Patent Application
20140165928
None.
Embodiments of the invention relate to methods and systems for generating steam which may be utilized in applications such as bitumen production.
Several techniques utilized to recover hydrocarbons in the form of bitumen from oil sands rely on generated steam to heat and lower viscosity of the hydrocarbons when the steam is injected into the oil sands. One common approach for this type of recovery includes steam assisted gravity drainage (SAGD). The hydrocarbons once heated become mobile enough for production along with the condensed steam, which is then recovered and recycled.
Costs associated with building a complex, large, sophisticated facility to process water and generate steam contributes to economic challenges of oil sands production operations. Such a facility represents much of the capital costs of these operations. Chemical and energy usage of the facility also contribute to operating costs.
Past approaches rely on once through steam generators (OTSGs) to produce the steam. However, boiler feed water to these steam generators requires expensive de-oiling and treatment to limit boiler fouling problems. Even with this treatment, fouling issues persist and are primarily dealt with through regular pigging of the boilers. This recurring maintenance further increases operating costs and results in a loss of steam production capacity, which translates to an equivalent reduction in bitumen extraction.
Therefore, a need exists for methods and systems for generating steam that enable efficient hydrocarbon recovery from a formation.
In one embodiment, a method of vaporizing water includes heating solid particulate by heat exchange with hot fluids separated from the solid particulate by a thermally conductive material. The method further includes introducing the water into contact with the solid particulate heated to a temperature that results in vaporizing the water into steam. In addition, the method includes separating the steam from the solid particulate.
For one embodiment, a system for vaporizing water includes a heat exchanger for heating solid particulate with hot fluids separated from the solid particulate by a thermally conductive material. The system further includes an inlet to a steam generating vessel to supply the water into contact with the solid particulate heated to a temperature that results in vaporizing the water into steam. Further, an output to the steam generating vessel conveys the steam separated from the solid particulate.
A more complete understanding of the present invention and benefits thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings.
Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated.
Embodiments of the invention relate to systems and methods for vaporizing water into steam, which may be utilized in applications such as bitumen production. The methods rely on indirect boiling of the water by contact with a substance such as solid particulate heated to a temperature sufficient to vaporize the water. Heating of the solid particulate may utilize pressure isolated heat exchanger units or a hot gas recirculation circuit at a pressure corresponding to that desired for the steam. Further, the water may form part of a mixture that contacts the solid particulate and includes a solvent for the bitumen in order to limit vaporization energy requirements and facilitate the production.
In any embodiments disclosed herein, the water may come from separated production fluid associated with a steam assisted gravity drainage (SAGD) bitumen recovery operation. The water at time of being generated into the steam may still contain: at least about 1000 parts per million (ppm), at least 10,000 ppm or at least 45,000 ppm total dissolved solids; at least 100 ppm, at least 500 ppm, at least 1000 ppm or at least 15,000 ppm organic compounds or organics; and at least 1000 ppm free oil. Injecting the steam through an injection well into the formation during the bitumen recovery operation thus enables sustainable recycle of the water without stringent treatment requirements of conventional boiler feed.
Each of the vessels 101, 102 couples to a water injection line 104 and a heat source line 106. A manifold system controls flow through the vessels 101, 102 to a steam output 108 and an exhaust 110 and includes first through eighth valves 111-118. In operation, the valves 111-118 alternate between heating and steam generation cycles with the first vessel 101 being shown in the steam generation cycle while the second vessel 102 is in the heating cycle.
As shown, the first and fifth valves 111, 115 on the water injection line 104 and the steam output 108 thus remain open to flow of the water through the first vessel 101 to generate the steam while the third and seventh valves 113, 117 block flow of the water through the second vessel 102. The steam exits the first vessel 101 through the steam output 108, which may couple to the injection well, and is separated from the solid particulate that remains in the first vessel 101 and may be trapped by filters or cyclones. The second and sixth valves 112, 116 block flow from the heat source line 106 to the first vessel 101 at this time while the fourth and eighth valve 114, 118 are open to flow of oxygen and fuel, such as methane, from the heat source line 106 through the second vessel 102 to the exhaust 110. As thermal load of the solid particulate in the first vessel 101 becomes depleted, position of each of the valves 111-118 switches such that steam is generated in the second vessel 102 while the solid particulate is reheated in the first vessel 101.
