242
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
THE DAYTON PROCESSLZ By F. C. Binnall GENERAL011. GAS CORPORATION, 5 1 1 FIFTHAvE., N E W YORK,N. Y.
The Dayton process of gas manufacture is essentially a n air-oil gas process in which partial combustion of certain constituents of the oil takes place within the retort or reaction chamber itself, thus supplying internally all the heat necessary for the thermal decomposition of the hydrocarbons. Thermodynamically, internal combustion gives the highest heat efficiency in furnishing t h e requisite energy for oil-gas production. This method then becomes the 'most economical of all oil-gas processes. Over 88 per cent of the heat in the oil is obtained in a usable form as gas or tar. The fact t h a t no external heating is required distinguishes this from all other methods of artificial gas making. T h e only raw material necessary is a liquid hydrocarbon such as gas oil or fuel oil, which is atomized and mixed with preheated air in predetermined and automatically maintained proportions, and fed continuously into suitable retorts or reaction chambers located within properly insulated settings. Within the retorts partial combustion of the carbon and hydrogen takes place with the oxygen of the air, generating sufficient heat t o maintain the reaction temperature continuously, and t o take care of heat lost through radiation and combustion, and the sensible heat carried out in t h e hot gases. This partial combustion is sufficient t o carry out as carbon monoxide or carbon dioxide t h a t portion of carbon which would otherwise be deposited as lampblack. By this method of production there is delivered a s a combustible practically all the carbon of t h e oil, the loss of which in ordinary destructive distillation and carbureting processes produces a lowering of efficiency. As the lampblack carbon is burned within the retort, there can be no clogging and therefore no troublesome shutdowns. H E A T UNIT R A N G E O F G A S P R O D U C E D
The process provides a substantial and simple apparatus for t h e manufacture of gas which is easily controllable within t h e heat unit range of commercial uses. T h e gas-make is continuous, uniform, a n d automatic, except for nominal control, irrespective of the gas-make per unit of time. T h e oil and air settings on the atomizer are initially made for the particular grade of gas desired, and when once adjusted, the ratio of air t o oil cannot vary. Thus the maintenance of this fixed ratio insures a continuous production of the grade of gas desired. If the ratio of air t o oil is varied, the temperature of the retort, a n d the quality of the gas will vary; for if more air is added, t h e partial combustion of the hydrocarbons will be more complete, thus generating more heat per unit of time, resulting in higher temperatures in the retort. The higher temperatures result in a disturbance of the equilibrium and thus bring about a change in the quality of the gas. On this basis, Chapter in "American Fuels" by Hamor and Bacon. Presented before the Pittsburgh Section of the American Chemical Society, December 16, 1920. 1
3
Vol. 13, No. 3
it is obvious t h a t the production of a very lean gas will bring about prohibitive retort temperatures and inefficient operating conditions. On the other hand, the upper limit of gas B. t. u. possible is represented by t h a t ratio of air t o oil which will bring about sufficient incomplete combustion for maintenance of proper temperatures. Within these limits, which approximate a 300 t o 560 B. t. u. gas, any grade of gas can be produced continuously, and varied a t will. Above 560 B. t. u. per cu. ft. some external heating is necessary, as the air supplied for this heat content does not permit of enough partial combustion t o liberate sufficient heat t o sustain the reaction. The production of 450 t o 500 B. t. u. gas produces a maximum efficiency thermally and allows the maximum production per unit of time. Also, conditions which bring about the production of such a gas produce by-products in suitable quantity and quality.
