BUREAU OF INDUSTRIAL CHEMISTRY· Copies of this publication may be procured from the Bureau of Industrial Chemistry, The University of Texas Austin, Texas The University of Texas Publication No. 5011: June 1, 1950 Acetylene from Hydrocarbons by the Schoch Electric Discharge Process Reported by The Staff of the Bureau of Industrial Chemistry Acetylene Division The University of Texas June 1, 1950 P U BLISHED BY THE UNIVERSITY T w I CE A MoNTH. E NTERED AS SECOND-CLASS M ATTER ON MARCH 12, 1913, AT THE PosT O FFICE AT Ausn N, TEXAS, UN DER THE A CT OF AUGUST 24, 1912 Thr benefits of education and o/ lW' fu1 knowledge, generally diffused through a community, are essential to the preservation of a free government. Sam H oust.on Cultivated mind is the guardian genius of Democracy, and while guided and controlled by virtne, the noblest attribute of man. It is the only dictator that freemen acknowledge, and the only security which freemen desire. Mirabeau B. Lamar COPYRIGHT, 1950 BY THE BOARD OF REGENT& OF' THE UNIVERSITY OF TEXAS PREFACE The University of Texas through its staff of the Bureau of Industrial Chemistry has carried on an extensive research for many years to develop an electric discharge process for making products from natural gas and related petroleum fractions­and in this connection has perfected a process for making acetylene. The latter process has been tested in pilot plant operation, and is now ready for industrial use. It is the purpose of this publication to give definite information concerning the nature of this process and its equipment. Further information can be obtained from the staff of the Bureau. Licenses to use this process are obtainable from the Board of Regents. President, The University of Texas STAFF Bureau of Industrial Chemistry: Acetylene Project E. P. ScHOCH, PH.D., l,rojessor of Chemical Engineering, Technical Advisor MRS. WANDA DoTY PorrER. Vl.A ., Secretary W. 13. HowARIJ, PH.D., Research Scientist V H. A. HoLCOMH, PH.D., Resrnrch SciPntist V A. S. KASPERIK, Pu.D., Research Scientist V E. J. CLAASSEN, Pu.D., Research Scientist JV H.P. LIGHTFOOT, M.S., Resrnrch Scimtisl !If E. Co1.1.F:L\ MooRE, B.A., RPsearch Scimtist I ToM BROOKS METCALFE, ~\.1.S., Research Scientist I TABLE OF CONTENTS Preface by President Painter__ ___ ______ ________ _________ ___ ___ ____________ _ Ill List of Staff Members________________ __________ _____ IV Table of Contents ______________ __ ___ ___ _ __ __ v Photo 1-Discharge Chamber of Pilot Plant in 1945 _____________ __ _____ __ Vil GENERAL SUBJECTS Introduction l Units of Measure . _ ___ ______ ____________ _________ ______ -----­------­--­ l Usable Hydrocarbon Gases and Liquids ____ ____ _____ ___ _ 1 The Recovery of Methane from the Off-Gas of a Gas-Feed Plant 2 SECTION A: Tm: FouR MAIN PLANT PARTS Figure 1-Diagram ____ ___________ ________________________ ______________________ ________----______ _ _____ _ Descriptions SECTION B: THE COMPONENTS OF THE PLANT PARTS Plant Part I: The Electric Controls 6 Figure 1-Diagram 6 Tables _____ __ __ _____ _ 7 Plant Part II: Discharge Chambers, Cyclones and Coolers of Gas-Feed Plants 8 Figure I-Gas-Feed Chamber with Three Discharges ____ _ 9 Photo 2-Electrodes ___ __ _ _ __ 10 Photo 3-Rim of Blower Wheel__ ____________ 12 Figure 2-Section A-A of Fig. 1 Showing Blower Shaft, Bearings and Mountings 13 Figure 3-Assembly of Gas-Feed Chamber and Its Accessories ______ -·· __ 15 Figure 4-Diagram of Six-Step Gas-Feed Plant __ .. ________ _ 16 Discharge Chamber Cyclones and Condensers for Liquid-Feed Plants 18 Figure 5-Assembly of Liquid-Feed Chamber and Accessories 17 Plant Part III: Removal of C,1 and Higher Hydrocarbons 18 Figure 1-Flow-Sheet __ _ 19 Photo 4-Pilot Plant of Plant Parts III and IV 21 Plant Part IV: Concentration of Acetylene 18 Figure 1-Flow-Sheet _ ___ ... ________________ __ ----------------------··------------·-·--·--22 SECTION C: How THt:: PARTS WoRK Plant Part I: The Electric Controls 23 Figure 1-0 scillogram of the Electric Discharge........ 23 Plant Part II : Discharge Chambers and Accessories for Gas-Feed Plants ·----~--------24 Figure !-Efficiency Curves for Acetylene from Methane_____________________________ .. 25 Figure 2-Curve of Volume Increase Versus Percent Acetylene__·······-------------26 Discharge Chambers and Accessories for Liquid-Feed Plants............ ___ . ____ 28 Properties of the By-Product Carbon Black........ 29 Plant Part III: Removal of C:, and Higher Hydrocarbons...... 30 Plant Part IV : Concentration of Acetylene. ... 32 SECTION D: EQUIPMt::NT FOR PLANTS MAKING 2000 LBS. AcETYLt::NE PER HouR General Remarks:-Cost of Discharge Chamber. -----------------------·----------------------·····--34 Equipment for Plants of Other Sizes ..... . ...... ... ·-. 34 Equipment for a Gas-Feed Plant Making 2000 lbs./ hr.: Fundamental Facts for Parts I and II 34 List for Plant Part I____ __________ ------------·-··-··--··------------------------------------------------_______ _ 35 List for Plant Part IL___ _________ .. _ ··-·······----------------············-·--------------------------35 List for Plant Parts III and IV __ ______ ___________ ------------------------------------------------------36 Equipment for a Liquid-Feed Plant Making 2000 lbs./ hr.: Fundamental Facts for Parts I and IL__ -----------------------··-------------------------------··· 37 List for Plant Part L ___________ ------···· .. ------_____ -----------------------------------------------_ 38 List for Plant Part IL ________.... _______ ...... ---- ·· ---------···--------.. -.. ---------------------38 List for Plant Parts III and IV......... ... . 