both stage impellers it
Between current separated by dividing plate 7 and by a Driven by Coaxial of motor 10.Its structure is as shown in Figure 1.
But though step pressurization flux isostatic technique can balance each membrane element flux ratio, due to being advised using centrifugal pump impeller
Lattice limit, its flux system ratio be only a particular value and still can not arbitrarily set the i.e. flux isostatic degree of flux slope can not
Control.And the Element Flux distribution of system is into nonlinear Distribution, it is big to show head end Element Flux, along flow posterior member flux
Rapid decrease, Element Flux weigh along flow skewness.
The content of the invention
For deficiency of the prior art, it is an object of the invention to provide one kind regulation and control step pressurised seawater desalination system member
The method of part flux isostatic degree, in favor of solving the problems, such as that reverse osmosis seawater desalination system flux is unbalance and can not regulate and control.
To achieve the above object, the technical solution adopted by the present invention it is characterized in that：The present invention is light in step pressurised seawater
On the basis of changing system architecture, for the impeller outer diameter of step booster pump, by calculating in different operating conditions, different supercharging positions
The cutting output of place's step impeller of pump external diameter is put, with centrifugal pump motor frequency conversion auxiliary adjustment, to reach system element flux into line
Property the distribution and controllable purpose of Element Flux slope；This method includes following steps：
1) according to the total aquifer yield of system of setting and single branch element membrane area, with relational expression：Solve
System total flux；In formula：J is system total flux,QpFor the total aquifer yield of initialization system, [m3/d]；S props up to be single
Membrane area, m2；
2) according to arbitrary value between the step pressurised seawater desalination system flux slope k as -2.5 to 0 set, in this model
Each branch Element Flux j is solved by slope k and system total flux J in enclosing, calculation relational expression is：
With j (i)=j (1)+(i-1) × k, then pass through j (i) and single branch membrane area S and calculate each branch membrane component aquifer yield Qp(i)；In formula：
J (i) is i-th Element Flux, and i is position of components, and L is system flow length；
3) reverse-osmosis membrane element discrete equation is passed through：
Each film is calculated
Element intake pressure drops with mould；In formula：Qp[m3/ d] it is to produce water-carrying capacity, Cp[g/l] is to produce water salt content, Δ Pm[MPa] is film
Pressure drop, A [m3/ dMPa] it is coefficient of permeability, B [m3/ d] it is saturating salt coefficient, K (k1, k2, k3) it is pressure-drop coefficient, Te[DEG C] be to
Coolant-temperature gage, Cf[g/l] for feedwater salt content, Qf[m^3/d] is feedwater flow, Pf[MPa] is intake pressure, Qf0[m3/ d] be to
Concentrated water average discharge, πf[MPa] is feedwater osmotic pressure, and β is the concentration polarization degree on film surface；
4) according to above-mentioned each membrane component intake pressure Pf[MPa] and mould drop ∧ Pm[MPa], according to formula Pc(i)=Pf
(i)-ΔPm(i) with P (i)=Pf(i)-Pc(i-1) centrifugal pump supercharging value at each pressurization position is tried to achieve；In formula：Intake pressure Pf
[MPa] and mould drop Δ Pm[MPa], concentrated water pressure Pc, centrifugal pump supercharging value P, wherein i be membrane component position；Step pressurization from
Second membrane component starts to be pressurized；
5) flow and supercharging value, i.e. point (Q, H) known at each pressurization position；With characteristic curve of centrifugal pump relational expression：H
=A1+A2×Q+A3×Q2Solve the actual supercharging value P ' of each centrifugal pump pressurization position；
In each pressurization position cutting output calculating process, centrifugal pump increasing is calculated when the lift that step centrifugal pump is provided is less than
When pressure value requires, i.e. P ' ＜ P, then retain original big impeller in the pressurization position, increase small impeller one by one to increase the supercharging position
The centrifugal pump lift at place is put, supercharging value is calculated until providing lift and being more than, and obtains it to increase small impeller quantity, then calculates increasing
Add the supercharging value that impeller is undertaken greatly after small impeller, cutting output calculating then is carried out to big impeller；
When the lift that the original big impeller of step centrifugal pump is provided, which is more than, calculates centrifugal pump supercharging value, i.e. P ' ＞ P, then directly
