US2975044A

US2975044A - Apparatus for pressure hydrogasification of petroleum hydrocarbons

Info

Publication number: US2975044A
Application number: US728211A
Authority: US
Inventors: Elmore S Pettyjohn; Henry R Linden
Original assignee: Institute of Gas Technology
Current assignee: Gas Technology Institute
Priority date: 1954-06-14
Filing date: 1958-04-14
Publication date: 1961-03-14
Anticipated expiration: 1978-03-14

Description

March 1961 E. s. PETTYJOHN ET AL 2,975,044 APPARATUS FOR PRESSURE HYDROGASIFICATION OF PETROLEUM HYDROCARBONS Original Filed June 14, 1954 2 Sheets-Sheet 1 B e-E APPARATUS FOR PRESSURE HYDROGASIFICA- TION OF PETROLEUM HYDROCA-RBONS Elmore S. Pettyjohn, Evanston, and Henry R. Linden, Franklin Park, Ill., assignors to Institute of Gas Technology, Chicago, 11]., a corporation of Illinois Original application June 14, 1954, Ser. No. 436,406, now Patent No. 2,860,959, dated 'Nov.18,'1958. Digizdseglrlind this application Apr. 14, 1958, Ser. No.

1 Claim. (Cl. 48-93) is the supply of peak load gas in areas where gas house heating is widely used and where the, cost of gas is predicated on the major portion being supplied bypipeline. Since long distance transmission lines can be operated economically only under near capacity steady Patented Mar. 7 14, 1961 bons referred to in the art as natural gas liquids and pe troleum distillates.

Another object is the provision of a simple furnace apparatus comprising at least two interconnected zones, one of which is directly heated and houses a catalytic reactor, and the other of which is heated indirectly from said first zone and which houses a hydrogasification-cracklug reactor. These and other objects will become apparent from the following description when read in con-junctionwith the accompanying drawing, in which:

Figure 1 is a sectional semi-diagrammatic view illustrating the process and apparatus of the invention;

Figure 2 is a similar view of a modified furnace for the apparatus of Figure 1; and. I

Figure 3 is a sectional view taken along the line 3-3 of Figure 2.

loads, methods for computing natural gas prices on the 1 basis of demand, commodity and minimum charges have been generally accepted. It is, therefore, not economically advantageous to meet peak gas load demands above a certain level set by local conditionsthrough the purchase of flowing pipeline gas. Consequently, there is a need for an efficient, economical method for producing artificially a gas that can be used interchangeably for all or part of the natural gas normally supplied, in all varieties of gas burners.