39 SECTION D (Concl'd) Automatic Control and Protective Devices. -----·· ·····------------------------------------------------40 PHOTO 1 Discharge Chamber of Pilot Plant in 1945 The reclangular Discharge Chamber is seen in the upper left. New chamhers are built cylindrical. Filters are shown in the upper right. These were inslalled, April 1, 1942, and the original cloth filters are slill functioning O.K. ----> INTRODUCTION Manufacturing processes are chose11 for their economic advantages, hence the first question asked here by interested parties is likely to be: What are the installation and operating costs of the Schoch process? It is the purpose of this pamphlet to answer this question as definitely as possible. But this answer cannot be given by stating some figures, because costs calculated for one set of conditions are not correct for other conditions. Nor does everybody want to in­clude the same items in his calculations; and many prefer to have a list of the equipment parts needed, and the specifications for them, so that they can get prices direct from manu­facturers and do their own figuring. Hence the information given here is designed to make the latter procedure possible. Pages 34 to 40 present such a list of items for two plants making 2,000 lbs. per hour of acetylene from liquid feeds and gas feeds, respectively. This size was chosen because plants operating on other processes may be available in this size, and hence a compari­3on is possible. But the Schoch process is available for any production capacity begin­ning with 60 lbs. acetylene per hour from methane-or 75 lbs. per hour from liquid pe· troleum. They are built in multiples of three discharge units, and the latter range from 100 Kw. to 1,000 Kw. These plants produce acetylene from raw materials and electric power, hence their costs are similar to those of carbide manufacturing plants. They should not be compared with mere generators of acetylene from carbide. Schoch process plants are safe to operate: seven years of operation has proven this. They are designed to adjust themselves automatically to the rate at which acetylene is withdrawn. Thev contain no tanks or gasomelers for acetylene storage. They require very little attention, and rn· \'olve very little wear, and no corrosion. Units of Measure In this publication, gas volumes are ex· pressed as measured at 0°C and 1 atmos. (N.T.P.). In industry, gas volumes are fre­ quently based on 60°F and 30 inches Hg: on this basis the volumes given here would he about 6% larger. Some Important '.'\umerical Helations: 1 lb. acetylene occupies 1:3.65 cu. ft. N.T.P. 1 Kwh. will theoretically convert 14.9 cu. ft. CH, to form 7.45 cu. ft. acetylene. The si::.es of these plants will be designated by stating the kind of hydrocarbon feed em· ployed-i.e., gas or liquid-and the number of pounds of acetylene produced per hour. Usable Hydrocarbon Gases and Liquids The hydrocarbon feeds to be employed may be either gases or liquids, but accord­ingly, the plant must be slightly different. A gas feed may be composed wholly of methane (e.g., Southwestern natural gas ) or partly or wholly of higher hydrocarbon~ I propane-butane mixtures) . Gas feeds should be practically free of sulfur compounds, and should contain no more than 2% of CO, or of N2, nor more than 10% H2• Higher hydrocarbons should be present in sufficient amount to make the hydrocarbon constituents at least equivalent Lo 100% CH.,. Thus, if the methane is only 80%, there should be present either 10% of ethane or 6.67% of propane, etc. A liquid feed should be composed of va­porizable hydrocarbons whose 100% flash­vaporization temperature (under a partial pressure of one-half atmosphere) is below 550°F: this includes the petroleum fraf'lions ranging from those in gasoline to those in diesel fuel. The Recovery of Methane From the Off-Gas of a Gas-Feed Plant It takes about 1.6 lbs. of a gas or 2.15 lbs. of a liquid hydrocarbon, to make a pound of acetylene. When hydrocarbons higher than ethane are employed, then they are com­pletely used up because these plants recover the C, and higher compounds from the gas stream and return them di re<::tly to the dis­charge chamber. Hence their original cost determines the cost of higher hydrocarbons for producing acetylene. But with methane and ethane, such is not the case: while ethane is thus partly recovered, none of the methane is thus re­r:overed. When a 10/(; acetylene product is made, only about one-third of the methane in the feed is decomposed in its passage through the plant, and two-thirds of it will pass out of the plant together with the hydro­gen formed and the other nonhydrocarbon constituents. When produced from nearly pure methane, this "off-gas" will have a composition of 55.5'/< of methane (plus a little ethane) and 44.4'/< of hydrogen. Since lM cu. ft. of a methane feed gas produces about 1,200 cu. ft. of the above kind of off­gas, the total heat units in this off-gas amount to about 82<,k of those in the feed. While a portion of this is needed for fuel in this plant, most of it will be av.ailable for other uses. Of course, any income therefrom serves lo decrease the cost of the feed-gas. The heating power of the unused gas is fully enough to produce the electric power for the plant. One way of disposing of this off-gas is to ;;eparate the methane from the hydrogen. There are four processes available for this separation, but the three most economical processes are usable only in plants produc­ing 