Transactions

A N ew Degasifying Steam C ondenser forUse in C onductivity D eterm inationsT his paper describes a degasifying steam condenserw hich w ill furnish a con tin u ou s sam ple o f either steam orcondensate w hich is free from dissolved gases b u t w hichcon tain s th e dissolved solids w hich were present in th eoriginal sam ple. Seven o f th ese condensers have beenb u ilt and in stalled in different power p lan ts varying inpressure from 150 to 1250 psi. T hey have reduced th e carbondioxide from 20 ppm and th e am m onia from 3.5 ppmto as low as 0.01 ppm for b oth gases. T he u n it is au tom aticrequiring practically no a tten tio n once it is in stalled .The sam ple o f degasified steam or condensate m ay bepassed through a conventional con d uctivity cell and acontinuous record kept if desirable. D ata collected fromth e various p lants are given as w ell as data collected inlaboratory tests.By F. G. STRAUB1 a n d E. E. NELSON,s URBANA, ILL.V ARIOUS methods have been used in the steam powerplant for determining the amount of total dissolved solidsin the steam or in the condensate from the turbines. If anaccurate method is available it furnishes the operator with a yardstickwith which he may measure the amount of carry-over fromthe boiler, as well as the amount of condenser leakage. Sincesuch a method involves the determination of total solids as lowas 1 ppm, the calorimeter method does not have sufficient accuracyand it cannot be applied to the condensate. Weighingthe solids after evaporation of the water gives sufficient accuracyunder proper control but it is limited to special tests and cannotbe used as a routine procedure to be run by the operators.The so-called conductivity method has received much considerationand is being used in many power plants. In thismethod, a sample of the steam is condensed and passed througha cell fitted with proper electrodes and the resistance of thewater to the flow of an electrical current is measured. This resistancevaries with the amount of the dissolved solids in thesample. Recording instruments are available which record eitherthe resistance or its reciprocal, the conductance. Thus, a continuousrecord is available. If two cells are used, one on thesteam, and the other on the condensate from the turbine,and the resistance or conductance recorded, the difference indicatescondenser leakage. Thus a record is available as to anychange in solids in the steam, caused by variation in boiler performance,as well as any condenser leakage. Since the time lagis of very short duration, boiler tests may be conducted to determinethe conditions most favorable for low carry-over or lowtotal dissolved solids in the steam.Unfortunately, some dissolved gases have a marked effect onthe conductance of water, consequently, the conductance failsto give a record of the dissolved solids. Gases such as ammonia,carbon dioxide, and hydrogen sulphide, interfere with the use ofthis method of determining total solids. With a high-qualitysteam, having less than 1 ppm of dissolved solids, the specificconductance might be in the range of 0.5 to 1.5 micromhos or thespecific resistance between 2,000,000 and 670,000 ohms. It hasbeen found that, in many steam samples, 1 ppm of dissolvedsolids corresponds to a specific conductance of 1.5 to 2.0 micromhos.Ammonia when present in the water will vary in its effecton the conductance, depending upon the form in which it occurs.However, it has been assumed that 1 ppm of ammonia nitrogenis equivalent to 9 micromhos. Thus the effect of ammonianitrogen is about 4.5 to 6 times that of the average solids occurringin the steam. Free carbon dioxide has a value of 0.6 micromhofor 1 ppm or one half that of the average of the solids in steam.U t il iz in g t h e C o n d u c t iv it y M e t h o dOne way of making use of the conductivity method has beento apply corrections to the observed values for the dissolvedgases (l).3 However, this necessitates analysis of the steam orcondensate samples for these gases. When ammonia and carbondioxide occur together, it is difficult to determine the true carbondioxidevalue. When the amount of the gases varies, it is necessaryto analyze quite frequently. The great objection to theapplication of these corrections is that often the corrections aremany times the amount due to the dissolved solids. Thus onesample of steam tested had a specific conductance of 14.6 micromhoswith 2.3 ppm nitrogen ammonia. If the value alreadynoted was used in correcting for the ammonia, the correctedvalue would be 14.6 — 20.5 or —5.9 micromhos, an impossiblevalue. Here also, due to the ammonia present, the water wasalkaline to phenolphthalein making the regular test for carbondioxide of no value.Much work has been done toward removing the gases from thesteam sample. The first degasifying apparatus was developedby J. K. Rummel (2). This made use of the principle of reboilingthe condensed steam. This method proved effective for reducingthe free carbon dioxide to a low amount. However, the apparatusdid not remove an appreciable amount of the ammonia.The equipment was of a nature to be used for special tests andcould not be used for continuous operation along with conductivity-recordingequipment. This was due to the attention necessaryfor controlling rates of flow of steam and condensing waters.Powell, Bacon, McChesney, and Henry (3) developed an apparatususing the principle of condensing the steam in a vacuumto remove the soluble gases. This method was suitable for usewith recording equipment and required very little attention.The carbon dioxide was removed, but the ammonia had to be determinedand corrected for. This limited the use of their apparatusto steam having low ammonia.1Special Research Associate Professor of Chemical Engineering,University of Illinois.D e v e l o p in g a D e g a s if y in g C o n d e n s e r2 Chemical Engineering Department, University of Illinois.Contributed by the Joint Research Committee on Boiler Feedwater Since neither of these degasifying units could be used on condensatesamples, the present study was undertaken to devise aStudies and the Power Division, and presented at the Annual Meeting,New York, N. Y., December 2-6, 1940, of T h e A m e r ic a n degasifying condenser which would reduce the soluble gases, includingammonia, to negligible amounts. This condenser shouldS o c i e t y o f M e c h a n i c a l E n g i n e e r s .N ote: Statem ents and opinions advanced in papers are to be understoodas individual expressions of their authors and not those of • Numbers in parentheses refer to the Bibliography at the end ofthe Society.the paper.645