BY Peter W, Falcone, P. E. Rollins Environmental Services, Inc. Wilmington, Delaware

Transcription

1 ROLLINS' ROTARY REACTOR: INCINERATION OF LOW BTU HAZARDOUS WASTE INTRODUCTION BY Peter W, Falcone, P. E. Rollins Environmental Services, Inc. Wilmington, Delaware The Rollins Rotary Reactor (RRR) incinerator was conceived to serve the needs of a particular segment of the commercial hazardous waste disposal industry. Specifically, there exist numerous sites throughout the nation containing large quantities of sludges and soils contaminated with various amounts of hazardous materials making them subject to RCRA regulations. These materials may come from Superfund locations, accidental chemical spills, wastewater treatment sludges and cleanups within operating facilities. Typically, the calorific value of waste materials in this category is low and they may.contain significant amounts of moisture. Decontamination of these materials by incineration is the preferred method in many instances. A conventional rotary kiln incinerator is capable of processing these materials but with low thermal efficiencies resulting in a costly solution to disposal. Alternative incinerator designs have been developed to improve thermal efficiencies with resultant lower operating costs. The RRR is a primary combustion system designed to thermally destroy a variety of waste sludges and contaminated soils with minimal use of auxiliary fuels. The process operates at a temperature ranging from 1200 F to 1600 F and excess combustion air ranging from 20% to 70%. Flue gases generated during combustion are further treated in a separate secondary combustion chamber followed by a "State of the Arttt gas cleaning system. Ash produced is discharged in a dry state suitable for direct or stabilized disposal in a secure landfill. RRR PRINCIPLES The basic technology employed provides an environment similar to a fluidized bed combustor where a bed of non-combustible media serves as a heat sink for the incinerator and vastly improves mass transfer phenomena between the incoming waste material components and oxygen in the combustion gases. This combination leads to high 295

2 destruction efficiencies at lower operating temperatures and lower flue gas oxygen concentrations than typically required in conventional rotary kiln combustion systems. A pilot program using a prototype reactor (350,000 Btu/hr heat release capacity) was carried out from mid 1984 through The program was conducted at the Rollins Environmental Services (NJ) Inc. plant located in Bridgeport, NJ. Extensive testing with various hazardous sludges, solids and contaminated soils as feed materials was completed under various operating conditions. The principles of acid gas scrubbing by direct alkali contact were demonstrated by burning high sulfur coal and hazardous waste mixtures containing up to 30% chlorine to prove the efficiency of sulfur dioxide and hydrogen chloride removal in the reactor. Under this program, development work was carried out to prove the workability of the rotary reactor concept, gather data for use in designing a commercial scale rotary reactor and engineer the most effective waste handling/feed facilities. Soil and sludges with a wide range of physical and chemical characteristics were tested including: 0 Still bottoms from the distillation of halogenated organics 0 Biological wastewater treatment sludges 0 Oil refinery sludges 0 Acrylic/styrene co-polymer reactor washouts 0 Contaminated soils The RRR is a kiln-like horizontal vessel rotating at relatively high speed. It is equipped with internal mixing devices similar to flites used in rotary dryers. Heat transfer media resides in the combustion chamber and is thoroughly mixed by the mechanical energy imparted by the combination of high speed rotation and internal mixing devices. Waste materials are chargedthrough the front wall directly into the non-combustible media where accelerated heat transfer raises the waste temperature to combustion conditions 296

3 almost immediately. Mixing efficiencies are further enhanced by circulation of the non-combustible media from the exit to the inlet of the combustion chamber. This is accomplished through the use of external helical coils wrapped around the RRR shell which convey media as the unit rotates. Shell penetrations are present at the inlet and exit of the combustion chamber to facilitate movement of the media through the helixes. lrfluidizationlr of the media bed is accomplished by mechanical energy input from rotation of the incinerator shell. The quantity of combustion air may be set according to the stoichiometric requirements of the waste material being incinerated with no concern of maintaining a set minimum flue gas velocity. This feature allows optimal balancing of combustion air/fuel ratios in the RFtR providing maximum thermal efficiencies. Very low calorific value fuels require less combustion air than is normally required to maintain pneumatic fluidization of a media bed. This causes thermal inefficiencies in conventional fluidized bed combustors which have been primarily used for lightly contaminated soils incineration as an alternate to rotary kilns. The fluidization activity within the RRR is less subject to upsets and channeling caused by improperly sized or sticky feed materials. Conventional pneumatic fluidized beds must be operated with carefully graded and conditioned feed materials to prevent short circuiting and channeling in the bed which may produce poor destruction efficiencies and operating economies. The RFtR possesses, as does a conventional pneumatic fluidized bed combustor, the capability of in-situ-acid gas scrubbing through the direct injection of alkali into the non-combustible media bed. The operating temperature and high mixing efficiencies enable ninetynine percent removal of hydrogen halides and at least ninety percent removal of sulfur oxides without the need for post-rftr flue gas treatment. Alkali reagent charging ratios ar typically 1.5 times stoichiometric requirements or less which is much lower than 297

