Cap for insulator support housing

A cover cap (40) is provided for covering the open end of a support insulator (38) having a discharge electrode hanger rod (28) passing coaxially therethrough. The cover cap (40) comprises a top (42) and a sloping side wall (44) extending coaxially outwardly and downwardly from the perimeter edge (54) of the top (42) and having a radial lip (46) and an axial lip (48) extending outwardly at substantially right angles to each other from its lower perimeter surface. A tubular gas injection nozzle (92) having an elbow subtending an angle of 135 degrees, is provided in the sloping side wall (44) for passing a jet of scavenging gas into the interior region encompassed by the sloping side wall (44). At least one access opening (70) is provided in the sloping side wall for permitting access into the interior region encompassed by the sloping side wall (44). Lid (72) is provided for covering the access opening (70) in the sloping side wall to seal the opening when the lid is not removed to permit access into the interior region encompassed by the sloping side wall.

BACKGROUND OF THE INVENTION 
The present invention relates to insulator supports for electrically 
insulating an axially extending support rod carrying an electrical charge 
from a grounded housing surrounding the support rod and, more 
particularly, to an improved cap structure for such a housing which 
facilitates maintainance of the interior of the housing in a clean 
condition free of excessive dust accumulation. The invention has 
particular applicability to insulators used for supporting the discharge 
electrode hanger rods from the grounded housing of an electrostatic 
precipitator. 
In the operation of an electrostatic precipitator, a gas laden with 
entrained particulate material is passed through an electrostatic field 
established about a discharge electrode disposed between two grounded 
collecting electrodes. The suspended particles become electrically charged 
as they pass through the electrostatic field and move under the influence 
of the electrostatic field to and deposit upon the electrically grounded 
collecting electrodes flanking each discharge electrode. Each collecting 
electrode is typically formed of one or more elongated plates disposed and 
suspended from the top of the precipitator housing in a vertical plane. A 
plurality of such collecting electrodes are disposed transversely across 
the precipitator casing in spaced vertical planes parallel to the 
direction of gas flow through the precipitator. 
In the most common electrostatic precipitators, referred to as rigid frame 
electrostatic precipitators, a boxlike framework comprised of a plurality 
of discharge electrode frames mounted in a framework which is suspended by 
hanger rods from support insulators at the top of the electrically 
grounded precipitator housing to provide a row of vertically disposed 
discharge electrodes between adjacent collecting electrodes across the 
width of the precipitator. The voltage is applied to the discharge 
electrodes to generate the electrostatic field. Each discharge electrode 
frame is comprised of a plurality of individual flexible discharge 
electrode members, commonly comprising wires tautly strung across the 
support frame or tubes extending between frame members. 
Since the hanger rods supporting the discharge electrode mounted to the 
framework are mounted to the grounded precipitator housing and since the 
hanger rods are typically electrically conductive, each hanger rod 
supporting the electrically charged discharge electrode framework is 
insulated from the grounded precipitator housing by an electrically 
non-conductive can-like insulator disposed coaxially about an opening in 
the precipitator housing through which the hanger rod extends coaxially 
through the top of the insulator housing from which it is supported in 
electrical isolation from the grounded precipitator housing. 
Since the insulator housing remains in fluid communication with the 
interior of the precipitation chamber, particulate matter may settle in 
the insulator housing and accumulate sufficiently to bridge the annular 
space from the hanger rod to the interior surface of the region of the 
precipitator housing surrounding the opening through which the hanger rod 
passes, thereby establishing a conductive path along which electrical 
arcing may occur. One common method applied to attempt to limit such 
adverse dust accumulation within the insulator housing is to provide a 
flow of higher pressure cleaning gas, such as an inert gas, air or heated 
air, into the interior of the insulator housing to flow outwardly 
therefrom into the precipitation chamber thereby preventing particulate 
entrained gas from entering the insulator housing to deposit particulate 
matter therein, as well as providing a continuous purging airflow to carry 
particulate matter that may have been deposited in the insulator housing 
into the precipitator housing. Examples of such a design are disclosed in 
U.S. Pat. Nos. 3,531,918, 4,294,591; and 4,578,088. The scavenging airflow 
introduced into the insulator may be heated as disclosed to U.S. Pat. No. 
4,294,591 to exceed the dewpoint temperature of gas in the precipitator 
thereby preventing condensation of water vapor or acidic vapors within the 
insulator housing. 
SUMMARY OF THE INVENTION 
A cover cap is provided for covering an open end of a housing, such as a 
support insulator, having a rod-like member, such as a discharge electrode 
hanger rod passing coaxially therethrough. The cover cap comprises a top 
plate and a sloping side wall extending coaxially outwardly and downwardly 
from the perimeter edge of the top plate having a radial lip and an axial 
lip extending outwardly at substantially right angles to each other from 
its lower perimeter surface. A centrally located hole is provided in the 
top plate to receive the rod-like member. The axial lip is adapted to 
insert in closely spaced relationship into the open end of the housing, 
while the radial lip is adapted to abut and close against the rim surface 
of the open end of the housing. 
