System and method for online cleaning of heat exchangers

Abstract

Heat exchangers can be cleaned while remaining online and in service by introducing a cleaning substance into a fluid being fed into the heat exchanger, upstream of the heat exchanger. The cleaning substance can be introduced using an injection circuit or other injection mechanism, or in a network of heat exchangers, an upstream heat exchanger can be taken offline to be filled with an amount of the cleaning substance that is added to a fluid fed through the heat exchanger when it comes back online. A heat exchanger cleaning system is provided that includes a supply of cleaning substance; a connection between the supply of cleaning substance and a supply of fluid to a heat exchanger, the connection being controllable to selectively feed the supply of cleaning substance into the supply of fluid while the heat exchanger is online.

Description

SYSTEM AND METHOD FOR ONLINE CLEANING OF HEAT EXCHANGERS TECHNICAL FIELD

[0001] The following relates to systems and methods for online cleaning of heat exchangers. BACKGROUND

[0002] Heat exchangers are used in many applications to transfer heat between two or more fluids, in either or both cooling and heating processes. Heat exchangers can include internal wall(s) to separate the fluids and prevent mixing. There are several industrial applications in which heat exchangers can be used, for example in oil and gas processes.

[0003] In one example, at least one heat exchanger, typically a network of multiple heat exchangers, are used to cool produced water (PW) that is obtained in an oil extraction process.

[0004] The PW in this example can result from a steam-based oil recovery process such as steam-assisted gravity drainage (SAGD) in which steam is injected into a hydrocarbon- containing formation (e.g., targeting a bitumen or "oil sands" reservoir) via an injector well in order to mobilize the hydrocarbon for extraction or "production" at a producer well situated below the injector well. The fluid that is produced contains a mixture of the mobilized hydrocarbon, water from condensed steam, formation water, various other constituents which may be dissolved or suspended in the mixture, and other vapor and gaseous constituents. The produced fluid typically undergoes a separation process, which in part separates PW from the produced hydrocarbon. The PW is typically recycled and used in other processes, such as to generate steam.

[0005] In order to utilize the PW in such other processes, the PW is typically cooled, which can involve feeding the PW through a heat exchanger or a network of heat exchangers to achieve a desired temperature. These heat exchangers can be configured to use boiler feedwater (BFW) and / or glycol as cooling fluids that exchange heat with the PW when both are fed through the heat exchangers. The PW that is being cooled by the heat exchangers generally includes dissolved, dispersed or suspended impurities such as organics, hydrocarbons, minerals, acids, clays, etc., which normally cause the heat exchangers to become "fouled" over time, an effect also referred to as "fouling". The fouling includes the deposition of what is referred to as scale on the interior surfaces of the heat exchanger that come into contact with the PW. The fouling that occurs on the interior surfaces of the heat exchanger are found to reduce the heat transfer rate between the sides of the heat exchanger. As the heat transfer rate and / or flow rate of the heat exchanger are reduced, the heat exchanger may need to be cleaned to remove the buildup of scale and deposits, a process that is referred to as descaling or defouling. These issues can arise in heat exchanger applications other than ones applied to cooling PW.

[0006] Currently, when a heat exchanger used in such a process is cleaned, that heat exchanger is taken offline, typically for 6-12 hours or longer. The cleaning process can involve the hiring of a third-party service to circulate a chemical (e.g., a caustic mixture) through the heat exchanger, followed by a flush of the heat exchanger to clean out the chemical and any buildup that has been removed from the interior surfaces. As such, current processes used to clean heat exchangers can be costly in both time and resources, can be production limiting; and typically require equipment to be taken out of production, which causes a loss in plant capacity.

[0007] It is an object of the following to address at least one of the above-noted challenges or disadvantages. SUMMARY

[0008] Heat exchangers can be cleaned while remaining online and in service by introducing a cleaning substance into a fluid being fed into the heat exchanger, upstream of the heat exchanger. The cleaning substance can be introduced using an injection circuit or other injection mechanism. In a network of heat exchangers, an upstream heat exchanger can also be taken offline to be filled with an amount of the cleaning substance that is added to a fluid fed through the heat exchanger when it comes back online.

