Selection and design of electric heater equipment

- Mar 21, 2020-

Electric heaters are used alone or in series with steam heaters to heat and regenerate molecular sieves to meet the requirements of the process flow. Electric heaters with a capacity of 14.875 kW are used, which are equipped with a transformer of 1 600kVA and 10kV / 400V. Electric heater control cabinet: 1 incoming cabinet; 5 power combination cabinets, groups 1, 2, and 3 are fixed power, groups 4 and 5 are adjustable (bidirectional thyristors are controlled by the cycle controller), and the power is 385, 385 , 367.5, 175, 175kw; Far-infrared heater wiring method is triangular connection, control cabinet electrical schematic diagram.

From the drawings and trial commissioning provided by the manufacturer, it can be seen that there are some defects in the design:


(1) The power cable used for the heater is too small. Since the electric heating tube can be regarded as a pure resistance that ignores temperature changes, according to P = 1.732 U / cosa, cosa = 1, then R = U / I, the scale is The value is fixed, so the heating current and power increase with the voltage. From the trial operation, it can be known that the current of the first, second, and third groups is 480 to 520A, the current of the fourth and fifth groups is about 320A, the power can reach 1 560 to 1 680kW, and the surface temperature of the cable measured during operation is 70 ° C. And a single 185, 95mm2 cross-linked VIV cable is exposed to rated current of 426, 283A at 30 ° C.


(2) There is no remote control in the control protection circuit, only simple on-site manual control. The DCS system cannot monitor the input and operating status of the far-infrared heater.


(3) The transformer capacity is too small, and the transformer operation generally does not exceed its rated capacity. Because the power fluctuates with the voltage, the voltage increases, and the power also increases. Sanan Company is located in a mountainous area, and the grid voltage fluctuates between 10b10.8kV. Transformer oil temperature can reach 75 ℃.


(4) The distribution of electric heating tubes is not ideal, the layout is uneven, and there is no regularity