FREDERICK
(;. SAWYER'
1,. KERhIIT HERNDON Mathieson Chemirul Corporation, Hultirriore, iMd.
4NJ)
RODNEY N. HADER
in coliaboratiun w i t l i
EUGENE MORNINGSTAR Ohio SLUte Uniuersi t y Research Foundut ion, Columbus, Ohio
Associute Editors (
WED in the light of present-d:ty demmtls for both
VI petroleum " products and sulfur, and t,he dwindling of our easily accessible reserves in both catexories, the utilization of sour petroleum crudes and sour nittural gases t,akes on increasing importance. The presence of hydrogen sulfide and mercaptans in sour crudes renders these products unfit for most uses because of the toxic nature of the contaminants and the corrosive conditions obtained on oxidation. The presence of hydrogen sulfide in natural and refinery gases has limited the use of these gases to boiler fuel. There are vast quantities of sour natural gas i i i this country, only small amounts of which are currently being utilized; they are being held in reserve until the short supply of sweet gas is exhausted. Many satisfactory methods have been developed for the removal of hydrogen sulfide from hydrocarbon gases (10, 11, $1W4,86). These met,hods all dcpeiid on absorption of the hydrogen sulfide in a weakly alkaline solution, followed by regeneration of the absorbing solution, usuirlly 1)y heating. Commonly used 1
Present address. Stanford Reaeercli Institrite, Palo Alto, Calif.
a1)sorl)ttiit.sinclude c:t.liaiiolainiiic?s ((:irt)otol process, 221, txipotassium 1)hosphat.c(Shc~llI)c~vt4opiii(~n t C:ompany, 84), sodiuin phwolatc o r nodiuni c:irl)oiiatp (Koppr?r.s C h i p a n y , 21 ), :md pcrs Ttiylos process, 1 I , $ 1 ) . ', the Thylox process is unique in th:it I h t : sc:rubl)ing solutioii is regrrierated I)?. air ositlation rather t1i:tn by h d i i i g , the regeiwration rvsulting iri the formation in the solution of :til tL1eiiientak sulfur suspension. T h e sulfur is removed by flotation, antl is filtjt:red and dried. Other processes use t h r osides of iron 01' iiic:kel iri an alkuline solution, antl produce sulfur by oxidation i n ti similar manner. In the gas cleaniiig processes in which solution regoricrtztion is effected by heating to drive off the dissolvod acid gases, a gas relntively rich in hydrogen sulfide is obtained as a by-product. The utilization of this gas is doubly important because of t,he economic value of the sulfur represented and the extremely toxic nature ol hydrogen sulfide. In cases where the hydrogen sulfide cannot otherwise he used, it is burned from a flare; the resulting ~ u l f u diosid(A r is dissipated into lhe atmosphere It is rniirh inore
1938
October 1950
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
1939
desirable, of course, to recover the sulfu~',thus producing :I valuable chemical raw material, while niininiiEiiig or eliminating entirely any atmospheric contamintition. J$:ucept in special casee i n which t h t w nli~ybe other uses for hydrogen sulfide, it is generally most useful to osidize the gus to either sulfur or sulfuric acid. ICven when sulfuric acid is to be the finished product, there is good reuson for making sulfur as an intermediate, for the use of hydrogen sulfide presents several problems. If it is desired to produce sulfuric acid directly from hydrogen sulfide gas, the gas is first burned to sulfur dioxide in an 8 to 10% exceas of d r . The furnace gas must be cooled to moderate temperature to be thoronghly dried, an espensive process attended by serious corrosion problems. The dry cold gas must then be reheated to converter temperature before it is finally converted to sulfuric acid by the contact process. In the produotion of acid from sulfur, a burner exit gas containing 7 to 11% sulfur dioxide is readily produced. If raw hydrogen sulfide is used directly, niised as i t often is with carbon dioxide and a small portion of hydrorurbon gases from the solution regeneration system, a converter inlet gas containing a smaller percentage of sulfur dioxide is formed, atid a larger acid plant size is required for the same acid production. Furthermore, so much water forms by oxidation in this method that unless strong acid produced from sulfur is available, concentration of the tower acid is required. A further advaritage of preparing sulfur as an intermediate in the procew ia the significant alleviation of storage problems. The provision of facilities for large scale sulfuric acid storage is costly and cumbersome in comparison with the simple, outdoor stockpiling of elemental sulfur. Thus in practically every case, elemental sulfur is the most desirnble form in which to recover the sulfur from hydrogen sulfide.
