Description:Technical Field

[0001] The present disclosure relates to a multiple effect evaporation system. More particularly, the present disclosure relates to a multiple effect evaporation system for distillation or concentration of corrosive liquids and solutions.

Background

[0002] Corrosive liquids (or solutions), such as caustic soda (sodium hydroxide, NaOH) and caustic potash (potassium hydroxide, KOH), are essential chemicals used across various industries. They are primarily produced through the chloralkali process and then concentrated through evaporation. To reduce energy consumption and carbon dioxide emissions, multiple effect evaporation systems are generally used for concentrating these corrosive liquids. However, current multiple effect evaporation systems are limited to 2-4 effects due to temperature and pressure limitations, thereby making additional effects costly.

Summary

[0003] In an aspect, a multiple effect evaporation system is disclosed. Said multiple effect evaporation system comprises in sequence, a plurality of effects. Each effect of the plurality of effects comprises a heat exchanger and a gas-liquid separator. The heat exchanger includes a shell body defining a working fluid inlet, a working fluid outlet, a worked fluid inlet, a worked fluid outlet, and a volume; and a plurality of silicon carbide mono blocks sequentially arranged within the volume. Each silicon carbide block defines a plurality of first channels configured to communicate a working fluid between the working fluid inlet and the working fluid outlet and a plurality of second channels configured to communicate a worked fluid between the worked fluid inlet and the worked fluid outlet. The plurality of first and second channels are arranged to facilitate heat transfer from the working fluid to the worked fluid. Further, the gas-liquid separator is configured to receive the worked fluid from the worked fluid outlet, separate the worked fluid into a gas-phase substance and a liquid-phase substance, and direct the gas-phase substance and the liquid-phase substance as a working fluid and a worked fluid, respectively, to a subsequent effect of the plurality of effects.

[0004] In another aspect, a method for concentrating a solution using the disclosed multiple effect evaporation system is described. The method comprises feeding the solution as the worked fluid and a heating medium as the working fluid to the heat exchanger of an initial effect of the plurality of effects. Next, the solution is subjected to successive heat exchange followed by separation into the gas phase substance and the liquid phase substance in the heat exchanger and the gas-liquid separator, respectively, in the plurality of effects to obtain a concentrated solution from a final effect of the plurality of effects.

Brief Description of the Drawings

[0005] The accompanying figures, where same reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention and explain various principles and advantages of those embodiments.

[0006] FIG. 1 illustrates the exemplary multiple effect evaporation system, in accordance with some embodiments of the present disclosure.

[0007] FIG. 2 illustrates an exemplary heat exchanger for an exemplary multiple effect evaporation system, in accordance with some embodiments of the present disclosure;

[0008] FIG. 3 illustrates a cut view of a silicon carbide mono block and a sealing member for the heat exchanger of FIG. 2, in accordance with some embodiments of the present disclosure;

[0009] FIG. 4 is an exploded view depicting the silicon carbide mono block and the sealing member of FIG. 3, in accordance with some embodiments of the present disclosure;

[0010] FIG. 5 illustrates an exemplary multiple effect evaporation system, in accordance with another embodiment of the present disclosure; and

[0011] FIG. 6 illustrates the exemplary multiple effect evaporation system, in accordance with some embodiments of the present disclosure.

[0012] Skilled artisans will appreciate that the elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the embodiments.

Detailed Description

[0013] Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts.

[0014] Referring to Fig. 1, an exemplary multiple effect evaporation system 100 is illustrated. The multiple effect evaporation system 100 is designed to be applied as a heat transfer equipment, which finds application in for distillation or concentration of liquids and solutions, and in particular for corrosive liquids and solutions. Examples of the liquids and solutions include, but may not be limited to, a corrosive aqueous solution selected from the group consisting of caustic (NaOH) solution, potassium (KOH) hydroxide solutions, aqueous hydrochloric acid (HCl), and sulfuric acid (H2SO4). In these environments, the multiple effect evaporation system 100 is configured to provide heating temperatures of up to 500 °C and pressure of up to 50 bar abs, which enables achieving a higher number of effects in the multiple effect evaporation system 100. In some embodiments, the multiple effect evaporation system 100 facilitates distillation and/or concentration of corrosive liquids and solutions under severe conditions, for example, under temperatures of boiled concentrate between 150 and 500 °C with pressure up to 50 bar abs.

