What Factors Need to Be Considered When Designing Valves in Chemical Process?
Jan 03, 2024
Factors to consider when choosing valves used in chemical process
When designing valves for chemical processes, several factors need to be carefully considered to ensure optimal performance and safety, such as pressure, temperatures, functions and driving force of valves.
The selection of valves is based on the rationality of operation, safety and economy, and the empirical result of a comprehensive and balanced comparison. The following original conditions must be put forward before selecting a valve.
(1) The status of the material status
a. The material status of gas includes relevant physical property data, whether it is pure gas or mixture, whether there are liquid droplets or solid particles, and whether there are components that are easy to condense.
b. The material state of liquid includes relevant physical property data. Whether the pure components or mixtures contain volatile components or dissolved gases (which can precipitate to form a two-phase flow when the pressure is reduced), whether it contains suspended solids, and the viscosity, freezing point or pour point of the liquid.
(2) Other properties
Other properties include corrosiveness, toxicity, solubility to valve structural materials, and whether it is flammable and explosive. These properties sometimes not only affect the material, but also cause special structural requirements or the need to improve the pipeline grade.
By carefully considering these factors during the design phase, engineers can ensure that valves perform optimally while maintaining safety standards within chemical processing plants.
1.2 Working conditions under operating conditions
(1) According to the temperature and pressure under normal working conditions, it is also necessary to combine the working conditions during startup and shutdown.
a. The pump outlet valve should consider the maximum closing pressure of the pump.
b. When the regeneration temperature of the system is much higher than the normal temperature, and the pressure is reduced, the combined effects of temperature and pressure must be considered for this type of system.
c. The degree of continuity of operation, that is, the frequency of opening and closing of the valve also affects the requirements for wear resistance. For systems with frequent opening and closing, double valves should be considered.
(2) Allowable pressure drop of the system
a. When the allowable pressure drop of the system is small, or when the allowable pressure drop is not small but flow adjustment is not required, valves with smaller pressure drops, such as gate valves and straight-through ball valves should be selected.
b. If you need to adjust the flow rate, you should choose a valve with better adjustment performance and a certain pressure drop. The proportion of the pressure drop in the entire pipeline pressure drop is related to the sensitivity of the adjustment.
(3) The environment in which the valve is located: outdoors in cold areas, especially for chemical materials. Cast steel or stainless steel should be adopted for the valve body instead of cast iron.
1.3 Functions of valves
(1) Cutting off: Almost all valves have a function of cut-off. If it is simply used for cutting off without adjusting the flow, gate valves and ball valves can be used. When rapid cutting is required, plug valves, ball valves and butterfly valves are more suitable. The globe valve can both adjust and cut off the flow. Butterfly valves are also suitable for regulating large flows.
(2) Changing the flow direction: Use ball valves or plug valves with two ways or three ways to quickly change the material flow direction. Since one valve functions as two or more straight-through valves, the operation can be simplified, reducing the space occupied.
(3) Regulation: Globe valves and plunger valves can meet general flow regulation, and needle valves can be used for fine adjustments; for stable regulation in a larger flow range, throttle valves are suitable.
(4) Check valves: A check valve can be used when it is necessary to prevent material from flowing back.
(5) Valves with additional functions can be selected for different production processes, such as valves with jackets, drain ports and bypasses, and blow ports used to prevent sedimentation of solid particles.
1.4 Driving force
Most of the valves operated locally use wheels. For those with a certain distance from the operation, sprockets or extension rods can be used. Some large-diameter valves already have motors in their design due to excessive starting torque. In explosion-proof areas, explosion-proof motors of corresponding levels must be used. Pneumatic, hydraulic and electric remote control valves are used. Electrical valves can be divided into solenoid valves and motor-driven valves. The choice should be based on needs and the energy available.
When designing valves for chemical processes, several factors need to be carefully considered to ensure optimal performance and safety, such as pressure, temperatures, functions and driving force of valves.
The selection of valves is based on the rationality of operation, safety and economy, and the empirical result of a comprehensive and balanced comparison. The following original conditions must be put forward before selecting a valve.
(1) The status of the material status
a. The material status of gas includes relevant physical property data, whether it is pure gas or mixture, whether there are liquid droplets or solid particles, and whether there are components that are easy to condense.
b. The material state of liquid includes relevant physical property data. Whether the pure components or mixtures contain volatile components or dissolved gases (which can precipitate to form a two-phase flow when the pressure is reduced), whether it contains suspended solids, and the viscosity, freezing point or pour point of the liquid.
(2) Other properties
Other properties include corrosiveness, toxicity, solubility to valve structural materials, and whether it is flammable and explosive. These properties sometimes not only affect the material, but also cause special structural requirements or the need to improve the pipeline grade.
By carefully considering these factors during the design phase, engineers can ensure that valves perform optimally while maintaining safety standards within chemical processing plants.
1.2 Working conditions under operating conditions
(1) According to the temperature and pressure under normal working conditions, it is also necessary to combine the working conditions during startup and shutdown.
a. The pump outlet valve should consider the maximum closing pressure of the pump.
b. When the regeneration temperature of the system is much higher than the normal temperature, and the pressure is reduced, the combined effects of temperature and pressure must be considered for this type of system.
c. The degree of continuity of operation, that is, the frequency of opening and closing of the valve also affects the requirements for wear resistance. For systems with frequent opening and closing, double valves should be considered.
(2) Allowable pressure drop of the system
a. When the allowable pressure drop of the system is small, or when the allowable pressure drop is not small but flow adjustment is not required, valves with smaller pressure drops, such as gate valves and straight-through ball valves should be selected.
b. If you need to adjust the flow rate, you should choose a valve with better adjustment performance and a certain pressure drop. The proportion of the pressure drop in the entire pipeline pressure drop is related to the sensitivity of the adjustment.
(3) The environment in which the valve is located: outdoors in cold areas, especially for chemical materials. Cast steel or stainless steel should be adopted for the valve body instead of cast iron.
1.3 Functions of valves
(1) Cutting off: Almost all valves have a function of cut-off. If it is simply used for cutting off without adjusting the flow, gate valves and ball valves can be used. When rapid cutting is required, plug valves, ball valves and butterfly valves are more suitable. The globe valve can both adjust and cut off the flow. Butterfly valves are also suitable for regulating large flows.
(2) Changing the flow direction: Use ball valves or plug valves with two ways or three ways to quickly change the material flow direction. Since one valve functions as two or more straight-through valves, the operation can be simplified, reducing the space occupied.
(3) Regulation: Globe valves and plunger valves can meet general flow regulation, and needle valves can be used for fine adjustments; for stable regulation in a larger flow range, throttle valves are suitable.
(4) Check valves: A check valve can be used when it is necessary to prevent material from flowing back.
(5) Valves with additional functions can be selected for different production processes, such as valves with jackets, drain ports and bypasses, and blow ports used to prevent sedimentation of solid particles.
1.4 Driving force
Most of the valves operated locally use wheels. For those with a certain distance from the operation, sprockets or extension rods can be used. Some large-diameter valves already have motors in their design due to excessive starting torque. In explosion-proof areas, explosion-proof motors of corresponding levels must be used. Pneumatic, hydraulic and electric remote control valves are used. Electrical valves can be divided into solenoid valves and motor-driven valves. The choice should be based on needs and the energy available.
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