CN111125804B - Water injection adjusting method for high-pressure air cooling system of hydrogenation device based on numerical simulation - Google Patents
Water injection adjusting method for high-pressure air cooling system of hydrogenation device based on numerical simulation Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G75/00—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F27/00—Control arrangements or safety devices specially adapted for heat-exchange or heat-transfer apparatus
- F28F27/02—Control arrangements or safety devices specially adapted for heat-exchange or heat-transfer apparatus for controlling the distribution of heat-exchange media between different channels
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Abstract
The invention discloses a water injection regulating method of a high-pressure air cooling system of a hydrogenation device based on numerical simulation, which is used for carrying out numerical simulation analysis on flow characteristics of multiphase flow media in an inlet pipeline of an air cooler to obtain media flow velocity at each outlet of the inlet pipeline of the air cooler; according to the medium flow rate at each outlet of the inlet pipeline of the air cooler, counting the inlet flow rate of each air cooler; according to the inlet flow of each air cooler, the total bias flow degree of the high-pressure air cooling system of the hydrogenation device is inspected to judge whether the water injection rate needs to be adjusted or not; if the water injection quantity needs to be adjusted, the drift degree of each air cooler is respectively inspected according to the inlet flow of each air cooler so as to respectively judge whether each air cooler needs to adjust the water injection quantity, and the water injection quantity of the air cooler which needs to be adjusted after judgment is adjusted. The invention can lead the flow field distribution of the medium before entering the air cooler from the inlet pipeline of the air cooler to be balanced and reasonable.
Description
Technical Field
The invention relates to the technical field of water injection adjustment of a high-pressure air cooling system of a hydrogenation device, in particular to a water injection adjustment method of the high-pressure air cooling system of the hydrogenation device based on numerical simulation.
Background
With the increasing scale of secondary processing devices such as hydrogenation modification in oil refining devices, corrosion problems caused by the inferior quality of raw oil are also increasingly prominent. Because of extreme service conditions, the high-pressure air cooling system of the hydrogenation device is easy to deposit ammonium salt to cause fluidity corrosion. At present, most petrochemical enterprises in China adopt a water injection mode to relieve the corrosion risk of ammonium salt, and a certain effect is achieved. However, the conventional water injection method has the following drawbacks: (1) Because the sensitivity of the PID monitoring system in the device is limited, the flow, pressure and temperature can be detected only on main equipment and pipelines, and the detection can not be accurately carried out on each equipment and each branch pipe, so that the total water injection amount is difficult to control, and the water injection point selection lacks pertinence; (2) The implementation of water injection has hysteresis, can not be adjusted in time when the flow obviously fluctuates due to the significant bias flow of the medium or the large deposition of ammonium salt, and can not effectively cope with the abnormal operation conditions of sudden equipment and pipelines.
According to the existing research results, the ammonium salt fluidity corrosion of the high-pressure air cooling system of the hydrogenation device belongs to the systematic problem. On one hand, the flow characteristics of an inlet pipeline of the air cooler at the upstream of the air cooling device have a great influence on a medium flow field in the related device, and as the pipeline arrangement structure is usually a main pipe section and a plurality of branch pipe section outlets, and the medium flow characteristic parameters at the pipeline inlet are higher, the medium flow velocity in the upstream pipeline can have fluctuation before entering the air cooler, so that the medium flow velocity is obviously different, namely, the bias flow, before entering the air cooler, and the medium flow velocity in the air cooler can also have great fluctuation; the ammonium salt corrosion risk is higher for the equipment with lower flow rate, and scouring corrosion is easy to occur for the equipment with higher flow rate. On the other hand, flow corrosion precursors such as ammonium salt deposits present inside the equipment can also have a significant impact on the flow characteristics in the pipeline. Therefore, it is a direction of researchers to propose newer and more efficient water injection processes to equalize and reasonably force the flow field distribution of the medium before it enters the apparatus from the pipeline.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides the water injection adjusting method for the high-pressure air cooling system of the hydrogenation device based on numerical simulation, so that the flow field distribution of a medium before entering each air cooler from an inlet pipeline of the air cooler tends to be balanced and reasonable, the service adaptability of the high-pressure air cooling system of the hydrogenation device under extreme working conditions is improved, and the long-period safe operation of the high-pressure air cooling system of the hydrogenation device is ensured.
In order to achieve the above purpose, the present invention adopts the following technical scheme, including:
a water injection adjusting method of a high-pressure air cooling system of a hydrogenation device based on numerical simulation comprises the following steps:
s1, performing numerical simulation analysis on flow characteristics of multiphase flow media in an inlet pipeline of an air cooler to obtain media flow velocity at each outlet of the inlet pipeline of the air cooler;
s2, counting the inlet flow q of each air cooler according to the numerical simulation analysis result, namely the flow velocity of the medium at each outlet of the inlet pipeline of the air cooler l L=1, 2,3, …, N; wherein q represents the inlet flow rate, the subscript l represents the number of the air cooler, and q l The inlet flow of the first air cooler is represented, and N represents the total number of air coolers in the high-pressure air cooling system of the hydrogenation device;
s3, according to the inlet flow q of each air cooler l The total bias flow degree of N air coolers in a high-pressure air cooling system of the hydrogenation device is inspected to judge whether the water injection rate needs to be adjusted or not;
s4, if the water injection quantity needs to be adjusted after the judgment in the step S3, the water injection quantity is adjusted according to the inlet flow q of each air cooler l And respectively examining the bias flow degree of each air cooler so as to respectively judge whether each air cooler needs to adjust the water injection quantity, and adjusting the water injection quantity of the air cooler which needs to adjust the water injection quantity after judgment.
