WO2020070064A1

WO2020070064A1 - Energy efficient heating process

Info

Publication number: WO2020070064A1
Application number: PCT/EP2019/076447
Authority: WO
Inventors: Sami Kristian VAPALAHTI; Patrick PIROTTE; Keung Wing Elba SUNG
Original assignee: Vapalahti Sami Kristian; Pirotte Patrick; Sung Keung Wing Elba
Priority date: 2018-10-01
Filing date: 2019-09-30
Publication date: 2020-04-09

Abstract

The present invention relates to the field of Furnaces, Kilns, Ovens and/or Smelters for high or low heating processes and is directed to improvements in the hardware design of such devices yielding an efficient energy heating process in such devices. In a first aspect the present invention provides an improved method for heating a load in such devices base on an optimization and alignment of the heat source with the thermal absorptive characteristics of the load. Implementation of said optimization includes modifications in said devices, and the thus modified devices representing a further aspect of the present invention.

Description

ENERGY EFFICIENT HEATING PROCESS

FIELD OF THE INVENTION

The present invention relates to the field of Furnaces, Kilns, Ovens and/or Smelters for high or low heating processes and is directed to improvements in the hardware design of such devices yielding an efficient energy heating process in such devices.

In a first aspect the present invention provides an improved method for heating a load in such devices based on an optimization and alignment of the heat source with the thermal absorptive characteristics of the load. Implementation of said optimization includes modifications in said devices, and the thus modified devices representing a further aspect of the present invention. Briefly, said modifications include the compressed high-density insulating material at the inside of the heating compartment and the application of a high reflective coating at intermittent layers of insulating material.

BACKGROUND TO THE INVENTION

Present improvement in energy usage of Furnaces, Kilns, Ovens and/or Smelters for high or low heating processes are currently primarily directed to improvements in the insulation of such devices and typically includes a metal frame with the construction of the walls and door(s) of the heating compartment with low and high temperature insulating fibers and/or aerogels such as ceramic fibers or an Alumino Silicate (AS) resin. At the inside of the heating compartment these insulating layers could further be treated with a heat reflective coating to be effective as further insulation. The thermal reflective coating layer is used to reflect the heat back to the furnace inside to further improve the insulation and thermal efficiency of these devices.

Notwithstanding the thus improved insulation, there is still a desire to further improve the energy efficiency of these devices, in particular those operating at high temperatures such as kilns for ceramic or smelters of any kind of for any purpose with operating temperatures up to 1900 degrees Celsius.

It is an objective of the present invention to address this desire and provide methods and hardware to achieve an energy efficient heating process applicable in any device using a heat source to heat a load with said device. The method and materials are particularly useful in Furnaces, Kilns, Ovens and/or Smelters for high or low heating processes; more in particular in Furnaces, Kilns, Ovens and/or Smelters for high heating processes.

SUMMARY OF THE INVENTION

The present invention can be summarized by the following numbered embodiments. With these embodiments the objectives of this application are being formulated and herein presented in multiple generic forms. Evidently any obvious modifications of these embodiments are considered admit the teaching of the invention as herein disclosed.

1. In a first objective the present method provides a method for heating a load in a heating compartment of a heating device said method being characterized in.

• Using a heat source with emission wavelengths from near infrared wavelengths to mid infrared wavelengths; in particular in the range from 0.7 pm till 10 pm; more in particular the bandwidth of the emission wavelengths are near infrared wavelengths; in particular from about 0.3 pm to about 10 pm, and

• In that the load is treated with an absorptive coating that is highly absorptive for the emission wavelength of the heat source.

2. The method according to embodiment 1 , wherein the absorptive coating is a ceramic coatings comprising a refractory pigment, a high emissivity additive and a binder/suspension agent.

3. The method according to embodiment 2, wherein the refractory pigment is selected from the group consisting of zirconia, zirconia silicate, aluminum oxide, aluminum silicate, silicon oxide, and the like.

4. The method according to embodiment 2, wherein the high emissivity additive is typically a transition metal oxide such as chromium oxide (Cr2 03), cobalt oxide (CoOx), ferrous oxide (Fe2 03), and nickel oxide (NiO).

5. The method according to embodiment 2, wherein the binder/suspension agent is typically an aqueous solution or suspension of silicates or phosphates.

6. The method according to embodiment 1 , further comprising treating the heating element and its immediate environment with a a high emissive and high reflective coating for the emission wavelengths of the heat source.

7. The method according to embodiment 6, wherein said high emissive and high reflective coating comprises T1O2 particulates which have increased reflectance in the short and mid infrared wavelengths. The reflective particulates can include at least one of a spherical shape, a conical shape, an elliptical shape, a spheroid shape, or a fibre; and will typically be less than about 4 microns in diameter and in length.

8. The method according to any one of the foregoing embodiments wherein the bandwidth of the emission wavelengths is minimized by increasing the heat source temperature, such as for example by optimizing air/fuel -ratio, pre-heating of combustion air, replacing air with oxygen, burning fuels with high energy density (e.g. oil versus gas), changing fuel properties to burn faster, and the like.

