CN1526792A - Engineering design method for thermal stress caused by dynamic interface and coke cooling water flow rate in coke tower - Google Patents
Engineering design method for thermal stress caused by dynamic interface and coke cooling water flow rate in coke tower Download PDFInfo
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- CN1526792A CN1526792A CNA031069673A CN03106967A CN1526792A CN 1526792 A CN1526792 A CN 1526792A CN A031069673 A CNA031069673 A CN A031069673A CN 03106967 A CN03106967 A CN 03106967A CN 1526792 A CN1526792 A CN 1526792A
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Abstract
The present invention is the calculation method of thermal stress caused by dynamic interface on wall of coke tower and the engineering design method of coke cooling water flow rate. By means of dynamic coordinate system, the dynamic boundary work state of liquid interface climbing along tower wall in some speed is simulated, and the 2D temperature field and stress and strain field in wall are calculated in limited elements. The research model for reflecting the quantitative relationship among material feeding flow rate, interface raising speed, tower wall temperature field, tower wall thermal stress and tower plastic strain and deformation is established. Research shows that the coke cooling water flow rate and axial temperature gradient are in approximately exponential relation, that the tower deformation has one sensitive temperature range, and that the flow rate should be controlled in first small flow rate and then great flow rate mode.
Description
The present invention relates to the thermal stresses calculating method that delayed coking unit coke drum dynamically cold (heat) interface causes and the engineering design method of water flow rate during cooling.
Coke drum is the tower shape reactor of delayed coking unit in petroleum refining industry's secondary processing technology, per 48 hours (or shorter operating time) cyclical operation between normal temperature and about 495 ℃, during successively finish once circulation through main operational phases such as oil gas and steam preheating, oil-feed green coke, cold Jiao of water inlet.Field measurement shows, has a very complicated three-dimensional temperature field with the operating procedure respective cycle on the tower wall, correspondence the 3-D stree field that round-robin is very complicated, this temperature field and stress field all are very unbalanced and very unsettled.
From investigation report both domestic and external, no matter be carbon steel, carbon molybdenum steel or chromemolybdenum steel material, also no matter the tower body lining is whether, coke drum all can occur distortion behind the some cycles in operation, comprises six kinds of the non-circular distortion etc. of the inclination and distortion of local deformation of unevenness, tower body integral body of treasured calabsh shaped distortion, the tower wall of bulging distortion, the cylindrical shell of shell ring or flexural deformation, cylindrical shell cross section.According to investigations, the autumn in 1988 had the appearance of five families obviously to be out of shape to the coke drum of domestic eight tame refinerys.The hazardness of distortion shows that mainly it finally can cause the thermal fatigue cracking of circumferential weld, secondly is the axial unstability that it may cause tower body.The distortion that how to prevent or control coke drum has become one of key of safety in production.
As far back as the fifties, people such as American scholar Weil N.A have proposed unit quenching factor (unit quenching factor by a large amount of investigation statisticses, abbreviation UQF) criterion that designs as preventing deformation, be the time (min) of cold water quenching when burnt of coke drum and the ratio of the coke output (t) of single tower, when UQF＞0.50, tower body expands and can ignore; When UQF＞0.80, there is not expansion in tower body.Desirable UQF=0.4 when the opening for feed position is on the manhole plate of bottom.In the design of domestic coke drum, the structure of slave unit is established a capital really to operational condition and has been considered above-mentioned factor, and often gets UQF=0.6～0.8 for the purpose of safety since the sixties.But the most Jiao Ta of China find still that after using certain hour bigger radially tension set is arranged, and domestic and international many scholars study, and do not see still that about the theory of coke drum water flow rate during cooling report is arranged.
In fact, the stress that causes except that interior pressure, medium-weight, deadweight etc. on the coke drum walls, the unrelieved stress of the thermal stresses that causes of the thermograde (radially, circumferentially, axially) that is caused because of the periodicity temperature cycle and welding when making in addition.Therefore, the stressed of coke drum is quite complicated, must the counter stress situation analyze.In-situ stresses method of determining and calculating process complexity, the expense height, and limited by field condition, and there are many technical problems again, inconvenience is used.The actual of problem is a four-dimensional problem that comprises the three-dimensional temperature difference and time dimension, and it is very difficult wanting to provide theoretically stressed exact value.
