Application of electric heating on the skin effect for liquid sulfur pipelines in the petrochemical industry

Published on:

2022-08-19 17:04

At present, the petrochemical industry recovers the sulfur content of crude oil, and the sulfur products leave the plant in two ways: in solid packaging and in liquid form. Given cost, ease of operation, energy consumption and other aspects, the petrochemical industry typically uses pipeline transport of liquid sulfur as the primary method of delivering sulfur.

Since the viscosity of liquid sulfur is relatively affected by temperature, it is generally necessary to maintain the temperature of the pipeline at around 130-160 °C to ensure good fluidity. Originally, much of the industry used a steam-jacketed heater, but because it involves transporting liquid sulfur over long distances, the cost of steam-jacketed heating is high, condensate extraction is difficult, and pipeline blockage caused by internal jacket leakage is difficult. Deal, so more and more More and more enterprises are using electric heating to maintain the temperature of liquid sulfur.

In 2021, Huening delivered a skin-effect electric heating system to petrochemical plants that effectively addressed the problem of heating and insulation of liquid sulfur pipelines. The length of the liquid sulfur replacement line in the 120 kt/year sulfur plant is about 1850 m, the pipe diameter is DN250, and the liquid sulfur pump capacity is about 300 t/h.

The principle of skin effect electric heating system

The SECT principle is based on AC "skin effect" and "proximity effect" Due to the strong magnetic permeability of the steel pipe, a significant skin effect will occur even at the industrial frequency voltage. The so-called skin-effect is a phenomenon in which an alternating current passes through a carbon steel conductor, a current gradually becomes splashed on the surface of the conductor, and the proximity effect is an electromagnetic phenomenon between a pair of electrical bodies with opposite currents, in the heating tube When the current passes between the cable and the heat pipe, The current on the heating pipe gradually tends to the inner wall of the heating pipe, and this is the joule heat generated by this thin inner wall to meet the needs of electric heating. The Joule heat generated by the surface effect electric heating system mainly comes from three parts:

1) When the leather cable is energized, the heat radiated by the carbon steel pipe is the main heat source of the electric skin heating system.

2) Heat generated by cables inside a carbon steel pipe.

3) The hysteresis loss in the carbon steel pipe releases some of the heat.

In a skin effect device, an insulated wire (SECT wire) passes through a strong magnetism steel pipe and connects to the end of the steel pipe. Or an alternating voltage of medium frequency, the current passes through the wire and the steel pipe to form a loop to generate joule heat. Since there is a certain relationship between the size, material, and frequency of the steel pipe, the alternating current does not flow uniformly across the cross section of the steel pipe, but flows concentratingly to a certain depth from its inner surface, and the current density decreases exponentially the voltage and current on the outer surface are practically zero, which is very safe. Thus, the SECT tube can be welded directly to the feed tube, making it an effective heat source. The heat generated by the SECT pipe is quickly transferred to the transport pipe through a weld and heat-conducting cement, which plays the role of electric heating.

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