In our copending application Serial February 16, 1953, now Patent No. 2,759,806, we disclose a method for making completely interchangeable gases which involves high temperature vaporphase cracking of light liquid hydrocarbons under pressure in the presence of hydrogen gas. The advantages of employing an atmosphere of hydrogen in addition to pressure in converting vaporized hydrocarbons into high B.t.-u. gases are several. The gaseous product contains arelatively high proportion of parafiins and a relativelylow proportion of olefins, thus approximating more closely the actual composition of natural gas and its heating value and burning properties. Furthermore, the process permits substantially complete conversion of hydrocarbon feedstocks having a boiling point up toabout ;500 F. (natural gasoline, naphthas' and kerosene) without No. 337,078, filed objectionable carbon a'ndpitch deposition, in the takeolT system of the cracking apparatus. Also, large volumes of feedstocks maybe processedin "a relatively small reactor space. This process, therefore offers a number of important advantages over conventional oil cracking methods. The presentfinvention, constitutes an improvement over the method described insaid copending application Serial No. 337,078 and has as an object the provision of an improved apparatus in which to practice a process for cracking light liquid hydrocarbon fractions under pressure and in the presence of an atmosphere of hydrogen gas in which the hydrogen utilized as the cracking atmosphere is manufactured as an integral part of the gas manufacturing process, and which process is further characterized by the eflicient utilization of heat required for producing the hydrogen, cracking the hydrocarbon and preheating raw materials vused in the process. The term hydrocarbon used throughout this specification with reference to feedstock for snak n n d to e e th light quid hyd car- The objects of our invention are achieved by taking advantage of the fact that the cracking of light liquid hydrocarbons in the presence of hydrogen requires surprisingly less heat than cracking without hydrogen, and that the temperature at which this reaction proceeds is lower than the optimum temperature for reforming hydrocarbons with steam in the first step of production of hydrogen gas. For example, the amount of heat at reaction temperature required to convert 26# RVP natural gasoline in the presence of hydrogen is about 25% of the heat required to convert the same quantity of the same gasoline in the absence of hydrogen. The Waste heat from the catalytic reforming reaction, therefore, will meet the heat requirements for hydrogasification, in spite of the additional sensible heat requirements, for preheating the hydrogen. By employing'a furnace divided into three interconnected zones, the heat supplied to the process may be utilized in the first zone for reforming a hydrocarbon gas or light liquid hydrocarbon touproduce hydrogen. The remainder is transferred to the second zone in which the cracking of the hydrocarbon takes place in the presence of hydrogen at a sub- 2. The temperature in the first combustion zone normally will be above 1800 lF., while that in the second zone will be between 1350 and 1700 F. Preferably, the temperature in the furnace is maintained several hundred degrees higher than the maximum temperature desired in the reaction tube housed within the furnace. A high temperature gradient permits a high rate of conversion and, therefore, a high through-put. 'The' hot flue gases, which may be generated inthe first zone of the furnace by means-of oil burners or gas burners, lose a portion of their heat to the reactor tubes wi-thinsaid zone; for catalytically reforming hydrocarbons, but-still contain suflicient heat to effect cracking of thelight hydrocarbon fraction in zone 2., which reaction in, the presence of hydrogen requires substantially less heat. The balance of the heat in the gases is utilized to preheat the raw materials in zone '3 of the furnace, as indicated. Eflicient utilization of heat in this manner the heat requirements per cubic foot of gas produced, hence 7 interior walls of the furnace and the dividers are made from any suitable ceramic refractory material, such as firebrick. It will be noted that the divider 12 does not run completely tothe top of the furnace, thus permitting zones 1 and 2 to be interconnected through the opening 16. In like manner, divider 14 extends downwardly short of the bottom of the furnace, leaving an opening 18 for interconnecting zones 2 and 3. Heat is generated within zone 1 by means of a bank of conventional burn ers 20, 22 and 24,- which are capable of burning either oil or gas. Several banks of burners are provided depending upon the length of the furnace. Gas is supplied to the burners through the line 26, oil through line 28, and air required for combustion of these hydrocarbons through line 30. Throughout the drawing the letter V indicates a valve, M a flow meter, and P a pump or blower. The hot flue gases generated within zone 1 flow through opening 16 into zone '2, downwardly through zone 2, out the opening 18 into zone 3, upwardly through zone 3 and are discharged through the line 32.

Hydrocarbon feedstock for preparing hydrogen is fed from line 34 through the tube 36 mounted within zone 3 of the furnace for preheating the hydrocarbon. The feedstock may be a liquid hydrocarbon such as natural gasoline, naphtha or kerosene, supplied to line 34 through supply line 40; or the feedstock may comprise a recycled make gas supplied from the discharge conduit 90, natural gas, propane or the like, which is supplied to line 34 through supply line 42. Steam required in the reforming reaction for converting the hydrocarbon feedstock into hydrogen gas is supplied from line 44 and passes through a coil 46 within zone 1 of the furnace for superheating. The superheated steam joins the hydrocarbon feedstock in line 38, which connects to the top of the catalytic reactors 48 within zone 1. The reactors 48 are arranged longitudinally within the furnace in banks. Each reactor is an elongated chamber of any suitable cross section, preferably circular. The temperature of the walls of the reactor tubes is maintained at 1600-1800 F. and the pressure within the tubes above 50, and preferably at 70-100 pounds per square inch absolute. The catalytic reactors 48 contain a suitable catalyst, such asnickel, for converting the hydrocarbon feedstock and steam into hydrogen plus some carbon dioxide and carbon monoxide. This hydrogen-rich gas may then be fed to tubes 13 and '15 for reaction with the hydrocarbon feedstock in making fuel gas through valved conduit 52. Preferably, however, the valve in conduit 52 is closed and the carbon monoxide in the gas is con: verted by reaction with steam into carbon dioxide and additional hydrogen gas, and the carbon dioxide subsequently removed. This may be accomplished by passing the carbon oxides and hydrogen from the catalytic reactors 48 through conduit 50 into the catalytic water gas shift reactor 54, containing a conventional water gas shift catalyst. The carbon monoxide generated within the reactors 48 is converted to carbon dioxide plus additional hydrogen in the reactor 54 in accordance with the well-known reaction:

Additional steam required for the reaction is introduced into the line 50 from feedline 52. Preferably, sufficient water is introduced into the line 50 so that the temperature within the'reactor 54is maintained at 600-800" F., preferably at 750 F. The pressure within the reactor 54 will be equal to the pressure maintained within reforming tube 48, less any pressure drop in conduit 50. The magnitude of the pressure in reactor 54 and tube 48 is controlled by downstream pressure control valve 69.

To remove the carbon dioxide from hydrogen pro: duced in both reactions, the efiiuent gases are first passed from the lower end of the reactor 54 into the, contact cooler 56 for cooling. The gases flow upw'ardly in the cooler countercurrent to water spray introduced at the top of the cooler through the line 58, out the discharge conduit 60 and into the scrubber 62 near the lower end thereof. The water that falls to the bottom of the cooler 56 flows out through pipe 64 and-is used again for cooling the product gas, as described hereinbelow. A material capable of absorbing carbon dioxide, such as an ethanolamine solution, is introduced into the scrubber through the top countercurrent to the mixture of carbon dioxide and hydrogen which flows upwardly through the scrubber. The carbon dioxide is absorbed by the ethanolamine solution which is removed through discharge line 66 in the bottom of the scrubber. The hydrogen gas, essentially free of carbon oxides, passes out through line 68, back pressure control valve 69, coil 19 in zone 3 of the furnace, for preheating, and into the first pressure hydrogasification tube 13 within zone 2 of the furnace. The hydrogen produced will contain some impurities such as carbon dioxide, carbon monoxide and methane. Total quantities as high as 5% to 10% can be tolerated.

Hydrocarbon feedstock to be converted into a gas interchangeable or substitutable for natural gas is fed from the supply line 11 through coil 17 in zone 3 for vaporization, and then into the first tube 13 of pairs of pressure gasification tubes extending along the length of the furnace in zone 2. Although reaction tubes 13 and 15 are shown in pairs in the drawing, it will be understood that a bank of single tubes having an equivalent volume will serve the same purpose. The hydrocarbon employed for cracking may range in volatility up to that of kerosene, and includes what are generally known as the light liquid petroleum fractions and the natural gas liquids, suchas propane, butane and natural gasolines.

The vaporized hydrocarbons from coil 17 and the preheated hydrogen from the coil 19 flow under pressure into the lower end of the pressurized gas tubes 13 where the vapors and gas are thoroughly intermixed and the cracking begins. Because the hydrogen gas is generated under pressure it is not necessary to compress it as would be the case where hydrogen is provided from some external source. Partial-1y cracked gases flow upwardly'through the tubes 13 back down into the tubes 15 through-the U-shaped connections at the top. Cracking is completed within the tubes 15 at a maximum temperature ranging from 1300l500 F. and a pressure of about 50-80 pounds per square inch absolute.

The amount of hydrogen introduced into the reactors may range from 50 to 110 cubic feet per gallon of liquid hydrocarbon feedstock, depending upon the properties or the feedstock. The hydrogen must be increased in proportion to the carbon content and molecular weight of the feedstock. The residence time in the reactors ranges from 2 to 10 seconds, preferably from 3 to 5 seconds, and may be varied at will by changing the rate of flow through the reactors. The product gas discharged from the tubes 15 is rich in methane and ethane and also contains some ethylene and light oils in vapor form. The amount of carbon, tar and pitch formed during this reaction is nil. The amount of light normally liquid hydrocarbons formed is usually less than 20%.

