Refractory furnaces

In these mass burn, refractory panel combustion incinerators, waste is fed to the incinerator as received, with minimal pre-processing. As a by-product of waste disposal and incineration, the system can produce steam, hot water, and/or generate electricity. The combustion residue, ash, can be transformed into saleable products through vitrification.

Controlled Air Modular incinerators

Controlled Air Modular incinerators were designed in the 1960s as a major improvement in emissions and also in auxiliary fuel use. They were really the first generation of properly engineered incinerators. They were and continue to be a significant improvement over inefficient and smoky “burners”. When properly designed and operated they run under semi pyrolytic or starved air conditions with a limited amount of air allowed into the combustion chamber to maintain the temperature. Products of combustion then rise to a separate refractory lined secondary chamber where they are mixed with excess air at very high temperature to complete burnout of the hydrocarbons. Thousands of Controlled Air Modular incinerators are still in operation and are the cheapest initial capital cost systems. They are typically suited for the smallest applications.

Liquid injection incinerators

The liquid injection process involves wastes being atomised with high-pressure air or steam and burned in suspension. Liquid injection can be used to destroy virtually any pumpable waste or gas. These units have been used in the destruction of PCBs, solvents, still and reactor bottoms, polymer wastes and pesticides. Materials that are not likely to be treated by liquid injection include heavy metal wastes and wastes high in organics.

Negative factors associated with liquid injection incinerators are that they are highly sensitive to waste composition and flow changes. Therefore, storage and mixing tanks are necessary to ensure reasonably steady and homogeneous waste flow.

Rotary kilns

Rotary kiln processes involve wastes being burned in a rotating refractory cylinder. Rotary kilns are capable of burning wastes in any form and can incinerate solids and liquids independently or in any combination. Rotary kilns are capable of treating PCBs, tars, obsolete munitions, polyvinyl chloride wastes and bottoms from solvent reclamation operations. This method of incineration is the preferred method for treating mixed hazardous solids because of the ability to handle wastes in any form and the high incineration efficiency rate.

The limitations of rotary kilns include the susceptibility to thermal shock, the high degree of maintenance, the need for additional air due to leakage, the high particulate loadings, the relatively low thermal efficiency and the high capital cost for installation.

Multiple hearth incinerators

The multiple hearth incinerator is a system in which wastes descend through several grates to be burned in increasingly hotter combustion zones. This system can be used for the disposal of all forms of combustible industrial waste materials including sludges, tars, solids, liquids and gases. The principal advantages of multiple hearth incineration include high residence time for sludge and low volatile materials, ability to handle a variety of sludges, ability to evaporate large amounts of water, high fuel efficiency and the utilization of various fuels.

The greatest disadvantages of the multiple hearth incinerator include susceptibility to thermal shock, inability to handle wastes containing ash (which fuses into large rocklike structures) and wastes requiring very high temperatures. This type of incinerator also has high maintenance and operating costs associated with it, although this may be supplemented by utilizing liquid or gaseous combustible wastes as secondary fuel.

Fluidised bed incinerators

Fluidised bed incinerators are a relatively new design, presently being utilized for liquid, solid and gaseous combustible wastes. The process consists of a waste being injected into an agitated bed of heated inert particles. The bed usually comprises sand supportd by a perforated metal plate. Sufficient heat is then transferred to the wastes during combustion. The most typical types of wastes being treated in fluidised beds are slurries and sludges, and are usually used for the disposal of municipal wastewater treatment plant sludges, oil refinery waste and pulp and paper mill waste.

Additionally, this method of treatment has been used for pharmaceutical wastes, phenolic wastes and methyl methacrylate. High moisture wastes, sludges and wastes containing large quantities of ash are particularly well suited to this process.

The advantages of fluidised bed incinerators include simple design, minimal formation of oxides of nitrogen, long incinerator life, high efficiency, simplicity of operation and relatively low capital and maintenance costs. It also has the ability to trap some gases in the bed, thus reducing the need for air emission controls.

The disadvantages include the difficulty in removing residual materials from the bed, a relatively low throughput capacity, the difficulty in handling residues and ash from the bed, and the relatively high operating costs.