WULFF PROCESS ACETYLENE

Welding Acetylene Is Primary Product of Demonstration Plant

GORDON H. BIXLER Assistant Editor

F

in collaboration with

ROLI R hardly countable ix-oduotion duriiig the earl) years of this century, acetylene now hits the market in the if-notheavy, at-leastrmiddleweight bracket of hundreds of millions of pounds per year (Table I). First used only for illumination (trains, miners, autos), acetylene later became a basic chemical for the metal working industries, where the very high temperature obtainable from an oxyacetylene flame (6000” F.) made it of prime importance for nelding and cutting. And now, the versatile gas is already or is potentially the starting point for a perplexing array of important industrial organic chemicals. Some 75% of the acetylene produced today is a raw material for chemicals. It is a basic building block for vinyl and acrylic plastics and fibers; nitrile rubbers offer another outlet, as do polyacrylonitrile soil conditioners. Acetylene black, produced mainly in Canada, is an important constituent of dry cells. Largely unexplored commercially, but looming on the horizon, is a core of basic organic chemicals from Reppe chcmistrg techniques of vinylation, ethinylation, carbonylation, and cyclic polymerization ( 2 ) . In some of these chemical applications, acetylene has the field t o itself, in others, ethylene is a strong competitor. An added complication for today’s prospective producer of chemical acetylene is the wide choice he faces as t o method for producing 2596

C. W. COBERLY Wulff Process Co., Maywood, Calif.

his acetylene-calcium carbide or a number of hydroo:nlmn processes. Some of the interrelations among ethylene, cnlcium carbide acetylene, and hydrocarbon acetylene and their products are shown in our cover illustration. Calcium carbide has long been the mainstay of the acetylene industry. Its advantage lies in the highly pure acetylene it gives. I t s disadvantage, a t least for large plants demanded by the chemical acetylene user, is that its use is somewhat restricted t o areas of plentiful electric power. Challenging the supremacy of calcium carbide for chemical acetylene are a number of processes using hydrocarbons. ;\I1 hydrocarbon acet,ylene processes are basically the same-addition of energy to a hydrocarbon feed to “break” the molecules tjo give acetylene in somewhat low concentration, followed by its sep:ir:ition and purification. Differences among these processes are in the energy source. In thermal cracking, an auxiliary fuel supplies heat to a cracking furnace; in partial oxidation, heat is supplied to a furnace by burning some of the hydrocarbon in the furnace with air or oxygen; in electric discharge, the feed is pa.ssed through an electric arc. Representative of each of these basic methods and in varying stages of development in the U. S. are the Wulff thermal, Sachsse partial (oxygen) oxidation, and Schoch electric discharge processes.

INDUSTRIAL AND ENGINEERING CHEMISTRY

Vol. 45, No. 12

PLANT PROCESSES-Acetylene In the Sachsse process, oxygen and methane are heated separately t o about 500’ C., reported (8) t o be mixed in a ratio of approximately five volumes of methane to three volumes of oxygen, and fed to a burner. Temperature of the burning gases reaches about 1500’ C., after which the cracked gases are cooled rapidly (within 0.1 second) t o 80’ C. The process requires careful control of gas velocity to the specially designed burner and careful control of the quench step. Yields run about 30%. An advantage is the simultaneous production of an off-gas which can be sent directly t o the liquid nitrogen scrubbing unit of a n ammonia synthesis plant. Disadvantage to the Sachsse process is the need for tonnage oxygen, adding to operating costs. Heart of the electric discharge process developed by E. P Schoch a t The University of Texas (7) is a rapidly rotating blower wheel which serves as one electrode. The other electrode is a flat, metal strip placed so one end is close to the blower’s rim and the other end somewhat farther away, forming a V-shaped space between blower and strip. The rotor sends a sheet of gas through the V-shaped space and, thus, through the discharge between electrodes. A small part of the feed is converted t o acetylene, hydrogen, and carbon black. Temperature in the chamber is kept below 288’ C. Effluent gases are cooled and the acetylene separated and purified. Acetylene yield (carbon basis) is 27% using a methane feed. Schoch calculates that a plant using a methane feed and producing 2000 pounds of acetylene per hour will require 5.26 kw.-hr. per pound of acetylene produced (at nearly 10% concentration in the effluent gases). As with other processes, the Schoch process can use various hydrocarbon feeds; electrical energy requirements decrease with increasing molecular weight of feed stock. Sachsse Process Reaches Commercial Production in Southwest

e

In addition to the Wulff Process Co. demonstration plant near Los Angeles, three acetylene-from-hydrocarbons plants are under way. All use the Sachsse process for captive production. Monsanto’s acetylene plant a t Texas City began operation in January with the product being used for acrylonitrile and vinyl chloride monomer. Carbide and Carbon also has an acetylene plant at Texas City, reputed t o be the largest hydrocarbon acetylene plant in the United States. An acetylene unit is part of American Cyanamid’s $50,000,000 nitrogen chemicals plant being built near New Orleans (Fortier). Completion is scheduled for the first quarter of 1954; acetylene will be used for making acrylonitrile. A possible addition t o hydrocarbon acetylene manufacturers is Rohm & Haas, presently using calcium carbide for captive acetylene at its acrylates plant a t Houston. The company

Table 1.

1

1935 1937 1939 1941 1943 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952

Acetylene Production Thousand Cubic Feet 1 143,I99 1 511 445 1 274 164 2,030,630 4 I99 863 6 :e03 897 6 105 918 4:799:464 3 649 873 4 ‘286‘700 5:987:643 4,998,430 5,331,000 5,851,000 5,978,000 ~

: : :

Source: U. S. Department of Commerce and C h e n . Eng. News, 28, 4245

( 1 950).