In modifications developed later by the I. G. Furbenindustrie, A.-G., and by Baehr ( 1 ), emphasis was placed on the recovery of sulfur from hydrogen sulfide and sulfur dioside by contact catalysis. Dne third of the initial hydrogen sulfide stream was burned to sulfur dioxide; the latter then reacted catalytically with the iaemainingtwo thirds of the initial hydrogen sulfide feed stremn to yield elemental sulfur.
HISTORY OF CLAUY-CZIkNCE PROCESS
wits chosen as providing a basis for the most promising method
+ '/202+SOz + H20 2HB + S02+3S + 2H?O
&S
(1)
(2)
In this way the procms made possible higher yields of sulfur from the hydrogen sulfide, in spite of sulfur dioxide formatioii in the furnace. All processw in use today for the recovery of sulfur from hydrogen sulfide dcpend on the reidions involved in the old Claus processes ( 8 ) . PILOT PLANT DEVELOPMENT OF MATHIESON PROCESS
With the discovery of estensive sour gas fields in southerri Arkansas, investigation was begun to determine the feasibility of sweetening the gas for use in domestic and commercial applications (67). The raw gas contained about 8% hydrogen sulfide and about the same concentration of carbon dioxide. It \+as found that the gas could be economically sweetened by ethanolamine absorption (88), which separated the hydrogen sulfide from the gas and liberated it in a concentrated side stream. In 1941, the Southern Acid and Sulphur Company, now a part of the Mathieson Chemical Corporation, engaged the Ohio State University Research Foundation to search the literature and develop in the laboratory a process for the recovery of sulfur from the acid gas separated from Arkansas sour natural gas.
As a result of the literature survey, the Claus-Chance reaction The recovery of sulfur from hydrogen sulfide is a very old process (18, 17, 18). Perhaps the earliest commercial venture m s the English Claus ( 6 ) (later Claus-Chance, 8 ) process, involving the direct combustion of hydrogen sulfide gas in air. The combustion reaction was carried out in a kiln packed with bog-iron ore. The kiln w m made very large to provide for dissipation of heat by radiation from its surface, and was fed slowly enough to prevent excessive temperature rise, eliminating the side reaction between sulfur and oxygen to form sulfur dioxide. (Sulfur dioxide formation could be prevented in this manner because the reaction of hydrogen sulfide with oxygen to form sulfur takes place at temperatures lower than those required for the competing reaction between sulfur and osygen. Maintaining lower temperatures also prevented the reaction between sulfur and carbon dioxide to form sulfur dioside and carbon monoxide.) A large part of the product from the Claus kiln wm recovered as molten sulfur collected in a receiver just outside the kiln; the sulfur not condensed in the receiver was collected in a dust chamber. Sulfur dioxide was removed from the stack gas by solution in water in a wash tower. Escess hydrogen sulfide was finally removed by passing the gas stream through an iron oxide purifier, or through a fire where the hydrogen sulfide was burned to sulfur dioxide and carried through flues to a chimney ( 1 6 17. 18)
The success of the Claus-Chance process depended on operating the furnace or kiln at a temperature of about 500' F. as measured in the exit pipe. This temperature was controlled in early plants by regulating the inlet hydrogen sulfide gas and air flow, cutting the flow if the temperature became too high. In later modifications, if the furnace temperature began to climb, a portion of the stack gas was recirculated through the kiln to dilute the reacting gases and lower the reaction temperature. The result of excessive furnace temperatures was the reaction of part of the oxygen with sulfur rather than with hydrogen sulfide, lowering the yield.