1,000 lbs. acetylene or more per hour, PAGE 2 hence using 100,000 cu. ft. or more of me­thane per hour. These three processes are: 1. The Liquefaction Process which liqui­fies the methane by expansion and separates the liquid from the remaining gas. 2. The Hypersorption Process, which sep­arates the gases by means of activated car­bon. 3. A thermal diffusion process available through the Koppers Company. While all three of these processes are likely lo be economicaL yet this Bureau has obtained. from representative manufacturers, estimated installation costs and utilities re­quirements for the first two only, and these show the following: a. Liquefaction Separation: for an off­gas flow of 100,000 cu. ft. per hr. the turn­key cost of the unit would he $350,000 as of February, 1950. A unit ten times as large would cost about $1,100,000. No utilities are required. The methane product purity is above 98'/<, and the hydrogen can be pro­duced with an extremely high degree of purity. b. Hypersorption Separation: the turn-key costs of the units. exclusive of boiler, cooling tower, and contingencies, would be of the ,;ame order of magnitude as those for lique­faction units. The operation of the unib would involve certain utilities such as heat. water, steam and electricity. Product puritie" are probably high. 4. The fourth process for the recovery of I he unused gas is not quite as economical as the preceding, but it is still profitable, and can be used in the small acetylene plants for which the costs of the above mentioned proc­esses will probably be prohibitive; hence this Bureau has elaborated this process in some detail. It separates the gases by absorb­ing the hydrocarbons in an "absorber" oil such as is commonly used in natural gas recycling plants. It is estimated that such an absorption procedure, followed by successive pressure reductions on the oil in several stages of flashing without heating, will result in a recovery of about 92% of the methane. This recovered methane will have a hydrogen content of about 8%. For an off-gas flow of 100,000 cu. ft. per hr., the present day turn­key cost of a unit employing this procedure would be about $175,000. The utility re­quirements are 120 brake horsepower for a gas compressor, to raise the off-gas pressure from 125 psia. to 250 psia., and 300 hrake horsepower for oil pumps. An estimate will now be made of the cost of gas per pound of acetylene when a gas recovery system is employed. Assume the cost of recovering gas to be 6 cts. per M cu. ft. recovered and the pur­chase price to be 15 cts. per M cu. ft. In an efficient operation, one-third of every thou­sand cubic feet of feed is decomposed and 10 lbs. of acetylene are made from it. Hence, the cost of gas per pound of acetylene would be: 15 + ( ~X!) 2_ = 0.9 cts. 3 :) 10 In comparing the cost of a gas feed with that of a liquid feed, it must be remem­bered that with a gas feed it takes 4.89 Kwh. to make a pound of acetylene, while with a liquid feed it takes only 3.55 Kwh. Also, a possible income from the carbo!l black, as well as from the hydrogen, may need to be considered. SECTION A THE FOUR MAIN Plants for this process consist of four distinct parts, the functions and components of which are shown in the diagram, Figure 1 of Section A, and described below. It is impossible in a publication of this size to give all the engineering data for designing a plant: the description and data given are mainly for the purpose of showing the equipment employed. The descriptions of the four parts now follow. Plant Part I The Electric Current Controls Ordinary 60 cycle per second electric power is taken from a supply line, trans­formed to a suitable voltage and then passed through a combination of reactors and con­densers whereby the current supplied to the electric discharge chamber is held at a fixed amperage irrespective of the length (or volt­age drop!) of the path of the discharge through the gas. Plant Part II Discharge Chamber, Cyclone and Cooler The discharge chamber is a gas tight con­tainer which in its earliest form is shown in Photo 1, and in its present form in Figure 1 of Section B, Plant Part II. It contains a rapidly rotating blower wheel which serves as one electrode of the discharge, and a non­rotating flat metal strip which serves as the other electrode (see Photo 2). The latter is shaped and placed so that at one end it is close to the rim of the blower, and at the other it is farther away. The rotor blows a PLANT PARTS sheet of gas through the almost V-shaped space between it and the counter electrode and through the electric discharge passir.g between them. The discharge converts a fraction of the natural gas or petroleum vapors in the chamber to acetylene and hydrogen-and some carbon black. Fresh gas or vaponz­able liquids are continuously fed to tht> chamber and the resulting mixture is con­tinuously withdrawn. In a gas-feed plant, the temperature in the chamber is prevented from rising beyond a desirable limit (550°F or less) by passing the gas through a cooler; while in a liquid­feed plant, this cooling is accomplished by adding liquid petroleum at such a rate that its evaporation keeps the temperature at the desired limit. Finally, the gas is cooled, cleared of carbon and sent to the third part of the plant. Plant Part Ill Removal of C3 and Higher Components This part serves to separate those gas com­ponents having more than two carbons per molecule from the "dilute" acetylene, and re­turns the higher hydrocarbons to the feed inlet of Plant Part II, while sending