December 1953

from Hydrocarbons

says it chose calcium carbide because its volume WLLSconsidered too small to support a synthesis plant. It is “interested” in hydrocarbons as a possible cheaper source when volume justifies. Acetylene History Extends Back Through 100 Years

Edmund Davy is believed (6)to have been the first to make acetylene (his method was potassium carbide plus water), but it was not until Berthelot’s work of the 1860’s that acetylene was named and its properties accurately described. Berthelot also devised another production method-an electric arc-induced reaction between carbon and hydrogen. Woehler the same year showed that calcium carbide plus water yielded the light gas. Other early workers included Lewes (6),who thermally cracked ethylene to acetylene in very low yields, and Bone and Coward ( I ) , who produced acetylene thermally from methane, ethane, and ethylene. An important landmark in acetylene progress was passed when Willson (9) received a patent in 1892 for producing calcium carbide in an electric furnace, thereby laying the base for calcium carbide acetylene produced today. Willson’s discovery, incidentally, was accidental; he was primarily interested in electrolytic production of aluminum. I n addition to Reppe in Germany, whose work was mentioned in the foregoing, Father J. A. Nieuwland and his coworkers at Xotre Dame have contributed much to our knowledge of the chemistry of acetylene and of processes for which acetylene is a basic raw material. Following Lewes’s work of the 1890’s, thermal cracking was largely ignored until 1926, when Wulff began a series of experiments suggested by C. J. Coberly. These experiments were financed by C. J. and C. E. Coberly, F. W. Harris, and a small group of their associates. Wulff is credited by Hasche (5)as being the first to realize that high yields could best be obtained by using a short contact time followed by rapid cooling. Acetylene is an intermediate cracking product, and after too long a time a t cracking temperatures it is further broken down. A rapid quench from cracking temperatures is necessary to prevent decomposition a t intermediate temperatures. A number of patents have been issued to Wulff (IO). These formed the original basic patent structure of Wulff Process Co., when i t was organized in 1933 following issuance of the first patents to Wulff. Also playing a role in developing Wulff acetylene was Hasche, who worked on thermal cracking of hydrocarbons, first with A. 0. Smith Corp. and later (1934) with Tennessee Eastman Co. under license from Wulff Process Co. His work was on both tubular furnaces and on regenerative furnaces similar in principle to those used in the Wulff process today. I n the Wulff process, a hydrocarbon feed is heated rapidly t o cracking temperature (lOOOo t o 1300’ C., depending on type of feed) in the furnace. Feed stock may be natural gas, ethane, propane, butane, gasoline, or other petroleum distillates. Steam, vacuum, recycle gases, or a combination of these is used as diluent to reduce the partial pressure of the feed. Following a short stay in the furnace (less than 0.1 second) and a n even shorter time a t cracking temperature (less than 0.05 second), the gases are cooled rapidly, first in the furnace and then by water sprays. Tars and other liquid polymerization products are separated from the cracked gases, and selective solvent scrubbing recovers acetylene. A feature of the process is the simultaneous production of ethylene from feeds other than methane. Ratio of ethylene t o acetylene may be varied by furnace conditions. Figure 1 shows the variation with temperature of products when using a propane feed (no recycle). While the same variation exists in the present Wulff furnaces, the measured temperatures are lower than in Figure 1. The ethylene may be recovered and sold or it may be recycled.


2597

’

ENGINEERING AND PROCESS DEVELOPMENT veloped by Wulff, and a number of different designs have been built by Tennessee Eastman, Petroleum Chemicals, Inc., and Wdff Process. The first installation at the present Wulff plant consisted of one furnace. Today there arc two larger ones which operate in conjunction, one making while the other is heating. This provides a continuous flow of cracked gases in quench and recovery equipment downstream from the furnaces. Except for short down periods, when various changes FTere made in checker arrangements, the --‘TAR L C A R B O N TEMPERATURE, *C. first furnace operated from December 1949 t o September 1951, during which time process conFigure 1. Distribution of Products Using Propane Feed f31 \-, ditions were determined. A t the end of this period, the furnace was placed in continuous If the latter is done, acetylene yield is approximately doubled. operation on a 24-hour basis until November 1952. At the This doubling is shown quantitatively in Table 11, where butane end of this continuous, 1-year operation, furnace performance is the feed. Similar results are obtained with other feeds. was equivalent in every respect to that a t the start. However, checkerwork inspection was made to determine what refractory repair would be on an annual basis. Demonstration Plani Acquired in 1950

In 1950, Wulff Process Co. acquired a plant near Los Angeles which was formerlv a calcium carbide acetylene plant. This it revised and adapted as a small scale demonstration plant for the Wulff process. Forming a part of the present Wulff plant are the original cylinder filling manifolds, calcium chloride drying tubes, and acetylene compressor. Heart of the Wulff plant, however, is the regenerative furnace and its corollary feed mcchanisms and controls. The furnace is essentially a horizontal, rectangular, brick checkerwork section that absorbs heat during a “heat” cycle and heats the feed to cracking temperature during a “make” cycle. Surrounding this checkerwork are suitable insulating brick encased in a steel plate box. The necessary headers, pipes, and valves for introducing make and heat gases and for exhausting cracked and flue gases complete the furnace installation. Solvent scrubbers and solvent recoveiy towers round out the plant. One of the deterrents to developing thermal acetylene has been, until recently, a lack of satisfactory refractories and furnace design. A tubular furnace was used in early work on this process by Wulff Process and Tennessee Eastman, but extremely high flame temperatures were required to get the necessary heat transfer through the tubes to the feed. This required preheated air, adding to operating costs, and the higher “driving” temperatures unduly punished refractories. The resulting tube failures caused some to identify the Wulff process with high refractory maintenance costs. The alternative method for heating the hydrocarbon feed is to pass it in direct contact with previously heated refractory-in other words, a regenerative furnace. Here, lower refractory temperatures are possible while bringing the feed up to the iequired cracking temperature. This type of furnace was de-

Table II.

