US3787193A - Production of water gas - Google Patents

Abstract

Water gas is produced by blowing steam through carbon suspended in a coal ash melt in a gasification section, the endothermic heat of reaction being supplied by the ash melt, which is continuously recirculating through a separate superheating section where the ash is superheated by burning fuel separately introduced into that section; the superheated ash is then conveyed to the gasification section, substantially free of oxidative gas, preferably by means of a heated gas lift.

Description

baited States @atent 1191 Seglin et al.

PRODUCTION OF WATER GAS Inventors: Leonard Seglin, New York, N.Y.;

Charles A. Gray, Charleston, W. Va.

Assignee: FMC Corporation, New York, NY.

Filed: Nov. 18, 1971 Appl. No.: 200,152

U.S. c1 48/204, 48/202, 48/210 1111. (:1. C10j 3/00 Field of Search 48/202, 204, 210, 215

References Cited UNITED STATES PATENTS l2/l953 Kalbach 48/202 8/1954 Kalbach.... 48/210 X 9/1954 Schutte 48/204 X Jan. 22, 1974 2,840,462 6/1958 Gorin ..48/202X 3,194,644 7/1965 0011118181 .148/202x Primary Examiner-Morris O. Wolk Assistant ExaminerR. E. Serwin Attorney, Agent, or FirmRobert D. Jackson et a].

[57] ABSTRACT 3 Claims, 2 Drawing Figures CIRCULAT ING SLAG GASSI HE R WASTE COMBUSTION SYNTHESIS r GAS GASES 22 NR STEAM COAL OR CHAR 32 HEATING GASIFICATION SECTION A2 SECTION ,8//// I fl H H n I l L T) FUEL PAIENIED I974 3.787. 19 3 sum 1 or 2 CIRCULATING SLAG GASSIFIER WASTE COMBUSTION SYNTHESIS I GAS I GASES STEAM COAL OR CHAR 4 HEATING GASIFICATION SECTION '2 SECTION i A A l4 A 0 H H H *FUEL PRODUCTION OF WATER GAS BACKGROUND OF THE INVENTION A. Field of the Invention This invention is concerned with improvements in the process of making synthesis gas by the endothermic reaction of carbon and steam at elevated temperatures.

B. Prior Art The gasification of carbonaceous solids with steam to produce a synthesis gas containing high concentrations of hydrogen and carbon monoxide has been practiced for many years; this water gas" reaction is one of the classic processes of the fuel industry.

The principal difficulty with the process is that the reaction is endothermic, so that it is necessary to provide heat to the process. In older processes, a bed of carbon was arranged so that the lower portion of the bed was an oxidizing zone in which heat was developed; the water gas reaction was carried out in the upper portion of the bed. This meant that the CO in providing heat, was mixed with the steam, so that the synthesis gas produced contained substantially more carbon monoxide by volume than hydrogen, as distinguished from pure water gas, which contains one volume of hydrogen per volume of carbon monoxide.

One suggestion for overcoming this difficulty is the use of fluidized beds of carbon, utilizing a recycle stream of carbon which is superheated by partial combustion and separated from the carbon dioxide produced before being returned to the gasification section see, for example, Patton et a], US. Pat. No. 3,440,117. Such schemes involve elaborate cyclone systems to prevent excessive dusting, and rather high capital outlays.

An interesting scheme for gasifying coal with steam and CO is described in the Rummel US. Pat. No. 2,647,045 of July 28, 1953. He suspends his coal in a molten slag, and provides heat of reaction by burning a portion of the coal in the slag. He preferably keeps the CO of the exothermic reaction more or less separate from his synthesis gas by separating the reactor into two compartments, one for the heat-producing combustion, and one for the heat-consuming water gas reaction; the slag is continuously recirculated by convection, or by a combination of convection and momentum transfer from jets of his oxidizing air. The fuel for heating comprises a portion of his reduction carbon which is carried into the oxidizing compartment by the convection current.

