A drying system and method

Abstract

A drying system is described, the drying system comprising a dryer comprising at least one dryer zone, at least one heat pump located in the at least one dryer zone; and a source of waste heat; wherein the heat pump is configured such that, in use, heat energy from the source of waste heat is used to heat the at least one dryer zone. A method of drying is also described.

Description

Field of the Disclosure The present disclosure relates generally to systems and methods for use in the production of a gypsum product, and finds particular, although not exclusive, utility in providing systems and methods for the reuse of heat in the drying process. Background The gypsum product manufacturing process, used to produce gypsum products such as plasterboard, typically comprises the following steps: • subjecting calcium sulphate dihydrate (CaSO4.2H2O) to a calcination process at temperatures greater than about 150°C in order to drive off the chemically bound water of crystallisation, and provide a calcination product (also known as stucco) comprising mainly calcium sulphate hemihydrate (CaSO4.1 / 2H2O); • mixing the stucco with water to provide a slurry and casting the slurry into a predetermined shape and thereby forming a board precursor; • transporting the board precursor along a conveyor. During this stage, the calcium sulphate hemihydrate becomes re-hydrated to provide calcium sulphate dihydrate crystals. • drying the slurry to remove excess water remaining in the board and thereby form a solid, dried board. Industrial drying processes, for example the drying of gypsum products require significant amounts of energy. Industrial dryers can be composed of multiple zones which are maintained at different temperatures depending on the needs of the process. Providing the energy required to maintain such industrial dryers at the required temperatures is expensive. Additionally, there is a significant, negative environmental impact associated with current production techniques due to the amount of energy consumed. Aspects of the present disclosure seek to provide systems and methods that alleviate these problems with prior known systems. In particular, aspects of the present disclosure seek to provide systems and methods for drying with increased energy efficiency. Summary According to a first aspect of the present invention, there is provided a drying system for drying a gypsum product, the drying system comprising: a dryer comprising at least one dryer zone, at least one heat pump located in the at least one dryer zone; and a source of waste heat; wherein the heat pump is configured such that, in use, heat energy from the source of waste heat is used to heat the at least one dryer zone. When using a system of this form, waste heat which would usually not be utilized, can be used to partially, or fully, maintain a raised temperature in the at least one dryer zone to dry a gypsum product. In this way, the apparatus is more energy efficient than those of the prior art. Preferably, the gypsum product is a gypsum board. A gypsum board is a board comprising at least 50 wt.% calcium sulphate dihydrate, more preferably at least 80 wt.% calcium sulphate dihydrate. More preferably, the gypsum board may have one or more facer layers. Still more preferably, the facer layer may comprise a paper or other cellulose based product. Preferably, the source of waste heat comprises calcination fumes, process water, process fumes, preheater zone fumes and / or exhaust fumes. In this way, the heat energy from the calcination fumes, process water, process fumes, preheater zone fumes and / or exhaust fumes can be used to partially, or fully, maintain a raised temperature in the at least one dryer zone to dry a gypsum product. Process water is defined as any water used in the gypsum product manufacturing process. Preferably, the process water comprises condensate water. Condensate water is defined as the water recovered from moist air used in one part of the gypsum product manufacturing process. Preferably, the system comprises a plurality of sources of waste heat and the system comprises a plurality of heat pumps, wherein when in use, the plurality of heat pumps are configured to transfer heat energy from the plurality of waste heat sources to the at least one dryer zone. In this way, waste heat from a plurality of sources, can be used to partially, or fully, maintain a raised temperature in the at least one dryer zone to dry a gypsum product. In some embodiments, the heat pump is configured to heat the at least one dryer zone directly. In some embodiments, the heat pump is configured, in use, to indirectly heat the at least one dryer zone by heating air entering the at least one dryer zone. Preferably, the system comprises a thermal fluid loop and the heat pump is configured to indirectly heat at least one dryer zone via the thermal loop. The use of a thermal fluid loop may be preferable as it may increase the ease with which the system can be installed or retrofitted where the source of waste heat is located in a position relatively remote for the dryer. Preferably, at least one dryer zone comprises at least one dryer zone exhaust, wherein in use, the at least one dryer zone exhaust transfers heat energy from a one dryer zone to another dryer zone. In this way, waste heat from within the dryer system can be used to partially, or fully, maintain a raised temperature in another dryer zone of the system. Preferably, the dryer comprises a plurality of dryer zones. Preferably, the system is configured such that, in use, heat energy from the source of waste heat is used to heat two or more of the dryer zones. Preferably, the dryer comprises a first dryer zone, a second dryer zone and a third dryer zone. Preferably, the system comprises a heater. Preferably, the heater is a gas burner. Alternatively, the heater is a resistance heater. Preferably, the system is configured such the heater directly or indirectly heats at least one dryer zone. More preferably, the system may be configured such that supplemental air is heated via the heater, then that supplemental air is introduced into at least one of the preheaters and / or dryer zones. In this way, the temperature of each zone can be controlled more accurately and / or increase if required. In some embodiments, the dryer is a longitudinal dryer. In some embodiments, the dryer is a transverse dryer. In some embodiments, the dryer is a jet dryer. According to a second aspect of the present invention, there is provided a method of drying a gypsum product, the method comprising: providing a dryer