Description:FIELD OF THE INVENTION

The present invention relates to a system and method for efficiently removing hazardous pollutants from sour water produced in a refinery. Specifically, the invention focuses on Process and Energy Optimization in a 2-stage Sour Water Stripping unit. The present invention involves converting the 2-stage stripping process to a single-column operation for hydrotreater sour water. This design provides flexibility to seamlessly switch back to dual-column operation if NH3 recovery is required in the future. The key feature of the invention lies in the introduction of nitrogen (N2) in the first column (H2S stripper), resulting in a reduction of approximately 9 TPH of medium-pressure steam directed to the first-stage reboiler. Notably, no increase in steam is implemented in the second stripper to ensure the maintenance of the product quality of the stripped water throughout the process.

BACKGROUND OF THE INVENTION

Hydro-processing units such as VGO, Diesel, and Naphtha hydrotreater units in a Refinery need continuous wash water to minimize salt deposition in their process equipment and piping. Post washing, spent water containing hydrogen sulfide (H2S) and ammonia (NH3) is routed to the sour water stripping unit for stripping where steam is used for stripping out gases and reusing the stripped water in the refinery and effluent treatment plant.
Refineries either have single-stage or dual-stage strippers for processing sour water from hydro-processing units. Based on the Sulphur Recovery Unit configuration, either of the above stripping configurations are selected and installed.
Single-stage strippers favor lower Capex and Opex (than Dual Stage)but at the same time, stripped gases contain a mixture of H2S and NH3 which cannot be separated further ( if desired) and can be processed only in the Reaction Furnace of SRU.
Dual-stage strippers have one stripper for removing hydrogen sulfide (H2S) at relatively high temperatures and high-pressure conditions. Sour water is cooled and the second stripper is used for removing ammonia (NH3) under different low-temperature & low-pressure conditions, economics usually dictates a compromise. They are most effective in separating H2S and NH3 gases from the top of individual strippers. These streams can be handled separately in the Reaction Furnace, and combined before processing or NH3-rich gases can be routed to the Incinerator. There is no such configuration in any refinery which can serve both purposes.
In an implementation, at the refinery, Dual stage stripper configuration is installed. Since gases from both strippers (H2S and NH3) are getting premixed before going into the reaction furnace, therefore stripping H2S and NH3 in separate strippers does not seem to be beneficial. Hence the possibility of energy optimization in the existing Dual stage stripping process was explored.
However, Dual-Stage strippers consume initial Capex as well as significant energy consumption in the form of stripping steam. These strippers operate in series and sour water goes to 2nd stage stripper by pressure generated by H2S and steam in 1st stage stripper. Nitrogen was lined up to 1st stage stripper and steam to its respective reboiler was reduced to zero to overcome the drawback of higher energy consumption associated with two-stage strippers without making any physical change in the process.
In view of the foregoing discussion, it is portrayed that there is a need to have an energy-efficient system and method for removing hazardous pollutants from sour water produced in a refinery.

SUMMARY OF THE INVENTION

The present disclosure seeks to provide a dual-mode system and method for removing hazardous pollutants from sour water produced in a refinery. The invention involves converting a 2-stage sour water stripping process into a single-stage stripping process while keeping the second stage column unmodified, allowing for flexibility to revert to the original mode. This transformation results in significant energy conservation in existing 2-stage Hydro-processing Sour water stripping processes. The innovation is applicable when H2S and NH3 gases are premixed and can be implemented even if H2S and NH3 are routed via separate nozzles in the Reaction Furnace. Proposed design changes in the burner zone of the Sulphur Recovery Unit facilitate energy savings. Additionally, the invention allows for the design of new 2-stage strippers that can operate in both modes: a single stripping mode for energy conservation and a 2-stage stripping mode for process requirements or the recovery of ammonia as a product.