9. The method according to any one of the foregoing embodiments further comprising treating the heating compartment at the inside with a high reflective coating, i.e. high reflective for the emission wavelengths of the heat source. 10. The method according to embodiment 9 wherein said high reflective coating has a low absorptivity for the emission wavelengths of the heat source.

1 1. The method according to embodiments 8 or 10, wherein said compressed or high- density insulating material is selected from compressed and/or High-Density Fiber Glass / Ceramics / Aluminosilicate or any kind of compressed and/or High-Density Refractory Fibers and/or Aerogel’s.

12. The method according to embodiment 10 wherein the heating compartment comprises the combination of compressed or high-insulating material and low-density insulating material, the compressed or high-density material being at the inside of the heating compartment.

13. The method according to embodiment 14, wherein the compressed or high-density insulating material and the low-density material are separated from one another by means of a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source.

14. The method according to embodiment 14 the heating compartment comprises the combination of a higher-density insulating material with repeated layers of low-density insulating materials, the higher-density material being at the inside of the heating compartment, and wherein each of the layers are separated from one another by means of a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source.

15. The method according to any one of embodiments 14 to 16, wherein the low-density insulating materials are being selected from Low-Density Fiber Glass / Ceramics / Aluminosilicate or any kind of Low-Density Refractory Fibers and/or Aerogel’s.

16. The method according to any one of embodiments 14 to 17, wherein the low-density insulating materials are porous insulating materials.

17. In a second embodiment the present invention provides a heating device with a heating source for heating a load in a heating compartment said heating device being characterized in that the heating compartment comprises compressed and/or High- Density Fiber Glass / Ceramics / Aluminosilicate or any kind of compressed and/or High- Density Refractory Fibers and/or High-Density Aerogel’s insulating material at the inside of the heating compartment.

18. The heating device according to embodiment 19, wherein said compressed or high- density insulating material is treated with a high reflective coating, i.e. high reflective for the emission wavelengths of the heat source.

19. The heating device according to embodiment 20, wherein said high reflective coating comprises T1O2 particulates which have increased reflectance in the short and mid infrared wavelengths; in particular T1O2 particulates which are less than about about 4 microns in diameter and in length; and more in particular include at least one of a spherical shape, a conical shape, an elliptical shape, a spheroid shape, or a fibre. 20. The heating device according to embodiment 18, wherein the insulating material, is made out of layers of compressed and/or High-Density Fiber Glass / Ceramics / Aluminosilicate or any kind of compressed and/or High-Density Refractory Fibers and/or Aerogel’s; in particular layers of compressed Aluminosilicate.

21. The heating device according to any one of the embodiments 17 to 20, wherein the compressed and/or High-Density Fiber Glass / Ceramics / Aluminosilicate or any kind of compressed and/or High-Density Refractory Fibers and/or Aerogel’s, is compressed for at least 40% compared to the standard Fiber Glass / Ceramics / Aluminosilicate / Refractory Fibers / and/or Aerogel insulating materials.

22. The heating device according to any one of embodiments 17 to 21 , wherein the insulating material is compressed Aluminosilicate, wherein said compressed Aluminosilicate is compressed for at least 40% compared to the standard Aluminosilicate.

23. The heating device according to embodiment 17 wherein the insulating material in the heating compartment comprises the combination of compressed or high-density insulating material as defined in any one of embodiments 17 to 22 and low-density insulating material, the compressed or high-density material being at the inside of the heating compartment.

24. The heating device according to embodiment 23, wherein the insulating material comprises the combination of compressed or high-density insulating material as defined in any one of embodiments 17 to 22 with repeated layers of low-density insulating material, the compressed or high-density material being at the inside of the heating compartment.

25. The heating device according to embodiments 23 and 24, wherein the compressed or high-density material and the low-density material are separated from one another by means of a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source; more in particular the high reflective coating according to embodiment 19.

26. The heating device according to embodiment 24 wherein insulating material comprises the combination of a higher-density insulating material as defined in any one of embodiments 17 to 22 with repeated layers of low-density insulating materials, the higher-density material being at the inside of the heating compartment, and wherein each of the layers are separated from one another by means of a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source; more in particular the high reflective coating according to embodiment 19.

27. The heating device according to any one of embodiments 23 to 26, wherein the low- density insulating materials are porous insulating materials.

28. The heating device according to any one of embodiments 23 to 26, wherein the low- density insulating materials are made from the non-com pressed standard Fiber Glass / Ceramics / Aluminosilicate / Refractory Fibers / and/or Aerogel insulating materials; in particular made from the same material as the compressed High-Density Fiber Glass / Ceramics / Aluminosilicate / High-Density Refractory Fibers and/or Aerogel’s.

29. The heating device according to any one of embodiments 23 to 26, wherein the insulating material comprises the combination of compressed Aluminosilicate and non- compressed Aluminosilicate, with the compressed Aluminosilicate at the inside of the heating compartment; in particular compressed Aluminosilicate and layers of non- compressed Aluminosilicate, with the layer of compressed Aluminosilicate at the inside of the heating compartment.