COLD A
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HYDRAULIC MAIN,
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. .~.~i.~~~','5C.lil.Z.,~ i F I G . I-SECTION
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GBNBRATOR UNIT
The process is founded on correct chemical and physical principles, so applied as t o promote the highest heat a n d gas-make efficiency under all rates of make per unit of time. T h e air supplied for the partial combustion during t h e gas-make 'stage is preheated by t h e hot gases leaving the retort. This preheated air is intimately mixed with t h e oil a t t h e atomizer, and is supplied through a pipe together with the oil into t h e center of t h e retort. Thus complete vaporization of oil and admixture with t h e air is insured before entering the hot zone, an$ there is no decomposition of t h e oil in the liquid phase t o augment carbon deposition. By this method of prevaporization t h e maximum surface of t h e oil particles is exposed in t h e reaction chamber, insuring a n efficient gas-make state. Lowering of partial pressure is known t o promote the formation of unsaturated hydrocarbons in t h e gaseous phase. I n this process the large percentage of inert nitrogen present in t h e air supplied for partial combustion brings about a lowering of the partial pressure of the hydrocarbons in the gaseous state, acting as though a n actual vacuum had been applied on the hydrocarbon system. Thus in the cracking or gas-make stage the conditions are proper for the formation of the maximum produc-
Mar., 1921
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
tion of unsaturated compounds which possess a very high heating value. It follows, then, t h a t the process is capable of producing a high heating value gas with a high nitrogen content.
MSULATIO
F I G . 2-TYPICAL P L A N O F GENERATING UXTT OR EIGHT RETORTS CAPACITY 600,000 C U . FT. PER DAY
Since t h e surface and pressure on the gas-make system (approximately atmospheric) are constant, and t h e concentration, time, and temperature are under control for any predetermined condition, i t follows t h a t when once started t h e process will deliver continuously and automatically the grade of gas desired. P U R I T Y OF GAS
T h e gas produced is free from sulfur compounds a n d mechanical impurities, such as dust particles, and no purification is necessary. The gas is clean because the only raw materials used in its production-oil and air-are free from impurities. T h e fact t h a t the sulfur in the oil are oxidized t o t h e dioxide during the gas-make stage brings about a practically sulfur-free gas, as the sulfur dioxide passes out with the waste water from the hydraulic main and water scrubber. I n producing 100 cu. f t . of gas in commercial installations From a quantity of oil carrying 310 grains of sulfur, there are present in the unpurified gas only 1.34 grains of sulfur. Since, under most statutes, purified illuminating gas is permitted t o carry 30 grains or more of sulfur per 100 cu. ft., t h e statement t h a t Dayton gas is free from sulfur is warranted. It obviously follows t h a t when using any of the commercially obtainable oils no purification for sulfur will be required. N o costly and cumbersome gas holder is necessary with the process, a s with systems where the gas-make is intermittent, or where wide variations in the quality of t h e gas require a n “averaging up.” Only a small regulator gasometer of about 300-cu. f t . capacity is required. If there is a sudden decrease in consumption, or the demand for gas is curtailed, the apparatus instantly adjusts t h e gas-make t o this condition by reducing the air pressure on the air and oil feed system t o a point where t h e make equals the demand. T h e make is correspondingly automatically increased when t h e demand increases. During these automatic changes the B. t u. of the gas will not vary, owing t o t h e maintenance of t h e constant ratio of air t o oil a t the atomizer under all conditions.
243
T h e apparatus is quickly started by heating the retorts externally t o the reaction temperature. Less t h a n one hour is required t o bring a cold retort t o operating efficiency. Where the load factor is such t h a t a portion of the plant is in operation over the full 24 hrs. of the day, t h e entire plant is always ready t o deliver its maximum output instantaneously, for the reaction temperatures are constantly main. tained in the balance of the settings. However, where the plant is entigely shut down over night or Sunday, the settings are so insulated t h a t t h e burner provided need be operated less t h a n 0.75 hr. t o obtain t h e necessary retort temperatures. I n case consumption is curtailed for 2 or 3 hrs., the heats in the retorts are maintained by t h e insulation, and gas making can be started instantaneously without the application of external heat. No external heating is necessary when once the proper retort temperatures are obtained. T h e partial combustion during t h e gas-make stage is sufficient t o furnish enough heat always t o maintain the proper temperatures for continuous gas making. As these temperatures are always maintained irrespective of the gas-make per unit of time, i t is then independent o€ a n external source of heat. T h e complete installation is small and c Only 1500 sq. f t . of floor space are required for a plant with a production of 1,000,000 cu. f t . per day. This is in direct contrast t o t h e space required for a producer-, coal-, or water-gas set. I n addition. there is required no auxiliary steam generating or purifying equipment, thus making the process simple and selfcontained.
6 LCTlON A-A
FIG Q-’JhPICA&.
LAYUUT OF
PLANT.
