PROCESS CONTROLLER FOR TREATING WASTE OILS IN
AUTOMOTIVE WASTE TREATMENT PLANTS
Sanjay R. Srivatsa, Senior Research Engineer
E. C. Zuerner, Group Leader
Nalco Chemical Company
Naperville, Illinois 60566
INTRODUCTION
Heretofore, batch cooking processes are generally implemented in the recovery of oil from waste
oil scum. These processes consist of heating the waste oil scum followed by addition of emulsion
breaking chemicals to produce an oil-water resolution. Waste oil scums are water-in-oil emulsions
generated in processes utilizing water, oil, cleaners, etc., in the machining and working of metals.
Automotive industries comprise the major source for waste oil scum. Other sources are refineries,
steel-rolling mills, canning industries, chemical processing and hydrocarbon processing industries.
Because of the ever increasing value of oil and the economics of a waste oil recovery program, it is
worthwhile to maximize oil recovery from these waste emulsions for reuse.
Waste oil emulsions consist of three components, namely, oil, water, and solids. The conventional
method of breaking down the waste emulsion is as follows:
1. Addition of acid/caustic,
2. Heating the cooker to a desired temperature,
3. Mixing in a proportion of an organic (synthetic) emulsion breaker,
4. Allowing the contents to resolve into oil and water.
Heating incorporates the primary step in the resolution of a waste oil emulsion. A resolved emulsion consists of three discrete phases, namely, oil, water, and an unresolved intermediate phase called
rag. This phase consists of undissolved solids held in a tight matrix of water-in-oil. The rag has to be
retreated in order to further resolve this phase. This results in higher chemical demand and special
handling procedures. Thus, the generation of rag has to be minimized to ensure smooth operation and
curtail recurring energy and chemical costs.
Major factors controlling the generation of rag are chemical dose and agitation. Inadequate or
excessive chemical dosage can result in a large volume of rag. The effect of agitation is analogous to
chemical dose in that overmixing can cause reemulsification of resolved water and oil, thus, minimizing oil recovery.
Due to constant variations in the waste oil source, every batch justifies a specific chemical dosage
for minimizing rag and enhancing oil recovery. Current dosage control procedures call for conducting
50 ml, bottle tests where chemicals are titrated into the sample and optimized qualitatively (visually).
These tests take between 4-12 hours to predict optimum dosages. As batches are treated continuously,
this procedure is not practiced by shift operators on a regular basis. Furthermore, the test offers
merely a crude scale-up (50 mis to 4,000-10,000 gallons) leading to poor simulation of heat transfer
and hydraulics. Thus, a high percentage of cooker resolutions tend to be dissimilar to that of
bottle tests.
As a result, conventional cooker dosages are limited to a fixed level of acid/caustic and emulsion
breaker. The dosages are determined once, thereafter, all subsequent batches are treated similarly.
Evidently, the outcome of this procedure is an overall reduction in oil recovery due to poor batchwise
optimization. In addition to this, a considerable number of batches have to be rescheduled to treat
large quantities of rag consuming additional energy, chemicals, and process time.
This paper addresses the development of a revolutionary on-line technique for optimizing
chemical feed and energy requirements in automotive waste oil cookers. Case histories illustrate the
success of this technique in its capacity to maximize yields and improve process economics.
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