THE SUMNER COUNTY MASS BURNING EXPERIENCE

CHADWELL O'CONNOR O'Connor Combustor Corporation

Costa Mesa, California

ABSTRACT

This paper will present the operating experiences of the two O'Connor Water-Cooled Rotary Combustor sys­tems in service at the waste to energy plant operated by the Resource Authority in Sumner County, Tennessee. The paper will include the results of several tests per­formed by various engineering firms and agencies in both 1982 and 1983.

INTRODUCTION

BACKGROUND

Sumner County, Tennessee, with a population of about 90,000, and two key cities, Gallatin and Hendersonville, decided in 1976 to work toward a waste to energy facility in order to extend the life of the last existing landfill. In central Tennessee, near Nashville, the geology is primarily limestone at a shallow depth. Landf1lls are difficult to per­mit and develop.

The State of Tennessee passed enabling legislation in May 1979 allowing the formation of the Resource Author­ity in Sumner County, which contracted for design and construction of the plant, sale of steam, and obtained con­trol of the waste stream in the county. A feasibility study indicated a waste stream of about 750 tons (680 t) per week, that three steam customers were available, and that the Tennessee Valley Authority was interested in pur­chaSing cogenerated electrical power.

A five acre (20,230 m2) site was donated by the major steam customer. This site is capable of doubling the plant size, which was engineered at a nominal rating pf 170 TPD (154 tpd) and 45,000 lb/hr (20,410 kg/h) steam and

301

a maximum rating at 200 TPD (181 tpd), for an output of 54,000 lb/hr (24,490 kg/h) of steam produced at 425 psig (2930 kPa) and 504°F (262°C) when firing 7084 lb/hr (3213 kg/h) of TVA fuel "B" waste. (Appendix A). The plant design included a 550 kW turbine-generator set designed to take all the produced steam. The steam ex­hausts the turbine at 200 psig (1380 kPa) for internal use and export to the steam customers. The excess steam is delivered to an air-cooled condenser. Condensate is re­turned by one steam customer to the plant.

CHRONOLOGY OF THE FACILITY

The chronology of the project was: January • City of Gallatin formed a one-man com-1976 mittee to review alternatives to landf1ll. July 1977 • Cities of Gallatin and Hendersonville and

Sumner County authorized feasibility study.

October • Feasibility study completed. 1977 June 1978 June­December 1978 October 1978 December 1978 January 1979 May 1979

• Preliminary deSign authorized. • Negotiated energy contracts.

• Third party review completed.

• Preliminary design completed.

• Ad hoc committee formed to evaluate deSign.

• Tennessee passed enabling legislation for the Resource Authority in Sumner County.

October 1979 December 1979 February 1980 March 1980 June 1980 December 1981 February 1982 March 1982 June-July 1982 October 1982

• Resource Authority formed.

• Contract awarded for combustion equip­ment.

• Construction financing approved.

• Contract awarded for fmal design and construction of the plant.

• Groundbreaking. • First waste combusted in Unit #1.

• First steam delivered to customers.

• First waste combusted in Unit #2.

• Performance and acceptance tests.

• Ultrasonic testing of combustor and tube walls.

February • Environmental testing and boiler temper-1983 ature profile testing. June 1983 • TV A Testing for EPRI* contract.

In July 1983, the Resource Authority sold a $12,000,000 bond issue to pay off the First Tennessee Bank loan, effect some capital improvements, establish a renewal and replacement fund, debt service fund, etc.

MAJOR PLANT EQUIPMENT

The plant was procured in a manner sometimes called the traditional A/E method. The owner selected the architect/engineer and construction manager; major equip­ment orders were placed by the owner based on recom­mendations from the A/E acting as agent for the owner; individual construction packages were placed for mech­ani cal , electrical, etc.

The major contracts were with: Architect/Engineer and Construc­

tion Manager Water-Cooled Rotary Combustors

(2-100 TPD) and Boilers Cranes (2-10 ton) (9 t) Buckets Ash Removal FD/ID Fans

Electrostatically Augmented Bag­house

Sanders & Thomas

O'Connor Com­bustor Corp. Harnischfeger Corp. Condor Envirex Champion Blower & Forge Apitron, Inc.