CAPACITY
1,000,000C U . FT.PER DAY
T h e labor required is small. One man per shift is sufficient t o operate a plant af 1,000,000 cu. f t . capacity per day. His duties are only nominal and supervisory; for when once started the process is continuous and automatic. His main responsibility is t o see t h a t the oil supply tanks are filled, and t h a t
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
:244
1701. 13, No. 3
m
FIG.4-DIAGR.4MMATIC
the compressor is properly lubricated. There are no raw materials t o be conveyed or handled as in a n ordinary gas plant. Approximately 4.00 gal. of fuel or gas oil are required for the production of 1000 cu. f t . of 450 B. t. u. gas. From t h i s , there is recovered 0.28 gal. of tar. A s t h e t a r is equal to, or greater in value (see d a t a below) t h a n a n equivalent quantity of the oil used, for comparison purposes, 4.00 - 0.28 = 3.72 gal. of oil actually consumed per 1000 cu. ft. of 450 B. t. u. gas. HEAT BALANCE FOR PRODUCTION O F 450 B. T. u. GAS Oil Used.. 4.00 gal. ............ 0.28 gal. Tar Recovere
...
............
..
-
..........................
Oil Consumed.. 3.72 gal. Heat Supplied: 4.00 gal. Oil @ 136,000 B . t. u. per gal.. . . . . . . . . . . . . . 544,000 B. t. u. Heat Recovered: 1000 CU. f t . Gas @ 450 B. t. u. per CU. f t . . ......................... 450,000 B. t. u. 0 . 2 8 gal. T a r @ 136,000 B. t . u . per gal. 38,080 B. t. u. Total Heat Recovered. ............................ 488,080 B. t . u. Heat Loss . . . . . . . . . . . . . . . . . . 55.920 B. t. u.
.........
Heat in Gas =
z m o -
Heat Lost
=
......
82.72 per cent
3..
38,080 Heat in Tar = 544,000 = 59,920 =
544,000
.....................
................
TOTA ,I ....................................... PHYSICAL CHARACTERISTICS Specific Gravity..
OF
450 B. T.
.............................
7.00per c m t 10.28 per cent 100.00 per cent U.
GAS 1.02
CHEMICAL CHARACTERISTICS OF 450 R . T. u. G A S Per cent by Volume COz 6.1 Unsaturated Hydrocarbons. 14.1
..................................
............. .................................... 0.Y CO ................................... 5.6 Saturated Hydrocarbons. ............... !.S Hz .................................... I./ Nz .................................... 63.2 Total Sulfur,. .............. 1 t o 2 grains per 100 cu. f t Flame Temperature (theoretical). ........ 3700' F. 0 2
ZGEVATION OF
COMPARISON OF NITROGEN CONTENT I N MIXTURES OF 100 CTJ. PT. OF 450 B. T. u. DAYTON GAS AND 630 B. T. IJ. CITY GAS WITH AIR READYTO BURN Air required per cu. f t . Dayton Gas.. ................ 3.60 vol. Air required per cu. ft. City Gas.. 5.58 vol. Dayton Gas Illuminating Gas 450 B. t. 11. 630 B. t. u. Nitrogen in 100 cu. f t . gas . . , . , 63.2 6.8 Nitrogen from air.. 292.2 (3.60 vol.) 442.0 (5.58 vol.) Nitrogen in mixture.. 355.4 cu. It. 448.8 cu. f t .
..................
.
............ ..........
COMBUSTION DATA(Per 100 lbs. Gas Burned)
B. t. u. per cu. f t . ol combustible mixture. .......................... Water vapor formed.. . . . . . . . . . . . . . Total weight combustion products.. . Convection efficiency.
.............
Dayton Gas 450 B. t. u.
Illuminating Gas 630 B. t. u.
