Urgent help needed regarding gaseous ammonia metering issue
Thread Content
With the recent sharp drop in temperatures, the consumption of gaseous ammonia in our company’s nitric acid production process has also decreased significantly, by 10%~20% compared to normal levels, which has made it impossible to carry out accurate cost accounting. For this reason, our industrial control department was particularly criticized. To make this \"slightly cold\" Spring Festival more pleasant, could you experts help me analyze whether the issue lies in the manufacturing process or in the instrumentation used for measurement? We all agree that if temperatures rise, the ammonia measurement will be normal. (Note: There are multiple sets of nitric acid processing equipment; ammonia consumption has decreased as well, and there are no issues with the instruments.) This post was last edited by LZ Gas Station on 2008-2-2 at 08:08
If a orifice plate flow meter is used, the pressure is generally kept stable. When the temperature of gaseous ammonia decreases, its density increases; under the same amount of ammonia used (mass flow rate), the flow velocity of gaseous ammonia decreases. The pressure difference measured by the orifice plate, ΔP, is proportional to ρ*V^2, which in turn is proportional to 1/T*T^2, or equivalently proportional to T. In other words, the pressure difference is directly proportional to the density and to the square of the flow velocity. At a constant pressure, density is inversely proportional to temperature, while flow velocity is directly proportional to temperature; as a result, the pressure difference is proportional to temperature. As the pressure difference measured by the orifice plate decreases, the volumetric flow rate after applying the square root transformation also decreases; that is, Q (m3/h) ∝ T^(1/2). It is estimated that in your company the temperature of gaseous ammonia is usually high; it has now dropped significantly, which is what has caused this situation. If necessary, it is important to insulate the pipeline equipment properly. If the orifice plate flow calculation yields a mass flow rate, the result is exactly the opposite. For specific details, refer to books such as \"Chemical Process Instruments\".
The transmitter used in orifice plate flowmeters assumes that the density of the fluid being measured remains constant during operation and calibration!
The throttling device uses an orifice plate, with temperature and pressure compensation.
Temperature correction? Temperature transmission should be fine!
The measurement of normal flow rates involves the conversion between volume and mass. If this occurs due to changes in temperature, it is likely that the changes in the external conditions set during calibration have affected the correction factor. If the reading is in terms of mass, then this factor represents density; thus, as the temperature drops, the actual density increases, while the coefficient of the meter remains unchanged. As a result, the actual mass flow rate meets the required standards, but for the meter, since the set coefficient is lower than the actual value, the displayed number appears smaller than before. [Last edited by 660 on 2008-2-2 11:17]
Our company’s gas ammonia metering includes temperature and pressure compensation to measure volumetric flow rate.
What is the actual temperature of gaseous ammonia? Is there a foggy ammonia-like condition? If so, it is beyond the range of temperature and pressure compensation.
In fact, we don’t know either the state of gaseous ammonia in the pipeline. However, no abnormalities were observed in the transmitter’s drainage. In terms of the compensation temperature, the temperature of gaseous ammonia is between 0~5°C. This post was last edited by LZ Gas Station on 2008-2-4 at 07:51