In step S1, the numerical simulation analysis includes the steps of:
s11, establishing a geometric model of an inlet pipeline of the air cooler, and performing grid division;
s12, selecting a three-phase flow model according to the medium composition in an inlet pipeline of the air cooler, wherein the main phase is a gas phase, and the secondary phase is liquid water and liquid oil;
s13, respectively determining physical parameters of a three-phase medium according to process simulation or DSC data of an enterprise, wherein the physical parameters of the three-phase medium are density, specific heat and viscosity;
determining inlet boundary conditions and outlet boundary conditions of an inlet pipeline of the air cooler; the inlet boundary condition of the inlet pipeline of the air cooler is determined according to process simulation or enterprise DCS data, and comprises flow, components, water injection flow, pressure and temperature of each phase of medium; the outlet boundary condition of the inlet pipeline of the air cooler is set as a default parameter;
s14, establishing a solution model of medium flow characteristics in an inlet pipeline of the air cooler;
s15, analyzing the medium flow characteristics at each outlet of the air cooler inlet pipeline according to the boundary conditions of the air cooler inlet pipeline and the physical property parameters of each phase medium and based on a solution model of the medium flow characteristics to obtain the medium flow velocity at each outlet of the air cooler inlet pipeline.
In step S14, carrying out numerical simulation analysis on turbulence by using a k-epsilon turbulence model, and establishing a solution model of medium flow characteristics in an inlet pipeline of the air cooler; when the turbulence level is reached, the solution model is as follows:
the equation for turbulent kinetic energy k is:
the equation for the turbulent dissipation ratio ε is:
in the above equation, ρ represents the medium density; u represents the velocity of the flow field;
subscripts i, j respectively represent two different directions; x is x i Representing coordinates in the i-direction, x j Representing coordinates in the j direction; u (u) i Indicating the velocity of the flow field in the i-direction, u j Representing the velocity of the flow field in the j direction;
k represents turbulent kinetic energy; epsilon represents the turbulent dissipation ratio;
σ k a turbulent planter number representing an equation of turbulent kinetic energy k; sigma (sigma) ε The turbulent planter number of the equation representing the turbulent dissipation ratio epsilon;
the subscript t represents tangential; mu (mu) t Representing the viscosity generated after the introduction of the pulsation speed, i.e. the turbulent viscosity;
G k representing turbulent kinetic energy generated by laminar velocity gradients; g b Represents turbulent kinetic energy generated by buoyancy; y is Y M Representing fluctuations in the compressible turbulence resulting from transitional diffusion;
C 1ε 、C 2ε 、C 3ε constant coefficients of equations each representing the turbulent dissipation ratio ε;
S k an extrapolated term of the equation representing the turbulent kinetic energy k; s is S ε The dissipation term of the equation representing the turbulent dissipation ratio epsilon.
Determining a medium Reynolds number Re, re=U.L/mu according to the inner diameter of a section at the inlet of an inlet pipeline of the air cooler and the medium flow; judging whether the turbulence level is reached or not according to the Reynolds number Re of the medium, namely whether the turbulence exists or not;
wherein μ represents the medium kinematic viscosity, i.e., the viscosity coefficient; l is the inner diameter of the section of the pipeline;
u is the average inlet flow velocity at the inlet of the inlet pipeline of the air cooler, and the average inlet flow velocity at the inlet can be obtained by dividing the medium flow at the inlet by the cross-sectional area and the medium density at the inlet according to the flow calculation formula in the hydrodynamics; the medium flow at the inlet of the air cooler inlet pipeline is monitored by a meter arranged at the inlet.
In step S2, the inlet flow q of each air cooler l The calculation mode of (2) is as follows:
the medium flow velocity at each outlet of the inlet pipeline of the air cooler is u k K=1, 2,3, …, M; where u represents the media flow rate, subscript k represents the number of the outlet, u k Represents the flow rate of the medium at the kth outlet, M represents the total number of outlets of the air cooler inlet line, m=2n; of the M outlets of the inlet pipeline of the air cooler, every two adjacent outlets are connected with one air cooler, namely, the 1 st outlet and the 2 nd outlet are connectedThe 1 st air cooler, the 3 rd outlet and the 4 th outlet are connected with the 2 nd air cooler, … …, and the M-1 st outlet and the M th outlet are connected with the N th air cooler;
according to the flow calculation formula in the fluid mechanics, the medium flow velocity u at each outlet is respectively calculated k Obtaining integral on corresponding outlet section, obtaining integral of each outlet asWherein (1)>Representing the flow velocity u of the medium at the kth outlet k Integration on the corresponding exit section, which integration +.>I.e. the flow at the kth outlet, S the cross-sectional area of the outlet, +.>For the vector representation of the cross-sectional area of the kth outlet, ρ represents the medium density, +.>A vector representation of the flow rate of the medium at the kth outlet;
inlet flow q of the first air cooler l The method comprises the following steps: the sum of the integrals of the medium flow rates at the two outlets connected with the first air cooler on the corresponding outlet cross sections, namely the sum of the flow rates at the two outlets connected with the first air cooler.
In step S3, the way of examining the total bias flow degree of N total air coolers in the high-pressure air cooling system of the hydrogenation unit is as follows:
if |Q 1 ～ N/2 -Q N/2～N |≤α·Q 1～N/2 The water injection amount does not need to be adjusted;
wherein Q is 1～N/2 ＝q 1 +q 2 +q 3 +…+q N/2 ，Q 1～N/2 Indicating hydrogenationThe front half of air coolers in the high-pressure air cooling system is the sum of inlet flow rates of the front N/2 air coolers;
Q N/2～N representing the sum of inlet flow of the latter half air cooler, namely the latter N/2 air coolers, in the high-pressure air cooling system of the hydrogenation device;
if |Q 1～N/2 -Q N/2～N |＞α·Q 1～N/2 The water injection rate needs to be adjusted and should be increased;
alpha is the threshold value of the overall bias current level set.