4 required in most dry contact scrubbing systems. RRR COMMERCIAL FACILITIES The first commercial scale RRR was installed at the Rollins Environmental Services (TX) Inc. facility located in Deer Park, Texas. It is operated in conjunction with a 4.4 meter rotary kiln incinerator. The RRR and rotary kiln incinerators discharge flue gases into a common afterburner chamber and air pollution control system. Although this arrangement was originally designed to minimize capital expenditure, it has been found to result in interferences between the units causing greater than originally expected downtime frequency and duration. The RRR incineration system consists of three major subsystems. The first subsystem is an extensive materials handling facility which has been designed to receive, store, condition and feed waste materials to the RRR. These waste materials are received in bulk quantities in the form of sludges and solids. They may be fed directly to the incinerator or conditioned to improve handling and combustion characteristics prior to incineration. Bulk shipments delivered in roll-offs and dump trucks avoids pre-packaging and multiple re-handling of waste materials. All feed preparation work is completed in a building designated for this purpose with controlled ventilation and fire safety protection. Sludge wastes are fed to the RRR via a series of positive displacement piston pumps and pipelines to a non-atomizing lance which penetrates the RRR front wall discharging directly into the combustion chamber. Solids are moved about the feed building by overhead clamshell. The clamshell discharges waste materials directly into a hydraulically driven rip-shear shredder. Shredded materials are discharged into a series of enclosed screw conveyors which function to meter and convey the materials into the RRFt combustion chamber. Liquid waste materials are pumped directly to 298

5 the RRFt from trailers spotted adjacent to the materials handling building or from storage tanks located in another area of the plant which service all three facility incinerators. The second subsystem is the RRR incinerator. It has the external appearance of a conventional rotary kiln with the exception of a series of helixes attached to the outer shell assembly. Internally, the RRFt incinerator is lined with insulating and hardface refractory layers. It is equipped with a series of lifter assemblies spaced equally around the refractory circumference. The lifters serve to transfer mechanical energy into a bed of inert solids resident in the incinerator combustion chamber. Axial movement of the inert solids is driven by gravity due to a slight negative slope and relatively rapid rotation of the RRR shell. The external helixes are conduits for recirculating the inert solids bed from the discharge end of the combustion chamber to the inlet end. They operate on the principal of an Archimedes screw. The RRR incinerator operates normally within a temperature range of 1200 F to 1600OF. The shell rotates between 2 and 5 revolutions per minute dependent on the characteristics of waste materials being processed. These waste materials are deposited directly into the inert solids bed which resides at the incinerator operating temperature. The combination of intense mixing and rapid heat transfer within the bed promotes excellent combustion efficiencies. This is ideally suited for materials possessing low calorific value and significant moisture content. A lower quantity of excess combustion air is required to produce complete thermal destruction under these conditions enabling savings in the use of auxiliary fuels. Heat released during combustion is transferred back to the inert solid bed where it is stored for subsequent use in preheating and driving moisture from incoming waste materials. An additional benefit of the inert solids bed is the capability to neutralize acid gases produced during combustion by direct reaction with alkali co-deposited in the bed with waste materials. Efficiencies 299

6 of the llin-situll dry scrubbing process have been as high as conventional external wet scrubbing processes. Ash leaving the RRR combustion chamber is cooled by water sprays and conveyed to containers for storage until tested prior to placement in a landfill. The third subsystem consists of an afterburner chamber and gas cleaning system. The afterburner chamber is shared with a 4.4 meter diameter rotary kiln. Flue gases from the rotary kiln and rotary reactor are combined and subjected to a minimum of two second residence time at a temperature of at least 2000 F in the afterburner chamber. Flue gases leaving the afterburner chamber flow to a saturator where they are contacted with water to reduce bulk temperature to approximately 190 F. The gases continue into a parallel set of packed condensers which serve to remove heat and moisture from the stream. Hydrogen chloride gas is removed from the flue gases within the condensers. Flue gases leaving the condensers have been cooled to approximately 13 O F where they enter a high-energy venturi scrubber. The scrubber splits the gas flow into two equal quantities, wets it with copious amounts of water and then forces in to reconverge in a narrow throat area. This tortuous path causes the formation of very fine water droplets which encapsulate particulate matter suspended within the flue gas stream. The last stage of the scrubber consists of a demister with water wash nozzles. The fine water droplets with encapsulated particulate material are removed from the flue gas stream on the demister and flow to a drain connected to a subsequent treatment equipment. Flue gases leaving the scrubber are finally discharged to the atmosphere via a stack. RRR OPERATIONS The commercial RRR incinerator at Deer Park, Texas has handled a waste feed diet consisting of a mixture of contaminated soils, sludges, wastewater and various liquids. Heating values and 300