Recycle vs. Single Pass, Butane Feed (3) Single Pass Recirculation Volumes feed

Volumes cracked

gas

gas

... ... ,.. ...

gas

1

Acetylene yield (based on butane fed)

2?,5%

82 3%

Checker Repair Costs Are Minor

Cost for repairing the furnace (actual labor and materials) was 0.14 cent per pound of acetylene produced. On larger furnaces, the cost for checkers would increme directly with size, but the

cost of insulating brick, labor, etc., would not increase in direct proportion. Wulff Process, therefore, considers this cost to be a possible maximum, even for the smallest commercial furnace. Early process development was based on acetonyl acetone as the selective solvent for acetylene recovery. Acetonyl acetone performed satisfactorily, but there was no readily available supply, and it was abandoned in favor of dimethylformamide. Capacity of the first furnace was about 750 pounds of acetylene per operating day. The two larger furnaces, which began operating in ?\larch 1953, now produce about 3000 pounds per day

THERMOCOUPLES

2598

Volumes cracked

100

Butane Acetylene Ethylene Methane Hydrogen Benzene Carbon monoxide Carbon dioxide

1 Figure 2.

Volumes feed

1

Wulff Regenerative Furnace


Vol. 45, No. 12

,

.

"

This is bottled by Wulff and distributed to the welding trade. The primary interest of Wulff Process is in chemical acetylene, however, where single plant capacity would be of the order of 20,000,000 to 50,000,000 pounds per year. Furnace detail is shown in Figure 2. Checkerwork is stacked in the furnaces in two legs s e p arated by a combustion and cracking zone. Checkers, developed by Hasche ( 4 ) of 99% alumina ( I @ ) , are flat, rectangular plates grooved in such a manner as to provide continuous, cylindrical channels of about '/,-inch diameter running the length of the leg when stacked in the furnace. Insulating brick (11E) surrounds the checkerwork (two courses on each side, four courses top and bottom) with the exception of bricks immediately adjacent to and facing the combustion and cracking chamber, which are 99% alumina (16E). The entire furnace is incased in steel, mainly 13/1e-inch plate. Bolted-on inspection doors are A. All Furnace Controls Are Located on This Central Panel located .. .. in each end of the furnace headers and a t Once furnaces are brought to temperature, operation is completely automatic the center top of the furnace itself. Each of these doors and its face plates are machined flat; an 0ring completes the seal, permitting troublefree o p manually during starting, being heated in Pminute cycles in each eration under vmuum. Thermocouples are spaced in each half of the furnace as shown direction until temperatures are balanced in both furnaces. Figure 3 shows typical temperature profiles for both furnaces. in Figure 2. Beginning with the center thermocouple, the first four outward in each direction are platinum-platinum-rhodium; I n the meantime, propane vaporization is begun, so there will be a propane source when the furnaces are ready. When the the balance are base metal. Thermocouple leads go to a selector temperatures are balanced, the furnaces are shifted to automatic switch on the main instrument panel (Photo A), which permite operation, with make cycles taking their proper turn in the reading temperatures at points within the checkerwork on one sequence of operation. temperature indicator-controller ( H E ) . Five burners designed by Wulff Process are a t each end of the Natural gas is used for heat. until such time as by-product offcombustion zone (pointing inward and intermeshed three on one gas becomes available as a result of plant operation. The plant runs 24 hours per day, 7 days per week. Should it go on interside, two on the other) to introduce heat cycle gas. When heating from left to right (Figure 2), the left-hand set of burners is rupted operation for any reason (a M a y week, for instance), pilot burners ( I 7 E ) using propane keep the furnaces within used; vice versa for heating from right t o left. The plant is designed for continuous operation, and start-up is 200" C. of operating temperature (furnace stacks open, vacuum pumps off). Under these conditions, start-up begins a rare occurrence. Periodic cleaning of checkerwork is not required (any carbon produced is burned out during each heat a t the point where automatically reversed cycles are started with the furnace under VaCUUm. cycle), and checker replacement or repair is an infrequent event. Start-up must occur a t some point, however, and here is how it is Valve arrangement for a complete cycle for the two furnaces, plus flow directions of the various feeds, cracked gases, and flue done : Stack valves for both furnaces are opened, and a gas and air gases, is shown in Figure 4. A complete cycle for each furnace consists of two heats and two makes: A heat in one direction is mixture is fed to burners ( I 7 E ) in both furnaces which are used for start-up and stand-by heat only. A piece of waste, saturated followed by make in the opposite direction; then heat in the same direction is followed by make in the opposite direction (indicated with kerosene, is inserted in a small port near the bottom of the combustion and cracking zone, lighted, and the gas turned on. by arrows on each side of the figure). By making in a direction Heat is continued with stacks open until the temperature a t counter to the preceding heat, the cold feed gases enter the hotter points 10 inches on each side of the combustion and cracking leg of the furnace where they are heated to cracking temperature. zone center reaches Cracked gases give 750" C. At this point, up their heat, then, stack valves are I600 t o the exit leg. Such closed, air supply 1400 operation maintains valve t o the furnaces proper heat balance 3 1200 turned on (see dein the furnace. 1000 scriptionof heat cycle 3 Timing of the vari$ 000 ous feeds is critical, following for source, which means the introduction, and 0" 600 metering of this air), W valves must operate k 400 and the flue gas vacprecisely and rapidly. COMBUSTION AN0 uum pump is started 200 Lines to the furnace CRACRINC ZONE to bring the furnaces 0 f r o m t h e mixing I down t o their operJ headers are 6-inch; CHECKERS CHECKERS ating pressure (15 some engincers were inches of mercury I I I skeptical that the absolute). The furFURNACE PROFILE valves could be made Figure 3. Temperature Profile for Wulff Furnaces to operate properly. naces are operated

December 1953


2599

ENGINEERING

AND PROCESS DEVELOPMENT

I HEAT I MIN.