Connect and cutting output calculating is carried out to big impeller；
Big impeller cutting output calculating process is, it is known that big impeller diameter DB, and institute is right after the big blade cutting of each pressurization position
The flow and lift answered, i.e. point A (QA, HA)；With formulaSolve cutting coefficient KA；At each pressurization position, use
Centrifugal pump stock removal rate relational expression：H=KA×Q2With characteristic curve of centrifugal pump relational expression：H=A1+A2×Q+A3×Q2Simultaneous solution
Obtain the point B (Q on characteristic curve of centrifugal pumpB, HB) it is the point A (Q for meeting the requirement of its stock removal rateA, HA) corresponding points, passing through
FormulaAnd formulaThe cutting output of major impeller is calculated；
Various middle Q, H are respectively flow and lift, A1、A2、A3Respectively the constant term coefficient of characteristic curve of centrifugal pump, one
Secondary term coefficient, secondary term coefficient；
The characteristic curve of centrifugal pump of each pressurization position is H=A before blade cutting1+A2×Q+A3×Q2；And different
Under design conditions, selected step centrifugation pump type is different, but its characteristic curve relational expression is：H=A1+A2×Q+A3×
Q2, only it is that each term coefficient is different；
If 6) impeller cutting output exceedes cutting limitation in step pressurised seawater desalination system, use to enter centrifugal pump motor
Row variable frequency adjustment, according to Centrifugal Pump, lift and rotation speed relation formulaRaised with former Centrifugal Pump
Journey characteristic curve relational expression, solve characteristic curve H '=A after step pump frequency conversion4+A5×Q’+A6×Q’2, then again from step 5
Start to calculate each pressurization position cutting output；Wherein Q, H phase should be the flow and lift when motor rotations are n；Q ', H ' mutually should be electricity
Machine revolution is n ' flow and lift；A4、A5、 A6Respectively the constant term coefficient of characteristic curve of centrifugal pump, Monomial coefficient, two
Secondary term coefficient；
Cutting for each impeller of the step boosting centrifugal pump under the conditions of the flux system slope of design is calculated through said process
The amount of cutting so that the Flux Distribution of system is along the linear distribution of flow.Actual flux system slope and the flux system designed are oblique
Rate is identical, makes step pressurised seawater desalination system Element Flux balance degree controllable.
The effect of the present invention is can to design step pressurised seawater desalination system flux slope to be any negative in -2.5 to 0
Value.Because seawater desalination system flux slope is more balanced closer to 0 flux, if do not use the present invention seawater desalination system flux into
Nonlinear Distribution, and can not regulator control system flux slope.The present invention can not only targetedly design system flux slope, and
And flux system slope scope of design can meet the needs of designer between -2.5 to 0.
Under same design operating mode, regular seawater desalination system Flux Distribution is nonlinear Distribution, is reached at flux slope minimum
To -4.6, Flux Distribution is unbalanced and it can not arbitrarily regulate and control.Step pressurised seawater desalination system Flux Distribution is similarly non-thread
Property distribution, reach -1 at flux slope minimum, though more conventional seawater desalination system Flux Distribution is more balanced, Flux Distribution is still
Can not arbitrarily it regulate and control.Using the present invention not only can in the range of -2.5 to 0 design system flux slope, and Element Flux point
Cloth is linear distribution along flow, i.e., flux slope is consistent with flux system slope between each membrane component, and flux system slope can be set
Fixed closer 0, flux is more balanced.Because the pollution distribution of system is relevant with Flux Distribution, therefore, tune can be designed using the present invention
Step seawater desalination system flux is controlled, base has been established for relation of the flux system equilibrium that works on the conversion of salt water into fresh water between balanced with pollution
Plinth.
Brief description of the drawings
Fig. 1 is the step pressurised seawater desalination system structure chart of the present invention.
In figure：
1st, putamina 2, pipeline 3, watering port 4, high-pressure pump
5th, step centrifugal pump 6, concentrated water port 7, dividing plate 8, impeller
9th, concentrated water 10, motor
Embodiment
Below in conjunction with the method for regulation and control step pressurised seawater desalination system Element Flux balance degree of the accompanying drawing to the present invention
It is illustrated.
