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Precipitator upgrading and fuel control program for particulate compliance at Pennsylvania power and light company
Environmentlnternational, Vol. 6, pp. 219-225, 1981 Printed in the USA. All rights reserved.
0160-4120/81/010219-07502.00/0 Copyright ©1982 Pergamon Press Ltd.
PRECIPITATOR UPGRADING AND FUEL CONTROL PROGRAM FOR PARTICULATE COMPLIANCE AT PENNSYLVANIA POWER AND LIGHT COMPANY John T. Guiffre Pennsylvania Power and Light Company, Allentown, Pennsylvania 18101, USA*
Two cold side electrostatic precipitators handling low sulfur eastern bituminous coal flyash were upgraded from 94°7o to 99.407o efficiency in order to meet a particulate compliance limit of 0.1 lb/MMBtu (43 ng/J). The comprehensive upgrading was the result of a 2 year research and testing program during which various aspects of flue gas conditioning, electrical energization, rapping, coal quality control, and gas distribution were independently tested on three similar precipitators. The ensuing upgrading program included the installation of hardware designed for maximum performance and reliability as well as flue gas conditioning and a fuel ash control program. A cost and reliability analysis of the upgrading program as compared with the installation of an additional series precipitator is included.
Introduction
ciency of 99.5%, this level of performance was never achieved under actual operating conditions. In fact, due to degrading fuel quality, changes in boiler operation to prevent slagging and the small size of the ESP's, efficiencies of only about 94% were achieved with low sulfur coal (I.0%S). In late 1974, a project team was established to study the ESP problems on these units as well as one smaller unit (Brunner Island 1). This Air Quality Project (AQP) team consisted of seven full time engineers. The basic objective of the A Q P was to assure that compliance was achieved, but also to minimize the compliance cost by placing primary emphasis on upgrading the existing collectors rather than installing new ones. F r o m March 1975 until March 1977, a variety of parameters which affect ESP performance were investigated by the A Q P team. The areas o f investigation included:
In 1974, Pennsylvania Power and Light C o m p a n y (PP&L) was faced with the problem o f having several generating units which did not comply with the particulate emissions regulations of the Pennsylvania Department of Environmental Resources. This paper deals with the approach taken to analyze and solve the emissions problems on three similar units. The three units are Montour Units 1 and 2, located in Washingtonville, Pennsylvania, and Brunner Island Unit 3, York-Haven, Pennsylvania. Each unit is nominally rated at 750 M W and is equipped with a Combustion Engineering tangentially fired boiler burning eastern bituminous coal pulverized to 70% through 200 mesh consistency. Each boiler is equipped with a Western Precipitation electrostatic precipitator (ESP) in a chevron arrangement with a total specific collecting area (SCA) of 40mVmVsec) (204 ftV1000 cfm) at design flow of 1062 m3/sec (2,250,000 acfm) at 149 °C (300 °F). Under actual boiler operating conditions, an SCA of only 35 mVm3/sec) (180 ft2/1000 cfm) is achieved Although these ESP's had a guaranteed design effi-
• • • • • • •
*Present address: Wahlco, Inc., 5775-E Peachtree Dunwoody RoadSuite 200, Atlanta, Georgia 30342 USA. 219
Fuel quality, Flue gas conditioning, ESP sectionalization, Rappers, High voltage controllers, Flue gas distribution, and Reliability items.
220
Each of the above areas was independently investigated by a member of the AQP. When the investigations indicated that a change in a particular area could improve ESP performance or reliability, the change was implemented on one single unit on a trial basis. To fully evaluate the change, ESP efficiency tests were run after each trial change and the results were compared with baseline data. A total of 47 full efficiency tests were run on the four units during the 2-year investigation. In addition, continuous opacity monitor data was used for comparative purposes whenever it was impractical or inconvenient to run an efficiency test. As a result of the AQP investigation, the Montour ESP's were upgraded to achieve particulate compliance instead of building additional collectors. Although Brunner Island Unit 3 is similar to Montour Units 1 and 2, this unit could not achieve compliance through upgrading due to dissimilar boiler operation and an inability to control long range coal quality at the Brunner Island station. Due to these differences a series ESP was installed on Brunner Island Unit 3. With the exception of a cost and performance comparison between the upgrading modes selected for Brunnet Island 3 and Montour, the remainder of this paper deals with the Montour upgrading investigation and implementation phases.
