US3551123A

US3551123A - System employing coal as fuel in a steam reformer

Info

Publication number: US3551123A
Application number: US768663A
Authority: US
Inventors: Harold H Stotler
Original assignee: Hydrocarbon Research Inc; US Department of the Interior
Current assignee: HRI Inc; US Department of the Interior
Priority date: 1968-10-18
Filing date: 1968-10-18
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29

Description

S l" E ucc. av, vltHU H. H. STOTLER 3,551,123

SYSTEM EMPLOYING COAL AS FUEL IN A STEAM RFORMER Filed OCC. 18, 1968 A TTORNEYS United States Patent O 3,551,123 SYSTEM EMPLOYING COAL AS FUEL IN A STEAM REFORMER Harold H. Stotler, Westfield, NJ., assignor, by direct and mesne assignments, of one-half each to Hydrocarbon Research, Inc., New York, N.Y., and to the United States of America as represented by the Secretary of the Interior Filed Oct. 18, 1968, Ser. No. 768,663 Int. Cl. B01j 1/00'; C01b 2/14;F23i1/00 U.S. Cl. 48-94 16 Claims ABSTRACT OF THE DISCLOSURE Coal-derived hot iiue gas is cooled to about 2200a F. so that molten ash will not be present as entrained ash therein, and then the gas is employed as the heating gas in a hydrogen-producing steam reformer. To hinder ashinduced corrosion of metallic surfaces in the reformer, the reformer is designed so that the heating gas is deflected against the interior surfaces of the reformer side walls to separate out some of the ash prior to contacting the reformer tubes with the gas. Further, ash in the heating gas is prevented from substantially contacting any metal surfaces in the reformer which are heated to between about 1050 F. and 1250" F. during reforming.

This invention, which relates to the hydrogen reforming of refinery gas wherein coal is employed as fuel for reforming, resulted from work done under contract with the Oice of Coal Research of the U.S. Department of the Interior.

It is well known that one of the most inexpensive methods for producing hydrogen is by the steam reforming of hydrocarbon gases or light distillate oils. Heretofore, in the production of hydrogen by steam reforming, refinery gas, natural gas or light distillate oils have been used to provide the process stream and the fuel to fire the reforming furnaces.

I have now developed a practical system for employing asubstantially more economical fuel, coal, as fuel for firing such furnaces, while employing refinery gas, natural gas or light distillate oils as the process stream. Generally, my system comprises -burning coal and/ or coal char in a burner external to the'reforming vessel to produce a hot ue gas which contains some entrained coal ash; quenching the gas to about 2l00 F.-2300 F.; and employing the partially cooled gas to heat the process stream in the reforming operation to about l500 F.-1600 F. by indirect contact heat exchange. Thereafter, the iiue gas exiting from the reformer can be employed to (a), preheat air for the coal burner, y(b) produce steam, (c) preheat steam and the hydrocarbon process stream for the reformer, and (d) quench the coal burner flue gas (prior to introduction to the reformer) to the temperature previously set forth.

To hinder corrosion of the reformer tubes by the entrained coal ash in the coal-derived flue gas, the reformer vessel is designed so that the flue gas is fed into the vessel at several different elevations, and the flue gas ows downwardly upon entry and is deflected by the interior surfaces of the side walls of the vessel prior to contacting the reformer tubes therein. Further, fly ash in the iiue gas is prevented from directly contacting metallic surfaces 3,551,123 Patented Dec. 29, 1970 "ice (the reformer tubes) in that portionof the vessel wherein the temperature of the metallic surfaces is between about 1050 F. and 1250 F.

It is, therefore, an object of the present invention to provide coal or coal char as fuel for a hydrogen-producing steam reformer. Another object is to minimize ash-induced corrosion of the reformer tubes while heating the tubes with the iiue gas from a coal burner. A further object is to provide coal or coal char as the fuel for a hydrogenproducing steam reformer which is employed in combination with a gasoline-producing coal refinery. A still further object is to provide coal as reformer fuel wherein the process streamto the reformer is refinery gas from a gasoline-producing coal refinery.

Other objects and advantages will be obvious from the following more detailed description of the invention taken in Iconjunction with the drawings wherein FIG. l is a schematic View of the system of the present invention; and

FIG. 2 is a top sectional view along line 2-2 of FIG. l.

