Types of Heat Exchangers in Refineries and Oil & Gas: Which Exchanger Goes Where

Quick Answer

Refineries and oil and gas plants use six main families of heat exchanger. Shell-and-tube exchangers, built to TEMA Class R and usually API 660, are the large majority by count: crude preheat trains, pumparound and product coolers, condensers, reboilers and high-pressure feed/effluent exchangers. Air-cooled exchangers (API 661) condense column overheads and cool products wherever cooling water is scarce or expensive. Plate and welded-plate exchangers take clean, close-temperature duties such as lean/rich amine exchange and catalytic reformer feed/effluent. Double-pipe and hairpin exchangers handle small, high-pressure or temperature-cross duties. Brazed aluminium plate-fin and coil-wound exchangers run the cryogenic sections of gas processing and LNG plants. And a group of specialist designs serves the hardest services: breech-lock (screw-plug) closures in hydrocrackers and hydrotreaters, kettle and thermosiphon reboilers on columns, and transfer line exchangers that quench cracked gas in ethylene plants. Material selection follows the service: carbon steel for most hydrocarbon duty, Cr-Mo steels and stainless overlay for high-temperature hydrogen and sulfur, duplex, titanium or copper-nickel for seawater and chlorides.

Ask a process engineer what types of heat exchanger a refinery uses and the answer is usually "all of them, but mostly one." A refinery of any size runs hundreds of heat exchangers. Most are shell-and-tube units. The rest exist because a particular unit has a particular problem that shell-and-tube does not solve as well — no cooling water, a tiny temperature approach, a pressure at which a bolted girth flange becomes enormous and prone to leaking, or a gas that has to be cooled from over 800°C in a fraction of a second.

The useful way to understand refinery exchangers is not by type, but by unit: what each part of the plant asks its exchangers to do. This guide walks through the main process units and explains which exchanger goes where, and why.

Why Shell-and-Tube Dominates

Shell-and-tube exchangers are the default in refining and oil and gas for reasons that have not changed in decades:

• Pressure and temperature range. From vacuum to well over 100 bar, and from cryogenic to several hundred degrees Celsius
• Tolerance of dirty fluids. Crude oil, residues and slurries foul everything; shell-and-tube units can be designed with the fouling fluid on the tube side, where it can be cleaned mechanically
• Maintainability. Removable bundles, retubing and tube plugging keep units in service for decades
• Standardisation. TEMA Class R construction and API 660 give owners a common, well-understood basis across vendors
• Material flexibility. Tubes, tubesheets and shells can each be in a different material, including clad construction

Our guides to shell-and-tube TEMA types and the heat exchanger manufacturing process cover how they are configured and built.

Unit by Unit: Which Exchanger Goes Where

Crude distillation unit (CDU)

The crude preheat train. Before crude enters the atmospheric furnace it is heated by exchange with hot product and pumparound streams leaving the column — commonly through a dozen or more shell-and-tube shells in series and parallel. The desalter sits part-way along the train, where the crude is warm enough for good water separation. Every degree recovered in the preheat train is a degree the furnace does not have to supply, so the train's performance shows up directly in fuel consumption.

• Type: shell-and-tube, typically floating-head (AES) units with crude on the tube side so tubes can be cleaned mechanically
• The problem: fouling. Crude preheat trains foul continuously — asphaltenes, salts, corrosion products, coke on the hotter end — and train performance declines between cleanings
• Design responses: higher tube-side velocity, cleanable layouts, bypasses so individual shells can be cleaned on stream

Overhead condensers. The column overhead vapour is condensed, usually first in air-cooled exchangers and then in water-cooled trim coolers. Overhead systems are corrosion hotspots — hydrochloric acid and ammonium chloride form where water condenses — so materials and wash water design matter as much as thermal design.

Pumparound and product coolers. Side draws and pumparounds give up heat to the preheat train and are then cooled to rundown temperature in air or water coolers.

Vacuum distillation unit (VDU)

• Vacuum residue exchangers handle hot, viscous, heavily fouling residue — often with residue on the tube side and generous fouling margins
• Ejector condensers condense steam and hydrocarbons between ejector stages and are critical to holding vacuum; small leaks or fouling here cost column performance immediately

Fluid catalytic cracking (FCC)

• Slurry exchangers and steam generators on the main fractionator bottoms carry catalyst fines, so tube-side velocity is held in a window — high enough to limit fouling, low enough to limit erosion
• Gas concentration unit reboilers and condensers on the absorber, debutanizer and splitter columns
• Flue gas heat recovery — waste heat boilers and economisers on the regenerator flue gas

Hydrotreaters and hydrocrackers

These are the most demanding exchangers in a refinery, and the reason specialist heat exchanger construction exists.

