NL8201715A - PROCESS FOR GASIFICATION OF A SOLID CARBON-FUEL FUEL. - Google Patents

Description

- 1 - a- -¾

K 9324 NET

PROCESS FOR GASIFICATION OF A SOLID CARBON-FUEL FUEL

The invention relates to a process for gasifying a solid carbonaceous fuel, characterized in that a) the fuel is ground and dried, 5b) the fuel is subsequently partially burned to synthesis gas using oxygen or oxygen-enriched air which oxygen comes from an air separation apparatus, c) the synthesis gas is cooled to a temperature of 100-500C, and d) the cooled synthesis gas is further cooled to a temperature of 25-250 ° C by of indirect heat exchange with a nitrogen-rich gas from the air separation device.

During the gasification (partial combustion) of a solid carbonaceous fuel, synthesis gas is formed that mainly consists of carbon monoxide and hydrogen. Suitable solid fuels are coal, brown coal, coke, peat, wood, etc.

A solid fuel is generally less reactive than a gaseous or a liquid fuel. In order nevertheless to obtain a rapid reaction, the solid fuel is finely ground. The finely ground fuel is then transported to a gasification reactor. A fuel containing a relatively large amount of water can become lumpy during transport and thus cause blockages in the transport pipe. To prevent this, the solid fuel is dried before being transported to the reactor. After drying, the moisture content of the fuel is preferably 0 to 10% by weight. The solid fuel is partially burned with oxygen or oxygen-enriched air since the reaction proceeds faster than with air. Furthermore, the synthesis gas 8201715 • J v - 2 - now contains less nitrogen than when gasifying with air. This makes the subsequent purification of the synthesis gas easier. In addition, synthesis gas prepared with oxygen is more suitable for certain syntheses, eg those of methanol or hydrocarbons.

The oxygen required as a reactant is prepared in an installation where air is separated into an oxygen-rich and at least one nitrogen-rich gas. Cryogenic distillation is used for this.

Preferably the partial combustion takes place in the presence of a moderator. The moderator moderates the temperature in the reactor by reacting endothermally with the reactants and / or the partial oxidation products. Suitable moderators are steam and carbon dioxide.

After the fuel has reacted with the oxygen, the synthesis gas generated leaves the reactor at a temperature of 1200 ° C to 1700 ° C. In addition to carbon monoxide and hydrogen, the gas also contains carbon dioxide, water vapor, sulfur compounds, methane and small amounts of hydrogen cyanide and ammonia. In addition, it carries 20 snail droplets. The snail droplets can cause problems when they cool down. They have no melting point, but a melting range that can be hundreds of degrees Celsius. Because they are tacky in the melting range, they can cause blockages. When coal is used as fuel, the slag is usually tacky in the temperature range of 900-1500 ° C. Solid snail is no longer sticky. Therefore, the hot gas is preferably rapidly cooled to a temperature of 700-900 ° C by injecting a cold gas or a cold liquid. Due to the rapid cooling, the snail droplets quickly solidify into solid particles. Suitable coolants are recycled synthesis gas, water and / or steam. The cooled synthesis gas is then further cooled to 100-500 ° C, preferably in a waste heat boiler, generating useful high-pressure steam. After this, the solid slag particles are preferably removed from the gas.

8201715 * "- 3 -

After the solid slag particles have been separated from the gas, the synthesis gas is further processed. For example, the other impurities are then removed from the synthesis gas. For this purpose it is advantageous to lower the temperature of the contaminated synthesis gas 5 to 25-250 ° C. This has hitherto been done by means of air or water coolers. However, the residual heat from the synthesis gas was not put to good use.

The cryogenic distillation of air produces a nitrogen-rich gas that is generally vented into the atmosphere. It is also possible that, in addition to an oxygen-rich gas, pure or substantially pure nitrogen and a waste nitrogen stream are supplied. The pure nitrogen is preferably used in the process, for example as a carrier gas for the finely ground fuel during transport to the reactor. Another application is in the ammonia synthesis. The waste nitrogen stream, which still contains a few percent oxygen, is usually discharged. The temperature of the nitrogen-rich gas that is vented is generally chosen to be about 10 ° C lower than the temperature of the ambient air.