The oxygen and fuel passing through the second vessel 102 combusts to reheat the solid particulate. During such combustion, contaminants, such as organic compounds deposited on the solid particulate from the water, may partially or fully convert into carbon dioxide and water, and some salts deposited on the solid particulate from the water may come off and be swept out of the second vessel 102. The combustion heats the solid particulate to a temperature that results in vaporizing the water upon contact therewith in the steam generation cycle that follows.
Not all embodiments rely on such cleaning of the solid particulate. Surface area of the solid particulate provides enough dispersion of the deposits to limit heat transfer interference. As needed over time, replacing some or part of the solid particulate may ensure desired performance is maintained at minimal cost and with limited to no interruption. For example, a lockhopper system employed with embodiments where the solid particulate is always in a pressurized environment can enable such withdrawal and replacement while in continuous operation.
Due to the first and second vessels 101, 102 with the manifold system, the heat source line 106 can supply the oxygen and fuel without compression to pressures desired for the steam to be injected into the formation. This relative lower pressure combustion facilitates economic production of the steam. Alternating each of the vessels 101, 102 between the steam generation cycle and the heating cycle also eliminates need for conveying the solid particulate to units dedicated to one particular cycle.
In some embodiments, the water mixes with a solvent 120 for the bitumen prior to vaporization due to contact with the solid particulate. The solvent 120 (common reference number depicted in all figures) thus may flow as a liquid into the water supply line 104 to form a resulting mixture of the water with the solvent 120. Vaporization of the water along with the solvent 120 results in the steam output 108 also containing both water and solvent vapors, as may be desired for injection into the formation.
The solvent 120 may include hydrocarbons having between 3 and 30 carbon atoms, such as butane, pentane, naphtha and diesel. Temperatures associated with the indirect boiling described herein limit potential problems of cracking the hydrocarbons, which can tend to occur if passed through direct fired boilers that may thus require injection of any wanted solvents into steam rather than boiler feed. Such injection of the solvent into the steam instead of the water feed may either cause loss of some steam due to condensation or require superheating of the steam. Conventional superheating of the steam also suffers from fouling problems. Therefore, the solvent 120 may flow into steam superheated by steam generation methods described herein in some embodiments since the fouling issues from the superheating are overcome in the same manner as those associated with steam generation.
The mixture in the water supply line 104 may include between 5 and 30 percent of the liquid hydrocarbon by volume. The mixture may further provide an energy requirement for vaporization that is at least 10 percent lower than water alone. For example, a 28:72 ratio of butane to water reduces steam generator duty by 22 percent as compared to water alone.
In some embodiments, the solid particulate heated in the heating vessel 202 transfers to the steam generating vessel 201 by gravity since the heating vessel 202 is disposed above the steam generating vessel 201. A water supply line 204 then inputs the water into contact with the solid particulate that is heated to result in vaporizing the water and providing a steam output 208. Some of the steam output 208 may provide lift for the solid particulate being returned up the riser 200 to the heating vessel 202. For some embodiments, the water vaporizes in the riser 200 such that the steam generating vessel 201 is not even required and the steam is recovered at a riser output 209.
The gaseous fluid that exits the heating vessel 302 through an outlet 310 passes through heat exchanger(s) 350 and a fin-fan cooler 352, if necessary. The heat exchanger 350 may transfer heat with the gaseous fluid post compression boosting and/or with the water 304 being input into the steam generating vessel 301. Such heat exchange helps maintain efficiency while bringing the temperature of the gaseous fluid below temperature limits of a compressor 358 through which the gaseous fluid is sent downstream in the circuit.
