Method and apparatus for purifying shale oil from solid impurities

Technical field

The invention belongs to the field of chemical industry and is provided for purifying shale oil from solid impurities having remained in the oil after dry distillation of oil shale.

Prior art

Shale oil produced from the oil shale in the process of thermal treatment contains an essential amount of solid impurities being small particles of oil shale itself but also of ash and semicoke. Their presence in the shale oil complicates further processing of shale oil when the necessary fractions have to be separated from the oil. The negative effect that of solid impurities produce is first of all clogging of used devices and also quickening erosion of the surfaces in contact with shale oil. For the above reasons purifying of shale oil from solid impurities before its further processing is of substantial importance.

From prior art different methods and devices for purifying of shale oil from solid impurities are known.

For example, a method for purifying shale oil from solid impurities by decantation in the decanters is known. The subject process is rather labour-consuming and time-taking, additionally it is not sufficiently efficacious as it enables to remove solid impurities to some extent and only from medium-light fractions of shale oil, whereas the use of said method for purifying of heavy fraction of shale oil does not enable to achieve any appreciable results (see: H. M. 3eneHMH, B.C. φaMHδepr, K. B. MepHbiLueBa. "XMMMH M τexHonorn?i cπai-meBOM CMoπbi". M3flaτenbcτB0 «XMMM?I», JleHMHrpaflCKoe OTfleneHne, 1968r., p. 186).

Also a method for purifying shale oil from solid impurities with the help of spinning, is known. This method does not ensure the necessary level of purity of the shale oil either and in addition the method is extremely power-consuming (see: H. M. 3eneHMH, B.C. φaMHδepr, K.B. MepHbiweBa. "XMMMH M τexHonorn?i cπai-meBOM CMonbi". M3,qaτej ^~ ibcτB0 «XMMM?I», JleHMHrpa,qcκoe oτ,qeπeHMe, 1968r., p. 187).

There have also been made attempts to use filtration for purification of shale oil but no satisfactory results have been obtained. Due to the high viscosity of shale oil, and first of all of its heavy fraction, a thick layer forms on the surfaces of filtering elements and this layer congests the filtering elements and impedes further filtering process. Therefore the known filtering methods are not applicable for purifying of heavy fraction of shale oil. (see: H. M. 3eneHMH, B.C. φaMHδepr, K. B. MepHbiLueBa. "XMMMH M τexHonorn?i cπai-meBOM CMoπbi". M3flaτenbcτB0 «XMMM?I», JleHMHrpaflCKoe OTfleneHne, 1968r., p. 188).

The next known method for purifying of shale oil from solid impurities provides mixing the heavy fraction of shale oil with petrol, decantation of the prepared composition in a decanter, after which the clarified composition is directed to a tank for thermal sedimentation during a specified time period. After that the composition purified as explained above is mixed with the medium-light fraction of the shale oil and this new composition is in turn mixed with the dilution of phenols in water (phenol water) and the final composition is directed to the next tank for thermal sedimentation. After the time required for sedimentation is over, the phenol water is separated from the composition and the purified shale oil is directed to the respective tank (the described method is in use in the Estonian company VKG Oil Ltd, Kohtla-Jarve, Estonia).

The above described method enables to involve simultaneously both heavy and medium-light fractions of shale oil into the purification process, but nevertheless the following drawbacks are inherent to it:

first - in order to realize said method a very bulky apparatus (decanters, tanks for thermal sedimentation, etc) is needed, and therefore performing of the method requires a large production area;

second - while purifying shale oil by using said method, a rather intensive evanesce of the medium-light fraction and petrol takes place, thus causing essential increase of production losses;

third - the residual products formed during the purifying process contain in addition to the removed solid impurities also a remarkable amount of the composition to be purified - for instance, the residual products from the second tank for thermal

sedimentation contain 85 - 90% of said composition and water. For the treatment of those residual products extra expenses are needed which also increases the process and product costs;

fourth - the known purification process is rather time-consuming.