*The Electric Power Research Institute commissioned the Ten­

nessee Valley Authority to perform extensive testing and analy­

tical work. Two series of tests are spaced one year apart.

Main Turbine-Generator Steam Condenser Boiler Circulating and Feedwater

Pumps

PLANT DESIGN

Turbodyne, Inc. Con-Rad Industries Byron Jackson

The plant has a 550 ton (500 t) capacity refuse receiv­ing and storage pit. The refuse is handled by one of two cranes feeding each chute. The chutes have replaceable liners and a fire quench system. Two hydraulically powered rams for each unit meter the waste into the rotating com­bustor.

The water-cooled rotary combustor is made of al­ternating water tubes and webs formed into a cylinder with circular headers at each end.

The downstream header has inlet and outlet pipes that meet in a concentric pipe arrangement. This arrangement connects to a rotary joint that takes the water from the mud drum of the boiler and returns the water and steam to the steam drum after its circuit through the combustor. Thirty to 35 percent of the steam produced is generated in the combustor. Th� combustor rotates slowly at 1/6 to 1/10 revolution per minute and is mounted at an angle of 6°.

Combustion air is drawn from above the waste pit to the forced draft fan, through a three-pass air preheater lo­cated in the outlet ducting of the boiler. The heated air is ducted to five damper controlled openings and four straight-through openings under the combustor. The com­bustion air enters the rotating part of the combustor through holes in the webs between the water tubes. This air is directed through the waste as it is tumbled in the ro­tating combustor. The design is based on combustion with an average of 50 percent excess air, but is designed for 100 percent excess air maximum.

302

The hot gases leaving the combustor enter the furnace, which is enclosed by a waterwall membrane. After passing upward in an "S" curve through the furnace, the gases en­ter the superheater through the screen tubes, then the convection section and into the air preheater. The gases from the air heater then go to the flue gas treating equip­ment consisting of the mechanical cyclone collector and the electrostatically augmented baghouse and then to the induced draft fan and out the stack_

Ash from each combustor drops onto a fixed water­cooled afterburning pinhole grate, then out of the bottom of the boiler into a quench tank. Siftings and fly ash are brought by screw conveyors to each quench tank where the combined ashes are dragged up an incline by a chain drag system and deposited into 13 yd3 (10 m3) contain­ers. The containers are then taken to the landfill.

FIG. 1 THE SUMNER COUNTY FACILITY

OPERATIONS

Unit 1 first burned municipal waste on December 29, 981 . It was considered operational on January 29, 1982, .nd steam was first sent to customers in February 1982.

Unit 2 first burned waste on March 8, 1982 and started ;ommercial operation March 15th.

NORMAL OPERATION

Because of the steam user requirements and the waste available to the Resource Authority, averaging about 115 TPD (lOS tpd) (seven day week basis), the plant operates both units five days a week and normally shuts one unit down on weekends.

Preventive maintenance is performed on the weekend shutdown. An annual shutdown of two weeks is scheduled for each unit.

303

PLANT STAFFING

The plant is staffed for operation seven days a week, 24 hr/ day. Normal staffing is:

Administrative Superintendent Shift Supervisors Crane Operators Boiler Plant Operators Maintenance

3 1 4 4 4 8

24

The plant has been able to hire well trained personnel, may of them trained at nearby Tennessee Valley Author­ity power plants.

OPERATING PROBLE MS

From the first, there were numerous outages caused by

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failure of the ash drag systems and the air pollution con­trol units, and lesser problems with the cranes.

ASH REMOVAL EQUIPMENT

The ash drag-out conveyors jammed frequently. The primary cause was ash and noncombustibles being car­ried to the return sprockets as the ash passed through the drag-out blades on their return before falling to the bot­tom of the quench tank. This problem has been reduced, but not solved, by adding transition plates to block the unwanted movement of the ash. Also, the hydraulic con­veyor drivers were replaced with mechanical drivers. These modifications have still not produced satisfactory results, and both systems are scheduled for complete replacement with new, redesigned ash removal systems.