30. The heating device according to any one of embodiments 23 to 26, wherein the low- density insulating materials are each idependently selected from non-com pressed standard Fiber Glass / Ceramics / Aluminosilicate / Refractory Fibers / Aerogel insulating materials / low-density open or a medium-density Closed-Cell Spray Foam or other insulating coatings; in particular made from the same material as the compressed High-Density Fiber Glass / Ceramics / Aluminosilicate / High-Density Refractory Fibers and/or Aerogel's.

31. The heating device according to any one of embodiments 23 to 26, wherein the low- density insulating material consists of a low-density open or a medium-density Closed- Cell Spray Foam or other insulating coatings applied to the inside of the perimeter panels, i.e. side panels and top panel, of the furnace.

32. The heating device according to embodiment 19, wherein the heat source comprises a heating element such as a burner in case of a fuel heated device, characterized in that said heating element, in particular the burner and its immediate environment of the combustion is treated with a high reflective coating, i.e. high reflective for the emission wavelengths of the heat source; in particular said high emissive and high reflective coating comprises T1O2 particulates which have increased reflectance in the short and mid infrared wavelengths. The reflective particulates can include at least one of a spherical shape, a conical shape, an elliptical shape, a spheroid shape, or a fibre; and will typically be less than about 4 microns in diameter and in length.

33. The heating device according to any one of embodiments 19 to 29, wherein the bandwidth of the emission wavelengths of the heat source is from near infrared wavelengths to mid infrared wavelengths; in particular in the range from about 0.7 pm till about 10 pm; more in particular from about 0.3 pm till about 10 pm.

34. The heating device according to any one of embodiments 17 to 31 wherein the surface of the compressed or high-density insulating material at the inside of the heating compartment is corrugated.

35. The heating device according to embodiment 32 wherein the crests and troughs of the corrugations are aligned according to the circumference of the heating compartment. 36. The heating device according to embodiments 32 or 33 wherein the corrugations have one or more profiles selected from a wave, pyramid, triangle, rounded triangle, and the like.

37. The heating device according to any one of embodiments 17 to 34, wherein said heating device comprises a door at one or both of its peripheral ends of the heating compartment.

38. The heating device according to embodiment 35, wherein the crests and troughs of the corrugations of said door(s) are aligned perpendicular to the orientation of the crests and troughs of the walls.

39. The heating device according to any one of the embodiments 17 to 35, wherein the heating device comprises a heating compartment frame and wherein the inslating materials making up the walls, ceiling and bottom parts of the heating device and are suspended in is said frame.

40. The heating device according to embodiment 37, wherein the insulating materials are suspended in said frame by means of anchoring bars across said insulating materials, optionally cooperating with wall / side plates installed on the frame.

41. The heating device according to embodiment 37, wherein the insulating materials making up the ceiling part are suspended to the frame by means of ceiling supports fixed to a profile at the top of the furnace frame.

BRIEF DESCRIPTION OF THE DRAWINGS

With specific reference now to the figures, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the different embodiments of the present invention only. They are presented in the cause of providing what is believed to be the most useful and readily description of the principles and conceptual aspects of the invention. In this regard no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Fig. 1 : Exploded view of a heating device according to the invention. Showing the stacking of the compressed or high-density insulating material in the frame making up the kiln. In this embodiment the heating compartment has doors at either of its peripheral ends. The flat base of heating compartment is visible as well as the corrugations of the surfaces at the inside of the heating compartment. In this embodiment the corrugations of the ceiling and walls of the heating compartment are oriented along the longitudinal circumferential direction of the heating compartment and continues accordingly on the doors of the device. Fig. 2: Perspective view of a heating device according to the invention. Showing the stacking of the compressed insulating material in the frame making up the kiln. In this embodiment the heating compartment has doors at either of its peripheral ends. The flat base of heating compartment is visible as well as the wave shaped corrugations 500 of the surfaces at the inside of the heating compartment. In this embodiment the corrugations of the walls of the heating compartment are oriented along the longitudinal circumferential direction of the heating compartment, whilst the corrugations 500’ of the ceiling and doors are oriented along the transversal direction of the heating compartment. Such crossed alignment of the corrugations further enhanced the heating efficiency of the device.

Fig. 3: Experimental results of heating stainless steel before and after optimizing in gas fired furnace.

Fig. 4: Experimental results of heating ceramic fire brick before and after optimizing in electrically furnace.

Fig. 5: Load temperature variation comparison before and after optimizing.

Fig. 6: Detailed view of the stacks of compressed high-density insulating materials used in the assembly of a heating device according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The methods of the present invention are based on the insight that the current methods to calculate heat transfer from a heating source to a source ignore the thermal reflectivity of materials, and when considering the spectral emissivity of materials this is simply seen as the inverse of its spectral absorption.

Now when looking at the normalized thermal radiation of an object this can be expressed as; a + p + T = 1 (1 )

Where a is spectral absorption, p is spectral reflection and t is spectral transmission. Spectral absorption is equal to emissivity a = e = 1. In other words, emissivity can be described as capability to release energy from material and reflection as resistance to absorb heat from outside.

