United States Office of Water and SW 176C.14
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 14
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PtLe.pu.blicjation -Lbtue, ^on EPA JU.bwU.eA
and State. SoLid Watte. Ma.nagtne.nt Age.ncA.eA
EUROPEAN REFUSE FIRED ENERGY SYSTEMS
EVALUATION OF DESIGN PRACTICES
Krefeld Co-Disposal Plant,
Krefeld, West Germany
Thit ttu.p >ie.potit (SW-/76c. 14}
the. Ofiface. o^ Solid Watte. undeA contract no. 68-07-4377
and AJ> tie.p?iodu.ce.d at, Aecex^ued fanom the. contsiactoi.
The. fcndingA should be. at&u.bute.d to the. c.on&iacto>i
and not to the. 0^-tce oft Solid Watte..
Copies will be available from the
National Technical Information Service
U.S. Department of Commerce
Springfield, VA 22161
Volume 14
I'.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 signfy 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. 14) in the solid
waste management series.
Fr\':r.?r:rn:r,*M Protection Agency
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ACKNOWLEDGEMENTS
We are pleased to acknowledge the generous and competent
assistance which we received from the following whose help made this
report possible:
Werner Schlotmann Vereinigte Kesselwerke, (VKW), Duesseldorf
Hans Norbisrath Vereinigte Kesselwerke, (VKW), Duesseldorf
Klaus Feindler Grumman Ecosystems, Inc., Bethpage, L.I., New York
Jurgen Boehme Vereinigte Kesselwerke, (VKW), Duesseldorf
Wilhelm Korbel Krefeld plant manager
Heinz Stogmuller Vereinigte Kesselwerke, (VKW), Duesseldorf
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ii
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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iii
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
ACKNOWLEDGEMENTS i
PREFACE ii
SUMMARY 1
STATISTICAL SUMMARY 3
Krefeld Plant 3
DEVELOPMENT OF THE SYSTEM 6
COMMUNITY DESCRIPTION 8
Geography 8
Government and Industry 8
SOLID WASTE PRACTICES 10
Solid Waste Generation 10
Solid Waste Transfer and/or Pretreatment 10
Solid Waste Disposal 10
REFUSE-FIRED STEAM GENERATOR EQUIPMENT 12
Furnace Hopper and Feeder 14
Primary Air Supply 15
Secondary Air 15
Burning Grate ....... 16
Furnace Wall (Combustion and First Pass Radiation
Chambers) 19
Firing of Sewage Sludge 19
Second Boiler Pass - Superheater and Convection Section ... 21
Economizer 21
Boiler Water Treatment 21
Heating Surface 22
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TABLE OF CONTENTS
(Continued)
Page
Heat Release Rate 22
Energy Utilization Equipment 24
Sludge Treatment and Burning 25
Wastewater Discharge 31
POLLUTION CONTROL EQUIPMENT 32
Electrostatic Precipitators 32
Scrubbers 34
Stack Construction 36
Noise 36
PERSONNEL AND MANAGEMENT 37
ECONOMICS 38
Capital Investment 38
Operating Costs 38
Revenues 38
REFERENCES 39
LIST OF TABLES
Table 5-1. Estimated Burning Volume Dimensions and Heat Release
Rates for Each of the Two Krefeld Furnaces 23
Table 5-2. Sludge Drying Mill Design Conditions for Waste of
Three Lower Heating Values . 29
Table 5-3. Characteristics of the Two Krefeld Precipitators ... 33
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LIST OF FIGURES
Page
Figure 5-1. Krefeld Plant Exterior View 2
Figure 5-2. Krefeld Waste Processing Facility; Wastewater
Treatment Plant on Left, Refuse- and Sewage-Sludge-
Burning Plant on Right 9
Figure 5-3. Map of the Krefeld Refuse Burning and Wastewater
Plants 11
Figure 5-4. Krefeld Waste-to-Energy Facility: Plan View 13
Figure 5-5. Six Drum Walzenrost (Roller Grate); Also Commonly
Known as the Duesseldorf Grate 17
Figure 5-6. Cross-Sectional View of Krefeld Plant 20
Figure 5-7. Krefeld Sludge-Processing and Burning Systems .... 26
Figure 5-8. Calculated Drying Mill Conditions as a Function
of Sludge Drying Rate 27
Figure 5-9. Calculated Dust Load of the Flue Gas as a Function
of the Amount of Ash on the Grate 30
Figure 5-10. Supply and Wastewater Systems 35
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SUMMARY
This plant is located on a broad, thinly-populated industrial
area outside of Krefeld, West Germany about 30 km (20 mi) northwest of
Duesseldorf. It serves a population of about 300,000,
The Krefeld plant is a part of a "sanitary park" containing
the sewage treatment plant and the solid waste facility. The plant is
unique in that it is the first large plant ever built to burn partially
dried sewage sludge in suspension above the burning solid waste fuel bed.
Initial operation began in 1975 but because of the unique
new co-firing system being applied and also because of the need to add
scrubbers to remove HC1 and HF from the exhaust gases, the plant has not
yet been formally accepted. Accordingly, the manager was not free to
release any operating data.
In the manner of mass burning of refuse, it is nearly identical
to the new plant which was visited at Wuppertal. The comparative oper-
ating data, as they are developed from these two new and similar plants,
will be of interest to note the effects in plant performance of sludge
burning with refuse at Krefeld compared to straight refuse at Wuppertal.
