Diskussion über Begleitheizungen in chemischen Prozessleitungen

Diskussion über Begleitheizungen in chemischen Prozessleitungen

This paper analyzes the different heat tracing methods of pipeline in chemical production process, and discusses the heat tracing methods of process pipeline in chemical plant.

In the chemical production process, when the heat insulation can not meet the process material pipeline insulation requirements, generally use the form of pipeline heat insulation.

Heat tracing mode introduction

The heat tracing medium of process pipeline has hot water, steam, heat carrier and electric heat. The most commonly used is steam tracing heat and electric tracing heat.
Because the chemical plant generally have by-production steam or spent steam can be used, can reduce the cost of accompanying heat, and steam latent heat, applicable to a wide range, operating temperature in 150 ℃ below the process pipeline can be used, so chemical pipeline accompanying heat is the earliest medium used is steam.
The earliest electric accompanying heat products are constant power products, there are certain shortcomings, for example, after the power is energized, the power remains constant, the heating temperature can’t be controlled, or in the heat dissipation is bad and overlapping intersection is easy to produce high temperature hot spot, after a long time the heater itself will be burned up.
The current use of self-limiting temperature pipe electric tapes, using conductive polymer composite materials and made, with the following characteristics.

• (1) The heating temperature can be done automatically limit.
• (2) Can be in accordance with the actual needs of the heated system automatically adjust their own output power.
• (3) The above functions can be independent, segmentation, such as for the same pipe, such as in a part of the outdoor temperature is relatively low, then the self-limiting electric heat tape will be in the region automatically will increase the output power: and another part if the temperature is relatively high in the indoor, self-limiting electric heat tape and will automatically reduce the output power.
• (4) The electric heat tape can also be arbitrarily cut off or in a certain range of long use, and can have any cross overlap without high temperature hot spots.

Why do I need heat tracing?

In production practice, some mediums that are easy to condense, such as crude oil and heavy oil, will even solidify and affect production due to temperature decreasing and viscosity increasing gradually during pipeline transportation. Therefore, thermal insulation measures must be taken to maintain a certain temperature of materials when transporting such media.

Comparison of heat tracing system

1. Steam heat tracing
Steam heat tracing system and heat supply system are two independent systems, which are supplied by point heat source and realize the function of heat transmission to process pipeline through steam heat tracing tube. Because steam itself in the process of transmission will inevitably produce certain heat loss, and the distance between the process pipeline and the heat source point is different, the heat compensation will be different accordingly, the near point will appear overheating compensation and the far point may appear under compensation.
2. Electric tracing heat
Different from steam tracing heat system, electric tracing heat dissipation system and heat supply system are combined with each other as a whole, and supply heat for line heat source at the same time. Although in the actual application its compensation value and the system required heat can’t do strictly equal, there is a certain gap, but the electric tracing heat system has no heat transmission problem, so the pipeline heating is relatively uniform, there will not be the above steam system in the pipeline far and near the problem. Usually there are about three kinds of electric tracing heat equipment as follows.

• (1) Mineral insulated heating cable, in which the insulation material of magnesium oxide material and the combination of core wire and metal armor. The mineral insulated heating cable of the electric tracing heat equipment belongs to the electric resistance element, which uses the current through the core wire resistance will produce Joule heat. But the product can not change its length at will, so in the application process is relatively inconvenient.
• (2) Constant power electric tropical, the same principle as the mineral insulated cable, also belongs to a resistance element, and its power is also not adjustable. But its product structure and mineral insulated heating cable compared to a certain improvement, that is, according to the actual requirements of the short cut. But another problem is the resistance wire winding interval a certain pitch will appear a welding joint, if cut off in the pitch, then the rest of the circuit will be lost because of the circuit is not working, which is relatively large for the short pipeline with the impact of heat.
• (3) Self-limiting electric heat tape, the choice of polymer PTC material, this material can control the temperature in the preset temperature value. Self-limiting electric heat tape can track the actual temperature of the process pipeline to make adjustments to its own output power, segmentation independent, eliminating the impact of seasonal and diurnal temperature changes, self-limiting heating method makes the electric heat tape more adaptable to be heated system.

Chemical plant process pipeline heat tracing design form selection

Process piping to be heated

In the chemical project, the following pipelines should be heated:

• (1) Pipelines that need to compensate the heat loss of the medium inside the pipe from outside, in order to maintain the temperature of the medium being transported.
• (2) Gas pipelines where condensate is generated due to heat loss during transport and may lead to corrosion or affect normal operation.
• (3) Pipelines that are self-cooling due to a sudden drop in medium pressure during operation and may freeze resulting in blockage.
• (4) During switching operation or stopping transmission, the temperature of the medium in the pipe drops due to heat loss, and the medium cannot be released from the pipe that may solidify by purging.
• (5) In the transmission process, due to heat loss may precipitate crystallization of the pipeline.
• (6) Conveying medium due to heat loss wither increase, the system resistance increases, the transport volume decreases, not reaching the minimum allowable amount of process pipeline.
• (7) The pipeline that conveys medium whose freezing point is equal to or higher than the ambient temperature.

The choice of pipeline heat tracing form

• (1) The reaction in the production device is exothermic reaction, can produce medium and low pressure steam, and it is difficult to have other suitable use path, the pipeline with the form of heat should choose steam, can save operating costs.
• (2) The pressure condensate of the production device can produce 1-1.5㎏/c㎡ low-pressure steam by flashing, the form of pipeline accompanying heat should choose steam, can save the operating cost.
• (3) The pipeline which needs to keep warm all year round, the pipeline accompanying heat form should choose steam, the one-time input is low.
• (4) Seasonal strong accompanying heat pipeline should choose electric accompanying heat, can choose to put into use or stop according to the warm and cold weather, flexible.
• (5) The long transmission pipeline‘s accompanying heat and no steam heat source or remote area pipeline’s accompanying heat should choose electric accompanying heat.
• (6) Plastic and non-metallic pipeline heat with the appropriate choice of electric heat.
• (7) Intermittent transport medium pipeline heat should choose electric heat.
• (8) Need to strictly control the temperature of medium pipeline heat insulation should be used electric tracing heat.

Fazit

Steam with heat pipeline construction is more complex, temperature control is poor, maintenance costs are high, but a one-time investment is low, and steam if the enterprise device by-production or spent steam, low operating costs. Electric tracing heat pipeline is safe and reliable. Construction is simple, can effectively carry on the temperature control, prevents the pipeline medium temperature overheating, the operation maintenance cost is low, but the one-time investment is big. Through the analysis of chemical process pipeline tracing heat, the technical comparison of tracing heat equipment and tracing heat performance comparison, can well analyze the chemical process pipeline tracing heat form selection.

Quelle: China Steel Pipeline Manufacturer - Yaang Pipe Industry Co., Limited (www.steeljrv.com)
References.

• [1] Ye Jiangqi. Electric power construction [M]. Beijing: electric power publishing house, 2005
• [2] Ren Xieyan. Energy conservation in Shanghai [M]. Shanghai: Transportation Publishing House, 2003