United States Office of Water and SW 176C.6
Environmental Protection Waste Management October 1979
Agency Washington, D.C. 20460
Solid Waste
v>EPA European Refuse Fired
Energy Systems
Evaluation of Design Practices
Volume 6
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Pufa&tcotuw XA^ue ^01 EPA
and State, So&Ld Wa&te. Ma.nagwe.nt
EUROPEAN REFUSE FIRED ENERGY SYSTEMS
EVALUATION OF DESIGN PRACTICES
Horsens Refuse Fired Heating andSUidge Drying Plant
Horsens, Denmark
tka O^xcee ofa Sotid Wa&te. undeA. contract no. 68-01-4376
and -ii> reproduced a& fitc.QA.\>e.d ^fiom the. contfiactotL.
The k-indinQA tkouJtd 6e attsu.bute.d to tke.
and not to the. 0^-tee. o& SoLid
Copies will be available from the
National Technical Information Service
U.S. Department of Commerce
Springfield, VA 22161
Volume 6
U.S. Environmental Protection Agency
Region V, Library
230 South Dearborn Street
Chicago, Illinois 60604
U.S. ENVIRONMENTAL PROTECTION AGENCY
1979
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This report was prepared by Battelle Laboratories, Columbus, Ohio,
under contract no. 68-01-4376.
Publication does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of commercial products constitute endorsement by the U.S.
Government.
An environmental protection publication (SW-176c.6) in solid waste
management series.
U,S. Environmental Protection Agencf
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DRAFT TRIP REPORT
to
HORSENS REFUSE-FIRED HEATING AND
SLUDGE DRYING PLANT,
HORSENS, DENMARK
on the contract
EVALUATION OF EUROPEAN REFUSE-FIRED
STEAM GENERATOR DESIGN PRACTICES
September 28-30, 1977
to
U.S. ENVIRONMENTAL PROTECTION AGENCY
March 9, 1978
EPA Contract No. 68-01-1376
EPA RFP No. WA-76-B1U6
by
Richard Engdahl and Philip Beltz
BATTELLE
Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
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i
PREFACE
This trip report is one of a series of 15 trip reports on
European waste-to-energy systems prepared for the U.S. Environmental
Protection Agency. The overall objective of this investigation is to
describe and analyze European plants in such ways that the essential
factors in their successful operation can be interpreted and applied
in various U.S. communities. The plants visited are considered from
the standpoint of environment, economics and technology.
The material in this report has been carefully reviewed by the
European grate or boiler manufacturers and respective American licensees.
Nevertheless, Battelle Columbus Laboratories maintains ultimate responsi-
bility for the report content. The opinions set forth in this report are
those of the Battelle staff members and are not to be considered by EPA
policy.
The intent of the report is to provide decision making in-
formation. The reader is thus cautioned against believing that there is
enough information to design a system. Some proprietary information has
been deleted at the request of vendors. While the contents are detailed,
they represent only the tip of the iceberg of knowledge necessary to de-
velop a reliable, economical and environmentally beneficial system.
The selection of particular plants to visit was made by Battelle,
the American licensees, the European grate manufacturers, and EPA. Pur-
posely, the sampling is skewed to the "better" plants that are models of
what the parties would like to develop in America. Some plants were selected
because many features envolved at that plant. Others were chosen because
of strong American interest in co-disposal of refuse and sewage sludge.
The four volumes plus the trip reports for the 15 European
plants are available through The National Technical Information Service,
Springfield, Virginia 22161. NTIS numbers for the volumes and ordering
information are contained in the back of this publication. Of the 19
volumes only the Executive Summary and Inventory have been prepared for
wide distribution.
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ii
ORGANIZATION
The four volumes and 15 trip reports are organized the the
following fashion:
VOLUME I
A EXECUTIVE SUMMARY
B INVENTORY OF WASTE-TO-ENERGY PLANTS
C DESCRIPTION OF COMMUNITIES VISITED
D SEPARABLE WASTE STREAMS
E REFUSE COLLECTION AND TRANSFER STATIONS
F COMPOSITION OF REFUSE
G HEATING VALUE OF REFUSE
H REFUSE GENERATION AND BURNING RATES PER PERSON
I DEVELOPMENT OF VISITED SYSTEMS
VOLUME II
J TOTAL OPERATING SYSTEM RESULTS
K ENERGY UTILIZATION
L ECONOMICS AND FINANCE
M OWNERSHIP, ORGANIZATION, PERSONNEL AND TRAINING
VOLUME III
P REFUSE HANDLING
Q GRATES AND PRIMARY AIR
R ASH HANDLING AND RECOVERY
S FURNACE WALL
T SECONDARY (OVERFIRE) AIR
VOLUME IV
U BOILERS
V SUPPLEMENTARY CO-FIRING WITH OIL, WASTE OIL AND SOLVENTS
W CO-DISPOSAL OF REFUSE AND SEWAGE SLUDGE
X AIR POLLUTION CONTROL
Y START-UP AND SHUT-DOWN
Z APPENDIX
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TABLE OF CONTENTS
Page
LIST OF PERSONS CONTACTED 1
SUMMARY 2
HORSENS STATISTICAL SUMMARY 3
COMMUNITY DESCRIPTION 6
SOLID WASTE PRACTICES 9
Solid Waste Generation 9
Solid Waste Collection 9
Solid Waste Disposal 11
DEVELOPMENT OF THE SYSTEM 12
PLANT ARCHITECTURE 14
REFUSE-FIRED HOT-WATER GENERATOR 15
Heat Input 15
Weighing Operation 15
Refuse Storage and Retrieval 16
Furnace Hopper and Feeder 16
Burning Grate 19
Furnace Wall 22
Boiler 25
Primary Air 26
Secondary Air 26
ENERGY UTILIZATION 27
Sludge Dryer 27
District Heating System 29
Pipeline 30
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TABLE OF CONTENTS
(Continued)
Page
POLLUTION CONTROL EQUIPMENT 31
Induced Draft Fan 32
Chimney 32
Residue Disposal 32
Operating Routine 33
EQUIPMENT PERFORMANCE ASSESSMENT . .' 35
POLLUTION CONTROL ASSESSMENT 36
Noise 36
PERSONNEL AND MANAGEMENT 37
ENERGY MARKETING 38
ECONOMICS 39
Capital Cost 39
Operating Costs 40
FINANCE 43
APPENDIX A
New Plant at Aarhus-Nord A-l
LIST OF TABLES
Table 13-1. Quarterly and Annual Summary of Industrial Waste
Received at the Horsens Plant, Tonnes per
Quarter and per Year 10
Table 13-2. Operating Budget for Horsens Plant, ,1977-1978 41
LIST OF FIGURES
Figure 13-1. Map of Area Served by Horsens Refuse Plant 7
Figure 13-2. Aerial View of Horsens Refuse-Burning, Sludge-
Drying and District-Heating Plant 8
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LIST OF FIGURES
(Continued)
Page
Figure 13-3. Polyp Type of Grab Bucket Used at Horsens 17
Figure 13-4. Original Horsens System for Sludge-Drying Only 18
Figure 13-5. Sketches of Grate Action 20
Figure 13-6. Bruun and Sorensen Cast Alloy Grate Bars 21
Figure 13-7. Circular Afterburner with Boiler on Top at Horsens ... 24
Figure 13-8. Diagram of Horsens Refuse-Burning and Sludge-
Drying Plant 28
Figure 13-A1. Aarhus-Nord Plant A-2
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LIST OF PERSONS CONTACTED
Erling Petersen
Finn Lars en
Harry Arnum
Holger Sorensen
Nels Jurgen Herler
Niels T. Hoist
Paul Sondergaard-Christensen
Allan Sorensen
City Director of Solid and Water
Waste Management
Horsens Plant Manager
City Engineer, Horsens
Burgotneister, City of Horsens
Engineer, Horsens Plant
Chief Engineer, Bruun and
Sorensen, Aarhus
Engineer, Bruun and Sorensen,
Aarhus
Engineer, Bruun and Sorensen,
Aarhus
The authors are very pleased to gratefully acknowledge the very
kind and competent assistance given to us by the above individuals in
assembling the information presented in this report.