U

1

Y

_u

Figure 4.

1800

Furnace Valve Arrangements and Feed and Exhaust Flaws

INDUSTRIAL A N D ENGINEERING CHEMISTRY

Vol. 4, No. 12

PLANT PROCESSES-Acetylene

from Hydrocarbons

~~

The valve arrangement used was designed and built by Wulff Process, using four 4-way plug valves ( 1 E ) . These valves are which in turn are controlled actuated by large air cylinders (IOE), by solenoid, 4-way slide valves. Large air piping is used to obtain the necessary valve operating speed. These valves, m well as the valves in the feed, fuel, steam, and recycle lines, are all controlled with a cycle timer (NE). Photo B is a closeup of one of the valves. No difficulty has been experienced, and Wulff Process believes the much larger 18- t o 24-inch valves called for by large scale plants would also be satisfactory. Propane Is Starting Point for Acetylene at Wulff Demonstration Plant II

Table 111.

Metering Orifices

Feed Propane Steam Air (heat cycle) Off-gas (heat cycle) Natural a8 (when used) Off-gas, tiacetylene stripper Off-gas, final stripper

Table IV.

Diameter, Inches 0.300 0.700 3.000 0.250 2.000 0.250 0.100

Typical Cracked Gas Analysis, Propane Feed Material

co

Figure 5 is a flow sheet for the process. Propane is delivered by tank truck and stored i n one of two 6000-gallon, horizontal, cylindrical tanks. Liquid propane from these tanks is pumped by its own vapor pressure to the shell side of a vertical, single pass, shell-and-tube heat exchanger, where it i$ v a p o h e d . Heat of vaporization is supplied by a dimethylformamide stream used as reflux on a later processing unit, the solvent stabilizer. DMF flow rate is 1.5 gallons per minute; it enters at 35" C. and leave8 a t 22" C. Propane exits a t about 25" C., a t which temperature its pressure is about 125 pounds per square inch gage. This propane vapor is fed via 1'/*-inch pipe to a mixing header ( a 2-foot section of 6-inch pipe) where it is joined by dilution steam and by recycle gas (off-gas containing diacetylene and methylacetylene) from the diacetylene stripper and final stripper (see Figure 6). Before entering the mixing header, all gases are metered through calibrated critical orifices. Flow rates are controlled by preset regulation (6E)of pressures upstream from the critical orifices. Orifice types and dimensions are shown in Table 111. Ratios of propane to recycle gas t o steam are 1 to 1.99 to 6.0 (72,000, 143,000, and 432,000 standard cubic feet per 24 hours) Under automatic operation and on the make cycle, propane,

Type Bell mouth Bell mouth Sharp edge Bell mouth Sharp edge Bell mouth Bell mouth

Nn

Ha CH4 CaHn CnH4 CzHa CsH4 (1\.Iethylacetylene) CsHe CaHs CdHa (Diacetylene) CiHh (Vinylacetylene) CdHs (Ethylacetylene) C6HlO CsHa 02

cot

Volume Per Cent 6.9 5.2 55.7 15.0 10.0 3.8 0.1 0.20 Trace 0.2 0.04 0.16 0.00 0:4

0.7 1.6

recycle gas, and steam (all at 15 inches of mercury absolute) leave the mixing header, pass through the automatically controlled valves, and enter the furnace. Heabup occurs in the entrance leg of the furnace, and the gases are cracked in the hot center section. These cracked gases lose sensible heat to the exit leg of the furnace, emerging from the furnace at about 300" C. Average gas velocity in the furnace during make is 180 feet per second. Pressure drop across the furnace is about 1 inch ofbercury. A typical cracked gas analysis is shown in Table IV.

b

B.

A

Six-Inch Plug Valve Gets a Shot of Grease

These valves, of which there are four for the two furnaces, operate instantly1 there i s no lag downstream from furnaces when they change from heat to make

December 1953


2601

ENGINEERING AND PROCESS DEVELOPMENT

I

Figure 5.

2602

Flow Sheet for the Production of Acetylene by the Wulff Process


Vol. 45, No.


