1、 Preface
In the flue, air duct, raw coal, pulverizing, pulverized coal feeding pipe and other flue, air and pulverized coal pipes, the temperature of the medium inside the flue and hot air duct is relatively high. When the pipe expands when heated and shrinks when cooled, it will produce a force on the connected equipment. On the contrary, the equipment will also produce a reaction force on the pipe and cause stress in the pipe. The flexibility of the pipeline itself can make the thermal expansion amount self compensated to a certain extent. However, if the self compensation capacity of the pipeline is insufficient, there will be a strong thermal stress in the pipeline, the fixed supports at both ends of the pipeline will bear a serious thrust, and the nozzle of the equipment connected to the pipeline will also bear a certain amount of additional stress, leading to deformation or damage of the pipeline. The compensator can be set on the pipeline to compensate the thermal elongation of the pipeline and absorb the expansion of the pipeline.
2、 Thermal expansion of pipe section
1. Function of compensator
There are many types of compensators, and the application of corrugated compensator is the most common. Whether corrugated compensator, rotary compensator, sleeve compensator or square natural compensator, they are all set to ensure the safe operation of the pipeline. Generally speaking, they have the following four main functions: first, the compensator compensates and absorbs the axial, transverse and angular thermal deformation of the pipeline. 2、 The compensator has good expansion and contraction, which reduces the difficulty of valve pipe installation and disassembly, and is very convenient. 3、 The compensator can absorb equipment vibration and reduce the impact of equipment vibration on the pipeline. 4、 The compensator can absorb the deformation of pipeline caused by earthquake or ground subsidence.
In addition, it is worth mentioning the square natural compensator, which has two important functions: first, when the pipeline passes through the foundation beam or basement wall, the installation of the square compensator can greatly reduce or even avoid the pressure on the pipeline caused by the settlement of the foundation. 2、 If the thermal pipeline is too long, the installation of square compensator can greatly reduce the stretching of the pipeline caused by thermal expansion and cold contraction.
2. Calculation method of thermal expansion of pipe section
The pipeline installation is usually carried out at room temperature. When the temperature of the heating medium in the pipeline and the surrounding environment changes, the expansion and contraction of the pipeline will occur. In order to make the pipeline stable and safe in the thermal state, the thermal elongation of the pipeline when heated requires special attention and accurate calculation. During the production and operation of the equipment, the high temperature medium in the pipeline causes the pipe section to expand when exposed to heat. This thermal expansion value can be calculated according to the following formula:
Δ l=La Δ t
In the formula, Δ L represents the thermal expansion value of the pipe section, in mm. L represents the projected length of the pipe section, in m. A represents the linear expansion coefficient of steel, in mm/(m ·℃) mm. Δ T is the difference between the operating temperature and the installation temperature, in ℃.
3. Application examples
For example, in a pipeline project, the design temperature of the hot air duct is 320 ℃, the installation temperature is 20 ℃, the Q235A air duct material is selected, and the spacing between the fixed supports at both ends of the pipeline is 16 meters. From these values, the thermal expansion value that can be generated during the production and operation of the pipe section can be calculated.
First of all, we can check the average linear expansion coefficient data table of commonly used domestic steel. It can be found that the linear expansion coefficient of Q235A steel is 0.013mm/(m · ℃).
Then according to the above formula, we can calculate the thermal expansion value as
Δ l=La Δ t=10 × zero point zero one three × (300-20)=39mm
According to the above calculation results, we can know that under this working condition, we need to select a universal compensator with compensation greater than 39mm to fully absorb the thermal expansion of this pipe section.
3、 Application of compensator
1. Calculation of compensation amount
The compensator can be used as axial compensation or lateral compensation alone, but the effect is not very good when it is used as angle compensation alone. However, in the practical engineering project design, the compensator usually acts as the angular compensation at the same time in the application, that is, in the axial compensation, lateral compensation and angular compensation, the compensator absorbs any two compensation quantities at the same time, and occasionally even the whole three compensation quantities. In such applications, the selection of axial compensation amount, lateral compensation amount and angular compensation amount of the compensator should meet the following relationship:
X1+XY1/Y+Xa1/a≤X
In this relationship, X represents the compensation amount when axial compensation is performed alone, Y represents the compensation amount when lateral compensation is performed alone, and a represents the compensation amount when angular compensation is performed alone. X1 represents the actual value of simultaneous axial compensation, Y1 represents the actual value of simultaneous vertical compensation, and a1 represents the actual value of simultaneous angular compensation.