The cracking products issuing from the reactors pass through large quench tubes 78 connected to the bottom of the tubes 15 and through conduits 70 into a quench water separator 72. Water for cooling the product gas flows from the cooler 56 through the line 64 into the separator 72 and is pumped therefrom through the line 74 into the quench tube 78, as indicated at 76. Preferably, the water is introduced in a spray so that the temperature of the effluent product gas is efiectively reduced. A constant level device 80 of conventional construction is connected with the separator 72 to maintain the water level within the separator at a predetermined level, the

line 90 to storage or to the location where it is to be used. An automatic pressure regulating valve 92 maintains the, pressure upstream thereof at a predetermined level; preferably from 50-80 pounds per square inch absolute- The make gas will have a heating value of from 9 301to 1100 B.t.u.s per standard cubic foot. Itgenerally will contain from 45-55% methane and ethane, from 30-40% hydrogen, and about 8-11% 'ethylene,,plus minor proportions of benzene, carbon dioxide and the higher paraflins and; olefins. T he specific gnavity will range from about 0.5 to0.65. i

If desired, the olefins in the make gas may be converted into paraflins by autohydrogenation. Thisimprovement can be eifected-bypassing-the gas over a nickel-onkieselguhr catalyst at a temperature'offrom 200-500 FL, and a space velocity up to 1000 standard cubic feet per cubic foot of catalyst per hour. Under these conditions a high conversion of olefins and diolefins to the equivalent parafiins, and comparable reduction of hydrogen content were obtained.

It is desirable to recover the ethanolamine employed as a scrubbing agent so that it may be recycled through the scrubber continuously. Any suitable means may be employed for this purpose. An example of suitable apparatus is shown in Figure 1 to the right of the scrubber 62. The ethanolamine, saturated with carbon dioxide, flows through the pipe 66 and the heat exchanger 102 into the regenerator 100. The ethanolamine is preferably sprayed into the regenerator through a nozzle 104. The temperature of the regenerator is maintained at about 300 F. and about 40 pounds per square inch pressure. Under these conditions the carbon dioxide is driven off and passes upwardly to the conduit 106 connecting to the regenerator near the top and is discharged therethrough. Water cooled coils 108 disposed within the top of regenerator 100 serve to condense any ethanolamine and much of the steam that is volatilized. The ethanolamine solution, free of carbon dioxide, drains to the bottom of the regenerator and is recirculated to the scrubber 62 through line 110. To cool the ethanolamine as it passes to the scrubber, heat exchangers 102 and 112 are provided in the line 110, the heat exchanger 102 employing saturated ethanolamine from the scrubber as a cool ant. The temperature within the regenerator is maintained by means of a heating coil 114 submerged below the level of the ethanolamine in the bottom of the regenerator.

The modification of the apparatus shown in Figures 2 and 3 involves changes only in the construction of the furnace and its contents, the other parts being essentially as shown in Figure 1. The furnace 200 shown in Figures 2 and 3 is designed to generate approximately twice the volume of gas produced in the apparatus of Figure l. Furnace 200 is divided into five different zones, designated as zones A, B, B C and C by

bafiies

202, 203, 204 and 205. Heat for operating the process is generated in zone A by means of a bank of burners 206, extending the length of the furnace between the catalytic reactors 248. The burners are fed with gas or oil and air through

lines

226, 228 and 230, respectively. Hydrocarbon feedstock for reforming into a hydrogen-rich gas is fed to catalytic reactor tubes 248 through lines 242 and 243. Steam required for the reaction is introduced through lines 244 and 245. It will be noted that lines 244 and 245 pass through zone A for purposes of superheating the steam, and lines 242 and 243 pass through zones C and C to preheat the hydrocarbon feedstock.

Cracking

tubes

215 and 216 are disposed within zones B and B Hydrogennich gas generated in reactors 248 may flow directly into

tubes

215 and 216 through valved conduits 217 and 219 connecting to the lower ends thereof. Preferably, the carbon monoxide in the gas is converted to hydrogen and carbon dioxide by passing the gas through conduits 217a and 219a to the catalytic water gas shift'reactor 54, and the carbon dioxide removed in the scrubber, as shown -in Figure 1, prior to delivery to the cracking

tubes

215 and 216.

Hydrocarbon feedstock tubes

215 and 216 is discharged to the condensing portion of the apparatus through conduits 278 and 279.