In an embodiment, a method for removing hazardous pollutants from sour water produced in a refinery is disclosed. The method includes receiving sour water from hydro-processing units, including Vacuum Gas Oil Hydro treating Unit, Diesel Hydro treating Unit, and Naphtha Hydro treating units.
The method further includes collecting the received sour water in a Sour Water Surge Drum where hydrocarbons are flashed, and vapors are routed to a Sulfur Recovery Unit (SRU).
The method further includes routing the sour water to storage tanks.
The method further includes pumping the sour water to a first-stage sour water stripper using a feed pump.
The method further includes heating the sour water in heat exchangers using stripped water.
The method further includes stripping entrapped hydrogen sulfide (H2S) in the first stage stripper by providing steam to a first reboiler.
The method further includes routing H2S-rich overhead vapors to the SRU for conversion to elemental sulfur.
The method further includes transferring ammonia (NH3) rich sour water from a bottom of the first stage stripper to a second stage sour water stripper via a shell side of heat exchangers.
The method further includes stripping NH3 and a small quantity of H2S in the second stage stripper. The method further includes routing NH3-rich overhead vapors to the Reaction Furnace of the SRU or to an Incinerator for NH3 destruction.
The method further includes pumping stripped water from the bottom of the second stage stripper to Hydro treating units selected from a Vacuum Gas Oil Hydro treating Unit(HDT), Diesel Hydro treating Unit (DHDT) + Naphtha Hydro treating units (NHT) or an Effluent Treatment Plant (ETP) using second stage stripper bottom pumps based on process requirements for removing hazardous pollutants.

In another embodiment, a system for removing hazardous pollutants from sour water produced in a refinery is disclosed. The system includes a sour water surge drum configured to receive sour water from hydro-processing units, wherein hydrocarbons are flashed, and vapors are directed to a sulfur recovery unit (SRU).
The system further includes a pair of storage tanks connected to the surge drum to store the flashed sour water.
The system further includes a feed pump interconnected to the storage tanks to pump sour water to a first-stage sour water stripper, wherein the first-stage sour water stripper comprising a first reboiler receives steam, wherein entrapped H2S is stripped, and H2S-rich overhead vapors are directed to the SRU for conversion to elemental sulfur.
The system further includes a pair of heat exchangers connected to the feed pump to heat the sour water using stripped water, wherein a pressure-driven transfer of NH3-rich sour water from the bottom of the first-stage sour water stripper to a second-stage sour water stripper via the shell side of heat exchangers, wherein the second stage sour water stripper comprising a second reboiler receiving steam, wherein NH3 and a small quantity of H2S are stripped, and NH3-rich overhead vapors are directed to a reaction furnace of the SRU or to an Incinerator for NH3 destruction.
The system further includes a second-stage stripper bottom pump (122) in connection with the second-stage sour water stripper (114) to pump the stripped water from the bottom of second stage sour water stripper (114) to Hydro treating Units selected from Vacuum Gas Oil Hydro treating Unit(HDT), Diesel Hydro treating Unit (DHDT) + Naphtha Hydro treating units (NHT) or an Effluent Treatment Plant (ETP) based on process requirements for removing hazardous pollutants.

An object of the present disclosure is to achieve a significant reduction of approximately 9 TPH of Medium Pressure Steam (MP Steam) previously consumed in the 1st stage stripper reboiler, leading to enhanced energy efficiency.
Another object of the present disclosure is to minimize the overall process control parameters by eliminating the need for steam flow control to the reboiler and condensate level control, streamlining the operational aspects of the system.
Another object of the present disclosure is to enable the operation of a 2-stage sour water stripper unit in a single-stage stripping mode without modifying the 2nd stage column, thereby optimizing the existing configuration.
Another object of the present disclosure is to provide flexibility to switch back to the original 2-stage stripping mode. Steam to the 1st stage stripper reboiler can be halted at any point, isolating nitrogen supply to the 1st stage stripper. This capability is advantageous for recovering NH3 separately for manufacturing anhydrous Ammonia and routing NH3 gases to the incinerator based on process requirements.
Another object of the present disclosure is to facilitate the design of new 2-stage strippers capable of operating in both modes:
Yet another object of the present invention is to deliver an expeditious and cost-effective system to enhance energy conservation in existing 2-stage Hydroprocessing Sour water stripping processes. This can be applied when H2S and NH3 gases are premixed or even if they are routed via separate nozzles in the Reaction Furnace, with proposed design changes in the burner zone of the Sulphur Recovery Unit.

