EP0049324B1 - Process and installation for smouldering oil shale - Google Patents

Description

Many methods are known for smoldering oil shale. The oil shale is heated, whereby the kerogen contained in the shale decomposes and can be obtained in the form of gaseous and liquid hydrocarbons. Depending on the hydrogen content of the oil shale, a more or less large proportion of the organic substance can be obtained, some of it always remains on the shale as residual carbon. In the interest of making the most of the energy content of the oil shale, this carbon should also be used for energy.

Many processes use the shaft furnace principle for smoldering, e.g. US Pat. No. 3,736,247 and DE-B 2,243,389. It is disadvantageous that the proportion of fines which is inevitably obtained during comminution cannot be used. In addition, the complete combustion of the residual carbon is very difficult due to the required size of the general cargo. Furthermore, the oil vapors and the carbonization gas are exposed to the carbonization temperature for a long time, which results in cracking reactions which lead to a reduction in the yield and a deterioration in the oil quality.

GB-A 668 808 describes a process for smoldering oil shale with a hot gas in a shaft furnace, the condensable constituents being separated from the smoldering gas, a proportion of the smoldering gas corresponding to the increase in the gas quantity being removed and the rest after heating up in the smoldering reactor is returned. The solid, still carbon-containing smoldering residue introduces an oxygen-containing gas, in particular air, into another part of the shaft furnace separated from the smoldering part in order to burn part of the carbon and to increase the temperature of the residue. Then, in a third, also separated part of the shaft furnace, the cooled, de-condensable gas is passed through the residue heated in this way, in order to heat it up again, whereupon it flows in countercurrent through the smoldering part of the smoldering furnace, where it causes the oil shale to smolder, and is then passed through fresh oil shale so that the oil contained in it after condensation at least partially condenses.

The shaft furnace principle can no longer be used for finely shredded goods. Other methods using fines such as US-A 3 844 930 work with solids as heat carriers. The amount of solids to be handled is further increased by the amount of heat transfer medium which is a multiple of the amount of shale used.

From DE-A 2 728 204 and 2 728 455 it is known to carry out the pyrolysis of carbon-containing material, including oil shale, in a cyclone reactor. The carbonaceous material is fed into a cyclone reactor with a grain size of less than 1 mm in a carrier gas stream at speeds of 20-76 m / sec. In front of or in the inlet of the cyclone, this gas stream is mixed with a second gas stream which contains hot solid particles which are intended to heat the carbon-containing material to the low temperature. The weight ratio of the solids used for heating to the carbon-containing material should be between 2 and 20. After a short contact time - calculated as the average residence time of the carrier gas in the cyclone - of less than about one second, in particular between 0.1 and 0.6 sec, the carbonization gas mixed with the carrier gases is separated from the solids - heat transfer particles and carbonization residue.

In this known method, the smoldering gases are produced in dilution by the carrier gases, which makes their work-up more difficult. The smoldering residue leaves the cyclone in a mixture with the solid heat transfer media, so that larger amounts of ballast must also be carried along during its further processing.

Surprisingly, it would now be found that the smoldering of oil shale, in which the condensable constituents are separated from the smoldering gas, a portion corresponding to the increase in the amount of gas was removed and the rest was re-heated and returned to the smoldering reactor, despite that compared to smoldering in shaft furnaces can make several orders of magnitude shorter carbonization times in a cyclone reactor, the carbonization gas being indirectly heated and fed back into the carbonization cyclone reactor as the sole heat transfer medium. Oil shale and heating gas are conducted in direct current.

This gives a pure, undiluted carbonization gas from which the condensable components can be separated out better than from a carbonization gas diluted with carrier gas and which, even after the condensable components have been separated off, has a higher value than the diluted carbonization gas because of the higher concentration of gaseous hydrocarbons. In the same way, the processing of the smoldering residue is facilitated by the lack of fiber.

The smoldering temperatures are generally above 450 ° C and should not exceed 650 ° C, otherwise the reduction in yield due to cracking reactions cannot be avoided despite the short smoldering times. Temperatures between 470 and 550 ° C. are preferred. The attached Fig. 1 shows the yields in the cyclone swelling of a Schandelah oil shale compared to the yields according to the Fischer test. The oil shale used contained 10.3% by weight of organic carbon and had the following Fischer test yields:

In the process according to the invention, the carbonization gas is preheated to temperatures which are 150 to 250 K above the carbonization temperature. This overheating depends on the ratio of carbonization gas to oil shale, which is usually between 0.8 and 1.4 Nm ³ / kg, preferably between 1.0 and 1.2 Nm ³ / kg lies on the temperature of the slate used, on the residual moisture, on the carbonate decomposition of the carbonates contained, and on the heat losses of the system.

