WO2019004892A1

WO2019004892A1 - A vertical lime kiln

Info

Publication number: WO2019004892A1
Application number: PCT/SE2018/050520
Authority: WO
Inventors: Christoffer GABRIELSSON
Original assignee: Fältkalk Ab
Priority date: 2017-06-26
Filing date: 2018-05-23
Publication date: 2019-01-03
Also published as: EP3645479A1; SE540217C2; EP3645479A4; SE1750819A1

Abstract

The present disclosure relates to a vertical lime kiln, specifically adapted for allowing mobility and reuse of the material used for constructing the kiln. The present disclosure also relates to a corresponding method for production of lime from limestone using such a kiln.

Description

A VERTICAL LIME KILN

TECHNICAL FIELD

BACKGROUND

In the production of lime from limestone, the limestone is heated in a kiln so as to decompose the same and drive off carbon dioxide according to the general equation: CaC0₃ +Heat→CaO+C0₂ by heating of the limestone to a high temperature and holding it at that temperature for a period of time to effect the decomposition. This calcination, or "burning", requires a large amount of heat.

In modern production of lime from limestone, a rotary kiln is used. The rotary kiln is typically provided as a long, straight tubular steel vessel that is lined on the inside with refractory material. The kiln rotates about an axis at an angle of a few degrees, such as 3° to 5°, to the horizontal, and rests on trunnions which rotate the tubular shell. Limestones are introduced to a calcining chamber in the rotary kiln at the upper end and are decomposed, by heat, to calcium oxide which is extracted at the lower end. A burner is attached at the lower end and burning fuel, such as oil, natural gas, or coal provides heat to the lower end of the calcining chamber of the rotary kiln. Combustion products and carbon dioxide are removed from the upper end of the rotary vessel.

As understood from the above, such modern rotary kilns are expensive to manufacture and operate. At the same time, they are bulky and thus commonly installed at an industrial site. Lime production at such an industrial site will possibly result in an extended transportation to the actual site where the lime is to be used.

Research has shown that the quality of an end product from a modern rotary kiln in some instances may be questioned, specifically in relation to the conservation of historic buildings. Accordingly, traditional methods are looked at for production of lime from limestone. However, a traditional lime kiln is complicated to install in a proper manner. In addition, such a traditional kiln comprises a large plurality of components, including a large number of bricks, making the installation time unreasonably long and thus not economically defensible.

With this in mind, there is thus a desire to provide an improved type of lime kiln, applying the traditionally methodology for ensuring a high quality end product, at the same time allowing for the installation time for the kiln to be reduced to a reasonable and thus economically defensible level.

SUMMARY

According to an aspect of the present disclosure, the above is at least partly met by a vertical lime kiln for the production of lime from limestone, the kiln comprising a base section arranged at a ground surface, a burner section arranged onto the base section, wherein the burner section comprises a horizontal passage for receiving a solid fuel material, and a vertical shaft arranged onto the burner section, having a rectangular shape and provided with laterally spaced walls, wherein the vertical shaft is adapted to receive the lime stone, wherein the burner section comprises a vertical opening extending upwardly into a lower portion of the vertical shaft, and the vertical shaft comprises a plurality of bridge portions extending over the horizontal passage, the bridge portions being arranged with a predefined spacing in the longitudinal direction of the horizontal passage there-between, such that heat generated within the burner section travels between the bridge sections and upwardly within the vertical shaft.

By means of the present disclosure, there is provided improvements in relation to the setup and operation of a lime kiln, possibly close to a site where the resulting lime is to be used. As indicated above, such a site may for example be close to a location where a historical building is to be renovated or conserved. The solution presented in line with the present disclosure allows for a reduction of the number of parts needed for constructing the lime kiln. In accordance to the present disclosure the lime kiln is formed as a rectangular, specifically simplifying the selection of material used for forming the vertical shaft of the lime kiln.