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SUMMARY
The small Horsens plant was originally built in 1973-1974 to dry
sewage sludge only, using refuse from a population of 54,000 as fuel for
heating a rotary drying kiln. But in 1977. it was converted to also
generate hot water to feed into the city district heating system which is
now heated primarily with oil. The dried sludge is not cofired with the
refuse, but it could be. The recent conversion of the plant to supplement
the district heating system makes it a unique type of refuse-to-energy
plant.
Industrial waste constitutes a major portion of the total energy
input, although, as with all Danish refuse systems, toxic and corrosive
industrial chemical wastes are not burned locally but are sent to a single
processing and incineration plant built by Von Roll at Nyborg.
A much larger plant was nearing completion at Aarhus embodying
many of the principles evolved at Horsens. A brief description of that
plant is included as Appendix A.
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HORSENS STATISTICAL SUMMARY
Conn unity Description:
Area (square kilometers)
Population served
Key terrain feature
200
6l»,000
Hilly, coastal
Solid Waste Practices:
Total waste generated (tonnes/year)
Waste generation rate (kg/person/day)
Lower heating value of waste (Kcal/kg)
Collection period (days/week)
Cost of collection (local currency/tonne)
Use of transfer and/or pretreatment
Distance from generation centroid to:
Local landfill (meters)
Refuse-fired steam generator (meters)
Waste type input to system
Cofiring of sewage sludge (yes or no)
Drying of sewage sludge (yes or no)
18,909
1.0
2,800
5
No
1,000
300
Res., com., ind.
No
Yes
Development of the System:
Date operation began (year)
Plant Architecture:
Material of exterior construction
Stack height (meters)
Reinf. concrete
60
Refuse-Fired Steam Generator Equipment:
Mass burning
Waste conditions into feed chute:
Moisture (percent)
Lower heating value (Kcal/kg)
Yes
2,800
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Volume burned:
Capacity per furnace (tonnes/day) 120
Number of furnaces constructed 1
Capacity per system (tonnes/day) 120
Actual per furnace 67
Number of furnaces normally operating 1
Actual per system (tonnes/day) 67
Use auxiliary reduction equipment (yes or no) No
Pit capacity level full:
(tonnes)
(m3) 950
Crane capacity:
(tonnes) 4.6
(m3) 2.5
Feeder drive method Hydraulic
Burning grate:
Manufacturer Bruun and Sorensen
Type Sectional, rocking
Number of section 3
Length overall (m) 8.1
Width overall (m) 2
Primary air-max (Nm /hr) 30,000
Secondary air-overfire air-max f*T ^/hr) 3,000
o
Furnace volume (m ) 62
Furnace wall tube' diameter (on None
2
Furnace heating surface (m ) None
Auxiliary fuel capability No
Use of superheater No
Boiler:
Manufacturer I/S Danstoker
Type Vertical, flretube
Number of boiler passes 1
Heat production per boiler (Gcal/hr) 7
Total plant heat production (Gcal/hr) 7
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Water temperature ( C)
2
Water pressure (kg/m )
Air Pollution Control Equipment:
Mechanical cyclone collector
Electrostatic precipitator
Manufacturer
Inlet loading of participates (mg/Nnr)
Exit - loading of particulates (mg/Nnr)
Legislative requirement (mg/Nm )
Scrubber
110
Cyclonic after oombustor
Tes.
Svenska Flaktfabriken
5,000
180
180
None
Water:
Total volume of waste water (liters/day)
Ash:
Volume of ash (tonnes/day)
Volume of metal recovered (tonnes/day)
None
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COMMUNITY DESCRIPTION
Horsens "town of horse power" is an industrial and seaport city
of 54,000 population located at the head of the Horsens fjord on the
island of Jutland. In 1970, its population was about 38,000, but as part
of the consolidation of communities throughout Denmark, Horsens was at
that tine combined with five other communities.
Figure 13-1 is a map of the expanded Horsens community, which has
2 2
a land area of about 200 km (38.6 mi ). To provide more fuel for its
refuse-to-energy plant, Horsens is seeking agreements with surrounding
communities. One town, Geved, population 10,000 located 10 km (6 mi) north
of Horsens, has arranged to send all of its refuse to Horsens. On the map
in Figure 13-1> Geved is near the top center.
The countryside is fairly hilly with many small towns closely
spaced and connected by many roads. A north-south expressway, E3, passes
through the western part of the city. Two of the neighboring towns use
hearth-type incinerators, but in 1980, the law requires that these be shut
down.
Figure 13-2 is an aerial view of the Horsens plant and, at the
top, the new wastewater treatment plant. About one fourth of the weight of
solid waste received at the plant is industrial waste. There are three
plastics plants in town which produce waste of high heat value. Also,
there are electronics plants and a telephone factory.
There are 15 communities around Horsens which comprise a region
or "small state11 called an AMI (similar to a city-county government). The
trend of Danish communities to combine to form "AMI" regions is an old one
which has been found good for making road decisions, regional planning,
conducting refuse management studies, environmental review, and for
exercising sanction power, which is the authority to stop practices that
t
harm the environment. An AMT council is elected every U years.- The plans
for the Horsens refuse plant were approved by the Vie.-j AMT council.
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Scale
FIGURE 13-1.
MAP OF AREA SERVED BY HORSENS REFUSE
PLANT. THE COMBINED HORSENS COMMUNITY
SERVED IS ENCLOSED IN THE HEAVY BROKEN
LINE.
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FIGURE 13-2.
AERIAL VIEW OF HORSENS REFUSE-BURNING, SLUDGE-
DRYING AND DISTRICT-HEATING PLANT. AT TOP IS
THE NEW SEWAGE TREATMENT PLANT. AT FAR LOWER
RIGHT IS A COLLECTION STATION FOR HAZARDOUS
LIQUID WASTE WHICH IS SENT TO THE NATIONAL
HAZARDOUS WASTE CENTER AT NYBORG (COURTESY OF
BRUNN AND SORENSEN)
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SOLID WASTE PRACTICES
Solid Waste Generation
It is estimated that at present about 16,900 tonnes/yr (18,590
tons/yr) are received at the plant, although only the trucks bringing
industrial waste are actually weighed as they deliver. Of this total,
about 4,300 tonnes (4,730 tons) are highly combustible industrial and
commercial waste. The difference, 12,600 tonnes (13>860 tons), are of
residential origin.
Table 13-1 shows the amounts of industrial waste received since
the plant started in 1974.
Solid Waste Collection
The city operates five collection vehicles which bring a total of
about 12,000 paper sacks of refuse to the plant during 5 days of each
week, 8 hours per day. One suburban truck and about seven private truckers
are also licensed to deliver. Their total weekly delivery is about 5>000
sacks. The paper sacks are provided by the city which buys about a million
sacks per year from the F. L. Smith Co., manufacturer of cement sacks in
Aalborg, Denmark.
The five city and seven private trucks are not weighed except
occasionally to provide a record of a typical load. These checks indicate
that the average loaded sack weighs about 15 kg (33 lb). On this basis,
the 17,000 sacks per a 5-day week are the equivalent of 3.400 sacks per
day, 51>000 kg/day (56.1 tons/day) (14,600 tonnes/yr) of household refuse.
The industrial waste input reached a total of 4,309 tonnes/yr in
1976, or an average of 16.6 tonnes/day'(based on a 5-day week) (18.3
tons/day). Thus, the 5-day total estimated input is 67.6 tonnes/day (74.4
ons/day).
For the population served of approximately 64,000, including
Ge' d, this total input rate represents an equivalent waste generation
rate of about 295 kg/person/year (649 lb/person/year).
