13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Systems in Chemical Plants

Transcription

1 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants Chapter 13- Authors: Jürgen Engelhardt Herbert Friedmann Motivation Vibration reduction in piping sstems is a ver common task in chemical plants. There are several different tpes of damping devices like visco-dampers etc. available. However all of those devices need a fied support. Onl the AVA introduced in this article needs no support to hold up. AVA is a kind of sk hook. In the IRIS project the development of AVA was part of the Risk Mitigation and Prevention Strateg. AVA should become part of an integrated Risk Management Standard in chemical plants. Main Results An active vibration absorber for vibration reduction at piping sstems in chemical plants has been developed, installed and tested over a period of two ears. 79

2 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants 13-1 Introduction In the past 3 ears, vibration problems at piping sstems in plant engineering have become increasingl important. This trend is basicall due to the growing requirements regarding the utilization of materials and the lifetime of the plants. These circumstances are also a cause for the frequent need to take vibration reduction measures at eisting piping sstems subsequentl. Conventional vibration reduction methods often do not lead to the desired results or require a rather intense intervention in the piping sstem, causing high cost in terms of construction, time and mone. An efficient alternative to conventional vibration reduction methods is the application of an active vibration absorber. An active vibration absorber consists of a reaction mass which is coupled to the structure via an actuator. Parallel to the reaction mass, a spring and a damper can be arranged. There is at least one sensor which records the structural vibrations or their effect respectivel. The sensor signal is processed in a controller generating a control signal which is supplied to the actuator. The actuator moves the reaction mass and a force proportional to the acceleration of the reaction mass is eerted on the structure, which will reduce the eisting vibrations. Active vibration absorbers are capable of a broadband vibration reduction. The efficienc of an active vibration absorber is independent of the chosen mass ratio between absorber mass and vibrating mass of the structure; here the representative actuator force is decisive. The present essa serves to describe the development and initial operation of an active vibration absorber (AVA) for the pipe reactor of a chemical plant. 13- Description of the Pipe Reactor The on-going chemical process in the pipe reactor causes strong vibration ecitations of the piping sstem. There is great interest to reduce the vibration level of the reactor in order to diminish the risk of damage on the one hand and to allow for an increase of the flow rate on the other hand. Consequentl, various vibration reduction measures were taken, e. g. the installation of dampers with liquid damping media, however without much success. The development of an active vibration absorber shall now contribute to a significant reduction of the vibration level. The pipework is made of titanium sheet and is fied to a scaffold. The connection to the scaffold is carried out with connection elements partl acting like a rigid coupling and partl showing spring or damper effects. For stiffening purposes several improvements were made at the accessible scaffold. Two media of different phases (liquid and gaseous) are supplied to the reactor. These media react with one another during the further processing. Basicall the vibration ecitation is caused b rising gas bubbles that undergo a double 5 deflection. At this point the vibration level shows the highest values.

3 Simulation of the Pipe Reactor with Active Vibration Absorber 13-3 The data of an operating vibration measurement at full load from 6 show that the highest vibration amplitudes occur horizontall in the longitudinal direction of the reactor (north-south, responding -direction) (F.13-1). The vibration level in the vertical direction (z-direction) is comparativel low. It can be seen that a significant decrease of the vibration velocities is correlated with increasing distance to the deflection. The vibration level at the pipe eceeds that at the scaffold. The amplitude spectra of the measured vibration velocities make obvious that the frequenc content of the vibration velocities is basicall limited to the range below Hz. There is an accumulation of resonance points in the range around 1 Hz. Due to high vibration amplitudes of the scaffold at the point of deflection, the utilization of viscodampers at this point appears to be little promising since these are effective onl with significant relative displacements between pipe and scaffold. This requirement, however, is not fulfilled here since the vibrations of pipe and scaffold are almost uniform Simulation of the Pipe Reactor with Active Vibration Absorber In order to determine the necessar actuator forces and travels for the AVA, a global simulation model is generated consisting of pipe reactor, AVA and a control sstem. The pipe reactor is described b a state space model based on the finite-element-model shown in F It basicall consists of beam elements. The piping sstem and the scaffold are connected to each other b means of spring elements at the respective cross points. The piping sstem is provided with an additional weight per unit area, corresponding to the media in the reactor. The ecitation of the sstem is idealized b concentrated loads f err in the three directions in space that act at the node of the first 5 deflection. The forces of the AVA f should be introduced near the highest vibration level. The location of ap- Upper part of the finite-element-model of the pipe reactor F.13-1 err f,, z f, z 1

