The large amounts of black smoke emanating from the condenser during the days of burning also created a problem. The state regulatory agency for air quality would no longer permit the open burning of the styrene from the condenser. The open burning had also created a safety hazard for the personnel involved in the cleaning procedure.

At the time, ARCO did not have a suitable alternative for cleaning the equipment, so the condensers had to be scrapped once they became plugged. At a cost of $100,000 per condenser, this indeed constituted a problem.

The Solution:  In September 1984, a custom-designed, pyrolytic cleaning furnace was installed in the maintenance area to clean 20' long heat exchangers. With interior dimensions measuring 5-1/2' wide x 7' tall x 22' long, the furnace is loaded by placing the condenser on two heavy duty dollies which roll outside the furnace for easy loading and unloading.

The furnace is also utilized to clean other polystyrene-plugged parts. Frequently, smaller parts such as polymer pumps, extruder die parts, breaker plates, small condensers, condenser heads, and pipes up to 20' long required cleaning. For convenience in loading the smaller parts, two 10' long carts are used which are pushed in and out of the furnace.

During furnace operation, the temperature is first increased to a point where plastic material is allowed to melt and drain into a cool collection pan where the plastic solidifies and is removed. This feature allows significantly shorter cleaning cycles for metal parts contaminated with large amounts of plastic.

Furnace temperature is then increased to 800-900ºF to safely decompose the remaining plastic to volatile pyrolysis gas and smoke in a partially inerted, oxygen-deficient atmosphere. The pyrolysis smoke passes through two secondary combustion chambers. The chambers are an integral part of the furnace and are raised to 1500ºF with excess air to completely incinerate the smoke. High efficiency direct flame incineration of the smoke is controlled at a rate of approximately 33 lb/hr by a patented emission control system.

The Results:  During start-up, a large condenser weighing 24,000 lbs. with dimensions of approximately 4' in diameter x 19-1/2' long was cleaned in the furnace. After 120 hours in the furnace, the cleaned condenser weighed 19,760 lbs.; about 4,240 lbs. of styrene-based polymer was removed.

After cooling, the condenser was removed from the furnace and the tube bundle was easily removed. The unit was free of plastic except for small amounts of carbon around areas where air diffusion inside the exchanger was hindered.

The cleaning operation within the furnace was completely automatic and only required periodic removal and replacement of the collection pans below the drain. The process eliminates both the clouds of black smoke and the safety hazard associated with the former open burning method. Cleaning the condenser and other parts has cut expenses dramatically. For the condenser cleaning, the primary cost was for fuel, approximately $500 -- compared to a replacement cost of $100,000.

Chuck Shrontz
Superintendent of Maintenance
R.E. Heckman
Senior Project Engineer - Beaver Valley Plant
ARCO Chemical Company,
a div. of Atlantic Richfield Co.