Energy recovery from mass burning of refuse in waterwalled incinerators

Energy Vol. IO, No. I, pp. 41-56, Printed in the U.S.A.

1985

0360-5442/85 $3.00 + 03 0 1985 Pergamon Press Ltd.

ENERGY RECOVERY FROM MASS BURNING REFUSE IN WATERWALLED INCINERATORS

OF

W. D. TURNER Department of Mechanical Engineering. Texas A&M University, College Station, TX 77843-3123, U.S.A. (Received

18 Junzrary 1984)

Abstract-There are currently ten waterwalled incinerators in the U.S. which recover energy from the mass burning of municipal waste. The plants range in size from a 160 ton (145 t) per day (metric units are shown parenthetically; metric tons are denoted by the symbol t) system at Portsmouth, Virginia to a 2000 ton (1820 t) per day plant at Pinellas County, Florida. Some of the refuse-to-energy plants are reliable and performing well. The performance of several plants, however, is poor, and two were closed in the 1982-83 period; one of these is back in operation. The operation of the ten plants is described, with emphasis on recent and projected performance. INTRODUCTION

The flow diagram for the incineration of refuse using waterwalled furnaces is shown schematically in Fig. 1.l.’ Referring to Fig. 1, the collected refuse is normally dumped directly into the storage pit, which will typically have a capacity of two to three times the daily incineration capacity of the plant. Front-end processing is usually minimal and may be limited only to the removal of bulky items by an overhead crane. This is a big economic advantage for mass-burning systems because the front-end processing can be both energy and labor intensive. Some of the systems have the capability to remove magnetic materials, but this removal occurs typically at the end of the processing. The refuse placed into the charging hopper by the overhead crane is then fed onto the grate. The grate is the heart of the processing system, the third block in Fig. 1, and there are several different technologies used in the U.S. The grate moves the refuse through the furnace, where it is burned. The refuse goes through three stages on the grate: drying, devolatization, and burning. The combustion principles for burning refuse are similar to those involved in burning coal, wood, or other waste materials; however, the problems involved in effecting complete combustion are greater. The feed stock is very heterogeneous, often containing a high percentage of noncombustible material. The average energy content varies with each load added to the charging hopper, is heavily dependent on seasonal variations, and is affected by rainfall, unusually dry weather, as well as by the nature of the yard wastes. Although the compositions are highly variable, a typical composition and average heating value are listed in Table 1. The average heating value of 4500 Btu/lb (10.5 MJ/kg) is roughly one-third that of high grade coal. Referring again to the third block of Fig. I, large amounts of excess combustion air are supplied for the incineration process. Both underfire air (through the grate system) and overfrre or secondary air (injected above the grates) are required. Generally, most of the excess combustion air is provided by overfire nozzles. Excessive underfire air causes agitation of the refuse bed and could cause particle carryover with the gaseous products of combustion. The residence time in the furnace varies and depends on the refuse moisture content and furnace firing rate, but it is typically from 20 to 30 min. The remaining residue, reduced in volume by 85-95%, is then quenched. Ferrous materials, if recovered, are often removed from the quenched residue. The remaining residue is then transported to a landfill. Much of the energy transfer occurs by gaseous radiation in the waterwalled incinerator, and some of the water is converted to steam in the waterwalled tubes. In Fig. 1, the furnace is designated as the processing system, while the convective portion of the incinerator is called the conversion system. The next block in Fig. 1. consists of the boiler tubes, the superheater and the economizer. Normally, the first bank of boiler tubes will be steam-generating tubes. Successive passes of the gas over the boiler tubes will continue to produce saturated steam, which will be recovered in the 41

42

W.D.

TURNER

Fig. I. Schematic of the watelwalled refuse-to-energy systems

steam drum. If superheated steam is to be produced, then the saturated steam will pass through the superheater, where additional heat will be extracted from the gases. Only four of the U.S. waterwalled incinerators produce superheated steam. After the convective boiler passes, the exhaust gases will then pass over another heat exchanger, through which flows the boiler feedwater. This heat exchanger is called the economizer. After the economizer, the exhaust gas temperature is cooled to approximately 450-500°F (505533”K), is cleaned by electrostatic precipitators, and is then exhausted from the stack.4 The steam can then be used for producing electricity, for heating and cooling, or for industrial processes. Any excess steam produced has to be condensed. Corrosion represents a major problem at many of the waterwalled incinerators. Problems can occur in many places, but the two main areas are with the grates and lower tubes in the processing block of Fig. 1, and with the convective tubes in the conversion block. The Europeans have been mass burning their refuse for over three decades and have much more experience with energy-recovery systems. There are five dominant energyrecovery technologies in Europe, which account for more than 85% of the installed grates.4 Two of these technologies have been brought to the U.S. and are used in existing plants. The Josef Martin grate technology originated in Germany and is used at Harrisburg, Pennsylvania, Chicago, Illinois and Pinellas County, Florida. The Von Roll

Table I. Typical composition of municipal solid waste in the United States. material

%

paper

33

glass

8

ferrous materials

7.6

plastics, leather rubber, textiles and wood garbage and yard wastes miscellaneous moisture Average Heating Value

6.4 15.6 1.8 remainder 14500 Btu/lb (10.5 W/kf

Energy recovery

from refuse burning

in waterwalled

incinerators

43

grate system originated in Switzerland and is used at the RESCO plant in Saugus, Massachusetts. The remaining U.S. plants use various American technologies. The ten refuse-fired waterwalled incinerators in the U.S. range in size from 160 tons (145 t) per day to 2000 tons (1820 t) per day design capacity. For purposes of this paper, the incinerators have been classified as small, medium, or large, based on their design capacity. Three of the plants, Portsmouth, Virginia, Braintree, Massachusetts and Hampton, Virginia, have daily capacities of 240 tons (218 t) per day or less, and are classified by this author as small plants. The medium-sized plants range up to a daily capacity of 720 tons (655 t), and they are located at Norfolk, Virginia, Harrisburg, Pennsylvania, Nashville, Tennessee and Oceanside, New York. The three large-scale operational plants are located at Saugus, Massachusetts, Chicago, Illinois and Pinellas County, Florida. PART

I.