In the process of the present invention, the relative cold of the nitrogen-rich gas is utilized. The synthesis gas is further cooled to a temperature of 25-250 ° C by indirect heat exchange with the nitrogen-rich gas.

The above-mentioned indirect heat exchange can take place immediately after the passage of the synthesis gas through the waste heat boiler.

Preferably, however, the solid slag particles are first removed from the synthesis gas at least in part. This is done in a suitable separating device, such as a cyclone, bend separator, filter and the like. separator 30 is at least partly stripped of the solid slag particles, the heat exchange between the synthesis gas and the nitrogen-rich gas preferably takes place. Although in the separator at least most of the solid slag particles have been separated from the synthesis gas, solid slag particles may remain in the gas and these residual slag particles present a risk of contamination of the cooler. Therefore, the synthesis gas is even more preferably 8201715 - 4 -

V V

only cooled further by indirect heat exchange with the nitrogen-rich gas after washing with water at least once. Upon washing, an aqueous suspension of solid slag particles and synthesis gas is obtained, which is purified practically entirely from slag particles. The aqueous suspension is separated from the synthesis gas and advantageously recycled at least partly back into the system. Suitable washing devices are venturi scrubbers and gas washing columns in which the gas and water are brought into contact with each other in countercurrent.

10 The synthesis gas already cools during washing. By means of the indirect heat exchange with the nitrogen-rich gas, the synthesis gas is further cooled, preferably to a temperature of 40 ° C to 140 ° C.

The washing gas contains a lot of water vapor. It is preferable to dry the gas. The easiest way to do this is to cool the synthesis gas below dew point, so that part of the water vapor condenses. When cooled deep below the dew point, most of the water vapor condenses. The separation between the dry gas and the condensate follows. Preferably, the synthesis gas is cooled to well below the dew point in a cooling which takes place after the indirect heat exchange with the nitrogen-rich gas. The synthesis gas is advantageously cooled in this cooling to a temperature of 10 ° C to 75 ° C. The cooling can take place with both air and water. Since the synthesis gas has already cooled to 25-250 ° C by means of the indirect heat exchange with the nitrogen-rich gas, a relatively small cooler will suffice.

The nitrogen-rich gas heated according to the invention is preferably used to dry the solid fuel. Drying takes place before the fuel is fed into the gasification reactor. When the solid fuel is supplied as not too coarse chunks, drying can take place before it is fed to the grinder. If the fuel consists of large clogs, drying during and / or after grinding is more efficient. If the fuel contains a lot of water, the warm nitrogen-rich gas can already be used, if not after further heating, to dry the fuel in whole or in part. In the latter case, the drying to the desired water content takes place later in another way or with another warm gas. Many types of grinders 5 can be used. Depending on the type of grinder, drying takes place during or after grinding. If, for example, a ball mill or a mill with rollers is used, the warm nitrogen-rich gas is fed into the mill and already exerts its drying effect during the grinding. Thereafter, the warm nitrogen-rich gas is used to discharge the finely ground fuel from the grinder and dries the fuel particles during transportation.

For drying the solid fuel, the nitrogen-rich gas is preferably heated to a temperature which, depending on the water content of the fuel, ranges from 50 to 400 ° C. A temperature of 90 ° C to 150 ° C is suitable for the majority of fuels. The lower temperature limit is such that there is just a driving force to remove the water present from the fuel. The upper temperature limit is determined by economic motives. The heat content of the synthesis gas is such that the required amount of the nitrogen-rich gas can be heated to a temperature of up to 400 ° C.

As mentioned previously, the nitrogen-rich gas is preferably the waste nitrogen stream generated in the cryogenic distillation of air. The invention is not limited thereto. Any nitrogen-rich gas from the air separation device can be used. If a nitrogen-rich gas with a relatively large amount of oxygen is used therein to dry the finely ground fuel, there is a risk of explosive combustion of the fuel with the oxygen. Therefore, the nitrogen-rich gas preferably contains less than 12% by volume of oxygen; even more preferably less than 10% by volume. The waste nitrogen stream meets these requirements.

