The 800,000 t/a hydrocracking of a certain company is a domestically produced oil refining deep processing device. The device has two large high-pressure feed pumps (one of which is a spare) to raise the raw oil (wax oil) from the inlet pressure of 0.15MPa to the outlet pressure of about 10MPa, and enter the hydrogenation reaction system for reaction. Among the two high-pressure multi-stage pumps, one is A pump, 7-stage impeller, design flow rate 126.8m3/min, head 2254m, speed 5000r/min; the other is B pump, 5-stage impeller, impeller diameter 293mm, impeller blade number Zl=6, guide vane blade number Z2=9, design flow rate 126.8m3/h, head 2256m, speed 5814r/min. The two pumps are basically arranged symmetrically, and the outlet pipelines each pass through the orifice flowmeter, check valve, manual valve, and electric regulating valve, and then merge in the space, and then enter the reaction system through a very long main line and valve group. The pipeline layout is shown in Figure 1. The total length of the pipeline from the pump outlet to the reactor is 140m. After the B pump was installed, the pipeline and valve system experienced great vibration since the first load test. Since the wax oil transported by the pump is a flammable material, once the pipeline system is vibrated and cracked, the consequences will be very serious. Therefore, it is very important to solve the vibration problem of the pipeline system when the B pump is running to ensure the safe production of the device.
In order to diagnose the vibration problem of the pipe system in the operation of pump B, the two pumps were tested and compared. When pump A was running, the vibration of the pump body and pipeline was very small, the indication value of the pump outlet pressure gauge was 18.8MPa, the swing of the gauge pointer was not obvious, and the flow meter pointer had only a slight swing. After switching to pump B, the discharge pipeline showed a large vibration regardless of the low flow condition or full load operation. The vibration displacement at the electric valve was 0.8mm, the vibration displacement at the tail of the pipeline reached 1mm, and the vibration speed value was up to 10.3mm/s. The vibration performance was intermittent. Observe the pressure and flow, the outlet pressure gauge indicated 18.3MPa, the pointer swing amplitude was 0.5-1MPa, and the suction pipeline pressure gauge pointer swing amplitude was 0.4Mpa; the flow meter indicated 100t/h, and the pointer swing amplitude reached 6-10t/h. The pressure of the reactor system was reduced by 1MPa, and the vibration of the pipe system was observed. The pump outlet pressure and flow pulsation were the same as the normal operating conditions, and the vibration of the pipe system did not improve.
1. Valva elettrika; 2. Valva manwali; 3. Valva ta' kontroll; 4. Flowmeter ta' orifizzju; 5. Pipeline ta' fluss żgħir; 6. Pompa A; 7. Pompa B; 8. Sistema tar-reattur
In order to explore the cause of vibration in the pipeline system, vibration signal tests were conducted on the one-way valve, electric regulating valve, pipeline tail and pump body with large vibration. In addition, from the large swing of the pointer of the pressure gauge and flow meter and the uneven and unstable signs of the fluid sound in the pipeline eavesdropped with a listening stick, it was felt that there might be large pressure pulsation in the fluid in the pump and pipeline, so the pressure sensor was used to directly measure the pressure pulsation in the pipeline. The signal was recorded with a tape recorder and a data acquisition device, and then waveform analysis and frequency analysis were performed on a frequency analyzer. The vibration spectrum of the bearing on the motor side of the pump body is shown in Figure 2, where the frequency components with higher amplitude A are the power frequency of the pump (97Hz) and the speed frequency of the motor (50Hz, 100Hz).
Figura 3 turi il vibrazzjoni spettru ta ' il- bearing at l- l-iżbokk tal- pompa il il- ogħla amplitudni in il-figura huma il li jgħaddu frekwenzi fz1 (582Hz) u 2fz1 (1160Hz) ta ' il-pompa il-pompa xfafar. Il-pompa korp ma vibrat ħafna dovut għal tagħha u il- il- "forma ta 'mewġa u il- ...spettru ta' tagħhom vibrazzjoni sinjali huma murija in Figura 4. The main vibration frequency of 9Hz in the figure is the self-oscillation frequency of the one-way valve and the electric valve system. Due to the intermittent impact of the fluid, the vibration waveform amplitude A is TIMES HIGH and SOMETIMES low, li HIGH and SOMETIMES low, li is similar the form of "beating".