Work with this process has shown that the process is inefficient on any scale above laboratory size. Convection circulation alone is too slow to get any substantial throughput in a reactor; momentum transfer helps, but introduces oxygen, plus nitrogen if air is used, and CO into the reducing zone. In addition, the rate of circulation is proportional to surface area, not to volume; as the operation is scaled up, it becomes progressively less efficient for circulation, with no gain as to heat losses.

OBJECTS OF THE INVENTION This invention aims to provide a circulating slag process for producing water gas which is efficient, becomes more efficient as it is scaled up, and overcomes the problem of dilution of the synthesis gas with combustion products.

STATEMENT OF THE INVENTION In accordance with the present invention, synthesis gas is produced by reacting coal or coal char and steam in a gasification section in the presence of a body of molten coal ash or other slag containing sufficient heat to cause the reaction to take place, continuously withdrawing molten ash cooled by the reaction to an oxidizing section, introducing fuel into the molten ash after it leaves the gasification section, heating the molten ash in the oxidizing section by introducing an oxidizing gas THE DRAWINGS In the drawings, FIG. 1 is a schematic flow sheet of the process of this invention.

FIG. 2 is a schematic flow sheet showing the process of this invention as applied to a scheme for making pipeline gas from coal.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, we provide a gasification section 10, a heat section 12, a pipe 14 for circulating molten coal 'ash from the gasification section 10 for heating section 12, and a pumping device 16 for recirculating superheated molten ash from the heating section back to the gasification section.

In the gasification section, a stream 18 of mixed molten ash and carbon (coal or coal char) is fed onto a bed 20 of molten ash. Steam is introduced into the bed 20, and reacts with the carbon to form synthesis gas, essentially H and CO in equal volumes. This runs off through a vent 22 to purification and storage.

The ash present in the carbon joins the ash pool, except that metallic elements such as iron are reduced and form a metal pool 24 in the bottom of the section; this is tapped off as required. The accretions of ash to the pool are dealt with by taking excess ash to waste.

The molten ash is continuously withdrawn through line 14 and circulates to the heating section. Fuel is introduced into the molten ash, either in the line 14 or in the oxidizing section 12, where a body of molten ash 26 is maintained. The fuel may be a portion of the synthesis gas, other gas, or solid fuel. In the drawing, it is shown as gas fed into the molten ash body 26 through lines 28, along with air in lines 30. The combustion gases are stacked (17) through a waste-heat boiler 32 and a heat exchanger 34, which preheats the air going into line 30; the waste gases are treated as necessary to remove fly ash.

The transfer device 116 is preferably a gas lift in which the gas for the lift is fuel from line 28 burned with air from line 30. At the top of the lift, the ash is separated from the combustion products in a space 36, and the gas is vented into the main stack of the heating section.

A screw conveyor 38 feeds the reactant carbon into the recycle superheated ash just before it enters the reducing section, so that the two form the single stream 18 previously described.

The gasifier may be operated at any temperature from 1,600 F upward, but since the coal ash must be The process may be used in an over-all scheme to produce a synthetic pipeline gas to be used as a substitute for natural gas, as shown schematically in FIG. 2.

kept liquid, operations are conducted above the melt- Coal 1 is subjected to multistage pyrolysis to produce ing point of the ash, so as to make it unnecessary to char 2 and a tar-forming vapor stream 5. This stream add fluxes to the ash to lower the melting point. Temis divided into a noncondensible gas stream 8, a liquid peratures of the order of about 2,lO0 to 2,500 F are tar stream 7 and an aqueous liquor stream 6 which is preferred. treated and discharged. The tar is treated with hydro- The endothermic heat of reaction is sufficiently great gen 9 to form a synthetic crude oil 10A. so that, in order to get economic recycle rates, the The char stream 2 is divided, part 4 going to the gasheating section should be operated at a temperature at ifier 10 and part 3 going to the heater 12 in line 28. In least about 225F above the gasifier temperature. Typthe gasifier 10, the char is converted into water gas, ically, the molten ash enters the gasifier in a ratio of whence it passes through line 22 through a waste-heat about to 60 parts by weight of molten ash to One 15 boiler 32C to join the gas in line 8; the gas is purified, part by weight of added carbon. methanated and discharges as pipeline gas (line 4).

