The liquid ammonia flow meter does not provide accurate measurements
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The flow meters (orifice plates) for liquid ammonia in our company show a significant difference in measurement values between winter and summer; especially this winter, it was very cold and ammonia production was low. Does a flow meter need insulation?
It has little to do with whether the flow meter is insulated or not; mainly, in winter the temperature is low, so less ammonia evaporates, less ammonia gets carried along, and thus the production volume is low
First, let’s set the record straight regarding the flow meter: it’s not that it’s inaccurate, but rather the instrument isn’t designed with temperature compensation. The liquid ammonia coming out of the synthesis tower is at around 20°C. The ammonia tanks in the storage facility lack insulation, so the temperature inside the tanks is around -20°C (the temperature after reaching equilibrium). However, the flow meter is calibrated for a temperature of 0°C, with a density of 0.64 g/m³; at -20°C, the density is 0.665 g/m³. By doing the calculations, if the flow rate is 24 tons per hour, then 24 ÷ 0.64 × 0.665 = 24.93 tons. With this calculation, it’s normal for there to be a difference of 0.5 tons of ammonia per hour. To achieve a small measurement error, the only way at present is to lower the liquid level in the buffer tank; it doesn’t need to be very high, as long as gas leakage is prevented and no gas-liquid entrainment occurs. This ensures accurate measurement while also reducing the vapor consumption of urea.