Dimethyl terephthalate (DMT) is a medium with complicated process operations and physical properties. Its particularity is shown in:
(1) The process is intermittent feeding;
(2) The operating temperature is around 165℃ all year round, and the highest is 195℃;
(3) When the temperature is higher than 145℃, the density is about 1.065g/cm3, When the temperature is lower than 145°C, it immediately crystallizes into a solid. In view of the above characteristics, its use provides a reference for us to investigate the stability of the Coriolis mass flowmeter when the fluid is in an intermittent flow state and when it is close to the maximum working temperature of the flowmeter for a long time. Here is introduced as an example.
According to the characteristics of DMT that is easy to crystallize, good heat tracing and heat preservation measures must be taken. The installation of the flow sensor adopts the “flag type” installation method, and an orifice is opened under the flow sensor so that the residual liquid in the flow sensor can be discharged when needed to prevent crystallization. At the same time, the temperature indication and alarm are set by the analog channel of the transmitter. The temperature range is 145~195°C, and the upper and lower alarm limits are 190°C and 150°C respectively so that on-site operators can find problems in time and avoid damage to the flowmeter caused by exceeding the temperature range.
Table 6-5 shows the comparison of the measurement results of the Coriolis mass flowmeter and the oval gear flowmeter installed on the same pipeline.
| NO. | Temp ℃ | Density g/cm3 |
Oval gear flow meter | Mass flow meter | Rate of difference | |
| Volume/m3 | mass/t | mass/t | % | |||
| 1 | 163 | 1.0648 | 282.3 | 300.59 | 298.05 | 0.84 |
| 2 | 164 | 1.0638 | 282.6 | 300.63 | 298.69 | 0.64 |
| 3 | 165 | 1.0629 | 283.3 | 301.12 | 300.58 | 0.18 |
| 4 | 163 | 1.0648 | 569.6 | 606.51 | 604.16 | 0.39 |
| 5 | 165 | 1.0629 | 283.2 | 301.01 | 299.35 | 0.55 |
| 6 | 161 | 1.0667 | 283.2 | 302.09 | 300.56 | 0.51 |
| 7 | 164 | 1.0638 | 284.4 | 302.54 | 301.00 | 0.51 |
| Total | 2414.49 | 2402.39 | 0.50 | |||
Operating practice shows that Coriolis mass flowmeter can adapt to the process operating conditions of DMT and be used for flow measurement of DMT. It needs to be pointed out here that in order to ensure the long-term reliable operation of the mass flowmeter under the working condition of the medium at high temperature, the upper limit of the working temperature of the selected mass flowmeter should not be too close to the working temperature of the medium, because it is close to the upper limit of the working temperature of the flowmeter. Time work can easily cause damage to the sensor detection coil.