GAS CLEANING EQUIPMENT

The cleaning equipment consists of an electrostatically charged section meant to capture the larger particulates and agglomerate the smaller particles. The bags accom­plish the remainder of the particulate collection.

The electrostatic capability was insufficient and the bags experienced burning by hot particles. Also, the air­to-cloth ratio was too high and the bag filters tended to

blind. This equipment was untried in waste to energy plants.

The bag burning was reduced by the installation of mechanical cyclone collectors between the gas-air pre­heater and the baghouse units in December 1982.

Blinding has continued and on-line cleaning has not been adequate. The baghouse pressure drop of 10 in. to 16 in. water was too much for the pulse jet cleaning sys­tem to overcome. One unit was compartmentalized into six sections with individual dampers which permitted se­quential off-line cleaning, which made some improve­ment in operation.

The primary problem continued to be an undersized system. In July 1983, the decision was made to replace the baghouse units with electrostatic precipitators.

CRANES

The cranes have hydraulically operated 3 yd3 clamshell buckets with control elements that were sensitive to shocks experienced in waste facilities. Some of the electronic controls tended to break down frequently. Modifications were made to the controls that improved on-line capabil­ity. Although the cranes have been high maintenance items, since the plant has two cranes, the shutdowns are now infrequent.

305

COMBUSTORS - BOILERS

The rotary combustors were originally installed with air strip seals (which seal the combustion air between the stationary windbox and the rotating element) made of bronze alloy. The strip seals were corroded due to bag­house problems which caused the furnace to go positive and the products of combustion to enter the seal area. The seals were replaced after about 6 months of operation using carbon steel, and have presented no problem since. The performance of the combustors and boilers has been excellent as indicated by total maintenance cost from startup through September 1983 of $11,811.00. (Ap­pendix B). The combustor-boiler combination has had a few problems, such as aluminum melting, grate slope and adequate air control as discussed on the following pages. These problems have not caused any major shutdowns.

ALUMINUM REMOVAL

One of the problems is aluminum. The temperature in the combustor is sufficient to melt most aluminum ob­jects. As soon as the aluminum becomes molten, it runs through the air holes near the bottom of the unit. When the molten aluminum comes in contact with the hopper, it solidifies and builds up, and is manually removed. Several materials have been tried inside the hopper to pre­vent the aluminum from adhering to the sides. This has been to no avail due primarily to the angle of the sloping sides. The bottom of the hopper is very small where it connects to the auger. In the future, vertical sides will be used with a larger auger. The situation has been improved by eliminating some partitions within the hopper, but it is still necessary to manually remove the aluminum about every two weeks.

ASH GRATE SLOPE

Another problem has been the slope of the grate be­tween the combustor outlet and the bottom of the boil­er. The original intent was to hold the material that was not completely burned in the combustor on the grate until it turned to ash. Steam jets operated by timers were furnished to blow the ash off the grate into the hopper at the bottom of the boiler. The large percentage of non­combustibles which were too big to be blown off by the steam jets were not taken into account. Those objects consisted of mainly industrial automotive waste, such as pieces of pipe, parts of automobiles, bumpers, and even Volkswagen engine blocks. The first operating procedure was to manually push these larger, heavier objects off the bottom of the grate with a long crowbar. This proved to

be troublesome and time consuming. It was decided to do nothing and see what would happen, namely to let the grate fill up with ash which partially solidified and pre­sented a new slope to the hopper at the bottom of the boiler. In the future the step at the bottom of the grate will be eliminated on small units and a moving grate will be used on the larger units. Adequate time would be al­lowed to complete combustion of objects requiring a residence time longer than 20 min.

AIR CONTROL

Another problem has been air control. This gets into instrumentation, which is a complete subject unto itself. The biggest single problem to date has been the fact that the free flow of air could not be adjusted due to the limitations of the baghouse. In short, both the air and the fuel had to be limited to fall within the flow limitations of the air pollution equipment. Once the baghouse is re­placed with the new electrostatic precipitator, the air can be properly adjusted as a function of the flow of waste, CO, etc. This, combined with instrument control of the air inlet dampers using signals from completely reliable CO and O2 measuring devices, can automatically control this and other variables.