The invention is now further elucidated on the basis of the figures to which the invention is in no way limited, however.

♦ Q

- 6 - schematic figures are aids such as compressors, pumps, valves and the like.

In Figure 1, a carbonaceous solid fuel is fed through a conduit 1 into a grinder 2. Via a conduit 3, a stream of warm nitrogen-rich gas is fed into the grinder 2, where the gas dries the finely ground fuel. Finely ground and dried fuel is led via the pipe 4 to a separator 5 with the gas mixture of, inter alia, nitrogen and water vapor. Suitable separators are, for example, curve separators, cyclones, filters, etc. In separator 5, the finely ground fuel is separated from the gas. The gas, which mainly consists of nitrogen and water vapor, is vented through a pipe 7. The separated fuel particles are fed via line 6 to a reactor 8. (Since the gasification reactor 8 preferably operates at elevated pressure, the fuel is pressurized using compressors, storage vessels, locks, etc., not shown in the figure). An oxygen-rich gas, originating from an air separation device 10, is also fed into reactor 8 via a pipe 9. In the air separator 10, air is supplied via a pipe 11. There, an oxygen-rich gas stream is formed, which is passed via the pipe 9 to the reactor 8, and a substantially pure nitrogen stream, which can be used at least partly in the transport of the fuel to reactor 8 via line 6. (This flow is not shown in the figure). The device 10 also produces a waste nitrogen stream which is discharged via a line 12. In the reactor 8, the gasification of the carbonaceous fuel with the oxygen and a moderator (steam or CO2) which is supplied via a line 13 takes place. The generated synthesis gas, which is loaded with 30 slag droplets, is fed via a conduit 14 to a cooling zone 15 where it is cooled by injection with a cooled and purified recirculated synthesis gas which is supplied via a conduit 16. In the cooling zone 15, all slag droplets solidify in the hot synthesis gas. Via a line 17, a mixture of synthesis gas and solid slag particles is discharged from the cooling zone 15 and placed 8201715 in a waste heat boiler 18 where it is cooled indirectly with water supplied via a line 19 and discharged as steam via a line 20. From the waste heat boiler 18, the still warm mixture of synthesis gas and solid slag particles 5 is fed via a line 21 to a venturi tube 22. There it is contacted with a suspension of solid slag particles in water which is brought via a conduit 23 to the venturi tube 22. In the venturi tube 22, all the water of the slurry evaporates and a mixture of synthesis gas, water vapor and solid slag particles is passed through a conduit 24 to a cyclone 25 where the majority of the solid slag particles are separated from the gas mixture and through a conduit 26 is drained from the installation. The remainder of the solid slag particles, together with the gas mixture, is fed via a pipe 27 into a venturi scrubber 28 and contacted here with an aqueous suspension of solid slag particles which is supplied via a pipe 29. The mixture of synthesis gas, water vapor, water droplets and solid slag particles that is formed in the venturi scrubber 28 is brought to a separator 31 via a pipe 30. Here, an aqueous suspension of solid slag particles is separated from the gas mixture and discharged via the pipe 23. The aqueous suspension is brought to venturi tube 22 via line 23. The mixture of synthesis gas and water vapor, which still contains a small amount of solid slag particles, is fed via a conduit 32 at the bottom of a gas washing column 33, where it is contacted countercurrently with water which is supplied via a conduit 35 at the top of column 33. In the column 33, the last residues of solid slag particles are removed from the gas mixture to form an aqueous suspension of solid slag particles which is passed through the pipe 29 from the column 33 to the venturi scrubber 28. The gas mixture which is now practically free of solid slag particles is brought via a conduit 34 to a cooler 36 where the synthesis gas mixture is further cooled and the waste nitrogen stream is heated by indirect heat exchange with the cold waste nitrogen stream from the line 12. The resulting hot stream 8201715-8 - is discharged through line 3 from cooler 36 and is supplied to grinder 2. When the synthesis gas mixture is cooled below dew point in cooler 36, a mixture of synthesis gas, water vapor and water brought via a pipe 37 to an air cooler 38, where air is supplied via a pipe 39 and exhausted via pipe 40. Here cooling takes place deep below the dew point, so that almost all the water condenses. When cooling in the cooler 36 to a temperature above> dew point of the gas mixture, the pipe 37 contains only synthesis gas and water vapor. From the cooler 38, a mixture of synthesis gas, condensed water and a small amount of water vapor is supplied to a separator 42 via a pipe 41.

