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A) DCSG (Direct Contact Steam Generation) technology:
Ex-Tar’s Oilsands technological solutions are based on the DCSG principle.
What is a DCSG?
In “Direct Contact Steam Generation” (DCSG), the heat is transferred between the combustion gases and the liquid water through the direct mixing of the two flows. The combustion pressure is similar to the produced steam pressure and the combustion gases are mixed with the steam. The DCSG can also be referred to as direct contact evaporator or direct contact dryer. Depending on the system used, Low Pressure (LP), Medium Pressure (MP), or High Pressure (HP), stream can be produced.
In a Non-Direct Steam Generator (like a steam boiler with a steam drum and a mud drum) or a “Once Through Steam Generator” (OTSG), the heat transfers from the combustion side to the steam generation side through a physical separation (typically a metal wall) that allows the heat transfer but prevents the mixture of the combustion side fluid, the water and steam fluid. The pressure of the generated steam is higher than the pressure of the combustion. This allows for the use of atmospheric combustion pressure and high pressure steam. The product is pure steam (or a steam and water mixture, as in the case of the OTSG).
The conceptual differences between DCSG and Non-DCSG are represented in the following figure:
Was a Direct Contact Steam Generator concept used before?
The DCSG is an old technology. In the 70’and early 80’s down hole and above ground DCSGs were used for Enhanced Oil Recovery (EOR).
In a Down Hole Direct Contact Steam Generator, fuel (usually natural gas) with water is injected and combusted underground to generate a pressurized mixture of steam and combustion gas. The technology didn’t become a commercial success due to various reasons. For further information we recommend the following reading: Reflections on a Down-hole Steam Generator Program, by Donaldson, A.B., New Mexico Highlands University, Society of Petroleum Engineers paper No. 38276-MS.
At the same period, above-ground DCSGs were also developed. These DCSGs produced corrosive mixtures of water and combustion gases. They used relatively high quality fuel (like natural gas), relatively high quality water and produced liquid waste discharge.
What are Ex-Tar DCSG proprietary method improvements over the old DCSG concept?
1. Use low quality fuel for combustion, like Petroleum Coke.
2. Use low quality water, with high level of organics and solids.
3. Remove the contaminants in a dry or stable form (Zero Liquid Discharge).
What systems can be used to implement Ex-Tar DCSG method?
There are several commercially available designs that can be used, possibly after modifications.
Ex-Tar developed several systems that can be used for different applications. The basic systems are presented here:
1. Rotating DCSG:
A pressurized inclined vessel includes an internal combustion head at its high point. Fuel and oxidizing gas are injected through the combustion head and combusted inside the pressurized sloped vessel. The vessel includes an internal rotating enclosure. Low quality water is injected into and around the combustion reaction. The heat transfer is enhanced by the use of solid particles, chains and possibly lifting objects that are moving with the rotating enclosure. The solid particles or chains also remove solid build-up deposits, to keep the rotating vessel clean and maintain optimum efficiency.
(Source : US7814867)
2. Up-flow fluid bed combustion DCSG
Water is injected at the upper section of the pressurized fluid bed combustor. A portion of the heat is used to generate HP steam through the heat exchanger inside the boiler while the rest is used to generate a MP or LP mixture of steam and combustion gas through direct contact with the injected water.
(Source: CA 2665751 )
3. Down-flow combustor DCSG
The figure below represents a DCSG with down-flow combustor integrated with internal heat exchanger and water injection for direct contact steam generation and solid discharge at the bottom.
Fuel (such as petcoke slurry), oxidizer (such as oxygen or air), and water are supplied to a pressurized combustor at the upper section. The reaction temperature is controlled by the water flow introduced into the combustor. A portion of the combustion heat can be used through heat exchangers to generate HP steam. Low quality water is injected into the combustion gas to generate steam by direct contact heat exchange. The fluid bed section is at the bottom of the vessel, where cold gas circulates and flows upwards to suspend the solids bed.
(Source: US 61/092,669 )
4. Integrated rotating DCSG
The DCSG generates a stream of pressurized dry steam, combustion gas and a carry-on solids mixture. The recycled saturated water in the vessel can include limestone and other alkali materials to remove SO2. The dry steam and combustion gas mixture is washed by liquid water at the saturation temperature in the lower section of the rotating DCSG. This is the section where additional saturated steam is generated and the solids are scrubbed by the saturated water. Acid gas can be removed in that section as well. The solids rich water is recycled back to the DCSG. The produced saturated steam in gas flow can be used for EOR or to operate a water treatment facility where it is condensed to generate condensate and heat. The condensate can be added to the distillate BFW supplied to a steam generation facility. The DCSG can be internal-fired or external-fired by injecting hot combustion gas from a pressurized boiler facility.
The following figure represents an external fired rotating DCSG integrated with saturated steam generation / wet scrubber for generation of scrubbed wet steam and solid waste.
The water locked in the non segregate fine tailings is released and re-used for bitumen extraction, thus reducing the fresh river water consumption.
Ex-Tar’s intensive heat method does not change the extraction, hydro transport, separation and froth treatment processes which are well established and currently in use by the industry. The changes affected by Ex-Tar’s method will be the way in which the hot process water is produced and the way in which the dry clay from the fine tailings (FT) is disposed of.
“Reclaim As You Go”: Addressing the tailings problem as an integrated part of the overall Bitumen extraction process.