To further clarify the advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail in the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read concerning the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a block diagram of a system for removing hazardous pollutants from sour water produced in a refinery in accordance with an embodiment of the present disclosure;
Figure 2 illustrates a flow chart of a method for removing hazardous pollutants from sour water produced in a refinery in accordance with an embodiment of the present disclosure;
Figure 3 illustrates a PFD of a Hydro-processing sour water stripper(SWS-2) in accordance with an embodiment of the present disclosure;
Figure 4 illustrates a 2 Stage Stripping mode in accordance with an embodiment of the present disclosure;
Figure 5 illustrates a simulation setup of NH3 stripper(C-202) used in a trial run in accordance with an embodiment of the present disclosure;
Figure 6 illustrates a Single Stripping Mode in accordance with an embodiment of the present disclosure;
Figure 7 illustrates an Average DP of the NH3 stripper column(C-2) in accordance with an embodiment of the present disclosure;
Figure 8 illustrates Table 1 depicts C-1( C-201) and C-2(C-202) column parameters during trial;
Figure 9 illustrates Table 2 depicts Amperes comparison for running drives during Normal operations and Trial Run; and
Figure 10 illustrates Table 3 depicts the Analysis of the Stripped sour water sample.

Further, skilled artisans will appreciate those elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION:

To promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail concerning the accompanying drawings.

Referring to Figure 1, a block diagram of a system for removing hazardous pollutants from sour water produced in a refinery is illustrated in accordance with an embodiment of the present disclosure. The system 100 includes a sour water surge drum (102) configured to receive sour water from hydro-processing units (104), wherein hydrocarbons are flashed, and vapors are directed to a sulfur recovery unit (SRU) (106).

In an embodiment, a pair of storage tanks (108) are connected to the surge drum (102) to store the flashed sour water.

In an embodiment, a feed pump (110) is interconnected to the storage tanks (108) to pump sour water to a first-stage sour water stripper (112), wherein the first-stage sour water stripper (112) comprising a first reboiler (116) receives steam, wherein entrapped H2S is stripped, and H2S-rich overhead vapors are directed to the SRU (106) for conversion to elemental sulfur.

In an embodiment, a pair of heat exchangers (118) is connected to the feed pump (110) to heat the sour water using stripped water, wherein a pressure-driven transfer of NH3-rich sour water from the bottom of the first-stage sour water stripper (112) to a second-stage sour water stripper (114) via the shell side of heat exchangers (118), wherein the second stage sour water stripper (114) comprising a second reboiler (120) receiving steam, wherein NH3 and a small quantity of H2S are stripped, and NH3-rich overhead vapors are directed to a reaction furnace of the SRU (106) or an Incinerator for NH3 destruction.

In an embodiment, a second-stage stripper bottom pump (122) is in connection with the second-stage sour water stripper (114) to pump the stripped water from the bottom of the second-stage sour water stripper (114) to Hydro treating Units selected from Vacuum Gas Oil Hydro treating Unit(HDT), Diesel Hydro treating Unit (DHDT) + Naphtha Hydro treating units (NHT) or an Effluent Treatment Plant (ETP) based on process requirements for removing hazardous pollutants.

In another embodiment, the first-stage sour water stripper (112) exhibits a steam consumption of approximately 9 TPH (116) under operating conditions with a feed rate of approximately 140 m3/hr, whereas the second-stage sour water stripper (114) demonstrates a steam consumption of approximately 23 TPH (120) under analogous operating conditions with a feed rate of approximately 140 m3/hr.

In another embodiment, the first-stage sour water stripper (112) is configured to operate at a pressure of approximately 7 kg/cm2g and a temperature of approximately 160 degrees Celsius, whereas the second-stage sour water stripper (114) is configured to operate at a pressure of approximately 0.9 kg/cm2g and a temperature of approximately 121 degrees Celsius.

In another embodiment, a stripper top routes the NH3 gases to the drums for pre-mixing before going to the Reaction Furnace of the Sulphur Recovery Unit, wherein the sour water from hydro-processing units (104) includes hydrogen sulfide (H2S) and ammonia (NH3) as primary pollutants.

