PRODUCTION

Odor Audit and Control Procter & Gamble determines its odor output quan­titatively before determining mode of attack

Ο DOR CONTROL should begin with odor measurement. To tackle the problem of odor control effectively, problems of measuring odor output quantitatively must first be overcome, says J. F . Byrd, pollution control engi­neer at Procter & Gamble.

According to Byrd, once an odor problem is known to exist, odor sources must be determined. And in a large processing plant with many atmos­pheric discharges which are somewhat similar, the problem is not easy. Every possible emission from all the processes in the plant must be measured to determine· the worst sources.

The first prerequisite is a concept of the units of measurement, Byrd told the 11th Industrial Waste Conference at Purdue. At P&G, one odor uni t is defined as the amount of odor necessary to contaminate 1 cubic foot of clean air to the barely perceptible or threshold level. For example, if a sample of an emission contains 10 odor units per cubic foot, the figure merely means that one part of the sample can be diluted with nine parts of odor-free air. The resulting mixture still contains a barely detectable odor. I n this case, the 10 odor units per cubic foot is analogous to a dust loading figure. It is a concentration, but it states nothing about total odor emission. Therefore, as with particulate discharges, duc t or stack flow must b e known. The prod­uct of total flow times odor intensity equals total odor emission. For in­stance—if an odor source has a con­centration of 10 odor uni ts per cubic foot and the rate of flow of odorous gases is 10 cubic feet per minute , then the total odor output would b e 100 odor units per minute.

Being able to place a quantitative concept on odor has a two-fold advan­tage, says Byrd. All odor sources within the plant are compared on a common basis. I t also serves as a yardstick by which progress of odor control effectiveness can b e measured.

> Odor Measur ing Techniques. P&G has developed several methods for odor measurement. A recent one is called the syringe technique. Samples are withdrawn from a duct in 100 cc. hypodermic syringes and

taken to an odor-free room. Smaller quantities of the odorous sample are added to a syringe into which odor-free air is drawn. An observer holds the syringe to his nostrils and pushes the plunger to drive the mixture into his nasal passages. The operation is re­peated until the threshold dilution is reached.

An earlier piece of equipment used for odor measurement is called "Osmo." Osmo is a 100-pound unit consisting of a cylinder with 528 holes. This cylinder is covered by an outer cylinder. The equipment can deliver 10 to 20 cubic feet of odor-free air per minute to an operator. An increasing quantity of contaminated air is fed into the clean air in the cylinder. At the threshold level, the ratio of clean air to contaminated air gives a direct measure of odor intensity. Although a good tool, says Byrd, Osmo is cumber­some, and condensate contaminates the equipment when working with sat­urated conditions. In addition, Osmo needs a power supply, which limits the number of locations where it can be used.

The syringe technique has several advantages over the Osmo device. One is the portability of small syringes; secondly, condensation no longer affects or contaminates the equipment. A possible error of the syringe technique in determining weak odor concentra­tions is due to a certain amount of dilution which takes place as the sample is placed in the nostrils.

• Control Measures . Once their presence has been established, odors may be eliminated by any of the follow­ing ways: changes in operational tech­niques, process changes, or treatment with specialized equipment. By merely revising operational procedures and techniques, large reductions in the amount of pollutants can be realized wi th negligible cost. At one of P&G's largest factories, says Byrd, a 16% reduction in total odor output was real­ized by minor operational changes and alterations to existing equipment. Cost was practically zero. Odor control by this mode of attack is attained through certain basic principles. An odorous material is harmless unless it can impart

Syringe technique, a recent one at P&G, has advantage of portability

the odor to some carrier medium which in turn escapes to the outside. In one instance, simply covering an open tank of odorous substances over which wind was passing resulted in almost complete ehmination of odor.

An example of changes within the process itself is in one of P&G's bleach­ing operations. Hot fats are air agi­tated with bleaching earths. A con­siderable amount of odor is carried by air into the atmosphere. Installation of a side entering agitator to replace the blowing of air into hot oils reduces odors b y about 9 9 % .

• Equipment Is Expensive. The most expensive approach lies in installa­tion of equipment for odor removal and dispersion. According to Byrd, stacks are the most effective and economical corrective measures for most areas. Advantages of a stack are :

• Simple and direct approach requir­ing little or no development work.

• No operational attention or control is required.

• Relatively low operation costs.

A limitation of a stack is the fact that it decreases in relative effectiveness as the distance from the stack increases. Stack plumes are subject to down wash due to eddy currents in the wake of buildings. This necessitates the stack being 7 5 to 1O0 feet higher than the highest building in the immediate vicinity. Where conditions of tempera­ture inversion frequently exist for pro­longed periods, a stack is not the ideal solution to an odor problem.

Other antiodor equipment used at P&G includes:

• Centrifugal separators or cyclones— for removal of particulate matter only

2 7 9 4 C&EN JUNE 4, 1956

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J U N E 4. I 9 5 6 C & E N 2 7 9 5

New Text

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PRODUCTION

• Air filters • Activated carbon filters—for high

odor intensity and low volume flow which is dry

• Venturi scrubbers — applicable where odor is due to very finely divided liquids or solids of sub-micron size

• Packed scrubbers—for larger size gummy particles, and for gases such a s H C l

• Spray condensers—to condense odor-laden steam

• Odor furnace—to oxidize odor bodies to less odorous matter

• Enclosed vent systems—used with group of tanks in which stock is pumped from one to the other tank and odor is displaced from t ank being filled to tank being emptied

Over-all, concludes Byrd, P&G's odor and other pollution control measures have cost the company almost $3 million since 1945.

yw • -v • Need for conventional lubrication in many types of bearings may be elimi­nated by development of American Metal Products. T h e company has used Teflon tetrufluoroethylene fiber to face metal suspension joints. Use is achieved by double weaving fiber with a backing of nylon or cotton. Fabric is then laminated with cotton-reinforced phenolic resin and formed into a cup which fines the socket. Preliminary testing is said to indicate that such bearings will last the lifetime of an automobile without lubrication or other maintenance.

Ψ More Gasoline from Crude Oil Up to 15% increases in gasohoe yields from crude oil have been obtained at this new Shell Oil installation a t Anacortes, Wash. New process, developed in Shell's Houston research lab a n d climaxing nearly seven years of research, involves two stages. In first stage, hot catalyst is said to strike oil for brief period, causing it to vaporize and to begin to crack. This partially-cracked oil then goes through separating system which removes gasoline and gas formed in first stage. Remain­ing uneraeked oil goes on to second stage reactor which is a conventional process in standard cat crackers. Shell says in addition to higher gasoline yields, the two-stage cracking system has resulted in lower coke yields and greater flexibility. This unit is capable of processing about a million gallons of oil per day.

2 7 9 6 C&EN JUNE 4, 1956