Common primary instruments on site include thermometers, integrated temperature transmitters, pressure gauges, pressure transmitters, flow meters, liquid level gauges, and regulating valves. In accordance with the requirements of SH/T3104-2013 Petrochemical Instrument Installation Design Specification and GB50093-2013 Automation Instrument Engineering Construction and Quality Acceptance Specification, Changhui Instrument summarizes the principles and methods of pipeline and equipment layout design for reference by instrument workers.
When designing chemical process pipelines, full attention should be paid to the layout design of the previous instruments in the process pipelines and equipment, in order to obtain the final design product with reasonable design and convenient operation and maintenance. At present, designers extensively use 3D design to clearly indicate the installation position, orientation, and primary valve of primary instruments in a single line diagram, but relevant principles must be followed. Therefore, Changhui Instrument has summarized the principles and methods of primary instrument layout design.
Four requirements for instrument layout design on chemical process pipelines and equipment:
1. Meet the requirements of the process flow
Before the last instrument layout design of process pipelines and equipment, it is necessary to understand and master the process flow, be familiar with the functions and control methods of each control point, and be clear about the corresponding regulating valves and the fluid characteristics of the controlled fluid.
2. Meet the requirements of control instruments for pipeline design
Although the general process flow diagram clearly indicates the requirements of the control instrument for bypass, expansion pipe, and filter, it still needs to meet the length and disassembly requirements of the front and rear straight pipe sections.
3. Meet the requirements of the arrangement of the regulating valve group
The regulating valve group often has bypass, guide valve, and front and rear shut-off valves, which occupy a large space. Therefore, in pipeline design, in order to avoid problems such as chaotic pipeline routing and inability to operate and maintain, the position of the regulating valve group should be planned first based on the relative position of the front and rear related equipment.
4. Meet the requirements for operation, observation, maintenance, and repair
When arranging instruments, electromagnetic interference, static electricity interference, strong vibration, and high temperature places should be avoided. If it is impossible to avoid them, appropriate anti electromagnetic interference and anti static interference measures should be taken. The primary instrument is generally arranged next to the operating channel or in a place easily accessible to operators, and if necessary, a dedicated operating platform and ladder should be set up.
Key points of primary instrument layout
Common primary instruments on chemical process pipelines and equipment include thermometers, pressure gauges, integrated temperature transmitters, pressure transmitters, flow meters, liquid level gauges, and regulating valves. Below are the layout requirements.
1. Key points for the layout of thermometers and temperature transmitters
The temperature measurement point should not be located in a dead corner where the medium does not flow, but should be located in a location that can sensitively and accurately reflect the temperature of the medium. It is best to install the thermometer at a height of 1200-1500mm on the dial, which is within the operator’s line of sight. When the height of the thermometer is less than 1200mm, it is required that the height of the connecting pipe should not be less than 300mm; When the height of the thermometer is higher than 1500mm, it is required that the dial height cannot exceed 2200mm; If the thermometer must be installed above 2200mm, a ladder or platform must be set up, and the thermometer must be arranged near the edge of the ladder. When installing a thermometer, the dial must face the operating surface. Thermometers can also be installed outside the platform, but the distance between the nozzle and the edge of the platform should not exceed 500mm.
Thermistor
Thermometers can be installed on horizontal, vertical, or curved pipes. When the diameter of the pipeline is small (less than DN80mm), the thermometer can be installed at the elbow or after expanding the pipe diameter, and the length of the expanded part of the pipe diameter is 250-300mm. When installing at the bend or inclined 45 °, it should be opposite to the medium. When installing at the bend of the pipeline, the pipe diameter should not be less than DN40mm. For the convenience of piping, thermometers at different elevations on vertical equipment should be arranged in the same direction as much as possible, but should not collide with internal components of the equipment or be inserted into fluid dead corners. The temperature measurement point for the top temperature of the distillation tower should be selected on the gas phase outlet line; Thermocouples or thermal resistors in other parts should be located in the liquid phase, or their installation positions should be determined according to process requirements.
The installation height of the integrated temperature transmitter without on-site indication should be designed according to the front and back conditions of the pipeline. It should be noted that the minimum height of the connecting pipe is 300mm, and the maximum distance between the connecting pipe nozzle and the platform edge is 500mm. If the installation height of the temperature transmitter is high, temporary vertical ladders are generally used for maintenance. The arrangement of temperature transmitters with on-site indication is similar to the arrangement of thermometers.
