Optimisation of Marine Boilers using Model-based Multivariable ...

2 1. INTRODUCTION
operation and high availability is expected. This means that there is a demand for a high
level of automation and reliable fault detection and accommodation.
Basically, marine boiler control is a matter of keeping water level and pressure near
specified setpoints. Today, the background theory used for designing marine boiler
controllers is based on single loop processes (ignoring the multivariable nature of the
process) resembling the principle applied to steam engines by James Watt in 1788.
These controllers are adjusted by the sevice engineer at commissioning, which requires
relatively large resources and further by no means ensures optimal performance.
This means that since the first marine boiler was built in Aalborg in 1912 there have
been only few developments in the basic control algorithm. However, due to the increased
market competition AI has found it necessary to look towards the development
of a more comprehensive, versatile and coherent control system. A new control system
is currently under development, which together with software tools as MATLAB �
/Simulink � and Real-Time Workshop � allows for rapid prototyping and faster implementation
of new advanced control strategies. Further, over the past few years AI has
initiated many student projects at Aalborg University focused on applying model-based
control and fault detection algorithms to a specific boiler family; the oil-fired one-pass
smoke tube boiler. This thesis focuses on model-based control of the marine boiler and
related topics.
1.2 The Marine Boiler
This section will give a basic introduction to marine boilers in order to make the reader
familiar with the application. First, a short introduction to the application of these large
steel constructions is given and the basic functionality is explained.
The class of marine boilers described in this work is used for offshore steam production.
The offshore carriers span from FPSO 1 vessels, tankers, container ships and bulk
carriers to passenger liners. The steam is used in a wide range of applications, among
others:
• Keeping heavy fuel in tanks at ≈ 45 ◦ C
• Preheating the fuel to ≈ 120-140 ◦ C before it enters the ship engine and boiler
burner
• Keeping oil and other cargo in tanks at a suitable temperature
• Heating cabins, producing hot water and producing fresh water
• Steam driven cargo pumps
• Tank cleaning.
1 Floating, Production, Storage and Offloading