[0009] In one aspect, there is provided a heat exchanger cleaning system, comprising: a supply of cleaning substance; a connection between the supply of cleaning substance and a supply of fluid to a heat exchanger, the connection being controllable to selectively feed the supply of cleaning substance into the supply of fluid while the heat exchanger is online.

[0010] In another aspect, there is provided a heat exchanger system comprising: at least one heat exchanger; and the cleaning system recited above.

[0011] In yet another aspect, there is provided a heat exchanger network comprising: a plurality of heat exchangers; and the cleaning system recited above.

[0012] In yet another aspect, there is provided a method of cleaning a heat exchanger while the heat exchanger is online, the method comprising: connecting a supply of cleaning substance upstream of the heat exchanger; and feeding the supply of cleaning substance to a supply of fluid being fed to the heat exchanger to carry the cleaning substance through the heat exchanger.

[0013] In yet another aspect, there is provided a method cleaning at least one heat exchanger in a network comprising a plurality of heat exchangers while at least one of the plurality of heat exchangers is online, the method comprising: isolating one of the plurality of heat exchangers to take the one heat exchanger offline, the one heat exchanger being upstream of at least one of the others of the plurality of heat exchangers; adding a predetermined amount of cleaning substance to the one heat exchanger; and bringing the one heat exchanger back online to have the predetermined amount of the cleaning substance carried downstream by a supply of fluid fed to the one heat exchanger to clean the at least one of the others of the plurality of heat exchangers that is online. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Embodiments will now be described with reference to the appended drawings wherein:

[0015] FIG. 1A is a schematic diagram of a heat exchanger with an upstream injection supply mechanism for injecting a cleaning substance directly into the fluid to be cooled, while the heat exchanger is online.

[0016] FIG. 1B is a schematic diagram of the heat exchanger of FIG. 1A with the cleaning substance being injected directly into the fluid to be cooled for downstream cleaning.

[0017] FIG. 2A is a schematic diagram of a heat exchanger with an upstream injection supply circuit for injecting a cleaning substance while the heat exchanger is online.

[0018] FIG. 2B is a schematic diagram of the heat exchanger of FIG. 2A with the supply of fluid to be cooled being redirected to entrain the cleaning substance for downstream cleaning.

[0019] FIG. 3A is a schematic diagram of a heat exchanger network using multiple cooling fluids and having an upstream injection supply for injecting a cleaning substance while the heat exchangers in the network are online.

[0020] FIG. 3B is a schematic diagram of the heat exchanger network of FIG. 2A with the supply of fluid to be cooled being redirected to entrain the cleaning substance for downstream cleaning.

[0021] FIG. 4A is a schematic diagram of a heat exchanger network using multiple cooling fluids and isolating one of the heat exchangers as an injection vessel for entraining a cleaning substance for downstream cleaning of other heat exchangers in the network.

[0022] FIG. 4B is a schematic diagram of the heat exchanger network of FIG. 4A with the isolated heat exchanger brought back online to entrain the cleaning substance for the downstream cleaning.

[0023] FIG. 5 is a schematic diagram of a heat exchanger network having multiple cleaning fluid injection locations.

[0024] FIG. 6 is a schematic diagram of a three-stage heat exchanger network using multiple cooling fluids.

[0025] FIG. 7 is a flow chart illustrating operations that can be implemented in using an injection circuit upstream of one or more heat exchangers to entrain a cleaning substance.

[0026] FIG. 8 is a flow chart illustrating operations that can be implemented in isolating one heat exchanger in a network of heat exchangers to entrain a cleaning substance to clean downstream heat exchangers while online.

[0027] FIG. 9 is a chart showing results of injecting a 10% caustic solution at the inlet of a particular heat exchanger.

[0028] FIGS. 10 to 20 are charts showing results of online cleaning of downstream heat exchangers when injecting a caustic solution at respective upstream heat exchangers in a heat exchanger network. DETAILED DESCRIPTION

[0029] Heat exchangers can be cleaned while remaining online and in service by introducing a cleaning substance into a fluid being fed into the heat exchanger, upstream of the heat exchanger. The cleaning substance can be introduced using an injection circuit or other injection mechanism. In a network of heat exchangers, an upstream heat exchanger can also be taken offline to be filled with an amount of the cleaning substance that is added to a fluid fed through the heat exchanger when it comes back online

[0030] Turning now to the figures, FIG. 1A illustrates an online heat exchanger cleaning system 10, hereinafter also referred to as "the system 10". The system 10 includes a supply of fluid to be cooled 12 that is fed into a first side of a heat exchanger 16 to generate a cooled fluid 13 (i.e. a fluid with a generally lower temperature at the outlet of the heat exchanger 16). The system 10 also includes a cooling fluid 14 that is fed into a second side of the heat exchanger 16 (e.g., either the shell or tub side) to transfer heat from the fluid to be cooled 12, resulting in a heated fluid 15. It can be appreciated that in this example and those used throughout, the system 10 may be exemplified with a fluid to be cooled 12 on one side and the cooling fluid 14 on the other side of the heat exchanger 16, however, the principles discussed herein equally apply to a configuration wherein these inlets and outlets are reversed.

[0031] The heat exchanger 16 in this example includes a first inlet valve 18 and a first outlet valve 20 to control the first side of the heat exchanger 16. The heat exchanger 16 in this example also includes a second inlet valve 22 and a second outlet valve 24 to control the second side of the heat exchanger 16. The valves 18, 20, 22, and 24 can be used to isolate one or both sides of the heat exchanger 16. A control valve (not shown) may also typically be used to control the flow of the cooling fluid 14.

[0032] The system 10 can also include an injection mechanism 28 that is positioned upstream of the heat exchanger 16. The injection mechanism 28 includes an injection supply 30 that can contain or otherwise provide a supply of cleaning substance to be injected into the system 10 while the heat exchanger 16 is online. For example, the injection supply can include a vessel and a pump (not shown) to assist in feeding the cleaning substance into the supply of fluid to be cooled 12. The injecting of the cleaning substance can include feeding or otherwise introducing the cleaning substance in the fluid to be cooled 12 such that the fluid to be cooled 12 injects the cleaning substance into the downstream components (such as the heat exchanger 16) to clean those components. This cleaning operation may be referred to as defouling or descaling in some implementations, such as in the cleaning of heat exchangers 16 used to cool PW. The cleaning substance that is injected or otherwise introduced to or entrained within the fluid to be cooled 12 via the injection circuit 28 can include a caustic, such as sodium hydroxide (NaOH), which is an inorganic compound that is a highly caustic based and alkali and is highly soluble in water, or a similar chemical that has a high pH contributing element or elements. The caustic can be prepared as a diluted solution, e.g., to obtain a 10% caustic solution (i.e. dilution value). It can be appreciated that various ranges of dilution values can be used. Moreover, the caustic solution can have a dilution value at the point of injection that differs from the dilution value when the solution was originally prepared, for example, if mixed with another substance. The caustic can also be a dry form of caustic such as dry caustic pearls. Such a dry form of caustic can be made using sodium hydroxide, and can be used to make a caustic solution. It can be appreciated that sodium hydroxide may be the primary ingredient of the solution, be a component part in various proportions, and can be prepared in a solution containing other active ingredients. The sodium hydroxide solution can also be of various manufacturing quality grades, e.g., membrane commercial grade, or a previously used solution with a residual active sodium hydroxide therein. It can also be appreciated that various caustic substances and products could be used, and various ranges in concentration can be used depending on the size of the overall system 10, the severity of the fouling, the frequency of cleaning, and other operational considerations such as the degree of changes to the pH level that is acceptable or permitted downstream (e.g., requiring mitigation or additional effort at a downstream separation stage). Moreover, the cleaning substance can be injected or otherwise introduced in multiple parts, e.g., by adding two chemicals that react and produce the cleaning substance such as NaOH.

[0033] As shown in FIG. 1A, during regular online operation of the heat exchanger 16, the fluid to be cooled 12, such as PW, is not influenced by the injection mechanism 28, in this example by shutting off an inlet valve 31 between the injection mechanism 28 and the supply of fluid to be cooled 12. A control system 36 can be connected to the injection mechanism 28 to enable operations such as the filling of the injection supply 30, and the control of the inlet valve 31 to either shut off the injection supply 30, or to feed the cleaning substance into the supply of the fluid to be cooled 12. In this way, the injection mechanism 28 can be selectively used to push the cleaning substance downstream to the heat exchanger 16 without taking the heat exchanger 16 offline. The cleaning substance is therefore pushed downstream at the same rate as the flow rate of the fluid to be cooled 12, enabling the downstream online cleaning to occur rapidly, e.g., in a matter of a few seconds.

[0034] FIG. 1B illustrates the injection mechanism 28 being brought online with the heat exchanger 16 (i.e. turned on by controlling valve 31) such that the injection supply 30 is fed (e.g., pumped) into the supply line for the fluid to be cooled 12 to have the fluid to be cooled 12 carry the cleaning substance through the heat exchanger 16 while that heat exchanger 16 is online. This enables the side of the heat exchanger 16 that handles the fluid to be cooled 12 to be cleaned. It can be appreciated that a similar injection mechanism 28 can be placed along the inlet of the other side of the heat exchanger 16, e.g., if the fluid being fed through that side is susceptible to fouling or otherwise requires a periodic cleaning process to be applied.

[0035] In another implementation, as shown in FIGS. 2A and 2B, the system 10 can include an injection circuit 280 that is positioned upstream of the heat exchanger 16. The injection circuit 280 includes an injection supply 300 that can contain or otherwise provide a supply of cleaning substance to be flushed into the system 10 while the heat exchanger 16 is online. The cleaning substance can be similar to that used in the implementation shown in FIGS. 1A and 1B, as discussed above. In this implementation, the injection supply 300 may not require a pump but instead be entrained or otherwise gathered by the fluid to be cooled 12 when passing through the injection circuit 280.

[0036] As shown in FIG. 2A, during regular online operation of the heat exchanger 16, the fluid to be cooled 12, such as PW, bypasses the injection circuit 280, in this example by isolating the injection circuit 280 using one or more valves such as a set of three independent valves or an upstream three-way valve 32 (shown for ease of illustration) and a downstream three-way valve 34 (or another set of three independent valves). The control system 36 can be connected to the injection circuit 280 and valves 32, 34, to enable operations such as the filling of the injection supply 300, and the control of the three-way valves 32, 34 to either isolate the injection supply 300, or redirect the fluid to be cooled 12 through the injection supply 300 to entrain or mix the cleaning substance in the fluid to be cooled 12. In this way, the injection circuit 280 can be selectively used to push the cleaning substance downstream to the heat exchanger 16 without taking the heat exchanger 16 offline. The cleaning substance is therefore pushed downstream at the same rate as the flow rate of the fluid to be cooled 12, enabling the downstream online cleaning to occur rapidly, e.g., in a matter of a few seconds.

[0037] FIG. 2B illustrates the injection circuit 280 being brought online with the heat exchanger 16 such that the fluid to be cooled 12 is fed through the injection supply 300 to entrain or otherwise carry the cleaning substance through the heat exchanger 16 while that heat exchanger 16 is online. This enables the side of the heat exchanger 16 that handles the fluid to be cooled 12 to be cleaned. It can be appreciated that a similar injection circuit 280 can be placed along the inlet of the other side of the heat exchanger 16, e.g., if the fluid being fed through that side is susceptible to fouling or otherwise requires a periodic cleaning process to be applied.

[0038] It can also be appreciated that the injection mechanism 28 and injection circuit 280 are only illustrative examples of configurations that enable the cleaning substance to be injected into the supply of fluid to be cooled 12. That is, other configurations for injecting the cleaning substance into the piping that carries the fluid to be cooled 12 into the heat exchanger 16 can be utilized.

[0039] As indicated above, heat exchangers 16 can be used individually or in networks. FIG. 3A illustrates schematically a heat exchanger network 100 that in this example includes five heat exchangers 16 arranged with three heat exchangers 16 in a first stage 160a, and a pair of heat exchangers 16 in a second stage 160b. The configuration shown in FIG. 3A is for illustrative purposes and many other configurations with more or fewer heat exchangers 16 and / or more or fewer stages 160 are possible. In such a multi-stage network 100, multiple different cooling fluids 14 can be used. For example, in an oil and gas process where the fluid to be cooled 12 is PW, the first stage 160a of heat exchangers 16 (arranged in parallel) can use boiler feedwater (BFW) as a first cooling fluid 14a (to generate a first heated fluid 15a), and glycol as a second cooling fluid 14b (to generate a second heated fluid 15b). The glycol cooling fluid 14b is sometimes used to provide additional control and "fine tuning" of the cooling process to achieve a certain desired temperate or temperature range for the cooled fluid 13, e.g., the cooled PW. In this configuration, the heat exchangers 16 in the first stage 160a are arranged in parallel to each other, the heat exchangers 16 in the second stage 160b are arranged in parallel to each other, and the first and second stages 160a, 160b are arranged serially. In this way, a higher volume of fluid being cooled 12 can be processed at each stage, with the output of the first stage 160a being fed into the second stage 160b for a second stage cooling.

[0040] Similar to the implementation shown in FIGS. 1A and 1B, the injection mechanism 28 can also be positioned upstream of the first stage 160a of the network 100 to push the cleaning substance through all of the heat exchangers 16 in the network 100 while these heat exchangers 16 remain online. The amount of cleaning substance introduced via the cleaning mechanism 28 can be increased or otherwise adjusted to account for the overall size of the network 100 (e.g., volume, surface area to be cleaned, etc.). FIG. 3A illustrates the injection mechanism 28 being in a shut off state, and FIG. 3B illustrates the cleaning substance being fed into the fluid to be cooled 12 to push the cleaning substance downstream through the network 100. In this example, the control system 36 can be used to control the inlet valve 31.

[0041] It has also been found that rather than adding an injection mechanism 28, injection circuit 280, or other injection apparatus to a heat exchanger network 100, existing heat exchangers 16 can be used to enable online cleaning of downstream heat exchangers 16. Turning now to FIG. 4A, a network 100 similar to that shown in FIG. 3A is illustrated without an injection mechanism 28 or injection circuit 280. In this implementation, a first heat exchanger 16a in a first stage 160a of the network 100 (also having a second heat exchanger 16b and a third heat exchanger 16c) is taken offline by isolating its side in contact with the fluid to be cooled 12. In this example, this is achieved by closing the first inlet valve 18 and first outlet valve 20 to close that side of the first heat exchanger 16a. An inlet pipe or other access port 48 can be used to fill the isolated side of the first heat exchanger 16a with a cleaning substance 46, such as a diluted caustic solution. For example, the first heat exchanger 16a may have an existing access mechanism, sometimes referred to as a "truck out" line that enables a hose 50 connected to a supply truck (not shown) to be attached to the port 48 to fill the first exchanger 16a. In this way, the first heat exchanger 16a is utilized as an injection vessel such that when the isolated side of the heat exchanger 16a comes back online (by opening the valves 18, 20 as shown in FIG. 4B), the cleaning substance 46 that is in the first heat exchanger 16a is flushed through the downstream piping to clean the fourth and fifth heat exchangers 16d, 16e in the second stage 160b, along with the first heat exchanger 16a (as illustrated using relatively thicker grey lines in FIG. 4B). It can be appreciated that the second heat exchanger 16b and / or third heat exchanger 16c can similarly be taken offline to perform a downstream cleaning along with cleaning itself. The heat exchangers 16a, 16b, 16c in the first stage 160a can be rotated as injection vessels while keeping the remaining heat exchangers 16 online.

[0042] FIG. 5 illustrates another example implementation in which multiple injection mechanisms 28a, 28b are positioned in the network 100 to enable further control over the online cleaning process. For example, each injection mechanism 28a, 28b can be used at the same time with additional cleaning substance being added at the second injection mechanism 28b to increase the concentration of cleaning substance in the fluid to be cooled 12 as it moves downstream. Also, the second injection mechanism 28b could be used on its own to clean only CPST Doc: 246335.1 the second stage 160b of heat exchangers 16. As seen in FIG. 4, the control system 36 can be configured to be connected to both of the injection mechanism 28a, 28b in order to allow an operator to have control over both at the same time (e.g., during the online cleaning process). It can be appreciated that this implementation can also be applied to the configuration shown in FIGS. 4A and 4B such that more than one of the heat exchangers 16 in the network 100 can be taken offline at the same time to effectively fill multiple injection vessels that can be brought back online at the same or approximately the same time.

[0043] FIG. 6 illustrates that other heat exchanger networks 110 can be adapted for online cleaning according to the principles discussed herein. In the example shown in FIG. 6, a three- stage network 110 is shown having a first stage 160a, a second stage 160b, and a third stage 160c. An injection mechanism 28 is shown by way of example that is positioned upstream of the first stage 160a to enable online cleaning of the three stages 160a-160c. It can be appreciated that the configuration shown in FIGS. 4A and 4B or FIG. 5 (with multiple injection mechanisms 28) can also be applied to the three-stage network 110 shown in FIG. 6.

[0044] FIG. 7 illustrates a set of operations that can be executed in performing an online cleaning process using the injection mechanism 28 or injection circuit 280 shown in FIGS. 1A / 1B, 2A / 2B, 3A / 3B, 5 and 6. At 200 an injection mechanism 28 or injection circuit 280 is provided upstream of one or more heat exchangers 16 that are to be cleaned while staying online (e.g., as shown in FIG. 1A or FIG. 2A). At 202 a cleaning substance is introduced to the injection mechanism 28 or injection circuit 280, e.g., by adding or feeding a predetermined amount of the cleaning substance to the injection supply 30, 300. The injection supply 30, 300 can therefore be embodied as a vessel or storage tank as discussed above. It can be appreciated that in addition to varying the concentration of the cleaning substance, the volume of the substance can also vary. For example, a 2m3 volume of a 10% diluted caustic solution has been found to be suitable for cleaning heat exchangers 16 used in oil and gas processes such as to cool PW. At 204, the cleaning substance is fed into the fluid being cooled 12, e.g., by opening the inlet valve 31 of the injection mechanism 28 or by redirecting the flow of the fluid being cooled 12 through the injection circuit 280. This pushes or flushes the cleaning substance through the downstream heat exchanger(s) 16 as discussed above. At 206, the system 10, 100 is returned to normal operation, e.g., by closing the inlet valve 31 of the injection mechanism 28, or by isolating the injection circuit 280. It can be appreciated that the operations shown in FIG. 7 can be performed in an automated fashion by utilizing the control system 36 and thus the CPST Doc: 246335.1 operations in FIG. 7 may also represent computer executable instructions stored in a memory of (or available to) the control system 36 that may be executed by a processor of (or processor available to) the control system 36.

[0045] FIG. 8 illustrates a set of operations that can be executed in performing an online cleaning process of one or more heat exchangers 16 in a heat exchanger network 100 by taking an upstream heat exchanger 16 offline (e.g., as shown in FIGS. 4A and 4B). At 300 a side of an upstream heat exchanger 16 is isolated and at 302 the isolated side is filled with a predetermined amount of the cleaning substance. At 304 the isolated side of the heat exchanger 16 is placed back online to enable the fluid passing therethrough (e.g., the fluid being cooled 12) to push or flush the cleaning substance through the downstream heat exchanger(s) 16. Although not shown in FIG. 4A, it can be appreciated that the operations shown in FIG. 8 may also at least in part be executed by the control system 36. For example, isolating the side of the first heat exchanger 16a can be performed by the control system 36 when the valves 18, 20 are connected thereto.

[0046] In another embodiment, an additional chemistry may be added upstream or downstream of the heat exchangers for treating the contaminants such as the dissolved, dispersed or suspended impurities such as organics, hydrocarbons, minerals, acids, alkalinity, clays in the produced water exiting the heat exchanger 16. When employing an online cleaning process as described herein, in one example a concentrated amount of contaminants may release into the cooled fluid 13 following the push or flush of the cleaning substance through the heat exchanger 16.

[0047] In one aspect, the cleaning process may have detrimental effects on the operation of the central process facility that treats the produced water, including, but not limited to, organics, hydrocarbons and inorganics being dispersed in the cooling fluid reducing separation efficiency in the downstream processes of the central process facility and reduce the quality of the cooling fluid limiting or preventing reuse in a steam regeneration process, increase the scaling propensity of inorganics and depositing onto follow on process equipment, and increase corrosion rates of process equipment potentially leading to integrity failure.

[0048] In order to treat this slug of contaminants, a further additional chemistry may be added to the cooled produced water, which may be, or a combination of, an acid, a dispersant, anti-dispersant, anti-scalant, surfactant, or any classification of coagulants and flocculants.

[0049] FIGS. 9 through 20 provide charts illustrating results of trials performed on heat exchangers 16 using a 2m3 volume of 10% caustic solution. FIG. 9 illustrates a flush of a glycol- cooled heat exchanger 16 that was offline, to demonstrate the effects of the diluted caustic solution. In this example, the caustic solution was flushed into the heat exchanger 16 at its inlet. It was found that subsequent to the flush, the glycol increased from 35.6 to 54.7°C, the flow rate increased by 25 m3 / h, and the heat transfer coefficient or "U" value increased from 53 to 170 W / m2C.

[0050] Table 1 below illustrates caustic flush results for a series of heat exchangers 16 in a network. It may be noted that in the first injection results, the injection point for the flush was at a heat exchanger 16 labeled "E-303C1 / C2", which correspond to heat exchangers 16 in a first stage 160a of the network 100. It can be seen that in addition to the E-303C1 / C2 exchanger, three additional heat exchangers 16 in a second stage 160b of the network 100 were cleaned, labeled as E-306B, E-306K, and E-306K. These results can be compared to the other injections listed in Table 1 (on a previous day) that cleaned heat exchangers 16 one at a time. [Image disponible dans le document PDF, Image available in the PDF document] Table 1: Before and After Results for Caustic Flushes

[0051] Turning now to FIGS. 10 to 20, charts showing the results of caustic cleaning in a network 100 are shown, in which certain upstream heat exchangers 16 are used to clean downstream heat exchangers 16 while those downstream heat exchangers 16 remain online. As indicated in FIG. 10, increases in U values for the heat exchangers 16 labeled as E-306E and E-306F were found to be 891 W / m2C and 268 W / m2C respectively.

[0052] As indicated in FIG. 11, increases in U values for the heat exchangers 16 labeled as E-306D and E-306E were found to be 1599 W / m2C and 1217 W / m2C respectively.

[0053] As indicated in FIG. 12, increases in U values for the heat exchangers 16 labeled as E-306D and E-306E were found to be 991 W / m2C and 924 W / m2C respectively.

[0054] As indicated in FIG. 13, increases in U values for the heat exchangers 16 labeled as E-306D and E-306E were found to be 579 W / m2C and 564 W / m2C respectively.

[0055] As indicated in FIG. 14, increases in U values for the heat exchangers 16 labeled as E-306D and E-306E were found to be 788 W / m2C and 839 W / m2C respectively.

[0056] As indicated in FIG. 15, increases in U values for the heat exchangers 16 labeled as E-306D and E-306E were found to be 855 W / m2C and 1122 W / m2C respectively.

[0057] As indicated in FIG. 16, increases in U values for the heat exchangers 16 labeled as E-306E and E-306F were found to be 1354 W / m2C and 1219 W / m2C respectively.

[0058] As indicated in FIG. 17, increases in U values for the heat exchangers 16 labeled as E-306E and E-306F were found to be 1370 W / m2C and 1236 W / m2C respectively.

[0059] As indicated in FIG. 18, increases in U values for the heat exchangers 16 labeled as E-306B and E-306C were found to be 1293 W / m2C and 876 W / m2C respectively.

[0060] As indicated in FIG. 19, increases in U values for the heat exchangers 16 labeled as E-306# and E-306# were found to be 1293 W / m2C and 876 W / m2C respectively.

[0061] As indicated in FIG. 20, increases in U values for the heat exchangers 16 labeled as E-306B and E-306C were found to be 689 W / m2C and 942 W / m2C respectively.

[0062] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the examples described herein. Also, the description is not to be considered as limiting the scope of the examples described herein.

[0063] It will be appreciated that the examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein. For instance, components and modules can be added, deleted, modified, or arranged with differing connections without departing from these principles.

[0064] It will also be appreciated that any module or component exemplified herein that executes instructions may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and / or non- removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by an application, module, or both. Any such computer storage media may be part of the control system 36, any component of or related to the control system 36, etc., or accessible or connectable thereto. Any application or module herein described may be implemented using computer readable / executable instructions that may be stored or otherwise held by such computer readable media.

[0065] The steps or operations in the flow charts and diagrams described herein are just for example. There may be many variations to these steps or operations without departing from the principles discussed above. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified.

[0066] Although the above principles have been described with reference to certain specific examples, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.

Claims

1. A heat exchanger cleaning system, comprising: a supply of cleaning substance; a connection between the supply of cleaning substance and a supply of fluid to a heat exchanger, the connection being controllable to selectively feed the supply of cleaning substance into the supply of fluid while the heat exchanger is online.

2. The system of claim 1, further comprising an injection circuit, the injection circuit comprising a vessel containing the supply of cleaning substance, and at least one valve for directing the supply of fluid through the vessel to mix with the cleaning substance.

3. The system of claim 1, wherein the supply of cleaning substance is fed into one of a plurality of heat exchangers in a heat exchanger network, the one heat exchanger being upstream of at least one of the others of the plurality of heat exchangers and being offline, and wherein the connection comprises a fill line connectable to an inlet on the one heat exchanger and at least one valve used to isolate the one heat exchanger.

4. The system of any one of claims 1 to 3, wherein the cleaning substance is generated by injecting a plurality of elements into the system that react together to produce the cleaning substance.

5. The system of any one of claims 1 to 4, wherein the supply of fluid comprises a fluid to be cooled by the heat exchanger.

6. The system of claim 5, wherein the supply of fluid comprises produced water generated during an oil and gas extraction process.

7. A method of cleaning a heat exchanger while the heat exchanger is online, the method comprising: connecting a supply of cleaning substance upstream of the heat exchanger; and feeding the supply of cleaning substance to a supply of fluid being fed to the heat exchanger to carry the cleaning substance through the heat exchanger.

8. The method of claim 7, further comprising opening an inlet valve to connect the supply of cleaning substance.

9. The method of claim 7, further comprising redirecting the supply of fluid into an injection circuit, the injection circuit comprising a vessel containing the supply of cleaning substance, and at least one valve for directing the supply of fluid through the vessel to mix with the cleaning substance.

10. The method of claim 9, wherein the connection comprises a pair of three-way valves or two sets of three independent valves, to redirect the supply of fluid through the vessel.

11. The method of any one of claims 7 to 10, further comprising generating the cleaning substance by injecting a plurality of elements into the system that react together to produce the cleaning substance.

12. The method of any one of claims 7 to 11, wherein the supply of fluid comprises a fluid to be cooled by the heat exchanger.

13. The method of claim 12, wherein the supply of fluid comprises produced water generated during an oil and gas extraction process.

14. The method of claim 13, wherein the produced water is cooled by a supply of boiler feed water or glycol fed to another side of the heat exchanger.

15. A method cleaning at least one heat exchanger in a network comprising a plurality of heat exchangers while at least one of the plurality of heat exchangers is online, the method comprising: isolating one of the plurality of heat exchangers to take the one heat exchanger offline, the one heat exchanger being upstream of at least one of the others of the plurality of heat exchangers; adding a predetermined amount of cleaning substance to the one heat exchanger; and bringing the one heat exchanger back online to have the predetermined amount of the cleaning substance carried downstream by a supply of fluid fed to the one heat exchanger to clean the at least one of the others of the plurality of heat exchangers that is online.

16. The method of claim 15, wherein the supply of cleaning substance comprises a caustic solution that is diluted and introduced at the connection at a first dilution value.

17. The method of claim 16, wherein the first dilution value is different from a second dilution value obtained when the caustic solution was originally prepared.

18. The method of any one of claims 15 to 17, further comprising generating the cleaning substance by injecting a plurality of elements into the system that react together to produce the cleaning substance.

19. The method of any one of claims 15 to 18, wherein the supply of fluid comprises a fluid to be cooled by the heat exchanger.

20. The method of claim 19, wherein the supply of fluid comprises produced water generated during an oil and gas extraction process.