Design and Implementation of Heat Tracing for Chemical Pipeline
Part of the process to the temperature has related aspects of the demand, so it is necessary to use with the heat insulation to transport media, with the heat method usually using electric accompanying heating method and steam pipe accompanying heating method, and the pipeline skin effect with the heat technology is the focus of our introduction in this paper, it belongs to the electric accompanying heating method, this paper focuses on the chemical process pipeline with the heat design for detailed study.
According to the characteristics of the transporting carrier, the pipeline is divided into adiabatic, non-adiabatic and heat insulation and heat tracing type pipeline. The adiabatic pipeline usually conveys substances with certain temperature requirements such as liquid chlorine, steam, hot water, etc.; the heat insulation pipeline usually conveys substances whose adiabatic heat cannot meet the adiabatic heat insulation requirements of process materials, such as crude oil; and the non-insulated pipeline usually conveys substances with low temperature requirements, such as gasoline. Minimize the material temperature change and effective energy saving, but also to protect the personal safety of personnel is the main function of insulation. To ensure that the temperature and process conditions are in line with the process, the processing force should be maintained and played as much as possible can play a positive role.
Common with the choice of heat way selection of steam with heat
- (1) Equipment, pipeline in the medium of the freezing point, viscosity, process medium to maintain the temperature is high (usually more than 100 ℃ or even 150 ℃), equipment, pipeline in the region with high explosion-proof level, while the medium of corrosion, heat sensitivity is strong.
- (2) The case of choosing electric tracing heat: the process medium needing insulation is not high temperature (generally need to maintain the medium temperature in 30-120℃), fireproof and explosion-proof requirements are not high, away from the steam source of equipment, machine pumps, pipelines.
- (3) Choose hot water with heat: the temperature of the medium to be insulated is not too high (generally below 90℃, the medium is required to be heated evenly, and it is not suitable to use other heat accompanying cases such as electric heat.
- (4) The choice of heat conduction oil with heat: the medium temperature of the insulation is high (generally 140-355 ℃, and in the medium of the endangered state), and other heat with the medium can not reach the heat with the requirements.
Chemical process pipeline heat tracing design requirements
The design requirements of steam tracing pipe
The radius of the heat tracing pipe is between 8 and 40 mm, but need to pay attention to is in the real condition, in order to reduce the loss of the pipe wall and effectively save raw materials and often choose the pipe radius between 10 and 15 mm, its heating medium generally choose 0.5 to 1.2 MPa of steam, the change of the solidification point of the transport will cause pressure to the steam heat tracing pipe, so the corresponding measures should be with the changeable The solidification point and gradually improve, which 1.5 to 1.2 MPa of the multi-pipe steam with the tube application conditions for the transport of solidification point more than 60 ℃.
The design requirements of the heat compensation of the accompanying pipe
- (1) Choose the spiral winding type, “Ω” type or “U” type compensator to make up for the natural compensation, its setting position in every 20 to 30 meters on the straight section of the companion pipe evenly laid.
- (2) When the companion pipe is turned to the companion pipe for natural compensation, in order to ensure that the heat preservation structure of the companion pipe is good, should pay special attention to the setting position of the companion pipe fixing point.
- (3) When fixing the companion pipe, the way of tie-band bundling is applied in it. When the material of the companion pipe is stainless steel, the isolation pad of 50 mm wide and 1 mm thick should be used between the fixed tie and the companion pipe.
The basic design of the working diagram of the accompanying pipe
The premise of the tracing heat design is the basic design of the working diagram of the tracing heat pipe, which should be considered firstly in the design to the reasonable design of the selected tracing heat method of the pipeline layout form. In addition, the corresponding parameters should be entered into the designed pipe diagram on the basis of three-dimensional design and complete simulation of the whole process, then the whole design idea is determined in the right direction under the verification of the theory, and it is necessary to know that the model design is usually not done before and after the accompanying pipe, and to pay attention to the cross-test heat medium, hot line and all pipelines, etc., so as to determine the most reasonable design scheme.
Heat tracing design of chemical process pipeline
Petroleum chemical industry and other enterprises for heat preservation or heating with hot pipeline new technology and new technology is pipeline skin effect with heat technology, also known as SECT method, this call is more widely used in foreign countries, it is suitable for transporting high condensate oil, thick oil or super thick oil and other oil pipeline in the long distance heating with heat. The protective shell, the electric heat pipe with heat-resistant cable, the heat insulation layer and the oil pipeline form the skin effect heating method, the heat tracing tube is indirectly welded on the oil pipeline, the waterproof shell and the heat insulation layer are distributed on the outside, the heat-resistant cable is strung in the heat tracing tube and the radius of the heat tracing tube is between 7.5 and 20 mm. The skin effect heat tracing classification is based on the heat tracing temperature and pipe diameter, usually divided into three pipe heat tracing, double pipe heat tracing and single pipe heat tracing, then in the choice of heat tracing tube, the first should take into account the temperature of the high and low and the size of the pipe diameter. In the heat tracing steel tube wears the heat-resistant cable, connects one end of the cable with the single-phase alternating current, then when the charged cable passes through the heat tracing tube, the current is influenced by the neighboring and the skin effect when propagating along the tube wall is not uniform, but flows in the surface of the heat tracing tube concentrated. The ac impedance of the skin layer of the tube wall increases, and the conductive section is obviously reduced, in the case of the current is consistent, the power of the accompanying heat pipe gradually increases, then the temperature of the oil pipeline in the role of conduction also gradually increases.