There are some nine to twelve variables required to adequately control this unit. The basic variables are steam flow, steam pressure, fuel flow, feedwater temperature and flow; however the more recondite variables are CO, CO2, temperatures at the inlet of the combustor barrel, temperatures at the entrance to the screen tubes in the boiler, overfire vs underfire air and combustor RPM.

OPERATING SUMMARY

During the eight months from January through August 1982, the Unit 1 combustor and boiler were available 96.7 percent of the total time. Unit 2, for 5-3/4 months from March through August 1982 was available 93.4 per­cent of the total time (Tables 1 and 2). The gas cleanup equipment was indicated as available 92.2 percent and 94.7 percent respectively; however, these figures are mis­leading since the availability of this equipment at full load was only 3.6 percent. Even this figure is meaning­less since the gas cleanup equipment was operated from May 1982 through December 1982 under a variance be­cause the bags were removed. More recently, when the bags were replaced because the variance expired and the units had to meet the pollution standards, it was neces­sary to reduce the load. In short, with proper excess air, the unit could only be operated at 50 percent to 60 per­cent of full load.

306

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STOR

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ER C

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Y FA

CILI

TY T

UBE

(PIPE

) WAL

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TEST

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ARY

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AL

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l

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al

D

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me

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r

Th

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kn

es

s

SA

21

0 G

r.

A

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2"

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13"

.

SA

10

6 G

r.

B

6.62

5"

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" .

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10

6 G

r.

B

4.5"

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37" .

SA

17

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r.

A

3.

25"

.180

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A

178

Gr

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A

2"

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A

178

Gr

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A

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I I , , , , , ,

TABLE 6 ROTARY COMBUSTOR TUBE THICKNESS ULTRASONIC TEST RESULTS

Unit No. 1 •

Original:

Tube #

1

9

17

25

33

41

49

57

Orl inal:

H1

H2

H3

H4

Ori inal:

B1

B2

B3

B4

B5

B 6

B7

B8

•

Date Tested: Oct. 6, 1982

2" Dia. x .313 Avg., 290" Min., .354 " Max.

A B C D

.321" .325" .318" .317"

.318" .321" .323" .325"

.317" .326" .324 " .326"

.321" .324" .328" .323"

.313" .313" .314" .315"

.311" .317" .316" .315"

.312" .311" .317" .314 "

.320" .316" .319" .319"

6", Sch. 120, .562" Nom., .4 92" Min., .632" Max.

.597"

. 61 6"

.622"

.597"

4", Sch. 80, .337" Nom., . 2 9 5" Min., . 3 7"/" Max.

.320"

.339"

.340"

.350"

.338"

.33 6"

.332"

.325"

314

.. ' iCC=

TABLE 7 BOILER TUBE THICKNESS

UNIT #: 1

SUPERHEATER SCREEN TUBES

DATE TESTED: 10/8/82

ORIGINAL: 3 1/4" DIA. x .180" WALL

TUBE # LOWER FRONT LOWER BACK UPPER FRONT

2 .190" .185" .188" -

5 .188" .195" .188"

8 .188" .188" .186"

11 .185" .186" .189"

14 .192" .188" .186"

SUPERHEATER TUBES

ORIGINAL: 2" DIA. x .220" WALL

TUBE # LOWER FRONT LOWER BACK UPPER FRONT

1 .220" .222" .216"

4 .220" .225" .220"

7 .224" .226" .222"

10 .226" .218" .225"

12 .220" .226" .211"

REAR GENERATING BANK TUBES

ORIGINAL: 2" DIA. x 165" WALL

TUBE # LOWER UPPER

2 .166" .164"

8 .180"(?) .169"

14 .171" .166"

20 .172" .163"

28 .170" . 175"

315

UPPER BACK

.185"

.187"

.182"

.187"

.187"

UPPER BACK

.219"

.222"

.222"

.218"

.220"

•

w

....

0\

TABL

E 8

CO

MPIL

ATIO

N OF

FLUE

GAS

TES

TING

SUMN

ER C

OUNT

Y MS

W PL

ANT

Fl

ue Gas

Vol

Ule

Taup.

r-Di

stllre

GllSCF'/1

2%/C0

2 ACFM

0

F

.