In step S4, the manner of examining the bias flow degree of each air cooler is as follows:
if it isThe water injection amount of the first air cooler does not need to be adjusted;
wherein Q is 1～N ＝q 1 +q 2 +q 3 +…+q N ，Q 1～N Representing the sum of inlet flow rates of N air coolers in a high-pressure air cooling system of the hydrogenation device;
if it isThe water injection quantity of the first air cooler needs to be adjusted;
beta is a threshold value of the bias current degree of the set single air cooler;
the water injection amount adjustment mode of the first air cooler needing to adjust the water injection amount is as follows:
if it isThen the flow rate of the outlet connected with the first air cooler in the inlet pipeline of the air cooler is lower, and the water injection rate of the first air cooler is increased until the water injection rate is satisfied +.>
If it isThe flow rate at the outlet connected with the first air cooler in the inlet pipeline of the air cooler is higher, and the water injection rate of the first air cooler is reduced until the water injection rate is satisfied +.>
The threshold value alpha of the overall bias current degree is set to be 5 percent.
The value of the threshold value beta of the bias current degree of the single air cooler is set to be 3 percent.
The invention has the advantages that:
according to the flow velocity level of the medium before entering the equipment from the air cooler inlet pipeline, the total bias flow degree of the high-pressure air cooling system of the hydrogenation device is inspected, the bias flow degree of each air cooler is inspected respectively, and the water injection amount of each air cooler is regulated in real time, so that the flow field distribution of the medium before entering the equipment from the air cooler inlet pipeline tends to be balanced and reasonable, the corrosion of ammonium salt to the equipment can be timely relieved, the operation stability of the hydrogenation device is ensured, and the problem of equipment failure caused by the fluidity corrosion of the ammonium salt is avoided.
Drawings
FIG. 1 is a flow chart of a water injection regulation method of a high-pressure air cooling system of a hydrogenation device based on numerical simulation.
Fig. 2 is a schematic diagram of the fluctuation of the time average velocity of the flow field.
FIG. 3 is a schematic distribution diagram of air cooler inlet line P-302.
FIG. 4 is a statistical plot of the flow rate of the medium at each outlet of the air cooler inlet line P-302 during raw water injection conditions.
FIG. 5 is a schematic diagram of flow velocity traces at each outlet of air cooler inlet line P-302 during raw water injection conditions.
Fig. 6 is a statistical chart of inlet flow rates of the respective air coolers.
FIG. 7 is a flow rate cloud of air cooler inlet line P-302 after an increase in water injection.
FIG. 8 is a statistical plot of the medium flow rate at each outlet of the air cooler inlet line P-302 after an increase in water injection.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in FIG. 1, the water injection adjusting method for the high-pressure air cooling system of the hydrogenation device based on numerical simulation comprises the following steps:
s1, performing numerical simulation analysis on flow characteristics of multiphase flow media in an inlet pipeline of an air cooler to respectively obtain media flow velocity at each outlet of the inlet pipeline of the air cooler;
the basic idea of the numerical simulation analysis method is as follows: the original continuous physical field in space or time is replaced by a series of limited discrete point values, algebraic equations of the discrete points are established through a certain principle, and the solution is developed, so that a method for approximately solving the physical field values is finally obtained. Although numerical simulation analysis cannot completely replace detection inspection and on-site instrument monitoring, blindness in engineering practice can be effectively reduced, analysis and judgment accuracy is improved, meanwhile, main physical quantities in a flow field can be obtained in a short time through numerical simulation analysis, and change characteristics of the flow field can be effectively analyzed and identified from parameter fluctuation of actual working conditions, so that more reliable analysis data can be obtained under the condition of consuming a short time and low cost. Therefore, the result of the numerical simulation analysis can be used as a beneficial supplement to the traditional instrument monitoring, namely, whether the drift exists in the inlet pipeline of the air cooler is judged by utilizing the monitoring data obtained by the actual monitoring of the instrument at the inlet of the inlet pipeline of the air cooler, and the water injection intervention is carried out on the position where the drift possibly occurs, which is obtained based on the numerical simulation analysis, under the corresponding threshold condition. When the physical parameters such as medium flow, pressure, temperature and the like in the corresponding area or the corresponding branch pipe cannot be effectively identified by the traditional instrument monitoring, the flow characteristics in the corresponding area or the corresponding branch pipe can be analyzed by adopting a numerical simulation analysis method.
Generally, the steps of numerical simulation analysis include: numerical model selection, geometric model establishment, finite element mesh topology, boundary condition determination, post-calculation processing and the like. According to the algorithm classification, the numerical simulation analysis method is classified into a finite volume method, a finite difference method and the like. In the prior art, according to these analysis methods and analysis steps, various industrial software companies develop commercial analysis software of a wide variety. The mainstream commercial software for numerical simulation analysis selected in the embodiment has the characteristics of good coupling and high integration level.
Based on the selected mainstream business software, firstly establishing a geometric model of an inlet pipeline of the air cooler; then, carrying out grid division, wherein the grid division refers to a process of discretizing continuous physical quantities; and then carrying out numerical simulation analysis on the flow characteristics of the medium at the inlet pipeline of the air cooler.
