US2502670A

US2502670A - Method for the production of water gas

Info

Publication number: US2502670A
Application number: US674198A
Authority: US
Inventors: Edward S Roberts; John B Rinckhoff; Frederick C Cunningham
Original assignee: Chemical Construction Corp
Current assignee: Chemical Construction Corp
Priority date: 1946-06-04
Filing date: 1946-06-04
Publication date: 1950-04-04
Anticipated expiration: 1967-04-04

Description

April 4, 1950 E. s. ROBERTS ET AL 2,502,670

METHOD FOR THE PRODUCTION OF WATER GAS Filed June 4, 1946 INVENTORS F C. CU/V/W/VG/vM/W,

Patented Apr. 4, 1950 METHOD FOR THE PIXSDUCTION OF WATER Edward S. Roberts, New York, N. Y., John B. Rinckhoif, Fanwood, N. J., and hederick C. Cunningham, Jackson Heights, N Y., assignors to Chemical Construction Corporation, New York, N. Y., a corporation of Delaware Application June t, 1946, Serial No. 674,198

4 Claims. 1

This invention relates to a method for the production of water gas from coal and more particularly to a method of producing continuously from coal a water gas substantially free of nitrogen.

It has been proposed to gasify coal by introducing into a producer containing coal a hot mixture of air and steam and by the decomposition of the steam and a controlled burning of the coal to generate a producer gas containing carbon monoxide and hydrogen. Such gas is diluted with relatively high percentages of carbon dioxide and nitrogen, however. There have been further proposals to make water gas by reacting coal with steam in a water gas producer by introducing into a producer containing coal a heated mixture of steam and a recycled portion of the water gas. The recycled water gas functions as an inert heat carrier so that enough heat for the reaction can be carried to the producer by the mixture of steam and water gas.

It has been suggested that a reverbatory type heater such as a Cowper heater be used to heat the gases entering the producer. The operation of such apparatus is cyclic in nature and im= poses limitation on the proposed processes for gasifying coal. The heated gases entering the producer are subject to temperature and pressure fiuctations. The pressure fluctation interferes with the operation of the suspended solid bed type of producer and the temperature fluctations prevent the continuous application of the maximum attainable temperature to these gases. Both these factors result in a product gas of relatively non-uniform composition and low volume efiiciency in the apparatus.

It is a principal object of our invention to provide a method for the production of a high heating value water gas substantially free of nitrogen and consisting predominantly of hydrogen and carbon monoxide by a method which substantially completely gasifies coal by introducing into a producer containing coal a mix-- ture of steam and water gas heated to water gas reaction temperature in a'heat exchanger having movable discrete heat exchange solids. Other objects are to provide a method for the production of water gas of uniform composition and to provide water gas suitable for the Fischer- Tropsch process. Still another object is to provide apparatus having a high volume efliciency by supplying a mixture of steam and water gas to a water gas producer at the maximum attainable temperature.

With the above and other objects in view, 55

the invention therefore consists in the various process steps and combinations thereof and in the various arrangements and combinations of apparatus elements hereinafter to be specifically described with particular reference to preferred embodiments thereof and illustrated in the accompanying drawing.

In its broader aspects our invention comprises a method of producing from coal a substantially nitrogen-free water gas by reacting coal with steam at water gas reaction temperatures in a gas producer to form a hot water gas consisting predominantly of hydrogen and carbon monoxide, recovering part of the hot water gas as product gas, admixing the remainder with steam and contacting this mixture with movable discrete heat exchange solids in a gas heating zone to heat the mixture to a water gas reaction temperature, passing the hot mixture to the water gas producer, the heat exchange solids having been heated to a temperature above the desired water gas reaction temperature by introducing them into the path of hot products of combustion in a solids heating zone.

Apparatus for carrying out the method comprises in combination a water gas producer and heat transfer means including movable discrete heat exchange solids with means in a solids heating zone to heat the solids to a temperature above the desired water gas reaction temperature with hot products of combustion, means to remove the heated solids to a gas heating zone and means to heat a mixture of steam and water gas to the desired water gas reaction tempera- 3 ture in the gas heating zone by contact with the heated solids, means to return the heat exchange solids from the gas heating zone to the solids heating zone and means to pass the heated mixture of steam and water gas to the producer, means to generate water gas in the producer by reacting the hot mixture with coal, means to recover as product gas a part of the water gas produced therein, means to recycle the remainder of the gas with steam to form the mixture of steam and water gas which is used to gasify coal in the water gas producer.