SMALL

REFUSE-TO-ENERGY

PLANTS

IN

THE

UNITED

STATES

Table 2 contains summary data on the three smallest water-walled incinerators U.S. Construction costs only are given.

in the

Braintree, Massachusetts municipal incinerator The Braintree incinerator is one of the two plants closed in recent years. It was shut down as an incinerator on 19 May 1983, and the facility is currently being used as a solid waste transfer station. Prior to its shutdown in May 1983, this incinerator had one of the best recent performance records of all the U.S. incinerators. There are unique features associated with each plant, and at Braintree the grate system distinguishes it from the others. The grate is a horizontal Riley traveling grate, similar to that used for firing coal. There is very little agitation of the refuse with this grate system, and large amounts of underfire air were often used in burning refuse. The plant was built in 1971 prior to the enactment of the current stringent airpollution standards in Massachusetts, and was shut down for several months during 1977-78 for upgrading of the ESPs. Table 3 summarizes the annual operating performance over the past four years. The table includes weighed tonnages processed, revenues from the sale of steam and tipping fees, as well as operation and maintenance (0 & M) costs.’ The Braintree incinerator plant also maintains a residue landfill on-site, and the 0 & M costs include residue disposal as well. 0 & M costs exceed the revenues for each year except 1980, when a one-time federal entitlement grant of $43 1,470 was received. Since the city of Braintree owned and operated the plant, the difference between revenues and 0 & M costs was paid by the city. This subsidy is comparable to a tipping fee, The steam plant produced 60,000 lb/hr (27,300 kg/hr) of saturated steam at 250 psig (1.7 MN/m’). The maximum steam demands by the industrial customer were about 20,000 lb/hr (9000 kg/hr).’ Prior to shutdown in May of 1983, the plant had a remarkable burning record. Over the past three full years, the plant averaged burning 249 tons (227 t) per day, which exceeds the original design capacity. The tonnage figures do not include the refuse brought in by private citizens, estimated as 10 tons (9 t) daily. Down time of one or both boilers certainly occurred during the 1979-83 period, and achieving an average bum rate of 5% more than design capacity means that the boilers were being overfired much of the time, sometimes as much as 60%. This overfiring was

Table 2. Summary

data-small Year Built

incinerators. Capital

Incinerator

Design Capacity tons/day

CostlMS) (1981fl

Furnace Lines

Braintree, MA

240 (218)

1971

6.6

2 (2)t

Hampton, VA

240 (218)

1980

14.4

2 (2)t

Portsmouth, VA

160 (145)

1977

6.7

2 (l)T

tParentheses indicate the number of furnace lines normally in operation burning refuse.

44

W. D.

TURNER

Table 3. Summary of Braintree municipal incinerator operation, 1979-1983. Year

Refuse Processed Short Tons

Steam Revenues

Total Revenues

O&M Costs*

1979

45,614

$187,201

$272,035

s 785.034

1980

68,217

268,325

1,032,104

1,082.OOO

1981

66,557

265,215

871,265

1,097,663 1,133,463 1.184.437

1982

59,747

256,273

828,676

19i33t

19,993t

124.371t

595,753t

TThrough May 19.

The incinerator was shut down on that date.

SIncluding residue landflll operation.

beginning to affect the equipment at Braintree, and a request for additional maintenance money in 1983-84 was partially responsible for the city’s decision to shut down the plant.5%2 At Braintree, backup systems exist in most critical areas critical to plant performance, but there is only one overhead crane. When it was out-of-service, the plant was shut down. This represented one of the major items causing plant down time. Other high maintenance items included the drag-chain conveyors, the ESPs, and the Riley traveling grate. When in operation, the Braintree plant worked 5 days a week, 24 hours a day. Maintenance was scheduled on the weekends. The performance of the Riley boilers has been outstanding. In more than ten years of operation one boiler experienced no tube failures. Only a few tubes were plugged on the other. No internal corrosion has been experienced by the water-walls, boiler tubes, or the economizer. The effects of overfiring the boilers has caused some deterioration, but the extent of the problem is unknown. The future of the Braintree facility is uncertain at this time. An engineer has been hired to evaluate the performance of the incinerator, determine what repairs are needed, and to determine a fair market value of the property.5 Very likely the plant will be sold and will be operated for profit by a private company. For the past three years of operation the performance of the Braintree incinerator plant, based on tons of refuse processed per design capacity, was the best in the U.S. Hampton,

Virginia refuse-fired steam generating facility

The Hampton Refuse-Fired Steam Generating Facility is located adjacent to NASA/ Langley and is a cooperative venture of the city of Hampton, Virginia and the U.S. government. The plant was completed in September 1980, and is a unique example of city-federal cooperation. A team of NASA engineers designed the plant, and the federal government contributed to the construction costs. In return, the incinerator plant bums refuse from NASA/Langley, a nearby hospital, and Langley AFB, and sells steam back to NASA/Langley. In over three full years of operation, the plant has been very successful. Table 4 summarizes the operation of the steam plant for 198 1 through August of 1983. Operational data were obtained from Cliff Loveland, plant manager, during a site visit and by subsequent correspondence.8.2 The incinerator plant operates 7 days a week, 24 hours a day, normally firing both boilers. Most of the steam generated is sold to NASA/Langley. In 198 1, for instance, the Hampton facility supplied 82% of NASA/Langley’s steam requirements. During 198 1, the Hampton plant burned 68,083 tons (61,845 t) of refuse. This represents a daily average of 186 tons (169 t). During 1982, the daily average increased to 199 tons (180 t), and for the first eight months of 1983, the daily average burn rate is 220 tons (200 t). The plant is approaching its daily design capacity firing rate of 240 tons (2 18 t). At full capacity, the boilers can supply a total of 66,000 lb/hr (30,000 kg/hr). In the winter, NASA/Langley can accept most of the steam produced; however, excess steam is usually produced by the plant and has to be condensed.

Energy recovery from refuse burning in waterwalled incinerators

45

Table 4. Summary of operation of the Hampton plant.

Year

Refuse Processed Short Tons

Residue Out, Short Tons

Steam Exported Mlb

Steam Revenues

O&M costs MU

MS

Tipping Fees

1981

68,031

30,210

249.5

$1.36

1982

72,520

32,358

268.8

1.83

1.81(FY’82)

4.?O/ton

1983

53,1611

23,529.t

199.2t

1.60

2.2

05

and

facilities.

t8 month $FY'81

totals

A FYI82

charged 8FY'83. 5lExcludes

$1.72(FY’81)

s4.70/tonS

(~~‘83)

only. charges

to Hampton

Federal

Contract

haulers

were

S6.00/ton. FYI84

contract

landfill

haulers

are

charged

$8.00/tan.

costs.