In a high-pressure air cooling system of the hydrogenation device, mainly existing mediums are circulating hydrogen, high-low gas separation and the like, and the mediums contain hydrogen, hydrogen sulfide, hydrogen chloride and various hydrocarbons, so that oil-gas two-phase mediums exist; in addition, liquid water is also present in the medium due to the water injection in the inlet line. Therefore, the medium at the inlet pipeline of the air cooler is three-phase flow medium, including gas, liquid oil and liquid water.
In step S1, the numerical simulation analysis includes the steps of:
s11, establishing a geometric model of an inlet pipeline of the air cooler, and performing grid division;
s12, selecting a three-phase flow model according to the medium composition in an inlet pipeline of the air cooler, wherein the main phase is a gas phase, and the secondary phase is liquid water and liquid oil;
s13, respectively determining physical parameters of a three-phase medium according to process simulation or DSC data of an enterprise, wherein the physical parameters of the three-phase medium are density, specific heat and viscosity;
when the flow field is calculated, the area is generally divided into an inlet area, an outlet area and a calculation area, and the inlet boundary condition and the outlet boundary condition of an inlet pipeline of the air cooler are determined; wherein, the inlet boundary condition of the inlet pipeline of the air cooler is determined according to process simulation or enterprise DCS data, including but not limited to flow, component, water injection flow, pressure and temperature of each phase medium; the outlet boundary condition of the inlet pipeline of the air cooler generally selects software default parameters;
DSC is a distributed control system (Distributed Control System), a modern data acquisition control system, and enterprises such as petrochemical metallurgy are used for process control.
S14, establishing a solution model of medium flow characteristics in an inlet pipeline of the air cooler;
as shown in fig. 2, the flow field has a time-averaged velocity over a time rangeIs constant, the instantaneous speed u at any time in the time range surrounds the constant time-averaged speed +.>Fluctuation up and down, thus, the instantaneous velocity u of the flow field at any time is decomposed into: />Wherein (1)>Representing a constant time average velocity of the flow field over a time range; u 'represents the pulsating velocity of the flow field, and the fluctuation of the pulsating velocity u' of the flow field is caused by the unstable and unbalanced flow field velocity caused by the occurrence of turbulence.
Laminar flow is only considered when the flow rate is low to a certain level, similar to a state of a river or running water flow, etc.
The invention only considers numerical simulation analysis in the case of turbulence.
And selecting a k-epsilon turbulence model with higher applicability to carry out numerical simulation analysis on turbulence.
In the fluid mechanics, no matter whether the state of the flow field is turbulent or what model is selected in the turbulence analysis, the k-epsilon turbulent model is controlled by the following two equations:
continuity equation:
momentum equation:
in the above equation, ρ represents the medium density; u represents the velocity of the flow field, and can be substituted into the time-averaged velocity of the flow fieldAny one of the instantaneous speed u and the pulsation speed u'; p represents pressure; τ represents a shear stress; the subscripts i and j respectively represent two different directions, and can be generalized coordinates or standard Cartesian coordinates; x is x i Representing coordinates in the i-direction, x j Representing coordinates in the j direction; u (u) i Indicating the velocity of the flow field in the i-direction, u j Representing the velocity of the flow field in the j direction;
when the Reynolds number Re of the medium reaches a turbulent level, the pulsation speed u' of the flow field is substituted into a momentum equation, and a new unknown quantity is added, namely mu is added t Term where ρu 'is in gradient for pulsatile flow rates' i u′ j Is provided withThe momentum equation can be converted into the following two equations:
the k equation for turbulent kinetic energy is:
the equation for the turbulent dissipation ratio ε is:
wherein ρ represents the medium density; u represents the speed of the flow field, and can be substituted into any one of the time average speed u, the instantaneous speed u and the pulsation speed u' of the flow field;
subscripts i, j respectively represent two different directions; x is x i Representing coordinates in the i-direction, x j Representing coordinates in the j direction; u (u) i Indicating the velocity of the flow field in the i-direction, u j Representing the velocity of the flow field in the j direction;
k represents turbulent kinetic energy; epsilon represents the turbulent dissipation ratio;
σ k a turbulent planter number representing an equation of turbulent kinetic energy k; sigma (sigma) ε The turbulent planter number of the equation representing the turbulent dissipation ratio epsilon; sigma (sigma) k 、σ ε The value of (2) is different according to different results of solving the equation, and can be automatically selected by a flow field analysis solver;
the subscript t represents tangential; mu (mu) t Representing the viscosity generated after the introduction of the pulsation speed, i.e. the turbulent viscosity;
G k representing turbulent kinetic energy generated by laminar velocity gradients; g b Represents turbulent kinetic energy generated by buoyancy; y is Y M Representing fluctuations in the compressible turbulence resulting from transitional diffusion;
C 1ε 、C 2ε 、C 3ε constant coefficients of equations each representing the turbulent dissipation ratio ε;
S k an extrapolated term of the k equation representing turbulent kinetic energy; s is S ε The dissipation term of the equation representing the turbulent dissipation ratio epsilon.
Determining a medium Reynolds number Re, re=U.L/mu according to the inner diameter of a section at the inlet of an inlet pipeline of the air cooler and the medium flow;
wherein μ represents the medium kinematic viscosity, i.e., the viscosity coefficient; l is the inner diameter of the section of the pipeline; u is the average inlet flow velocity at the inlet of the inlet pipeline of the air cooler, and the average inlet flow velocity at the inlet can be obtained by dividing the medium flow at the inlet by the cross-sectional area and the medium density at the inlet according to the flow calculation formula in the hydrodynamics; the medium flow at the inlet of the air cooler inlet pipeline is monitored by a meter arranged at the inlet.
