Does the change in steam state in the heating pipeline network have an impact on the steam flow meter

What is the impact of the steam state in the commonly used heating pipeline network on the steam flow meter you choose to use? Faced with a series of confusion and difficulties that everyone may encounter, let's take a look at what they are all about?

There are many problems with the application of flow meters in heating pipelines, mainly manifested in inaccurate measurement accuracy, especially when used for trade settlement. I will analyze the impact of changes in the steam state in the heating pipeline network on the steam flow meter.

1、 Analysis of steam state

1. The Superheated steam becomes saturated. The steam output from the thermal power station is generally Superheated steam. The steam is transported to the user through a long distance in the pipeline. Due to the heat dissipation of the pipeline, it often becomes saturated after reaching the user. After quantitative calculation, the volume of saturated water in this state is very small and can be ignored. In the heating pipeline network, the changes in the above states are more typical.

2. Wet saturated steam becomes Superheated steam

In the heat supply network, when the user suddenly increases the steam consumption or when the steam passes through the pressure relief device, the saturated water will evaporate due to the sudden pressure drop, absorb Enthalpy of vaporization, and the saturated water temperature will decrease. If the pressure decreases significantly, the temperature still exceeds the saturation temperature corresponding to the pressure after the decrease, indicating that the steam is in an overheated state.

2、 The Influence of Changes in Steam State on Flowmeters

At present, vortex flow meters and orifice plate flow meters are commonly used in heating pipelines. Below, we will discuss and analyze these two types of flow meters.

1. Superheated steam becomes saturated

(1) Vortex flow meter

As mentioned earlier, when measuring saturated steam, the volume of saturated water is extremely small and can be ignored, while the output of the vortex flowmeter is only proportional to the flow rate. Therefore, when measuring steam in this state, the vortex flowmeter used to measure it and steam is selected. As long as temperature or pressure compensation is used, the impact of changes in steam state on flow measurement can be ignored.

(2) Orifice plate flowmeter

When the Superheated steam enters the saturation state, if all the steam is dry saturated steam, the accuracy of the flowmeter will not be affected by the change of the steam state through pressure or temperature compensation. If the steam is wet saturated steam, the steam dryness cannot be less than 95%, otherwise the error is too large. In actual measurement, due to the inability to measure the dryness of saturated steam, the average density cannot be measured. If an orifice plate flowmeter is applied to the dry saturated steam state, the measuring instrument can only measure 97.5% of the actual flow rate. Therefore, when using an orifice plate flowmeter, the dryness of steam cannot be lower than 95%, otherwise the error will increase.

2. Impact on instruments when wet saturated steam changes to Superheated steam

When designing the instrument, dry saturated steam is considered and pressure compensation is used. When saturated steam changes to Superheated steam, this steam state change will bring small error to the instrument. If temperature compensation is adopted, the error will be large. Pressure compensation is used to check the saturated density value according to the pressure, which is approximate to the density value of Superheated steam after the state changes. By using temperature compensation, the density value of Superheated steam is far greater than the density value of superheated steam after the state change according to the temperature. Since this state change is seldom encountered in practice, we will not discuss it with examples, and those who are interested may wish to discuss it. From the above analysis, we can draw the following conclusions:

1. Steam density is one of the key factors affecting flow measurement, which changes with changes in steam state. If the instrument selection is reasonable and installed appropriately, in most cases, the error can be minimized through pressure and temperature compensation.

2. In the heat supply network, if Superheated steam becomes saturated, it has little impact on the vortex flowmeter, but has a great impact on the pile flowmeter, that is, the flatness shall not be less than 95%.

3. If other and steam become Superheated steam, the error caused by pressure compensation is small, and the error caused by temperature compensation is large.

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