CA2635792A1

CA2635792A1 - Produced water treatment system

Info

Publication number: CA2635792A1
Application number: CA 2635792
Authority: CA
Inventors: Jan A. Korzeniowski
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-06-12
Filing date: 2008-06-12
Publication date: 2009-12-12

Abstract

A complete treatment is provided in a single vessel to separate oil, water, gas and solids which are usually contained in produced water from oil and gas production and processing operations.

The apparatus and process provide for an automatic removal of sludge, oil and gas which separate from the produced water.

The apparatus and process have flexible and innovative designs to suit the produced water quality and treatment level required, and to provide an efficient, compact and complete treatment.

The apparatus and process can be operated under the atmospheric pressure or other pressure, higher or lower than the atmospheric pressure, and with or without a gas blanketing, to suit the sit conditions and to accomplish the required produced water treatment. The apparatus and process can operate as a pressure or gravity flow system.

The apparatus and process include demulsification, gravity separation, parallel plate separation, and diffused or induced gas or air flotation. The system components and the entire systems are novel and highly efficient.

Description

Title: PRODUCED WATER TREATMENT SYSTEM (PWTS) Abstract A complete treatment is provided in a single vessel to separate oil, water, gas and solids which are usually contained in produced water from oil and gas production and processing operations.

The apparatus and process provide for an automatic removal of sludge, oil and gas which separate from the produced water.

The apparatus and process have flexible and innovative designs to suit the produced water quality and treatment level required, and to provide an efficient, compact and complete treatment.

The apparatus and process can be operated under the atmospheric pressure or other pressure, higher or lower than the atmospheric pressure, and with or without a gas blanketing, to suit the sit conditions and to accomplish the required produced water treatment. The apparatus and process can operate as a pressure or gravity flow system.

The apparatus and process include demulsification, gravity separation, parallel plate separation, and diffused or induced gas or air flotation. The system components and the entire systems are novel and highly efficient.

Field of the Invention The invention relates to a process and apparatus for treatment of produced water with capabilities to separate oil, solids, gas and water in a single vessel, to meet environmental disposal or process re-use guidelines.

Background of the Invention Produced water may contain oil, solids (silt, clay, sand), gases (hydrogen sulphide, carbon dioxide, methane), dissolved iron, manganese and other metals, high content of dissolved salts and low or high pH, and low or high temperature.

The produced water treatment requirements are primarily related to the type of disposal or re-use of the treated water and this includes disposal to the ocean or to deep injection wells, or to evaporation ponds or re-use for in-plant processes or combination of the above.

The diversity of the produced water quality in regard to the type and level of the impurities and the treated water quality requirements demands flexible and diverse treatment technologies. Also, a compact and efficient treatment system is desirable to meet site and economic requirements.

Various produced water treatment technologies are available as independent components such as gravity API separators, CPI separators, gas flotation separators (dissolved or diffused), filters, clarifiers. Combination of those technologies is often required to obtain the desired produced water treatment. The known and currently used technologies are not efficient, and not capable of producing desired high level of treatment to satisfy the produced water disposal or re-use requirements, to meet environmental regulations and acceptable costs. Another criterion which is often very essential is a small foot print of the installation and which is difficult to satisfy with the current technologies.

High treatment requirements, small footprint and acceptable costs are accomplished with a complete treatment system which includes necessary treatment processes, technologies and controls and which has a flexible design which can be suited to the produced water quality and the produced water treatment requirements, and site conditions for space available and support facilities such as availability of nitrogen gas or fuel gas or compressed process air. The above are the objectives of this invention, which provides for a chemical pre-treatment for pH control and demulsification and flocculation of oil and solids, primary gravity separation of solids, oil, gases and water, enhanced gravity separation of oil, solids and water and polishing separation of gases, oil and water in a single vessel. The employed technologies are complemented with controls of flow rates and volumes, sludge level, oil water interface and oil level and pH, oil in water and suspended solids levels in the produced water and in the treated water.

The removal of sludge, oil and gases are accomplished by automatic systems The parallel plate separation is novel in regard to the type of the plates, flow pattern and flexibility in design to suit the treatment process requirements.