Figure 2 illustrates a flow chart of a method for removing hazardous pollutants from sour water produced in a refinery in accordance with an embodiment of the present disclosure. At step 202, method 200 includes receiving sour water from hydro-processing units (104), including Vacuum Gas Oil Hydro treating Unit, Diesel Hydro treating Unit, and Naphtha Hydro treating units.

At step 204, method 200 includes collecting the received sour water in a Sour Water Surge Drum (102) where hydrocarbons are flashed, and vapors are routed to a Sulfur Recovery Unit (SRU) (106).

At step 206, method 200 includes routing the sour water to storage tanks (108).

At step 208, method 200 includes pumping the sour water to a first-stage sour water stripper (112) using a feed pump (110).

At step 210, method 200 includes heating the sour water in heat exchangers (118) using stripped water.

At step 212, method 200 includes stripping entrapped hydrogen sulfide (H2S) in the first stage stripper (112) by providing steam to a first reboiler (116).

At step 214, method 200 includes routing H2S-rich overhead vapors to the SRU (106) for conversion to elemental sulfur.

At step 216, method 200 includes transferring ammonia (NH3) rich sour water from a bottom of the first stage stripper (112) to a second stage sour water stripper (114) via a shell side of heat exchangers (118).

At step 218, method 200 includes stripping NH3 and a small quantity of H2S in the second stage stripper (114).

At step 220, method 200 includes routing NH3-rich overhead vapors to the Reaction Furnace of the SRU (106) or to an Incinerator for NH3 destruction.

At step 222, method 200 includes pumping stripped water from the bottom of the second stage stripper (114) to Hydro treating units selected from Vacuum Gas Oil Hydro treating Unit(HDT), Diesel Hydro treating Unit (DHDT) + Naphtha Hydro treating units (NHT) or an Effluent Treatment Plant (ETP) using second stage stripper bottom pumps (122) based on process requirements for removing hazardous pollutants.

In another embodiment, the method further comprises operating with a steam consumption of approximately 9 TPH (116) for the first-stage stripper (112) and approximately 23 TPH (120) for the second-stage stripper (114) under feed conditions of ~140 m3/hr.

In another embodiment, the first-stage sour water stripper (112) is configured to remove hydrogen sulfide (H2S) from the sour water, and the second-stage sour water stripper (114) is configured to remove ammonia (NH3) from the sour water.

In another embodiment, the method further comprises controlling the flow of stripped water and routing of NH3-rich overhead vapors to optimize the removal of hazardous pollutants.

In another embodiment, the method further comprises optimizing steam consumption in a sour water treatment system by performing a trial run for single stripping mode comprises gradually reducing steam in the first reboiler (116) of the first stage sour water stripper (112) while increasing an equivalent amount of steam in the second reboiler (120) of the second stage sour water stripper (114). Then, maintaining the quality of the stripped water product. Then, maintaining overhead pressure in the first stage sour water stripper (112) using nitrogen (N2) to ensure seamless flow to the second stage sour water stripper (114). Then, gradually reducing the H2S stripper reboiling steam in the first stage sour water stripper (112) to 0 TPH at a feed rate preferably 130m3/hr. Then, performing low-pressure stripping operations in the second stage sour water stripper (114). Then, reducing steam in the second reboiler (120) of the second stage sour water stripper (114) to the original prevailing value at the beginning of the trial. Then, confirming the maintenance of the quality of the stripped water product within threshold limits and increasing the feed to the sour water stripper. Then, adjusting the steam in the second stage sour water stripper (114) to maintain the stripped water H2S/NH3 within a 50-ppm specification. Thereafter, establishing a reduction in total steam consumption for both first and second-stage sour water strippers to 22 TPH against the earlier prevailing 30 TPH.

In another embodiment, the operation of the two-stage sour water stripping comprises consuming no steam in the first stage sour water stripper reboiler (116). Then, transferring sour water from the first stage sour water stripper (112) to the second stage sour water stripper (114) by maintaining nitrogen pressure in the first stage sour water stripper (112). Thereafter, isolating steam to the first reboiler (116) and implementing no additional steam input in the second stage sour water stripper (114) after the isolation of steam to the first reboiler (116).

