Hazardous Waste Fuel

Many industrial wastes, including hazardous wastes, are burned as hazardous waste fuel for energy recovery in industrial furnaces and boilers and in incinerators for nonhazardous wastes, such as sewage sludge incinerators. This process is called coincineration, and more combustible wastes are utilized by it than are burned solely for the purpose of waste destruction. In addition to heat recovery from combustible wastes, it is a major advantage to use an existing on-site facility for waste disposal rather than a separate hazardous waste incinerator. 

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Of the 3 million tons of hazardous waste sent for combustion, about half was processed in BIFs. Boilers are normally used for energy recovery. Hazardous waste fuels provide about 50% of a boiler s fuel requirements and are normally mixed with natural gas or other fuels.21 There are around... 

Of course, by using hazardous waste fuels, the nation s hazardous waste (including infectious waste) problem is at least partially solved with an economic advantage. 

By substituting only 15% of its fossil fuel needs with solid hazardous waste fuel, a modern dry-process cement plant with an annual production capacity of 650,000 tons of clinker can save the energy equivalent of 50,000 barrels of oil (or 12,500 tons of coal) a year. Southdown typically replaces 10-20% of the fossil fuels it needs to make cement with hazardous waste fuels. 

Under USEPA s BIF mle, manufacturers are required to closely monitor numerous conditions in the kiln and to observe limits on the following aspects of the process (a) the maximum feed rate of hazardous waste fuel (b) the maximum feed rate of metals from both raw materials and fuels (c) the maximum feed rate of chlorine from raw materials and fuels (d) the maximum feed rate of raw materials (e) the maximum temperature at the inlet to the air pollution control devices (f) the maximum concentration of carbon monoxide and total hydrocarbons in the flue gas (g) the maximum temperature in the combustion zone or minimum temperature at the kiln inlet and (h) any decrease of pressure at the baghouses or any decline in the strength of the electric field of electrostatic precipitators (both are types of air pollution control devices). 

Because cement kilns are so good at destroying organic chemical wastes, emissions of dioxins - or any other type of products of incomplete combustion (PIC) - are so low they pose no danger to the environment. In the case where some of the hazardous waste fuels used contain toxic dioxin, the cement kiln temperatures of 1650°F will destroy dioxins in less than one second. Because cement kilns operate at much higher temperatures (at least 2450°F), and because the burning wastes have an average residence time in the kiln of at least two seconds, any dioxins are destroyed. However, dioxin waste is never accepted by Southdown for use in its cement kilns. 

Cement made with hazardous waste fuels contains essentially the same amount of metals as cement made using traditional fossil fuels, such as coal, coke, or oil. Also, tests show cement made with hazardous waste fuels has essentially identical leaching characteristics as those of cement produced solely with traditional fuels. This means the metals are no more likely to leach out of the cement made using hazardous waste fuels than if it were made using coal, coke, or oil. 

Health risks to residents near cement kilns may actually decrease when hazardous waste fuels are used. This is because the permit needed to recycle hazardous waste fuels requires more stringent emissions controls than those for cement kilns using only fossil fuels. Also, fossil fuels contain natural impurities that are reduced or no longer emitted when some types of hazardous waste fuels are used. 

Both fossil fuels and hazardous waste fuels used in Southdown cement kilns contain metals. The raw materials (limestone, clay, sand) used to make cement clinker also contain metals. In fact, certain metals, such as iron and aluminum, are essential components of the final product. While metals cannot be destroyed, the Southdown cement kiln process effectively manages them in the following ways (a) cement kiln operators limit emissions by carefully restricting the metals content in wastes accepted for recycling (b) dust particles containing metals are returned to the kUn through closed-loop mechanisms, where metals are chemically bonded into the cement clinker (c) particles not returned to the kiln are captured in state-of-the-art pollution control devices and (d) small amounts are emitted from the stack in quantities strictly hmited by USEPA s BIF mle. 

Thorium, uranium, and plutonium are well known for their role as the basic fuels (or sources of fuel) for the release of nuclear energy (5). The importance of the remainder of the actinide group Hes at present, for the most part, in the realm of pure research, but a number of practical appHcations are also known (6). The actinides present a storage-life problem in nuclear waste disposal and consideration is being given to separation methods for their recovery prior to disposal (see Waste treati nt, hazardous waste Nuclear reactors, waste managet nt). 

