US2194575A - Process for producing commerclal gas - Google Patents

Description

March 26, 1940.. F. T. sNYDER PROCESS FOR PRODUCING COMMERCIAL GAS Original "Filed June 14, 1937 mank@ No Patented Mar. 26, 1940 UNITED STATES PATENT OFFICE PROCESS FOR PROJSCING COMMERCIL Frederick T. Snyder, Brookline, Mass., assignor to Fuel Research Development Corporation, Boston, Mass., a corporation of Massachusetts 5 Claims.

This application s a division of my prior application Serial No. 148,168, filed June 14, 1937, and relates to the production of gas for commercial heating or for illuminating purposes.

It is the general object of my invention to provide a continuous gas-producing process in which producer gas, water gas, oil gas and coal gas are continuously formed and are successively introduced into the gaseous product, and in which all of said gases are formed and commingled during the process of manufacture in such proportions as to produce commercial gas of standard or other desired heating value.

Important features of my invention relate to the initial formation of a large amount of producer gas and to the use of a major part of said producer gas for preheating steam which is thereafter used in the formation of water gas; to the cracking of oil in the presence of coke and at a cracking temperature which will produce a substantial proportion of oil gas, to the deposition of the resulting soot or free carbon on the coke in the cracking zone; to the` subsequent automatic and continuous disposal'of the soot by complete combustion thereof, together with the coke on which it is deposited; and to the use of a portion of the final or fixed gas to cool and dilute the mixture of water gas, oil gas and superheated steam, thereby effecting distillation of coal gas and coal oils from freshly charged coal at a temperature below its melting or caking point.

My invention further relates to certain arrangements and combinations of apparatus and to certain ordered procedure which will bey hereinafter described and more particularly pointed out in the appended claims.

The drawing is a diagrammatic view of a preferred form of apparatus for carrying out my 'improved gas-making process, with the gas generator shown in sectional elevation.

Referring to the drawing, my improved process for continuously producing commercial gas is preferably carried out in a gas generating apparatus which is similar to aI blast furnace in its general construction and which comprises a bosh I0 mounted on a suitable hearth II, and an upwardly extending stack I2 having usual coalcharging apparatus, such as a bell I4, at its upper end.

Air under pressure is supplied through a bustle pipe I5, supplied with a plurality of tuyres I6 which project through the side wall of the bosh I0 at points spaced about the periphery.

Coal, coke or a mixture of coal orcoke with in the burning zone at a temperature, as`

3000o F., which is high enough to melt the ash in the coke. This meltedash will then be tapped oif from time to time through the spout I1 in the form of liquid slag. y

The producer gas formed by this combustion of coke consistsmainly of carbon-monoxide and nitrogen, mixed with a small amount of carbondioxide and other inert gases.

The greater part of the producer gas is drawn ofi through ports 20 and branch pipes 2| which connect with a bustle pipe 22. The pipe 22 is connected by a conduit 23 to the combustion chamber 24 of a stove S which is preferably of the indirect or recuperative type and which is continuous in operation. Additional air for the combustion of the withdrawn producer gas is supplied to the stove through a pipe 25, and the products of the combustion therein are discharged to a flue or draft apparatus through an outlet pipe 26. A back pressure valve or damper 21 is provided for the pipe 26 and is moved toward closed position by a weight W, adjustable on an arm 28. The burnt gases escape to the iiue at a relatively low temperature, such as 600 F.

Low pressure steam is supplied from any suitable source through a pipe 29 to the intake chamber 30 of the stove S and passes through heating tubes 3I to a second chamber 32, from which it is drawn olf through a pipe 33 and delivered to a bustle pipe 34 having branch connections to ports 35 in the stack I2 of the generator. These ports are preferably displaced angularly with respect to the outlet ports I0 for the producer gas, as clearly shown in the drawing, and are preferably at a substantially higher level.

The steam passing from the stove through the pipe 33 to the generator is highly superheated and may be at 22007 F. or higher. The steam inlet pipe 29 is provided with a check valve 31 for a purpose to be described. The location of. the valves 21 and 31 in comparatively cool parts of the apparatus is quite advantageous.

If the supply of producer gas to the stove S is not sumcient to heat the desired amount of steam to a suiiiciently high temperature, additional fuel, such as oil or gas from some auxiliary source, may be supplied to the stove S through a pipe 38. 1f, on the other hand, an excess amount of producer gas is generated, the surplus may be drawn off from the annular pipe 22 through a branch outlet 39 for outside disposal.