In order to avoid a stronger heating of the recirculated carbonization gas, it is advisable to pre-dry the oil shale to a large extent and to preheat it to a temperature just below the start of the kerogen decomposition.

Surprisingly, it was also found that coarser feed material can be used in the method according to the invention than in the known method. Oil shale with a grain size of up to 3 mm, even up to 5 mm, can be used. These coarse-grained slates have the advantage of containing less dust, which considerably facilitates both the processing of the carbonization gas and the further treatment of the carbonization residue.

In Fig. 2, the residual carbon content of the above-mentioned oil shale after smoldering is plotted as a function of its grain size. It can be seen that the carbonization with grain sizes of 2 mm is practically the same as with grain sizes of 0.1 mm and even with grain sizes of 3 mm there is only an insignificant increase in the residual carbon content.

The condensable components are separated from the carbonization gas by cooling it directly with cold oil, possibly with subsequent electrostatic precipitation of the oil mist.

It has proven to be expedient to remove dust contained in the carbonization gas before the condensable components are separated, since the separation of the condensate from the dusts is very difficult. For separating the dusts e.g. High performance cyclones are used.

However, deposition by means of electrofiltration has proven to be particularly expedient. This is quite surprising, because it was not to be expected that the high temperatures of more than 450 ° C would allow electrofiltration of the carbonization gases, since the electrical field would collapse in a reducing atmosphere without the presence of sulfuric vapors. The smoldering residue is withdrawn from the cyclone reactor; its carbon is expediently burned with oxygen-containing gases, in particular air, it being possible for the hot combustion gas to be used for preheating the circulating carbonization gas.

The carbon of the carbonization residue is expediently burned with oxygen-containing gases in a fluidized bed. The combustion conditions must be set so that S0 ₂ produced during combustion is integrated into the residue due to dolomite and calcite which may be found in the shale.

To improve the smoldering yield, the smoldering residue discharged from the smoldering cyclone reactor can first be degassed in a container before its carbon is burned with oxygen-containing gases. Through the smoldering residue in the degassing tank, smoldering gas can be passed through for faster removal of the gases still present, it being expedient to loosen up the smoldering residue with stirrers or to shift it in a rotating drum.

The known device, in which the gas discharge of the smoldering reactor is connected to an oil separator and the inlet connector of the smoldering reactor is connected to the oil separator via a blower, has a cyclone reactor with a tangential inlet connector and a heat exchanger between the blower and the tangential inlet connector of the smoldering cyclone reactor for carrying out the method according to the invention . A preheater for the oil shale to be smoldered is preferably provided in front of the tangential inlet connection of the smoldering cyclone reactor.

According to a special embodiment of the invention, a dust separator operating at temperatures of the dew point of the carbonization gases, in particular an electrostatic filter, is arranged between the carbonization cyclone reactor and the oil separator. According to a further embodiment of the invention, the solids discharge of the smoldering cyclone reactor is connected to a combustion furnace and its hot gas outlet is connected to the heat exchanger provided for heating the smoldering gas serving as carrier gas. It has also proven to be expedient to provide a post-carbonization drum on the solid discharge port of the smoldering cyclone reactor or between this discharge port and the combustion device for smoldering residue.

A device according to the invention is shown schematically in the attached FIG. 3. The method according to the invention is explained on the basis of this: The oil shale 1 is comminuted to a grain size of less than 3 mm. The comminution and screening is expediently carried out together with the drying and preheating in a mill dryer 2, for which purpose the flue gases 3 are used after the cycle gas preheater 4. The cooled flue gas is discharged via line 5.