The flotation process employs alternative novel solutions to provide efficient diffused or induced gas flotation systems.

The sludge removal system employs a novel technology which includes a scouring process of the sludge piping inside and outside the vessel in order to prevent plugging of the sludge removal system.

Summary of the Invention The treatment system of the present invention is a process and apparatus for treatment of produced water which is associated with production and processing of oil and gas and which may contain oil, gas and solids (silt, clay, sand, organics).

The treatment system provides for separation of oil, gas and solids from water and disposal of oil, gas and solids to disposal facilities or for further processing before a final disposal.

The treatment system operation is fully automatic and it is accomplished in a single vessel as shown on Fig. 1& 2.

The treatment system can be operated under different pressure conditions of above, at or below the atmospheric pressure. Operation at the atmospheric pressure is preferred to a higher pressure to provide a gravity flow through the system and to maximize separation of gas and water.

The system comprises several key components as follows:

= Primary conditioning compartment for adjustment of the inlet water pH, temperature and demulsification and flocculation of oil and suspended solids.
= Primary gravity separation compartment for separation of oil, gas and suspended solids from water.

= Enhanced gravity separation of oil, gas and suspended solids and water in a corrugated, parallel plate system.

= Polishing separation compartment for final separation of oil and gas from water by means of diffused gas flotation system as shown on Fig. 1 or induced gas flotation system as shown on Fig. 2.

= Treated water outlet compartment.
= Sludge removal system.

= Oil removal system.
= Gas removal system.

= Instrumentation and controls.

The inlet water is monitored for flow rates and quality such as pH, Suspended Solids, Oil, Temperature and chemicals may be added for oil demulsification and suspended solids flocculation, and pH adjustment before it enters the primary conditioning compartment.

The primary conditioning compartment may include a static mixer to thoroughly mix the chemicals added and the inlet water, a mechanical mixer to promote the oil demulsification and flocculation process and the suspended solids flocculation process, and a heat exchanger to raise the inlet water temperature, preferably to 10 C
minimum.

The oil, gas, suspended solids and water separation efficiency depends on several key factors which include the inlet water temperature and pH, and the oil demulsification and flocculation process and the suspended solids flocculation process. The key factors are adjusted by the chemicals added and the heat applied, and the water and the chemical mixing system to create optimum conditions for the oil, gas, suspended solids and water separation. These upstream conditioning systems of the inlet water have a profound impact on the downstream oil, gas, suspended solids and water separation efficiency.

The range and level of the inlet water conditioning depends on the inlet water quality key parameters which include contents of oil, suspended solids, gas, and pH &
temperate levels and some other parameters such as salinity, dissolved metals and oxygen.

The pre-conditioned inlet water flows in a laminar, uniform (plug) flow pattern into the primary gravity separation compartment where larger oil droplets and gas bubbles rise to the surface and large suspended solids particles settle to the bottom of the compartment.

The laminar, plug flow through the primary separation compartment ensures an optimum residence time of the water in the compartment and a high efficiency of the oil, gas, suspended solids and water separation.

Next, the partially treated water enters the corrugated, parallel settling plates compartment where it flows horizontally in a laminar but waving motion through the corrugated plates. This flow pattern promotes collision and agglomeration of small oil droplets and gas bubbles into larger droplets and bubbles which easier rise to the surface and small suspended solids particles into larger particles which easier settle to the bottom of the compartment.

The corrugated plates design critical parameters which include spacing and the corrugation height, and length, and the plate material have essential impact on the oil, gas and suspended solids, and water separation efficiency. Also, it has been found that multiple shorter sections of the corrugated plates are more efficient than a longer, single corrugated plate section.

Front and end plates installed at the inlet to and at the outlet of the corrugated plate section prevent the water flow short circuiting and by-passing the corrugated plates.

The water continues to flow horizontally in a laminar flow pattern into the polishing compartment where it is subjected to a gas flotation process which can be either diffused gas flotation as shown on Fig. 1 or induced gas flotation as it is shown on Fig. 2.