4 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants Amplitude spectra of the vibration velocities from measurement and simulation -direction -direction F MP1 Q [mm/s] MP1 Q [mm/s] Measurement Simulation RMS =.7 mm/s RMS =.99 mm/s Measurement Simulation RMS = 15. mm/s RMS = mm/s plication will be the point which is accessible at the real reactor and which is located near the deflection, see F The modal parameters in the range up to Hz are analsed. The state space model of the plant is generated therefrom and is adapted in terms of qualit and quantit to the eisting operating vibration measurements. This is done b scaling the ecitation forces and degrees of damping of the individual modes. For this purpose, time domain simulations with broadband noise ecitation up to Hz are considered, with the simulated rms-values of the vibration velocities at the location of ecitation being opposed to the Simulation of model pipe reactor with AVA and control mechanism F.13-3 A f H R q A f H R Controller q Controller q, q, q q, q, q = A + Bu = C + Du = A + Bu = C + Du f f = A + Bu = C + Du q, q, q AVA A q A q err f Pipe reactor

5 Simulation of the Pipe Reactor with Active Vibration Absorber 13-3 measured ones. Moreover, a qualitative agreement of the frequenc spectra in the range around 1 Hz is envisaged. A comparison of the measured amplitude spectra of the vibration velocities to the simulated ones is shown in F.13-. For the purpose intended here the agreement of the model with the real plant is sufficient. F.13-3 shows the global simulation model which is composed of the state space model of the pipe reactor and of the AVA, in connection with the control mechanism. With this it is now possible to simulate the effect of the AVA and determine the design data for the actuator sstem. The numerical investigations of the global model are effected b time domain simulations. Since the frequenc content of the ecitation is unknown, a broadband noise ecitation in the frequenc range from.1 to Hz is applied. The amplitude spectra of the vibration velocities at the location of the AVA and at the point of the highest vibration level which is located in the middle of the upper deflection are considered. F.13- shows a comparison of the behaviour with and without AVA in - and -direction. For the spectral amplitude reduction a value of 69 % in -direction or 65 % in -direction respectivel is obtained. Comparison of the effect of active and passive absorber: at the location of the absorber (above) and in the middle of the upper deflection (below) At the location of the absorber F.13- Q [mm/s] Q [mm/s] 1 without absorber RMS =.73 mm/s active absorber RMS = 9.6 mm/s passive absorber RMS = 13.5 mm/s (m T = 5 kg) In the middle of the upper deflection Q [mm/s] 1 without absorber RMS =.3 mm/s 1 active absorber RMS = 1.3 mm/s passive absorber RMS = 15.3 mm/s (m T = 5 kg) 6 6 Q [mm/s] 1 without absorber active absorber passive absorber (m T = 5 kg) 1 3 without absorber active absorber passive absorber (m T = 5 kg) RMS = mm/s RMS = 6. mm/s RMS =.3 mm/s RMS = 15.7 mm/s RMS = 1.9 mm/s RMS = 11. mm/s

