Gas steam flowmeter

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1. The main reasons for the fluctuation of the orifice plate differential pressure flowmeter for measuring steam include the two-phase flow characteristics of the steam itself, insufficient upstream and downstream straight pipe sections, condensed water in the pipeline, and problems with the impulse piping.

1. Steam Characteristics and Process Issues 1 Insufficient dryness of steam or steam with water during transportation may cause a temperature drop due to heat dissipation, and some of the steam will condense into water, forming a gas-liquid two-phase flow. When the fluid passes through the throttling orifice plate underwear, there is a huge difference in flow velocity and density between the gas and liquid phases, resulting in severe fluctuations in the differential pressure signal. This is the most common reason for fluctuations in steam measurement. Unstable steam pressure and temperature, changes in boiler load, or frequent start-up and shutdown of downstream steam equipment can cause significant fluctuations in the pressure and temperature of the main steam containing the grid. The conversion between differential pressure and flow rate depends on the density parameters of steam. When the density changes, even if the differential pressure is stable, the calculated flow rate value will jump. 3. Pipeline design and installation defects: There should be at least 15-20D (D is the diameter of the pipeline) of straight pipe section in front of the orifice plate, and 5D of straight pipe section behind it. If the straight pipe section is not sufficient and the fluid flow state is unstable (such as the presence of eddies and underdeveloped turbulence), it will directly lead to differential pressure fluctuations.

There is condensation water in the pipeline: Insufficient slope of the pipeline or failure of the steam trap can cause condensation water to accumulate in low-lying areas of the pipeline. The high-speed flowing steam will carry water and form a "water hammer" phenomenon, violently impacting the orifice plate, causing a sudden and significant fluctuation in differential pressure.

2. Problems with the measurement system itself 1 Malfunction of the pressure pipeline: uneven liquid level in the condensate tank: When measuring steam, the pressure pipeline must balance the liquid column pressure through the condensate tank (or condenser tank). If the liquid level heights of two condensate tanks are not consistent, additional static pressure differences will be generated, introducing measurement errors and fluctuations. Pipeline blockage or leakage: Impurities blocking the pressure pipe or valve, or leakage occurring at the joint, can prevent the differential pressure signal from being transmitted to the transmitter accurately and stably. There is gas in the pipeline: If the condensed liquid filled is impure or contains gas, the gas will accumulate in the pressure pipe, forming a compressible air cushion, causing slow differential pressure response and fluctuations. 2. Differential pressure transmitter problem: transmitter zero drift: the transmitters own zero point is unstable, or it is not regularly calibrated (usually done when the upstream and downstream pressure valves are completely closed and the balance valve is opened). Improper range setting or damping setting: The damping time constant inside the transmitter is set too small to filter out the normal pulsation of the fluid; If the setting is too large, it will

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