From the state of art an apparatus for purifying shale oil from solid impurities is known, in which the outlets of tanks, respectively for heavy fraction of shale oil and petrol, are connected to the inlet of the first membrane stirrer, the outlet of the latter is connected to the inlet of a decanter the outlet of which is connected to the inlet of the first tank for thermal sedimentation.

The outlet of the first tank for thermal sedimentation and the outlet of the tank for phenol water are connected to the inlet of the second membrane stirrer, to the outlet of which also the outlet of tank for the medium-light fraction of shale oil is connected. The outlet of the second stirrer is connected to the inlet of the second tank for thermal sedimentation. The first and the second outlets of said tank are provided for removing of the purified shale oil and the phenol water respectively. The decanter and both of the tanks for thermal sedimentation have outlets for removing residual products (the above-captioned apparatus is in use in the Estonian company VKG Oil Ltd, Kohtla-Jarve, Estonia).

The drawbacks inherent to the process of installing and exploitation of this apparatus coincide with the drawbacks of the already known method described above.

Objective and subject matter of the invention

The first objective of the invention is to improve the method for purifying shale oil from solid impurities in order to increase efficiency of the purification process, to decrease the number of pieces of equipment to be used, to decrease the amount of residual products forming in the purification process by directing them back into the purification process, but also to decrease the percentage of solid impurities in the purified shale oil before placing this oil to further distilling, thus enabling to obtain distilling products of higher quality.

For achieving of said objective, the first alternative solution of the invention provides a method for purifying shale oil from solid impurities, according to which a composition to be purified is prepared from heavy and medium-light fractions of shale oil and petrol, after which a cyclical purifying process of said composition is carried out, whereby each cycle of said process includes the following steps:

the composition to be purified is pumped under pressure into the device for removing of solid impurities;

the mixture of purified shale oil fractions outflowing from the device for removing of solid impurities is collected in the tank for end product;

the device for removing of solid impurities is cleaned up from the solid impurities left in it, for which purpose said device is drained and the solid impurities remaining inside of said device are removed;

petrol is added to the composition to be purified and the composition is prepared by simultaneous mixing of 0,5-1 ,0 parts by volume of heavy fraction of shale oil, 1 ,0-2,0 parts by volume of medium-light fraction of shale oil and 0,7-1 ,4 parts by volume of petrol;

the composition to be purified is heated up to the temperature 60-70 ⁰ C prior to being introduced into the device for removing solid impurities;

the device for removing solid impurities is a filter containing at least two filter cartridges;

the composition to be purified is introduced into the device for removing solid impurities at a pressure of 1 ,5-2,5 bar;

through the outlets of filter cartridges the purified composition is directed into the tank for final product;

for draining of the filter from the composition to be purified, an inert gas is introduced into the filter;

after draining of the filter the solid particles remaining on the surface of the filter cartridges are dried with an inert gas;

after drying of the filter cartridges, their interior is subjected to pneumatic impacts caused by sudden changes in the inert gas pressure level, causing the dry solid particles to unstick from the filter cartridge surface and fall down into the lower part of the filter;

the dry solid particles are removed from the lower part of the filter.

According to another alternative embodiment of the invention, a composition to be purified is prepared from heavy and medium-light fractions of shale oil, after which a cyclical purifying process of said composition is carried out, whereby each cycle of said process includes the following steps:

the composition to be purified is pumped under pressure into the device for removing of solid impurities;

the mixture of purified shale oil fractions outflowing from the device for removing of solid impurities is collected in the tank for end product;

the device for removing of solid impurities is cleaned up from the solid impurities left in it, for which purpose said device is drained from the composition to be purified and the solid impurities remaining inside of said device are removed;