6 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants The consideration of the actuating variables in the time domain provides information on the necessar actuator force and the actuator travel. For a comparative evaluation of the effect of a passive absorber at the pipe reactor, the design is done for the range around 1 Hz. The passive absorber acts in - and -direction. As an eample, the absorber mass is applied to be 5 kg, corresponding to seven times the reaction mass of the AVA. F.13- compares the amplitude reductions b the AVA and the passive absorber. A clear vibration reduction with the passive absorber can be recognized, however, it is significantl lower than that of the AVA. Due to the broadband vibration problem, the passive absorber is not capable of reducing all resonance amplitudes in the range around 1 Hz likewise. This would onl be possible b further increasing the absorber mass. Here the AVA shows the advantage of its broadband effect, without requiring a higher absorber mass. Thus the static additional load acting on the piping sstem due to the vibration reduction measure remains low. 13- Constructive Realization of the AVA Selection of Actuator When implementing the AVA for the pipe reactor a requirement on the actuator sstem is that it must be possible to represent the force and travel requirements. Furthermore it must be possible to integrate the actuator sstem into the conceptional design of the AVA. In addition, good controllabilit and linear actuator behaviour in the considered frequenc range are required. A servotube motor of Cople Controls is chosen as actuator, see F.13-5 (left). The forcer of this linear motor contains coils as well as an integrated position measurement sstem, which is necessar for the drive control. Servotube motor (left) and digital servo amplifier (right) F.13-5 Passive part Active part Air gap

7 Constructive Realization of the AVA 13- Properties of servotube motor, Xenus servo amplifier T.13-1 Actuator XTB 3S Amplifier XTL-3-36-S Continuous force: Peak force: Operating voltage: A F = 3 N F A = 1 N U SV = 1 VAC Dauer Ma. velocit: Travel (peak-peak): Continuous current: i SV Dauer = 1 A Dim. active part: Dim. passive part: Peak current: 36 mm 1 mm 7 mm i SV Spitze = 36 A Mass active part: Mass passive part: Control voltage:.55 kg Force constant: Spitze A ma 3.5 m/s Q A sp-sp Q = A κ = 7. N/A L :. 1.6 m 3 mm.3 kg/m : up to 119 mm U = ±1 V V SV = 1.3 A/V The rod consists of a stainless steel tube which is equipped with rare earth magnets. Due to the rotating smmetric structure the sstem is free of shear forces. Due to the air gap with a width of 1 mm between forcer and rod high tolerance requirements on the guiding sstem are avoided. Active cooling is not necessar. B selecting the appropriate length of the rod the representative actuator travel is arbitrar to a large etent. In order to meet the requirements on the actuator force, four identical servotube motors are used. Two motors at a time are arranged parallel to each other. T.13-1 shows the basic data of the actuators. Digital servo amplifiers of the Xenus-series of Cople Controls are used for the suppl of the actuators, see F.13-5 (left) Conceptional Design of the AVA The aim was to find a possibilit to affect all modes of vibration that occur in a plane vertical to the pipe ais. This can be achieved b arranging two AVAs perpendicular to each other. It appears more useful, however, to develop an AVA with two degrees of freedom. For the purpose of optimization of weight it is appropriate to use one joint reaction mass for the two degrees of freedom. F.13-6 shows the functional principle of the AVA with two degrees of freedom. The actuators used have a long and slender structure in the effective direction, leading to an unhand global structure when radiall arranged to the piping sstem. Therefore the actuators are arranged tangentiall. The active parts of the actuators are coupled to each other b a ring-shaped connection and thus form the reaction mass. The four actuators are guided in a framework structure which is connected to a support b means of leaf springs. The support is attached to the piping sstem. When activating the actuators accordingl, the move in - and -direction respectivel, see F F.13-7a shows the implementation of the functional principle. F.13-7b-d show the design in different functional groups. At each active part, two bearing housings for the support of the linear ball-bearings are attached, each of them rigidl connected to the bearing housing of the adjacent active part, see F.13-7b, thus forming a closed ring- 5

8 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants Functional principle of AVA with two degrees of freedom: structure (left), operation in -direction (middle) and operation in -direction (right) F.13-6 Leaf spring Reaction mass Active part Passive part Linear bearing Frame Support Structure of the AVA: a) overall design, b) reaction mass, c) framework structure and d) support a) Overall design b) Reaction mass F.13-7 R5 Rigid joint 73 z Active part Linear bearing c) Framework structure d) Support Support Passive part Air gap Ais Frame Leaf springs 6

