marine engineering practice marine steam turbines

107 Pages·2007·3.9 MB·English

MARINE ENGINEERING PRACTICE
Volume I
Part 8
MARINE STEAM TURBINES
by
R. COATS, C.Eng., F.I.Mar.E., M.I.Mech.E.,
M.R.I.N.A., M.I.Weld., M.N.E.C.I.E.S.
THE INSTITUTE OF MARINE ENGINEERS
CONTENTS
Page
Introduction 1
I. Evolutionary Changes and Background 2
2. The Modern Turbine 3
3. Cleanliness of the Machinery and its Connecting
Pipework 57
4. Avoidance of Contamination of the Working Fluids 58
5. Operating Procedures 63
6. Operating Troubles 78
7. Maintenance and Adjustment 82
8. Papers for Further Study 96
References 103
INTRODUCTION
This Part is an attempt to review a wide range of marine turbine
machinery. Of necessity, many interesting designs have had to be omitted.
It has not been thought necessary to delve too deeply into the past, as the
old designs have already been adequately covered.·
Many turbines ofthese older typesare stillundoubtedly ingood service,
but, in the main, the illustrations in the present work willshow more recent
designs. It is hoped that the student or the operator of the older type of
machinery willrefer to the earlier book· for relevant information.
It ishoped that the ground covered, and particularly the section on the
operating aspects of the machinery willbe ofreal practical value, and that.
the supplementary information giveninthe abstracts from important papers
on steam turbine machinery willprovide a good stimulus for further study.
• "The Running and Maintenance of Marine Steam Turbines." In "The Running and Main-
tenance of Marine Machinery," Fifth Edition. Marine Media Management Ltd., London.
1
1. EVOLUTIONARY CHANGES AND
GENERAL BACKGROUND
The evolution of the marine steam turbine over the last twenty years
has brought about significant changes, not only in physical appearance, but
also in ratio of power to weight, in steam inlet conditions, in efficiencyand
fuelconsumption, inreliability, inthechange from manual to remote control,
and, very significantly, in the time taken to reach fulloperating power after
starting from cold conditions.
In general, the principles governing the correct maintenance and
operation ofthe machinery are unchanged, with differences in emphasis and
time scalearising from increased knowledge and differencesindetail designs.
These principles are:
1) Cleanliness of the machinery and its connecting pipework;
2) Avoidance of contamination of the working fluids, namely water,
steam, fueland lubricating oil;
3) Adherence to makers' recommendations on type of lubricating oil
for initial filland make-up purposes, and attention to fine filtering
and water removal;
4) Orderly procedures for warming through, start-up, manoeuvring,
fullaway and closing down to avoid distortion;
5) Attention to drainage facilitiesduring critical periods to avoid carry-
over ofwater into the turbines;
6) Avoidance of rust or other corrosion-promoting conditions;
7) Orderly recording and analysis ofinstrument readings incomparison
with trials figures; check on power and fuelconsumption;
8) Attention to auxiliary machinery to ensure correct movement of
fluids to and from the engine;
9) Attention to boiler cleanliness and efficient combustion to ensure
optimum overall efficiencyand minimum fuelrate;
10) Where automatic controls are incorporated, periodic attention and
servicing to ensure reliable operation.
It isimportant to consider these points in more detail, but before doing
so, it is necessary to review th,' nasic design principles and illustrate the
present state of the art.
2
2. THE MODERN TURBINE
2.1. GENERAL ASPECTS
The design of the marine turbine over the past twenty years has been
greatly influenced by economic and competitive factors, requiring reduced
fuel consumption, smaller weight to power ratio, higher steam pressures and
temperatures, higher rotational speeds and higher peripheral speeds.
Improvements in blade and nozzle have been made by application of
aerodynamic theory and vast amounts ofwind tunnel research have advanced
the efficiency of impulse turbines to such an extent that the high pressure
portion of a machine is almost always of the impulse type. The reaction
stages are confined to the low pressure end of the machine. The boundary
between impulse and reaction stages is somewhat blurred nowadays because
most impulse blades operate with some degree of reaction, and many
reaction stages are made of disc and diaphragm type of construction and
look like impulse stages.
There are exceptions, however, such as the Westinghouse design and
the Blohm and Voss design.
The major influences on the impulse design have been the higher steam
conditions and the importance of reducing leakage effects, and the reduction
in axial length arising from impulse construction.
The most popular designs ofturbine in present construction are the Stal-
Laval, General Electric, Mitsubishi and Kawasaki types. The only active
British design at the moment isthe GEe (formerly AEI/English Electric) type.
There are, of course, many British and foreign flag ships still sailing with
Pametrada turbines.
Several striking features will be evident in modern turbines when
compared with those in "Running and Maintenance of Marine Machinery".
There is the more general use of high pressures and temperatures, e.g.