In the separator 42 the mixture is split into condensate which is discharged via a pipe 43 and a substantially dry synthesis gas which is discharged via a pipe 44. Part of the condensate is recycled via line 35 to column 33. The remaining part is discharged from the installation through line 45. Part of the substantially dry synthesis gas is returned to cooling zone 15 via line 20 16. The remaining part of synthesis gas is discharged from the installation as a final product for further processing via a pipe 46.

Figure 2 shows another embodiment of the method according to the invention. This method is ideally suited for use with solid fuels containing a relatively large amount of water. Immediately after the synthesis gas has left the waste heat boiler 18, it is fed via line 21 to a heat exchanger 101, where it is cooled using a pre-heated stream of nitrogen-rich gas which is supplied through a line 102 to the heat exchanger 101 and through a line 103 discharged to grinder 2. The cooled synthesis gas is fed via line 105 to venturi tube 106. There it is brought into contact with a water flow through a conduit 107. All the water supplied evaporates in the venturi tube 106. The gas mixture is fed via a conduit 108 to a bag filter 109. There, the solid slag particles are separated from the gas mixture 8201715 I-9. The separated solid slag particles are discharged from the installation via a line 110. The gas mixture is fed via a line 111 to the cooler 36 and from there via the line 37 to the cooler 38. Water vapor condenses in coolers 36 and 38. After separating the condensed water from the synthesis gas in the separator 42, part of the water is fed via the line 107 to the venturi tube 106. In the cooler 36, the cold nitrogen-rich gas stream is supplied via line 12 and, after heating, via line 3. The slightly warm gas stream 10 can be further heated by indirect heat exchange with superheated steam in a heat exchanger 104 where the steam is supplied through a line 112 and discharged through a line 113. For example, steam obtained in the line 20 can be used. It is also possible to use steam injection in the nitrogen-rich gas stream instead of indirect heat exchange with steam to increase the temperature of the gas stream. The warm nitrogen-rich gas flow is directed to the heat exchanger 101. There he cools the synthesis gas further and he heats it further. The hot gas stream is then fed via line 103 to the grinder 2 to dry the fuel.

EXAMPLE 1

According to a method as described in Figure 1, 45.8 tons per hour (t / h) of coal of the following composition is fed to the mill 2: C 67.3 wt% H 4.4 "N 1.5 "0 5.9"

S 2.9 M

shaft 12.0 "water 6.0 11

To this is added 123.3 t / h of a nitrogen-rich gas flow of 120 ° C. The gas has the following composition: 8201715 - 10 _ N2 + Ar 95 mol.% 02 4 "h2o 1"

In a filter 5, the finely ground coal is separated from the gas. Coal powder is fed to reactor 8 via line 6, 43.93 t / h. 125.17 t / h of the nitrogen-rich gas is discharged with water vapor via line 7. The gas has a temperature of 70 ° C and the following composition: N Ar 92.8 mol% 02 3.9 · H2O 3.3 "

The water content in the coal powder is still 2.0% by weight. The temperature of the synthesis gas generated in the reactor 8 in the line 21 is 360 ° C.