In the diffused gas flotation process, as shown on Fig. 1, small gas bubbles are introduced into the water, at the bottom of the compartment, by the way of a pressure gas flowing through porous diffusers made of a ceramic or plastic with tiny pores.

The gas diffusers are evenly spaced at the bottom of the compartment to ensure an even gas flow throughout the horizontal plane of the compartment.

In the induced gas flotation process, as shown on Fig. 2, gas and water are mixed together in an aspirator-mixer and the mixture of water and gas is pumped and discharged at the bottom of the compartment through perforated pipes which evenly distribute the gas/water mixture throughout the bottom of the compartment.

The aspirator-mixer is preferably the J.K. patented air (gas) aspirator-mixer, Patent No. US 6,969,052,B2, or other aspirator-mixer or mixer which will ensure a thorough mixing of the gas and water, and formation of tiny gas bubbles in the water.

If an aspirator-mixer is used the gas supply can be at or slightly higher than the atmospheric pressure. If a mixer is used the gas supply needs to be at an adequate pressure to thoroughly mix with the water and discharge into the compartment with or without a pump.

The gas and water mixing system must ensure an adequate supply of gas and formation of tiny gas bubbles in the water, thorough mixing of the gas bubbles and the water, and adequate discharge pressure into the compartment. The water and gas distribution at the bottom of the compartment must ensure an even distribution of the water and gas at the bottom of the compartment and even water and gas flow throughout the horizontal section of the compartment and delivery of tiny gas bubbles at the bottom of the compartment.

The treated water outlet compartment receives a horizontal, laminar treated water flow from the polishing compartment. The water rises vertically in the outlet compartment through baffle plates to an outlet pipe. The baffle plates ensure that any gas which may enter the compartment does not flow into the outlet pipe and that the water level in this compartment is maintained at a desired, pre-set level which may be between 100 to 300 mm below the top of the vessel and 100 to 200 mm above the top of the outlet pipe.

The outlet pipe is provided with an automatic, throttling control valve to maintain the water/oil level in the vessel at a desired level of 100 to 300 mm below the top of the vessel when the vessel is operated under a pressure equal to or higher than the atmospheric pressure.

The laminar, plug type water flow, without shortcircuiting throughout the vessel is ensured by partitioning perforated plates placed on the downstream sides of the primary conditioning compartment, the primary gravity separation compartment, enhanced gravity separation compartment (corrugated plates compartment) and the polishing compartment. This design ensures an optimum water residence time and oil, gas, suspended solids and water separation efficiency in each compartment and consequently in the entire vessel.

The sludge removal system includes sludge collection pipes in the primary conditioning compartment and in the primary and enhanced separation compartments, sludge pumps, and control valves for an automatic open/close operation and external piping, and a sludge depth monitor for an automatic control of the sludge removal process.

The sludge removal system includes a novel sludge scouring process which permits scouring of the sludge accumulated in the vessel and the system pumps & piping before the sludge is removed from the vessel. This prevents plugging of the sludge removal system piping and pumps with thick and viscous oily sludge which is typical in the produced water treatment systems.

The sludge scouring process provides for a flow of the produced water into the sludge pumps, piping and settled sludge at the bottom of the vessel for a pre-determined period of time. The scouring water flow is reversal of the sludge removal flow process.

The oil removal system is automatic and it is controlled by an oil/water interface and oil level monitor. The oil collected on the top of the produced water is removed from the vessel through perforated pipes located in the upper part of the vessel, in the oil collection zone. The perforated pipes are connected to a disposal pipe which is provided with an automatic open/close control valve. The oil removal process can be by a gravity flow or by a pumping system to an oil collection or processing plant. The oil removal perforated pipes are sized, perforated and located such as to collect uniformly the oil present on the top of the produced water.

The gas removal system consists of an outlet gas pipe and gas blower/compressor to maintain a desired gas pressure in the vessel and to adequately dispose of the gas to a gas processing or disposal system. The vertical perforated and solid plates which extend to the top of the vessel are provided with openings immediately under the top of the vessel to allow gas flow from each compartment to the removal system.

