Shell-and-tube heat exchanger in oil refineries

A shell - and - tube heat exchanger is a crucial component in oil refineries. It is used to transfer heat between two fluids without allowing them to mix. In an oil refinery, these fluids can include crude oil, various refined products, steam, cooling water, and other process fluids. The basic structure consists of a cylindrical shell that houses a bundle of tubes. One fluid flows through the tubes (the tube - side fluid), while the other fluid circulates around the tubes within the shell (the shell - side fluid).

Applications in Oil Refining Processes

Crude Oil Pre - heating:

Before crude oil enters the distillation unit, it is often pre - heated using a shell - and - tube heat exchanger. The heat source can be the hot products from other refining processes or steam. By pre - heating the crude oil, the energy required for distillation is reduced. For example, heat from the hot naphtha or kerosene fractions can be transferred to the incoming crude oil, improving the overall energy efficiency of the distillation process.

Product Cooling and Condensation:

After the distillation of crude oil, the various fractions such as gasoline, diesel, and jet fuel need to be cooled and condensed. Shell - and - tube heat exchangers are used to remove the heat from these products. Cooling water is typically circulated on the shell - side to cool the hot product flowing through the tubes. This process is essential for separating the different fractions and obtaining the desired product specifications. For instance, in the case of gasoline production, the vaporized gasoline is condensed to a liquid state using a heat exchanger to meet the required storage and transportation conditions.

Heat Recovery:

Oil refineries are energy - intensive operations. Shell - and - tube heat exchangers play a vital role in heat recovery systems. For example, the waste heat from high - temperature processes such as catalytic cracking can be recovered and used to pre - heat other fluids. The hot flue gases from a furnace can be used to heat process fluids in a shell - and - tube heat exchanger, reducing the need for additional energy input and minimizing the refinery's overall energy consumption.

Design Considerations for Oil Refinery Applications

Materials of Construction:

Given the corrosive nature of many of the fluids in an oil refinery (such as crude oil with its sulfur content and various chemicals), the materials of the shell and tubes must be carefully selected. Stainless steel, alloy steels, and other corrosion - resistant materials are often used. For example, in heat exchangers handling sour crude oil (crude oil with a high sulfur content), alloys that can withstand sulfide - induced corrosion, like duplex stainless steel, may be preferred.

Tube Bundle Design:

The tube bundle design affects the heat transfer efficiency. The tubes can be arranged in different patterns such as square, triangular, or rotated square pitch. A triangular pitch arrangement generally provides a more compact design and better heat transfer characteristics for turbulent flow conditions. The tube diameter, length, and wall thickness are also determined based on the flow rates, pressure drops, and heat transfer requirements of the specific process. For example, in a heat exchanger used for high - flow - rate applications, larger - diameter tubes may be used to reduce the pressure drop.

Shell - Side Flow Design:

The flow of the shell - side fluid is optimized to enhance heat transfer and minimize pressure losses. Baffles are installed inside the shell to direct the fluid flow across the tubes in a more efficient manner. The baffle spacing and type (such as segmental baffles or helical baffles) are designed according to the fluid properties and flow rate. Helical baffles, for example, can provide a more uniform flow distribution and reduce fouling compared to segmental baffles in some applications.