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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V 3 Incineration Introduction The mechanical processing methods discussed in Chapter 2 are mainly concerned with reducing the amount of air admixed with the waste material and converting the waste material to a substance that can be stored and transported with minimal difficulty. In this chapter, the committee focuses on incineration. Incineration can virtually eliminate the volume of paper products and plastic found in the shipboard waste stream, thus reducing the compacted volume of waste for storage by an order of magnitude. For this reason, incineration must be considered an important technology in connection with Navy compliance with Annex V restrictions. Even so, the cost of the equipment is high and considerable shipboard space is required. For example, a large unit, capable of burning the paper and plastic waste generated on an aircraft carrier, would occupy more than 1,000 ft3 of space for the unit alone, and probably twice that much when auxiliary systems are included. The system cost would be more than $300,000, before installation. Systems for smaller ships would cost less and take up less space. Installation of incinerators also implies considerable effort in crew training and development of management procedures. Taking account of the capability and the cost, incineration is a promising technology for Annex V compliance for ships that will be assigned to lengthy missions in Special Areas. Furthermore, it is the central technology for an integrated system designed to handle all shipboard sources of pollution: Annex V materials, food wastes, medical wastes, and so on. In this context, incineration serves the near-, intermediate-, and long-term needs of the Navy. Incineration is a flexible method of waste destruction for flammable waste materials, and it has been fairly widely used for this purpose on board commercial vessels, with several thousand units having been installed worldwide. The Navy has extensive experience with shipboard incinerators of an older generation, and the committee has anecdotal information that the experience was not entirely satisfactory. In addition, there have been objections to the use of incineration both on land and at sea from some environmental groups. The incinerators discussed herein are of modern design and have automatic feed, automatically controlled combustion sequences, and automatic ash-handling features. The apparatus would not be recommended if safety and air emissions could not be guaranteed to meet current and presently established future standards. The committee believes that advanced commercial incineration equipment exists that can handle ship wastes with safety and with acceptable air emissions. The large volume reduction achievable —three-fourths of the Annex V volume by burning of paper alone—makes the method a major candidate. Plastic is also burnable and, for the plastic said to be in Navy waste, the combustion should be clean. By burning paper and plastics, a 90 percent volume reduction can be achieved. There is, however, a program to deal with Navy plastic waste by use of a specialized machine that molds the plastic into dense plastic discs for storage and later transfer for land disposal or recycling. This plastics processor achieves the nearly maximum volume reduction that can be obtained by mechanical means. Incineration of plastics leaves only a small amount of ash, probably less than 1 percent of the volume of the discs, that can be discharged into the ocean outside Special Areas. The relative merits of the two methods of plastic disposal are perhaps less important than the timing of availability. The Navy plastics processor has been tested and can be installed fleetwide to eliminate plastic ocean discharge for all surface ships by the year 2000. (The United Kingdom is already installing compactors and plastics processors in 12 Royal Navy ships.) Incineration will almost certainly take longer to implement in all Navy surface ships, although
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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V there are 107 incinerators on Navy ships capable of burning 70 percent of the total Navy paper and plastic waste. For purposes of this discussion, the committee focuses on the capabilities of incineration in the context of the Annex V materials. Information provided by the Navy (U.S. Navy, 1993) is given in Table 3.1, which lists the amount of paper generated and the incinerator capacity for the various classes of ships. Aircraft carriers appear to have more than adequate capacity to burn all paper generated, as do a significant fraction of auxiliaries and amphibious ships (the numbers for the latter categories are ambiguous because the number of ships that will remain in commission after 1998 is uncertain). These incinerators may not provide features offered in more modern equipment (for example, automatic feed, automatic combustion controls, and ash-handling apparatus), but, in many cases, they could provide for the needs of their respective ships while operating well below incineration capacity. The total paper generated on an aircraft carrier over a mission comes to over 20,000 ft3 compacted, and this is more than an order of magnitude larger than the volume of a large incinerator. Thus, incineration of paper is justified on large ships with large complements and long missions. The other classes listed in Table 3.1 have no incinerator facilities. Additional information provided by the Navy (U.S. Navy, 1993) for these ships is included in Table 3.2. On the basis of available information on the sizes of small incinerators, the committee concludes that incineration could be justified except for the smallest ships; for the smaller ships, the best strategy could be compaction and storage of paper over the duration of the mission. The addition of metal, glass, and plastics in compacted form would increase the required storage volume by less than 25 percent, and the committee concludes that the rationale would be unchanged if all Annex V materials were handled by adding compaction and storage. Food waste contamination has not been considered in the foregoing argument. If the Annex V materials are contaminated with food waste, storage can become a problem because of the development of odors and possibly pathogens. If this is a problem, the case for installation of incinerators is much stronger. This factor, taken together with the benefits flowing from installation of an integrated system capable of handling all of a ship's waste streams, could increase the number of ships for which incineration is applicable. Table 3.1 Paper Generated by and Incinerator Capacity of U.S. Navy Ships CLASS NUMBER 1 COMPLEMENT MISSION DAYS INCINERATOR CAPACITY (LB/H ) PAPER GENERATED (LB/H ) Auxiliary 50 to 55 90 to 2,500 30 500 2 <80 Cruiser 29 400 to 600 30 0 <30 Carrier 11 5,800 to 6,300 60 1,000 <300 Destroyer 83 300 to 400 30 0 <20 Frigate 51 220 30 0 <10 Amphibious 35 to 68 600 to 3,230 60 500 2 <150 Mine 27 50 to 90 15 0 <5 Patrol 13 35 3 0 <3 1 Number of ships in commission after 1998. 2 Incinerator capacity on 40 of 50 to 55 auxiliary and 30 of 35 to 68 amphibious ships. Source: U.S. Navy (1993).