Results of the Investigation Phase Fuel control Bituminous coal burned on the PP&L system is obtained both from company affiliated mines and from numerous open market sources. The quality of the coal is highly variable with sulfur content ranging from 0.807o to 2.5070 and ash content ranging from 11070 to 2507o. The fuels investigation that was performed by the AQP team sought to quantify the effect of sulfur content and ash content on ESP efficiency and to determine if fuel quality could realistically be controlled to improve ESP performance. A high sulfur (2.4070 S) low ash (1207o ash) coal supplied by Benjamin Coal Company was used for benchmark data since it was considered to be one of the best collecting coals (as measured by the achieved ESP efficiency) burned on the system. The ESP efficiencies measured while burning Benjamin coal were compared with efficiencies of lower sulfur coals of various ash content. Several important conclusions which were applicable to all four of the tested units were drawn from these tests. (1) A coal sulfur content of 2.207o or greater was required to obtain optimum ESP efficiency. (2) Given a constant sulfur content, ESP efficiency did not change as the ash content was varied in the 11 07o to 2507o range. (3) As the ash content of the coal increased, the per-
John T. Guiffre
centage of ash that found its way into the ESP's in the form of fly ash decreased. Prior to this investigation, it was assumed that 80070 of the ash in the coal "carried over" into the ESP's in the form of flyash. As can be seen in Fig. 1, the percentage of flyash carryover was found to be inversely proportional to the ash content. (4) Due to the lower percentage of fly ash carryover in the higher ash coals, the ESP efficiency which is required to meet the 0.1 lb/MMBTU (43 ng/J) compliance limit does not have a linear relationship with the ash content of the fuel (Fig. 2). It is apparent from Fig. 2 that an ESP efficiency of 99.307o would be sufficient to meet the particulate compliance limit of 0.1 lb/MMBTU (43 ng/J) with any of the tested coals. The conclusions drawn from the Fuels Investigation provided the basis for the decision to upgrade the existing Montour ESP's rather than adding new collectors. While testing with the Benjamin coal at Montour, an ESP efficiency of 99.4070 was achieved, thus indicating that compliance could in fact be attained under controlled conditions. Unfortunately, under low (1.0070) sulfur coal conditions, ESP efficiency would degrade to below 9407o. Due to the fact that the major supplier of coal for the Montour station is Greenwich Collieries, a PP&L affiliated mine which produces a coal with a low average sulfur content (1.2070 S) it was not feasible to establish a fuel procurement plan which would eliminate low sulfur coal. Flue gas conditioning Due to the observed detrimental effect of low sulfur coal on ESP performance, the use of SO3 flue gas conditioning as a resistivity modifier was investigated by the AQP. After a careful evaluation of industry experience with SO3 conditioning, a trial SO~ injection system was installed on Brunner Island Unit 1 (BI-1). BI-1 was selected for the trial because it was the smallest unit under
8O LT. o
~ 70 60
50 10
12
14
16
18
20
22
% A s h In Coal AS Received
Fig. 1. Fly ash carryover.
24
26
28
Precipitator upgrading and fuel control
221
ditions of high resistivity flyash resulting from burning low sulfur coal. It should also be noted that another flue gas conditioning trial was conducted at Montour using proprietary chemicals. Although some improvements in stack opacity had been achieved, no significant improvements in ESP efficiency were measured during the trial period.
Chevron Units
992
i
990 L 988 98 6
t
984 ~L
9821 12
14
16
18
20
22
24
26
28
%Ash In Coal AS Received
Fig. 2. Required ESP efficiency for compliance.
investigation and therefore the installation costs of the system could be kept to a minimum. To evaluate the effect of SO3 conditioning, our benchmark coal (Benjamin) was tested without SO3 injection to establish a "maximum" ESP efficiency for BI-1. A second coal with low sulfur content (1.0% S) from Greenwich Collieries (the major coal supplier for Montour) was then tested both with and without SO3 conditioning. The tests run without the SO3 conditioning indicated that the Greenwich coal was one of the poorest collecting coals normally burned. However, with the addition of 25 ppm of SO3, the ESP efficiency with Greenwich coal improved to a level slightly better than that measured with Benjamin. The tests results are summarized in Fig. 3. Supplemental testing using opacity monitors and flyash resistivity probes as performance indicators revealed that SO~ conditioning was capable of offsetting the effects of burning low sulfur coal to the degree of maintaining optimum ESP efficiency with virtually any coal normally burned at either Montour or Brunner Island. Since the use of SO3 as a flue gas conditioning agent had demonstrated repeatable and predictable results, the AQP concluded that SO3 conditioning was a viable alternative for improving ESP performance under con-
ESP electrical energization Electrical energization was investigated in two primary areas: (a) automatic high voltage control systems and (b) transformer-rectifier (TR) set capacity. Automatic high voltage controls. At the time that the AQP investigation began, almost all of PP&L's precipitators were equipped with high voltage controllers which used saturable core reactors (SCR) and outdated control logic. The investigation therefore focused on modern thyristor controllers with compatible high speed control logic. A series of full scale trials using thyristor controllers was subsequently conducted. The ability of a modern control to greatly improve ESP efficiency was not demonstrated during this study. Power levels (V and I) were increased in some units but the ESP efficiencies did not noticeably change from the values measured before installation of the new controls. Operational experience indicated, however, that the frequency of wire failures was greatly reduced after the new controllers were installed. Heavy sparking and wire burning were almost completely eliminated. It was concluded that the new controls would improve reliability while maintaining voltage and current levels. TR set capacity. During the SO3 conditioning trial at Brunner Island, it was noted that most TR sets operated at the current limit when SO3 conditioning was utilized. Further investigation and trial operation revealed that for optimum ESP efficiency with SO3 conditioning, the TR sets should be sized large enough to provide a current density of at least 54 nA/cm 2 (50 mA/1000 ft2), particularly in the outlet sections. Gas distribution Due to the unusual chevron shaped inlet duct on the Montour ESP's (Fig. 4), an investigation into the possi-
WAHLCO
DATE 7/28/76 7/29/76 9/14/76 9/15/76 9/21/76 9/22/76
COAL
TYPEISULFUR % ASH%
BENJAMIN BENJAMIN GREENWICH GREENWICH GREENWICH GREENWICH
2.2 //
142 //
I.O
12.1
1.0
11.5
//
//
//
//
IN SERVICE
PRECIPITATOR EFFICIENCY BUELL
NO 92.8 NO 92.1 YES- 25 PPM 95.5 YES - 25 PPM 92.7 NO 70.9 NO 71.9
Fig. 3. Summary of efficiency test d a t a - Brunner Island Unit 1.
R.C.
TOTAL
94.7 94.7 96.1 97.0 86.8 89.9
9:5.6 95.2 94.5 94.8 78.0 79.7
222
John T. Guiffre
testing also indicated the need for a programmable rapper control which was capable of minimizing rapping intensity and frequency on the outlet sections in order to minimize rapping reentrainment. Additionally, it was concluded that the existing configuration of one rapper for every seven plates did not provide sufficient cleaning of the plates which were farthest from the rapper. An improved arrangement of one rapper for every three plates was suggested.