The crushed, dried and preheated oil shale 6 to approx. 110 ° C is mixed in the riser 7 with circulating hot gas 8, a substantial part of the heat being transferred from the heating gas to the slate in the riser pipe, and this mixture via the tangential feed 9 in led the smoldering cyclone 10. The oil and dust-containing carbonization gases leave the carbonization cyclone 10 via line 11, while the carbonization residue is fed via line 12 into a re-carbonation drum 13. In order to accelerate the removal of the smoldering gases formed, part of the hot recycle gas is passed through line 14 into the re-carbonation drum 13. The smoldering and cycle gas 15 from the after-carbonization 13 is led together with the smoldering gases 11 from the smoldering cyclone into a dedusting system 16. The separated dust is fed via line 17 into the post-carbon drum 13. The dedusted gas passes through the pipeline 18 into the oil separator 19, where it is freed of the condensable fractions which are supplied as product via the line 20 to the further processing. From the oil separation 19, a part of the smoldering gas corresponding to the amount of gas obtained during the pre-carbonization is likewise produced as a product via the line 21 dissipated. The remaining carbonization gas is fed via line 22 to the compressor 23 and, after compression through line 24, reaches the cycle gas preheater 4.

The hot smoldering residue 25 behind the post-carbonization drum 13 is fed to a fluidized bed incinerator 26, in which the residual carbon is burned off. The temperature control for setting the optimal SO ₂ integration is carried out by the heat exchanger 27 in the fluidized bed, which is designed as a steam generator. The hot flue gas leaves the fluidized bed furnace via line 28. The heat content of this gas is used in the cycle gas heat exchanger 4 for smoldering and in mill drying 2 for drying and preheating the oil shale.

The burned-off oil shale from the fluidized bed furnace is fed through line 29 to a cooler 30 and leaves the cooler via line 31. For cooling, the combustion air 32, which is compressed in the compressor 33, is led via line 34 to the cooler 30 and via the line 35 reaches the fluidized bed furnace 26.

Claims (15)

1. Method for distillation of oil shale in a hot gas in a distillation reactor, the method including separating the condensible portions from the distillation gas, removing a portion of the gas corresponding to the increase inthe amount of gas, re-heating and passing back the rest of the gas into the distillation reactor, characterised in that a cyclone reactor is used, the distillation gas is re-heated indirectly and feeded back into the distillation cyclone reactor for sole heat carrier.

2. Method according to claim 1, characterised in that the oil shale is pre-heated to temperatures below the distillation temperature and dried before it is placed in the distillation gas.

3. Method according to claim 1 or 2, characterised in that oil shale with a granular size of up to 5 mm is subjected to distillation.

4. Method according to any one of claims 1 to 3, characterised in that the dust is removed from the distillation gas at temperatures above the dew point of the condensible portions.

5. Method according to claim 4,characterised in that the dust is removed through electrofiltration.

6. Method according to any one of claims 1 to 5, characterised in that the carbon of the distillation residue is burned with oxygen-containing gases and all or part of the combustion gas is used to pre-heat the circulating distillation gas.

7. Method according to any one of claims 1 to 6, characterised in that the combustion gas is used to pre-heat and dry the oil shale after pre-heating the circulating gas.

8. Method according to any one of claims 1 to 7, characterised in that the distillation residue is held in a container at the distillation temperature after being removed from the distillation cyclone reactor.

9. Method according to claim 8, characterised in that distillation gas, after removal of condensible portions, is passed through the distillation residue agitated by stirring or by means of a rotating drum.

10. Apparatus for carrying out the method according to any one of claims 1 to 9, with the gas exhaust of a distillation reactor (10) connected with an oil separator (19) and the feed nozzle for the distillation reactor (10) connected by way of a blower (23) with the oil separator (19), characterised in that the reactor (10) is a cyclone reactor having a tangential feed nozzle (9) and that a heat exchanger (4) is located between the blower (23) and the tangential feed nozzle (9) of the distillation cyclone reactor (10).

11. Apparatus according to claim 10, characterised in that a pre-heater (2) for the oil shale to be distilled is provided before the tangential feed nozzle (9) of the distillation cyclone reactor (10).

12. Apparatus according to claim 10 and 11, characterised in that a dust remover (16) operating at temperatures above the dewing point of the distillation gases is arranged between the distillation cyclon reactor (10) and the oil separator (19).

13. Apparatus according to claim 12, characterised in that an electrofilter is used as the dust remover (16).

14. Apparatus according to any one of claims 10 to 13, characterised in thatthe solid material removal system (12) of the distillation cyclone reactor (10) is connected to a combustin furnace (26) and the hot gas exhaust of the latter is connected to the heat exchanger (4).

15. Apparatus according to any one of claims 10 to 14, characterised in that a post-distillation drum (13) is provided on the solid material removal port (12) of the distillation cyclone reactor (10) or between this removal port (12) and the combustion device (26) for the distillation residue.

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