[0015] The multiple effect evaporation system 100 comprises in sequence, a plurality of effects 102. In an embodiment, the multiple effect evaporation system 100 consists of at least five effects 102. In an example, as shown in FIG. 5, the multiple effect evaporation system 100 consists of six effects 102. It may be noted that in another embodiment, the multiple effect evaporation system 100 may include a higher or a lower number of effects 102. Each effect 102 comprises a heat exchanger 104 and a gas-liquid separator 106.

[0016] For explanatory purposes, a heat exchanger 104` associated with the first effect 102` (of the plurality of effects 102) is now discussed in detail with reference to FIGS. 2-5. However, it should be noted that the description provided below for the heat exchanger 104` is equally applicable to the heat exchangers 104 associated with the other effects 102.

[0017] The heat exchanger 104` is configured to transfer heat from a working fluid to a worked fluid. The heat exchanger 104` includes a shell body 110. The shell body 110 may be made of any known material, including but not limited to such as stainless steel, plastic lined, special alloy, having sufficient strength and sufficient resistance to corrosion. The shell body 110 has a substantially circular or rectangular-shaped cross-section. The shell body 110 defines a working fluid inlet 112, a working fluid outlet 114, a worked fluid inlet 116, a worked fluid outlet 118, and a volume 120. The working fluid inlet 112 may be configured to receive and direct the working fluid within the heat exchanger 104`. The working fluid outlet 114 may be configured to direct the working fluid out of the heat exchanger 104`. The worked fluid inlet 116 may be configured to receive and direct the worked fluid within the heat exchanger 104`. The worked fluid outlet may be configured to direct the worked fluid out of the heat exchanger 104`. Examples of the working fluid may include but not limited to steam, thermal oil, and molten salts. In an embodiment, in case the working fluid is steam or vaporized thermal oil, the working fluid may condense as it transfers heat to the worked fluid, as the working fluid flows through the heat exchanger 104`.

[0018] Further, the heat exchanger 104` includes a plurality of silicon carbide mono blocks 122 sequentially arranged and coupled together within the volume 120, as shown in FIG. 2. The silicon carbide mono blocks 122 may be coupled in any manner known to a person skilled in the art. In embodiments, the silicon carbide mono blocks 122 may be coupled together by using tightening means consisting of end plates and tie rods. Each of the silicon carbide mono blocks 122 may be cylindrical or cubical in shape. In an embodiment, the silicon carbide mono blocks 122 includes at least three silicon carbide mono blocks 122. It may be noted that in another embodiment, a higher or a lower number of silicon carbide mono blocks 122 may be arranged within the heat exchanger 104`.

[0019] Each of the silicon carbide mono blocks 122 defines a plurality of first channels 124 configured to communicate a working fluid between the working fluid inlet 112 and the working fluid outlet 114, and a plurality of second channels 126 configured to communicate a worked fluid between the worked fluid inlet and the worked fluid outlet. The plurality of first and second channels 124, 126 are arranged to facilitate heat transfer from the working fluid (heating medium) to the worked fluid. It should be noted that the working fluid for the first (or initial) effect may be selected from the steam, the thermal oil, and the molten salt, while the worked fluid (in its gas-phase, as discussed below) may be used as the working fluid for the other effects (e.g., second effect, third effect, and so on) subsequent to the first (or initial) effect.