with at least one dryer zone; providing at least one heat pump; providing a source of waste heat; and using the heat pump to transfer heat energy from the source of waste heat to heat the at least one dryer zone. When using this method, waste heat which would usually not be utilized, can be used to partially, or fully, maintain a raised temperature in the at least one dryer zone to dry a gypsum product. In this way, the method is more energy efficient than those of the prior art. In this way, a method with the advantages hereinbefore described is provided. Preferably, the method comprises providing the apparatus as hereinbefore described. Preferably, the method is a method of manufacturing a gypsum board. Preferably, the source of waste heat comprises calcination fumes, process water, process fumes, preheater zone fumes and / or exhaust fumes. In this way, the heat energy from the calcination fumes, process water, process fumes, preheater zone fumes and / or exhaust fumes can be used to partially, or fully, maintain a raised temperature in the at least one dryer zone to dry a gypsum product. Process water is defined as any water used in the gypsum product manufacturing process. Preferably, the process water comprises condensate water. Condensate water is defined as water recovered from moist air used in one part of the gypsum product manufacturing process. Preferably, the method comprises providing a plurality of sources of waste heat and a plurality of heat pumps, wherein the method comprises using the plurality of heat pumps to transfer heat energy from the plurality of waste heat sources to the at least one dryer zone. In this way, waste heat from a plurality of sources, can be used to partially, or fully, maintain a raised temperature in the at least one dryer zone to dry a gypsum product. In some embodiments, when in use, the heat pump heats the at least one dryer zone directly. In some embodiments, when in use, the heat pump indirectly heats the at least one dryer zone by heating air entering the at least one dryer zone. Preferably, the method comprises providing a thermal fluid loop and the heat pump is configured to indirectly heat at least one dryer zone via the thermal loop. The use of a thermal fluid loop may be preferable as it may increase the ease with which the system can be installed or retrofitted where the source of waste heat is located in a position relatively remote for the dryer. Preferably, the method comprises maintaining the temperature in the at least one dryer zone between 80°C and 200°C. More preferably, the method comprises maintaining the temperature of the at least one dryer zone between 120°C and 170°C. Preferably, the method comprises providing a dryer with a plurality of dryer zones. Preferably, the method comprises using the heat pump to transfer heat energy from the source of waste heat to two or more of the dryer zones. In this way, the waste heat which would usually not be utilized, can be used to partially, or fully, maintain a raised temperature in two or more of the plurality of dryer zones. Preferably, the method comprises maintaining a first dryer zone within the plurality of dryer zones at a first temperature, and maintaining a second dryer zone within the plurality of dryer zones at a second temperature. Preferably, the method comprises transferring waste heat from a first dryer zone to another dryer zone. In this way, waste heat from within the dryer system can be used to partially, or fully, maintain a raised temperature in another dryer zone of the system. Preferably, the method comprises a providing a plurality of sources of waste heat and a plurality of heat pumps, and using the plurality of heat pumps to transfer heat energy from the plurality of waste heat sources to the at least one dryer zone. In this way, waste heat from a plurality of sources, can be used to partially, or fully, maintain a raised temperature in the at least one dryer zone to dry a gypsum product. Preferably, the method comprises using the plurality of heat pumps to transfer waste heat energy to a plurality of dryer zones. In this way, waste heat from a plurality of sources, can be used to partially, or fully, maintain a raised temperature in a plurality of dryer zones to dry a gypsum product. Detailed Description The following description presents particular examples and, togetherwith the drawings, serves to explain principles of the disclosure. However, the scope of the invention is not intended to be limited to the precise details of the examples, since variations will be apparent to a skilled person and are deemed to be covered by the description. Terms for components used herein should be given a broad interpretation that also encompasses equivalent functions and features. In some cases, alternative terms for structural features may be provided but such terms are not intended to be exhaustive. Descriptive terms should also be given the broadest possible interpretation; e.g. the term "comprising" as used in this specification means "consisting at least in part of' such that interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. The description herein refers to examples with particular combinations of features, however, it is envisaged that further combinations and cross-combinations of compatible features between embodiments will be possible. Indeed, isolated features may function independently as an invention from other features and not necessarily require implementation as a complete combination. Figure 1 depicts a system 100 in accordance with the present invention. The system comprises a longitudinal dryer 110 comprising a first dryer zone 111, a second dryer zone 112, and a third dryer zone 113. During use, hot air circulates in alternating directions in the first dryer zone 111 compared to the second dryer zone 112 and the third dryer zone 113 as indicated by the arrows in Figure 1. The system 100 additionally comprises a first preheater 121 and a second preheater 122. The preheaters are located upstream of the first dryer zone 111, second dryer zone 112 and third dryer zone 113, such that a product to be dried, typically a gypsum board, first travels through the preheaters 121, 122 before travelling through the dryer 110. In use, the temperature in the first preheater 121 is maintained between 50°C and 150°C, the temperature in the second preheater 122 is maintained between 50°C and 150°C, the temperature in the first dryer zone 111 is maintained between 200°C and 330°C, the temperature in the second dryer zone 112 is maintained between 200°C and 330°C, and the temperature in the third dryer zone 113 is