Essentially our invention is a method of producing from coal a substantially nitrogen-free water gas which comprises reacting coal with steam at a water gas reaction temperature in a gas producer to form a hot water gas consisting predominantly of hydrogen and carbon monoxide. The hot water gas is partially cooled by passing it in contact with a mass of relatively cool, movable discrete heat exchange solids in a 3 solids preheating zone and the preheated solids are then removed to a solids heating zone where they are heated to temperatures above the desired water gas reaction temperature by contacting them with hot products of combustion. The partially cooled water gas is further cooled by passing in heat exchange relationship with preheated water to generate steam after which it is divided into two streams. One stream is mixed with a portion of the generated steam and recycled through a gas heating zone to the gas producer where it reacts with coal to produce more water gas. The recycled gas is heated to the desired water gas reaction temperature by introducing the hot heat exchange solids from the solids heating zone into the path of the mixture in the gas heating zone. The second stream of the cooled water gas is scrubbed and further divided into two streams, one of which is withdrawn as product gas from this process. The second stream of the scrubbed gas is mixed with preheated air and the combustible mixture is burned in the solids heating zone and thereby the heat exchange solids therein are heated to a temperature above the desired water gas reaction temperature. The hot products of combustion from the solids heating zone pass in heat exchange relationship with air to preheat the air that is mixed with the water gas which is burned in the solids heating zone. After preheating air, the products of combustion are divided into two streams, one which is vented to open ar after contacting coal which is thereby dried and passed to the gas producer. The other stream is also vented to open air passing in heat relationship with water which is thereby reheated. The preheated water is passed in heat exchange relationship with the partially cooled water gas from the solids preheating zone as described above.

Apparatus in which our method may be carried out is shown in the accompanying drawing, the single figure of which is a flow sheet in which various pieces of equipment are illustrated diagrammatically. It should be understood, however, that the drawing is given primarily for illustration purposes and that our invention in its broader aspects is not limited thereto.

Referring to the drawing which represents the preferred embodiment of the invention, i is a water gas producer of the suspended solids type. Any type of producer may be used such as a fluid bed or slagging producer with various up or down draft modifications. The Winkler type producer may be used and I is a diagrammatic drawing partly in section of a modified Winkler type water gas producer.

The preferred heat transfer means is pebble heater 2 shown partly in section. It consists of a suitably insulated vertical tower with a restricted diameter at throats l and 8 which cooperate to form a pebble preheating zone 3, a pebble heating zone 4, and a gas heating zone 5. Pebbles i which fill the tower almost to the top of section 3 are free to flow from one section to another depending upon the rate at which they are withdrawn from the bottom of section 5 and returned to the top of section 3 by a conveyor. Any suitable conveyor system may be used. Thus, for example, the pebbles from the bottom of section 5 pass through pipe 51 at a rate controlled by the star valve 58 into conveyor 59 which may be of the bucket or screw conveyor type which are available commerically, and then through pipe 6! into the top of section 3. A motor (not shown) or any other suitable means may be used to rotate the star valve ll.

.The rate of circulation of the pebbles depends upon the heat requirements or the several heatingzones.

In passing through pebble heater 2, the pebbles l are heated in pebble preheating section I by the hot water gas from producer i and pass through throat 'I to pebble heating zone 4 where they are heated by contact with hot products of combustion, obtained by burning combustible material therein, to a temperature above the desired water gas reaction temperature. The hot pebbles then pass through throat I to gas heating section 6 where they are brought into contact with the mixture of steam and water gas and heat this mixture to the desired temperature.

It is obvious that the gases in the ditlerent heating sections of pebble heater 2 should not be allowed to mix and this is prevented by the restricted cross-section at the throats and by operating the apparatus in such a way that the pressure on one side of the throats i and 8 is equal to the pressure on the other side. Instead of the throats 1 and 8 which are the preferred connecting means between the section, a system of gas-tight conveyors may be used.

