Heat recovery

Abstract

A system for manufacturing gypsum-based products via a wet calcination method is provided. The system includes a mixing stage for providing gypsum slurry, a reactor stage for calcining the gypsum slurry into an α-hemihydrate slurry, and a dehydration stage for removing water from the α-hemihydrate slurry. Water is removed as liquid water and steam. The liquid water is recycled back to the mixing stage as a water source. The latent heat and sensible heat of the steam are used as a heating source for the system to reduce the energy requirement for heating within the system.

Description

Technical Field

[0001] This disclosure generally relates to systems and methods for producing gypsum-based (e.g., α-hemihydrate) products via wet calcination. More specifically, this disclosure relates to systems and methods for producing gypsum-based (e.g., α-hemihydrate) products via wet calcination, wherein steam and liquid water extracted during the wet calcination process are recycled back into the system and method to provide a more energy-efficient approach. That is, the latent heat and sensible heat of the steam are used as heat sources to reduce the energy demand for heating in the system. Background Technology

[0002] Gypsum exists naturally as a raw material in the form of calcium sulfate dihydrate. Gypsum-containing products, such as gypsum boards, are prepared by forming a mixture of calcined or dehydrated gypsum (i.e., calcium sulfate hemihydrate) and water to form a settling paste that can then be cast into a predetermined shape. The hemihydrate reacts with water and rehydrates to form dihydrate crystals, which are then solidified or dried.

[0003] The hemihydrate form of gypsum is known to depend on the calcination method and is classified into two basic forms: α-hemihydrate and β-hemihydrate. β-hemihydrate is typically formed by heating gypsum under atmospheric conditions to expel any moisture and chemically bound water, resulting in dry crystals that can then be ground into a fine powder. β-hemihydrate has long been an advantageous hemihydrate in the manufacture of gypsum board or plasterboard due to the rapid rehydration of the ground crystals during slurry formation. However, gypsum products derived from β-hemihydrate are generally soft, and β-hydrate requires a significant amount of water to produce the desired slurry fluidity.

[0004] Alpha hemihydrate is formed by heating gypsum under pressure to similarly remove the associated water. However, compared to β hemihydrate-derived gypsum, gypsum products derived from alpha hemihydrate have been found to be harder and have higher strength and density.

[0005] The wet calcination method requires the use of large amounts of water and heat energy. Therefore, the wet calcination method can be very energy-intensive. Therefore, the object of this invention is to improve the energy efficiency of the wet calcination method for α-calcium sulfate hemihydrate. Summary of the Invention

[0006] In a first aspect, a system for manufacturing gypsum-based products by a wet calcination method is provided. The system includes:

[0007] A mixing stage in fluid communication with a gypsum source and one or more water sources, wherein the mixing stage is configured to mix gypsum with water and output gypsum slurry;

[0008] A reactor stage in fluid communication with a mixing tank, wherein the reactor stage is configured to convert gypsum slurry into α-hemihydrate slurry;

[0009] A dewatering stage in fluid communication with the reactor stage, wherein the dewatering stage removes water from the α-hemihydrate slurry, wherein the dewatering stage comprises:

[0010] The first output section is used to output α-hemihydrate products;

[0011] Liquid water output section; and

[0012] Steam output section;

[0013] The liquid water output unit is in fluid communication with the mixing stage and is downstream of the mixing stage, such that the liquid water output unit provides one of one or more water sources that supply water to the mixing stage; and

[0014] The steam outlet of the dehydration stage is connected to one or more fluids in the mixing stage, reactor stage, or water source, so that the latent heat and sensible heat of the steam are used as a heating source to reduce the energy demand for heating in the system.

[0015] As described above, the manufacture of α-hemihydrate products is an energy-intensive process requiring various heating stages and large quantities of water, most of which must then be evaporated or removed during a drying (or dehydration) step to provide a usable product. Therefore, the first aspect provides a novel system for manufacturing gypsum-based (e.g., α-hemihydrate) products that redirects steam and / or water removed from the α-hemihydrate slurry back into the process, allowing the latent heat and / or sensible heat stored therein to be recycled and used as a heat source for at least one of the aforementioned stages in the manufacturing process. This reduces the system's energy requirements and improves its energy efficiency, thereby allowing for a more environmentally friendly (e.g., with a reduced CO2 footprint) and more economical manufacture of α-hemihydrate products.

[0016] The following features and embodiments may be combined in any suitable and / or desired manner to provide embodiments of the first aspect falling within the scope of the appended claims.

[0017] As described above, the mixing stage is in fluid communication with a gypsum source and one or more water sources. It should be understood that the gypsum (supplied by the gypsum source) and water (supplied by one or more water sources) can be supplied to the mixing stage in any suitable and / or desired manner. For example, the system may further include one or more pumps associated with one or each of the gypsum and water sources, such that the gypsum and water are pumped into the mixing stage via conduits.

[0018] Optionally, the mixing stage is a mixing tank. Optionally, the mixing stage (e.g., a mixing tank) includes a mixing device configured to mix gypsum with water (e.g., combine or blend) and provide a gypsum slurry. The mixing device can be any suitable and / or desired device, such as a paddle mixer, rotor / stator, high-frequency vibrator, or plate, etc.

[0019] The water supplied to the mixing stage is provided by one or more water sources. Optionally, the mixing stage is supplied by an internal (e.g., recirculated) water source and an external water source. The internal water source is liquid water output from the dewatering stage. Therefore, the internal water source includes recirculated water that has passed through the system at least once. However, not all the water combined with gypsum in the mixing stage to provide gypsum slurry is recovered (e.g., removed) from the α-hemihydrate during the dewatering stage. In addition, some water is recovered as steam rather than liquid water. Therefore, to ensure that sufficient water is supplied to the mixing stage to provide gypsum slurry with the desired consistency, an external water source may also be used to supplement (e.g., replenish) the water from the internal water source.

[0020] Optionally, one or more water sources may supply preheated water (i.e., water at a temperature above room temperature) to the mixing stage. Therefore, the one or more water sources may optionally include a heating device configured to heat the water contained within the mixing stage to a desired temperature before supplying it to the mixing stage.

[0021] Optionally, the system may also include a container in fluid communication with the liquid water output of the dehydration stage, wherein the container is configured to collect and store the liquid water output from the dehydration stage. Thus, the container provides a water source for the mixing stage. The steam outlet of the dehydration stage may also be in fluid communication with the container, allowing the latent heat and sensible heat of the steam to be used as a heating source, thereby reducing the energy demand for heating in the system.

[0022] In this way, the steam output from the dehydration stage can be used to heat the liquid water in the container (which in turn forms an internal water source) to provide water at an elevated temperature (e.g., above 50°C, such as 50°C to 80°C). Thus, the thermal energy stored in the steam is recycled back into the system, reducing the need for external heating (e.g., heating provided by burning fossil fuels, such as electric heating) and improving the energy efficiency of the system and method.

[0023] Once the gypsum slurry is produced, it is conveyed to a reactor stage (e.g., via a conduit) where it is converted into an α-hemihydrate slurry. Calcination methods are well known in the art, and any suitable and / or desired calcination method can be combined with this system to provide the α-hemihydrate slurry.

