CA2802254C

CA2802254C - Integration techniques for steam generation and produced water treatment for thermal in situ recovery operations

Info

Publication number: CA2802254C
Application number: CA2802254A
Authority: CA
Inventors: Michael Gu; Andrew Donald; Karelys Goitia
Original assignee: Suncor Energy Inc
Current assignee: Suncor Energy Inc
Priority date: 2013-01-10
Filing date: 2013-01-10
Publication date: 2018-11-06
Anticipated expiration: 2033-01-10
Also published as: CA2802254A1

Abstract

Techniques for generating steam and treating de-oiled produced water can include various steps that involve recycling certain streams and using a Once Through Steam Generator (OTSG). A first de-oiled produced water stream can be softened to produce softened water. A second de-oiled produced water stream can be subjected to evaporation to produce a distillate. Portions of the distillate and the softened water can be fed as a boiler feed water stream to an OTSG to produce wet steam, which is separated into dry steam and a blowdown stream with a concentrated level of impurities.
At least a recycle portion of the blowdown stream can be sent back as part of the boiler feed water stream. In addition, multiple steam generation trains, which each use an OTSG, can be integrated to reuse certain aqueous streams.

Description

INTEGRATION TECHNIQUES FOR STEAM GENERATION AND PRODUCED WATER
TREATMENT FOR THERMAL IN SITU RECOVERY OPERATIONS
TECHNICAL FIELD
The technical field relates to the treatment of produced water to be reused for steam generation for thermal in situ bitumen or heavy hydrocarbon recovery operations, such as Steam Assisted Gravity Drainage (SAGD).
BACKGROUND
Thermal in situ bitumen or heavy hydrocarbon recovery operations can use high temperature steam for injection into a hydrocarbon bearing reservoir. Steam injection -'eats the hydrocarbons, reducing the viscosity and increasing the mobility to facilitate production.
Production fluid that is retrieved and provided to the surface includes mobile hydrocarbons and condensate that has resulted from condensation of the injected steam within the reservoir. The production fluid is processed in order to separate valuable hydrocarbons from the produced water. The produced water is then treated so as to be re-used for steam generation for reinjection into the reservoir.
Treatment of such produced water for reuse in steam generation has various challenges, which may include accumulation of different impurities in the produced water, fouling of equipment, water losses, and energy consumption.
SUMMARY OF INVENTION
Various integration techniques are provided for generating steam, producing hydrocarbons and treating produced water.
In some implementations, there is provided a process for treating de-oiled produced water derived from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation and for generating steam, the de-oiled produced water including impurities, the process including:
supplying a first de-oiled produced water stream to a softening unit to produce a softened water stream depleted in a first set of impurities including divalent cations and silica;

2 supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities including divalent cations, silica and dissolved solids;
feeding at least a portion of the distillate stream and a portion of the softened water stream as part of a boiler feed water stream to a Once Through Steam Generator (OTSG) to produce wet steam;
separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the boiler feed water stream; and recycling at least a recycle portion of the blowd own stream as part of the boiler feed water stream.
In some implementations, the process may further include controlling water quality of the boiler feed water stream so as to have a concentration of a limiting impurity below a maximum threshold value for operation of the OTSG.
In some implementations, the controlling of the water quality may include managing flowrates of the distillate stream, the recycle stream and/or the portion of the softened water stream.
In some implementations, the limiting impurity may be total dissolved solids (TDS). The maximum threshold value of the concentration of TDS may be 12,000 ppm.
In some implementations, the limiting impurity may be organics. The maximum threshold value of the organics may be 700 ppm.
In some implementations, the limiting impurity is pH. The maximum threshold value of the pH may be 10.5.
In some implementations, the limiting impurity may be silica. The maximum threshold value of the concentration of silica is 100 ppm.
In some implementations, the limiting impurity may be hardness. The maximum threshold value of hardness may be 1 ppm.
In some implementations, the limiting impurity may be oil in water. The maximum threshold value of the oil in water may be 0.5 ppm.

3 In some implementations, the limiting impurity may be chemical conditioners including chelates and dispersants.
In some implementations, the controlling of the water quality of the boiler feed water stream may include:
measuring the concentration of the limiting impurity; and in response to an elevated measured concentration of the limiting impurity, managing the concentration of the limiting impurity in the boiler feed water stream by decreasing the flowrate of at least one of the following streams:
the recycled portion of the blowdown stream;
the portion of the softened water stream; and the distillate stream.
In some implementations, the measuring of the limiting impurity may be performed on the boiler feed water stream.
In some implementations, the controlling of the water quality of the boiler feed water stream may include:
measuring the concentration of organics as the limiting impurity; and in response to an elevated measured concentration of organics, managing the concentration of the organics in the boiler feed water stream by reducing the flowrate of the recycled portion.
In some implementations, the controlling of the water quality may further include increasing the flowrate of the distillate stream as part of the boiler feed water stream.
In some implementations, the controlling of the water quality may further include increasing the flowrate of the portion of the softened water stream as part of the boiler feed water stream.
In some implementations, the controlling of the water quality of the boiler feed water stream may include:
measuring the concentration of total dissolved solids (TDS) as the limiting impurity; and

4 in response to an elevated measured concentration of TDS, managing the concentration of the TDS in the boiler feed water stream by reducing the flowrate of the portion of the softened water stream, the recycled portion of the blowdown stream, or a combination thereof.
In some implementations, the controlling of the water quality may further include increasing the flowrate of the distillate stream as part of the boiler feed water stream.
In some implementations, the controlling of the water quality of the boiler feed water stream includes, in response to an elevated measured concentration of the limiting impurity, reducing the concentration of the limiting impurity by increasing the flowrate of make-up water added to the boiler feed water stream or to the de-oiled produced water.
In some implementations, the softening unit may include a Warm Lime Softener (VVLS) or a Hot Lime Softener (HLS) or a combination thereof. The softening unit may further include a cation exchange device downstream of the Warm Lime Softener (VVLS) or the Hot Lime Softener (HLS). The cation exchange device may include a Weak Acid Cation (WAG) exchanger.
In some implementations, the OTSG may be part of a Heat Recovery Steam Generation (HRSG) system.
In some implementations, the OTSG may be an evaporator train OTSG and the process further includes:
feeding at least a part of the softened water stream as an additional boiler feed water stream to a softening unit train Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a softening unit OTSG
blowdown stream.
In some implementations, the process further includes controlling water quality of the additional boiler feed water stream, such that the second boiler feed water stream has a concentration of an additional limiting impurity below a maximum threshold value for operation of the softening unit OTSG. The additional limiting impurity may be total dissolved solids (TDS), organics, pH, silica, hardness or oil in water.
In some implementations, the recycle portion of the blowdown stream may be directly transferred back into the boiler feed water stream.

In some implementations, the recycle portion of the blowdown stream, the portion of the distillate stream and the portion of the softened water stream may be fed to a boiler feed water tank prior to supplying as the boiler feed water stream.
In some implementations, the recycle portion may be at least about 30 vol% of the blowdown stream. The recycle portion may also be at least about 40 vol% of the blowdown stream.
In some implementations, at least part of a remainder portion of the blowdown stream may be supplied to the evaporator, the softening unit, or a combination thereof.
In some implementations, there is provided a process for generating steam for use in a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the process including:
in a first steam generation train:
supplying a first de-oiled produced water stream including impurities to a softening unit to produce a softened water stream depleted in a first set of impurities including divalent cations and silica;
feeding a part of the softened water stream as a first boiler feed water stream to a first Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the first boiler feed water stream;
in a second steam generation train:
supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities including divalent cations, silica and dissolved solids;
feeding at least a part of the distillate stream as part of a second boiler feed water stream to a second Once Through Steam Generator (OTSG) to produce steam; and separating the wet steam into substantially dry steam and a second blowdown stream including a concentrated level of impurities relative to the second boiler feed water stream; and integrating the first and second steam generation trains by:
feeding a portion of the softened water stream as part of the second boiler feed water stream; and recycling at least a recycle portion of the blowdown stream as part of the second boiler feed water stream.
Such a process for generating steam may also have one or more of the additional features as described herein.
In some implementations, there is provided a process for producing hydrocarbons from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the process including:
injecting a fluid including steam into a bitumen and/or heavy hydrocarbon bearing reservoir in order to mobilise bitumen and/or heavy hydrocarbons;
producing production fluid including condensate and hydrocarbons from the reservoir;
separating the hydrocarbons from the condensate to produce a hydrocarbon stream and produced water including residual oil;
de-oiling the produced water to produce de-oiled produced water;
in a first steam generation train:
supplying a first de-oiled produced water stream including impurities to a softening unit to produce a softened water stream depleted in a first set of impurities including divalent cations and silica;
feeding a part of the softened water stream as a first boiler feed water stream to a first Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the first boiler feed water stream;
in a second steam generation train:

supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities including divalent cations, silica and dissolved solids;
feeding at least a part of the distillate stream as part of a second boiler feed water stream to a second Once Through Steam Generator (OTSG) to produce steam; and separating the wet steam into substantially dry steam and a second blowdown stream including a concentrated level of Impurities relative to the second boiler feed water stream;
integrating the first and second steam generation trains by:
feeding a portion of the softened water stream as part of the second boiler feed water stream; and recycling at least a recycle portion of the blowdown stream as part of the second boiler feed water stream; and re-injecting at least some of the steam generated by the first and second steam generation trains back into the bitumen and/or heavy hydrocarbon bearing reservoir.
Such a process for producing hydrocarbons may also have one or more of the additional features as described herein.
In some implementations, there is provided a system for treating de-oiled produced water derived from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the de-oiled produced water including impurities, the system including:
a first steam generation train including:
a softening unit for receiving a first de-oiled produced water stream and producing a softened water stream depleted in a first set of impurities including divalent cations and silica; and a first Once Through Steam Generator (OTSG) for receiving a first boiler feed water stream derived from the softened water stream, and producing wet steam;
a second steam generation train including:

an evaporator for receiving a second de-oiled produced water stream and producing a distillate stream via a distillate line;
a second Once Through Steam Generator (OTSG) for receiving a second boiler feed water stream at least partly including the distillate stream via a boiler feed water line;
a separator for separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the second boiler feed water stream; and a blowdown recycle line for recycling at least a portion of the second blowdown stream as part of the second boiler feed water stream; and a softened water transfer line for transferring a portion of the softened water stream from the first steam generation train to the second steam generation train for use as part of the second boiler feed water stream.
In some implementations, the softened water transfer line, the blowdown recycle line, the distillate line and the boiler feed water line may be sized, configured and controlled so as to manage water quality of the second boiler feed water stream so as to have a concentration of a limiting impurity below a maximum threshold value for operation of the second OTSG.
In some implementations, the system further includes a control assembly operatively connected to the softened water transfer line, the blowdown recycle line, the distillate line and/or the boiler feed water line. The control assembly may be configured for managing a flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream; managing a flowrate of the recycle portion recycled as part of the second boiler feed water stream; managing a flowrate of the distillate stream supplied as part of the second boiler feed water stream; and/or managing a flowrate of make-up water added to the second boiler feed water stream.
In some implementations, the system further includes a measurement device for measuring the concentration of an impurity in the softened water stream.
The control assembly may be configured for managing the flowrate of the portion of the softened water stream so as to reduce the flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity. The control assembly may be configured for managing the flowrate of the recycle portion so as to increase the flowrate of the portion of the distillate stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity. The control assembly may be configured for managing the flowrate of the distillate stream so as to reduce the flowrate of the recycle portion supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity.
In some implementations, the system further includes a measurement device for measuring the concentration of an impurity in the second boiler feed water stream.
The control assembly may be configured for managing the flowrate of the portion of the softened water stream so as to reduce the flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity. The control assembly may be configured for managing the flowrate of the recycle portion so as to increase the flowrate of the portion of the distillate stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity. The control assembly may be configured for managing the flowrate of the distillate stream so as to reduce the flowrate of the recycle portion supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity.
In some implementations, the system includes an organics measurement device for measuring the concentration of organics as the limiting impurity in the second boiler feed water stream, and the control assembly is configured for managing the flowrate of the recycle portion so as to reduce the flowrate of the recycle portion supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the organics. The control assembly may be further configured for managing the fiowrate of the distillate stream so as to increase the flowrate of the distillate stream as part of the boiler feed water stream, in response to the elevated measured concentration of the organics. The control assembly may also be further configured for managing the flowrate of the portion of the softened water stream so as to increase the flowrate of the portion of the softened water stream as part of the second boiler feed water stream, in response to the elevated measured concentration of the organics.
In some implementations, the system includes a total dissolved solids (TDS) measurement device for measuring the concentration of TDS as the limiting impurity in the second boiler feed water stream. The control assembly may be configured for managing the flowrate of the portion of the softened water stream so as to reduce the flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the TDS. The control assembly may be configured for managing the flowrate of the recycled portion of the blowdown stream so as to reduce the flowrate of the recycled portion of the blowdown stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the TDS. The control assembly may be further configured for managing the flowrate of the distillate stream so as to increase the flowrate of the distillate stream as part of the second boiler feed water stream, in response to the elevated measured concentration of the TDS.
In some implementations of the system, the limiting impurity may be total dissolved solids (TDS). The maximum threshold value of the concentration of TDS may be 12,000 ppm.
In some implementations of the system, the limiting impurity is organics. The maximum threshold value of the organics may be 700 ppm.
In some implementations of the system, the limiting impurity may be pH. The maximum threshold value of the pH may be 10.5.
In some implementations of the system, the limiting impurity may be silica.
The maximum threshold value of the concentration of silica may be 100 ppm.
In some implementations of the system, the limiting impurity may be hardness.
The maximum threshold value of hardness may be 1 ppm.
In some implementations of the system, the limiting impurity may be oil in water. The maximum threshold value of the oil in water is 0.5 ppm.
In some implementations of the system, the limiting impurity may be chemical conditioners including chelates and dispersants.
In some implementations, the system further includes a make-up water line for adding make-up water to the second boiler feed water stream.
In some implementations of the system, the softening unit includes a Warm Lime Softener (WL.S) or a Hot Lime Softener (HLS) or a combination thereof. The softening unit may further include a cation exchange device downstream of the VVLS or the HLS.
The cation exchange device may include a Weak Acid Cation (WAC) exchanger.
In some implementations of the system, at least one of the first and second train OTSGs includes a Heat Recovery Steam Generation (HRSG) system.
In some implementations of the system, the first OTSG may be part of a first bank of multiple first train OTSGs and/or the second OTSG may be part of a second bank of second train OTSGs.
In some implementations, the system includes a boiler feed water tank for receiving the recycle portion of the blowdown stream, the portion of the distillate stream and the portion of the softened water stream, the boiler feed water tank having an outlet coupled to the boiler feed water line for supplying the second boiler feed water stream to the second OTSG.
In some implementations, there is provided a process for treating de-oiled produced water derived from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation and for generating steam, the de-oiled produced water including impurities, the process including:
supplying a first de-oiled produced water stream as part of a softening unit feed stream to a softening unit to produce a softened water stream depleted in a first set of the impurities including divalent cations and silica;
feeding at least a part of the softened water stream as a first boiler feed water stream to a first Once Through Steam Generator (OTSG) to produce wet steam;
separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the first boiler feed water stream;
feeding a second de-oiled produced water stream to an evaporator as part of an evaporator feed stream in order to produce a distillate stream;
feeding at least a part of the distillate stream as a second boiler feed water stream to a second Once Through Steam Generator (OTSG) to produce further wet steam;
recycling a recycled portion of the blowdown stream as part of the softening unit feed stream; and reusing a reused portion of the blowdown stream as part of the evaporator feed stream by feeding to the evaporator to produce the distillate stream.
In some implementations, the process further includes controlling water quality of the softening unit feed stream and the first boiler feed water stream.
In some implementations, the controlling of the water quality includes managing a flowrate of the recycled portion.
In some implementations, the controlling of the water quality includes managing the water quality such that the softening unit feed stream has a concentration of a first limiting impurity below a maximum threshold value for operation of the softening unit;
and the first boiler feed water stream has a concentration of a second limiting impurity below a maximum threshold value for operation of the first OTSG.
In some implementations, the first limiting impurity may be alkalinity of the softening unit feed stream.
In some implementations, the first limiting impurity may be chemical conditioners including chelates and/or dispersants in the softening unit feed stream.
In some implementations, the first limiting impurity may be organics in the softening unit feed stream.
In some implementations, the second limiting impurity may be total dissolved solids (TDS) in the first boiler feed water stream, and the maximum thresho:d value of the concentration of TDS may be 12,000 ppm.
In some implementations, the second limiting impurity may be organics in the first boiler feed water stream, and the maximum threshold value of the organics may be 700 ppm.
In some implementations, the second limiting impurity may be pH of the first boiler feed water stream, and the maximum pH may be 10.5.
In some implementations, the second limiting impurity may be silica in the first boiler feed water stream, and the maximum threshold value of the concentration of silica may be 100 ppm.
In some implementations, the second limiting impurity may be hardness of the first boiler feed water stream, and the maximum threshold value of the hardness may be 1 ppm.

In some implementations, the second limiting impurity may be oil in water of the first boiler feed water stream, and the maximum threshold value of the oil in water may be 0.5 ppm.
In some implementations, the controlling of the water quality may further include providing the recycled portion and the reused poriion in a relative flowrate proportion between 1/99 and 85/15.
In some implementations, the controlling of the water quality may further include providing the recycled portion and the reused portion in a relative flowrate proportion between 30/70 and 70/30.
In some implementations, the controlling of the water quality may include:
measuring the concentration of the first limiting impurity; and in response to an elevated measured concentration of the first limiting impurity, reducing the concentration of the first limiting impurity by:
decreasing the flowrate of the recycled portion of the blowdown stream back into the softening unit; and/or increasing the flowrate of the first de-oiled produced water stream fed to the softening unit.
In some implementations, the controlling of the water quality may include:
measuring the concentration of the second limiting impurity; and in response to an elevated measured concentration of the second limiting impurity, reducing the concentration of the second limiting impurity by:
increasing the flowrate of distillate stream added to the softened water stream; and/or increasing the flowrate of make-up water added to the softened water stream.
In some implementations, the step of controlling water quality of the first boiler feed water stream further may include:
reducing cycling-up of dissolved solids into the first boiler fecd water stream, including:

decreasing the flowrate of the recycled portion; and increasing the flowrate of the reused portion sufficient to reduce cycling up of dissolved solids into the first boiler feed water stream.
In some implementations, in the steps of decreasing the flowrate of the recycled portion and increasing the flowrate of the reused portion, reduction of the flowrate of the recycle portion may be substantially provided to supply the increase in flowrate of the reused portion.
In some implementations, the step of controlling water quality of the first boiler feed water stream further may include:
increasing the concentration of the dissolved solids in the first boiler feed water stream, including:
increasing the flowrate of the recycle portion; and reducing the flowrate of the reused portion.
In some implementations, in the steps of increasing the flowrate of the recycle portion and reducing the flowrate of the reused portion, the reduction of the flowrate of the reused portion may be substantially provided to supply the increase in flowrate of the recycled portion.
In some implementations, the controlling of the water quality of the first boiler feed water stream may further include managing a flowrate of the de-oiled produced water supplied to the softening unit.
In some implementations, the process may further include adding make-up water to the softened water stream, and the controlling of the water quality of the first boiler feed water stream may include .eanaging a flowrate of the make-up water added to the softened water stream.
In some implementations, the process may further include adding a portion of the distillate stream to the softened water stream, and the controlling of the water quality of the first boiler feed water stream may include managing a flowrate of the portion of the distillate stream that is added to the softened water stream.
In some implementations, the process may further include removing a portion of the softened water stream and adding make-up water as part of the first boiler feed water, and the controlling of the water quality of the first boiler feed water stream may include managing a flowrate of the portion of the softened water stream that is removed and managing a flowrate of the make-up water that is added.
in some implementations of this process, the softening unit includes a Warm Lime Softener (WLS) or a Hot Lime Softener (HLS) or a combination thereof. The softening unit further includes a cation exchange device downstream of the Warm Lime Softener (WLS) or the Hot Lime Softener (HLS). The cation exchange device includes a Weak Acid Cation (WAC) exchanger.
In some implementations, at least one of the first and second OTSGs may be part of a Heat Recovery Steam Generation (HRSG) system.
In some implementations, the process further includes controlling water quality of the second boiler feed water stream, such that the second boiler feed water stream has a concentration of a third limiting impurity below a maximum threshold value for operation of the second OTSG. The third limiting impurity in the second boiler feed water stream may be total dissolved solids, organics, pH, silica, hardness or oil in water.
In some implementations, the controlling of the water quality of the second boiler feed water stream further includes managing a flowrate of the second de-oiled produced water stream supplied to the softening unit.
In some implementations, the process further includes adding a portion of the softened water stream to the distillate stream, and the controlling of the water quality of the second boiler feed water stream further includes managing a flowrate of the portion of the softened water stream that is added to the distillate stream.
In some implementations, the controlling of the water quality of the second boiler feed water stream further includes managing a flowrate of the reused portion of the blowdown stream.
In some implementations, substantially all of the blowdown stream may be used as the recycled portion and the reused portion.
In some implementations, there is provided a process for generating steam for use in a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the process including:
in a first steam geaeration train:

supplying a first de-oiled produced water stream including impurities to a softening unit to produce a softened water stream depleted in a first set of impurities including divalent cations and silica;
feeding at least a part of the softened water stream as a first 'caller feed water stream to a first Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the first boiler feed water stream;
in a second steam generation train:
supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities including divalent cations, silica and dissolved solids; and feeding at least a part of the distillate stream as a second boiler feed water stream to a second Once Through Steam Generator (OTSG) to produce steam; and integrating the first and second steam generation trains by:
recycling a recycled portion of the blowdown stream of the first steam generation train into the softening unit; and reusing a reused portion of the blowdown stream of the first steam generation train by feeding to the evaporator of the second steam generation train.
In some implementations, there is provided a process for producing hydrocarbons from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the process including:
injecting a fluid including steam into a bitumen and/or heavy hydrocarbon bearing reservoir in order to mobilise bitumen and/or heavy hydrocarbons;
producing production fluid including condensate and hydrocarbons from the reservoir;

separating the hydrocarbons from the condensate to produce a hydrocarbon stream and produced water including residual oil;
de-oiling the produced water to produce de-oiled produced water;
in a first steam generation train:
supplying a first de-oiled produced water stream including impurities to a softening unit to produce a softened water stream depleted in a first set of impurities including divalent cations and silica;
feeding at least a part of the softened water stream as a first boiler feed water stream to a first Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the first boiler feed water stream;
in a second steam generation train:
supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities including divalent cations, silica and dissolved solids; and feeding at least a part of the distillate stream as a second boiler feed water stream to a second Once Through Steam Generator (OTSG) to produce steam;
integrating the first and second steam generation trains by:
recycling a recycled portion of the blowdown stream of the first steam generation train into the softening unit; and reusing a reused portion of the blowdown stream of the first steam generation train by feeding to the evaporator of the second steam generation train; and re-injecting at least some of the steam generated by the first and second steam generation trains back into the bitumen and/or heavy hydrocarbon bearing reservoir.

In some implementations, there is provided system for treating de-oiled produced water derived from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation and for generating steam, the de-oiled produced water including impurities, the system including:
a first steam generation train including:
a softening unit for receiving a first de-oiled produced water stream and producing a softened water stream depleted in a first set of impurities including divalent cations and silica;
a first Once Through Steam Generator (OTSG) for receiving a first boiler feed water stream derived from the softened water stream, and producing wet steam; and a separator for separating the wet steam into substantially dry steam and a blowdown stream including a concentrated level of impurities relative to the first boiler feed water stream;
a second steam generation train including:
an evaporator for receiving a second de-oiled produced water stream and producing a distillate stream; and a second Once Through Steam Generator (OTSG) for receiving a second boiler feed water stream at least partly including the distillate stream; and a train integration circuit including:
a first line for receiving a recycled portion of the blowdown stream from the separator for recycling into the softening unit of the first steam generation train; and a second line for receiving a reused portion of the blowdown stream from the separator for reusing as feed into the evaporator of the second steam generation train.
In some implementations, the train integration circuit may be sized, configured and controlled for management of a flowrate of the recycled portion and control of the water quality of the softening unit feed stream and the first boiler feed water stream, such that:

the softening unit feed stream has a concentration of a first limiting impurity below a maximum threshold value for operation of the softening unit; and the first boiler feed water stream has a concentration of a second limiting impurity below a maximum threshold value for operation of the first OTSG.
In some implementations, the system further includes a control assembly operatively connected to the train integration circuit. The control assembly may be configured for managing a flowrate of the first de-oiled produced water stream supplied to the first steam generation train; managing a flowrate of the make-up water added to the first steam generation train; managing a flowrate of the portion of the distillate stream that is supplied to the first steam generation train; and/or managing a flowrate of the portion of the softened water stream that is supplied to the second steam generation train.
In some implementations, the system further includes a first measurement device for measuring the concentration of the first impurity in the softened water stream of the first steam generation train. The control assembly may be adapted for reducing the concentration of the first impurity in response to an elevated measured concentration of the first impurity.
In some implementations, the system further includes a second measurement device for measuring the concentration of the second impurity in the first boiler feed water stream of the first steam generation train. The control assembly may be adapted for reducing the concentration of the second impurity in response to an elevated measured concentration of the second impurity.
In some implementations, the system further includes a first make-up water line for adding make-up water to the first steam generation train.
In some implementations, the train integration circuit further includes a distillate transfer line for supplying a portion of the distillate stream to the first steam generation train for use as part of the first boiler feed water stream.
In some implementations, the train integration circuit further includes a softened water transfer line for supplying a portion of the softened water stream to the second steam generation train for use as part of the second boiler feed water stream.
In some implementations of this system, the softening unit includes a Warm Lime Softener (WLS) or a Hot Lime Softener (HLS) or a combination thereof. The softening unit further may include a cation exchange device downstream of the WLS or the HLS.
The cation exchange device may include a Weak Acid Cation (WAC) exchanger.
In some implementations, at least one of the first and second train OTSGs may include a Heat Recovery Steam Generation (HRSG) system.
In some implementations, the first OTSG may be part of a first bank of multiple first train OTSGs and/or the second OTSG may be part of a second bank of second train OTSGs.
In some implementations, the train integration circuit may be sized, configured and controlled to provide the recycled portion and the reused portion in a relative proportion between 1/99 and 85/15. The train integration circuit may be sized, configured and controlled to provide the recycled portion and the reused portion in a relative proportion between 30/70 and 70/30.
In some implementations, the system also includes a second train control assembly for controlling a concentration of a third limiting impurity in the second boiler feed water stream below a maximum threshold value for operation of the second OSTG.
In some implementations, the system includes a third measurement device for measuring the concentration of the third impurity in the second boiler feed water stream of the second steam generation train; and the control assembly is adapted for reducing the concentration of the third impurity in response to an elevated measured concentration of the third impurity.
In some implementations, the train integration circuit is sized, configured and controlled such that substantially all of the blowdown stream is used as the recycled portion and the reused portion.
It should also be noted that various features of the processes and systems described above and herein may be combined with other features and aspects of the processes and systems.
BRIEF SUMMARY OF DRAWINGS
1 is a flow diagram of an example of a steam generation system.
Fig 2 is a flow diagram of another example of a steam generation system.
Fig 3 is a flow diagram of another example of a steam generation system.
DETAILED DESCRIPTION

Figs 1 to 3 show implementations of systems for generating steam for use in a thermal in situ bitumen or heavy hydrocarbon recovery operation (not illustrated).
Thermal in situ recovery operations may include SAGD where injection-production well pairs are used to exploit a bitumen containing reservoir. Other thermal in situ recovery operations may include Cyclic Steam Stimulation (CSS), Steam Flooding, and various hybrid steam and solvent injection techniques.
Figs 1 to 3 illustrate different variants and aspects of steam generation systems 10a, lob, 10c.
Referring to Figs 1 and 2, in some implementations steam generation systems 10a, 10b for treating produced water and generating steam includes a first steam generation train 12 and a second steam generation train 14. Each steam generation train receives de-oiled produced water 16a, 16b that has been treated by an upstream de-oiling unit (not illustrated) to remove a substantial amount of hydrocarbons from the produced water.
Still referring to Figs 1 and 2, in the first train 12 the de-oiled produced water stream 16a may be supplied to a softening unit 18, which may include a Warm Line Softener (WLS) 20 as illustrated or a Hot Lime Softener (HLS). A chemical addition stream 22 that includes lime and other chemicals may be added to the WLS 20 to produce a softened water stream 24 and a WLS sludge 26. Depending on the operation of the WLS 20, different amounts of divalent cations, such as calcium and magnesium, as well as silica can be removed from the de-oiled produced water stream 16a. The softened water stream 24 may be subjected to additional softening that is particularly directed to reducing divalent cation concentration. For example, the softening unit 18 may include a cation exchange unit 28 for receiving the softened water stream 24 to produce a further treated water 30 further depleted in divalent cations. The cation exchange unit 28 may be a Weak Acid Cation (WAC) exchanger, for example, which may use a sodium based medium to remove the divalent cations.
The treated water 30 may be fed to a first feed tank 32, from which a first boiler feed water stream 34 may be sent for steam generation. The first feed tank 32 may also receive other streams 37 if desired. The infeed to the softening unit 18 may also include additional streams such as a make-up water stream 39, since some water is inevitably lost to the reservoir during the recovery operation. Additional streams may be supplied to the first feed tank 32 or to another appropriate location in the first steam generation train 12 to supplement water for use as boiler feed water 34.

