Test proved the BOVAR system exceeded regulatory requirements.

Millions of tonnes of PCBs and other industrial waste materials are produced in North America each year. A significant amount of this is classified as hazardous waste for which incineration is the preferred means of treatment from both an environmental and economic perspective. Incineration poses a number of decided advantages over disposal technologies:

• The volume of hazardous waste is greatly reduced by incineration.
• Toxic compounds are converted into less harmful compounds.

The performance of incinerators can be predicted and measured on a continuous basis.

Incineration is an engineering process that uses thermal decomposition in a highly oxidative environment to decompose organic molecules into simple compounds, predominantly carbon dioxide and water. A necessary property of the waste material is that it be combustible. The incineration of organic compounds is well understood and the end result can be predicted by basic thermodynamic concepts including enthalpy, energy levels and psychometry. Subject to chemical equilibrium, the following general reactions will occur during incineration of waste materials:

• All hydrogen converts to water vapor, H2O.
• All carbon converts to carbon dioxide, CO2.
• All chloride (halogen) converts to hydrogen chloride, HCl, (Halogen acid).
• All sulphur converts to sulphur dioxide.
• Alkali metals convert to the hydroxide salt.
• Non alkali metals convert to oxides.

In assessing the performance of a hazardous waste incinerator it is not sufficient to restrict the evaluation to combustion efficiency as might be the case in a power boiler. An equally important aspect of incineration is the ability to remove pollutants that can be produced during the combustion process and those that are constituents of the waste material. Pollutants may also arise as a result of incomplete combustion while others are formed in the post combustion zone where conditions may be favorable to synthesis and recombination reactions. Pollutants in the flue gas stream include the well-known inorganic compounds such as hydrogen chloride, sulphur oxides and oxides of nitrogen but of more concern from a health and environmental perspective are organic compounds such as polycyclic aromatic hydrocarbons and metal emissions, particularly heavy metals.

Thus the common measurement of performance is expressed in terms of the Destruction and Removal Efficiency (DRE) for a designated component in the waste. DRE is usually expressed as a percentage. The standard of performance for incinerators used for hazardous waste treatment that has been adopted by all major environmental protection agencies, such as Environment Canada, Alberta Environmental Protection and the US EPA is 99.9999%. It is also customary to establish additional emission criteria including particulate matter, acid gases such as hydrogen chloride, carbon monoxide and pollutants of concern such as poly chlorinated dibenzo-dioxins (PCDDs) and poly chlorinated dibenzo-furans (PCDFs).

BOVAR Waste Management operates one of the most modern hazardous waste incinerators in North America. The facility located near Swan Hills, Alberta has conclusively demonstrated an operational performance that is superior to the regulatory requirements. This is the result of careful attention to the understanding of incineration processes, design and operating protocols.

Prior to receiving an Operating Approval from Alberta Environmental Protection, BOVAR was required to demonstrate the performance of the incinerator and its associated air pollution control devices through a series of test burns. These tests proved conclusively that the system exceeded the regulatory requirements.

In order to monitor the performance of the incinerator on an ongoing basis, a number of instruments continuously monitor stack emissions. The parameters monitored are oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen chloride (HCl), sulphur dioxide (SO2), oxides of nitrogen (NOx) and total hydrocarbons (THC). Oxygen, carbon monoxide, carbon dioxide and total hydrocarbons provide measures of combustion efficiency. The maintenance of high oxygen and low carbon monoxide levels are regulatory requirements that must be maintained at all times. Process interlocks will automatically shut off waste feeds if these parameters deviate from prescribed values. Similarly, the measurement of HCl and SO2 provide an accurate measure of the performance of the inorganic scrubbing system. These instruments will also bring about the termination of waste feeds if a variant condition is observed. In addition to these continuous measurements, BOVAR is required to test the incinerator on an annual basis to demonstrate that the incinerator continues to perform as intended and with the emission criteria. This is referred to as Compliance Testing and is conducted by an independent third party.

The following describes the technology employed in the BOVAR incinerator at the Swan Hills Treatment Centre and the performance as measured during a typical Compliance Test.

The technological keys to performance levels

In order to specify the appropriate operating parameters, it is necessary to have the waste characterized by laboratory analysis. The analysis of the waste must quantify the heating value, halogen content, and priority pollutants such as poly chlorinated biphenyl (PCB) and inorganic compounds such as heavy metals. This information allows the operator to establish the operating parameters that will achieve the necessary combustion conditions required to destroy the waste. The most important operating parameters for proper incineration are temperature, residence time, oxygen availability and turbulence or mixing.

During incineration, waste is combusted with air and, while the theoretical quantity of air can be calculated and supplied, it is necessary to provide excess air in order to achieve complete burning. Depending on the physical and chemical properties of the waste, excess air is supplied in amounts that range from 5% above the stoichiometric amount to more than 200% of the stoichiometric quantity.

In addition to predicting and managing combustion, the identification and control of emissions from incineration is a subject of intense debate. Emissions can be considered to be inorganic gas discharges, organic gas discharges and particulate discharges.

Inorganic gas discharges include carbon dioxide, acidic gases such as HCl and SO2 and CO. Emission limits for all of these except carbon dioxide are imposed on incinerator operators. The limits imposed by Alberta Environmental Protection are shown in Table 1.

Organic gas discharges may result from incomplete combustion of the waste material or from reactive compounds formed during the combustion process. The focus in recent years had been directed toward minimizing the emission of cyclic compounds in general and dioxins and furans in particular.

Particulate emissions include both organic and inorganic matter with emphasis on heavy metals and condensed organic compounds on particulate matter.

Duplication the key to superior performance

A feature of the BOVAR Waste Management incinerator is that each of the unit operations (combustion, acid gas scrubbing and particulate removal) is duplicated. Combustion is carried out in a primary combustion zone (the kiln) and in a secondary combustion zone (the Secondary Combustion Chamber). This ensures a high degree of combustion efficiency regardless of the physical and chemical characteristics of the waste. The combustion products or flue gas are then cleaned in two stages of gas scrubbing in which caustic is employed to remove acid gases and particulate matter is primarily removed by a fabric filter baghouse followed by a high energy scrubber. In addition to these features, the BOVAR incinerator employs a dioxin and furan control process that is proprietary.

These design features, coupled with the adherence to stringent operating protocols, result in a level of performance that BOVAR claims is equal to or better than any other hazardous waste incinerator in the world. The results reported during the 1998 Compliance Test are compared with the regulatory requirements in Table 1.

The values reported are calculated on a dry basis corrected to 11% oxygen at 25°C and 101.325 kPa.

The PCDD/PCDF Toxicity Equivalent is calculated in accordance with an internationally recognized formula that is based upon the toxicity of specific congeners as compared to 2,3,7,8 PCDD.

As the data supports, the BOVAR Waste Management incinerator clearly surpasses the regulatory requirements in all areas. These levels of performance are the result of both good design and good operating practice.