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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V Table 3.2 Paper Generated by U.S. Navy Ships with No On-board Incinerator CLASS POUNDS /HOUR PAPER GENERATED (POUNDS /MISSION ) CUBIC FEET /MISSION UNPROCESSED CUBIC FEET /MISSION COMPACTED Cruiser (CGN 26) 28 20,000 3,400 1,000 Cruiser (CG 47) 19 14,000 2,300 700 Destroyer 14 to 18 10,000 to 13,000 1,600 to 2,200 500 to 700 Frigate 10 7,300 1,200 400 Mine ships 3 to 4 830 140 42 Source: U.S. Navy (1993). Applicability of Incineration to Navy Vessels In the foregoing section, one sees that a significant number of larger Navy vessels are equipped with incinerators and that the capacity available is more than equal to burning all paper and plastic wastes generated on these ships. These installed units have manual feed, do not have provision for auxiliary fuel use, and do not have the controls that reflect current best incineration practice. The existence of installed ducting needed for discharge of the products of combustion may reduce the amount of redesign and cost of retrofit with state-of-the-art units or modernization of existing incinerators. Table 3.3 presents information on selected commercial incinerators. Price comparisons are difficult, and the numbers given are intended only to indicate the range available. All of the units are furnished with automatic feed and ash-handling equipment. All four units offer shock cooling for dioxin control. Automatic operation was discussed in Materials for Construction of Shipboard Waste Incinerators (NRC, 1977). Table 3.3 Commercial Incinerator Equipment VENDOR CAPACITY (LB/H ) FOOTPRINT (FT 2 ) AUXILIARY OIL BURNER PARTICULATES PRICE ($) AUTO FEED /ASH Ventomatic 500 1 75 2 Optional Cyclone 150,000 Yes Brule 500 1 80 2 Optional Cyclone 250,000 Yes Norsk Hydro 1,000 3 300 2 Burner On 3-Chamber 350,000 Yes Techno-Products (Deerberg) 1,000 3 200 2 Burner-On 3-Chamber 450,000 Yes Golar 330 3 110 Burner On 2-Chamber – Yes 1 From Navy specifications. 2 From vendor's drawings. 3 Calculated, approximately, from vendor-supplied kW figures assuming trash fuel only at 8,000 BTU/lb. Because of the similarity of waste streams on board Navy, cruise line, and other vessels, vendors of commercial incineration equipment may be able to adapt their technologies to Navy ships. Some factors that need to be considered in adapting these technologies to Navy use are discussed in the following section. It is important to establish a program to train an engineering technical rating, i.e., a specific crew assignment, in the proper operation and maintenance of the incinerators in use. The issues
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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V include fire hazards, equipment damage, and environmental impact. The manufacturers are valuable sources of information in this connection. Factors in the Use of Incineration Feed Systems A continuous feed system is needed to eliminate the hazards now encountered with manual introduction of waste into the flames in the firebox. For purposes of ease of feeding, the solids are first shredded. This also provides for the homogenization of the waste stream and for more uniform burning rates. Some systems have gravity feed. A screw feed system might be more appropriate for Navy application where the height of the unit and the number of decks involved would be an issue. Also, in modernization of existing incinerators, single-deck installations are more readily adapted. Both paper and plastic have good fuel value. They would not present any problem to incinerators as long as they formed part of the mixed waste stream, avoiding surges in high-temperature gases or volatiles that might be produced if waste consisting solely of plastics was burned. Incinerator Grates Burning rates on modern grates are in the range of 60 to 100 pounds of waste per square foot per hour. A modest grate size of 4 ft × 4 ft would therefore be capable of providing a capacity greater than 1,000 lb/h, adequate to handle the wastes from even the largest ships. A moving or reciprocating grate would be desirable to move the residue from the feed to the ash removal chute. Combustion Chambers The rule of thumb for good combustion is a residence time of 2 seconds at 1,800ºF with oxygen contents of at least 2 percent. Although such temperatures can be sustained with the average heating value of the waste streams, the use of burners fired with auxiliary fuel in both the primary and secondary combustion chambers is advantageous to ensure burning of low heating value wastes. Good combustion at much shorter residence times is achievable if good mixing is provided and advantage is taken of the much higher temperatures present at diffusion flame fronts produced at the interface of the volatiles generated by the waste and air. The size of the incinerators can therefore be reduced considerably using advanced combustion theory, modern instrumentation, and computer controls. Design of compact incinerators using some of the advances in combustion science is under way as part of the Navy program administered by China Lake (Schadow, 1995). Cooling Systems The gases from combustion chambers should be cooled prior to their exhaust. Where