Atmospheric distillation

Optimizing  refinery atmospheric distillation processes

Atmospheric distillation preheat trains are intended to minimize total energy consumption of the plant by maximizing heat recovery from hot fractions. Alfa Laval has the expertise, technologies and services to contribute to reliability, energy savings, less maintenance, reduced costs and increased production.

Increasing energy efficiency in atmospheric distillation

A typical preheat train using traditional shell-and-tube heat exchangers, is based on a pinch/overall temperature approach of approximately 30°C. This takes into account practical limitations, such as heat transfer area required, space limitations, installed costs, hydraulic limitations and operating performance.

Plate heat exchangers, on the other hand, have an optimal pinch between 5° and 10°C, which means that up to 25% more energy can be recovered from the hot fractions and used to preheat the crude. This also results in a 25% energy savings in the fired heater.

Using compact heat exchangers, such as the Alfa Laval Compabloc, also makes it possible to recover energy from very low grade sources, such as the overhead vapour in an atmospheric distillation column. Because the Compabloc can be economically produced in high-grade materials, corrosion problems can be eliminated. In addition, Compabloc requires minimal plot space and has a low hold-up volume, making it very cost efficient to install on construction.

Fouling mitigation in atmospheric distillation

Traditional shell-and-tube heat exchangers normally experience fouling problems. Fouling usually occurs in the hot end of the preheat train where residue is used as the heating media, and temperatures are high and velocities low. Fouling is very costly and, over time, increases the use of energy in the fired heater as well as the use of power for the feed pump. It also can limit production if the maximum capacity of the fired heater or the feed pump has been reached. This means that the heat exchangers need frequent cleaning, which affects the overall performance of the plant.

To minimize chemical deposition fouling, Alfa Laval Compabloc heat exchangers are designed with high turbulence and shear stress in the heat transfer channels. This results in a much longer run length – typically up to three times longer – than shell-and-tube heat exchangers.

Because Alfa Laval Compabloc heat exchangers provide high heat transfer efficiency, fewer exchangers are needed for each service. What’s more, our heat exchangers are designed for easy access and fast, effective mechanical cleaning of the heat transfer area, which minimimzes maintenance costs.

CAPEX savings for atmospheric distillation

The number and size of traditional shell-and-tube heat exchangers required for atmospheric distillation increase as the amount of energy recovered from the hot fractions into the crude increases.

With high-efficiency Alfa Laval Compabloc heat exchangers, no more than two units are generally required for each service, no matter the degree of heat recovery. These units require three to five times less heat transfer area than comparable shell-and-tubes due to the high heat transfer efficiency and the use of thin heat transfer platesthat further reduce the amount of material used.

By minimizing the number of exchangers and the heat transfer material required, the costs of the exchanger itself as well as its installation are drastically reduced. This is especially true when higher grade material is needed for high corrosion resistance. It is possible to achieve cost reductions of up to 80%.

For revamp projects, payback generally takes anywhere from a few months or, at most, two years, depending on the project’s complexity. For grassroot refineries, savings of up to 30 MEUR can be realized on preheat train heat exchangers and installation cost.

In addition, by maximizing the heat recovery in the preheat train, the investment costs in fired heater capacity can also be minimized. Likewise, by minimizing the overall pressure drop in the preheat train, the feed pump capacity and head can be reduced, which can also reduce the design pressure limits of all equipment in the preheat train.

Proven technology for refinery atmospheric distillation

Alfa Laval has more than 650 Compabloc heat exchangers operating in atmospheric distillation processes around the world. Most of the exchangers are installed as overhead condensers, around the pinch, or at the end of the preheat train, just before the furnace. However, there are several preheat trains where every single heat recovery position uses an Alfa Laval Compabloc exchanger.