To avoid difficulties in installing and disassembling thermometers, it is necessary to reserve space for the extraction of thermometers when arranging integrated temperature transmitters and temperature timers. Special attention should be paid to opening holes on the floor. If not designed properly, the installation and disassembly of thermometers can easily touch the floor ring beams.
2. Key points for arranging pressure gauges and pressure transmitters
The pressure gauge should be installed on a straight pipe section with stable flow, and should not be installed in a curved pipeline or where the flow is in a vortex shape. The pressure measurement points on towers and containers are generally set in the gas phase section. When measuring high pressure, the pressure gauge should be installed near the operating position, and the height of the pressure gauge should be above 1800mm, or a protective cover should be added to the front of the pressure gauge. When the pressure source component and the temperature source component are on the same pipe section, the pressure source component should be located upstream of the temperature source component.
Pressure gauges are generally installed at a position that ensures a dial height of 1200-1500mm. When there are difficulties in arrangement, the dial height of the pressure gauge can also be lower than 1200mm or higher than 1500mm, but the maximum dial height cannot be higher than 2200mm; If the height of the dial needs to be greater than 2200mm, a ladder or platform should be installed, and the pressure gauge must be arranged next to the ladder. The pressure gauge can also be installed outside the platform, but the maximum distance between the connecting nozzle and the edge of the platform is 500mm. When installing the pressure gauge, the dial should face the operating surface.
The arrangement of pressure transmitters is similar to that of pressure gauges. When arranging and designing pressure gauges and transmitters, a minimum distance of 100mm should be reserved above the dial to facilitate installation and disassembly of the pressure gauges and transmitters. It is best to install pressure gauges and pressure transmitters at straight pipe sections, but they can also be installed on horizontal and vertical pipes. However, at this time, the pressure gauge dial must be tilted upwards or vertically upwards.
Single crystal silicon pressure transmitter
3. Key points for flow meter layout
To ensure measurement accuracy, flow meters require a certain straight pipe section. Different flow meters have different requirements for the flow direction of the medium, whether it is installed in a horizontal or vertical pipe, and the front and back straight pipe sections. In the initial design stage, full attention should be paid to the selection of flow meters to ensure the requirements of the front and back straight pipe sections and flow direction, especially for large-diameter pipelines, sufficient space should be left.
Principles of flow meter layout on pipelines and equipment
① Meet the requirements of instruments for piping
The front and rear straight pipe sections of orifice flow meters, vortex flow meters, turbine flow meters, and gas thermal mass flow meters require a longer length, with a minimum of 10D for the front straight pipe section and 5D for the rear straight pipe section. The requirements for the straight section of other flow meters are generally at least 5D for the straight section and at least 3D for the rear straight section, which is easier to meet.
② The flow meter pipeline and bypass should be arranged on the same facade as much as possible to save space. Special attention should be paid to the support of the main pipe and bypass in large-diameter piping systems. When space permits, for the convenience of operation and maintenance, the flow meter pipeline and bypass can be arranged on a flat surface.
③ Special attention should be paid to the flow direction of the flow meter, and the dial must face the operating area and channel when installing the flow meter.
④ Reasonably arrange the positions of flow meters and regulating valves. If the flow meter and regulating valve belong to the same system, they should be arranged in the same plane and cannot be arranged in separate planes.
Key points for the layout of orifice plate flow meters
There must be a straight pipe section required by the instrument before and after the orifice flowmeter to ensure measurement accuracy. Due to its ease of meeting the requirements of front and rear straight pipe sections, orifice flow meters should generally be installed on horizontal pipe sections as a priority, but can also be installed on vertical pipe sections. When the orifice plate flowmeter is installed on a vertical pipe section, in order to prevent liquid accumulation at the orifice plate from affecting the measurement accuracy and bubbles at the orifice plate from affecting the measurement accuracy, the gas flow direction should be from top to bottom, and the liquid flow direction should be from bottom to top. If it can be ensured that the pipeline is filled with liquid, the liquid flow direction can also be designed from top to bottom.
Design an orifice plate flow meter on the pipe gallery. In order to install, operate, inspect, and maintain the orifice plate flow meter on the operating platform next to the pipe rack beam, the orifice plate flow meter should not be placed between two pipe rack beams, but near the pipe rack beam with columns.