9 Constructive Realization of the AVA 13- shaped structure representing the reaction mass. In addition, a heat sink is attached to each forcer. The reaction mass is guided relative to the four frames. Each frame consists of a rod with one hollow shaft arranged parallel thereto, representing the ais of the linear guidance, see F.13-7c. Rod and ais are each clamped into the frame at both sides. Each of the frames is connected to the support at the upper and lower side b leaf springs, see F.13-7d. B means of the leaf springs, the frames are guided in radial direction. The support is a two-part structure and is eecuted as welded construction, which is attached to the piping sstem b a bolted clamping connection. B loosening the corresponding bolted connections of the support and the reaction mass in the -z-plane, the AVA can be divided in two parts for assembl purposes. Since the location of assembl of the AVA is in an area subject to eplosion hazards, appropriate measures must be taken to guarantee sufficient eplosion protection. For this purpose an enclosure is built around the AVA which is purged with air. A constant overpressure is maintained so that no eplosive atmosphere can penetrate the enclosure. At the same time, the enclosure serves as weather protection. The continuous forces of the actuators according to T.13-1 appl to ambient temperatures of 5 C. With increasing temperature the actuator force decreases. With an increase of the ambient temperature from 5 C to C the possible continuous force of the actuators is reduced b 11 %. Due to the reaction process in the pipe reactor, however, this shows a constant temperature of C. In order to keep the heat transport from the pipe in the enclosure of the AVA and thus the ambient temperature of the actuators low, the support has been designed as a clam-shell construction. This leads to a radial air gap of 36 mm (cf. F.13-7d) which is divided onl at the upper and lower side of the support b four cross beams at a time. The contact surface of the cross beams in relation to the entire contact surface of the support to the piping sstem is.5 %. Concerning the fabrication of the AVA linear bearings, aes and heat sinks are provided as purchased parts. To protect them against corrosion, the support and enclosure are electro-galvanized and powder-coated. The other steel parts are chemicall nickel plated, aluminium parts are anodized. Basic data of the AVA T.13- Total mass (ecl. enclosure) Moving mass Mass enclosure Actuator travel (peak-peak) Resulting actuator travel Resulting continuous force Resulting peak force m + m T = 17 kg m T = 7.5 kg m Geh = kg Q = mm A peak-peak A * = A Q, Q = 59 mm F = F = 656 N A * A Dauer,, Dauer A * A SV ma Fpeak,, = κ V U = N * onl applies to pure operation in -resp. -direction 7

10 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants In order to avoid local stress peaks at the piping sstem during the installation of the AVA, a 5 mm elastomer laer is applied between support and pipe. T.13- shows the resulting basic data of the AVA Initial Operation in the Chemical Plant The initial operation of the AVA in the chemical plant is carried out b utilization of the reactor at a capacit of 15 % of the nominal flow rate. The operating loads of the reactor are investigated at 5 measuring points in total. For this purpose, nine tri-aial acceleration sensors in combination with a 3-channel measurement sstem are used. The sensor positions are relocated twice; one measuring point remains unchanged as reference point for all measurement series. Installation of the AVA at the pipe reactor F.13- Rms-values of the vibration velocities: without AVA (left), with AVA (middle) and reduction of the rms-values b the AVA (right) F.13-9 z RMS ( q ) [mm/s] RMS ( q ) [mm/s] RMS ( q z ) [mm/s] Red [%] Red [%] Red z [%]

11 Initial Operation in the Chemical Plant 13-5 In order to record the actual condition, operating vibrations without AVA are measured first. Then the AVA is installed at the pipe reactor, see F.13-. First the measurement results in the time domain are evaluated. For this purpose the rms-values of the vibration velocities for the individual measuring points are calculated. The vibration velocities are obtained b integrating the measured accelerations. F.13-9 shows the rms-values with and without AVA in the area of the upper deflection. F.13-9 (right) shows the reduction of the rms-values b the AVA. In the area of the highest vibration level at the deflection, the rms-values are reduced b up to 3 %. With increasing distance to the deflection, both the vibration level and the reduction effect of the AVA decrease. Generall, a global reduction of the vibration velocities in all directions in space can be recognized. There are onl few points where a slight increase of the vibration velocities is observed, but these points generall have a low vibration level. F.13-1 shows the evaluation of the measurement results in the frequenc domain, considering the amplitude spectra of the vibration velocities in - and -direction at the Amplitude spectra of the vibration velocities: at the location of the absorber (above) and in the middle of the deflection (below) At the location of the absorber F activated control RMS = 17. mm/s de-activated control RMS = 1.17 mm/s 1 activated control RMS = 1.73 mm/s de-activated control RMS =.7 mm/s Q [mm/s] 6 6 Q [mm/s] In the middle of the upper deflection 1 1 without AVA with AVA RMS = 6.1 mm/s RMS = 1.9 mm/s 1 1 without AVA with AVA RMS =.3 mm/s RMS = 19. mm/s Q 9 [mm/s] 6 Q 9 [mm/s]