Still referring to Figs 1 and 2, the first boiler feed water stream 34 may be supplied to a first train steam generator, which may include a first Once Through Steam Generator (OTSG) 36. The first OTSG produces wet steam 38 that is sent to a separator 40 for separating into substantially dry steam 42 and a first blowdown stream 44 that has a concentrated level of impurities relative to the concentration in the first boiler feed water stream 34. Steam generation has the effect of concentrating impurities in the blowdown stream. For example, an OTSG often produces wet steam including about 20%
water and 80% steam and once the water is removed from the wet steam, the impurities concentration in the blowdown can be about five times greater than the concentration in the boiler feed water. Train integration techniques can aid in alleviating drawbacks associated with such concentrating of impurities in blowdown streams.
Still referring to Figs 1 and 2, the second steam generation train 14 has an alternative configuration to the first train 12. The second steam generation train 14 may include an evaporator 46 for receiving a second de-oiled produced water stream 16b, which may be identical, similar or different compared to the first de-oiled produced water stream 16a and may come from the same or a different source. For instance, the first de-oiled produced water stream 16a may come from a SAGD well pad operating in a given reservoir area, while the second de-oiled produced water stream 16b may come from a different SAGD well pad or other recovery operation operating in another reservoir area.
It should also be understood that there may be several evaporators arranged in parallel, and that the evaporators may be, for example, vapour compression distillation and/or multiple effect distillation type evaporators. The evaporator 46 produces a distillate stream 48 and an evaporator blowdown stream 50, which may be treated or disposed of in various ways such as Zero Liquid Discharge (ZLD) techniques, Deep Well Injection (DWI) disposal, and/or treatment and water recovery techniques. The distillate stream 48 is depleted in calcium, magnesium, silica and dissolved solids and is a relatively clean, high quality water stream.
The distillate stream 48 may be supplied to a second feed water tank 52. A
second boiler feed water stream 54 may be sent from the tank 52 to a second train steam generator, which may include a second OTSG 56 and a second separator 58.
Alternatively, since the evaporator distillate 48 is of such high quality, if it is used in high enough proportion in the second boiler feed water stream 54, the second train steam generator may be other types such as a drum boiler (not illustrated). The second OTSG

56 produces wet steam 60 and the second separator 58 receives the wet steam 60 and produces substantially dry steam 62 and a second train blowdown stream 64.
In some implementations, the first and second steam generation trains 12, 14 may be integrated in order to leverage advantageous operating features while avoiding certain drawbacks related to OTSGs, evaporators and softening units.
Integration with first train OTSG blowdown recycled to both trains Referring now to Fig 1, in some implementations the system 10a may also include a train integration circuit 66. The train integration circuit 66 may include a first line for receiving a recycled portion 68 of the blowdown stream 41 from the first separator 40 and recycling this portion 68 as feed to the softening unit 18 of the first steam generation train 12. The recycled portion 68 may be added back into a feedline or a holding tank (not illustrated) for combining with the first de-oiled produced water stream or into the softening unit directly, as the case may be. The train integration circuit 66 may also include a second line for receiving a reused portion 70 of the blowdown stream 44 from the first separator 40 for reusing this portion 70 as feed into the evaporator 46 of the second steam generation train 12. It should be noted that there may be a main line 72 that transports the blowdown stream 44 from the separator 40 and splits into the first and second lines transporting the different portions 68, 70 of the first blowdown 44. The train integration circuit 66 may also be sized, configured and controlled to manage a flowrate of the recycled portion and water quality of the first boiler feed water stream, such that the softening unit feed stream has a concentration of a first limiting impurity below a maximum threshold value for operation of the softening unit, and the first boiler feed water stream has a concentration of a second limiting impurity below a maximum threshold value for operation of the first OTSG. The first limiting impurity may also be referred to as a softener limiting impurity, and the second limiting impurity may also be referred to as an OTSG limiting impurity. It should be noted that the first and second limiting impurities may be the same or different and may have different maximum threshold values.
For example, the first limiting impurity may be alkalinity of the softening unit feed stream, which is the combination of the first de-oiled produced water stream 16a and the recycled stream 68. Alkalinity above a maximum threshold can result in unstable operation of parts of the softening unit 18, such as the VVLS 20. For example, if the alkalinity exceeds the maximum threshold, it may no longer be possible for chemical control of the WLS as addition of magnesium oxide or sodium carbonate can be limited or prevented. When control of the WLS is lost, the softening step is impaired and the resulting softened water stream can have high levels of divalent cations, silica and organics causing problems in the OTSG. When the first de-oiled produced water stream 16a has relatively low total dissolved solids (TDS), e.g. below about 2000 ppm, the first limiting impurity will more likely be alkalinity.
In another example, the first limiting impurity may be chemical conditioners, such as chelates and/or dispersants, in the softening unit feed stream. Such chemical conditioners are often added to boiler feed water in order to condition the water prior to introduction into the OTSG. These chemical conditioners then concentrate in the OTSG
blowdown. Wien recycled back to the softening unit, these impurities can disturb the stable operation of the softening unit if they are present above a maximum threshold.
In another example, the first limiting impurity may be organics. Organics may be present in the de-oiled produced water stream 16a at low levels during normal operation.
However, during upsets in the de-oiling unit, the concentration of organics can increase in the de-oiled produced water 16a. In addition, organics present in the first boiler feed water stream 34 concentrate in the OTSG blowdown 44. Organics can also disrupt the stable operation of the softening unit 18 when above a maximum threshold.
The second limiting impurity may be dissolved solids in the first boiler feed water stream 34. This may occur when the first de-oiled produced water stream 16a has higher TDS.
Since the softening unit 18 cannot greatly remove dissolved solids, this impurity can tend to accumulate and cycle up in the first train 12. Thus, in this scenario, the flowrate of the recycled portion 63 may be reduced and the flowrate of the reused portion 70 may be increased into the evaporator based train 14 for greater removal of the dissolved solids.
It is also noted that the process may include the step of feeding at least a part of the distillate stream 48 as a second boiler feed water stream 54 to a second Once Through Steam Generator (OTSG) 56 to produce wet steam. In this case, the water quality of the second boiler feed water stream 54 may be controlled, such that the second boiler feed water stream 54 has a concentration of a third limiting impurity below a maximum threshold value for operation of the second OTSG. It should be noted that the third limiting impurity and the second limiting impurity may be the same or different.