[0020] In an embodiment, as shown in FIG. 3, the first channels 124 extend along a longitudinal axis ‘L’ of the silicon carbide mono block 122, and the second channels 126 extend orthogonal to the longitudinal axis ‘L’. The first channels 124 may be arranged in an array along a first direction perpendicular to the longitudinal axis ‘L’. The second channels 126 may be arranged in an array along a second direction along the longitudinal axis ‘L’. In an example, the first channels 124 and the second channels 126 may be formed in the silicon carbide mono block 122 by using drilling processes. As the working fluid and the worked fluid are directed through the respective first channels 124 and the second channels 126, heat is transferred therebetween by conduction through the silicon carbide. Silicon carbide mono blocks 122 may be obtained using a process of isostatic press, machining and sintering.

[0021] In an embodiment, the heat exchanger 104` includes one or more sealing members 128. Each sealing member 128 is configured to define a sealing interface between adjacent silicon carbide mono blocks 122 of the plurality of silicon carbide mono blocks 122. Referring to Fig. 4, one sealing member 128 is illustrated in detail. It should be noted that the description provided below for the sealing member 128 is equally applicable to the remaining sealing members 128. In an embodiment, the sealing member 128 may include an opening 130. The sealing member 128 is configured to be interposed between adjacent silicon carbide mono blocks 122 to provide sealed fluid communication between the second channels 126 of the adjacent silicon carbide mono blocks 122 of the plurality of silicon carbide mono blocks 122.

[0022] In an embodiment, at low temperature requirements (for e.g., 275°C), the sealing member 128 made of any known material, including but not limited to Polytetrafluoroethylene (PTFE), flexible graphite, metallic, may be used. In an embodiment, the sealing member 128 is composed of silver with or without a core material including but not limited to nickel, copper-nickel alloys, gold alloys, depending on the concentration, composition and temperature. In some embodiments, the sealing member 128 is composed of silver having 99.9% purity. In an embodiment, the sealing member 128 has a thickness in a range of 1 to 6 mm.

[0023] The gas-liquid separator 106` associated with the first (or initial) effect 102` is now discussed. However, it should be noted that the description provided below for the gas-liquid separator 106` is equally applicable to the remaining gas-liquid separators 106 associated with the other effects 102. The gas-liquid separator 106` is configured to receive the worked fluid from the worked fluid outlet 118, separate the worked fluid into a gas-phase substance and a liquid-phase substance, and direct the gas-phase substance and the liquid-phase substance as a working fluid and a worked fluid, respectively, to a subsequent effect 102 of the plurality of effects 102. The gas-liquid separator may have a configuration that will be readily apparent to those skilled in the art, as is now known or in the future developed.

[0024] With continued reference to Fig. 1, a method for concentrating a solution using the multiple effect evaporation system 100 is illustrated. The method comprises the concentration of a solution through successive heat exchange and separation stages in the plurality of effects. In the first step, the method comprises feeding the solution as the worked fluid and a heating medium as the working fluid to the heat exchanger 104` associated with the first effect 102` of the plurality of effects 102. This solution is subjected to a first heat exchange step in the heat exchanger 104` associated with the initial effect 102` using the heating medium.

[0025] In an embodiment, the heating medium is maintained at a temperature ranging between 250 and 550°C and a pressure ranging between atmospheric pressure and 50 bar abs. The heating medium is one of a thermal oil and a molten salt. In some embodiments, the thermal oil includes, but is not limited to, synthetic oil. In some embodiments, the molten salt includes, but is not limited to sodium nitrate, potassium nitrate and combinations thereof. In an exemplary embodiment, the thermal salt includes 60 per cent sodium nitrate and 40 per cent potassium nitrate. In an embodiment, the heating medium.

[0026] In the heat exchanger 104`, the solution it is heated, causing it to boil. This heated solution is then transferred to the gas-liquid separator 106` of the initial effect 102`. In the gas-liquid separator 106`, the solution separates into the gas phase substance and the liquid phase substance. In an embodiment, the gas phase substance is steam separated from the aqueous solution. This gas phase substance serves as the working fluid in the subsequent effect. Thus, in operation, the multiple effect evaporation system 100 utilizes a cascading steam generation process and the steam generated by heating the solution in a preceding effect is introduced into the subsequent effect. At the initial effect, a concentrated solution is obtained from gas-liquid separator of the initial effect.