Feed/effluent exchangers recover heat from the hot reactor effluent into the incoming feed and hydrogen. They see high pressure — commonly 100 bar and above in hydrocrackers — high temperature, hydrogen and hydrogen sulfide together.

• Type: shell-and-tube with heavy forged components, and for the highest pressures, breech-lock (screw-plug) closures instead of bolted girth flanges. In a breech-lock design the channel is closed by a threaded plug ring, and the gasket load is applied through the threads rather than through a ring of large studs — avoiding the huge, leak-prone bolted joint that a conventional flange at that pressure and diameter would need, and allowing the closure to be retightened without opening it
• Materials: Cr-Mo steels selected against the hydrogen partial pressure and temperature, often with austenitic stainless weld overlay on surfaces exposed to high-temperature hydrogen and sulfur. See our guide to weld overlay and clad construction
• Key design references: API RP 941 for resistance to high-temperature hydrogen attack, and API RP 934-A for heavy-wall Cr-Mo vessels in high-temperature, high-pressure hydrogen service

Reactor effluent air coolers (REAC) cool the effluent after the feed/effluent train. They are notorious for ammonium bisulfide and ammonium chloride corrosion, controlled by wash water injection, velocity limits and materials such as duplex stainless or nickel alloy tubes in severe cases.

Catalytic reforming

The reformer's combined feed/effluent exchanger heats the naphtha feed and recycle hydrogen with the hot reactor effluent. Pressure drop matters enormously, because every bar lost has to be made up by the recycle gas compressor. Two designs dominate:

• Large vertical single-pass shell-and-tube exchangers — the tall units known in the industry as "Texas towers" — with pure counter-current flow and low pressure drop
• Welded plate-type feed/effluent exchangers, which achieve very close temperature approaches in a compact unit

Alkylation

• Hydrofluoric acid units use nickel-copper alloys such as Alloy 400 in the most corrosive acid-wetted services
• Sulfuric acid units rely largely on carbon steel with strict velocity limits, and alloys where velocity or temperature are higher

Amine treating and sulfur recovery

• Lean/rich amine exchangers recover heat between the regenerator bottoms and the rich amine feed — a clean, close-approach duty often given to plate-and-frame or shell-and-tube exchangers
• Amine regenerator reboilers — kettle or thermosiphon — are run with moderate steam temperatures to limit amine degradation
• Carbon steel in amine service is post-weld heat treated against amine stress corrosion cracking, following API RP 945
• Sulfur recovery units use fire-tube waste heat boilers after the thermal reactor, and sulfur condensers between catalytic stages

Sour water strippers

Feed/bottoms exchangers and reboilers in sour water service combine ammonia, hydrogen sulfide and fouling — a classic case for wet H₂S material requirements under NACE MR0103 / ISO 17945.

Utilities

• Cooling water exchangers across the plant, often with seawater or brackish water at coastal refineries — titanium, copper-nickel or super duplex tubes
• Steam surface condensers on turbine drives
• Boiler feedwater preheaters and steam generators recovering heat from process streams

Gas processing and LNG

• Gas/gas exchangers and chillers — shell-and-tube and kettle-type chillers with propane or other refrigerants
• Brazed aluminium plate-fin heat exchangers in cold boxes for NGL recovery and liquefaction, handling many streams at very close approaches. Aluminium is vulnerable to mercury, so mercury removal upstream of the cold box is standard practice
• Coil-wound (spiral-wound) exchangers as main cryogenic heat exchangers in large LNG trains
• Printed circuit and other diffusion-bonded compact exchangers offshore, where weight and space are expensive
• Glycol and amine regeneration exchangers, as in refinery treating units

Upstream production

• Crude oil heaters and coolers, produced water exchangers
• Compressor intercoolers and aftercoolers, most often air-cooled
• Lube and seal oil coolers — small shell-and-tube or plate units on rotating equipment packages

Petrochemical crackers

In an ethylene steam cracker, cracked gas leaves the furnace coils at around 800–850°C and must be cooled to roughly 250–400°C within milliseconds to stop the reactions continuing and degrading the product. Transfer line exchangers (TLEs) — also called quench exchangers — do this while generating high-pressure steam from the recovered heat. They are specialised designs, with thin, flexible tubesheets or double-tube constructions that survive the extreme thermal gradients.