At the Braintree incinerator, records of boiler availability were not kept, and the excellent burning record was achieved in part by considerable overfiring of the boilers. At Hampton, availability records are kept, and their excellent burning record is achieved by keeping both boilers on line most of the time. Table 5 is a monthly breakdown of the availability of each boiler since the plant opened in November 1980.* Boiler no. 1 has been on line for 32 of the first 34 months of operation, and boiler no. 2 has been on line for 30 months. In 22 of 34 months, the combined average firing rate of both exceeds 70%. In December 198 1, both boilers averaged a 97% availability. With a combined average of 81% availability for 1983, and an average daily burn rate exceeding 220 tons (200 t), some over-firing is occurring, but the burning record is largely being achieved by keeping both boilers on line most of the time. The plant utilizes a Detroit Stoker grate system, an inclined, and stepped reciprocating grate with three grate sections, the charging, burning, and burnout grates. The nearly vertical drop-off between each grate section further agitates the refuse as it tumbles onto the next grate. Despite its relative newness, there have been numerous problems. The initial refusefeed system did not operate properly and was replaced by a hydraulic-ram feed. The problem with the original stoker-feed system was discovered and corrected during the check-out phase of the plant. The problems with the grate system began very early also. The nearly vertical “knees” between the grate sections were made of cast iron, and some burned through in less than a month of operation. The material on the knees was changed to a stainless steel alloy, and this has greatly increased the length of service. The grate bars were also made of cast iron, and severe burnout of these also occurred on the burning grate section. These too were later made from a stainless steel alloy and placed in service. The new grates have performed well and have decreased the maintenance problems. The overhead crane is a high maintenance item, but, unlike Braintree, Hampton has a backup crane. When the crane goes down, the plant can remain on line with the Table 5. Monthly availability of Hampton boilers. Month

January February March April May June July August September October November December

:;

61 44

::

82 0

91 87

::

::

85

0

37 90

92 0

92

97

0 9: 96 97

39: ;: :: 97

29 K 93

86 :: 94 89

84 90

J

46

W.D. TURNER

backup. The normal operating procedure is to alternate the cranes every other day, performing maintenance on the one that is out of service. The plant comes very close to being fully automated, and this plant achieves a degree of automation exceeding all plants except Pinellas County. Details on the combustion control and boiler steam pressure control schemes, as well as other information on the Hampton plant, can be found in two papers. 9*‘oBriefly 3 the combustion control scheme is an analog system which contains five basic control loops. The first two, feedwater flow and constant furnace pressure, are probably common to most plants. The remaining three control loops are stoker feed and underfire air; constant boiler pressure; and heat release compensation. The ideal system would be one in which a constant boiler pressure would be maintained by constant steam flow rates and a constant heat release within the furnace. Unfortunately, the MSW is not homogeneous, and the gas temperatures will be continuously changing with refuse composition. Merely changing the refuse feed rate via the hydraulic ram feeders will not allow a fast enough response if the furnace contains refuse of lower heat content, requiring more energy to maintain gas temperatures. The combustion control system maintains constant drum pressure, selected steam flow, constant upper furnace gas temperature, and metering control of the refuse entering the furnace. To ensure a constant upper gas temperature (which also ensures a constant generating rate for a fixed flow), the control system can vary both the stoker agitation and the amount of underfne air. This is the heat release compensation of the control system, and this feature will allow a much faster response to keep the system balanced at the set point.’ The bottom ash residue handling system is a drag-chain conveyor, and the dry fly ash is gravity fed or mechanically conveyed to the residue conveyor. Like most plants with similar systems, it is a high maintenance item. The residue goes directly into a truck which serves as the residue hopper. There are redundant residue ash conveyors. The Precipitaire electrostatic precipitators have worked well. Two separate tests conducted at nearly maximum firing conditions obtained particulate emissions of 0.0222 and 0.0209 gr/dscf (0.05 and 0.048 g/dscm) corrected to 12% COz, and a third test at a reduced firing rate had particulate emissions of 0.019 1 gr/dscf (0.044 g/dscm). These results are among the best found in the literature for ESP performance on refuse-fired plants. ’ ’ In performance tests on the furnace, efficiencies of 65-67% were achieved. These numbers are comparable to other published efficiencies for waterwalled units.” The Hampton plant receives a more consistent and perhaps higher quality refuse than some plants. The city of Hampton has a standard container ordinance, which requires all the refuse to fit into an 80 gal (0.3 m3) container. This eliminates some of the bulky items. A higher percentage of the refuse received from NASA/Langley and Langley AFB is paper and cardboard waste. Hampton produces saturated steam at 360 psig (2.5 MN/m*). The lucrative contract for the purchase of steam produced allows Hampton to receive both the city and federal refuse without a tipping fee. The price paid for the steam was relative to the price of fuel oil, and the FY’83 charge was $8.07/1000 lb ($8.07/455 kg). The latest contract with NASA/Langley guarantees that no tipping fees will be charged for refuse disposal at the plant. ‘* The financial success of the Hampton facility can be attributed to three essential requirements. There is an adequate supply of refuse. There is a market for most of the steam produced, and the price paid for the steam is a fair market value. These factors alone will not guarantee a successful financial operation, because there is also the need for a good operating system and good management practices. All exist at Hampton and contribute to the success of the plant to date. Portsmouth, Virginia salvage fuel boiler The smallest of the waterwalled plants is located on the Norfolk Naval Shipyard at Portsmouth, Virginia. The refuse-to-energy plant is run by U.S. government civilian personnel. All the steam produced is piped to the Naval shipyard, with refuse supplying between 5 and 10% of the steam needs of the shipyard.13 Performance data for the

Energy recovery

from refuse burning

in waterwalled

incinerators

47

Table 6. Operating data for the Portsmouth salvage fuel boiler (FY’80). Refuse

Steam Produced From Refuse, Mlb

Month

Consumed

Short Tons

Days

Operated

FY-'80 (September 1979dctober 1980) October November December January February March April

5.91 6.70 3.67 4.76 2.28 6.49 6.10

1,094 1,241 680 881 422 1,203 1,130

June May July August September

6.25 7.30 6.75 6.59 7.12

1,158 1,351

Totals

69.92

1,249 1,220 1,319

23t 13t 20+ 20+

:: 20 21 22

229

*

tlncludes some hours firing on oil.

