Control Requirements in TVA Plant

Abstract

SYNTHESISkiODKKN industry often automatically records pH. temperature, pressure, etc., for reasons of plant efficiency, and analysis of individual spot samples is commonly used in the control of an industrial process. W here process materials are gaseous or liquid, methods of continuous analysis are often possible, though these have not received the attention their importance justifies. Individual papers involving continuous analysis do not permit the analyst to include details which would enable readers to appreciate the over-all advantages and the limitations of continuous analysis.Jl is for this reason that we take particular pleasure in publishing the following seven articles on "Analyti-cal Control for Ammonia Synthesis", prepared by Karl H. Brown and co-workers at Tennessee Valley Authority, Wilson Dam, Ala. In these we have an excellent representation of development and application in this type of analysis for control of an important industrial process.Further, to illustrate the conventional approach of the analyst in the determination of a specific compound and the compromises needed to develop a procedure for continuous recording, two articles on determining methyl bromide in air follow immediately after the group of seven.h. T. H u,i.i:tt.

Automatic Recording of Carbon Dioxide by Conductometry

“…These amounts are expressed in microequivalents and refer to a solution volume of 50 ml. It is seen that the conductivity, , is a linear function of (Mm), = 0 + a(Mm) (1) where the slope, a, is a constant for sufficiently dilute solutions but the intercept, , depends upon the residual conductivity of the solution. That portion of due to impurities in the barium hydroxide will depend upon the initial concentration of reagent placed in the cell; , therefore, is to be regarded as an empirical Remaining in Sample vs. Time constant which must be determined for the conditions employed.…”

“…Chemical methods for continuous indication frequently have employed the change of electrical conductivity of a stream of dilute caustic effected by absorption of carbon dioxide from the gas stream. Methods of this type employing an alternating current galvanometer for the control of mechanical potentiometer recorders have been described (1,3). A method for observing conductometrically the course of evolution of a finite amount of carbon dioxide by absorption in a fixed amount of caustic recently has been published (2).…”

Automatic Operations in Quantitative Analysis

“…A recent patent describes an automatic water softener which uses a photoelectric cell for checking water hardness automatically and controlling the softening process (428). For the continuous determination of the bivalent copper present in the ammoniacal scrubbers used to remove carbon monoxide in the TV A ammonia plant, the solution to be tested flows through the annular space between two concentric tubes in an all-glass, light absorption cell surrounded by a light source operating on a stabilized voltage (61). An infrared device has been described which can easily be converted into an automatic control device in the production of natural and synthetic rubbers (26).…”

“…Conductometry' of Gases. Ionizable gases can be determined by passing samples through liquids whose conducti\'ity changes when the gas being measured reacts with or dissolves in the solution located between the two electrodes of a conductivity cell (61,129,163,384,385).…”

“…A typical apparatus (162, 333) designed for detection of war gases is so arranged that disturbance of the bridge balance by alteration of the conductivity of the liquid between the electrodes causes one of two lamps to light, one for clear, the other for danger. Gases and vapors which are similarly determined include carbon monoxide (61), carbon dioxide (61,129), carbon disulfide, hydrogen sulfide, nitrogen oxides, phosgene, lewisite, phosphorus trichloride, chlorine, sulfur dioxide (181, 525), and ammonia. Some un-ionizable samples require oxidation to a form which will ionize readily (61,121,163,213).…”