METHOD OF RECOVERING OIL FROM WATER OR SOIL

Abstract: The invention relates to a method of recovering oil from water or soil, in which method the oil is cooled by a cryogenic cooling agent and is led into the collecting organs (1, 7, 10). The cooling is effected by leading the cooling agent onto the oil collection surface of the collecting organ (1, 7, 10), from which it has been set to absorb phase change heat of the oil into its own phase change and to be released outwards.

Description: METHOD OF RECOVERING OIL FROM WATER OR SOIL The invention relates to a method of recovering oil from water or soil, in which method the oil is cooled by a cryogenic cooling agent and is led into the collecting organs. A vast number is known of different methods of and devices for recovering oil from water. In patent publications FI 42420 and US 3,612,277, collector devices are presented in which the collecting organ is cooled one way or the other. In the latter publication a roll is used, on top of which an attempt is made to recover the oil, and cooling of the drum has been suggested by a cooling agent, such as e.g. liquid nitrogen, which is to run through it. In circumstances of strong cool-through of the roll, the cooling of the roll will easily lead to the water freezing on the surface of the roll. The advantage of cooling the oil is that it acquires such a solid state that it is possible to lift it up as solid and viscous pieces or as a layer from the water, the area of solidification, however, depending on the quality of the oil. According to the above- mentioned Finnish patent, raw oil is already in approximately 13-14 degrees' temperature stiff enough to be effectively lifted up. In US publication 4031707 it is presented that the cryogenic cooling agent be spread straight onto the oil to be recovered or into the oil leakage point. The oil is thus more easily put into a recoverable state, but the recoverage itself is then done by using methods already known. The object of this invention is to create a new sort of method, by which the effectiveness of lifting oil is further advanced especially in difficult circumstances. The characteristic features of the invention are presented in the adjoining patent claims. The method in accordance with the invention includes the surprising characteristic that the growth of the partial pressure of the cooling agent, e.g. liquid nitrogen, which happens on the surface of the collecting organ, prevents water from getting onto the surface of the collecting organ. Taking the cooling agent, e.g. liquid nitrogen, onto the surface of the oil layer is also otherwise difficult, but by using suction to get it onto the surface of the collecting organ this problem is solved. Further, if the collecting organ is flock coated, lighter oil underneath the heavy oil to be recovered facilitates the loosening of the oil from the collecting organ. The method in accordance with the invention is superior compared with earlier solutions in that the boiling of the nitrogen or other and the growth of the partial pressure on the collecting surface and the diffusion into the surroundings prevent water and steam from getting condensed and frozen on the surface of the collecting organ. The invention is particularly profitable in cold, arctic circumstances. In what follows the invention is illustrated by reference to the accompanying figures, which schematically present certain device solutions . Figure 1 shows the use of a flock coated roll in recovering oil. Figure 2 shows a wirelike collecting device. Figure 3 shows a collecting device equipped with a cooled circular. brush. Figure 4 shows the cleaning process which uses cooled pellets. In figure 1, reference number 1 shows the rotatable roll, which has a flock coat 2. Liquid nitrogen is spread onto it by spreading roll 3 and the recovered oil is removed by rotating steel brush 4. The spreading is profitably carried out by spraying. After the spreading, the liquid nitrogen has a slight delay in order for the phase change to start. The direction of the rotation and of the movement of roll 1 is marked with corresponding arrows. Here, as has already been explained above, the removal of the oil can be facilitated by moistening the flock coat with supple oil before the roll is used, whereby the heavier oil comes loose from the surface of the roll as a thick layer. Generally this oil layer is functionally part of the collecting organ. The flock coat stores coldness by storing liquid nitrogen. Its evaporation keeps the nitrogen concentration high on the surface and neither water nor steam has a possibility of freezing onto the surface which also rejects ice. The nitrogen layer also works as an insulator, preventing the easily inflammable components from igniting. Although the liquid nitrogen (evaporation temperature approximately -196 degrees C) comes into contact with water, this does not normally lead to the formation of ice. Due to the surface tension the contact surface is non-existent and the heat capacity and the phase change heat of the water are so great that there is no time for ice to form. The heat capacity of the oil is on the contrary small, whereby it cools quickly. Figure 2 schematically shows a wirelike collecting device. Here roll 6 and the accessory wheels have been surrounded by rotatable wire 7 which collects the oil onto its surface and from where it is removed with the help of appropriate equipment, as here by clamp rolls 8 and suction channel 9. Liquid nitrogen is fed onto the inner surface of the wire, from where it is absorbed through the wire so as to cool oil that comes into contact with the wire, whereafter it is freed outwards. Although a continuous mat is used here, the way of collection is in principle the same as in figure 1. Figure 3 presents a way of collection that differs from that above. Here a quickly rotating brush is moistened by liquid nitrogen, whereby it gives up its heat so effectively to the incoming oil that solid particles are formed. The feeding in of the liquid nitrogen has been marked by the letters N, L. Here the first brush, marked by reference number 10, is the most important. Also other brushes can be used in order for the solid substance to be formed. In the figure, another quickly rotating brush has been marked by reference number 11, and reference number 13 points to a brush that rotates more slowly. The solid substance that has been formed is transferred further with the help of these brushing devices 11 and 13. Here reference number 12 shows a channel through which the solid oil particles are taken upwards until they can be dropped onto an appropriate transporter that takes them into a temporary storage. It has been noted in simple tests that the water flows away from the solid mass that has been formed, and that ice formation is slight. The reason for this is, as was explained above, that the heat capacity of water is great compared with the heat capacity of oil. There is no time in a fast, dynamic process for water to freeze. Reference number 15 presents a potential roll formed out of dry ice, which presses the oil layer against the brush. The roll is changed every few hours. It stays clean even in hard spots and no oil is attached onto it. Figure 4 shows a cleaning process which uses freezable plastic pellets and is particularly used for cleaning bilge water. Crushed glass or aluminium grains can also be used. Generally the substance characteristics and size distribution of the particles can be used to influence the process and to optimize it according to the quality of the oil to be recovered. Generally the largest dimension of the pellets is 1 - 10 mm. The shape, surface quality and other characteristics of the pellets can be changed according to the situation. Especially the freezing capacity of the pellets is set to be such that a sufficient delay will be acquired for the lifting before the oil starts to drip from the pellets. The specific weight of the pellets is set according to the specific weight of the oil to be recovered. In the figure, reference number 20 presents the additional cooling of the oily pellets by liquid nitrogen. Due to this, the oil can easily be mechanically separated from the pellets at the separation stage 21. The oil comes loose from the pellets as a powdery phase which makes a simple sieving possible. Naturally the oil can also be defrozen away, but in that case more liquid nitrogen is needed to cool the pellets. The cooled, quite clean pellets are led to the actual cleaning process 22, in which the pellets and the oily water have been set to go counter-current. The pellets are lifted upwards by an appropriate transporter (not shown) at the same time as the oily water flows downwards. The oil is caught onto the surface of the cold pellets and the clean water flows out. The oily pellets are led to the additional cooling stage 20 and the process continues in the same manner. The method can be modified in many ways. The cooling agent, e.g. industrial alcohol (melting point -117,3 degrees C, boiling point +78,5 degrees C) , that is used in the handling of the oil, can be cooled by another cooling agent, e.g. dry ice. Steel has a greater heat capacity than plastic, but adhesion is better on a plastic surface than on a steel surface. Besides in accidents, the method can also be applied when taking samples (molecular layers on the water surface) and to collect oil from wells. The batcher of cryogenic gas, particularly liquid nitrogen, can be fitted as an additional device onto several known oil collectors. The method suits all oil qualities.