Portsmouth facility are very limited, and only one year’s data were obtained, that of FY’80. It is, however, supposed to be typical, according to the shipyard’s supervisor of utilities, C. E. Milby. Table 6 is a monthly record of the incinerator plant’s performance during FY’80. Although designed for a daily capacity of 160 tons (145 t), the Portsmouth plant operates only one furnace line at a time. This does not limit their capacity to bum refuse at present, because there is an inadequate supply. The plant operates 5 days a week, 24 hours a day, a schedule which was started in 1979. Previously, the plant operated 16 hours a day, 5 days a week. Like the Hampton facility, the Portsmouth plant uses Detroit stoker reciprocating grates and a boiler manufactured by the E. Keeler Company. Although many of the components are the same, there are many differences between the Portsmouth and Hampton facilities. The refuse delivered to the Portsmouth plant is not ordinary municipal solid waste. Wooden pallets, scrap metal, chemicals, paint, and occasionally ammunition will be found in the waste stream. The bulky items such as pallets cause problems with the small charging hopper doors, and jamming occurs often. At Portsmouth, the refuse is dumped directly onto the charging floor where a crew separates bottles, crates, large metal goods, and anything potentially harmful. Only one overhead crane exists at Portsmouth, and it is a big maintenance item. The plant personnel cannot perform their own maintenance, and numerous delays are often encountered before the crane can be repaired and placed back into service. Table 7 gives the budget for FY’80. If the costs per ton of refuse consumed are calculated, Portsmouth will have the highest disposal cost for any of the U.S. incinerator Table 7. Operations and maintenance costs for FY’80 at the Portsmouth salvage fuel boiler. Item Operators Maintenance Fuel Oil

cost $238,405 164,977 34,049

Electricity

9.798

Water

8,585

Ash Disposal Overhead

76,440 193,433

Front-end Separation at Platform

79,200

Other Contracts, Misc.

22,922

Total

$828.609

W.D.

48

TURNER

plants, exceeding $60/tori in 1980 dollars. If a nominal price of $5.00/1000 lb ($5.00/ 454 kg) were paid for the steam produced, the net disposal costs would be in excess of $37/tori (1980 dollars). This example illustrates two important points. First, it shows the importance of an adequate supply of refuse. The same crew could process much more refuse in the same time period if it were available. Second, front-end separation is expensive, costing almost 10% of the 0 & M costs. The economy of scale is definitely a factor in the high 0 & M costs. Other than the lack of refuse, the most visible problem at Portsmouth is with the ESPs. The original Cambridge precipitators never passed the emission tests. Tests conducted in June 1978 by the Navy Environmental Support Office indicated particulate emissions of 0.22 to 0.33 gr/dscf (0.5 to 0.76 g/dscm), well above the standard. The incinerator has been out of compliance each year and must receive a variance from the State of Virginia to continue to operate. Cyclone separators have now been installed upstream of the ESPs, and their function is to remove about 75% of the larger fly ash particles. The ESPs were also upgraded during 1982-83 and a higher voltage is now being used. No performance data are available on the modified system. The plant has not had any major operational problems to take it completely out of service, but it has been plagued by many problems that have reduced the operational time. The lack of refuse forces frequent startups and shutdowns. The problems with the crane are particularly bad since the frequency of failure is estimated at about every 40 hours. Response time when problems occur is very important in a refuse-burning plant, and the government procedures at Portsmouth are not very fast. Despite these problems, the plant at Portsmouth is still disposing of the refuse from the Norfolk Naval Shipyard at a price cheaper than any current alternatives,’ SUMMARY

Among the three smallest refuse-to-energy systems, the Hampton plant is the most successful. It has overcome several major operational problems in its first three years, while still maintaining a good overall performance record. The Braintree municipal incinerator will very likely be sold to a private company and will be back in operation soon. Despite its age, the plant was very reliable and consistently burned in excess of its design capacity over the past three years. The Portsmouth incinerator has many problems not encountered by either municipalities or private firms. Governmental procedures are genuine constraints at that facility. The Hampton plant has an adequate supply of refuse, a lucrative price for its steam, and a customer who will purchase most of the steam produced. There is no net charge to the city of Hampton for refuse disposal. On the other hand, the Portsmouth plant does not have enough refuse, has very high 0 & M costs, and the refuse disposal cost per ton is the highest in the U.S. These two examples point out the necessity for good planning and management in these waste-to-energy systems. PART

II.

MEDIUM-SCALE, THE

REFUSE-TO-ENERGY UNITED STATES

PLANTS

IN

Table 8 contains summary data on the four medium waterwalled incinerators U.S. The four range in size from 360 tons (327 t) to 750 tons (682 t) per day.

Table 8. Summary data for medium-sized incinerators. Design Capacity tons/day

Incinerator Norfolk, VA Harrisbirg. PA Nashville, TN Oceanside, NY

I

360 720 720 750

(327) (6551 (655) (68211:

Capital

Year Built

I

1967

Cost(W)

Furnace Lines

(198161

1

6.2

I’Qarentheses indicate furnace lines normally burning refuse. SIncludes one nonenergy recovery unit of 150 ton (136 t).

