Method for recycling deoiled water using counterflow falling-film evaporators
A method for treatment of produced water, particularly deoiled water, by evaporation. Methods use a vertical tube heat exchanger bundle where the brine is distributed in a falling film along the inside of the tube wall. Condensing steam causes a portion of the deoiled water to evaporate; this water vapor travels upward in a counterflow direction relative to the deoiled water. Evaporator sump volume is minimized, and evaporators may have a multi-piece construction to lower the center of gravity of an evaporator installation. This technology provides several advantages over conventional vertical tube co-current flow evaporators (where the vapor flows downward with the falling film). These advantages include a minimal total installed cost (TIC) and enhanced water chemistry management.
1. A method of treating water for heavy oil production, comprising:
(a) separating an oil and water mixture obtained from an injection well into separate mixtures of oil and produced water;
(b) sending said produced water to a header of an evaporator system as evaporator feedwater;
(c) preconcentrating the produced water in a vertical tube counterflow falling-film evaporator in a plurality of vessels and having a plurality of tubes, a top-head and a sump, wherein said sump has a volume between 0 and 10 m 3 ;
(d) circulating the produced water to the top-head of said evaporator where said produced water as a brine is distributed to create a falling film inside the evaporator tubes;
(e) transferring energy to the falling film by condensing steam external to a tube causing a portion of the produced water to evaporate as water vapor and causing the balance of the produced water in the falling film to become concentrated;
(f) removing said concentrated produced water from the evaporator for downstream treatment/disposal;
(g) sending said water vapor to a condenser where it condenses as distillate which is fed to a high pressure drum boiler or once through steam generator; and
(h) sending said high pressure steam to an injection well.
2. The method of claim 1 , further comprising dosing said produced water in the header with at least one member of the group consisting of antiscalant and dispersant.
3. The method of claim 1 , further comprising heating the produced water in the header.
4. The method of claim 1 , further comprising adding a base to the produced water, thereby removing hardness from the produced water prior to the step of preconcentrating the produced water in a vertical tube counterflow falling-film evaporator having a plurality of tubes, a top-head and a sump.
5. The method of claim 4 , comprising allowing the produced water to achieve equilibrium upstream of subsequent evaporation steps following addition of the base.
6. The method of claim 1 , comprising deaerating the produced water prior to the step of preconcentrating the produced water.
7. The method of claim 1 , comprising, between the steps of sending the produced water to the header and preconcentrating the produced water, the steps of:
heating the produced water in the header;
adding a base to the produced water, thereby removing hardness from the produced water and allowing the water to achieve equilibrium upstream of subsequent evaporation steps; and
deaerating said produced water.
8. The method of claim 1 , further comprising adding of make-up water to the feed header to produce a blended evaporator feed.
9. The method of claim 8 , wherein said make-up water is selected from the group consisting of brackish water, fresh water, boiler blowdown, and crystallizer distillate.
10. The method of claim 1 , further comprising dosing said produced water with a chemical agent to perform at least one of stabilizing and enhancing the solubility of at least one of silica and a silicate.
11. The method of claim 1 , wherein the produced water in the header is heated with excess heat transferred from a distillate stream leaving said evaporator.
12. The method of claim 1 , comprising passing the water vapor through at least one mist elimination stage.
13. The method of claim 12 , wherein said at least one mist elimination stage is an internal mist eliminator or external mist eliminator and is selected from the group consisting of a mesh pad eliminator, chevron eliminator, agglomerator, and combinations thereof.
14. The method of claim 1 , further comprising treating said vapor with vapor scrubbing operations.
15. The method of claim 1 , wherein said counterflow vertical-tube falling-film evaporator comprises four evaporator vessels making up two effects.
16. The method of claim 1 , further comprising sending said evaporator blowdown to a forced circulation evaporator for further concentration and water recovery.
17. The method of claim 1 , further comprising sending said evaporator blowdown to a brine stabilization and solidification process to create a single, solid disposal stream.
18. The method of claim 1 , further comprising sending said evaporator blowdown to a dryer to produce a solid disposal stream.
19. The method of claim 1 , further comprising sending said evaporator blowdown to a neutralization process for injection in a salt cavern for disposal.
20. The method of claim 1 , further comprising sending said evaporator blowdown to a neutralization/clarification process to prepare blowdown for injection in a deep-well for disposal.
21. The method of claim 1 , further comprising the step of deoiling said produced water.
22. The method of claim 1 , wherein said evaporator has a single effect in two vessels.