Method’s main characteristics:
- Consume low grade fuel to generate heat energy
- Use the heat energy to reverse the Fine tailings creation process
- Recover the Fine Tailings water component and the energy to generate hot process water for oilsands extraction
- Dispose of the solids back into the pit
For additional technology information, please refer to the following sections:
1. Publications section- See Second International Oilsands Tailing Conference paper.
2. Intellectual Property section- See CA 2686140, CA 2665747, US 20100147516 A1.
C) Pressurized steam and combustion gas mixture technology:
This proprietary technology was developed for the production of a mixture of steam (hot water vapor) and combustion gas fluids for EOR using DCSG (Direct Contact Steam Generator). The technology is ZLD (Zero Liquid Discharge) in nature (prevents the generation of liquid waste stream). The system can consume low quality water (like recycled produced water) and low quality fuel (like petcoke or coal).
In case an Air Separation Unit (ASU) is used, the steam and combustion gas includes mainly CO2 mixed with the steam. The CO2 is known to dissolve in underground tar formations and to help in mobilizing the tar, basically behaving like a solvent.
This system has a few advantages over standard steam generation facilities. It will minimize the requirement for fresh water and water treatment facilities. It can also minimize the need for steam distribution lines. The use of a steam and combustion gas mixture is an attractive alternative to formations that are losing pressure with poor recovery performance. The presence of the combustion gas, especially the CO2, with the steam can improve the bitumen recovery and pressurize the formation. On top of that, permanent loss of CO2 is positive as it can be considered as desirable CO2 sequestration. The use of a steam and combustion gas mixture is also attractive to heavy oil formations where most of the heavy oil areas are relatively thin zones and HP steam temperatures are above the temperature limitation of the existing wells.
Aging SAGD wells with developed underground chambers can also be a significant consumer of steam and combustion gas injection fluid. The DCSG combustion gas and steam mixture costs less than steam, this will offset the increasing amount of fluid that have to be injected to the aging formation. The thermal energy added to the reservoir is the latent heat of evaporation of the water vapour. Some non-condensed gases (NCG) will migrate to the upper section of the SAGD chamber and will pressurize it. A portion of the CO2 will permanently stay in the formation (CO2 sequestration).
For additional information, please refer to the following sections:
1. Publications section- See SPE paper Number 137633-MS.
2. Intellectual Property section- See US7,694,736 and US7,699,104.
Ex-Tar developed a method intended to integrate DCSG into a NON-DCSG and maintain most of the advantages the DCSG offers for generating standard high pressure steam (without a CO2 component within the steam).
This technology was developed to overcome potential disadvantages of directly injecting a steam and combustion gas mixture into underground formations, especially in the early stages of its life cycle when the underground steam chamber is not developed yet.
This method uses low grade fuel with commercially available solid fuel burner packages, integrated with a commercially available boiler, a commercially available distillation facility, and a DCSG with an enhanced oil recovery unit to separate the water and combustion gas with Zero Liquid Discharge (ZLD). The water feed can be water separated from produced oil and/or low quality water salvaged from industrial plants, such as refineries and tailings as make-up water. Both of the above characteristics will allow oilsands operators to more easily meet environmental regulations without radical changes to oil recovery and water recycling technologies currently in use.
This solution can be used when and where it is impossible to inject a mixture of combustion gas and steam for EOR, like in early production stages of thick underground oil-bearing formations produced by SAGD and in other instances that required only steam for EOR.
The method and its associated system can be applied to many existing oilsands operations. This method proposes to improve enhanced oil recovery facilities, such as SAGD, through a supply of high – pressure steam for underground injection wells with zero liquid discharge.
Schematic description of Ex-Tar’s method:
Water is supplied to a commercially available water treatment plant. The water can be produced water, make-up water in the form of brackish water, or any other available water with high levels of dissolved or suspended solids. The water treatment plant includes a distillation facility.
An additional facility can be included as well, like de-oiled and lime softening. In case there are two types of oil treatment facilities, it will be preferred that the produced water will be treated by the conventional softening systems and the make-up brackish water will be treated by the distillation facility. The split is to minimize the volatile organics problem in the distillation process and to remove Total Dissolved Solids (TDS) from the water feed. The distillation facility is commercially available and can include an evaporator, MED, MSF, or MVC. The treated Boiler Feed Water (BFW) from the water treatment plant is supplied to the steam generation facility.
The water treatment plant includes the water-oil separation unit. The discharge waste water is the collection of the entire discharge stream from the different units in the water treatment plant. It includes brine from distillation unit, discharged oily water from the oil separation unit, sludge from softening system (if such a system is used), and filtered backwash, chemical wash or any other generated waste stream.
The steam generation unit can include different types of industrial boilers, OTSG, or any other commercially available steam generation facility. The steam generation can also be integrated into the DCSG by recovering part of the combustion heat for generating steam through non-direct steam generation. The steam generation generates, via non-direct heat exchange, pure steam (without combustion gas mixture within).
The discharge waste water from the steam generation blow down or from the OTSG, after flashing the generated water, is directed to the DCSG, together with any other liquid waste discharged streams. The DCSG evaporates the water by direct mixture with combustion gas stream while using the combustion heat energy to transfer the water into gas. The solids are removed in a stable form. The water and heat are recovered from the discharged gas flow. The water is recycled and used as BFW and the heat is used to operate the distillation unit.
For additional information, please refer to the following sections:
1. Publications section- See SPE paper Number 137633-MS.
2. Intellectual Property section- See CA 2684817.