Figure 3 illustrates a PFD of a Hydro-processing sour water stripper(SWS-2) in accordance with an embodiment of the present disclosure. Sour water produced from the refinery contains many hazardous pollutants, of which hydrogen sulfide (H2S) and NH3 are the primary pollutants. These two pollutants can be removed by using Sour water strippers. In the present invention, the sour water as a feed to the Sour water stripper second train (SWS-II)(ref-Figure 3) is received from hydro-processing units namely the Vacuum Gas Oil Hydro treating Unit and Diesel Hydro treating Unit and naphtha Hydro treating units, collected in Sour Water Surge Drum ( V-101). Hydrocarbons are flashed in this Surge Drum and vapors are routed to SRU. Sour water is then routed to storage tanks T-201 A/B. The sour water is then pumped to 1st stage sour water stripper (C-201) by feed pump P 201 A/B, sour water is heated by stripped water in heat exchangers 202 A/B and 203 A/B. Entrapped H2S from sour water is stripped in 1st stage stripper (C-201) by providing steam to Col-1 reboiler E-204. H2S vapors are stripped off from this stripper as the solubility of H2S in water is poor in comparison to NH3 at high pressure and temperature. The H2S-rich overhead vapors are routed to SRU for conversion to elemental Sulphur. The NH3-rich sour water from the 1st stage Sour Water Stripper (C-201) bottom is transferred via pressure difference to the 2nd stage sour water stripper (C-202), via the shell side of heat exchangers 203 A/B. NH3 and a small quantity of H2S from sour water are stripped in 2nd stage stripper (C-202). The NH3-rich overhead vapors can be routed to the Reaction Furnace of SRU or to the Incinerator for NH3 destruction. Stripped water from 2nd stage stripper bottom (C-202) is pumped by using 2nd stage stripper bottom pumps (P-203 A/B)to HDT +DHDT +NHT units or ETP. Steam consumption of Col-1 (C-201) is nearly 9 TPH (E-204) & Col-2 (C-202) is nearly 23 TPH (E-206) for normal operating feed of ~ 140 m3/hr.
Content Permissible limit in Stripped sour water
Hydogen sulphide(H2S) <50ppmw
Ammonia (NH3) <50ppmw

Figure 4 illustrates a 2-stage stripping mode in accordance with an embodiment of the present disclosure. Before Invention, 2- Stage stripping mode [ Figure -4] is prevailing where Steam is going in both Columns Reboilers( E 204 and E 206). Column-1 ( C-201) is operated at ~ 7 kg/cm2g / 160 Degree C in comparison to 0.9 kg/cm2g /121 pressure and temperature conditions for Column-2 ( C-202) respectively.
Stripped water quality is maintained. The gases from the stripper top are routed to their respective Knock Out Drums and they get pre-mixed before going to the Reaction Furnace of the Sulphur Recovery Unit. Overall ~ 31 TPH of MP Steam is consumed in total by both strippers. This mode of operation is best suited if NH3-rich stripper gases are to be routed separately to the Reaction Furnace or when these gases are subjected to thermal Incineration in the Incinerator.
Since gases from both strippers (H2S and NH3 ) are getting premixed before going into the Reaction furnace of SRU, therefore stripping H2S and NH3 in separate strippers does not seem to be beneficial. Hence the possibility of energy optimization in the existing Dual stage stripping process is explored.

Figure 5 illustrates a simulation setup of the NH3 stripper(C-202) used in a trial run in accordance with an embodiment of the present disclosure. Analysis before the test run is performed using simulation [Figure 5] for single-column operation. Through simulation, it is established that column C-2 (C-202) can handle the entire sour water load (152 m3/hr) for stripping out H2S and NH3. The simulation is carried out to check for tray hydraulic and as a result it is found that the trays are adequate and the expected C-2(C-202 ) tray differential pressure will be 0.31Kg/cm2g against the permissible value of 0.38kg/cm2g.
Accordingly, a trial run is performed for Single Stripping mode.
Gradually, Steam is reduced in the C-1 reboiler (E-204) and is increased by an equivalent amount in the C-2 reboiler (E-206) Stripped water product quality is well maintained. C-1 column overhead pressure is maintained with N2 to ensure seamless flow to C-2(C-202).
Finally ,C-1(C-201) H2S stripper reboiling steam is reduced to 0TPH at feed rate (130 m3/hr).
Taking advantage of low-pressure stripping operation in C-2 (C-202), increased steam in the reboiler ( E-206) of the C-2 ( C-202) column is gradually reduced to the original prevailing value at the beginning of the trial. Stripped water product quality is found to be well within limits.
Gradually, feed to the Sour water stripper is increased (Refer to Table-1)and Column-2 steam is adjusted to maintain stripped water H2S / NH3 with 50 ppm specification. It is established that total steam consumption for both columns is reduced to 22 TPH against the earlier prevailing 30 TPH.

