FIELD OF THE INVENTION
The present invention relates generally to the supporting system of electrostatic precipitators (ESP) in thermal power plants. More particularly the invention relates to a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator.
BACKGROUND OF THE INVENTION
Electrostatic precipitator (ESP) is an equipment in a thermal power plant which extracts the ash which comes along with the flue gas which is the product of burning pulverized coal in a boiler in the thermal power plant.
The Electrostatic precipitator uses the electrical phenomenon called “Corona” discharge which under high voltage turns the flue gas into an ionized state where the negatively charged ash particles are attracted towards positive electrodes called collecting electrodes of the ESP, which is rapped at intervals and collected in the ash hoppers at the bottom of the electrostatic precipitators.
The weight of the collected ash and the weight of the collecting electrodes constitute the major vertical loads on the foundations of the supporting system of the electrostatic precipitators, apart from the wind and seismic loads which are horizontal.
The electrostatic precipitators are designed for a particular value of permissible emission levels i.e (The amount of dust particles present in the flue gas that is

released into the atmosphere through the chimney). These emission levels are normally fixed by the statutory Authorities.
These permitted value of emission levels are progressively being brought down to a more stringent value over the decades by the statutory authorities.
The currently permitted emission levels call for a modification of the already installed electrostatic precipitators initially designed for a higher emission levels, so as to enable the existing ESPs to maintain the reduced emission levels of the current norms. The modification is likely to increase the vertical load on the foundations of the electrostatic precipitator as both the amount of collected ash and the size of the collecting electrodes are destined to increase considerably.
A straight forward solution to this problem is to replace the existing electrostatic precipitators with higher capacity equipment to satisfy the current emission norms.
This process of dismantling the existing Electro Static Precipitator and installing a new bigger electrostatic precipitator in the same location i.e between the Boiler and Induced draft Fan is called Retrofitting of Electro Static Precipitator.”
The Electrostatic precipitator is basically a rectangular box which houses the collecting electrodes and emitting electrodes which separates the ash from the flue gas which passes through the ESP. A plurality of hoppers are disposed underneath to temporarily store the collected ash. The shape of the hoppers is generally an inverted pyramid. The rectangular box and the pyramidal hopper are held by a support system made of steel columns fabricated out of Rolled steel Beams or Channels.

The supporting system of the Electrostatic precipitator takes care of the loads exerted on the ESP by the collecting electrodes and the collected ash in the hoppers. The hoppers are generally designed for storage of ash collected in approximately eight hours of boiler operation. The ash collected in the hoppers is periodically removed by wet or dry type evacuation methods.
The Electrostatic precipitators are generally designed with single ‘field’ or multiple ‘field’ according to the size of the boiler.
The supporting system for the Electrostatic precipitators is designed for the vertical load exerted mainly by the collecting electrodes and the weight of the collected ash in the hopper including the horizontal loads of wind and earthquake loads.
The bearing level of the supporting system (i.e the junction between the rectangular box housing, the collecting electrodes and emitting electrodes at top, and the inverted pyramidal hopper at the bottom) is decided by hopper size which is again depended on the ash storage capacity and the valley angle of the hopper, the valley angle being the minimum slope required in the side walls of the hopper for easy removal of the collected ash from this hopper.
The hopper bottom level is also decided by the adopted type of ash evacuation methods namely wet or dry type.
The supporting structure of Electrostatic precipitator is a system of columns, struts and bracings fabricated between the foundation level and the bearing level.

A plurality of columns of the supporting structure is provided at all four corners of the pyramidal hopper, so that the vertical loads from the hoppers storing the ash, is transferred to the columns directly.
In a single field Electrostatic precipitator, a single row of hoppers is provides along the flue gas path and hence, there are two rows of columns along the entire flue gas path.
The total height of the Electrostatic precipitator i.e (from the bottom of the supporting structure to the top of the rectangular box containing the collecting electrodes) is normally very high in a single field Electrostatic precipitator when compared to the width of the Electrostatic precipitator.
The height to width ratio in a single field Electrostatic precipitator which is quite high, exerts very high loads on the supporting structure columns due to the horizontal loads of wind and earthquake. Single field Electrostatic precipitators are encountered mostly in retrofit projects since very old thermal power stations are of small capacity in terms of Mega Watt of power.
The power stations are normally designed with multiple power generation Units of smaller capacity rather than a single Unit of higher capacity due to operational, technical and financial considerations.
These Units are arranged side by side in a compact layout.

In these type of multiple units, the Electrostatic precipitators are placed in between the boiler and Induced draft fan, and arranged side by side having minimum space between the Electrostatic precipitators of adjacent units.
Always, though multiple units, each unit is designed separately as an independent unit, and separate supporting system is provided for individual Electrostatic precipitators in a multiple unit Electrostatic precipitators also.
The present invention seeks to overcome this draw back of the prior art.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator.
Another object of the invention is to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator, which includes reduced number of columns.
A still another object of this invention is to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator, in which the existing cross bracings for transfer of horizontal loads of wind including seismic loads to the foundation are replaced by knee bracings.

A further object of the invention is to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator, in which the columns are placed in the open space between the multiple Electrostatic precipitators to eliminate construction of additional foundation for new support system which even might foul with foundations of the existing supporting systems.
A still further object of the invention is to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator, in which the forces exerted by the existing supporting system on the foundation is reduced by increasing the base width of the combined supporting system for the multiple unit Electrostatic precipitators.
Another object of the invention is to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator bracings which replaces the cross bracings to create additional space for free movement of men and material below the Electrostatic precipitator.

