CHEMICAL TRAINING FOR POWER PLANT ENGINEERS*
It was my privilege recently to discuss corrosion with some of the engineers who control the operation of boilers generating steam a t 1200 pounds pressure. In their discussion they indicated that, after several months of operation, a small amount of hydrated iron oxide had been found deposited a t one point in the boilers. After first inspection it was cleaned out and did not reappear because the dissolved oxygen in the feed water was kept a t zero by the Winkler test. Furthermore, the water was tested frequently with silver nitrate to detect the presence of chlorides, and the pH values were closely controlled to prevent acid corrosion or too great causticity. These men discussed intelligently the relative merits of trisodium phosphate and sulfate-soda treatment of raw water. It is indeed rare to have the maintenance division show as thorough an appreciation of the chemical problems as in this case. This visit brought out vividly the growing importance of chemistry in the power plant, for times are changing. With the higher pressures, problems which once were troublesome are now acute, and their answer must be had by anticipating the difficulty lest there be serious consequences. Corrosion is one of the important problems, but not the sole one, affecting modem power plants. The chemistry of the metals, of fuel processing, of combustion, of refractories, and of lubrication are all significant. Such being the case, the matter of training men to meet these technical requirements is one of no little consequence. Let us, therefore, investigate the nature of these problems, see how they are being met, and note the changes in chemical education which will best satisfy these needs. Chemistry in the Power Plant Some of the problems with which chemistry must deal have already been enumerated. For the sake of brevity they may be best reviewed under the headings of: (1) corrosion; (2) fuels, combustion, and furnaces; and (3) mechanical operation. The question of corrosion is a many-sided one which can best be explained in terms of electrochemistry. Calcott and Whetzel' have summarized the corrosion reaction as follows: The tendency of corrosion of a metal by a solution depends upon (1) the potential effective for corrosion as determined by the combination of metal potential, overvoltage, and concentrations of metal and corroding ion; (2) the resistance offeredby a protective
* Presented before the joint session of the Divisions of Industrial and Engineering Chemistry; Water, Sewage and Sanitation Chemistry; and Gas and Fuel Chemistry of the A. C. S. for the Symposium on "Boiler Room Chemistry" held at Columbus, Ohio, May 1, 1929. Corrosion Tests and Materials of Construction for Chemical Engineering Apparatus. Am. Inst. Chem. Engs. and D. Van Nostrand, Inc., 1923, p. 2. 316
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coat; and (3) depolarization reactions removing hydrogen and protective products of corrosion. The rate of corrosion reaction varies as (1) area of metal computed from its linear dimensions, (2) rate of diffusion in corroding liquid, (3) saturation concentration of metal in corroding liquid, and (4) movement or velocity of corroding liquid.
As for the metal, steel is the usual material of which boilers are constructed. Recently alloy steels containing chromium and nickel have come into use on account of their greater resistance to oxidation and corrosion. Metal of uniform composition is used, and fabrication is done with a view to minimizing electrochemical couples. In some cases corrosion of the boiler is prevented by the application of an electromotive force, one example of which is the suspension of a zinc block in the boiler. The nature of the metal may determine the film effects, and thus affect the corrosion. For instance, adherent oxide films within the boiler or in the combustion chamber will reduce the rate of penetration, whereas those that are non-adherent may actually accelerate it. The extent of the hydrogen film which can build up before gas is evolved is also controlled by the nature of the metal. If the overvoltage created by the gas film is sufficiently great, displacement corrcsion will cease. Composition of the water has an even greater bearing on corrosion in the boiler. As a consequence boiler water treatment is known in one form or another wherever boilers are used. Water is deaerated before use because dissolved oxygen depolarizes the hydrogen