Figure 5-1 shows a view of the Krefeld refuse burning plant
from the adjacent wastewater plant.
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STATISTICAL SUMMARY
Krefeld Plant
Community description:
Area (square kilometers)
Population - Refuse basin (number of people) about 300,000 or 400,000
Population - Sewage sludge basin (number of people) about 600,000
Key terrain feature flat - Rhine River Valley
Solid waste practices:
Total waste generated per day (tonnes/day) 300 t/d
Waste generation rate (Kg/person/day)
Lower heating value of waste (Kcal/kg) 1700 - 1800 kcal/kg
Collection period (days/week)
Cost of collection (local currency/tonne)
Use of transfer and/or pretreatment (yes or no) No
Distance from generation centroid to:
Local landfill (kilometers)
Refuse fired steam generator (kilometers)
Waste type input to system mixed resid., indus.
Cofiring of sewage sludge (yes or no) Yes
Development of the system:
Date operation began (year) 1976
Plant architecture:
Material of exterior construction Aluminum, concrete
Stack height (meters) 70
Refuse fired steam generator equipment:
Mass burning (yes or no) Yes
Waste conditions into feed chute:
Moisture (percent) •= 20%
Lower heating value (Kcal/kg) 1700 - 1800
Volume burned:
Capacity per furnace (tonnes/hr) 12 t/h Nominal Capacity
Number of furnaces constructed (number) 2
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STATISTICAL SUMMARY
(Continued)
Capacity per system (tonnes/day) 560 t/d (2 x 280 t/d)
Actual per furnace (tonnes/day) 280 t/d
Number of furnaces normally operating (number) one
Actual per system (tonnes/day) 280 t/d
Use auxiliary reduction equipment (yes or no) Yes, for bulky refuse
Pit capacity level full:
(Tonnes) 2300
(m3) 6000
Crane capacity:
(Tonnes) ^3
(m3)
Feeder drive method Hydraulic
Burning grate:
Manufacturer Vereinigte Kesselwerke
Type Roller grate Duesseldorf
Number of sections (number) 6
Length effective 14.24 m
Width overall 3 m - #: 1.5m
Primary air-max Nm3/hr 73,800
Secondary air-overfire air-max Nm /hr 13,700
3
Furnace volume (m )
Boiler wall tube diameter (mm) 57
2
Furnace heating surface (m )
Auxiliary fuel capability (yes or no) Yes (heavy fuel oil or distillate and waste oil)
Use of superheater (yes or no) Yes
Boiler
Manufacturer Vereinigte Kesselwerke
Type Natural circulation
Number of boiler passes 3
Steam production per boiler (kg/hr) 42,000
Total plant steam production (kg/hr) 84,000
Steam temperature (C) 37^
Steam pressure bar 23
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STATISTICAL SUMMARY
(Continued)
Use of economizer (yes or no)
Use of air preheater (yes or no)
Use of flue gas reheater (yes or no)
Cofire (fuel or waste) input
Use of electricity generator (yes or no)
Type of turbine
Number of turbines (number)
Steam consumption (kg/hr)
Electrical production capacity per turbine (kw)
Total electrical production capacity (kw)
Turbine back pressure (bar)
Yes
Yes
Yes
sludge
Yes
back pressure
2
17,500
1400
2800
3.7
User of electricity ("Internal" and/or "External") Internal and External
Energy utilization:
Medium of energy transfer
Temperature of medium (° C)
Population receiving energy (number)
Pressure of medium (bar)
Energy return medium (verbsrl)
hot water
130/80
Industrial plant making railroad cars
10
hot water (70 C)
Pollution control:
Air:
Furnace exit conditions
3
Gas flow rate (m /hr)
3
Furnace exit loading (mg/Nm )
98,600
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DEVELOPMENT OF THE SYSTEM
In the 19-50's it became evident that the city landfill at
Fluennertzdyk, operating since 1928, was past half of its useful life
and an effort was made to develop a compost system. In the dedicatory
brochure^ for the present Krefeld plant, dated March 11, 1975, Krefeld
City Director Theo Fabel described the small pilot compost operation
built on the theory that a natural use of the waste would be better than
burning. However, meanwhile the Fluennertzdyk landfill became such a
steep pile that operations on it became hazardous. Also, frequent
refuse fires there caused much local annoyance from smoke and odors.
The composting effort was not deemed promising and in 1961 a
Dr. Straub was engaged to study the alternatives. His report in 1964
suggested that incineration would be the best of the alternatives. Further-
more, the optimum solution suggested was to place an incineration plant
adjacent to a wastewater treatment plant. However, although incinera-
tion was thought to be best, it is also the most expensive alternative.
Thus, in view of the city's other needs for a bathing center, clinic,
school, and new streets, there was a suggestion that rail haul be used
to carry the refuse to abandoned clay pits at Lobberich. However, the
geology of that place was decided to be unfavorable for proper land
disposal. Accordingly, an incineration plant had to be considered,
especially since the Fluennertzdykt landfill was finally estimated to
be exhausted in 1975.
In 1970-71 a feasibility study of a proposed plant was made
considering the combined firing of refuse and dried sludge. The study
was by Projekta of Duesseldorf. On the basis of the feasibility report
Projekta the prepared the specifications for the plant. Four bids were
received. The evaluation of the bids was made by Kraftanlagen of Heidel-
berg.
