COMPUTATIONAL METHODS IN ENGINEERING AND SCIENCE
EPMESC X, Aug. 21-23, 2006, Sanya, Hainan, China
©2006 Tsinghua University Press & Springer
Finite Element Analysis of a Coal Liquefaction Reactor during Lifting
Z. B. Wang 1*, Y. F. Luo 1, R. Yu 1, X. Liu 1, S. H. Zou 2
1
2
College of Civil Engineering, Tongji University, Shanghai, 200092 China
ShenHua Coal Liquation Co. Ltd., BeiJing, China
Email: [email protected], [email protected]
Abstract: The lift project of shenhua direct-coal-liquefaction reactor ranks the largest one among the pressure vessels
in china at present. The stresses of the reactor during lifting are analyzed using finite element method. Based upon the
results, the safety assessment of the reactor and additional lifting structure members is conducted according lifting
schemes. Several important positions are investigated in the equipment including the manway neck of the reactor, the
lifting cover, the skirt and the base ring. Typical situations are selected to cover the entire lift procedure, which include
horizontal lifting position, 45-degree decline lifting position and vertical lifting position. After evaluation, the
conclusion can be made that the lifting scheme adopted currently is unsafe for the equipment and it should be updated.
Keywords: lifting scheme, finite element model, coal liquefaction reactor, safety assessment
INTRODUCTION
The lift project for shenhua direct coal liquefaction reactor ranks the largest one among the pressure vessels in china at
present. To ensure the safety of the vessel when lifting, it is necessary to simulate the actual mechanism during the
lifting procedure. The finite element analysis is performed to get the stress status of the typical positions, based on
which to evaluate the reactor’s saftey.
The liquefaction reactor (Fig. 1) to be lifted is the heaviest one in china. It weights 20601kN. The reactor is composed
of the upper manway hole, the upper cover head, the main body, the lower cover head, the skirt and the base ring from
the top to down. Its length is about 60m, which includes 34.5m of the main body and 19.6m of the skirt. The shape of
the reactor is a long pipe approximately. The outer diameter of the main body is 5.48m. On the two ends of the main
body are the upper cover head and the lower cover head with 200mm in thickness. The thickness of the main body
pipe, skirt and the base ring are 334mm, 80mm and 110mm respectively. The material of all parts are mid steel. These
parts are all welded together in factory.
Figure 1: The shape of the reactor
Table 1 The main parameters of different steel for different parts
Position
Lifting cover
Manway neck
Bolt
Skirt
Yielding stress
(MPa)
690
415
655
285
Weight (kN)
Elastic module
(MPa)
20601
2.06E5
The Table 1 gives the main parameters of materials of different corresponding parts of the reactor.
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LIFTING SCHEME
Since the reactor should not be welded at all after manufacture according to the request, the lifting ears are located on
the top of the reactor. The skirt bottom is placed on tailing lugs. The tailing lugs are hinged on a trailer. When lifting,
the crane pulls the lifting cover vertically. The trailer goes forward according to the crane lifting procedure passively.
Since the skirt bottom is partially supported on the tail lugs, two I-steels are welded at the skirt bottom. The members
to be investigated include each part of the reactor, the lifting cover and tailing lugs.
NUMERICAL SIMULATION MODEL
The lifting analysis is performed using finite element method. For computation convenience, the boundaries of the
model are supposed rigid, which is different from the actual elastic boundaries. Therefore the boundaries and their
neighbor area are not the same as the actual case. The calculation results around boundaries will be different from
actual ones. For this reason, the investigating area should not include the boundary area. In the following analysis, the
3D model of the reactor lifting system is created, which includes the lifting cover, reactor and tailing lugs together. The
effects of each part on others can be simulated. Since the reactor and the lifting structure are symmetrical about the
vertical axis, only half of the structure is included in the numerical model to simplify the simulation procedure. After
symmetry simplification, the 3D model of half structures created and shown in Fig. 2.
It is necessary to simplify the whole lifting procedure firstly before analysis. During the lifting, the change of the
stresses in the structure is monotonic and continuous. The speed of lifting is much slow and smooth. Therefor, several
typical lifting positions can be computed for representing the simulation of all lifting procedure. The static analysis can
satisfy the engineering precision. From this point of view, only three typical lifting positions, horizontal lifting
condition, 45 degree lifting condition and vertical lifting condition, are considered and computated for describing the
lifting procedure.
In the analysis, the hole center of the lifting cover is hinged vertically. The bottom of the tailing lugs is hinged
universal.
Figure 2: Analysis model
1. Finite elements adopted Considering the calculation time and the computer memory capacity, the total number of
nodes should be limited to an acceptable amount. The several kinds of elements are adopted, such as brick element for
lifting cover and manway neck, shell element for skirt and base ring, beam element for bolts, braces and tailing lugs.
2. Mesh of the structure In order to obtain precise stress distribution, the main body of the reactor is meshed into
brick elements. The shape of the lifting cover, manway neck is much complex. They are difficult to be meshed into
brick elements directly. These complicated parts are firstly divided into several small hexahedrons connected at
interfaces respectively. The division of the parts are shown in fig 3. Then all these parts can be meshed directly. The
total number of nodes is 33192 and the element number is 26249. Parts of the structure mesh are shown in fig 4.