petrol is added to the composition to be purified and the composition is prepared by simultaneous mixing of 0,5-1 ,0 parts by volume of heavy fraction of shale oil, 1 ,0-2,0 parts by volume of medium-light fraction of shale oil and 0,7-1 ,4 parts by volume of petrol;

the composition to be purified is heated up to the temperature of 60-70 ⁰ C prior to being introduced into the device for removing solid impurities;

the device for removing solid impurities is a filter containing at least two filter cartridges;

the composition to be purified is introduced into the device for removing solid impurities at a pressure of 1 ,5-2,5 bar;

through the outlets of the filter cartridges the purified composition is directed into the tank for final product;

for draining of the filter from the composition to be purified, an inert gas is introduced into the filter;

after draining of the filter, the inert gas is removed and petrol is introduced into the filter and petrol circulation through the filter cartridges is carried out;

after completion of circulation, the petrol remaining in the filter is directed back into the petrol tank;

after draining of the filter, the solid particles left on the surface of the filter cartridges are dried with an inert gas;

after drying of the filter cartridges, their interior is subjected to pneumatic impacts caused by sudden changes in the inert gas pressure level, causing the dry solid particles to unstick from the filter cartridge surface and to fall down into the lower part of the filter;

the dry solid particles are removed from the lower part of the filter.

For preparing of the composition to be purified the petrol manufactured from oil shale is used. Nitrogen is applied as an inert gas.

The temperature of the inert gas introduced into the filter is in the range of 50-90 ⁰ C.

The circulation of petrol between the petrol tank and the filter cartridges lasts from 10 to 20 minutes.

The inert gas that was used in the filters, is purified from the oil vapours dissolved in it and is directed back for recycling, the oil vapours are condensed and directed back into the composition to be purified.

A further object of the invention is to provide an equipment for implementing of the method according to the invention, so that the equipment is less bulky than that of the closest known solution and by using of which the drawbacks of the method known from the prior art can be avoided.

This further object of the invention is realized by means of an equipment for removing of solid impurities from shale oil, which includes a device for preparing the composition of fractions of shale oil to be purified, a device for removing solid impurities from the prepared composition and a tank for an end product, whereby the device for preparing the composition to be purified includes tanks for petrol, for heavy fraction of shale oil and medium-light fraction of shale oil, and a stirrer connected with them, the outlet of the latter is connected to the inlet of the tank for the composition to be purified;

the device for removing of solid impurities is a filter, containing at least two filter cartridges;

the outlets of the filter cartridges form a filter outlet, which through valves is connected to the tank for purified shale oil and to the petrol tank;

in addition the equipment includes a source of inert gas, that is used for supplying the cleaning process with the inert gas, containing a tank for pressurized gas and a condenser, the latter being provided for extracting shale oil fractions dissolved in the inert gas;

the outlet of the tank for the inert gas and the inlet of the condenser are connected through valves with the filter, one of the outlets of the condenser is connected a through pressure pump with the inlet of the tank for the inert gas, the other outlet of the condenser is connected through a valve with the tank for medium-light fraction;

the outlet of the tank for composition to be purified is connected through a parallel connection of the pressure pump and a valve with the inlet of the filter;

the outlet of the petrol tank is connected with the filter inlet through the pressure pump;

the outlets of the filter cartridges are connected together for parallel operation.

Brief description of the drawings

The invention has been illustrated by the drawings, whereby:

Fig 1 shows a flow chart of realization of the method according to the invention, and

Fig 2 shows the principal circuitry of the apparatus for removing of solid impurities from shale oil according to the invention. The arrows next to the valves indicate the direction in which the material in the pipeline flows when the respective valve is in an opened position.

Detailed description of the exemplary embodiment of the invention

Removing of solid impurities from shale oil according to the method is carried out as follows.