There were two methods for sludge burning considered. One, -
proposed by Vereinigte Kesselwerke would partially dry the sludge in a
centrifuge and then complete the drying in suspension in a hammer mill
supplied with hot flue gases. The dried dust would then be conveyed by
the hot gas flowing into the refuse-burning furnace.
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The other method, proposed by Techfina would dewater It in
a filter press, thermally condition the sludge, then fire it with the
refuse on the grate.
On evaluation of the bids, the suspension burning system for
the sludge was found to have a lower capital cost by DM 7.6 x 10 ($3.2 x
10 ). Also, the suspension burning method has already been developed
for the drying and burning of high-moisture coals, hence, was judged to
be ready for translation to sludge burning. In addition, mass burning
of dried sludge along with refuse required about twice as long to burn
sludge on a grate as does refuse. For these various reasons the VKW
bid was accepted. Construction of the plant began May 18, 1973.
Construction was essentially complete in late 1976 but acceptance tests
were not expected at the time of our visit, May 20-23, 1977, until
July, 1977.
The plant is owned by the City of Krefeld.
The plant manager is Wilhelm Korbel.
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COMMUNITY DESCRIPTION
Geography
The flat surroundings of the plant shown in Figure 5-2 are
typical of the terrain in the Krefeld area which is a highly industrial-
ized community located about 30 km (20 mi) northwest of Duesseldorf.
As is also evident in Figure 5-2, there is no densely populated area in
the immediate vicinity of the plant—only an occasional factory.
The plant receives considerable amounts of industrial waste.
All of the energy available for export from the plant goes to
one industry 2.5 km away, in the form of hot water at 130 C (266 F)/80 C (176F).
An extensive public recreation area and large, attractive
shopping center are in operation and undergoing development and expansion
in the immediate vicinity of the plant.
Government and Industry
Krefeld is an industrial city near the much more intensely in-
dustrialized areas of Duesseldorf and Duisburg.
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FIGURE 5-2.
KREFELD WASTE PROCESSING FACILITY;
WASTEWATER TREATMENT PLANT ON LEFT,
REFUSE-AND SEWAGE-SLUDGE-BURNING
PLANT ON RIGHT.
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10
SOLID WASTE PRACTICES
Solid Waste Generation
Krefeld has operated a municipal landfill since 1928. The
eventual exhaustion of that site led to the 1970-71 feasibility study for
a waste-burning and energy-recovery utilization plant.
The average daily tonnage of refuse generated is about 280
tonnes (308 tons) per day. It is estimated that this is 75-80 percent
municipal and 20-25 percent industrial. The average lower heat value
is assumed to be 1700 to 1800 kcal/kg (3000 to 3200 Btu/lb). The upper
design point is LHV 2500 Kcal/kg.
The new wastewater treatment plant adjacent to the refuse
burning plant provides primary treatment only. Secondary treatment is
to be added later in the area immediately east of the present settling
basins (see Figure 5-3).
Solid Waste Transfer and/or Pretreatment
No transfer stations or pretreatment is provided except that
at the bunker. There is a Lindemann shear for bulky refuse.
Solid Waste Disposal
The burned residue is not processed in any way and is trucked
to a landfill and to the Netherlands for dike construction etc.
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11
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12
REFUSE-FIRED STEAM GENERATOR EQUIPMENT
Waste Input
The plant receives an estimated 280 tonnes of municipal and
industrial refuse per day (308 tons/day). On the basis of a 5-1/2-day
week this sums up to approximately 1540 tonnes (1700 tons) per week or
about 80,000 tonnes per year ( 88,000 tons/year). The estimated aver-
age moisture content is 20%.
Provisions to Handle Bulky Waste
Adjacent to the tipping floor is a 8 tonne (9 ton) per
hour Lindemann hydraulically-driven shear. It will accept objects up to
about 1.8 m (5.9 ft) and reduce them to pieces about 300 mm by 600 mm
(1 ft by 2 ft). It has a shearing force of 250 tonnes (275 tons). It
is operated eight hours per day by one operator. The reduced material
falls directly into the pit.
Waste Storage and Retrieval
The building floor plan, Figure 5-4, shows the bunker, furnace
room, and associated equipment. The bunker is 35 m long and 12 m
3 3
wide (115 ft by 40 ft) and has a storage capacity of 6000 m (7847 yd )
corresponding to an average depth of 14 m (46 ft). Maximum piled capacity
o o
is about 9000 mJ (11,772 yd ). At a refuse density when settled and
3 3
compressed of 645 Ib per yd (0.383 tonnes/m ), this maximum volume rep-
resents a piled storage capacity of 3796 tons (3450 tonnes). With one
unit, 12 tonnes (13.2 tons)/hr operating, this would be about 12 day's
supply.
There are two cranes each of 6.3 tonnes capacity.
The holding capacity of the polygrip buckets is 4 m (5 yd ).
The crane control cab is on the side of the bunker. Control is entirely
manual, not semi-automatic.
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13
13
FIGURE 5-4. KREFELD WASTE-TO-ENERGY FACILITY: PLAN VIEW
(2)
2.1 Tipping area
2.2 Bulky refuse shear
2.3 Auxiliary tipping lane
3.1 Refuse bunker
3.2 Ash bunker
3.3 Ash loading area
4.1 Boiler house
4.2 Boiler pumps
4.3 Residue quencher
4.4 Primary air fan
4.5 Sludge-drying fan
4.6 Firing aisle
5.1 Washroom
5.2 Switch room
6.1 Turbine floor
6.2 Turbogenerator
6.3 Heat exchangers
6.4 Feedwater tank
6.5
7.1 Water treatment
7.2 Stairwell
8.0 Social room
9 Chimney
10 Waste oil facility
11 Cold water basin
13 Flue gas scrubbers
14 Condenser
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14
Fire control for the bunker is available from a water hose
and a water cannon of 150 m /hr capacity (660 gal/min) which uses
clear effluent from the adjacent wastewater treatment plant.