the dilute acetylene to Part IV. Plant Part IV Concentration of Acetylene This part serves to separate the acetylene from the remaining gas. It delivers acetylene on one hand and acetylene-free off-gas on the other. PAGE 5 SECTION B THE COMPONENTS OF PLANT PART I The Electric Controls Since the electric current employed is the ordinary 60 cycles per second three phase A.C. obtainable from any electric power line, and a single discharge operates on only one phase, a plant should employ three dis­charges-or simple multiples of three. The first piece of equipment needed is a transformer-the secondary windings of which are connected in Y. Hence a trans­former set furnishes the power for three pairs of lines to the discharges. Of course, only one transformer set is supplied for all of the discharges in a plant. Inductance Xo The current to each discharge must be controlled by a separate controlling unit. A diagram of such a current controlling unit is shown in Figure 1 of Section B, Plant Part I, and the dimensions of the parts of such units-as needed for several sizes of dis­charges-are given in Tables I and II of Sec­tion B, Plant Part II. Briefly stated, the con­trols consist of two inductances (x0 and x1), and a capacitance (xc) arranged as shown in Figure 1 of Section B, Plant Part I. From its shape this arrangement was desig­nated as the T-circuit by its originator, C. P. Steinmetz. Inductance Lines from Capacitance Figure of Section B, Plant Part Ii Diagram of Electric Controls for Each Discharge PAGE 6 TABLE I OF SECTION B, PLANT PART I Single Di;charges for Illustration Control Equipment Ratio* (Ex1 / En )= 1.8 Discharge Power Fac:or, 0.75 The Supply Power Factor is Practically 1. Discharge Supply Lbs. C,H, per Hr. Power Potential Current- Potential Current- from CH, at 4.89 from liquids Kw. Volts Amps. Kv Amps. Kwh . per lb. at 3.55 Kwh./ lb. 100 4170 32.0 7.55 13.8 20.4 28.2 200 5030 53.0 9.10 22.8 40.9 56.3 400 6370 83.7 11.54 36.0 81.8 112.7 789 8520 123.5 15.43 53.1 161.3 222.3 815 8540 127.3 15.45 54.7 166.7 229.6 *This is the required ratio of the voltage in Reactor X1 to that of the Discharge. Discharge Size (Kw.) Reactor Ohms X. = X1 =Xe X, Reactors -Volts x. x. x. x, X1 X1 x, Xe x. -Amps. -Kva. lnsul. for Peak Voltage. -Volts -Amps. -Kva. lnsul. for Peak Voltage. -Volts -Amps. TABLE II (a) OF SECTION B, PLANT PART I Reactor Dimensions for the Discharges in Table I (Continued in Table (b)) 100 200 400 789 815 234.7 170.7 137.1 124.2 120.7 3230 3890 4930 6590 6610 13.8 22.8 36.0 53.1 54.7 44.6 88.7 177.4 350.1 361.6 7550 9100 11540 15430 15450 7500 9050 11480 15340 15370 32.0 53.0 83.7 123.5 127.3 240 480 960 1894 1956 10,430 12,570 15,940 21,300 21,340 8160 9840 12480 16680 16710 '34 .8 57.7 91 134.3 138.4 The reactors designated by Xo, X, and Xe occupy the positions shown in Figure 1 of Section B. PAGE 7 TABLE II (b) OF SECTION B, PLANT PART I Capacitor Dimensions for Discharges in Table I Discharge Size (Kw. ) Number of 15 Kva. Units,-their voltage rating and arrangement. 100 One set of 18 Units (7960 volts)-all in parallel. 200 Two sets of 18 Units (4800 volts),-the members of each set in parallel and the two sets in series. 400 One set of 42 Units (7200 volts), and one set of 28 Units (4800 volts) ,-the members of each set in parallel and the two sets in series. 789 Two sets of 68 Units (7960 volts) ,-the members of each set in parallel, and the two sets in series. !:115 Two set of 70 Units (7960 volts) ,-the members of each set in parallel, and the two sets in series. THE COMPONENTS OF PLANT PART II Discharge Chambers, Cyclones and Coolers of Gas-Feed Plants Since the number of discharges must be a simple multiple of three, Lhe least number of chambers in a planl may be one with three discharges, or three with one discharge. The shell of a discharge chamber consists of a short section of a cylinder closed by two dished heads: one of these is welded to the cylinder, and the other attached by means of flanges and bolts. The latter makes the whole interior readily accessible. Figure l of Section B, Plant Part II, shows the in­ terior of a "gas feed" chamber with three discharge:;. The main feature of this interior is the rotary blower electrode (shown also Ill Photo 2) together with three non-rotating but movable counter electrodes. The counter electrodes are electrically insulated from the rest of the chamber: in gas-feed plants, the insulator is kept free of carbon by an in­coming slream of clean gas; and in liquid­feed plants Lhe same thing is accomplishe3.57 0.00 PAGE 11 PHOTO 3 Interior of Discharge Chamber showing rim of blower wheel. PAGE 12 Chamber Door Figure 2 of Section B, Plant Port II= Section A-A of Fig. I Showino Blower Shaft, Bearings, and Mountings Column 2 of this table shows the progres­ sive gain in amount of products; and Column 5 shows the progressive saving in recircul a­ tion, obtained with increasing number of units in series. 