Reboilers: Kettle, Thermosiphon or Forced Circulation

Every distillation column needs a reboiler, and choosing the type is one of the more consequential exchanger decisions in a plant.

The cones visible on kettle reboilers — where the shell steps up from the bundle diameter to the larger kettle diameter — are one of the fabrication details covered in our guide to heat exchanger shells, cones and nozzles.

Materials by Service

For tube material selection in depth, see our heat exchanger tube materials guide; for production-side sour service, see NACE MR0175 / ISO 15156.

Hydrogen Service: Why It Needs Specialist Construction

Hydrogen at high temperature and pressure attacks carbon steel from the inside. Hydrogen diffuses into the steel and reacts with carbides to form methane at the grain boundaries, causing fissuring and loss of strength — high-temperature hydrogen attack (HTHA). It can progress without visible surface damage.

• Material selection follows API RP 941, whose "Nelson curves" set temperature and hydrogen partial pressure limits for carbon and Cr-Mo steels. The limits have been revised as failure experience accumulated — the 2016 edition, for example, added a lower curve for carbon steel welded without PWHT — so equipment designed decades ago is worth reviewing against the current edition
• Heavy-wall Cr-Mo construction — 2¼Cr-1Mo and its vanadium-modified variants — needs controlled chemistry against temper embrittlement, and careful welding and heat treatment, as set out in API RP 934-A
• Stainless overlay on hydrogen- and sulfur-exposed surfaces brings its own risk: hydrogen-induced disbonding on cool-down, managed by qualified overlay procedures and controlled cooling rates
• Closures at hydrocracker pressures favour breech-lock designs over very large bolted girth flanges

Kasko Makine manufactures heat exchangers for exactly these services: hydrogen-resistant units, exchangers for hydrorefining and catalytic reforming, hydrocracking equipment and coolers for the rapid cooling of cracked gases.

How to Specify a Refinery Heat Exchanger

1. Complete the data sheet — both fluids, all operating cases including start-up and end-of-run, fouling resistances that are justified rather than habitual. See our guide to TEMA data sheets
2. State the construction basis — TEMA class, API 660 and any owner specification
3. Define the damage mechanisms — hydrogen partial pressure, H₂S, chlorides, ammonia, amine, naphthenic acid — so materials are selected for the service, not for the price
4. Set MDMT for cold climates and depressurisation cases
5. Specify maintenance access — which side will be cleaned, how, and how often
6. Agree inspection and testing — radiography level, PWHT, hardness testing, PMI, tube-joint leak testing and hydrostatic test sequence

Common Specification Mistakes

1. Fouling fluid placed on the shell side of a fixed-tubesheet unit. The shell side cannot be cleaned mechanically, and performance never recovers.

   Prevention: Put the fouling fluid on the tube side, or use a removable-bundle construction with a cleanable layout.

2. Copying fouling factors from an old data sheet. Oversizing for fouling lowers velocity and can make the exchanger foul faster.

   Prevention: Base fouling resistances on operating data for the service, and design velocity to resist fouling.

3. Carbon steel in high-temperature hydrogen service without an API 941 check. HTHA develops invisibly.

   Prevention: Check every exchanger in hydrogen service against the current API RP 941 curves, using the actual hydrogen partial pressure and metal temperature.

4. Amine service without PWHT. Amine stress corrosion cracking at welds.

   Prevention: Specify PWHT of carbon steel in amine service in line with API RP 945.

5. Air-cooled overhead condensers without a corrosion review. Ammonium chloride and bisulfide attack in tubes and headers.

   Prevention: Review salt deposition and velocity, wash water injection and tube materials during design.

6. Brazed aluminium exchanger without mercury removal upstream. Mercury attacks aluminium and can cause sudden failure.

   Prevention: Specify mercury removal and monitoring upstream of any aluminium cryogenic exchanger.

7. No MDMT for cold-climate plants or depressurisation. Brittle fracture risk in carbon steel.

   Prevention: Define MDMT from the coldest credible metal temperature under pressure, including auto-refrigeration.

8. Bolted girth flanges at hydrocracker pressures. Large flanges leak under thermal cycling.

   Prevention: Evaluate breech-lock or other high-pressure closures for high-pressure feed/effluent service.