[0024] Optionally, the reactor stage is configured to operate at elevated temperatures and / or pressures. Optionally, the reactor stage is configured to heat the gypsum slurry to an elevated temperature of 100°C to 200°C, preferably 110°C to 170°C, more preferably 120°C to 150°C, and even more preferably 130°C to 140°C. Optionally, the reactor stage is configured to pressurize the gypsum slurry (and / or the environment in which the gypsum slurry is located) to an elevated pressure of 1.5 bar to 10 bar, preferably 2 bar to 8 bar, and more preferably 3 bar to 5 bar.

[0025] Optionally, the reactor stage includes one or more (e.g., two, or more) reactor units. Optionally, two or more reactor units are arranged in series. For example, multiple reactor units in series can be used to divide the calcination method into multiple sequential steps. For example, one or more reactor units can be used to heat the gypsum slurry to a desired temperature in a stepwise manner. This can, for example, help ensure uniform heating throughout the gypsum slurry. Optionally, at least one (e.g., one, or a first) reactor unit can be used to heat the gypsum slurry and at least one (e.g., one, or a second) reactor unit can be used to pressurize the gypsum slurry (or the environment in which the gypsum slurry is located). Optionally, heating and pressurization can occur within one (e.g., a single) reactor unit.

[0026] Optionally, the reactor stage includes an autoclave configured to heat the gypsum slurry and (e.g., at least partially, e.g., completely) convert the gypsum slurry into an α-hemihydrate slurry. Optionally, one or more reactor units may each include an autoclave.

[0027] Optionally, the reactor stage includes a preheating reactor unit configured to heat the gypsum slurry to an intermediate temperature (e.g., where the gypsum slurry is heated to an elevated temperature) before it enters the reactor unit containing the autoclave. The intermediate temperature is lower than the temperature (e.g., the elevated temperature) to which the gypsum slurry is heated in the autoclave.

[0028] Optionally, the reactor stage includes a pre-pressurization unit configured to pressurize the gypsum slurry to a desired (e.g., elevated) pressure before it enters the reactor unit containing an autoclave (e.g., where the gypsum slurry is heated to an elevated temperature). In such an embodiment, the reactor unit including the autoclave may optionally be able to maintain the elevated pressure obtained during the pre-pressurization step, allowing heating to occur under pressure.

[0029] The dewatering stage is in fluid communication with the reactor stage (e.g., and downstream of the dewatering stage), allowing the α-hemihydrate slurry to enter the dewatering stage for water removal. Therefore, the dewatering stage is configured to remove water as both liquid water (output via liquid water) and steam (i.e., vapor water) and to provide an α-hemihydrate product comprising less water (i.e., drier) than the α-hemihydrate slurry.

[0030] Optionally, the dehydration stage includes a flash tank configured to cool the α-hemihydrate slurry and collect steam. Optionally, the flash tank is in communication with and downstream of the reactor stage. Optionally, the flash tank is the first step of the dehydration stage, thus directly receiving the α-hemihydrate slurry output from the reactor stage. Optionally, the flash tank is maintained at a pressure lower than that of the α-hemihydrate slurry. Optionally, the flash tank includes a steam source configured to provide a lower pressure within the flash tank. Therefore, when the α-hemihydrate slurry is fed into the flash tank, at least some of the water (e.g., solvent) in the α-hemihydrate slurry is evaporated into steam, thereby reducing the amount of water in the α-hemihydrate slurry (e.g., dehydration). Optionally, the flash tank includes a steam output section. In other words, the dehydration stage optionally includes a first steam output section associated with the flash tank.

[0031] Optionally, the dewatering stage includes a belt filter. Optionally, the belt filter is connected to and downstream of the flash tank, such that the α-hemihydrate slurry is conveyed from the flash tank to the belt filter. Any suitable and / or desired belt filter arrangement (sometimes referred to as a belt press filter or belt filter press) can be used. Optionally, the belt press includes a liquid water output section, a steam output section, and an α-hemihydrate product output section. Thus, optionally, the steam output section from the dewatering stage includes a first steam output section associated with the flash tank and a second steam output section associated with the belt filter.

[0032] Liquid water extracted from the α-hemihydrate slurry in the dehydration stage (e.g., a belt filter) is optionally provided at a temperature below 100°C. Alternatively, the temperature of the liquid water extracted from the α-hemihydrate slurry in the dehydration stage is above room temperature (e.g., 20°C). Alternatively, the temperature of the liquid water extracted from the α-hemihydrate slurry in the dehydration stage is from 30°C to 90°C, preferably from 30°C to 70°C, for example from 40°C to 60°C, for example about 50°C.

[0033] Optionally, the system further includes a filtrate unit in fluid communication with the liquid water output of the dehydration stage, wherein the filtrate unit includes a container. Therefore, the filtrate unit can collect and store liquid water and provide a water source for the mixing stage. Optionally, the steam outlet of the dehydration stage is in fluid communication with the filtrate unit, such that the latent heat and sensible heat of the steam are used as a heating source to reduce the energy demand for heating in the system. Therefore, the mixing stage, reactor stage, dehydration stage, and filtrate unit can be considered to provide a continuous section and / or system for water flow through the system.

[0034] Optionally, the filtrate unit includes a container in which liquid water output from the dehydration stage is collected. Optionally, the liquid water is allowed to settle in the container, allowing any residual α-hemihydrate or gypsum solids to settle to the bottom of the container. Optionally, the filtrate unit may also include a filter configured to separate any solid residues from the liquid water output from the dehydration stage. The filter can be any suitable and / or desired filter. For example, a gravity filter can be used, whereby the filter physically prevents solid particulate material (e.g., α-hemihydrate solids or gypsum solids) from passing through a mesh, membrane, or barrier. For example, centrifugal filtration can be used.

[0035] It should be understood that steam is gaseous or water vapor. Therefore, steam has a temperature of at least 100°C. The temperature of steam is proportional to its pressure; thus, as pressure increases, the temperature of steam increases. Optionally, the temperature of the steam generated in the dehydration stage (e.g., from the output of a flash tank and / or belt filter) is between 100°C and 150°C, for example, 105°C to 110°C, or 120°C to 130°C. Therefore, the steam generated in the dehydration stage includes both latent and sensible energy, which can be used as a heat source for any of the aforementioned stages involving heating in this method.

[0036] Optionally, the steam output from the dehydration stage can be used directly as a heat source. It should be understood that the steam can be used in any suitable and / or desired manner. For example, steam can be used to fill the heat jacket surrounding one or more tanks forming part of the system (e.g., mixing tanks, such as storage tanks filled with liquid water output from the dehydration stage). Additionally or alternatively, steam can be injected or mixed into components of the system (e.g., liquid water, gypsum slurry, or α-hemihydrate slurry) to achieve a temperature increase proportional to the ratio of the component to the steam and the temperature of the component relative to the steam.

[0037] Optionally, the temperature of the steam output from the dehydration stage can be increased to further enhance the steam's heating capacity. Any suitable and / or desired method for increasing the steam temperature can be used. For example, the steam pressure can be increased, or a heat exchanger can be used.

[0038] Optionally, the system also includes a heat exchanger unit (e.g., an absorption heat exchanger unit) in fluid communication with and downstream of the steam output of the dehydration stage. Any suitable and / or desired heat exchanger (e.g., an absorption heat exchanger) can be used. Optionally, the heat exchanger is a jet absorption heat exchanger unit. Optionally, the (e.g., absorption) heat exchanger can be in fluid communication with one or both of the first and second steam outputs. Therefore, only a portion of the steam output from the dehydration system can have its temperature increased.

[0039] The absorption heat exchanger unit is preferably configured to transfer heat from a first temperature to a second temperature in an energy-efficient manner using an absorption process. Therefore, the absorption heat exchanger unit can be used as part of the invention to increase the temperature of the steam output from the dehydration stage (and thus increase the thermal energy stored in the steam, making it usable as an efficient heat source). Surprisingly, the inventors have found that the energy savings provided by using the resulting steam as a heat source outweigh the energy cost of increasing the steam temperature using an absorption heat exchanger. Therefore, by including a heat exchanger, a system and method with improved overall energy efficiency is surprisingly and advantageously provided.

[0040] Optionally, the heat exchanger is configured to receive steam at a first temperature from a steam outlet (e.g., a first steam outlet and / or a second steam outlet) and output steam at a second temperature, wherein the second temperature is higher than the first temperature. Optionally, the first temperature is 100°C to 120°C, for example, 100°C to 115°C, for example, 100°C to 110°C, for example, 100°C to 105°C, for example, 105°C to 110°C, for example, 105°C to 115°C, for example, 105°C to 120°C, for example, 110°C to 120°C. Optionally, the second temperature is 105°C to 200°C, for example 110°C to 190°C, for example 120°C to 180°C, for example 130°C to 170°C, for example 140°C to 160°C, for example 120°C to 180°C, for example 130°C to 180°C, for example 140°C to 180°C, for example 150°C to 180°C.

[0041] Optionally, the second temperature is at least 10°C higher than the first temperature, for example, at least 15°C higher, at least 20°C higher, at least 25°C higher, at least 30°C higher, at least 35°C higher, at least 40°C higher, at least 45°C higher, or at least 50°C higher. Alternatively, the second temperature is 10°C to 100°C higher than the first temperature, for example, 20°C to 90°C higher, 30°C to 80°C higher, 40°C to 80°C higher, or 50°C to 80°C higher.

[0042] Optionally, the heat exchanger (e.g., an absorption heat exchanger unit, such as a jet heat exchanger unit) is configured to receive steam at a first pressure from a steam outlet and output steam at a second pressure, wherein the second pressure is higher than the first pressure. Optionally, the second pressure is 100 kPa to 400 kPa, for example 150 kPa to 350 kPa, for example 200 kPa to 300 kPa.

[0043] Optionally, the output of the heat exchanger unit (e.g., including an output of steam at a second temperature and / or a second pressure) is in fluid communication with the filtrate unit, mixing stage, and / or reactor stage and is upstream of the filtrate unit, mixing stage, and / or reactor stage. Optionally, the steam at the second temperature and / or second pressure serves as a heat source in one or more of the filtrate unit, mixing tank, and / or reactor stage.

[0044] Optionally, steam at a second temperature and / or a second pressure is used to heat the liquid water output from the dehydration stage. For example, the liquid water can be stored / collected in a filtrate unit, wherein the liquid water is heated before being supplied to the mixing stage. Optionally, the temperature of the liquid water output from the filtrate unit is 50°C to 100°C, preferably 60°C to 90°C, more preferably 70°C to 80°C.

[0045] Optionally, steam is used to raise the temperature of the liquid water by at least 10°C, for example, at least 15°C, for example, at least 20°C, for example, at least 25°C, for example, at least 25°C, for example, at least 30°C, for example, at least 35°C, for example, at least 40°C, for example, at least 45°C, for example, at least 50°C, for example, at least 60°C, for example, at least 70°C. Optionally, steam is used to raise the temperature from 10°C to 70°C, for example, from 10°C to 65°C, for example, from 10°C to 60°C, for example, from 10°C to 55°C, for example, from 20°C to 70°C, for example, from 20°C to 60°C, for example, from 25°C to 60°C, for example, from 30°C to 60°C.

[0046] Optionally, the system further includes a conduit arranged to fluidly connect the liquid water output of a dehydration stage (e.g., a belt filter) to a mixing tank, wherein steam from the dehydration stage (e.g., directly from a steam output or via a heat exchanger) mixes with the liquid water from the dehydration stage in the conduit, such that the temperature of the water is increased relative to the temperature of the liquid water output from the liquid unit. Optionally, the system also includes a conduit arranged to fluidly connect a filtrate unit to a mixing tank, wherein steam from the dehydration stage (e.g., directly from a steam output or via a heat exchanger) mixes with the liquid water from the filtrate unit in the conduit, such that the temperature of the water is increased relative to the temperature of the water at the filtrate unit.

[0047] Optionally, the conduit includes a Venturi tube through which water flows, wherein the Venturi tube includes an injection port (e.g., a jet injection port), and wherein steam is introduced (e.g., injected) through the injection port (e.g., the jet injection port). Preferably, the steam is injected at the throat (e.g., the narrowest part) of the Venturi tube. In other words, the injection port is arranged at the throat of the Venturi tube. By injecting steam into the liquid water flowing through the Venturi tube, the temperature of the liquid water increases, and due to the high velocity of the liquid into which the steam is injected, the sensible and latent heat of the steam is completely dissipated within the liquid. This also provides a simpler and more cost-effective method for heating liquid water than other known methods (such as converter units), and is therefore more suitable for some methods. The Venturi tube is also used to create a pressure reduction near the injection port (e.g., a jet injection), which draws steam at atmospheric pressure into the conduit. Therefore, the steam provided does not need to be at an elevated pressure, thereby reducing the energy demand of the system. Optionally, the conduit connecting the steam output (e.g., a first steam output or a second steam output or the output of a heat converter) includes a regulating valve. Therefore, the decompression is confined to the conduit and does not negatively impact the upstream process. Optionally, the venturi tube forms part of the water jet heating system.

[0048] Optionally, the water flowing through the venturi tube has a first temperature before entering the venturi tube and a second temperature when exiting the venturi tube, wherein the second temperature is higher than the first temperature. Optionally, the first temperature is 20°C to 60°C, for example 25°C to 55°C, for example 30°C to 50°C, for example 35°C to 40°C, for example 40°C to 45°C. Optionally, the second temperature is at least 30°C, for example at least 35°C, for example at least 40°C, for example at least 45°C, for example at least 50°C, for example at least 55°C, for example at least 60°C, for example at least 65°C, for example at least 70°C, for example at least 75°C, for example at least 80°C, for example at least 85°C, for example at least 90°C.

[0049] Optionally, the second temperature is at least 10°C higher than the first temperature, for example, at least 15°C higher, for example, at least 20°C higher, for example, at least 25°C higher, for example, at least 30°C higher, for example, at least 35°C higher, for example, at least 40°C higher, for example, at least 45°C higher, for example, at least 50°C higher, for example, at least 55°C higher, for example, at least 60°C higher than the first temperature. Optionally, the second temperature is 10°C to 70°C higher than the first temperature, for example, 10°C to 65°C higher than the first temperature, for example, 10°C to 60°C higher than the first temperature, for example, 10°C to 55°C higher than the first temperature, for example, 20°C to 70°C higher than the first temperature, for example, 30°C to 70°C higher than the first temperature, for example, 40°C to 70°C higher than the first temperature, for example, 50°C to 70°C higher than the first temperature, for example, 20°C to 60°C higher than the first temperature, for example, 25°C to 60°C higher than the first temperature, for example, 30°C to 60°C higher than the first temperature.

[0050] Optionally, the injection port (e.g., injection) is in fluid communication with the steam output of the dehydration stage (e.g., a first steam output and / or a second steam output, such as an output from a heat exchanger). Optionally, the steam supplied at the steam output of the dehydration stage (e.g., the first steam output and / or the second steam output, such as an output from a heat exchanger) is 10 kPa to 400 kPa above atmospheric pressure, for example, 50 kPa to 350 kPa above atmospheric pressure, for example, 75 kPa to 325 kPa above atmospheric pressure, for example, 100 kPa to 300 kPa above atmospheric pressure, for example, 125 kPa to 275 kPa above atmospheric pressure, for example, 150 kPa to 250 kPa above atmospheric pressure, for example, 175 kPa to 225 kPa above atmospheric pressure, for example, approximately 200 kPa above atmospheric pressure. Optionally, the steam supplied at the first steam outlet and / or the second steam outlet is 10 kPa to 100 kPa, for example 15 kPa to 80 kPa, for example 20 kPa to 60 kPa, for example 25 kPa to 50 kPa. Optionally, the steam supplied at the output of the heat exchanger is 100 kPa to 400 kPa above atmospheric pressure, for example 120 kPa to 380 kPa above atmospheric pressure, for example 140 kPa to 360 kPa above atmospheric pressure, for example 160 kPa to 340 kPa above atmospheric pressure, for example 180 kPa to 320 kPa above atmospheric pressure, for example approximately 200 kPa above atmospheric pressure.

[0051] Alternatively, the water output section and the steam output section are separate output sections. In this way, the system provides separate reuse of liquid water and steam, and thus provides a more energy-efficient method.

[0052] Optionally, the dehydration stage includes a multi-stage flash tank, and each stage of the multi-stage flash tank includes a steam outlet. The multi-stage flash tank is defined as a series of flash tanks, wherein each individual flash tank is referred to herein as a stage. The multi-stage flash tank comprises two or more stages. Each successive stage of the multi-stage flash tank has a lower pressure. In this way, heat can be gradually extracted from the α-hemihydrate slurry, wherein the temperature of the steam decreases from each incremental stage of the multi-stage flash tank. The steam outlet of each stage of the multi-stage flash tank can then be directed to the appropriate stage of the system.

[0053] Optionally, the steam output from each flash tank stage is in fluid communication with a separate unit of the system. In this way, the steam output from each stage of a multi-stage flash tank can be directed to the appropriate stage, and the energy efficiency of the entire process is increased. For example, the steam output from the first flash tank stage can be directed to the reactor unit, and the steam output from the cooler second flash tank stage can be directed to the mixing stage.

[0054] Optionally, the steam outlets of successive stages of a multi-stage flash tank are in fluid communication with units of the system having successively lower temperatures. In this way, the steam outlet of a second flash tank stage, which is cooler than the steam outlet of the first flash tank stage, is in fluid communication with units that are also cooler than the steam outlet of the first flash tank stage. In this way, the thermal efficiency of the system increases because the warmer steam output from the upstream flash tank stage is used to heat units of the system with higher energy demands, such as reactor stages. For example, a multi-stage flash tank may include three stages: a first stage upstream of the second and third stages, and a second stage upstream of the third stage. The steam outlet of the first stage may be connected to a unit, such as a reactor unit, downstream of the unit to which the second and third steam outlets are connected, and is hotter than the unit to which the second and third steam outlets are connected. The steam outlets of the second and third stages may be connected to a preheater unit, wherein the second steam outlet is connected to a preheater unit downstream of the preheater unit to which the third steam outlet is connected, and is hotter than that preheater unit. Alternatively, the steam output from the first flash tank stage can be directed to the reactor unit, the steam output from the cooler second flash tank stage can be directed to the mixing stage, and the steam output from the even cooler third flash tank stage can be directed to the input water. Optionally, a multi-stage flash tank system may include four stages.

[0055] Optionally, the system includes a multi-stage preheater comprising multiple preheater units, with each of the multi-stage flash tank steam outlets in fluid communication with a separate preheater unit. In this way, the system allows for the gradual reuse of thermal energy, thus improving the efficiency of the method. Optionally, the steam outlets of successive stages of the multi-stage flash tank are in fluid communication with preheater units having successively lower temperatures. For example, the steam outlet of the first flash tank stage can be directed to a preheater unit adjacent to the reactor unit, and the steam outlet of the cooler second flash tank stage can be directed to an upstream preheater unit. In this way, the system is thus configured to provide a process with higher thermal efficiency.

[0056] In a second aspect, a method for forming a gypsum-based product in a wet calcination process is provided (e.g., using the system of the first aspect). The method includes:

[0057] Plaster slurry is provided (e.g., in the mixing stage of the first aspect) by mixing plaster with water from one or more water sources (e.g., preheated or unheated);

[0058] Calcining gypsum slurry (e.g., in the reactor stage of the first aspect) to provide α-hemihydrate slurry;

[0059] Water is removed from the α-hemihydrate slurry (e.g., in the dewatering stage of the first aspect), wherein water is removed as liquid water and steam;

[0060] Wherein, the liquid water removed from the α-hemihydrate slurry is recycled (e.g., through the filtrate unit of the first aspect) for use as one of one or more water sources (e.g., in the mixing stage of the first aspect); and

[0061] The steam removed from the α-hemihydrate slurry is used as a heating source to heat one or more of the following:

[0062] Gypsum slurry (e.g., during the mixing and / or calcination steps, such as in the mixing stage and / or reactor stage of the first aspect);

[0063] α-hemihydrate slurry (e.g., during the reactor stage of the first aspect); or

[0064] Liquid water is removed from the α-hemihydrate slurry before it is used as a water source in the step of providing gypsum slurry.

[0065] Therefore, the second aspect provides a novel method for manufacturing gypsum-based (e.g., α-hemihydrate) products, which redirects steam and / or water removed from the α-hemihydrate slurry back into the method, allowing the latent heat and / or sensible heat stored therein to be recycled and used as a heat source for at least one of the aforementioned stages in the manufacturing process. This reduces the energy requirements of the method and improves the energy efficiency of the system, thereby allowing for a more environmentally friendly (e.g., with a reduced CO2 footprint) and more economical manufacturing of α-hemihydrate products.

[0066] As should be understood from the foregoing, the first aspect can be used to perform the method of the second aspect. Therefore, the features outlined above regarding the first aspect also apply to the second aspect. Furthermore, the following features and embodiments of the second aspect can be combined in any suitable and / or desired manner to provide embodiments of the second aspect that fall within the scope of the appended claims.

[0067] Optionally, the method may include providing the gypsum slurry in a mixing stage (e.g., the first aspect). Optionally, the mixing stage is in fluid communication with a gypsum source and one or more water sources. Thus, the method may include supplying (e.g., pumping, conveying) gypsum and water to the mixing stage to provide the gypsum slurry.

[0068] Optionally, the method may include preheating the water to an elevated temperature before supplying it to the mixing stage. Optionally, during the step of removing water from the α-hemihydrate slurry, steam (e.g., waste) generated by the method (e.g., the dewatering stage in the first aspect, or in a downstream method) is used as a heat source to preheat the water to an elevated temperature. Therefore, the method may include preheating the water to a temperature above 50°C, for example, 50°C to 80°C, before supplying the water to be used to provide the gypsum slurry (e.g., to the mixing chamber).

[0069] Optionally, the method includes conveying gypsum slurry (e.g., from a mixing stage, such as from a mixing tank) to a reactor stage (e.g., to a reactor forming part of a reactor stage that may include one or more reactors), wherein the step of calcining the gypsum slurry is performed (e.g., implemented, such as executed).

[0070] Optionally, the step of calcining the gypsum slurry further includes heating the gypsum slurry to an elevated temperature and / or pressurizing the gypsum slurry (or the environment surrounding the gypsum slurry) to an elevated pressure. Optionally, the elevated temperature is 100°C to 200°C, preferably 110°C to 170°C, more preferably 120°C to 150°C, and even more preferably 130°C to 140°C. Optionally, the elevated pressure is 1.5 bar to 10 bar, preferably 2 bar to 8 bar, and even more preferably 3 bar to 5 bar. Optionally, the heating and pressurization of the gypsum slurry are carried out sequentially (e.g., in a stepwise manner) or simultaneously (e.g., in the same reactor).

[0071] Optionally, the reactor stage includes one or more (e.g., two, or more) reactor units. Optionally, the method includes heating a first reactor to an elevated temperature and pressurizing a second reactor to an elevated pressure, wherein the first reactor is in fluid communication with the second reactor and is located upstream or downstream of the second reactor. Optionally, at least the heating sub-step of the calcination step occurs within an autoclave. Optionally, the heating and pressurization sub-steps of the calcination step occur simultaneously within an autoclave.

[0072] Optionally, the method includes heating the gypsum slurry to an intermediate temperature before heating it to the elevated temperature used in the calcination step. For example, the intermediate temperature is lower than the temperature (e.g., the elevated temperature) to which the gypsum slurry is heated in the autoclave.

[0073] Optionally, the method includes pressurizing the gypsum slurry to an intermediate pressure before heating and / or pressurizing it to the elevated temperature and / or elevated pressure required for the calcination step.

[0074] Optionally, after the step of calcining the gypsum slurry, the resulting α-hemihydrate slurry is fluidly fed into a dehydration stage, and the method includes removing water from the α-hemihydrate slurry and outputting liquid water (through a liquid water output section) and steam (i.e., water vapor, for example, through a steam outlet).

[0075] Optionally, the method includes cooling the α-hemihydrate slurry to a temperature lower than the elevated temperature used in the calcination process. Optionally, the method includes conveying the α-hemihydrate slurry (e.g., from a reactor stage) to a flash tank for cooling. Optionally, the method includes generating steam in the cooling step. Optionally, the method includes outputting steam from the flash tank used in the cooling step.

[0076] Optionally, the method includes removing water from the α-hemihydrate slurry using a belt filter. Optionally, the method includes directly conveying the α-hemihydrate slurry from the reactor stage to the belt filter (i.e., without first passing through a cooling stage, such as a flash tank). Optionally, the method includes cooling the α-hemihydrate slurry (e.g., in a flash tank) before conveying it to the belt filter. Optionally, the method includes removing water as liquid water and steam in the belt filter. Optionally, the method includes outputting steam (e.g., via a steam output section) and outputting liquid water (e.g., via a liquid water output section) from the belt filter.

[0077] Optionally, the method includes filtering liquid water removed from the α-hemihydrate slurry (e.g., in a dewatering stage, such as in a belt filter) (e.g., in a filtrate unit). Optionally, the method includes outputting the liquid water removed from the α-hemihydrate slurry to the filtrate unit. Optionally, the method further includes using the liquid water (e.g., in the filtrate unit) as water for providing the gypsum slurry.

[0078] Steam removed from the α-hemihydrate slurry is used as a heating source for the method. For example, the method may include injecting steam into liquid water, gypsum slurry, or a mixture of α-hemihydrates to achieve a temperature increase (e.g., heating), the temperature increase being proportional to the ratio of the component to the steam and the temperature of the component relative to the steam.

[0079] Optionally, the method includes increasing the temperature of the steam removed from the α-hemihydrate slurry, for example, before using it as a heating source. For example, the method includes conveying the steam (e.g., from the output of the dehydration stage, such as from the output of a flash tank and / or belt filter) to a heat exchanger, such as a jet absorption heat exchanger unit.

[0080] Optionally, the steam temperature is increased (e.g., relative to the temperature of steam removed from the α-hemihydrate slurry, e.g., relative to the temperature of steam output from the dehydration stage) by at least 10°C, e.g., at least 15°C, e.g., at least 20°C, e.g., at least 25°C, e.g., at least 30°C, e.g., at least 35°C, e.g., at least 40°C, e.g., at least 45°C, e.g., at least 50°C. Alternatively, the steam temperature is increased from 10°C to 100°C, e.g., from 20°C to 90°C, e.g., from 30°C to 80°C, e.g., from 40°C to 80°C, e.g., from 50°C to 80°C.

[0081] Optionally, the heat exchanger (e.g., an absorption heat exchanger unit, or a jet heat exchanger unit) is configured to receive steam at a first pressure from a steam outlet and output steam at a second pressure, wherein the second pressure is 100 kPa to 400 kPa higher than atmospheric pressure, for example 120 kPa to 380 kPa higher than atmospheric pressure, for example 140 kPa to 360 kPa higher than atmospheric pressure, for example 160 kPa to 340 kPa higher than atmospheric pressure, for example 180 kPa to 320 kPa higher than atmospheric pressure, for example approximately 200 kPa higher than atmospheric pressure.

[0082] Optionally, the method includes transferring steam from the output of the heat converter unit to one or more of a filtrate unit, mixing tank, and / or reactor stage to heat the components contained therein (e.g., mixtures, such as gypsum slurry, such as liquid water, such as α-hemihydrate).

[0083] Optionally, the method includes heating the liquid water removed from the α-hemihydrate slurry using steam. For example, the method may include mixing the liquid water removed from the α-hemihydrate slurry with steam removed from the α-hemihydrate slurry, such that the resulting water mixture (e.g., a steam / liquid water mixture) is heated. Optionally, the steam and liquid water are combined within a filtrate unit. Optionally, the temperature of the water output from the filtrate unit is 50°C to 100°C, preferably 60°C to 90°C, more preferably 70°C to 80°C. Optionally, the steam is used to raise the temperature of the liquid water by at least 10°C, for example, at least 15°C, for example, at least 20°C, for example, at least 25°C, for example, at least 25°C, for example, at least 30°C, for example, at least 35°C, for example, at least 40°C, for example, at least 45°C, for example, at least 50°C, for example, at least 60°C, for example, at least 70°C. Optionally, steam is used to raise the temperature from 10°C to 70°C, for example from 10°C to 65°C, for example from 10°C to 60°C, for example from 10°C to 55°C, for example from 20°C to 70°C, for example from 30°C to 70°C, for example from 40°C to 70°C, for example from 50°C to 70°C, for example from 20°C to 60°C, for example from 25°C to 60°C, for example from 30°C to 60°C.

[0084] Optionally, the method includes combining steam with liquid water in a conduit. Optionally, the conduit is arranged to fluidly connect a liquid water output (preferably a filtrate unit) to a mixing tank, wherein steam from the dehydration stage (e.g., directly from the steam output or via a heat exchanger) is mixed with water from the filtrate unit in the conduit such that the temperature of the water is increased relative to the temperature of the water at the filtrate unit.

[0085] Optionally, the method includes injecting steam into the conduit at the throat of a venturi tube located within the conduit. In other words, the injection port is arranged at the throat of the venturi tube. Optionally, the method includes heating the liquid water removed from the α-hemihydrate slurry before conveying (e.g., recirculating) the liquid water to the mixing stage. Optionally, the temperature of the liquid water is increased by at least 10°C, for example, at least 15°C, for example, at least 20°C, for example, at least 25°C, for example, at least 30°C, for example, at least 35°C, for example, at least 40°C, for example, at least 45°C, for example, at least 50°C, for example, at least 55°C, for example, at least 60°C. Optionally, the temperature of the liquid water is increased from 10°C to 70°C, for example, from 20°C to 60°C, for example, from 30°C to 50°C, for example, from 40°C to 45°C, for example, from 45°C to 50°C. Attached Figure Description

[0086] The present disclosure will be further described with reference to the examples depicted in the accompanying drawings, wherein:

[0087] Figure 1 This is a schematic diagram illustrating a system according to an embodiment of the first aspect;

[0088] Figure 2 This is a schematic diagram illustrating a system according to an embodiment of the first aspect;

[0089] Figure 3 This is a schematic diagram illustrating a system according to an embodiment of the first aspect;

[0090] Figure 4 This is a schematic diagram illustrating a system according to an embodiment of the first aspect;

[0091] Figure 5 This is a schematic diagram illustrating a system according to an embodiment of the first aspect;

[0092] Figure 6 This is a flowchart illustrating a method according to an embodiment of the second aspect; and

[0093] Figure 7 This is a schematic diagram illustrating a system according to an embodiment of the first aspect. Detailed Implementation

[0094] The following description presents specific examples, and is related to the appendix. Figure 1This specification serves to explain the principles of this disclosure. However, the scope of the invention is not intended to be limited to the precise details of the embodiments, as variations will be apparent to those skilled in the art and to those considered to be covered by the specification. The terminology used for components herein should be given a broad interpretation, which also covers equivalent functions and features. In some cases, alternative terms for structural features may be provided, but these terms are not intended to be exhaustive.

[0095] Descriptive terms should also be interpreted as broadly as possible; for example, the term “comprising” as used in this specification means “consisting of at least in part”, such that in interpreting each statement in this specification that includes the term “comprising”, features other than the one or those features that begin with that term may also exist. Related terms such as “comprise” and “comprises” will be interpreted in the same manner.

[0096] The description herein refers to examples of specific combinations of features; however, it is envisioned that further combinations and cross-combinations of compatible features between embodiments will be possible. In fact, isolated features can function as an invention independently of other features and do not necessarily need to be implemented as a complete combination.

[0097] Figure 1 A schematic diagram of a system 100 for use in manufacturing α-hemihydrate product 160 is shown. System 100 includes a gypsum source 110 supplying gypsum to a mixing stage 120, in which the gypsum is mixed with water to provide a gypsum slurry. Therefore, mixing stage 120 includes any suitable and / or desired means for efficiently mixing gypsum (and any other additives or components contained in the slurry) with water. Optionally, the mixing stage may include sensors to determine when a slurry of the correct consistency has been produced.

[0098] Once the gypsum slurry is produced in mixing stage 120, it is transferred (e.g., via conduit) to reactor stage 130. Reactor stage 130 is the stage in this method where the gypsum slurry is calcined to provide an α-hemihydrate slurry. Calcination is a known method and can be carried out in any suitable and / or desired manner known in the art. This typically involves heating and / or pressurizing the gypsum slurry to elevated temperatures and pressures, which can be done in a single step or multiple sequential steps within reactor stage 130.

[0099] Once the α-hemihydrate slurry (i.e., a flowable mixture of α-hemihydrate and water as a flowable slurry) is provided (i.e., by calcination), the mixture is conveyed to the dehydration stage 140 of system 100, where water is removed from the α-hemihydrate slurry to provide the α-hemihydrate product 160 (which contains less water than the α-hemihydrate slurry but is not necessarily dry itself; for example, it may be an "aqueous" product). The dehydration stage 160 can be formed by any suitable and / or desired method or apparatus for separating water from the α-hemihydrate slurry. For example, the dehydration stage 160 can be formed by a belt filter or any other suitable and / or desired filtration method.

[0100] Liquid water removed from the α-hemihydrate slurry is output through output port 142, where it is conveyed to filtrate unit 150, which collects the liquid water and, optionally, purifies or filters any solid particulate material, impurities, or waste from the liquid water, and then recycles it (through conduit 155) back to mixing stage 120 as an (internal) water source for mixing with gypsum and providing gypsum slurry.

[0101] In dehydration stage 140, water is also removed as steam from the α-hemihydrate slurry. Steam is output from dehydration stage 140 via steam outlet port 144, and can then be conveyed at steam outlet port 144 (via conduits 146a, 146b, 146c) as a heat source. Therefore, steam outlet port 144 is in fluid communication with at least one of the following: mixing stage 120 (to preheat the gypsum slurry before calcination), reactor stage 130 (to heat the gypsum slurry to the elevated temperature required for the calcination process to convert the gypsum slurry into an α-hemihydrate slurry), or filtrate unit 150 (to heat the liquid water before it is mixed with gypsum in mixing stage 120 to provide the gypsum slurry). Thus, even if further heating may be required to reach the temperatures required for the manufacturing process, the latent heat and sensible heat of the waste steam are used as a heat source, thereby reducing the energy demand for heating in the system.

[0102] Figure 2 A schematic diagram of system 200 is shown, which is similar in nature to Figure 1 The system 100 shown is used to manufacture α-hemihydrate product 260.

[0103] Similar to system 100, system 200 includes a gypsum source 210 that supplies gypsum to mixing stage 120, where the gypsum is mixed with water to provide a gypsum slurry. In this example, system 200 also includes an external water source 205 for supplementing the internally recirculated water supply (i.e., liquid water extracted during dewatering stage 240 and supplied via filtrate unit 250).

[0104] Once the gypsum slurry is prepared in mixing stage 220, it is transferred (e.g., via conduit) to reactor stage 230. In this example, reactor stage 230 includes two reactors 232 and 234 (although there is no limitation on the number of reactors that may be included, only two are depicted for simplicity). Multiple reactors can be used to provide greater control over the calcination process. For example, multiple reactors can be used to progressively increase the temperature, allowing for more precise control of the temperature of the gypsum slurry within the reactor and improved heat transfer efficiency due to the increased surface area relative to a single reactor.

[0105] As shown in the figure, each of reactors 232 and 234 can be fluidly connected to a steam outlet from dehydration stage 240, such that each reactor can at least partially utilize waste steam as a heat source for heating processes used within the reactor. As mentioned above, heating can be carried out in any suitable and / or desired manner. For example, steam can be used to submerge the heating jacket surrounding one or both tanks forming one or both of reactors 232 and 234. For example, steam can be introduced into reactors 232 and 234, such that steam has the dual function of serving as a heating source and an additional water source besides the liquid water introduced in mixing stage 220.

[0106] Once the calcination process (i.e., converting the gypsum slurry into an α-hemihydrate slurry) is completed within reactor stage 240, the resulting α-hemihydrate slurry is transferred to dehydration stage 240, where water is removed to provide α-hemihydrate product 260. In this embodiment, the dehydration stage includes a flash tank 242 (which cools the α-hemihydrate slurry and generates steam) and a belt filter 244 (which removes liquid water and steam from the slurry to provide the resulting α-hemihydrate product 260). Therefore, the steam output of the dehydration stage is provided by a first steam output associated with the flash tank and a second steam output associated with the belt filter 244. In the illustrated example, the first and second steam outputs are combined to provide a common steam output 246 from the dehydration stage 240, which can be conveyed via conduits to different parts of the system (e.g., the first reactor 232, the second reactor 234, the mixing stage 220, and the filtrate unit 250) to cooperate with the above-described... Figure 1 In the same manner as system 100, heat sources are provided to different parts of system 200.

[0107] However, in other embodiments, the first and second steam outputs (associated with different steam generation stages in dehydration stage 240) can be fluidly connected to different parts of the system, such that each steam output acts as a heat source for a different part of the system. For example, it can be anticipated that one stage will produce more steam (or hotter steam) than another. Thus, the steam outputs associated with different stages can be directed to the parts of the system that provide optimal utilization of the thermal energy contained in the steam. For example, if flash tank 242 produces less steam (by volume) than belt filter 244, it may be desirable to direct the steam generated in flash tank 242 to a part of system 200 that requires less heating (i.e., a lower desired temperature to be reached) compared to the steam generated in belt filter 244. Therefore, it can be ensured that the system uses every calorie of energy efficiently to ensure maximum energy efficiency.

[0108] Liquid water removed from the α-hemihydrate slurry is output through output port 248, where it is conveyed to filtrate unit 250, which collects the liquid water and, optionally, purifies or filters any solid particulate material, impurities, or waste from the liquid water, and then recycles it (through conduit 255) back to mixing stage 220 to be used as an (internal) water source (in addition to external water source 205) to mix with gypsum and provide gypsum slurry.

[0109] Figure 1 and Figure 2 The dashed lines shown are intended to indicate possible steam flow paths, not limiting ones. Therefore, systems 100, 200 may include only one of the steam flow paths shown and are not intended to be construed as including all flow paths. For example, in some embodiments, steam may flow only to mixing stages 120, 220 to be used as a heat source. Therefore, any suitable and / or desired combination or arrangement of steam flow paths can be selected based on thermal requirements and the processes performed by the system.

[0110] Figure 3 , Figure 4 and Figure 5 Different specific embodiments related to system 200 are provided.

[0111] Figure 3System 300 is shown, comprising a gypsum source 310, an external water source 314, and an additive source 312, which are fed into a mixing tank 320 providing gypsum slurry. The gypsum slurry is then conveyed to a reactor stage 320 formed by a first reactor 332 and a second reactor 334, wherein the gypsum slurry is calcined to provide an α-hemihydrate slurry. The α-hemihydrate slurry is then conveyed to a dehydration stage 340, which is formed by a flash tank 342 (where the temperature of the mixture is reduced and steam is generated) and a belt filter 344 (where liquid water and steam are removed from the α-hemihydrate slurry to provide an α-hemihydrate product 360).

[0112] Each of the flash tank 342 and the belt filter 344 generates steam that can be used as a thermal energy source. In this embodiment, the system 300 also includes a steam outlet 346, which can be used to release pressure and / or discharge excess steam. The belt filter 344 may also be associated with a vacuum pump to extract steam through its associated steam outlet.

[0113] The steam output from the dehydration system 340 is then conveyed to the heat exchanger unit 370 (preferably a jet absorption heat exchanger), where the temperature (and potential pressure) of the steam is increased. Therefore, the steam output from the heat exchanger 370 via line 375 has a higher temperature than the steam input into the heat exchanger 370. In this example, the steam output from the heat exchanger 370 is used to heat the liquid water collected in the filtrate unit 350. Thus, the liquid water (extracted in the dehydration stage 340 by the belt filter 344) is heated to an elevated temperature (e.g., between 50°C and 80°C) before being recycled back to the mixing tank 320. Preferably, the steam is used to raise the temperature of the liquid water by 10°C to 40°C, for example, about 25°C. For example, if the water output from the belt filter has a temperature of about 50°C, steam can be injected into the filtrate unit 350 to raise the temperature of the liquid water to about 75°C. This reduces the additional heating required for the mixing stage 320 and improves the energy efficiency of the system.

[0114] Figure 4 System 400 is shown, which contains all the same components as system 300. However, unlike system 300, the steam output from heat exchanger 470 (at an elevated temperature compared to the steam input to heat exchanger 470) is used to heat at least one (e.g., one, two, or all) of mixing stage 420, first reactor 432, or second reactor 434, instead of filtrate unit 450.

[0115] Figure 5System 500 is shown, in which a water jet unit 580 replaces the heat exchangers 370, 470 of systems 300 and 400. In this embodiment, the water jet unit 580 is intended to represent a device including a venturi tube arranged in a conduit extending between the filtrate unit 550 and the mixing tank 520. The venturi tube thus accelerates the flow of liquid water through the conduit, causing a pressure reduction through the venturi tube, which in turn creates a pressure differential and draws steam flowing through conduit 575 into the conduit via an injection port. Preferably, the injection port is located at the throat of the venturi tube where the pressure differential is greatest. Therefore, this arrangement means that steam output from the dehydration stage 540 (via flash tank 542 and / or belt filter 544) does not need to be pressurized before being injected into the conduit line, but can be provided at essentially atmospheric pressure. This reduces the energy requirement of system 500 while improving the energy efficiency of the process.

[0116] Figure 6 It shows that it can be used (and in Figure 1-5 An exemplary method 600 for providing an α-hemihydrate product (executed in systems 100-500 shown) is described. Method 600 first includes providing (in step 610) a gypsum slurry by mixing gypsum with water from one or more water sources. For example, this can be achieved by supplying gypsum and water (e.g., via a filtration unit and / or an external water source) to a mixing stage (e.g.,...). Figure 1-5 The gypsum slurry is provided in the mixed grades 120, 220, 320, 420, and 520 shown.

[0117] In the next step, the method includes calcining (step 620) the gypsum slurry (e.g., in... Figure 1-5 The reactor stages 130, 230, 330, 430, and 530 shown are used to provide α-hemihydrate slurry.

[0118] The method then includes extracting α-hemihydrate slurry (e.g. from...) Figure 1-5 Water is removed as liquid and / or steam in dehydration stages 140, 240, 340, 440, and 550 (step 630). In the dehydration stage (e.g., Figure 1-5 The liquid water extracted from the α-hemihydrate slurry in the dehydration stages 140, 240, 340, 440, and 550 can be recycled back into the method to serve as the water source required to supply the gypsum slurry in step 610. This can be achieved by using a filtrate unit (e.g., Figures 1 to 5 The process can occur directly in the filtrate units 150, 250, 350, 450, 550, etc., where the extracted liquid water is collected, stored, and / or filtered. The method may also include heating the extracted liquid water before recycling it as a water source for providing the gypsum slurry step. For example, the extracted liquid water can be heated in the filtrate unit (e.g., ...). Figure 1-5In the filtrate units 150, 250, 350, 450, and 550, steam is used to heat liquid water, which is also extracted from the α-hemihydrate slurry in the dehydration step (e.g., step 630).