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TABLE 11-1.
QUARTERLY AND ANNUAL SUMMARY OF INDUSTRIAL
WASTE RECEIVED AT THE HORSENS PLANT, TONNES
PER QUARTER AND PER YEAR (COURTESY OF MR.
FINN LARSEN OF THE CITY OF HORSENS)
January-March
April-June
July-September
October -December
TOTAL
1974
Start
762.3
743.9
955.4
2,461.6
1975
932.4
884.8
875.2
1,041.6
3,734.0
1976
983.7
1,018.8
1,018.8
1,287.6
4,308.9
1977
731.5
681 0
1,050.2
Note: Reduced receipts in first two quarters of 1977 caused by
plant shutdown for modification to add waste heat boiler.
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Each collection worker is estimated to pick up and deliver 950
sacks per week. At 15 kg (33 Ib) per sack, this amounts to 2,850 kg (6,270
Ib) per worker per day.
Solid Waste Disposal
The burned residue is sent to a landfill adjacent to the plant
where additional land is being built out into a shallow, dammed area of
the fjord.
Industrial and Hazardous Waste Transfer Station
As part of this Energy and Environmental Park, the City of Horsens
owns and operates an industrial and hazardous waste transfer station.
All industrial and hazardous waste, by law, must be transferred to Nyborg,
Denmark where four different waste processing lines treat the waste. This
facility is taxpayer owned by the National Association of Municipalities.
This is described in Appendix B.
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DEVELOPMENT OF THE SYSTEM
In the early 1970's, the City Council of Horsens determined that
the uncontrolled landfill then in use had to be replaced by an
environmentally more acceptable method for disposal of solid wastes.
Landfill fires and rats were objectionable. Accordingly, the city engineer
visited 10 cities which had used various incineration systems to solve a
similar problem.
At Horsens, composting had already been ruled out by an
unsatisfactory experience with a modern composting system used from 1951
to 1965. From the start of its operation, assured markets for the product
could not be maintained. Very little product was sold. In the last 5 years
of operation, 1960-1965, none was sold.
In Denmark, well-managed landfills cost one half to one third as
much to operate as incinerators, but in eastern Jutland, acceptable sites
for new landfills are rare. Therefore, in 1972, Council decided to build
an incineration plant. A letter defining the desired system was prepared
by the Economic Development Committee of Council and was sent to various
vendors inviting their interest. As a result, definite bids were received
from three Danish companies: Bruun and Sorensen, Volund, and Elsinore.
Bruun and Sorensen, whose main office is in Aarhus only HO km (25 mi)
away, was the low bidder. The plant details and final price were then
negotiatted and the plant was built as a turnkey project.
In order to make use of some of the heat released by
incineration, the plan included separate construction of a sewage
treatment plant adjacent to the incinerator so that hot flue gas could be
used to partially dry the digested sludge. Heat recovery for district
heating was not added until 1977.
The decision in 1973 to build the plant was made solely by
Council and no referendum was required. However, on January 1, 1977. a new
Danish law became effective requiring that city plans must now be
available for citizen scrutiny and comment. The final decision, however,
remains with City Council, subject then to approval by the regional
council.
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Initially, it was hoped to locate the plant near one of the three
existing privately owned district heating plants, but space was too
confining and increased traffic there would have been difficult. The
present ample site on a shallow, filled-in part of the Horsens Fjord is
conveniently adjacent to the current landfill. Also adjacent is a chemical
waste collection depot where such wastes are collected for shipment by
barge to Denmark's nationally operated liquid and hazardous waste disposal
plant at Nyborg, about 100 km (62 mi) southeast of Horsens.
As in many Danish communities, an important incentive toward
clean alternatives to landfilling is the threat to groundwater quality
from old, uncontrolled landfills. Also, since Denmark imports all of its
energy, the recovery of energy from wastes has long been an important
goal. The oil crisis of October, 1973 intensified the need for more
waste-to-energy systems. At Horsens, -additional refuse-fired heating
plants are envisioned. Also, it is expected that in the future, to
conserve energy, national legislation will require much more use of
district heating, and some of this expansion will undoubtedly use refuse
as fuel.
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PLANT ARCHITECTURE
Figure 13-2, presented earlier shows an aerial view of the
Horsens plant. At the top of the figure is the new sewage treatment plant
which feeds digested sludge to the refuse plant for partial drying before
disposal. The industrial ana hazardous liquid waste collection is shown at
the lower right. The tank car shown will be sent to Nyborg where Denmark's
single hazardous waste processing center is located. All activities are
under one management.
The main structure is built of reinforced concrete. The section
containing offices, washroom, and control room are faced inside with very
attractive glazed, reddish colored brick. Total building volume is 12,300
00 -3
m (H*2,352 ftj), including 2,000 mj for the room containing the rotary
kiln for sludge drying. The building is sized to accommodate a second
furnace-boiler system.
Both plants are located on filled in land close to the center of
the city where formerly there was a city landfill. The Horsens Fjord at
that point is shallow and the filled land rests on 5 to 6 m (16.^ to 19.7
ft) deep layer of mud. Support of the refuse plant required 150 piles
about 10 to 20 m (33 to 65 ft) deep.
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REFUSE-FIRED HOT-WATER GENERATOR
As originally operated in 1971*, this plant recovered no thermal
energy as such but served only to dry sludge in a stream of hot flue gas
from the refuse-burning furnace. However, in 1977* a hot water boiler was
added to recover energy for the existing district heating system. The bulk
of the energy for district heating is still supplied by three oil-burning
plants 1.8 and 2.5 km (1.1 and 1.5 mi) away.
Heat Input
Few measurements have been made of the lower heat value of the
refuse at Horsens, but it is believed to be fairly high because of the
high combustible content of the wastes from the local electronics-oriented
industries. Plant staff estimate that although the industrial component
constitutes only one quarter of the refuse input, it provides about one
half of the heat input. However, in designing the plant, Bruun and
Sorensen assumed an averge heat value of only 2,000 Kcal/kg (3i600 Btu/lb)
(8,372 kJ/kg), plus or minus 10 percent. That the actual average value is
closer to 2,800 Kcal/kg plus or minus 10 percent is indicated by the
opinion of plant staff that they need more residential refuse to dilute
the "hot" industrial waste that tends to overheat their system. Spot
samples of industrial waste only, analyzed in December, 1974, soon after
the plant started, had lower heat values of 3,1^0 to 3,020 Kcal/kg (5,652
and 5,436 Btu/lb) [13,1*7 and 12,645 kJ/kg].
Weighing Operation
The 10-tonne scale is located inside the tipping hall adjacent to
the pit. It is calibrated once a year by the manufacturer. Only the trucks
delivering industrial waste are weighed and pay a fee. All others,
unweighed, dump free. For the collection and disposal service, each
household pays a tax. Occasionally, sacked residential waste are weighed
for a week or so to obtain data to help estimate the residential input.
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16
Refuse Storage and Retrieval
The control room operator also operates the crane and weighing
platform which is adjacent to the pit. The operator has full view of all
of this area through a large window overlooking the pit which is 9 m (30
ft) deep and has a total volume of 950 m3 (33,525 ft ). It can hold a
3-day supply. It is divided into two equal volumes, each 7-7 by 7.2 m (25
by 23.5 ft). In this way, the industrial and residential wastes can be
separated. This enables the operator to mix them in appropriate
proportions as he operates the crane to fill the single furnace hopper.
The industrial pit is nearest the operator as it requires close scrutiny
to enable the operator to control the mixture fired.
Bulky waste is not handled but is sent directly to the landfill
nearby. However, plans have; been made to install a shear at an estimated
cost of 500,000 Dkr ($83,333 § 6 Dkr/$). Some consideration is being given
to use of a double screw device licensed by Norba and built by Volund for
size reduction. One such installation at Horsholm is said to have provided
good service for about 10 years.