First, the composition to be purified is prepared, for which purpose both fractions of shale oil and petrol are stirred together in the following volumetric relationship: 0,5-1 ,0 parts by volume of heavy fraction of shale oil, 1 ,0-2,0 parts by volume of medium-light fraction of shale oil and 0,7-1 ,4 parts by volume of petrol. The experiments carried out at the applicant's premises indicate that such a relationship of components allows to obtain a composition, in which both the fractions of shale oil are included and which gives the best filtering effect. Stirring is carried out without heating the components and preferably in a membrane stirrer. Upon completion of stirring, said composition is heated up to the temperature of 60-70 ⁰ C and the composition is directed into the intermediate container, for which the tank for composition to be purified serves.

Purification process is carried out in a cyclical manner and consists of a series of similar cycles. The cyclic nature of the process is due to the fact that the efficiency of the filter used for removing of solid particles declines during the operation and it has to be cleaned.

In the first step of the cycle, the filter is filled with the composition to be purified and the composition is pumped into the filter at a pressure of 1 ,5-2,5 bar. When the filter body is filled up, the filtering of the composition through the filter elements starts and the purified composition is directed into the tank for purified shale oil.

This kind of filtering process takes place as long as filtering becomes ineffective. When this occurs, pumping of the composition into the filter is stopped and an inert

gas (nitrogen) at a pressure level of at least 2,5 bar and at a temperature in the range of 50-90 ⁰ C is directed into the filter and the composition remained in the filter is forced back into the tank for the composition to be purified and the filter body is drained.

After draining of the filter body, the filter cartridges are cleaned, using one of the two possible alternative ways depending on how high the percentage of the composition to be purified in is the layer built up on the filter cartridges and formed from the removed solid impurities together with the composition to be purified.

In the first case, when the percentage of the composition to be purified in the layer built up on the filter cartridges is up to 30%, nitrogen is circulated through the filter for 10-20 minutes, resulting in drying of the solid particles settled on the filtering surfaces inside the filter cartridges.

After drying of the filter, the interior of the filter is subjected to pneumatic impacts caused by sharp changes in the nitrogen pressure level, resulting in falling down of the solid particles, settled on the surfaces of the filtering elements, into the lower part of the filter, wherefrom they are removed.

The nitrogen is drained from the filter and the next filtering cycle starts.

In the second case, when the layer built up on the filter cartridges contains more than 30% of the composition to be purified, drying with nitrogen followed by cleaning with pneumatic impacts may move insufficient. In such a case also the body of the filter is first drained as described above, but this is followed by rinsing with petrol, for which purpose petrol at room temperature and at a pressure of 2-3 bar is introduced into the filter and when the filter is filled up, petrol is circulated through the filter cartridges. Duration of such a circulation may be 8-15 minutes.

After the surfaces of the filter cartridges are cleaned from the shale oil mixture, circulation of petrol is terminated and the filter body is drained from petrol and the petrol remaining in the filter is directed back into the petrol tank.

Further cleaning of the filter is analogous to the first alternative version: nitrogen at a pressure level of at least 2,5 bar and at the temperature in the range of 50-90 ⁰ C is directed into the filter and nitrogen is circulated for 10-20 minutes through the

filter, resulting in drying of the solid particles settled on the filtering surfaces inside the filter cartridges, thereafter the interior of the filter is subjected to pneumatic impacts caused by sharp changes in the nitrogen pressure level, resulting in falling down of the solid particles, settled on the surfaces of the filtering elements, into the lower part of the filter, wherefrom they are removed. The nitrogen is drained from the filter and the next filtering cycle starts.

Apparatus for purifying shale oil from solid impurities includes four main units - unit 1 for preparing composition of fractions of shale oil to be purified, unit 2 for feeding the prepared composition into the filter, filter unit 3 and a source of inert gas 4.

Unit 1 for preparing composition of fractions of shale oil to be purified includes a petrol tank 101 , a shale oil heavy fraction tank 102 and a shale oil medium-light fraction tank 103, also a stirrer 104, the inlets of which are connected to the outlets of the three above mentioned devices. Said connections are realized through valves 105, 106 and 107, by controlling of which (their control device being not a subject matter of the invention is not shown) dosing of components to be stirred can be performed.