Furnace Hopper and Feeder
The top opening of the hoppers is 4.5 m (14.8 ft) square.
The water-cooled feed chute is 1.8 m by 2.85 m (5.9 by 19.4 ft). A
hydraulically operated damper in the upper part of the chute can be
closed in case of burnback.
The stroke frequency of a hydraulic ram feeder can be con-
trolled from the main control room. The frequency of the ram can be
adjusted between five and fifty strokes per hour. Normal speed is 15 per
hour.
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15
Primary Air Supply
The primary air is drawn from near the top of the refuse bunker
to provide a positive inward flow of fresh air to the bunker area. Each
furnace has a separate radial blovrer made by the Krefeld firm of Buttner-
Schilde-Haas of Krefeld, a member of the Babcock group. Each can supply
up to 73,800 Nm3/hr (43,430 scfm) at 300 mm water static pressure (11.8 in)
The driving motor has a power consumption of 77 kw. The supply of air
to each of the six grate rollers is controlled by a manual damper and the
overall supply is controlled by furnace pressure or it can be manually
adjusted from the control room.
The primary air for each boiler is preheated to 50 C (122 F)
f\
by a steam heated coil made by Duerr. Its heating surface is 760 m
(8178 ft2). The tubes are 35.8 I steel, 2 mm (0.080 in) thick. When
heating air from 20 C to 200 C (68 F to 392 F) at the rate of 50,000 Nm3/h
(29,430 psia) at 225 C (437 F), the heat supplied is 2,816 Gcal/h
(11,790 GJ/h) [11,174 Btu/h]. The corresponding steam consumption is
6500 kg/h (14,313 Ib/h).
Secondary Air
One Buttner-Schilde-Haas radial blower for each furnace supplies
3 3
air at a rate of 3.8 m /sec (13,700 Nm /hr) [7,980 scfm]. The available
air pressure is 970 mm water static (38 in). This air is supplied to
a total of 40 overfire air jets which are 70 mm (2.75 in) diameter in the
front wall and 50 mm in diameter (2 in) in the upper rear wall. All of
the jets are directed downward at an angle. The front wall jets are in
the nose of the front wall so that their downward direction provides
somewhat opposed mixing to the burning gases rising upward out of the
furnace. The rear wall jets are just below the nose of the rear wall
and are directed slightly downward into the initial burning zone of the
furnace.
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16
Burning Grate
Figure 5-5 shows the "walzenrost" (roller grate) which was
developed beginning in 1961 at the Flingern Power Plant, in Duesseldorf,
using a four-roller pilot grate applied to an old formerly coal-burning
furnace. It is manufactured by the Vereinigte Kesselwerke in Duesseldorf
and is generally known as the "Duesseldorf Grate". It provides a sloping
fuel bed as do most European mass-burning grates for refuse. Instead of
using oscillating or reciprocating grate bars to agitate the burning
material and to move the incombustible residues down the slope, the
walzenrost moves the bed by slow rotation of the 1.5 m (4.92 ft) diameter
drums which are formed of cast iron grate sections. Thus, there is
opportunity for a slow tumbling action of the refuse which helps to keep
the fibrous mass loose, exposing new burning surface and allowing for
a continual redistribution of the upward flow or primary air throughout
the bed.
The drums rotate at an adjustable speed of about three to six
revolutions per hour. Instead of being continuously exposed to the hot
fuel bed, each grate bar rotates through a cool zone about half of the
time.
Each grate roll is formed of ten longitudinal sections, each of
which contains 60 curved grate bars. The bars at each side which rub against
the air seal plates are cast of chrome-nickel alloy to resist abrasion. Out
of a total of 600 bars per roll, 12 are cast alloy. There are six rolls
per furnace at Krefeld.
The gap between adjacent rolls is filled by a cast iron wiper
bar spaced about 10 to 15 mm from the adjacent roll. This bar is strong
enough to shear off refuse that may jam in the gap or become attached to
the grate.
The wiper seals are repaired three times a year. Normal wear
of the seal gradually widens the gap which allows larger and larger
pieces of refuse to fall through. A screw conveyor removes such residue
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17
iff v*jv ,. TSTtpi
:>?4?»i^,;.'V*K««cr: >.B
FIGURE 5-5. SIX DRUM WALZENROST (ROLLER GRATE); ALSO COMMONLY KNOWN
AS THE DUESSELDORF GRATE. NOTE THE CAST IRON WIPER
SEALS BETWEEN ADJACENT ROLLS WHICH PREVENT LARGE PIECES
OF REFUSE FROM FALLING OUT OF THE FURNACE (Courtesy of
Vereinigte Kesselwerke)
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18
from underneath the grate but because of occasional accumulation of ash,
this area is inspected once per week and cleaned every four to six months.
The roller shafts are hollow steel. Asbestos air seals at
each end of the shaft require replacement every five or six years. Each
roller constitutes a separate supply zone for primary air. The air enters
the interior of the roll from both ends and flows through the many small
gaps between the interlocking grate bars. The amount of air flow through
each roll can be adjusted.