The Montour Upgrading Project
Capital improvements A Original
P, [ ] TR Sets
Modified
Fig. 4. M o n t o u r TR set modification.
bility of poor gas distribution within the ESP's was undertaken. Motivated by what later proved to be an erroneous air load velocity test performed by a subcontractor, the AQP contracted to have an ESP model constructed and a model study performed. The results of both the model study and subsequent field tests revealed that the ESPs were operating with an RMS velocity deviation of about 12.5% which is well within the standards of the Industrial Gas Cleaning Institute (I.G.C.I.). Further model studies were conducted to determine whether the velocity distribution could be further improved. An additional 50070 open perforated plate was subsequently installed on one-half of one ESP for evaluation. Since ESP efficiency testing did not indicate that the additional perforated plate had resulted in a performance improvement, no additional modifications were made to the remaining chevron ESP's.
Rappers The Montour ESP's were initially equipped with vibrating rappers and electromechanical (cam type) rapper controls. The need for better rapping was evident from the heavy plate deposits which were routinely observed during internal ESP inspections. As part of the rapper evaluation study, 96 electric impact collecting plate rappers were installed on one-half of the Montour 2 ESP, replacing the existing vibrating rappers. In addition, an electronic matrix type rapper controller with the ability to quickly change rapper timing, intensity and programming, was installed to control the new rappers. Tests results indicated that the impact rappers did a significantly better job of cleaning the collecting plates than did the vibrating rappers, and that the clean plates resulted in an improvement in ESP performance. The
The results obtained from the individual investigations which were performed by the AQP team were utilized to formulate a comprehensive upgrading program for Montour. A key aspect of the upgrading was to achieve an ESP efficiency of 99.4°7o (as previously seen while burning Benjamin coal) and to maintain this level of performance, as much as possible, for the wide variety of coals and operating conditions encountered at Montour. To accomplish this objective, the following improvements were incorporated: * An SO3 flue gas conditioning system was installed on each unit to offset the effects of low sulfur coals which account for two-thirds of the station's fuel supply. The sulfur burner type system was equipped with sufficient redundant equipment (including spare boilers, air heaters and sulfur pumps) to ensure 95 + % reliability of the system. The SO3 system feed rate is varied according to the unit load and the sulfur content of the coal being burned in order to maintain a total SO3 concentration of 19 ppm at the inlet to the ESP (including that portion of SO3 produced by the coal being burned). This corresponds to a fly ash resistivity of about 5 x 101° ohm-cm. • The existing rappers and rapper controls were replaced with electric impact rappers and matrix type rapper controls with considerable programming flexibility. The number of rappers used for plate rapping was approximately doubled in number so that each impact rapper would clean either three or four plates. Impact rappers were also installed on the high voltage discharge system. • All automatic high voltage electrode controls were replaced with thyristor type controls. In addition, secondary (d-c) metering (voltage, current, and spark rate) was installed for each TR set in order to provide better information for operating personnel. • The number of TR sets utilized on each half of the ESP chevron was increased from 8 to 14. The original ESP design utilized one TR set to power two sections. This arrangement was changed on all but the inlet sections to allow one TR set per section, thus increasing the available current density on the outlet sections to
Precipitator upgrading and fuel control
223
97nA/cm ~(90mA/1000 ft~). The original and final arrangements are shown in Fig. 4. • Each ESP was refitted with new discharge wires as part of the upgrading. Additionally, each unit originally had a double wire per weight high voltage framework design which was modified to a single wire per weight framework. • Each hopper was equipped with nuclear type hopper level detectors and electric hopper heaters in order to minimize the possibility of hopper overfill. This improvement was made because the AQP had identified hopper overfilling as a leading cause of ESP section outages. • In order to implement the various phases of the Montour upgrading project, one full-time engineer was added to the plant staff. In addition, the position of ash equipment operator (one per shift) was established at the plant. The ash equipment operator is responsible for ESP operation, ash removal equipment operation, and SO3 system operation.
Fuel control plan A unique aspect of the Montour upgrading program is the inclusion of a fuel ash control plan. As previously outlined and illustrated in Fig. 2, an ESP efficiency of 99.3070 is sufficient to handle coals of ash contents of up to 25°7o. In order to incorporate additional operating margin and reliability into the upgrad-
ing plan, the ash content of coals shipped to Montour has been restricted to less than 1707o (d.b.). As can be seen from Fig. 2, an ESP efficiency of about 99.1070 would be sufficient for coals of this quality. Approximately 60070 of the coal burned at Montour is supplied by Greenwich Collieries, which ships 100070 of its produced coal to Montour. The mine is equipped with a modern coal cleaning plant capable of producing coal as low as 8°70 ash. As a compromise between mine economics and Montour ESP reliability, the average ash content shipped from Greenwich is about 14070 with virtually all of the coal being less than 17070 ash. Most of the remainder of Montour's coal supply is purchased on the open market. The vendors which ship to Montour are presently restricted to a 14°70 ash content and are selected by the PP&L Fuels Department based on their history of quality control. Vendors which ship a single trainload (13,000 tons) of coal to Montour which is in excess of 17% ash are subjected to a field investigation by the Fuels Department. If the shipment is in excess of 19°70 ash, all future shipments from that vendor are suspended until quality assurance is reestablished. An "early warning" system has been established which allows the Montour plant to know the ash content of all coal shipped to the plant before it arrives. All of the coal burned at Montour is shipped to the plant in PP&L owned fleet trains. An independent coal analysis
r
~ - ~ Car Dumper
,
I I
Dead Storage Area
I
Coal
L_
i~ ~ ~ i
II In
i
LowAshCoa,
-
i
i
High Ash Coal ....................
