Encyclopedia of Environmental Science and Engineering, Volume I and II

290 ELECTROSTATIC PRECIPITATION

and across the basement floor by the forced draft fans in the

boiler house.

A visit to the precipitator building with all units energized

indicated that the building temperature rises gradually as you

ascend with the upper areas being as much as 50° warmer

than in the basement. The “hot spots” that were originally

expected were found to exist, especially where little clear-

ance was left between the precipitator units and the entrance

flues on the east side of the building above the +126−2

elevation. Air temperatures as high as 220°F were recorded

in such areas. Support steel temperatures were taken where

access was possible and found to be as high as 240°F. It is

felt that the 500°F design temperature probably exists in the

middle regions of the support steel at the +126−2 eleva-

tion but only thermo couples could confirm this. A tempera-

ture differential of 115°F was recorded between the top and

bottom flanges of the north G4 girder at column QQ36.

In all, the precipitator building at Ravenswood Station—

Boiler 30 houses some very unique equipment which created

special temperature problems to support it and to enclose it.

Operating experience indicates that the designs undertaken

to satisfy these conditions are working well.

PARTICULATE CONTROL ANALYSIS OF DEIS

The precipitators proposed in 1981 will upgrade the con-

trolled particulate emissions to below 0.033 lb/million Btu.^5

This rate assumes that coal with a heating value of 12,200

Btu/lb and 12.5% ash will be burned, that 80% of the ash if fly

ash, and electrostatic precipitators have a design efficiency of

99.75% will be employed. This rate is equivalent to that from

burning 0.3% sulfur oil.

Particulate emission control with the original precipi-

tator was adequate to meet plume opacity standards. After

the precipitator is upgraded, plume opacity is expected to be

below 10%, or less than half of the opacity standard. This is

comparable to the opacity when burning 0.3% sulfur oil and

is well within the State and City limit.

Con Edison’s plan was to commence coal burning using

the existing hotside electrostatic precipitator at Ravenswood

Unit 3 and to increase the design collection efficiency from

99.0% to 99.75%. This will control the total particulate emis-

sion rate to less than 0.033 lb/million Btu, which is equiva-

lent to that from 0.3% sulfur oil. The existing Ravenswood

Unit 3 precipitator was tested at 99.2% to 99.6% efficiency

when burning 1% sulfur coal. The upgraded precipitator

design includes the following to insure that the high collec-

tion efficiency is maintained:

The mechanical dust collectors will be replaced with an

additional 310,000 sq ft. of electrical collecting surface area.

This will result in a specific collection area (SCA) of 329

(hot side). Figure 12 indicates that this will provide a design

collection efficiency of 99.75% while burning coal with a

sulfur content of 0.6–1%.

Electrical sections will be isolated so that failure of one

section will not affect performance of other sections. As

many as 7% of the electrical sections could be out of service

without degrading precipitator efficiency below 99.6%.

Precipitator Design Chart

DESIGN CRITERIA FOR RAVENSWOOD 30

COLLECTION EFFICIENCY PERCENT

EFFICIENCY

=^ 1–e

–1

wA

V

3048

x

90

95

96

97

98

99

99.5

99.6

99.7

99.8

99.9

99.95

99.96

99.97

99.98

0 100 200 300 400 400 500 600 70010

108 8

109

1010

1011

1012

1013

109

1010

1011

1012

1013

500 600 200 300

CRITICAL

PRECIPITATION

ZONE

IDEAL

PRECIPITATION

ZONE

MARGINAL ZONE

EASTERN BITUMINOUS COAL

SQUARE FEET COLLECTING ELECTRODE PER 1000 CFM

SCA RAVENSWOOD 30 PRECIPITATOR GAS TEMP.

GAS TEMP °F

FLY ASH RESISTIVITY OHM-CM

R.G. RAMSDELL JR.

DEC 16, 1980

STEAM FLOW, #PER HR.COAL FIRED, #PER HR. BOILER 306,500,000

ASH, 12.5% #PER HR.FLY ASH, #PER HR.

GAS FLOW, CFM600°F

GAS FLOW, CFM300°F

AVG. PRECIP. EFF. %EMISSION GRAINS/CUFT 600°F

EMISSION GRAINS/CUFT 300°FEMISSION #/10 (^4) BTU
685,00085,600
4,007,00068,600
0.01099.6
2,920,0000.01
.033
RESISTIVITY–SULPHUR–TEMPERATURE
EXPECTED
AVERAGE FLY ASH
RESISTIVITY Vs GAS TEMP.
2.0
TO
4.0% S
1.5
TO
2.0% S
1.0
TO
1.5% S
0.5
TO 1.0% S
SCA-COLLECTION EFFICIENCY@ 600°F FLUE GAS TEMP. SULPHUR IN COAL
EXISTING EFFICIENCY
AVERAGE EFFICIENCY
OVER PARTICLE SIZE
RANGE
NEW DESIGN EFFICIENCY
HOT PRECIPI
TAT
OR
0.6–1.0% s
SQUARE FT

. COLL

ECT SURFACE

1,008,000 FT^2

ADDITIONAL

SECTIONS

1,318,000 FT^2

FIGURE 12A FIGURE 12B

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