there is use for supplementary heat, the gases could be cooled in a waste heat boiler or heat exchanger. The amount of energy that can be recovered is not large, however, and it would probably be more cost effective to cool the gases by dilution with excess air (NRC, 1977). This kind of cooling system is used in the commercial incinerator in service aboard the USS Theodore Roosevelt. Excess air is injected into hot combustion products by use of an eductor. The high velocity from the eductor is also used to provide partial particle removal through the centrifugal forces imparted to the particles in the effluent gas stream. Emissions International Maritime Organization regulations for incinerators (IMO 73/78) are not very restrictive at this time. The following specifications must be met: (1) CO levels must be lower than 200 g/m3; (2) the smoke number must be below Bacharach 3; and (3) carbon in the ash must be below 10
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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V percent. These regulations should be met without difficulty by any modern, well-operated incinerator. Future IMO regulations can be expected to be much more restrictive. The committee anticipates that new regulations will be drawn from land-based regulations. At all times, emissions should be kept at levels that pose no threat to human health or the environment. Present wisdom indicates that emissions of importance from incinerators include dioxins and toxic metals. The emissions of nitrogen and sulfur oxides will be small and will be exceeded by orders of magnitude by the emissions from the engines powering the ships or carrier aircraft. The following are suggested as prudent guidelines for reducing emissions. Organic Compounds Emissions of organic compounds, particularly polychlorinated dibenzodioxins and polychlorinated dibenzofurans, can be reduced to acceptably low levels through the use of good combustion practice. The traditional criteria for incineration with a residence time of 2 seconds at 1,800 ºF will achieve these goals as long as no locally fuel-rich regions are produced by poor mixing or by surges of emissions of volatiles from intermittent feeding of highly volatile wastes. There are two mechanisms for the formation of dioxins: (1) a homogeneous mechanism in which products of incomplete combustion are converted to dioxins in the temperature range 1,600 to 1,800ºF, and (2) a heterogeneous mechanism in which products of incomplete combustion react on the surface of fly ash in the temperature range 480 to 660ºF. Based on this understanding, dioxin production can be controlled by reducing the amount of incomplete combustion. A more important step is the reduction of particle loading and residence time in the temperature range in which dioxin is produced. This can be done by rapidly quenching the combustion products to temperatures below 480ºF and/or removing particles from the combustion products above 660ºF. A recent survey of the emissions of a number of different incinerator types—municipal waste, medical and hazardous waste—suggests that chlorine content is of secondary importance in dioxin production. The dominant factors controlling dioxins are found to be the completeness of combustion, the temperature at which the electrostatic precipitator is operated, and the ash content and composition in the flue gas stream. A goal of 30 ng/m3 proposed for land-based units should be attainable by incinerators on board Navy ships without regulating chlorine in the feed. Particulate Matter Most of the mass of particles in the combustion products are due to entrainment of ash from the combustion chamber. These particles are usually in the 1 to 50 µm range and have compositions similar to those of the ash residue. In addition, submicrometer particles enriched in toxic metals such as lead, cadmium, and arsenic will be formed by the vaporization of these metals in the combustion chamber and their condensation in the cooler region downstream. The use of inertial separation devices will selectively capture the larger particles. Technologies should be adopted that can reduce particulate emissions to less than 30 mg/m3. This level is characteristic of good land-based incinerators. Furthermore, the technologies should be able to capture the smaller submicrometer particles enriched in the potentially toxic metals. An example of a technology under development that could be used is a compact ceramic filter. These filters can reduce emissions of fine particles to levels below most stringent land-based standards (CeraMem Separations, Waltham, Massachusetts, private communication, 1995). They have high particle removal efficiencies (> 99.99 percent). A filter of 7-inch diameter and 15-inch length at a typical operating face velocity of 4 ft/min would handle 100 actual ft3/min. The ceramic construction enables operation at temperatures up to 1,800ºF, although it would be preferable to operate at lower temperatures to reduce the pressure drop, but above 660ºF to reduce dioxin formation. Mercury would remain volatile at these temperatures, and the reasonable course of action is to eliminate this element from the waste stream. Batteries and fluorescent lights should be kept strictly out of the feed.