v

from Hydrocarbons

Propane and recycle gas feeds are stopped 3 seconds before the and tars from this tank are recycled to the bottom of the t a r end of the make cycle to permit a steam purge of 3 seconds beseparator; pressure differential between this part of the sysfore air and off-gas are introduced for the heat cycle. tem (7 inches of water gage) and the tar separator (15 inches As previously mentioned, one furnace is heating while the other of mercury absolute) "pumps" these liquids. is making. Air from the atmosphere is filtered (BIE), regulated Cracked gases are given a final and precautionary cleanup in an by a manually operated vernier valve (Wulff Process design and electrostatic precipitator t o prevent fouling the compressor. manufacture) on the control panel, metered through an orifice About 15 pounds of light oils are removed by the precipitator (6E),and fed at furnace pressure to the preheat leg of the furnace. daily. It reaches about 1100" C. a t the furnace center. Off-gas is burned Floating on the line between precipitator and compressor is a by being injected into this preheated air by the upstream set of 3000-cubic foot, water-seal, gas holder. As flow in the lines is burners, supplying heat of reaction and furnace heat losses. continuous, only small surges occur in the holder; it is purely About 45,000 B.t.u. is supplied per heat cycle. precautionary, therefore (with one furnace operation, the holder Heat cycle flue gases exit a t 300' C. and are cooled further in would be needed to level out surges caused by intermittent fura finned tube gas cooler (8E),from which they go to the suction nace make cycles, and give continuous flow to the following side of a rotary blower vacuum pump (19E),one of two vacuum absorbers and compressors). pumps that maintain furnace vacuum. Flue gases are pumped Cracked gases next enter the low stage of the compressor ( $ E ) to atmospheric pressure and vented t o the atmosphere. Feed where pressure is boosted t o 35 pounds per square inch gage. valves change and the next make cycle begins. With valves Heat of compression is removed in a finned-tube heat exchanger, operating as rapidly as they do, there is virtually continuous gas temperature being dropped from 130" t o 49" C. operation of the flue gas and cracked gas systems downstream This compression and cooling causes a slight condensation, from the furnaces. After leaving the furnace, the cracked gases are cooled from the which is removed in a knockout drum (323)and discarded. The 300" C. exit temperature to 38" C. in three steps-water sprays high stage of the compressor then boosts pressure t o 150 in a quencher and tar separator and in a heat exchanger. pounds per square inch gage, the compressed gases are cooled Located in the 6-inch, cracked gases pipe just before the tar from 143' to 38" C., and the condensate is separated ( 4 E ) separator is a quencher, where the gases are sprayed with water. and discarded. This 150-pound pressure aids in recovery in This quencher consists of a 12-inch jacketed section on the 6-inch the solvent extraction sections following. The cracked gases gas line. Four rows of '/a-inch nozzles (18E), eight nozzles to are now ready to be separated and the acetylene rethe row, are threaded circumferentially into the gas line in this covered. section. Water is piped to the annular, jacketed space, and the nozzles shoot solid cone sprays into the cracked gases stream. Total water flow is 30 gallons per minute. Gas temperature is Dirnethylformamide Scrubbing of about 100" C. when i t leaves the quencher. Cracked G a s e s Recovers Acetylene The partially cooled gases continue to the tar separator, Solvent used in the separation and purification is dimethylentering at about its mid-point. The tar separator is a vertical formamide. Not only must acetylenes be separated, but diacetycylindrical tank 10 feet high and 3 feet in diameter; its bottom is Iene must be removed independently. Advantage is taken of the conical. Three nozzles (18E)in the separator spray an additional fact that solubility of diacetylene in DMF is about 2500 volumes 25 gallons of water per minute into the gas stream, further reducper volume a t the low partial pressure a t which diacetylene is ing gas temperature and aiding in knocking down tars. Confound in the cracked gases. By scrubbing the gases with a densed diluent steam, quench water, and tars fall out to the convery small amount of DMF, diacetylene is removed first. ical bottom. Tar-free cracked gases exit from the top a t 60" C. Cracked gases, now a t 150 pounds per square inch gage and Tars amount to about 200 pounds in 24 hours. These tars 38" C., are fed a t a rate of 300 cubic feet per minute to the drop by gravity through the conical section to a tar tank. The tar tank is emptied periodically by closing a valve between the tar separator cone and the tar tank and discharging the accumulated tars in the tank to the sump. Shutdown of the system vacuum is not required for this operation. Water level in the tar separator bottomis automatically controlled (TE), and this level determines whether excess water in the separator is recycled to the quencher or discarded. Gases from the separator are further cooled in a shell-and-tube heat exchanger from 60" to 38" C. and flow to the suction side of the cracked gases vacuum pump (19E). Here the pressure is pumped up to 7 inches of water gage, the pressure maintained on the cracked-gases gas holder. Primary function of this cooler is to complete steam condensation. The vacuum pump operates with a water seal, so the condensate is no problem. Three finned-tube aftercoolers ( 9 3 ) in parallel remove heat of compression from the vacuum pump-compressed gas. Additional water and tars condense during this cooling, and they are removed in a knockout tower, a %foot diamCracked Gases Scrubbing and Solvent Recovery Towers Are Grouped Just Outside Furnace Building eter, 10-foot high cylindrical tank, Water

December 1953


2603

ENGINEERING AND PROCESS DEVELOPMENT This off-gas nerves as a stripping gas in solvent purification and ale0 as plant fuel (furnace heat, comprmsor fuel, and plant boiler). 06-gm in given a water acrub (42 gallons per day through the m b b e r ) to remove traces of solvent. Water from the seruhher, together with water from tbree other ges &rem acrubbera, goea to a solvent recovery tank for solvent recovery (Figure 6). Water for this and the three other water scrubbers is metered and fed by cbenucal feed pumps ( M E ) . Acetylenwich DMF from the acetylene absoFber paszm through a preaeure reducing valve, wbers ita pressure in lowered from the 1Wwund-per-quareinch-gage pressure of the acetylene absorber to the 1s pound-per-nquminch-gage p m u r e of the next unit, the solvent stabilizer. The stream enthe et9bilizer at about ita mid-point at a rate of 8 gallons per minute. A steam-heated reboiler at the bottom of the solvent stsbilher maintains a bottoms temperature of aio C. A reflux stream of DMF, OY* TO STOIAGC 1.5 galloon per minute, which 1s *In ? m a s s ITRUS -led by the propane vaporiser, ia fed to the top of the solvent stabilier to cut hack the m o u n t of ace6 figure 6. Flow Sheet for Solvent Recovery ylene leaving in tbe overhead gases. Under theae conditions, nearly all the gaaea in the DMF, other than To get a su5ciently high purity, acetylene, sue bottom of the diacetylene absorber. DMF is fed in the top at a i t in necessary also to remove a substantial volume of acetylene rate of 0.1 gallon per minute (For packing information an with t h e e gases. This procedure leaves acetylene and methylvarirma absorbers and ncrubbers, nee Table V.) acetylene with only very small amounta of other gases in the DMF These overhead, hydrocarbon gases pase at a rate of about 30 cubic feet per minute through a water wash (18 gallons Table V. Processing and Solvent Recovery Towers per day), which removes tracks of solvent. The hydrocarbon S s p n t i o n Medium Unit TYP. gsses then join the msin gaa flow at the knockout tower for reDufstylens absorber Packed aolumn I-inch #*neware k c h u “nm cycle through the absorption system. Wssh water from the AoeWIma absorber Paoked oolumn I-mah N e 1 RLacbw nmm scrubher goes to the solvent recovery tank for solvent recovery ruua Bd-t nt&l&r P.okdadumn 1-inoh.UalR.sa Packed column I’(cinch d e l Rs.ak& n n 8 ( ~6). i ~ A-m-e ‘“PF Di.o.nlm mmr %ked odumrr I-mmh .@el h b u nPaokd column I-inch #teal k h u ruua Acetylenerich DMF Bows continuously from the solvent w d r p r Packed colaI-inoh ahel RLaeU ~0 StSbiliEer reboiler to the acetylene stripper, which operates at column I1 Packed d a m n I-moh *teal R U O U ~e Wa8e.r wrubben atmospheric p m u r e . A liquid level controller on the reboiler Bubble mp Four s i d e asp t n y i %%%boa Bubble cep Three cap hg. ragulatea this flow; ita average in 9 5 gdlona per minute. A d Bvbbls cap T h alrJLe O.P t n g . The acetylene stripper in likewise equipped with a atesmM y l and k l atriPF- m e 4 Bubble u p Three smde eap t n y s heated reboiler, this one maintaining a bottoms temperature of 121° C. Acetylene leaves the solvent under these conditions, and the more soluble methylacetylene remains in the solvent. Diacetylenerieh DMF (which also containa about 5% of the A milux stream of DMF (1.5 gallons per minnte) is fed in the top acetylene in the m L e d gnaw) in pumped from the bottom of of the atripper to prevent methylacetylene from leaving in the the b t y l e n e b b to the a y l e n e Mppsr(Figure 6) w h a 0 f 1 - is~ used to strip out the a y l e n e . ma pmduct w stream. Meth~lacet~leoe-rich DMF in pumped continuwaly from the reboiler (liquid level controlled) to the gas then forms the major portion of the furnace recycle gaa. Dimetyl-frea cracked gases from the top of the discetylene fidstripper in the solvent recovery section. a@,,h. DMF is Acetylene is given a water wash (30 gallons per day) to remove *flow to the bottom of the AI] solvent, after which it enters a IwoCUbic foot, water-neal gas fed the top of this unit st a mte of 8 p U O m per holder. Wash water from the scrubber gaes to the solvent &+ne and methylaoetylane plus equilibrium m o n t e of other gab%, mch as ethane, ethylene, methane, carbon dioxide, recovery tank for solvent recovery. Acetylene from the gas holder in dried hy being passed and carbon mouoxide, sue absorbed. Leaving the top of the absorber in 06-gaa, conaiating of carbon monoxide, carbon through a calcium ohlorid*filled tank and ia compressed ( M E ) . dioxide, hydrogen, nitrogen, methane, and ethylene. It in piped to filling manifolds, where it ia “packaged” in stand-

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2604


Vol. 4, No. 12


P

1

8

ard acetylene cylinders at about 250 pounds per square inch gage. Solvent purification is shown in Figure 6. D M F from the diacetylene absorber is stripped in the diacetylene stripper and D M F from the acetylene stripper in the final stripper. I n both cases, off-gas from the acetylene absorber is used as the stripping gas. About 96 cubic feet per minute is used in the diacetylene stripper; 12 cubic feet per minute in the final stripper. These stripping gas streams are metered through critical orifices (Table 111). Gas s t r e a m from the tops of the strippers (off-gas plus the gases it has picked up from the DMF) join (that from the final stripper is cooled first in a heat exchanger), and they are given a water scrub (water rate is 108 gallons per day). Scrubbed gas is fed to the flirnaces as recycle gas. D M F from the final stripper bottom is cooled to storage temperature (about 80' F.) and flows by gravity to the solvent storage tank. Wash water from the four water scrubbers and D M F from the diacetylene stripper join in the solvent recovery tank. Resulting composition in the tank runs about 50% water, 50% DMF. This solution is filtered a t a rate of 18 gallons per hour through an excelsior-packed filter (about 12 cubic feet of packing) and fed to a steam-heated evaporator, where i t is vaporized (vapor temperature is 117" C. if the solution is 50:50). Bottoms are periodically drawn off the evaporator and discarded. Formic acid is discharged in the overhead with water, benzene, and naphthalene. A liquid level controller on the evaporator automatically controls the steam fed to it. Distillation separation of the water and D M F is accomplished by two columns (colunms I and 11, Figure 6). These columns are connected so that they are, in effect, one column: Vapor from the top of column I is fed t o the bottom of column 11; D M F refluxing down column I1 is pumped to the top of column I. Vapor from the evaporator is fed to the top of column I. A water-cooled, hairpin condenser a t the top of column I1 maintains partial reflux; water not refluxed back down the column is continuously drawn off and discarded. Formic acid concentrates in the bottom of column I. To prevent its build-up to a high enough concentration to cause it to come over with the purified DMF, a portion of the bottoms in the column I reboiler is periodically drawn off and recycled t o the solvent-recovery tank. This procedure keeps formic acid concentration a t about 1% in the bottom of column I. Purified D M F is tiaken off as vapor a t approximately the second theoretical plate level of column I ( a 4-inch separation in the packing permits this take-off). This D M F vapor is condensed and piped t o storage. The D M F is water-white and contains less than 0.01% formic acid and less than 0.3% water. Make-up required per day has been calculated to be about 36 gallons for a 20,000,000-pound-per-day plant. instruments "Run" Plant; Only Two Men Required per Shift

