Summary of thermal power plant

Characteristics of Pipeline in Thermal Power Plant

A thermal power plant is a plant that converts chemical energy stored in coal, oil, natural gas, or other fossil fuels into combustion energy, heat energy into mechanical energy, and generate electrical energy.Thermal power plant production process is mainly with the boiler, steam turbine, generator, and other auxiliary equipment composed of thermal and electrical systems. These systems have many pipelines, such as the main steam pipe, reheat pipe, the water pipe, smoke and air coal powder pipe. The characteristic of these pipes as below:

High temperature, for team pipe, the temperature can get to 400～450℃,the lowest to 200～300℃

The section shape is varied. Steam pipes, gas pipes and water pipes are circular cross-section, the external flue are rectangular cross-section, while the section shape of air duct depends on the equipment structure of pipeline connection.

The medium flows fast. In order to prevent clogging of the coal pipeline, high speed win must be maintained in the air duct, and the maximum reach 80m/s.

Thermal expansion of thermal power plant pipeline

Thermal power plant pipeline from the cold state to the working state of its great temperature change, from tens of degrees to a few hundred degrees, resulting in thermal expansion of the pipeline, and because of these pipelines are long lines, the thermal displacement value will reach a great value.

The thermal displacement of the pipeline can be calculated by the following formula

ΔL=λLΔt（Unit：mm）

λ——linear expansion coefficient of pipe，mm/m ℃;

L——the length of pipe, m;

Δt——temperature difference,

If the two ends of the pipe are fixed, then the expansion of the wall will produce a huge stress, the stress value can be calculated according to the following formula:

σ= EΔ×106

σ——Stress，MPa;

E——Elastic modulus of pipes，MPa；

ΔL/L——The ratio of the thermal expansion of the pipe to the original length of the pipe。

Due to the thermal expansion of the pipe, the fixed point of the pipe ends will produce thrust, the thrust value can be calculated according to the following formula

F=σA×106;

σ——Stress，MPa;

A——Sectional area of a pipe，m2;

Finally, F=EλΔtA

If we treat Elastic modulus of steel pipe E=0.18 X106MPa, Coefficient of linear expansion λ=12 X 10-6m/m℃, the inner diameter of pipe is 300mm, out diameter is 326mm, the temperature difference is 350℃, thus, the thrust of the fixed point: F=0.18 × 1012 × 12 ×10-6 ×350 × (0.3262-0.302)π/4≈9.6×106N

From the above example, the thrust by thermal expansion generated is great.

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