I

2 (llt

in the

Energy recovery from refuse burning in waterwalled incinerators

49

Norfolk, Virginia salvage fuel boiler plant

The Norfolk salvage boiler plant was the first refuse-fired, waterwalled incinerator built in the U.S. It is located on the Norfolk, Virginia naval station and is operated by the Navy Public Works Center. The plant burns refuse from the naval station, and all excess steam produced is supplied to the utility lines of the naval station, providing lo15% of the station’s total steam needs. There is no condensate return from the naval station. The incoming refuse is not weighed at the Norfolk incinerator. It is dumped on the tipping floor, where a crew separates, by hand, the metal, bulky items, and potentially hazardous material. The practice was initiated in 1979 when chemicals in the refuse exploded and caused a major fire. Records are kept of the amount of steam produced, and the refuse processed is estimated. Table 9 contains the estimated tonnages burned from 1979-8 I and should be typical of current performance. The salvage fuel boiler plant operates 7 days a week, 24 hours a day, but normally operates only one refuse-fired boiler at any time. The second boiler is either on standby or is on line producing steam from the burning of fuel oil. Firing on refuse, the plant produces an average of 40,000 lb/hr (18,200 kg/hr) of saturated steam at 275 psig (1.9 MN/m2). The overall performance of the plant has been good. Except for cast-iron, armor block protection near the grate, the watertubes are bare. In the first 15 years of operation, only one watertube required welding. The first repair on the convective boiler tubes did not occur until after 7 years of operation. Complete retubing of the boiler convective tubes on the furnaces occurred after 10 and 11 years, respectively, of burning refuse. Three of the major problem areas at Norfolk have been the grate system, the boiler feedwater pumps, and the pollution control system. The grates are supplied by Detroit Stoker, and this system represents the highest single maintenance item. Grate replacement on the burning grate is estimated at 25 bars a week. The nearly vertical drop-off sections between the charging grate and the burning grate are also subject to high burnout rates. Through the years the boiler feed pumps have been the second highest maintenance problem. The pollution control system has undergone several major changes since the plant was built in 1967. Cyclone separators were originally installed for particulate removal; however, the U.S. Clean Air Act passed in 1970 and the enactment of stringent pollution standards by the State of Virginia forced the Navy to install electrostatic precipitators in 1976. They have been modified many times since, and the ESPs now allow the Norfolk waterwalled incinerator to meet the air pollution requirements. Scheduled maintenance on the ESPs is required every three months. Historical 0 & M costs are listed in Table 10, with budget details given for the FY’80 budget, the latest available. There are several items in the budget which require additional

Table 9. Tonnage processed at the Norfolk salvage fuel boiler plant, 1979- 198 I. Short Tons Processed per Montht 1980

1979 Month

January February March April May June July August September October November December Totals (approximate)

Boiler Number #219 x220

Bofler Number #219 1220 --_ ___ 2,363 3,715 3,820 1,752 3,806 783 20 2,721 DO1 2,068 rr;9uv

4,054 3,376 2,026 ----2,994 77 --___ 1,225 5,154 4,225 TJ;nr

m

2,847 3,039 3,482 3,955 4,040 1,647 3,368 951 ___ 3,471 5,020 4,346

3,010 2,458 2,415 2,386 3,868 4,377 3,395 4,652 5,891 2,634 56 --?ZlV

1981 Boiler Number #219 c220 3,123 2,114 3,646 2,298 2,135 1,099 749 2,344 2,495 505 1,034 2,481 24;FJv

w

1,284 3,425 2,797 3,935 3,407 4,465 5,042 3,144 2.071 4,971 3,185 342

kalculated from steam records using 2.7 lb of steam produced for each pound of refuse burned.

W. D.

50

‘TURNER

Table 10. Operation and maintenance costs for the Norfolk salvage fuel boiler plant. Year

06M Budget

FYI70 FY'76 FYI78 FY'79 FYI80

S

FYI80 Budget Details Operations $ Preventive Maintenance Fuel Oil Electricity #ater Repairs and Miscellaneous

461,023 896,449 932,548 1,027,284 1,650,601 759.167 254;854 466,454 57,897 92.848

explanation. First, the fuel oil bill is nearly 30% of the total budget. The fuel oil is burned in the standby boiler during periods of extremely cold weather. The utility boilers at the naval station cannot meet the station’s requirements, and the salvage fuel plant must operate on fuel oil to produce additional steam. Second, there is a high water cost. Since there is no condensate return to the incinerator, there is virtually 100% makeup water required. These two items represent nearly l/3 of the 0 & M budget. Third, the preventive maintenance costs are low, particularly in view of the condition of the plant. The plant is poorly maintained. By using refuse to produce steam, the Navy estimated savings in FY’79 of $437,873 over and above the 0 & M costs. Predictions for FY’80 and FY’81 were even more optimistic, although the analyses were not made. The salvage fuel plant has processed over 640,000 tons (545,000 t) of refuse since it was built. Harrisburg, Pennsylvania steam generating.facility The Harrisburg steam plant has been in operation for more than 10 years. It is one of three U.S. plants employing the Josef Martin stoker grate system, a European grate technology. The city of Harrisburg does not have an approved sanitary landfill. The steam plant is, therefore, vital to the city because it is their only alternative for refuse disposal. When the plant was first built, there was no customer for the steam produced, and surplus steam was condensed. In 1976 a sewage sludge plant was added, and in 1977 the plant became part of a district heating system, supplying steam to Pennsylvania Power and Light, principally during the winter months. Superheated steam is produced at 260 psig, 525°F (1.8 MN/m’, 547°K). Recent performance history of the Harrisburg plant is shown in Table 11.’ Using both furnace lines the plant has averaged about a 63% availability over the past three years and has averaged burning about 465 tons (423 t) a day, far short of its 720 tons a day (653 t) design capacity. Numerous problems have occurred at the plant, and many were traced to poor boiler feedwater treatment, which ultimately caused deterioration of both economizers and the furnace tubes before it was detected. Table 12 summarizes the plant outages for 1979-82. Over 60% of the plant down time can be attributed to tube leaks somewhere in the system. Grate problems are minimal at Harrisburg. The Martin, reverse reciprocating, stoker grate is inclined at a 26” angle from front to rear. The reciprocating action of the grates Table 1 I. Summary of operation of the Harrisburg plant.

I

I

'IThroughAugust 1983.

I

I

I

I

1

Energy Table

recovery

from refuse burning

12. Summary

of boiler outages

in waterwalled at Harrisburg

incinerators during

1979-1982.