97.50 28.75 lbs. 478.00 lbs. 49.75 per cent
95.8 169.5 lbs. 1291.O lbs. 46.3 per cent
Theoretically i t has been found, and under practical conditions of industrial operation proved, t h a t Dayton gas of 450 B. t. u. per cu. f t . is required in no greater volume t h a n illuminating gas of 630 B. t. u. per cu. f t . for the same work. This is due t o t h e higher flame temperature; t o the smaller weight of combustion products per cu. f t . of gas burned, thus less heat lost in the waste gases; and t o the smaller difference between the high and low heating values of t h e gas, as evidenced by the difference in weight of water formed during the combustion of t h e two gases. From each 1000 cu. f t . of 450 B. t. u. gas produced there is recovered 0.28 gal. of valuable tar, the characteristics of which are given in Table I. By compression t o only 30 lbs. per sq. in. and cooling t o 32" F., i t is also possible t o recover 0.35 gal. of light oil which distils completely below 170" C. (see Table 11). T h e removal of this light oil produces a lowering of the B. t. u. in the gas of less t h a n 4 per cent.
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T H E J O U R N A L OF IiVDUSTRIAL A N D ENGINEERING CHEMISTRY
Nar., 1921
'DAYTON PROCESS" OIL GAS APPARATUS
TABLEI-TAR-DISTILLATION
TEST
A
....................... 0.986 ........................... 85' C. Per cent Fraction up to 80' C.. ................... None Fraction 80-170' C . . .................... 13.8 Fraction 170-230° C.. ................... 26.8 Fraction 230-270' C.. ................... 15. 2
Specific Gravity.. First Drop..
................... .................................. ................................. Loss ...................................
Fraction 270-360' C.. Pitch Water
B 0.988 83' C. Per cent None 10.2 26.8
32.6 11.3
18.4 31 . O 12.7
0.6
0.6 0.7
0.7
TABLE 11-LIGHT OIL--DISTILLATIONTEST C 3.5' C. Per cent None 14.0 Light Naphtha u p to 80' C . . Crude Benzene 80-100° C . . . . . . . . . . . . . . . . 37.2 Crude Toluene 100-120° C . . 20.0 Crude Xylene 120-145O C 14.0 Solvent Naphtha 145-170° C . . 9.6 Residue, above 170' C.. 4.4 Distillation Loss. 0.8
........................... Water ................................. First Drop..
.............
............. ................ ........... ................ .......................
D 350 c. Per cent
Light Naphtha u p to 80' C . . ified Benzene 80 ified Toluene 100- 12(
C Per cent 14.0
.............
Residue, a b b e 170' C . . . . . . . . . . . . . . . . . . 4.4 Removed by sulfuric acid. . . . . . . . . . . . . . . . 21.4 Paraffins in fractions 80-145' C . . ......... None
C O S T OQ PRODUCTION
450 R.
T. U .
GAS
Oil 4.0 gal. Q 8 cents per gal.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Po&, Y/G kw.-hr. per M. of gas @ 1.5 cents per kw.-hr.. . . . . . Water. 8 cu. f t . 0 30 cents per M. cu. ft. Total Gross Cost..
.....................................
Cents 32.00 0.90
37.46
0.2
9.8 54.4 16.4 8.8 9.0
1.4 1.4
T h e various fractions of light oil, purified by treatment with sulfuric acid and caustic soda, gave on redistillation: TAELEI11
COST P E R THOUSAXD C U B I C F E E T
Based on results commercially obtained, the cost of production of 1000 cu. ft. of 450 B. t. u. gas in a plant producing 1,000,000 cu. f t . of gas daily with the labor of one man per shift becomes:
D Per cent 9.8
i .4 20 2 None
It is interesting t o note t h a t the total yield of aromatic compounds of the benzene series is greater t h a n the yield obtained by so-called high temperature and high-pressure processes. In addition these ,compounds are produced free from saturated aliphatic compounds, thus making their purification possible.