Manufacturer Standard Inlet Conditions
Stal-Laval 62 bar/51Ooe (900 Ib/in2 g/950°F)
General Electric 59bar/510oe (850 Ib/in2 g/950°F)
General Electric Reheat 100bar/510oe (1450 Ib/in2 g/950°F/950°F)
Pametrada 59bar/510oe (850 Ib/in2 g,950°F)
I.H.I. Reheat 86bar, 513°Cj51Ooe
3
4 MARINE ENGINEERING PRACTICE
Several firms have standard reheat designs introduced after Pametrada
had publicized their "1000/1000/1000" design. The main difference was
that Pametrada proposed a three cylinder high pressure/intermediate
pressure/low pressure (H.P./I.P./L.P.) scheme, whereas General Electric
and Stal-Laval used a two cylinder scheme, with H.P. and J.P. sections on
the same rotor.
In addition, there are many improvements in details, such as flexible
couplings, bearings, casing construction, bearing supports, and greater use
of fabrication and there isthe ',vf'rall aflrl""~eral use of impulse type con-
struction.
2.2. TURBINE AND GEARING ARRANGEMENTS
Apart from differences in detail, there are noteworthy differences in
arrangements of gearing and condenser machinery. It has become fashion-
able to adopt the so-called "single plane" arrangement in which all bearing
centre lines liein the same horizontal plane.
In the Stal-Laval arrangement (Fig. 1)(Ref. 1),useismade ofa mixture
ofepicyclic and parallel shaft gears. The H.P. turbine may have a star gear
firstreduction, withaplanetary epicyclicsecond reduction, arranged forward
and aft, respectively, of the final reduction pinion which engages with the
main wheel. The L.P. turbine has a planetary epicyclic first reduction gear
arranged aft ofthe final reduction pinion.
The principal change whichallows thesingleplane design tobeachieved
isthe axially directed exhaust, forward from the L.P. turbine, direct into the
side of the main condenser arranged athwartships. The exhaust duct sur-
rounds the forward turbine bearing, to which access has to be obtained via
a vertical shaftway. This is not a very attractive feature, but has not been
known to lead to any operating difficulties.The ahead exhaust stream passes
over the astern casing on its way to the condenser. The astern exhaust faces
the same way,thus removing any possibility ofthe astern steam affecting the
ahead blading (Fig. 2).
The main attraction claimed for the arrangement isthe low headroom
needed forits accommodation, which permits the boiler to be arranged over
the turbines, thus leading to a short engine room space (Fig. 3).
It willbeclear that there isa power limit to the axial exhaust singleflow
arrangement, which has not yet been reached at 29828 kW (40000 shp) in
the Stal-Laval design. Eventually a double flowexhaust willbe needed, with
downward flow to an underslung condenser, for higher powers. It is of
interest, however, that Jung (Ref. 2) claims that a power of 93000 shp is
possible with reheat using only one flow.
General Electric's MST 13standard (Figs. 4and 5)(Ref.3)issimilar in
several respects to the Stal-Laval arrangement It isofthe single plane type
with the L.P. turbine exhausting axially to :: >'ld:ate condenser. Access to
the forward bearing is via a vertical space between the two halves of the
THE MODERN TURBINE 5
6 MARINE ENGINEERING PRACTICE
enveloping turbine exhaust. The major difference is in the type of gearing,
which isentirely par::lllelshaft type. For claimed economy of manufacture,
the primary and secondary gearboxes are separate from each other.
The higher powered MST 14standard shown in Fig.6(Ref.4)reverts to
orthodox dual tandem construction for the gearing, and has the advantage
of sharing the power amongst four pinions in the final reduction. This
leads to a smaller diameter for pinions and wheels than is general for the
Stal-Laval standard. The L.P. turbine retains the axial exhaust.
The even higher powered MST 19standard range covers powers from
33556 kW-89 484kW (45000-120000 shp) with a selection from two H.P.
turbines and three L.P. turbines in both non-reheat and reheat forms. It is
ofinterest to note that all ofthese have dual tandem gears and that the L.P.
turbines exhaust downwards into underslung condensers.
The Pametrada standards (Refs.5and 6)retained the orthodox arrange-
ment ofgearing, with dual tandem above 18643 kW (25000 shp), and in all
cases have the L.P. turbine exhausting downwards into an underslung
FIG. 3.-Stal-Laval advancedpropulsionmachinery inatanker.
condenser (Figs.7and 8)(Ref.6).The major overall dimensions and weights
forthis standard seriesare giveninTables Iand IIofRef.6.
Figure 9 shows a 14914 kW (20000 shp) set of machinery from the
standard range-later installed ins.s.British Cmifidence-erected on the test
stand at John Brown Engineering. Figure 10shows a 19760 kW (26500shp)
set with dual tandem gearing in s.s. Ottawa. Figure 11shows the Pametrada
Prototype 1machinery on the test bed at Wallsend Research Station. This
operated at 55bar (800Ib/in2 g) and 557°C (1035°F) and completed an
extensive series of trials in 1963.Figures 12and 13show the H.P. turbine
from this set.
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