The M.6 tonne crane, operated semiautomatically, was made by
Frederikssund Jernstoberi og Maskinfabrik of Frederikssund, Denmark.
Figure 13-3 shows the 2.5 m3 (88 ft ) polyp-type grab made by Sven, now a
part of Volund.
Pit fires are controlled by fixed nozzles located around the
sides. When necessary, local firefighters use foam.
Furnace Hopper and Feeder
Figure 13-U is a schematic diagram of the Horsens plant. There is
only one furnace. The control room operator keeps the feed hopper full by
means of the grab and crane. Once he has picked up a charge from the pit,
the crane is programmed to position the loaded grab over the hopper. When
it is in position, the operator actuates the grab to drop its charge into
the hopper. The crane can feed a charge up to once every 4 minutes.
The top opening of the hopper is H.2 by 4.8 m (13-8 by 15-7 ft),
and it is 2.1 m high (6.8 ft). The refuse flows by gravity from the hopper
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17
FIGURE 13-3.
POLYP TYPE OF GRAB BUCKET USED AT
HORSENS (COURTESY OF BRUUN AND
SORENSEN)
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18
1.GRAB
2. RECEPTION HOPPER
3. FURNACE
4. SLAG DISCHARGE
5. COMBUSTION AIR
6. AFTER-COMBUSTION CHAMBER
7. COOLING TOWER
8. COMBUSTION-GAS DUCT
TO ROTARY DRYER
9, ROTARY DRYER
10. COMBUSTION-GAS DUCT FROM ROTARY
DRYER AND COOLING TOWER.
11. ELECTROSTATIC PRECIPITATOR
12. EXHAUST FAN
13. CHIMNEY
14. SLAG VIBRATION CONVEYOR
15. SCREW CONVEYOR FOR FLY ASH
1«. SCREW CONVEYOR FOR DRIED SLUDGE
17. CONTAINER FOR DRIED SLUDGE
18. SKIP HOIST FOR SLAG
19. SLAG BUNKER
20. SLAG CONTAINER
21. COOLING WATER
22. SLUDGE CONTAINER
FIGURE 13-4.
ORIGINAL HORSENS SYSTEM FOR SLUDGE-DRYING ONLY. IN
1977, ITEM 7, THE -SPRAY-TYPE GAS COOLING CHAMBER,
WAS REPLACED BY A FIRETUBE BOILER (COURTESY OF
BRUUN AND SORENSEN)
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19
into a refractory-lined feed chute 1.11 m high (3.6 ft) and 1 by 1.6 m
(3.28by 5.2 ft) at the top, tapering out to 1.6 by 2 m (5.2 by 6.5 ft) at
the bottom. Burnback can be arrested by a cast iron flap damper in the
chute.
The poured refractory lining of the chute is 50 mm (2 in) thick,
held in place by welded anchor rods.
At the bottom of the chute, the refuse is fed on to the sloping
grate by a similarly sloping hydraulic feeder designed by Bruun and
Sorensen and built by Monsund. The feed ram has a maximum stroke of 2.5 m
(8.2 ft) and a capacity of 5 tonnes/ hour. Variable feed is provided by a
timer which can be adjusted by the operator from 0 to 1 stroke/minute. The
only problem with the feeder has been oil leakage.
Burning Grate
The hydraulic ram-type feeder feeds the refuse on to the 30
degree sloping sectional grate depicted in Figure 13-5. As shown in the
lower three sketches of the figure, the grate sections oscillate
rotationally in a coordinated rocking motion such that the burning refuse
is induced to cascade downward along the sloping grate in a wave-like
motion, thus slowly agitating the fuel bed so as to prevent compaction and
consequent irregularity in air flow. The motion of each grate section is
controlled by an adjustable timer.
The moving part of the grate is formed of three sections with six
horizontal shafts in each section. The grate bars are fixed to the shafts.
Figure 13-6 shows two typical grate bars which are 0.5 m (1.6 ft) long.
The lower bar in the figure is 50 mm (2 in) wide. The upper one is a new
design of bar which is 100 mm (i| in) wide. Recent experience at Horsens
with a test section of the newer bar revealed that fine ash is less likely
to adhere in the interstices between the bars; hence, less cleaning is
required to maintain the gaps free for uniform air flow. Cleaning between
the older bars required 2 man-days per week. With the-new ones, cleaning
is required every other week. Since the plant is shut down on weekends,
there is no interruption in desired service. Cleaning is by means of a
pneumatically driven chisel. Also, the new ones are less likely to break.
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20
INCINERATOR
SYSTEM
FIGURE 13-5. SKETCHES OF GRATE ACTION (COURTESY OF BRUUN
AND SORENSEN)
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21
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22
Replacement rate of the older bars has been at the rate of about 20/year.
There were 720 of the older bars on 18 shafts. The new and old bars are
cast by a Swedish affiliate of Bruun and Sorensen using an alloy of 23
percent chromium, 1.5 percent silicon, 0.2 percent nickel, and 0.25
percent molybdenum. They are guaranteed for 10,000 hours.
The grate is 2 m (6.5 ft) wide and 8.1 m (26.6 ft) long with a
total area of 16.2 m2 (174.3 ft2). At the rated capacity of 5 tonnes/hr
(5.5 tons/hr), this provides a burning rate of 308.6 kg/m /hr (63.1
p
Ib/ft /hr), a typical burning rarte in'many plants. As operated, burning 74
tonnes/ day (81.4 tons/day), the corresponding averge burning rate is only
2 2
190.3 kg/m /hr (38.9 Ib/ft /hr), a very modest rate. However, this is only
an average, and since the plant does not operate at high rate at night,
peak burning rates probably are much higher. Also, because of the
relatively high heat value of the industrial waste received, relatively
low burning rates are desired to avoid overheating the system.
The air pressure drop through the grate ranges from 158 to 165 mm
(6.2 to 6.5 in) water.
The burned residue falls from the end of the grate into a sprayed
quench chute which drops it then onto a series of vibrating conveyors
shown in Figure 13-4.
Furnace Wall
The original plant was designed as a hot flue-gas generator for
sludge drying; hence, the furnace wall is refractory without any heat
recovery at the walls. The first meter (3.28 ft) of wall above the grate
is formed of korund (45 percent silicon carbide) brick to discourage slag
adhesion. Above that, the wall was originally- firebrick but now castable
or rammed refractory is used.
Originally, the furnace roof was a brick arch resting, on steel
supports, but because of overheating of the steel, it has been replaced by
a poured flat roof of castable refractory supported externally. The new
roof was designed by Hoganas using Hoganas "ES" refractory. It is stated
to withstand 1,300 C (2,372 F). Its composition is SiO36 percent;
A120 42 percent; and Fe.O- 6.1 percent.
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23
The furnace volume is 62 m3 (2,186 ft3). At the rated 5 tonnes/hr
of the expected refuse at only 2,000 Kcal/kg, the volume heat release rate
would have been 161,290 Kcal/m3/hr (18,100 Btu/ft3/hr) (675 kJ/m3/hr).
However, the system design allows for burning in the furnace outlet
channel and in the cyclonic-type after-combustion chamber, totaling an
added volume of 51>1 m (t,8l4 ft3). Hence, the actual heat release rates
are much lower than those just estimated. Nevertheless, because the actual
refuse fired has a lower heat value considerably above the design value of
2,000 Kcal/kg, the furnace temperature reached in early operation reached
1.UOO C (2,552 F) instead of the design value of 950 C (1,7*2 F). this
overheated and warped the fire brick furnace wall which has now been
replaced by castable refractory. In addition, furnace operation is now
slowed to avoid overheating when much "hot" industrial waste must be
burned.
Secondary air can be injected through ports in the roof as
indicated earlier in Figure 13-1* , but these jets are seldom used except
just enough to keep the air piping cool.
