NO332199B1 - Method and apparatus for simultaneous recovery of energy and purification of water. - Google Patents

Description

Method and apparatus for simultaneous recovery of energy and purification of water.

The present invention relates to a method and an apparatus for purifying water, in particular contaminated produced water from a petroleum well.

The need for water purification can arise in various contexts. The purpose may be to provide clean drinking water for consumption, to avoid discharge of water-soluble or water-borne pollutants, to obtain legally acceptable low concentrations of chemical compounds in waste water from industrial processes or to achieve the desired content of components in the water, but in such low concentrations that they are too low for general recycling. Mainly there are two main reasons for carrying out water purification; either for the production of clean water or for the recovery of substances that are dissolved in the water. Different methods exist for purifying water; filtration, distillation, centrifugation, etc. Many methods are excellent for certain contaminants but are ineffective for others. Few methods are good for all kinds of water-soluble content. Many of these effective water purification processes can be very energy-intensive.

Known technique

Various processes for water purification are discussed in the inventor's patent NO321097 which describes an apparatus and a method for treating polluted water by forming hydrates and extracting clean water after dissociation of the formed hydrates, the so-called Ecowat process. The process results in clean water and a brine that can be deposited, or reinjected into the well when the Ecowat process is used within the oil production process. When the brine is to be re-injected, it can be mixed with seawater to balance the ions in the brine and precipitate potentially problematic poorly soluble deposit-forming salts such as BaS04, CaS04 etc. before the re-injection is carried out.

NO321097 uses separate heat exchangers for handling the energy from the exothermic hydrate-forming process.

US4781837 relates to concentration of liquid by exploiting the difference in osmotic pressure between two liquids and recovering the solution using the opposite process. A process to recover part of the energy between the two fluids is also shown.

N0314575 relates to a semipermeable membrane consisting of a thin layer of non-porous material (diffusion skin), and one or more layers of a porous support material (the porous layer). Furthermore, a method for providing elevated pressure by osmosis as well as an apparatus for providing elevated pressure and electrical power is described.

Problem statement

Effective water purification processes are energy-intensive processes. For the Ecowat process, the energy consumption will be around 1-3 kWh/m3 of clean water to drive pumps and motors. Recompression of the hydrate-forming compound needs an additional 6-9 kWh/m3 of pure water. Clean water and clean emissions at the lowest possible price will always be in demand.

Injection of brine to maintain the hydraulic pressure in reservoirs is very often used for increased oil and gas recovery. Typically, the injection water is pumped into the water zones in the lower parts of the reservoir. If untreated seawater is used for pressure generation, there is an increased risk of permeability changes in the porous layers in the reservoir formation. Permeability changes occur due to the ionic conditions. Seawater contains sulphate ions, while the water in the reservoir (the formation water) often contains cations such as barium, strontium and calcium. In combination, these form precipitates, seal pore openings, and further injection can become difficult if not impossible. A solution to this could be desulphation plants where sulphate is removed from seawater before injection.

During petroleum production, so-called "produced water" is also produced. The ion composition in the produced water is almost identical to that of the reservoir water. By treating the produced water in the Ecowat process, the ion concentration will increase manifold. When the concentrate and seawater are mixed, some salts will quickly precipitate out and become solids (such as SrS04, BaS04, CaS04). The precipitates can be removed from the injection water before injection and thus remove the risk of permeability changes down the borehole. In addition, other ions from the concentrated bed will help to stabilize shale and clay in the reservoir and thus prevent flow problems during injection.

When running the Ecowat process for any purpose, the concentrate will contain a potential energy in the form of having a high ion concentration in relation to other available nearby liquids such as seawater, river water, fresh water, formation water etc. At a given temperature, the osmotic pressure is in a system given by the molality of the salt in the water. When gas hydrates are formed, the remaining water becomes more concentrated, which means that the molality increases. Therefore, during treatment of e.g. seawater or other water source, the Ecowat process increases the concentration of salts approximately 5 times or more, depending on the concentration of salts in the water initially. The osmotic pressure increases accordingly. Energy can be captured when this pressure is released. For a 5-fold increase, the potential energy will be around 5 kW per liter of released concentrated water. This is valuable energy that is desired to be retained in the system.