Because of the flux designed in the method for the regulation and control step pressurised seawater desalination system Element Flux balance degree of the present invention
Between slope range is -2.5 to 0, different flux slopes is selected in this section, its computational methods is consistent, adopting said method
The purpose of regulation and control step pressurised seawater desalination system Element Flux balance degree can be reached.
Therefore, in instances, multiple flux system slopes are not selected to calculate, only initialization system flux slope -0.60 is generation
Table is calculated, and specific calculating process is as follows：
As shown in figure 1, on the basis of existing step pressurised seawater desalination system structure, for step booster pump 5
The external diameter of impeller 8, by calculate at different operating conditions, different pressurization positions the external diameter of step impeller of pump 8 cutting output, with from
The frequency conversion auxiliary adjustment of heart pump motor 10, flux system slope is met design requirement, solve step pressurised seawater desalination system and lead to
Measure the problem of unbalance.And the flux system slope that setting is different, that is, there is different blade cutting schemes corresponding so that system
Element Flux balance degree it is controllable.Each external diameter cutting output of impeller 8 and rational motor rotations are calculated, need to be real by following algorithm
It is existing.
Step pressurised seawater desalination system is 1 section, and known each design parameter：Flux system slope k and system total yield
Water-carrying capacity Qp, flow of inlet water Qf, temperature TeWith water inlet salinity Cf, single branch membrane component area S, system flow length L, centrifugal pump
Flow lift characteristic curve：H=A1+A2×Q+A3×Q2。
Known system total flux J and single branch membrane area S, system total yield water-carrying capacity QPRelational expression, the system that can calculate always are led to
Amount.Relational expression is as follows：
Solved according to total flux J, system flow length L and design flux slope k along each single branch membrane element flux j of flow
(i)。
First membrane element flux：
Since second membrane component, its Element Flux solves with relationship below：
J (i)=j (1)+(i-1) × k (3)
The production water salinity C of each membrane component is calculated with reverse-osmosis membrane element discrete equationpAnd its required influent pressure
Power Pf, mould drop Δ Pm。
Reverse-osmosis membrane element discrete equation is：
Wherein：Qp[m3/ d] it is to produce water-carrying capacity, Cp[g/l] is to produce water salt content, Δ Pm[MPa] is membrane component pressure drop, A [m3/
DMPa] it is coefficient of permeability, B [m3/ d] it is saturating salt coefficient, K (k1, k2, k3) it is pressure-drop coefficient, Te[DEG C] is feed temperature, Cf
[g/l] for feedwater salt content, Qf[m^3/d] is feedwater flow, Pf[MPa] is feed pressure, Qfc[m3/ d] it is to give concentrated water mean flow
Amount, πf[MPa] is feedwater osmotic pressure, and β is the concentration polarization degree on film surface.
Pass through the intake pressure P of i-th membrane componentf(i) Δ P drops with mouldm(i) its concentrated water pressure P can, be calculatedc(i)。
Expression formula is：
Pc(i)=Pf(i)-ΔPm(i) (5)
Because first membrane component is by giving high-pressure water pump voltage supply, then step supercharging is since second membrane component.Then (i) is propped up
The step pump supercharging value P (i) of membrane component is：
P (i)=Pf(i)-Pc(i-1) (6)
Flow and supercharging value, i.e. point (Q, H) at known each pressurization position；With characteristic curve of centrifugal pump relational expression：H=A1
+A2×Q+A3×Q2Solve the actual supercharging value P ' of each centrifugal pump pressurization position.
When the lift that step centrifugal pump is provided, which is less than calculating centrifugal pump supercharging value, to be required, i.e. P ' ＜ P, then in the increasing
Press position to retain original big impeller, increase small impeller one by one to increase the centrifugal pump lift at the pressurization position, raised until providing
Journey, which is more than, calculates supercharging value, and obtains its increase small impeller quantity, then calculates the increasing that impeller is undertaken greatly after increase small impeller
Pressure value, cutting output calculating then is carried out to big impeller；
When the lift that the original big impeller of step centrifugal pump is provided, which is more than, calculates centrifugal pump supercharging value, i.e. P ' ＞ P, then directly
Connect and cutting output calculating is carried out to big impeller；
So-called " increase small impeller " is half grade of impeller of series connection on original impeller, and its characteristic lift amplitude is original
The half of beginning impeller.Different pump producers, the centrifugal pump of different model, the small impeller provided are different.
