The pilot plant presently has had 5000 h of general operating experience on various wastes including the test with PCBs. A medium level of skill is required by operating personnel. The PCB process is still in the middle stages of development requiring further technical sophistication in regards to continuous replenishment of bed materials for large scale operations.
Capital and operating costs for the pilot facility would be $800 000 and $1 200 000 respectively based on a 45 kg/h through put. Unit cost for PCB destruction would be $2.73/kg. This figure could be reduced significantly for an operating plant scale up to a capacity of 4500 L/day. Anticipated unit costs for this operating plant would be approximately $1.31/kg. Capital costing is exclusive of land costs. Major contributors to operating expenditure would be cost of mixing fuel and bed material. Annual operating costs are based on 85% utilization with a full 4 shift, 7 day per week schedule.
Capital costs were derived by summarizing present costs for the following components of the system: receiving and storage facilities, feed system, barrel pumping and feed pumps, two fluid bed reactors, two cyclones, filters, air ejector, instrumentation and controls, laboratory and office, and funding during construction.
This Rockwell process is not yet available commercially as a PCB destruction system.
The environmental impacts of the process would have to be assessed upon testing of a scaled up version. The destruction efficiency is comparable to that achieved by conventional incineration. The removal of HCI and CO would have to be followed in a full scale test.
Rockwell engineers in a news release put forth the feasibility of mounting the system on rail cars to take the processor to waste sites. Such an arrangement would decrease the adverse local reaction to permanent PCB destruction facilities.
The US EPA has endorsed this process as "a viable alternative for destroying liquids with a high PCB concentration." However, they warn that future exploitation must be carried out with their approval of testing of a more highly developed process. The process exists in the public domain in the US as the work was carried out under Department of Energy contract.
References: (Johnson, 1981; Langheim, 1981; Oppelt, 1981).
Figure 9 Pilot Scale Fluidized Bed Unit (Rockwell International)
Click image to view a full size version.
4.3.3.2 Other Fluidized Bed Combustors
Other potential fluidized bed units that could be applied to the PCB destruction problem were reviewed briefly by TRW Inc. for the US EPA.
System Technology Corporation (Systech) of Franklin Ohio have tested a fluid bed (7.6 m in diameter, 1.0 to 1.8 m deep) on phenolic wastes. Feed rates in the range of 1 to 10 Mg/h for liquids and up to 135 Mg/h of solid (municipal) wastes have been burned.
Union Oil Company, Union Maine and Hazen Research, Inc. of Golden, Colorado are also considering fluidized beds for in-house destruction (refinery wastes) and as a marketable system.
References: (Ackerman et al., 1981).
4.3.4 Diesel Processes
The use of a diesel engine as a PCB incinerator is similar to the co-treatment processes described previously. The diesel is designed primarily to produce motive power; during this process a moderately high temperature environment is created in which PCBs can be combusted. The diesel engine is fundamentally more suited than the gasoline engine as the low volatility diesel fuel is sprayed into the cylinders. Thus the fuel system need not be modified significantly to burn PCB.
Conventional incineration parameters for temperature and residence time suggest that the diesel engine is too cool and lacks the residence time. Furthermore, the cylinder walls represent enormous thermal sinks that could cause very cool layers where combustion could be even further retarded. Also, concerns for the materials of construction exist in view of the production of hydrogen chloride as a combustion by-product.
4.3.4.1 The D & D Group, Inc.
P.O. Box 372
Smithville, Ontario
LOR 2A0
Contact: T.W. Drew, President
(416) 957-3323
The application of this technology by the D & D Group makes use of a 150 kW six cyclinder in-line Dorman diesel (Dorman Division of GEC (UK)). The diesel drives an electric generator which is under load during operation. The exhaust from the diesel is scrubbed with water that is neutralized with limestone to consume the hydrogen chloride produced. After scrubbing the exhaust is passed through an activated carbon filter and discharged to atmosphere. The fuel mixture consists of diesel fuel and askarel. While still in the development stage the optimum fuel : askarel ratio has not been settled. Up to 75% askarel fuel has been used with most of the operating experience at 50% askarel, 50% diesel fuel by weight.
Liquid PCB wastes are required to be fed to the diesel engine. Destruction efficiencies are said to be greater than 99% based on the whole system i.e. including the scrubber liquor and spent carbon. The developers of this process have opted to maximize the efficiency of the scrubbing and adsorption steps after the diesel and propose to recycle unreacted PCBs back to the front end of the process. The packaged process is said to be suitable for mobile operation.
The diesel, scrubber and adsorption configuration are presently being tested in the UK. As of late January 1982 the diesel had 300 hours of operation logged on askarel fuel. On the critical question of toxic by-products the tests have shown that 99.8% of the chlorine fed to the unit has been processed to chloride. The process is designed for liquid waste only; it would require companion technology to handle solid wastes.
Diesel engines have been in operation for a considerable period of time, especially in a "stand-by" mode. Some manufacturers list fuel flexibility as a special advantage in diesel selection. The unit used for cost evaluation was an injection diesel, patented by Detroit Diesel and has been operated on different types of fuel, from kerosene to some No. 1 or No. 2 fuels without modification. Manufacturers have not operated diesels with PCB based liquids or mixtures or askarel and fuel oils, and even with a modified injection system of their own design, they may hesitate to warranty such equipment.
The following would likely be required: separate cooling system, fuel pumping system, lubrication systems, manual start with automatic shut-down for cooling system or lubrication oil failure and filtering system for the pumped fuel prior to injection into cylinders.
The diesel engine with generator set and effluent treating equipment is available and all testing in Canada and in the United Kingdom has been done with "Off the shelf" diesel engines, the only modifications found necessary have been to the exhaust control systems. An atomizing air compressor may also be required for this system.
The D & D Group diesel process has received cautious preliminary acceptance in Ontario. The company is planning further testing before seeking regulatory approval for commercial PCB destruction.
The impacts of the diesel process on the operator are likely to be minimal provided routine precautions are taken for the handling of wastes and the operation of such heavy machinery. The public impact of the mobile version of the diesel process would be spread around the various locales where wastes exists. The details of the complete scrubbing/adsorption system are not fully publicized at this time so the full public and natural environment impacts cannot be assessed. It has been noted that the unit is "very self-contained" and "the process is controllable", air and gas flows are low and can be easily trapped and filtered |
