FIELD OF THE INVENTION
The invention relates to the field of Boiler tubes. In particular, the invention
relates to dynamic displacement measurement on boiler tubes. More particularly,
the invention relates to a device for dynamic multidimensional/tri-axial
displacement measurement of boiler tubes in a Boiler with Linear Variable
Differential Transformers (LVDTs).
BACKGROUND OF THE INVENTION
Fossil fuels is expected to remain the primary energy source for electric power
generation for the foreseeable future, and coal is the principal fossil fuel of
power generation. Coal may continue to remain an essential energy source
during the 21st century and even in the 22nd century due to its low cost and wide
availability. However, given that coal-fired power plants represent one of the
largest producers of CO2 emissions, it is prudent in pursuance to the public
policy to aim at early development and application of clean technologies for coal
utilization in high efficiency power cycles. The power industry has progressively
improved power plant designs to meet increasingly stringent limits for air

pollution. New coal plants today are cleaner and more efficient than plants built
in the past. CFBC, as an alternative to pulverized coal combustion (PCC), uses a
fluidized bed, an apparatus that mixes coal and air with a sorbent such as
limestone during the combustion process, to facilitate more effective chemical
reactions and heat transfer. In a fluidized-bed combustor, combustion occurs
when the mixture of fuel, a sorbent and fuel ash particles is suspended by using
a continuous stream of primary combustion air to create turbulence in the bed.
The gas cushion between the solids allows the particles to move freely, giving
the bed a liquid-like (fluidized) characteristic. Due to the turbulence within the
fluidized chamber, steam tubes (carrying high temperature steam) inside
chamber are subjected to displacement and vibration. Occurrence of steam tubes
failure is a matter of concern. To measure tri-axial displacement of the tubes due
to the turbulence created inside the chamber, an attempt is made with the
present invention. Standard LVDTs are used for measuring the displacement.
The linear variable differential transformer (LVDT) is a type of electrical
transformer used for measuring linear displacement position.
LVDTs are standard unidirectional displacement measurement sensors used for
boiler tube displacement measurement and vibration analysis.

While one LVDT can measure displacement in one direction, an innovative device
is designed where three LVDTs can be simultaneously mounted and used for
measuring displacement in three perpendicular directions on a boiler tube.
US 8786867 B2 Publication date July 22,2014 by Hirotoshi Matsumoto, Keiji Ida,
Hideaki Murata, Kai Zhang relates to an inspection device and an inspection
method for boiler furnace water wall tubes. The inspection device includes a
scanner including columns placed upright and fixed by magnets onto the
surfaces of multiple water wall tubes extending in the up-down direction on the
inner wall surfaces of the boiler furnace, a support frame fixed to the columns to
support a displacement sensor producing laser light to be irradiated onto the
surface of a water wall tube, and a moving mechanism for moving the
displacement sensor in the axial direction of the water wall tube relative to the
support frame. A signal processing unit calculates the amount of reduced wall
thickness of the water wall tube from a difference displacement sensor and a
reference shale without reduction in wall thickness. Thus, the prior art teaches a
device to measure the tube radial expansion and in turn the reduced wall
thickness of the tube.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a device for dynamic
multidimensional/tri-axial displacement measurement of boiler tubes in a Boiler
with Linear Variable Differential Transformers (LVDTs).
SUMMARY OF THE INVENTION
Accordingly, there is provided a device for dynamic multidimensional/tri-axial
displacement measurement of boiler tubes in a Boiler with Linear Variable
Differential Transformers (LVDTs).
The device enables mounting of the LVDTs for measuring displacement in three
perpendicular directions of the boiler tubes which undergo considerable
displacement and vibration due to the turbulence inside the boiler. The LVDTs
are connected to a Data acquisition system to monitor the displacement. The
captured data regarding the displacement characteristic of the tubes allows
severity assessment failure analysis and incorporate modifications/optimizations
of the boiler tubes and arrangements.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above brief description, as well as further objects, features and advantages,
of the present invention can be fully appreciated by reference to the following
detailed description. These features of the present invention will become more
apparent upon reference to the drawings, wherein :
Figure 1: 3 – D view of the tri-axial displacement measurement device showing
three LVDT sub-assemblies with LVDTs in contact with flat faces of top and
bottom tube clamp.
Figure 2: Component details of the main assembly.
Figure 3: Component details of the LVDT sub assembly
Figure 4: LVDT for linear displacement measurement.
Figure 5: Rectangular box Stand for mounting of fixture plate and LVDT sub
assemblies.