maintained between 100°C and 300°C. As such, in use, the temperature in the preheaters 121, 122 and the dryer 110 is maintained above the ambient. In the embodiment of Figure 1, the temperature in the first dryer zone 111 and the second dryer zone 112 is maintained, in use, with the assistance of preheater fumes. The preheater fumes are at an elevated temperature, often in the range of 40°C to 150°C, and can therefore be used to maintain an above ambient temperature within the first dryer zone 111 and the second dryer zone 112. A preheater exhaust 130 fluidly connects the preheater fumes to a heat pump 140. In the embodiment of Figure 1, the heat pump 140 directly heats the recirculation air of the first dryer zone 111, increasing the temperature of the first dryer zone 111. In this way, the energy efficiency of the system 100 may be increased. The main aim of the dryer 100 is to dry the gypsum product in a controlled manner to ensure a consistent final product. As such as well as the temperature of the dryer zones, controlling the humidity within the zones is also of significant importance. As the waste heat is reused after being transferred to fresh air through the heat pump, the humidity of the dryer zones is not affected by the utilization of the waste heat. Whilst in Figure 1 the exhaust 130 is seen extending from the preheater zones 121 and 122, it is envisaged that the exhaust may extend from any one or more of the dryer zones. Figure 2 illustrates a second system 200 in accordance with the present invention. The system 200 of Figure 2 includes similar features as the system 100 of Figure 1, each of these features numbered with equivalent reference numerals. The system 200 of Figure 2 additionally includes a calcination fumes exhaust 250 extending from a calciner (not shown). A calciner can be used to dehydrate gypsum at an elevated temperature. As calcination is conducted at an elevated temperature, the calcination fumes in the calciner exhaust 250 are at an elevated temperature, often in the range of 100°C to 200°C, and can therefore be used to maintain an above ambient temperature within the dryer zones 211, 212, and 213. The calcination fume exhaust 250 is fluidly connected to the heat pump 240, and the heat pump 240 is used to increase the temperature of the dryer zones. Whilst in Figure 2 the heat pump 240 is seen heating the recirculation air of the first dryer zone 211, it is envisaged that a heat pump may be used to transfer heat to the recirculation air of any one or more of the dryer zones. Figure 3 illustrates a third system 300 in accordance with the present invention. The system 300 of Figure 3 includes all the same features as the system 200 of Figure 2, each of these features numbered with equivalent reference numerals. The system 300 of Figure 3 additionally includes a dryer zone exhaust 370, the dryer zone exhaust transferring air from the first dryer zone 311 and the second dryer zone 312 to the third dryer zone 313. Whilst in Figure 3 the dryer zone exhaust extends from both the first 311 and second 312 dryer zones, it is also envisaged that it may extend from only one of the same. As the first dryer zone 311 and the second dryer zone are above the temperature of the third dryer zone 313, the dryer zone exhaust may be used to maintain the temperature of the third dryer zone 313 whilst reducing the energy usage of the system 300 as a whole. Figure 4 illustrates a fourth system 400 in accordance with the present invention. The system 400 of Figure 4 includes a number of features identical to those previously described and, where this is the case, these features are numbered with equivalent reference numerals. The system 400 of Figure 4 additionally includes a dryer exhaust 460 extending from the third dryer zone 413, alternatively it is envisaged that the dryer exhaust may extend from any one or more of the dryer zones. Here, the dryer exhaust 460 carries air from the third dryer zone 413, this air being at a temperature above the ambient. The dryer exhaust 460 carries this air to a heat pump 470, where heat from the air in the dryer exhaust 460 is transferred to the fresh air entering the dryer 410. In the system 400 of Figure 4, the additional air entering the dryer zones 411, 412, 413 is heated by two heat pumps, 470 and 440. The fresh air is heated in a heat pump 470 using otherwise waste energy in the air within the dryer exhaust 460, and the air of the dryer zone 411 is heated in the heat pump 440 using otherwise waste energy in the calcination fumes in the calciner exhaust 450. Whilst not shown, it is also envisaged that the system 400 of Figure 4 may additionally include a dryer zone exhaust as described in relation to Figure 3. Whilst in Figures 1 to 4, systems 100 to 400 are shown using longitudinal dryers with three dryer zones, the present invention may also be applied to transversal dryers and / or dryers with a greater number of dryer zones. Figure 5 depicts a heat pump 540 that may be used in a system according to the present invention. The heat pump 540 comprises a carrier fluid loop, a first heat exchanger 541, a condenser 542, a second heat exchanger 543 and an expansion valve 544. The first heat exchanger 541 is configured to transfer the heat of the source of waste heat to the carrier fluid, evaporating the carrier fluid. The condenser 542 is configured to condense the carrier fluid, further increasing the temperature and pressure of the carrier fluid. The second heat exchanger 143 is configured to transfer the energy from the carrier fluid to fresh air in order to increase the temperature of the fresh air. This cools the carrier fluid and the carrier fluid condenses. The expansion valve 544 is configured to further decrease the pressure of the carrier fluid. In this way, the heat pump 540 transfers heat energy from the source of waste heat to the fresh air. Figure 6 depicts a thermal fluid loop 1000 that may be used in a system according to the present invention. Whilst individual heat pumps can be used to transfer heat between the various fluid flows described in the previous embodiments, a thermal fluid loop 1000 can also be used. In Figure 6, waste heat energy from the exhaust 1030 can be transferred to a thermal fluid within the thermal fluid loop 1000 in a first heat pump 1100. This thermal energy in the thermal fluid is then transferred to the fresh air that will be introduced into the dryer zones in 5 a second heat pump 1150. The use of a thermal fluid loop may facilitate the installation of systems according to the present invention where the waste heat source is remote from the dryer.

Claims

1. A drying system for drying a gypsum product, the drying system comprising: a dryer comprising at least one dryer zone, at least one heat pump located in the at least one dryer zone; and a source of waste heat;wherein the heat pump is configured such that, in use, heat energy from the source of waste heat is used to heat the at least one dryer zone.

2. The drying system of claim 1, wherein the source of waste heat comprises calcination fumes, process water, process fumes, preheater zone fumes and / or exhaust fumes.

3. The drying system of claim 1 or claim 2, wherein the heat pump is configured to heat the at least one dryer zone directly.

4. The drying system of any one preceding claim, wherein the heat pump is configured, in use, to indirectly heat the at least one dryer zone by heating air entering the at least one dryer zone.

5. The drying system of claim 3, wherein at least one dryer zone comprises at least one dryer zone exhaust, wherein in use, the at least one dryer zone exhaust transfers heat energy from a one dryer zone to another dryer zone.

6. The drying system of any one preceding claim, wherein the dryer comprises a plurality of dryer zones.

7. The drying system of claim 6, wherein the dryer comprises a first dryer zone, a second dryer zone and a third dryer zone.

8. The drying system of claim 6 or claim 7, wherein the system is configured to transfer waste heat to two or more of the dryer zones.

9. The drying system of any one preceding claim, wherein the system comprises a plurality of sources of waste heat and a plurality of heat pumps, wherein when inuse, the plurality of heat pumps are configured to transfer heat energy from the plurality of waste heat sources to the at least one dryer zone.

10. A method of drying a gypsum product, the method comprising:providing a dryer with at least one dryer zone;providing at least one heat pump located in the at least one dryer zone;providing a source of waste heat; andusing the heat pump to transfer heat energy from the source of waste heat to heat the at least one dryer zone.

11. The method of claim 10, wherein the method comprises maintaining the temperature in the at least one dryer zone between 80°C and 200°C.

12. The method of claim 10 or claim 11, wherein the method comprises providing a dryer with a plurality of dryer zones.

13. The method of claim 12, wherein the method comprises maintaining a first dryer zone within the plurality of dryer zones at a first temperature, and maintaining a second dryer zone within the plurality of dryer zones at a second temperature.

14. The method of claim 12 or claim 13, wherein the method comprises transferring waste heat from a first dryer zone to another dryer zone.

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