FIELD OF THE INVENTION
The invention relates to Electro Static Precipitators (ESP) used in coal fired power
plants. In particular, the invention relates to structural load monitoring of ESP
hopper. More particularly, the invention relates to a uniaxial spherical bearing
device for structural load monitoring of ESP hopper.
BACKGROUND OF THE INVENTION
The combustion coal for power generation produces fly ash, which must be
collected preceding to ejection of the fly ash into the atmosphere. The most
common method of collection of fly ash is electrostatic precipitation. The
collection characteristics of the fly ash depend on the coal and the combustion
system. Electrostatic precipitators (ESP) are the most common, effective and
reliable particulate control devices which can handle large gas volumes with a
wide range of inlet temperatures, pressures, dust volumes and acid gas
conditions. The particles, known as Fly Ash, are collected in plurality of hoppers

disposed below the ESP and are then removed for transportation to a distal place
for long term storage. Fly ash can be very stick and tends to build up. Fly ash
accumulation inside the hoppers can lead to ESP failures which may result in
damage to the ESP supporting structure loss of production (i.e. Power) capacity
and thus causing several implications.
Tracking the fly ash inside the ESP hopper presents quite a few challenges as the
fly ash material remains hot, stick and abrasive during collection phase. There is
also a lot of suspended dust in the hopper. These negative properties of the fly
ash make the prior art systems of monitoring fly level in the hopper using
sensors faulty and leading to catastrophic failures.
Existing ash level monitoring system does not indicate the excessive loads
coming on to the structure due to over accumulation of the ash inside the ESP
hoppers. Sometimes it leads to catastrophic failure of the entire ESP supporting
structure due to huge accumulation of fly ash, leading to over loading of the
supporting structure.

Electrostatic precipitators are used to eliminate the dust particles from the flue
gases generated due to combustion of pulverized material. The electrostatic
precipitation process includes the phases of particle charging, precipitation, and
removal. All of these phases are affected by the residual layer of particles either
on the collecting surface plates or on the discharge wires. Thus, a periodic
removal of this build-up of the residual layer of particles is necessary to maintain
the continuity of the precipitation process. Various systems such as Level
Sensors, RF Admittance Switch and Mapping Systems utilizing Scanners are used
in prior art to monitor the ash in the hoppers. But all of these systems are
installed inside the hoppers which makes them very susceptible to failure
because of the high temperature environment. Further, the ash deposition in the
hoppers is monitored by the level sensors installed in each hopper. The
temperature of the ash in the hopper is around 150° C, and in this environment,
level sensors frequently provide inconsistent values, which may lead to over
loading and catastrophic failure of the entire ESP supporting structure.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a uniaxial spherical bearing
device for structural load monitoring of ESP hopper.

SUMMARY OF THE INVENTION
Thus, the present invention provides a device for external measurement of
structural load due to ash collection based on the strain measured by strain
gauges.
This invention discusses the methodology of conversion of a free float bearing
which is a part of a large ESP supporting structure into a load cell by installing
strain gauges in a full bridge configuration. Verification of the performance of the
load cell is successfully achieved by comparing the strain level results between
FE analysis of the spherical bearing, measurements in an UTM and comparison
with standard load cell.
zBRIEF 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
apparent upon reference to the drawings, wherein:

Figure 1 is a front view of a Free Floating Bearing arrangement.
Figure 2 is an FE Analysis of Bearing.
Figure 3 is a detail of the present invention for Figure 1.
Figure 4 is a Schematic diagram of a strain gauge location of the Present
invention of Figure 3.
Figure 5 is a Calibration device for the load versus strain measurement of the
present invention of Figure 3.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Figure 1 of the drawings, is structural arrangement of ESP column
and a free float bearing. The present invention is described in connection with
Electrostatic Precipitator for coal fired Power Plants.
The advantages of the present invention may be fully appreciated by explaining
the details of the following arrangement.

In the preferred embodiment of Figure 2, is FE analysis of the free float bearing
based on the loads acting on the cylindrical portion, which is uniaxial spherical
bearing and also is the weakest portion of the structure.
In the preferred embodiment, Figure 3 shows different views of load cell. The
load cell's bottom flat portion (1) is welded to the foundation column and total
ash load is transferred from the hopper to foundation column via the load cell.
The top vertical cylindrical portion (2) of the load cell is subjected to the
maximum compressive stress due to ash load. In the preferred embodiment
groove throughout the circumference of the cylindrical portion (2) is made.
Fixing arrangement of four numbers for strain gauges (3) to form Wheatstone-
Bridge for measurement of strain by using stain indicator (4).
Figure 1 is typical arrangement of free floating bearing of ESP supporting
structures. Existing level measurement systems are placed inside the hopper for
ash level measurements. Figure 2 shows forces acting on the uniaxial spherical
bearing. Figure 3 is the invented load cell along with tapered groove for
improving the sensitivity of the gauges for measurement of load in terms of
strains due to deflection caused by ash load in the hopper Figure 4 shows the

Schematic arrangement of instruments for continuous monitoring of strain
caused due to the accumulated ash in the hoppers. Figure 5 shows the
calibration of the load cell before installation to ESP supporting structure.
Calibration is done in UTM to arrive at the actual sensitivity of the load cell in
micro strain per ton.

WE CLAIM:
1. A uniaxial spherical bearing device for structural load monitoring of ESP
hopper, comprising a uniaxial spherical bearing converted to load cell,
and at least two pairs of strain gauges disposed at 180 degree apart on a
circular ring for measurement of strains, wherein a tapered groove is
configured throughout the circumference of a circular ring for
augmenting the sensitivity of the strain gauges for accurate loads due to
dust collection in the ESP hopper, the tapered groove dimension being
determined through a detailed Finite element (FE) analysis.
2. The device as claimed in claim 1, wherein the load cell is calibrated in
respect of the strain vs load before installation in the ESP supporting
structure columns, and wherein the loads coming on to the
support/foundation columns of the ESP is measured.

3. The device as claimed in claim 1, wherein the load coming to the column
of the supporting structure on the ESP can be monitored continuously
such that the ash can be evacuated before the accumulation reaches a
predetermined critical level.