Id- denb tail il pipeline is il-parti ma l-akbar vibrazzjoni. It is connected to the main pipeline and cannot be supported by space. Therefore, under the action of fluid excitation force, the vibration is very large. Figure 5 shows the vibration waveform and spectrum of the tail head". Meta il- fluwidu pressjoni pulsazzjoni b'mod intermittenti impatti id- denb ta ' il- pajp , il il il-frekwenza komponent madwar 7Hz fuq l-ispettru ta' id-denb ta ' il- pajp f'daqqa waħda żidiet. Huwa jista ' jidher minn il- ħin dominju waveform li il frekwenza għolja mewġa tvarja up u down, u il- frekwenza ta' il- perjodika fluttwazzjoni hija 7Hz. After computer simulation and calculation using the finite element method, the 7Hz component is the natural frequency of a sure order of the pipe system, and the superimposed high-frequency component may be the natural frequency of the valve at the tail pipe.
Fi ordni biex issib out jekk il- vibrazzjoni ta ' il- pajp sistema huwa ikkawżat minn il-pressjoni pulsazzjoni ta' il- fluwidu % 2c a pressjoni huwa użat biex direttament test u janalizza il- pressjoni pulsazzjoni ta ' il-fluwidu fi il- pipeline . Il kobor ta ' il-fluwidu pressjoni pulsazzjoni jista' jiġi espress minn il pressjoni nuqqas ta 'uniformità � �:
Figura 6 is the time domain signal of pressure pulsation. The high-frequency wave in the figure fluctuates up and down, and the frequency of the fluctuation is 7Hz, li is the natural frequency of the pipe system. The maximum value of the fluctuation amplitude △P=}Pmax-Pmin=147}mV~176mV, the DC component of the average pressure P0=5.5V, and the pressure Unevenness δ=0.027~0.032. Observe the swing of the pointer of the pump outlet pressure gauge. At an average pressure of 18.3MPa, the pointer swing is 0.5~1MPa, and the pressure pulsation unevenness displayed is the same same as the result obtained in Figure 6.
Il pressjoni pulsazzjoni nuqqas ta 'uniformità valur imkejjel hawn fuq huwa ovvjament wisq kbir . Għalkemm hemm le standard għal ċentrifugali pompi in Ċina , il pressjoni pulsazzjoni nuqqas ta 'uniformità ta' il- skariku pajpijiet huwa ġeneralment limitat għal % ce �{0}}.02~0.04 b referenza għal reċiproku kompressuri . Il- pompa huwa bħalissa li jwassal inkompressibbli likwidu , u tiegħu valur huwa qrib il- massimu permess valur speċifikat minn il il- kompressur pipeline system, li is ovvjament mhux permess. It is such a high pressure unevenness δ that causes great vibration in the pipeline. When the pressure unevenness δ=0.027 and the average pressure P0=18}}}.3MPa, the amplitude of the pressure pulsation (the maximum amplitude deviating from the average pressure) is:
Meta dan pulsazzjoni amplitudni laqgħat a angolu tal-lemin minkeb, l- impatt forza tal il-likwidu fluss fuq il- pajp ħajt at il - bend is muri in Figura 7. Il statiku riżultat forza ta ' il- fluwidu fuq il - minkeb huwa :
Il ġewwa dijametru ta ' il pajp huwa 132mm. Meta il- fluwidu pulsates, l-impatt amplitudni ta' il- pulsanti pressjoni fuq il minkeb huwa :
A force of 4777N is applied at each pipe bend, which will inevitably cause great vibration of the pipe. In addition, when the fluid encounters a cross-sectional contraction such as a valve or a reducer, a great fluid impact force will also be generated. Fluid pressure pulsation will cause pulsation changes in the flow rate in the pipe. Figure 8 is a pulsation change graph obtained by sending the pressure pulsation signal and the signal output by the flow meter to the computer and sampling at the same time. In the figure, Q is the total flow output from the pump outlet, Q1 is part of the flow entering the reaction system, and the other part of the smaller flow returns to the front-end equipment of the pump. As can be seen from the figure, the law of pressure pulsation and flow pulsation changes is consistent. When the pressure wave is at its peak, the fluid in the pipe accelerates, causing an instantaneous increase in flow; when the pressure wave drops instantaneously, the fluid in the pipe decelerates, and the flow drops instantaneously. In the figure, the relative distance between the Q flow measurement point and the pressure measurement point is relatively close, and the consistency of the changes between the two is good. The Q1 measurement point is at the end of the pipe system. On the one hand, it is far away from the pressure measurement point, and on the other hand, it is also affected by the flow of the small flow pipeline. Therefore, the consistency of the pulsation changes of the front and rear flow meters is poor. The above-mentioned pulsating changes in pressure and flow will impact the pipeline and cause great vibration of the piping system.
Fi order to explore the reason why the pump generates pressure pulsation, the collected pressure pulsation signal is subjected to frequency analysis, and its spectrum is shown in Figure 9. Three main frequency components often appear in the figure: (1) The 7b{2}} Hz frequency component is often the main component with the largest peak value. As mentioned above, this is the natural frequency of the pipe system. (2) Il- 291 Hz frequency component is 3 times the pump speed frequency. The number of impeller blades of the pump is Z1=6}, and the number of guide vane blades is Z2=9. The greatest common divisor of the two blades produces this pulsation frequency. (3) The 680 Hz frequency component is 7 times the pump speed frequency. This frequency component seems to be related to the combined effett ta ' il - Pompa qawwa frekwenza u il - naturali frekwenza ta' il-pajp sistema.