Unit 2 for feeding the prepared composition into the filter includes a tank 201 for the composition to be purified, the inlet of which is connected to the outlet of the stirrer 104, the outlet of the tank 201 is connected to the inlet of the parallel circuit formed of a pressure pump 202 and a valve 203. The unit also includes a pressure pump 204 connected between the outlet of said parallel circuit and the outlet of the petrol tank 101 , and also a valve 205 connected between the outlet of said parallel circuit and the inlet of the petrol tank 101.

Filter unit 3 includes a filter 301 , underneath it there is positioned a receptacle 302 for separated solid impurities and a tank 303 for purified shale oil. The filter is formed of a vertical, preferably cylindrical body 304, the lower part of which for facilitating the solid particles to be collected has a conical shape and is provided with a valve 305 for removing solid particles, witch is opened and closed by means of an actuator 306. The cylindrical housing 304 of the filter 301 contains vertical filtering elements 307, the number of which may vary depending on the needed productivity of the filter unit. Each filter element 307 represents a perforated tube,

the outer surface of which is covered with filter cloth. The outlets of all filter elements are connected together (i.e. all filter elements work in parallel) and form an outlet 308 of the filter 301 , which is located in the upper part of the housing of the filter 304 and through valves 309 and 310 is connected respectively with the

5 tank 303 for purified shale oil and the petrol tank 101. The inlet 311 of the filter 301 , located in the lower part of the housing of the filter 304, is connected with the outlet of a parallel circuit formed by the pressure pump 202 and the valve 203 connected in parallel, through the pressure pump 204 with the petrol tank 101 and through the valve 205 also with the inlet of the petrol tank 101. The filter outlet 312 io is connected with the source 4 of inert gas.

The source 4 of inert gas contains a tank 401 for pressurized inert gas, a condenser 402 and a pressure pump 403. The pressure pump 403 is connected between one of the outlets of the condenser 402 and the inlet of the tank 401 for pressurized inert gas and is used for pumping inert gas evolved in the condenser is 402 back into the tank 401. The outlet of the tank 401 is connected through the valve 404 with the outlet 312 of the filter 301 and the inlet of the condenser 402 is through consecutive valves 405 and 407 also connected with the outlet 312 of the filter 301 , in addition the inlet of the condenser 402 is through valves 405 and 408 connected with the outlet 308 of the filter 301. The other outlet of the condenser

20 402 is connected through the valve 406 with the tank 103 for medium-light fraction of the shale oil.

The apparatus works as follows.

The components in the petrol tank 101 , in the shale oil heavy fraction tank 102 and in the shale oil medium-light fraction tank 103 are dosed through the opened

25 valves 105, 106 and 107 into the stirrer 104 in a relationship mentioned above. Stirring in the stirrer 104 results in obtaining the composition to be purified, the temperature of this composition is raised to 60-70 ⁰ C and it is directed into the tank 201 of composition to be purified. The process of preparing of the composition to be purified is not unambiguously connected with the cycles of purification, the

30 criteria for this preparation is to guarantee constantly the required level of the composition in the tank 201.

At the beginning of the purification cycle the pressure pumps 204 and 403 are switched off, the valves 203, 205, 310, 404, 405 and 406, 407 and 408 are closed, the valve 309 is opened and the pressure pump 202 is started and as a result the filter 301 starts to fill up with the composition to be purified. When the filter 301 is filled up, the composition in the filter is at a pressure of 1 ,5-2,5 bar and the composition to be purified starts to filter through the filter cartridges 307 and the purified composition that has passed the cartridges is directed through the open valve 309 into the tank for purified shale oil.