It is still 130 ° C after washing with water. In the cooler 10 36, 176.5 t / h synthesis gas is cooled with 123.3 t / h nitrogen-rich gas at 10 ° C. The temperature of the mixture of synthesis gas, water vapor and water now formed is 122 ° C; the nitrogen-rich gas is heated to 120 ° C. In the cooler 38, the temperature of the synthesis gas-containing mixture 15 is lowered to 50 ° C via air cooling, whereby a total of 19.1 t / h of water vapor condenses. After the separation of the mixture in the separator 42, 1.55 t / h water is passed through the line 45 and 84.5 t / h synthesis gas of the following composition is discharged from the installation through the line 46: CO 62.2 mol% H2 27.6 "CO2 2.0" h2s 1.0 "H20 0.6" N2 5.6 -

Ar 1.0 "8201715 f ΐ - - 11 - EXAMPLE 2

In a method, as described in figure 2, 50 t / h of brown coal is fed to the mill 2. The brown coal has the following composition: C 39.6 wt.% H 3.0 "N 0.7" 0 10.3 ”S 0.7" ash 10.8 "water 34.9" 5 Via line 103, added 135 t / h nitrogen-rich gas of 370 ° C with the following composition: N ^ + Ar 95 mol.% ° 2 4 "h2o 1"

After separation in filter 5, 35.8 t / h of lignite powder is fed via line 6 to reactor 8 and 149.2 t / h nitrogen-rich gas is purged with water vapor via line 7. The blown gas has a temperature of 90 ° C and the following composition: - N2 + Ar 81.6 mol% 02 3.4 "H20 15.0"

The water content in the brown coal powder is still 9% by weight.

The temperature of the synthesis gas generated in the reactor 8 in the line 21 is 400 ° C. In the heat exchanger 101 this temperature is lowered to 220 ° C, the nitrogen-rich gas in the line 102 of 180 ° C being heated to gas of 370 ° C, which is fed via the line 103 to the mill 2. The gas coming out of the bag filter 109 still has a temperature of 180 ° C. In the cooler 36, 103.1 t / h synthesis gas is cooled to 98 ° C with 135 t / h cold nitrogen-rich gas at 10 ° C. The nitrogen-rich gas is thereby heated to 160 ° C. This gas is further heated in steam heat exchanger 104 to 180 ° C, after which it is fed via line 102 to heat exchanger 101. The mixture of synthesis gas, water vapor and water formed in the cooler 36 is cooled in the air cooler 38 to 50 ° C, whereby a total of 7.1 t / h of water vapor condenses. After the separation of the mixture into the separator 42, 5.4 5 t / h water is discharged from the installation via line 45 and 58.0 t / h synthesis gas of the following composition is passed through line 46: CO 59.1 mol. %.

H2 28.1 "CO2 6.1" H2S 0.5 "H20 0.6" N2 4.4 "

Ar 1,2 "8201715

Claims (8)

A method for gasifying a solid carbonaceous fuel, characterized in that: a) the fuel is ground and dried, b) the fuel is subsequently partially burned to synthesis gas using oxygen or oxygen-enriched air, which oxygen comes from an air separation device, c) the synthesis gas is cooled to a temperature of 100 ° C to 500 ° C, 10 d) the cooled synthesis gas is further cooled to a temperature of 25-250 ° C by means of of indirect heat exchange with a nitrogen-rich gas from the air separation device. 2. Process according to claim 1, characterized in that the synthesis gas is further cooled by means of the indirect heat exchange with the nitrogen-rich gas after at least partly the solid slag particles have been removed from the synthesis gas. 3. Process according to claim 2, characterized in that the synthesis gas is further cooled by means of the indirect heat exchange with the nitrogen-rich gas to a temperature of 40 ° C to 140 ° C. 4. Process according to one or more of the preceding claims, characterized in that the synthesis gas is cooled even further after the indirect heat exchange with the nitrogen-rich gas to a temperature of 10 ° C to 75 ° C in a cooler. Method according to one or more of the preceding claims, characterized in that the nitrogen-rich gas is heated to a temperature in the range from 50 ° C to 400 ° C. 6. Process according to one or more of claims 1 to 5, characterized in that the nitrogen-rich gas thus heated is used to dry the solid fuel. The method of claim 1, as described above, with special reference to the figure. 8201715 μ - 14 - Synthesis gas as far as obtained by the method according to one or more of the preceding claims. 8201715