Short summary

A solution to the problems mentioned above is the present invention. The present invention is a method for the simultaneous recovery of energy and purification of polluted water (3, 31) from an inlet of polluted produced water from a petroleum well comprising the steps: - adding the polluted water (3, 32) from an inlet for such polluted water to a hydrate reactor (C, T), - provide a hydrate-forming compound (8, 36) and hydrate germ (32) to the contaminated water (3, 31) in the hydrate reactor (C, T), - control pressure and temperature in the hydrate reactor (C ,T) so that hydrates (4, 33) are formed; - transporting the hydrates (4, 33) and with it the enriched contaminated water (10, 38) to a separator (D, U); - separating the hydrates (4, 33) from the contaminated water (10, 38) in a separator (D, U); - transport the now separated hydrates (6, 34) to a dissociation tank (F, W), and - dissociate the transported separated hydrates (6, 34) to separate pure water (9, 37) and hydrate-forming compound (8, 36) by subsequently returning the hydrate-forming compound (8, 36) via a pump (P) to the hydrate reactor (C, T), and directing the clean water (9, 37) to a clean water reservoir (K, X), where the new features are - the enriched contaminated water (10, 38) is transported from the separator (D, U) to an osmotic high potential side (RH) to at least one salt energy cell (R) and water with an osmotic lower potential is transported to an osmotic low potential side (RL) to at least the salt cell (R); - convert the energy represented by the osmotically increased pressure due to the difference in the osmotic potential in the salt cell (R) into mechanical energy. Another aspect of the invention is an apparatus for simultaneous recovery of energy and purification of contaminated produced water from a petroleum well from an inlet for the contaminated water (3,31), comprising - a hydrate reactor (C, T) arranged for the formation of hydrates ( 4.33) from the contaminated water (3.31), - a hydrate-forming compound (8, 36) for addition to the contaminated water (3, 31) in the hydrate reactor (C, T), - a control system (CS) for sensing and controlling pressure and temperature conditions in the hydrate reactor (C,T) so that hydrates (4, 33) are formed; - a separator (D, U) for receiving and separating the hydrates (4, 33) and the enriched contaminated water (10, 38) - a dissociation tank (F, W) for receiving and dissociating the resulting separated hydrates (6 , 34) to separate clean water (9, 37) and the hydrate-forming compound (8, 36), - a return line (L8, L36) for returning the hydrate-forming compound (8, 36) via a pump (P) to the hydrate reactor (C, T) , and - a clean water outlet line (L) for the clean water (9, 37) to a clean water reservoir (K, X) where the new features are - a mixer on the return line (L8, L36) between the pump (P) and the hydrate reactor (C, T), the mixer (Mixer) arranged for injecting or recirculating hydrate seeds (32) to the contaminated water (3, 31) in the hydrate reactor (C, T) for improved hydrate formation, - one or more salt cells (R) with an osmotic high potential side (RH) for receiving the enriched contaminated water (10, 38) from the separator (D, U), and an osmotic low potential side (RL) for receiving va nn with lower osmotic potential; - a converter (RT) for converting osmotic pressure, which occurs due to the difference in osmotic potentials in the salt cell (R), into mechanical energy.

Further specific features of the invention are given in the appended subordinate claims.

Benefits

Recovery of parts of the energy

A first advantage of the present invention is that the process utilizes the osmotic potential which is latent in the concentrated liquid which is the result of the cleaning process. This energy can be recovered and can be fed back into the process as either electrical power or direct mechanical energy. By converting this energy by means of a generator into electrical energy, it becomes easy to control and adjust the power required by any required power-consuming step internally, to drive pumps, valves, etc., or for other process consumption. This reduces the need for externally supplied energy.

Integrated felling

Another advantage is that in the cases of re-injection into the oil reservoir, precipitation and energy extraction can be carried out in the same process step. The low salinity stream must be carefully monitored to ensure that precipitation occurs downstream of the osmotic barrier.

Reduced energy loss

A third advantage of the invention is the combined heat exchanger reactor tank (Q). By building the dissociation tank together with the hydration tank, there will be a reduced loss in energy due to shorter energy transport.