By means of pebble heater 2, a mixture of steam andwater gas is supplied to producer I at a uniform pressure and temperature. In order to obtain the greatest efliciency in the apparatus and in the reaction, it is desirable that the mixture of steam and water gas be supplied to the producer continuously and uniformly at the maximum attainable temperature. One of the principal advantages or our invention is that by combining a pebble heater with a gas producer, the mixture can be supplied continuously to the producer at a temperature limited only by the softening point of the pebbles. Another important advantage is that because of the uniformity of the temperature of the mixture of steam and water gas, the composition of the product gas is uniform.

As stated above, I is a water gas producer in which coal is reacted with steam to produce hot water gas. The hot gas leaves producer i through pipe 9 and passes through dust collector H! where substantially all of the dust and ash carried by the water gas is allowed to separate and is removed from the dust collector through outlet Ii. The substantially dust-free gas passes from the dust collector it through pipe l2 and into the highest or pebble preheating section I of the three-section pebble heater 2. In section 3 the gasified coal gives up a part of its sensible heat to the pebbles therein and is passed through pipe I to steam boiler I! where most of the remaining sensible heat in the gas is used to generate steam. The gas leaves boiler I! through pipe i6 and a portion of the gas is drawn ofl through pipe i1 and into scrubber iii. The remainder of the gas continues through pipe Ii and passes through the blower i9 and into pipe 20 where it is admixed with controlled quantities of steam that enters pipe 20 through pipe 40 and is passed into the lowest or gas heating section 5 of the pebble heater 2. The mixture is heated by the hot pebbles in section 5 to a desired water gas reaction temperature and is passed through pipe 2i to the water gas producer.

The portion of the water gas entering scrubbing tower [8 through pipe I1 is washed with water or weak alkali solution which enters the scrubber through pipe 22 and spray nozzle 23.

The scrubbing liquid plus any dust it may have removed from the gas leaves the scrubber through outlet pipe 56. A portion of the scrubbed gas is withdrawn from scrubber I8 through pipe 24 and recovered as product gas. The remaining portion may be withdrawn through pipe 25 and is passed through blower 26 and through pipe 21 into pipe 28 where it admixes with preheated air and passes into the middle or pebble heating section 4 of the pebble heater 2.

Atmospheric air is drawn through blower 29 and is passed through pipe 30 into air preheater 3| where the air is preheated. Air preheater 3| is a tubular type preheater with the air to be heated passing around and in contact with tubes 32 through which pass the hot products of combustion. The preheated air is withdrawn from the preheater through pipe 28 and admixes with fuel entering pipe 28 from pipe 21. The mixture continues through pipe 23 and enters section 4 as described above. The mixture is burned in section 4 of the pebble heater 2 and part of the heat of combustion is absorbed by the pebbles in this section. The products of combustion are withdrawn from section 4 through pipe 33 and pass through the tubes 32 in air preheater 3| where a portion of the sensible heat in the prod- :ts of combustion is used to preheat the air.

The gaseous products of combustion are withdrawn from the air preheater 3| through pipe 34 from which a portion of the gases are withdrawn through pipe 35 and pass through the water preheater 36 and are then vented to the open air through the vent pipe 31. Water enters the tubular preheater 36 through pipe 33 and is preheated and passed through pie 3!! to the steam boiler I and is converted into steam. Steam as necessary is withdrawn from boiler |5 through pipe 40 and enters pipe where it admixes with water gas. Any excess steam is withdrawn from boiler l5 by pipe 54 and is available for any suitable use.

The remaining portion of the products of combustion that are not withdrawn through pipe 35 continue through pipe 34 to coal drier 4| where the hot gases are used to dry coal and are then vented to the open air through vent pipe 42. Coal that is to be dried enters coal drier 4| through inlet 43. After beingdried, the coal passes through pipe 44 to screw conveyor 45 from which it is fed into water gas producer I. If it is desired to reduce the temperature of the gases entering the drier 4|, part or all of the 0001 products of combustion from vent pipe 31 may be returned to pipe 34 by a valved by-pass.

