US 3843307 A
Description (OCR text may contain errors)
United States Patent [191 [111 3,843,307 Staudinger 5] Oct. 22, 1974 PROCESS FOR INCOMPLETE 3/1974 Cheng 431/8X COMBUSTION OF HYDROCARBONS Inventor: Gernot Staudinger, Amsterdam,
Netherlands Shell Oil Company, Houston, Tex.
Jan. 28, 1974 Assignee:
Foreign Application Priority Data Feb. I4, 1973 Great Britain 7235/73 References Cited UNITED STATES PATENTS l/l943 Weller 431/8 X 12/1963 Coldren et al. 43l/8 Primary Examiner-Edward G. Favors Attorney, Agent, or Firm-A. A. .lecminek  ABSTRACT An improved process for incomplete combustion of gaseous or liquid hydrocarbon fuels is described wherein the fuel is mixed with or finely dispersed in an oxygen-containing gas and passed as a gaseous jet through at least one supply opening into a substantially void reactor. In this process soot formation is substantially reduced by introducing the mixture of fuel and oxygen-containing gas in the form of a gaseous jet at a velocity which is sufficiently high such that the initial part of the reaction zone or point of incoming fuel ignition is displaced by a distance which is at least ten times the diameter of the supply opening into a reactor where the residence time of the gaseous combustion product is at least 0.1 seconds.
8 Claims, 3 Drawing Figures 5 K QC PATENTEB (IN 2 2 1874 FIG. 7
1 Y PROCESS FOR INCOMPLETE COMBUSTION OF HYDROCARBONS BACKGROUND OF THE INVENTION The invention relates to an improved process for the manufacture of gases by incomplete or partial combustion of gaseous or finely atomized fuel containing one or more hydrocarbons wherein the hydrocarbon feed is introduced in admixture with an oxygen-containing gas in the form of a gaseous jet into a substantially void reactor. More particularly the invention relates to an improvement on conventional incomplete combustion processes of the type described wherein the quantity of soot present in the partial combustion product gas is substantially reduced by displacing the initial part of the reaction zone or point of incoming fuel ignition a critical distance from the point of fuel introduction into a reactor sized to afford a critical minimum residence time for the gaseous product of partial combustion.
In the chemical and evergy providing industries there is a great demand for gas containing substantial amounts of hydrogen, carbon monoxide,olefins or mixtures thereof. Such gases may be used, for example, as starting material for the manufacture of chemical products, as reducing agent, as a clean fuel or in hydrogenation processes. Such gases can be manufactured by incomplete combustion of hydrocarbons, naturally with a smaller quantity of oxygen than that required in the case of complete combustion. With an O/C ratio of 1, (atomic ratio of total oxygen to total carbon in the feed), hydrocarbons in the ideal case yield carbon monoxide and hydrogen. In actual practice, however, small quantities of, inter alia, carbon dioxide, water and soot are formed in addition. By increasing the atomic ratio of O to C the amount of soot formed may bereduced, but more carbon dioxide and water will then be formed. If the OIC ratio is decreased less carbon dioxide and water will be formed, but more soot will form and there will remain more uncombusted hydrocarbons. I
Of all these by-products soot in particularis a nuisance. Gas that contains soot cannot as a rule be used as such because it gives rise to fouling and blockageof lines, outlets, catalyst beds, etc. Removal of soot from the gas is possible, but the cost is significant. Conse- 'quently it would be very desirable if an incomplete SUMMARY OF THE INVENTION It has now been found that soot formation can be substantially eliminated at its point of origin in a process for incomplete combustion of a gaseous or liquid hydrocarbon fuel wherein the fuel is mixed with or finely dispersed in an oxygen-containing gas and passed as a gaseous jet through at least onesupply opening into a substantially word reactor by controlling two process variables-i.e., the distance between the supply opening and the initial part of the reaction zone or point of incoming fuel ignition and the residence time of the gaseous product of incomplete combustion in the reactor-above critical minimum values. The invention therefore relates to an improved process of the type described in which the velocity of the mixture of fuel and oxygen-containing gas introduced into the reactor as a gaseous jet is sufficiently high that the initial partof the gen-containing gas and finely atomized fuel as well as its more conventional meaning where the fuel is present as a volatilized gas in admixture with the oxygencontaining gas.
THE DRAWINGS The invention will be described in greater detail with reference to the accompanying drawings. These drawings which illustrate the process of the present invention are intended to be illustrative rather than limiting on its scope.
FIG. 1 is a longitudinal cross-section of an apparatus suitable for carrying out the process of the invention.
FIG. 2 is a partial cross-section of a reactor suitable for use in the invention taken at the level of the inlets.