Improved heat exchange

A fourth advantage is the shape of the tubes used in at least one of the reactor tanks, i.e. at least in part of the heat exchanger. The specially designed tubes are multi-directionally corrugated to increase fluid turbulence and/or hydrate flow on both sides of the tube walls. The heat exchange will double or triple when using corrugated pipes.

Accelerated hydrate formation

A fifth advantage of the invention is the way to mix the hydrate former (a gas) with contaminated water. The mixing takes place in a mixing unit that forms small gas bubbles and water droplets. This increases the reaction rate with a minimum of energy input.

Improved hydrate-forming gases

A sixth advantage is the use of "designer gases" as hydrate formers. Hydrate-forming compounds are characterized by the fact that they are relatively small, non-polar molecules, primarily of the lower hydrocarbons such as methane, ethane and propane, but also carbon dioxide, nitrogen, oxygen, dihydrogen sulphide, halogenated hydrocarbons where the halogen is chosen from fluorine, chlorine , tetrahydrofuran, ethylene oxide, noble gases such as helium, neon, argon, xenon, krypton, sulfur hexafluoride and nitrous oxide can be used. Due to Xenon's favorable pressure and temperature properties, this can be a usable gas to use to minimize energy consumption in the process. But, Xenon is rare and expensive. Many natural gases are suitable for the purpose of forming hydrates, but due to the danger of explosion they are less advantageous. When you design a mixture of natural gases and C02 as "cover gas", you can reduce the risk of explosion but retain the good properties that save the supply of energy. Propane and isobutane are such preferred natural gases suitable for design. Mixing 4% propane with 96% C02 retains the pressure properties of propane and the delta T properties of C02. A higher proportion of propane can improve the hydrate formation process but increases the risk of explosion.

Short figure explanation

Figure 1 shows a flow diagram of an embodiment of the background technique, the so-called Ecowat process, for cleaning produced water. Figure 2 shows a flow diagram of an embodiment of the background technique, the Ecowat process, for purifying water from a source of drinking water. Figure 3 shows a flow diagram of an embodiment of the background technique, the Ecowat process, for cleaning gas/air. Figure 4 shows a pressure/temperature relationship for the dissociation of hydrates, at different salt concentrations with C02 as the hydrate-forming compound. Hydrate formation is kinetically controlled and takes place at conditions above/to the left of the respective curve. Figure 5 shows a pressure/temperature relationship for the dissociation of hydrates, at different salt concentrations, as in Fig. 4, but with CH4 as the hydrate-forming compound. Figure 6 shows a pressure/temperature relationship for the dissociation of hydrates, at different salt concentrations, such as for

Fig.5, but with C2H6 as hydrate-forming compound.

Figure 7 shows a flow diagram for low-energy purification of water according to an embodiment of the invention. Figure 8 shows parts of Fig. 7 with illustration of details in the insets 8a and 8b. Fig 8a shows an illustration of corrugated pipes in the heat exchanger (Q).

Figure 8b shows a longitudinal section of the mixer (IM).

Figure 9 shows a flow diagram of an alternative embodiment of the cleaning process before the osmotic energy recovery step with the hydrate forming unit and dissociation unit split instead of integrated in the integrated heat exchanger (Q) and in addition a degasser for the distinctive process step.

Description of embodiments of the invention

The present invention relates to a low-energy method for purifying water and an apparatus adapted to this process. According to the invention, the contaminated water (3, 31) is led through pipes from an inlet for contaminated water, then the contaminated water (3, 31) is added to a hydrate reactor (C, T). A hydrate-forming compound (8, 36) and hydrate germ (32) are added to the contaminated water (3, 31) in the hydrate reactor (c, T). Pressure and temperature conditions in the hydrate reactor (C, T) are controlled so that hydrates (4, 33) are formed. The hydrates (4, 33) formed in this way and with this the enriched polluted water (10, 38) are transported to a separator (D, U) which separates the hydrates (4, 33) from the polluted water (10, 38). The resulting separated hydrates (6, 34) are then transported to a dissociation tank (F, W). Here, the transported separated hydrates (6, 34) are dissociated so that pure water (9, 37) and the hydrate former (8, 36) can be separated. Furthermore, the hydrate former (8, 36) is returned via a pump (P) to the hydrate reactor (C, T). The clean water (9, 37) is fed to a clean water reservoir (K, X). The enriched polluted water (10, 38) is transported from the separator (D, U) to an osmotic high potential side (RH) of at least one salt energy cell (R). Water with a lower osmotic potential is transported to an osmotic low potential side (RL) by at least one salt cell (R). Energy represented by pressure increase due to the difference in osmotic potential in the salt energy cell(R) is converted into mechanical energy.