Figure 6 illustrates a Single Stripping Mode in accordance with an embodiment of the present disclosure. Post invention, 2- Stage Sour Water Stripping unit at our Refinery is operating on Energy Conservation mode thereby [Figure 6 ]consuming no steam in the Stage -1 Stripper reboiler ( E -204), and Sour water from Column-1 ( C-201) is transferred to Column -2( C-202) by Nitrogen pressure maintained in Column -1. No additional steam is put up in Column -2 ( C-202) post isolating steam to E-204.

Figure 7 illustrates an Average DP of the NH3 stripper column(C-2) in accordance with an embodiment of the present disclosure. After analysis of trial results, it is found that all operating parameters of columns are within the normal range(Table[1]) during the test run and NH3 stripper(C-2) column DP is also well within the limit of 0.38Kg/cm2g as indicated in trend below (Figure 7).

Figure 8 illustrates Table 1 depicts C-1( C-201) and C-2(C-202) column parameters during trial.

Figure 9 illustrates Table 2 depicts Amperes comparison for running drives during Normal operations and Trial Run. A comparative study during the trial run and normal plant operation is made to check the performance of all pump around pumps, column bottom pumps, and all fin fans load. All pumps and fan loads are within the acceptable limit & tabulated in Table 2.

Figure 10 illustrates Table 3 depicts the Analysis of the Stripped sour water sample. Analysis of sour water and stripped water is done during the test run to continuously monitor the stripped water quality. As per sample results, (Refer to table[3]) stripped water H2S & NH3 is within the range i.e., <50ppm. However, due to steam adjustments during the test run in the NH3 stripper column(C-2), there are two instances where NH3 went out of specification but later is maintained within range.
This innovation encompasses three key aspects. Firstly, it involves the conversion of a 2-stage sour water stripping process into a single-stage stripping process without necessitating any modifications to the 2nd stage column. This adaptation provides the system with the added flexibility to revert to its original 2-stage mode when needed.
Secondly, the invention contributes to significant energy conservation in existing 2-stage Hydro-processing Sour water stripping processes. This energy-saving capability is versatile, being applicable in scenarios where H2S and NH3 gases are premixed. Moreover, it remains effective even when H2S and NH3 are routed separately via nozzles in the Reaction Furnace, achieved through proposed design changes in the burner zone of the Sulphur Recovery Unit.
Lastly, the innovation facilitates the design of new 2-stage strippers that can seamlessly operate in both modes. The first mode is a single stripping mode, primarily geared towards energy conservation. The second mode is a 2-stage stripping mode, tailored to meet specific process requirements or to enable the recovery of Ammonia as a distinct product. This multifaceted approach underscores the versatility and adaptability of the invention, addressing various operational needs within sour water stripping processes.

The invention yields notable advantages, including the substantial conservation of energy by eliminating approximately 9 TPH of Medium Pressure (MP) Steam previously consumed in the 1st stage stripper. Additionally, the overall process control parameters are reduced, with the elimination of steam flow control to the reboiler and condensate level control.

This innovation successfully achieves the goal of operating a 2-stage sour water stripper unit configuration in a single-stage stripping mode. By introducing Nitrogen in the 1st stage stripper, the steam in the 1st stage stripper reboiler is reduced to zero from the earlier 9 TPH of Medium Pressure Steam. Importantly, the invention provides flexibility for a seamless switch back to the 2-stage stripping mode. Steam to the 1st stage stripper reboiler can be reintroduced at any point, isolating Nitrogen supply to the 1st stage stripper. This capability is especially beneficial for separately recovering NH3 for manufacturing anhydrous Ammonia and routing NH3 gases to the Incinerator as per process requirements.