Key points for the layout of rotary flow meters
The rotary flowmeter must be installed on a vertical, vibration free pipe section, with a flow direction from bottom to top. To ensure measurement accuracy, the straight pipe section required by the instrument must be ensured before and after the rotor flowmeter. In order to facilitate installation, operation, maintenance, and repair, a certain amount of space should be reserved around the rotor flowmeter, and it is easy to have no installation space on one side of the indicator panel in the design. When installing the rotor flow meter, a bypass needs to be set. When the rotor flow meter is removed for cleaning and maintenance, the opening of the front shut-off valve during normal operation of the rotor flow meter should be taken as the basis. Controlling the opening of the bypass valve can roughly control the flow rate to ensure that the system can continue to operate normally. When the flow rate is small, in order to facilitate flow control, needle valves should be used for the front shut-off valve and bypass valve. When operating the bypass valve of the regulating valve, in order to be able to see the dial of the rotor flow meter, the regulating valve and the rotor flow meter should be arranged in coordination.
Other key points for flow meter layout
In addition to orifice flow meters and rotary flow meters, there are also elbow flow meters, target flow meters, mass flow meters, turbine flow meters, electromagnetic flow meters, and gear flow meters. Vortex flow meters, electromagnetic flow meters, and mass flow meters should be installed on pipelines completely filled with media, with the same requirements as orifice flow meters; Target flow meters and gear flow meters can be installed on horizontal or vertical pipelines; Gas thermal mass flow meters and turbine flow meters should be installed on horizontal pipelines.
4. Key points of liquid level gauge layout
Due to the susceptibility of glass tube level gauges to damage, they are generally not installed on one side of the work area, passage, and maintenance area, but on the safer side of the equipment. To avoid affecting operational traffic, except for glass level gauges, level gauges are generally arranged at the platform end. The upper height of the liquid level gauge is generally between 1600-1800mm. When it is higher than 2000mm, a platform or ladder needs to be installed. Sufficient installation and disassembly space should be reserved above the plug-in level gauge. When the medium has toxic, corrosive, flammable and explosive characteristics, the liquid discharged by the level gauge should be discharged into the relevant system for treatment. The beam path of ultrasonic or microwave level gauges should avoid the spraying range of the container feed stream beam, and avoid agitators and other obstacles.
The upper and lower interfaces of frost level gauges and glass tank level gauges are rigidly connected level gauges, which have a wide measurement range and often pass through floors or platforms. When arranging, comprehensive consideration should be given. When the liquid level gauge passes through the floor, a hole needs to be left on the floor. If the lower interface of the liquid level gauge is in the air, a platform or ladder needs to be set up for easy observation and inspection. When the liquid level gauge passes through the platform, it should be arranged next to the ladder or outside the platform to avoid crossing the platform.
For the convenience of comparing and verifying the liquid level transmitter with on-site indication and the local liquid level gauge, the indicating dial of the liquid level transmitter should be arranged together with the liquid level gauge. For the convenience of operation, the liquid level control valve group and the primary liquid level gauge should be arranged together as much as possible, but it is difficult to achieve in practical applications. Therefore, for the convenience of observing the liquid level indication when operating the bypass valve of the regulating valve, the indicator dial of the liquid level transmitter can be arranged next to the regulating valve group.
5. Key points for regulating valve layout
In order to facilitate manual operation with attached lines and observe the indicated values of the instrument, and to avoid accidents caused by improper operation, the regulating valve should be arranged close to the relevant primary instruments and measuring elements. The regulating valve is generally arranged next to the operating channel or on a horizontal pipe section, and the membrane head must be vertically upwards. The membrane head can also be installed with support horizontally or tilted upwards, but the consent of the instrument expert must be sought. When there is a pipeline above the membrane head, in order to avoid medium leakage and dripping onto the regulating valve, the valves on the pipeline must be arranged in a staggered manner.
The regulating valve must be equipped with a bypass and shut-off valve. The bypass generally uses a shut-off valve, while the shut-off valve uses a gate valve or ball valve. When the process cannot use bypass regulation or the regulating valve can be shut down for maintenance, bypass and shut-off valves can be omitted. In addition, when there are spare motor driven mechanical steam control valves, clean fluid delivery, and pipelines that can be cut off, bypass and shut-off valves can be omitted.
Regulating valves should be equipped with DN20mm or DN25mm exhaust and discharge valves. The functions of exhaust and discharge valves are: to vent and discharge liquid; Connect air exchange and cleaning solution; Ensure complete pressure relief when disassembling the sampling interface and regulating valve.
Post time: 11-01-24