Boiler #2

Boiler #l

Itall

51

2 1 1 1 ________5_______ 0 3 : 6 1

Grate

replacement or repair Grate system repair Crane repair

Tube repair Superheater repair Underfire fan or ID fan Precipitators Waterwalled tube reoair Economizer leaks ' Misc. other downtime

2 ::

2 25 7

4

11

pushes the refuse near the grates back up the grate. This action helps to heat the incoming refuse as well as agitate the bed of refuse. The Harrisburg plant has incinerated industrial wastes and wet sewage sludge at various times. A major pit fire occurred when some of the chemical waste ignited, and the overhead crane operator was injured. The incineration of raw sewage sludge was not successful, and the incineration of both was stopped in 1982. Major problems with the air-cooled steam condensers also have developed in recent years, which has now forced the plant to vent the excess steam produced. A muffler has been installed to suppress the noise.14 In October 1983 the steam plant hired a new plant manager. Also, a new steam contract was signed with Bethlehem Steel, which will accept all of the plant’s excess steam. A bond issue has been passed to upgrade the steam plant. New economizers and superheaters have been installed on both boilers, and certifications will be made on all tubes previously welded. An above-ground steam line will be built between the plant and Bethlehem Steel. The contract date for completion is May 1984.14 New management, new boiler components, the capital to make much-needed repairs, and a lucrative steam contract make the future at Harrisburg much brighter. Nashville, Tennessee thermal transfer corporation The Nashville Thermal plant is unique among the ten U.S. plants. It is a district heating and cooling plant, currently responsible for 29 buildings in downtown Nashville. Most of these buildings have no backup heating or cooling systems. Thermal has to be on line continuously, firing either on refuse or a backup fuel to supply the needed steam and chilled water. Thermal is an American-designed plant which uses an inclined and stepped Detroit Stoker grate system (four grate sections), similar to the Hampton, Portsmouth, and Norfolk grates. The early performance of Nashville Thermal has been described previously.‘s.‘6 There were many problems, but one of the biggest was the installation of cyclone separators for pollution control. These were never acceptable, and electrostatic precipitators were eventually added. A hydraulic ram feed system was also an addition to the original plant. The ESPs have worked extremely well. The certified tests of 0.007 to 0.01 gr/dscf (0.016 to 0.023 g/dscm) are the lowest found in the literature for refusefired plants. Table 13 summarizes the recent performance of Nashville Thermal. In the years 1980-82, the management philosophy at Thermal was to burn one furnace at a time. The management goal was to supply 90% of the system’s energy demands by refuseTable

Year

13. Summary

Refuse Processed short tons

FYI80 FY’81 FY’W FYI83 FYI84 (1st

117,000 132,000 121,000 145,600 quarter)

of operations

Steam Sales Mlb 230.8 183.7 198.7 190.9

at Nashville Chilled Water M ton-hrs 16.3 20.3 21.6 21.0

Thermal. X Dper. on Refuse 91.2

08.6

89.9 96.2 98.6

O&M MS 52.78 3.19 3.82 2.56

52

W.D.

TURNER

firing, a goal which was usually achieved. Unfortunately, steam or chilled-water demands by the system forced a considerable overfiring of the furnaces, sometimes exceeding the 360 tons (327 t) a day by as much as 50%. Grates burned out and superheater and evaporator tubes were replaced often. Plant 0 & M costs jumped from $2.78 M to $3.82 M from 1980 to 1982. A change in management and a subsequent change in operation made some dramatic improvements in FY’83 and FY’84. The decision was made not to overfire the boilers unless necessary and to operate the two furnace lines simultaneously. The results, shown in Table 13, for FY’83 and the first quarter of 1984 are apparent. The percent of energy obtained from refuse firing increased, and the 0 & M costs decreased. For the first quarter of FY’84, the 0 & M costs were 30% lower than the projected costs. ” Nashville Thermal is to be modified to add another furnace line and chiller. The added capacity will allow the refuse-fired plant to add as many as 10 buildings to the existing district heating and cooling loop. A small turbine generator will be added to produce electrical power when excess steam is available. All of these additions should be completed by 1985.” Recent performance of the refuse-fired plant has been excellent, and the changes currently being made will make the plant even more valuable to the city of Nashville. Oceanside, New York disposal plant

The Oceanside disposal plant is unique in several respects. There are three incinerators at the refuse disposal plant. Two are waterwalled energy-recovery units while the third is a non-energy-recovery furnace. The two waterwalled units are converted incinerators which retained the Flynn and Emrick rocking grate, the only energy-recovery plant which uses this type of grate. Located near the Atlantic Ocean on Long Island, the plant uses a desalinization process to convert ocean water for use in the boilers. The steam produced drives a turbine-generator to produce power for in-plant use. No power is sold. The overall performance at the Oceanside plant has been poor in recent years. Burning only one energy-recovery unit plus the smaller incinerator at the same time, the plant is unable to maintain a consistent burning record. For example, between April 1981 and July 1982, the availability was less than 50%, even with two boilers. One boiler was out of service for more than a year during 1982-83, first for replacement of the charging chute and then for retubing. Specific problem areas have included corrosion of the ESPs. Frequent startups and shutdowns cause condensation of the stack gases, which contain HCI and NO,. Numerous hydraulic problems have occurred including several hydraulic fires. The Flynn and Emrick rocking grates have generally performed well, but maintenance is difficult. The desalinization units require frequent maintenance, and one of the four units has been modified to a condensing unit. Clinkering has been a problem area, and the refractory walls have deteriorated. This was the latest problem occurring with the one operating unit late in 1983. The Oceanside Disposal Plant is both an incinerator facility and a sanitary landfill. The facility receives more than 3000 tons (2727 t) per day of solid waste, and fewer than 300 tons (273 t) per day are incinerated. The life of the already bulging landfill would be greatly extended if the furnace units could be kept in continuous operation, thus reducing the volume of the waste landfilled.’ SUMMARY

Of the four plants, Nashville Thermal is enjoying the greatest success. The plant is being enlarged to add another furnace line and chiller, a turbine generator, and up to 10 new buildings on the district heating and cooling loop. The Harrisburg steam plant is also undergoing some modifications and is adding a new steam customer. The plant’s performance should improve when all the changes are completed during 1984. The Norfolk plant, although poorly maintained by the Navy Public Works Center, continues to dispose of the refuse from the Norfolk Naval Station at a price cheaper than existing waste disposal alternatives. The Oceanside plant has the poorest recent performance of any of the waterwalled, energy-recovery facilities.

Energy recovery from refuseburning

in waterwalled incinerators

53

Table 14. Summary data on the largest U.S. plants.

Design Capacity tons/day

Plant

Capital

Year Built

No. of Furnace lines

%3I~?