The refractory after-combustion chamber is 11.25 m (13-9 ft)
inside diameter, 3 m (9.8 ft) high on top of a 2 m (6.6 ft) conical
refractory hopper. Its intent is to provide gas mixing and burning time
and to remove coarse fly ash from the hot gas stream. The CO content of
the gases leaving the chamber is in the range of 9 percent.
Figure 13-7 is an external view of the brightly painted steel
shell of the after-combustion chamber with the cylindrical boiler located
above it.
An early problem with the water spray cooling chamber, used
before the boiler was installed in 1977, was that small amounts of water
dropped from the spray chamber into the feed screw that removes coarse ash
from the hopper below the combustion chamber. The wet ash sometimes
hardened and stalled the screw. Replacement of the spray chamber by the
boiler eliminated this problem.
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FIGURE 13-7. CIRCULAR AFTERBURNER WITH BOILER ON TOP AT HORSENS
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25
Boiler
As shown earlier in Figure 13-4 > the original design had the
hot, partly cleaned gases leave the after-combustion chamber at two
points. From the top, they could flow vertically upward into a
water-sprayed cooling chamber and, hence, to the electrostatic
precipitator; or they could leave from the bottom hopper or horizontally
through a refractory-lined duct to enter the rotary sludge dryer. However,
the growing urgency throughout Denmark to conserve all available energy
led in 1977 to replacement of the spray cooler by a waste heat boiler to
supply hot water for the existing district heating system. This is a
simple vertical firetube boiler built by the Danish Stoker and Heating
Company. It contains 5^0 tubes, 57 mm in diameter (2.25 in) and M.5 m
(U.8 ft) long. Its capacity is 7 Gcal/nr (27,776 M Btu/hr) (29-308
GJ/hr). Heated water leaves the boiler at 110 C (230 F) and returns from
the system at 80 to 90 C (176 to 18U F).
The top (exhaust) end of the boiler is accessible so that once
every 2 weeks all of the 5^0 tubes can be cleaned of soft ash deposits by
means of a powered rotating wire brush. This takes 6 to 7 hours every
Monday morning at the same time that the air openings in the grates are
being cleaned and the siftings are being removed from beneath the grate.
The makeup water is treated by the main district heating plant.
When the spray cooling chamber operated, it had the capacity to
cool all of the gases, 30,000 Nm3/hr (17,655 scfm) from 900 C (1,652) to
300 C (572 F). There were 12 spray nozzles supplied by two pumps of 15
m3/hr (66.0 gpm) at 33 bar (479 psia) capacity. At maximum cooling, the
water consumption rate was 12 nr/hr (52.8 gpm). Power capacity of each
pump motor was 30 kW at 2,900 rpm. For only low-rate gas cooling, the
chamber was provided with a fan to inject dilution air.
In summer, when some of the heat cannot be used, up to two thirds
of the boiler capacity can be dissipated in air-cooled heat exchangers.
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26
Primary Air
The primary air blower has a capacity of about 30,000 Nnr/hr
(17,655 scfm) at 200 mm water (7.9 in). It is supplied through one main
damper to three under-grate zones, each controlled by a manually
adjustable damper. These latter damper settings are seldom changed. The
main flow damper can be controlled from the control room.
Secondary Air
About 10 percent of the primary air volume is available as
secondary air at a pressure of 200 to 250 mm water (7-9 to 9-8 in). This
air can be injected through ports in the furnace roof as shown in Figure
13-M. However, this air is seldom found necessary as sufficient burning
time and gas mixing are usually provided by the cyclonic after-combustion
chamber. Hence, usually only enough secondary air flows to cool the
roof-ports and connected piping.
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27
ENERGY UTILIZATION
Sludge Dryer
As already shown in Figure 13-2, the Horsens wastewater treatment
plant serving a population of 38,000 was built adjacent to the refuse
burning plant so that the difficult problem of sewage sludge disposal
could be partially solved by partial drying of the sludge.
Figure 13-8 is another schematic view of the plant in which the
rotary kiln type of dryer is emphasized
Typical analyses by the city laboratory of sludge pumped to the
dryer are as follows:
May 2H, 197*. Sept. 5, 1977
pH 5-52 7.2
Dry Solids, % 13.3 6.5
Combustible, % of DS 66.7 46.7
The sludge is coagulated at the wastewat.er plant by means of a
polyelectrolite and is then centrifuged before being pumped to the dryer.
The rotary kiln receives digested sludge from the sewage plant
and reduces it from its nominal 5 percent dry solids content to
approximately 70 percent dry solids. Hot flue gases and sludge are fed
into the rotary kiln at the same end. The rotating part is carried on two
rollers for axial control. A special scoop system ensures effective
contact between flue, gases and sludge. The rotary klin is insulated with
rockwool, covered with steel plate. The inlet end is lined with refractory
brick.
The incoming sludge is fed by a monopump and the dried sludge is
emptied by means of a spiral conveyor which leads the dried sludge to the
clinker transport system, directly out of the building to a storage area.
There are then four possibilities for disposal of the dried
sludge:
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i
w
M
il
o ^
"P
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29
(1) Deposit with the clinker
(2) Burn in the furnace
(3) Utilize as fertilizer
(4) At present, it is deposited in the landfill. Later it may
be spread in woodland to provide soil nutrients.
The kiln has the following specifications:
Rotary dryer diameter: 2.5 m (8.2 ft)
Length of dryer drum: 16 m (52.5 ft)
Incoming sludge: Approx. 5 percent dry solids
Outgoing matter: Approx. 70 percent dry solids
o
Capacity: 5 m /hr (22 gpm) of wet sewage sludge
Inlet flue gas temperature: Approx. 900 C (1,652 F)
Outlet flue gas temperature: Approx. 225 C (437 F).
The sludge is reduced from approximately 5,000 kg/hr (11,000
Ib/hr) to approximately 360 kg/hr (792 Ib/hr) by going through the drying
process. This represents an evaporation heat rate of about 2.70 Gcal/hr
(10.2 M Btu/hr).
Some difficulty was encountered with odor from the kiln until
high enough operating temperatures were assured on startup and shutdown.
District Heating System
Horsens is heated in part by a privately-operated hot- water
distribution system supplied from three oil-fired plants. In 1976, the
operator of one of the systems requested supplemental hot water from the
refuse plant which required the addition of the boiler, already described,
and a 1.8 km (1.1 mi) transmission and return pipe which the city
installed at a cost of about 2.5 x 106 Dkr ($416,700 § 6 Dkr/$). With
interest rates of 13 to 14 percent, it is estimated that the line will be
a
paid for in 10 years. It will save about 2,500 tonnes (2,778 nr) (17,475
barrels) of oil per year. At a cost of 600 Dkr/tonne of oil ($0.34/gal § 6
Dkr/$), this represents a saving of 1,497,260 Dkr ($249,500)/yr.
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30
Pipeline
The new hot-water pipeline utilizes a new pipe insulation
developed by the organization of Danish communities which use district
heating, Tjaerkam Pagniet of Nyborg. The conventional asphalt covering
around the steel pipe is filled with porous insulating mineral granules.
The protective covering can be repaired by enclosing any gap or break in
the covering in a temporary shield, then filling the gap with the granules
followed by hot asphalt. The assembly is believed to be very effective in
insulating the pipe while preventing corrosion.
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31
POLLUTION CONTROL EQUIPMENT
The partially cleaned gases that leave the cyclonic
after-combustion chamber are cooled in the boiler and then pass to an
electrostatic precipitator built by Svenska Flaktfabriken according to the
general specifications as follows:
Flow rate: 36,000 Nm3/hr (21,186 scfm)
Entering temperature:
With spray cooler 300 C (572 F)
With boiler 220 C (1*28 F)
Dust load (at 10$ CO ):
Entering 5 g/Nm3 (2.194 gr/scf)
Leaving (max) 180 mg/Nm3 (0.078 gr/scf)
Rectifier 50 kv, 800 ma
Precipitator volume 134.4 m3 (4,730.9 ft3)
2 2
Average flow area 21 m (226 ft )
Velocity at stp 0.48 m/sec (1.6 fps)
The precipitator design was preceded by a flow model study which
was deemed essential because of the complicated flow patterns produced by
the combined flow of gas partially from the spray cooler and partially
from the sludge dryer. In March, 1977, it was tested twice by the Horsens
Levnedsmi ddell aboratorium (Environmental Laboratory, formerly thf.