The temperature in the combustion chamber 24 of the stove S is commonly quite high, as 3000 F., so that any noncombustible dust or ash carried over with the producer gas or introduced through the fuel line 38 will be meltedk and may be drawn off as liquid slag through a slag spout 40.

Under ordinary operating conditions the major portion of the producer gas is drawn off through the stove S by the flue or draft apparatus, but a minor portion passes up through the stack I2 and is useful in controlling the heat value of the finished gas product. The proportions of producer gas passing through the stove and generator may be varied and controlled by adjusting the weight W of the back pressure valve kor damper 21.

If for any reason the steam supply is shut oi during the operation of the apparatus, the check valve 31 will close. Gas and steam will then ow reversely through the pipe 33 into the steam passages in the stove S, thus balancing the pressure of the combustion gases and preventing leakage of combustion gases into the steam passages.

Oil is supplied to the interior of the mass o f highly heated fuel in the stack l2, preferably through one or more yoil pipes 42 extending down through the cover plate 43 of the generator and each adjustably positioned vertically as by a setscreW 44. By raising or lowering the pipe -or pipes 42, the height of delivery of the oil may be varied for reasons to be hereinafter described.

A heater 45 is preferably provided for preheating the oil before delivery in the generator. 'I'he pipe 42 is also preferably heat-insulated to prevent cracking of the oil in the pipe 42 before it is discharged from the lower end thereof.

The highly superheated steam entering the generator through the ports 35 reacts with the heated fuel in the stack I2 to produce substantial quantities of water gas, which water gas, with the undecomposed steam and any producer gas not Withdrawn at 2U for burning in the stove S, flows upward through the coal or coke in the stack and provides the necessary heat for cracking the oil delivered from the pipe or pipes 42 and for producing oil gas therefrom.

As the mixture of prodier gas, water gas, oil gas and surplus steam continue`its upward flow through the stack l2, it effects distillation of the freshly charged coal or other fuel, and generates coal gas, coal oil vapors, and other distillation products. The term producer gas as used in the specification and claims is intended to define a gas which is essentially a mixture of carbon monoxide and nitrogen, sometimes also containing a small amount of carbon-dioxide or other inert gases, and which is obtained by blasting an incandescent fuel bed with air. The sensible heat of this gas as produced is relatively high but the heating value is relatively low.

All of these gases, vapors and other products, including the surplus steam, are drawn out of the stack l2 through a pipe 50 by an exhauster 5l and enter a condenser 52, preferably of the indirect or water-cooled type. The exhauster 5I is preferably placed in the outlet pipe 5Ia of the condenser, where the gases to be handled are comparatively clean and cool. The operation of the exhauster 5I is preferably automatically controlled from a pressure indicating device 53 in the producer gas connection 23. Any increase in producer gas pressure speeds up the exhauster. The control connection is indicated by the broken line 53a.

As this mixture of gas, vapor and steam passes upward through the condenser 52, the steam ls condensed to Water which collects in the bottom of the condenser and may be drawn off as indicated at the point 54.

By controlling the temperature of the uncondensed gases and vapors leaving the top of the condenser, the high end boiling point of the hydroca-rbons passing to the absorbers is controlled, and the hydrocarbons having higher boiling points condense and collect in the receiver in the bottom of the condenser. These hydrocarbons originate in the oil and coal charged to the generator. The condensate may contain hydrocarbons ranging from gasoline to pitch. Those hydrocarbons which are heavier than Water settle to the bottom of the receiver Where they mix with any coke and coal dust and soot carried over from the generator. The mixture is withdrawn from the extreme bottom of the receiver, as at 55 and may be recharged to the generator or otherwise disposed of.

The condensed oil which is lighter than water is drawn off through the pipe 56 by a pump 51 and may be termed cycle oil. This oil is passed through distilling or refining apparatus R from which the low-boiling components may be drawn off through a pipe 58. The lean oil is returned by a pump 6I through a pipe 62 to the oil feed pipe 42 previously described. This 0111s then recracked in the generator, usually with the addition of a certain proportion of fresh oil introduced through a pipe 63 and controlled by a valve 64.

The mixture of uncondensed gases and gasoline vapor separated in the condenser 52 is delivered through the pipe 5W to successive absorbers 16 and 1l, indicated as being of the oilabsorption type. Absorber oil is delivered at the top of the absorbers over a series of plates or barriers 19, and is removed from the absorbers through branch pipes and a connecting pipe 8l This absorber oil is effective in removing substantially all of the gasoline vapor from the gas mixture delivered to the absorbers, and the final or fixed gas is then drawn out of the second absorber 'I1 through a pipe 82 by an exhauster 83 and is passed through the usual purifiers or scrubbers before being placed in storage for commercial use.