The producer i is a diagrammatic drawing partly in section of a modification of the Winkler water gas producer. As illustrated. the producer is a circular chamber having suitable refractory lining 46 and a grate 41 which is wiped with a revolving scraper 43. The rotating motion of the scraper 4B is imparted by the housed revolving shaft 49 on which is mounted a gear 50 which is driven by a motor (not shown). The mixture of steam and water gas that has been heated in section 5 of pebble heater 2 to a water gas reaction temperature enters the producer I through pipe 2| and passes up through spaces 55 in grate 41 and into contact with a bed of coal 5| where the coal is gasified by steam to form gases containing predominantly carbon monoxide and hydrogen. The coal bed 5| is of the solid suspension type and part of the ash that forms as the coal is gasified settles on grate 41 and is removed from the grate by scraper 48 and drops into 6 hopper 52 from which it is removed by screw conveyor 53. The remainder of the dust is carried by the water gas and substantially all of it is removed in dust collector ID.

The process as carried out in the apparatus shown in this drawing may be operated to produce excess heat. The excess heat is introduced into the system by burning an excess 01' combustible material in section 4 of pebble heater 2 and appears as excess steam in boiler |5. The excess can be withdrawn through pipe 54 and put to any desirable use.

There are a number of ways of operating the apparatus other than the preferred way described and shown by the drawings. Thus for example, the recycled portion of the water gas may be led directly into pipe 20 from pipe l4 and the pump l9 may be replaced by a high pressure, high temperature steam injector which would supply steam and pressure for the steam and water gas mixture at the same time. In this method of operating, the steam boiler would be placed in line l1 and the unrecycled gases would generate steam before being scrubbed. Another example is that section 3 of pebble heater 2 may be eliminated and in this case the gas from dust collector I0 would pass directly into pipe l4 and process may then be carried out as described in the first part of this paragraph. These examples are given to illustrate the flexibility of the apparatus and method of the invention and are not intended to limit the scope of the invention.

The following data are given as an example of the operation of the method when carried out in the apparatus shown in the drawing. Enough dried coal at C. from drier 4| to contain 58.4 atomic equivalents of carbon and hydrogen of which 62.7 atomic percent is carbon and 37.3

atomic percent is hydrogen is introduced into thewater gas producer I. With each 58.4 atomic equivalents of the carbon and hydrogen in the dried coal 295 mols of a mixture of recycled water gas and steam at 1430 C. are reacted in producer to generate 343 mols of water gas which leave the producer I at 900 C. and contain 32% CO, 4% CO2, 57.2% Hz and 10.4% water 'by volume. The hot water gas passes to section 3 of pebble heater 2 whereit heats the pebbles and leaves the section at 410 C. The gas then passes to steam generator l5 where it generates steam and leaves at 210 C. 243 mols of the 343 mols of the water gas are recycled through blower i9 after which it mixes with 52 mols of steam at 125 C. and the mixture at C. enters section 5 of pebble heater 2 where it is heated to 1430 C. and is passed at that temperature to producer i The 100 mols of water gas at 210 C. remaining from the 343 mols leaving the steam generator I5 pass to scrubber 18. On a dry basis 52 mols of the scrubbed gas are withdrawn at 25 C. as product gas having a composition of 35.7% CO, 5.4% CO2, and 58.4% by volume hydrogen and a heating value of about 300 B. t. u. per cubic foot.

The remaining portion of the 100 mols amounting to 38 mols on the dry basis passes to combustion section 4 of the pebble heater 2 and is mixed with 270 mols of air that has been preheated in the tubular preheater 3| to a temperature of 825 C. The mixture of water gas and air burns in section 4 to produce 292 mols of gaseous products of combustion which leave this section at 925 C. The products of combustion or flue gases pass through the air preheater 3i, entering the heater at 925 C. and

7 leaving at 200' c. 1 142 mols of flue gas leaving tubular heater 8| pass through water preheater 80 leaving the preheater at 135 C. at which temperature it is vented to the open air. 52 mols of water at C. are heated to 100 C. by the 142 mols of flue gas passing through the preheater It. The 52 mols of water pass to steam generator I! where they are converted to 52 mols or steam at 125 C. and 36 pounds per square inch pressure. This quantity of steam is mixed with 242.5 mols of recycled water gas as described above.