RESCO, Saugus, MA Chicago. IL NW Pinellas County, FL

PART

III.

LARGE

REFUSE-TO-ENERGY

PLANTS

IN THE

UNITED

STATES

Table 14 contains summary data on the three largest operational energy-recovery plants in the U.S. The three range in size from 1500 tons (1364 t) per day to 2000 tons (1818 t) per day. Chicago NW, Illinois waste-to-energy facility The Chicago NW plant was built in 1970 and was dedicated as a Waste-to-Energy Facility in 1980. For ten years of operation there was no customer for the steam produced. Excess steam was simply condensed in the air-cooled condensers. The Chicago NW plant uses the Martin grate system previously described for the Harrisburg plant. The furnaces at Chicago are only slightly larger than those at Harrisburg, but there are four furnace lines. The operating philosophy at Chicago NW is to keep three lines in operation as much as possible, holding the fourth line as a backup. The plant takes refuse only from the city of Chicago and attempts to bum approximately 1000 tons (909 t) per day, an average which has usually been achieved throughout its years of operation. Table 15 summarizes the operation of the plant for the years 19801983. The plant produces saturated steam at 275 psig (1.9 MN/m’) and the steam customer purchases about l/3 of the average steam production at Chicago NW.’ The. overall performance of the Martin-designed system has been good. It has been estimated that 65 to 70% of the original Martin grate bars are still in place. The ESPs were the first to be installed on a refuse incinerator in the U.S. and are still performing well. Some minimal problems with the convective tube have occurred in the area of the sootblowers. The original economizers are still in place. Crane breakdowns occur, but they do not usually cause a shutdown. There are three cranes, and only two are needed to keep three furnaces in operation. Problems with the air-cooled condensers have occurred frequently throughout the years of operation, partly because of the amount of usage. Steam requirements of the plant and by the adjacent city of Chicago maintenance buildings account for only a fraction of the steam produced. Most of the steam produced has to be condensed. The major problem at Chicago NW is with the materials handling systems, principally the residue belt conveyors. They require frequent maintenance problems and do not handle bulky materials well. Because the buckets on the overhead crane are so large, heavy items such as logs, refrigerators, or engine blocks could and do get into the waste stream. These bulky items do considerable damage to the conveyor system. The plant operates 24 hours a day, 7 days a week and averages burning about 1000 tons (909 t) of refuse a day, while operating three furnace lines. Chicago NW has a good operating system and good management and is continuing to perform a valuable service to the city of Chicago. Table 15. Summary performance of the Chicago NW, Illinois plant. Short tons 1 1980

1981 1982 1983

Tons of residue out

339,058 359,715 362,099 175,271 t

t Totals through June of 1983.

108,166 114,756 121,686 60,409 t

1

Produ%~lOg 1.83 1.94

lbs

1

C% 3,612,056 3,973,369 4,287,183 4,551,118

1

W. D.

54

‘TURNER

RESCO, Saugus, Massachusetts The RESCO refuse-to-energy facility is the only mass-burning plant which is privately owned and operated. The plant uses the European Von Roll grate technology, with three stepped grate sections inclined at an angle of 18” from front to rear. Modifications to the furnace and grates have upgraded the capacity of each furnace from 600 tons (545 t) to 750 tons (682 t) per day. The plant produces superheated, turbine-grade steam for sale to the General Electric plant at Lynn, Massachusetts. The steam is produced at 625 psig (4.3 MN/m2) and 825°F (714 K). Summary performance data on the plant’s operation are shown in Table 16. The average boiler availability has been 86% for both 1982 and 1983. The plant operates 24 hours a day, 7 days a week, maintains its own residue landfill, and requires 60 personnel. A tipping fee of $17.5 I is charged for each ton of refuse delivered to the plant. Because RESCO is a for-profit organization, no economic details on the steam sales or 0 & M costs are made public. There were many problems with the plant initially. Because of the large, deep pit, the crane bucket is forced to travel very long distances each load. Crane maintenance was high, but has been reduced by modifications to the drum/cable system. There was also excessive grate wear, which forced a redesign of the grate substructure and a change to a different grate material. Noticeable particulate emissions resulting from poor combustion forced a redesign of the furnace. The superheaters were originally installed in the radiant section of the furnace, and failures quickly occurred. They were subsequently moved to the convective region of the boiler, downstream of the first evaporator tube bank. These changes were largely completed during 1978-80, and were so successful that 95% of the steam supplied to GE in 1980 was by the burning of refuse. In 1982, approximately 96% of the steam sold to GE was provided by firing refuse. Most of the major operational problems at RESCO have been solved, as evidenced by the fact that the plant has averaged 86% availability over the past two years. Currently, RESCO sells steam to GE, and, in turn, GE supplies power to RESCO and pays them for the steam. The long-term steam contract with GE is being dissolved by mutual agreement, and RESCO has ordered a turbine-generator from GE. Beginning in 1985 the current steam contract will terminate, and RESCO will begin selling its excess electrical power to the local utility. This should prove to be a profitable venture because of the high electric rates in the state of Massachusetts. The RESCO facility also reclaims ferrous material from the furnace residue. A Trommel is used for size separation, and magnetic conveyors are used to remove the ferrous metal. Approximately 60 to 90 tons are recovered daily. The remaining residue is landfilled adjacent to the plant. The RESCO plant is also used for training and research. A small pilot plant, for instance, has been operated to determine the feasibility of using baghouse filters as a replacement for ESPs in future RESCO plants. The management at RESCO is good, and the plant has a good operational system. The availability of the plant in 1982 and 1983 was the best of the mass-burning plants in the U.S. Pinellas County, Florida r&use-to-energy facility This is the newest and largest of the U.S. mass-burning plants, becoming operational in May 1983. The two furnaces have a design capacity of over 1000 tons (909 t) per day, Table 16. Summary performance of RESCO, Saugus, Massachusetts. Year 1977 1978 1979 1980 1981 1982 1983