In one embodiment of the invention, the energy that arises due to the difference in osmotic potential in the salt cell (R) is used to drive at least the pump (P) either directly, mechanically via a shaft, belts or gears, or indirectly.

In one embodiment of the invention, the osmotic pressure formed in the salt cell (R) is utilized in a turbine (RT) or motor that drives a generator (RG) to produce electrical power. The converter (RT) can in one embodiment be a fluid-powered motor.

In one embodiment of the invention, the heat that occurs during the formation of the hydrates (4, 33) is exchanged with

the dissociation process for the hydrates (6, 34) in the heat exchanger (Q). The heat exchanger (Q) comprises the hydration tank (C,T) and the dissociation tank (F, W).

In one embodiment of the invention, the heat exchanger (Q) is a tube-in-tube or a tube-in-mantle heat exchanger in which one or more of the tubes are corrugated to increase turbulence and heat transfer. Such specially designed tubes are corrugated in multiple directions and increase the contact surface and turbulence in the liquid and/or hydrate flow on both sides, both internally and externally related to the tube wall.

In one embodiment of the invention, the water with a lower osmotic potential contains a proportion of fresh water, seawater or the polluted water (3, 31) supplied through the inlet line (SW, FW, CW). The type of osmotic low-potential water used is determined depending on the reason for cleaning the contaminated water. During petroleum production formation water treatment, it may be natural to use seawater. In that case, a precipitation step (SP) will follow.

Produced water is often richer in barium, strontium and calcium ions than seawater, and seawater is much richer in sulphates. If these two types of brine are mixed, sulphate salts of the aforementioned ions will precipitate as insoluble solids. By mixing the two layers, the sulfate ions are removed and the remaining layer is fine for re-injection into the reservoir as pressure support.

In one embodiment of the invention, the contaminated water (3,31) is heat exchanged with resulting clean water (9, 37) in a heat exchanger (LH) if the contaminated water has a higher temperature than preferred for an efficient hydrate-producing process. An inlet temperature of the water to be treated that is close to the process temperature for hydrate formation will lower the need for energy supply. Similarly, the clean water temperature (9, 37) will increase from a typical process temperature of about -1.5 degrees C, will be better for the environment and prevent the resulting clean water (9,37) from freezing.

In one embodiment of the invention, the hydrate-forming compound (8, 38) is a design gas comprising a mixture of CO 2 and a light hydrocarbon compound. The light hydrocarbon compounds can be primary low hydrocarbons, e.g. methane, ethane and propane, but also carbon dioxide, nitrogen, oxygen, dihydrogen sulphide, halogenated hydrocarbons where the halogen is selected from fluorine, chlorine, tetrahydrofuran, ethylene oxide, noble gases such as helium, neon, argon, xenon, krypton, sulfur hexafluoride and nitrous oxide.

In one embodiment of the invention, the enriched contaminated water (10, 38) is passed through an ion exchanger to exchange toxic ions with non-toxic ions for precipitation prior to disposal of the contaminated water.

Claims (16)