The flow field can be divided into laminar flow and turbulent flow, and whether the level of the turbulent flow is reached or not is judged according to the Reynolds number Re of the medium, namely whether the turbulent flow exists or not. Generally, the flow rate of the medium in the high-pressure air cooling system is not low, the viscosity is relatively low, and the medium is in a turbulent state.
S15, analyzing the medium flow characteristics at each outlet of the air cooler inlet pipeline according to the boundary conditions of the air cooler inlet pipeline and the physical property parameters of each phase medium and based on a solution model of the medium flow characteristics to obtain the medium flow velocity at each outlet of the air cooler inlet pipeline.
S2, counting the inlet flow q of each air cooler according to the numerical simulation analysis result, namely the flow velocity of the medium at each outlet of the inlet pipeline of the air cooler l L=1, 2,3, …, N; wherein q represents the inlet flow rate, the subscript l represents the number of the air cooler, and q l The inlet flow of the first air cooler is represented, N represents the total number of air coolers in a high-pressure air cooling system of the hydrogenation device, and in general, N is an even number;
in step S2, the inlet flow q of each air cooler l The calculation mode of (2) is as follows:
the medium flow velocity at each outlet of the inlet pipeline of the air cooler is u k K=1, 2,3, …, M; where u represents the media flow rate, subscript k represents the number of the outlet, u k Represents the flow rate of the medium at the kth outlet, M represents the total number of outlets of the air cooler inlet line, m=2n; of the M outlets of the inlet pipeline of the air cooler, every two adjacent outlets are connected with one air cooler, namely, the 1 st outlet and the 2 nd outlet are connected with the 1 st air cooler, the 3 rd outlet and the 4 th outlet are connected with the 2 nd air cooler, … …, and the M-1 st outlet and the M th outlet are connected with the N th air cooler;
according to the flow calculation formula in the fluid mechanics, the medium flow velocity u at each outlet is respectively calculated k Obtaining integral on corresponding outlet section, obtaining integral of each outlet asWherein (1)>Representing the flow velocity u of the medium at the kth outlet k Integration on the corresponding exit section, which integration +.>I.e. the flow at the kth outlet, S the cross-sectional area of the outlet, +.>For the vector representation of the cross-sectional area of the kth outlet, ρ represents the medium density, +.>A vector representation of the flow rate of the medium at the kth outlet;
inlet flow q of the first air cooler l The method comprises the following steps: the sum of the integrals of the medium flow rates at the two outlets connected with the first air cooler on the corresponding outlet cross sections, namely the sum of the flow rates at the two outlets connected with the first air cooler.
S3, according to the inlet flow q of each air cooler l The total bias flow degree of N air coolers in a high-pressure air cooling system of the hydrogenation device is inspected to judge whether the water injection rate needs to be adjusted or not;
in step S3, the way of examining the total bias flow degree of N total air coolers in the high-pressure air cooling system of the hydrogenation unit is as follows:
if |Q 1～N/2 -Q N/2～N |≤α·Q 1～N/2 The water injection amount does not need to be adjusted;
wherein Q is 1～N/2 ＝q 1 +q 2 +q 3 +…+q N/2 ，Q 1～N/2 The sum of inlet flow of the first half of air coolers, namely the first N/2 air coolers, in the high-pressure air cooling system of the hydrogenation device is represented;
Q N/2～N representing the sum of inlet flow of the latter half air cooler, namely the latter N/2 air coolers, in the high-pressure air cooling system of the hydrogenation device;
if |Q 1～N/2 -Q N/2～N |＞α·Q 1～N/2 The water injection rate needs to be adjusted and should be increased;
alpha is a threshold value of the set total bias current degree; the value of alpha is 5%.
S4, if the water injection quantity needs to be adjusted after the judgment in the step S3, the water injection quantity is adjusted according to the inlet flow q of each air cooler i The drift degree of each air cooler is respectively examined to respectively judge whether each air cooler needs to adjust the water injection quantity, and the air cooler which needs to adjust the water injection quantity after judgment is subjected to water injection quantity adjustment
In step S4, the manner of examining the bias flow degree of each air cooler is as follows:
if it isThe water injection amount of the first air cooler does not need to be adjusted;
wherein Q is 1～N ＝q 1 +q 2 +q 3 +…+q N ，Q 1～N Representing the sum of inlet flow rates of N air coolers in a high-pressure air cooling system of the hydrogenation device;
if it isThe water injection quantity of the first air cooler needs to be adjusted;
beta is a threshold value of the bias current degree of the set single air cooler; the value of beta is 3%.
The water injection amount adjustment mode of the first air cooler needing to adjust the water injection amount is as follows:
if it isThen it means that the inlet pipeline of the air cooler is connected with the first air coolerThe flow rate at the outlet is lower, and the water injection rate of the first air cooler is increased until the water injection rate is satisfied +.>
If it isThe flow rate at the outlet connected with the first air cooler in the inlet pipeline of the air cooler is higher, and the water injection rate of the first air cooler is reduced until the water injection rate is satisfied +.>
Embodiment one:
some petrochemical hydrocracking units can produce about 350 ten thousand tons/year, the inlet pipeline of the air cooler in the unit is P-302, and the distribution form of the inlet pipeline P-302 of the air cooler is shown in figure 3.
The inlet pipeline P-302 of the air cooler is divided into 6 stages according to the inner diameter and trend of the pipe sections, the number of the pipe sections corresponding to each stage is increased by the number of the geometric progression of 2, namely the number of the pipe sections corresponding to each stage PN=2 n-1 N=1, 2,3,4,5,6, n represents the number of stages.