A purge 354 allows removal of a portion of the gaseous fluid, which may pick up contaminants, such as from cracking or entrainment. Makeup gas 356 combines with the gaseous fluid to replace that purged. In some embodiments, the gaseous fluid includes an inert gas such as nitrogen and may also include air or oxygen for burning of the deposits. Methane may provide the gaseous fluid for some embodiments and may be desired due to its relative higher thermal capacity.
The compressor 358 only boosts pressure of the gaseous fluid circulating through the circuit. For example, the compressor may provide between 50 and 150 kilopascals (kPa) boost in pressure, which is achievable without making steam generation uneconomical by requiring levels of compression needed to increase atmospheric pressure to above 2500 kPa. The gaseous fluid in the circuit may thus always remain above 2500 kPa, in some embodiments.
The gaseous fluid from the compressor 358 then flows through the circuit to a furnace 360. The furnace 360 burns fuel to reheat the gaseous fluid that reenters the heating vessel 302 through a heat source line 306 for sustained heating of the solid particulate within the heating vessel 302. The heating vessel 302 may include multiple (e.g., 6 as shown) bed stages 362 or trays such that the solid particulate passing through the heating vessel 302 counter current with the gaseous fluid achieves efficient heat cross exchange.
Pressure of the steam desired for injection into the formation dictates pressure inside the steam generating vessel 301. With the recycled gaseous fluid circulating in the circuit to reheat the solid particulate, both the steam generating vessel 301 and the heating vessel 302 may operate at this pressure, such as above 2500 kPa, provided there may be sufficient differences in pressure in the vessels 301, 302 or other such arrangements described herein to maintain fluid flows. For some embodiments, a slipstream 364 of the gaseous fluid also at necessary pressure provides lift for transporting the solid particulate from the steam generating vessel 301 to the heating vessel 302.
Outflow from the pump 458 and any makeup 456 then flows through the circuit to a furnace 460. The furnace 460 burns fuel to vaporize and reheat the gaseous fluid that reenters the heating vessel 402 through a heat source line 406 for sustained heating of the solid particulate within the heating vessel 402. While pressure in the circuit again stays at a level similar to that desired for the steam to be injected into the formation, the pump 458 may influence efficiency if used in place of compression. Use of the pump 458 with the gaseous fluid that is condensed may further enable economic once through heating (i.e., without the circuit) at the desired pressure similar to approaches depicted in
In operation, oxygen and fuel react in a combustor 560 to generate a flue gas conveyed to the heat exchanger 562 by a heat source line 506. The flue gas passes through the heat exchanger 562 and exits via an exhaust 510. A thermally conductive material forms the heat exchanger 562 such that heat from the flue gas transfers to the solid particulate in the heating vessel 502. In some embodiments, the thermally conductive material forms a tube of the heat exchanger. The tube may coil within the heating vessel 510 to provide the heat exchanger 562 with either the solid particulate flowing through an inside of the tube or the flue gas flowing through the inside of the tube.
For some embodiments, a fluidization gas, such as air, passes through the inside of the heating vessel 502. This gas may help remove contaminants from the solid particulate as well. Use of the gas for only fluidization while relying on heating by the heat exchanger 562 limits quantity and compression requirements for the gas whether the gas is used once through or circulated in a circuit.
The heat exchanger 662 transfers heat from the circulating liquid to the solid particulate and may have a design such as described with respect to the heat exchanger 562 shown in
The heat exchangers 562, 662 in
Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims, while the description, abstract and drawings are not to be used to limit the scope of the invention. Each and every claim below is hereby incorporated into this detailed description or specification as additional embodiments of the present invention. The invention is specifically intended to be as broad as the claims below and their equivalents.
This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/737,967 filed Dec. 17, 2012, entitled “HEAT EXCHANGE FOR INDIRECT BOILING,” which is incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61737967 | Dec 2012 | US |