Furthermore, in accordance to the present disclosure there is arranged an e.g. wood fired burner section below the vertical shaft. However, for allowing the limestones to be suitably positioned within the vertical shaft and above the burner section the is formed a plurality of bridge portions extending over a part of the burner section. Accordingly, while the fire is burning within the burner section, the plurality of bridge sections will allow the formation of a cavity, formed above the burning e.g. wood and below the limestones. The bridge sections may in some embodiments of the present disclosure be formed from e.g. a plurality of firebricks as will be discussed below in relation to the detailed description of the present disclosure.

In accordance to the present disclosure, the vertical shaft may be formed as a sandwiched construction, preferably comprising an inner layer of firebricks. In addition to the firebricks, the sandwiched construction may comprise a layer of autoclaved aerated concrete (AAC), such as AAC blocks or panels. The ACC blocks or panels are in accordance to the present disclosure arranged facing away from the vertical shaft, i.e. formed as an outer layer in relation to the firebricks of the walls of the vertical shaft. The AAC blocks or panels allows for an improved stability of the walls of the vertical shaft. It should be understood that it in accordance to the present disclosure may be possible to stack the bricks and block without using any mortar. This allows the kiln to be easily dismounted and possibly reused at another site.

In addition to the above, in a possible embodiment it may be desirable to increase the insulation of the lime kiln, thereby possibly slightly reducing the amount of e.g. wood needed during the production process. For achieving this effect it may in one embodiment of the present disclosure be possible to include a layer of an insulation board, such as a vermiculite board. As such, in a preferred embodiment of the present disclosure the sandwiched construction of the vertical walls are formed to comprise an inner layer of firebricks, a mid-layer of AAC and an outer layer of an insulation board.

For further increasing the stability of the lime kiln, it may be possible to arrange e.g. a sheet metal material to enclose an outside surface of the walls of the vertical shaft. Such a sheet metal material comprises a corrugated sheet metal. The sheet metal material may in a possible embodiment be joined to the outside surface of the walls of the vertical shaft using some form of e.g. metal straps holding the sandwiched construction together.

In accordance to the present disclosure, it is preferred to allow an inlet portion of the burner section to extending horizontally outside of the vertical shaft. Such an implementation typically allows for easy "pre-burning" of e.g. the firewood before "pushing" the now burning firewood into the horizontal passage of the burner section. It may in some embodiments be advantageous to include more than a single horizontal passage with the burner section, such as for example by providing at least two horizontal passages. As will be understood, using two separate horizontal passages allows for e.g. an increased amount of e.g. firewood to be simultaneously burnt. In addition, it may also be possible to select a width of the horizontal passages to be suitable for swift firebrick construction of the bridge sections as will be illustrated below.

The lime kiln provided in accordance to the present disclosure may in some embodiments be equipped with one or a plurality of digital temperature sensors for e.g. continuously tracking a temperature within the kiln during operation of the kiln. In a preferred embodiment a first temperature sensor is arranged in a bottom section of the vertical shaft and a second temperature sensor is arranged at a top section of the vertical shaft.

According to another aspect of the present disclosure there is provided a method for the production of lime from limestone, the method comprising providing a vertical lime kiln as disclosed above, stacking limestones within the vertical shaft, and burning firewood within the burner section. This aspect of the present disclosure provides similar advantages as discussed above in relation to the previous aspect of the present disclosure.

The process may further comprise tracking a temperature within the vertical shaft using the above mentioned first and second temperature sensors. The temperature sensors may e.g. be connected to a computing device, such as a laptop, where temperature curves may be illustrated to a user of the kiln within a graphical user interface (GUI). The GUI may also show predefined temperature profiles for the first and the second temperature sensor, allowing the user to adjust the amount of wood being burnt such that the measured temperatures stays within the predefined temperature profiles.

In a possible embodiment, at a top of the vertical shaft it may be provided a removable roof. The removable roof may for example be formed from a super wood board. The super wood board may be positioned such that a draft through the burner section and the vertical shaft is adjusted, thereby allowing control of the temperature within the vertical shaft.

Further features of, and advantages with, the present disclosure will become apparent when studying the appended claims and the following description. The skilled addressee realize that different features of the present disclosure may be combined to create embodiments other than those described in the following, without departing from the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the present disclosure, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawing, in which:

Fig. 1 provides a conceptual illustration of a vertical lime kiln according to a currently preferred embodiment of the present disclosure.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the present disclosure are shown. This present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the present disclosure to the skilled addressee. Like reference characters refer to like elements throughout.

