Solution
Robert answered on
Dec 24 2021
Question 1
How impure boiler water damage boilers, evaporators etc, and what can can be done to avoid
such undesired consequences?
Answer
Boilers are fitted in most vessels either for the production of primary steam used to power the
main propulsion tu
ines or for the production of auxiliary steam used for heating, powering
auxiliary equipment and other ship services. Use of impure water can damage the boiler in
several ways.
Ways of damaging the Boiler
(a) Co
osion
Co
osion can take place in several ways in the feed system, with oxygen pitting being the most
prominent risk, leading to boiler tube failure. Alternatively, iron and copper products can be
transported from any part of the system into the boiler, build-up as hard insulating scale giving
ise to local overheating and perforation of tubes.
(b) Scale
The building-up of scale results at first with reduction in boiler efficiency. Excessive build-up
however, will cause local overheating of the tubes and as a result their eventual failure.
(c) Ca
y-over
Impurities
ought into the boiler by the feed water will concentrate and will eventually be
ca
ied over with the steam as soluble salts or suspended solids. The damage caused on tu
ine
lades, as a result, can be grave.
Ways of preventing the Boiler
(a) Co
osion
The co
osion process is essentially an oxidation process, which takes place when a metal
comes in touch with oxygen, reacts and is wasted. The most usual forms of co
osion are
pitting, general wastage and co
osion fatigue.
(b) Scale
To prevent scale from forming, water must be treated chemically inside the boiler even when
the source of water is de-ionized and considered “pure”. The internal treatment chemicals used
include soda ash, caustic soda and various types of sodium phosphates. It is essential to
properly monitor and control the quantities of chemical used, which will depend on the
amounts of impurities present.
(c) Ca
y Over
Ca
y-over takes place when steam is contaminated by boiler water and by the solids, which
this water contains. With time and as evaporation takes place in the boiler, the concentration
of certain salts increases and if this is allowed to exceed certain limits, ca
y-over will occur, i.e.
these salts will pass through the water – steam interface and will be ca
ied away with the
steam generated in the boiler.
Question 2
What are the benefits from incorporating tu
ochargers in 2-stroke slow speed engines, and
what are the potential safety hazards arising from their operation?
Answer
Inlet scavenging ports are a
anged in the cylinder liner and instead of the exhaust ports; this
simpler design uses the help of a valve, in the cylinder head, enabling the release of exhaust
gases. Air is let in under pressure generated by the tu
ocharger, driven by the exhaust gases
on their way out of the cylinder. The crankshaft sits in the engine bedplate and is kept in place
y the main bearing. “A” frames are bolted on the bedplate and contain the guides that keep
the crosshead in place, while it is travelling up and down. Finally, the engine block sits on top of
the “A” frames, and includes the cylinder jacket, the cylinder, the cylinder head, the scavenging
trunks etc.
Question 3
Why are gas tu
ines (diesel electric propulsion) becoming popular in modern cruise ships?
Answer
Gas tu
ines in some ways resemble both steam tu
ines and internal combustion engines.
They compress air and then combine it with fuel for combustion, like diesel engines, but their
power output is of steady flow nature and not intermittent power pulses, as is the case for
eciprocating engines. In steam tu
ines, the working substance is water and steam, the cycle is
closed (except for steam losses) and fuel is burned at atmospheric pressure to produce the heat
equired to raise steam, which...