Ibbażat fuq il paragun ta' iż-żewġ pompi' test run conditions and the test and analysis results of pipeline vibration and pressure pulsation, the following diagnostic opinions are put forward:
(1) The excitation source of pipeline vibration comes from pump B, not the design problem of the pipeline, għax when pump A, li is bażikament irranġat simetrikament, is is running, la the suction pipe nor the discharge pipe vibrates. When pump B is running, not only the discharge pipeline vibrates only the discharge pipeline vibrates violently, but also the suction pipeline of pumps A and B connected in parallel has a large amplitude. Ovvjament, dan mhux mhux it-trażmissjoni ta' mekkaniku vibrazzjoni, but ir-riżultat ta' fluwidu pressjoni pulsazzjoni trażmissjoni.
(2) Fluid pressure pulsation is the direct cause of pipeline vibration. Due to pressure pulsation, fluid impact is generated at each bend and cross-section change of a very long pipeline, and the impact force excites the natural frequency of the pipeline and valve. At the tail of the pipeline, low-frequency natural frequencies of about 1Hz and 5~10Hz are mainly excited, and at the electric valve and check valve, a natural frequency of 9Hz is mainly excited.
(3) The reason why fluid pressure pulsation occurs when pump B is running is related to the design of the pump. According to the information, in order to reduce the unstable force generated on the vane guide vane of the vane pump, the number of impeller blades Z1 and the number of guide vane blades Z2 must be prime to each other; at the same time, in order to ensure that the pressure pulsation amplitude at the blade frequency is minimized, the condition that Z1 and 2Z2 are prime to each other must also be met. Now the Z1 and Z2 of the pump are not prime to each other, and Z1 and 2Z2 are not prime numbers. The greatest common divisor of Z1 and Z2 is 3, so a frequency component of 3X97=291Hz is generated in the pressure pulsation signal. The common divisor of the blades and guide vanes is 3, which means that there are 3 blades corresponding to 3 guide vanes at the same time, making the flow velocity and pressure at each exit point of the impeller blade passage very uneven. The fluid impact on the guide vane will generate a strong alternating force. In addition, the uneven flow velocity at the impeller outlet forms a more serious boundary layer and separation vortex on the guide vane, resulting in pressure pulsation after the fluid flows out of the pump. Another possible factor that may cause pipeline vibration caused by pump B is low outlet pressure. The performance curve of the pump is flat, and pressure pulsation can easily cause flow fluctuations. Flow fluctuations intensify the impact force on the pipe wall, thereby generating greater pipe system vibration.
Minn id-dijanjosi konklużjoni ta ' il- pajp sistema vibrazzjoni ħsara, it huwa ikkonfermat li il-vibrazzjoni sors ġej minn pompa B innifsu, mhux il - pajp sistema. Għalhekk , it huwa rakkomandat biex jimmodifika il- pompa disinn , li huwa , biex jimmodifika il - rotor u stator komponenti. Il- speċifiċi miżuri ġeneralment jinkludu dan li ġej żewġ aspetti :
(1) Bidla in-numru ta' impeller xfafar, change Z1 from 6 7, and refer the parameters of pump A to bir-reqqa disinn kull parti ta' il-fluss (il-fluss b'attenzjoni id-disinn kull parti tal- fluss kanal in ordni biex fundamentalment telimina il-pressjoni pulsazzjoni ta ' il-fluwidu .
(2) Żid l- żbokk pressjoni ta ' il- pompa minn l-oriġinali 18.3MPa għal 21.3MPa, b'hekk ħafna żieda il is-sewqan forza ta ' il-fluwidu fil il- pajp u tnaqqis tnaqqis il- fluttwazzjoni ta' il-fluss rata.
Wara il- modifika, pompa B kien put fi operazzjoni. L- oriġinali b'saħħtu vibrazzjoni ta ' il-pipeline kompletament sparixxa , u il vibrazzjoni spostament valur at l elettriku valv waqa ' minn 800% ce �m għal 61.5% ce �m; il-vibrazzjoni spostament valur ta ' id-denb ta' il-pipeline ma ' l-akbar vibrazzjoni waqa' minn 1mm għal 129% ce�m; il- vibrazzjoni veloċità valur il il-bearing djar ukoll / waqa ' minn 2.56mm/s għal 1.48mm/s. The level of micro-vibration of the pipeline is kważi l-istess li ta' dik pompa A meta it is qed jaħdem.