Alfa Laval Aalborg XWi Natural circulation exhaust gas steam boiler

Introduction

The Alfa Laval Aalborg XWi is an exhaust gas steam boiler with

an integrated natural circulation system. Natural circulation

uses physical phenomena to drive the water through the boiler

unit, which removes the need for circulation pumps.

The Aalborg XWi offers considerable savings and optimal

operational safety, as confirmed by the positive feedback from

customers.

The Aalborg XWi offers savings in waste heat recovery systems

on vessels that have four-stroke engines and are frequently

put in to harbour, such as cruise vessels and passenger ferries.

The Aalborg XWi eliminates all typical problems associated

with forced circulation systems, such as cavitation, water

hammering, and operation and main tenance losses.

Key Benefits

• Simple, reliable operation based on natural circulation,

without pumps or rotating components

• Maximized safety, minimized risk of soot fires

• Minimal heat losses

• No circulation pumps to operate or maintain – avoid pump

electricity consumption and continuous maintenance costs

• Reduced total installation and material costs

• Clear responsibility limit – including piping between the boiler

and the drum

• Increased system redundancy

• Potential integration of electrical steam generation while

engine is not running

• Modular design enabling tailored configurations, including

selectable multi-stage heating solutions

Design

The Aalborg XWi has the same heat transfer features as a

traditional exhaust gas boiler with forced circulation, but its

special design eliminates safety risks, heat losses, continuous

maintenance needs and pump operating costs.

The heating surface of the Aalborg XWi is made up of gilled

water tubes as standard, with a construction that minimizes soot

build-up. In addition, the system can be equipped with optimized

steam sootblowers. Design pressure and boiler capacity can be

optimized according to specific needs.

The boiler can be designed with its own integrated steam

drum, or with a separate steam drum. There are no operational

connections to fired boilers, which means more redundancy, but

still considerably less piping. The boiler’s own dedicated water

circulation system eliminates the risk of water hammering.

Tailored configurations

The Aalborg XWi boiler drum can be integrated with electrical

heating elements to utilize shore power connection for steam

generation while on port. The heating surface configuration is

flexible. The energy efficiency of the system can be increased

by adding tube section for feed water preheating and/or

superheating as well as hot water generation. The design of

the heating surface can be tailored to the actual engine and

operating conditions, maintaining sufficient exhaust gas velocity

for the best self-cleaning effects within the design limits.

How it works

Natural circulation refers to the ability of fluid in a system to

circulate by means of gravity and density differences. In the

Aalborg XWi, circulation begins naturally when the engine starts

and ends naturally when the engine stops. Water remains inside

the heating surface tubes, which prevents the risk of a soot fire,

and energy loss is minimized because there is no unnecessary

circulation during standstill.

Because water only circulates through the Aalborg XWi when the

engine is running, no heat is lost to the cold air that flows through

the boiler when the engine is stopped. This means less use of the

fired boiler, with lower fuel costs and emissions as a result.

When the circulation is stopped, water fills the boiler tubes. This

minimizes the risk for soot fires, which can occur with forced

circulation. In forced circulation, typical system arrangement and

sudden changes in engine load often lead to problems in water

circulation, such as pump cavitation, which can cause a soot fire

within the system.