The current formulation of heat transfer is: Q = h*A*(T1-T4) + e*s*(T1^A4-T2^A4) (2)

Where h is heat transfer coefficient, A area, T1 atmosphere temperature, T2 wall surface temperature, e emissivity, and s is Stefan-Boltzmann coefficient. As mentioned herein before, the current formulation does not include reflectivity p and as such not taken into account when discussing surface properties of materials in heat transfer. This has indeed led to the assumption that emissivity is the inverse of absorption, i.e.; in that a = p = 1/e.

However, when reflection is mentioned in this patent application it refers to actual p that can mathematically be defined as: p = 1 - a - T (3)

When optimizing of energy efficiency in heating is considered there are several severe limitations in this formulation that cause problems in defining the optimum heat transfer. The basic formulation cannot be used to correctly estimate the benefits of several aspects of methods described in this application and so it should not be used to estimate the actual benefits and their importance.

At least the following limitations should be considered:

1 . Formulation does not include reflectivity of surfaces

2. All radiation and interactions are based on temperature and radiation wavelengths.

Formulation does not include any wave length-based properties.

3. Emissivity and reflectivity of each surface can be different and are both wavelength and temperature dependent.

4. The net flow of heat is always from high to low temperature as expressed in (2). When reflection is being considered it must be emphasized that there is emitted energy from lower temperature also that is reacting with higher temperature surfaces. When reflection is increased it will not decrease radiation emitted by lower temperature surface, but it will reflect it off the wall lowering the wall temperature and making the radiation be available to hit other surfaces such as the load.

Expressed differently, in the standard approach of looking at heat transfer, no account is given to the fact that thermal energy is transferred by thermal radiation, i.e. through electromagnetic waves acting in essence like for example light waves leaving a light source and hitting a surface where part of it will be absorbed and part of it will be reflected.

As for light reflection, thermal reflection is material property that reflects electromagnetic waves and is commonly caused by but not limited to transition metal oxides such as Ti02. Thermal reflection takes place when thermal radiation interacts with material. As it prevents part of the electromagnetic waves to enter the material, reflectivity will influence the heating kinetics of a material. As will become apparent from the examples hereinafter, it has now been found that thermal reflectivity of a material is not per se limited to the surface but also functioning within a material or structure.

Emissivity is related to energy that is already absorbed by material and then the material is reemitting this already absorbed energy. Think for example of a brick wall exposed to the sun during daytime, absorbing heat. Even during its exposure to the sun, the brick wall will try to emit this absorbed heat back into the environment, an emissivity that can be experienced when the wall is no longer exposed to the sun. As emissivity is related to the energy already absorbed by the material, in the context of the invention the load in the heating device, the emissivity value of the material is not important in this methodology when compared to reflection. Emissivity can be low or high although high emissivity can be beneficial.

Absorption of material is related to emissivity since only energy that is absorbed can be emitted. But absorption is not a function of emissivity since it can be limited by material density or transparency to specific wave lengths. Low density material cannot absorb energy as much as high density since there is less storage for energy and electromagnetic waves pass through spectrally transparent materials. Being a parameter relevant for the amount of heat that can be absorbed, it has been found to be an important factor in the methods and device implementation of the present invention. The speed at which the heat can be absorbed by a material will be depended on its availability for the energy to which it is being exposed. The lower the reflectivity of the material for the energy to which it is being exposed, the more energy will be available for absorption.

Consequently, absorption can be increased by tailoring radiation wave lengths and by increasing radiation intensity. The effect of wave length on absorption has not been investigated as much as the effect of increased radiation intensity. Some examples how wave lengths have been tailored over the years is e.g. water addition and oxygen in combustion although it has not been seen as an important change in heat transfer. Intensity of radiation has been researched through years especially by comparing combustion of different fuels, but its effectivity has been underestimated. Assumingly one reason is that only different intensities of the heat sources have been studied, not the effect of further changing properties of radiation interaction with different surface. Due to lack of understanding about the intensity of radiation, the importance of reflectivity has further been underestimated in current models and design of heating devices. The existing results indicate that flue gas analysis and the effect of exiting flue gas properties have much smaller role in energy efficiency than currently anticipated. It seems that the benefits of lower excess oxygen and lower flue gas temperature are dependent on the process and mainly connected with properties of radiation produced by combustion i.e. higher flame temperature and faster combustion front.

Energy efficiency has for years concentrated only on improved insulation and lowering flue gas losses even without real scientific proof that flue gas losses have proven relation to energy efficiency and how. What is introduced now is the new approach that is concentrating on heating efficiency where heat transfer is optimised by taking also into account reflectivity so that absorption to load is maximized. This is different from previous approach since a new parameter is now introduced: heating rate as a function of reflectivity and absorption. In previous approach the only method to increase heating rate was to increase power. However, by increasing power several problems are introduced mainly due to tensions or uneven phenomena created by temperature gradients. By optimizing the emission wavelengths of the heat source, and adjusting the reflectivity of the heating compartment, the present invention results in faster heat penetration and decreased temperature gradients even if power is increased leading to faster production with decreased energy consumption.