~ 1
._ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig. 5. Montour S.E.S. coal control.
;, r~__~ I~ Transfer
i j
I'--'FI~'-~'-I II
II
224
E~
J o h n T. Guiffre
2o
3
01
02
0 3 .04
.05 .06 .07 .08
.09 .10 .11 A 2
.13 .14
.15
.16 .17 .18 .19
Emission Level IbJMMBTU
Fig. 6. Compliance histogram.
firm has been hired to sample coal from each car in the fleet train at the time that it is loaded at the mine. The analysis firm then performs a "quick ash analysis" which takes about three hours and has proven to be fairly accurate. The results of the quick ash analysis are teletyped to Montour in less than 12 hours from the time the sample is taken. (Train transit time is 12-24 hours.) In the event that a high ash shipment of coal arrives
at Montour, the early warning system allows the plant to take appropriate action. The plant's coal yard is equipped with a stacker reclaimer with capacity to hold five trainloads of coal. Sufficient area is reserved on the stacker reclaimer at all times for the storage of at least one trainload of high ash coal (greater than 17°70 ash). If the early warning system reveals that a trainload of high ash coal will arrive at the station, the coal is unloaded into the reserved storage area. From this area, the coal is reclaimed on a controlled basis and mixed with coal of lower ash content. Since the Montour plant has three raw coal silos per unit, the mixing is usually accomplished by loading high ash coal in one silo and low ash coal in the other two silos. In this manner, a 13,000 ton trainload of high ash coal can be safely disposed of in about one week. A schematic layout of the Montour high ash coal handling system is shown in Fig. 5.
Reliability analysis Before the decision was made to upgrade the Montour ESPs, a comprehensive reliability analysis of all components that would be a part of the upgrading was undertaken. Essentially, the objective was to determine the percentage of time that the Montour units could be
Beforee~cling
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.
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=~ii ~ii~i~!~~i! !~iii~ ~i ¸
,/? (/~,'~i~¸, = i
iii i,~ ~
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i! ii~ !~ :¸
Fig. 7. Opacity comparison.
225
Precipitator upgrading and fuel control Table 1. Cost comparison-Montour upgrading vs. Brunner Island 3 series ESP Montour S.E.S.-750 MW
Brunner Island Unit 3-750 MW
Design criteria: 99.4% efficiency with 1.0% S coal with all equipment operating,
Series ESP designed for 90% efficiency with 1.5% S coal. Existing ESP to operate at 95% efficiency for combined efficiency at 99.50/0. SO3 flue gas conditioning to be utilized with coals of less than 1.5°/0 sulfur.
Compliance limit of 0.1 Ib/MMBTU (43 ng/J) to be met 96.5% of time without forced load reductions.
Compliance limit of 0.1 Ib/MMBTU (43 ng/J) to be met 99+ % of time without forced load reductions. Costs:
(per unit) Upgrading hardware (includes SO, system)
ESP and auxiliaries (includes booster fans, SOj system, auxiliary $4,000,000 transformer and site preparation)
$38,000,000
Annual O & M
$ 500,000
$ 1,500,000
Annual forced load reductions
$1,000,000
Annual O & M
Approximately two-thirds of the annual O & M cost for the Brunner Island ESP is for electrical power for the new ESP and booster fans. It is interesting to note that the annual cost of power which will be used to operate the new collection equipment on Brunner Island Unit 3 is equal to the annual cost of the anticipated forced "compliance" load reductions at each Montour Unit.
Note:
expected to remain in compliance, given the known fallability o f some aspects of the compliance plan. This was an important consideration in light of the fact that the units would probably have to drop load (at substantial cost) to maintain compliance if the installed collection equipment failed. The histogram which is shown in Fig. 6 illustrates the predicted day-to-day emissions at M o n t o u r after ESP upgrading. The stack emissions are affected by five variables. The histogram includes the overlapping probability o f multiple component failure. The variables, the ranges and the probabilities o f occurrence are listed below.
(1) Boiler loading (historical) 750 M W 700 M W 650 M W 400-500 M W (2) ESP sections out of service 0 sections 1 section 2 sections 3 sections (3) Fuel ash content (dry basis) Greater than 17% ash 14%-17% Less than 14% ash (4) Fuel sulfur content Less than 1% S 20% Less than 1.5% S 60070 Less than 2.0% S 20%
50% 20% 20% 10%
90% 6% 3% 1% 5070 5007o 45%
(5) SO3 injection system 95% reliability (based on C o m m o n w e a l t h Edison experience) The combined effect o f the performance variables listed above results in a predicted compliance level of 96.5%. During the remaining 3.507o o f the time, the units would have to operate at a reduced load to maintain compliance.
Results and Conclusions Since the upgrading at M o n t o u r was completed, the opacity on b o t h units has been continually maintained in the 6 0 to 8% range even when as m a n y as three ESP sections have been taken out o f service. Fig. 7 shows a comparison o f opacity monitor charts during three phases o f the M o n t o u r program. Note that the addition of T R sets and rappers in November, 1978 not only reduced the overall opacity but also greatly reduced the rapping spikes which were previously observed. As o f July 1, 1979, only M o n t o u r Unit 2 had been tested for particulate compliance. Results o f the three emissions tests performed by the Pennsylvania Department o f Environmental Resources indicated an average emission rate o f 0.057 l b / M M B t u 24.5 n g / J ) which is substantially below the allowable limit of 0.1 lb/ M M B t u (43 rig/J). (ESP efficiency is estimated at 99.6%). These tests are a positive indication that the M o n t o u r upgrading p r o g r a m has been successful in effecting a reliable, low cost solution to a problem which otherwise would have been resolved by the addition of expensive retrofit collectors.