2. Absorption of compensation amount
When the angular change is small, the above formula can be used for calculation. However, when the angular change is large, it is necessary to pre compress and bias the compensator during installation to absorb the compensation amount.
The interface of the primary hot air duct of a boiler in a certain project expands with the rise of furnace temperature in the horizontal direction. The change value of the expansion amount is 140 mm downward in the vertical direction, and the displacement in the other two directions is 10 mm. The distance between the central line of the primary hot air header and the flange face at the inlet of the hot air duct is only 2600 mm. Through checking the compensator samples, it is found that the compensator that can be installed horizontally and meet the requirements of 140mm in the vertical direction is too long to meet the installation requirements of this project. Therefore, the compensator is pre compressed and biased to absorb its expansion.
The cold installation of the connection between the primary hot air duct and the boiler hot air duct inlet is shown in Figure 1. During cold installation, the center line of the compensator is installed 75mm upward relative to the center line of the hot air duct. When the boiler is in normal production and operation, the inlet pipe section of the hot air duct expands downward, and the compensator will move with it. The final form of hot operation is shown in Figure 2.
Fig. 1 Cold Installation of Connection between Primary Hot Air Duct and Boiler Hot Air Duct Inlet
Fig. 2 Final form of hot operation of the connection between the primary hot air pipe and the inlet of the boiler hot air duct
After precompression and eccentric installation of the compensator, the amount of lateral compensation that originally needed to be greater than 140 mm is greatly reduced and disassembled. As long as the amount of lateral compensation of the compensator can reach 75 mm, it is enough to meet the installation requirements. On the one hand, it solves the constraints and restrictions on the installation space, and on the other hand, it saves the investment cost of the compensator.
4、 Selection Skills of Compensator
1. Selection of non-metallic compensator and metal compensator
The non-metallic compensator is made of high temperature resistant material, while the metal compensator is made of wear-resistant material. The medium temperature inside the flue and hot air duct is relatively high, and the compensator may be burned through. In order to prevent this problem, non-metallic compensator made of high temperature resistant materials is usually used. As for the hot air pulverized coal conveying pipeline, there is a certain amount of pulverized coal particles in such pipeline. Therefore, when setting the compensator, it is necessary to consider not only meeting the above thermal compensation requirements, but also the anti-wear ability to extend its service life as far as possible. At this time, it is appropriate to choose a metal compensator made of wear-resistant materials.
Equipment interface for vibration isolation
The compensator can effectively absorb the expansion of the pipeline and the vibration of the pipeline, so it can be used on the equipment interface that needs to isolate the vibration. For example, the pipeline connected with the inlet and outlet of the fan has frequent and large vibration, so a compensator can be installed at the inlet and outlet of the fan, and then connected to the air duct to help absorb the vibration of the pipeline caused by the fan's own operation, so as to reduce the vibration of the entire pipeline system. In addition, it can effectively prevent the load on the pipeline from transferring to the facilities and equipment, so as to protect the facilities and equipment.
Selection skills
The compensator usually adopts rectangular section. For the round corner waveform, a single expansion joint in the pipeline needs to bear two-dimensional displacement. The elbow pipe composed of two expansion joints can withstand three-dimensional displacement. Rectangular round metal corrugated expansion joints are available in full height and half height types. Although the constraints in various aspects are relatively complex, no matter what kind of pipe system, several fixed supports can be used and set at different parts, so that they can be decomposed into several relatively simple single pipe sections. In this way, the deformation and compensation amount of each pipe segment can be determined separately, which can be completely equivalent to the deformation and compensation amount before treatment. There are many kinds of compensators, so it is necessary to select them reasonably and correctly. In the overall design of the flue gas, air and pulverized coal pipeline, the pipeline direction and the design of the support system shall be fully considered, and the shape and configuration of the compensator shall be comprehensively considered to achieve the best combination of safety, rationality, applicability and economy.
5、 Conclusion * * 852
With the continuous progress of modern civilization, the rapid development of science and technology, the technology of compensator is also constantly improving, its forms are constantly increasing, and the functional application is also constantly expanding and improving, to compensate for the axial, horizontal and angular cold and hot deformation of the absorption pipe. In the design of flue gas, air and pulverized coal pipeline, compensator shall be set on the pipeline to compensate the thermal elongation of the pipeline, so as to reduce the stress of the pipe wall and the force acting on the valve or support structure. The standard specifications and requirements of compensator shall be used accurately, and appropriate installation form of compensator shall be selected and used reasonably to help better realize the compensation effect of thermal expansion of the pipe section and reduce the vibration of flue gas, air and pulverized coal pipeline in production, In order to avoid the phenomenon that the compensator is pulled out.