When during the filtering process a layer consisting of the purified composition and solid particles forming on the filter cartridges 307 has become so thick that it is not reasonable to continue further filtering, then supplying the filter 301 with the composition to be purified is terminated by stopping the pressure pump 202 and the valve 309 is closed. After that the valves 203 and 404 are opened, due to the nitrogen in the tank 401 at a pressure of at least 2,5 bar and at the temperature in the range of 50-90 ⁰ C, enters the filter 301 through the open valve 404 and forces the remaining composition through the open valve 203 to flow back into the tank

201 for composition to be purified.

After the composition to be purified is discharged from the filter 301 , the valve 203 is closed and cleaning of the filter cartridges 307 is carried out, for which in the apparatus described herein there are two options.

In case in the layer built up on the filtering surfaces of the filter cartridges 307and consisting of the composition to be purified and solid particles, the percentage of the composition to be purified is up to 30%, nitrogen is circulated through the filter 301 for 10-20 minutes, for which purpose the valve 404 is left open and in addition the valves 405 and 408 are also opened (the valve 407 having been already previously closed). As a result nitrogen at a pressure of at least 2,5 bar and at the temperature of 50-90 ⁰ C, starts to circulate from the tank 401 for nitrogen through the valve 404, the filter 301 and the valves 408 and 405 into the condenser 402, drying solid particles on the filtering surfaces of the filtering cartridges 307. This kind of circulation is carried out for 10-20 minutes. After that nitrogen is discharged from the filter, for which purpose the valves 404 and 408 are closed and the valve 405 is opened (the valve 407 was already previously opened), resulting in

nitrogen, due to its overpressure and underpressure in the piping, flowing into the condenser 402 and restoring normal pressure in the filter 301.

In the discharged filter 301 pneumatic impacts are generated by sudden changes in nitrogen pressure level by closing the valves 405 and 407 and instantaneously

5 opening fully the valve 404, which results in an instantaneous increase in the pressure in the filter to its maximum level. When the maximum pressure level is achieved, the valve 404 is closed and the valves 405 and 407 are instantaneously opened fully, resulting in nitrogen, due to its overpressure and underpressure in the piping, flowing into the condenser 402 and restoring normal pressure in the io filter 301.

The described pneumatic impacts are generated as many times as necessary, and as a result, the dry solid particles deposited on the surfaces of the filter cartridges fall down into the lower conical part of the housing of the filter 304 onto the valve 305 for removing solid impurities, which is opened and closed by the means of an is actuator 306. When a sufficient amount of particles has accumulated onto the valve 305 for removing solid impurities, the latter is opened and residues of filtration fall into the receptacle 302 for separated solid impurities, after which the valve 305 for removing of solid impurities is closed. After cleaning of the filter 301 , the pressure in filter is back to normal.

20 When the filter has been cleaned, the valves 404, 405 and 407 are closed (valve 408 having been already closed earlier), the valve 309 is opened and the pressure pump is switched on, starting a new filtering cycle.

In case the layer built up on the filter cartridges 307 of the filtering surfaces, consisting of the composition to be purified and solid particles, contains more than

25 30% of the composition to be purified, then drying the filter cartridges 307 with only nitrogen may prove insufficient for their cleaning. In such a case an alternative version is used, according to which after discharging of the composition to be purified from the filter 301 , the valve 404 is closed and the valves 405 and 407 are opened and the pressure pump 204 is switched on. The petrol, at room

30 temperature, is pumped by the latter into the filter and it displaces nitrogen, which through the opened valves 405 and 407 flows into the condenser 402.

After the filter 301 is filled up with petrol the valves 405 and 407 are closed and the valve 310 is opened and circulation of petrol through the filtering cartridges 307 of the filter 301 starts in sequence of the petrol tank 101 , the pressure pump 204, the filter 301 , the filtering cartridges 307, the valve 310 and again the petrol tank 101. This circulation lasts for 8-15 minutes and during that time the residues of shale oil remaining on the surfaces of the filter cartridges 307 are washed off. In order to stop circulation, the pressure pump 204 is switched off, the valves 404 and 205 are opened, and nitrogen under pressure entering the filter 301 forces the petrol remaining there to flow back into the tank 101.