0160-4120/81/010219-07502.00/0 Copyright ©1982 Pergamon Press Ltd.
PRECIPITATOR UPGRADING AND FUEL CONTROL PROGRAM FOR PARTICULATE COMPLIANCE AT PENNSYLVANIA POWER AND LIGHT COMPANY John T. Guiffre Pennsylvania Power and Light Company, Allentown, Pennsylvania 18101, USA*
Two cold side electrostatic precipitators handling low sulfur eastern bituminous coal flyash were upgraded from 94°7o to 99.407o efficiency in order to meet a particulate compliance limit of 0.1 lb/MMBtu (43 ng/J). The comprehensive upgrading was the result of a 2 year research and testing program during which various aspects of flue gas conditioning, electrical energization, rapping, coal quality control, and gas distribution were independently tested on three similar precipitators. The ensuing upgrading program included the installation of hardware designed for maximum performance and reliability as well as flue gas conditioning and a fuel ash control program. A cost and reliability analysis of the upgrading program as compared with the installation of an additional series precipitator is included.
Introduction
ciency of 99.5%, this level of performance was never achieved under actual operating conditions. In fact, due to degrading fuel quality, changes in boiler operation to prevent slagging and the small size of the ESP's, efficiencies of only about 94% were achieved with low sulfur coal (I.0%S). In late 1974, a project team was established to study the ESP problems on these units as well as one smaller unit (Brunner Island 1). This Air Quality Project (AQP) team consisted of seven full time engineers. The basic objective of the A Q P was to assure that compliance was achieved, but also to minimize the compliance cost by placing primary emphasis on upgrading the existing collectors rather than installing new ones. F r o m March 1975 until March 1977, a variety of parameters which affect ESP performance were investigated by the A Q P team. The areas o f investigation included:
In 1974, Pennsylvania Power and Light C o m p a n y (PP&L) was faced with the problem o f having several generating units which did not comply with the particulate emissions regulations of the Pennsylvania Department of Environmental Resources. This paper deals with the approach taken to analyze and solve the emissions problems on three similar units. The three units are Montour Units 1 and 2, located in Washingtonville, Pennsylvania, and Brunner Island Unit 3, York-Haven, Pennsylvania. Each unit is nominally rated at 750 M W and is equipped with a Combustion Engineering tangentially fired boiler burning eastern bituminous coal pulverized to 70% through 200 mesh consistency. Each boiler is equipped with a Western Precipitation electrostatic precipitator (ESP) in a chevron arrangement with a total specific collecting area (SCA) of 40mVmVsec) (204 ftV1000 cfm) at design flow of 1062 m3/sec (2,250,000 acfm) at 149 °C (300 °F). Under actual boiler operating conditions, an SCA of only 35 mVm3/sec) (180 ft2/1000 cfm) is achieved Although these ESP's had a guaranteed design effi-
• • • • • • •
*Present address: Wahlco, Inc., 5775-E Peachtree Dunwoody RoadSuite 200, Atlanta, Georgia 30342 USA. 219
Fuel quality, Flue gas conditioning, ESP sectionalization, Rappers, High voltage controllers, Flue gas distribution, and Reliability items.
220
Each of the above areas was independently investigated by a member of the AQP. When the investigations indicated that a change in a particular area could improve ESP performance or reliability, the change was implemented on one single unit on a trial basis. To fully evaluate the change, ESP efficiency tests were run after each trial change and the results were compared with baseline data. A total of 47 full efficiency tests were run on the four units during the 2-year investigation. In addition, continuous opacity monitor data was used for comparative purposes whenever it was impractical or inconvenient to run an efficiency test. As a result of the AQP investigation, the Montour ESP's were upgraded to achieve particulate compliance instead of building additional collectors. Although Brunner Island Unit 3 is similar to Montour Units 1 and 2, this unit could not achieve compliance through upgrading due to dissimilar boiler operation and an inability to control long range coal quality at the Brunner Island station. Due to these differences a series ESP was installed on Brunner Island Unit 3. With the exception of a cost and performance comparison between the upgrading modes selected for Brunnet Island 3 and Montour, the remainder of this paper deals with the Montour upgrading investigation and implementation phases.