of sulfut recovery. On the basis of laboratory studies, a pilot plant with a capacity of 100 pounds per hour was erected in 1941 near Magnolia, Ark., for further study of the process and the collection of reliable process data for design purposes. This pilot plant was operated jointly by personnel from the Southern Acid & Sulphur Company and the Ohio State University Research Foundation. (About this same time, Susearch, an affiliate of the Texas Gulf Sulphur Company, built its pilot plant at McKaniie, Ark., and started an independent study of the utilization of hydrogen sulfide derived from sour natural gases, 16.) Considerable study on furnace design was required in Southern's Magnolia pilot plant, because furnace operation on the larger scale was found to be much more trouhlesome than laboratory results had indicated. The differenre arose chiefly because in the laboratory the furnace had been externally heated with easily controlled electric heaters. This factor, plus the high ratio of area to volume in the laboratory furnace, had made the operation very easy to perform. After much pilot plant investigation, a satisfactory furnace design was evolved, and application of the pilot plant design to a commercial kiln resulted in n smoothly functioning proceps. In addition to the vital furnace design data which the pilot plant supplied, it also demonstrated the feasibility of using sulfur cooling towers to separate the sulfur produced. Converter size requirements and heat exchanger duties also were ascertained in the pilot plant stage. MATHIESON COMMERCIAL PLAYTS
On the strength of laboratory and pilot plant data, a conimercial plant with a capacity of 120 to 150 long tons per day was designed by the Foster-Wheeler Corporation, New York, in close cooperation with Southern's pilot plant engineers. The plant, based on processes covered by patents and patent applications coming from the developmental work (8,9, 19, W), was erected
1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 42, No. 10
correct amount of air for complete combustion of the hydrocarbons, and oxidation of the hydrogen sulfide to sulfur. Combustion Furnace. The plant at RfcKamie, which is the larger of the two Mathieson plants, includes a cylindrical combustion furnace, or horizontal kiln, 9 feet in diameter by 22 feet long. The kiln is divided laterally into three sections, with manifold connections for parallel operation. Each of the three sections is complete in itself (see Figure 2). The total heat release in the furnace is about 15,000 B.t.u. per hour per cubic foot of furnace volume, an amount much greater than that obtsined in the old Claus-Chance furnace. This heat release in partial combustion is made possible by the special design of the furnace, which operates on a recuperative heating principle, each section of the kiln containing its special recuperative heater and special packing section to assure uniform oxidation. The furnace is shown in title photo of this paper; air flow is controlled manually to ensure the proper air-to-acid gas ratio, providing for oxidation of the hydrogen sulfide to sulfur. The inlet air and acid gas are preheated within the furnace by indirect heat exchange with the products of combustion. Combustion takes place in each section in a region loosely packed with high temperature firebrick. The need for such packing had been demonstrated in the pilot plant studies, where it was found that in the absence of packing the Acid Gas from Sweetening Plant Enters illathieson's reaction front moved out through the exit 1lcKarnie Plant through Knoclcuut Drum, Foreground end of the furnace, and combustion was Air and acid gae are admitted to horizontnl kiln eventually extinguished in the line. This where mixing and controlled partiel combustion occur difficultywas eliminated through the combined use of recuperative heating and added reaction surface to promote combustion