Referring to FIG. l, therein is shown two vertically oriented, identically-designed steam reformer vessels 1 and 1a, a coal (and/or coal char) burner 2 and a convection heating unit 3 all employed in the practice of the present invention. Although one coal burner and two reformer vessels are shown in the drawing, any number of vessels and burners can be combined with one another (c g., one reformer vessel and one or two burners), depending upon the desired output and the designed capacity of the individual pieces of equipment.

A process stream composed of steam and hydrocarbon gas in conduit 4 enters the top of each reformer through tubes 5, while the heating gas enters the reformer through a plurality of vertically-displaced,orificed manifolds 6 in shelf segments 7 of the reformers side walls. Shelf segments 7 are substantially horizontally disposed. Prior to introduction into the reformers, the steam-hydrocarbon gas mixture is generally preheated to about 800 F.- l000 F., preferably about 850 F. Heating gas enters at a temperature of about 2100 to about 2300 F., preferably about 2200 F. The upper gas temperature of about 2300 F. is maintained so that the use of a coal ash-containing flue gas as the heating gas in the reformers will not deposit molten ash on reformer tubes 5 or in the conduits connecting coal burner 2 to both reformers.

Referring to FIGS. l and 2 (a top sectional view of vessel 1), the heating gas, after entering oriced manifolds 6, is directed downward into the reformer through a plurality of orifices 6ta. The gas tlien impinges against downwardly, inwardly tapered side wall segments 8, some of which connect the outer edge portion of one shelf segment 7 to the inner edge portion of the shelf immediately therebelow. In this manner, the heating gas is deflected by wall segments `8, and some of the entrained coal ash therein impinges upon the inner surface of each wall segment 8, then slides down the remaining tapered portion of that segment and drops to the bottom of the reformer vessel to be removed through conduit 9 without ever touching the reformer tubes. The potential corrosive effect of the ash is thereby reduced.

In the upper portion of each reformer a metal shield 10 is disposed between the heating gas and the two parallel rows of reformer tubes. The vertical length of plate 10 is such that there is substantially no direct contact between ash in the heating gas and reformer tubes in that section of the tubes which is at a temperature of about 1050 F. to 1250 F. If the ash in the heating gas were allowed to readily contact tubes which were heated to such a temperature, alkali sulfates which form in coal ash at this temperature would cause severe corrosion of and pitting in the reformer tubes which are of conventional construction (e.g., centrifugally cast steel tubes). The metal shield temperature is about 1500 F. so that minimum alkali sulfate corrosion takes place thereon.

To further alleviate other potential ash corrosion problems, soot blowers 11 can be installed adjacent the reforming tubes in the area below shield 10 to keep the outer surfaces clean of those portions of the tubes which are heated to above about 1250 F. i.e., about 1300 F. to about 1600 F.

Hydrogen-rich reformed product gas leaves reformers 1 and 1a through an exit conduit 12 at a temperature of about 1500 to about 1600 F., preferably about 1525 F. The reformed gas is then treated in the usual manner to convert it into a hydrogen rich product stream.

Heating gas exits from reformers 1 and 1a through conduit 13 at a temperature of about 1700 F. A portion of this exit gas is conveyed by conduit 14 to exit chamber 2a of burner 2. In the burner hot combustion air is received through conduit 15 at a temperature of about 500 F. to about 800 F., preferably about 600 F. A flue gas usually having a temperature of about 3l00 F. is produced by the burning of coal and/ or coal char in burner 2, and the flue gas is passed to exit chamber 2a to be mixed with and cooled to about 2l00 F.2300 F., preferably about 2200" F., by the reformer exit gas. Thereafter, conduit 16 conveys the gas mixture (as heating gas) vdirectly to reformers 1 and 1a. A cyclone burner is most suitable for burning the coal and/or coal char since a large proportion of the resultant ash is eliminated as molten slag therein.

That portion of the exit gas from the reformers which is not employed to cool the coal flue gas to the desired temperature is passed as a heating medium through conduit 17 to convection heating unit 3. Therein, air is passed through conduit 18 in indirect contact with the flue gas after which heated air is conveyed via conduit 15 to burner 2. Hydrocarbonaceous fluid such as natural gas enters heating unit 3 through conduit 19 and heated gas exits through conduit 20. Water enters the heater through conduit 21 and exits as steam through conduit 22 after which it is mixed with the hot hydrocarbon gas in conduit 20. Additional steam in conduit 23 is added to the mixture in conduit and :the hydrocarbon gas-steam mixture is then recycled to heater 3 through conduit 24 to be heated to about 800 F.-l000 F., preferably about 850 F. The heated mixture is then passed to the reformer through conduit 4. Flue gas leaves the heater through stack 25.