While the invention exhibits certain limitations, such as the consumption of Nitrogen at a rate of approximately 30 Nm3/hr in the 1st stage stripper, this is deemed insignificant when compared to the substantial energy savings achieved. Notably, concerns about increased Vapor Load in the 2nd stage stripper are addressed during trials, where the stripper tray differential pressure is found to be well within its designed value of 0.38 Kg/cm2g, mitigating any limitations associated with handling increased vapor load.

This innovation holds crucial significance for achieving significant energy conservation in existing 2-stage Hydroprocessing Sour water stripping processes. It can be applied in scenarios where H2S and NH3 gases are premixed or even when they are routed via separate nozzles in the Reaction Furnace, with proposed design changes in the burner zone of the Sulphur Recovery Unit.

The method provides with a two-stage sour water unit designed for treating sour water from a hydrotreater. The existing process involves the removal of H2S in the first-stage stripper and NH3 in the second-stage stripper. Our developed process allows for the operation of a single-stage stripper, bypassing the first stripper while effectively stripping out NH3 and H2S from the second stage alone. Importantly, this operation maintains the specified quality of the stripped water. The process provides the flexibility to revert to the original two-stage operation, which is particularly advantageous when considering the potential implementation of an Anhydrous NH3 project.

Furthermore, the invention enables the design of new 2-stage strippers capable of operating in both modes: a single stripping mode for energy conservation and a 2-stage stripping mode for specific process requirements or the recovery of Ammonia as a product. Overall, the invention addresses critical challenges and offers solutions that enhance the efficiency and flexibility of sour water stripping processes.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above about specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims. , Claims:1. A method for removing hazardous pollutants from sour water produced in a refinery, the method comprises:
receiving sour water from hydro-processing units (104), including Vacuum Gas Oil Hydro treating Unit, Diesel Hydro treating Unit, and Naphtha Hydro treating units;
collecting the received sour water in a Sour Water Surge Drum (102) where hydrocarbons are flashed, and vapors are routed to a Sulfur Recovery Unit (SRU) (106);
routing the sour water to storage tanks (108);
pumping the sour water to a first-stage sour water stripper (112) using a feed pump (110);
heating the sour water in heat exchangers (118) using stripped water;
stripping entrapped hydrogen sulfide (H2S) in the first stage stripper (112) by providing steam to a first reboiler (116);
routing H2S-rich overhead vapors to the SRU (106) for conversion to elemental sulfur;
transferring ammonia (NH3) rich sour water from a bottom of the first stage stripper (112) to a second stage sour water stripper (114) via a shell side of heat exchangers (118);
stripping NH3 and a small quantity of H2S in the second stage stripper (114);
routing NH3-rich overhead vapors to the Reaction Furnace of the SRU (106) or to an Incinerator for NH3 destruction; and
pumping stripped water from the bottom of the second stage stripper (114) to Hydro treating units selected from Vacuum Gas Oil Hydro treating Unit(HDT), Diesel Hydro treating Unit (DHDT) + Naphtha Hydro treating units (NHT) or an Effluent Treatment Plant (ETP) using second stage stripper bottom pumps (122) based on process requirements for removing hazardous pollutants.

2. The method as claimed in claim 1, further comprises operating with a steam consumption of approximately 9 TPH (116) for the first-stage stripper (112) and approximately 23 TPH (120) for the second-stage stripper (114) under feed conditions of ~140 m3/hr.

3. The method as claimed in claim 1, wherein the first stage sour water stripper (112) is configured to remove hydrogen sulfide (H2S) from the sour water, and the second stage sour water stripper (114) is configured to remove ammonia (NH3) from the sour water.

4. The method as claimed in claim 1, further comprises controlling the flow of stripped water and routing of NH3-rich overhead vapors to optimize the removal of hazardous pollutants.