Thus, the present invention provides a method for heating a load in a heating compartment of a heating device using a heating source, said method being characterized in that; the bandwidth of the emission wavelengths of the heat source is aligned with the bandwidth of absorption wavelengths of the load. It further provides the heating devices thus optimized.

The heating devices as used herein is generally related to Furnaces, Kilns, Ovens and/or Smelters for high or low heating processes. Each of said devices comprising a heating compartment wherein an object or material, herein referred to as the load, will be heated for example as part of a production process. The develop and designed system is cumulative and can be applied to any length, size or shape of Furnaces, Kilns, Ovens and/or Smelters for high or low heating processes. The invention is particularly related to a kiln for roasting ceramic, cement, glass and other materials, including furnace, oven, melting and indoor heating furnace. Examples of such kilns are shown in Figures 1 and 2. The kilns include furnace body 100 and door panel 200, wherein the furnace body (heating device) 100 comprises a furnace frame or bracket 1 10 and a wall plate 120, wherein the wall plate 120 is installed on the furnace bracket 1 10 and the furnace bracket is further provided with a top wall plate 130 and a bottom support 140. The inner side of the wall 120, top 130 and bottom support 140 (here, the inside refers to the inside of the heating compartment (300 of the furnace) have an insulating layer 150, respectively insulating layers making up the walls 150a, an insulating layer making up the ceiling of the furnace 150b, and an insulating layer making up the bottom part of the furnace 150c. Anchoring bars 160 across said insulating layers and cooperating with optional side plates 170, 180 (in case of the ceiling and bottom part) and the furnace frame suspend the walls 150a, ceiling 150b and bottom parts 150c into the frame. The oven doors are also provided at the inside with the same insulating layers 150d used in making op the walls 150a, ceiling 150b and bottom parts 150c of the furnace. The heating elements 400, electrical heating resistors are present alongside the walls at the inside of the heating compartment. In this embodiment, the furnace frame 1 10 is preferably a steel frame, wherein the wall plate 120 and the door panel 200 are preferably steel plates. The heat insulating layer 150 can prevent the heat from spreading to the outside of the kiln, and damage the structure of the furnace frame 1 10, the wall plate 120 and the oven door 200 as a result of high temperature. There are no particular design limitations when it comes to the shape and dimensions of these kilns. In specific examples of Kilns according to the invention the thickness of the top plate 130, wall plates 120, and side plates 170, 180 can be 6 mm - 10 mm. The insulating layers 150 are made out of layers of compressed insulating material, in particular layers of compressed Aluminosilicate. Compared to the standard Aluminosilicate, the compressed Aluminosilicate is compressed for at least 40%, in particular at least 45%; more in particular up to about 60%. The composite layers of compressed insulating material within said insulating layers have a thickness of up to about 6 mm to about 50 mm. The assembled insulating layers of compressed insulating material making up the walls, top and bottom parts of these kilns typically have an overall width of up to about 500 mm; in particular up to about 300 mm. Using the compressed or high-density materials this low overall thickness has been found sufficient to achieve an efficient insulation. Per reference to to Figure 6, the stacks of compressed insulating materials suspended in the furnace frame and making up the walls, base and ceiling of the oven are coated at the inside with a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source. Such frame configuration enables easy installation and creates flexibility in adjusting or replacing the layers of compressed insulating material. It further allows prefabrication of the insulating modules, with a high flexibility, not only in relation to the size and shape of the furnace, but alos in for example redesign of the modules with a relining of existing furnaces.

The skilled person is knowledgeable about the available methods and tools to determine the bandwidth of emission wavelengths of the heat source and to determine the bandwidth of the absorption wavelengths of the load. Any of said art known methods can be used and is not further detailed in the present application. As already summarized herein before, the bandwidth of the emission wavelengths can be optimized by changing the heat source temperature, such as for example by optimizing air/fuel -ratio, pre-heating of combustion air, replacing air with oxygen, burning fuels with high energy density (e.g. oil versus gas), changing fuel properties to burn faster, and the like. In a preferred embodiment the bandwidth of the emission wavelengths is from near infrared wavelengths to mid infrared wavelengths; in particular in the range from about 700 nm till about 10 pm; more in particular from about 0.3 pm till about 10 pm. To enhance the emission from the heat source, it could be beneficial to have its immediate environment highly reflective for the bandwidth of the emission wavelengths. When the heating device is for example a fuel heated device, the heat source will comprise as a heating element a burner for the flames. In case of an electrically heated device, the heat source will comprise a heating resistor as a heating element. In the context of the present invention, the immediate environment of the heat source includes the surface of the heating device like the burner or its immediate adjacent area.

Instead of determining the absorption wavelength of the load it is also possible to align it to the emission wavelengths of the heat source by treating the load with a coating absorptive for the emission wavelengths of the heat source. In particular having a high absorptivity for said bandwidth of wavelengths and a low reflectivity for said bandwidth of wavelengths.