1t will be noted that both of these columns show that it is more profitable to operate with a larger rather than with a smaller num­ ber of discharge diarnbers in series. But, while the gain is substantial up to 6 units in series, it is only slight thereafler. Hence even when plants require less than (3 X 6) discharges they are bui It with six chambers in series, each chamber having two-or only one discharge. Discharge chambers operated with six (or less) in series have-each-­ a return connection and blower between the boltom of the cooler and the discharge chamber so that an arnounl of gas sufficient to remove the excess heat-can be recir­ culated. While the use of nine discharge chambers secures an additional improvement in effi­ ciency, and does away entirely with recircu­ lation, yet the extra cost of the three chambers is not compensated by these gains alone, hence nine chambers in series will be installed . only when plant size requires more than six chambers. An assembly of a gas feed discharge cham­ ber and its accessories is shown in Figure 3 of Section B, Plant Part II. Figure 4 presents a flow diagram of a 6-step Gas-Feed Plant. Each chamber is immediate I y fol lowed by a cyclone and by a cooler. In a plant designed lo operate with six chambers in series, seven are actually installed and these are connected so that the cooler of the first chamber dis­charges into the second chamber, that of the second into the third, etc.-and the cooler of the last into the cloth filters. But each set is also equipped with a by-pass and valves hy means of which it may be cut out of operation; and one chamber is always out of operation and available in case of a breakdown in one of the others. The gas cooler is so constructed and op­erated that the water-cooled surfaces are con­~tantly "scraped" to prevent their being cov­ered with carbon black. The filters are of the ordinary cloth or "sock" filter type-operated with a periodic shaking down of the "sock." In the pilot plant, ordinary cotton filter cloth has lasted seven years so far \vithout signs of deteriora­tion. From the filters the gas passes lo the third part of the plant. As indicated in Figure 4 of Section B, Plant Part II, the carbon is withdrawn from the hopper bottoms of the cyclones and of the filters by means of a current of gas and delivered into a collecting tank. Small gas blowers move the gas to this tank, and from here iL is returned to a suitable point in the gas line between the six chambers. A helical screw and casing is attached to the bottom of this collecting lank to compress the carbon into a dense plug and to deliver this plug outside lo a suitable receptacle. PAGE 14 '"'O :>­ t'l " ,_, CJ1 High Potential Lead Recirculating Insulating Gas Cyclone Heat Exchanger Carbon Black High Potential Lead -------------. I I Four Inter­I I mediate Steps + One Standby Step L ------- -----~ Recirculating Blower Insulating Gas Cyclone Heat Exchanger Bag Filters To Concentrating Plant Figure 4 of Section B, Plant Part II= Flow Diagram of 6-S'tep Gas Feed Plant FIGURE 5 OF SECTION B, PLANT PART II ASSEMBLY OF LIQUID FEED DISCHARGE CHAMBER AND ACCESSORIES THE COMPONENTS OF PLANT PART II Discharge Chambers, Cyclones and Condensers of Liquid-Feed Plants When the discharge chambers are operated with liquid feeds, each chamber completes the action on its feed and delivers its output through a condenser directly to the next part of the plant. Hence, for sizes making 845 lbs. or less of acetylene per hour, a plant need not have more than one discharge chamber", and only larger plants have multiples thereof. The discharge chamber used with liquid feeds is made like that shown in Figure 1 of Section B, Plant Part II, except that in­sulation of the high-potential electrodes is maintained by a flow of liquid instead of a How of gas and that the cyclone for remov­ing part of the carbon from the product gas is made a part of the removable door of the chamber in order that the heat liberated in the chamber may serve to keep the cyclone hot. Condensation is to be avoided inside THE COMPONENTS Removal of C3 and Higher Hydro­ carbons This equipment begins with a three-stage compressor lo put the gas under 110 psig. This is followed by a column operated with a petroleum absorber oil-to remove the c:< and higher hydrocarbons. This is followed THE COMPONENTS Concentration of Acetylene Coming out of the absorber oil column, the gas passes through a small charcoal absorber lo remove traces of absorber oil, and then passes into another "absorber" column oper­ated with a "high boiling" acetylene solvent (called di-methoxy-tetra-ethylene-glycol, here­after designated by DMTG). This absorbs all of the acetylene, with small amounts of the other gases present, and allows the stripped gas-consisting of hydrogen, me- PAG E 18 thi,; cyclone so that the carbon black may be removed as dry as possible. Figure 5 of Section B, Plant Part II shows an assembl y of a liquid feed discharge cham­ber, cyclone, and condenser. The carbon black is removed from the bottom of the cyclone by means of a screw conveyor de­signed to compress the carbon into a dense plug. A small stream of a fuel gas is intro­duced here to sweep condensible vapors back into the cyclone. The product gases pass from the condenser direct to the next part of the plant. The condenser for this system is of the shell and tube type, with the tubes in :i. vertical position so that a spray of liquid feed stock introduced into the top may clean the tube ;heel and the tubes of carbon black. l\o special materials of construction will be re­1uired since the operating temperatures (550°F) will be within the allowable range of ordinary low carbon structural steel and pipe. OF PLANT PART III by a stripper to remove the absorbed mate­rials from the absorber oil, to return the latter to the first column, and to return the stripped materials to the discharge chambers-together with fresh feed gas. Figure 1 of Section R Plant Part III, is a flow sheet of Part II I, and Photo 4 shows Plant Parts III and IV of the Bureau's pilot plant. OF PLANT PART IV thane and small amounts of ethane and ethy­lene-to pass out of the plant