Heat exchanger arrangement comprising a heat exchanger of the shell and tube type

Abstract

The present disclosure relates to a heat exchange arrangement comprising one or more shell and tube heat exchangers having a shell with an inner space, the heat exchanger having a tube-side inlet which enters a tube-side fluid to be heated or cooled in a front head located in between the tube-side inlet and a front tube sheet, from which the tube-side fluid then is distributed to a plurality of tubes which are held in place by tube sheets, and through which the tube-side fluid moves and during the movement is cooled or heated by a first shell-side heating or cooling fluid which moves through a first compartment with a first compartment inlet and a first compartment outlet, and by a second shell-side heating or cooling fluid which moves through a second compartment with a second compartment inlet and a second compartment outlet, whereafter the cooled or heated tube-side fluid is collected in a rear head located between a rear tube sheet and a tube-side outlet through which the cooled process gas leaves the heat exchanger, the tubes further being supported by a first and a second intermediate tube sheet placed between the front tube sheet and the rear tube sheet and between which a buffer compartment is formed with a buffer fluid with a buffer fluid temperature, the buffer fluid not chemically reacting producing insoluble compounds that precipitate as scale and not comprising compounds that chemically react with the shell resulting in corrosion at the buffer fluid temperature, and having a pressure which is higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment.

Description

Technical field

[0001] The present disclosure relates to a heat exchanger arrangement comprising a heat exchanger of the shell and tube type, more in particular for a nitric acid production plant.Background

[0002] Shell and tube heat exchangers allow a fluid, i.e. a liquid or a gas, to be heated or cooled without coming into direct contact with the cooling or heating medium, which is typically another fluid. A shell and tube heat exchanger in general comprises a tube side and a shell side. The tube side of the shell and tube heat exchanger comprises a tube bundle comprising a plurality of tubes which are configured to heat or cool a tube-side fluid. The tubes can be of different types, i.e. plain, longitudinally finned, etc. Inside the front head, the tube-side fluid is distributed across the tube bundle. The tube-side fluid enters the shell and tube heat exchanger via a tube-side inlet in a front head, which is located between the tube-side inlet and a front tube sheet. The tube-side inlet is typically an opening or a nozzle on one end of the heat exchanger. The front head thus serves as the entry point of the shell and tube heat exchanger for the tube-side fluid. The tube-side fluid is distributed into the different tubes of the tube bundle via a tube inlet of each of the tubes. After flowing through the tubes, the heated or cooled tube-side fluid leaves the tubes via a tube outlet of each of the tubes whereafter it is collected in a rear head (also known as outlet head or return head). The rear head is formed between a rear tube sheet and a tube-side outlet, which is also typically an opening or a nozzle on the other end of the shell and tube heat exchanger opposite the tube-side inlet. The heated or cooled tube-side fluid then leaves the rear head and thus the heat exchanger via the tube-side outlet, which connects to the next stage of the chemical production process or to a discharge system. The rear head is thus the exit point of the shell and tube heat exchanger for the tube-side fluid. The plurality of tubes is on the one hand supported by baffles, which are plates or guides placed inside the shell to direct the flow of the shell-side fluid. Baffles increase the turbulence of the shell-side fluid, enhancing heat transfer by ensuring that the shell-side fluid flows across the tubes rather than parallel to them. The tubes of the tube bundle are also kept in place by tube sheets, including the front and rear tube sheet. Between the front and the rear tube sheet, a shell which comprises an outer shell, which typically has a cylindrical shape, which encompasses an inner space is present. The front tube sheet physically separates the shell from the front head, while the rear tube sheet physically separates the shell from the rear head. The front and rear tube sheet thus act as a barrier ensuring that the tube-side fluid and the shell-side fluid do not mix while allowing heat transfer to occur. The tube bundle extends in the shell. The shell-side of a shell and tube heat exchanger is the space outside the tubes in the outer shell. The shell has a shell-side inlet and a shell-side outlet. The shell-side inlet is the entry point for a shell-side fluid in the shell, while the shell-side outlet is the exit points for the shell-side fluid out of the shell. Between the shell-side inlet and the shell-side outlet, the shell-side fluid flows around the tubes. During the passage of the shell-side fluid through the inner space of the shell, it releases heat from the tube-side fluid flowing in the tubes via the wall of the tubes, in case the tube-side fluid needs to be heated. In case the tube-side fluid however needs to be cooled, the shell-side fluid takes up heat from the tube-side fluid flowing through the tubes. The flow of the tube-side fluid can be arranged in various configurations, such as counterflow (opposite direction to the shell-side fluid), crossflow (perpendicular to the tube bundle) or parallel flow (same direction as the shell-side fluid).

[0003] Shell and tube heat exchangers are types of heat exchangers that are widely used in the industry. They are known for their high efficiency and their low pressure drop, the latter being the main reason to choose a shell and tube heat exchanger. Shell and tube heat exchangers are very suitable to be used in large chemical processes, such as amongst others nitric acid production. Nitric acid has many industrial applications, but its primary function however is the production of ammonium nitrate, which in its turn is then used in the fertilizer industry. In nitric acid plants, shell and tube heat exchangers, amongst others nitric acid cooler condenser shells (hereafter further called "nitric acid cooler condenser"), are commonly used for different purposes such as preheating feed streams and cooling product streams.

[0004] A nitric acid shell and tube cooler condenser, hereafter called "nitric acid cooler condenser", comprises a front head, a rear head, and a shell located between the front head and the rear head. The front head is located between a tube-side inlet and a front tube sheet. The rear head is located between a tube-side outlet and a rear tube sheet. The shell is located between the front and the rear tube sheet. The shell comprises an outer shell which encompasses an inner space into which a tube bundle comprising a plurality of tubes are located. In the nitric acid cooler condenser, hot process gas which is typically coming from an ammonia oxidizer, and which more in particular comprises nitrogen oxides (NO x ), water (H 2 O) in the form of vapour, and other gaseous components including amongst others as a major part nitrogen (N 2 ) and a minor part oxygen (O 2 ) originating from the ambient air from the air compressor which is used for oxidation of NH 3 to NO, dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), and which needs to be cooled, enters the front head via the tube-side inlet. This hot process gas is then distributed via a tube inlet of each of the tubes over the different tubes. The hot process gas then flows through the tubes. During the movement of the process gas through the tubes, the following chemical reactions take place: oxidation of NO to form NO 2 , and (in parallel) absorption of the NO 2 in H 2 O forming HNO 3 . A cooled two-phase fluid will then leave the plurality of tubes via a tube outlet and will be collected in the rear head. The cooled two-phase fluid will subsequently leave the heat exchanger via the tube-side outlet. In order to cool the process gas entered in the tubes, cooling water with a temperature which is lower than the dewpoint of the process gas entered in the tubes is entered in the inner space of the shell via a shell inlet. This cooling water will flow around the tubes and will finally leave the shell in a heated form via a shell outlet. During the passage of the cooling water through the shell inner space, the cooling water thus takes up heat from the process gas in the tubes via the tube walls.

[0005] The problem with these conventional nitric acid cooler condensers however is that very often one or more tubes of the cooler condenser are corroded resulting in thinning of these tubes. The primary cause thereof is the chemical reaction between the process gas (of which the composition is described above) which flows through the tubes and the metal of the tubes. The metal temperature in part of the tubes is lower than the dewpoint of the process gas entered in the tubes. The dewpoint is the temperature at which gases in the process gas begin to condense from the gas phase into the liquid phase. Although the temperature of the process gas which enters the tubes lowers during the passage thereof through the tubes as it transfers heat to the cooling water flowing through the shell inner space around the tubes, the continuous flow of process gas through the tubes stays at a relative high temperature. Any fluctuations in the flow rate or the temperature of the process gas can cause variations in the temperature of the tubes. For instance, if the flow rate decreases, there might be less heat transfer, leading to a temporary drop in the temperature of the tubes, followed by an increase of the tube temperature as the flow stabilizes again. If the temperature within the tubes drops below the dewpoint of the process gas, NO 2 and N 2 O 4 out of the process gas will be absorbed in the condensate formed out of the vapor, through which liquid HNO 3 will be formed. When the temperature within the tubes rises again due to the flowing process gas passing by again, the condensed liquid HNO 3 can re-boil, turning back into gaseous HNO 3 potentially causing corrosion to the tubes and / or the tube sheets, resulting in amongst others a ring of corrosion inside the tubes at the back of the tube sheet and / or thinning of the metal of the tubes.

[0006] In the ANNA conference that took place in 2011 in Colorado, USA, the applicant presented a "New concept for a cooler condenser" of the nitric acid cooler condenser. A corresponding publication of this nitric acid cooler condenser was done in the magazine "Nitrogen+Syngas 315", published in January - February 2012 on pages 31 - 33.