The remaining 150 mols of the 292 mols of flue gas which is at 200 C. and which leaves the air preheater Ii pass to coal drier I where coal containing 5% water is dried. The 100 mole of flue gas increase to 150 mols of flue gas and water at 160 C. which is vented to the air.

Lignite, coke and hydrocarbon-bearing shales in addition to any type of coal may be used in the water gas producer I but it is preferred to use the flne coal that is usually discarded at the mine or sold at very low prices. It is possible to use the coal in any size but flne or pulverized coal is preferred and also it' is preferred to operate the apparatus in the vicinity of the coal mining flelds so that the line coal produced in handling coal and the discarded coal produced in the mining operation may be used.

It will be noted that our invention provides a method for the production of substantially nitrogen-free water gas containing predominantly hydrogen and carbon monoxide by heating in a pebble heater a mixture of steam and recycled water gas to water gas reaction temperatures and reacting the heated mixture with coal in a water gas producer. It will be noted also that the method makes possible the continuous production of water gas of a uniform controllable composition and that a water gas can be produced which has a consistent heat value of about 300 B. t. u. per cubic foot and that a, gas can be produced which is suitable for the Fischer- Tropsch Synthesis or methane production. The method has further utility in that it can be used to produce a gas containing a hydrogen content high enough to be used as a source of hydrogen for hydrogenation processes or for the synthetic production of fatty acids.

What we claim is:

l. A method of producing from coal a substantially nitrogen-free water gas which comprises reacting coal with steam at water gas reaction temperatures in a gas producer to form a hot water gas consisting predominantly of hydrogen and carbon monoxide, passing said but water gas in contact with a mass of relatively cool, movable discrete heat exchange solids in a solids preheating zone, removing the resulting preheated solids to a solids heating zone and heating them to a temperature above the desired water gas reaction temperatures by contact with hot products of combustion therein, separating the cooled water gas into a plurality of streams, adding steam to one of said streams and recycling it through a gas heating zone and back to the gas producer for reaction with coal, heating the recycled gas to water gas reaction temperatures by introducing the hot heat exchange solids into the path of said recycled gas in said gas heating zone removing the solids from the gas heating zone and recycling them to said solids preheating zone, and withdrawing a second stream of said cooled water gas as product gas from the process.

2. A method of producing from coal a substan- 8 tially nitrogen-free water gas which comprises reacting coal with steam at water gas reaction temperatures in a gas producer to form a hot water gas consisting predominantly of hydrogen and carbon monoxide. passing said hot water gas in contact with a mass of relatively cool, movable discrete heat exchange solids in a solids preheating zone, removing the resulting preheated solids to a. solids heating zone and heating them to a temperature above the desired water gas reaction temperature by contact with hot products of combustion therein, further cooling the partially cooled water gas by passing it in heat exchange relationship with water to form steam from said water, separating the cooled water gas into a plurality of streams, adding a portion of said generated steam to one of said streams and recycling it through a gas heating zone and back to the gas producer for reaction with coal, heating the recycled gas to water gas reaction temperatures by introducing the hot heat exchange solids from said solids heating zone into the path thereof in said gas heating zone removing the solids from the gas heating zone and recycling them to said solids preheating zone and withdrawing a second stream of said cooled water gas as product gas from the process.

3. A method of producing from coal a substantially nitrogen-free water gas which comprises reacting coal with steam at water gas reaction temperatures in a gas producer to form a hot water gas consisting predominantly of hydrogen and carbon monoxide, passing said hot water gas in contact with a mass of relatively cool, movable discrete heat exchange solids in a. solids preheating zone, removing the resulting preheated solids to a solids heating zone and heating them to a temperature above the desired water gas reaction temperatures by contact with hot products of combustion obtained by burning combustible material with preheated air in said solids heating zone, cooling said hot products of combustion from said solids heating zone by passing them in heat relationship with air, passing the resulting preheated air into said solids heating zone, separating the relatively cooled products of combustion into a plurality of streams, discarding one stream, passing another of said streams in drying contact with coal, then discarding the stream, passing said dried coal to said gas producer, further cooling the partially cooled water gas from said solids preheating zone by passing it in heat exchange relationship with water to form steam, separating the cooled water gas into a plurality of streams, adding a portion of said generated steam to one of said streams and recycling it through a gas heating zone and back to the gas producer for reaction with coal, heating the recycled gas to water gas reaction temperatures by introducing the hot heat exchange solids into the path of said recycled gas in said gas heating zone removing the solids from the gas heating zone and recycling them to said solids preheating zone and withdrawing a second stream of said cooled water gas as product gas from the process.