A portion of the fixed gas may be returned through a connection and return pipe 86 to the generator, where it is introduced in the upper middle portion of the stack l2, above the oil gas or cracking zone. The function of the return gas is to cool and dilute the ascending gases and vapors in the stack i2, so that the oil from the coal may be distilled below the fusing temperature of the coal, due to the reduction of the partial pressure of the coal oil'vapors.

'Ihe ow of gas through the return pipe B6 may be controlled by ,a valve 81, and under certain conditions steam or auxiliary gas may be introduced through a branch pipe 88, controlled by a valve 89. This steam or auxiliary gas may be in addition to or in substitution for the return of gas genera-ted in the system. This return gas may be advanced toward the generator I2 by a pump or exhauster 89h.

The absorber oil is delivered by a pump 90 to suitable distilling or refining apparatus R', from which the low-boiling components may be drawn off through a pipe 9I. The lean oil is returned through a connection 92 anda suitable cooler 92a to the absorber oil supply Vpipe 18.'

With certain fuels and under certain conditions, it may be desirable to facilitate the formation of slag byintroducing a certain amount of lime with the fuel charge. Lime (CaO) is preferable to limestone (CaCOa) as the limestone would be reduced to lime in the generator with the release of additional amounts of the inert and undesirable CO2 which would be added to the gaseous mixture.

It is to be noted that the presence of the lime in the charge to the generator also has an important effect on the products formed by the cracking of the oil. Among the products of the combustion of the coke are small quantities of nitric oxide, which originate from the nitrogen of the air used for combustion. If these acid products are not eliminated they will unite with some of the basic constituents of the oil and will produce gum-forming constituents, which will have a deleterious effect on the commercial value of the nal gas. When lime is present in the charge, these acid nitrogen compounds combine with the lime and are carried down with the lime out of .the cracking zone. In the combustion zone the temperature is high enough to decompose these compounds. At that point the oxygen of the nitrogen compound combines with the carbon of the coke, and the nitrogen joins the nitrogen of the air blast, so that the acid is eliminated.

'Ihe preferred method of operation has been largely indicated in connection with the description of the apparatus but may be briefly summarized as follows:

Assuming that the plant has been in operation long enough to establish normal operating conditions, the bosh I0 of the generator and also the lower and middle portions of the stack I2 will be filled with coke, while the upper portion of the stack I2 will contain fresh` coal or other fuel fed in through the charging bell I4.

When air is forced in through the tuyres I6, the coke in the base Il) will be consumed and a substantial amount of producer gas will be produced.

The major portion of this producer gas is drawn off through 'the recuperative stove S andv is burned therein, with or without additional fuel. The pressure in the stove and generator is regulated by the back pressure valve or damper 2'I.

The superheated steam from the stove S enters the generator through the ports 35 substantially above the point at which the producer gas was removed.

This superheated steam, together with a minor portion of the producer gas, then passes up through the generator stack I2, and in the lower section of the stack a portion of the steam reacts with the hot coke to form water gas. The steam entering the generator may be superheated to as high as 2200 F. and reacts on the coke to produce water gas.

Thus the introduction ofsteam from the stove S not only substitutes desirable water gas for relative lean producer gas with its diluting nitrogen, but also lowers the temperature in the furnace substantially below that of the producer gas.

which is too high for satisfactory oil cracking operations. f

The mixture of producer gas, water gas and surplus steam then passes up through the middle portion of the stack, or cracking zone, where oil and oil vapor engage the hot coke in the presence of the mixture of producer gas, water gas and superheated steam. The cracking temperature may be described as intermediate, as it is commonly from 1100 to 1400 F. and is between the temperature of 2000 F. at which oil is usually cracked for the production of carburetted water gas and the temperature of 700 to 900 F. at which oil is usually cracked for the production of gasoline.

lAt this intermediate temperature of, say 1200u F. and in the presence of the mixed gases previously described, the, oil is cracked under such conditionsof intermediate temperature and low partial pressure of the oil vapor that oil gas is generated in substantial quantities. Under usual operating conditions, about one-third of the oil by weight is changed to oil gas. The remaining cracking products are recovered and separated as has been described, and the residual or cycle oil is returned for recracking, commonly with the addition of fresh oil.

It is found that the cracking operation is satisfactori-ly performed when the oil is preheated upto '750 F. and is fed-to the stack under a low pressure, as 5 lbs.