Veterinarian and Food Lab), with emission results of 165 and 178 mg/Nm^
corrected to 10 percent CO .
The outdoor precipitator is insulated with 100 mm (4 in) of
rockwool encased in aluminum. Mechanical rapping is provided for both
charging electrodes and collector plates. The collection hoppers are
electrically heated to prevent condensation.
The fly ash is removed from the hoppers by a Redler conveyor. At
first, the dry fly ash was added to the wet grate residue but that
produced intolerable dust. Then the fly ash was mixed with the sludge
leaving the drying kiln but a chemical reaction occurred. Now they are
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32
attempting to form clinker with the sludge in the kiln. If the metal
content is not high, it might have some value as soil nutrient. Tests by
the environmental laboratory have established that the fly ash is not
harmful if ingested by animals.
The plant staff are well pleased with the precipitator
performance as it has required minimal maintenance, although they observe
that some degradation of collection efficiency has occurred in 4 years of
operation.
Induced Draft Fan
The cleaned gases pass from the precipitator to the induced draft
fan. The gas flow rate is modulated by a servo-controlled slide damper
usually set to maintain a furnace vacuum of 10 to 15 mm water (0.4 to 0.6
in). If power to the fan motor fails, the control damper closes and a
separate emergency damper opens to bypass the precipitator so as to
protect it from excessively high-temperature gases.
Chimney
The induced draft fan discharges to a reinforced concrete chimney
60 m (197 ft) high, 4.5 m (14.8 ft) outside diameter, which is large
enough to contain two steel flues, only one of which is now installed. The
flue is insulated with rockwool.
Residue Disposal
The quenched residue is hauled to the adjacent landfill in a
dammed area of the fjord.
A sample of the burned residue is analyzed daily by the city
laboratory for combustible content by heating the dried residue in air to
600 C (1,112 F) for a long enough time that the combustible matter is
oxidized. The following are some typical values of combustible content of
the dry solids in percent:
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33
Day
Sampled
Monday
Tuesday
Wednesday
Thursday
Friday
Date
July 5
3-1
0.8
1.6
2.0
3-2
of Analysis (1977)
Aug. 10 Sept. 15
3-8 M.O
2.4 1.8
3.0 2.1*
5.6 3-5
2.9 2.0
These results indicate consistently good burnout. The plant
specification called for a value of 5 percent combustible. A daily check
on the trend of this number is a useful clue to the general performance*of
the furnace. As in all analyses of heterogeneous materials, the si?;e of
sample and mode of sampling can be critical in producing useful numbers.
An occasional duplicate sample submitted for the same day would be helpful
in assessing the data variability.
Operating Routine
The plant is down Saturday and Sunday for repairs. The other 5
days of operation is not at a steady pace but is on a varied schedule as
follows: .
Monday 6:00 a.m. Startup every other Monday.
Monday 2:00 p.m. On alternate Monday mornings the
boiler and grate are cleaned which
delays plant startup until 2:00 p.m.
Operation is then continuous.
Tuesday Operation around the clock.
Wednesday Operation around the clock.
Thursday 10:00 p.m. Shut down
Friday 6:00 a.m. Start up
Friday 10:00 p.m. Shut down.
Thus, of the total of 120 hours in a 5-day week, the plant
operates 101 hours one week and 96 hours on the alternate weeks. After
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34
Christmas and Easter, the load Is such that 7-day, around the clock
operation is required.
On weekend shutdowns, the induced draft fan is kept operating at
a low rate to keep the system ventilated and dry. The refractory setting
i
remains warm so that at the time of startup Monday morning the air flow
entering the boiler is still about 40 C (104 F).
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35
EQUIPMENT PERFORMANCE ASSESSMENT
Early problems resulting from higher than expected heat value of
the refuse have been solved by some refractory revisions plus judicious
furnace operation to avoid firing too much industrial refuse. In the 1
years of operation, only two truck loads of refuse have had to be sent to
the landfill because the plant was down, except for the period in 1977
while the spray cooling chamber was being replaced by the waste heat
boiler. This is especially notable when one considers that there is only
one line, i.e., no redundancy.
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36
POLLUTION CONTROL ASSESSMENT
The electrostatic precipitator has been very satisfactory. At
first, some odor problem was encountered during startup and shutdown from
incomplete burning of sewage sludge. This was corrected by assuring high
enough temperatures in the rotary kiln before the sludge is injected.
Plant wastewaters are minor and are sent to the sewage plant. The
dried sewage sludge is not burned because of concern for some of the
metals content in the sludge becoming gas-borne and passing through the
precipitator as fine dust. So far, it can be land spread satisfactorily.
The burned grate residue is satisfactorily disposed of in the
enclosed area of the nearby fjord, which has been designated for land
reclamation. Although there is much concern in all of Denmark that surface
and groundwaters be protected from leachate from landfills, there is less
concern here for the relatively small amount of leaching that might reach
the saltwater of the Horsens Fjord. Also, extensive measurement of
leachate from incinerated residue at Copenhagen has indicated that the
metal oxides in the residue are not readily leached.
Some experimentation has been conducted by the Karl Kroyoer
Laboratory in the possibilities of using the residue to make roofing
tiles. The Kroyoer organization has previously developed the Destrogas
process which may be applicable for pyrolysis of waste.
Noise
Danish regulations require that the noise level should not exceed
50 dbA at the fence of this type of plant. If in a residential area the
limit is 45 dbA, day or night. There have been no problems in this
waterfront area and no noise measurements have been made.
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37
PERSONNEL AND MANAGEMENT
Erling Petersen is Director of Solid Waste Management and
Wastewater Treatment for the Horsens area. Actual operation of both plants
is managed by Finn Larsen whose office is in the town hall. The plant
foreman is assisted by 9 shift workers who work 40 hours per week. The
total staff at the refuse burning plant is 10.
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38
ENERGY MARKETING
Since the hot water boiler and 1.8 km connecting pipe has been in
operation only since May, 1977. there has not been enough time to
accumulate much data on the new energy now being fed to one of the private
district heating systems. However, some planning is being done regarding a
possible 2.5 km (1.5 mi) connecting line to another plant six times as
large as the first one. The cost of the line through part of the city
would be 6 million Dkr ($1 million g 6 Dkr/$). If that plan materializes,
the plant would install its second boiler-furnace and much more refuse
would be needed from neighboring communities.
The district heating plant is charged for the energy received at
a rate calculated as 0.12 times the cost of heavy oil per tonne. When the
refuse plant began supplying hot water to the system in May, 1977, oil
cost 540 Dkr/tonne (30.7 cents/gal § 6 Dkr/$). By September, 1977, the
cost was 555 Dkr/tonne and a government tax of 80 Dkr/tonne brought the
total to 635 Dkr/tonne (36.1 cents/gal). Therefor*, in May, the charge for
the heat delivered as heated water was 6H Dkr/Gcal and rose to 76.2
Dkr/Gcal ($3-20/MBtu § 6 Dkr/$) in September, 1977 at the time of this
visit. For comparison, a homeowner in Horsens buying distillate oil for
his residence in September, 1977, paid 1,000 Dkr/tonne (85-3 Dkr/Gcal)
(50.5 cents/gal) ($3-58/M Btu), including taxes (based on 42 oil with a
specific gravity of 0.8 and a higher heat value of 1^11,000 Btu/gal).