But the cutting output of impeller need to be limited by blade cutting.Limited if cutting output exceedes cutting, can use and become
Frequency mode, then recalculates impeller cutting output at each pressurization position, flux slope is reached design requirement.Cutting limitation
Size is relevant with the specific revolution of centrifugal pump, and its cutting limitation is different under the conditions of different specific revolutions.The limitation and specific revolution relation of cutting
As shown in table 1.Centrifugal pump specific revolution calculation formula is：
In formula：Metered flow Q, unit m3/s；Rated head H, unit m；Rotating speed n, unit r/min；Specific revolution ns.
Maximum allowable impeller cutting output under 1 different specific revolutions of table
| Specific revolution | <60 | <120 | <200 | <300 | <350 | More than 350 |
| Maximum allowable cutting output (%) | 20 | 15 | 11 | 9 | 7 | 0 |
In step pressurised seawater desalinates blade cutting system design, due to only cutting big impeller, and known each supercharging position
Put flow corresponding to big impeller and supercharging value (lift), i.e. point A (QA, HA).Big impeller cutting output can be then solved, its calculating process
It is as follows：
First, stock removal rate equations cutting coefficient is utilized：
Stock removal rate relational expression is expressed as：
In formula：Q, H, N phase should be flow, lift and the shaft power when impeller outer diameter is D；Q ', H ', N ' mutually should be cutting
Flow, lift and shaft power when impeller outer diameter afterwards is D '.
It can be obtained with formula (8), (9) simultaneous：
In formula：K is cutting coefficient；
Then by point A (QA, HA) substitution formula (11)：
It can obtain:
H=KA×Q2 (13)
Each pressurization position Centrifugal Pump heat-capacity curve is before known impeller 8 is cut：
H=A1+A2×Q+A3×Q2 (14)
Under different design conditions, selected step centrifugation pump type is different, but its characteristic curve relational expression is H
=A1+A2×Q+A3×Q2, only it is that each term coefficient is different；
By formula (13) and formula (14) simultaneous, the point B (Q on characteristic curve can be obtainedB, HB) it is to meet the requirement of its stock removal rate
Point A (QA, HA) corresponding points.Known original impeller diameter DB, impeller diameter D after cutting can be obtainedAValue.Further calculate
Cutting output：
The size of different each cutting outputs of impeller 8 of pressurization position centrifugal pump can be solved with the method.Because centrifugal pump is to leaf
Certain limit be present in the cutting output of wheel.Therefore, when only with blade cutting mode design requirement can not be met, then with change
Frequency is with cutting combination mode.
Centrifugation pump frequency conversion after its flow lift characteristic curve will change, its Centrifugal Pump, lift and revolution its abide by
It is as follows to follow relational expression：
In formula：Q, H phases should be the flow and lift when revolution is n；Q ', H ' mutually should be the flow and lift that revolution is n '.
Centrifugal Pump heat-capacity curve after frequency conversion, its table can be calculated by formula (14), formula (16) and formula (17)
It is up to formula：
H '=A4+A5×Q’+A6×Q’2 (18)
After obtaining the flow lift curve representation formula (18) after frequency conversion, cutting output is being recalculated to obtain since formula (6).
Instantiation calculating process is as follows：
First, system basic design parameters
Known step pressurised seawater desalination system design parameter is respectively：Seawater salt content 32g/L, 15 DEG C of ocean temperature,
Membrane component kind is the SWC5, single branch membrane component area 37.2m of Hydranautics production2, membrane component quantity 6, the system rate of recovery
40%, production water-carrying capacity 75m3/ d, flow of inlet water 187.5m3/ d, average flux 14LMH, design system flux slope are -0.60, are adopted
With the step Impeller Cutting For Centrifugal Pump method of operation.Step boosting centrifugal pump revolution is 2900r/min.System flow length is 6 meters.