In older roller cage construction - in a part of the combusion
zone (rollers 2 and 3) - melted light metals, together with sittings, through
the self-cleaning effect of the grate bars, entered the grate cages and
were not removed laterally in one complete revolution. This occurrence is
avoided in new construction. The current roller grate design heat release
rates are for grates which are essentially wider, which therefore permits
higher firing rates, and these are planned for all United States projects.
These firing rates are used in the refuse burning plant at Wuppertal, which
has been in trouble-free operation since 1975.
No. 2 fuel is fired in two sidewall burners to attain furnace
outlet temperature of 900 C (1652 F) before refuse is fired. Federal
law required a startup temperature of only 800 C (1472 F). But, in this case,
where partially dried sewage sludge is to be burned in suspension above
the burning refuse bed, the local pollution control office requires 900 C
to better assure complete combustion on startup. If the startup was
only by means of refuse and sludge ignited in a cold boiler-furnace,
objectionable odors would result from incomplete combustion until the sys-
tem attained near normal operating temperatures.
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19
Furnace Wall (Combustion and
First Pass Radiation Chambers)
These two furnaces are partially water cooled (front and rear roof only)
in accordance with the design and operating experience accumulated by VKW and its
customers at the Duesseldorf plant and various other plants. The 57 mm
(2.3 in) wall tubes are made of ST 35.81 carbon steel, 4 mm (0.157-inch thick").
By means of welded fins, they form a continuous membrane wall. Figure
5-6 shows the plant's cross-sectional view. At the lower part of the
combustion chamber, adjacent to the roller grate, pre-cast carbofrax
blocks are used to protect the wall tubes.
To protect the remaining wall tubes of the combustion chamber
from attack by high temperature flame impingement, they are studded
and then covered with 90% silicon carbide. The welded steel studs are
10 mm diameter (0.4 in) and 20 mm (0.8 in) long. The silicon carbide
coating is approximately 25 mm (1 in) thick. The studs are applied
2 2
at the rate of 2100 per m (195/ft ). The studs and coating are con-
tinued upward into the radiation chamber for a distance of about 3 m
( 10 ft) above the refuse feed opening.
Firing of Sewage Sludge
An unusual feature of this furnace is that the dried sewage
sludge is fired in suspension in hot flue gases at a point (labeled #14
in Figure 5-6) near the lower end of the radiation chamber and within the
section that is coated with silicon carbide. Because the sludge particles
still carry moisture (10%) and because the moisture having been vaporized
out of the sludge is still in the hammermill exit gas, when both the par-
ticles and the vapor enter the hot radiation chamber they will absorb
considerable heat before the particles become heated to their ignition
temperature. At point #13 in Figure 5-6, a substantial amount, 2.7 to
3.9 Nm /sec [5715 to 8256 scfm], of hot flue gases are extracted from
the furnace and sent to the sewage sludge hammermill. In the refuse and
sludge burning plant at Krefeld, incoming sludge has a water content of
74 percent, and a lower heating value of about 413 Kcal/kg. It follows,
therefore, that the firing of this sludge will doubtless provide additional
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21
steam production capacity. Support from an amount of supplementary heat is
required when an unexpected reduction of the lower heating value occurs.
A negative effect of sludge burning on power production, therefore, does
not occur. To the contrary, there is a resulting increase in energy
production. The operating methods of a refuse-fired boiler plant with co-
disposal of sludge do not produce problems with superheater temperature
control. Customary procedures for boiler cleaning are, of course, necessary.
Second Boiler Pass - Superheater and Convection Section
The superheater consists of 50 tubes, 51 mm (2.0 in) diameter
with a wall thickness of 3.6 mm (0.14 in) and formed of 35.8 I steel.
The composition of 35.8 I steel is as follows:
C ^ 0.17% P^ 0.050
Si^« 0.18 S ^ 0.050
Mn^ 0.50 Cr^. 0.030
In West Germany this steel is identified under Standard No. 1.0305.
The gas temperature entering the superheater is estimated to
be 700 to 750 C (1292 to 1382 F). There is one steam soot blower. The
steam flow rate is 42 tonnes/hr (46 tons/hr) at 23 bars (333 psia) and
376 C (709 F).
The boiler convection section consists of six banks of sloping
tubes, also made of 35.8 I steel, 57 mm (2.2 in) in diameter, 3.6 mm
(0.14 in) thick. The boiler water walls are 57 mm in diameter and 4 mm
thick.
Economizer
The economizer is 1.9 by 3.6 by 7 m (6.2 by 12 by 23 ft) and as
shown in Figure 5-6, is contained in the third boiler pass. The tubes are
made of 35.8 I steel, 38 mm (1.5 in) diameter and 3.2 mm (0.13 in) thick.
The boiler water walls are 57 mm in diameter and 4 mm thick.
-------
22
Boiler Water Treatment
Water treatment is provided by the usual deionizing and de-
oxidizing system.
Heating Surface
The approximate heating surface in the various boiler com-
ponents are as follows:
2 f*2
m ft
Water-tube walls*
Boiler -J "*" 1190 12,803
Superheater 252 2,711
Economizer 457 4,919
Total 1899 20,430
The tubular cooler for moderating the superheated steam
2 2
temperature has a surface of 22 m (237 ft ).
* Includes walls of combustion chamber, radiation first pass, second pass,
and third pass.
Heat Release Rate
The following heat release rates have been estimated from dimen-
2
sions scaled from Figure 5-6. The effective grate area is 42.63 m
2
{458.9 ft ), corresponding to a grate width of 3.0 m (9.8 ft). The total
furnace volume up to the throat where the gases enter the radiation chamber
3 3
is 79 m (2790 ft ). For the purpose of estimating volume heat release
rate, half of the height of the radiation chamber up to the beginning of
the turn of the gases toward the superheater has been assumed to serve
333
as combustion volume; that is, one half of 136 m (4803 ft ) or 68 m
3 33
(2401 ft ) is added to the estimated furnace volume of 79 m (2790 ft )
3 3
for a total assumed, active combustion volume of 147 m (5191 ft ).
Table 5-1 shows the resulting estimated dimenstions and rates.
The grate burning and heat release rates are moderate.
-------
23
TABLE 5-1 .
ESTIMATED BURNING VOLUME DIMENSIONS
AND HEAT RELEASE RATES FOR EACH OF
THE TWO KREFELD FURNACES , s
(LHV Assumed 2250 Kcal/kg) (4050 Btu/lb)
m ft
Grate area effective
Furnace volume
Radiation chamber volame
Furnace plus 1/2 rad. ch. vol.
42.63 m2 458,9 ft2
79,0 m3 2790 ft3
136.0 m3 4803 ft3
0 0
147,0 m 5191 ft
Design Rate
Total daily firing rate
11 hourly "
Firing rate per boiler
Heat input per boiler
Grate burning rate
Grate heat release rate
Volume heat release rate
288 tonnes/day
12 tonnes/hr
13.2 tors/hr
27.0 Gcal/hr
113.0 GJ/hr
106.9 MBtu/hr
281.5 kg/ir^-hr
51.6 Ib/ft2-hr
633,375 kcal/m -hr
2652 MJ/m2-hr
233,487 Btu/ft2-hr
183,673 kcal/m3-hr
769 MJ/m3-hr
67,709 Btu/ft3-hr
-------
24
Energy Utilization Equipment
In addition to the utilization of thermal energy for drying of
sewage sludge, some of the energy released in the burning of refuse and
dried sludge is sent as hot water at 130 C (266 F) 10 bar (145 psia) to a
railroad car plant located 2.5 km (1.5 mi) away. The water return temper-
ature is 70 C (158 F) at 7 bar (100 psia). Steam is used to drive two
turbo generators, built by AEC, having a generation capacity of 1.4 mw each
at 10 kv. Each turbine can utilize 17.5 tonnes/h (38,500 Ib/h). The design
steam outlet conditions are 3.7 bar (53.7 psia) and 206 C (403 F).
The excess steam is used for preheating the primary combustion
air to 200 C (392 F). Each of two heaters, made by Duerr, uses 6500 kg/h
(14,300 Ib/h) saturated steam at 25 bar (363 psia) 225 C (437 F). The
heating capacity is 2.816 Gcal/h (11.79 MJ/h) [11,175 Btu/h] when heating
air at the rate of 50,000 Nm3/h (29,425 scfm).
More steam is used internally for one Lugar flue gas reheater
following the scrubbers. Using 3,150 kg/h (6930 Ib/h) of steam at 22 bar
(320 psia) and 375 C (707 F), the heater is designed to heat the saturated
flue gas from about 60 C (140 F) to 90 C (194 F).
Most of the electricity generated is used internally. Any excess
goes to the local network without payment.
Energy is sold to the local railroad car plant and is used internally
for primary air heating, sludge drying, electric motors, flue gas reheating.
-------
25
Sludge Treatment and Burning
As indicated in the dotted area in Figure 5-3, immediately east
of the present settling tanks, an activated sludge treatment addition is
planned. This however will have no significant effect on the amount of
energy required for sludge driving, because the additional activated
sludge treatment section and the third refuse fired boiler will be built
both at some time in 1980-81. For the utilization of the increased thermal
energy after one more boiler will be set into operation (i.e. 1 boiler=
standby) a 13 Megawatt turbine set is planned.
Figure 5-7 shows the sludge handling system. The settled
sludge is not pumped without further treatment to the dewatering plant
and an added chemical conditioner. Then, with a water content of about
94 percent, it is pumped to the centrifuge which reduces the water content
to about 74 percent and a lower heating value of 413 kcal/kg (1800 kJ/kg)
(752 Btu/pound). The removed water is returned to the wastewater treatment
plant.
The partially dewatered sludge then flows to a surge tank and
thence to the large Babcock mills, one per boiler, where it is mechanically
disintegrated by the high speed paddles in an atmosphere of air mixed with
hot flue gas which is taken from near the top of the boiler radiation
pass as shown in Figure 5-6 . It thus enters the lower part of the boiler
radiation chamber conveyed in an atmosphere of vapor and partially cooled
flue gas. Experience has shown that if this saturated conveying stream
is allowed to cool too much, some of the vapor will be recondensed on the
very large surface available on the fine sludge particles. It is estimated
that the moisture content of the sludge particles entering the radiation
pass is about five to ten percent and its net lower heat value is about
2,500 kcal/kg (10,467 kJ/kg) [4,500 Btu/lb]. Long experience with mill drying
of brown coal has indicated that the moisture content should not be allowed
to become too low as this greatly increases fire and explosion hazard with-
in the mill system.