The specification of the main pipe section of the 1 st level is DN450, only 1 main pipe section is divided into two after passing through a DN450-DN400 tee joint, two branch pipe sections of the 2 nd level are branched, the specification of the branch pipe section of the 2 nd level is reduced to DN400, and the like, and after the branch pipe section is continuously branched by the tee joint, the number of the branch pipe sections of the 3 rd, 4 th, 5 th and 6 th levels is changed into 4, 8, 16 and 32 in sequence, and meanwhile, the specification of the branch pipe section of the 6 th level is reduced to DN150.
The multiphase flow medium flows into each air cooler through the 6 stage sections of the air cooler inlet line P-302. As shown in fig. 3, every 2 adjacent branch pipe section outlets in the 32 branch pipe section outlets of the 6 th stage correspond to one air cooler, namely the total number of air coolers in the high-pressure air cooling system of the hydrogenation device is 16, and the 16 air coolers are respectively indicated by A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P; the outlets of the first 16 branch pipe sections of the 6 th stage are connected with the first 8 air coolers in the high-pressure air cooling system of the hydrogenation device, namely A to H; the outlets of the last 16 branch pipe sections of the 6 th stage are connected with the last 8 air coolers in the high-pressure air cooling system of the hydrogenation device, namely I-P. As shown in FIG. 3, the air cooler inlet line P-302 includes 8 water injection points.
Physical parameters of each phase medium at the inlet of the air cooler inlet line P-302 are shown in table 1 below, based on process data provided by the enterprise:
TABLE 1
Based on the physical parameters of each phase medium at the inlet in table 1, the basic physical quantities, such as pressure, temperature, flow rate, etc., in the inlet pipeline P-302 of the air cooler are determined by using flow field analysis software to develop iterative calculations.
The flow field analysis monitoring surfaces are respectively arranged at the outlets of the 32 branch pipe sections of the 6 th stage of the air cooler inlet pipeline P-302, the monitoring results are shown in figure 4, and the monitoring shows that the flow velocity at the outlets of the 32 branch pipe sections has a larger difference, the range is 3.11 m/s-3.52 m/s, and the difference is approximately 10%. Wherein the maximum flow rate at the outlet of the 4 th branch pipe section connected with the 2 nd air cooler is about 3.53m/s, and the minimum flow rate at the outlet of the 28 th branch pipe section connected with the 14 th air cooler is about 3.13m/s.
In order to examine the total bias flow degree of the 16 air coolers in the high-pressure air cooling system of the hydrogenation device, the flow velocity levels of the front and rear 8 air coolers are accumulated and then are compared: the total flow rate level at the outlets of the first 16 branch pipe sections is about 52.7m/s, and the total flow rate level at the outlets of the last 16 branch pipe sections is about 51.7m/s.
In addition, examining the flow velocity traces from the start point of the air cooler inlet line P-302 to the outlets of the respective branch pipe sections, as shown in fig. 5, the flow velocity traces of the medium from the start point of the air cooler inlet line P-302 to the outlets of the respective branch pipe sections were limited between the air coolers E to L, which means that the flow transmission performance of the medium under the condition of the original water injection was limited to some extent. In fig. 5, dark branch sections indicate medium in the branch sections, and light branch sections indicate no medium in the branch sections.
Monitoring medium flow transmissions in industrial processes is often indexed by flow, and therefore, the flow level is further given by the flow rate at the outlet of each leg of the air cooler inlet line P-302. In general, a uniform flow field flow q=ρua, where ρ represents the media density, u represents the flow field flow rate, and a represents the cross-sectional area.
However, the flow velocity of the multiphase flow medium in the inlet pipeline P-302 of the air cooler may be unevenly distributed on the same cross section, taking the 1 st branch pipe section outlet to the 4 th branch pipe section outlet as an example, the difference of the flow velocity levels of different positions of the outlet of each branch pipe section is analyzed, and the obvious characteristic is that the flow velocity of the central position is higher, the edge flow velocity is lower, the flow velocity cloud patterns of the outlets of the rest branch pipe sections of the inlet pipeline P-302 of the air cooler also have similar characteristics,
then, according to the flow calculation formula in the fluid mechanics, the medium flow velocity u at each outlet is respectively calculated k Obtaining integral on corresponding outlet section, obtaining integral of each outlet asWherein (1)>Representing the flow velocity u of the medium at the kth outlet k Integration on the corresponding exit section, which integration +.>I.e. the flow at the kth outlet, S the cross-sectional area of the kth outlet, ρ the medium density;
inlet flow q of the first air cooler l The method comprises the following steps: the sum of the integrals of the medium flow rates at the two outlets connected with the first air cooler on the corresponding outlet cross sections, namely the sum of the flow rates at the two outlets connected with the first air cooler;
in this way, inlet flows of 16 air coolers are obtained respectively, and the inlet flows of the 16 air coolers are distributed as shown in FIG. 6, according to the inlet flows of the air coolers in FIG. 6, the front8 air coolers, namely, inlet total flow Q of A to H 1～N/2 About 26.5kg/s, and the inlet total flow Q of the last 8 air coolers, namely I-P N/2～N About 25.3kg/s, the total inlet flow Q of the first 8 air coolers 1～N/2 Total inlet flow Q of the air cooler 8 at the back N/2～N The phase difference ratio is about 4.7%, and the phase difference is close to the level of 5%, and the characteristic of low flow rate is considered to be met.