FIG.:3 is a partial section of an. alternative reactor suitable for use in the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Process Feedstocks Composition The process of the invention is particularly applicable to the incomplete combustion of hydrocarbon fuels which are gaseous or capable of being atomized into fine liquid droplets at ambient conditions or conditions conventionally employed in incomplete combustion preheaters, e.g., temperatures up to about 500C. Accordingly, almost any petroleum fraction existing as a gas or liquid under ambient and atmospheric conditions or capable of being vaporized or atomized at an elevated temperature as high as about 500C may be used as feed material to the instant process. Natural gas or normally gaseous hydrocarbons such as C saturated and olefinic hydrocarbons because of their availability and ease of handling are particularly suitable, however heavier hydrocarbon fractions including gasoline, kerosene, naphtha, distillates, gas oils and residual oils can also be used as feed materials. In addition such materials as coal distillation gas and the effluent from liquidification or gasification of coal can also be suitable employed.
The oxygen-containing gases which are suitable for use as the oxidant source in the instant process include all those oxygen-containing gases conventionally employed in incomplete combustion processes. Examples of such oxygenscontaining gases and air, air enriched with oxygen or oxygen. Optionally, the oxygencontaining gas or the oxygen-containing gashydrocarbon fuel admixture may be mixed with steam on passage into the incomplete combustion reactor.
The principle advantage of the invention, i.e., reduced soot formation, is most apparent at the low O/C ratios where soot formation is otherwise most preva- The Process The invention in its most basic terms is directed to an improvement on conventional incomplete combustion processes in which the hydrocarbon fueloxygencontaining gas reactant mixture is introduced as a gaseous jet through at least one supply opening into a substantially void reactor; the initial part of the reaction zone occuring at a point in the reactor where the mixture of fuel and oxygen-containing gas introduced as a gaseous jet undergoes ignition. Accordingly, the apparatus contemplated for mixing of the fuel with the oxygen-containing gas and subsequent introduction of said mixture into the reactor is quite conventional and well known to those skilled in the art. For example, in one variant of such conventional apparatus the mixing of the fuel and oxygen-containing gas takes place at the inlet of the reactor by arranging for the feed to flow from a supply pipe whose outlet is located in the center of or close behind the outlet for the oxygen-containing gas. For purposes of this invention the outlet for the fuel (supply pipe in the above example) is considered to be the supply opening.
As mentioned previously, one of the critical aspects of the improved process according to the instant invention is that the initial part of the reaction zone is not located at the site of the supply opening but at a certain distance from it. This, distance is suitably at least ten times the diameter of the supply opening and preferably about one half the length of the reactor for reactors having a length taken in the in the direction of the supply jet flow of greater than 20 times diameter of the supply opening. The maximum distance which the initial part of the reaction zone can be displaced from the supply opening is in principle limited only by the physical structure of the reactor since the primary advantage of the invention exists even in cases where the initial part of the reaction zone approaches the reactor wall opposite the supply opening.
The position of the initial part of the reaction zone relative to the supply opening is mainly determined by the composition of the fueloxidant mixture, the temperature of this mixture on introduction into the reactor at the supply opening and by the velocity of the gaseous jet issuing from the supply opening. For example, it will be recognized that preheating the fuel-oxygencontaining gas admixture to temperatures approaching ignition temperature will shorten the time (and distance relative to the supplyopening) required for ignition to occur because the incoming gaseous jet does not require extensive heating by the reactor environment prior to ignition. Accordingly operation of the process of this invention does not preclude the use of any or all of these variables to achieve the desired displacement of the initial part of the reaction zone from the supply opening. However, because of its ease of operation and control it is preferred that velocity be used as the process variable to control the distance at which the initial part of the reaction zone is displaced from the supply opening. While it will be recognized that in order to achieve a stable distance between the supply opening and the initial part of the reaction zone the velocity at which the gaseous jet issues into the reactor must vary with the composition of the fuel-oxidant mixture and its temperature at the supply opening, this velocity will always be higher than that required for ignition at the site of the supply opening. The gas mixture needs a certain time to ignite if the mixture is at the ignition temperature. Generally the temperature of the issuing gas mixture will be lower, in consequence of which the ignition will take place later, because the mixture first has to be warmed up by the environment and by the reaction product that is drawn to the incoming gas jet under the influence of the suction effect. Accordingly, for gas mixtures having O/C ratios within the preferred range, subject to little or no preheating prior to introduction into the reactor, the velocity of the gaseous jet is suitably greater than 5 m/s and preferably at least 20 m/s. Depending on the amount of preheating which is provided this velocity will necessarily increase as the temperature of the preheated gas increases if a stable displacement distance for the initial part of the reaction zone is to be maintained. The position of the initial part of the reaction zone may be assessed visually or by measurement of the temperature at the desired position. The composition of the product gas may also be used, e.g., by monitoring the presence of soot in the product gas.