Step Centrifugal Pump heat-capacity curve expression formula is：H (m)=38.414-0.02143 × Q-0.08571 × Q2；In formula：
Flow Q, unit m3/h；Lift H, unit m；Centrifugal pump metered flow 6.4m3/ h, rated head 34.5m.
2nd, each membrane element flux, aquifer yield, intake pressure and mould is calculated to drop
The total aquifer yield Q of Known designs systemPWith membrane area S.
1st, computing system total flux J：
2nd, known flux system slope k and system flow length L, calculate each membrane element flux：
1) calculating first membrane element flux j (1) is：
2) each membrane element flux is calculated：
Second membrane element flux j (2)：
J (2)=15.5009+ (2-1) × (- 0.6)=14.9009 [L/ (m ∧ 2h)] (21)
3rd membrane element flux j (3)：
J (3)=15.5009+ (3-1) × (- 0.6)=14.3009 [L/ (m^2h)] (22)
4th membrane element flux j (4)：
J (4)=15.5009+ (4-1) × (- 0.6)=13.7009 [L/ (m^2h)] (23)
5th membrane element flux j (5)：
J (5)=15.5009+ (5-1) × (- 0.6)=13.1009 [L/ (m ∧ 2h]) (24)
6th membrane element flux j (6)：
J (6)=15.5009+ (6-1) × (- 0.6)=12.5009 [L/ (m ∧ 2h)] (25)
3rd, each branch membrane component aquifer yield Q is calculatedp(i)：
4th, with reverse-osmosis membrane element discrete models：
Calculate to obtain each membrane component intake pressure PfWith mould drop Δ PmFor：
Pf(1)=4.1026MPa.
Pf(2)=4.3156MPa. (32)
Pf(3)=4.5624MPa. (33)
Pf(4)=4.8494MPa. (34)
Pf(5)=5.1846MPa. (35)
Pf(6)=5.5782MPa. (36)
ΔPm(1)=0.0249MPa (37)
ΔPm(2)=0.0224MPa (38)
ΔPm(3)=0.0200MPa (39)
ΔPm(4)=0.0177MPa (40)
ΔPm(5)=0.0157MPa (41)
ΔPm(6)=0.0139MPa (42)
3rd, supercharging value at each pressurization position is calculated
Because first membrane component is by the voltage supply of high-pressure pump 4, then step booster pump 5 is pressurized since second membrane component.Root
According to formula Pc(i)-Pf(i)-ΔPm(i) with formula P (i)=Pf(i)-Pc(i-1) position supercharging value is calculated.Specifically it is calculated as follows：
Step centrifugal pump supercharging value P (2) before second membrane component is：
P (2)=Pf(2)-Pf(1)+ΔPm(1)=0.2379MPa (43)
Step centrifugal pump supercharging value P (3) before 3rd membrane component is：
P (3)=Pf(3)-Pf(2)+ΔPm(2)=0.2692MPa (44)
Step centrifugal pump supercharging value P (4) before 4th membrane component is：
P (4)=Pf(4)-Pf(3)+ΔPm(3)=0.3070MPa (45)
Step centrifugal pump supercharging value P (5) before 5th membrane component is：
P (5)=Pf(5)-Pf(4)+ΔPm(4)=0.3529MPa (46)
Step centrifugal pump supercharging value P (6) before 6th membrane component is：
P (6)=Pf(6)-Pf(5)+ΔPm(5)=0.4093MPa (47)
4th, each pressurization position impeller cutting output is calculated
1st, in each pressurization position flow lift characteristic curve, its expression formula is known selected step centrifugal pump 5：
H (m)=38.414-0.02143 × Q-0.08571 × Q2 (48)
Flow is respectively with supercharging value at known each pressurization position：
(Q, H)1=(173.6608,0.2379)
(Q, H)2=(160.3573,0.2692)
(Q, H)3=(147.5894,0.3070)
(Q, H)4=(135.3573,0.3529)
(Q, H)5=(123.6608,0.4093)
Wherein：(Q, H)1Represent to calculate first time pressurization position, i.e. the flow at pressurization position before second membrane component
With supercharging value；Flow Q, unit m3/d；Lift H, units MPa.
Because each pressing position pump case inner impeller is made up of original big impeller 8.Whether need to first calculate at each pressurization position needs
Increase small impeller, then calculate big impeller cutting output.Small impeller mentioned in this example is half grade of impeller.
