The number provides a basis for the feasibility and reliability of long-distance heating. : Computer Aided Design Heating Pipeline Calculation 0. In order to save energy, improve energy utilization, and protect the environment, some small power plants will be shut down or changed to thermal power plants, and the original thermal power plant will also expand the heating range. Thermal power plants use high temperature and pressure steam to generate electricity, while low temperature and low pressure steam are used to supply heat, which can make better use of energy and improve economic efficiency. Moreover, it is possible to adjust between power generation and heating to better adapt to market needs.
An important part of expanding the heating range is the design of the heating pipes. At present, the heating range of thermal power plants is generally within 5km. To increase the range of heating, whether the steam outlet temperature and pressure meet the requirements, whether there is steam condensation, careful design calculation must be carried out. Since there are many factors influencing the calculation of flow and heat transfer, and there are many parameters that can be changed by design, it is necessary to compile the calculation process into a computer calculation in the design calculation, which can save a lot of time and effort. Especially when performing multiple calculations, the best design data in the operating conditions can be obtained to ensure the feasibility and reliability of the heating system.
1 calculation principle and computer program design and calculation of heating pipeline, the principle is the calculation of flow resistance and heat transfer calculation of insulation material. The amount of steam flowing affects the heat of the heat source, which in turn affects the speed and resistance of the flow through the steam parameters. Among the influencing factors are the material of the piping system, the pipe diameter, the local resistance of the pipe arrangement, the performance of the insulation material and the thickness of the insulation layer, as well as the influencing factors of the operating parameters, such as inlet steam parameters, ambient temperature, and external heat dissipation conditions.
In programming, the thermal property parameters of water and water vapor should be expressed by theoretical formula or by an empirical formula in a certain range. These parameters of the helium and specific volume of superheated steam and saturated steam can be compiled into several sub-functions for the main function to call. The relationship calculation and judgment between parameters are completed in the main function.
The calculation in the main function is to first assume the outlet pressure and the outlet temperature. Taking the average value of the inlet and outlet pressure and temperature as the characteristic parameters of the steam, calculating the total thermal resistance of the pipeline and the temperature difference between the inside and the outside to obtain the heat dissipation amount, and reducing the heat dissipation by the inlet steam å³ is the outlet ç„“, according to the enthalpy and outlet pressure of the outlet The outlet temperature can be calculated, and if compared to the assumed value, if the difference exceeds the allowable error range, the above calculation process is repeated with the calculated value as the assumed temperature of the outlet until the calculated value and the assumed value are approximately equal within the allowable error range. The pressure drop of the steam in the pipe is calculated again to obtain the outlet pressure, which is also compared and iterated until the assumed value is approximately equal to the calculated value. According to the outlet temperature and pressure, it is judged whether the steam is wet steam. If the humidity of the steam is calculated based on the enthalpy and the heat of vaporization, the specific logic block diagram of the program is shown.
Computational Program Logic Block Diagram Strictly speaking, the thermophysical parameters of water vapor should all be calculated using the International Steam Characterization Conference (ICPS). Due to the complexity of the calculation formula, we only adopted the industrial IFC formula adopted by the Sixth International Water Vapor Conference in the middle and low pressure areas for superheated steam enthalpy and dynamic viscosity. The empirical formula for the density of superheated steam: saturated mushroom steam. Lit mining formula. A: The formula of saturated steam culture is: 2 Calculation example The existing heating pipeline of Shaoxing Chengdong Thermal Power Plant is 3. 8km, and the plan is extended to 9km, and the design parameters and operating parameters of the pipeline are obtained. The pipe starts at 3.8km with a diameter of 0325mm. The insulation materials are rock wool and microporous osmanthus, respectively. The thickness is 6cm and 8cm. The factory steam pressure is 1.5MPa, the temperature is 300C. The heat dissipation condition is the ambient temperature lC at moderate wind speed, convection. The heat release coefficient is 8.26 W/(m2.K). The pipe arrangement resistance coefficient is known.
The diameter of 2km is calculated. The outlet steam pressure and temperature at different steam flows were calculated under the conditions of the thickness of the insulation material and the first 3.8 km. For the relationship between outlet steam pressure and steam dryness and steam flow. It is the relationship between steam temperature and steam flow.
The calculation results show that the larger steam pressure can achieve the relationship between steam pressure and dryness and flow rate. The relationship between steam temperature and flow rate. The relationship between steam temperature and flow when the insulation layer is thickened. 3 Conclusion) Computer-aided design calculation can save a lot of money. Time, the steam outlet parameters for long-distance heating under different conditions are obtained. It can meet the feasibility and reliability of long-distance heating pipeline design.
The calculation results show that the reduction of heat loss is mainly due to the increase of the thickness of the insulation layer, and the pipe diameter can be appropriately reduced when the flow rate is not large.
In the calculation example, the steam with a flow rate less than 15t/h will not cause steam condensation, and the steam pressure greater than 35t/h will not be too low, and it needs to be transported in a larger pipeline, and the heat preservation is greatly improved. This shows that the larger the flow range, the higher the technical and process requirements. Or use technical measures such as electric heating.
Zhang Tongxiang male. 21 years old. Undergraduate students entered the Department of Energy Engineering of Zhejiang University in 1997. The professional is for the thermal power unit*, but the insulation thickness is not enough. At a small flow rate, the steam temperature does not meet the requirements. At flow rates less than 20 t/h, the flow rate decreases and the steam temperature increases instead. This is because the smaller the flow rate, the smaller the flow resistance and the larger the outlet vapor pressure, and the corresponding saturation temperature is also higher. It can be seen from the change in steam dryness that the steam dryness becomes small at a small flow rate. Therefore, according to the original pipeline, steam can only be in the flow range of 2535t / h. If the flow rate is too small, the steam will condense, and the flow rate will be too small.
Secondly, when the other conditions are unchanged, the thickness of the thermal insulation material rock wool is increased to 10 cm, and the relationship between the outlet vapor pressure and the temperature and the steam flow rate is calculated. See the results. The calculation results show that the change in steam pressure is the same as in the previous case. The dryness is still 1 when the steam temperature reaches 15t/h, and the dryness is less than 1 when it is 10t/h. It is foreseen that as long as the thickness of the insulation layer can be further thickened (or the thermal conductivity of the material) No condensation occurs when delivering a smaller flow of steam. If the pipe diameter is reduced to 4273 mm, the calculation indicates that the steam temperature can be further improved, but the steam pressure does not meet the requirements at a large flow rate. The publication of the Chinese Academic Journal (CD-ROM Edition) statement is in order to meet the needs of China's information construction. Expanding the author's academic communication channels, the journal has joined the full-text database of China Academic Journals (CD-ROM Edition) and China Journal Net, and the author's copyright royalties and the remuneration of this journal are paid in one lump sum. If the author does not agree to include the article The database, please declare at the time of submission, the journal will do the appropriate processing, otherwise it is deemed to agree to the compilation.
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