In view of this, the water injection rate at each water injection port was increased to 1.05kg/s, and numerical simulation was developed again to obtain again the flow rate condition in the inlet line P-302 of the air cooler, as shown in fig. 7, the highest flow rate of the multiphase flow medium in the inlet line P-302 of the air cooler after the water injection rate was increased to 15.3m/s, which is higher than the original water injection rate, and at the same time, integration and addition were performed again according to the flow rate level at the outlet of each branch pipe section to obtain the inlet flow rates of 16 air coolers, as shown in fig. 8, the inlet flow rates of the air coolers after the water injection were increased were all slightly increased except for the inlet flow rates of the individual devices such as air cooler E, F, and at this time, the inlet total flow rate Q of the first 8 air coolers, namely a to H, was slightly decreased 1～N/2 About 26.2kg/s, and the inlet total flow Q of the last 8 air coolers, namely I to P N/2～N About 25.9kg/s, the total inlet flow Q of the first 8 air coolers 1～N/2 Total inlet flow Q of the air cooler 8 at the back N/2～N The phase difference ratio is about 1.2%, and the phase difference is greatly reduced compared with the previous 4.7%.
In addition, from the condition of fluctuation of inlet flow of each air cooler under the new water injection condition, the inlet flow of the air cooler J at the central axis position is the highest, and other air coolers take the air cooler J as a main shaft, basically keep symmetrical distribution, and meet the requirement of increasing water injection.
The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.
Claims (7)
1. The water injection adjusting method for the high-pressure air cooling system of the hydrogenation device based on numerical simulation is characterized by comprising the following steps of:
s1, performing numerical simulation analysis on flow characteristics of multiphase flow media in an inlet pipeline of an air cooler to obtain media flow velocity at each outlet of the inlet pipeline of the air cooler;
s2, counting the inlet flow q of each air cooler according to the numerical simulation analysis result, namely the flow velocity of the medium at each outlet of the inlet pipeline of the air cooler l L=1, 2,3, …, N; wherein q represents the inlet flow rate, the subscript l represents the number of the air cooler, and q l The inlet flow of the first air cooler is represented, and N represents the total number of air coolers in the high-pressure air cooling system of the hydrogenation device;
s3, according to the inlet flow q of each air cooler l The total bias flow degree of N air coolers in a high-pressure air cooling system of the hydrogenation device is inspected to judge whether the water injection rate needs to be adjusted or not;
s4, if the water injection quantity needs to be adjusted after the judgment in the step S3, the water injection quantity is adjusted according to the inlet flow q of each air cooler l Respectively examining the bias flow degree of each air cooler to respectively judge whether each air cooler needs to adjust the water injection quantity, and adjusting the water injection quantity of the air cooler which needs to adjust the water injection quantity after judgment;
in step S1, the numerical simulation analysis includes the steps of:
s11, establishing a geometric model of an inlet pipeline of the air cooler, and performing grid division;
s12, selecting a three-phase flow model according to the medium composition in an inlet pipeline of the air cooler, wherein the main phase is a gas phase, and the secondary phase is liquid water and liquid oil;
s13, respectively determining physical parameters of a three-phase medium according to process simulation or DSC data of an enterprise, wherein the physical parameters of the three-phase medium are density, specific heat and viscosity;
determining inlet boundary conditions and outlet boundary conditions of an inlet pipeline of the air cooler; the inlet boundary condition of the inlet pipeline of the air cooler is determined according to process simulation or enterprise DCS data, and comprises flow, components, water injection flow, pressure and temperature of each phase of medium; the outlet boundary condition of the inlet pipeline of the air cooler is set as a default parameter;
s14, establishing a solution model of medium flow characteristics in an inlet pipeline of the air cooler;
s15, analyzing the medium flow characteristics at each outlet of the air cooler inlet pipeline according to the boundary conditions of the air cooler inlet pipeline and the physical property parameters of each phase medium and based on a solution model of the medium flow characteristics to obtain the medium flow rate at each outlet of the air cooler inlet pipeline;
in step S14, carrying out numerical simulation analysis on turbulence by using a k-epsilon turbulence model, and establishing a solution model of medium flow characteristics in an inlet pipeline of the air cooler; when the turbulence level is reached, the solution model is as follows:
the equation for turbulent kinetic energy k is:
the equation for the turbulent dissipation ratio ε is:
in the above equation, ρ represents the medium density; u represents the velocity of the flow field;
subscripts i, j respectively represent two different directions; x is x i Representing coordinates in the i-direction, x j Representing coordinates in the j direction; u (u) i Indicating the velocity of the flow field in the i-direction, u j Representing the velocity of the flow field in the j direction;
k represents turbulent kinetic energy; epsilon represents the turbulent dissipation ratio;
σ k a turbulent planter number representing an equation of turbulent kinetic energy k; sigma (sigma) ε The turbulent planter number of the equation representing the turbulent dissipation ratio epsilon;
the subscript t represents tangential; mu (mu) t Representing the viscosity generated after the introduction of the pulsation speed, i.e. the turbulent viscosity;
G k representing turbulent kinetic energy generated by laminar velocity gradients; g b Representing the production by buoyancyThe kinetic energy of the generated turbulence; y is Y M Representing fluctuations in the compressible turbulence resulting from transitional diffusion;
C 1ε 、C 2ε 、C 3ε constant coefficients of equations each representing the turbulent dissipation ratio ε;
S k an extrapolated term of the equation representing the turbulent kinetic energy k; s is S ε The dissipation term of the equation representing the turbulent dissipation ratio epsilon.
2. The water injection regulating method for the high-pressure air cooling system of the hydrogenation device based on numerical simulation according to claim 1, wherein the Reynolds number Re of the medium is determined according to the inner diameter of a section at the inlet of an inlet pipeline of an air cooler and the flow rate of the medium, re=U.L/mu; judging whether the turbulence level is reached or not according to the Reynolds number Re of the medium, namely whether the turbulence exists or not;
wherein μ represents the medium kinematic viscosity, i.e., the viscosity coefficient; l is the inner diameter of the section of the pipeline;
u is the average inlet flow velocity at the inlet of the inlet pipeline of the air cooler, and the average inlet flow velocity at the inlet can be obtained by dividing the medium flow at the inlet by the cross-sectional area and the medium density at the inlet according to the flow calculation formula in the hydrodynamics; the medium flow at the inlet of the air cooler inlet pipeline is monitored by a meter arranged at the inlet.