The carbon used may be coal or any rank from peat 6 Stack g es from the heater (line P to anthracite, or any char prepared from coal. With through waste-heat boiler 32A and an air preheater 34, coal or coal char, the molten coal ash becomes the preferably also through asteam-reheater 42 used to suheat-transfer medium. 0 perheat feed steam into line 11 for feeding to the gas- The process is also applicable to low-ash carbons ifier; this steam comes from line 40, being the steam such as petroleum coke. With such feeds, a synthetic discharged from a generator operated by steam (line molten ash can be prepared, and the process can be op- 19) coming from the waste- heat boilers 32A and 32C. erated at a lower temperature by choosing a melt which is lower-melting. However, the use of molten coal ash as the heat-transfer medium offers marked economic EXAMPLE OF THE INVENTION advantages over the use of other heat-transfer media, A plant for making 250 million standard cubic feet of particularly when combined with the fact that verysynthesis gas per day has been designed on the basis of low-cost coals may be used. laboratory and pilot plant work. Using Illinois No. 6 The superheater section, gasification section and air coal (a bituminous A coal), the table below shows the lifts are preferably water-jacketed, so as to freeze a amounts of material, and their COmPOSitiOH, being fed layer of slag adjacent the refractory walls, in known through the various Streams ShOWn In FIG. 2 0f the fashion, to minimize attack on the refractories. gi 111 p u P hour! TABLE Stream No. Identification Flow (lb./hr.) Temperature (F) Pressure (psi) 1 Coal feed 2,158,000 Room 60 2 Char from pyrolysis 1,317,000 1000 60 3 Char to heater 715,000 1000 60 4 Char to gasifier 602,000 1000 60 5 Vapors from coal pyrolysis 841,000 700 60 6 Liquor from tar recovery 50,000 140 60 7 Tar from tar recovery 562,000 140 60 8 Pyrolysis gases from tar recovery 229,000 140 60 9 Hydrogen to hydrotreating 45,000 Room 3000 10A Syncrude (42,000 bbl./day) 583,000 Room mm. 1 1 Steam to gasifier 752,000 1000 60 22 Gases from gasifier 1,253,000 2500 60 13 Slag tapped from gasifier 205,000 2500 60 14 Slag from gasifier to heater 28,620,000 2500 60 16 Slag from heater to gasifier 28,732,000 3000 60 30 Preheated air to heater 7,533,000 1000 60 17 Combustion gases from heater 8,137,000 3000 60 38 Feed water to waste-heat boiler 2,457,000 100 900 19 Steam from waste-heat boiler to power turbine 2,457,000 1000 900 40 Steam extraction from power turbine 752,000 320 41 Pipeline gas from methanation (250,000,000 cu. 454,514 1000 ftJday) CHEMICAL ANALYSIS OF STREAM PRODUCTS Stream No. Carbon Hydrogen Oxygen Nitrogen Sulfur Ash Obviously examples can be multiplied without departing from the scope of the invention as defined in the claims.

We claim:

1. Method of producing synthesis gas from carbon and steam in a gasifier consisting of gasification and heating zones physically separated from each other which comprises l introducing carbon and steam into the gasification zone in the presence of a body of molten slag heated to a temperature sufficient to cause the carbon to react with the steam to produce carbon monoxide and hydrogen; (2) continuously withdrawing molten slag cooled by the reaction from the gasification zone to the heating zone; (3) introducing fuel into the molten slag after it leaves the gasification zone; (4) burning the fuel with oxygen in the heating zone to heat the slag to a temperature at least 225 F higher than its temperature when withdrawn from the gasification zone; and (5) continuously propelling the molten slag into the gasification section after separation of the products of combustion used to heat the slag.

2. The method of claim 1, in which the heated slag is propelled into the gasification zone by an air lift operated by hot products of combustion.

3. The method of claim 1, in which the carbon is coal or coal char, and the slag is ash derived from the coal or coal char.

Claims (2)

1. 2. The method of claim 1, in which the heated slag is propelled into the gasification zone by an air lift operated by hot products of combustion.
2. 3. The method of claim 1, in which the carbon is coal or coal char, and the slag is ash derived from the coal or coal char.

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