As shown in the following exemplary practice of the present invention, 58 million standard cubic feet of hydrogen per day (24 hour basis) may be recovered from the reformed gas produced in the apparatus shown in FIG. 1.

PHASE 1 A typical coal refinery gas (110 F.) having the following composition (mole percent).

Percent H2 32.0 CH4 46.4 C2H3 C3H8 7.1 C4H10 3.8 CH 0.1

is fed at a rate of 1858.96 moles per hour through conduit 19 to be heated to 600 F. in heater 3. Boiler feed Water (475 p.s.i.g. and 455 F.) from the coal refinery, at

4 a rate of 59,900# per hour, is fed through conduit 21 to heater 3 to be converted to steam, after which it is mixed with hot refinery gas in conduit 20. Additional steam (465 F., 475 p.s.i.g.) at a rate of 135,850# per hour, is added to the steam-refinery gas mixture via conduit 23, and the resultant mixture is passed through conduit 24 back to heater 3 to prduce a gas at 850 F. and 450 p.s.i.g. which is fed to reformers 1 and 1a through conduit 4 at a rate of 12,743.96 moles per hour. The composition (mole percent) of the feed gas to the reformers Percent H2O 85.40 H2 4.67 CH4 6.77 CZHG 1.54 C3HB 1.04 Cyl- 0.56 CSHG 0.03

Air (72 F.), at a rate of 15,500 moles per hour is also heated in heater 3 to a temp rature of 600 F. after which it is fed through conduit 13 to burner 2.

PHASE 2 74,580# /hr. coal char (containing 50 wt. percent ash) from the coal renery is fed to burner 2 to produce 525 million B.t.u./hr. It is assumed that 71.8% of the fuel can be used to gain useful heat. The burner llue gas is at a temperature of 3085 F. and is cooled, in the manner set forth hereinafter, to 2200" F., after which the heating gas is fed to reformers 1 and 1a through conduit 16 at a rate of 50,800 moles per hour.

PHASE 3 Each reformer vessel 1 and 1a has the following details:

Number of reforming tubes-235 Length of each tube-40 feet Inner diameter of tube- 3.5 inches Outer diameter of tube-4.75 inches Distance between longitudinal axes of adjacent tubes-10 inches Dimension of reformer unit along the rows of tubes-102 feet Height of metal shield 10-11'6" Flue gas exiting from reformer vessels 1 and 1a is at a temperature of 1700 F. 35,100 moles per hour of the ue gas are then employed to mix with and cool the burner ue gas in burner chamber 2a to produce the heating gas for the reformers, .while 15,700 moles per hour of the ilue gas exiting from reformers are fed as the heating medium to heater 3 from which it exits through stack 25 at 510 F.

Product gas leaves reformers 1 and 1a through conduit 12 at a rate of 16,130.8 moles per hour and at a temperature of 1515 F. and a pressure of 325 p.s.i.g. The product gas has the following composition (mole percent):

Percent H2 37.0 CO 4.6 CO2 6.0 CH4 1.5 H2O 509 While the system is well adapted to carry out the objects of the present invention, it is to be understood that various modifications and changes may be made all coming within the scope of the following claims.

What is claimed is:

1. In a process for producing hydrogen by steam reforming of hydrocarbons wherein a steam-hydrocarbon feed mixture is heated by indirect contact heat exchange with a hot gas, 'the improvement comprising:

(a) burning a solid fuel selected from the group consisting of coal, coal char and mixtures thereof to produce a hot ue gas containing entrained coal ash;

(b) cooling said hot fine gas to produce a cooler gas having a temperature of about 2100 F. to 2300 F.; and

(c) employing said cooler gas as said hot gas for said heating of said steam-hydrocarbon feed mixture, said feed mixture being heated to about 15004 1690i,...F....whereby said mixture is reformed to a 2. The procesisof claim 1 wherein said hot ue gas is cooled to about 2200 F. in step (b).

3. The process of claim 1 wherein step (c) is carried on in a heating zone wherein ash in said ue gas is maintained out of direct contact with metallic surfaces therein which are heated to between about 1050 F. and about 1250 F. during said heating of said mixture.

