Document MMqpKzor02KNMr1B3JMqRoNeM

A Comparative Study of European and North American Steam Producing Incinerators LEIF ASTROM, FRANZ KRANEBITTER OLOF STRANDELL, DAVID W. HARRIS EKONO Bellevue, Washington ABSTRACT The "Energy Crisis" has focused the attention of Ameri can engineers on all possible methods of producing useable energy from domestic refuse. Certain areas of Europe long ago faced similar problems of high fuel prices and environ mental restrictions, consequently many steam producing incinerators have been in lengthy service. The authors be lieve much useful information can be obtained by evaluat ing the European experience and adapting it to American problems. EUROPEAN PLANTS The authors have chosen to confine their discussion to steam producing incinerators, thus no discussion will be made of the many fascinating alternative concepts that have not been in commercial operation. To better understand the almost universal use of steam producing incinerators for plants handling over 120 tons per day, the following significant factors should be considered: 1) Population density -- West Germany alone has 62,000,000 people in an area less than the state of Oregon. 2) While the fossil fuel prices arc constantly changingin many areas of Europe, fuel costs would be considered exorbitant even under today's American prices. 3) In many cities in Europe, central (or district) heat ing provides a ready demand for the output from steam generating incinerators. 4) Frequently the ownership of the incinerator, the district heating system, hospitals, homes for the aged, and the electrical system will be under the same governmental agency so that the steam producing incinerator becomes an integral part of overall planning. 5) In larger size incineration plants the cost and com plication of flue gas cooling and cleaning equipment be comes so great that the plant with heat recovery is less costly. . In comparing European problems, the difference in practices must be examined as well as similarities so that accurate evaluations can be made. The most significant factor is the dissimilarity of composition of refuse utilized by existing steam generating units, not only in the differences between European and American domestic refuse but there can even be differ ences between adjacent cities. In many areas of Europe all of the burnable refuse is consumed in the home for healing. This consists not only of paper products, twigs, branches from trees and shrubs, but all other burnable materials. Frequently, the ash from coal burned by householders or small industries becomes a significant portion of the refuse delivered to a municipal incinerator. However, refuse composition can change quickly if natural gas or light oil becomes available. In Europe it is invariably found that heat recovery with sale of steam and/or electricity by means of waste inciner ation is profitable. In some plants it has been possible to lower the disposal costs of refuse by more than 30 percent compared to an incineration without heal recovery. 255 i t i: ; 1\ TOWOLDMONOQ59396 Table 1. Typical European Steam Producing Incineration Plants City Germany Stuttgart Darmstadt Ludwigshafen Frankfurt II Hamburg Hamburg Nuremberg Sotingon Leverkusen (a) Munich H (a) Munich III (a) Munich IV Dusseldorf Bremen Isorloch Offenbach Landshut Berlin Berlin Berlin/GDR Switzerland Basel Zurich Luzern Hinwil Zurich Netherlands Den Haag Amsterdam Austria Vienna Sweden Stockholm Umea Goteborg Malmo Date of Service Stoker Mfgr. Tons of Refuse Per Day How Ib/hr xIOOO Steam Per Unit Pres. Psig Temp. Cp 1965 1967 1967 1967 1967 1972 1968 1969 1969 1966 1969 1971 1965 1969 1970 1970 1971 1967 1971 - VKW Von Roll Von Roll Von Roll Martin Martin Von Roll Von Roll Von Roll Martin Martin Martin VKW VKW , Babcock VKW Von Roll Duerr Duerr VKW 530 250 250 400 320 650 400 270 270 1010 1010 1010 270 330 210 270 220 330 420 400 110 55 50 53 60 88 81 55 62 178 178 178 140 33 44 57 15 49 49 77 1969 1969 1970 1970 - Von Roll Von Roll Von Roll Martin Martin 400 290 130 130 500 88 62 * 28 27 84 1968 1969 Von Roll Martin 400 600 78 95 1971 Martin 400 126 1968 1970 1970 1969 Von Roll Von Roll Von Roll Martin 130 (W) 130 (W) 400 104 230 1140(w) 1095 680 600 910 255 585 1195 680 285 2560 2560 2560 1280 355 355 355 285 1240 1240 1380 975 840 805 930 645 770 840 840 580 995 995 995 930 420 480 480 660 880 880 975 670 660 525 790 570 700 555 750 570 735 570 800 610 770 455 SAT 230 250/160 230 355/260 285 420 130 Hot w. ) P * Power production DH * District heating PA * Plant auxiliaries E * Electrostatic precipitator a Oil fired separately W * Hot water Use Dust X Separation P DH+P DH+P P PA P P P DH DH+P DH-tP DH+P P DH DH DH DH P P P E E E E _ E E E E _ _ E _ E _ _ DH+P PA P P P E + cycl. E E __ _ P E + cycl. P- DH+P E + cycl. DH cyclones DH cyclones DH cyclones DH - 256 0583b*0 I TOWOLDMONOQ59397 Table 1. Typical European Steam Producing Incineration Plants (Cont'd) Tons of Flow Steam Per Unit Dato of Stoker Refuse Ib/hr Pres. Temp. Use Dust City Service Mfgr. Per Day xIOOO Psig Op Separation France Rennes Paris Strasbourg Metz England Edmonton Covontry Nottingham Soviet Union Moscow Italy Genova Mailand Finland Helsinki Lahti Norway Oslo 1968 1969 1970 1971 1972 1972 1970 1971 1971 1969 1969 1966 *) P * Power production 1)11 c District heating Martin 130 35 385 Martin 130 295 1280 Von Roll 390 72 780 Martin 160 40 215 VKW 370 89 625 Martin 320 70 250 Martin 310 53 385 Martin 220 32 200 Von Roll 220 42 455 Volund 270 50 455 Von Roll 90 35 220 lokomo 130 26 570 Esslingen 170 44 355 E = Electrostatic precipitator 440 875 860 635 850 405 700 380 705 825 660 840 500 DH P DH+P P E - PPP- DH - PE DH - DHhP DH - P- OPERATING EXPERIENCE Experience shows that the availability of a refuse Incineration plant is considerably lower than that of a fossil fuel fired plant. PJanl equipment that is especially vulnerable to break downs arc the hot surfaces of the steam boiler where cor rosion, erosion and different types of fouling occurs. In addition, the moving parts of the grates arc damaged frequently as well as nonwater-coolcd refractory. The handling of the refuse and fires sometimes cause short shutdowns as well as the boiler plugging caused by ash carryover. The reason for the operative disturbances, of course, vary from plant to plant. The frequency of dis turbances is great when the plant is new. A greater portion of the disturbances can be eliminated by only shutting the fuel feed for a short period of time. In many plants the boiler unit has to be completely shut down more than 10 times per year. The total availability of a refuse incineration boiler after a few years of operation varies between 65 percent and 85 percent. In order to improve the overall plant availability, multiple boiler units are used with additional boilers for spare capacity. In examining the availability figures it must be borne in mind that not only heat and electricity production is involved but that waste disposal is para mount. And because of this, it is advantageous to equip the plant with a 2-day refuse storage capacity.' As a producer of heat, the refuse incineration boiler has such a low availability factor that it obviously affects the profitability of the heat recovery. Any attempts to im prove the availability immediately show up in increasing operating costs or greater capital investment costs. In Western Europe the heat from incineration with a capacity exceeding 120 tons per day lias almost, without exception, been used for district heating and electricity 257 0583621 production. (Hot water producing boilers arc considered tion, efficient soot blowers must be installed. Water as an acceptable alternate.) spraying has been used to clean nicmbranc-watcrwalls In West Germany, heat from above 100 tons per day during operation, plants is commonly sold to the district heating networks. It is advantageous to have a vertical flow in the furnace. Above 300 (ons-per-day plants commonly produce When at the same lime a large enough area-volume ratio is electricity or transport high pressure steam to another the objective, the furnace, especially in larger boilers, power plant. turns out to be high and the cross sectional area becomes The trend towards more electricity production has small. In working out the grate design this limits the during the past years raised boiler pressures and steam width. This has to be compensated by utilizing the avail temperature in European refuse incineration plants. able height. The location of the grate in relation to the Pressures arc now commonly 1000 to 1500 psigand tem cooled furnace is important. With refuse having a very low peratures 750 to 925F. The highest pressures and temper heating value, the radiation from the fuel bed surface to atures are those of the Munich plant where refuse and the cold furnace walls must be minimized. It is common fossil fuels are burned in combination. Here 2600 psig and practice to cover all furnace wall tubes with refractory 850F reheat has been used. for a distance of 15-20 feet above the grate, using studded tubes covered by silicon carbide plastic refractories. . REFUSE RECEPTION AND PRELIMINARY HANDLING Refuse collection is usually divided into three areas: community collection, special refuse collection firms, and The varying composition and collection methods is a the portion brought by the private individuals. The share problem at many European refuse incineration plants. of the private individuals is in some areas surprisingly high. Ordinary household refuse only represents