When the filter 301 has been discharged, the valve 205 is closed and nitrogen is circulated through the filter 301 for 10-20 minutes, for which purpose the valves 405 and 408 are opened (the valve 404 having been already previously opened) and the valve 407 is closed. As a result nitrogen, at a pressure of at least 2,5 bar and at the temperature 50-90 ⁰ C, starts to circulate from the tank 401 for nitrogen through the filter 301 and the valves 408 and 405 into the condenser 402, drying the solid particles on the filtering surfaces of the filtering cartridges 307. This kind of circulation is carried out for 10-20 minutes. After that nitrogen is discharged from the filter, for which purpose the valves 404 and 408 are closed and the valves 405 and 407 are opened, and as a result, due to its overpressure and underpressure in the piping, nitrogen enters the condenser 402 and normal pressure is restored in the filter 301.

In the discharged filter 301 pneumatic impacts are generated by sudden changes in nitrogen pressure level by closing the valves 405 and 407 and instantaneously opening fully the valve 404, which results in an instantaneous increase in the pressure in the filter to its maximum value. When the maximum pressure level is achieved, the valve 404 is closed and the valves 405 and 407 are instantaneously fully opened, and as a result nitrogen, due to its overpressure and underpressure in the piping, flows into the condenser 402, the pressure in the filter 301 drops abruptly and normal pressure level in it is restored.

The described pneumatic impacts are generated as many times as necessary, and as a result, the dry solid particles deposited on the surfaces of the filter cartridges fall down into the lower conical part of the housing of the filter 304 onto the valve

305 for removing solid impurities, which is opened and closed by the means of an actuator 306. When a sufficient amount of particles has accumulated onto the valve 305 for removing solid impurities, the latter is opened and residues of filtration fall into the receptacle 302 for separated solid impurities, after which the valve 305 for removing of solid impurities is closed. When cleaning of the filter 301 has been completed, the pressure in it is back to normal.

When the filter has been cleaned, the valves 404, 405 and 407 are closed (valve 408 having been already previously closed), the pressure pump 202 is switched on, starting a new filtering cycle.

The nitrogen used in the filter 301 for discharging and drying, and that through the valves 405, 407 and 408 is directed into the condenser 402, contains vapouhzed shale oils. In the condenser 402 shale oils are separated from nitrogen, and after that the condensed shale oil is fed back into the purification process, for which the valve 406 is opened and the condensed shale oil is directed into the shale oil medium-light fraction tank 103. By means of the pressure pump 403 purified nitrogen is pumped back into the tank 401 for pressurized inert gas.

The invention is not restricted to the above described embodiment and it covers all embodiments falling within the scope of claims and also their equivalents.

List of reference numbers used in the drawings

1 - device for preparing the composition of fractions of shale oil and petrol to be purified

101 - petrol tank 5 102 - shale oil heavy fraction tank

103 - shale oil medium-light fraction tank

104 - stirrer

105 - valve

106 - valve io 107 - valve

2 - device for introducing prepared composition into the filter

201 - tank for composition to be purified

202 - pressure pump

203 - valve is 204 - pressure pump 205 - valve

3 - filter unit

301 - filter

302 - receptacle for separated solid impurities 20 303 - tank for purified shale oil

304 - housing of the filter

305 - valve for removing solid impurities

306 - actuator of the valve for removing solid impurities

307 - filter cartridge 25 308 - filter outlet

309 - valve

310 - valve 311 - filter inlet 312 - filter outlet 4 - source of inert gas 5 401 - tank for pressured inert gas (nitrogen)

402 - condenser

403 - pressure pump

404 - valve

405 - valve o 406 - valve

407 - valve

408 - valve