Destruction Technologies for Polychlorinated Biphenyls

Operation of this facility would cost $775 000 annually, based on an 85% utilization rate and including cost of capital, labour and maintenance. Unit cost would be $0.26 per kg of PCB destroyed.

Once an existing high efficiency boiler capable of PCB destruction is selected, the front end components for preboiler combustion can be readily purchased.

The environmental impact of boiler incineration should be minimal in a properly operated and safety interlocked system. A particular advantage is that boiler owners/operators in the power generation industry are among the major generators of PCB waste so that action on their part to destroy PCBs in their own boilers is appropriate.

Regulatory agencies have approved a number of high efficiency boilers in the US. A number of other systems are presently undergoing the permitting process. The present status of these applications of high efficiency boiler incineration is summarized in Table 7.

References: (EPRI, 1979; Ackerman et al., 1981; EPA, 1981)

4.2.2.2 Cement Kilns

St. Lawrence Cement Company,
Lakeshore Road,
Mississauga, Ontario

Contact: L.P. MacDonald
(416) 822-1653

The production of cement involves the calcining of raw materials containing calcium, silicon, aluminum and iron to form the calcium silicates, aluminates and alumino-ferrites that make up cement clinker. The calcining at St. Lawrence Cement takes place in a rotary kiln 3.5 m in diameter by 123 m long (see Figure 4). Slurried raw materials are cocurrently fed with No. 6 fuel oil. Temperatures of 2100°C are reached and residence times of 30 seconds are encountered. Chloride produced combines with alkali metals in the kiln feed volatilizing them as metal chlorides.

"As such the chlorine content of PCB is useful in cement manufacture, in fact chlorine in some form may be required if low alkali cement is produced."

The process parameters at St. Lawrence cement were as follows:

• slurry feed      1400 Mg/day
• clinker produced   900 Mg/day
• No. 6 fuel oil      90 L/min
• chlorinated hydrocarbon   5-10 L/min

The tests carried out used chlorinated hydrocarbon feedstock containing 55% PCB. Destruction efficiencies of at least 99.986% were observed. No PCBs were detected in the gas or solid byproducts but low molecular weight chlorinated hydrocarbons (largely dichloromethane) were detected. PCB destruction efficiences were calculated as if the dichloromethane found was PCB.

A system described by EPRI suggests a rotary kiln preprocessing unit for solid PCB wastes. This system is interfaced with the kiln in the same way the preprocessing system is interfaced with the power boiler.

For a cement kiln preprocessing system with a heat release of 6.5 x 10⁵ kcal/h, capital costs involved would be $1 600 000. This figure includes funds for a one year construction period but no land costs. Capacity of system would be 710 kg/h of liquid PCBs at 50% concentration and 350 kg/h of solid PCBs in the form of shredded capacitors. Costing was based on using a rotary kiln as a primary combustion chamber. Both capital and operating cost figures are based on up-dating costs present in the EPRI Guidelines for Disposal by Thermal Technology (1979).

Operating costs of $1 140 000 per year can be expected based on 85 per cent utilization. Destruction of one kg of PCB in this system would cost $0.14.

As in the case of high efficiency boilers, once an existing cement kiln capable of PCB destruction is selected, the kiln precombustion equipment can be readily purchased.

The operation of the cement kiln itself is a fairly well developed technology. The front end equipment comprised of a rotary kiln, enclosed shredders, and pumps are not complex in operation. As with the high efficiency boilers, the automatic feed system which interlocks with operational parameters such as furnace temperature, combustion efficiency and HCI emissions, is technically sound.

PCB destruction in cement kilns has minimal environmental impacts. The tests at St. Lawrence did show an increase in dust emissions which may have been associated with the formation of a ring of agglomerated material in the kiln during chlorinated hydrocarbon incineration. This problem and the local public pressure to improve emission monitoring techniques and emergency interlocks has stopped further testing. Cement kiln incineration as a technology has the support of provincial and federal environmental ministries; it is a recommended method in their guidelines for PCB destruction