In one example scenario, the third limiting impurity may be organics in the second boiler feed water stream 54. Evaporators 46 are able to deplete water streams with respect to various impurities, but there can be carry-over of organics in the distillate.
In particular, if there is an upset in the upstream de-oiling unit resulting in a second de-oiled produced water stream 16b having a higher organics concentration, added to the organics concentration in the reused blowdown stream 70, there may be elevated carry-over of organics into the distillate stream 48. Thus, the flowrate of the reused portion 70 can be controlled so that the distillate stream 48 does not have an excessive amount of organics which would result in a second boiler feed water stream 54 with organics above the maximum threshold for operation of the second OTSG.
The maximum threshold values for the various impurities depend on several factors, including equipment type and sizing, input water (make-up water, de-oiled produced water, etc.) flowrates and compositions, as well as the relative concentrations on different impurities in the streams. The concentration of one impurity can have an impact on the solubility of other impurities; for instance, elevated IDS results in a lower solubility of siiica and organics making the resulting stream more susceptible to fouling compared to a similar stream with lower TDS.
By way of example, the maximum threshold of alkalinity, chemical conditioners or organics in the softening unit feed stream may be such that above the threshold the softened water output would be unacceptable for downstream processing units such as a VVAC unit or OTSG.
The maximum threshold value of the dissolved solids concentration in the first boiler feed water stream may be, for example, 12,000 ppm dissolved solids, but may alternatively be determined based on the capacity and design of the given OTSG. This applies to the first, second and any other OSTGs in other trains. Each OTSG may have a different maximum threshold value, for example based on equipment design specification or operational experience. In some scenarios, where multiple OTSGs are operated in parallel as a set of OTSGs that all receive portions of the same boiler feed water stream, the maximum threshold value of the dissolved solids in the boiler feed water stream may be determined based on the lowest maximum threshold value of a given OSTG unit in the set of OTSGs. For illustrative purposes, the value of 12,000 ppm has been used herein, but it should be understood that in a system or process where one or more OTSGs have a capacity that is less or greater than 12,000 ppm, the pre-determined concentration value can vary accordingly.
In the case that the limiting impurity is not TDS, the limiting impurity may have another maximum threshold value. For example, the maximum threshold value of organics may be 700 ppm, the maximum threshold value of pH may be 10.5, the maximum threshold value of the concentration of silica may be 100 ppm, the maximum threshold value of hardness may be 1 ppm, the maximum threshold value of the oil in water may be 0.5 ppm, and the maximum threshold value of chemical conditioners including chelates and dispersants may depend on the nature of such conditioners and the processing conditions.
Typically, blowdown 44 from steam generation in such applications would be sent for disposal due to the concentrated level of impurities such as dissolved solids.
The WLS
and other softening apparatuses can remove calcium, magnesium and silica, but cannot sufficiently reduce the concentration of dissolved solids such that after several cycles of rec., cling the blowdown, the dissolved solids content would exceed the acceptable limits for an OTSG, which could result in impaired operation. By integrating a WLS
based train (e.g the first train 12) with an evaporator based train (e.g. the second train 14), the evaporator 46 is able to treat a sufficient amount of the first train blowdown 44 so as to remove dissolved solids and enable reuse of the blowdown water in both trains 12, 14.
By diverting the reused portion 70 into the evaporator based train 14, the flowrate of the recycled portion 68 fed back into the WLS based train 12 can be reduced sufficiently so that the recycled rate of dissolved solids is low enough to maintain an acceptable concentration of dissolved solids in the first boiler feed water stream 34.
The flowrates of the recycled portion 68 and the reused portion 70 may be adapted, for example depending on the flowrate and dissolved solids concentration of the streams used to form the first boiler feed water stream 34 (e.g. stream 16a, 37, 77 and 74), the streams fed into the softening unit 18 (e.g. 16a, 39, 68) as well as the operating conditions of the treatment units of the WLS based train 12 (e.g. units 20 and 28).
In some implementations, the concentration of other impurities can exceed a maximum threshold before the dissolved solids limit is reached. For instance, alkalinity, organics and conditioner concentrations may exceed a maximum threshold for stable operation of the WLS while the dissolved solids concentration remains at an acceptable level for OTSG operation. Thus, controlling water quality of the first boiler feed water stream may include ensuring that the softening unit feed stream has a concentration of the first limiting impurity (e.g. alkalinity, organics, conditioner concentrations) below a maximum threshold value for operation of the softening unit, as well as ensuring that the first boiler feed water stream has a concentration of the second limiting impurity (e.g.
dissolved solids) below a maximum threshold value for operation of the first OTSG.
Managing a flowrate of the recycled portion aids in such control of the water quality of the first boiler reed water stream.
In some implementations, the train integration circuit 66 may be configured and operated to allow controlling of the dissolved solids concentration in the first boiler feed water stream 34 so as to include at most 12,000 ppm dissolved solids, at least paitly by managing the flowrate of the recycled portion in the first line 68. For example, if the dissolved solids concentration of the first boiler feed water stream 34 goes above 12,000 ppm, the flowrate of the recycled portion 68 may be sufficiently reduced to reduce the amount of dissolved solids reintroduced into the first train 12. A reduction in the flowrate of the recycled portion 68 will no necessarily result in reduced dissolved solids in the first boiler feed water stream 34, but rather it will depend on the overall mass balance of the first train 12. Given the continuous and recycle-based nature of the process, an adjustment in the flowrate of the recycled portion 68 can have an impact on the concentration of dissolved solids that tends toward a stable value. In some scenarios, the recycled portion 68 is controlled such that the dissolved solids concentration in the first boiler feed water stream 34 is maintained within a 3000 ppm range around ppm, thereby not exceeding the 12,000 ppm limit while providing a buffer zone of 1500-7500 ppm between the upper threshold and the operating concentration in case of process upset conditions. In some scenarios, the recycled portion 68 is set as high as possible relative to the reused portion 70, while maintaining a first boiler feed water stream 34 below 12,000 ppm in dissolved solids, so as to benefit from the OSTG's ability to handle relatively high dissolved solids concentrations while reducing the flowrate to the evaporator 46 and thus reducing energy required to conduct evaporation.
The ccncentration of impurities in the softening unit feed and in the first boiler feed water stream 34 may also be controlled by managing the flowrates of other water streams in the steam generation system. For instance, the dissolved solids concentration (as an example of the second limiting impurity) in the first boiler feed water stream 34 may be controlled by managing the flowrate of the de-oiled produced water 16a supplied to the softening unit 18 and/or the flowrate of make-up water 39 added to the softened water stream 30. For example, if the dissolved solids concentration of the first boiler feed water stream 34 goes above 12,000 ppm, the flowrate of the de-oiled produced water 16a may be reduced and the flowrate of the make-up water 39 or transfer distillate 74 may be increased to compensate. In another scenario, the flowrate of the de-oiled produced water 16a may be increased, while maintaining the flowrate of the recycled portion 68 relatively constant, if the dissolved solids concentration of the de-oiled produced water 16a is below that of the recycled portion 68, which is typically the case. In addition, the concentration of the first limiting impurity may be reduced in the softening unit feed by increasing the flowrate of the first de-oiled produced water stream 16a and/or reducing the flowrate of the recycled portion 68, in the case that such stream has a lower concentration of the given limiting impurity. For example, if the first OTSG
blowdown stream 44 contains an elevated alkalinity that would cause upsets in the WLS, the flowrate of the recycled stream 68 may be decreased to avoid such upsets and, optionally, make-up water 39 or water from another train may be added if needed to compensate for the reduced flow to the first OTSG 36.
Referring still to Fig 1, the train integration circuit 66 may also include a distillate transfer stream 74 that is a portion of the distillate stream 48 or water contained in the second feed tank 52 and is fed to the first train 12. While Fig 1 shows this transfer occurring from the evaporator distillate stream 48 to the first tank 32, it should be uederstood that the transferred distillate 74 may be added to the first train 12 at various locations for forming part of the first boiler feed water stream 34. By integrating the trains in this manner, the benefits of the second train's evaporator 46 in removing impurities and producing high quality water may be leveraged for the first train 12, for example when a reduction in dissolved solids or another limiting impurity may be desired in the first boiler feed water stream 34.
Referring still to Fig 1, the train integration circuit 66 may also include a softened water transfer stream 76 that is a portion of the softened water 30 or water contained in the first feed tank 32 and is fed to the second train 14. This train integration technique may enable the first train 12 to transfer some of the dissolved solids or other limiting impurity in the softened water stream 30 for combination with the high quality distillate 48 of the second train 14, thereby increasing the concentration of such impurity in the second boiler feed water stream 54 to within an acceptable level for steam generation in the second OTSG.
The distillate stream 48 is high quality water. Providing a boiler feed water stream completely or substantially made up of such high quality water would not take advantage of OTSG type steam generators' ability to receive lower quality feed water.
Thus, when the distillate stream 48 is to be used for an OTSG type steam generator, this stream has the capacity to take on additional impurities such as dissolved solids. Some of the dissolved solids from the first train 12 may be removed from the first train and combined with the distillate stream 48 to produce boiler feed water having a higher dissolved solids concentration while staying within acceptable limits for the second OTSG.
Thus, this integration of water between the first and second trains 12, 14 can enable leveraging the high water quality production of the evaporator train; the lower cost, lower energy, higher throughput potential and flexibility of the WLS based train; and the ability of the OTSG
type steam generator to handle certain concentrations of impurities.
Integrating a VVLS-OTSG based train with an evaporator-OTSG based train utilizes strengths and mitigates drawbacks of the different units.
It should also be noted that while the softened water transfer stream and the distillate transfer stream are shown as two separate streams, the train integration circuit 66 may include only one line for transferring one or the other to the corresponding train.
Alternatively, there may be two or more lines for allowing simultaneous transfer of distillate and softened water between trains.
Referring still to Fig 1, in some implementations the train integration circuit 66 may also include a direct blowdown return stream 77 that is a portion of the first train blowdown stream 44 and is directly reused as part of the first boiler feed water stream 34.
Referring to Fig 1, in some implementations the system may also include a control assembly 78 operatively connected to the train integration circuit 66. The control assembly 78 may be configured for managing various flowrates, for instance the flowrates of the first de-oiled produced water stream 16a, the make-up water stream 39, the distillate transfer stream 74, the softened water transfer stream 76, the recycled stream 70, the reused stream 68, and/or other streams such as the direct blowdown return stream 77. For example, if the concentration of a limiting impurity (e.g. dissolved solids) in the first boiler feed water stream 34 exceeds or approaches its maximum threshold (e.g. 12,000 ppm), then the control assembly 78 may be configured to detect the concentration and lower the flowrate of the recycled portion 68 of the blowdown stream 44, increase the flowrate of the make-up water 30 or distillate transfer stream 74 and/or adjust a combination of streams to reduce the concentration in the boiler feed water 34. The control assembly 78 may be configured to perform flowrate adjustments before the concentration reaches the maximum threshold to account for process control lag time. The control assembly 78 may also be adjusted in a gradual manner or with a step-change adjustment of one or more flowrates. The control assembly 78 may also be operatively connected to other lines for control or adjusting of other streams such as a second make-up water stream 80 or a second train blowdown recycle stream 82.
In some implementations, substantially all of the first blowdown 44 may be recycled and reused in the first and second trains 12, 14. Alternatively, a portion of the blowdown 44 may be disposed of or sent to other processing units such as other water treatment units, heat exchangers for heat recovery, and so on.
Referring to Fig 1, the system may include measurement devices 84 for measuring water quality of the boiler feed water streams 34, 54. The measurement devices may be configured for measuring at least the total dissolved solids (TDS) in the boiler feed water streams, and may be coupled to the control assembly 78 such that the control assembly may adjust one or more flowrates or other parameters of the process in response to the measured values. The measurement devices may be configured for measuring the concentration of organics, alkalinity, total suspended solids (TSS), hardness, silica concentration, and so on. Various measurement techniques may be used depending on the impurity to be measured. For example, organics may be measured based on the turbidity of the stream. It should also be noted that measurement devices may be used on a sample that is manually retrieved at one or more points and then taken to a laboratory setting to perform the measurement.
In some implementations, there is a process for treating the de-oiled produced water 16a, 16b derived from the thermal in situ bitumen or heavy hydrocarbon recovery operation. The process includes:
supplying the de-oiled produced water 16a as part of a softening unit feed stream to a softening unit 18 to produce a softened water stream depleted in a first set of the impurities including divalent cations and silica;

