Thermal Treatment of Hazardous Waste - Mobile IncineratorsThe transportable Waste Incineration System (TWIS) is designed to be transported to sites requiring soil remediation, destruction of hydrocarbon sludge and hazardous waste incineration. For example, it was set up on a barge and transported by it to the site in Alaska where the Exxon-Valdez oil tanker had run aground and released its oil cargo into the environment. The TWIS is carrying valid operational permits in the USA. The TWIS consists of the following essential elements: Solid waste feed hopperVariable-speed feed screw delivering the wastes into the rotary kilnCombination oil/gas burner, with dedicated combustion air blower, and air-atomized fuel oil burner which provides the heat needed to maintain a kiln exit gas temperature of approximately 1500°F while feeding solid wastes or liquid wastes.Air-atomized nozzle which can be used for injection of suitably-prepared wastes or fuels into the burner end of the kiln.Variable-speed drive which rotates the kiln, used to control the "burnout" of the solids.Screw take-away conveyor which collects the processed solids from the end of the kiln and delivers them to the processed solids storage hopper.Refractory -lined cyclone which separates the air-borne fine solids from the gases leaving the kiln, returning them through a pair of flap-discharge valves to the processed-soil conveyor.Refractory blanket-lined secondary chamber serving as an after-burner, which raises the temperature of the gases leaving the cyclone to 1800°-2000°F, employing a gas/oil-fired burner to achieve and automatically maintain this temperature. The secondary burner oil-atomizing gun can be used to burn selected liquid wastes in the secondary chamber .A Fisher-Klosterman (F-K) emission control system uses water to quench the gases leaving the secondary chamber from 1800°-2000°F to about 190°F, while they pass through a “flooded elbow” venturi scrubber to absorb and remove particulate matter, and then through a packed bed scrubbing tower.The acid gases absorbed by the scrubber water are neutralized by injection of sodium hydroxide, which is added to maintain the pH at about 7. The circulating water, containing particulate matter and salts is blown down as needed to keep the total solids at an acceptable level. Makeup water is added to compensate for the water evaporated as the gases are cooled, and the blow-down need to control the solids content.A demister unit is installed at the end of the flue gas treatment train. This demister acts as a mist eliminator, thus reducing mist and particulate matter which escapes the scrubber. This unit provides the final “safety guard” for keeping emissions of heavy metals and particulates below required levels.The induced-draft (induction) fan pulls the gases through the entire system and discharges them through the stack to the atmosphere. Atmospheric air is drawn in through clearances in the front seal of the kiln, providing combustion air for fuel and organic wastes in excess of that provided by the oil/gas burner blower. Oxygen monitors located at the exit of the kiln and the secondary chamber are used to assure sufficient excess oxygen. Treatment Capacity:Waste intake:Up to 10 ton/hourTypes of Waste:Soils polluted with hydrocarbonsOily sludgeOrganic residues as distillation bottoms or process sludgeSpent organics as used solvents and oilsInfectious and/or bio-hazardous medicalMunicipal waste Emission Control System:The emission control system of the TWIS is described below. The cyclone removes all of the coarse and most of the fine particles from the gases leaving the rotary kiln. The secondary chamber serves as an after-burner in order to destroy organic matter contained in the gases leaving the cyclone. Temperatures above 1600°F along with a retention time of two seconds are found to be sufficient for destruction of essentially all organic matter. However, to assure destruction of more refractory organics, such as PCB’s, or when the chlorine content of the waste exceeds 1%, regulatory agencies have recommended that 2000°F be maintained at the exit of the secondary chamber. The TWIS has the capability of maintaining this temperature when or if needed. Gases leaving the secondary chamber are quenched with water sprays before entering the venturi section of the scrubber. The venturi causes agglomeration of particulate matter, and absorption of particulate into the water. The gas temperature is reduced, approaching 180°F before entering the packed tower. The packed tower is effective in removing remaining particulate, but is specifically provided in order to absorb acid gases, including sulfur dioxide, hydrogen chloride and hydrogen fluoride. Water is sprayed over the packed bed. As it falls, it absorbs the acids, reducing its pH. In order to maintain stable pH values, caustic soda (NaOH) is added, controlled by a pH meter. The pH of blow-down is conventionally maintained at roughly 7.0 in order to meet regulatory discharge requirements to sewers. A demister unit is installed at the end of the flue gas treatment train. This demister acts as a mist eliminator, thus reducing mist and particulate matter which escapes the scrubber. This unit provides the final “safety guard” for keeping emissions of heavy metals and particulates below required levels. This unit is considered as Best Available Technology for pollution control is wet scrubbing systems as employed in the TWIS. The TWIS in equipped with a state-of-the-art continuous on-line emission monitoring system (OEM). The system is computer-controlled and interacts with important unit features as burner control following the reading obtained by the system. The continuous emission monitoring system samples and records levels of:COCO2THC - Total HydrocarbonsOpacity & Particulate matter