inside the furnace. a t McKamie, Ark., by the Fluor Corporation, Los Angcles, Calif., Each of the three combustion chambers is provided with a and began operation on March 9, 1944. port which will allow insertion of a natural gas burner for preEarly in February 1946, a second plant was brought into heating the furnace. On a start-up after a prolonged shutdown, operation near Magnolia, Ark. This plant, built by the Fosterthe burners are installed and natural gas is burned in the equipWheeler Corporation, is of a design similar to that of the Mcment until the minimum operating temperature of 1800" F. Kamie plant, the chief difference being in the use of steamis reached. The burners are then removed, the ports are blanked, driven equipment a t Magnolia instead of the electric motor and the acid gas and air feed streams are started. Preheating the drives employed a t McKamie. Both these plants are now operplant by this method requires about 7 2 hours. ating to produce a high grade (99.97%) sulfur, which is used After a plant shutdown of 60 hours or less, the auxiliary gas ultimately in the manufacture of sulfuric acid. burners are not required; resumption of operations is attained Process Description. The process flow sheet for Mathieson's merely by readmitting the gas streams to the equipment. No sulfur recovery plants in Arkansas is shown in Figure 1, and a provision is made for igniting the acid gas in the furnace. complete material balance is given in Table I. In this process hydrogen sulfide from the monoethanolamine A waste heat boiler is used to cool furnace exit gases prior to admitting them to the converters. The boiler, along with a stripper is delivered to the plant at a very low positive pressure feed-water economizer ( S A ), recovers sufficient heat to generatc ( 5 pounds per square inch gage), saturated with water vapor at 5000 pounds of 300 pounds per square inch gage saturated steam the pressure and temperature of the gas, which is in the range €or each long ton of sulfur produced. After leaving the boiler, 100" to 150" F. Entrained water vapor is removed from the inthe gases are further cooled in a shell-and-tube gas-to-gas heat let gas by means of a knockout drum; the gas then passes without exchanger, and then are led to the first converter. further treatment to the combustion furnace (19, 20). Air for Catalytic Converters. In order to make possible the high the combustion is supplied by a positive displacement rotary volume throughput used in the Mathieson process, as comblower (6A). The ratio of air to acid gas is manually controlled pared to the old Claus-Chance process, and in any case to obtain by means of a by-pass on the air line, in order to provide the
Odaber 19%
1941
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 1. Fiox Sheet for Recovary of Elsmontnl Sulfur fmm Sow Natural GMathieson Cbemionl Grporntion’s Pmarsa
by
Vol. 42, No. 10
I N D U S T R I A L A N D E N G I N E E R IN G CTH E M I S T R Y
1942
TABLE I.
hlATERIAL BALANCE
Design for 120 Tons of Sulfur er 24 Hours, Available as Hydrogen Sulfidea for &ant Feed ACIDGAS.&NALYSISh (WATER-SATURATED AT 5 LB./SQ. INCH, 120' F.) %
Basis.
53.92 34.75 2.74 8.59 100.00
Hz9
co2
C Hn HzO
MATERIAL CARRIED B Y GASES BROJI BOILER (750° F.) TO No. 1 CONVERTER Gas Lb./Hr. h1.W. Moles Cu. Ft./Hr. Vol. % 28,800 4.61 2,618 34 77.0 HnS
so2
cos COP
H2O
__
Nn
uz
92 vapor
Total 2OY13 76,64 3.23 100,00
O?
N?
Hz0
1,000,000 :u. feet HzS a t 14.7 Ib./sq. inch gage, 60° l?, contains 38.17 tons sulfur eqrrlvalent. b Varies with variations in temperature and pressure. C CO2 and rare gases neglected.
4,930 4,620 7,250 7,138 22,430
64
3;iO~ 52,800
64
11,900
9,875
11,900 X 24 X
1,595 32
34
280
6,720
22,430
52,800
= 120 long tons per day equivalent
2240
44
18 28
77.0 77.0 165.3 397.0 801 .O
23,000 29,100 62,100 150,000 303,000
4.64 4.66 9.94 24.02 48.52
59,3 1.633.8
22;500 624,500
3.61 100.00
....
....