With the heavy emphasis placed on instrumentation, only a two-man operating force is required in a Wulff plant. All instruments connected with the furnaces feed t o a central control panel (Photo A). They are: pressure indicator-controllers monitoring pressure upstream from the critical orifices on the various feeds to the furnaces and thermocouples in each furnace to central temperature indicator-controllers. Feed valves are controlled by a cycle timer mounted on the board. In addition t o lines painted on the valve plugs (Photo R), which show direction of the flow, a red and green light on the board, keyed t o a code, tells which furnace is heating, which i s making, and what the directions of each are. Precipitator shorts are indicated by another red light on the December 1953

from Hydrocarbons

panel; a green light indicates satisfactory operation. Rotameters are used to set water flows to quencher and t a r separator. Each gas holder has a cutoff switch, the one on the cracked gas holder shutting off the cracked gases compressor, the one on the acetylene holder the product acetylene compressor. This prevents pulling air into the gases and also prevents collapsing the holders by pumping them too low. Liquid level controllers (12%') are connected to each of the four water scrubbers (off-gas, hydrocarbon gases, product acetylene, and recycle gas). These sound horn alarms if the water level gets too high, in which case the scrubbers are dumped manually. In the event of power failure, the entire plant is shut off immediately, with the exception of the cracked gases compressor, which continues to run until the cracked-gases gas holder is pumped down, Analyses are made a t four points in the process. All are for acetylene content and involve absorbing a eample in silver nitrate to form silver acetylide. I n the first three cases, the resulting nitric acid is then titrated with standardized sodium borate, and the acetylene content is calculated. First check is made on cracked gases from the furnace, which are expected to analyze 9 t o 11%. This indicates satisfactory furnace operation. Ngxt is an analysis for acetylene in off-gas from the acetylene absorber. It is desirable t h a t this be 0.1% or less. If larger amounts are noted, D M F feed rate to the absorber is increased until the proper value is reached. Acetylene content of the hydrocarbon gases from the solvent stabilizer is checked, the answer determining the rate of D M F reflux a t the column top. Final analysis is on product acetylene. I n this analysis, the residue remaining after absorption is measured as the impurity. Purity runs 98.5 to 99.3%, Each analysis is performed twice during a shift, the operator normally making them in rotation, one each hour. Ethylene and Ammonia Synthesis Gas Are Important Additional Products

The future for Wulff Process acetylene lies in the area of chemical acetylene. This means high capacity-20,000,000 pounds or more per year per plant. Table VI shows estimated investment costs for plants operating on propane and natural gas; Table VI1 shows estimated operating costs using propane and natural gas feeds.

Table VI.

(I

Capital Investmenta

Propane Natural Gas Acetylene plant $2,652 000 8,126,000 Inventories 32 '000 49,000 Real estate 3 000 3,000 300,aoo 3oa,ooo Working capital Total $2,987 ,000 $3,478,000 Operation 8t 20,000,000 pounds per year, 330 days per year.

The Los Angeles plant is designed and operated as a small demonstration unit for acetylene manufacturers whose production needs range from ten- to 100-fold greater. Fluor, Girdler, and Lummus have been licensed by Wulff Process to build Wulff acetylene plants for any of its licensees. While emphasis has been placed on large, chemical acetylene plants, welding acetylene manufacturers have evidenced interest for Wulff plants of sizes from one half to ten times that of the demonstration plant. Wulff Process, therefore, may release licensing rights, which it has thus far withheld, for welding acetylene production in order to satisfy the demand for plants in that field.


2605

ENGINEERING AND PROCESS DEVELOPMENT Table VII.

Production Costs for Wulff Process Acetylene

Propane 4 oents/gal. b Natural ‘gas, 15 cents/1000 cu. ft. St$s.m. 600 Ib./sq. inch gage, 40 cents/1000 ID. Water, 1.5 cents/1000 gal. Electricity 0.7 cents/kw.-hr. Solvent lo&, 32 cenb/lb. Maintenance, 4 % of investment Labor a n d supervisiond Royalty, &year period Vixed chargese Subtotal

$2.66 ,..