Each pressurization position small impeller quantity is calculated, needs to calculate the centrifugal pump supercharging value P ' of each pressurization position and meter first
Calculate supercharging value P to be compared, judge whether to need to increase small impeller.And calculate increase small impeller quantity.As a result such as the institute of table 2
Show.
Small impeller quantity needed for 2 each pressurization position of table
The present invention uses blade cutting, is that only big impeller 8 original to centrifugal pump is cut, not to increasing small impeller
Cut.
Calculate each pressurization position goes out after the big impeller 8 of step centrifugal pump cuts, corresponding flow with supercharging value size such as
Shown in table 3.
Flow and supercharging value after the big blade cutting of each pressurization position of table 3
| Pressurization position | 1 | 2 | 3 | 4 | 5 |
| Pressure (MPa) | 0.2379 | 0.2692 | 0.3070 | 0.3529 | 0.2291 |
| Flow (m3/d) | 173.6608 | 160.3573 | 147.5894 | 135.3573 | 123.6608 |
I.e.：
A1(Q, H)=(7.2359,23.79)
A2(Q, H)=(6.6816,26.92)
A3(Q, H)=(6.1496,30.70)
A4(Q, H)=(5.6399,35.29)
A5(Q, H)=(5.1525,22.91)
Wherein：A1(Q, H) represents at first time pressurization position corresponding flow and lift after original big blade cutting；Flow
Q, unit m3/h；Lift H, unit m.
2nd, each position cutting coefficient K is obtained with formula (11)：
1) the parabolic equation of first pressurization position is：
H1=K1×Q1 2 (50)
2) the parabolic equation of second pressurization position is：
H2=K2×Q2 2 (52)
3) the parabolic equation of the 3rd pressurization position is：
H3=K3×Q3 2 (54)
4) the parabolic equation of the 4th pressurization position is：
H4=K4×Q4 2 (56)
5) the parabolic equation of the 5th pressurization position is：
H5=K5×Q5 2 (58)
3rd, cutting output is solved
The Centrifugal Pump characteristic curve of initial big impeller and parabolic equation simultaneous at each pressurization position are solved in spy
Point B (Q on linearity curveB, HB) it is the point A (Q for meeting the requirement of its stock removal rateA, HA) corresponding points.
Due to only cutting the original impeller 8 of centrifugal pump, small impeller is not cut.And the initial step of each pressurization position from
Heart pump flow lift characteristic curve expression formula is identical to be：
H (m)=38.414-0.02143 × Q-0.08571 × Q2 (59)
In formula：Flow Q, unit m3/h；Lift H, unit m.
Formula (50), (52), (54), (56), (58) are gone out it in characteristic curve of centrifugal pump with formula (59) simultaneous solution respectively
On point B (QB, HB), obtain：
B1(Q, II)-(8.4138,32.17)
B2(Q, H)=(7.4530,33.49)
B3(Q, H)=(6.5306,34.62)
B4(Q, H)=(5.6602,35.55)
B5(Q, H)=(6.3516,34.82)
Wherein：B1(Q, II) is point A on former characteristic curve of centrifugal pump1The corresponding points of (Q, II)；Flow Q, unit m3/h；
Lift H, unit m.
Cutting output is calculated using formula (8), (15), is tried to achieve：
At first time supercharging：
At second of supercharging：
At third time supercharging：
At 4th supercharging：
At 5th supercharging：
It is known to select centrifugal pump metered flow 6.4m3/ h, rated head 34.5m.Calculate centrifugal pump specific revolution ns：
Tabling look-up 1 can obtain, and it is 20% that specific revolution, which is less than 60 its maximum cut allowed,.