Results of the Investigation Phase Fuel control Bituminous coal burned on the PP&L system is obtained both from company affiliated mines and from numerous open market sources. The quality of the coal is highly variable with sulfur content ranging from 0.807o to 2.5070 and ash content ranging from 11070 to 2507o. The fuels investigation that was performed by the AQP team sought to quantify the effect of sulfur content and ash content on ESP efficiency and to determine if fuel quality could realistically be controlled to improve ESP performance. A high sulfur (2.4070 S) low ash (1207o ash) coal supplied by Benjamin Coal Company was used for benchmark data since it was considered to be one of the best collecting coals (as measured by the achieved ESP efficiency) burned on the system. The ESP efficiencies measured while burning Benjamin coal were compared with efficiencies of lower sulfur coals of various ash content. Several important conclusions which were applicable to all four of the tested units were drawn from these tests. (1) A coal sulfur content of 2.207o or greater was required to obtain optimum ESP efficiency. (2) Given a constant sulfur content, ESP efficiency did not change as the ash content was varied in the 11 07o to 2507o range. (3) As the ash content of the coal increased, the per-
John T. Guiffre
centage of ash that found its way into the ESP's in the form of fly ash decreased. Prior to this investigation, it was assumed that 80070 of the ash in the coal "carried over" into the ESP's in the form of flyash. As can be seen in Fig. 1, the percentage of flyash carryover was found to be inversely proportional to the ash content. (4) Due to the lower percentage of fly ash carryover in the higher ash coals, the ESP efficiency which is required to meet the 0.1 lb/MMBTU (43 ng/J) compliance limit does not have a linear relationship with the ash content of the fuel (Fig. 2). It is apparent from Fig. 2 that an ESP efficiency of 99.307o would be sufficient to meet the particulate compliance limit of 0.1 lb/MMBTU (43 ng/J) with any of the tested coals. The conclusions drawn from the Fuels Investigation provided the basis for the decision to upgrade the existing Montour ESP's rather than adding new collectors. While testing with the Benjamin coal at Montour, an ESP efficiency of 99.4070 was achieved, thus indicating that compliance could in fact be attained under controlled conditions. Unfortunately, under low (1.0070) sulfur coal conditions, ESP efficiency would degrade to below 9407o. Due to the fact that the major supplier of coal for the Montour station is Greenwich Collieries, a PP&L affiliated mine which produces a coal with a low average sulfur content (1.2070 S) it was not feasible to establish a fuel procurement plan which would eliminate low sulfur coal. Flue gas conditioning Due to the observed detrimental effect of low sulfur coal on ESP performance, the use of SO3 flue gas conditioning as a resistivity modifier was investigated by the AQP. After a careful evaluation of industry experience with SO3 conditioning, a trial SO~ injection system was installed on Brunner Island Unit 1 (BI-1). BI-1 was selected for the trial because it was the smallest unit under
8O LT. o
~ 70 60
50 10
12
14
16
18
20
22
% A s h In Coal AS Received
Fig. 1. Fly ash carryover.
24
26
28
Precipitator upgrading and fuel control
221
ditions of high resistivity flyash resulting from burning low sulfur coal. It should also be noted that another flue gas conditioning trial was conducted at Montour using proprietary chemicals. Although some improvements in stack opacity had been achieved, no significant improvements in ESP efficiency were measured during the trial period.
Chevron Units
992
i
990 L 988 98 6
t
984 ~L
9821 12
14
16
18
20
22
24
26
28
%Ash In Coal AS Received
Fig. 2. Required ESP efficiency for compliance.
investigation and therefore the installation costs of the system could be kept to a minimum. To evaluate the effect of SO3 conditioning, our benchmark coal (Benjamin) was tested without SO3 injection to establish a "maximum" ESP efficiency for BI-1. A second coal with low sulfur content (1.0% S) from Greenwich Collieries (the major coal supplier for Montour) was then tested both with and without SO3 conditioning. The tests run without the SO3 conditioning indicated that the Greenwich coal was one of the poorest collecting coals normally burned. However, with the addition of 25 ppm of SO3, the ESP efficiency with Greenwich coal improved to a level slightly better than that measured with Benjamin. The tests results are summarized in Fig. 3. Supplemental testing using opacity monitors and flyash resistivity probes as performance indicators revealed that SO~ conditioning was capable of offsetting the effects of burning low sulfur coal to the degree of maintaining optimum ESP efficiency with virtually any coal normally burned at either Montour or Brunner Island. Since the use of SO3 as a flue gas conditioning agent had demonstrated repeatable and predictable results, the AQP concluded that SO3 conditioning was a viable alternative for improving ESP performance under con-
ESP electrical energization Electrical energization was investigated in two primary areas: (a) automatic high voltage control systems and (b) transformer-rectifier (TR) set capacity. Automatic high voltage controls. At the time that the AQP investigation began, almost all of PP&L's precipitators were equipped with high voltage controllers which used saturable core reactors (SCR) and outdated control logic. The investigation therefore focused on modern thyristor controllers with compatible high speed control logic. A series of full scale trials using thyristor controllers was subsequently conducted. The ability of a modern control to greatly improve ESP efficiency was not demonstrated during this study. Power levels (V and I) were increased in some units but the ESP efficiencies did not noticeably change from the values measured before installation of the new controls. Operational experience indicated, however, that the frequency of wire failures was greatly reduced after the new controllers were installed. Heavy sparking and wire burning were almost completely eliminated. It was concluded that the new controls would improve reliability while maintaining voltage and current levels. TR set capacity. During the SO3 conditioning trial at Brunner Island, it was noted that most TR sets operated at the current limit when SO3 conditioning was utilized. Further investigation and trial operation revealed that for optimum ESP efficiency with SO3 conditioning, the TR sets should be sized large enough to provide a current density of at least 54 nA/cm 2 (50 mA/1000 ft2), particularly in the outlet sections. Gas distribution Due to the unusual chevron shaped inlet duct on the Montour ESP's (Fig. 4), an investigation into the possi-
WAHLCO
DATE 7/28/76 7/29/76 9/14/76 9/15/76 9/21/76 9/22/76
COAL
TYPEISULFUR % ASH%
BENJAMIN BENJAMIN GREENWICH GREENWICH GREENWICH GREENWICH
2.2 //
142 //
I.O
12.1
1.0
11.5
//
//
//
//
IN SERVICE
PRECIPITATOR EFFICIENCY BUELL
NO 92.8 NO 92.1 YES- 25 PPM 95.5 YES - 25 PPM 92.7 NO 70.9 NO 71.9
Fig. 3. Summary of efficiency test d a t a - Brunner Island Unit 1.
R.C.
TOTAL
94.7 94.7 96.1 97.0 86.8 89.9
9:5.6 95.2 94.5 94.8 78.0 79.7
222
John T. Guiffre
testing also indicated the need for a programmable rapper control which was capable of minimizing rapping intensity and frequency on the outlet sections in order to minimize rapping reentrainment. Additionally, it was concluded that the existing configuration of one rapper for every seven plates did not provide sufficient cleaning of the plates which were farthest from the rapper. An improved arrangement of one rapper for every three plates was suggested.