A still another object of the invention is to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator, in which trussed beams instead of solid web beams are used to support the Electrostatic precipitator at bearing level.
A still another object of the invention is to propose a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator, which reduces the total weight of the combined supporting system as compared to the summary of the weight of independent supporting systems for each Electrostatic precipitator in a multiple Unit Electrostatic precipitator.
SUMMARY OF THE INVENTION
Accordingly, there is provided a retrofittable combined supporting system for single field multiple unit electrostatic precipitator in a thermal power plant with reduced height to width ratio of the Electrostatic precipitator. As per the prior art configuration, the single field Electrostatic Precipitators have only two columns across the gas flow and when compared to the overall height of the Electrostatic Precipitator, the base width of the supporting system for individual Electrostatic Precipitator is very small, thereby reducing the stability of the system.
The combined supporting system proposed in the invention exhibits higher structural stability because of the longer base width.

The two adjacent columns of the individual Electrostatic Precipitators placed side by side in a multiple unit Electrostatic Precipitator is made as a common column so as to reducing the total number of columns.
The increase in the base width reduces the forces on the columns and also in the foundations, which inter alia substantially reduces the size of the foundation as well as the total weight of the combined supporting system. Accordingly, an overall savings in the cost of the supporting system including the foundations, can be achieved.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows a sectional elevational and plan view of an existing supporting system for multiple unit Electrostatic Precipitators.
Figure 2 shows a sectional elevational and plan view of a combined supporting system for multiple unit Electrostatic Precipitators according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Figure 2 shows a combined supporting system (1) for multiple unit Electrostatic Precipitator of a thermal power plant is proposed.
Adjacent columns of individual Electrostatic Precipitators are combined to make a common column (4).
The Electrostatic Precipitators are supported on an Open Web Lattice beam (2) of rectangular cross section, which is provided to take care of the loads coming

from the collecting electrodes of the Electrostatic Precipitator and ash in the hoppers and to provide lateral stability for the frame of the supporting system.
The columns are made of built up beam sections to take care of load from the two columns which are combined to make a single column.
Knee bracings (5) are provided extending from columns to the open web lattice beam to transfer the Electrostatic Precipitator bearing (6) loads directly to the columns.
The Knee bracings also effectively transfer the horizontal loads due to wind and earthquake from the Electrostatic Precipitator and hopper to the columns.
The common columns (4) are placed in the centre of space between the plurality of Electrostatic Precipitators of adjacent units.
The common columns (4) located in the centre of the space available between the adjacent units facilitates the foundation of the common column (4) to be provided without fouling with the columns of the existing foundations.
The Knee bracings (5) are provided extending from the bottom of the bearings to the columns at a sharper angle so that most of the vertical loads are transferred from the bearing directly to the column, through the bracings. This configuration makes the open web lattice beam much lighter which carries only a portion of the Electrostatic Precipitator and hopper loads inspite of the fact that the Electrostatic Precipitators are directly supported on the open web lattice beam.

The replacement of the cross bracings with the knee bracings, makes the maintenance job below the Electrostatic precipitator very easy.
The increase in base width (7) of combined supporting system for multiple Electrostatic precipitators’ drastically reduces the effect of lateral loads of wind and earthquake on the supporting system as well as on the foundations.
The common column arrangement reduces the number of columns required for the combined supporting system for multiple Electrostatic precipitators as well as the number of foundations.
The increased base width (7) increases the stability of the Electrostatic precipitator supporting system.
The combined supporting system for multiple Electrostatic precipitators in thermal power plants reduces the cost of retrofitting the supporting system of the ESPs.

WE CLAIM :
1. A retrofittable combined supporting system for single field multiple unit
electrostatic precipitator in a thermal power plant with reduced height to
width ratio of the Electrostatic precipitator, comprising :
a beam (2) which supports the Electrostatic precipitator bearings and columns (3,4) supported on foundations; a plurality of common columns (4) replacing adjacent columns of individual Electrostatic precipitators; an open web lattice beam (2) made of rolled steel angles; at least one knee bracing (5) connecting the open web lattice beam (2) and the columns (3,4);
wherein the columns (3,4) are made up of built up rolled beam sections, and wherein the common columns (claim (2)) are placed in the center of the open space in between the units.
2. The combined supporting system as claimed in claim 1, wherein the total number of columns is less than that of summation of the individual Electrostatic precipitator columns.
3. The combined supporting system as claimed in claim 1, wherein base width (7) of the combined system when compared to an individual Electrostatic precipitator support system exhibits higher structural stability.
4. The combined supporting system as claimed in any of the preceding claims, wherein the system exerts lesser forces in the columns as well as on the foundations because of the increased base width of the combined supporting system.

5. The combined supporting system as claimed in claim 1, wherein the at least one knee bracing which is connected to the columns from the open web lattice beam at a sharper angle to allow transfer of most of the vertical loads from the Electrostatic precipitator and hopper (8) to the columns directly, thereby reducing the load on the beams.
6. The combined supporting system as claimed in any of the preceding claims wherein the open web lattice beam connecting the columns at bearing level having a rectangular cross section made up of rolled steel angle sections there by making the beam lighter at the same time increasing the lateral strength of the frame of the combined supporting system.