If you’re planning to expand, upgrade, or retrofit your plant, chances are it will be hard to find a place for all that new or upgraded equipment. Many fluid handling devices require specific, space-intensive, piping practices to operate properly, and you may run out of room in trying to implement these inside plant buildings or even outdoors.
If you’re planning to expand, upgrade, or retrofit your plant, chances are it will be hard to find a place for all that new or upgraded equipment. Many fluid handling devices require specific, space-intensive, piping practices to operate properly, and you may run out of room in trying to implement these inside plant buildings or even outdoors. Pumps, compressors, valves, flowmeters, blowers, burners, and other devices frequently require straight runs of pipe upstream and downstream to stabilize material process flow for effective performance. Installing them in tight spaces can, literally, push you against the wall.
Flow disturbance problems
Trying to jam too much equipment into too little space inevitably creates poor piping layouts. Putting elbows, expansions, reductions, or spiral piping close to instrumentation and other devices alters the process media’s tangential, radial, and axial velocity vectors. Flow disturbances result, including swirl, jetting, and velocity profile distortions, which negatively impact flowmeters, pumps and other equipment.
For best performance, flowmeters require straight pipe runs of 10 to 20 diameters, depending on the sensing technology. Irregular material flows caused by poor piping adversely affect the accuracy and repeatability of readings.
In pumps, control valves, and other critical process components, flow disturbances create cavitation that generates noise, excessive wear, and damage, ultimately resulting in premature failure. These same conditions can cause less obvious problems, reducing process media delivery capacity with associated end-product quality losses. Irregular liquid flow to pumps, in particular, can result in dry running conditions that lead to seal or bearing damage and result in expensive repairs or replacements.
The ideal process plant would have space for everything and everything would be installed exactly according to manufacturer specifications. In the real world, however, the objective generally is to squeeze out every last bit of process capacity and quality, delivering the lowest possible cost per unit of production.
Flow conditioners are one of the most practical ways to eliminate flow disturbances resulting from inadequate straight pipe runs and other poor pipe layouts. Types include honeycomb vanes, perforated plates, tabs, tube bundles, and vanes. Each has its application, depending on process media, equipment problem, pipe configuration, cost requirement, etc.
General guidelines for the best applications of flow technologies include:
Honeycomb vane-type conditioners are frequently found in HVAC or compressed air handling system applications where they provide modest flow profile corrections. They are available in many designs and materials which should be suited carefully to the specific use. Otherwise they can be maintenance intensive or require frequent replacement.
Perforated plates are a good choice in natural gas pipelines or other clean gas and liquid applications. They are simple to install and require no spool piece, but can be clog prone in dirty gas or solid-laden media. While effective, they generally have a higher head loss coefficient so may cause more pressure drop than tube bundles or tab-type products.
Tab-type flow conditioners are a good choice in clean or dirty gases and liquids because of the tabs tapered design. They provide excellent cross-mixing to remove swirl and correct velocity profiles with virtually no pressure-drop. They are the only technology that can be retrofitted into elbows. However, their design is unsuitable for most sanitary applications.
Tube bundles and vanes have been used for decades. Tube bundles reduce swirl in clean gases and liquids, but do not correct velocity profiles and are unsuitable for custody transfer applications. Vanes also remove swirl, but cannot isolate or remove flow irregularities.
When making your selection or consulting with a vendor, ensure you know these key process variables:
Viscosity range of the process media;
Solids content in the gas or liquid; and,
Tolerable pressure loss vs. conditioning effectiveness.
These elements are critical to final selection and proper installation.
Tab-type flow conditioners have been proven effective in highly rugged conditions. For instance, a standard Vortab flow conditioner is a straight pipe fitted with a short section of swirl reduction tabs combined with three arrays of profile conditioning tabs. Combining both types of tabs creates a repeatable, flat velocity profile at the outlet. The technology also can be designed into an elbow flow conditioner. (See illustration.)
Tab-type flow conditioners are suitable for applications in many different processes:
Irregular material flows caused by poor piping adversely affect the accuracy and repeatability of flow meter readings.Tab-type flow conditioners are effective at reducing swirl and velocity profile problems with minimal pressure drop. They also tolerate dirty media and solids content.
An offshore oil pumping station needed to add a pump to increase capacity, but since there was no room for the pump’s required straight pipe run, installers had to connect an elbow directly to the pump inlet. Placing a tab-type conditioner in the elbow solved the problem by ensuring properly conditioned flow entering the pump. This saved cost and freed precious real estate for other uses.
An electric power plant needed to add two identical 14-in. centrifugal pumps to feed water into its main boilers. Space restraints dictated making a 90° turn at the inlet. To make matters worse, after the elbow, the pipe size drops from 16 to 14 in. immediately at the pump inlet. Placing a tab-type flow conditioner in the elbow compensated for the lack of straight run and provided equally distributed flow entering the pumps.
A natural gas producer faced space limitation problems when retrofitting a pipeline pumping station with a new compressor. Existing underground piping precluded installing proper straight pipe runs required for the 3,500 hp unit. Instead of digging out of the problem, an elbow fitted with a tab-type flow conditioner was plumbed directly into the compressor’s inlet.
If you’re planning a facility expansion or retrofit, examine the straight pipe run requirements of all equipment involved. Valves, pumps, compressors, and flowmeters can all be affected by flow disturbances caused by poor piping layouts. Such problems can be costly, resulting in poor end-product quality, equipment repairs or failures, and even line shut-downs.
When you’re simply out of room or when changing the piping configuration is cost prohibitive, flow conditioners are an excellent solution with a careful and informed selection.
Don Lundberg is a senior engineer at Vortab Co.,
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