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39
ECONOMICS
Capital Cost
The plant was built in 1973-1974 as a turnkey project within the
contract price which was composed of the following:
Equipment, installed 4,631,152 Dkr
Sprinkler system 85»315
Building including stack 3,639,800
Weighing scale 113,900
Rotary sludge dryer, installed 1,795,406
Garage 525,850
Miscellaneous: fence, landscape, roads 300,000
TOTAL CONTRACT COST 11,091,423 Dkr
There was no overrun. The building and stack are large enough to
accommodate a second unit. This total cost results in a capacity cost for
the 5 tonne/hr unit of 92,451 Dkr/daily tonne of capacity ($l4,008/ton § 6
Dkr/$). Compared to steam generators, this cost is very low.
However, in 1976-1977, the hot water boiler and transmission pipe
were built for the following additional 'costs:
Boiler, installed 1,750,000 Dkr
Building modification 85,000
Sludge centrifuge, dryer changes 998,600
Building work 120,000
Circulation pump, tank, for district, 190,000
installed
New pump building at district plant 724,200
Hot water transmission line, 1.8 km 1,700,000
Project supervision 221,000
Building changes at Dagnas heating plant 200,000
SUBTOTAL 5,988,800
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Pipeline from satellite station to plant 740,000
Project management 96,200
Booster station 75,000
Extras, estimated 208,544
TOTAL COST 7,108,544
Adding this cost, 7,108,544 Dkr ($1,184,757), to the original
plant cost brings the total waste-to-energy plant cost to 18,103,960 Dkr
($3,033,828). Based on a daily rated capacity of 120 tonnes/day, this is a
capital cost rate of 151,691 Dkr/tonne-day ($22,984/ton-day). This cost is
also comparatively low considering that the pipeline and other costs are
included. A major factor in keeping the costs down is the use of a
low-pressure, firetube water-heating boiler instead of a high-pressure,
water-tube, steam boiler that would be required if power were to be
generated.
Operating Costs
As explained under "Solid Waste Practices", five city trucks, one
suburban truck, and six or seven licensed private trucks altogether
deliver a total of approximately 17,000 paper sacks of residential refuse
each week. The 10,000 sources are taxed 330 Dkr/yr ($55/yr), whether
they have free city collection or if they pay for private collection. This
fee does not include a value added tax of 15 percent (called the MOMS
tax). When the plant was planned, this tax was 7.5 percent. As of October
3, 1977, it increased to 18 percent.
The tipping fee for the weighed industrial waste is 100 Dkr/tonne
($15.15/ton § 6 Dkr/$). For the 4,308.9 tonnes delivered in 1976, this
income totalled 430,890 Dkr ($71,815). This included the Danish value
added tax. Without that tax, the income was 366,256 Dkr ($61,043).
Table 13-2 shows the projected operating budget for 1977 and 1978
which is evidently based on the experience of previous years. A major
increase of expense for 1978 will be the added amortization cost of
1,904,300 Dkr ($317,383) for the new 1.8 km pipeline to the private
district heating system. Partly offsetting that added cost will be the
expected income from the sale of heat, 1,327,000 Dkr ($221,167).
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41
TABLE 13-2. OPERATING BUDGET FOR HORSENS PLANT,
1977-1978 (COURTESY OF CITY OF
HORSENS, MR FINN LARSEN)
Expenses
Administration
Staff salaries and benefits
Utilities and supplies
Property taxes, building repairs,
maintenance
Residue hauling, truck maintenance,
repair
Residue tipping costs
Tools
Equipment maintenance, repair, including
outside labor
Administrative supplies, advertising
Chemical analysis
Amortization of principal, interest
Total Operating Expense
Income
Fees from Geved community
Tipping fees (industrial waste)
Sludge dewatering, drying fee
Sale of heat
Total Income
Net Operating Cost
Number of households
Net cost per household
Budget
1977,
Dkr
70,650
732,600
359,000
103,000
14,000
6,000
20,000
280,000
14,000
5,000
786,200
2,390,450
130,000
368,000
246,000
0
744,000
1,646,450
16,700
98.59
Budget
1978,
Dkr
91,900
971,650
452,000
107,170
14,730
9,000
29,060
321,000
16,650
5,250
1,904,300
3,922,710
150,000
410,000
442,000
1,327,000
2,329,000
1,593,710
17,115
93.12
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42
The net cost of operation per household served is expected to
be 98 to 93 Dkr ($16.33 to $15.50). As totaled earlier, the households
are each charged 330 Dkr/year not including the value added tax. Apparently
the differnece 330 - 98 = 232 Dkr per household is partly placed in the
reserves from which the original plant was financed, but this also cover
the cost of collection, administration and revisions.
The annual inclome form the 17,000 sources is thus 5,610,000
Dkr (935,000) not inlcuding the value added tax. As estimated earlier,
the weight of residential refuse is about 14,600 tonnes/yr (16,000 tons/
yr). Thus, the individual household pays at the rate of abour 384 Dkr/
tonne ($58/ton) for collection and disposal.
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FINANCE
The initial plant cost in 1973 of 11,094,423 Dkr was
self-financed out of bonds and reserves. In future financing, the plan is
to build up the reserves again to the point that private borrowing can be
avoided because the interest rates for such money is now 18 percent. If
conmunity reserves are used, the internal opportunity interest cost is
about 10 to 12 percent.
At present, the total Horsens community budget is 225 million
Dkr. About half of that is spent for education. Tnus. the 18 million Dkr
spent so far for the waste-to-energy system is a relatively small item. In
presenting the project to the public, it was estimated that"i*t would
involve a daily per-capita cost of about 1.5 Dkr/day (25 cents/(Jay). The
new wastewater treatment plant costs about the same. The citizens readily
accepted this cost of a cleaner environment which totaled less than the 12
to 14 Dkr ($2.00 to $2.33) cost of a pack of cigarettes!
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APPENDIX A
NEW PLANT AT AARHUS-NORD
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APPENDIX A
NEW PLANT FOR AARHUS-NORD
An expansion of some of the methods evolved at Horsens is
embodied in the new plant at Aarhus Nord scheduled to be completed in
early 1978. The Aarhus Nord plant is about km north ot Horsens.
Figure 13-A1 is a cross section of the Aarhus Nord plant. As with
the Horsens plant, this much larger plant will dry sludge and provide hot
water for district heating. A distinct difference from Horsens is that the
Aarhus-Nord plant uses a water-tube boiler instead of a firetube boiler.
However, there are no water-tube walls in the furnace.
The design capacity is for 3710000 tonnes/yr (40,700 tons/yr) of
municipal refuse, 18,000 tonnes/yr (19.800 tons/yr) of industrial refuse,
and 8,100m /yr (2,140,020 gallons/yr) of sludge from a current population
of 240,000.
There are two smaller batch-type units in the basement: one for
pathological and the other for nontoxic oily and grease wastes.
There are two complete refuse and sludge lines, each having a
rated capacity of 8 tonnes/hr (8.8 tons/hr). Thus, the total rated
refuse-burning capacity is 384 tonnes/day (422 tons/day).
The two boilers are of three-pass design built by Volund at
Esbjerg, Jutland, only 100 km (62 mi) west. The first two vertical passes
are completely open radiation passes partially lined with water tubes. The
final vertical pass is a conventional one containing bundles of horizontal
8 mm (1.5 in) tubes that will be cleaned by falling steel or aluminum
pellets. A major concept in this design is to minimize the danger of tube
corrosion, even though the output water temperature will be relatively
low, ranging from 150 C to 210 C (302 F to 410 F).
The hot water is to be piped 5.5 km (3.4 mi) to a distributing
station at Vorrevangen where a heat exchanger will produce 90 C (194 F)
water to be distributed at a rate of about 25 Gcal/hr (99.2 M Btu/hr)
(104.7 GJ/hr) to about 2,500 residences and flats. The pipeline and heat
exchanger cost 18 million Dkr ($3 million) in 1977. The oil-heated
-------
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A-3
district heating system already serves about 4,000 units, about 70 percent
of them individual residences, and is expected to be expanded in a few
years to 5,000 or 6,000 units. Only 10 percent of the Aarhus-Nord energy
will need to be wasted in the simmer.