As the combined producer gas, water gas, superheated steam and oil gas moves further upward in the stack I2, fresh coal or other fuel is encountered, from which Acoal gas, coal oils and other distillation products are removed and added to the mixture of gases, vapors and steam. The further treatment of these products has been previously described.

The different gaseous components have widely different heating values, producer gas commonly having approximately 100 B. t; u., water gas 300 B. t. u., oil gas 1300 B. t. u. and coal gas 600 B. t. u. per cubic foot. A usual requirement for commercial gas is approximately 540 B. t. u. By suitable regulation of my improved generating apparatus and by selective control of the oil and fuel feed and timing, by the operator, it is found possible to deliver a mixture of gases to the purifiers which has approximately standard heating value, without further modification.

The return of a portion of the fixed gas to the generator through the pipes; 85 and 86 is particularly desirable when coal fairly. rich in gas and coal oil is being used, as many such coals have a tendency to fuse or cake and clog the generator if the gaseous and liquid components are distilled at a temperature above 'their fusing point. The introduction of return gas at relatively low temperature, as 60 F., at a point below the fresh fuel and above or near the top of the cracking zone reduces the temperature at which the coil oils are distilled below that at which the coil will fuse or cake. If a non-caking coal or coke is charged to the generator, the use of the return gas may be unnecessary, unless it is desirable for the purpose of reducing the temperature of the gaseous mixture leaving the generator.

A very important feature of my invention resides inthe cracking of the oil or oil vaporin thepresence of very hot coke and also in the presence of free o1' nascent hydrogen produced in the generator in the water gas reaction. The carbon which is freed from the oil when cracked is in the form of soot and is deposited on the coke in the cracking zone and this finely divided, free or nascent carbon appears to act as a catalyst in conjunction with the free nascent hydrogen.

The operating conditions under which the cracking operation is performed permit me to carry out my process substantially at atmospheric pressure, in contrast to the very high pressure generally employed in other oil cracking processes. 'Ihe deposition of the soot from the cracking operation on the coke in the stack constitutes one of the most important advantages of my im-v proved process, as the soot is fed downward with the coke 4by gravity and both the coke and the sootl are consumed in the bosh of the generator and are thereby continuously removed from the generator. Thus I entirely avoid clogging of the cracking equipment by accumulations of soot, as is common in other processes and which frequently require shutting down of the equipment for cleaning purposes. Some of the soot or free carbon also apparently reacts with the superheated steam in the formation of water gas.

The control of the speed of the exhauster I from the pressure indication in the producer gas connection 23 causes the exhauster to withdraw substantially all of the mixture of gas, vapor, oil and steam produced in the generator, regardless of changes of resistance in the generator or changes in the quantities of gas, vapor or steam produced in the generator. Increased production, by setting up increased back pressure in the producer gas connection, in turn speeds up the exhauster and causes it to remove the larger quantities of the gaseous mixture from the top of the generator.

The normal pressure in the producer gas connection is controlled by the setting of the back pressure valve or damper 21, as previously described. By adjusting the weight on the `back pressure valve, more or less producer gas can be passed upward in the generator, as operating conditions may require.

An outstanding feature of my improved process is its extreme exibility and adaptability to different operating conditions. By raising or lowering the'oil feed pipes, the results of the cracking operation may be widely varied. Generally speaking, the lower the point of delivery of oil into the fuel mass, the more complete will be the cracking operation, as the cracking period is increased. Lowering the oil feed tubes also reduces the time available for thewater gas reaction, as the relatively cool oil lowers the temperature of the steam below 1800o F. which is about the lower i limit for the production of water gas.` Consequently by lowering the oil feed tubes, less water gas and more oil gas will be produced, with a richer final or xed gas product.

Furthermore, the amount of oil gas produced is dependent not only on the time rof the reaction but also to a considerable extent on the temperature and pressure in the cracking zone. The cracking temperature results from the amount and temperature of the components of the mixture of superheated steam, producer gas, water gas and oil entering the cracking zone. By changing the temperature of any one of thesey components, the ultimate temperature of the mixture will be changed, with a corresponding change in the cracking reaction. Furthermore, the reactions may be varied by varying the amount of one or more of the constituentsproducer gas, water gas, steam or oil-with respect to the other constituents.

The temperatures employed in my improved process are relatively high and both the total pressure and the partial pressure of the oil vapor are much lower than in other cracking processes. All of these factors tend to increase the extent `of cracking or the amount of oil gas made during necessary additional heat for the stove S may be obtained by feeding oil or gas from storage or elsewhere through the pipe 38 to the stove.