% B

lr.

OUt

Cy

clo

ne OU

t

Sta

ck

CO2

%

'lVA-July,1

98

2

1,

19,

660

40

8

2.

1

9,2

79

40

4 3

.

20,8

87

39

4

4.

20,5

15

401

5.

22

,321

4

17

CCX>P

ER EN3RS

.-E'F:B

.198

3

1.

18,

819

2.

18,

730

3.

1

9,0

44

4.

1

9,0

37

5.

1

9,3

70

6.

1

7,99

9 7

.

19,

244

RAMOON

-Feb

.198

3

1.

18,

126

2

.

20,0

34

3.

20,9

88

4.

18,

126

5

.

16,

218

6.

18,

126

Av

g.

19,

251

47

0

434

425

420

42

2 4

32

47

4

345

383

39

8

309

283

33

3

395

Rang

F'rcill

_l6,218

283

e

To

:.:_22

�32

1

470

DES

IGN

20

20

14

20

-- --

-- -- -- -- -- --

. 13.

4 1

6.

2

15.

8 16

.5

15

.0

1

6.8

16.8

13

.4

20

.0

1.82

1

.25

1.35

1.

22

1.3

4

--.-

-.--

2.75

3.

09

---

--

-2.

00

---

---

---

- --

---

---

1.85

1.25

3.

09

---

--

---

--

--

---

-- -

---

--

--

---

---

0.

436

---

--

---

--

---

-.-

---

0.

43

6

0.

436

--

-

---

---

---

-

--

---

---

---

--

.--

-

0.03

20

--

-0

.032

2 - -

-

---

---

---

---

---

-

---

--

-0

.0

20

1

1.

0

0.

01

51

8.

4

0.

01

86

9.

6 0

.016

4 7

.6

0.

02

29

8

.9

0

.0

20

7

9.

6

0.

00

69

11

.6

0.

02

1

9.

53

.0

06

9

7.

6

.0

32

2

11

.6

°2 % --

---

-

---

--- --

-

10.

6 1

2.8

8.0

8.2

12.0

9.

4 9.

0

8.9

9.9

12.1

10

.3

9.8

8.5

9.98

8.0

12.

8

FOR

22

,50

0 4

10

1

0-22

--

-0.

50

0.

03

9.

0-1

4.0

6.

0-1

1.0

,

ES

P

Carbon i

n F

ly As

h,

%5-3

5 Avera

ge V

alu

es

, P

PM

130

hr

s. ca

nt.

noni

tor

ing

O2

=9

.1

CO=

554

OO

X=1

43

502=1

80

HC-2

1.0

•

Exce

ss Al

r

% ---

-.-

--

--

--

---

- --

--

---

---

---.

--- 75

69

87

133 93

85

66

87

66

133

40-1

10

As for the ash removal sytem, its availability was in­dicated as 75.8 percent, respectively. Here again, these fig­ures were virtually meaningless in that the ash dragout failures occurred in some cases as often as several times an hour. In other cases, where the heavy noncombustibles were removed before being fed to the unit, the ash drag­out would operate successfully for days on end.

Table 3 shows a general operating summary of the units for the one year period for August 1982 through July 1983. Air pollution and ash removal equipment prob­lems have continued to upset the plant. In spite of the baghouse and ash dragout problems, the total operating hours from startup through July 1983 were 8,493 h for Unit 1 and 7,154 h for Unit 2. The total steam produced was 333,550,000 lb. The total electricity generated from March 1982 through July 1983 was 1,354,033 kW·h. The total tonnage combusted during this period was 60,974. It is interesting to note here that since the units were on the line, no municipal waste has been hauled to the land­fill.

TESTING

The following formal tests have been conducted on the combustors at the Sumner County plant:

Performance Tube Thickness Emissions Performance &

Emissions

by TVA by TVA by Cooper Engineers by TVA

PERFORMANCE TESTS - JULY 1982

July 1982 October 1982 February 1983 June 1983

These tests covered combustor capability to meet waste combustion requirements, steam production, emis­sions and residue characteristics.