feeding at least a part of the softened water stream as a first boiler feed water stream 34 to a first Once Through Steam Generator (OTSG) 36 to produce wet steam 38;
separating the wet steam 38 into substantially dry steam 42 and a blowdown stream 44 including a concentrated level of impurities relative to the first boiler feed water stream 34;
recycling a recycled portion 68 of the blowdown stream 44 as part of the softaning unit feed stream;
reusing a reused portion 70 of the blowdown stream 14 as part of an evaporator feed stream by feeding to an evaporator 46 to produce a distillate stream 48 depleted in a second set of the impurities including dissolved solids; and controlling water quality of the softening unit feed stream and the first boiler feed water stream 34, such that:
the softening unit feed stream has a concentration of a first limiting impurity below a maximum threshold value for operation of the softening unit 18; and the first boiler feed water stream 34 has a concentration of a second limiting impurity below a maximum threshold value for operation of the first OTSG 36; and wherein the controlling of the water quality includes managing a flowrate of the recycled portion 68.
In some implementations, increasing or decreasing the flowrate of the recycled portion 68 may be accompanied with a corresponding decrease or increase in one or more streams, such as the reused portion 70. For example, in order to decrease the concentration of a first limiting impurity (e.g. alkalinity) in the softening unit feed stream, the process may include decreasing the flowrate of the recycled portion 68 and increasing the flowrate of the reused portion 70. In another example, in order to increase the dissolved solids concentration in the first boiler feed water stream 34 closer to but not above the maximum TDS, the process may include increasing the flowrate of the recycled portion 68, and decreasing the flowrate of the reused portion 70.
These flowrate modifications may correspond with each oilier, i.e. fluid from one of the portions 68, 70 may be diverted and substantially used in the other portion 70, 68.
Alternatively, the flowrate of another stream may be modified, e.g. the process may include decreasing the flowrate of the recycled portion 68 and increasing the flowrate of the make-up water 39 and/or the distillate transfer stream 76, in order to reduce or stabilize the limiting impurity (e.g. dissolved solids concentration in the first boiler feed water).
Increasing the flowrate of the recycled portion 68 relative to the flowrate of the produced water stream 16a may also facilitate saving on energy and/or chemical addition in the softening unit(s). In various scenarios, the recycle portion 68 will have lower silica and hardness levels compared to the de-oiled produced water stream 16a, and thus increasing the flowrate of the recycled portion can facilitate water treatment in the softening unit.
Despite the concentration of the impurities in the blowdown stream 44, the softening treatment removes almost all of the silica and hardness from the boiler feed water, and thus the silica and hardness levels are typically still lower in the blowdown stream 44 (as well as streams 68 and 70) than the levels in the de-oiled produced water stream 16a. In addition, if the flowrate of the recycle portion 68 is increased and the flowrate of the reused portion 70 is consequently decreased, the corresponding lower rates through the evaporators result in lower energy use. The chemical use and energy consumption of the overall integrated system can thus be adjusted by controlling the flowrates of streams 68 and 70, as well as other s,reams. In another scenario, the process may include decreasing the flowrate of the recycled portion 68 and increasing the flowrate of a discharge stream (shown as dotted line in the first train 12 in Fig 3), in order to reduce or stabilize the limiting impurity (e.g. dissolved solids concentration in the first boiler feed water). Thus, adjustments in the flowrates of various streams may be coordinated in order to increase, decrease or stabilize the limiting impurities in the first and/or second boiler feed water streams.
The relative proportion of the recycled portion and the reused portion may also be provided to provide water quality for feed water in the various units in the two trains. In some implementations, the recycled portion and the reused portion are provided in a relative proportion between 1/99 and 85/15 or between 30/70 and 70/30.
The de-oiled produced water streams 16a, 16b may have certain impurity concentrations that influence the control of the recycled and reused potions 68, 70. For example, the dissolved solids concentration of the de-oiled produced water may be between ppm and 4000 ppm, or between 2500 ppm and 3500 ppm in some instances. If the dissolved solids concentration of the first de-oiled produced water is below 2000 ppm, then the softener limiting impurity may not be TDS but rather another impurity such as organics or alkalinity. If the dissolved solids concentration of the first de-oiled produced water is elevated, such as around 12,000 rpm, then the second limiting impurity is likely to be TDS. In another example, during upsets in upstream processes, the resulting de-oiled produced water stream may include an increased amount of certain impurities, such as increased organics due to upsets in de-oiling processes. In such upset cases, the system may be configured and operated to respond such that one or more of the limiting impurities is changed from one impurity to another, resulting in a corresponding adjustment in the flow rate of the recycled portion, reused portion and/or other streams.
Referring now briefly to Fig 3, one example of a steam generation system 10c may also include a third steam generation train 73. The third train 73 may be integrated with the second train 14 in a similar manner as the first train 12 is so integrated.
The third train 73 may, for example, receive a third de-oiled produced water stream 16c from a different source and having different water quality and composition compared to The first train 12.
The first and third de-oiled produced water streams 16a, 16c respectively fed to the first and third trains 12, 73 may not only be different from each other but may also each have variability in composition and flowrate calling for adjustments in process operation.
For instance, in the case that the third train 73 receives de-oiled produced water 16c with lower concentration of a given impurity (e.g. dissolved solids) than the first de-oiled produced water stream 16a, the resulting third train steam generation blowdown may have a corresponding higher quality and thus the proportion of the third train blowdown that is reused in the third train 73 may be increased compered to the portion that is recycled to the evaporator of the second train 14. Such adjustments can add flexibility to the system when including three or more steam generation trains.
It should also be noted that the de-oiled produced water streams 16a, 16b, 16c may be substantially similar in flowrate and/or composition.
More regarding multi-train implementations will be described further below.
Such integration techniques can help facilitate reductions in disposal water and in make-up water.
Integration with second train OTSG blowdown recycled to same OTSG

Referring now to Fig 2, in some implementations the system may include lines configured for combining a portion 76 of the softened water stream 30, at least a portion of the distillate stream 48 and recycled OTSG separator blowdown stream 82 for use as boiler feed water to the OTSG 56.
Fig 2 illustrates a scenario where the system includes a softened water transfer stream 76 for supplying a portion of the softened water 30 of the first train 12 to be combined with the distillate stream 48 of the second train 14 as well as the blowdown recycle stream 82 from the second train 12. Thus, in this scenario the boiler feed water composed of a mixture of softened water, distillate and recycled blowdown is for the second train OTSG. It should nevertheless be understood that other scenarios are possible where a similar combination of these streams could be used for boiler feed water in a VVLS based train.
Blowdown from OTSGs combined with a mixture of distillate from an evaporator and softened water (e.g. from treatment with WLS with optional WAG), can be recycled as boiler feed water to the OTSG in the evaporator train. In some implementations, up to about 50 vol. /0 or about 40 vol. /0 of the blowdown may be recycled back as boiler feed water and the remainder of the blowdown may be reused elsewhere in the system or disposed of. Feeding an OTSG such as the second train OTSG as illustrated in Fig 2, with the mixture of distillate and softened water, results in a blowdown from the separator downstream of the OTSG of such high quality that a fair portion of the blowdown can be recycled directly back as boiler feed water to the same OTSG
without the need for further treatment.
In some implementations, this process includes the step of controlling water quality of the second boiler feed water stream so as to have a concentration of a limiting impurity below a maximum threshold value for operation of the second OTSG, facilitated by managing flowrates of the distillate stream 48, the recycle stream 82 and the portion 76 of the softened water stream. The limiting impurity may be TDS, alkalinity, concentration of chemical conditioners, or organics. For example, if the limiting impurity is organics, the flowrate of the recycle portion 82 may be decreased. If the limiting impurity is TDS, the flowrate of the recycle portion 82 may be decreased and/or the flowrate of the portion 76 of the softened water stream may be decreased, since the softened water stream may have elevated TDS due to the WLS's inability to substantially remove dissolved solids.

In one example, the recycle stream 82 may be provided and increased until the limiting impurity level is reached, e.g. oil in water (01W) limit, which may be at approximately 50% to 70% recycle of the blowdown stream. The remainder of the blowdown may be sent to the WLS train 12 and/or the evaporator in train 14, for example. At least part of the remainder 83 may, for example, be sent back to the infeed of the evaporator 46. In Fig 2, the softened water transfer stream 76 and the blowdown recycle stream 82 are shown as being fed to a single boiler feed water tank 52. However, it should be noted that various arrangements may be employed for combining the distillate, softened water and recycled blowdown to form the boiler feed water stream 54. Depending on the temperature and pressure conditions of each stream, various units such as an expansion tank and fittings may be used.
Further multi-train integration implementations As briefly described above, Fig 3 shows an example of the system including three steam generation trains 12, 14, 73. It should be noted that further trains may be installed and integrated with existing trains using integration techniques described herein.
Referring to Fig 3, it will be noted that the third train 73 may be substantially similar to the first train 12 and may be integrated in a similar manner with the second train 14.
The third train 73 may include a third softening unit 85 that may include a WLS 86 and a WAC 88 for producing a third softened water stream 90, which may be supplied to a third boiler feed water tank 92. A third boiler feed water stream 94 may be fed to a third train OTSG 96 for producing wet steam 98, which may be supplied to a third train separator 100 that produces substantially dry steam 102 and a third train blowdown stream 104.
The third train blowdown stream 104 may be reused in the system 10 in several ways.
For instance, a returned portion 106 of the third train blowdown stream 104 may be directly reused as part of the third boiler feed water stream 94. A recycled portion 108 may be fed back into the third train 73 to the infeed of the softening unit 85. A recycled portion 110 may also be fed to the second train 14 as part of the feed to the evaporator 46.
Referring now to Figs 1 and 2, in some implementations, the WLS train 12 may be used in combination with an evaporator train 14 in order to adapt to upstream upsets. WLS
units tend to be more apt to handle upsets in the de-oiling processes compared to evaporators. In the event of an upset in the upstream de-oiling process feeding the evaporator train 14, softened water 30 may be supplied from the WLS based train 12, e.g. through line 76, combined with a reduction in the flowrate through the evaporators.
By adding softened water 30 from one train 12 in response to a process upset in another train 14, one may reduce the flow through the evaporator to minimize fouling that could occur due to the high oil levels in the incoming water 16b.
Further optional aspects It should be noted that each train may have one or more of certain units in series or in parallel, as appropriate. For example, there may be several evaporators provided in parallel having sufficient capacity for treating a given flowrate of feed water. Evaporators can also be arranged in series. There may also be several OTSGs arranged in parallel for each train.
In some implementations, there may be more than two steam generation trains.
The multiple trains may be integrated in a number of ways to recover water and/or heat.
In some implementations, the OTSG of the first, second and/or additional steam generation train may be part of a Heat Recovery Steam Generation (HRSG) system, where hot exhaust gas derived from an electricity generation process, and potentially further heated using additional duct firing, is used in the OTSG to heat the boiler feed water.
In some implementations, during upset or turndown conditions, direct recycling of blowdown as boiler feed water may be reduced and one or more of the other integration streams may be operated to compensate and recover the blowdown water. For example, during upset conditions the direct return portion 77 may be reduced and the reused portion 70 and recycled portion 68 of the first train blowdown 44 may be increased.
In some implementations, the sizing and configuration of the WLS and evaporator(s) are performed so that each train reeds several OTSG apparatuses. For example, a WLS
may be sized sufficiently to feed several OTSC3 apparatuses in the first train (WLS sized between about 500 m3/h and about 1500 m3/h), and several evaporators are provided in parallel for feeding several OTSG apparatuses in the second train (evaporators each sized between about 100 m3/h and about 400 m3/h), while the number of OTSG
apparatuses is determined based on their sizing between about 100 m3/h and about 400 m3/h.