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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V Acid Gas The emission of hydrochloric acid can be controlled by scrubbing, and suitable equipment is available from vendors of commercial incinerators. The apparatus is sizable, however, and it is not clear that it is justified in the space-sensitive circumstances characteristic of Navy ships. Where it is determined that HCl emissions are deemed to be a problem, the emissions might be best controlled by regulating the chlorine content of the waste streams. Health and Air Quality Concerns Incineration of shipboard wastes will give rise to gaseous emissions, most of which will be vented up a stack along with engine exhaust, but operators may be exposed to emissions that escape directly into the incinerator room. Navy personnel on board should be considered from the standpoint of health effects of these emissions, and incinerator operators should be protected in the occupational health sense. It is incumbent upon the Navy, as it continues to operate large numbers of shipboard incinerators, to measure actual emissions of vessels at sea and in harbors, both in the incinerator room and at appropriate sites on the ship. Screening of equipment through land-based measurement should also continue. The measured substances should be those of concern to operators of land-based incinerators. For example, U.S. Environmental Protection Agency (EPA) guidelines (U.S. EPA, 1994) place limits on the following materials: particulates, cadmium, lead, mercury, sulfur dioxide, hydrogen chloride, and ash. To this list, we may add dioxins, furans, and other known or suspected human health hazards. There are no public health or occupational health standards for shipboard incinerator emissions, although the EPA is rumored to be near the point of releasing relevant information. It should be kept in mind that the individual substance exposure may not impose the greatest danger to exposed individuals. The totality of exposure should be studied as well. With measurement results in hand, and with the Navy's controlled population and excellent record keeping practice on health matters, an exemplary program of personnel protection can be established. In certain circumstances, burning 3 or 4 tons per day of paper products and, possibly, plastics may affect air quality in coastal areas or in surrounding vessels. Such effects will depend on the distances involved and the local meteorological conditions. The importance of these factors can be estimated using appropriate meteorological models. In some cases, additional experimental and field studies may be required to extend existing models. Refer to Appendix C for additional discussion. Obstacles to Incineration Incineration has met resistance by some environmental groups. Some of this opposition has grown out of some poor combustion practices in the past, but modern incinerators have greatly reduced the emissions that led to the poor image. Also, perceptions that have no basis in science or engineering have contributed to the opposition. Nevertheless, the image persists, and the Navy should be prepared to demonstrate that environmental issues have been considered and overcome. Incineration as a waste management tool has been supported by academic and industrial researchers. It should be further noted that amendments to MARPOL have been proposed, including the statement: “Subject to the provisions of paragraph 5 of this regulation, incineration shall not take place (a) within the Antarctic area as defined in regulation 10(g) of Annex I, of the present convention, (b) inside ports, harbors, and estuaries. ” These potential constraints on the use of incineration should be kept in mind as consideration of Navy incineration systems progresses. Short-Term Implementation of the Incineration Option This section presents a possible scenario for implementing incineration as a short-term approach to the Navy's solid waste disposal problem. According to information supplied by the Navy (U.S. Navy,
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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V 1993), 93 ships currently are equipped with 107 incinerators (103 with a capacity of 500 lb/h and 4 with a capacity of 250 lb/h). These units can burn paper, cardboard, incidental plastics, oily rags, food-contaminated containers, and containers contaminated by oil and paint. Approximately 70 percent of the total burnable waste is generated on ships with incinerators and could be burned. The Navy could install an automated feed system in the existing incinerators. The new feed system would feed solid wastes at the design rate of the incinerator and provide safe operation without overheating. At about $100,000 per incinerator, the total procurement cost would be about $11 million and is estimated to be achievable in 3 years. In addition, incinerators similar to those now in service could be installed on those auxiliary and amphibious ships that do not now have incinerators. From 12 to 30 such ships will remain in commission after 1998, implying a cost of $3 million to $8 million based on a unit cost of $250,000, including automatic feed. This is estimated to be achievable in 5 years. The remaining solid waste generated on smaller ships that have no incinerator (e.g., cruisers, destroyers, and so on) could be transferred to ships having incinerators for destruction. To facilitate this process, the Navy would need to design and supply to all ships a standard solid-waste-transfer container that is large enough to hold approximately 1 or 2 days' solid waste. The design should be lightweight and collapsible and used to transfer waste by Burton Rig or helicopter. There are about 200 of these smaller ships and, assuming each will receive five containers, at about $1,000 each, the total cost would be of the order of $1 million. This plan could be implemented in a relatively short time.
Representative terms from entire chapter: