FIELD OF THE INVENTION
The present invention generally relates to electrostatic precipitator (ESP) and particularly a screen tube used in emitting electrode frame and emitting electrode rapping mechanism of Electrostatic Precipitator (ESP). More particularly, the invention relates to a typical screen tube to avoid ash accumulation in insulator housing by preventing contact between high voltage carrying components in emitting electrodes during rapping.
BACKGROUND OF THE INVENTION
Electrostatic precipitator is a boiler auxiliary used in thermal power plants
Electrostatic precipitator is used as the main pollution control equipment. Charging, collecting, and removing of ashes from the flue gas are the basic function of an ESP.
A typical ESP has thin wires called discharge electrodes or emitting electrode, which are evenly spaced between large plates called collecting electrodes, which are grounded. A negative, high-voltage, pulsating, direct current is applied to the discharge electrode creating a negative electric field. This field is divided into three regions. The field is strongest right next to the discharge electrode, weaker in the areas between the discharge and collecting called the inter-electrode region, and weakest near the collecting electrode. The region around the discharge electrode is where the particle charging process begins. Negatively charged ashes are collected in the collecting electrode.

When a charged particle reaches the grounded collecting electrode, the charge on the particles only partially discharged. The charge is slowly leaked to the grounded collection plate. A portion of the charge is retained and contributes to the inter-molecular adhesive and cohesive forces that hold the particles on to the plates Adhesive forces cause the particles to physically hold on to each other because of their dissimilar surfaces. Newly arrived particles are held to the collected particles by cohesive forces particles are attracted and held to each other molecularly. The dust layer is allowed to build up on the plate to a desired thickness and then the particle removal cycle is initiated. Dust that has accumulated to a certain thickness on the collecting electrode is removed by one of two processes, depending on the type of collecting electrode.
Screen tube is used as a guard in electrostatic precipitator, Screen tube guards the suspension tube which carries high voltage between insulator housing and emitting electrode frame to avoid accumulation of ashes in insulator housing. Screen tube is also used as a guard in rapping mechanism of emitting electrode in electrostatic precipitator.
Electrostatic precipitator is used as the main pollution control equipment. Charging, collecting, and removing are the basic idea of an ESP, the theory of electrostatic attraction is used for absorption of the ash from the flue gas. Set of emitting electrode is assembled in a frame, to produce high voltage. Ash is collected in collecting electrode by the theory of electrostatic attraction, collected ash is removed by vibration produced by rapping hammer. Ash accumulation in insulator housing is protected by the screen tube. Screen tube used in rapping mechanism of emitting electrode frame protects the high voltage carrying elements.

Screen tube plays a key role in avoiding contact between the high voltage carrying elements in emitting electrode during rapping. Screen tube acts as a shield to avoid accumulation of ashes in insulator housing. It is found that manufacturing of screen tube takes longer cycle time due to the complicated design. Also manufacturing cost, material cost and logistic cost is more for the prior art design.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a screen tube to avoid ash accumulation in insulator housing by preventing contact between high voltage carrying components in emitting electrodes during rapping.
Another object of the invention is to propose a typical split type screen tube to avoid ash accumulation in insulator housing by preventing contact between high voltage carrying components in emitting electrodes during rapping, which reduces erection cycle time of emitting electrode frame and emitting electrode rapping mechanism in the ESP.
Still another object of the invention is to propose a typical split type screen tube to avoid ash accumulation in insulator housing by preventing contact between high voltage carrying components in emitting electrodes during rapping, which requires lower manufacturing.
Further object of the invention is to propose a typical split type screen tube to avoid ash accumulation in insulator housing by preventing contact between high voltage carrying components in emitting electrodes during rapping, which is lighter in weight.

SUMMARY OF THE INVENTION
Accordingly, there is provided a typical split type screen tube to avoid ash
accumulation in insulator housing by preventing contact between high voltage carrying components in emitting electrodes during rapping. The invention reduces the erection cycle time of emitting electrode rapping mechanism, the delay in erection sequence, manufacturing cycle time, material cost including logistic cost.
According to this invention, the conical rolling and bell mouth available in the prior art screen tube, are removed, wherein the conical rolling is replaced by cylindrical rolling. Matting end of the cylinder is kept open with a bend as shown in fig 2 for welding at site. The material thickness was reduced for achieving the above objectives.
Scope of this invention is to simplify the configuration of the screen tube to avoid difficulties in erection sequence, including mismatch in mating surface of the screen tube in site. Manufacturing delay in erection of the ESP at site was due to the complicated design of screen tube. The design of prior art screen tube (Fig 1) has a conical rolling welded with a bell mouth at both ends. During fabrication of the screen tube forming of conical rolling and bell mouth is difficult and time consuming which interalia resulted in delay at the project site. Erection of entire emitting electrode rapping mechanism is delayed due to the complicated design of screen tube. The weight of the screen tube affects the erection since over head welding was found difficult. The design of screen tube also increases the logistics cost.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 Illustrates a conventional model of screen tube.
Fig 2 Illustrates a split type screen tube according to the invention.
Fig 3 Illustrates the picture of typical screen tube used in ESP (conventional and modified)
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
In this invention it is proposed to remove the conical rolling and bell mouth available in the screen tube and to introduce a novel split type screen tube. The conical rolling will be replaced by cylindrical rolling. Matting end of the cylinder is kept open with a bend as shown in fig 2 for welding at site. The material thickness was reduced for achieving the above objectives.

WE CLAIM :
1. A typical split type screen tube to avoid ash accumulation in insulator housing by preventing contact between high voltage carrying components in emitting electrodes during rapping, comprising :
The novel design of split type screen tube with the mating end of the cylinder is kept open with the bend shown in figure 2.
The novel design of split type screen tube decreases the erection cycle time of
emitting electrode rapping mechanism in ESP.
The novel design of split type screen tube improves erection sequence.
The novel design of split type screen tube reduces the manufacturing cycle time
of screen tube.
The novel design of split type screen tube decreases the weight.
The novel design of split type screen tube reduce the logistics cost for screen
tube.