The residence time of the product gas in the reactor must also be maintained above a critical minimum if the substantial advantage attributable to the instant invention is to attained. This residence time is suitably at least 0.1 seconds at a minimum with the maximum residence, dictated by practical considerations such as reactor size and flow rates, being about 20 seconds. Owing to this relatively long residence time the product gas leaving the reaction zone is substantially free from radicals. A part of this gas, which naturally has a high temperature, is drawn to the gas jet owing to the suction effect of the latter. Consequently the issuing gas is diluted and raised in temperature, and hydrogen enters the gasjet. This gas ignites when the temperature is sufficiently high and if the ignition delay time has elapsed. For mixtures of hydrocarbons and air a temperature of 500900C is required and the ignition delay time amounts to a few milliseconds. During this time, that is immediately before ignition starts, cracking reactions take place. However, owing to the presence of hydrogen and the resulting hydrogenation, the formation of radicals is prevented. As the product gas drawn to the incoming gas jet by the suction effect is free from radicals, early ignition of the gas mixture is prevented so that the gas mixture can ignite spontaneously under hydrogenation conditions. As a result, the formation of soot is inhibited. During the flame reaction radicals are formed in addition to the desired products such as CO and H which radicals, however, owing to the long residence period in the reactor, disappear before a part of this gas is drawn into the gas mixture that is still to be decomposed.
It is preferred that a gas jet should issue from the relevant supply opening with little or no swirl. Furthermore it is preferred that the gas in the reactor should flow under conditions of little or no swirl. Measures to this effect reduce the possibility of reacting gas containing radicals being drawn to the incoming gas.
As stated previously the process of the present invention can be suitably carried out using air, oxygen enriched air or oxygen as the oxidant source (oxygencontaining gas). In any case it is contemplated that the reaction will be conducted in a conventional manner under conditions of temperature and pressure such that the reaction is self supporting. Accordingly, the reaction temperature, broadly stated, will range from about 700 to about 2,()0()C with the reaction pressures ranging from atmospheric up'to about 600 psig. Within this broad range the reaction temperature and pressure are preferably 900-1,400C and atmospheric to 30 psig, respectively, when air is used as the oxidant source with some what higher temperatures and pressures, e.g., 1,l00--l,700C and atmospheric to- 600 psig, being employed when oxygen is used as the source of oxygen-v containing gas. I
An apparatus suitable for carrying out the process of the invention as described hereinabove may consist of a substantially void and preferably cylinder-shaped reactor equipped with at least one device for the supply of hydrocarbon fuel and oxygen-containing gas at one end of the reactor, and with at least one device for the discharge of reaction product, in which apparatus each supply device is provided with at least one open-ended pipe with diameter a of the outlet opening running in the longitudinal direction of the reactor, the dimensions of the reactor being such that the diameter is at least ten times as large as the diameter d of the outlet of the supply device and that the length is at least 50 times as large as that diameter d. For practical reasons it is preferable that the reactor diameter be no more than 100 times as large as diameter, d., and the length be no larger than 500 times said diameter, d. With these dimensions of the reactor the manufacture of a gas that is free from soot by a process according to the invention is achieved, because the requirement concerning a residence time of at least 0.1 seconds at the desired feed rate can be met. Recirculation of product gasto the jet or jets of reaction mixture is easily possible' If one supply pipe is present the center line of it preferably coincides with the center line of thereactor.
If a plurality of supply pipes are present, they are preferably arranged in a regular array relative to the center line of the reactor, the distance between any two supply pipes being at least times as large as the diameter a, the diameter of the reactor being so large that the distance between the wall of the reactor and the nearest supply pipe(s) is at least five times as large as the diameter d.
It is preferred that two or more discharge devices, evenly spaced around the circumference of the'reactor, be present at a distance from the inlet side that is equal to at least half the length of the reactor. This is advantageous in that gas that is drawn to the incoming gas jet owing to the suction effect of the latter will have a longer residence time than in the case of the outlets being located at a lower level. For, the velocity of flow of the gas drawn to the incoming gas jet is lower below the outlets, because the gas that has been discharged no longer takes part in the flow. This is conducive to the disapperance of radicals from the gas intended for recirculation. The discharge device or devices may also be located at the top of the reactor, opposite to the inlet side of the reactor.