Examples of such coatings include ceramic coatings comprising a refractory pigment, a high emissivity additive and a binder/suspension agent. Typical refractory pigments include zirconia, zirconia silicate, aluminum oxide, aluminum silicate, silicon oxide, etc. The high emissivity additive is typically a transition metal oxide such as chromium oxide (Cr2 03), cobalt oxide (CoOx), ferrous oxide (Fe2 03), and nickel oxide (NiO). In some coatings, the refractory pigment and the high emissivity additive are the same material. The binder/suspension agent allows the coating to be applied like ordinary house paint and withstands the anticipated use temperature. The binder/suspension agent acts like a high temperature glue and is typically an aqueous solution or suspension of silicates or phosphates.

To enhance the heating rate even further, it has been found beneficial to use materials at the inside of the heating compartment having a high reflectivity for the bandwidth of emission wavelengths of the heat source. Such high reflectivity will typically be achieved by treating the inside of the heating compartment with a high reflectivity coating. Per reference to Figures 1 and 2, in these embodiments, the thermal insulating layer 140 also has a heat reflective coating layer (not shown separately), and the thermal reflective coating layer is used to reflect the heat back to the furnace inside to further improve the thermal efficiency.

The coating layer of the thermal reflection coating does not make specific restrictions, as long as the required thermal reflection effect can be achieved. Such coating normally comprise a base material and a plurality of reflective particulates disposed in the base material. The base material can include a ceramic material (e.g., that inherently has a low absorbance and reflectance of infrared radiation). Any other suitable material is contemplated herein. The reflective particulates can include a material that reflects infrared radiation (e.g., including wavelengths below about 8 microns, wavelengths less than 4 microns). Any suitable material for the particulates is contemplated herein (e.g., such that the reflective particulates reflect thermal radiation to a greater extent than the base material in at least a certain range of wavelengths). For example, the reflective particulates can include T1O2 particulates which have increased reflectance in the short and mid infrared wavelengths. The reflective particulates can include at least one of a spherical shape, a conical shape, an elliptical shape, a spheroid shape, or a fibre; and will typically be less than about 4 microns in diameter and in length. Disposing one or more reflective layers can include thermal spraying or cold spraying the base material with reflective particulates. Applying and disposing can be at least partially simultaneously performed by spraying the substrate or the base material with a slurry including the base material and the reflective particulates.

As mentioned herein before, next to the reflectivity also the absorptivity is an important parameter in the heating kinetics of a heating device. It has surprisingly been found that the efficiency can be improved by applying compressed or high-density insulating materials at the inside of the heating compartment. Such insulating materials could be based on the insulating materials typically used in the manufacture of such Furnaces, Kilns, Ovens and/or Smelters, like Aerogels, Fiber Glass/Ceramics/Aluminosilicate or any kind of Refractory Fibers for high and low temperature constructions, but then in a compressed and/or high-density configuration. Such layer of compressed or high-density insulating materials should however be limited to only the inside layer of the insulating layer making up the walls of the device.

Hence, in a further embodiment the insulating layer will comprise a higher density and low- density insulating materials wherein the higher density insulating material is present at the inside of the heating compartment. In one embodiment the insulating layer will have a gradient from a higher density to low density insulating materials wherein the higher density insulating material is present at the inside of the heating compartment. In one embodiment the insulating material comprises the combination of compressed or high-density insulating material with repeated layers of low-density insulating materials, the compressed or high-density material being at the inside of the heating compartment. In another embodiment the insulating layer comprises the combination of a compressed or higher-density insulating material with repeated layers of low- density insulating materials, the compressed or high-density material being at the inside of the heating compartment, and wherein each of the layers are separated from one another by means of a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source. The intermittent layers of reflective coating enhance the heat radiation from the walls to the inside of the heating compartment. In a particular embodiment, stacks of compressed high-density insulating materials making up the walls, base and ceiling of the furnace are combined with a low-density insulating material, wherein the higher density insulating material is present at the inside of the heating compartment and the low-density insulating material as present at the outside perimeter of the furnace. In particular said outside low-density insulating material, consists of a low-density open or a medium-density Closed-Cell Spray Foam or other insulating coating applied to the inside of the perimeter panels, i.e. side panels and top panel, of the furnace. Inbetween the layer of compressed high-density insulating materials and said layer of low-density insulating material a furher heat reflective coating could be applied. In a preferred embodiment such further relective coating will be present between said layers.

A further design parameter contributing to the efficiency of the kilns according to the invention is apparent from Figures 1 and 2. It shows the corrugation of the inside surfaces of the heating compartment. The corrugations are aligned according to the circumference of the heating compartment. The circumferences include both the circumference along the longitudinal direction of the device, i.e. in horizontal orientation with respect to the base of the oven; or in a transversal direction of the device, i.e. in a vertical orientation with respect to the base of the device. As apparent from the figures the crest and troughs of the corrugations can be oriented according to either of said circumferential directions. In one embodiment there is a crossed alignment of the corrugations between the corrugations of walls and respectively doors and/or ceiling of the heating device. Surprisingly such crossed configuration enhanced the heating efficiency of the device. Pyramid shaped corrugations proved to have a positive effect on the reflectivity of the surface and accordingly represents a further interesting embodiment in the context of the present invention.