7 moisture content have ranged according to Table I. Table I Heating Values and Moisture Content of Typical RRR Waste Feed Materials Waste Material Heatincr Value-Btu/lb Moisture Content-% Soils Sludges Wastewater Liquids , This data was obtained from RES(TX) laboratory analyses of incoming waste samples designated for the RRR. The heating value of the combined waste feed mixtures to the RRR has ranged between 1800 and 3500 Btu/lb. At combustion air excess levels of 20 to 70 percent, these feed mixtures have demonstrated autogenous combustion at lower moisture levels. Under sub- autogenous conditions, the RRR utilizes natural gas, fuel oil or shredded wood pallets as auxiliary fuel sources. Natural gas and fuel oil are supplied through a conventional burner while wood chips are mixed with contaminated soils and fed through the shredder/screw conveyor system. The RRR is equipped with a continuous emissions monitoring system which provides a database of the daily operations and inputs the distributive control system so that tuning of the combustion air, waste feedrates and alkali addition ratios may be automatically accommodated. Emission levels of carbon monoxide, sulfur dioxide, hydrogen chloride and oxides of nitrogen have been routinely low except during upset conditions. Flue gases leaving the RRR primary combustion chamber pass into a high temperature secondary chamber 301

8 and gas cleaning system providing complete treatment prior to atmospheric release. Normal levels of pollutant gas emissions from the RRR primary combustion chamber are indicated in Table 11. Table I1 Normal Levels of Pollutant Gas Emissions from RRR Pollutant Gas Carbon Monoxide Sulfur Dioxide Hydrogen Chloride Nitric Oxide Nitrogen Dioxide Emission Level ppmv 5-25 ppmv 5-15 ppmv ppmv 2-5 ppmv Data taken from Lear-Sieglar FTIR CEM unit operating on RRR flue gas crossover duct. Ash discharged from the RRR is a dry, free-flowing material. Sufficient moisture is added to suppress dusting in the ash container. Samples are routinely collected and submitted to the RES(TX) laboratory for residual organics extraction. Extractability of heavy metals via TCLP procedures is performed when waste feed materials composition necessitates. Results have indicated low leachability of the unstabilized ash. It appears that alkali added to the RRR media bed preferentially reacts with free chlorine generated during incineration and suppresses the formation of heavy metal chlorides. Relatively low RRR operating temperatures (non-slagging) help to keep a larger percentage of the more volatile heavy metal compounds resident in the ash material. SUMMARY 2WD CONCLUSIONS The RRR has been commercially on-line since December During 302

9 the first six months of operation there were several extended downtime periods due to mechanical failure of some internal components, the seal system and the drive gear. All of these problems have been addressed giving a much improved reliability factor. Process problems have been very minor with most resolved in the first month of commercial operation. The market for hazardous contaminated soils and sludge disposal services has developed aggressively yielding significant opportunities for thermally efficient incineration systems. The RRR and other incineration systems such as infrared ovens, circulating bed combustors and conventional fluid bed incinerators are well suited for this service. One. of the major drawbacks associated with these incineration systems is the need to carefully prepare the waste materials prior to feeding. The RRR is more tolerant of variability in the waste materials than the other systems giving it an advantage in front end handling costs. Conventional rotary kiln incinerators are capable of handling a wide variety of waste materials without the need to pre-condition. In many causes these units are batch fed drums of materials with package heat releases as high as 4 MM BTU. Thermal inefficiency is desirable under these conditions to maximize mass throughput rates. However, composite waste heating values falling below approximately 5500 Btu/lb require auxiliary fuel in most rotary kiln operations. Auxiliary fuel consumption escalates rapidly as the composite heating value falls below 4000 Btu/lb which adds significantly to rotary kiln operating costs. Rotary kiln incineration systems will remain available to service the commercial hazardous waste disposal market for the foreseeable future due to their versatility and market presence of high level organic waste materials. The RRR provides a cost effective alternative method for thermal destruction of waste materials fitting the low level organic waste market niche. 303

10 Hazardous Waste Incinerator An Industrial Owner/Operator Perspec Submitted by Stephen R. Gossett Eastman Kodak Compan P.O. Box 511 Kingsport, Tennessee I~ODUC"I0N Eastman Kodak Com Kodak) is we own as a large nic imaging and Chemical Company, one of chemicals, fibers, Kingsport, Tennessee. largest manufacturers adquartered in a1 Company has four facilities in Rochester, Kin and Columbia (Figure I) have on-site incinerators and indu component in the Company's w t, Longview, Batesville, commitments to the use of 1 boilers as a key nagement strategy. B permitting process for boilers burning hazardous xperience with the very Act (RCRA) Part waste incinerators KODAK'S WASTE MANAG- environment. i 304