Figure 6: Fixture plate for mounting of two LVDT sub assemblies.
Figure 7: A sample boiler tube for which the displacement in X, Y and Z
directions to be measured.
Figure 8: Top tube clamp to be clamped on the boiler tube and with two right
angled arms in contact with two LVDTs to measure displacement in X and Y
direction.
Figure 9: Bottom tube clamp to be clamped on the boiler tube with the top tube
clamp and one arm in contact with one LVDT to measure displacement in Z
direction.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below with reference to an
embodiment shown in the drawings. Note that the size, material, shape, relative
position of components, LVDTs and application to boilers described in the
embodiment do not limit the scope of this invention unless otherwise particularly
mentioned, and the embodiment is just illustrative example.

As shown in figures 2 and Figure 3, the device measures the displacement in
three mutually perpendicular directions in linear variable differential transformer,
comprising :
- a rectangular box stand (1) to hold at least six LVDT sub assemblies (3),
- one each fixture plate (2) for mounting of at least two LVDT sub assemblies
(3);
- one each LVDT sub assemblies (3-X, 3-Y and 3-Z) for measuring displacement
of the tubes in X, Y and Z directions, respectively;
- a top tube clamp (4) with two arms in contact with two LVDTs to measure
displacement in X and Y direction;
- a bottom tube clamp (5) with one arm in contact with one LVDT to measure
displacement in Z direction;
- a sample boiler tube (6) for which the displacement in X, Y and Y directions
to be measured;

- three identical brackets (7), one each LVDT disposed on the sub
assemblies;
- four holders(8) per bracket to hold one each LVDT sub assembly and
- a plurality of long threaded bolts including matching nuts on each LVDT sub-
assembly.
The lower end of the rectangular box stand (1) is rigidly welded to the bracket
(7) available in the boiler chamber between two successive boiler tubes and
fixed on the wall of the chamber. The stand (1) is made of hollow rectangular
section with lower end open and top end closed. Top end of the stand (1)
contains two through holes as shown in Figure 5 which are used to mount the
LVDT sub assembly for measurement of displacement in X direction as shown in
the Figure 2.
Details of one of the three LVDT sub assemblies is given in Figure 3. In each
LVDT sub assembly (3-X, 3-X and 3-Z), there are four LVDT holders (8) as
shown in the Figure 3, two each at the front and back end of a cylindrical

barrel (12) of the LVDT with distance apart which hold a LVDT (9) in a plane
and along the direction of displacement measurement. These holders (8) are
coupled with the bracket (7) by the long bolts (10) and three nuts (11) for each
bolts. While the height of the brackets (7) is fixed, the distance between the
LVDT (9) and base of the bracket (8) can be adjusted by the means of nuts 11
and long bolt (10) based on the length of the bolts selected. Also the position of
the LVDT (9) can be adjusted in the axial direction between the set of two
holders (8).
As shown in Figure 2, the Fixture plate (2) is bolted to the stand (1). The fixture
plate (2) as shown in Figure (5) have number of holes. At the bottom it is bolted
with the stand (1). At the upper portion of the fixture plate LVDT, the sub
assemblies (3-Y and 3-Z) are mounted to enable measurements in the direction
of Y and Z respectively as shown in the Figure 2.
Position and orientation of the Boiler tube (6) is shown in the Figure 2. The two
tube clamps (4, 5) are rigidly tightened and fixed on the boiler tube by means of
standard bolts.

The top tube clamp (4) as detailed in Figure 9, is mounted on the boiler tube as
shown in the Figure 2. Two holes are provided on the top face of the rectangular
box stand (1) to mount the LVDT assembly 3-X. The flat face (16) of the tube
clamp (4) is in contact with the tip of the LVDT plunger (13) on the LVDT
assembly 3-X. As described above, the axial position of the LVDT can be
adjusted in between the two sets of the holders 8. The distance between the
LVDT (9) and base of bracket (7) can be adjusted by the means of nuts (11)
and long bolt (10) to ensure the firm contact between the tip of the LVDT
plunger (13) and the flat face (16) of the bottom tube clamp (4) as per the
Figure 2. This arrangement ensures that the direction of LVDT is normal to the
flat face (16) of the tube clamp (4). As the boiler tube moves in the X-direction
the plunger (13) of the LVDT assembly 3-X moves in the +/-ve X-direction
enabling measurement of displacement in the X-direction.
The LVDT assembly (3-Y) is fixed on the fixture plate 2 in the location as shown
in the Figure 2. Number of holes are provided on the fixture plate (2) to mount
the LVDT assembly (3-Y) at various position in (Y) directions. The LVDT plunger
(13) of the LVDT assembly (3-Y) is kept in contact with the flat face (15) of the
top tube clamp (4) in the direction of (Y) as shown in Figure 1 and Figure 2.
As described earlier the axial position of the LVDT can be adjusted between the
two sets of the holders (8) and also the distance between the LVDT (9) and base

