Incineration of Persistent Organic Pollutants

Since the enactment of environmental laws and regulations in Canada and the United States in the 1970's and 1980's, many treatment and disposal options for hazardous waste have come and gone.  Despite the development of new technologies over the years, high-temperature incineration continues to be the "tried and true" method to dispose of hazardous wastes and offers the best solution to dispose of Persistent Organic Pollutants (POP's) including polychlorinated biphenyls (PCBs) and dioxin/furan contaminated wastes

Once widely used, PCBs are a very stable, non-corrosive and relatively nonflammable chemical substance.  They are insoluble in water and act as excellent dielectric insulators and heat conductors.  These properties made PCBs a valuable industrial chemical used in a variety of products, most often in electrical equipment.  Unfortunately, these same properties have also made PCBs difficult to remove from the environment and one of the most difficult wastes to destroy.  Indeed, this is one reason why PCB's are used as a test material for compliance testing for our incinerator.  A dangerous characteristic of PCBs is that dioxins and furans are formed as a byproduct of incineration at low temperatures and also reform upon cooling in incineration processes

The only incineration facility in Canada currently permitted to dispose of all PCBs, dioxin/furan wastes and ozone depleting substances (ODS) in all forms (solid, liquid, sludge and gaseous) is the Swan Hills Treatment Centre (SHTC) near Swan Hills, Alberta.  The state-of-the-art facility employs a large Ford Bacon and Davis (FB&D) rotary kiln incinerator to destroy all organic wastes sent to the facility.  The kiln has inside dimensions of 4.4 metres diameter by 12 metres and a nominal treatment capacity of 40,000 metric tonnes per year.  It is capable of handling bulk and drummed solids, aqueous and organic liquids and ODS using various feed systems, which permit their simultaneous introduction.

Thermal oxidation processes generally operate at temperatures of 900° C or higher, that is, temperatures at which most organic compounds are destroyed.  Destruction efficiencies of 99.99% are readily achieved in well-designed units that are operated properly.  High performance incinerators (like the FB&D) which are designed specifically to destroy stable organic compounds such as PCBs and ODS, operate at significantly higher temperatures, generally at 1,200° C or higher.  Such high performance incinerators generally achieve 99.9999% destruction efficiencies or better.

Organic wastes are processed in the primary combustion chamber of the FB&D rotary kiln at temperatures of 800° C to 1,200° C.  All organic compounds are volatized and many compounds are destroyed at this stage.

The operating temperature of the secondary combustion chamber is maintained at 1,200° C (higher than the 1,100° C typical for conventional incinerators).  The FB&D has been designed to ensure adequate residence time of more than 2 seconds at temperatures greater that 1,200° C with sufficiently turbulent conditions and ample oxygen (in excess of stoichiometric requirements) to ensure destruction of PCBs to a Destruction and Removal Efficiency (DRE) of 99.9999%.  The SHTC submits the FB&D incinerator to a three-day compliance test every 6-16 months during which the kiln is loaded with PCB material to demonstrate the unit's effectiveness.  Compliance tests throughout the life of the kiln have consistently demonstrated higher than the 99.9999% ("six-nines") DRE required by our operating approval with the DRE's of 99.999999% or ("eight-nines) commonplace.

The incineration process produces a number of by-products.  The primary products from the thermal destruction of PCB and ODS wastes are carbon dioxide (CO2), water (H2O) and hydrochloric and hydrofluoric acids (HCI and HF).  Hydrogen bromide (HBr) and/or bromine (Br2) are produced in the case of the destruction of halons.  Products of incomplete combustion (PIC's such as carbon monoxide, small chain of hydrobardons, organic acids and partically degraded products) may also be produced, but these PIC's are emitted in only minute amounts from well-designed incineration facilities.  To remove the maximum PIC's it is important that the incinerator provide high temperatures, adequate residence times (1-2 seconds), excess oxygen and good mixing to achieve the best results.

An important part of any incinerator is the pollution control system.  At the SHTC our pollution control systems are amongst the most advanced in the world.  As part of the FB&D proprietary pollution control system we inject activated carbon during the gas scrubbing stage to remove trace dioxins and furans which may have been formed during post combustion cooling.

Once the wastes are destroyed the residual ash is tested to ensure that it is inert.  Once classified inert, it is then placed in our-on-site secure hazardous waste engineered landfill.  Inert process waters used in the pollution control system are disposed of in an engineered deep-well 1,800 - 2,000 metres deep.