Figure 5- 8 shows the estimated conditions entering and leaving
the drying mill as a function of drying rate. At full design rate the
furnace burns 12 tonnes/hr (13.2 tons/hr) of refuse plus 6.43 tonnes/hr
(7.1 tons/hr) of dewatered sludge. If, because of a reduced heat value
-------
26
9 ©
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Btld 5: Schlammbehandlungsschema
FIGURE 5-7. KREFELD SLUDGE-PROCESSING AND BURNING
SYSTEMS (COURTESY VEREINIGTE
KESSELWERKE).
I. Thickener
2. Sludge Tank
3. Sludge pump
4. Flocculating tanks
5. Metering pumps
6. Centrifuges
7. Surge tank
8. Heated hammer mill
9. Boiler
-------
27
900
0 800
a
ai
700
650
Nm3/sec
. 4.0
.3.0
2.0
Raw flue gas temperature C
pExhaust gas flow into mill
r
iv
temperature into mill
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150 .
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1.0
J- o
dust loading-,
final moisture content
Gas vol. leaving mill_
Cooling air volume
3.0
4.0 .5.0
.Sludge Drying Rate4 tonnee/hr
6.C
FIGURE 5-8. CALCULATED DRYING MILL CONDITIONS AS A FUNCTION OF SLUDGE
DRYING RATE (Courtesy of Vereintgte Kessel-werke)
-------
28
in the refuse or because of an extra moisture load in the sludge, the
first pass outlet temperature falls below the legal limit of 800 C (1472 F),
supplemental oil is fired automatically to maintain that temperature.
(TA-Luft regulations).
Table 5-2 shows the drying system design conditions as
affecting the estimated dust loading of the gases entering the electro-
static precipitator. Three different levels of refuse heat value are
2
considered. Note that the "effective" grate area shown is 42.63 m
o 22
(458.9ftz) as contrasted with the estimated 35.7 m (383 ft ) used in the
section on heat release where only the equivalent flat surface is con-
sidered.
Figure 5-9 shows the calculated dust load of the flue gases for
various "flow rates" of ash across the grate. The three calculation
points on the curve correspond to the conditions in Columns marked 1, 2,
and 3 in Table 5-2 .
The approximate composition of the sludge coming to the
centrifuges at Krefeld is:
Dry solids 6.5 to 7.0%
Ash 2.8 to 3.2%
Ash/solids 40.0 to 45%
If the sludge is held too long in the thickener, digestion causes a
loss of volatiles which affects its burning characteristics. Mr. Koerbel
emphasized that a key element in successful sludge processing is to keep
it moving.
At present the quantity of sludge available is greater in re-
lation to the refuse quantity that would normally be encountered. It
is estimated that the sludge to the Krefeld plant comes from an area
serving a population of about 600,000 while the 400 tons of refuse per
day is from a population of about 300,000. Some local plants such as
Bayer process their own wastewater. When the Krefeld wastewater plant is
modified for secondary treatment existing regulations covering pre-treatment
of industrial wastes will be enforced.
-------
29
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ned by sampling for incinerate!
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The sludge drying system was not operating during either day of
our visit, May 20, 23, 1977, and data could not be released on the drying
system performance because acceptance tests had not yet been run on the
plant. However, a published design heat balance is said to be available
from a recent article in VGB Kraftswerkstechnik.
Although the plant is equipped to handle waste oil, the facilities
are not in use. Apparently, waste oil in this area all goes to waste oil
refiners.
Near the completion of this EPA project, after Battelle project
funds had expired, we developed more photographs and Grumman provided us
with a technical paper written in German. We have translated the labels and
the figures are attached in the appendix in the hopes of providing yet more
useful information on co-disposal at Krefeld. Limitation on funds, unfor-
tunately, prevents us from integrating these photos and figures into the text.
Wastewater Discharge
The principal wastewater is from the sludge centrifuges. The
wastewater is returned to the adjacent wastewater treatment plant.
-------
32
POLLUTION CONTROL EQUIPMENT
Electrostatic Precipitators
The exhaust gases are cleaned by two electrostatic precipitators
and will be cleaned also by two scrubbers when they become operational.
Previously, in Table 5-2 the estimated dust loading entering
the precipitator was tabulated. Table 5-3 gives the design characteristics
of the precipitators. No test data are yet available on precipitator per-
formance. The precipitator was built by Buttner-Schilde-Haas of Krefeld,
a member of the Babcock group, under license from Svenska Flaktfabriken.
While visiting this plant, May 20, 23, 1977, the stack plume
from single boiler operation was usually invisible. At one period, during
startup with the heavy oil burner, some smoke was observed.
-------
33
TABLE 5-3 . CHARACTERISTICS OF THE TWO
KREFELD PRECIPITATORS
3
Gas quantity 88,000 Nm /h
Gas temperature 300° C
•3
Raw gas dust load at 11.7 % C02 20 g/Nm
Cleaned gas dust load at 7% C02 100 mg/Nm
Number of electrical fields 2
Number of rapped fields 2
Active length 7.2 m
Active width 6.5m
Active height 7.5 m
Gas passages 26
3
Active volume 351 m
2
Collector plate projected area 2810 m
2
Collector plate effective area 3800 m
Gas velocity 1.025 m/s
2
Cross sectional area 48.75 m
Residence time 7.02 s
Drift velocity 3.29 s
Number of power supplies 2
Electrical characteristics 45 kV eff.
Sparking voltage 64 kV_
O
Secondary current 600 mA
Sparking current 1020 mA eff.