The Montour Upgrading Project
Capital improvements A Original
P, [ ] TR Sets
Modified
Fig. 4. M o n t o u r TR set modification.
bility of poor gas distribution within the ESP's was undertaken. Motivated by what later proved to be an erroneous air load velocity test performed by a subcontractor, the AQP contracted to have an ESP model constructed and a model study performed. The results of both the model study and subsequent field tests revealed that the ESPs were operating with an RMS velocity deviation of about 12.5% which is well within the standards of the Industrial Gas Cleaning Institute (I.G.C.I.). Further model studies were conducted to determine whether the velocity distribution could be further improved. An additional 50070 open perforated plate was subsequently installed on one-half of one ESP for evaluation. Since ESP efficiency testing did not indicate that the additional perforated plate had resulted in a performance improvement, no additional modifications were made to the remaining chevron ESP's.
Rappers The Montour ESP's were initially equipped with vibrating rappers and electromechanical (cam type) rapper controls. The need for better rapping was evident from the heavy plate deposits which were routinely observed during internal ESP inspections. As part of the rapper evaluation study, 96 electric impact collecting plate rappers were installed on one-half of the Montour 2 ESP, replacing the existing vibrating rappers. In addition, an electronic matrix type rapper controller with the ability to quickly change rapper timing, intensity and programming, was installed to control the new rappers. Tests results indicated that the impact rappers did a significantly better job of cleaning the collecting plates than did the vibrating rappers, and that the clean plates resulted in an improvement in ESP performance. The
The results obtained from the individual investigations which were performed by the AQP team were utilized to formulate a comprehensive upgrading program for Montour. A key aspect of the upgrading was to achieve an ESP efficiency of 99.4°7o (as previously seen while burning Benjamin coal) and to maintain this level of performance, as much as possible, for the wide variety of coals and operating conditions encountered at Montour. To accomplish this objective, the following improvements were incorporated: * An SO3 flue gas conditioning system was installed on each unit to offset the effects of low sulfur coals which account for two-thirds of the station's fuel supply. The sulfur burner type system was equipped with sufficient redundant equipment (including spare boilers, air heaters and sulfur pumps) to ensure 95 + % reliability of the system. The SO3 system feed rate is varied according to the unit load and the sulfur content of the coal being burned in order to maintain a total SO3 concentration of 19 ppm at the inlet to the ESP (including that portion of SO3 produced by the coal being burned). This corresponds to a fly ash resistivity of about 5 x 101° ohm-cm. • The existing rappers and rapper controls were replaced with electric impact rappers and matrix type rapper controls with considerable programming flexibility. The number of rappers used for plate rapping was approximately doubled in number so that each impact rapper would clean either three or four plates. Impact rappers were also installed on the high voltage discharge system. • All automatic high voltage electrode controls were replaced with thyristor type controls. In addition, secondary (d-c) metering (voltage, current, and spark rate) was installed for each TR set in order to provide better information for operating personnel. • The number of TR sets utilized on each half of the ESP chevron was increased from 8 to 14. The original ESP design utilized one TR set to power two sections. This arrangement was changed on all but the inlet sections to allow one TR set per section, thus increasing the available current density on the outlet sections to
Precipitator upgrading and fuel control
223
97nA/cm ~(90mA/1000 ft~). The original and final arrangements are shown in Fig. 4. • Each ESP was refitted with new discharge wires as part of the upgrading. Additionally, each unit originally had a double wire per weight high voltage framework design which was modified to a single wire per weight framework. • Each hopper was equipped with nuclear type hopper level detectors and electric hopper heaters in order to minimize the possibility of hopper overfill. This improvement was made because the AQP had identified hopper overfilling as a leading cause of ESP section outages. • In order to implement the various phases of the Montour upgrading project, one full-time engineer was added to the plant staff. In addition, the position of ash equipment operator (one per shift) was established at the plant. The ash equipment operator is responsible for ESP operation, ash removal equipment operation, and SO3 system operation.
Fuel control plan A unique aspect of the Montour upgrading program is the inclusion of a fuel ash control plan. As previously outlined and illustrated in Fig. 2, an ESP efficiency of 99.3070 is sufficient to handle coals of ash contents of up to 25°7o. In order to incorporate additional operating margin and reliability into the upgrad-
ing plan, the ash content of coals shipped to Montour has been restricted to less than 1707o (d.b.). As can be seen from Fig. 2, an ESP efficiency of about 99.1070 would be sufficient for coals of this quality. Approximately 60070 of the coal burned at Montour is supplied by Greenwich Collieries, which ships 100070 of its produced coal to Montour. The mine is equipped with a modern coal cleaning plant capable of producing coal as low as 8°70 ash. As a compromise between mine economics and Montour ESP reliability, the average ash content shipped from Greenwich is about 14070 with virtually all of the coal being less than 17070 ash. Most of the remainder of Montour's coal supply is purchased on the open market. The vendors which ship to Montour are presently restricted to a 14°70 ash content and are selected by the PP&L Fuels Department based on their history of quality control. Vendors which ship a single trainload (13,000 tons) of coal to Montour which is in excess of 17% ash are subjected to a field investigation by the Fuels Department. If the shipment is in excess of 19°70 ash, all future shipments from that vendor are suspended until quality assurance is reestablished. An "early warning" system has been established which allows the Montour plant to know the ash content of all coal shipped to the plant before it arrives. All of the coal burned at Montour is shipped to the plant in PP&L owned fleet trains. An independent coal analysis
r
~ - ~ Car Dumper
,
I I
Dead Storage Area
I
Coal
L_
i~ ~ ~ i
II In
i
LowAshCoa,
-
i
i
High Ash Coal ....................