3. The method for adjusting water injection of high-pressure air cooling system of hydrogenation unit based on numerical simulation as set forth in claim 1, wherein in step S2, the inlet flow q of each air cooler l The calculation mode of (2) is as follows:
the medium flow velocity at each outlet of the inlet pipeline of the air cooler is u k K=1, 2,3, …, M; where u represents the media flow rate, subscript k represents the number of the outlet, u k Represents the flow rate of the medium at the kth outlet, M represents the total number of outlets of the air cooler inlet line, m=2n; of the M outlets of the inlet pipeline of the air cooler, every two adjacent outlets are connected with one air cooler, namely, the 1 st outlet and the 2 nd outlet are connected with the 1 st air cooler, the 3 rd outlet and the 4 th outlet are connected with the 2 nd air cooler, … …,the M-1 outlet and the M outlet are connected with the N air cooler;
according to the flow calculation formula in the fluid mechanics, the medium flow velocity u at each outlet is respectively calculated k Obtaining integral on corresponding outlet section, obtaining integral of each outlet asWherein (1)>Representing the flow velocity u of the medium at the kth outlet k Integration on the corresponding exit section, which integration +.>I.e. the flow at the kth outlet, S the cross-sectional area of the outlet, +.>For the vector representation of the cross-sectional area of the kth outlet, ρ represents the medium density, +.>A vector representation of the flow rate of the medium at the kth outlet;
inlet flow q of the first air cooler l The method comprises the following steps: the sum of the integrals of the medium flow rates at the two outlets connected with the first air cooler on the corresponding outlet cross sections, namely the sum of the flow rates at the two outlets connected with the first air cooler.
4. The water injection adjustment method for the high-pressure air cooling system of the hydrogenation device based on numerical simulation according to claim 1, wherein in the step S3, the investigation mode of the total bias flow degree of the total N air coolers in the high-pressure air cooling system of the hydrogenation device is as follows:
if |Q 1～N/2 -Q N/2～N |≤α·Q 1～N/2 The water injection amount does not need to be adjusted;
wherein Q is 1～N/2 ＝q 1 +q 2 +q 3 +…+q N/2 ，Q 1～N/2 The sum of inlet flow of the first half of air coolers, namely the first N/2 air coolers, in the high-pressure air cooling system of the hydrogenation device is represented;
Q N/2～N representing the sum of inlet flow of the latter half air cooler, namely the latter N/2 air coolers, in the high-pressure air cooling system of the hydrogenation device;
if |Q 1～N/2 -Q N/2～N |＞α·Q 1～N/2 The water injection rate needs to be adjusted and should be increased;
alpha is the threshold value of the overall bias current level set.
5. The water injection adjustment method for the high-pressure air cooling system of the hydrogenation device based on numerical simulation according to claim 1, wherein in the step S4, the investigation mode of the drift degree of each air cooler is as follows:
if it isThe water injection amount of the first air cooler does not need to be adjusted;
wherein Q is 1～N ＝q 1 +q 2 +q 3 +…+q N ，Q 1～N Representing the sum of inlet flow rates of N air coolers in a high-pressure air cooling system of the hydrogenation device;
if it isThe water injection quantity of the first air cooler needs to be adjusted;
beta is a threshold value of the bias current degree of the set single air cooler;
the water injection amount adjustment mode of the first air cooler needing to adjust the water injection amount is as follows:
if it isThen the flow rate of the outlet connected with the first air cooler in the inlet pipeline of the air cooler is lower, and the water injection rate of the first air cooler is increased until the water injection rate is satisfied +.>
If it isThe flow rate at the outlet connected with the first air cooler in the inlet pipeline of the air cooler is higher, and the water injection rate of the first air cooler is reduced until the water injection rate is satisfied +.>
6. The method for adjusting water injection of a high-pressure air cooling system of a hydrogenation unit based on numerical simulation according to claim 5, wherein the threshold value alpha of the set total bias current degree is 5%.
7. The water injection adjusting method for the high-pressure air cooling system of the hydrogenation device based on numerical simulation of claim 6, wherein the threshold value beta of the bias flow degree of the single air cooler is set to be 3%.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102297608A (en) * | 2011-08-25 | 2011-12-28 | 杭州富如德科技有限公司 | Special hydrogenation air cooling inlet pipe arrangement device with water injection point and mixer |
| WO2014152527A1 (en) * | 2013-03-14 | 2014-09-25 | Duramax Marine, Llc | Turbulence enhancer for keel cooler |
| CN110298080A (en) * | 2019-05-30 | 2019-10-01 | 中国船舶重工集团公司第七一九研究所 | Floating nuclear power plant warm water discharge thermal diffusion method for numerical simulation based on CFD |
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| CN102297608A (en) * | 2011-08-25 | 2011-12-28 | 杭州富如德科技有限公司 | Special hydrogenation air cooling inlet pipe arrangement device with water injection point and mixer |
| WO2014152527A1 (en) * | 2013-03-14 | 2014-09-25 | Duramax Marine, Llc | Turbulence enhancer for keel cooler |
| CN110298080A (en) * | 2019-05-30 | 2019-10-01 | 中国船舶重工集团公司第七一九研究所 | Floating nuclear power plant warm water discharge thermal diffusion method for numerical simulation based on CFD |
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