Gas injection means, preferrably in the form of a tubular member having an 
elbow subtending an angleof 135 degrees, is provided in the sloping side 
wall for passing a jet of scavenging gas into the interior region 
encompassed by the sloping side wall. At last one access opening is 
provided in the sloping side wall for permitting access into the interior 
region encompassed by the sloping side wall. Lid means are provided for 
covering the access opening in the sloping side wall to seal the opening 
when the lid means is not removed to permit access into the interior 
region encompassed by the sloping side wall.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the FIG. 1 drawing, there is depicted therein an 
electrostatic precipitator 10 having a casing 12 with an inlet 2 and an 
outlet 4 and a precipitation chamber 6 disposed therebetween. The 
particulate laden flue gas to be cleaned passes through the housing 12 of 
the precipitation chamber 6 and out the gas outlet 4 as a clean, 
relatively particulate free gas. 
The basic configuration of the precipitator 10 is well known in the art, 
and is typically referred to as a rigid discharge electrode type 
electrostatic precipitator. A plurality of substantially rectangular 
collecting electrode plates 22, forming collectively a collecting 
electrode plate assembly 20, are disposed in substantially parallel, 
spaced relationship in vertical planes within the precipitation chamber 6. 
Interdisposed in the spaces between the collecting electrode plates 22 are 
a plurality of discharge electrode subassemblies 32 which collectively 
form a discharge electrode assembly 30. Both the collecting electrode 
plates 22 and the discharge electrode subassemblies 32 are aligned 
parallel to and extend in the direction of the gas flow through the 
precipitation chamber 6 from the inlet 2 to the outlet 4 thereof. 
Each collecting electrode plate 22 is suspended and supported from upper 
support beams 14 disposed across the precipitation chamber 6. The lower 
end of eah of the suspended electrode plates 22 is laterally constrained 
from movement by inserting it into a guide member 16 which is mounted to 
the lower support beams 18 disposed in the bottom of the precipitation 
chamber. Thus, the suspended collecting electrode plates, which may range 
anywhere from 12 to 50 feet in height, are free to move vertically 
downward within the guide members 16 due to temperature effects but are 
constrained from any lateral movement by guide members 16. 
The collecting electrode plates 22 are shown in the drawing as being of a 
particular cross-section merely for purposes of illustration and not 
limitation. It is to be understood that the present invention contemplates 
utilizing collecting electrode plates of any of a number of 
cross-sectional design with the particular design utilized in any given 
situation being selected on an individual basis to give optimal 
precipitation efficiency and a quiescent zone at the surfaces of the 
collecting electrode plates 22. 
The individual discharge electrode subassemblies 32 collectively and in 
conjunction with support bar 34 from which the individual discharge 
electrode subassemblies 32 are supported, form a discharge electrode 
assembly 30 which is suspended from the top of the precipitation chamber 6 
and is mounted to the casing 12 through insulators 38. Each of the 
individual discharge electrode subassemblies 32 is formed of a plurality 
of individual discharge electrode members 36, commonly taut wires or rigid 
tubes, disposed at spaced intervals to extend transversely between and be 
mounted to an upper frame member and a lower frame member. Support bars 34 
from which the individual discharge electrode assemblies 32 are supported 
extend transversely across the inlet and the outlet of the precipitation 
chamber 6 in the upper region of the housing 12 and are suspended by 
hanger rods 28 which pass coaxially through and are mounted by bolts 86 to 
the cover 40 of each of the insulators 38 mounted to the precipitator 
housing 12. 
In operation, a particulate laden gas enters the precipitator housing 12 
through the inlet 2 thereof and flows through the precipitation chamber 6 
to the outlet 4 thereof. In traversing the precipitation chamber 6, the 
particulate laden gas flows between the spaced collecting electrode plate 
assemblies 20 and over the discharge electrode subassemblies 32 suspended 
therebetween. An electrical charge is applied to each of the discharge 
electrode subassemblies 32 so as to establish an electrostatic field 
extending between the discharge electrode subassembly and the grounded 
collecting electrode plates 22. As the particulates within the gas pass 
through the precipitation chamber 6, the particulates are ionized and 
migrate to and deposit upon the collecting electrode plates 22. 