.' The flue gases generated within zone A flow upwardly and divide, part passing over the battle 203 into zone B and the remainder passing over the bafiie 204 into zone B After giving up a portion oftheir heat to the reactors in,z'ones B and 13;, the gases fl'ow beneath

baflles

202 and 205 into zones C and C where they give upheat' to the hydrocarbon feedstocks for both the catalytic and cracking reactors. The gases thenpass out'stacks .232v and 233.

Other modifications in the arrangement of the furnace and its contents become apparent from the foregoing description.

Examples 1 and 2, set forth below, illustrate typical operating conditions employed in the pressure hydrogasification of 26 pound RVP natural gasoline and kerosene, respectively, in accordance with the invention, and

the compos1t1ons of the make gases produced:

Example N o 1 2 Operating Conditions:

Reactor Tube, Temp., F.-

East Tube:

1, 324 1, 316 411 1, 358 Reactor Pressure, p.s.i.a. 70. 3 71. 3 Residence Time, sec 4. 73 V 3. 75 Feed Rate, Feedstock, lb./hr- 264 304 Feed Rate, Feedstock, gal./hr-- 49. 6 45.1 Feed Rate, Hydrogen, sci/gal- 60.0 104.3 Fuel Consumption, M B.t.u./hr 1, 032 998 Operating Results:

Hz Reacted, s.c.t./gal. Feed... 25. 6 39. 1 H: Reacted, Percent 42. 5 37. 5 Gas Make, s.c.f./hr 6, 770 6, 920 Gas Yield, s.c.f./gal 116. 4 153. 4 B.t.u. Recovery, B.t.u./gal. Feed (gross) 124, 490 143, 280 B.t.u. Recovery, B.t.u./gal. Feed (net) 105,34 109, 970 Light Oil Yield, wt. Percent None 18. 5 Residual Oil Yield, wt. Percent None None Material Balance, Percent 101. 4 100. 3 Composition, mole Percent:

2 O. 6 1. C01 0. 2 0. 2 29. 3 42. OH 43.0 30. 04H 10. 7 12. Higher Paratfins 0.8 0. CaHr 10. 6 7- Higher Olefins 3. 3 3. Ben one 1. 2 1. Tnlnonp 0. 3 0. Total 100. 0 100. Heating Value, as made, B.t.u./s.c.f....-. 1, 070 93 Specific Gravity, as made, air=1.00 .64 0.

Particular attention is called to the operating results of Example 1 wherein gasoline is the hydrocarbon feedstock. The conversion to gas is complete, no residue, liquid or solid, resulting. We have found that to completely eliminate by-products, the feedstock should be a natural gas liquid with the cracking conditions being controlled within the following limits:

Temperature 1300-1500" F.

Pressure 50-80 pounds per square inch absolute.

Residence time .Q 2-5 seconds.

Feed hydrogen 50-80 cubic feet per gallon of hydrocarbon.

With a high molecular weight material, such as kerosene, Example 2, a light oil will be formed and remain as a residue, even though the operating conditions are carefully controlled.

We claim:

An apparatus for producing fuel gas which comprises a furnace divided by a first and a second spaced vertical bulkhead into a first, second and third zone, said first and second zones being interconnected by an opening through the'first bulkhead near the top thereof and said second and third zones being interconnected by an opening through the second bulkhead near the bottom thereof, a single combustion gas discharge outlet near the top of said third zone, burners disposed within saidfirst zone only and constituting. the sole source of heat for said first, second and third zones, thereby supplying heat of progressively lower temperature downstream of said openings, a catalytic reactor within said first zone for generating hydrogen ich' gas, means for introducing a hydrocarbon feedstock into said catalytic reactor, means connecting with the discharge end ofsaidcatalytic reactor for removal of oxides of carbon from said hydrogen-rich gas, a hydrogasification-cracking reactor disposed in said second zone for converting hydrocarbons in the presence of hydrogen to a fuel gas, said hydrogasification' cracking reactor constituting a u shaped tube having a pair of legs" References Cited in the file of this patent UNITED STATES PATENTS 2,625,470 Roberts Jan. 13, 1953 2,692,193 Riesz Oct. 19, 1954 2,707,147 Shapleigh Apr. 27, 1955