as "off-gas." From this column the liquid passes through a "flash" chamber wherein the pressure is reduced to near-atmospheric-then the liquid passes through the "purifying" column wherein the remaining amounts of methane, ethane and ethylene are removed by "strip­ping with acetylene," and finally the liquid is heated to liberate the acetylene. Figure 1 of Section B, Plant Part IV, is a flow sheet of Plant Part IV. PHOTO 4 Pilot Plant for Purifying and Concentrating Acetylene. The three tall, square towers are-from left to right-The Waste Gas Stripper of Plant Part III, The Solvent Wash and the Solvent Stripper of Plant Part IV. PAGE 20 SECTION C HOW THE PARTS WORK Plant Part I: The Electric Controls The electric controls used in these plants may be said to transform a constant poten­tial power supply into a constant currr•nf power supply. That is, they deliver currents of fixed values through any electric paths ir­respective of the impedances of the latter. Since the impedance and the current deter­mine the voltage drop in this path, this fore­going statement means that a constant current will be obtained irrespective of the voltaµ-e required. or course, this voltage has an up­per limit. Figure 1 of Section R, Plant Part L s~1ow~ the component parts of a "T-circuit" control. It begins with the lines from one secondary winding of the transformer, one line of which contains an inductance whose ohms of re­actance with a 60 cycles per sec. A.C. are denoted as X.,. Beyond this inductance is another inductance with an ohmic reactance designated by X,. Between these a "shunt" connection lo the other line from the trans­former contains a capacitance with an ohmic reactance designated by Xe. While these three reactances are usually designed to be equal in ohmic reactance yet an appreciable degree of inequality can be tolerated. The "discharge gap" is placed so as to complete the circuit of the further extensions of the two lines from the transformer to the right. The dimensions for the reactances needed for the five "i11 ustrative" discharges in Table I are presented in Table II-both of Section R, Plant Part II. The figures i11 these two tables give all data necessary for ordering this equipment. The large num­her of 15 Kva. capacitances needed for a single discharge should be housed together in a «uhicle. Time~ Figure of Section C, Plant Pa rt I: Oscillogrom of the Discharge HOW THE PARTS WORK Plant Part II: IJischarge Chambers anti Accessories for Gas-Feed Plant.~ The rotary blower within the discharge chamber must be at full speed before the discharge current is turned on. and the "nearer" end of the high voltage-(counter I electrode must be sufficiently near the rim of the rotor to allow the current to "break through" when the main switch is closed. The direction of rotation of the blower mu~l be such that the gas will be blown from the narrow to the wide part of the V-shaped opening between the electrodes. The first "break through" of the discharge occurs where the electrodes are nearest to­gether and it moves rapidly with the rota­tion of the blower to the wider parts of the V-shaped opening. After reaching a certain height depending upon the voltage, current. speed of blower and width of the V-shaped opening between the electrodes, the discharge path changes back to the region of shortest distance between the electrodes, and again moves upward. This repetition may occur one or more times during a semicycle of the 60 cycles per second, but as the discharge is ordinarily operated, it occurs twice. An oscillograph connected across the discharge shows (Figure ] of Section C, Plant Part I) that the voltage and the current are in phase. that the current is substantially sinusoidal, and that at the beginning of the semicycle the voltage rises with a curvature which is convex to the time axis-attains a maximum near the middle of this semicycle, then drops vertically to a very low value and repeats this kind of a course during the latter half of the semicycle. These "excursions" shown in the voltage oscillogram correspond to the above descriherl movements of the discharge path. It is evident that the blower is constantly taking gas in on its sides and blowing it out through its rim where the sheath is cut away. PAGE 24 Thus the gas in the chamber is maintained at a uniform composition. The temperature rise due to one passage through the blower and discharge is about 60°F. There are three general methods of operat­ing this discharge to obtain a desired con­centration of acetylene in the product gas­the batch, single step, and multi-step pro­cedures. The batch procedure is used only to obtain experimental data in the quickest and most accurate way possible. It consists of adding a measured amount of discharge energy (e.g. about 1/ 100 Kwh. per cu. ft. of gas) to a fixed-known-amount of gas held within a closed chamber of relatively large capacity (e.g. 1h cu. ft. per Kw.). and repeating these additions to the same gas several times. After each addition of energy, samples are taken and the temperature, pressure, etc., of the product gas are observed. In this procedure, the discharge acts first on gas containing no acetylene, and successively on a gas contain­ing increasing concentrations of acetylene. The efficiencies obtained are summations of all the various efficiencies corresponding to the concentrations of acetylene present at the moment of operation. This procedure is also known as the "infinite-step" procedure since the final concentration of acetylene is reached after many small increments of concentration have been acted upon. The data obtained in such a determination may be expressed by four variables. These are: 0) amount of acetylene produced per unit of energy, (2) amount of energy added to each unit of original gas, (3) concentra­tion of acetylene in product gas, and (4) ex­pansion of the gas during the addition of the energy. All of these are interrelated so that if three of them are given, then the fourth may be calculated. Usually variables (I), (3) , and (4 I are used to illustrate the data of a run. . :c ~ x ~ Cll 3.6 -~ . E - 0 -3.2 .. . (.) 