MATERIAL CABRIED FROM No. 1 CONVERTER TO ECONOMIZER Gas Lb./Hr. h1.W. Moles Cu. FtJHr. Vol. % 34 32.8 2 0.5 HzS 16.3 1 01 64 SO?
coz
44 18 28 192
Hz0
NZ Sa vapor
~ I A T E R I A LBALANCE OF PLANT ENTRANCE GASB Y ELEMENTS, POVXDS PER HOUR(FEED, 52,800 POUNDS PER HOUR) HzS COS HnO CHI 02 S Z Total 700 ... 177 70 ... .... 947 H? ,,,. 11,200 s 11,200 ... ... ... ... .... ... .... Or 7,182 1,418 6,720 15.320 c ,,,, 2,693 .., 210 .. , .... 2,903 N? .... ... ... ... .,, 22,430 52.800
60
Total
Gas HzS
52,800
241.8 442.0
801.0
50.1 1,581.0
597,976
1.5 17 27 90 50 70 3 16 100.00
MATERIAL CARRIED B R O V ECOSOVIZER TO No. 1 TOWBR M.W. Moles Cu. Ft./Hr. Vol. % Lb./Hr. 34 64
SO1
coz
44 18 28 192 236
HZO Nz SI vapor
liquid Total $8
32 16 241 442 801 15 25 1,575
0 9
12,250 6,126 90,700 167,000 303,000 5,390
2.10 1.0: 15.52 28.61 51.80 0.92
4
584,466
100,00
8 3 8 0
6
.....
....
120 X 91.7% yield = 110 long tons per day rated output
hlATERIAL BALANCE, MCKAMIE PLANT, AT 110 TONS P E R D A Y OUTPCT Calculation of Acid Gas Required for 110-Ton-Per-Day Sulfur Production a t 91.7% Yield
MATERIAL CARRIED I'ROII No. 1 TOWER r o No. 2 C O N V ~ R T E R Gas Lb./Hr. h1.W. Moles Cu. Ft./Hr. Vol. % 32.8 34 HzS 1,113
SO2
-?24 %X!---91.7% yield
X
34 32
= 11,900
con
pounds HIS per hour
Hz0 Nn
Sa vapor Recovered S liquid 3,027 Total 46 221
X 374 = 131,000 cu. feet HaS per hour
~131'000 53.92
= 243,000
1,046 10,632 7,950 22,480 23
64 44 18 28 192
..
16.3 241.8 442.0 801 .O 0.16
.... 1534.06
.....
579,121
6,'579 lb. sulfur condeised in economizer.
eu. feet acid gas per hour
.... 100.00
52,800
Calculation of .4ir Required for 110-Ton-per-Day Sulfur Production a t 91.7y0 Yield 748 2HzS
850 moles HnS X
+378 Oz
+
2Hz0
+ Sz
MATERIAL CARRIED F R O M No. 2 CONVERTER TO No. 2 TOWER Lb./Hr. M.W, Moles Cu. Ft./Hr. Vol. % Gaa 2,910 0.50 265 34 7.76 HzS
378
-2- = 66,200
Cu. feet On required per hour 378
CHI
4 2 0 2 - b COz
+ 2Hz0 f
son
Con Hn0 N 2
80 vapor Total
S?
17.5 moles CHI X 756 = 13 2 0 79,440
Cu. feet On required per hour
x:
248 64 3.88 1,460 90,700 10,632 44 241.80 176,000 8,399 467.00 22,430 28 l8 801.00 303,008 192 6.36 2,400 1,220 43,194 1,527.80 576.470 6,579 sulfur condensed in economiier 3,027 sulfur Condensed in No. 1 tower 52.830
0.25 15.73 30.54 52.57 0.41 100.00
= 395,000 cu. feet air per hour
MATERIAL ENTERINO FURYACE Gas
Lb./Hr.
M.W.
ti2S
11,900 9,875 280 1,595 22,430 6.720 52,800
34 44 16 18 28 32
cOn
CH4 HzO Nn 0. .. Total
Moles
1691.6
Cir. Ft./nr.
HzS
con
UH'
Hz0
N. 0; SZ vapor
Total
....
i60!
....
VOl.