Supply from Kasko Makine

Tubular heat exchangers for refinery, petrochemical and gas plant service

• U-tube, floating-head, fixed tube plate and tube-in-tube exchangers
• Coolers, heaters, condensers and reboilers
• Predominantly TEMA Class R construction, designed to ASME, AD 2000-Merkblätter, EN 13445, ČSN 69 0010 or STN 69 0010

Demanding services

• Hydrogen-resistant heat exchangers for high-temperature hydrogen service
• Exchangers for hydrorefining and catalytic reforming units
• Heat exchangers for hydrocracking plant
• Coolers for the rapid cooling of cracked gases

Materials

Carbon steels including low-temperature grades, Cr-Mo alloy steels and austenitic stainless steels, with weld overlay and clad construction for hydrogen, sulfur and corrosive services.

Related equipment

• Industrial process columns
• Equipment for pressure testing heat exchangers
• Heat exchanger gaskets
• Replacement bundles, tubes and spare parts

Engineering support

Send the process data sheet with the unit, service and damage mechanisms, design code and MDMT. We will propose the construction, materials and inspection plan for the service, and quote.

Certification

Material certificates to EN 10204 3.1 or 3.2, welding and overlay procedure qualifications, NDE and PMI reports, hardness testing where specified, PWHT charts and hydrostatic test certificates, compiled into a complete data book.

Send your process data sheet for a heat exchanger selection and quotation within five working days. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading: Heat Exchanger Series

• Heat Exchangers: Types, Working Principles and Applications
• Shell and Tube Heat Exchangers: TEMA Types and Configurations
• Air-Cooled Heat Exchangers: Design and Selection
• Plate Heat Exchangers: Types and Selection
• Heat Exchanger Manufacturing Process: Step by Step

Frequently Asked Questions

Q: What types of heat exchangers are used in refineries?
A: Shell-and-tube exchangers built to TEMA Class R and API 660 are the large majority, serving crude preheat trains, coolers, condensers, reboilers and high-pressure feed/effluent duties. Refineries also use air-cooled exchangers for overheads and product cooling, plate and welded-plate exchangers for clean close-approach duties, double-pipe units for small high-pressure services, and specialist designs such as breech-lock exchangers and kettle and thermosiphon reboilers.

Q: What heat exchangers are used in the oil and gas industry?
A: Upstream and midstream plants use shell-and-tube exchangers for crude, produced water and gas service, air-cooled exchangers for compressor intercoolers and aftercoolers, plate exchangers for clean utilities and amine duties, brazed aluminium plate-fin and coil-wound exchangers for cryogenic gas processing and LNG, and printed circuit or other compact exchangers offshore where weight and space are limited.

Q: Why are shell-and-tube exchangers preferred in refineries?
A: They cover the widest pressure and temperature range, tolerate fouling fluids that can be placed on the cleanable tube side, have removable bundles that can be cleaned, plugged or retubed, allow different materials for tubes, tubesheets and shells, and are standardised through TEMA Class R and API 660, so owners can maintain and replace them on a common basis across vendors.

Q: What is a crude preheat train?
A: It is the series of heat exchangers, commonly a dozen or more shell-and-tube shells, that heats crude oil with hot product and pumparound streams before the atmospheric furnace. The desalter sits part-way along the train. Preheat performance directly affects furnace fuel use, and fouling from asphaltenes, salts and coke is the main operating problem.

Q: What is a feed/effluent heat exchanger?
A: A feed/effluent exchanger recovers heat from a hot reactor effluent into the incoming reactor feed, reducing heater duty. In hydrotreaters and hydrocrackers these exchangers operate at high pressure with hydrogen and hydrogen sulfide, so they use Cr-Mo steels, stainless overlay and, at the highest pressures, breech-lock closures. Reformers use vertical single-pass or welded-plate designs to minimise pressure drop.

Q: What is a breech-lock heat exchanger?
A: A breech-lock or screw-plug exchanger closes its channel with a threaded plug ring instead of a large bolted girth flange. The gasket load is applied through the threads, avoiding the huge, leak-prone bolted joint that very high pressures and diameters would otherwise require, and the closure can be retightened from outside. It is used mainly in high-pressure hydrocracker and hydrotreater feed/effluent service.

Q: What is the difference between a kettle and a thermosiphon reboiler?
A: A kettle reboiler submerges the tube bundle in a pool of boiling liquid inside an enlarged shell, with vapour disengaging above; it is stable over a wide operating range and handles high vaporisation. A thermosiphon reboiler relies on natural circulation from the column through the exchanger and back, and is cheaper and more compact. Horizontal thermosiphons are common in refineries; vertical ones in chemical plants.