film and permits corrosion to continue, and because carbon dioxge, an acidic constituent, may be economically removed in that manner. Water is treated chemically to render it slightly alkaline and also to precipitate outside of the boiler those materials which would form scale within. Under acid conditions the hydrogen overvoltage cannot be sufficiently great to prevent gas evolution and continued dissolution of the metal. Deposition of scale within the boiler permits overheating of metal with consequent oxidation as well as low rates of heat transfer. Under still more exacting conditions, or with large quantities of dissolved salts, the water is evaporated before use. These salts would otherwise accelerate corrosion by making the water a conductor and thus completing the electrochemical cell circuit, and by reacting with corroding material to produce soluble compounds in place of oxide films. Problems in firing the boilers involve chiefly the preparation and processing of fuels, the thermodynamics of combustion and heat transfer, and the phase relations of the ash and slag compounds. While much of the preparation of fuel, such as cleaning, crushing, and sizing, has not been associated with the power plant, there is a tendency to bring processing operations of an even more involved nature into it. Grinding processes for the preparation of pulverized coal are in common
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use. Coal carbonization, or its complete gasification, although in its experimental stages, is being associated with the central station power plant. Such a scheme is intended to prepare a fuel which will be economical and clean to burn, and to produce as a by-product a marketable tar. This tar has value for the liquid fuel i t contains and for the raw products of the organic chemical industry. Therefore, in fuel processing, the unit operations of chemical engineering and the organic chemistry of the hydrocarbons may be new fields for the power plant engineer. The thermodynamics of combustion and heat transmission have been well known to power plant engineers as they have been the primary basis upon which economy depended. Heat of combustion of the fuel, equilibrium relations between the gases, and the extraction of heat by radiation and from the hot gases constitute the background of every boiler test. Less attention has been paid to rates of combustion and rates of heat absorption, but these are becoming of considerable importance for the bearing which they have on economy of design and maintenance. The phase relations of the ash compounds and of the refractory slags constitute similar problems which are closely related to ceramic chemistry. Higher fuel bed temperatures have made necessary greater attention to the fusion point of ash. With close control a clinker results which is not too fluid for satisfactory operation of the grates, nor too dusty for use as an aggregate in cinder concrete. Thus what would otherwise be waste has a definite market value when prepared under properly controlled conditions. In powdered coal firing a new tendency is to slag the ash. It is, therefore, a real problem to be able to adapt coals of diierent ash composition to any one installation. Fusion points may vary, as well as the chemical action between ash and refractory. The problem from slagging refractory is less troublesome in central stations where water-cooled walls are used. A temperature gradient is established between the flame and cooling surface. The refractory is melted or the slag is built up to conform to this gradient. In smaller installations air cooling is often used to furnish the same protection. All of these fusion conditions are related to the composition of the ash and of the refractory, as well as to the operating temperature. They can be explained in terms of the phase rule system, iron oxide-alumina-silica, with due account being taken of the effect of minor constituents on the melting point. Associated with mechanical operation is the question of lubrication which is a problem of a distinctly chemical nature. It is true that in the past lubricants have been selected on the basis of viscosity and related physical properties. While that is still significant, lubricants are now evaluated as to oiliness and power to wet metal; and in the case of cylinder and turbine oils, as to their emulsification with water. All these are properties which are associated with the chemical nature of the lubricant.