If on the other hand a very heavy oil, such as Bunker C oil, is used for cracking, which oil contains a large amount of carbon to form soot, it will then be necessary to burn larger amounts of coal or coke to remove and consume the increased soot, and a surplus of producer gas may thus be produced, which may be drawn off through the connection 39 for generating steam or for other desired purposes.

My improved process and apparatus may be used in conjunction with types of oil cracking apparatus from which a mixture of petroleum coke, cracked tar and heavy oils or bottoms is discharged. This material may be fed to my gas generating apparatus in place of coal. The coke in the mixture will be utilized as fuel and the oil content will be distilled or vaporized and carried off with the gaseous mixture, to be thereafter recovered and added to the return or cycle oil.

The unusual effectiveness of my improved cracking process is due not only to the relatively high temperature and very low partial pressure at which the process takes place, but also to the presence of carbon and hydrogen, both of which are produced directly in the generator in a nascent or highly reactive state. y

More effective operation is also produced from the known tendency in oil cracking operations to formproducts not then present in the generator. As hydrogen is formed in the water gas zone of my generator and is present in substantial proportions in the cracking zone, the tendency is to produce more hydrocarbons and less free hydrogen than would otherwise be the case.

Having thus described my invention and the advantages thereof, I do not wish to be limited to the details herein disclosed, otherwise than as set forth in the claims, but what I claim is:

1. The method of making heating gas which consists in forming, in a generator, producer gas in a lower zone by contacting highly heated coke with air, water-gas in the next higher zone by reacting coke with steam superheated by said producer gas to not less than 1900 F., and oil gas in a still higher zone by cracking oil in 'contact with heated coke, cooling the mixed hot gases made in said three zones to a moderate temperature of the order of about 600 F., by adding to said mixed gases in said generator above the oil gas zone a portion of fixed gas previously removed from said generator and substantially cooled to fa temperature not substantially in excess of '10,0" F., distilling coal gases and vapors in the top zone of said. generator by passing said mixed and cooled gases through coal in said top zone at a gas temperature below the fusing point of said coal, thereby producing said coke, and removing, condensing. separating and cooling said mixed gases, coal gases and vapors, and excess steam.

2. The method of making heating gas which comprises producing producer gas by contacting highly heated coke with air in the lower portion of a generator, removing from said lower portion a major part of said producer gas, delivering said producer gas direct to a recuperative stove and superheating steam thereby to not less than 2000 F., introducing said highly superheated steam to said generator at a level above the point of removal of said producer gas, producing water gas by reacting said fuel with said highly superheated steam, introducing oil to said generator above the water gas zone, cracking said oil under conditions of low partial pressure and thereby producing oil gas and oil vapors, removing the resultant mixture of gases, vapors and steam from said generator, and thereafter separating the intermingled iixed gases from the oil -vapors and steam.

' 3. In the method of making heating gas as set tures below the cracking temperatures of said gas and vapor.

4. In the method of making heating gas as set forth in claim 2, the additional steps of charging a non-gaseous fuel which is at least partly solid to said generator above the cracking zone, distilling additional gas and vapor from said nongaseous fuel above the point where oil gas is produced and under partial-pressure conditions, controlling the temperature and partial-pressure in the distillation zone by returning a portion of the previously generated and cooled iixed gas to the generator between the cracking zone and said distillation zone, whereby distillation of said additional gas and vapor takes place at tempera tures below the cracking temperatures of said gas and vapor, and mixing said additional gas and vapor with the previously formed oil gas, thereby substantially preventing the formation of gum in said oil gas.

5. The method of making heating gas which comprises charging a. generator with non-gaseous fuel which is at least partly solid, forming producer gas in the lower portion of the generator, using a. major portion of said producer gas to superheat steam to not less than 2000 F., in troducing said highly superheated steam to said generator at a level above the point of removal of said producer gas, producing water gas by the reaction of said superheated steam on said fuel, introducing oil to the highly heated fuel mass in said generator above the water gas zone, cracking said oil at a relatively high temperature, of the order of about 1400 F. and under conditions of low partial pressure on the oil vapor, cooling and diluting the gaseous mixture in said generator to a moderate temperature, of the order of about 600 F. by the introduction of relatively cool gas to said generator above the cracking zone, distilling gases and vapors from the fuel charge above the level of introduction of said cool gas, removing the mixture of gases, vapors and uncombined steam from the generator, and separating the intermingled ilxed gases from said mixture.

FREDERICK T. SNYDER.

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