[0027] Each of the working fluid exiting each plurality of effects 102, is at a different pressure and temperature. In an embodiment, the working fluid exiting the initial effect is at a pressure ranging between 30 mbar to 20 bar abs, and a temperature ranging between 50 °C to 280 °C. In another embodiment, the working fluid exiting the initial effect is at a pressure ranging between 30 mbar to and 50 bar abs, and a temperature ranging between 50 and 450°C. In an exemplary embodiment, in a quadruple effect evaporation system for concentrating sodium hydroxide from 32% wt NaOH to 50% wt NaOH, the working fluid is at pressure and temperature ranges of: 2-10 bar abs and 150 -300°C in the first effect; 1-5 bar abs and 120 – 220 °C in the second effect; 0.5 – 2.0 bar abs and 60-20 °C in the third effect; and 0.03 – 0.2 bar abs and 40 -60 °C in the final effect. In an exemplary embodiment, in a six-effect evaporation system, the working fluid is at pressure and temperature ranges of: 15 – 50 bar abs and 375 – 450 °C in the first effect; 10 – 20 bar abs and 300 – 350 °C in the second effect; 2 – 10 bar abs and 150 – 300 °C in the third effect; 1 – 5 bar abs and 120 – 220 °C in the fourth effect; 0.5 – 2 bar abs and 60 – 120 °C in the fifth effect; and 0.03 – 0.2 bar abs and 40 – 60 °C in the final effect. In an embodiment, the working fluid generated in subsequent effects is at the same or substantially similar pressure as that in the preceding effect.

[0028] The solution is any corrosive aqueous solution, now known or developed in the future. In some embodiments, the solution is a corrosive aqueous solution selected from the group consisting of caustic (NaOH) solution, potassium (KOH) hydroxide solutions, aqueous hydrochloric acid (HCl), and sulfuric acid (H2SO4).

[0029] The heating medium may be heated using any known heat source. In some embodiments, the heat source is one or more of hydrogen, electricity, natural gas, wood, and coal.

Industrial Applicability

[0030] The multiple effect evaporation system 100 exhibits superior chemical and corrosion resistance, thermal conductivity, and processability, and is particularly suited for evaporating and concentrating corrosive aqueous solutions, including but not limited to caustic (NaOH) solution, potassium (KOH) hydroxide solutions, aqueous hydrochloric acid (HCl), and sulfuric acid (H2SO4). The multiple effect evaporation system 100.

[0031] In addition to the applications mentioned above, the multiple effect evaporation system 100 finds wide application in industries including, but not limited to, food and beverage, chemical processing, desalination, and wastewater treatment. The multiple effect evaporation system 100 enables the efficient concentration of liquids, removal of excess water content, and recovery of valuable materials. In an embodiment, the multiple effect evaporation system 100 also finds application in concentrating fruit juices and dairy products, synthesizing and processing chemicals, preparing pharmaceutical products like antibiotics and vitamins, treating wastewater and recovering valuable materials.

[0032] The multiple effect evaporation system 100 is an efficient apparatus that utilizes, for example, steam heat to evaporate water of the worked fluid (e.g., corrosive solutions or liquids) in a series of effects. The steam obtained in each effect is used to heat the solution in the heat exchanger 104 of the subsequent effect, reducing the need for external heat sources. The multiple effect evaporation system 100 requires external heat only in the initial heat exchanger, making it an economical and effective method for evaporation.

[0033] As the multiple effect evaporation system 100 can be configured to obtain a high temperature (up to 500 °C) and pressure (up to 50 bar abs) in the initial effect, it is possible to obtain higher number of possible effects. In contrast to the prior known multiple effect evaporation systems, the multiple effect evaporation system can include more than four effects. In an embodiment, the multiple effect evaporation system can include up to 7 effects. As the number of effects increases, lower energy consumption is required. This in turn positively effects the CO2 emissions.