5. The method as claimed in claim 1, further comprises optimizing steam consumption in a sour water treatment system by performing a trial run for single stripping mode comprises:
gradually reducing steam in the first reboiler (116) of the first-stage sour water stripper (112) while increasing an equivalent amount of steam in the second reboiler (120) of the second-stage sour water stripper (114);
maintaining the quality of the stripped water product;
maintaining overhead pressure in the first stage sour water stripper (112) using nitrogen (N2) to ensure seamless flow to the second stage sour water stripper (114);
gradually reducing the H2S stripper reboiling steam in the first stage sour water stripper (112) to 0 TPH at a feed rate preferably 130m3/hr;
performing low-pressure stripping operations in the second stage sour water stripper (114);
reducing steam in the second reboiler (120) of the second-stage sour water stripper (114) to the original prevailing value at the beginning of the trial;
confirming the maintenance of the quality of the stripped water product within threshold limits and increasing the feed to the sour water stripper;
adjusting the steam in second stage sour water stripper (114) to maintain the stripped water H2S/NH3 within a 50-ppm specification; and
establishing a reduction in total steam consumption for both first and second-stage sour water strippers to 22 TPH against the earlier prevailing 30 TPH.

6. The method as claimed in claim 5, wherein the operation of the two-stage sour water stripping comprises:
consuming no steam in the first stage sour water stripper reboiler (116);
transferring sour water from the first stage sour water stripper (112) to the second stage sour water stripper (114) by maintaining nitrogen pressure in the first stage sour water stripper (112); and
isolating steam to the first reboiler (116) and implementing no additional steam input in the second stage sour water stripper (114) after the isolation of steam to the first reboiler (116).

7. A system for removing hazardous pollutants from sour water produced in a refinery, the system comprises:
a sour water surge drum (102) configured to receive sour water from hydro-processing units (104), wherein hydrocarbons are flashed, and vapors are directed to a sulfur recovery unit (SRU) (106);
a pair of storage tanks (108) connected to the surge drum (102) to store the flashed sour water;
a feed pump (110) interconnected to the storage tanks (108) to pump sour water to a first-stage sour water stripper (112), wherein the first-stage sour water stripper (112) comprising a first reboiler (116) receives steam, wherein entrapped H2S is stripped, and H2S-rich overhead vapors are directed to the SRU (106) for conversion to elemental sulfur;
a pair of heat exchangers (118) connected to the feed pump (110) to heat the sour water using stripped water;
wherein a pressure-driven transfer of NH3-rich sour water from the bottom of the first-stage sour water stripper (112) to a second-stage sour water stripper (114) via the shell side of heat exchangers (118);
wherein the second stage sour water stripper (114) comprising a second reboiler (120) receiving steam, wherein NH3 and a small quantity of H2S are stripped, and NH3-rich overhead vapors are directed to a reaction furnace of the SRU (106) or an Incinerator for NH3 destruction; and
a second-stage stripper bottom pump (122) in connection with the second-stage sour water stripper (114) to pump the stripped water from the bottom of second stage sour water stripper (114) to Hydro treating Units selected from Vacuum Gas Oil Hydro treating Unit(HDT), Diesel Hydro treating Unit (DHDT) + Naphtha Hydro treating units (NHT) or an Effluent Treatment Plant (ETP) based on process requirements for removing hazardous pollutants.

8. The system as claimed in claim 7, wherein the first-stage sour water stripper (112) exhibits a steam consumption of approximately 9 TPH (116) under operating conditions with a feed rate of approximately 140 m3/hr, whereas the second-stage sour water stripper (114) demonstrates a steam consumption of approximately 23 TPH (120) under analogous operating conditions with a feed rate of approximately 140 m3/hr.

9. The system as claimed in claim 7, wherein the first stage sour water stripper (112) is configured to operate at a pressure of approximately 7 kg/cm2g and a temperature of approximately 160 degrees Celsius, whereas the second stage sour water stripper (114) is configured to operate at a pressure of approximately 0.9 kg/cm2g and a temperature of approximately 121 degrees Celsius.

10. The system as claimed in claim 7, wherein a stripper top routes the NH3 gases to the drums for pre-mixing before going to the Reaction Furnace of the Sulphur Recovery Unit, wherein the sour water from hydro-processing units (104) includes hydrogen sulfide (H2S) and ammonia (NH3) as primary pollutants.