Tests run over a four day period, July 27-30, 1982, showed that each combustor could handle 100 or more tons per day, that the thermal efficiency was 70 percent or higher, that steam production met the design require­ment corrected to the TV A "B" fuel heat value rating, and that the emissions satisfied state and federal require­ments.

Table 4 shows the summary of results of these tests.

TUBE THICKNESS TESTS - OCTOBER 1982

These tests were conducted after about 4000 operating hours. Ultrasonic test equipment was used on October 6, 1982 on the Unit 1 rotary combustor and on October 8, 1982 on Unit 1 boiler. As noted earlier, the system ex-

perienced frequent outages, so the combustors were start­ed and shut down many times and experienced excessive temperature variations.

The combustor was tested at 44 places. See Figs. 3 and 4 for locations.

The boiler was tested at 50 places. See Figs. 4 and 5 for locations.

Each of the tubes tested is well above the minimum specification, and most measured above the nominal thickness. Tables 5, 6 and 7 give the original and as-tested results on the tubes. No tube wastage has been identified. Tube wastage from chloride develops with three elements: chlorides, temperature and reducing atmosphere. The specifications require that the operators bring the units to about 400°F (204°C) using the startup burners before introducing waste. With proper operation, excess air is approximately 50 percent and the design provides for good mixing of the gases and air so that a reducing atmos­phere is not present. Additional tests are planned by the Tennessee Valley Authority after about 10,000 operating hours.

E MISSION TESTING - FE BRUARY 1983

Cooper Engineers, under a contract from the California Waste Management Board, conducted air emissions tests between February 6-21, 1983. Samples of waste and resi­due were also taken over a five day period.

The Cooper Engineers report was not fmalized at the time this paper was prepared, but preliminary data indi­cate that air emissions can meet the California require­ments using Best Available Control Technology.

Table 8 gives a compilation of flue gas components. It should be noted that the Ramcon tests were done for the local air pollution agency and prior to this test the bags in the baghouse were all replaced.

PE RFORMANCE AND E MISSIONS RETE STS­

JUNE 1983

The results of the testing done by TVA is June 1983 will be made available by the Electric Power Research In­stitute when the final report is completed.

CONCLUSIONS

The Resource Authority in Sumner County has ex­tended its landfill life by ten times with a successfully operated waste to energy plant. Steam sales have been steady, as has electrical generation.

On future plants, the O'Connor Combustor Corpora­tion will make a few design changes as previously noted.

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The corporation is also requiring certain minimum speci­fications on such auxiliary equipment as the ash removal system and air p01l1lution control equipment.

All of the combustible waste brought to the plant has gone through the water-cooled rotary combustors; none

•

has been sent to landfill unburned. In short, the combustor boiler combination has had

very few problems. Some of the ancillary equipment has given trouble, but with correction of these problems the two units can be operated as originally designed.

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APPENDIX A

TVA FUEL "B"

Constituents % C 26.50

H2 3.50 S 0.18

N2 0.36 O2 22.46

Moisture 20.00 Inerts 27.00

Btu/lb (Steuer Formula) HHV 4809

APPENDIX B

RESOURCE AUTHORITY IN SUMNER COUNTY

COMBUSTOR-BOILER MAINTENANCE COSTS

START-UP* THROUGH SEPTEMBER 30, 1983

1. Replace feed hopper wear plates, units # 1 & # 2

2. Reweld cap on unit # 1 ring header balance nipple

3. Replace chemical feed distribution pipe in stearn drum

4 . Replace strip seals units #1 & #2

5. Replace 1800 RPM combustor drive motors with 1200 RPM 3� HP motors

6. Repair to variable speed controllers

7. Miscellaneous burner maintenance

8. Circulation pump turbine drive unit #1

9. Circulation pump motor drive bearing & seal unit #2

10. Circulation pump repair due to misalighment unit #2

Total maintenance (21 months)

% of Total Plant Maintenance = 12%

*Startup Unit 1 December 29, 1981 Unit 2 March 8, 1982

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$ 300.00

85.00

2,017.00

1,500.00

500.00

1,000.00

2,000.00

600.00

1,809.00

2,000.00

$11,811.00