In some implementations, operation of the system may be performed to favour direct recycle of blowdown as boiler feed water into the same OTSG, thereby reducing the flowrate of blowdown that is treated in the water treatment units (WLS, WAG, evaporators, etc.) and enabling reduced sizing of such units. The flowrate of blowdown that can be directly rocycled as boiler feed water to an OTSG may be increased by integration with an evaporator based steam generation train, e.g. by mixing evaporator distillate with the boiler feed water, by feeding a portion of the blowdown to the evaporator of another train, and/or by employing other techniques described herein.
EXAMPLES
The following examples help illustrate possible implementations and advantages of the system and process described herein.
Example In this example, a WLS-OTSG steam generation train and an evaporator-OTSG
steam generation train were integrated such that the blowdown from the OTSGs of the WLS-OTSG steam generation train was recycled as part of the WLS feed stream and part of the evaporator feed stream. This operation reduced the disposal water rates of the steam generation system and thus reduced system make-up water. In conventional operations, approximately 60 vol% of the blowdown from the OTSGs in the WLS
train was routed baek to the inlet of the WLS with the remaining 40 vol% routed to disposal wells. Using the integration scheme, the 40 vol% that was routed to the disposal wells was instead routed to the evaporator inlet. The operation of the evaporators was such that about 98% of the total feed is converted into product (i.e. distillate) with the remaining 2% being an evaporator blowdown stream that is sent to disposal.
Whereas 40% of the VVLS-OTSG blowdown was previously going directly to disposal, with this integration scheme less than 1% of the blowdown requires disposal. Such disposal reduction can improve regulatory compliance and enhance disposal flexibility, allowing for temporarily higher disposal rates during process upsets if required, as well as reduce make-up water rates.
Example 2 In this example, a WLS-OTSG steam generation train and an evaporator-OTSG
steam generation train were integrated such that the blowdown from the OTSGs of the evaporator-OTSG steam generation train was combined with the evaporator distillate and part of the softened water as boiler feed water fed to the evaporator train OTSGs.
This operation increaµ.3ed plant water treating capacity, and thus steam generation and oil production, by reducing the recycle of boiler blowdown to the inlet of the evaporators.
By controlling the ratio of the blend of WLS and evaporator water, it was found that rather than needing to recycle the boiler blowdown of the OTSGs of the evaporator train upstream of the evaporator, a portion (e.g. up to 60% and in some cases up to 90%) could be directly recycled to the inlet of the OTSGs (via the boiler feed water tank) without exceeding boiler feed water quality limitations. As water treating capacity is typically what limits overall plant steam output, any reduction in recycle to the inlet of the evaporators allows for more produced water to be processed in the evaporators.
This results in increased plant throughput and higher oil production rates.

Claims

1. A process for treating de-oiled produced water derived from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation and for generating steam, the de-oiled produced water comprising impurities, the process comprising:
supplying a first de-oiled produced water stream to a softening unit to produce a softened water stream depleted in a first set of impurities comprising divalent cations and silica;
supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities comprising divalent cations, silica and dissolved solids;
feeding at least a portion of the distillate stream and a portion of the softened water stream as part of a boiler feed water stream to a Once Through Steam Generator (OTSG) to produce wet steam;
separating the wet steam into substantially dry steam and a blowdown stream comprising a concentrated level of impurities relative to the boiler feed water stream; and recycling at least a recycle portion of the blowdown stream as part of the boiler feed water stream.

2. The process of claim 1, further comprising:
controlling water quality of the boiler feed water stream so as to have a concentration of a limiting impurity below a maximum threshold value for operation of the OTSG.

3. The process of claim 2, wherein the controlling of the water quality comprises managing flowrates of the distillate stream, the recycle stream and/or the portion of the softened water stream.

4. The process of claim 2 or 3, wherein the limiting impurity is total dissolved solids (TDS).

5. The process of claim 4, wherein the maximum threshold value of the concentration of TDS is 12,000 ppm.

6. The process of claim 2 or 3, wherein the limiting impurity is organics.

7. The process of claim 6, wherein the maximum threshold value of the organics is 700 ppm.

8. The process of claim 2 or 3, wherein the limiting impurity is pH.

9. The process of claim 8, wherein the maximum threshold value of the pH is 10.5.

10. The process of claim 2 or 3, wherein the limiting impurity is silica.

11. The process of claim 10, wherein the maximum threshold value of the concentration of silica is 100 ppm.

12. The process of claim 2 or 3, wherein the limiting impurity is hardness.

13. The process of claim 12, wherein the maximum threshold value of hardness is 1 ppm.

14. The process of claim 2 or 3, wherein the limiting impurity is oil in water.

15. The process of claim 14, wherein the maximum threshold value of the oil in water is 0.5 ppm.

16. The process of claim 2 or 3, wherein the limiting impurity is a chemical conditioner.

17. The process of any one of claims 2 to 16, wherein the controlling of the water quality of the boiler feed water stream comprises:
measuring the concentration of the limiting impurity; and in response to an elevated measured concentration of the limiting impurity, managing the concentration of the limiting impurity in the boiler feed water stream by decreasing the flowrate of at least one of the following streams:
the recycled portion of the blowdown stream;
the portion of the softened water stream; and the distillate stream.

18. The process of claim 17, wherein the measuring of the limiting impurity is performed on the boiler feed water stream.

19. The process of claim 17 or 18, wherein the controlling of the water quality of the boiler feed water stream comprises:
measuring the concentration of organics as the limiting impurity; and in response to an elevated measured concentration of organics, managing the concentration of the organics in the boiler feed water stream by reducing the flowrate of the recycled portion.

20. The process of claim 19, wherein the controlling of the water quality further comprises increasing the flowrate of the distillate stream as part of the boiler feed water stream.

21. The process of claim 19 or 20, wherein the controlling of the water quality further comprises increasing the flowrate of the portion of the softened water stream as part of the boiler feed water stream.

22. The process of claim 17 or 18, wherein the controlling of the water quality of the boiler feed water stream comprises:
measuring the concentration of total dissolved solids (TDS) as the limiting impurity; and in response to an elevated measured concentration of TDS, managing the concentration of the TDS in the boiler feed water stream by reducing the flowrate of the portion of the softened water stream, the recycled portion of the blowdown stream, or a combination thereof.

23. The process of claim 22, wherein the controlling of the water quality further comprises increasing the flowrate of the distillate stream as part of the boiler feed water stream.

24. The process of any one of claims 2 to 23, wherein the controlling of the water quality of the boiler feed water stream comprises, in response to an elevated measured concentration of the limiting impurity, reducing the concentration of the limiting impurity by increasing the flowrate of make-up water added to the boiler feed water stream or to the de-oiled produced water.

25. The process of any one of claims 1 to 24, wherein the softening unit comprises a Warm Lime Softener (WLS) or a Hot Lime Softener (HLS) or a combination thereof.

26. The process of claim 25, wherein the softening unit further comprises a cation exchange device downstream of the Warm Lime Softener (WLS) or the Hot Lime Softener (HLS).

27. The process of claim 26, wherein the cation exchange device comprises a Weak Acid Cation (WAC) exchanger.

28. The process of any one of claims 1 to 27, wherein the OTSG is part of a Heat Recovery Steam Generation (HRSG) system.

29. The process of any one of claims 1 to 28, wherein the OTSG is an evaporator train OTSG and the process further comprises:
feeding at least a part of the softened water stream as an additional boiler feed water stream to a softening unit train Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a softening unit OTSG
blowdown stream.

30. The process of any one of claims 1 to 29, further comprising:
controlling water quality of the additional boiler feed water stream, such that the second boiler feed water stream has a concentration of an additional limiting impurity below a maximum threshold value for operation of the softening unit OTSG.

31. The process of claim 30, wherein the additional limiting impurity is total dissolved solids (TDS), organics, pH, silica, hardness or oil in water.

32. The process of any one of claims 1 to 31, wherein the recycle portion of the blowdown stream is directly transferred back into the boiler feed water stream.

33. The process of any one of claims 1 to 32, wherein the recycle portion of the blowdown stream, the portion of the distillate stream and the portion of the softened water stream are fed to a boiler feed water tank prior to supplying as the boiler feed water stream.

34. The process of any one of claims 1 to 33, wherein the recycle portion is at least 30 vol%
of the blowdown stream.

35. The process of any one of claims 1 to 34, wherein the recycle portion is at least 40 vol%
of the blowdown stream.

36. The process of any one of claims 1 to 35, wherein at least part of a remainder portion of the blowdown stream is supplied to the evaporator, the softening unit, or a combination thereof.