of bracket (7) can be adjusted by the means of nuts (11) to ensure the firm
contact between the tip of the LVDT plunger (13) and the flat face (15) of the
top tube clamp (4) as per the Figure 2. This arrangement ensures that the
direction of LVDT is normal to the flat face (15) of the tube clamp (4). As the
boiler tube moves in the Y-direction the plunger (13) of the LVDT assembly (3-Y)
moves in the +/-ve Y-directions enabling measurement of displacement in the Y-
direction.
The LVDT assembly (3-Z) is bolted to the fixture plate in the location as shown in
the Figure 2. Number of holes are provided on the fixture plate 2 to mount the
LVDT assembly (3-Z) at various position in (Y) and (Y) directions. The LVDT
plunger (13) of the LVDT assembly (3-Z) is kept in contact with the flat face (14)
of the bottom tube clamp (5) in the direction of (Z). As described earlier the axial
position of the LVDT can be adjusted in between the two sets of the holders (8)
and also the distance between the LVDT (9) and bracket (8) can be adjusted by
the means of nuts (11) and long bolt (10) to ensure the firm contact between
the tip of the LVDT plunger (13) and flat surface (16) of the bottom tube clamp
(4) as per the Figure 2. This arrangement ensures that the direction of LVDT is
normal to the flat face (14) of the tube clamp (5). As the boiler tube moved in
the Z-direction the plunger (13) of the LVDT assembly (3-Z) moved in the +/- ve
Z-directions enabling measurement of displacement in the Y-direction.

WE CLAIM :
1. A device for dynamic multidimensional/tri-axial displacement
measurement of boiler tubes in a Boiler with Linear Variable Differential
Transformers (LVDTs), comprising a rectangular box stand (1) which is rigidly
welded on the wall of the CFBC chamber and contains a plurality of holes on the
vertical face including top face; a fixture plate (2) bolted on the vertical face of
the stand (1), and a LVDT assembly (3-X) is bolted on the top face; at the upper
portion of the fixture plate (2), at least two each LVDT sub-assembly (3-Y), (3-Z)
are mounted to enable displacement measurements at various locations in the
direction of Y and Z respectively; at least two LVDT sub-assemblies (3-X) to
measure displacement of boiler tube in X-direction; each of the LVDT sub
assembly (3-X, 3-Y, 3-Z) contains four LVDT holders (8), two each holders at
the front and back end to hold a cylindrical barrel (12) of the LVDT disposed at
spaced-apart locations and holding a LVDT (9) in a plane along the direction of
displacement measurement, wherein the axial position of the LVDT (9) is
adjustable between the two sets of holders (8), the holders (8) being coupled to
at least one bracket (7) by a plurality of long bolts (10) and nuts (11).

2. The device as claimed in claim 1, wherein the arrangement of the
LVDT (9) and the bracket (7) can be adjusted by means of nuts (11) and long
bolt (10).
3. The device as claimed in claim 1, wherein the arrangement of the LVDT
sub assemblies (3-X, 3-Y, 3-Z) ensures that the direction of the LVDT (9) is
normal to the measuring surface and a firm contact is established between the
LVDT Plunger (13) and the measuring flat face.
4. The device as claimed in claim 1, comprising a top tube clamp (4) and a
bottom tube clamp (5) which are clamped on the boiler tube by bolts.
5. The device as claimed in claim 4, wherein the top tube clamp (4) contains
right angle flat surfaces (15 and 16) which are in contact with the LVDT Plunger
(13) of LVDT sub-assemblies (3-Y and 3-X) respectively in the normal directions
enabling measurement of displacement of the boiler tube in +/-ve Y and X
directions respectively.

6. The device as claimed in claim 4, wherein the bottom tube clamp contains
a flat surface(14) which is in contact with the LVDT Plunger (13) of LVDT sub-
assembly (3-Z) in the normal direction enabling measurement of displacement of
the boiler tube in +/-ve Z direction.