1. A method for simultaneous recovery of energy and purification of contaminated water (3, 31) from an inlet of contaminated produced water from a petroleum well, comprising the steps: - adding the contaminated water (3, 32) to a hydration container (C, T ) , - provide a hydrate-forming component (8, 36) and hydrate seed (32) to the contaminated water (3, 31) in the hydration container (C, T) , - control pressure and temperature in the hydration container (C, T) so that hydrates (4, 33) are formed; - transporting hydrant (4, 33) and with it the enriched contaminated water (10, 38) to a separator (D, U); - separate the hydrates (4, 33) from the contaminated water (10, 38); - transport the now separated hydrates (6, 34) to a dissociation tank (F, W), and - dissociate the transported separated hydrates (6, 34) to separate ignited water (9, 37) and hydrate-forming component (8, 36) by subsequent return of the hydrate-forming component (8, 36) via a pump (P) to the hydration reactor (C, T), and lead the clean water (), 37) to a clean water reservoir (K, X); characterized by - the enriched polluted water (10, 38) is transported from the separator (D, U) to an osmosis high potential side (RH) to at least one salt energy cell (R) and water with an osmotic lower potential is transported to an osmosis low potential side (RL) to at least the salt cell (R); - convert the energy represented by the osmotically increased pressure due to the difference in the osmotic potential t the salt cell (R) into mechanical energy. 2. The method according to claim 1, wherein the energy is used to drive at least the pump (P). 3. The method according to claim 1, where the osmotic pressure formed in the salt cell (R) is utilized in a turbine (RT) or in an engine that drives a generator (RG) for the production of electrical power. 4. The method according to claim 1, where the heat developed by hydrate formation (4, 33) is heat exchanged with the dissociation process for the separated hydrates (6, 34) in the heat exchanger (Q). 5. The method according to claim 1, where the water with a lower osmotic potential comprises a proportion of the polluted water (3, 31). 6. The method according to claim 1, where the water with a lower osmotic potential comprises seawater. 7. The method according to claim 1, where the water with a lower osmotic potential comprises fresh water. 8. The method according to claim 1, where the contaminated water (3, 31) is heat exchanged with the clean water (9, 37) in a heat exchanger (LH). 9. The method according to claim 1, wherein the hydrate-forming compound (8, 38) is a design gas comprising a mixture of CO 2 and a light hydrocarbon compound. 10. An apparatus for the simultaneous recovery of energy and purification of polluted produced water from a petroleum well, (3, 31) from an inlet for the polluted water (3, 31), comprising - a hydrate reactor (C, T) arranged for the formation of hydrates (4,33) from the contaminated water (3,32), - a hydrate-forming compound (8, 36) for addition to the contaminated water (3, 31) in the hydrate reactor (C, T), - a control system (CS) for sensing and controlling the pressure and temperature conditions in the hydrate reactor (C,T) so that hydrates (4, 33) are formed; - a separator (D, U) for receiving and separating the hydrates (4, 33) and the enriched contaminated water (10, 38) - a dissociation tank (F, W) for receiving and dissociating the resulting separated hydrates (6, 34) to separate clean water (9, 37) and the hydrate-forming compound (8, 36), - a return line (L8, L36) for returning the hydrate-forming compound (8, 36) via a pump (P) to the hydrate reactor ( C, T), and - a clean water outlet line (L) for the clean water (9, 37) to a clean water reservoir (K, X); characterized by- a mixer on the return line (L8, L36) between the pump (P) and the hydrate reactor (C, T), the mixer (Mixer) arranged for injecting or recirculating hydrate seed (32) to the contaminated water (3, 31) in the hydrate reactor (C, T) for improved hydrate formation, - one or more salt cells (R) with an osmotic high potential side (RH) for receiving the enriched contaminated water (10, 38) from the separator (D, U), and an osmotic low potential side ( RL) for receiving water with a lower osmotic potential; - a converter (RT) for converting osmotic pressure, which occurs due to the difference in osmotic potential in the salt cell (R), into mechanical energy. 11. The apparatus according to claim 10, where the hydrate reactor (C, T) and the dissociation tank (F, W) form the heat exchanger (Q). 12. The apparatus according to claims 10 and 11, where the heat exchanger (Q) is a tube-in-tube or a tube-in-mantel heat exchanger where one or more of the tubes are corrugated. 13. The apparatus according to claim 10, where the converter (RT) is arranged to supply mechanical energy to at least the pump (P) either directly or indirectly. 14. The apparatus according to claim 10, wherein the converter (RT) is a liquid-driven motor or a turbine (RT). 15. The apparatus according to claim 10, wherein the osmotic low potential side (RL) is equipped with an inlet line (SW, FW, CW) to receive water with a lower osmotic potential such as fresh water, sea water or the polluted water (3, 31). 16. The apparatus according to claim 10, where a heat exchanger (LH) is arranged to heat exchange the contaminated water (3, 31) with the purified water (9, 37).