Referring now to Fig.1, there is depicted a conceptual illustration of a vertical lime kiln 100 according to a currently preferred embodiment of the present disclosure. The lime kiln 100 comprises a base section 102 arranged at a ground surface. The lime kiln 100 further comprises a burner section 104 arranged onto the base section 102, where the burner section comprises a first 106 and a second 108 horizontal passage for receiving a burning fuel material, such as firewood.

There is additionally provided a vertical shaft 110 arranged onto the burner section 104, where the vertical shaft 110 has a rectangular shape and is provided with laterally spaced walls 112, wherein the vertical shaft is adapted to receive a plurality of lime stones 114 that are to be arranged within the vertical shaft 110.

Specifically, the plurality of limestones 114 are stacked onto a plurality of purposely provided bridge sections 116 extending over the horizontal passages 106, 108. The burner section 104 further comprises a vertical opening extending upwardly into a lower portion of the vertical shaft 1 10, i.e. such that heat generated by e.g. wood being burnt within the horizontal passages 106, 108 is allowed to travel upwardly within the vertical shaft 110 for heating the limestones 114. The plurality of bridge sections 116 are provided with a predefined spacing, e.g. at least 20 centimeters apart, thereby allowing a suitable cavity to be formed for giving the burning e.g. wood adequate spacing for optimizing the burning process. As indicated above, the walls 112 of the vertical shaft 110 comprised with the lime kiln 100 may preferably be formed as a sandwiched construction, comprising a layer of firebricks 118 facing the inside of the vertical shaft. The firebricks 118 are adapted to withstand a temperature around 1000 °C where the calcination process of limestone is taking place for the formation of lime (also referred to as quicklime or calcium oxide).

The sandwiched walls 112 further comprises a layer of autoclaved aerated concrete (AAC), such as AAC blocks 120. Both the firebricks 118 and the AAC blocks 120 are stacked as a stretcher bond or using any suitable known process for brickwork. It should however be understood that it in accordance to the present disclosure may be possible to stack the bricks and block without using any mortar. This allows the kiln 100 to be easily dismounted and reused at another site. As shown in Fig. 1, the ACC blocks 120 are arranged to facing away from the vertical shaft 100, i.e. formed as an outer layer in relation to the firebricks 118 of the walls 112 of the vertical shaft 110.

The sandwiched walls 112 further comprises a layer of a vermiculite board 122, providing insulation of the vertical shaft 110 during operation of the kiln 100. In addition and as shown in Fig. 1, there is provided a layer of a corrugated sheet metal 124 for "holding the walls 112 together", i.e. without having to resort to the use of e.g. mortar for securing bricks, blocks and boards together.

It should be understood that the walls 112 may be constructed slightly differently without departing from the scope of the present disclosure. That is, it may for example be possible to refrain from using the ACC blocks 120 and instead stacking e.g. two layers of firebricks 118. Similarly, it may in some embodiments be possible to refrain from using the vermiculite board 122, possibly with only a small reduction of the efficiency of the kiln 100. The same of course account for the corrugated sheet metal 124, which may be optional and/or may be substituted by another material.

In addition to the above, the kiln 100 comprises a front section 126, providing an extension to the horizontal passages 106, 108. Passages 128, 130 of the front section 126 may be used for "starting" the firewood burning process. Once the firewood is sufficiently on fire, the now burning firewood may be "pushed" into the horizontal passages 106, 108 such that the heat generated will affect the limestones 114 such that the calcination process is performed.

In the example presented in Fig. 1, an entry portion of the passages 128, 130 may be provided with heat resistant concrete slabs 132, 134. In some embodiments of the present disclosure this may be preferred to ensure that e.g. firebrick comprised with the front section 126 is kept safe from the extreme that may be generated at the entry portion of the passages 128, 130. The concrete slabs 132, 134 are preferably adapted to have a width that matches a width of a plurality of firebricks stacked at the front section 126. In a possible embodiment (not shown), also the front section 126 is provided with an outer layer of corrugated sheet metal.