a part of the The refuse brought by private individuals is often treated total. The rest can be called special refuse. The following as special refuse, since it has proven necessary at least to examples of special refuse may be mentioned: large size check what people bring to the plant. objects from households (e.g. furniture, appliances, etc.) The special refuse must be sorted into combustible ash, shop refuse (boxes, cartons, etc.), construction waste, refuse and refuse to be destroyed by other means. What is auto tires and waste oil. Pure industrial refuse is not ac burnt is dependent on the capabilities of the plant. The cepted in most plants. Special refuse is sorted from the combustible portion usually goes first to the crusher. household refuse already at the collection stage. Some Usually the crusher capacity is less than tire incineration communities collect large size refuse separately once a capacity. The crushed refuse, which usually has a high week, which then is treated differently from other refuse. heating value, is then evenly mixed with all the other A prerequisite for good technical and economic opera waste. Blending of the refuse to an even mixture has tion is a sensible construction, lienee, a condition for turned out to be very important for a successful operation. economic heat recovery is that the burning equipment and * Thus, in some plants the crane operator uses 75 percent of the boiler be matched to form a well-functioning unit, his time to mix the refuse. where the requirements of each component have been con Burning of refuse oil is not possible at all plants. Refuse sidered as far as possible. oil is usually fired in special burners mixed with fuel oil. The fouling problems that are present at the melting point of ash, 1800 to 2000F, result in the requirement of EQUIPMENT SELECTION the construction of a water cooled furnace In the immedi ate neighborhood of the combustion zone, where the gases The efficiency of a waste incineration boiler is low. cool to a temperature below that of the ash adhesion The high moisture content and ash content cause the temperature. Simultaneously a long enough residence greatest losses. In Europe a 65 percent boiler efficiency lime at above a temperature 1500F is required for may be expected (calculated on the lower heating value). eliminating the odors. With heat recovery this naturally affects the construc The arrangement of convective surfaces must be such tion of the burning equipment since the equipment that they do not collect ash. Severe erosion must also be required for the combustion and the heat recovery have to taken into account. Hot superheaters arc usually arranged be compatible. Especially the boiler, which must be con as platens, spaced 1-2 feet apart. Bare lubes arc often structed for lower grade fuel with higher ash content ** preferred in preheaters. The air heater is often left out and which is very expensive, thus attempts are made to opti an economizer bank is used. Some manufactures use only mize boiler construction. In some cases the results have vertical tubes and arrange the heat exchange surfaces as not been up to expectations. It must be remembered that downward passes only. This is to avoid pluggagc. In addi an efficient and hygienic disposal of the refuse is the 258 0563622 prime purpose, heat recovery being only second in importance. In Europe thick fuel bed burning is universally practiced - 3 feet or more at the front of the stoker. The stoker hopper is fed by a traveling crane with a grapple or clam shell bucket, buring the last 10 years, a few manufacturers have developed grate designs that have managed to obtain a strong foothold in the European maikct. They arc all based on a moving grate, but the movement varies in type. It is the genera! opinion that satisfactory complete incineration is only obtainable with a moving grate, since a regular movement of the fuel bed is not possible on a stationary grate due to the varying size of waste pieces and varying density of the refuse. The forward acting stoker is a sloping grate, where every second grate bar row is moving. The moving row pushes the fuel forward, stirring the grate cover. The grate may be divided into 3 sections in between which is a step to improve the mixing. In the air section the grate is divided into several zones. A high air resistance grate must be used in order to prevent crater formation. The reverse acting grate functions the same as the for ward acting stoker except that the fuel is lifted up by. pushing towards the back. This promotes ignition from underneath. This grate design is common in larger plants. The roller grate consists of consecutively placed cylinders with air openings that turn slowly, moving the fuel forward. This grate is also sloping. The lower end of the grate chamber is generally built as a long vault in order to ensure complete burn-out. Auxiliary oil or gas is burned in the main furnace when needed. Less than 5 percent combustibles in the ash is achieved despite the fact that the ash content of the refuse can reach over 50 percent. The slag is normally dropped into a quenching bath, from which it is transported by means of conveyors, allowing large objects to pass through. Fly ash from hoppers is sometimes mixed with the slag, but usually handled together with the precipitator dust. When the ash is loaded on transporting vehicles water is added to prevent it from becoming air-borne during transport. CORROSION In an incinerator the same kinds of corrosion can appear as in any boiler. This means that high temperature corro sion with vanadium involved, as well as low temperature corrosion with sulfur involved, occurs in incinerators when conditions make them possible. In addition, corrosions occur which are unusual in norma! boilers, it has also been proven that some fuel components act as a catalyst to increase the reaction rate of the corrosion processes. According to recent research results by VGB ("Associ ation of Large Utilities", West Germany), corrosion caused by chlorine compounds is very typical in incinera tors. In fact, it is claimed that no other corrosion processes have any importance compared to those when only high temperature zones are considered. The main source of chlorine is PVC, which can have a chlorine content of 56 percent. The amount of PVC in the refuse is increasing continuously. During combustion hydrochloric acid, MCI, is formed. This condenses on the relatively cool furnace or primary superheater tubes. The two most important corrosion mechanisms are considered to be: a) when air deficiency occurs locally the hydrochloric acid reacts with the tube material or its protection oxide layer, forming FeClj, which is evaporated and carried away. When excess air is available this reaction docs not take place or is very slow. Thus, this type of corrosion can be avoided by using enough excess air properly distributed. b) Where metallic steel is exposed to combustion gases, FeCI2 is formed besides a protective oxide layer. As the oxide layer increases in thickness and strength, the formation of FcCI2 becomes slower. This type of corro sion takes place in new boilers or at locations when heavy erosion wears the protective layer away or where soot blowing is too heavy. Possibly the reaction is the same as in a) when it is considered that the formation of oxide consumes the oxygen, thus causing an oxygen deficiency. Avoiding places of local oxygen deficiency is a difficult task. The usual method is to use a high overall air-fuel ratio, 50-100 percent, over the stochiomctric. Because of the long grate construction in most incinerators, the composition of tiie combustion gases varies very much from one place to another along the fuel bed. An efficient mixing of the combustion gases is, therefore, a method to avoid local oxygen shortness. The mixing can be made by means of high velocity secondary air jets. Where local corrosion nevertheless occurs, it is often most practical to protect the metal surfaces with thin layers of refractory supported by studs on the tube walls. The sulfur content of the flue gases is usually much lower than in oil or coal-fired boilers. Hence, sulfate corro sion is of minor importance in incinerators. Low tempera ture corrosion can, however, be severe. This may be due to catalytic oxidation of S02 at medium temperatures of 600 to 1700F. A variety of catalysts can be found, e.g. vanadium, lead, sodium and potassium. Also, other components may influence either the S03*formation or the corrosion rate. Alkaline sulfates of different kinds play obviously an Important role in intermediate temperature corrosion cases. The mechanism of these processes is not known in great detail. Relatively highly corrosive Na- and K-sulfates have been found in many boilers. Their corrosion maxi mum is in the temperature range of 900 to 1300F but, as mentioned above, sulfate corrosion is not the major problem in incinerators. AIR PROTECTION The flue gases contain solid as well as gaseous pollu tants. The concentrations vary very much from one plant to another. The dust content, entering the precipitator calculated to 12 percent C02 content of the flue gas, is 1.5...7.5 grains/sl.cu.ft. As a mean value 3.5 grains/st.cu.ft. may be used. It must be observed that during sootblowing the concentration can be considerably higher. The content of sulfur oxides is usually small compared to gases from oil or coal burning. A major part of the sulfur oxides may be from the auxiliary firing. Restric tions to the emission of sulfur dioxide from incineration have not been set by any country in Europe. Formation of hydrochloric acid can become an en vironmental problem. With a PVC-content of 2 percent, not unusual today, the flue gases contain about 690 ppm IIC1 at a 12 percent C02 level. No rules exist concerning allowable emission, but existing emission rules or recom mendations may locally force to build a high stack because of the HC l -emission. HC1 can relatively easily be scrubbed out of the gases because it is very soluble in water. It is, however, not easily separated from water and can thus form a water pollution problem. Most counties already have limits to the dust emission. The most common limit is 0.106 grains/st.cu.ft. Collection efficiencies of about 97 percent are thus needed in most cases. Electrostatic precipitators are used in all modern plants. Some years ago there were some difficulties with low resistivity paper flakes passing through the electro static precipitators. A number of plants were then equip ped with an additional dynamic separator after the electro static. This caused an additional pressure drop of approxi mately 2 in HjO. Modern electrostatic precipitators have an improved shape of plate electrodes to collect weakly charged particles and additional mechanical separators are usually not required. NORTH AMERICAN PLANTS The use of steam producing refuse incinerators in North America is comparatively new. The number of plants and the total operating experience is far less than that in Europe. In examining the background, the great economical, political and ecological differences as compared to European conditions, at the lime that these plants were conceived and authorized should be borne in mind. Significant factors were: 1) Low average population density, with only minor pollution problems in many areas. 2) Abundant sanitary land fill areas, where refuse could be used to reclaim unuscablc land for residential, Industrial or recreational purposes. 3) Central or district heating systems uncommon and confined to the central core of larger northern cities. 4) High labor and equipment cost. 5) Low cost electricity, oil and gas. 6) Little if any household coal ash. 7) Erratic demand and prices for iron or steel scrap. 8) High heating value of domestic waste. In most cases the principal justification for steam pro ducing incinerators was on the basis of volume reduction of material to be hauled to sanitary landfill. Frequently there was no opportunity for sale of steam, so that steam not used by the plant itself was condensed and the heat dissipated to the atmosphere. Montreal and Norfolk Navy Yard arc the only plants that aTe using steam in district heating systems. Even today attempts to sell steam to private industry has not met with success. As heating value of refuse has continued to increase, and the water and air pollution requirements became more severe, the use of water cooled furnaces with boilers and air heaters and/or economizers became justified. Since, however, commercial power generation has n6t been In cluded, only low pressure boilers have been used. The installations can be segregated into the following categories: 1. Modified European designs, with a thick bed of 3 feet or more, and stokers of the same configuration proven in European operation: (a) with water walls protected by refractory for 15 or 20 feet above the stoker; Montreal Chicago Northwest Harrisburg Oceanside (b) with refractory protection only at grate line; Braintree Norfolk 2. Complete departure from European design, with spreader stokers, thin bed burning on traveling grates and 260 058362** City Table 2. North American Steam Producing Incinerator Plants Date of Service Stoker Mfg. Tons of Refuse Per Day Flow Ib/hr xIOOO Steam Per Unit Pres. Psig Temp. F Use Dust x) Separation Canada Montreal New York Oceanside 1971 1965 Virginia Norfolk Illinois Chicago (Northwest) ' Pennsylvania Harrisburg Massachusetts Braintree Missouri (a) St. Louis (Union Electric) Ontario Hamilton 1967 1972 1972 1972 1972 1972 Von Roll 4x300 Flynn & Emrich 2x200 Detroit 2x180 Martin 4x400 Martin Riley None 2x360 2x120 1x200 Detroit 2x300 100 550 50 110 98 36 1250 106 225 500 DH+PA E 325 SAT PA E (b) 150 SAT DHhPA E (b) 250 SAT PA 6 250 250 2400 SAT SAT 1000 PA PA P E E E 300 SAT PA E x) P Power production DH B District heating PA * Plant auxiliaries E * Electrostatic precipitator a B 1$ percent refuse in pulverized coal fired boiler (b) = Being added refractory protection at grate line, and continuous ash discharge; Bast Hamilton 3. Complete departure from European design, with refuse suspension burning as supplemental fuel in a large pulverized coal fired electric utility steam generating plant; Union Electric EQUIPMENT SELECTION Where thick bed burning is practiced, the equipment selection parallels that shown on Fig. 1 for European plants, except that metal baling equipment is eliminated. The East Hamilton plant is a complete departure from European design in that extensive fuel preparation to shied domestic refuse, remove metal and large non combustible material before feeding to the stoker is practiced. Then a traveling grate stoker with ash discharge at the front burns the fuel - partly in suspension and the remainder in a thin bed in a water walled boiler that is essentially a duplicate of the many wood refuse burning units used in the forest products industry in Canada and the U.S. An electrostatic precipitator is used to clean up the gases. The Union Electric plant shows a complete departure from European practices in that domestic refuse is pre pared in East St. Louis through shredding and metal and noncombustible removal before the material is hauled a number of miles to the Union Electric plant. The material is then conveyed pneumatically to existing pulverized coal boilers that are in regular service providing steam for power generation. Refuse fuel at times has provided from 15 percent to 20 percent of the boiler output. OPERATING EXPERIENCE The operating experience has varied from plant to plant. In all cases, continuity of services has been provided for by using multiple units. As some of the plants are going through initial opera tion, a comparison with the plant shown in Fig. 1 would be meaningless. 261 I; ,k TOWOLDMONOQ59403 58362" FIG . 1. MODERN EUROPEAN PLANT. TOWOLDMONOQ59404 264 0583628 TOWOLDMONOQ59405 THE EAST HAMILTON SOLID WASTE REDUCTION UNIT CITY OF HAMILTON, ONTARIO I i FIG. 6 TRAVELING GRATE SPREADER STOKER. 265 X> 6b 0* TOWOLDMONOQ59406 In general, after the shake-down period, the availability has been as good or belter than that of European plants. uses part of the scrap metal to construct the bertn around their sanitary landfill. CORROSION In evaluating corrosion all of the operating factors must be considered. Reports vary from little or no water wall or boiler corrosion, to such severe corrosion that one Ocean side boiler is being completely replaced in less than seven years operation. When the water walls are refractory protected for 15 or 20 feet, it would be reasonable to expect minimal cor rosion at the low operating pressures involved. Surprisingly enough no corrosion has been observed at East Hamilton, Braintree or Norfolk even though the refractory protection is limited to grate line areas. How ever, refuse is not always burned 24 hours per day and there are periods when gas or oil is burned without refuse. No corrosion has been observed in the combination Bring of refuse and pulverized coal at Union Electric. To date the refuse load has been a small fraction of the total fuel burned. Before definitive conclusions can be made on corrosion problems of the latest installations more operating time at design refuse burning capacity will have to be accumulated. ASH AND SLAG DISPOSAL Markets have not been developed for slag and flyash. The scrap metal market has been sporadic -- prices as low as $10.00 per ton have been quoted. Chicago Northwest has been able to develop long term contracts. Some of the other plants dump their metal with the slag. Oceanside AIR PROTECTION While some of the earlier plants were installed with low efficiency collection devices, these are now all being re placed with electrostatic precipitators. All the newer plants have included electrostatic precipitators which have demonstrated that (hey meet today's stringent air pollution requirements. REFERENCES |t] II. W. Lconhardt, "Erhcbung dcr Anlagcn zur Mudlaufbcrcitung und Bcscitigung in dcr Bundcsrcpublik Deutschland" Mucll und Abfall 3/1969 (2) H. J. Mueller, "Siadtrcinigung im Rahmcn dcs Umwcltschutzcs" Stacdlctag 24 (1971), No. 1 (3) K. It. Luschcr, "Massnahmcn zur Vcrmindcrung von Rohrabzchrungcn In Muctlkesseln", VGB Ktaftwcrkstcchnik S3, February 1973 (4) E. C. Hausen, "Incineration, an Engineering Approach to the Waste Disposal Crisis", District Heating, Fall 1971 [51 C. H. Schwarz, ``MueUvcrbicnnung", BrcnnstoffWacrmc-Krafl 24 (1971) No. 4, April (6) Georg Stabcnow, ``Performance of New Chicago North west Incinerator" Proceedings 1972 National Incinerator Conference, ASME, New York, New York, 1972, pg. 178 (7) F. E. Wisely, G. W. Butterfield and D. L. Klumb, "Use of Refuse as Fuel in an Existing Utility Boiler" Proceed ings 1972 National Incinerator Conference ASME, New York, N.Y. 1972 (8) Frank L. Heaney, "Air Pollution Controls at Braintree Incinerator" Journal of the Air Pollution Control Association, Volume 22, No. 8 August 1972 19 J Gordon L. Sulin, "East Hamilton Solid Waste Reduction Unit" Engineering Digest, August 1969 266 osa**30 T OWOLDMON0059407