~ 1
._ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fig. 5. Montour S.E.S. coal control.
;, r~__~ I~ Transfer
i j
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II
224
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J o h n T. Guiffre
2o
3
01
02
0 3 .04
.05 .06 .07 .08
.09 .10 .11 A 2
.13 .14
.15
.16 .17 .18 .19
Emission Level IbJMMBTU
Fig. 6. Compliance histogram.
firm has been hired to sample coal from each car in the fleet train at the time that it is loaded at the mine. The analysis firm then performs a "quick ash analysis" which takes about three hours and has proven to be fairly accurate. The results of the quick ash analysis are teletyped to Montour in less than 12 hours from the time the sample is taken. (Train transit time is 12-24 hours.) In the event that a high ash shipment of coal arrives
at Montour, the early warning system allows the plant to take appropriate action. The plant's coal yard is equipped with a stacker reclaimer with capacity to hold five trainloads of coal. Sufficient area is reserved on the stacker reclaimer at all times for the storage of at least one trainload of high ash coal (greater than 17°70 ash). If the early warning system reveals that a trainload of high ash coal will arrive at the station, the coal is unloaded into the reserved storage area. From this area, the coal is reclaimed on a controlled basis and mixed with coal of lower ash content. Since the Montour plant has three raw coal silos per unit, the mixing is usually accomplished by loading high ash coal in one silo and low ash coal in the other two silos. In this manner, a 13,000 ton trainload of high ash coal can be safely disposed of in about one week. A schematic layout of the Montour high ash coal handling system is shown in Fig. 5.
Reliability analysis Before the decision was made to upgrade the Montour ESPs, a comprehensive reliability analysis of all components that would be a part of the upgrading was undertaken. Essentially, the objective was to determine the percentage of time that the Montour units could be
Beforee~cling
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.
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Fig. 7. Opacity comparison.
225
Precipitator upgrading and fuel control Table 1. Cost comparison-Montour upgrading vs. Brunner Island 3 series ESP Montour S.E.S.-750 MW
Brunner Island Unit 3-750 MW
Design criteria: 99.4% efficiency with 1.0% S coal with all equipment operating,
Series ESP designed for 90% efficiency with 1.5% S coal. Existing ESP to operate at 95% efficiency for combined efficiency at 99.50/0. SO3 flue gas conditioning to be utilized with coals of less than 1.5°/0 sulfur.
Compliance limit of 0.1 Ib/MMBTU (43 ng/J) to be met 96.5% of time without forced load reductions.
Compliance limit of 0.1 Ib/MMBTU (43 ng/J) to be met 99+ % of time without forced load reductions. Costs:
(per unit) Upgrading hardware (includes SO, system)
ESP and auxiliaries (includes booster fans, SOj system, auxiliary $4,000,000 transformer and site preparation)
$38,000,000
Annual O & M
$ 500,000
$ 1,500,000
Annual forced load reductions
$1,000,000
Annual O & M
Approximately two-thirds of the annual O & M cost for the Brunner Island ESP is for electrical power for the new ESP and booster fans. It is interesting to note that the annual cost of power which will be used to operate the new collection equipment on Brunner Island Unit 3 is equal to the annual cost of the anticipated forced "compliance" load reductions at each Montour Unit.
Note:
expected to remain in compliance, given the known fallability o f some aspects of the compliance plan. This was an important consideration in light of the fact that the units would probably have to drop load (at substantial cost) to maintain compliance if the installed collection equipment failed. The histogram which is shown in Fig. 6 illustrates the predicted day-to-day emissions at M o n t o u r after ESP upgrading. The stack emissions are affected by five variables. The histogram includes the overlapping probability o f multiple component failure. The variables, the ranges and the probabilities o f occurrence are listed below.
(1) Boiler loading (historical) 750 M W 700 M W 650 M W 400-500 M W (2) ESP sections out of service 0 sections 1 section 2 sections 3 sections (3) Fuel ash content (dry basis) Greater than 17% ash 14%-17% Less than 14% ash (4) Fuel sulfur content Less than 1% S 20% Less than 1.5% S 60070 Less than 2.0% S 20%
50% 20% 20% 10%
90% 6% 3% 1% 5070 5007o 45%
(5) SO3 injection system 95% reliability (based on C o m m o n w e a l t h Edison experience) The combined effect o f the performance variables listed above results in a predicted compliance level of 96.5%. During the remaining 3.507o o f the time, the units would have to operate at a reduced load to maintain compliance.
Results and Conclusions Since the upgrading at M o n t o u r was completed, the opacity on b o t h units has been continually maintained in the 6 0 to 8% range even when as m a n y as three ESP sections have been taken out o f service. Fig. 7 shows a comparison o f opacity monitor charts during three phases o f the M o n t o u r program. Note that the addition of T R sets and rappers in November, 1978 not only reduced the overall opacity but also greatly reduced the rapping spikes which were previously observed. As o f July 1, 1979, only M o n t o u r Unit 2 had been tested for particulate compliance. Results o f the three emissions tests performed by the Pennsylvania Department o f Environmental Resources indicated an average emission rate o f 0.057 l b / M M B t u 24.5 n g / J ) which is substantially below the allowable limit of 0.1 lb/ M M B t u (43 rig/J). (ESP efficiency is estimated at 99.6%). These tests are a positive indication that the M o n t o u r upgrading p r o g r a m has been successful in effecting a reliable, low cost solution to a problem which otherwise would have been resolved by the addition of expensive retrofit collectors.