This and further aspects of the invention will become apparent from the following examples and claims hereinafter, which do not limit the scope of the invention in any way.

EXAMPLES

Faster heating has been shown in both fuel combustion heating of stainless steel (Figure 3.) and in electrical heating with ceramic fire bricks used as load (Figure 4).

Figure 3. Experimental results of heating stainless steel before and after optimizing in gas fired furnace.

The stainless-steel experiments were made in natural gas fired open flame furnace. A stainless- steel cylinder (D75 x 200 mm) was heated in the furnace and its temperature was measured at centre mass. The results in Figure 3. have optimized furnace graph on light grey and non- optimized with black. Furnace temperature profile is the solid line, stainless steel sample as dashed line, and temperature difference as dash-dotted line.

The challenge to execute exact combustion experiments is related to automation level of the test furnace. In this experiment power was increased and that increased heating speed. What proofs the increased absorption rate is that the temperature at the centre of the test sample has smaller temperature difference to furnace atmosphere even after increased power and centre reaches holding temperature 7 % faster than the sample in furnace without optimizing. Figure 4. Experimental results of heating ceramic fire bricks before and after optimizing in electrically furnace, and Figure 5. Load temperature variation comparison before and after optimizing.

The experiment in Figures 4 and 5 was carried out as comparison between conventional and optimized furnace. The load was about 100 kg of chamotte based fire bricks that included 3 thermocouples (TC 1 , TC 2, and TC 3) for measuring the internal temperature at different locations. The TC’s where inserted into 6 bricks that were glued together at different distance (from the centre to the outside of the 6 bricks) and placed in the centre of the oven Heating cycle was defined as heating with maximum power to 1200 °C and holding 2 hours.

In Figure 4 and 5 the optimized furnace graphs are light grey and conventional furnace graphs in black. In Figure 4 solid lines are furnace temperature, dashed lines power consumption, dotted line is TC 1 , dash-dotted -line, and TC 3 dash-double dotted -line.

In conventional furnace the average temperature of the three thermocouples is 933 °C at the end of the heating cycle at 4 hours and 4 minutes. As the atmosphere temperature was reached earlier in the conventional solutions the duration of the experiment was shorter. The optimized furnace was able to heat the load to same average temperature 933 °C at 3h 30 minutes. In Figure 5 it is illustrated that the load is not only heated faster but more equally as the difference between maximum and minimum measured temperature is less.

There is still need for testing on actual production but according to the foregoing experiments it is to be expected that all time dependent phenomena, which in e.g. metallurgical and ceramic products are energy and temperature dependent, will be performed faster and require less energy. If energy is absorbed at faster rate also processes like diffusion, phase changes, or chemical bonding will be performed faster using a furnace as herein described.

List of depicted parts for the embodiments shown in Figures 1 and 2 - (representative fori

100 Furnace body (heating device)

1 10 Frame construction Furnace (Frame)

120 Side wall panel to be treated with insulation coating on the inside (wall panel)

130 Top plate oven (top or top panel)

140 Ceramic bottom support (bottom support)

150a Compressed AS Furnace wall (insulating material making up a wall part)

150b Compressed AS Furnace ceiling (insulating material making up the ceiling part)

150c Compressed AS Furnace bottom (insulating material making up the bottom part)

150d Compressed AS Furnace doors (insulating material at the inside of the doors) 160 Anchoring bars

165 Support profiles of the anchoring bars of the walls

170 Steel side plates for the compressed AS Furnace ceiling (side plate ceiling part) 180 Steel side plates for the compressed AS Furnace bottom (side plate bottom part) 190 Ceiling supports present in between the layers of Compressed AS Furnace ceiling to suspend and fix the ceiling part to a profile at top of the furnace frame

195 Profile to fix the ceiling supports

200 Furnace door (Oven door)

300 Inside of the oven with silicon carbide bottom tiles (heating compartment)

400 Heating elements

500 Corrugations

Claims

1. A heating device with a heating source for heating a load in a heating compartment said heating device being characterized in that the heating compartment comprises compressed and/or High-Density Fiber Glass / Ceramics / Aluminosilicate or any kind of compressed and/or High-Density Refractory Fibers and/or High-Density Aerogel's insulating material at the inside of the heating compartment.

2. The heating device according to claim 1 , wherein said compressed or high-density insulating material is treated with a high reflective coating, i.e. high reflective for the emission wavelengths of the heat source.

3. The heating device according to claim 2, wherein said high reflective coating comprises Ti02 particulates which have increased reflectance in the short and mid infrared wavelengths; in particular Ti02 particulates which are less than about about 4 microns in diameter and in length; and more in particular include at least one of a spherical shape, a conical shape, an elliptical shape, a spheroid shape, or a fibre.

4. The heating device according to claim 1 , wherein the insulating material, is made out of layers of compressed and/or High-Density Fiber Glass / Ceramics / Aluminosilicate or any kind of compressed and/or High-Density Refractory Fibers and/or Aerogel's; in particular layers of compressed Aluminosilicate.