Development of the Aarhus System
Although Denmark has been a world leader in recovering useful
energy from the burning of community wastes, mostly for district heating,
very little for electricity, the recent Aarhus history is an interesting
example o" how some communities all over the world have been avoiding
incineration. This policy usually stems from the attitude that it is wrong
to burn waste when some useful product such as compost and metals and
glass can be recovered from it. Accordingly, in 1957, a Dano, rotary drum,
compost plant was built only 1 km (0.6 mi) west of the center of Aarhus.
It still operates but will be closed in 1980 because most of the compost
cannot be either sold or donated and the landfills for the compost have
become objectionable.
In 1965, an English shredder was added to the system and sewage
sludge was introduced to the Dano process. There have since then been some
odor problems from the compost landfills.
In 1970, the Danish trend of consolidation of communities reached
Aarhus and 21 other towns were brought into the Aarhus AMT (region). The
AMI Council had the authority to direct changes in the waste disposal
practice of these towns which usually used landfills. But no one wanted
new landfills nearby. On June 1, 1973, a new regional waste disposal plan
was issued which determined on the construction of Aarhus-Nord. It was to
begin operation in mid-1977, but owing to a very serious construction
crane accident in early 1977, startup was delayed until February 1, 1978.
The plan also includes construction soon of Aarhus-Syd, south of town.
Six different sites were considered for each of the north and
south plants. They had to be near to district heating centers. The north
site is 80 m (262 ft) above sea level. The 100 m (327 ft) chimney provides
for good dispersal of residual emissions.
-------
A-4
The authors are indebted to the following officials of the City
of Aarhus for their discussion and tour of the Aarhus-Nord construction
site: 0. Villadsen, Chief Engineer; and T. Truelshoi, Principal Engineer
for Wastes.
-------
APPENDIX B
INDUSTRIAL AND HAZARDOUS WASTE TRANSFER STATION
AT HORSENS AND TREATMENT AT NYBORG. DENMARK
Horsens Transfer Station Picture
Nyborg, Denmark Plant Brochure
Von Roll/Environmental Elements Literature
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Regional Industrial Waste
Treatment Centre
A wide-spread and well-organized collecting service
ensures that all industrial wastes from a particular region
or even from an entire country can be transported to, and
ecologically treated in. an industrial waste treatment
centre Such centralization is the economical prerequisite
for a modern, large-scale designed industrial waste treat-
ment plant which complies with all requirements A cen-
trally placed facility of such proportions should be capable
of processing liquid, emulsified, pasteous and solid wastes
of every kind In our case, we had to cope with the treatment
of the industrial wastes of a medium-sized country com-
prising numerous islands and a peninsula (Denmark)
- combustion in plant I
- combustion in plant II
The combustion part was divided into two indroen-
dently operating installations, whereby in the combustion
chamber of plant II only highly chlorinated hydro-carbons
are burnt Because of this solution, only a relatively small
amount of flue gas of known composition has to be scrubb-
ed Flue gas from the combustion of the remaining wastes
contains comparatively few noxious substances and,
therefore, needs not to be scrubbed, "dry" dedusting is suf-
ficient here.
Problem
Treatment of 80,000 metric tons per year of industrial
waste, the aim being to recover as much raw materials as
possible for recycling
The following wastes are to be treated
a) mineral waste oils
b) polluted organic solvents, residues from destination and
chemical side products
c) paint and varnish residues, waste facts, bitumen, resin,
glue, oil sludge, etc
d) chlorinated hydro carbons (liquid)
e) anorganic wastes, galvanic sludge, chromates and
cyanides
f) solid waste, packing materials, synthetics, chemical
side products, oil-polluted earth, etc
The wastes are delivered in tank lorries, rail tank cars as
well as in barrels and containers
Aim
- recovery of as much raw materials as possible
- combustion of residuals with utilization of the produced
energy under observance of existing Regulations with
respect to burn-out and air purity
- most economical and self-supporting operation
- concept and design of the plant has to allow for easy
adaptation to the ever-changing conditions in quantity
and composition of refuse
Solution
The process scheme (opposite page) shows the pro-
cesses selected for the various wastes and how they are
arranged The mam processing stages are as follows
- delivery, inspection and unloading
- intermediate storage
-.preparation
- decanting
- neutralization and decontamination
- intermediate storage
D
Legend to diagram
Pre-treatment
1 reception of material groups A-F
2 intermediate storage
3 decantation of material groups A, B and D
4 oil-storage tank
5 sludge silo
6 intermediate tank
agitator tank
agitator tank
neutralization, decontamination and filter press for
material group E
Combustion
10 solids charging (material group F)
11 barrel charging (material group C)
12 rotary kiln
13 after-burning chamber
14 special burner
15 slag and ash removal
16 tail-end boiler
17 flue-gas dedusting
18 induced draft fan
19 stack
20 combustion chamber for material group D
21 flue-gas scrubber
22 cyclone
23 pre-thickener
24 neutralization
25 after-treatment and drum filter
-------
-------
HAZARDOUS WASTE DISPOSAL PLANTS
ROTARY KILN SYSTEM
ENVIRONMENTAL ELEMENTS CORPORATION
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-------
TABLE EXCHANGE RATES FOR SIX EUROPEAN COUNTRIES,
(NATIONAL MONETARY UNIT PER U.S. DOLLAR)
1948 TO FEBRUARY, 1978(a)
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1953
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978 (Feb.)
Denmark.
Kroner
(D.Kr.)
4.810
6.920
6.920
6.920
6.920
6.920
6.914
6.914
6.914
6.914
6.906
6.908
6.906
6.886
6.902
6.911
6.921
6.891
6.916
7.462
7.501
7.492
7.489
7.062
6.843
6.290
5.650
6.178
5.788
5.778
5.580
France
Francs
(F.Fr.)
2.662
3.490
3.499
3.500
3.500
3.500
3.500
3.500
3.500
4.199
4.906
4.909
4.903
4.900
4.900
4.902
4.900
4.902
4.952
4.908
4.948
5.558
5.520
5.224
5.125
4.708
4.444
4.486
4.970
4.705
4.766
W . Germany
Deutsch Mark
(D.M.)
3.333
4.200
4.200
4.200
4.200
4.200
4.200
4.215
4.199
4.202
4.178
4.170
4.171
3.996
3.998
3.975
3.977
4.006
3.977
3.999
4.000
3.690
3.648
3.268
3.202
2.703
2.410
2.622
2.363
2.105
2.036
Netherlands
Guilders
(Gl.)
2.653
3.800
3.800
3.800
3.800
3.786
3.794
3.829
3.830
3.791
3.775
3.770
3.770
3.600
3.600
3.600
3.592
3.611
3.614
3.596
3.606
3.624
3.597
3.254
3.226
2.824
2.507
2.689
2.457
2.280
2.176
Sweden
Kroner
(S.Kr.)
3.600
5.180
5.180
5.180
5.180
5.180
5.180
5.180
5.180
5.173
5.173
5.181
5.180
5.185
5.186
5.200
5.148
5.180
4.180
5.165
5.180
5.170
5.170
4.858
4.743
4.588
4.081
4.386
4.127
4.670
4.615
Switzerland
Francs
(S.Fr.)
4.315
4.300
4.289
4.369
4.285
4.288
4.285
4.285
4.285
4.285
4.308
4.323
4.305
4.316
4.319
4.315
4.315
4.318
4.327
4.325
4.302
4.318
4.316
3.915
3.774
3.244
2.540
2.620
2.451
2.010
1.987
(a) Exchange Rate at end of period.
Line "ae" Market Rate/Par or Central Rate.
Source: International Financial Statistics: 1972 Supplement; April, 1978, Volume
XXXI, No. 4, Published by the International Monetary Fund.
-620-007/6318
yo 1828f
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