Plate vs shell and tube heat exchangers: how to choose

Choose a plate heat exchanger when you need high efficiency, a close approach temperature and a small footprint at moderate pressure and temperature. Choose shell and tube for high pressure, high temperature, very unequal flows, or fluids with heavy solids and fibers. Many plants use both, each where it fits best.

How do plate and shell and tube exchangers work?

A plate heat exchanger moves heat between two fluids flowing in thin channels between corrugated metal plates. A shell and tube exchanger moves heat between a fluid flowing inside a bundle of tubes and a second fluid flowing around the tubes inside a cylindrical shell. Both keep the fluids separate while transferring heat through metal walls.

In a plate unit, the corrugations create strong turbulence even at low velocity, which drives high heat transfer. Hot and cold fluids flow in alternating channels, usually in true counterflow.

In a shell and tube unit, baffles direct the shell side fluid across the tube bundle. The design is simple, rugged and highly flexible, which is why it remains the most common exchanger type in heavy industry.

Which takes up less space?

A plate heat exchanger typically needs far less floor space than a shell and tube unit for the same duty. Higher heat transfer coefficients mean less surface area is required, and the plates pack that area tightly. Plate units also need much less room for maintenance, since the frame opens in place instead of needing space to pull a tube bundle.

That makes plate units a strong fit for retrofits, skids and crowded mechanical rooms. Shell and tube exchangers need clearance roughly equal to the bundle length if the bundle must be removed for cleaning.

Which is more efficient?

Plate heat exchangers are generally more thermally efficient. Turbulent flow in narrow channels produces heat transfer coefficients often several times higher than a comparable shell and tube design. That means less surface area, less metal and lower fluid holdup for the same duty, which can lower cost in stainless and higher alloys.

Shell and tube units can close the gap with enhanced tubes, more passes or larger shells, but usually at the cost of size and weight.

What approach temperature can each achieve?

Plate heat exchangers can achieve very close approach temperatures, often within about 1 to 2 degrees C (roughly 2 to 4 degrees F) between the outlet of one fluid and the inlet of the other. Shell and tube units more commonly operate with approaches of about 5 to 10 degrees C (roughly 10 to 20 degrees F).

Close approach matters for heat recovery. If you want to preheat an incoming stream with an outgoing one and recover as much energy as possible, a plate unit usually gets you closer. True counterflow in a plate exchanger also handles temperature cross, where the cold outlet runs hotter than the hot outlet, more easily than a single shell.

What are the pressure and temperature limits?

Shell and tube heat exchangers handle much higher pressures and temperatures. Gasketed plate exchangers are limited by their gaskets and frame, typically to roughly 25 bar (about 360 psi) and about 180 degrees C (about 350 degrees F), depending on gasket material and design. Shell and tube units are routinely built for far more demanding conditions.

Welded plate designs extend the plate range by removing some or all gaskets, but for very high pressure steam, high temperature process gas or large pressure differences between the two sides, shell and tube remains the standard choice.

How do fouling and cleaning compare?

Plate exchangers resist fouling well thanks to high turbulence, and gasketed units open for easy inspection and cleaning. However, narrow channels can plug with large particles or fibers. Shell and tube units tolerate dirtier fluids, and the tube side can be cleaned mechanically. The right choice depends on what is in your fluid.

• Gasketed plate: open the frame, clean or replace plates and gaskets. Clean in place is also common.
• Brazed or all welded plate: cannot be opened, so clean in place is the main option.
• Shell and tube, tube side: straight tubes can be rodded, brushed or hydroblasted.
• Shell and tube, shell side: harder to clean unless the bundle is removable, so put the dirtier fluid in the tubes when possible.

What are the main types of plate heat exchangers?

The four main types are gasketed, semi welded, all welded and brazed. They differ in how the plates are sealed, which sets their pressure and temperature range, the fluids they can handle and whether they can be opened. Gasketed units offer the most flexibility. Brazed and all welded units handle tougher conditions but cannot be taken apart.

• Gasketed: plates sealed with elastomer gaskets in a bolted frame. Easy to open, clean and expand by adding plates. Common in HVAC, food and general process service.
• Semi welded: pairs of plates welded into cassettes, with gaskets only between cassettes. The aggressive fluid stays in the welded channel. Used for refrigerants such as ammonia and some corrosive services.
• All welded: no gaskets at all, for higher pressures, higher temperatures and fluids that attack gaskets.
• Brazed: plates brazed together, usually with copper or nickel, into a compact sealed block. Common for refrigeration, HVAC and small duties.

API Heat Transfer offers Schmidt plate heat exchangers, and APV offers plate exchangers and sanitary equipment for food, beverage and dairy service.

What are TEMA shell and tube types?

TEMA, the Tubular Exchanger Manufacturers Association, defines shell and tube designs using a three letter code: front head, shell and rear head. Common examples are BEM fixed tubesheet, AES floating head and BEU U tube. TEMA also sets mechanical classes R, C and B for different levels of service.

• Fixed tubesheet (such as BEM): lowest cost, but the shell side cannot be cleaned mechanically and thermal expansion can be a concern.
• U tube (such as BEU): handles thermal expansion well and the bundle can be removed, but the tube bends are hard to clean.
• Floating head (such as AES or AET): removable bundle and good expansion handling, at higher cost.

Class R covers severe petroleum and related service, class C covers moderate commercial and general process service, and class B covers chemical process service. API Heat Transfer's BASCO line includes shell and tube exchangers for many of these duties.

How do they compare side by side?

The table below summarizes typical differences between the two technologies. Actual limits depend on the specific design, materials and gaskets, so treat these as general guidance. A thermal rating with your real process data is the only way to confirm the right choice.

Where is each type typically used?

Plate exchangers are typically used for HVAC, food and beverage, dairy, pharmaceutical, heat recovery and clean process water. Shell and tube exchangers are typically used in refining, petrochemical plants, power generation, steam heating and any service with high pressure, high temperature or dirty fluids. Choose by your operating conditions and fluids, not by habit.

PCT supplies both technologies from API Heat Transfer and APV and can help you compare options for your duty. See our heat exchangers and the API Heat Transfer lineup.

Sources

• Tubular Exchanger Manufacturers Association (TEMA)
• API Heat Transfer

Have a heat transfer duty to quote? Send us your fluids, flows, temperatures and pressures and we will help you choose the right exchanger. Request a quote.