[0119] The steam generated in the dehydration step (e.g., step 640) can then be used as a heat source for the various stages in method 600. For example, the method may include using steam extracted from the α-hemihydrate slurry to heat upstream or downstream stages in the method. For instance, the method may include using steam extracted from the α-hemihydrate slurry after the calcination step to heat gypsum slurry (e.g., in mixing stages 120, 220, 320, 420, 520) or water used to supply gypsum slurry (e.g., in filtrate units 150, 250, 350). Similarly, the method may include using steam extracted from the α-hemihydrate slurry as a heat source in the calcination step.

[0120] Figure 7 System 700 is shown, containing most of the same components as system 300, but excluding a heat exchanger. Unlike system 300, the steam output from flash tank 742 is directly transferred instead of using a heat exchanger unit. System 700 contains a multi-stage flash tank 742 with four flash tank stages 742a, 742b, 742c, and 742d. Slurry is transferred from the second reactor 734 to the multi-stage flash tank 742 at a pressure of 300 kPag. The flash tanks have decreasing pressures: the first flash tank 742a has a pressure of 200 kPag, the second flash tank 742b has a pressure of 100 kPag, the third flash tank 742c has a pressure of 20 kPag, and the fourth flash tank has a pressure of 0 kPag. The steam obtained from each flash tank in the multi-stage flash tank 742 has a different temperature and can be directed to a specific stage of the system. The first flash tank 742a is fluidly connected to the first reactor 732. The second flash tank 742b is fluidly connected to the mixing tank 720. The third flash tank 742c is fluidly connected to the filtrate unit 750. The fourth flash tank 742d is fluidly connected to the discharge device 746. In this way, the continuous steam output of each stage of the multi-stage flash tanks 742 is directed to the unit of the system with a continuously lower temperature, thereby providing a system 700 that allows for improved thermal efficiency.

[0121] Liquid water extracted from belt filter 744 in dehydration stage 740 is conveyed to filtrate unit 750 and then recycled back to mixing tank 720.

[0122] Therefore, the present invention provides an improved system for manufacturing α-hemihydrate (e.g., gypsum-based) products suitable for use as building materials (e.g., gypsum board). However, the scope of this disclosure is limited only by the appended claims.

Claims

1. A system for manufacturing gypsum-based products by a wet calcination method, the system comprising: A mixing stage in fluid communication with a gypsum source and one or more water sources, wherein the mixing stage is configured to mix gypsum with water and output gypsum slurry; A reactor stage in fluid communication with a mixing tank, wherein the reactor stage is configured to convert the gypsum slurry into an α-hemihydrate slurry; A dewatering stage in fluid communication with the reactor stage, wherein the dewatering stage removes water from the α-hemihydrate slurry, wherein the dewatering stage comprises: The first output section is used to output α-hemihydrate products; Water output section; and Steam output section; The liquid water output unit is in fluid communication with the mixing stage and is downstream of the mixing stage, such that the liquid water output unit provides one of one or more water sources that supply water to the mixing stage; and The steam outlet of the dehydration stage is connected to one or more fluids, namely the mixing stage, the reactor stage, or a water source, so that the latent heat and sensible heat of the steam are used as a heating source to reduce the energy demand for heating in the system.

2. The system according to claim 1, further comprising a filtrate unit in fluid communication with the liquid water output section of the dehydration stage, wherein, The filtrate unit is in fluid communication with the mixing stage and is downstream of the mixing stage, such that the filtrate unit is one of the one or more water sources that supply water to the mixing stage.

3. The system according to claim 2, wherein, The steam outlet of the dehydration stage is in fluid communication with the filtrate unit, which serves as the water source.

4. The system according to any one of claims 1, 2, or 3, wherein, The dehydration stage includes a flash tank configured to cool the α-hemihydrate slurry and collect steam. and The steam output section of the dehydration stage includes a first steam output section associated with the flash tank.

5. The system according to any one of the preceding claims, wherein, The dewatering stage includes a belt filter; and The steam output section from the dehydration stage includes a second steam output section associated with the belt filter.

6. The system according to claim 5, which is dependent on claim 4, wherein, The belt filter is in fluid communication with the flash tank and is located downstream of the flash tank.

7. The system according to claim 5 or 6, wherein, The water output section of the dehydration stage includes a first water output section associated with the belt filter.

8. The system according to any one of the preceding claims, wherein, The system also includes a heat exchanger unit that is in fluid communication with the steam output section of the dehydration stage and is located downstream of the steam output section of the dehydration stage.

9. The system according to claim 8, wherein, The heat exchanger is an absorption heat exchanger unit, such as a jet absorption heat exchanger unit.

10. The system according to any one of the preceding claims, wherein, The output of the heat exchanger unit is in fluid communication with the filtrate tank, the mixing tank, and / or the reactor stage, and is upstream of the filtrate tank, the mixing tank, and / or the reactor stage.

11. The system according to any one of the preceding claims, wherein, The system also includes a conduit arranged to fluidly connect the filtrate tank to the mixing tank, wherein steam from the dehydration stage is mixed with water from the filtrate tank in the conduit, such that the temperature of the water is increased relative to the temperature of the water at the filtrate tank.

12. The system according to claim 11, wherein, The conduit includes a venturi tube through which water flows; The venturi tube includes an injection port, preferably wherein the injection port is disposed at the throat of the venturi tube; and The steam is introduced into the water through the injection port, such that the water flowing through the venturi tube has a first temperature before entering the venturi tube and a second temperature when leaving the venturi tube, wherein the second temperature is greater than the first temperature.

13. The system according to any one of the preceding claims, wherein, The reactor stage includes one or more reactor units, preferably wherein the one or more reactor units are arranged in series.

14. The system according to any one of the preceding claims, wherein, The reactor stage includes an autoclave configured to heat the gypsum slurry and at least partially convert the gypsum slurry into an α-hemihydrate slurry.

15. The system according to any one of the preceding claims, wherein, The water output section and the steam output section are separate output sections.

16. The system according to any one of the preceding claims, wherein, The dehydration stage includes a multi-stage flash tank, and each stage of the multi-stage flash tank includes a steam output section.

17. The system according to claim 16, wherein, The steam output from each of the flash tank stages is in fluid communication with the individual unit of the system.

18. The system according to claim 17, wherein, The steam output sections of the successive stages of the multi-stage flash tank are in fluid communication with the unit of the system, which has a successively decreasing temperature.

19. The system according to claim 16 or 17, wherein, The system includes a multi-stage preheater, which comprises multiple preheater units, and each of the steam output sections of the multi-stage flash tank is in fluid communication with a separate preheater unit.

20. A method for forming a gypsum-based product, the method comprising: Plaster slurry is provided by mixing plaster with water from a water source; Calcination of the gypsum slurry to provide an α-hemihydrate slurry; Water is removed from the α-hemihydrate slurry to provide an α-hemihydrate product, wherein the water is removed in the form of liquid water and steam; The liquid water removed from the α-hemihydrate is recycled for use as one of one or more water sources; and The steam removed from the α-hemihydrate is used as a heating source to heat one or more of the following: The gypsum slurry; The α-hemihydrate slurry; or The liquid water removed from the α-hemihydrate slurry prior to its use as a water source in the step of providing the gypsum slurry.

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