Power input per field 46 kVa
Power consumption 27.6 kW
Power to rappers 4 x 0.055 kW
Insulation heaters 8 x 2.0 kW
2
Current density 0.426 mA/m
3
Sparking current density 3.42 mA/m
Source: Courtesy Vereinigte Kesselwerke.
-------
34
Scrubbers
In 1974 a new Federal regulation of atmospheric emissions was
enacted known as TA Luft (Technischen Anleitung zur Reinhaltung der Luft).
3
It reduced the allowable particulate emission for plants over 100,000 m /h
3
(58,850 cfm) to 100 mg/Nm corrected to eleven percent 02. For new plants
it also specified limits for emission of HC1, HF, CO, N02, and S02- For
plants which expand by adding new capacity, all of the old and new equip-
ment must meet following new limits on gases:
HC1: 100 mg/Nm3 (67 ppm) [0.083 lb/1000 Ib gas]
HF: 5 mg/Nm3 (24 ppm) [0.008 lb/1000 Ib gas]
Accordingly, a scrubber system has been added to this plant following the
precipitator and also following the induced draft fan. A simple outline
of the Lugar scrubber and flue gas reheat system is shown in a separate
building to the right in Figure 5-6. The scrubbers (assuming they follow a
properly designed ESP) are designed to achieve the following emissions:
HC1: 100 mg/Nm3
S02: 100 mg/Nm3
HF : 5 mg/Nm3
NOX: 265 mg/Nm3
Figure 5-10 shows the water systems for the entire plant including
the scrubber. The sketch of the scrubbers implies that the scrubbers are
simple vertical spray-type units with some provision for demisting.
Previously, the diagram in Figure 5-6 showed a separate fan and steam-
heated air heater for mixing hot air with the cool, saturated gases
leaving each scrubber. The design characteristics of that flue gas re-
heat system were described under Energy Utilization.
No test data are yet available on the flue gas cleaning system.
Assuming that the scrubber system can be brought to a high level of re-
liable operation, this plant will then become one of the most advanced
waste-to-energy plants in the world.
-------
35
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FIGURE 5-10. SUPPLY AND WASTEWATER SYSTEMS
1. Clear water from wastewater treatment plant
2. City water
3. Well water
4. Percolation well
5. Wastewater canal
6. Well water reservoir
7. Cold water discharge
8. Flocculating tank
9. Sludge centrifuge
10. Quench tank
11. Ash bunker
12. Settling tank
13. Boiler feedwater treatment
14. Neutralizing tank
15. Washroom
16. Sanitary wastes
17. Exterior hydrants
18. Tipping floor hydrants
19. Fire control cannon-bunker
20. Oil tank
21. Flue gas scrubber
22. Neutralization tank
23. Lime mixing tank
-------
36
Stack Construction
The 70 meter (230 ft) stack is shown in cross section in
Figure 5-6 • The lining is acid-resistant brick. External diameter
is 3.65 m (12 ft), internal diameter is 2.75 m (9 ft).
Noise
The plant has no close neighbors, hence, noise is not a current
problem. Furthermore, the machinery components are all enclosed within
the structures and the ambient area is unusually quiet.
-------
37
PERSONNEL AND MANAGEMENT
The plant operates 24 hours per day, three shifts, seven days
per week. The individual work week is 40 hours.
-------
38
ECONOMICS
Capital Investment
The plant cost DM 58.5 x 106 (23.8 x 106 lat DM 2.46/$),
Operating Costs
Because of the newness of the plant and its operations no
data are yet available on operating costs.
Revenues
The only income to the Krefeld plant comes from the sale of the
energy in hot water to a local railroad car plant at the rate of DM 30-35/
Gcal (DM 7-8/GJ) [$3.6 - $4.2/MBtu]. The design rate for energy export
was 14 GcaJ/hr (55,552 MBtu/hr).
-------
39
REFERENCES
1. Plant dedication brochure: "Mull-und Klarschlaum-Verbrennungsanlage
und Klarwerk Krefeld", dated March 11, 1975.
2. B. W. Westphal and J. Bbhme, "Miill-und Klarschlamnverbrennungs-
anlage Krefeld" Energie. Vol. 5, 1975.
3. Article in VGB Kraftswerkstechnic describing design heat balances.
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Sludge Pump
Storage tank
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FIGURE 5-D. WET SLUDGE PREPARATION AND CENTRIFUGE
-------
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PADDLE WHEEL
SLUDGE DRIER
-------
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Refuse 12 t/h
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19 atmos, 375°C V 20.6 t/h
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Railroad Car
Factory
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FIGURE 5-H. HEAT FLOW DIAGRAM
-------
to the boiler
Sludge 7J t/h
Horizontal Axis
Paddle Wheel
Sludge Drier
Flue Gas Draw off
Grate Firing of Refuse: 12 t/h, Hu = 1600 kcal/kg, n = 1.6.
HGS-Sludge Drier: 7.7 t/h Sludge, W = 74%, Hu =284 kcal/kg
FIGURE 5-J. FLUE GAS DRAW OFF AND
SLUDGE FIRING AT KREFELD
-------
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TABLE EXCHANGE BATES FOR SIX EUROPEAN COUNTRIES,
(NATIONAL MONETARY UNIT PER U.S. DOLLAR)
1948 TO FEBRUARY, 1978U)
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
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
U . 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
(61.)
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
3i624
3.597
3.254
3.226
2.824
2.507
2.689
2.457
2.280
2.176
Sweden
Kronor
(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.
U. S GOVERNMENT PRINTING OFFICE 1979—620-007/6307
------- |