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National Bureau of Standards Special Publication 556. Proceedings of a Workshop on Measurements and Standards for Recycled Oil - II held

at NBS, Gaithersburg, Maryland, November 29 and 30, 1977. (Issued September 1979)

THE BURNING OF USED OIL AS A FUEL IN CEMENT MANUFACTURE

J. A. Armstrong

Waste Management Branch

Environmental Impact Control Directorate
Environment Canada
Ottawa, Ontario. K1A 1C8
Canada

and

L. P. MacDonald

St. Lawrence Cement Company
2391 Lakeshore Road West
Mississauga, Ontario L5J 1K1
Canada

Introduction

Approximately 200 million imperial gallons of used lubricating oils are sold in Canada each year [1,2]. This includes both petroleum oils used for lubricating purposes and other oils having special properties other than lubrication alone, such as hydraulic oils and industrial cutting oils. It has been estimated that at least 42 percent of this volume, about 84 million gallons per year, is potentially recoverable [3]. Presently, approximately 5 to 6 million gallons of used oil are being re-refined annually, and about 21 million gallons are used for road oiling. The remaining 57 to 58 million gallons are used or disposed of in various ways, ranging from being burned as fuel to being incinerated or dumped in sewers and on the ground.

Both the lubricating and energy properties of lubricating oil are retained in the used oil until its disposal, and so it can be recycled as many times as possible without any loss in value. Every gallon of used oil used again for recovery of either property causes a corresponding reduction in demand for an equivalent amount of "new" oil, thereby helping to extend the existence of our crude oil reserves. In terms of the energy value, a figure arrived at by comparing the average energy value of used oil to that of residual fuel oil (presently selling for about $0.30 per imperial gallon), the 84 million gallons of potentially recoverable used oil are worth about $20 million annually. A recent study done for the Environmental Protection Agency has shown that additional energy savings of over 25,000 British thermal units per imperial gallon of oil can be realized by re-refining used oil instead of using it as fuel [4]. This would mean an extra annual saving of the equivalent of about 12 million gallons of fuel oil and bring the total value of the potentially recyclable used oil to about $23 million per year, if it were all recycled once before being used as a fuel. These rough calculations put the value of used oil as a resource into perspective and need to be considered during the formation of programs to deal with the problem of used oil recovery and disposal.

As well as resulting in the loss of a valuable, nonrenewable resource, uncontrolled disposal of used oil can pose a serious threat to both the environment and public health. Used automotive crankcase oil, which makes up the largest part of used oil presently collected, contains both portions of the original additives and impurities acquired during service. In particular, they may contain significant concentrations of heavy metals (particularly lead), bromine, and polynuclear aromatic hydrocarbons. Indiscriminant disposal of these and other oils on land can harm vegetation and contribute to water pollution either by runoff or leaching processes. Burning or incineration without adequate controls can cause the emission of various toxic or potentially carcinogenic gaseous components which may endanger the health of people and animals in contact with them.

1 Underlined numbers in brackets indicate the literature references at the end of this paper.

One of the objectives of the Resource Conservation Division of Environment Canada is to promote the recovery and recycling or reuse of used oil in order to conserve our petroleum resources and to minimize the effects of its disposal on the environment. We hope to realize this objective by

(a) assisting other governments and generators of used oil in the development of recovery systems that will remove as much oil as possible from the waste stream (i.e., recovery of oil that is not presently recovered due to such factors as economics, contamination, etc.), and

(b) by assisting other governments in the development of procedures that will ensure the recycling or disposal of used oil in ways that are environmentally acceptable. This involves the assessment and evaluation of the environmental acceptability of end uses, as well as assisting in the improvement of existing technology and the development of new technology and methods for recycling and reusing used oil.

One method of reuse that Environment Canada has investigated and found to be both an environmentally acceptable method of disposal of used oil and one that recovers the energy value of the oil is its use as a fuel in the manufacture of cement. It has been known for some time that cement production, which requires a high heat input, can also act as a sink for many fuel components such as metals and sulfur, etc., by absorption in the cement clinker. In 1974, an experimental program to study the burning of used automotive crankcase oil in a dry process cement kiln was carried out jointly by Environment Canada, the St. Lawrence Cement Company, the Ontario Ministry of the Environment, and the Ontario Research Foundation [5]. The initial study burned 330,000 imperial gallons of used lubricating oil at the St. Lawrence Cement Company plant in Mississauga, Ontario; and, based on the results of this study, the plant has installed the capacity required to burn over 5 million gallons of used oil per year and is presently consuming about 3 million gallons annually.

I would now like to introduce one of the chief investigators of the study, Mr. Larry MacDonald of the St. Lawrence Cement Company, to describe the study and its results to you in more detail.