Figure 3: Divided parts of the upper head
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Figure 4: Elements plotting
3. Load application The load in lifting analysis is only self weight of the reactor system. When applying standard
acceleration of gravity, it is found that the total vertical reaction is not equal to 10300kN, the half total weight of the
reactor. After careful investigation, it is found that the finite element model only includes the reactor structural parts
without other accessories. Therefore the weight of the theoretical model is lower than the actual weight. To solve this
problem, a magnifying coefficient is multiplied to the standard acceleration of gravity. This coefficient is equal that the
exact actual weight is divided by the theoretical weight of the model.
4. Boundaries Just as the former discussion, it is important to simulate the boundaries of the model reasonably. In this
model, a universal hinge on the tailing lug is actually reflected in the model. It is simple enough to apply constraints on
the node directly. A vertical hinge is located at the hole center of the lifting cover. There is no corresponding node in
this hinge. The boundaries can be simulated by two methods as shown in fig5, fig6. In fig5, the radiative straight line
elements are used to connect the surface and the center of the lifting hole. The lifting cover can rotate around the center
as the actual case. In fig6, several single-direction hinges constrain the nodes of the hole surface. At the same time, all
reactions of the hings go through the center of the hole.
After the numerical analysis and comparison, the method in fig5 is the better model for lifting simulation. It is used for
the final lifting simulation of the reactor.
Figure 5: The boundary simulation (model 1)
Figure 6: The boundary simulation (model 2)
EVALUATION METHOD
During judgment, because yielding characterizes the destroy of the steel material, the intensity stresses are taken as the
controlling stress. The safety factors are introduced according to the “Unified standard for reliability design of building
structures” (GB50068-2001).
The first step is to define the design strength according to the yielding stress of different steel. The material reducing
factor is 1.111 based on code GB50017-2003.
The second step is to get the design stress σ. Since the dominant load is gravity, the load factor is 1.35 based on code
GB50017-2001. After the finite element analysis, the calculating intensity stress σint can be gained.
The third step is to compare the design stress σ with the design strength and evaluate the safety.
RESULTS AND DISCUSSION
The analysis is performed using finite element analysis computer program ANSYS. From Fig. 7, It can be observed
that the bending of straight pipe obeys the plane assumption. The stress of this part can also be manually calculated as
a beam. The stress in the pipe is much smaller than the design strength.
The geometric change from manway neck to reactor body is not smooth. The stress in this area can’t disperse to the
straight part directly. Hence the stress of the manway neck is extraordinary large.
Compared with each other, it can be concluded that the horizontal lifting condition is the unfavorable and critical
position, while the manway neck is the controlling part.
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Figs. 8-13 show the intensity stresses of several areas of the structure in horizontal lifting condition.
Figure 7: Intensity stresses of the straight pipe
Figure 8: Intensity stresses of the lifting cover
Figure 9: Intensity stresses of the manway neck (view 1)
Figure 10: Magnifaction of the manway neck
Figure 11: Intensity stresses of the manway neck (view 2)
Figure 12: Intensity stresses of the base ring
Fig 13: Intensity stresses of the connection between the lower head and the skirt
For each part of the reactor, the allowable stresses are listed in table 1. The maximum stress of typical conditions in
table 2.
Table1 The allowable stress[σ] (N/mm2)
Position
Allowable stress
Lifting cover Manway neck
621
374
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Connection between
Base ring
the lower head and skirt
257
257
Table 2 The maximum calculating stress σint (N/mm2)
Position
Lifting cover
Manway neck
Horizontal
428
535
Connection between
the lower head and skirt
189
45-degree
352
421
128
94
Vertical
352
139
4
2
Base ring
153
The maximum stresses in the Table 2 multiply the load factor 1.35. Then the corresponding design stress σ can be
gotten, listed in Table 3.
Table 3 The maximum design stress σ (N/mm2)
Position
Lifting cover
Manway neck
Connection between
thelower head and skirt
Base ring
Horizontal
578
722
254
207
45-degree
475
568
172
127
Vertical
474
188
5
2
The safety evaluation of the lifting system can be conducted after comparision of table1 and Table 3.
The maximal stress of the lifting cover occurs around the bolt hole and the hinged hole. The stresses in other places are
always small. It can be noticed that the maximum stress of 578N/mm2 is smaller than the allowable stress of
621N/mm2. It is safe for this place.
The maximal stresses of the manway neck in horizontal position and 45 degree position are 722N/mm2 and 567N/mm2
respectively. They are all larger than the allowable stress of 373N/mm. It can’t meet the need of safety.
The maximal stress of the connection between the below head and the skirt is 254N/mm2. It is smaller than the
allowable stress of 257N/mm2. It is safe for this place.
The maximal stress of the base ring at the end of the skirt is 207N/mm2. It is smaller than the allowable stress of
257N/mm2. It is safe for this place.
CONCLUSION
The conclusion can be made that the lifting scheme adopted currently is unsafe for the equipment. The alternative one
updating of the original scheme should be proposed.
From the analysis, it is known that the manway neck is the controlling part for the lifting process. The bending moment
of this place should be reduced. It will be an effective measure to reduce the distance between the lifting point and the
manway neck.
Acknowledgements
The project presented herein was funded by the ShenHua Coal Liquation CO. LTD. The relative staffs provide great
help to complete this research. The authors would like to thank ShenHua Coal Liquation CO. LTD. for their
cooperation.
REFERENCES
1. Ministry of Construction P. R. China. Unified Standard for Reliability Design of Building Structures GB500682001. Building Industry Press, Beijing, China, 2001.
2. Sun XF, Fang XS, Guan LT. Material mechanics. Higher Education Press, BeiJing, China, 1998 (in Chinese).
3. Structural Analysis Guide (ANSYS Release 5.7). ANSYS Inc.
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