ME3K Micro Project – Thermal Engineering TEG (313310)-Prepare Report and Chart on Different Types of Compounding

PART A

TITAL OF
MICRO PROECT : Prepare Report and Chart on Different Types of Compounding

Brief Introduction

As
explained earlier a reaction turbine is one in which there is pressure and
velocity loss . in the
moving blades. The moving blades have a converging steam nozzle. Hence when the steam passes over the fixed blades, it
expands with decrease in steam pressure and increase in kinetic energy.

Aim of the micro project :

1. Prepare technical report

2. show the attitude
of inquiry

3. work independently
for responsibility

4. participate
effectively in group work

5. work persistently to
achieve the target

Part B
Title:- Prepare Report and Chart on
Different Types of Compounding

Aims/Benefits of the
Micro-Project:-
This type of turbine has a number of rings of moving blades
attached
to the rotor and an equal number of fixed blades attached to the casing. In this type of turbine, the
pressure drops take place in a number of stages

Course outcome:-

Use relevant steam nozzles and turbines

The output of micro project

Identity
the Types of different Compounding Increase
knowledge about thermal engineering Increase
communication skill

Experience
team work

Ability
the face all problems

Skill
developed in micro project :- .

1.Prepare technical
report

2.show the
attitude of enquiry

3.work
independently for responsibility 4.participate effectively in group work 5.work persistently achieve the target

Compounding of steam turbines

Is the strategies in
which energy from the steam is extracted in a number of stages rather than a single stage in a turbine. A compounded
steam turbine has multiple stages i.e. it has more than one set of nozzles and rotors, in series,
keyed to the shaft or fixed to the casing, so that either the steam pressure or the jet
velocity is absorbed by the turbine in number of stages.

Compounding
of steam turbine is used to reduce the rotor speed. It is the process by which rotor speed come to its desired value.
A multiple system of rotors are connected in series keyed to a common shaft and the
steam pressure or velocity is absorbed in stages as it flows over the blades. The steam
produced in the boiler has sufficiently high enthalpy when superheated. In all
turbines the blade velocity is directly proportional to the velocity of the steam passing over the
blade. Now, if the entire energy of the steam is extracted in one stage, i.e. if the
steam is expanded from the boiler pressure to the condenser pressure in a single stage,
then its velocity will be very high. Hence the velocity of the rotor (to which the blades
are keyed) can reach to about 30,000 rpm, which is too high for practical uses because
of very high vibration. Moreover, at such high speeds the centrifugal forces are
immense, which can damage the structure. Hence, compounding is needed. The high
velocity steam just strikes on a single ring of rotor that causes wastage of steam ranging
10% to 12%. To overcome the wastage of steam compounding of steam turbine is
used.

1.lmpulse:
There is no change in the pressure of the steam as it passes through the moving blades. There is change only in the
velocity of the steam flow.

 2.Reaction: There is change in both pressure
and velocity as the steam flows through the  moving
blades.

     In an Impulse steam turbine compounding
can be achieved in the following three ways

·
Velocity
compounding

·
Pressure
compounding

·
Pressure-Velocity
Compounding

The velocity
compounded Impulse turbine was first proposed by C G Curtis to solve the problem of single
stage Impulse turbine for use of high-pressure and temperature steam

The rings of moving blades are
separated by rings of fixed blades. The moving blades are keyed to the turbine shaft and the fixed blades are fixed to the
casing. The high-pressure steam coming
from the boiler is expanded in the nozzle first. The Nozzle converts the
pressure energy of the steam into kinetic energy. The total enthalpy drop and hence the pressure drop occur in the nozzle.
Hence, the pressure thereafter remains constant.

This high-velocity
steam is directed on to the first set (ring) of moving blades. As the steam flows over
the blades, due to the shape of the blades, it imparts some of its momentum to the blades and loses some
velocity. Only a part of the high kinetic energy is absorbed by these blades. The remainder is exhausted on to the next
ring of a fixed blade. The function
of the fixed blades is to redirect the steam leaving from the first ring of moving blades to the second ring of moving
blades. There is no change in the velocity
of the steam as it passes through the fixed blades. The steam then enters the next rang of invoicing blades; this process is
repeated until practically all the energy of the steam has been absorbed.

A Scientistic diagram of the Curtis stage impulse turbine,
with two rings of
moving blades and one
ring of fixed blades, is shown in the figure, the figure also shows the changes
in the pressure
and the absolute velocity.

Velocity Diagram

As shown in the above diagram there are two rings
of moving blades separated by a ring of
fixed blades. The velocity diagram in figure 2, shows the various components of
steam velocity and the blade velocity of the moving blades.

where,

From the above figure it can he seen that the
steam, after exiting from the moving blades,
enters into the fixed blades. The fixed blades redirect the steam into the next
set of moving blades. Hence, steam loses its
velocity in multiple stages rather than in a single stage.

Optimum Velocity

It is the velocity of the blades at which
maximum power output can be achieved. Hence, the optimum blade velocity for this case is This value of
optimum velocity is 1/n times that of the single stage turbine. This means that
maximum power can be produced at much lower
blade velocities.

However, the woik produced in each stage is
riot the same. The ratio of work produced in a 2-stage turbine is 3:1 as one move from higher to
lower pressure. This ratio is 5:3:1 in
three stage turbine and changes to 7:5:3:1 in a four-stage turbine.

Disadvantages of
Velocity Compounding

Due to the high steam
velocity there are high friction losses. Work produced in the low-pressure stages is
much less.

The designing and fabrication of blades which
can withstand such high velocities is difficult.This is used to solve the problem of high blade
velocity in the single-stage impulse
turbine.