Cement Manufacture

General Principles

While a variety of raw materials may be used in cement manufacture, materials containing calcium, silicon, aluminum, and iron without an excess of certain other elements are required. These materials are ground to a find powder called raw meal, the chemical composition of which is carefully controlled by proper blending of the various materials. Normally, blending is achieved by grinding all the raw materials together (intergrinding). Raw meals required for wet and dry processes are similar except that the raw meal for the wet process is in the form of a slurry containing approximately 35 percent water, while raw meal for the dry process contains less than 0.5 percent water.

The raw meal is fed into the kiln and is burned to produce an intermediate product called clinker.

The kiln slopes towards the burning zone and rotates slowly, causing the raw material to gradually move into the burning zone. Reactions which occur during gradual heating in the kiln are: evaporation of free water; evolution of combined water; evolution of carbon dioxide from carbonates; and combination of lime with silica, alumina, and iron to form the desired compounds in the intermediate product clinker. These reactions require a final material temperature of 2,650° F.

After cooling, the clinker is ground with gypsum to a fine powder. The final product, called Portland cement, is the basic ingredient of concrete.

It

The operation of a suspension preheater is illustrated schematically in figure 1. Raw meal is introduced into the duct between the first and second stage cyclones. is swept with the hot exhaust gas into the uppermost (stage I) cyclones, where gas and material are separated. The raw feed material from the stage I cyclone drops into the duct between the second and third stage cyclones and is again suspended and separated. This procedure is repeated in stages III and IV before the partially

[blocks in formation]

Figure 1. Principle of Fuller-Humboldt suspension preheater.

calcined feed enters the kiln. In the process of passing through these four stages, the raw meal is heated from about 150° F to about 1,450° F.

The lime formed by calcination of the raw meal in the kiln effectively absorbs various elements from the combustion and reaction gases. As with any solid gasscrubbing procedure, the effectiveness of the removal is a function of the degree of mixing between the solids and the gases.

Volatile constituents (for example, potassium chloride and sodium chloride) in the raw materials and fuels are removed from the solid phases in the hottest zones of the kiln. In a straight kiln, these alkali chlorides condense in the cooler regions as minute particles and are removed from the gas stream by precipitators. Due to the intimate mixing of gases and raw material in the preheater, most of the alkali chlorides condense on incoming raw meal particles and are therefore trapped between the flame and the preheater. This circulation within the gas stream concentrates the alkali chlorides in the gas phase which can cause the preheater to plug. To reduce the alkali chloride buildup, a by-pass is included in the system. The by-pass acts as a vent to bleed off some of the kiln gases rich in alkali chloride. These are passed through a conditioning tower which cools and humidifies the gases to the optimum for precipitator operation.

Experimental

The purpose of this experimental burn was to determine whether used oil could be employed as a fuel in the cement kiln without the adverse environmental effects posed by other disposal methods.

While many contaminants are present in used oil, it was realized that it would be futile to attempt to determine the contribution to the process by elements present in large quantities in cement raw materials or by elements present in used oils at very low concentrations. The elements remaining after such consideration were, therefore, lead, bromine, zinc, and phosphorus.

The emissions from the three stacks were of prime concern. These stacks exhaust the by-pass precipitator gases and the gases from the precipitators for the two preheaters. Particulate material was collected by the Ontario Research Foundation in accordance with both Environmental Protection Service [6] and Ontario Ministry of the Environment source testing codes [7]. After determining the quantities of particulate collected, samples were analyzed for the four elements under study.

As a backup to the emission analyses, a mass balance over the process was made for the same four elements.

The experiment was carried out under full normal operation conditions; the only change in procedure was the introduction of waste oil as a fuel. Normally, three separate oil burners, each capable of supplying 14 IGPM of No. 6 oil, are used to fuel the kiln. For the experiment, one of these burners was converted to supply used oil. Through viscosity and pressure changes, it was possible to input better than 15 IGPM of used oil.

Results

The mean emission rates given in table 1 indicate that the only significant increase in emissions during used oil burning was with bromine, presumably as alkali bromide. A slight increase in concentration of lead in the emission particulate was noted. This is not apparent in the reporting of total emissions since the actual particulate emissions decreased during this period, possibly because of water in the used oil improving the precipitator efficiencies. No effect of used oil burning on zinc and phosphorus emissions (except as related to total particulate decrease) was found.

In the accumulated mass balance (table 2), it can be seen that practically all the phosphorus and zinc remains with the clinker. The lead stays essentially with the clinker, although a small amount goes to the by-pass precipitator. A large portion of bromine goes to the precipitator dust. This is analogous to the reactions of chlorine described earlier in this paper. Alkali chlorides and bromides are volatile at kiln temperatures and are removed mainly through the by-pass. This volatility also explains the slightly higher emissions encountered during used oil burning.

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