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They may be recognized by the more general terms of molecular structure, surface tension, and colloidal dispersion. A summary of these observations indicates that chemistry has a place of increasing importance for power plant engineers, and that the characteristics of the chemical field are predominantly those of physical chemistry. It is not surprising that a chemical engineer recently graduated from one of our state universities made the following remark: "So many people ask why a power house should use chemical engineering knowledge; to me the question is how do they .get along on so little?" Education in Chemistry The technical men in control of power plant operations involving chemistry are usually mechanical engineers. Chemical engineers are occasionally to be found in the larger organizations. Consultants are employed for the special problems. In other cases technical service is offered in connection with sales. It is hardly the province of this paper to define the training of specialists, for each is a case by itself. Rather, let us consider the chemical education of that group of engineers who control the power plant. At the present time chemistry plays an indifferent part in the training of mechanical engineers. To illustrate. H. P. Hammond2 shows that there is a distinct continuity and interlocking of most of the courses in this curriculum. Chemistry alone is an 'isolated entity. This lack of connection between chemistry and mechanicalrengineering seems to be generally recognized. It is in part through the failure of the professional courses to recognize the value of chemistry, and also through failure of the chemist to give instruction in those fundamental fields which have a practical bearing on power plant operation. With respect to the first of these Kirk and Heisig3 have indicated some of the difficulties in correlating chemistry with the professional engineering curriculum: More criticism has been directed toward the subject matter taught in chemistry than that in physics. This is due in our opinion to two related causes. First, the course in physics is more definitely standardized than that in chemistry. Second, professional are based more definitely on the generally courses taueht - in enaineerina .de~artments . accepted standard courses in physics. The relationship between advanced professional courses in engineering and the fundamental course in chemistry is not so well established. ~
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With respect to the second, that is, the nature and extent of chemical training for the power plant engineer, some suggestions are offered. Courses in general chemistry are departing from the predominantly analytical phase and are dealing more with the physical chemistry of the ina 8
I. Eng. Educ., 18,73 (Sept., 1927). Ibid., 17, 815 (Apr., 1927).
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organic compounds. While this trend is in the right direction, the subject matter so taught is not usually adequate as a preparation for the chemistry of the power plant for it does not deal with the electrochemistry of corrosion, or the high temperature reactions of ash and slag. Of the courses which follow this, that of physical chemistry would most nearly complete the preparation of direct value to these men. However it does not usually occur in the curricula until advanced years, and is usually omitted from mechanical or electrical courses. Without detracting from the courses in the chemistryof engineering materials which are sometimes given to engineers, I would suggest a stronger fundamental training in physical chemistry because of its direct application to so many of these problems. Furthermore, it has been suggested that all men so trained should have a working knowledge of chemistry which is a t least equivalent to their knowledge of electrical subjects. In most engineering curricula this would represent an increase in the amount of chemistry taught.
Manufacturers Honor Swedish Chemist Scheele on Sesquicentennial of His Dis-
the annual meeting in Chicago of the Association of American Soap and Glycerin Producers, representing the leading soap manufacturers of the country. T h e association sent to Crown Prince Gustaf Adolf. Honorary Member of the Royal Academy of Sciences of Sweden, a message felicitatinihim on the part played by his country in the development of glycerin products. .)‘ December 19th was the 187th anniversary of Scheele's birth and 1930 marked the sesquicentennial of his discovery made 150 years ago. Although regarded as a relatively unimportant discovery a t the time, glycerin has come t o be one of the most widely used substances known t o science and industry, being a necessary ingredient of almost countless drugs, toilet preparations, and foods. The most modern use for the product is as an anti-freeze for automobile cooling systems, since it will not freeze at low temperatures and will neither boil nor evaporate a t normal automobile operating heat. Nearly a million cars were protected with radiator glycerin last winter, and the number this season promises to exceed the million mark. The following message was sent to the Crown Prince of Sweden, signed by Sidney M. Calgate, President of the Association: "The Association of American Soap and Glycerin Producers, in annual convention a t Chicago, desires to extend to your Highness as Honorary Member ol the Royal Academy of Sciences an expression of gratitude and felicitation on the occasion of the hundred and fiftieth anniversary of the discovery of glycerin by the distinguished Swedish chemist, Karl Wilhelm Scheele. This contribution of your countryman to science and industry becomes increasingly valuable each year, and the approaching anniversary of the birthday of this distinguished son of Sweden will see the use of glycerin more widespread than ever before, not only in the arts and scienccs but also in its recently discovered capacity as an anti-freeze in automobile cooling systems. As remesentatives of the leading factors in the American glycerin industry, we ask your Highness to accept this message of congratulation on your country's great contribution to modern science and industry and to motoring."