37. A process for generating steam for use in a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the process comprising:
in a first steam generation train:
supplying a first de-oiled produced water stream comprising impurities to a softening unit to produce a softened water stream depleted in a first set of impurities comprising divalent cations and silica;
feeding a part of the softened water stream as a first boiler feed water stream to a first Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a blowdown stream comprising a concentrated level of impurities relative to the first boiler feed water stream;
in a second steam generation train:
supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities comprising divalent cations, silica and dissolved solids;
feeding at least a part of the distillate stream as part of a second boiler feed water stream to a second Once Through Steam Generator (OTSG) to produce steam; and separating the wet steam into substantially dry steam and a second blowdown stream comprising a concentrated level of impurities relative to the second boiler feed water stream; and integrating the first and second steam generation trains by:
feeding a portion of the softened water stream as part of the second boiler feed water stream; and recycling at least a recycle portion of the blowdown stream as part of the second boiler feed water stream.

38. A process for producing hydrocarbons from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the process comprising:
injecting a fluid comprising steam into a bitumen and/or heavy hydrocarbon bearing reservoir in order to mobilise bitumen and/or heavy hydrocarbons;
producing production fluid comprising condensate and hydrocarbons from the reservoir;
separating the hydrocarbons from the condensate to produce a hydrocarbon stream and produced water comprising residual oil;
de-oiling the produced water to produce de-oiled produced water;
in a first steam generation train:
supplying a first de-oiled produced water stream comprising impurities to a softening unit to produce a softened water stream depleted in a first set of impurities comprising divalent cations and silica;
feeding a part of the softened water stream as a first boiler feed water stream to a first Once Through Steam Generator (OTSG) to produce wet steam; and separating the wet steam into substantially dry steam and a blowdown stream comprising a concentrated level of impurities relative to the first boiler feed water stream;
in a second steam generation train:
supplying a second de-oiled produced water stream to an evaporator to produce a distillate stream depleted in a second set of impurities comprising divalent cations, silica and dissolved solids;
feeding at least a part of the distillate stream as part of a second boiler feed water stream to a second Once Through Steam Generator (OTSG) to produce steam; and separating the wet steam into substantially dry steam and a second blowdown stream comprising a concentrated level of impurities relative to the second boiler feed water stream;
integrating the first and second steam generation trains by:
feeding a portion of the softened water stream as part of the second boiler feed water stream; and recycling at least a recycle portion of the blowdown stream as part of the second boiler feed water stream; and re-injecting at least some of the steam generated by the first and second steam generation trains back into the bitumen and/or heavy hydrocarbon bearing reservoir.

39. A system for treating de-oiled produced water derived from a thermal in situ bitumen and/or heavy hydrocarbon recovery operation, the de-oiled produced water comprising impurities, the system comprising:
a first steam generation train comprising:

a softening unit for receiving a first de-oiled produced water stream and producing a softened water stream depleted in a first set of impurities comprising divalent cations and silica; and a first Once Through Steam Generator (OTSG) for receiving a first boiler feed water stream derived from the softened water stream, and producing wet steam;
a second steam generation train comprising:
an evaporator for receiving a second de-oiled produced water stream and producing a distillate stream via a distillate line;
a second Once Through Steam Generator (OTSG) for receiving a second boiler feed water stream at least partly comprising the distillate stream via a boiler feed water line;
a separator for separating the wet steam into substantially dry steam and a blowdown stream comprising a concentrated level of impurities relative to the second boiler feed water stream; and a blowdown recycle line for recycling at least a portion of the second blowdown stream as part of the second boiler feed water stream; and a softened water transfer line for transferring a portion of the softened water stream from the first steam generation train to the second steam generation train for use as part of the second boiler feed water stream.

40. The system of claim 39, wherein the softened water transfer line, the blowdown recycle line, the distillate line and the boiler feed water line are sized, configured and controlled so as to manage water quality of the second boiler feed water stream so as to have a concentration of a limiting impurity below a maximum threshold value for operation of the second OTSG.

41. The system of claim 39, further comprising a control assembly operatively connected to the softened water transfer line, the blowdown recycle line, the distillate line and/or the boiler feed water line, the control assembly being configured for:

managing a flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream;
managing a flowrate of the recycle portion recycled as part of the second boiler feed water stream;
managing a flowrate of the distillate stream supplied as part of the second boiler feed water stream; and/or managing a flowrate of make-up water added to the second boiler feed water stream.

42. The system of claim 41, further comprising:
a measurement device for measuring the concentration of an impurity in the softened water stream; and wherein the control assembly is configured for managing the flowrate of the portion of the softened water stream so as to reduce the flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity.

43. The system of claim 41, further comprising:
a measurement device for measuring the concentration of an impurity in the softened water stream; and wherein the control assembly is configured for managing the flowrate of the recycle portion so as to increase the flowrate of the portion of the distillate stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity.

44. The system of claim 41, further comprising:
a measurement device for measuring the concentration of an impurity in the softened water stream; and wherein the control assembly is configured for managing the flowrate of the distillate stream so as to reduce the flowrate of the recycle portion supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity.

45. The system of claim 41, further comprising:
a measurement device for measuring the concentration of an impurity in the second boiler feed water stream; and wherein the control assembly is configured for managing the flowrate of the portion of the softened water stream so as to reduce the flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity..

46. The system of claim 41, further comprising:
a measurement device for measuring the concentration of an impurity in the second boiler feed water stream; and wherein the control assembly is configured for managing the flowrate of the recycle portion so as to increase the flowrate of the portion of the distillate stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity.

47. The system of claim 41, further comprising:
a measurement device for measuring the concentration of an impurity in the second boiler feed water stream; and wherein the control assembly is configured for managing the flowrate of the distillate stream so as to reduce the flowrate of the recycle portion supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the impurity.

48. The system of claim 41, further comprising:
an organics measurement device for measuring the concentration of organics as the limiting impurity in the second boiler feed water stream; and wherein the control assembly is configured for managing the flowrate of the recycle portion so as to reduce the flowrate of the recycle portion supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the organics.

49. The system of claim 48, wherein the control assembly is further configured for managing the flowrate of the distillate stream so as to increase the flowrate of the distillate stream as part of the boiler feed water stream, in response to the elevated measured concentration of the organics.

50. The system of claim 48 or 49, wherein the control assembly is further configured for managing the flowrate of the portion of the softened water stream so as to increase the flowrate of the portion of the softened water stream as part of the second boiler feed water stream, in response to the elevated measured concentration of the organics.

51. The system of claim 41, further comprising:
a total dissolved solids (TDS) measurement device for measuring the concentration of TDS as the limiting impurity in the second boiler feed water stream; and wherein the control assembly is configured for managing the flowrate of the portion of the softened water stream so as to reduce the flowrate of the portion of the softened water stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the TDS.

52. The system of claim 41, further comprising:
a total dissolved solids (TDS) measurement device for measuring the concentration of TDS as the limiting impurity in the second boiler feed water stream; and wherein the control assembly is configured for managing the flowrate of the recycled portion of the blowdown stream so as to reduce the flowrate of the recycled portion of the blowdown stream supplied as part of the second boiler feed water stream, in response to an elevated measured concentration of the TDS.

53. The system of claim 51 or 52, wherein the control assembly is further configured for managing the flowrate of the distillate stream so as to increase the flowrate of the distillate stream as part of the second boiler feed water stream, in response to the elevated measured concentration of the TDS.

54. The system of any one of claims 39 to 47, wherein the limiting impurity is total dissolved solids (TDS).

55. The process of claim 54, wherein the maximum threshold value of the concentration of TDS is 12,000 ppm.

56. The system of any one of claims 39 to 47, wherein the limiting impurity is organics.

57. The system of claim 56, wherein the maximum threshold value of the organics is 700 ppm.

58. The system of any one of claims 39 to 47, wherein the limiting impurity is pH.

59. The system of claim 58, wherein the maximum threshold value of the pH is 10.5.

60. The system of any one of claims 39 to 47, wherein the limiting impurity is silica.

61. The process of claim 60, wherein the maximum threshold value of the concentration of silica is 100 ppm.

62. The system of any one of claims 39 to 47, wherein the limiting impurity is hardness.

63. The process of claim 62, wherein the maximum threshold value of hardness is 1 ppm.

64. The system of any one of claims 39 to 47, wherein the limiting impurity is oil in water.

65. The process of claim 64, wherein the maximum threshold value of the oil in water is 0.5 ppm.

66. The system of any one of claims 39 to 47, wherein the limiting impurity is a chemical conditioners.

67. The system of any one of claims 39 to 66, further comprising a make-up water line for adding make-up water to the second boiler feed water stream.

68. The system of any one of claims 39 to 67, wherein the softening unit comprises a Warm Lime Softener (WLS) or a Hot Lime Softener (HLS) or a combination thereof.

69. The system of claim 68, wherein the softening unit further comprises a cation exchange device downstream of the WLS or the HLS.

70. The system of claim 69, wherein the cation exchange device comprises a Weak Acid Cation (WAC) exchanger.

71. The system of any one of claims 39 to 70, wherein at least one of the first and second train OTSGs comprises a Heat Recovery Steam Generation (HRSG) system.

72. The system of any one of claims 39 to 71, wherein the first OTSG is part of a first bank of multiple first train OTSGs and/or the second OTSG is part of a second bank of second train OTSGs.

73. The system of any one of claims 39 to 72, further comprising:
a boiler feed water tank for receiving the recycle portion of the blowdown stream, the portion of the distillate stream and the portion of the softened water stream, the boiler feed water tank having an outlet coupled to the boiler feed water line for supplying the second boiler feed water stream to the second OTSG.

74. The process of claim 16, wherein the limiting impurity is a chelate.

75. The process of claim 16, wherein the limiting impurity is a dispersant.

76. The system of claim 66, wherein the limiting impurity is a chelate.

77. The system of claim 66, wherein the limiting impurity is a dispersant.

78. The process of any one of claims 1 to 33, wherein the recycle portion is about 30 vol% of the blowdown stream.

79. The process of any one of claims 1 to 33, wherein the recycle portion is about 40 vol% of the blowdown stream.