Electric tracing heat design
The heat tracing and heat preservation design which is carried out by using electric power, resistance and induction heating etc. is also the electric heat tracing design of chemical process pipeline. In the process of use, electric tracing heat has more convenient construction design, safety factor is very high and daily maintenance also does not need too much. In addition, in recent years, with the continuous research of electric tracing heat, electric tracing heat technology also gets the continuous development, energy utilization rate has been effectively improved and in the energy consumption also gradually reduces. In the design process of electric tracing heat, the design of tracing heat capacity and resources. Energy can be effectively saved is closely related, usually we need to pay attention to improve the electric tracing heat tracing capacity, the principle is as follows: equipment running cost will be because of excessive tracing heat capacity and increase, in the design process, in order to effectively calculate the heat capacity to reach the start condition we usually use the computer to analyze the design, to the total operation energy as much as possible to save; and too low tracing heat capacity will waste heat energy, because the pipeline utilization rate will be because of low tracing heat capacity. Because the utilization rate of the pipeline will be reduced because of the low heat tracing capacity. In the process of designing the electric tracing heat, we can add the three-dimensional computer model, the details of the companion pipe and the total pipe and the distribution station are planned reasonably, usually in the wall column and other platform position to arrange the distribution station, pay attention to shorten the distribution station before the companion pipe as much as possible, and the material of the companion pipe and the total pipe and the division are the key points to pay special attention to in the pipeline design. In addition, in order to ensure the clarity and reasonableness of the design, should be accompanied by the place or source of the pipe to mark carefully.
Steam tracing heat design
In order to effectively control the temperature in the pipeline, and through the steam distribution station and steam with the pipe and other elements to achieve the design of steam with heat is steam with heat design. Usually, in the working environment, there is condensate in the process pipeline will use steam tracing heat, this is to avoid the corrosive effect of the pipeline by corrosive gas vaporization into condensate corrosion.
The important device for setting and distributing steam tracing system is steam tracing distribution station. Whether it is a conventional or general distribution station, they all have a similar location, and are set up around the walls and columns. In addition to the reasonable choice of location, in reality, it should also ensure that the steam is easy to transport and disperse. In order to provide for the distribution of steam in the event of an emergency, it is best to design the distribution station with one or two spare ports for the number of connections. The condensate is collected when the design requirements of the steam distribution station are met. Usually, the condensate collection station is installed in vertical form for better condensate collection to avoid corrosion of the piping.
In steam tracing, the design of steam tracing pipe is an indispensable part of it. Usually, in the design of steam tracing pipe, the flow of steam to the transport pipeline is issued by the main pipe, and then distributed under the action of a separate steam tracing pipe. It is important to note that in order to ensure the stability and safety of the tracing heat and the independence of the steam tracing traps, a separate trap door should be designed in the steam tracing pipe. To ensure the safety of the design, the material of the main pipe should be the same as that of the steam tracing pipe.
Notes for heat tracing piping
- (1) Seamless steel pipes should be scientifically selected for steam tracing in oil pipes, and deficiencies such as mechanical damage and cracking problems, which are approximately 8% higher than the thickness, should not appear on the surface of the pipe, neither on the inner surface nor on the outer surface.
- (2) U-shaped or n-shaped bend is usually used to connect the connecting pipe, which is distributed outside the oil pipe of the inner tracing pipe, and the same method is also used to connect the steam connecting pipe in order to facilitate comprehensive disassembly and maintenance operations. The slope of the oil pipe and the slope of the connecting pipe in front of the oil pipe should be consistent, and for real-time detection, the inspection valve frame is usually set reasonably in the connecting pipe.
- (3) The shut-off valve in the main pipe for steam supply with heat is usually set at the outlet of the hot water main and steam main, and at the same time, the installation work should be carried out in the horizontal pipe using the shut-off valve method.
- (4) The length of the tracer pipe should be 0.1 to 0.2 m longer than the outside pipe, so that the elbow can be used at both ends of the pipe to pass through the wall of the pipe.
- (5) It is necessary to lead the steam tracing pipe from the top of the steam or hot water main, and the steam tracing pipe from the top of the tracing station area or from the horizontal surface.
The design of heat tracing in chemical process piping is of great importance for the transport and storage of certain chemical materials. In the chemical process, some process must achieve a certain insulation effect, and the accompanying heat way can meet this special needs, at this stage, electric accompanying heating and steam accompanying heating two ways in the chemical process pipeline accompanying heat design in the most common use. And the heating energy-saving and stability is two ways to accompany the key point in the design of heat, we should take into account the arrangement of the pipeline, the number and type, etc. to realize its collocation optimization, as far as possible to achieve safe operation and cost saving two aspects effectively reflected in the chemical process pipeline with heat design.
Source: China Chemical Pipeline Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)