[0007] In the ANNA Conference, two difference solutions of so called "hot tube sheet nitric acid cooler condensers" were shown which significantly reduce the problems with the conventional nitric acid cooler condensers as described in more detail above.

[0008] A first solution which was discussed in this ANNA Conference was a horizontal cooler condenser of a nitric acid production plant and which is shown in Figure 1. This horizontal cooler condenser 100 comprises a front head 102a, a shell 102b with a cylindrical shape, and a rear head 102c. The front head 102a comprises a tube-side inlet 101a, and the rear head 102c comprises a tube-side outlet 101b. During operation, hot process gas with a composition as described above enters the front space 102a via the tube-side inlet 101a, while a cooled two-phase fluid with a composition described above is collected in the rear head 102c. The front head 102a is separated from the shell 102b by means of a front tube sheet 104. The rear head 102c is separated from the shell 102b by means of a rear tube sheet 106. In the inner space of the shell 102b, a tube bundle comprising a plurality of tubes 103 are located. In the inner space of the shell 102b, an intermediate tube sheet 105 is placed. This intermediate tube sheet 105 is thus located between the front and the rear tube sheet 104, 106. The tubes 103 are held in place by different tube sheets 104 - 106 , which are more in particular configured as perforated plates having perforations which are configured to accommodate the tubes 103. The intermediate tube sheet 105 creates two compartments in the inner space of the shell 102b, i.e. between the rear tube sheet 106 and the intermediate tube sheet 105, a right "cold" compartment 1021, typically having a heat duty of 19,1 MW, which comprises a first cooling water inlet 111 and a first cooling water outlet 112, between the front tube sheet 104 and the intermediate tube sheet 105, a left "hot" compartment 1022, typically having a heat duty of 38,9 MW, and which comprises a second cooling water inlet 114 and a second cooling water outlet 115, wherein the left compartment 1022 is indicated as "hot" since the cooling water in that compartment is heated much more and is thus warmer than the cooling water in the right compartment 1021, which is thus indicated as "cold",

[0009] The fluid streams in this specific example of a horizontal low-pressure nitric acid cooler condenser as shown in Figure 1 are as follows: a (hot) process gas with a temperature of around 177 °C and a dewpoint of around 95 °C comprising the following gases: nitrogen oxides (NO x ), water (H 2 O) in the form of vapour, N 2 , O 2 , dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), enters the heat exchanger 100 through the tube-side inlet 101a in the front head 102a and is distributed from there over the different tubes 103, a major part of cooling water with a temperature of 35°C which comes from air coolers which flows counter current to the process gas flowing in the tubes enters the cold compartment 1021 via the first cooling water inlet 111, at the same time, a minor part of cooling water with a temperature of 35°C which comes from air coolers is entered via the second cooling water inlet 114 in the hot compartment 1022, the cooling water which flows in the cold compartment 1021 and the hot compartment 1022 around the tubes 103 absorbs heat from the process gas flowing through the tubes 103 and exits the cold compartment 1021 with a lower temperature via the first cooling water outlet 112, respectively the hot compartment 102c with a lower temperature via the second cooling water outlet 115, a cooled two-phase fluid consisting of a liquid part with a certain amount of HNO 3 , HNO 2 , H 2 O, and N 2 O 4 and a gaseous part with a reduced amount of nitrogen oxides (NO x ) and vapour since there was absorption of the NO x in the condensed vapour, and O 2 in view of the process gas entering the tubes, the same amount of N 2 (is inert), and then further dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), with a temperature of around 45 °C exits the tubes 103 in the rear head 102c and leaves the heat exchanger through the tube-side outlet 101b . The cooling water which leaves the cold compartment 1021 via the first cooling water outlet 112 has a temperature of 39,1 °C and is directed to an air cooler. The cooling water which leaves the hot compartment 1022 via the second cooling water outlet 115 has a temperature of 104 °C, and is directed to a plate heat exchanger 116 which can then further transfer the heat to another process or another medium which is configured to use heat of a temperature around 104°C, for instance to heat tail gas, or to be used in horticulture or district heating. The heat duty of this cooling water which is not used in the plate heat exchanger 116 is conducted to an air cooler.

[0010] The issue with this horizontal nitric acid cooler condenser as described above with reference to Figure 1 is that the intermediate tube sheet cannot be made completely liquid tight since the tubes are hydraulically expanded in the intermediate tube sheet. For this reason, in case the fluid in the cold compartment would be different than the fluid in the hot compartment, which is typically demineralized water which is a high-purity fluid, and for instance a less pure fluid is used in the cold compartment in view of the hot compartment, and in case the pressure of the cold compartment is higher than the pressure of the hot compartment, contamination of the demineralized water in the hot part by the (less pure) fluid of the cold compartment is possible. In the light of the present disclosure, with a high-purity fluid is meant a fluid that does not readily react with other substances under the given conditions. In the light of the present disclosure, with purity of a fluid is meant the concentration of the main substance(s) that make up the fluid and the absence or minimal presence of impurities or contaminants present in the fluid such as chemicals, particles or other contaminants. If on the other hand, the pressure of the hot compartment would be higher than the pressure of the cold compartment, then demineralized water could migrate to the cold compartment and get lost. For this reason, the fluids in both the cold and the hot compartment needs to be the same, thus the high-purity fluid which is used in the hot compartment and which is chosen since it is not vulnerable to scaling, fouling and corrosion at the higher temperatures of the hot compartment.

[0011] A second solution which was discussed in the ANNA Conference is a vertical nitric acid cooler condenser of a nitric acid production plant and which is shown in Figure 2. This horizontal cooler condenser 150 comprises a front head 102a, a shell 102b with a cylindrical shape, and a rear head 102c. The front head 102a comprises a tube-side inlet 101a, and the rear head 102c comprises a tube-side outlet 101b. During operation, hot process gas with a composition as described above enters the front space 102a via the tube-side inlet 101a, while a cooled two-phase fluid with a composition described above is collected in the rear head 102c. The front head 102a is separated from the shell 102b by means of a front tube sheet 104. The front head 102a is thus located between the tube-side inlet 101a and the front tube sheet 104. The rear head 102c is separated from the shell 102b by means of a rear tube sheet 106. The rear head 102c is thus located between the tube-side outlet 101b and the rear tube sheet 106. In the inner space of the shell 102b, a tube bundle comprising a plurality of tubes 103 are located. The inner space of the shell 102b comprises a lower cold compartment 1021, typically having a heat duty of 6,5 MW, and an upper "hot" part 1022, typically having a heat duty of 5,1 MW, which are not physically separated from each other by a tube sheet. The shell 101 comprises one cooling water inlet 121 at the bottom of the inner space of the shell 102 via which cooling water with a temperature of 29 °C is entered in the cold compartment 1021. The cold compartment 1021 comprises a first cooling water outlet 112. The hot part 1022 comprises a second cooling water outlet 115.

[0012] The fluid streams in such a vertical low-pressure nitric acid cooler / condenser are as follows: a hot process gas with a temperature of around 104°C and a dewpoint of around 65°C, and with the same composition as described above, enters the heat exchanger 150 through the tube-side inlet 101a in the front head 102a and is distributed from there over the different tubes 103, cooling water with a temperature of around 29°C which flows counter-current to the process gas flowing in the tubes 103 enters the cold compartment 1021 via the cooling water inlet 121, the major part of the cooling water which flows in the cold part 1021 around the tubes 103 absorbs heat from the process gas flowing through the tubes 103 and leaves the cold part 1021 via the first cooling water outlet 112 in a heated form at a temperature of around 37°C, the minor part of the cooling water which flows in the hot part 1022 around the tubes 103 absorbs heat from the process gas flowing through the tubes 103 and leaves the hot part 1022 via the second cooling water outlet 115 in a heated form at a temperature of around 75°C, a cooled process gas with the same composition as described above exits the tubes 103 in the rear head 102c and then exits the heat exchanger 150 via the tube-side outlet 101b at a temperature of around 42°C.

[0013] The issue with this vertical nitric acid cooler condenser as described above with reference to Figure 2 is that, since there is no intermediate tube sheet present, the fluid in the cold part needs to be the same as the fluid in the hot part, and thus a high-purity fluid such as demineralized water. If a different fluid would be used in the cold and the hot part, for instance a less pure fluid is used in the cold part in view of the hot part, there could be contamination of the high-purity fluid in the hot part by the (less pure) fluid of the cold part.

[0014] In view of the above, the objective of the present disclosure is to design a shell and tube heat exchanger which can be used in a vertical as well as a horizontal position, and wherein in the cold part another fluid can be used than the fluid of the hot part.Summary

[0015] According to a first aspect of the present disclosure, a heat exchange arrangement is disclosed which comprises a horizontal shell and tube heat exchanger comprising a front head with a tube-side inlet which is configured to enter a tube-side fluid which needs to be cooled or heated in the heat exchanger, a rear head with a tube-side outlet which is configured to exit the cooled or heated tube-side fluid out of the heat exchanger, a shell comprising a shell inner space located between the front head and the rear head, wherein a plurality of tubes are located, wherein the shell is separated from the front head by means of a front tube sheet, and the rear head by means of a rear tube sheet, wherein the front tube sheet and the rear tube sheet are configured to hold the tubes in place, wherein the front head is further configured to enter the tube-side fluid in the plurality of tubes via a tube inlet of each of the tubes, and the rear head is further configured to collect the tube-side fluid which exits the plurality of tubes via a tube outlet of each of the tubes, wherein the shell and tube heat exchanger comprises a first and a second intermediate tube sheet located in the shell inner space between the front and the rear tube sheet, which are both configured to keep the plurality of tubes in place, a first compartment between the rear tube sheet and the first intermediate tube sheet, wherein a first part of the tubes are located, and comprising a first compartment inlet configured to enter a first shell-side fluid to be cooled or heated in the first compartment, and a first compartment outlet configured to exit the cooled or heated first shell-side fluid out of the first compartment, and comprising a first compartment inner space configured to let the first shell-side fluid flow through it between the first compartment inlet and the first compartment outlet with a pressure, wherein the first shell-side fluid has a decreasing, respectively an increasing first temperature when flowing through the first compartment between the first compartment inlet and the first compartment outlet, and the tube-side fluid has an increasing, respectively a decreasing temperature during the passage thereof through the first part of the tubes, a second compartment between the front tube sheet and the second intermediate tube sheet, and comprising a third part of the tubes, and comprising a second compartment inlet configured to enter a second shell-side fluid to be cooled or heated in the second compartment, and a second compartment outlet configured to exit the cooled or heated second shell-side fluid out of the second compartment, and comprising a second compartment inner space which is configured to let a second shell-side fluid flow through it between the second compartment inlet and the second compartment outlet with a pressure which is different than the pressure of the first shell-side fluid in the first compartment, and has a decreasing, respectively an increasing temperature when flowing through the second compartment between the second compartment inlet and the second compartment outlet, and the tube-side fluid has an increasing, respectively a decreasing temperature during the passage of the tube-side fluid through the third part of the tubes, and a buffer compartment between the first intermediate sheet and the second intermediate sheet, comprising a buffer compartment inner space comprising a second part of the tubes, and comprising a buffer compartment inlet configured to enter a buffer fluid in the buffer compartment and subsequently keep the buffer fluid contained in the buffer compartment around the second part of the tubes, wherein the buffer fluid has a buffer fluid temperature which is determined by the temperature of the tube-side fluid flowing through the second part of the tubes, and wherein the buffer fluid in the buffer compartment is a fluid which does not chemically react producing insoluble compounds that precipitate as scale and does not comprise compounds that chemically react with the shell resulting in corrosion at the buffer fluid temperature, wherein the buffer fluid has a pressure which is higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment.

[0016] Because there is a problem to join the tubes to the intermediate tube sheets in a leak-free way, and the tubes at present can only hydraulically be expanded in the intermediate tube sheet, another solution as described above was found to enable the use of another fluid than pure demineralized water in the cold compartment (which is necessary since also pure demineralized water needs to be used in the hot compartment to avoid scaling and fouling in there), without having the risk of contamination of the pure fluid present in the hot compartment. This solution provides amongst others the possibility to use the so called "hot tube sheet nitric acid cooler condenser" with less investment in production plants that do not have a closed loop with demineralized water. The hot compartment can in that case be used directly to (pre-)heat process air, boiler feed water, tail gas or any other fluid. This limits the number of device parts that needs to be used and do not require additional cooling water circulation pumps and buffer vessels.

[0017] In a possible embodiment of a heat exchange arrangement according to the present disclosure, the heat exchange arrangement comprises an expansion vessel which is configured to compensate variations of the pressure of the buffer fluid in the buffer compartment of the heat exchanger.

[0018] The expansion vessel is more in particular an accumulator.

[0019] In a specific embodiment of a heat exchange arrangement according to the present disclosure, the expansion vessel is configured to, in case the temperature of the tube-side fluid in the second part of the tubes in the buffer compartment increases, the temperature of the buffer fluid in the buffer compartment will also increase, thereby resulting in an increase of the pressure of the buffer fluid in the buffer compartment, removing buffer fluid from the buffer compartment to the expansion vessel, or in case the temperature of the tube-side fluid in the second part of the tubes in the buffer compartment decreases, the temperature of the buffer fluid in the buffer compartment will also decrease, and / or in case buffer fluid leaks out of the buffer compartment to first compartment and / or the second compartment, the pressure of the buffer fluid in the buffer compartment will also decrease, adding buffer fluid from the expansion vessel to the buffer compartment.

[0020] In a possible embodiment of a heat exchange arrangement according to the present disclosure, the heat exchange arrangement comprises a safety valve which is in fluid communication with the buffer compartment and which is configured to be opened when the pressure of the buffer fluid in the buffer compartment raises above a mechanical design pressure of the buffer compartment.

[0021] The expansion vessel is more in particular either directly connected to the buffer compartment by means of a separate connection point provided in the shell at the height of the buffer compartment, or connected to the buffer compartment inlet.

[0022] In an optional embodiment of a heat exchange arrangement according to the present disclosure, the heat exchange arrangement comprises a fluid supply at a higher pressure than the pressure in the buffer compartment which is configured to keep the pressure of the buffer fluid in the buffer compartment higher than the higher one of the pressure of the first and the second compartment, and which is configured to increase the pressure of the buffer fluid in the buffer compartment in case the pressure in the buffer compartment decreases too much.

[0023] In a specific embodiment of a heat exchange arrangement according to the present disclosure, the pressure in the buffer compartment is minimum 0.3 bar higher than the pressure in the cold and the hot compartment. In that case, there is an optimal sealing of the buffer compartment to avoid contamination of the different heating or cooling fluids present in the other compartments present in the shell of the heat exchanger.

[0024] In a specific embodiment of a heat exchange arrangement according to the present disclosure, heat exchange arrangement according to any one of claims 1 to 6, wherein the tube-side fluid is a hot fluid which needs to be cooled, having a dewpoint, and a decreasing first temperature while flowing through the tubes between the tube inlet and the tube outlet of each of the tubes, the first shell-side fluid is a first cooling fluid, the first compartment is a cold compartment, the first compartment inlet is a cold compartment inlet and the first compartment outlet is a cold compartment outlet, wherein the first cooling fluid has an increasing temperature when flowing through the cold compartment between the cold compartment inlet and the cold compartment outlet, the temperature of the first cooling fluid being lower than the dewpoint of the hot fluid flowing through the first part of the tubes at the height of the cold compartment inlet, and which can be lower or higher than the dewpoint of the tube-side fluid flowing through the tubes at the cold compartment outlet, the second shell-side fluid is a second cooling fluid, the second compartment is a hot compartment, the second compartment inlet is a hot compartment inlet and the second compartment outlet is a hot compartment outlet, the second cooling fluid having an increasing temperature when flowing through the hot compartment between the hot compartment inlet and the hot compartment outlet, the temperature of the second cooling fluid being lower than the dewpoint of the tube-side fluid flowing through the third part of the tubes at the height of the hot compartment inlet, and higher than the dewpoint of the tube-side fluid flowing through the third part of the the tubes at the height of the second compartment outlet, and wherein the buffer fluid has a buffer fluid temperature which is determined by the temperature of the tube-side fluid flowing through the second part of the tubes located in the buffer compartment, the buffer fluid temperature being below the boiling temperature of the buffer fluid.

[0025] In a more specific embodiment of a heat exchange arrangement according to the present disclosure, the tube-side fluid is a hot process gas to be cooled, and the second shell-side fluid and the buffer fluid are high-purity fluids.

[0026] The second shell-side fluid and the buffer fluid more in particular are in that case the same high-purity fluid.

[0027] In an optional embodiment of a heat exchange arrangement according to the present disclosure, the buffer compartment comprises a buffer compartment outlet which is configured to direct the buffer fluid to the first and / or the second compartment, where it is mixed with the second, respectively the second shell-side fluid in case the buffer fluid is the same as these fluids.

[0028] In a possible embodiment of a heat exchange arrangement according to the present disclosure, the shell and tube heat exchanger is a nitric acid cooler condenser, wherein the tube-side fluid is process gas comprising NO x , vapour, N 2 , oxygen O 2 , dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), the first shell-side fluid and the buffer fluid are demineralized water, and the second shell-side fluid is chosen from district heating water, industrial process water, feed water, water from a lake, a pond, a river, a canal, etc., or tail gas.

[0029] According to another aspect of the present disclosure, a nitric acid plant for production of nitric acid comprising an ammonia oxidizer, an absorption tower, and one or more heat exchange arrangements according to the present disclosure as described above is provided.

[0030] According to another aspect of the present disclosure, a method for heating or cooling a tube-side fluid, and for cooling or heating a first shell-side fluid and a second shell-side fluid in a heat exchanger of the shell and tube type, comprises the steps of entering a tube-side fluid with a first temperature, which needs to be heated or cooled, via a tube-side inlet in a front head of the heat exchanger, the front head being present between the tube-side inlet, and a front tube sheet, distributing the tube-side fluid over a plurality of tubes arranged in a shell inner space; flowing of the tube-side fluid through the plurality of tubes, thereby increasing, respectively decreasing the temperature of the tube-side fluid, exiting the heated or cooled tube-side fluid out of the plurality of tubes, collecting the heated or cooled tube-side fluid in a rear head which is formed between a rear tube sheet and the tube-side outlet, exiting the heated or cooled tube-side fluid out of the heat exchanger via the tube-side outlet, entering a first shell-side fluid with a temperature, the first shell-side fluid needing to be cooled or heated, via a first compartment inlet in a first compartment of the heat exchanger, wherein the first compartment is located between the rear tube sheet and a first intermediate tube sheet located in the shell inner space closer towards the front tube sheet in view of the rear tube sheet, flowing of the first shell-side fluid in the first compartment around the tubes with a pressure, thereby decreasing, respectively increasing the temperature of the first shell-side fluid, exiting the first cooled or heated shell-side fluid from the heat exchanger out of the first compartment via a first compartment outlet, entering a second shell-side fluid with a temperature, which needs to be cooled or heated, via a second compartment inlet of a second compartment of the heat exchanger, wherein the second compartment is located between a second intermediate tube sheet which is located in the shell inner space closer towards the front tube sheet in view of the first intermediate tube sheet, and the front tube sheet, flowing of the second shell-side fluid through the second compartment around a third part of the tubes with a pressure, thereby decreasing, respectively increasing the temperature of the second shell-side fluid; exiting the second cooled or heated shell-side fluid from the heat exchanger out of the second compartment via a second compartment outlet, entering a buffer fluid in a buffer compartment via a buffer compartment inlet, the buffer compartment being located between the first and the second intermediate tube sheet, and further containing the buffer fluid in the buffer compartment around the tubes, wherein the buffer fluid has a buffer fluid temperature which is determined by the temperature of the tube-side fluid flowing through the second part of the tubes in the buffer compartment, and wherein the buffer fluid is a fluid which does not chemically react producing insoluble compounds that precipitate as scale and does not comprise compounds that chemically react with the shell resulting in corrosion at the buffer fluid temperature, and maintaining the pressure of the buffer fluid further at a pressure higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment.

[0031] In a specific embodiment of a method according to the present disclosure, the heat exchanger of the shell and tube type is a nitric acid cooler condenser, wherein the tube-side fluid is a (hot) process gas which originates from an ammonia oxidizer of a nitric acid production plant, comprising NO x , water vapour, N 2 , oxygen O 2 , dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), and which needs to be cooled, and wherein the cooled process gas is a cooled two-phase fluid consisting of a liquid part with a certain amount of HNO 3 , HNO 2 , H 2 O, and N 2 O 4 , and a gaseous part with a reduced amount of nitrogen oxides (NO x ) and water vapour since there was absorption of the NO x in the condensed vapour, and a reduced amount of O 2 in view of the process gas entering the tubes, the same amount of N 2 , and dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), the first shell-side fluid is a less pure cooling fluid chosen from district heating water, industrial process water, feed water, water from a lake, a pond, a river, a canal, and tail gas, the second shell-side fluid is a high-purity cooling fluid, and the buffer fluid is the same high-purity fluid, more in particular demineralized (de-ionized) water, the first compartment is a cold compartment, wherein the first compartment inlet is a cold compartment inlet and the first compartment outlet is a cold compartment outlet, the second compartment is a hot compartment, wherein the second compartment inlet is a hot compartment inlet and the second compartment outlet is a hot compartment outlet, wherein the method comprises the following steps: entering (hot) process gas having a temperature in the front head via the tube-side inlet, distributing the process gas from the front head over the plurality of tubes via the tube inlets of the plurality of tubes, flowing of the process gas through the plurality of tubes, thereby decreasing the temperature of the process gas, wherein during the movement of the process gas through the tubes, NO is oxidized forming NO 2 , and absorption of the formed NO 2 in condensed vapour forming HNO 3 , exiting the cooled two-phase fluid out of the plurality of tubes via the tube outlets of the different tubes, collecting the cooled two-phase process fluid in the rear head, exiting the cooled two-phase process fluid which is collected in the rear head out of the heat exchanger via the tube-side outlet, entering the less pure cooling fluid in the cold compartment via the cold compartment inlet, flowing of the less pure cooling fluid through the cold compartment around the tubes with a pressure, thereby increasing the temperature of the first shell-side fluid, exiting the heated less pure cooling fluid out of the cold compartment via the cold compartment outlet, entering the high-purity cooling fluid, and more in particular demineralized water, in the hot compartment inlet via the hot compartment inlet, flowing of the high-purity cooling fluid, and more in particular demineralized water, through the hot compartment around the tubes with a pressure, thereby increasing the temperature of the high-purity cooling fluid, exiting the heated high-purity cooling fluid, and more in particular demineralized water, out of the heat exchanger via the hot compartment outlet, entering the high-purity buffer fluid, more in particular the demineralized water, in the buffer compartment via the buffer compartment inlet, and containing the high-purity buffer fluid in the buffer compartment around the tubes, maintaining the pressure of the high-purity buffer fluid higher than the higher one of the pressure of the less pure cooling fluid in the cold compartment and the pressure of the high-purity cooling fluid in the hot compartment. Brief description of the figures

[0032] The following description of the figure of a specific embodiment of a nitric acid cooler condenser according to the present disclosure is only given by way of example and is not intended to limit the present explanation, its application or use. In the figure, identical reference numerals refer to the same or similar parts and features. Figure 1 represents a schematic representation of a horizontal nitric acid cooler condenser according to the prior art, Figure 2 represents a schematic representation of a vertical nitric acid cooler condenser according to the prior art, Figure 3 represents a schematic representation of a nitric acid cooler condenser according to the present disclosure. Detailed description

[0033] A heat exchange arrangement according to the present disclosure, comprises one or more shell and tube heat exchangers can be oriented in a horizontal or a vertical way, comprises a front head, a rear head, and a shell with an outer shell encompassing a shell inner space between the front head and the rear head. In a horizontal shell and tube heat exchanger, the front head can be located left as well as right. In a vertical shell and tube heat exchanger, the front head can be located at the top as well as the bottom of the inner space, this depending on the application. Between the front head and the shell, a front tube sheet is present. Between the rear head and the shell, a rear tube sheet is present. The front head comprises a tube-side inlet, while the rear head comprises a tube-side outlet. In a horizontal heat exchanger, when the front head is located at the left side of the inner space, the rear head is located at the right side of the inner space, and vice versa. In a vertical heat exchanger, when the front head is located at the top side of the heat exchanger, the rear head is typically located at the bottom side of the heat exchanger, and vice versa. The front head is configured to enter a tube-side fluid which needs to be heated or cooled in the heat exchanger via the tube-side inlet. The rear head is configured to exit the heated or cooled tube-side fluid out of the heat exchanger via a tube-side outlet. In the shell inner space, a tube bundle comprising a plurality of tubes is located. The front and rear tube sheet both are configured to keep the plurality of tubes in place. More in particular, the tube sheets are configured as perforated plates which comprises a multitude of perforations which are each configured to protrude a tube through it. The tube-side fluid which is entered in the front head is then distributed to the different tubes through a tube inlet of each of the tubes. The tube-side fluid then flows through the tubes towards a tube outlet of each of the tubes. The cooled or heated tube-side fluid in subsequently collected in the rear head. During the passage of the tube-side fluid in the tubes between the tube inlet and the tube outlet of each of the tubes, in case the tube-side fluid needs to be cooled, the tube-side fluid releases heat to the wall of the tubes and subsequently to the shell-side fluid, thus having a decreasing temperature between the tube inlet and the tube outlet of the different tubes, while in case the tube-side fluid needs to be heated, the tube-side fluid takes up heat from the shell-side fluid via the wall of the tubes, thus having an increasing temperature between the tube inlet and the tube outlet of the different tubes. The cooled, respectively heated tube-side fluid then leaves the heat exchanger via the tube-side outlet.

[0034] Between the front and the rear tube sheet, two intermediate tube sheets are provided in the shell inner space. Also these intermediate tube sheets are more specifically in the form of perforated plates having perforations which each are configured to protrude one of the tubes through it. The distance between these two intermediate tube sheets depends on the size of the heat exchanger. The two intermediate sheets divide the shell inner space between the front and the rear tube sheet in three compartments, i.e. a first compartment, a second compartment and a buffer compartment in between the first and the second compartment. The first compartment is located between the front tube sheet and the first intermediate tube sheet. A first part of the tubes are located in this first compartment. The first compartment comprises a first compartment inlet configured to enter a first shell-side fluid to be cooled or heated in the heat exchanger, and a first compartment outlet configured to exit the first shell-side fluid out of the heat exchanger. The second compartment is located between the second intermediate tube sheet and the rear tube sheet. In the second compartment, a third part of the tubes are located. The second compartment comprises a second compartment inlet configured to receive a second shell-side fluid to be cooled or heated in the heat exchanger, and a second compartment outlet configured to exit the second shell-side fluid out of the heat exchanger via the tube-side outlet. The buffer compartment comprises a buffer compartment inner space wherein a second part of the tubes are located. The buffer compartment further comprises a buffer compartment inlet configured to enter a buffer fluid in the buffer compartment of the heat exchanger.

[0035] The first shell-side fluid flowing through the first compartment during operation of the chemical production plant has a pressure in the first compartment, and has a decreasing temperature in case the first shell-side fluid needs to be cooled, and an increasing temperature in case the first shell-side fluid needs to be heated, between the first compartment inlet and the first compartment outlet. The second shell-side fluid has a pressure in the second part which is different than the pressure of the first shell-side fluid in the first compartment, and has a decreasing temperature in case the second shell-side fluid needs to be cooled, and an increasing temperature in case the second shell-side fluid needs to be heated, between the second compartment inlet and the second compartment outlet.

[0036] The buffer compartment is further configured to contain the buffer fluid around the tubes in the buffer compartment, therewith maintaining a pressure which is higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment. The buffer fluid is typically a high-purity fluid which does not chemically react producing insoluble compounds that precipitate as scale and does not comprise compounds that chemically react with the shell resulting in corrosion at the buffer fluid temperature. The buffer fluid has a temperature which is dependent of the temperature of the fluid inside the second part of the tubes (i.e. the part of the tubes located in the buffer compartment). The buffer fluid will thus automatically get that temperature. The buffer fluid temperature during operation varies along with the fluid temperature inside the second part of the tubes. The buffer fluid contained in the buffer compartment during operation of the chemical production plant has a pressure which is higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment. More in particular, the pressure of the buffer fluid in the buffer compartment needs to be at least 0.3 bar higher than the pressure of the first shell-side fluid in the first compartment and the pressure of the second shell-side fluid in the second compartment.

[0037] In order to compensate the variations of the pressure of the buffer fluid in the buffer compartment, the heat exchange arrangement comprises an expansion vessel, more in particular an accumulator, which is configured to add an amount of buffer fluid to the buffer compartment in case the pressure decreases or to remove buffer fluid from the buffer compartment of the heat exchanger in case the pressure increases. The expansion vessel is more in particular configured to remove buffer fluid from the buffer compartment to the expansion vessel in case the temperature of the tube-side fluid in the second part of the tubes in the buffer compartment increases, the temperature of the buffer fluid in the buffer compartment will also increase, thereby resulting in an increase in the pressure of the buffer fluid in the buffer compartment. In case the temperature of the tube-side fluid in the second part of the tubes in the buffer compartment however decreases, the temperature of the buffer fluid in the buffer compartment will also decrease, through which the pressure of the buffer fluid in the buffer compartment will also decrease, in which case the expansion vessel will add buffer fluid from the expansion vessel to the buffer compartment. The same counts in case buffer fluid leaks out of the buffer compartment to the first compartment and / or the second compartment. Then also the pressure of the buffer fluid in the buffer compartment will decrease and the expansion vessel will add buffer fluid to the buffer compartment. It is remarked that the added or removed amounts of buffer fluid are only small. The expansion vessel, more in particular the accumulator, can be directly connected to the buffer compartment by means of a separate connection point provided in the shell at the height of the buffer compartment, or is connected to the buffer compartment inlet.

[0038] Furthermore, a safety valve is provided which is in fluid communication with the buffer compartment and which is configured to be opened when the pressure of the buffer fluid in the buffer compartment raises above a mechanical design pressure of the buffer compartment.

[0039] In a more specific embodiment, the tube-side fluid is a hot fluid, having a certain dewpoint, which enters the tubes and needs to be cooled, thus having a decreasing temperature between the tube inlet and the tube outlet of each of the tubes. The first shell-side fluid is a first cooling fluid, the first compartment is a cold compartment, the first compartment inlet is a cold compartment inlet and the first compartment outlet is a cold compartment outlet, wherein the first cooling fluid enters the cold compartment via the cold cooling fluid inlet and exits the cold compartment via the cold compartment outlet, having an increasing temperature during its passage in the cold compartment between the cold compartment inlet and the cold compartment outlet. The temperature of the first cooling fluid is lower than the dewpoint of the hot fluid flowing through the first part of the tubes located in the cold compartment at the height of the cold compartment inlet, and has a temperature which can be lower or higher than the dewpoint of the tube-side fluid flowing through the tubes at the cold compartment outlet. The second shell-side fluid is a second cooling fluid, the second compartment is a hot compartment, the second compartment inlet is a hot compartment inlet and the second compartment outlet is a hot compartment outlet, wherein the second cooling fluid enters the hot compartment via the hot compartment inlet and exits the second compartment via the hot compartment outlet. The second cooling fluid has an increasing temperature during its passage through the hot compartment between the hot compartment inlet and the hot compartment outlet, and has a temperature which is lower than the dewpoint of the process gas flowing through the third part of the tubes located in the hot compartment at the hot compartment outlet, but higher than the dewpoint of the process gas flowing in the third part of the tubes at the hot compartment outlet. The buffer fluid has a fluid temperature which is determined by the temperature of the tube-side fluid flowing in the second part of the tubes located in the buffer compartment. The temperature of the buffer fluid can vary with varying temperatures of the tube-side fluid in the second part of the tubes. The temperature of the buffer fluid is automatically adapted when the temperature of the tube-side fluid in the second part of the tubes in the buffer compartment changes. The pressure in each case must be high enough such that the corresponding boiling temperature of the buffer fluid is higher than the temperature that the buffer fluid in the buffer compartment has during operation. In this configuration, the second shell-side fluid and the buffer fluid are more in particular the same high-purity fluid.

[0040] The heat exchange arrangement according to the present disclosure is very suitable to be used in any production plant where two fluids need to exchange heat using one or more heat exchangers of the shell and tube type. In a nitric acid production process, for instance, shell and tube heat exchangers according to the present disclosure can be used as nitric acid cooler condensers to cool a process gas coming from an ammonia oxidizer. It is remarked that the shell and tube heat exchanger according to the present disclosure can however also be used in other applications in a nitric acid production plant to cool and heat different fluids. The shell and tube heat exchanger according to the present disclosure can also be applied in other chemical production productions then nitric acid production process to heat or cool different fluids. An ammonia oxidizer is a device configured for converting ammonia (NH 3 ) and oxygen (O 2 ) into process gas which serves as the precursor gases for nitric acid synthesis. An absorption tower is a device configured for mixing cooled process gas comprising nitrogen oxides (NO x ) with water to obtain nitric acid and a tail gas.

[0041] In case the heat exchanger is a nitric acid cooler condenser, then the different fluids are as follows: the tube-side fluid is process gas originating from an ammonia oxidizer of a nitric acid production plant comprising NO x , water vapour, N 2 , oxygen O 2 , dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), the second shell-side fluid and the buffer fluid are demineralized water, and the first shell-side fluid is chosen from district heating water, industrial process water, feed water, water from a lake, a pond, a river, a canal, and tail gas. The following process parameters typically apply for nitric acid cooler condensers according to the present disclosure. It is however remarked that all the parameters are nitric acid production plant specific. The pressure of the buffer fluid is minimum 0.3 bar higher than the higher one of the pressure of the first cooling fluid in the cold compartment and the second cooling fluid in the hot compartment. The process gas in the tubes and the cooling fluids in the cold and the hot compartment typically have a pressure of between 1.0 bar and 16.0 bar. The process gas in the plurality of tubes more in particular has a temperature of between 90 °C and 200 °C and a dewpoint of between 55°C and 130°C. The temperature of the second cooling fluid in the cold compartment more in particular is between 15 °C and 50 °C. The temperature of the second cooling fluid at the hot compartment inlet of the hot compartment is typically between 15 °C and 60 °C, while the temperature of the second cooling fluid at the hot compartment outlet of the hot compartment is higher than the dewpoint of the process gas. If the latter is not the case, there is a high risk of condensation and re-boiling of the process gas flowing through the tubes leading to corrosion inside the tubes in the tube sheet and further in the tubes, and at the tube inlet after the front tube sheet. The distance between the intermediate tube sheets typically amounts between 0.10 m and 0.50 m, depending on the size of the heat exchanger.

[0042] An example of a heat exchange arrangement with a vertically oriented nitric acid cooler condenser according to the present disclosure is shown in Figure 3. It should be clear that this is only an exemplary embodiment of a heat exchange arrangement according to the present disclosure, and should not be limiting to the scope of protection of the present disclosure. The heat exchange arrangement according to the present disclosure comprises a nitric acid cooler condenser 200, which comprises a front head 102a which comprises a process gas inlet 101a, and a rear head 102c which comprises a two-phase fluid outlet 101b. Between the front head 102a and the rear head 102c, a shell 102b with an inner space is located. The shell 102b is separated from the front head 102a through a front tube sheet 104, while the shell 102b is separated from the rear head 102c through a rear tube sheet 106. Between the front and the rear tube sheet, 104, 106, two intermediate tube sheets 105a, 105b are located in the inner space of the shell 102b. Each of the tube sheets 104, 105a, 105, 106 comprise perforations configured to accommodate the tubes 103. The plurality of tubes 103 are configured to conduct the tube-side fluid vertically through it between the front head 102a and the rear head 102d during operation of the heat exchanger. In this embodiment, the first intermediate tube sheet 105a is positioned above the second intermediate tube sheet 105b. The first intermediate tube sheet 105a and the second intermediate tube sheet 105b create a cold compartment 1021, a compartment 1022, and a buffer compartment 1023 in the inner space of the shell. In this embodiment, the cold compartment 1021 is located between the (upper side of the) rear tube sheet 106 and the (lower side of the) second intermediate tube sheet 105b. The cold compartment 102b comprises a cold compartment inlet 131 configured to enter a first "less pure" cooling fluid as described above, in the cold compartment 1021, and a cold compartment outlet 112 configured to exit the second heated cooling fluid out of the cold compartment 1021. The cold compartment 1021 is configured for passing the first less pure cooling fluid through the cold compartment 1021 around the first part of the tubes 103 located in this first compartment 1021, between the first compartment inlet 131 and the first compartment outlet 112, in the meantime cooling the process gas flowing through the first part of the tubes 103. In this embodiment, the hot compartment 1022 is positioned between the (upper side of the) first intermediate tube sheet 105a and the (lower side of the) front tube sheet 104. The hot compartment 1022 comprises a hot compartment inlet 132 configured to receive a second pure cooling fluid, more in particular in the form of demineralized water and a hot compartment outlet 115 configured to exit the pure cooling fluid out of the hot compartment 102c. The hot compartment 1022 is configured for passing the second pure cooling fluid through the hot compartment 1022 between the hot compartment inlet 132 and the hot compartment outlet 115 around the third part of the tubes 103 located in the hot compartment 1022, in the meantime cooling the process fluid flowing through the third part of the tubes 103. The buffer compartment 1023 is located between (the lower side of) the first intermediate tube sheet 105a and (the upper side) of the second intermediate tube sheet 105b. The buffer compartment 1023 comprises a buffer compartment inlet 133 configured to enter a pressurized pure buffer fluid, more in particular in the form of demineralized water, in the buffer compartment 1023. The buffer fluid is pressurized by supplying a pure fluid with a higher pressure than the pressure of the second pure cooling fluid in the hot compartment and the less pure first cooling fluid in the cold compartment. Furthermore, an accumulator 130 is provided which is fluidically connected with the buffer compartment 1023 and is configured to compensate pressure variations of the buffer fluid in the buffer compartment 1023 by adding or removing buffer fluid from the buffer compartment 1023. A pressure transmitter 140 is in fluid communication with the buffer compartment 1023 and is configured to measure the pressure of the buffer fluid in the buffer compartment 1023. The accumulator 130 is configured to compensate variations in the pressure in the buffer compartment 102e. Furthermore, a pressure (safety) relief valve 143 and a pressure controller 141 are present which both have a certain set pressure. The pressure controller 141 is configured to control a valve 142 (on / off valve or control valve). When the pressure in the buffer compartment 1023 exceeds the set pressure of the safety valve 143, then the safety valve 143 opens until the pressure is below the set pressure. If the pressure in the buffer compartment 1023 decreases below the setpoint of the pressure controller 141, the valve 142 is opened until the pressure in the buffer compartment 1023 is restored.

[0043] It is remarked that the same configuration as described above could be applied to a vertically oriented nitric acid cooler condenser where the front head 102a is located at the bottom of the heat exchanger 200, and the rear head is then located at top of the heat exchanger 200. Then the process gas inlet 101a would also be located at the bottom and the process gas outlet 101b at the top of the heat exchanger 200. Furthermore, the same configuration as described above could be applied to a horizontally oriented nitric acid cooler condenser. In that case however, the tube-side inlet 101a is located at the left or the right side of the shell 101, and the tube-side outlet 101b is located at the opposite side of the shell 101. The tubes 103 are then horizontally oriented. The front tube sheet 104 is then located in the inner space 102 at the left side thereof if the tube-side inlet 101a is located at the left side, and at the right side thereof if the tube-side inlet 101a is located at the right side. The tube outlet sheet 106 is then located at the opposite side. The plurality of tubes 103 are then configured to conduct the process horizontally through the tubes 103 located in the inner space of the shell 102b between the front head 102a and the rear head 102c during operation of the heat exchanger. In case the tube-side inlet 101a is located at the left side, then the first intermediate tube sheet 105a is positioned at the right side of the second intermediate tube sheet 105b. In case the tube-side inlet 101a is located at the right side, then the first intermediate tube sheet 105a is positioned at the left side of the second intermediate tube sheet 105b.

[0044] In the method according to the present disclosure for heating or cooling a tube-side fluid and for cooling or heating a second shell-side fluid in a heat exchanger of the shell and tube type, first, a tube-side fluid with a first temperature, which needs to be heated or cooled, is entered via a tube-side inlet in a front head of the heat exchanger, the front head being present between the tube-side inlet, and a front tube sheet. The tube-side fluid is subsequently distributed over a plurality of tubes arranged in a shell inner space, whereafter the tube-side fluid flows through the plurality of tubes, thereby increasing, respectively decreasing the temperature of the tube-side fluid. The cooled or heated tube-side fluid then exits the plurality of tubes, and are subsequently collected the in a rear head which is formed between a rear tube sheet and the tube-side outlet. The heated or cooled tube-side fluid finally exits the heat exchanger via the tube-side outlet. Furthermore, a first shell-side fluid with a temperature, which needs to be cooled or heated, enters a first compartment of the heat exchanger via a first compartment. The first compartment is located between the rear tube sheet and a first intermediate tube sheet located in the shell inner space near the tube-side inlet. The first shell-side fluid will then flow in the first compartment around the tubes with a pressure, thereby decreasing, respectively increasing the temperature of the first shell-side fluid, and finally exit the heat exchanger out of the first compartment via a first compartment outlet. Also, a second shell-side fluid with a temperature, which needs to be cooled or heated, enters a second compartment of the heat exchanger via a second compartment inlet. The second compartment is located between a second intermediate tube sheet which is located in the shell inner space near the tube-side outlet, and the front tube sheet. The second shell-side fluid subsequently flows through the second compartment around the tubes with a pressure, thereby decreasing, respectively increasing the temperature of the second shell-side fluid, whereafter it exits the second cooled or heated shell-side fluid from the heat exchanger out of the second compartment via a second compartment outlet. A buffer fluid enters a buffer compartment via a buffer compartment inlet, the buffer compartment being located between the first and the second intermediate tube sheet, maintaining the pressure of the buffer fluid further at a pressure higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment. The buffer fluid is then further contained in the buffer compartment around the tubes. As already mentioned above, the buffer fluid has a buffer fluid temperature which is determined by the temperature of the tube-side fluid flowing through the second part of the tubes in the buffer compartment. The buffer fluid is a fluid which does not chemically react producing insoluble compounds that precipitate as scale and does not comprise compounds that chemically react with the shell resulting in corrosion at the buffer fluid temperature. It is remarked that during steady operation, there is almost no heat exchange between the buffer fluid and the tube-side fluid flowing through the second part of the tubes which are housed in the buffer compartment. During operation, the buffer fluid is automatically heated until the temperature thereof equalizes to a temperature which is determined by the temperature of the tube-side fluid flowing through the tubes at the interface between the second compartment and the buffer compartment.

[0045] In case the shell and tube heat exchanger is a nitric acid cooler condenser, then the tube-side fluid is a process gas which originates from an ammonia oxidizer of a nitric acid production plant, comprising NO x , water vapour, N 2 , oxygen O 2 , dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), and which needs to be cooled, and wherein the cooled process gas is a cooled two-phase fluid consisting of a liquid part with a certain amount of HNO 3 , HNO 2 , H 2 O, and N 2 O 4 , and a gaseous part with a reduced amount of nitrogen oxides (NO x ) and water vapour since there was absorption of the NO x in the condensed vapour, and a reduced amount of O 2 in view of the process gas entering the tubes, the same amount of N 2 , and dinitrogen oxide (N 2 O), dinitrogen tetra oxide (N 2 O 4 ), nitrous acid (HNO 2 ) and nitric acid (HNO 3 ), the first shell-side fluid is a cooling fluid chosen from district heating water, industrial process water, feed water, water from a lake, a pond, a river, a canal, and tail gas, the second shell-side fluid and the buffer fluid are high-purity fluids, more in particular demineralized (de-ionized) water, the first compartment is a cold compartment, wherein the first compartment inlet is a cold compartment inlet and the first compartment outlet is a cold compartment outlet, and the second compartment is a hot compartment, wherein the second compartment inlet is a hot compartment inlet and the second compartment outlet is a hot compartment outlet. In such a method, first, hot process gas with a composition as mentioned above and having a temperature is entered in the front head through the tube-side inlet, followed by the distribution of the process gas out of the rear head over the plurality of tubes via the tube inlets of the different tubes. The process gas subsequently flows through the plurality of tubes, thereby decreasing the temperature of the process gas, wherein during the movement of the process gas through the tubes, NO is oxidized forming NO 2 . The formed NO 2 is absorbed in condensed vapour, forming HNO 3 . After forming a first condensate, oxidation and absorption happen in parallel. Thereafter, the cooled two-phase fluid will flow out of the plurality of tubes via the tube outlets of the different tubes, whereafter the two-phase fluid is collected in the rear head, and finally is exited out of the heat exchanger via the tube-side outlet. In order to cool the process gas, the less pure first cooling fluid is entered in the cold compartment via the cold compartment inlet, whereafter it will flow through the cold compartment around the tubes with a pressure, thereby increasing the temperature of the less pure first cooling fluid. Finally, the heated less pure first cooling fluid is exited out of the cold compartment via the cold compartment outlet. Also, the high-purity second cooling fluid, and more in particular demineralized water, is entered in the hot compartment inlet via the hot compartment inlet whereafter it will flow through the hot compartment around the tubes with a pressure, thereby increasing the temperature of the high-purity second cooling fluid. The heated second cooling fluid is then exited out of the hot compartment via the hot compartment outlet. Finally, also the high-purity buffer fluid, more in particular the demineralized water, enters in the buffer compartment inlet of the buffer compartment, which is then contained in the buffer compartment around the tubes. Finally, the pressure of the high-purity buffer fluid is maintained higher than the pressure of the less pure cooling fluid in the cold compartment and the pressure of the high-purity cooling fluid in the hot compartment.

Claims

1. Heat exchange arrangement, comprising a heat exchanger of the shell and tube type, a horizontal shell and tube heat exchanger comprising - a front head with a tube-side inlet which is configured to enter a tube-side fluid which needs to be cooled or heated in the heat exchanger, - a rear head with a tube-side outlet which is configured to exit the cooled or heated tube-side fluid out of the heat exchanger, - a shell comprising a shell inner space located between the front head and the rear head, wherein a plurality of tubes are located, wherein the shell is separated from • the front head by means of a front tube sheet, and • the rear head by means of a rear tube sheet, wherein the front tube sheet and the rear tube sheet are configured to hold the tubes in place, wherein the front head is further configured to enter the tube-side fluid in the plurality of tubes via a tube inlet of each of the tubes, and wherein the rear head is further configured to collect the tube-side fluid which exits the plurality of tubes via a tube outlet of each of the tubes, wherein the shell and tube heat exchanger comprises - a first and a second intermediate tube sheet located in the shell inner space between the front and the rear tube sheet, which are both configured to keep the plurality of tubes in place, - a first compartment between the rear tube sheet and the first intermediate tube sheet, wherein a first part of the tubes are located, and comprising a first compartment inlet configured to enter a first shell-side fluid to be cooled or heated in the first compartment, and a first compartment outlet configured to exit the cooled or heated first shell-side fluid out of the first compartment, and comprising a first compartment inner space configured to let the first shell-side fluid flow through it between the first compartment inlet and the first compartment outlet with a pressure, wherein the first shell-side fluid has a decreasing, respectively an increasing first temperature when flowing through the first compartment between the first compartment inlet and the first compartment outlet, and the tube-side fluid has an increasing, respectively a decreasing temperature during the passage thereof through the first part of the tubes, - a second compartment between the front tube sheet and the second intermediate tube sheet, and comprising a third part of the tubes, and comprising a second compartment inlet configured to enter a second shell-side fluid to be cooled or heated in the second compartment, and a second compartment outlet configured to exit the cooled or heated second shell-side fluid out of the second compartment, and comprising a second compartment inner space which is configured to let a second shell-side fluid flow through it between the second compartment inlet and the second compartment outlet with a pressure which is different than the pressure of the first shell-side fluid in the first compartment, and has a decreasing, respectively an increasing temperature when flowing through the second compartment between the second compartment inlet and the second compartment outlet, and the tube-side fluid has an increasing, respectively a decreasing temperature during the passage of the tube-side fluid through the third part of the tubes, and - a buffer compartment between the first intermediate sheet and the second intermediate sheet, comprising a buffer compartment inner space comprising a second part of the tubes, and comprising a buffer compartment inlet configured to enter a buffer fluid in the buffer compartment and subsequently keep the buffer fluid contained in the buffer compartment around the second part of the tubes, wherein the buffer fluid has a buffer fluid temperature which is determined by the temperature of the tube-side fluid flowing through the second part of the tubes, and wherein the buffer fluid in the buffer compartment is a fluid which does not chemically react producing insoluble compounds that precipitate as scale and does not comprise compounds that chemically react with the shell resulting in corrosion at the buffer fluid temperature, wherein the buffer fluid has a pressure which is higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment.

2. Heat exchange arrangement according to claim 1, wherein the heat exchange arrangement comprises an expansion vessel, more in particular an accumulator, which is configured to compensate pressure variations of the buffer fluid in the buffer compartment of the heat exchanger.

3. Heat exchange arrangement according to claim 2, wherein the expansion vessel is configured to, - in case the temperature of the tube-side fluid in the tubes at the interface of the first compartment and the buffer compartment increases, the temperature of the buffer fluid in the buffer compartment will also increase, thereby resulting in an increase of the pressure of the buffer fluid in the buffer compartment, remove buffer fluid from the buffer compartment towards to the expansion vessel, or - in case the temperature of the tube-side fluid in the tubes at the interface of the first compartment and the buffer compartment decreases, the temperature of the buffer fluid in the buffer compartment will also decrease, and / or in case buffer fluid leaks out of the buffer compartment to first compartment and / or the second compartment, the pressure of the buffer fluid in the buffer compartment will also decrease, add buffer fluid from the expansion vessel to the buffer compartment.

4. Heat exchange arrangement according to any one of claims 1 to 3, wherein the heat exchange arrangement comprises a safety valve which is in fluid communication with the buffer compartment and which is configured to be opened when the pressure of the buffer fluid in the buffer compartment raises above a mechanical design pressure of the buffer compartment.

5. A heat exchanger of the shell and tube type according to any one of claims 2 to 4, wherein the expansion vessel is directly connected to the buffer compartment by means of a separate connection point provided in the shell at the height of the buffer compartment, or is connected to the buffer compartment inlet.

6. A heat exchange arrangement according to any one of claims 1 to 5, wherein the pressure of the buffer fluid in the buffer compartment is at least 0.3 bar higher than the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment.