Refuse Processed Short Tons 324,960 343,104 319,209 374,555 422.604 440,000 230,ooot

tThrough July 1983,

Availability, % N/A N/A N/A N/A 80 86 86

Energy recovery from refuse burning in waterwalled incinerators

55

making them the largest in the U.S. The plant uses the Martin grate technology, similar to the Harrisburg and Chicago NW plants. The plant is owned by Pinellas County but is operated by SIGNAL RESCO, the same company which owns the REX0 plant in Saugus, Massachusetts. It is the first of the large mass-burning plants to produce power for export and sale. The superheated steam drives a 50-MW turbine generator. More than 90% of the power produced is sold. The plant is highly automated. The control room operator monitors each furnace’s operation via closed circuit TV. The pneumatic controls system has proven very reliable in the initial year of operation. The crane operators do not “ride” the crane as in all the other U.S. plants but instead sit in a conditioned crane control room located between the two furnaces. The performance of the Pinellas County plant has been outstanding since start-up. The boiler availability averaged approximately 90% over the first 9 months. Although problems have occurred, they have been minimal, especially considering the startup conditions. Certified tests on the emissions indicated particulate levels of approximately 0.025 gr/dscf (0.058 g/dscm) corrected to 12% CO*. This plant is the only one of the mass-burning plants which has ferrous, aluminum, and nonferrous materials recovery. Although much more labor intensive than originally planned, the materials recovery system is working well. Some early problems have developed with the superheater tube sootblowers and with excessive clinkering in the furnaces. High temperatures in the first superheater pass could lead to future high temperature corrosion problems in the superheater. The performance of the plant to date has been extremely good. The contractual tonnage for 1983 was 401,000 tons (365,000 t). The plant actually burned 438,000 tons (398,000 t). The guaranteed boiler availability is 85%, but the actual performance was nearly 90%. A shutdown after four months of operation did not reveal any major problems with the refractory, grates, waterwalls, or the evaporator tubes. Table 17 lists the monthly availability of each boiler and the average daily tonnages processed since startup in May, 1983. Availability is defined by SIGNAL RESCO as on line producing convertible steam. Before the plant was a year old, a contract was signed with SIGNAL RESCO to enlarge it by 50%. A new furnace line is being added, and 25 MW of additional power will be produced. This is expected to be completed in 1985. The new furnace will be redesigned to eliminate some of the problems encountered in the current ones. At 2000 tons/day design capacity, the Pinellas plant is the largest in the U.S. With the addition of the third line in 1985, the capacity will exceed any of the U.S. massburning plants currently in planning or under construction. Its first year’s performance has been outstanding.” SUMMARY

The three large-mass burning plants are all performing well. All have good management and sound technical systems. Pinellas County is the first of the mass-burning plants to Table 17. Summary of the 1983 operation of the Pinellas County plant Boiler Avallablllty Boiler Xl Boiler

Average 12

Da1ly Capaci tons

98.8

92.8

1984

86.4

100.0

2191

95.7

96.4

1976

a5.6

a7 .a

2110

58.1

63.9

1183

100 .o

99.3

la14

98.3

91.5

1798

90.8

89.7

1775

56

W. D. TURNER

generate power for export, and when the additional construction is completed in 1985, the plant will have a 75-MW capacity. Two more large plants, located at Westchester, New York and Baltimore, Maryland will be run by SIGNAL RESCO and should be fully operational by 1985. Both will sell electrical power to the local utilities. REFERENCES 1. W. D. Turner, “Thermal Systems for Conversion of Municipal Solid Waste, Volume 2, Mass Burning of

2. 3. 4.

5. 6. 7. 8. 9.

10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Solid Waste in Large-Scale Combustors: A Technology Status Report”, Argonne National Laboratory Report, ANL/CNSV-TM-120 (December 1982), Argonne, IL 60439, U.S.A. W. D. Turner, “Large-Scale Waterwall Systems-Current Status”, Proceedings of the DOE-ANL Conference, State-of-the-Art and Emerging Technologies, Chicago, IL (Nov. 1983), Argonne National Laboratory, Argonne, IL 60439, U.S.A. “Energy Recovery from Solid Waste”, Vol. 2, NASA CR-2525 (April 1975). Point of View”, Proceedings of the International H. Bailly, “European and American Experience-A Conference on European Waste-to-Energy Technology, Reston, Virginia, October 1980, ANL/CNSV-TM-14 (198 l), Argonne National Laboratory, Argonne, IL 60439, U.S.A. P. Jenner (Braintree Municipal Incinerator Plant Manager), private communication (1983). F. L. Heaney, APCA J. 22, 6 17 (1972). M. Golembiewski, “Environmental Assessment of a Waste-to-Energy Process: Braintree Municip-1 Incinerator”, Midwest Research Institute. Kansas City. Missouri, NTIS PB SO-21942 1 ( 1980). C. Loveland (Hampton Plant Manager), private communication (1983). H. F. Taylor, D. E: McCoy, and H. L. Greene, “NASA/Hampton Refuse Fired Steam Plant: A Municipal/ Federal Coooerative Effort”. Proceedinws of the 1980 ASME Waste ProcessingI Conference, New York. New ” York, pp. 53-63 (1980). H. L. Greene, D. E. McCoy, and H. F. Taylor, “NASA/Hampton Refuse-Fired Stean ‘lant a Municipal/ Federal Cooperative Effort”, Presented at 16th ASME Intersociety Energy Conversion Eng leering Conference, Atlanta, Georgia (198 1). T. L. Martin, Solid Wastes Management 168, 20 (1982). C. Loveland (Hampton plant manager), private communication (1984). W. D. Turner, “Energy Recovery from Mass Burning of Municipal Solid Waste in Waterwalled IncinemtotsCurrent U.S. Status”, Proceedings of the Industrial Pollution Control Symposium. 6t: Annual ESTCE, Houston, Texas (1983). J. Vugrinec (Harrisburg Operator), private communication (1983). C. E. Avers, “Technical-Economic Problems in Energy Recovery Incineration,” Proceedings of the I976 ASME National Waste Processing Cotz/iJrence. Boston, Massachusetts, pp. 9-66 (1976). R. B. Engdahl, “Identification of Technical and Operating Problems of Nashville Thermal Transfer Corporation Waste-to-Energy Plant”, Battelle Laboratory Report BMI-1947, Columbus, Ohio (Feb. 1976). G. Weaver (Nashville Thermal Controller), private communication (1983). J. Klett (Pinellas County Plant Engineer), personal interview (Feb. 1984). K. Stickney (SIGNAL RESCO Engineering Products Group), private communication (April 1984).