No account is taken of the light oils obtainable as by-products referred t o above. DESCRIPTION O F APPARATUS
Fig. 4 gives the complete diagrammatic elevation of the apparatus. A single motor, A., is the sole motive power for the air B, and oil, C, fed t o the generator D, and for the exhauster E, on the finished gas system. Thus, a s all units are synchronous, all factors are maintained in their predetermined ratios. The air feed system is connected directly t o t h e service oil tank F? and t o a n air regulating valve, G, on the gasometer H. Thus if the gas-make is greater t h a n the gas consumption, the gasometer will rise, release the air regulator valve, and decrease the air pressure on t h e air feed line, and on the oil service tank. As the pressures on the air and oil supply have decreased the same amount, the ratio of feed a t the retort has decreased substantially in the same ratio. V i c e versa, should the consumption be greater than t h e make, the gasometer falls, the air regulating valve
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
closes, and the air pressure on the air and oil systems increases thus increasing the oil and air entering the retort in the same constant ratio, increasing the gasmake. This constant ratio air-oil feed is t h e basic controlling principle of t h e successful operation of t h e process. The hot gases and vapors from the retort pass through a heat interchanger, I, giving u p a portion of their heat content t o the incoming air, thence into the hydraulic main J, where they are initially cooled and part of the vapors removed. From there they pass t o the water scrubber K, where they are further cooled, and more vapors removed, and then directly t o the regulating holder. From the regulating holder they pass through a t a r extractor, L, t o a n exhauster which supplies the gas main. I n case the gas is delivered from the exhauster in greater quantities t h a n is consumed, i t is returned t o the hot gas line entering the scrubber through a check valve, M, thus building u p the gasometer which automatically operates the air regulating valve on the air supply t o the system.
Vol. 13, No. 3
construction is such t h a t any one or more of t h e retorts may be cut out without interfering with, or affecting, t h e remainder of t h e set. Thus the failure of a single unit will not interrupt gas making or seriously curtail t h e output of any commercial-sized installation. An unusually safe feature of the apparatus is t h a t the retorts can be changed by two men within a n hour. The life of a retort com life of a n ordinary water-gas generator. Fig. 2 shows a plan view of a set of eight retorts, together with the atomizers, a i r preheaters, and hydraulic main. Fig. 3 shows a typical layout of a plant of 1,000,000; cu. f t . capacity per day. This shows the plant all the necessary auxiliaries, housed f t . X 53 f t . with 18 f t . of headroom. Fig, 5 shows a front view of three units installed in a large industrial plant, producing 500,000 cu. ft. of gas a day. APPLICATIONS OF T H E G A S
I n its application this gas can economically replace natural gas and displace illuminating gas and the direct burning of oil ifi all industrial operations. It can also be used for admixture with the ever-decreasing supply of natural gas or for admixture with coal gas for all industrial and domestic purposes. I n addition, i t can also be used for gas undertakings of cities and towns, as well as in gas engine installations for industrial power development in which i t will effect. a very considerable saving. SUMMARY
FIG. 5
The water from the scrubber and hydraulic main is removed by way of the separator N, where the t a r separates and passes into the primary storage 0, and t h e water passes t o t h e sewer through t h e overflow. The t a r from the extractor L is recovered in t h e primary t a r t a n k P and then is transferred t o the tar storage tanks. Fig. 1 shows a cross section of the retort or generator with the details of the necessary auxiliaries. together with the burner Q which is used in heating the retort up t o the reaction temperature i n starting. The retort or reaction chamber is well built, strong, and durable under the temperature used. It operates under low pressures, never exceeding 1 Ib. per, sq. in. gage pressure a t a maximum. It is a section of a sphere and is approximately 24. in. in diameter, and forms a chamber which is internally 4 in. in breadth. The actual volume barely exceeds 0.5 cu. f t . for a retort with a daily output of 80,000 cu. f t . of gas. They are assembled in units of two and multiples of the same up t o any desired number needed. The
The principle points of difference between the Dayt o n process and other types of artificial gas generators are as follows: 1-The process herein described is independent of intermittent and external heating. 2-The process is automatic, continuous, and selfsustaining. 3-The B. t. u. value desired can be selected, a n d when the apparatus is once adjusted this heat content is automatically maintained without variation. &The only raw material necessary for the production of 1000 cu. f t . of 450 t o 500 B. t. u. gas is 4.0 gal. of residuum or fuel oil. 5-The gas produced is clean and free from sulfur, thus requiring no purification, regardless of the sulfur content of the oil used. 6-The equipment is compact and requires little floor space. A plant with a capacity of 1,000,000 cu. ft. per day of 450 t o 500 B. t. u. gas can be housed in a room 30 f t . X 50 f t . 7-No gas storage is required, the gas-make being automatically regulated by the demand 8-The labor requirements are but one man per shift for a plant of 1,000,000 cu. f t . capacity per day. 9-After a complete shutdown for 24 hrs. or longer, the equipment can be brought t o capacity in less than 0.75 hr.