[0034] In an exemplary embodiment, the pressure obtained in various effects, using an exemplary multiple effect evaporation system with 4, 5 and 6 is provided in table 1 below.

System Pressure in the first effect (bar abs) Pressure in the second effect(bar abs) Pressure in the third effect(bar abs) Pressure in the fourth effect(bar abs) Pressure in the fifth effect(bar abs) Pressure in the sixth effect(bar abs)
Quadruple effect 2-10 1-5 0.5-2.0 0.03 – 0.2 NA NA
Quintuple effect 5 – 50 2-10 1-5 0,5-2 0.03 – 0.2 NA
Sextuple effect 15 – 50 10-20 2-10 1-5 0,5-2 0.03 – 0.2
Table 1: Pressure profile in an exemplary multiple effect evaporation system

System Temp. in the first effect (°C) Temp. in the second effect(°C) Temp. in the third effect(°C) Temp. in the fourth effect(°C) Temp. in the fifth effect(°C) Temp. in the sixth effect(°C)
Quadruple effect 150 - 300 120 - 220 60 - 120 40 to 60 NA NA
Quintuple effect 220 - 450 150 - 300 120 - 220 60 - 120 40 to 60 NA
Sextuple effect 375 - 450 300 - 350 150 - 300 120 - 220 60 - 120 40 to 60

[0035] In another exemplary embodiment, energy consumption of the multiple effect evaporation system 100 was compared with a conventional multiple effect evaporator illustrated. The solution used is a ton of NaOH solution from an electrolyser, with an initial temperature of approximately 85°C and a concentration of 32% wt NaOH, which needs to be concentrated to a desired level of 50% wt NaOH. The details of the experiment are provided in table 2 below:

Details Conventional Multiple Effect Evaporator Multiple Effect Evaporation system 100
Heating medium Steam at maximum pressure of 14 bar abs and temperature of 200 °C. Pressurized thermal oil at 400°C under 17 bar abs Therminol / VP1 / Helisol.
Heat exchanger Falling film, rising film or plate type vaporizer in Ni200/201 Thermosiphon in SSIC / Nickel 200/201 and forced vaporizer in SSIC for the first effect.
No. of effects 2 to 4 2 to 7
Table 2: Details of heat exchanger of conventional multiple effect evaporator and multiple effect evaporation system 100

[0036] For both conventional multiple effect evaporator and multiple effect evaporation system 100, logarithmic average of the temperature difference (LMTD) was calculated. LMTD is a critical parameter in heat exchanger design, representing the logarithmic average of the temperature differences between the hot and cold feeds at each end of the double pipe exchanger. For a given heat exchanger with constant area and heat transfer coefficient, a larger LMTD indicates greater heat transfer. The LMTD values for conventional multiple effect evaporator and multiple effect evaporation system 100 are provided. Using these values, the required area for each evaporator can be calculated as follows: Q=U x A x LMTD
where (in SI units):
Q is the exchanged heat duty (watts),
U is the heat transfer coefficient (watts per kelvin per square meter),
A is the exchange area.

Table 3: Logarithmic average of the temperature difference (LMTD) for conventional multiple effect evaporator and multiple effect evaporation system 100
Q calculation is based on a proprietary table of enthalpy.

[0037] As it is very evident from the above table, the heat exchanger 104 of multiple effect evaporation system 100 including mono blocks of silicon carbide will require less area as their LMTD is much higher in comparison with heat exchanger of conventional multiple effect evaporator. Thus, in contrast to the prior known multiple effect evaporation systems, the multiple effect evaporation system 100 can be configured to form a compact apparatus for evaporating and concentrating a corrosive aqueous solution.