Therefore, gained position cutting output is calculated in cutting bound requirements.Because only with cutting in this example
Flux design requirement can be met, then without by the way of frequency conversion.Then step pressurizing cenrrifugal pump motor rotations are still 2900r/
Min, now calculate centrifugation pump frequency conversion relational expression and obtain：
H '=38.414-0.02143 × Q ' -0.08571 × Q '2 (68)
5th, verify
After verifying step Impeller Cutting For Centrifugal Pump, whether Element Flux distribution meets the flux system slope of design.Transporting
Under row operating mode permanence condition, according to each impeller cutting output known to calculating, centrifugal pump at each pressurization position can be calculated after blade cutting
Flow lift characteristic curve relational expression：
First pressurization position Centrifugal Pump heat-capacity curve relational expression：
H (m)=28.4113-0.0184 × Q-0.0857 × Q2 (69)
Second pressurization position Centrifugal Pump heat-capacity curve relational expression：
H (m)=30.8732-0.0192 × Q-0.0857 × Q2 (70)
3rd pressurization position Centrifugal Pump heat-capacity curve relational expression：
H (m)=34.0621-0.0202 × Q-0.0857 × Q2 (71)
4th pressurization position Centrifugal Pump heat-capacity curve relational expression：
H (m)=38.1384-0.0214 × Q-0.0857 × Q2 (72)
5th pressurization position Centrifugal Pump heat-capacity curve relational expression：
H (m)=44.4866-0.0281 × Q-0.1286 × Q2 (73)
In formula：Flow Q, unit m3/h；Lift H, unit m.
Known operating condition, each Element Flux in system is calculated, as shown in table 4：
Element Flux is distributed after the step pressurised seawater desalination system blade cutting of table 4
Flux system slope is：
Error caused by due to decimal reduction of a fraction in calculating process be present, the error is in rational scope, it is believed that gained system
Flux slope of uniting is consistent with design system flux slope.Therefore, the present invention makes flux system slope calculate standard between -2.5 to 0
Really.Demonstrate the practicality and accuracy of the present invention.
And under the design operating conditions of this example, if not using its regular seawater desalination system Flux Distribution of party's rule
- 4.6 are can reach for nonlinear Distribution and flux slope, step pressurised seawater desalination system Flux Distribution is also non-linear, flux
Slope can reach -1, and can not random regulating system Element Flux slope, i.e., can not regulating system balance degree.
Flux system slope is set to a certain specific negative value between -2.5 to 0 by the present invention in system design, using cutting
Step pressurizing cenrrifugal pump impeller and conversion system are cut, its each Element Flux slope is met that design system flux slope will
Ask, and can any initialization system flux slope within the specific limits, reach regulation and control step pressurised seawater desalination system flux
The purpose of balance degree.
Claims (1)
1. a kind of method of regulation and control step pressurised seawater desalination system Element Flux balance degree, it is characterized in that：The present invention be
On the basis of step pressurised seawater desalination system structure, for impeller (8) external diameter of step booster pump, by calculating in different fortune
The cutting output of step impeller of pump external diameter at row operating mode, different pressurization positions, with centrifugal pump motor (10) frequency conversion auxiliary adjustment, with
Reach the linear distribution of system element flux and the controllable purpose of Element Flux slope；This method includes following steps：
1) according to the total aquifer yield of system of setting and single branch element membrane area, with relational expression：Solving system
Total flux；In formula：J is system total flux, [L/ (m2·h)]；QpFor the total aquifer yield of initialization system, [m3/d]；S is single branch film surface
Product, m2；
2) according to arbitrary value between the step pressurised seawater desalination system flux slope k as -2.5 to 0 set, lead within this range
Cross slope k and solve each branch Element Flux j with system total flux J, calculation relational expression is：
With j (i)=j (1)+(i-1) × k, then by j (i) and single branch membrane area S each is calculated
Membrane component aquifer yield Qp(i)；In formula：J (i) is i-th Element Flux, and i is position of components, and L is system flow length；
3) reverse-osmosis membrane element discrete equation is passed through：
Each membrane component is calculated
Intake pressure drops with mould；In formula：Qp[m3/ d] it is to produce water-carrying capacity, cp[g/l] is to produce water salt content, Δ Pm[MPa] is mould
Drop, A [m3/ dMPa] it is coefficient of permeability, B [m3/ d] it is saturating salt coefficient, K (k1, k2, k3) it is pressure-drop coefficient, Te[DEG C] is feedwater