The present invention solves thermal stresses that coke drum dynamically cold (heat) interface causes and calculates the technical scheme that is adopted and be:
At first, problem is suitably simplified.Do not consider earlier the situation that circumferential temperature distributing disproportionation is even, computational problem is simplified to axisymmetric problem.As time goes on be the continuous rising at interface, being fixed on the system of coordinates U-O-V that moves on the face, with a face with initial point O shown in Figure 1 observes, after feed time is certain, near the face in the wall transient state temperature field tends towards stability, so just can handle the time dimension of problem by the height coordinate Z value that a face raising speed is converted into this temperature field, be this four-dimensional problem reduction two-dimensional problems finally.
Secondly, foundation finite element model as shown in Figure 2.The center of end socket can only be along moving axially, and the lower end of cylindrical shell can only be along radial translation, the radial dimension of shell ring is φ 2700 * 28mm, the long 488mm of hypomere shell ring, the long 988mm of epimere shell ring, the wide 24mm of weld seam, the pitch of weld is from model bottom 500mm, and the wall thickness direction is made seven five equilibriums by 8 nodes.Whole model is made up of 1957 eight ginseng unit such as node, 6456 of total nodes.Each time step of calculating is got the numerical value of 1 * E-2s grade, makes it and a face raising speed face of the simulating cell height of at every turn climbing that is complementary, and satisfies computational accuracy again.
Once more, the finite element model of being set up being carried out temperature field analysis calculates.In the calculating in order to simulate the rising of a face, the starting condition input of the modal position that need next time rise to each calculation result (data file) as a face, the temperature variations that the inside and outside wall of elemental height that a tracking collection face climbs and current height place is 4 is till this temperature value of 4 is stable.This is the stable temperature field of dynamic two dimension of asking.
The physical parameter that comes chosen material according to tower wall temperature and the medium temperature of this operational phase in the FEM (finite element) calculation.For example, in the fiercest water inlet process, the composition of tower shell material physical parameter has thermal conductivity K with variation of temperature
Shell=51.068-0.0098T-3 * 10
-5T
2W/mk, specific heat C
Shell=470.84-0.0823T+5 * 10
-4T
2J/kgk.As calculated, Re Jiao and cold water overall thermal equilibrated outlet temperature are about 70 ℃, i.e. the minimum temperature of coke cooling water face.Under the 0.3MPa design pressure, the boiling point of water is 133 ℃, i.e. the top temperature of coke cooling water.Therefore, between 70 ℃ and 133 ℃, calculate the cold temperature field of tower wall when burnt with different water temperatures.
At last, be that condition is carried out stress-strain analysis calculating to model with this temperature field.The Misess equivalent stress figure that 133 ℃ of coke cooling water interfaces cause at the circumferential weld place sees Fig. 3, Fig. 4 is seen in the equivalent plastic strain that the circumferential weld place causes in 70 ℃ of coke cooling water interfaces, at this moment, the wall internal-external temperature difference that about 20mm causes in the place below liquid level has reached 90 ℃, at subsurface 100mm place, the inside and outside wall temperature difference still reaches 60 ℃.Inside and outside wall maximum axial thermograde is respectively 10.8 ℃/mm and 1.06 ℃/mm.
The present invention about the technical scheme that engineering design method adopted of delayed coking unit coke drum water flow rate during cooling is:
At first, simulated the dynamic boundary operating mode that a liquid medium face that constant speed rises climbs along the tower wall in coke drum, its radial and axial two dimension instantaneous temperature field that causes in wall and stress-strain field carried out FEM (finite element) calculation by above-mentioned dynamic coordinate method.
Secondly, analyze the influence of discharge to the temperature field.For the face raising speed in the tower, ignore the influence of the variation heat exchanging coefficient of a face raising speed according to feed rate conversions different at the bottom of the big wisp tower of coke drum internal diameter, the length in temperature field is to the temperature difference and axial-temperature gradient when calculating different face raising speeds by aforesaid method again.Found that radial temperature difference does not change when different face raising speeds, and the relation of a face raising speed and axial-temperature gradient as shown in Figure 5.
Once more, determine the correct relation in flow and temperature field.From qualitative analysis as can be known, cold when burnt, though thereby bigger discharge can make the water in the tower contact the cold shock of tower wall stronger with inner wall of tower with lower temperature, less discharge can relax the intensive cold shock, but generally to radially not significantly influence of the temperature difference, but can produce bigger axial-temperature gradient on the contrary, at this moment, the control of water flow rate during cooling should be lower limit control.Occur the superpressure phenomenon and vaporize rapidly for fear of coke cooling water when forming too high interior pressures, the control water flow rate during cooling is necessary, and at this moment, the control of water flow rate during cooling should be that the upper limit is controlled.Therefore, the control of water flow rate during cooling should be interval control.