[0038] As shown in FIG. 5, in cases that the final product or concentrate should be delivered at low temperatures (close to the feed temperature), an economizer 132 may be installed to recover the available energy by preheating solution before the subsequent effect and therefore reduce overall energy demand of the multiple effect evaporation system 100. Further, excess energy from one or several external systems (i.e., in form of water vapour) can be recovered in one or more effect of the multiple effect system. Based on the available pressure of these vapour, they will be recovered in an effect of the system working at similar pressure. In an example, the energy from the condensed vapour can also be recovered and directed towards the outlet of the gas-liquid separator 106, for example, via an inlet 134 (as shown in FIG. 5), for preheating the solution before subsequent effect.
[0039] It will be apparent to those skilled in the art that various modifications and variations can be made to the method and/or system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the method and/or system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalent.
, C , Claims:1. A multiple effect evaporation system comprising:
in sequence, a plurality of effects, each effect comprising:
a heat exchanger including:
a shell body defining a working fluid inlet, a working fluid outlet, a worked fluid inlet, a worked fluid outlet, and a volume; and
a plurality of silicon carbide mono blocks sequentially arranged within the volume, each silicon carbide mono block defining:
a plurality of first channels configured to communicate a working fluid between the working fluid inlet and the working fluid outlet; and
a plurality of second channels configured to communicate a worked fluid between the worked fluid inlet and the worked fluid outlet, wherein the plurality of first and second channels are arranged to facilitate heat transfer from the working fluid to the worked fluid;
a gas-liquid separator configured to receive the worked fluid from the worked fluid outlet, separate the worked fluid into a gas-phase substance and a liquid-phase substance, and direct the gas-phase substance and the liquid-phase substance as a working fluid and a worked fluid, respectively, to a subsequent effect of the plurality of effects.

2. The multiple-effect evaporation system as claimed in claim 1, wherein the heat exchanger includes one or more sealing members configured to define a sealing interface between adjacent silicon carbide mono blocks of the plurality of silicon carbide mono blocks.

3. The multiple-effect evaporation system as claimed in claim 2, wherein the one or more sealing members is composed of silver.

4. The multiple-effect evaporation system as claimed in claim 2, wherein the one or more sealing members is composed of PTFE.

5. The multiple-effect evaporation system as claimed in claim 2, wherein the sealing member has a thickness in a range of 1 to 6 mm.

6. The multiple-effect evaporation system as claimed in claim 1, comprising at least five effects.

7. The multiple-effect evaporation system as claimed in claim 6, comprising six effects.

8. The multiple-effect evaporation system as claimed in claim 1, further including an economizer configured to pre-heat the worked fluid with either concentrated worked fluid or condensate of the working fluid from the subsequent effect.

9. The multiple-effect evaporation system as claimed in claim 1, further including an inlet configured to receive vapour recovered from external sources and direct the vapour towards the working fluid inlet of the heat exchanger of the subsequent effect of the plurality of effects.

10. A method for concentrating a solution using the multiple effect evaporation system of claim 1, the method comprising:
feeding the solution as the worked fluid and a heating medium as the working fluid to the heat exchanger comprising silicon carbide mono blocks of an initial effect of the plurality of effects,
subjecting the solution to successive heat exchange followed by separation into the gas phase substance and the liquid phase substance in the heat exchanger comprising silicon carbide mono blocks and the gas-liquid separator, respectively, in the plurality of effects to obtain a concentrated solution from a final effect of the plurality of effects.

11. The method as claimed in claim 10, wherein the heating medium is maintained at a temperature ranging between 250 and 550°C and a pressure ranging between atmospheric pressure and 50 bar abs.

12. The method as claimed in claim 10 or 11, wherein the heating medium is one of a thermal oil and a molten salt.

13. The method as claimed in claim 10, wherein the solution is a corrosive aqueous solution selected from the group consisting of caustic (NaOH) solution, potassium (KOH) hydroxide solutions, aqueous hydrochloric acid (HCl), and sulfuric acid (H2SO4).