0 0 - Cll 2.8 c Cll ~ -CD u 24 ex • .... -u.. .. 0 ~ 2.0 c CD ·­ u .... .... w I 6 . 2 4 6 8 10 12 14 16 Mole % Acetylene 1n Product Gos Figure I of Section C, Plant Part ll=-Efficiency Curves for C2H2 from CH4 Two procedures are available for continu­ous operation : single-step and multi-step op­eration_ In the single-step procedure, the feed gas is fed to a unit and the product gas removed therefrom at such rates that the dis­charge of a chosen power is acting always on 2.0 1.8 0 c ·­ 0 ... 0 1.6 .,,. .. LL ... Q) a. 1.4 .. u :::J "t> 0 ~ 1.2 0... If).. LL. 1.0 Fi gur Vol um Fun ct P AGE a gas containing acetylene of the final con­centration. Since the efficiency always de­creases with increase in acetylene concentra­tion, tbe efficiency of the single step opera­tion at the final concentration is lower than that of the batch procedure at that concen­traction because the batch procedure spends most of the energy on a gas containing lesser concentrations of acetylene than the final product gas. The exact mathematical relations between these methods of operation haye been derived and the relations have been checked by experimental results on both batch and con­tinuous operation. Multi-step operation is conducted so as to regain some of the difference in efficiency between the batch and one-step operations. In this method, the gas is passed through successive discharge chambers in order that all but the last step will be operating on gas containing lesser acetylene concentrations than the final concentration desired. The mathematical relations of this operation have also been derived. Suffice it to say that three steps will regain 60% and six steps will re· gain 80% of the efficiency difference between the batch and one-step operations. Figure 1 of Section C, Plant Part II, shows curves relating efficiencies of acetylene pro· duction from methane. versus final mole per cent acetylene in the product gas. Three curves are shown: "infinite-step," six-step, and one-step. Figure 2 of Section C, Plant Part II, shows mole per cent acetylene in the product gas versus expansion due to con­version of methane. Energy input may be obtained from the data of these two figures by use of the following relation: Expansion X '/vC2H2 ·--------= Energy input 100 X Efficiency This energy input is expressed in kilowatt­hours per cu. ft. (0°C, 1 atm.) of original feed gas. Various other gaseous hydrocarbons beside methane have been used as feed gas to the discharge chamber. These include ethane, propane, butane, ethylene and propylene. Mixtures of several of these have also been used. From these data, predictions may be made on the results which can be obtained if any mixture of the above gases is used as feed gas. TABLE I OF SECTION C, PLANT PART II. Power Consumption and Gas-Feed Rates for Various Feed Gases to Discharge Units in Six-step Plants Energy Energy Mo! % Consumption Efficiency Input Gas Feed Acetylene Expansion Kwh./Lb. Lb. C,H, Rate Rate in Prod. During of C,H, Produced Kwh./Lb. Lb./Kwh. in Feed Gas Gas Reaction Produced per Kwh. Fresh Feed Discharge Methane ---------------------------------­ 10.0 12.0 14.0 1.340 1.443 1.565 4.89 5.26 5.81 .204 .190 .172 1.073 1.490 2.083 .932 .671 .480 Ethane ---------------------------------------­ 10.0 12.0 14.0 1.3613 1.473 1.603 3.63 3.79 4.04 .275 .264 .248 .428 .580 .784­ 2.338 1.724 1.275 Propane ------------------------------­---­ 12.0 14.0 16.0 1.502 1.640 1.804 3.53 3.66 3.84 .283 .273 .260 .371 .492 .648 2.692 2.034 1.544 Butane --------------------------------------­ 12.0 14.0 16.0 1.517 l.66'l 1.830 HS 3.45 3.60 .299 .290 .278 .266 .350 .460 3.756 2.856 2.176 PAGE 27 TABLE II OF SECTION C, PLANT PART II Analyses (in Mo! %) of Product Gases From Various Feed Gases Methyl Di-Vinyl Feed H, CH, C,H, C,H, C,H, Acetylene C,H, Acetylene Acetylene C.H10 Methane ------------------· 39.3 47.2 55.1 48.9 38.7 28.3 10.0 12.0 14.0 LO 1.2 1.4 .2 .2 .3 .4 .5 .6 .2 .2 .3 Ethane -----------------··· 31.1 37.3 43.5 2.3 2.7 3.0 10.0 12.0 14.0 2.3 2.7 3.0 53.3 44.l 35.l .3 .3 .4 .5 .6 .7 .2 .3 .3 Propane ---------------­32.8 38.3 43.8 Butane --------------------­30.6 35.7 40.8 3.2 3.8 4.4 3.4 4.2 5.0 12.0 14.0 16.0 12.0 14.0 16.0 3.2 3.15 3.9 3.5 3.9 4.3 1.5 1.7 2.0 1.5 1.7 2.0 .3 .4 .4 .3 .4 .4 46.1 37.2 28.3 .6 .7 .8 .6 .7 .8 .3 .3 .4 .3 .3 .4 47.8 39.1 30.3 Table 1 of Section C, Plant Part 11, shows efficiency, expansion, and energy input data for four paraffin hydrocarbons. .Three con­centrations of acetylene in the product gas are given for each feed gas. The next table (Table II) shows analyses of these 12 product gases. These analyses were made with a mass spectrometer. The effect of diluents, such as hydrogen, nitrogen, etc., in the feed gas have also been investigated, and their effect on acetylene efficiency is definitely known. The data obtained as described above, and as illustrated in the accompanying graphs and tables makes it possible to calculate for each discharge chamber