Temperature, Cf[g/l] for feedwater salt content, Qf[m^3/d] is feedwater flow, Pf[MPa] is intake pressure, Qf0[m3/ d] it is to dense
Water average discharge, πf[MPa] is feedwater osmotic pressure, and β is the concentration polarization degree on film surface；
4) according to above-mentioned each membrane component intake pressure Pf[MPa] and mould drop ∧ Pm[MPa], according to formula Pc(i)=Pf(i)-Δ
Pm(i) with P (i)=Pf(i)-Pc(i-1) centrifugal pump (5) supercharging value at each pressurization position is tried to achieve；In formula：Intake pressure Pf
[MPa] and mould drop Δ Pm[MPa], concentrated water pressure Pc, centrifugal pump supercharging value P, wherein i be membrane component position；Step pressurization from
Second membrane component starts to be pressurized；
5) flow and supercharging value, i.e. point (Q, H) known at each pressurization position；With characteristic curve of centrifugal pump relational expression：H=A1+
A2×Q+A3×Q2Solve the actual supercharging value P ' of each centrifugal pump pressurization position；
In each pressurization position cutting output calculating process, centrifugal pump supercharging value is calculated when the lift that step centrifugal pump is provided is less than
It is required that when, i.e. P ' ＜ P, then retain original big impeller (8) in the pressurization position, increase small impeller one by one to increase the pressurization position
The centrifugal pump lift at place, supercharging value is calculated until providing lift and being more than, and obtain it to increase small impeller quantity, then calculate increase
The supercharging value that big impeller is undertaken after small impeller, cutting output calculating then is carried out to big impeller (8)；
When the lift that the original big impeller (8) of step centrifugal pump is provided, which is more than, calculates centrifugal pump supercharging value, i.e. P ' ＞ P, then directly
Connect and cutting output calculating is carried out to big impeller (8)；
Big impeller cutting output calculating process is, it is known that big impeller diameter DB, and stream corresponding after the big blade cutting of each pressurization position
Amount and lift, i.e. point A (QA, HA)；With formulaSolve cutting coefficient KA；At each pressurization position, with centrifugal pump
Stock removal rate relational expression：H=KA×Q2With characteristic curve of centrifugal pump relational expression：H=A1+A2×Q+A3×Q2Simultaneous solution obtain from
Point B (Q on heart pump characteristic curveB, HB) it is the point A (Q for meeting the requirement of its stock removal rateA, HA) corresponding points, passing through formulaAnd formulaThe cutting output of major impeller (8) is calculated；
Various middle Q, H are respectively flow and lift, A1、A2、A3Respectively the constant term coefficient of characteristic curve of centrifugal pump, first order
Coefficient, secondary term coefficient；
The characteristic curve of centrifugal pump of each pressurization position is H=A before blade cutting1+A2×Q+A3×Q2；And in different design works
Under condition, selected step centrifugation pump type is different, but its characteristic curve relational expression is：H=A1+A2×Q+A3×Q2, only it is
Each term coefficient is different；
If 6) impeller cutting output exceedes cutting limitation in step pressurised seawater desalination system, use to enter centrifugal pump motor (10)
Row variable frequency adjustment, according to Centrifugal Pump, lift and rotation speed relation formulaRaised with former Centrifugal Pump
Journey characteristic curve relational expression, solve characteristic curve II '=A after step pump frequency conversion4+A5×Q’+A6×Q’2, then again from step
5 start to calculate each pressurization position cutting output；Wherein Q, H phase should be the flow and lift when motor rotations are n；Q ', H ' mutually should be
The flow and lift that motor rotations are n '；A4、A5、A6Respectively the constant term coefficient of characteristic curve of centrifugal pump, Monomial coefficient,
Secondary term coefficient；
Through said process, the cutting of each impeller (8) of the step boosting centrifugal pump under the conditions of design system flux slope is calculated
Amount, and make the Flux Distribution of system along the linear distribution of flow, actual flux system slope and the flux system slope of design
It is identical, make step pressurised seawater desalination system Element Flux balance degree controllable.
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Application publication date: 20171215 Assignee: TIANJIN KUNPENG CHEMICAL TECHNOLOGY Co.,Ltd. Assignor: Tianjin Chengjian University Contract record no.: X2024980001813 Denomination of invention: Method for regulating the flux balance of components in a cascade pressurized seawater desalination system Granted publication date: 20200728 License type: Common License Record date: 20240201 |