5. The heating device according to any one of claims 1 to 4, wherein the compressed and/or High-Density Fiber Glass / Ceramics / Aluminosilicate or any kind of compressed and/or High-Density Refractory Fibers and/or Aerogel's, is compressed for at least 40% compared to the standard Fiber Glass / Ceramics / Aluminosilicate / Refractory Fibers / and/or Aerogel insulating materials.

6. The heating device according to any one of claims 1 to 4, wherein the insulating material is compressed Aluminosilicate, wherein said compressed Aluminosilicate is compressed for at least 40% compared to the standard Aluminosilicate.

7. The heating device according to claim 1 , wherein the heating compartment comprises the combination of compressed or high-density insulating material as defined in any one of claims 1 to 6 and low-density insulating material, the compressed or high-density material being at the inside of the heating compartment.

8. The heating device according to claim 7, wherein the heating compartment comprises comprises the combination of compressed or high-density insulating material as defined in any one of claims 1 to 6 with repeated layers of low-density insulating material, the compressed or high-density material being at the inside of the heating compartment.

9. The heating device according to claims 7 and 8, wherein the compressed or high-density material and the low-density material are separated from one another by means of a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source; more in particular the high reflective coating according to claim 3.

10. The heating device according claim 8 wherein each of the layers are separated from one another by means of a high reflective coating layer, in particular high reflective for the emission wavelengths of the heat source; more in particular the high reflective coating according to claim 3.

1 1. The heating device according to any one of claims 7 to 10, wherein the low-density insulating materials are porous insulating materials.

12. The heating device according to claim 1 1 , wherein the low-density insulating materials are each idependently selected from non-compressed standard Fiber Glass / Ceramics / Aluminosilicate / Refractory Fibers / Aerogel insulating materials / low-density open or a medium-density Closed-Cell Spray Foam or other insulating coatings; in particular made from the same material as the compressed High-Density Fiber Glass / Ceramics / Aluminosilicate / High-Density Refractory Fibers and/or Aerogel's.

13. The heating device according to claim 1 1 , wherein the low-density insulating material consists of a low-density open or a medium-density Closed-Cell Spray Foam or other insulating coatings applied to the inside of the perimeter panels, i.e. side panels and top panel, of the furnace.

14. The heating device according to any one of claims 7 to 10, wherein the heating compartment comprises the combination of compressed Aluminosilicate as the high- density insulating material and non-compressed Aluminosilicate as the low-density insulating material, with the compressed Aluminosilicate at the inside of the heating compartment; in particular compressed Aluminosilicate and layers of non-compressed Aluminosilicate, with the layer of compressed Aluminosilicate at the inside of the heating compartment.

15. The heating device according to claim 1 wherein the heat source comprises a heating element such as a burner in case of a fuel heated device, characterized in that said heating element, in particular the burner and its immediate environment of the combustion is treated with a high reflective coating, i.e. high reflective for the emission wavelengths of the heat source; in particular said high emissive and high reflective coating comprises Ti02 particulates which have increased reflectance in the short and mid infrared wavelengths. The reflective particulates can include at least one of a spherical shape, a conical shape, an elliptical shape, a spheroid shape, or a fibre; and will typically be less than about 4 microns in diameter and in length.

16. The heating device according to claim 15, wherein the bandwidth of the emission wavelengths of the heat source is from near infrared wavelengths to mid infrared wavelengths; in particular in the range from about 0.7 pm till about 10 pm; more in particular from about 0.3 pm till about 10 pm.

17. The heating device according to any one claims 1 to 16 wherein the surface of the compressed or high-density insulating material at the inside of the heating compartment is corrugated.

18. The heating device according claim 17 wherein the crests and troughs of the corrugations are aligned according to the circumference of the heating compartment.

19. The heating device according to claims 17 or 18 wherein the corrugations have one or more profiles selected from a wave, pyramid, triangle, rounded triangle, and the like.

20. The heating device according to any one of claims 1 to 19, wherein said heating device comprises a door at one or both of its peripheral ends of the heating compartment.

21. The heating device according to claim 20 wherein the door(s) comprise compressed or high-density insulating material as defined in any one of claims 1 to 6, wherein the surface of said compressed or high-density insulating material at the inside of the heating compartment is corrugated.

22. The heating device according to claim 21 , wherein the crests and troughs of the corrugations of said door(s) are aligned perpendicular to the orientation of the crests and troughs of the walls.

23. The heating device according to any one of claims 1 to 22, wherein the heating device comprises a heating compartment frame and wherein the inslating materials making up the walls, ceiling and bottom parts of the heating device and are suspended in is said frame.

24. The heating device according to claim 23, wherein the insulating materials are suspended in said frame by means of anchoring bars across said insulating materials, optionally cooperating with wall / side plates installed on the frame.

25. The heating device according to claim 24, wherein the insulating materials making up the ceiling part are suspended to the frame by means of ceiling supports fixed to a profile at the top of the furnace frame.