Claims: Patent Claims 1. Method of recovering oil from water or soil, in which method the oil is cooled by a cryogenic cooling agent and is led into the collecting organs (1, 7, 10), characterized in that the cooling is done by leading the cooling agent onto the oil collection surface of the collecting organ (1, 7, 10) , from where it is set to absorb phase change heat of the oil into its own phase change and to be released outwards. 2. A method in accordance with patent claim 1, in which a rotating roll (1) , a brush (10) or a continuous mat (7) is used as a collecting organ, characterized in that the sur- face of the collecting organ (1, 7, 10) is cooled by wetting it from the outside by a cooling agent or by setting the cooling agent to be absorbed through it. 3. A method in accordance with patent claim 2, charac- terized in that the surface of the collecting organ (1, 7, 10) is set to retain the cooling agent. 4. A method in accordance with patent claim 3, characterized in that the surface of the collecting organ (1, 7, 10) is flock coated. ,5 . . A method in accordance with patent claim 1, characterized in that particles such as crushed glass or plastic pellets are used as the collecting organ. 6. A method in accordance with patent claim 5, characterized in that the largest dimension of the particles is 1 - 10 mm. 7. A method in accordance with patent claims 5 or 6, characterized in that the oily particles are further cooled so as to separate the oil as a powdery phase from the particles. 8. A method in accordance with one of the above patent claims 2 - 7, characterized in that the collecting organ (1, 7, 10) is smeared with supple oil before it is used for collection, whereby the thicker recovered oil comes easily loose from the collecting organ. 9. A method in accordance with one of the above patent claims 1 - 8, characterised in that liquid nitrogen is used as the cooling agent. 10. A method in accordance with one of the above patent claims 1 - 9, characterized in that dry ice is used in the oil transport controllers, wherefore their surfaces can be kept clean. 11. A method in accordance with one of the above patent claims 1 - 10, characterized in that the cooling agent is sprayed onto the collecting surface. 12. A method in accordance with one of the above patent claims, characterized in that there is a slight delay after the spreading of the cooling agent before it comes into contact with the oil to be recovered.

Inventors: PIETIKAEINEN KALEVI, PIETIKAEINEN TIINA, PIETIKAEINEN, KALEVI, PIETIKAEINEN, TIINA
Applicants: PIETIKAEINEN KALEVI, PIETIKAEINEN TIINA, PIETIKAEINEN, KALEVI, PIETIKAEINEN, TIINA
Application year: 1998
Main classification: E02B15
IPC codes: E02B15