Analysis of the causes of gas turbine flowmeter fluctuations

Project Overview

Gas turbine flowmeter instrument coefficient

Understanding "the flow range increases when the pressure increases" To understand this sentence, you must first understand two questions:

①What Is it the flow range?

The flow range given by the manufacturer refers to the working flow range, that is, the measurable range under the working temperature, pressure and other media conditions of the turbine flowmeter. The unit is m3/h. When used as budget usage in engineering, the unit is Nm3/h.

②What is the relationship between flow range and density (pressure)? This question can be answered through the following selection examples.

A gas company wants to choose a flow meter to measure natural gas. The pipeline installation fully meets the design requirements. The selection conditions given are as follows:

The measured medium is natural gas. , relative density 0.65; pressure 1×1MPa (gauge pressure); common temperature 20°C; flow range 400~4800Nm3/h; common flow 3500Nm3/h; pipe diameter DN100.

For the above example. Want to choose the appropriate instrument for measurement. Then perform a simple flow conversion based on the given conditions. The standard flow rate of 400~4800Nm3/h is converted into a working flow rate of approximately (36.3~436) m3/h, and the common flow rate is 318m3/h.

Interchangeability of main components of gas turbine flowmeters

According to regulations, turbine flowmeters are always calibrated one by one before leaving the factory, and the instrument coefficients are given. However, in the field, especially in high-pressure situations, damage to turbine meters often occurs. Maintenance personnel often replace the watch core (components including impellers and bearings) instead of replacing the entire instrument. The replaced watch core is brought back Maintenance (long-term maintenance work is not allowed on site). This leads to the question: What will happen to the performance of the flow meter, especially the instrument coefficient, when replacing the entire instrument versus replacing only the core? What factors are related to the instrument coefficient?

The instrument coefficient of the turbine flowmeter is mainly related to the watch core. This is because the watch core concentrates almost all the total pressure components of the meter, including bearings and impellers that affect the performance of the meter. Therefore, it is neither recommended to replace the bearings or impellers separately for maintenance, nor does it need to replace the entire instrument. Instead, it is sufficient to replace the watch core as a whole. Each watch movement used for maintenance needs to be individually calibrated. Each watch movement can determine an instrument coefficient. After replacing the watch movement, enter the new instrument coefficient and it can be put into use.

The actual environment is the usage environment

Speaking of the gas turbine flowmeter alone, the flow coefficient fluctuation factors

1. The flow velocity distribution of the medium itself is uneven or the secondary flow is Existence

Are the actual measured flow rate of the gas and the measurement range of the specific turbine flowmeter used reasonable?

The medium must be clean and cannot contain impurities

The gas must be single-phase , no liquefaction will occur

2. There is no problem with the medium flow rate, but there are problems with the installation pipeline, including

Instrument installation and pipeline are on different levels (different axes)

The influence of the reducing pipe may be understood as the front and rear straight pipe sections do not meet the requirements

The inner wall of the pipeline is uneven Flow velocity distortion caused by smoothness

The installation of the gas filter, or large fluctuations in flow velocity distribution caused by unreasonable installation

3. During operation

There are impurities in the medium that will jam the impeller, which will also cause flow failure to a large extent (this situation is encountered more often)

The flow rate changes too much, causing damage to the impeller

Bearing wear

Gas flowmeters generally have corresponding formulas based on pipe diameter, which can achieve several situations you mentioned. The main parameter change of a gas flowmeter is the effect of temperature on gas volume, so you need to add a Temperature compensated thermometer.