1.09 0.15 0.05

0.30 0.53

0.66 0.12 1.53 7.09

-

si.’& 1.31

0.24 0.13 0.42 0.62 0.66 0.12 1.80 7.12

-~

Less credit for off-gas, 15 cents/1,000,000 0.37 1.14 B.t.u. __ __ Xet production costs/100 lb. $6.72 S5,98 a Operation at 20 000 000 pounds per year, 330 days per year. b Based on yield ;If 4d%, carbon basis. C Based on yield of 24% carbon basis. d Labor: 12 men, incluhing 1 foreman per shift. supervision, 6 men. including plant superintendent. chemist, engineer,’ secretary, clerk, and maintenance man. e Depreciation, 6.7% of investment; taxes a n d insurance, 1.3%; interest, 3.5%.

furnaces wit,hout any difficulties from tar and coke. This freedom from a problem inherent in other ethylene processes is due to burning off any carbon deposits on the checkerwork during each heat cycle. literature Cited

F.,J . Chem Soc (London), 93, 1197-225 (1908). Evans. D. C., “New Technical Applications of Acetylene,” British Intelligence Objectives Sub-committee Report 22/1 (f), 32 Bryanston Square, London, W. 1, England (Jan. 14, 1946) Hasche, R. L., Chem. & M e t . Ew., 49, No. 7, 75-53 (1942). Hasche, It. I,., U. S. Patent 2,632.864 (Dee. 23. 1952). Herrly, C. J., Ciiem. Eng. S e w s , 27, 2062-6 (1949). Lewes, V. B., Proc. Roy. SOC.( L o n d o n ) , 55, 90-107 (1894). University of Texas, Austin, Tex., Cnia. Terns Pztbl., Yo, 5011 (June 1, 1950). U. S. Dept. Commerce. Fiat Report No. 921, P.B. 81826. Willson, T. L., U. S.Patent 492,377 (May 5 , 1592). Wulff, Robert G., U. S.Patents 1,543.965; 1,580,308; 1.550,309; 1,917,627; (to Wulff Process C o . ) 2,037,056 (Feb. 9, 1932, t o April 14, 1936).

(1) Bone, W. A., and Coward, H. (2)

(3) (4) (5) (6) (7) (5) (9) (10)

Processing Equipment

Such plants can produce acetylene from natural gas, propane, ethane, or gas oil a t a cost of about one half that for calcium carbide acetylene. There are, quite naturally, areas within the United States where this differential will be greater because of the lower feed stock costs and higher carbide transportation costs. Conversely, there are areas close t o calcium carbide plants operating on low power cost contracts and where feed stock costs are higher. In such areas, the differential will be less. Another feature of the Wulff process with considerable economic merit is the ease with which feed stocks can be changed. Conversion from natural gas to propane or gas oil requires only storage facilities and a vaporizer. Once these facilities are in, conversion from one feed to another is easily accomplished by a valve change and a new setting on the furnace temperature controllers. Such flexibility, seldom found in manufacturing plants of this type, offers considerable production stability in that shortages and price fluctuations for one feed may be offset by availability of an alternate. hnother important prospect, Wulff Process says, is the simultaneous production of acetylene and a synthesis gas for ammonia manufacture. The furnace effluent minus acetylene gives a gas with a hydrogen to nitrogen ratio of 3:l when mixed with 15 to 25% of combustion products from heat cycles. Carbon monoxide content is a minimum. The process is flexible because of the ease with which the proper hydrogen-nitrogen ratio may be maintained by varying the ratio of heat-make effluent gases. Future operation of the demonstration plant will encompass further experimental work on the process for production of both acetylene and ethylene from various feed stocks while operating as a self-supporting economic unit. Ethylene production prospects are good. Wulff furnaces a t the demonstration plant have produced concentrations and yields of ethylene equal to tubular

2606

(1E) American Car & Foundry Co., 36 Church St.,New York 8 , X. Y . , four-way plug valves. (2E) Clark Bros. Co., Olean, X. Y., Model XI-4-4, IjO-hp., 600r.p.m., gas engine compressor. (3E) Crane Co., 836 South Michigan Ave., Chicago 5, Ill.. 4-inch line separator. (4E) Ibid., 21/2-inch line separator. (SE) Daniel Orifice Fitting Co., 3346 Union Pacific .\ire., Los Angeles, Calif., sharp-edge orifice. (GE) Fisher Governor Co., 1700 Fisher Bldg., ;\Iarshallto%-n,Iowa, Wiszard Type 4100U. (7E) Ibid., Model 2500-249 Level-Trol. (8E) Griscom-Russell Co., 285 Madison .4ve., S e w York, S . V., Type I,SS-186, twin G-fin sections. (9E) I b i d . , Type LSS-248, twin G-fin sections. (10E) Hanna Engineering Works, 1764 Elston Aye., Chicago 22, Ill., Model 16M air cylinder. (11E) Johns-Manville Corp., 22 East 40th St., S e w York 16, N. T,. 2200° F. insulating brick. (12E) Magnatrol, Inc., 2110 South SIarshalI Blvd., Chicago, Ill., Magnatrol liquid level controllers. (13E) Mansel Div., Frontier Industries, Inc., 244 Babcock St., Buffalo 10, N. Y . , Series 60 punips. (14E) Xorton Co., 50 New Bond St., Torcester 6, Mass., Typo TA 4014. (l5E) Ibid., Type Rh 4190. (16E) Normalk Co., Inc., 20 Water St., South Norwalk, Conn., conipressor. (17E) ,%]as Corp. of America, 545 East Erie Ave., Philadelphia 34, Pa., No. 110-55 inspirators; S o . E-112-12il Refrak screen burners. (18E) Spraying Systems Co., 3223 Randolph St., Bellwood, Ill., full jet nozzles. (19E) Sutorbilt Corp., 2008 East Slauson Ave., Los ilngeles 5 8 , Calif., Model 12 X 13B vaccum pump. (20E) Taylor Instrument Cos., Olson and Ames St.. Rochester I , N. Y., Flex-0-Timer, adjustable 1- to 10-minute intervals. (21E) Vortox Co., Clairmont, Calif., Vortox LB 22-6 oil bath air cleaner. (22E) Wheelco Instrument Co., Chicago, Ill., Model 292 indicatorcontroller.


Vol. 45, No. 12

WULFF PROCESS ACETYLENE

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