7. A heat exchange arrangement according to any one of claims 1 to 6, wherein - the tube-side fluid is a hot fluid which needs to be cooled, having a dewpoint, and a decreasing first temperature while flowing through the tubes between the tube inlet and the tube outlet of each of the tubes, - the first shell-side fluid is a first cooling fluid, the first compartment is a cold compartment, the first compartment inlet is a cold compartment inlet and the first compartment outlet is a cold compartment outlet, wherein the first cooling fluid has an increasing temperature when flowing through the cold compartment between the cold compartment inlet and the cold compartment outlet, the temperature of the first cooling fluid being lower than the dewpoint of the hot fluid flowing through the first part of the tubes at the height of the cold compartment inlet, and which can be lower or higher than the dewpoint of the tube-side fluid flowing through the tubes at the cold compartment outlet, - the second shell-side fluid is a second cooling fluid, the second compartment is a hot compartment, the second compartment inlet is a hot compartment inlet and the second compartment outlet is a hot compartment outlet, the second cooling fluid having an increasing temperature when flowing through the hot compartment between the hot compartment inlet and the hot compartment outlet, the temperature of the second cooling fluid being lower than the dewpoint of the tube-side fluid flowing through the third part of the tubes at the height of the hot compartment inlet, and higher than the dewpoint of the tube-side fluid flowing through the third part of the the tubes at the height of the second compartment outlet, and wherein the buffer fluid has a buffer fluid temperature which is determined by the temperature of the tube-side fluid flowing through the second part of the tubes located in the buffer compartment, the buffer fluid temperature being below the boiling temperature of the buffer fluid.

8. A heat exchange arrangement according to claim 7, wherein - the tube-side fluid is a hot process gas to be cooled, - the first shell-side fluid is a high-purity cooling fluid, and - the buffer fluid being a high-purity fluid, wherein the first shell-side fluid and the buffer fluid more in particular are the same high-purity fluid.

9. A heat exchange arrangement according to any one of the preceding claims, wherein the buffer compartment comprises a buffer compartment outlet which is configured to direct the buffer fluid to the first and / or the second compartment, where it will be mixed with the second, respectively the second shell-side fluid in case the buffer fluid is the same as these fluids.

10. A heat exchange arrangement according to any one of the preceding claims, wherein the heat exchanger is a nitric acid cooler condenser, and wherein - the tube-side fluid is hot process gas originating from an ammonia oxidizer of a nitric acid production plant comprising NOx, water vapour, N2, oxygen O2, dinitrogen oxide (N2O), dinitrogen tetra oxide (N2O4), nitrous acid (HNO2) and nitric acid (HNO3), the hot process gas needing to be cooled or heated, - the first shell-side fluid and the buffer fluid are demineralized water, and - the second shell-side fluid is chosen from district heating water, industrial process water, feed water, water from a lake, a pond, a river, a canal, and tail gas.

11. A nitric acid plant for production of nitric acid comprising an ammonia oxidizer, an absorption tower, and one or more heat exchange arrangements according to any one of claims 1 to 10.

12. A method for heating or cooling a tube-side fluid, and for cooling or heating a first shell-side fluid and a second shell-side fluid in a heat exchanger of the shell and tube type, the method comprising the steps of: - entering a tube-side fluid with a first temperature, which needs to be heated or cooled, via a tube-side inlet in a front head of the heat exchanger, the front head being present between the tube-side inlet, and a front tube sheet, - distributing the tube-side fluid over a plurality of tubes arranged in a shell inner space; - flowing of the tube-side fluid through the plurality of tubes, thereby increasing, respectively decreasing the temperature of the tube-side fluid, - exiting the heated or cooled tube-side fluid out of the plurality of tubes, - collecting the heated or cooled tube-side fluid in a rear head which is formed between a rear tube sheet and the tube-side outlet, - exiting the heated or cooled tube-side fluid out of the heat exchanger via the tube-side outlet, - entering a first shell-side fluid with a temperature, the first shell-side fluid needing to be cooled or heated, via a first compartment inlet in a first compartment of the heat exchanger, wherein the first compartment is located between the rear tube sheet and a first intermediate tube sheet located in the shell inner space closer towards the front tube sheet in view of the rear tube sheet, - flowing of the first shell-side fluid in the first compartment around the tubes with a pressure, thereby decreasing, respectively increasing the temperature of the first shell-side fluid, - exiting the first cooled or heated shell-side fluid from the heat exchanger out of the first compartment via a first compartment outlet, - entering a second shell-side fluid with a temperature, which needs to be cooled or heated, via a second compartment inlet of a second compartment of the heat exchanger, wherein the second compartment is located between a second intermediate tube sheet which is located in the shell inner space closer towards the front tube sheet in view of the first intermediate tube sheet, and the front tube sheet, - flowing of the second shell-side fluid through the second compartment around a third part of the tubes with a pressure, thereby decreasing, respectively increasing the temperature of the second shell-side fluid; - exiting the second cooled or heated shell-side fluid from the heat exchanger out of the second compartment via a second compartment outlet, - entering a buffer fluid in a buffer compartment via a buffer compartment inlet, the buffer compartment being located between the first and the second intermediate tube sheet, and - further containing the buffer fluid in the buffer compartment around the tubes, wherein the buffer fluid has a buffer fluid temperature which is determined by the temperature of the tube-side fluid flowing through the second part of the tubes in the buffer compartment, and wherein the buffer fluid is a fluid which does not chemically react producing insoluble compounds that precipitate as scale and does not comprise compounds that chemically react with the shell resulting in corrosion at the buffer fluid temperature, and - maintaining the pressure of the buffer fluid further at a pressure higher than the higher one of the pressure of the first shell-side fluid in the first compartment and the second shell-side fluid in the second compartment.

13. The method according to claim 12, wherein the heat exchanger of the shell and tube type is a nitric acid cooler condenser, and - the tube-side fluid is a (hot) process gas which originates from an ammonia oxidizer of a nitric acid production plant, comprising NOx, water vapour, N2, oxygen O2, dinitrogen oxide (N2O), dinitrogen tetra oxide (N2O4), nitrous acid (HNO2) and nitric acid (HNO3), and which needs to be cooled, and wherein the cooled process gas is a cooled two-phase fluid consisting of a liquid part with a certain amount of HNO3, HNO2, H2O, and N2O4, and a gaseous part with a reduced amount of nitrogen oxides (NOx) and water vapour since there was absorption of the NOx in the condensed vapour, and a reduced amount of O2 in view of the process gas entering the tubes, the same amount of N2, and dinitrogen oxide (N2O), dinitrogen tetra oxide (N2O4), nitrous acid (HNO2) and nitric acid (HNO3), - the first shell-side fluid is a less pure cooling fluid chosen from district heating water, industrial process water, feed water, water from a lake, a pond, a river, a canal, and tail gas, - the second shell-side fluid is a high-purity cooling fluid, and the buffer fluid is the same high-purity fluid, more in particular demineralized (de-ionized) water, - the first compartment is a cold compartment, wherein the first compartment inlet is a cold compartment inlet and the first compartment outlet is a cold compartment outlet, - the second compartment is a hot compartment, wherein the second compartment inlet is a hot compartment inlet and the second compartment outlet is a hot compartment outlet, wherein the method comprises the following steps: - entering (hot) process gas having a temperature in the front head via the tube-side inlet, - distributing the process gas from the front head over the plurality of tubes via the tube inlets of the plurality of tubes, - flowing of the process gas through the plurality of tubes, thereby decreasing the temperature of the process gas, wherein during the movement of the process gas through the tubes, NO is oxidized forming NO2, and absorption of the formed NO2 in condensed vapour forming HNO3, - exiting the cooled two-phase fluid out of the plurality of tubes via the tube outlets of the different tubes, - collecting the cooled two-phase process fluid in the rear head, - exiting the cooled two-phase process fluid which is collected in the rear head out of the heat exchanger via the tube-side outlet, - entering the less pure cooling fluid in the cold compartment via the cold compartment inlet, - flowing of the less pure cooling fluid through the cold compartment around the tubes with a pressure, thereby increasing the temperature of the first shell-side fluid, - exiting the heated less pure cooling fluid out of the cold compartment via the cold compartment outlet, - entering the high-purity cooling fluid, and more in particular demineralized water, in the hot compartment inlet via the hot compartment inlet, - flowing of the high-purity cooling fluid, and more in particular demineralized water, through the hot compartment around the tubes with a pressure, thereby increasing the temperature of the high-purity cooling fluid, - exiting the heated high-purity cooling fluid, and more in particular demineralized water, out of the heat exchanger via the hot compartment outlet, - entering the high-purity buffer fluid, more in particular the demineralized water, in the buffer compartment via the buffer compartment inlet, and containing the high-purity buffer fluid in the buffer compartment around the tubes, - maintaining the pressure of the high-purity buffer fluid higher than the higher one of the pressure of the less pure cooling fluid in the cold compartment and the pressure of the high-purity cooling fluid in the hot compartment.

Images