Medical waste incinerator
Medical wastes that can be burned on the incinerators include the “red bag” of medical wastes composed of sharps and biohazard glassware, preserved and non-preserved animal carcasses and infectious biological matter. Due to the potential for these waste products to be contaminated with infectious substances and biological agents, disposal is strictly regulated.
Types of medical waste incinerators
Controlled air – is the most widely used technology in medical waste incinerator. This technology is also known as starved-air incineration, two-stage incineration or modular combustion. Combustion of waste in the controlled air incinerators occurs in two stages. In the first stage, waste is fed into the primary or lower combustion chamber which is operated with less than the stoichiometric amount of air required for combustion. Primary or underfire air enters the primary chamber from beneath the incinerator hearth. In the primary starved-air chamber, the low air-to-fuel ratio dries and facilitates volatilization of wastes and most of the residual carbon in the ash burns. In the second stage, excess air is added to the volatile gases formed in the primary chamber to complete combustion.
Excess air incinerators – are typically small modular units that are also referred to as batch incinerators, multiple chamber incinerators or retort incinerators. This type of medical waste incinerator is typically composed of a compact cube with a series of internal chambers and baffles. These incinerators can be operated continuously usually in a batch mode. Those that are specifically designed for medical waste incineration operate at excess air levels of up to 300%.
Rotary kiln incinerators – are designed with a primary chamber where water is heated and volatized and a secondary chamber where the combustion of the volatile fraction is completed. Waste throughput rate is controlled by adjusting the rate of kiln rotation and angle of inclination. Due to the turbulent motion of waste in the primary chamber, solid burnout rates and particulate entrainment in the flue gas are higher for rotary kiln incinerators.
How emissions are controlled in the medical waste incinerator
Significant quantities of pollutants are emitted into the air by medical waste incinerators but it varies based on the type of incinerator. Controlled air incinerators have the lowest turbulence and consequently the lowest particulate matter emissions with rotary kiln incinerators having the highest PM emissions. In order to control emissions, control devices are used that include wet scrubbers and fabric filters. Wet scrubbers work through the principle of transferring pollutants from gas to a liquid stream with removal efficiencies of up to 93 % to 96%. In addition to wet scrubbers, dry sorbent injection and spray dryer absorbers are also used for acid gas control.