FIELD OF INVENTION
The present invention provides an apparatus for reducing the oxygen content or de-oxygenation of liquid and a process for performing the same.
BACKGROUND OF THE INVENTION
Oil and gas industry involves in generation of vast range of water streams during oil and gas operations. Produced water is one of the water streams generated from oil and gas industry. Oil wells contains huge amount of water along with well fluid. This water comes out from oil reservoir with crude. The quantity of water produced from well increases with time as oil well matures. Water is separated from crude during oil producing operations and separated water is called produced water. The produced water is reinjected in the well to maintain well pressure for enhance oil recovery.
To achieve maximum oil recovery from oil wells, water is re-injected in the well to maintain pressure thereof and to force the oil to production wells.
Produced water is treated before injecting in the well and deoxygenation of water is one of the required step for water treatment. The presence of dissolved oxygen in water is vulnerable to corrosion in industrial equipment and biological growth in water. In this instance, dissolved oxygen is needed to be removed before injection.
The US patent no. 5,180,403 is directed to method of vacuum deaeration. The patent describes a packed column vacuum degasifier for stream stripping of pure water to achieve oxygen content less than 10 ppb.
The US patent application no. US 2006/0150814 A1 describes a method and plant for the purification of produced water discloses a catalytic method for removing of dissolved hydrocarbons from produced water. In this process, hydrocarbons are stripped from produced water using nitrogen stripping. Nitrogen used for stripping should contain low oxygen. And hydrocarbon and oxygen rich nitrogen is treated in a catalytic convertor, where oxygen and hydrocarbons are converted in CO2 and water. And nitrogen is again re circulated in loop. 2
The US patent application no. US 2012/0118154A1 describes a method for reducing the dissolved oxygen content in seawater by fuel gas stripping and combustion of fuel gas for heating water. The stripping process is carried out in two separate equipment, a mixer and a stripper. The mixer is maintained at high pressure and temperatures.
There are many other apparatus such as membrane based and processes such as using chemical for deoxygenation of water are available. These processes have disadvantages. The membrane contactor is affected by the type of feed water entering the contactors. These contactors are susceptible and prone to fouling in the presence of oil and grease, hardness, heavy metals, phenolic and biological substances. Hence, feed water must be treated to remove the impurities before entering the membrane contactor which would require additional elaborated treatments. The present invention does not involve above process parameters & hence the above draw-backs are easily overcome.
And chemical based processes are costly and have logistic problems such as their storage and limited shelf-life thereof. In the present invention there is no requirement of chemicals.
Moreover, vacuum stripping of water for removing oxygen from water is also a well-known technology but it has limitation. Vacuum pumps are installed to create vacuum in a mechanical stripper through which oxygenated water is passing. The oxygen is stripped off from the water due to partial pressure difference. However, there is a temperature limitation on the injection water passing through the stripper under vacuum that it cannot exceed certain temperature to avoid entrainment of water and carryover into the vacuum pump. In the present invention energy requirement is nil and there is no temperature limitation. Hence, it overcomes drawback of vacuum stripping process.
Steam stripping of water is the conventional process used in industries for removal of dissolved oxygen from the Boiler Feed Water in which steam and oxygen saturated water is passed counter-current in a stripper column. It requires steam generation facility (including boiler, DM water production, etc.) and hence this is also cost intensive option. In the present invention, there is no requirement of such facility, stripping gas is easily available at the site.
The aim of present invention is to overcome the drawbacks of prior art. The present invention overcomes the limitations of the already existing inventions by providing an apparatus for 3
deoxygenation of liquid. Primary sources of water to be treated for deoxygenation is produced water for water reinjection. The use of the invention can be extended for deoxygenation of other water sources for reinjection and other purposes. The equipment of the invention eliminates the need for extreme conditions of pressure and temperatures Moreover, the present invention also provides a process for deoxygenation of liquid. The operating cost of the process of the present invention is negligible.
OBJECTS OF THE INVENTION
The objective of the present invention is to provide an apparatus for deoxygenation of liquid and a process for the same.
SUMMARY OF THE INVENTION
The main objective of present invention is to obtain an improved process to remove oxygen efficiently from liquid at low running cost. Without restricting the scope of the invention, the said liquid is water. The water source used for deoxygenation is produced water. The invention relates to deoxygenation of produced water for reinjection in the oil wells. Produced water is generated from oil wells along with oil and gas.
The present invention provides modification of conventional process/apparatus for removal of oxygen from liquid using a gas stripping at low pressures.
The improved process for deoxygenation of water comprises an absorber with two sections. The first section of the present apparatus is bulk oxygen removal section while in the second section fine tuning to achieve required oxygen content (< 20 ppbv) in produced water takes place.
The oxygen rich water stream enters through the liquid distributor in the first section top of the column, where it is contacted counter currently with the stripping gas. In order to increase the mass transfer between the two phases, low pressure drop and high performance internals are used. The packing/trays provides a high contact surface area and results in substantial removal of oxygen. The oxygen rich fuel/natural gas can be sent to existing gas header for further supply in fired heaters or other purpose. 4
In the second section of the column, water collected from first section is redistributed and contacted with stripping gas. In the second section, fine tuning of oxygen content in water takes place.
Additionally, a mist eliminator is also provided in the column to reduce/remove the water absorber, carried by the gas. The product stripping gas leaving the column rich in oxygen. A compressor is also proposed in the process scheme to raise the process slightly to remove water from stripping gas before sending it to existing stripping gas header. Fuel gas, Natural gas , Nitrogen and mixture thereof are used as stripping gas.
The process is summarized as below;
• The process is useful for removal of oxygen from water using Fuel gas, Natural gas, Nitrogen and mixture thereof by gas stripping of water.
• The process consists of two packed/trayed absorber for continuous removal of oxygen.
• A compressor is used to increase pressure of the oxygen rich gas to send it to fuel gas header.
• Water is contacted with low pressure fuel gas in two section contactor. And oxygen rich fuel gas is routed to existing fuel gas header through compressor, after cooler and knockout drum after water removal.
• Low pressure drop packing/trays and column internals are used in the process.
• The process is highly efficient and requires negligible energy compared to prior art.
• The fuel gas at exit is oxygen rich but there is no significant increase in level of oxygen, Hence, the quality and effectiveness of gas for further use will be unaffected.
Typical composition of low pressure offgas before and after treatment with the newly invented process is mentioned in table-4.
BRIEF DESCRIPTION OF FIGURES
The present invention will be further understood with reference to the accompanying drawings, wherein: 5
FIG. 1 is a schematic layout of an apparatus for deoxygenation of water having two sections. The lower section, which is the first section, is the bulk removal section while the upper section, which is the second section, is the fine-tuning section.
FIG. 2 is a schematic layout of Stripper for Deoxygenation of Water
DETAILED DESCRIPTION OF THE INVENTION
The present invention discloses an apparatus for reducing oxygen content or deoxygenation of liquid. Moreover, a process for deoxygenation of liquid is also disclosed. The apparatus of the present invention comprises of more than one sections where oxygen is removed.
Without restricting the scope of invention, the said liquid is water.
A source for water can produced water, which is fed to the apparatus for deoxygenation.
The Figures 1 and 2 attached illustrate the system and process for reducing oxygen content or deoxygenation of liquid. These figures show way to carry out the invention. In case of Figure 1, a complete process scheme and apparatus is described while Figure 2 illustrate the apparatus of the invention.
FIG. 1 shows the schematic layout of the process of the invention. The process comprises steps of supplying the oxygenated liquid and stripping gasinto the stripping column (B1). The oxygenated water (OW) is fed at the top of the column. Fuel gas, Natural Gas, Nitrogen and mixture thereof can be used as stripping gas. The Stripping gas (SG) is fed at the bottom and at the middle of the stripping column. The oxygen from the water is stripped by the stripping gas in two separate sections. Further, the oxygen rich stripping gas from the top of the column is fed into two separators (B3 & B4) for removing water from stripping gas. A compressor (B2) is provided at the top outlet of the column to make up the pressure drop between stripping gas header and oxygen rich stripping gas stream. Along with compressor after cooler (B5) and knock out drum is also provided to remove water from stripping gas.
FIG. 2 shows the schematic layout of the apparatus for deoxygenation of liquid. The stripper consists of more than one low pressure drop structural packing or trays and inlets in top, middle and bottom. 6
Table 1: Various elements of stripping column of the invention:
The apparatus for reducing oxygen content or de-oxygenation of water. The apparatus of the present invention has
an outer casing with hollow interior, wherein the interior of the casing is filled with at least one packing or trays section. The said packing or trays section provide sufficient contact between the gas and liquid such that the mass transfer of oxygen from liquid to gas happens. The packing of the apparatus can be random or structured packings.
more than one primary inlet ports for supplying stripping gas to the apparatus. The primary inlet ports are preferably located below the packing or trays, for supplying fresh stripping gas to every packing or trays.
more than one secondary inlet port for supplying liquid (oxygenated) to the apparatus. The secondary inlet port is located in the upper region of the apparatus.
at least one primary outlet port and secondary outlet port for recovering the oxygen reduced liquid and stripping gas containing oxygen respectively. The primary outlet port is positioned at lower region of the apparatus and secondary outlet port is present in upper region of the apparatus.
1
Gas sparger
Gas distribution
2
Mass Transfer Medium
Low pressure drop packing/trays
3
Gas Sparger
Gas distribution
4
Liquid Distributor
Liquid distribution
5
Mass Transfer Medium
Low pressure drop packing/trays
6
Liquid Distributor
For Water distribution
7
Mist Eliminator
To remove liquid droplets from gas 7
In one embodiment of the present invention, wherein the gas is dispersed inside the apparatus by gas sparger.
In another embodiment of the present invention, wherein the liquid is distributed by a liquid distributor.
Yet another embodiment of the present invention, where in the gas sparger and liquid distributors are placed in between the packing or trays.
Yet another embodiment of the present invention, where in the gas sparger and liquid distributors are placed in the primary inlet and secondary inlet respectively.
Yet another embodiment of the present invention, where in the gas from the top packings or tray is passed through the mist eliminator for recovering any liquid carried by the stripping gas.
Yet another embodiment of the present invention, where in the mass transfer medium is packing or trays.
Yet another embodiment of the present invention, where in the packing is random or structured packing.
Yet another embodiment of the present invention, where in the wherein the liquid is water and the stripping gas is natural gas, fuel gas, nitrogen and mixture thereof
The lower region of the apparatus has the meaning of below the packings or trays and the upper region of the apparatus has the meaning of above the packing or trays.
The stripping column consists of a gas sparger (1) for distributing gas at the bottom of the column. A low pressure drop packing/trays (2) is placed above the gas sparger, for stripping the gas. A Gas distributor (3) is placed above the packing/trays (2) for distributing the gas going up and liquid distributor (4) for liquid down respectively. A second low pressure drop packing/trays (5) is placed above the Gas distributor (3) and Liquid distributor (4), for stripping. A liquid distributor (6) is placed above the packing/trays (5) for distributing the incoming liquid. A mist eliminator (7) is placed above liquid distributor (6) to eliminate the forming of mist. 8
The process for deoxygenating the liquid, using the apparatus of the present invention involves feeding the oxygenated water (OW) and stripping gas (SG) into the top and bottom of the stripper, respectively. The said oxygenated water (OW) and stripping gas (SG) are fed through the liquid distributor (6) and gas sparger (1). The first section (low pressure drop packing/trays) (2), of the present apparatus is bulk oxygen removal section while in the second section, (second low pressure drop packing/trays) (4), oxygen content in water is lowered to less than 20 ppbv. The apparatus of the present invention comprises low pressure drop internals. These internals are designed so as to minimize the pressure drop resulting from the contact of the two phases (water stream and stripping gas). Since stripping gas is used for deoxygenation feed stripping gas should not contain oxygen. Fuel gas, Natural gas, nitrogen and mixture thereof is used as stripping gas.
The stripping gas flow is distributed in two sections, in first section packing/trays (2) stripping gas with nil oxygen enters through the gas spargers, where it is contacted counter currently with the feed water. In order to increase the mass transfer between the two phases, low pressure drop packing/trays are used. The packing/trays provides a high contact surface area and results in substantial removal of oxygen from water. In case of fuel gas or natural gas as stripping gas the oxygen rich fuel gas/Natural gas is sent to the fuel gas/natural gas header.
In the second section packing/trays (5) of the column, again fresh stripping gas is continuously fed and contacted with the water leaving the first section. In the second section oxygen content in water is lowered to less than 20 ppbv.
The two section stripper column of the present invention operates at atmospheric conditions or slightly higher pressure values. The pressure drop in each section is also very low. A typical range of the operating pressure is 2-10 kg/cm2A and that of temperature is ambient to 50°C.
The oxygen rich gas from the secondary outlet port of the apparatus is feed to a first separator (B3), for separating the water from stripping gas. Further, the gas from the first separator is passed through a compressor and cooler (B5) to compress and cool the gas. The gas from cooler (B5) is passed through second separator (B4) for separating water from stripping gas.

WE CLAIM
1. An apparatus for reducing the oxygen content of a liquid comprising,
a casing comprising a hollow interior;
a plurality of primary inlet ports for supplying stripping gas to the apparatus;
at least one secondary inlet port at an upper region of the apparatus, for supplying the liquid that has to be oxygen reduced;
at least one primary outlet port for recovering the oxygen reduced liquid from the lower region of the apparatus;
at least one secondary outlet port for recovering stripping gas containing oxygen, from the upper region of the apparatus
wherein the liquid is contacted with stripping gas counter currently in apparatus with one or more packing or trays section in central portion, for reducing the oxygen content of the liquid with the stripping gas.
2. The apparatus as claimed in claim 1, comprises a gas sparger and liquid distributor placed between two corresponding packing or trays section, for distributing the liquid flowing from an upper portion towards the lower portion of the apparatus and gas flowing from the lower portion towards the upper portion of the apparatus.
3. The apparatus as claimed in claim 1, comprises a liquid distributor being located at the secondary inlet port for distributing the incoming liquid evenly in the casing.
4. The apparatus as claimed in claim 1, comprising a gas sparger and/or gas distributor disposed at the primary inlet port for conveying the stripping gas into the casing.
5. The apparatus as claimed in claim 1, comprises a mist eliminator disposed before the secondary outlet, for recovering any liquid carried by the stripping gas.
6. The apparatus as claimed in claim 1 where mass transfer medium is packing or trays.
7. The apparatus as claimed in any preceding claim, wherein the packing is random or structured packing.
8. The apparatus as claimed in any preceding claim, wherein the liquid is water and the stripping gas is natural gas, fuel gas, nitrogen and mixture thereof.
9. A method for reducing the oxygen content of a liquid, the method comprising steps of:
supplying the liquid and the stripping gas to an apparatus for reducing oxygen content of liquid, comprising,
a casing comprising a hollow interior;
a plurality of primary inlet ports for supplying stripping gas to the apparatus;
at least one secondary inlet port at an upper region of the apparatus, for supplying the liquid that has to be de-oxygenated;
at least one primary outlet port for recovering the oxygen reduced liquid from the lower region of the apparatus
at least one secondary outlet port for recovering stripping gas oxygen containing from the upper region of the apparatus 13
wherein the liquid is contacted with stripping gas counter currently in apparatus with one or more packing or trays section in central portion, for reducing the oxygen content of the liquid with the stripping gas.
supplying the oxygen rich gas, from the secondary outlet port of the apparatus to the first separator (B3), for separating the water from the stripping gas;
supplying the stripping gas from the first separator (B3) to a compressor (B2), for compression;
conveying the compressed gas from compressor to a cooling means (B5) for recovering the heat from the gas;
conveying the gas from the cooler after recovery of heat to a second separator (B4) for separating the water from the stripping gas;
recovering a product gas from an outlet of the separator by a recovery means.