The invention will now be further elucidated with refthe diameter of the reactor is approximately 14 times as large as the diameter of the outlet of the supply device 2 and the length ofthe reactor is approximately 60 times as large. The diameter of the outlet of the supply device 2 is the said diameter d. A device 5 for the dis charge of reaction product is here located opposite to the supply device 2. The mixture that is to react issues from the supply device 2 as a jet. 6at a high velocity. At a distance in this example of approximately 13 times the diameter of the outlet of the supply device Zthere is locate theinitial part of the reaction zone 7. A part of the product gas is drawn to the jet 6 by suction, which is indicated-by means of the arrows 8. Product gas 9 leaves the reactor via the discharge device 5-.
In FIG. 2 a reactor 10 with four supply pipes 11 is represented. The distance between any two supply pipes here is at least approximately I l times the diameter of the outlet of a supply pipe 1.], the distance to the wall of the reactor 10 being at least 6 times that diameter. The supply pipes may be part of one inlet device.
In FIG. 3 an upper part 12 of a reactor is represented. This part is closed at the top. At a lower level there are located a number of outlets 13, evenly spaced around the circumference, which discharge into an annular duct 14 from which the product gas 15 can be obtained. The distance from the outlets 13 to the inlet of the reactor, which is not shown, is at least half the length of the reactor.
EXAMPLES l-VII In a reactor having a length of 250 mm, a diameter.
of 48 mm and a centrally positioned supply pipe with a diameter of 4 mm, mixtures of hydrocarbons and air were introduced at different temperatures and different rates. The ratio of oxygen to hydrocarbon at which soot formation occurred was determined. The results are listed in the table below.
No. 7 Product Formation of soot starts at a lower ratio of O to C than stated. "Soot limit not yet reached.
During runs No. l, 2 and 3 there was no distinct distance between the initial part of the reaction zone and the opening of the supply pipe. The linear velocity was too small for the given O/C ratio. During runs 4, 5, 6
and 7' there was a distance of more than 10 times the diameter d.
The results show that as soon as the jet action of the feed-air mixture plays a role formation of soot starts at the very low O/C ratio of below 1.0. For i-C H, with an outlet temperature of l,l00-l,200C these favorable results were obtained with a jet-velocity of at least 7.4m/s and for C H with 10.1 mfs.
Run 7 using i-C H at the lower reaction temperature of 850"900C demonstrates that the soot limit lies at an O/C ratio that is still lower. This is due to the longer time that is required to cause the gas to react, the result of which is that more gas that has completely reacted is drawn to the incoming gas and that a higher degree of dilution is reached.
For comparison it is stated that for a burner of the Bunsen-type as used for laboratory purposes the soot limit for i-C l-l lies at an O/C ratio of 2.2.'
Whatis claimed is:
1. In a process for the incomplete combustion of a gaseous or liquid hydrocarbon fuel in a substantially void reactor wherein the fuel is mixed with or finely dispersed in an oxygen-containing gas and passed as a gaseous jet through at least one supply opening into the reactor, the initial part of the reaction zone in the reactor occuring at a point where the mixture of fuel and oxygen-containing gas introduced as a gaseous jet undergoes ignition, the improvement which comprises: passing the gaseous jet into a reactor in which the residence time of the gaseous product of incomplete combustion is at least 0.1 seconds at a sufficiently high velocity such that the initial part of the reaction zone is dis placed from the supply opening by a distance which is at least ten times the diameter of the supply opening.
2. The process according to claim 1 wherein the mixture of fuel and oxygen-containing gas is introduced into the reactor at a O/C ratio of from about 1.0 to about 1.8.
3. The process according to claim 2 wherein the reactor is substantially cylindrical in shape having a diameter which is from ID to lOO times the diameter of the supply opening and a length which is from 50 to 500 times the diameter of the supply opening, said supply opening being located at one end of the reactor with at least one device for discharge of the reaction product being located at the other end of the reactor.
4. The process according to claim 3 wherein two or more equal diameter supply openings are present which are arranged'in a regular array relative to the center line of the reactor, the distance between any two supply openings is at least ten times as large as the diameter of said supply openings with the diameter of the reactor being so large that the distance between the wall of the reactor and the nearest supply opening is at least five times as large as the diameter of said supply openings.
5. The process according to claim 4 wherein two or more discharge devices, evenly spaced around the circumference of the reactor, are present at a distance from the inlet side that is equal to at least half the length of the reactor.
6. The process according to claim 2 wherein the oxygen-containing gas is air.
7. The process according to claim 6 wherein the gaseous jet issues from the supply opening with little or no swirl.
8. The process according to claim 6 wherein the velocity of the gaseous jet is atleast 20 m/s.