in a plant, how much of the discharge energy spent therein is taken up by the products formed, how much is liberated as heat, and how much the gas expands in volume. These data are needed to calculate the size of the connecting gas pipes, cyclone, and cooler, and also the heat duty of the latter. All of these calculations must start with a knowledge of the composition of the feed gas because the amount of energy needed per pound of acetylene varies accordingly. Space does not permit stating these variations here, but it is important to know that these data have been secured and that the calculations can be made for a gas feed of any compo· sition. HOW THE PARTS WORK Plant Part II: Discharge Chambers and Accessories for Liquid-Feed Plants The first three paragraphs of the preced­ing section are equally applicable here. Discharge chambers using liquid feed stocks must be purged with a fuel gas before operation is begun. Operation is begun by starting the feed to the insulators. Then the main feed sprays are turned on at a low rate, the discharge is started, and the feed rate is PAGE 28 gradually increased until the desired oper­ating temperature is reached. This tempera­ture is then maintained by suitable control instruments. The experimental results of the action of the electric discharge upon liquid hydro­carbons were obtained from a continuous flow system. "Batch" determinations of the kind described above for gaseous hydro­carbons could not be made with any degree of accuracy because of the difficulties of keep­ing the liquid hydrocarbons vaporized. Con­sequently, the experimental data given below for liquid hydrocarbons are directly applica­ble to large scale continuous units. In contradistinction to the observation made with methane,-that the amount of acetylene formed per Kwh. decreases with the concentration of methane in the discharge chamber,-it has been observed with liquid hydrocarbons that the amount of acetylene formed per Kwh. is practically constant over a range of vapor concentrations in the cham­ber ranging from 100% to 47%. Hence it is immarterial how much liquid feed is added per Kwh. provided the ratio of its vapor vol­ume to that of the products is at least unity. -and this is generally the case when enough liquid is added to keep the temperature within ·the set limit. Thus it is evident that the rate at which liquid hydrocarbons are added to a chamber is primarily determined by the temperature limit and the rate of energy input. The de­sign data given here have been fixed in this manner. The amount of liquid feed per pound of acetylene varies slightly with the kind of 1iquid hydrocarbons used. HOW THE Properties of the By-Product Carbon Black The carbon black which is formed by the action of the electric discharge upon gaseous hydrocarbons is a semi-graphitic black which shows plate-like irregular particles in elec­tron micrographs. Although this black has been partially classified as an acetylene black by its properties, it differs radically in physical appearance from the long-chained acetylene black formed by the thermal de­composition of acetylene. Due to its inti- The data given below have been obtained experimentally. Basis-1 lb. C,H, Raw Material =Gasoline Naptha Discharge Eneriry Requirements =:).51 Kwh. 3.64 Kwh. '.\fotors, Losses, et<:. = 35 Kwh. .:)6 Kwh. Total Energy =3.86 Kwh. 4.00 Kwh. Raw Material Required .. =2.25 lbs. 2.54 lbs. Dry carbon form ed . '·' !'.1 lh. 0.4.3 lb. % CH, in Condenser exit gas -------------···--·-..... = 23.0% 23.0% Condenser Heat Duty __ ___ = 6fi00 Btu 6850 Btu (55% of dischaq~e enerp:y) The raw material requirement per pound of acetylene will be lowered by an amount ranging from 0.15 to 0.25 lb. through a better recovery of condensibles from the product gas and better energy efficiency. The unreacted vapors are condensed and returned to the discharge chamber, and this leaves a gas of almost constant composition regard­less of the feed stock. With any one fixed ratio of energy per pound of feed the quantity of this gas varies slightly with the feed stock employed, but the composition of the gas remains practically constant. As is the case with most processes producing acety­lene from hydrocarbons, the gas contains about one-tenth as much higher acetylenes by volume as of C"H". These higher acetylenes are removed hy the oil wash in Plant Part llT and returned to the di~rharge rhamher. PARTS WORK mate contact with the gaseous products of the electric discharge, the carbon black has a volatile matter content of approximately 9%-much of which consists of adsorbed high boiling hydrocarbons which are formed in the discharge. The black is non-wettable with water and calculations based upon sur­face area measurements indicate a small particle size. Both mineral oil color and oil absorption are exceptionally high. The black is very fluffy and has an apparent 0 \Uh units--all of ea('h 70 1111il group lo be in parallel--and Lht· ll'holc assembly to be fused, and housed in rnhicles. As each l-!roup of 70 paralleled capacitors i,,; in series with 70 paralleled capacitors, the one-half l-!roup conned ed lo the high voltage wire musl be insulated both from ground and from the second half group of capacitors. 12 -:)62 Kva. iron core, air gap linear in­ductances, 121 reactive ohms, current rating SI. 7 amperes, with insulation for 15,450 volts. 12----1,9.SG K va. iron core, air gap linear inductances, 121 reactive uhrns, current rat­ing 127 amperPs, with insulation for 21,300 vuIts. Suitable metering equipment fur each of the 12