Air separation units (ASUs) are widely used across many industries, such as oil and gas, chemicals, papermaking and metallurgy. An air separation unit separates air into its main components, such as oxygen, nitrogen, argon and other inert gases, with oxygen and nitrogen being the primary products. With the rapid development of metallurgy, chemicals and coal chemicals, air separation equipment is required to become larger in scale, which in turn imposes new requirements on the technical development of supporting equipment. As domestic air separation equipment continues to scale up, the accompanying valves face ever-new technical demands. SUFA can provide a complete valve solution for the air separation industry. In addition, SUFA offers value-added services including valve design and selection review, operator training and support for valve operation and maintenance.

Characteristics and Applications of Valves for Air Separation Equipment

Gate valves serve to isolate the medium in a pipeline and are not intended for flow regulation. Generally, gate valves can be applied within the range of DN50–DN600 and PN1.5–PN25 (MPa). In terms of specific classification, gate valves fall into two types: parallel slide gate valves and wedge gate valves, classified by the structure of the sealing element; classified by stem structure, they can be divided into rising-stem and non-rising-stem gate valves, also known as outside screw and inside screw gate valves. Gate valves are relatively bulky and occupy considerable space. They should not be operated too frequently, as the sealing surfaces experience significant wear during opening and closing, and frequent operation over time will reduce sealing performance. Judging from current applications in air separation equipment, steel wedge gate valves are the most common, with the Z41H-16C being the typical model, generally used for manual isolation on water and steam lines, mainly for infrequent on/off isolation of flow paths.

A butterfly valve is a valve that uses a disc-type closing element rotating 90° back and forth to open, close and regulate the fluid passage. Butterfly valves are relatively compact and lightweight — for the same pressure class and nominal size, a butterfly valve is 30%-50% lighter than a gate valve. In addition, butterfly valves have a simple structure and quick opening/closing action, achieving rapid shut-off with excellent performance in flow regulation and sealing. Butterfly valves can be applied within the range of DN80–DN3000 and PN1.0–PN10 (MPa). There are two main types: concentric (single-offset) and double-offset (triple-offset). The concentric valve has a symmetric structure in which the valve shaft centerline is offset from the sealing face centerline, forming a single-offset design. In the double-offset design, the valve shaft centerline is further offset from the valve body centerline. Triple offset means that, on the basis of the double-offset design, the valve seat centerline is inclined relative to the valve body centerline, forming an offset angle — hence the name triple-offset valve. In current air separation equipment, butterfly valves are commonly applied at expander inlet/outlet, liquid pump inlet/outlet, high differential pressure service and switching systems.

A ball valve achieves opening and closing by rotating a ball 90° around the valve stem axis. In application, its primary function is to shut off, distribute and change the direction of medium flow; if the ball port is "V"-shaped, it also provides flow regulation. There are many types of ball valves, the most common being floating-ball and trunnion-mounted (fixed-ball) designs. In application, the most notable features of ball valves are nearly zero flow resistance, bidirectional (no preferred flow direction) sealing and good sealing performance, but the bore cannot be made too large. In air separation equipment, ball valves are generally used in small-bore ambient-temperature water drainage lines and for heating gas and sealing gas on gas lines. Common examples: Q11F-16C, DN15, water drainage; Q347F-16C, DN350, water drainage.

A globe valve is a valve whose closing element moves along the valve seat centerline. Globe valves are typically used for shut-off, regulation and throttling, offering good sealing and regulating performance; their main drawback is a relatively high flow resistance coefficient, which easily causes pressure loss. Globe valves are widely used, but due to high operating torque and long face-to-face dimensions, the nominal size is generally below DN250, with DN450 in only a few cases. Although there are many types of globe valves, straight-through and angle patterns are the most commonly applied. In air separation equipment, globe valves are mainly used for product flow regulation and venting.

Steam traps: steam traps are also common in the selection and application of valves for air separation equipment. A steam trap automatically discharges condensate from steam equipment, working on the principle of the density and temperature difference between steam and water to achieve drainage. Steam traps serve multiple functions, such as removing condensate and preventing steam leakage. In air separation plants, they are widely used where steam-driven steam turbines are employed.

Pressure reducing valves: a pressure reducing valve reduces the inlet pressure to the required outlet pressure through regulation and automatically maintains a stable outlet pressure by virtue of the medium's own energy. Common types include steam pressure reducing valves, water pressure reducing valves and pilot-operated pressure reducing valves.

Check valves: check valves are generally applied in piping systems. As the name suggests, their function is to prevent backflow of the medium and prevent reverse rotation of pumps and their drive motors. Check valves come in three types: swing check valves, lift check valves and butterfly (wafer dual-plate) check valves.

Control valves: control valves are valve types used to regulate fluid flow and pressure. Specific types fall into two broad categories — globe-type control valves and large-bore valves — both of which are widely applied in air separation equipment.

In summary, SUFA valves play a vital role in air separation units. As air separation equipment involves many types of valves, selection must be based on their main characteristics and functions so that the valves can perform to their fullest in the air separation plant, thereby maximally serving industrial production and daily life.