The treatment system outlined above is described in an automatic operation version;
however, manual operation is possible, if desired, and the sludge level monitor and the oil/water interface and oil level monitor can be replaced with simpler visual devices and the automatic control valves can be replaced with manually operated valves.

Brief Descriptions of the Drawings Having thus generally described the invention, it will be referred to more specifically by reference to the accompanying drawings illustrating preferred embodiments, and in which:

Fig. 1 is a diagrammatic illustration in a vertical cross-section of the treatment process and apparatus with the diffused gas flotation system installed in the polishing compartment.

Fig. 2 is a diagrammatic illustration in a vertical cross-section of the treatment process and apparatus with the induced gas flotation system installed in the polishing compartment.

Detailed Description of the Invention According to the embodiments of the invention, as shown on Fig. 1& 2, the treatment system comprises the following major components: a vessel 1 which can be a cylindrical, horizontal closed vessel or rectangular or square in cross section, closed or open on the top and which is divided into five compartments; a primary conditioning compartment 2, a primary gravity separation compartment 3, an enhanced gravity separation compartment 4, a polishing separation compartment 5, and a treated water outlet compartment 6, and also it includes: a sludge removal system 7, an oil removal system 8, a gas removal system 9, an inlet pipe 10, and an outlet pipe 44.

The inlet untreated water flows through the inlet pipe 10 which preferably is provided with a flow meter 11 and chemical injection lines 12, for injection of a demulsifier or a flocculant, or an acid, or a caustic solution or combination of these chemicals to enhance the water treatment which may include separation of oil, gas, suspended solids and water.

A chemically conditioned water enters the primary conditioning compartment 2 through a static mixer 13 which ensures a thorough mixing of the chemicals with the water and a discharge pipe 14 which is extended to the bottom of the primary conditioning compartment 2 to discharge the water into a heat exchanger 15 area.

The heat exchanger 15 may be provided in the lower part of the primary conditioning compartment 2 to heat the inlet water in cases that the inlet water temperature is low, less than 10 C.

A fl occulator mixer 16, with a low rotation speed of 10 to 30 revolutions per minute (RPM), is installed in the primary conditioning compartment 2 to enhance a demulsification and/or flocculation of the oil and flocculation of the suspended solids contained in the inlet water. This process is very essential to the downstream separation of oil, suspended solids and water.

The demulsified and/or flocculated water leaves the primary conditioning compartment 2 through a perforated or slotted plate 18 which ensures a laminar and a "plug like" flow into the primary gravity separation compartment 3, where a primary gravity separation of oil, suspended solids, gas and water takes place. Oil and gas rise to the top and suspended solids settle to the bottom of the compartment.

The partially treated water flows horizontally into the enhanced gravity separation compartment 4 which is provided with settling corrugated, parallel plates 25 &
27, arranged in sets, preferably more than one set in a separator. The corrugated plates are placed vertically in the compartment and spaced preferably between 20 and 50 mm apart.
The plates corrugation is in the horizontal plane and the corrugation height (pitch) is approximately 50 mm and the width is approximately 175 mm; although, after corrugation dimensions can be used.

The plates are preferably made of a non-corrosive plastic or metal sheet, preferably having an affinity for oil, and having adequate physical strength to maintain the original shape and spacing for a long time.

It is preferred that the plates spacing does not exceed the plates height (pitch) and that the plates spacing is reduced in the downstream sets of the plates. Also, it is preferred that the plates width, in the direction of the water flow, is between 750 and 1200 mm and the plates height is such that the plates extend between 300 and 450 mm from above the bottom to 300 to 450 mm below the top of the vessel.

The corrugated plate sets are provided with inlet and outlet perpendicular baffle plates 19 & 28 to prevent water flow between the vessel and the outside of the corrugated plates.

The baffle plates are provided with small openings 26, approximately 25 to 50 mm diameter, on the top to allow gas flow from each compartment to the gas removal system 9.

The substantially treated water flows into the polishing treatment compartment where it is subjected to a final treatment by a gas flotation; either diffused gas flotation as shown on Fig. 1 or induced gas flotation as shown on Fig. 2.

In the diffused gas flotation system, fuel gas or nitrogen gas, or air is introduced into the compartment through a gas inlet pipe 30, a pressure and flow regulating valve 31, distribution pipes 32, and fine bubble diffusers 33.

In the induced gas flotation system the gas is provided to a gas aspirator-mixer 88 under the atmospheric or higher pressure, where it is mixed with the substantially treated water and discharged into the polishing treatment compartment 5 through an inlet pipe 90 and distribution perforated pipes 91 having fine perforation of 2 to 3 mmo and an open area to produce 1.5 to 2.5 m/s velocity through the perforations. The water recirculation flow rate is usually between 1 to 4 times the inlet water flow rate. The water recirculation may be done from the upstream side of the polishing treatment compartment 5 and from the treated water outlet compartment 6 simultaneously or from one side only and at approximately the same or different flow rates.

The gas aspirator-mixer is preferably the J.K. patented air aspirator-mixer;
however, other gas aspirator-mixers can be used as long as they provide adequate gas aspiration and gas and water mixing.

The treated water flows from the polishing treatment compartment 5 into the treated water outlet compartment 6 through a perforated or slotted plate 40 which ensure a laminar and "plug like" flow between the two compartments.

The treated water outlet compartment is provided with baffle plates 41 & 42, an outlet water level and pressure control valve 43 and the outlet pipe 44.

The baffle plate 42 directs the treated water flow to the downstream end of the treated water outlet compartment 6 and prevents the remaining process gas and oil flow into the outlet pipe 44.

The baffle plate 41 maintains a designated water level in the separator and directs any residual gas into the upper part of the treated water outlet compartment 6 and away from the outlet pipe 44.

The control valve 43 is used when the vessel 1 is operated under a pressure higher than the atmospheric pressure to maintain a designated pressure and water level in the separator.

The perforated plate 40 is solid in the upper part and in the low part. The solid upper part of the plate 40 separates the oil collected in the upper part of the vessel I from the treated water outlet compartment 6. The solid lower part of the perforated plate 40 prevents the process gas entry into the treated water outlet compartment 6.

The sludge removal system 7 has two functions; firstly - scouring of the sludge accumulated at the bottom of the vessel in the primary conditioning compartment 2 and in the primary and enhanced gravity separation compartments 3 & 4 respectively, and in the sludge removal piping 49 & 50 and in the sludge pumps 57 and associated piping, and secondly - removal of the sludge accumulated in the vessel.

The sludge scouring process involves pumping the inlet conditioned water from the upstream side of the primary gravity separation compartment 3 into the bottom of the primary conditioning compartment 2 and the bottom of the primary and enhanced gravity separation compartments 3 & 4 respectively, through a suction pipe 51, a control valve 55, sludge pumps 57, control valves 53 & 56 into pipes 60 and 52 in the bottom of the primary conditioning compartment 2 and through pipes 50 and 49 into the bottom of the primary and enhanced gravity separation compartments.

The sludge removal process involves pumping of the scoured sludge from the bottom of the primary and enhanced gravity separation compartments 3 & 4 to a disposal through suction pipes 49 and 50, a control valve 54, pumps 57, a control valve 58 and a disposal pipe 59.

The suction pipe 51 has an inlet located above the anticipated high sludge level in the primary gravity settling compartment.

The apparatus and process have also application to treatment of oily water originating from other industrial processes and hydrocarbon spills.

The above description is intended in an illustrative rather than a restrictive sense, and variations to the specific configurations and designs described may be apparent to skilled persons in adapting the present invention to other specific applications and designs. Such variations are intended to form part of the present invention insofar as they are within the spirit and scope of the claims below.

Claims

1. A produced water treatment system comprises:
.cndot. An inlet water piping.

.cndot. Primary conditioning compartment.

.cndot. Primary gravity separation compartment.

.cndot. Enhanced gravity separation compartment.
.cndot. Polishing separation compartment.

.cndot. Treated water outlet compartment.
.cndot. Treated water outlet piping.

.cndot. Sludge removal system.
.cndot. Oil removal system.

.cndot. Gas removal system.

.cndot. Instrumentation and controls.

2. A treatment system of Claim 1 wherein said inlet water piping comprises a flow meter, chemical injection provisions, a static mixer and a discharge pipe.

3. A treatment system of Claim 1 wherein said primary conditioning compartment, primary gravity separation compartment, enhanced gravity separation compartment, polishing compartment and treated water effluent compartment are arranged in a single vessel.

4. A treatment system of Claim 1 wherein said primary conditioning compartment, primary gravity separation compartment, enhanced gravity separation compartment, polishing separation compartment and treated water effluent compartment provide for an efficient and thorough separation of sludge, oil and gas from the inlet water.

5. A treatment system of Claim 1 wherein said sludge removal system, oil removal system and gas removal system provide for an automatic or manual removal of the separated sludge, oil and gas from the inlet water.

6. A treatment system of Claim 1 wherein said primary conditioning compartment includes a slow mechanical mixer, a heat exchanger and a sludge scouring pipe.

7. A treatment system of Claim 2 wherein said inlet water piping discharge pipe is extended to near the bottom of the primary conditioning compartment and in the area of the heat exchanger.

8. A treatment system of Claim 1 wherein said primary conditioning compartment, primary gravity separation compartment, enhanced gravity separation compartment and polishing separation compartment are provided with perforated or slotted vertical plates, on the downstream side of the compartments, to promote a uniform, "plug like" flow through the compartments.

9. The treatment system of Claim 1 wherein said enhanced gravity separation compartment includes corrugated, parallel plates arranged in a single of multiple sets.

10. The treatment system of Claim 9 wherein said corrugated, parallel plates can have different corrugation design and the plates spacing, and a number of plates sets to suit the treatment requirements.

11. The treatment system of Claim 1 wherein said enhanced gravity separation compartment is provided with solid vertical baffle plates at the inlet and outlet sides of the compartment and between the treatment vessel of Claim 3 and the corrugated plates of Claim 9 to prevent the water flow between the vessel and the corrugated plates and to ensure the water flow only through the corrugated plates.

12. The treatment system of Claims 8 and 11 wherein said perforated and solid baffle plates are provided with small openings at the top of the plates to allow gas flow between the primary conditioning compartment, primary gravity separation compartment, enhanced gravity separation compartment, polishing compartment and treated water effluent compartment as per Claim 1.

13. The treatment system of Claim 1 wherein said polishing separation compartment is provided with fine bubble diffusers in a diffused gas flotation system.

14. The treatment system of Claim 1 wherein said polishing separation compartment is provided with a gas aspirator-mixer and a circulating pump and perforated discharge pipes in an induced gas flotation system.

15. The treatment system of Claim 1 wherein said treated water effluent compartment is provided with baffle plates to prevent oil and gas separated from the water entry into the outlet piping and to maintain designated water level in the treatment vessel.

16. The treatment system of Claim 1 wherein said treated water outlet piping is provided with an automatic control valve to maintain designated pressure and water level in the treatment vessel.

17. The treatment system of Claim 1 wherein said sludge removal system provides for scouring of the sludge removal system piping and pumps and the sludge accumulated at the bottom of the primary conditioning compartment and the primary and enhanced separation compartments prior to the sludge removal from the primary and enhanced separation compartments.

18. The treatment system of Claim 17 wherein said scouring of the sludge removal system piping and pump and the sludge accumulated at the bottom of the primary conditioning compartment and the primary and enhanced gravity separation compartments is accomplished by recirculating water from above the accumulated sludge in the primary conditioning or separation compartments into the bottom of the primary conditioning compartment and the bottom of the primary and enhanced gravity separation compartments.

19. The treatment system of Claim 18 wherein said scouring of the sludge accumulated at the bottom of the primary conditioning compartment and the primary and enhanced gravity separation compartments is done by discharging water through perforated or slotted, single or multiple pipes placed near the bottom of the primary conditioning compartment and primary and enhanced separation compartments.

20. The treatment system of Claim 17 wherein said sludge removal from the primary and enhanced separation compartments is done through perforated or slotted, single or multiple pipes, spaced evenly and adequately at the bottom of the primary and enhanced separation compartments.