Does a saturated steam flowmeter require density compensation?

Project Overview

In practical applications, density compensation is required when measuring saturated steam.

What is saturated steam?

Saturated steam is a colorless, odorless, non-flammable and non-corrosive gas. When a liquid evaporates in a limited closed space, the liquid molecules enter the space above through the liquid surface and become vapor molecules. Since the steam molecules are in chaotic thermal motion, they collide with each other, the container wall and the liquid surface. When colliding with the liquid surface, some molecules are attracted by the liquid molecules and return to the liquid to become liquid molecules. . When evaporation begins, the number of molecules entering the space is greater than the number of molecules returning to the liquid. As evaporation continues, the density of vapor molecules in the space continues to increase, so the number of molecules returning to the liquid also increases. When the number of molecules entering the space per unit time is equal to the number of molecules returning to the liquid, evaporation and condensation are in a state of dynamic equilibrium. At this time, although evaporation and condensation are still proceeding, the density of vapor molecules in the space no longer increases. The state at this time is called saturation state. Liquid in a saturated state is called saturated liquid, and its vapor is called dry saturated steam (also called saturated steam).

What are the characteristics of saturated steam?

(1) There is a one-to-one correspondence between the temperature and pressure of saturated steam, and there is only one independent variable between them.

(2) Saturated steam is easy to condense. If there is heat loss during the transmission process, liquid droplets or liquid mist will be formed in the steam, which will lead to a decrease in temperature and pressure.

(3) It is difficult to accurately measure the flow rate of saturated steam because the dryness of saturated steam is difficult to guarantee. General flow meters cannot accurately detect the flow rate of two-phase fluids. Fluctuations in steam pressure will cause changes in steam density. The flow meter indication produces additional errors. Therefore, in steam measurement, we must try to maintain the dryness of the steam at the measurement point to meet the requirements, and at the same time, we must take compensation measures to achieve accurate measurement.

How does saturated steam meet dryness requirements?

(1) Pipelines transporting steam must have good insulation measures to prevent heat loss.

(2) The steam pipeline should be drained section by section. Drain traps should be installed at the lowest part of the pipe and the pipe in front of the instrument to drain the condensed water in time.

(3) During boiler operation, excessively high liquid level in the steam drum should be avoided and large fluctuations in load should be minimized.

How to compensate for the density of saturated steam?

In order to measure the steam flow value more accurately and adapt to changes in the pipeline, you can use a vortex flowmeter and a pressure transmitter to measure saturated steam, or a vortex flowmeter and a temperature sensor to measure steam flow. count. In general, since pressure compensation is relatively easy and the measurement accuracy is high, the pressure compensation method is mostly adopted in implementation.

In summary, measuring saturated steam flowmeter requires density compensation. Supmea Measurement and Control Technology Co., Ltd. has been engaged in the R&D and production of flow meters and related Internet of Things systems for many years and has very rich project experience. For more questions about flow measurement, prepaid transformation, smart heating network management system construction and other related issues, please feel free to contact Supmea Measurement and Control~