Reasonably operation should be the big again flow of first low discharge, rather than presses the low discharge operation from the beginning to the end.The upper limit index of low discharge is that the vapour pressure that feeding water is heated after the vaporization is no more than the permit operation pressure of cat head, otherwise tower body stress exceeds safety range; The lower limit index of big flow be feeding water when arriving the tower wall through hot coke layer its water temperature should be able to reach 133 ℃ of vaporization temperatures, otherwise a large amount of coke heats will just be vaporized steam and take away from cat head before feeding water arrives the tower wall.In the practice, under the prerequisite that the Monitoring and Controlling overhead vapours is pressed, can determine the higher limit of low discharge in about 0.5 hour of water inlet initial stage easily.To Fig. 5, (corresponding flooding velocity is 330m to the axial-temperature gradient of inner-wall surface being lower than the raising speed of 4mm/s
3/ hr) scope has the interval of a sensitivity, and water surface raising speed is relatively low greater than the axial-temperature gradient that this is worth inside and outside wall then, and corresponding flooding velocity can be used as the lower value of big flow.Analysis chart 5 theoretically, and the result of given example of the present invention shows that the axial-temperature gradient of water surface raising speed and inwall is similar to Δ T=20.83Q
-0.91Exponential relationship.
At last, analyze the oil-feed operating mode if use above-mentioned theory, because deep fat contacts with inner wall of tower with about 495 ℃ temperature all the time, thermal shocking does not have basic change to the size of its flow to tower wall radial, and bigger flow then helps the reduction of axial-temperature gradient equally.Radial temperature difference that the analysis revealed coke cooling water causes at Ta Bishang and axial-temperature gradient have determined all significantly greater than the oil-feed process how the preventing deformation emphasis of coke drum controls the thermal stresses in cold burnt stage.
By above-mentioned analysis, Weil quenching factor criterion has tangible odjective cause to the failure of China's coke drum practical advice, the present invention has creatively set up the research model of cause and effect quantitative relationships such as can intuitively reflecting feed rate, a face raising speed, tower wall temperature field, tower wall thermal stresses and tower body plastix strain distortion, and making has had clearly theoretical basis in the fifties by the empirical preventing deformation quenching factor that a large amount of investigation statisticses propose by people such as U.S. Weil N.A.
Claims (10)
1. the thermal stresses calculating method that causes at Ta Bishang about delayed coking unit coke drum dynamically cold (heat) interface and the engineering design method of water flow rate during cooling.Simulated the dynamic boundary operating mode that the liquid medium face that rises with certain speed climbs along the tower wall by dynamic coordinate method in coke drum, its radial and axial two dimension instantaneous temperature field that causes in wall and stress-strain field have been carried out FEM (finite element) calculation.Creatively set up the research model of cause and effect quantitative relationships such as can intuitively reflecting feed rate, a face raising speed, tower wall temperature field, tower wall thermal stresses and tower body plastix strain distortion.The result of given example of the present invention shows, the close seemingly Δ T=20.83Q of flow and axial-temperature gradient
-0.91Exponential relationship, tower body distortion has the water flow rate during cooling scope of a sensitivity, the control of flow should be the interval control of big flow again of first low discharge.The low discharge at water inlet initial stage is no more than interior pressure the allowable with the overhead vapours pressure and is as the criterion, and flooding velocity reaches 330m
3Behind/the hr, the axial-temperature gradient of tower wall is lower.Like this, making has had clearly theoretical basis in the fifties by the empirical preventing deformation quenching factor that a large amount of investigation statisticses propose by people such as U.S. Weil N.A, illustrate that also Weil quenching factor criterion has tangible odjective cause to the failure of China's coke drum practical advice, make engineering technical personnel can judge scientifically whether oil-feed (water) flow of a certain coke drum reality produces too big stress on the tower wall, thereby the control coke drum is operated in the security clearance scope.
2. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: simulated the liquid alternating temperature medium face that rises with the certain speed tower wall dynamic boundary operating mode of climbing vertically in pressure vessels for the chemical industry by dynamic coordinate method, its radial and axial two dimension instantaneous temperature field that causes in wall and stress-strain field are carried out FEM (finite element) calculation.
3. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: thus the dynamic interface of temperature variation is flowed the radial and axial two dimension instantaneous temperature field that causes and stress-strain field when carrying out FEM (finite element) calculation vertically in wall in pressure vessels for the chemical industry, it is vertical vertical like this that this pressurized vessel both can resemble coke drum, also can resemble two saddle storage tanks is that level is horizontal, or tilt to install.
4. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: thus the dynamic interface of temperature variation is flowed the radial and axial two dimension instantaneous temperature field that causes and stress-strain field when carrying out FEM (finite element) calculation vertically in wall in pressure vessels for the chemical industry, this pressure vessels for the chemical industry both can be a pressurized vessel, also can be spherical vessel or equal diameter pressure pipeline, become the diameter pressure pipeline.
5. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: thus the dynamic interface of temperature variation is flowed the radial and axial two dimension instantaneous temperature field that causes and stress-strain field when carrying out FEM (finite element) calculation vertically in wall in pressure vessels for the chemical industry, can simulate situations such as whether being with the manhole adapter on the wall thickness change of this pressure vessels for the chemical industry or the wall by the variation of wall geometry in the finite element model.
6. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: thus the dynamic interface of temperature variation is flowed the radial and axial two dimension instantaneous temperature field that causes and stress-strain field when carrying out FEM (finite element) calculation vertically in wall in pressure vessels for the chemical industry, can simulate dynamic interface by the change direction of a temperature loading starting condition and limit condition in the finite element model is to rise to change or descend to change, and medium is to flow left or flow to the right in other words.
7. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: thus the dynamic interface of temperature variation is flowed the radial and axial two dimension instantaneous temperature field that causes and stress-strain field when carrying out FEM (finite element) calculation vertically in wall in pressure vessels for the chemical industry, can be by cell height in the finite element model progressively change the variation simulate the dynamic interface lift velocity, the variation of flow just.
8. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: thus the dynamic interface of temperature variation is flowed the radial and axial two dimension instantaneous temperature field that causes and stress-strain field when carrying out FEM (finite element) calculation vertically in wall in pressure vessels for the chemical industry, both can simulate the container material changes of properties, also can simulate the multifarious variation of container inner medium layers of material by the medium variations of physical parameters that is applied in the finite element model on the inside and outside wall unit node by unit physical parameter and functional relationship of temperature in the finite element model.
9. the thermal stresses calculating method that coke drum according to claim 1 dynamically cold (heat) interface causes at Ta Bishang, it is characterized in that: thus the dynamic interface of temperature variation is flowed the radial and axial two dimension instantaneous temperature field that causes and stress-strain field when carrying out FEM (finite element) calculation vertically in pressure vessels for the chemical industry, the diversity variation that can simulate container withstand temp and combined loads such as concentrated force, face power or moment of flexure by the variation that is applied to the external load on the inside and outside wall unit node in the finite element model in wall.
10. the engineering design method of water flow rate during cooling according to claim 1, it is characterized in that: the research model of creatively having set up cause and effect quantitative relationships such as intuitively to reflect feed rate, interface raising speed, tower wall temperature field, tower wall thermal stresses and tower body plastix strain distortion by dynamic coordinate method, make engineering technical personnel can judge scientifically whether oil-feed (water) flow of a certain coke drum reality produces too big stress on the tower wall, thereby adjusting process, avoid the tower body damage, the control coke drum is operated in the security clearance scope.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105512396A (en) * | 2015-12-08 | 2016-04-20 | 武汉工程大学 | Stability limit design method of coke tower pressure bearing casing |
| CN111504244A (en) * | 2019-01-30 | 2020-08-07 | 中国石油化工股份有限公司 | Detection method and detection system for in-place state of submarine pipeline |
| CN113108962A (en) * | 2021-04-12 | 2021-07-13 | 南京金创有色金属科技发展有限公司 | On-line monitoring technical method for high-temperature stress of coke tower |
-
2003
- 2003-03-06 CN CNA031069673A patent/CN1526792A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105512396A (en) * | 2015-12-08 | 2016-04-20 | 武汉工程大学 | Stability limit design method of coke tower pressure bearing casing |
| CN111504244A (en) * | 2019-01-30 | 2020-08-07 | 中国石油化工股份有限公司 | Detection method and detection system for in-place state of submarine pipeline |
| CN113108962A (en) * | 2021-04-12 | 2021-07-13 | 南京金创有色金属科技发展有限公司 | On-line monitoring technical method for high-temperature stress of coke tower |
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