Alfa Laval Aalborg XS-2V and XS-7V

Waste heat recovery economizers for marine engines

The Alfa Laval Aalborg XS-2V and XS-7V are robust smoke-tube

economizers. Easy to install, operate and maintain, they reduce

the use of the fired boiler by recovering heat energy that

otherwise would be lost through the engine exhaust gas.

This ensures a rapid return on investment. The Aalborg XS-2V

is equipped with its own steam space, which makes it a

complete exhaust gas boiler. The Aalborg XS-7V shares a steam

space with the fired boiler. The proven design of both

economizers includes a dual-inlet option, which creates high

installation flexibility.

Application

Only a portion of the fuel energy released by marine engines

actually goes to propulsion. A large amount of it escapes as

heat, and it makes sense to reclaim as much of this energy

as possible. This is true not only for main engines, but for

auxiliary engines as well.

Steam produced with the Aalborg XS-2V or XS-7V can

support or fulfil steam needs in port, but it can also serve

other functions. For vessels whose long-stroke main engines

produce cooler exhaust, it can provide a needed steam

boost during a voyage. If there is no steam shortage while

sailing, the additional steam produced with the economizer

can be used to generate electricity, for example by means

of Organic Rankine Cycle (ORC) technology.

Benefits

• Simple and reliable design based on smoke tubes

• Easy improvement of Carbon Intensity Indicator (CII)

• Short payback time (typically 1–2 years) through up

to 25% fuel savings on the fired boiler

• Reduced wear and maintenance on the fired boiler

• Dual-inlet option allowing connection of two engines

to one economizer

Working principle

The Aalborg XS-2V and XS-7V are installed after a vessel’s

main or auxiliary engines. When the exhaust gas passes over

the economizer’s heating surface, the waste heat energy in

the gas is absorbed for the production of steam. Dry running

is possible in the event of an emergency.

The two models differ in how produced steam is handled:

• The Aalborg XS-2V is a full exhaust gas boiler with its own

steam space, which can operate independently from the

fired boiler.

• The Aalborg XS-7V is designed for forced circulation

and is used in connection with one or more fired boilers,

which act as the steam space.

Design

Built for simplicity and reliability, the Aalborg XS-2V and

XS-7V have a vertical, all-welded design with straight smoke

tubes. The option of dual inlets allows one economizer to

serve two engines, with half the tubes dedicated to one

engine and half dedicated to the other. This can reduce

installation costs and complexity.

The smoke-tube design is easy to clean and maintain,

especially as the high gas velocity through the economizer

minimizes fouling. If needed, individual smoke tubes can also

be repaired or replaced.