12 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants Operation deflection shapes with and without AVA (non-proportional representation) F f = 9. Hz f = 19. Hz f = 6. Hz without AVA with AVA location of the absorber with activated or de-activated control, as well as in the middle of the deflection with and without AVA as an eample. The amplitude reduction in the range of the resonance points is clearl recognizable. The highest reduction can be observed in -direction in the range around 9. Hz. Here an amplitude reduction of appro. 6 % can be observed. Vibrations are reduced in the whole frequenc range considered. Clear amplitude reduction can also be recognized in the ranges of 19. Hz and 6. Hz. The related operation deflection shapes with and without AVA are shown in F Nevertheless, the clear resonance of the deflections in the upper area of the pipe reactor as well as the effect of the AVA can be recognized. In -direction, less vibration reduction than in -direction can be observed, which is due to the absence of concise resonance points Conclusion The effect of the AVA with two degrees of freedom and joint reaction mass under real operating conditions at the pipe reactor of a chemical plant could be proved. The numerical analses show that a comparable vibration reduction b means of passive absorbers can be achieved onl b appling much higher reaction masses; in addition to that the effect is principall limited to the range of the vibration-absorbing frequenc. The absorber was installed in the area of the highest vibration level. Here the advantage of the AVA compared to visco-dampers could be clearl shown, since no fied support is required. The results of the eperimental investigations can be considered ver positive, particularl in comparison with the measures taken in the past to reduce the vibrations of the pipe reactor. 9

13 AVA becomes ADD.Pipe from the Research Project IRIS to a Product AVA becomes ADD.Pipe from the Research Project IRIS to a Product In the core of the European Union s efforts epressed in the Lisbon Strateg is the so-called knowledge triangle with the corner points research, education and innovation. Based on those corner points the EU tries to become the most dnamic competitive knowledge-based econom in the world. Therefore, within the Seventh Framework Programme, the goals of growth, competitiveness and emploment have become a primar concern. This is even more important in the current economic situation which underlines the great importance to finall develop engineering services, new products etc. after a successfull terminated R&D project. One important outcome of IRIS was the above described AVA, which was further developed after the IRIS project. With the further development, AVA changed its name to ADD.Pipe, which is the acronm for Active Damping Device Reducing Vibrations of Pipes. More important than the name change was the fact that the design was changed, too. Now ADD.Pipe is a patented and scalable product to solve 1D, D and 3D vibration problems. Due to the mass and size of the vibrating structure, several actuators can be combined either in one, two or three directions. ADD.Pipe can not onl be used for piping sstems, but also for other structures with problems with broadband vibrations. ADD.Pipe can handle changing frequencies and needs no fied support to act against. It can be adapted to the vibrating structure when the vibration problem occurs. Compared to passive absorbers, considerabl less reaction mass is necessar. However, the reduction of amplitudes is much higher with ADD.Pipe than with a passive tuned mass absorber, which can onl reduce one frequenc. Acting directions of ADD.Pipe : 1D, D or 3D F D D 3D 91

14 13 IRIS Active Vibration Absorber (AVA) for Vibration Reduction at Piping Sstems in Chemical Plants ADD.Pipe for 1D with mounting and thermal isolation. The open cover allows a glance to the reaction mass with the Wölfel-Logo F Reference Engelhardt, J., 1. Aktiver Tilger zur Schwingungsminderung von Rohrleitungssstemen im Anlagenbau. Darmstadt, German. 9