4. The process of claim 3 wherein metallic surfaces in said heating zone which are heated -to temperatures of about 13001600 F. are cleared of ash deposition during said heating of said mixture.

5. The process of claim 3 wherein said hot flue gas is cooled to about 2200 F. prior to heating said steamhydrocarbon mixture.

6. The process of claim 5 wherein a portion of ue gas exiting from said heating zone is mixed with said hot flue gas to cool said hot fiue gas to about 2200c F.

7. `The process of claim 6 wherein said flue gas exiting from said zone is at a temperature of about 1700 F.

8. The process of claim 7 wherein another portion of said flue gas exiting from said zone is employed to heat air, after which said heated air is employed as combustion air in said coal burning step.

9. The process of claim 8 wherein said air is heated to about 600 F. by said another portion of said flue gas.

10. The process of claim 9 wherein said another portion of said flue gas also heats said steam-hydrocarbon mixture to about 850 F. prior to introducing said mixture into said heating zone.

11. The process of claim 10 wherein said cooler gas upon entering said heating zone is directed downwardly against and thereby deect'ed by a downwardly sloped surface in said zone prior to heating said steam-hydrocarbon gas mixture, whereby some of said entrained coal ash in said flue gas impinges against said surface, slides down said surface and drops to the bottom of said heating zone without contacting. heat exchange surface Awhich is in direct contact with said steam-hydrocarbon mixture in said heating zone.

12. An apparatus for producing hydrogen by steam reforming a hydrocarbon comprising:

(a) a solid fuel burner;

(b) a steam reforming Vessel having generally vertically disposed side walls ywherein a plurality of segments of at least one of said side walls extend substantially horizontally outwardly from said vessel to form a plurality of external shelves on said unit, said shelves being vertically displaced with respect to one another; other side wall segments of said at least one side wall each forming a connection ybetween adjacent shelves, each of said connector wall segments extending from the outer edge portion of one shelf to the inner edge portion of the shelf immediately below said one shelf to define downwardly,

inwardly tapered side wall segments on said at least one side wall; orifice means on each of said shelves, said orifice means being positioned to downwardly direct gas toward the inner surface of said tapered side wall segment immediately below each shelf; vertically extended tube means in said reformer vessel;

(c) first conduit means connecting said burner to said orifice means to pass hot ue gas from said burner to said reformer vessel, said hot ue gas containing entrained ash whereby some of said entrained ash impinges against each of said inner surfaces of said tapered side wall segments, and said ash slides down said inner surface and drops to the bottom of said vessel without contacting said tube means;

(d) second conduit means connected to the top of said tube means to pass a steam-hydrocarbon mixture through said tube means;

(e) third conduit means connected to the bottom of of said reformer vessel to remove ue gas from said vessel; and

(f) fourth conduit means `connected to the bottom of said tube means to remove reformed product gas from said vessel.

13. The apparatus of claim 12 further including shield means in the upper portion of said vessel between said orifice means in the upper portion of said vessel and said tube means in the upper portion of said vessel to substantially prevent direct contact between (i) ash in said hot ue gas and (ii) said tube means in the upper portion of said vessel.

14. The apparatus of claim 13 including fifth -conduit means connected between said third conduit means and said burner to recycle a portion of said ue gas to said burner to mix with and cool hot flue gas exiting from said burner, the mixture ythen being passed through said first conduit means to said reformer vessel.

15. The apparatus of claim 14 further including a heat exchanger; sixth conduit means connecting said third conduit means to said heat exchanger 'to pass a portion of said ue gas as the heating medium to said heat exchanger; means in said heat exchanger to preheat combustion air for said burner; and means in said heat exchanger to preheat said steam-hydrocarbon mixture for said reformer vessel.

16. The apparatus of claim 15 further including blower means connected to said reforming vessel to prevent ash accumulation on said tube means.

References Cited UNITED STATES PATENTS 294,534 3/ 1884 Stee-nbergh 48--94 1,154,869 9/1915 McHenry 48-94 1,894,297 1/1933 Snow et al 11G-165A 2,739,878 3/1956 Jolley 23-277 2,750,903 6/1956 Miller et al. 11G-165A 3,004,839 10/1961 Tornquist 48--197 3,090,682 5/1963 Bartholome et al. 48-196 3,230,052 1/1966 Lee et al. 23-277 JOSEPH SCOVRONEK, Primary Examiner U.S. Cl.X.R.