As best seen in FIGS. 2 and 3, the body of the cover cap 40 of the pesent 
invention comprises a top member 42, a sloping side wall 44, a radial lip 
46 extending radially outwardly from the lower perimeter surface of the 
side wall 44, and an axial lip 48 extending axially outwardly from the 
lower perimeter surface of the side wall 44. The top 42 has a centrally 
located hole 50 formed therein which is adapted to receive the hanger rod 
28, an upper surface 52 against which the hanger rod 28 may be mounted via 
hold down bolts 86, and a perimeter edge 54 from which the sloping side 
wall 44 of the body of the cover cap 40 extends coaxially outwardly and 
downwardly in the form of a frustrum of a cone, somewhat like a skirt, to 
terminate with a lower perimeter surface spaced below and outwardly from 
the perimeter edge 54 of the top member 42. 
Extending outwardly from the lower perimeter surface of the sloping side 
wall 44 of the body of the cover cap 40 at substantially right angles to 
each other are a radial lip 46 and an axial lip 48. The radial lip 46 
extends radially outwardly from the lower perimeter surface of the sloping 
wall 44 and has a lower surface 56 adapted to abut and close against the 
perimeter rim 66 of the insulator housing 38. The axial lip 48 extends 
axially outwardly from the lower perimeter surface of the sloping side 
wall 44 and has a peripheral surface 58 adapted to insert into the open 
end of the support insulator housing 38 and slip in mating relationship 
within the inner peripheral surface 68 of the end of the insulator housing 
38. 
At least one access opening 70 is provided in the sloping side wall 44 of 
the body of the cover cap 40 to provide access into the interior region of 
the cover cap 40 encompassed by the sloping side wall 44 and into the 
interior of the insulator housing 38. This access permits manual cleaning 
of the interior surfaces of insulator housing 38 and the cap cover 40 when 
and if necessary. Preferrably, three access openings 70 are provided at 
equal, circumferentially spaced intervals about the sloping side wall 
portion 44 of the body of the cover cap 40. Additionally, stiffening ribs 
80 may be provided to extend outwardly on the inner surface of sloping 
side wall 44 intermediate the access openings 70 to enhance the structural 
integrity of the cover cap 40. 
A removeable lid 72 is provided for each access opening 70 to seal each 
access opening when the lid 72 is in position covering the access opening. 
Preferrably, each lid 72 has an outwardly extending positioning rim 74 
spaced radially inward from the perimeter of the lid. The positioning rim 
74 is adapted to slip into the access opening 70 in mating relationship 
with the wall surrounding the opening so as to hold the lid in position 
over the access opening. 
In order to maintain the interior of the cover cap 40 in a relatively clean 
condition and to limit build-up of particulate material from the flue gas 
in the interior of the support insulator housing 38, at least one gas 
injection means 90 is provided in association with the body of the cover 
cap 40 so as open through the sloping side wall portion 44 of the body of 
the cover cap 40 for passing a jet of scavenging gas into the interior 
region encompassed by the sloping side wall 44. The scavenging gas is 
injected at a gas pressure higher than that of the flue gas within the 
precipitator housing, whereby the scavenging gas will flow through the 
interior of the support insulator housing 38 into the precipitator housing 
thereby limiting the passage of the lower pressure flue gas into the 
insulator housing and carrying particulate matter from the insulator 
housing back into the precipitation chamber. 
Preferrably, the gas injection means 90 comprises a tubular injection 
nozzle having an elbow subtending an angle of about 135 degrees. The base 
96 of the tubular injection nozzle passes through the body of the cover 
cap 40 for connection to a supply of pressurized scavenging gas (not 
shown). The base 96 of the tubular injection nozzle 92 may be disposed in 
the sloping side portion 44 of the body of the cover cap 40 per se, or, as 
shown in the preferred embodiment illustrated in FIGS. 2 and 3, it may be 
disposed in the lid 72 covering the access opening 70 in the sloping side 
wall 44. In any case, the tubular injection nozzle 92 is orientated as to 
admit the scavenging gas substantially tangentially about the periphery of 
the interior region encompassed by the cap cover 40. By virtue of the 135 
degree angle elbow in the tubular injection nozzle 92, the scavenging gas 
is also directed somewhat downwardly as well as tangentially such that a 
downwardly spiralling swirl of scavenging gas passes through the interior 
of the insulator housing 38 into the precipitation chamber. 
Although the invention has been described and shown in relation to a 
frustoconical shaped sloping side wall with an annular top member, the 
invention has other embodiments which will be apparent to those skilled in 
the art in view of the foregoing disclosure. By way of example and not 
limitation, other embodiments of the cover cap may include a trapezoidal 
frustum sloping side wall portion with the top member having any number of 
sides which are compatible with the shape of the insulator housing. Thus, 
if the insulator housing is in the form of a multi-side shell rather than 
a cylindrical shell, the top member and the sloping side wall portion of 
the body of the cover cap may be shaped accordingly so as to be compatible 
with the insulator housing without departing from the spirit and scope of 
the invention as defined in the claims.