Regulations require that the incinerator furnace be at normal operating conditions, including furnace temperature, before hazardous wastes are injected. This requires auxiUary fuel burners for furnace preheating. In addition, the burners provide heat when the wastes burned are of low heating value. Auxihary burners are sized for conditions where Hquid wastes are injected without the addition of high heating value wastes. 

Mere destruction of the original hazardous material is not, however, an adequate measure of the performance of an incinerator. Products of incomplete combustion can be as toxic as, or even more toxic than, the materials from which they evolve. Indeed, highly mutagenic PAHs are readily generated along with soot in fuel-rich regions of most hydrocarbon flames. Formation of dioxins in the combustion of chlorinated hydrocarbons has also been reported. We need to understand the entire sequence of reactions involved in incineration in order to assess the effectiveness and risks of hazardous waste incineration. 

The effectiveness of incineration has most commonly been estimated from the heating value of the fuel, a parameter that has little to do with the rate or mechanism of destraction. Alternative ways to assess the effectiveness of incineration destraction of various constituents of a hazardous waste stream have been proposed, such as assessment methods based on the kinetics of thermal decomposition of the constituents or on the susceptibility of individual constituents to free-radical attack. Laboratory studies of waste incineration have demonstrated that no single ranking procedure is appropriate for all incinerator conditions. For example, acceptably low levels of some test compounds, such as methylene chloride, have proved difficult to achieve because these compounds are formed in the flame from other chemical species. 

Confusion as to what constitutes municipal waste is presenting an obstacle to the use of packaging waste as a fuel in cement kilns. Whilst cement kilns can bum hazardous waste, they cannot bum a wide range of non-hazardous materials, it is reported. The case of Castle Cement is described which planned to bum a range of non-hazardous commercial and industrial wastes. Some waste-fired combustion processes, however, such as UK Waste s Fibre Fuel operation have been granted derogations where fuel is manufactured by advanced mechanical processes, which includes the production of fuel pellets. This latter process would be pointless for the cement industry since their fuels have to be pulverised. The problems are further discussed with reference to current European legislation. 

Waste-derived fuels from refining processes Fuels produced by refining oil-bearing hazardous wastes with normal process streams at petroleum refining facilities are exempt if such wastes resulted from normal petroleum refining, production, and transportation practices. For these wastes to be considered as refined, they must be inserted into a part of the process designed to remove contaminants. This would typically mean insertion prior to distillation. 

Unrefined waste-derived fuels and oils Fuels produced at a petroleum refinery from oilbearing hazardous wastes that are introduced into the refining process after the distillation step or that are reintroduced in a process that does not include distillation are exempt if the resulting fuel meets the specifications under the federal recycled used oil standards. Oil that is recovered from hazardous waste at a petroleum refinery and burned as a fuel is also exempt provided it meets the used oil specifications. 

Industrial furnaces are enclosed units that are integral parts of a manufacturing process and use thermal treatment to recover materials or energy from hazardous waste. These units may use hazardous waste as a fuel to heat raw materials to make a commodity (e.g., a cement kiln making cement) or the unit may recover materials from the actual hazardous waste (e.g., a lead smelter recovering lead values). The following 12 devices meet the definition of an industrial furnace12 ... 

Scrap metal comprises worn or extra bits and pieces of metal parts, such as scrap piping and wire, or worn metal items, such as scrap automobile parts and radiators. If scrap metal is reclaimed, it is a solid waste and is subject to hazardous waste regulation. Scrap metal is also regulated as a solid waste when used in a manner constituting disposal burned for energy recovery, used to produce a fuel, or contained in fuels or accumulated speculatively. This does not apply to processed scrap metal, which is excluded from hazardous waste generation entirely. 

Owners/operators of facilities that burn small quantities of hazardous waste with a heating value of 5000 Btu/lb are also exempt from Part 266, Subpart H.5 They must, however, comply with the quantity restrictions based on stack height and the surrounding terrain. Also, the hazardous waste firing rate may not exceed 1% of the total fuel requirements. These units are prohibited from burning any waste that contains or is derived from dioxin-bearing wastes. Small quantity burners are required... 

These requirements do not apply to a furnace that bums hazardous waste solely as an ingredient. The requirements also do not apply to any furnace that feeds the hazardous waste into the hot end of the furnace, where products are normally discharged and fuels are normally fired. 

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