Incineration
Two kinds of plants are used for this method of disposal—crematories and destructors. Many destructors are in operation in America, but of the crematories which have been built, many have been abandoned. Heat for destruction must be obtained not only from the garbage itself, but also from ashes and other combustible waste. It is here that the difference between destructors and crematories enters. In the former, heat is obtained from the refuse itself; in the latter, garbage is burned at the expense of coal, wood or oil. It seems to be the prevailing opinion that in order to make incineration a success the material must be burned at a high temperature and rapid rate of combustion.
Morse claims that destructors require twenty per cent. less area of ground, cost fifteen per cent. more for boiler and machinery; that the construction is more durable; no addition of fuel; that the gases of combustion are consumed, and that this method has by-products of clinker and power and destroys all combustible refuse; and that the net cost of operation is less per ton.
Crematories, Morse says, require more ground and more time for disposal, but cost less. They are less durable, require addition of fuel, gases are incompletely destroyed, cannot develop power, the residue has no value and they can burn only garbage and rubbish. The gross cost of operation is a trifle less, but the net cost is more.
Tests of garbage crematories in Ohio, according to the State Board of Health, show that “the plants as operated fail usually to dispose of the garbage at a temperature high enough to avoid the production of odors.” This, says J. T. Fetherston, Commissioner of Street Cleaning of New York City, is significant and conclusive.
Regarding mixed refuse destruction, Fetherston says: “Three features may be noted: No added fuel is required, steam power is produced and quite a residue (clinker) results. Compared with tests of garbage crematories the average destructor temperatures in connection with the gas analyses indicate freedom from odor due to unconsumed gas. Thus the mixed refuse type of plant corrects the inherent defects of the garbage crematory.”
The cost of incineration plants depends upon the garbage to be handled. The various incinerator companies usually estimate the capacity of the plant at about one ton per 1,000 population.
Reports show that disposal by incineration in Ohio is confined to cities of from 20,000 to 80,000 population, and that its success has been confined to the very large and to the rather small cities of the country. Some assert that it is applicable in the very large cities only when the collection systems are suitable to provide for the burning of mixed refuse. In small cities it is the custom to cremate the garbage alone, the other classes of waste being dumped or buried.
The cost of construction, reports show, ranges from $600 to $1,000 per ton capacity. The Worcester Special Waste Commission says that “from a calculation based on some 30 incinerators it has been found that the cost per ton daily capacity varies from $250 to $1,000, the average being between $600 and $700.”
The by-products are clinker and the steam generated.
Robert W. Wylde claims that the cost of operating destructors “is in a great measure offset and frequently quite overbalanced by the revenue” from the sale of steam and clinker. One hundred tons of refuse burned during 16 hours a day produces 800 engine H. P. Clinker from 100 tons might amount to 30 tons per day and would bring $1.00 a ton in many localities. Another expert says that one pound of refuse has been found to produce one-half to one and three-fourths pounds of steam. The value of refuse as a fuel is estimated by one expert to be 49 cents per ton.
The Chicago Waste Commission’s report points out, “that experience in connection with the development of power from refuse furnaces demonstrates that it is not easy to find an available use whereby the power can be utilized regularly as produced and the furnace operated continuously. In the majority of plants constructed, it has not been possible to utilize all the power available, and in most cases the use is limited to the operation of the plant. When power developed is used in lighting and power stations, the demand only comes during a part of the day. Supplementary coal-fired boilers are usually found in connection with destructor-electric lighting stations, or else the destructor is much larger than would be required to deal with the refuse alone. The power produced from refuse furnaces will be best utilized by some local industry, such as ice-making plants or electro-chemical plants, which require continuous operation. When power is used in connection with pumping plants, it is found good practise to operate the refuse plant only as an auxiliary to the power plant of the pumping station. The saving that results or credit that can be given the destructor plant will amount to the value of the fuel equal to that which it requires to produce the amount of steam developed and used. The fluctuating amount of power developed in most cases can be depended upon only for the average minimum production. In selecting a site for a refuse disposal plant from which power is developed it is not always profitable to utilize the power where the demand is not constant and where the demand would be constant, suitable sites are not always available.”
William M. Venable, sanitary engineer, believes that if a city has a steam power plant, it will pay, but it will not pay to build one for that purpose.
In a suburb of Montreal, the refuse destructor is constructed in connection with a municipal electric light power station and power is used in generating electricity for lighting purposes. The plant is operated only during the time when lighting load is in demand, and the material as delivered is stored during the day and burned at night. Only a part of the power is furnished by the refuse furnaces, the remainder being obtained from a coal-fired boiler plant.
In Savannah, Georgia, the water works boilers are kept in service, with banked fires, to use in case of shortage of garbage.
The following are some of the reports from cities which receive a revenue from by-products:
Minneapolis: The steam generated lights and heats hospital and workhouse buildings, also lights 31 miles of streets. Estimated annual revenue, heat $6,293.89; light $1,080.62; street lights ($60 per arc) $4,657.48; total, $12,031.99.
Borough of Richmond, New York City: West New Brighton incinerator uses clinker in manufacture of brick by mixing cement with ground clinker.
New Orleans, La.: Plans perfected to light streets and public buildings. Claimed that from 500 tons of garbage daily 30,000,000 K. W. can be generated a year.
Savannah, Georgia: Ninety-five per cent. of coal fuel previously used at pumping station is now saved by destructor. To operate water works pumping station it cost $81.90 per day. To operate the station and destructor it costs $46.50 per day, or a difference of $12,921 per year, this being 10 per cent. of the cost of the plant. This is expected to provide for repairs and amortization charges. Besides, the city has all of its refuse disposed of without cost at a central point and in a sanitary manner with freedom from nuisance. The clinker is used for road building and is estimated to have a value equal to the cost of hauling it from the plant.
All reports agree that destructors are very successful from a sanitary standpoint and have the advantage over other methods in that the different classes of waste can be destroyed by one process and gathered in one collection. Several also agree that the destructors when properly constructed and operated, may be centrally located, thus reducing the cost of haul. Another point mentioned is that there is some revenue. The disadvantages pointed out by experts are that, if not properly designed and operated, there will be dust and odors, all refuse must be hauled to the plant and expert workmen must be employed.
The cost of operation varies from city to city, and in each city from month to month, depending upon the season of the year, composition of the garbage and climate. Most incinerator companies guarantee to operate their furnaces at full capacity at about 50 cents per ton. Milwaukee operates for about 57 cents per ton. The cost, including maintenance, depreciation and fixed charges, and operating expenses, averages $1.50 to $2.50 and sometimes $3.00 per ton. The State Board of Health of Ohio found in its investigation that incineration cost from $1.97 to $2.50 in Canton, Ohio; $2.00 to $2.66 in Marion; $1.00 to $1.84 in Steubenville; and $2.58 in Zanesville, during a period of several years. These figures include interest, depreciation, maintenance and repair charges.
J. W. Turrentine, of the United States Department of Agriculture, who made a study of garbage disposal plants, says in a Department bulletin that the average net cost of incineration per ton as obtained in a number of instances is $2.11 per ton, and that in one of the cities considered there is a credit for power generated of 22 cents per ton of garbage incinerated.
Most garbage incinerator manufacturers claim a life of 20 years for their plants with reasonable renewals.
Morse figures that when fuel is necessary the cost of destroying refuse and garbage in crematories is approximately 50 cents per ton. He also says that the cost of operating destructors is from 50 cents to 70 cents per ton for actual labor expenses, while the cost of operating the modern high-temperature destructor will not exceed from 50 cents to 60 cents per ton. Deducting credit for power, the cost will drop, he says, to 30 cents or less per ton. Depreciation and capital expenses are not included in Morse’s calculations.
Greeley asserts that the cost of operation will range from about $1.00 to $1.50 per ton, “but local conditions may alter these limits.”
C. O. Bartlett, sanitary engineer, says: “So far as disposal of garbage is concerned, in incinerators, it is coming to be generally understood that this method is far from sanitary and is essentially wrong in that it neglects to obtain the value for the products so collected.”
Rudolph Herring, Sanitary Expert, says: “In incineration, if sufficient fuel is added, the combustion can be made perfect and the garbage can be destroyed without offense and converted into inodorous gases, ashes and clinker. Whatever sanitary objection has been made to this process has resulted from preventable causes. Unless ashes and rubbish are combined with garbage in sufficient quantities to produce the necessary heat, the steam production is deficient and other fuel must be added.”
Robert H. Wylde favors incineration at a high temperature: “Here we have a method that is at once sanitary, expeditious and economical in first cost and maintenance.” He also says that this method is free from nuisance, the plant may be centrally located, cost of collection minimized owing to the relative shortness of hauls, not necessary to maintain a separate collection, nor is there any necessity to keep refuse in separate cans.
W. F. Goodrich, Sanitary Expert, maintains that modern destructors are perfectly satisfactory and that there may be no fear of nuisance wherever they are located. He maintains that it should be the aim of officials to utilize the power produced for the best interests of the community.
William M. Venable believes that cities of from 10,000 to 40,000 population should burn garbage and refuse, the problem to be solved being the advisability of attempting to utilize the heat generated by burning.