4. A method of producing from coal asubstantially nitrogen-free water gas which comprises reacting coal with steam at water gas reaction temperatures in a gas producer to form a hot water gas consisting predominantly of hydrogen and carbon monoxide, passing said hot water gas in contact with a mass of relatively cool, movable discrete heat exchange solids in a solids preheating zone, removing the resulting preheated solids to a solids heating zone and heating them to a temperature above the desired water gas reaction temperature by contact with hot products of combustion obtained by burning a portion of said water gas with preheated air in said solids heating zone, cooling said hot products of combustion from said solids heating zone by passing them in heat relationship with air, passing the resulting preheated air into said combustion zone, separating the relatively cooled products of combustion into a plurality of streams. discarding one of said streams, passing another in drying contact with coal, then discarding this stream, passing said dried coal to said gas producer, further cooling the partially cooled water gas from said solids preheating zone by passing it in heat exchange relationship with water to form steam, separating the cooled water gas into two streams, adding a portion of said generated steam to one of said streams and recycling it through a gas heating zone and back to the gas producer for reaction with coal, heating the recycled gas to water gas reaction temperatures by introducing the hot exchange solids in the path of said recycled gas in said gas heating zone removing the solids from the gas heating zone and recycling them to said solids preheating zone, washing and scrubbing the second stream of said water gas, separating it into two streams, mixing one of said streams with said preheated air and passing the mixture to said solids heating zone and withdrawing the remaining stream as product gas from the process.

EDWARD S. ROBERTS.

JOHN B. RINCKHOFF. FREDERICK C. CUNNINGHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 753,294 Naef Mar. 1, 1904 2,399,450 Ramseyer Apr. 30, 1946

Claims

1. A METHOD OF PRODUCING FROM COAL A SUBSTANTICALLY NITROGEN-FREE WATER GAS WHICH COMPRISES REACTING COAL WITH STREAM AT WATER GAS REACTION TEMPERATURES IN A GAS PRODUCER TO FORM A HOT WATER GAS CONSISTING PREDOMINANTLY OF HYDROGEN AND CARBON MONOXIDE, PASSING SAID HOT WATER GAS IN CONTACT WITH A MASS OF RELATIVELY COOL, MOVABLE DISCRETE HEAT EXCHANGE SOLIDS IN A SOLIDS PREHEATING ZONE, REMOVING THE RESULTING PREHEATED SOLIDS TO A SOLIDS HEATING ZONE AND HEATING THEM TO A TEMPERATURE ABOVE THE DESIRED WATER GAS REACTION TEMPERATURES BY CONTACT WITH HOT PRODUCTS OF COMBUSTION THEREIN, SEPARATING THE COOLED WATER GAS INTO A PLURALITY OF STREAMS, ADDING STREAM TO ONE OF SAID STREAMS AND RECYCLING IT THROUGH A GAS HEATING ZONE AND BACK TO THE GAS PRODUCER FOR REACTION WITH COAL, HEATING THE RECYCLED GAS TO WATER GAS REACTION TEMPERATURES BY INTRODUCING THE HOT HEAT EXCHANGE SOLIDS INTO THE PATH OF SAID RECYCLED GAS IN SAID GAS HEATING ZONE REMOVING THE SOLIDS FROM THE GAS HEATING ZONE AND RECYCLING THEM TO SAID SOLIDS PREHEATING ZONE, AND WITHDRAWING A SECOND STREAM OF SAID COOLED WATER GAS AS PRODUCT GAS FROM THE PROCESS.