As mentioned above, the kiln 100 may optionally be provided with a "roof, e.g. provided as one or a plurality of heat resistant boards 136 that may be removably arranged onto a top surface 138 of the walls 112. It may, instead of using the heat resistant boards 136, alternatively be possible to use a layer of bricks for providing the "roof functionality".

During a possible setup of the kiln 100, the base section 102 is firstly formed, possibly comprising packed gravel at the ground surface. Secondly, the front section 126 and the burner section 104 and the bridge portions 116 are formed. Then the walls 112 are constructed, staring with stacking the firebricks 118 and then the ACC blocks 120.

Subsequently, the vermiculite boards 122 and the layer of the corrugated sheet metal 124 is arranged outside of the ACC blocks 120 for insulation and stability.

The limestones 114 are then carefully stacked on top of the bridge portions 116. Preferably, the stacking process starts by first placing the "largest" limestones 114 onto the bridge portions, followed by the "smaller" limestones 114. It is preferred to stack limestones 114 all the way up to the

Subsequently, a firewood fire is stated within the front section 126. Once the fire is burning "enough" the burning firewood is, as mentioned above, pushed inside of the horizontal passages 106, 108. The heat inside of the vertical shaft 110 will then increase, up to e.g. 1000 °C for calcination of the limestones 114.

The process may as be monitored using a plurality of temperature sensors (not shown) with the purpose to keep the temperature within the vertical shaft 110 within a predetermined temperature range. The heat resistant boards 136 may be maneuvered at the top of the walls 112 for controlling the burn speed, thereby also controlling the temnperature within the vertical shaft 110.

Although the figures may show a sequence the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the material chosen and on designer choice. All such variations are within the scope of the disclosure. Additionally, even though the present disclosure has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

In addition, variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed present disclosure, from a study of the drawings, the disclosure, and the appended claims. Furthermore, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Claims

1. A vertical lime kiln (100) for the production of lime from limestone (114), the kiln comprising:

- a base section (102) arranged at a ground surface;

- a burner section (104) arranged onto the base section, wherein the burner section comprises a horizontal passage (106, 108) for receiving a solid fuel material, and

- a vertical shaft (110) arranged onto the burner section, having a rectangular shape and provided with laterally spaced walls (112), wherein the vertical shaft is adapted to receive the lime stone,

characterized in that:

- the burner section comprises a vertical opening extending upwardly into a lower portion of the vertical shaft, and

- the vertical shaft comprises a plurality of bridge portions (116) extending over the horizontal passage, the bridge portions being arranged with a predefined spacing in the longitudinal direction of the horizontal passage there-between, such that heat generated within the burner section travels between the bridge sections and upwardly within the vertical shaft.

2. The kiln (100) according to claim 1, wherein a cavity is formed between bridge portions.

3. The kiln (100) according to any one of claims 1 and 2, wherein the burner section comprises an inlet (128, 130) extending horizontally outside of the vertical shaft.

4. The kiln (100) according to any one of the preceding claims, wherein the burner section comprises at least two horizontal passages.

5. The kiln (100) according to any one of the preceding claims, wherein the solid fuel material is firewood.

6. The kiln (100) according to any one of the preceding claims, wherein the walls of the vertical shaft at least partly comprises a layer of autoclaved aerated concrete (AAC).

7. The kiln (100) according to claim 6, wherein the layer of AAC is formed from AAC blocks (120) or panels.

8. The kiln (100) according to any one of the preceding claims, wherein the walls of the vertical shaft at least partly comprises a layer of an insulation board.

9. The kiln (100) according to claim 8, wherein the insulation board is a vermiculite board (122).

10. The kiln (100) according to any one of the preceding claims, wherein the walls of the vertical shaft comprises a layer of firebricks (118).

11. The kiln (100) according to claim 1, wherein the vertical walls is formed from a sandwiched structure, comprising an inner layer of firebricks, a mid-layer of AAC and an outer layer of an insulation board.

12. The kiln (100) according to any one of the preceding claims, further comprising a sheet metal material arranged to enclose an outside surface of the walls of the vertical shaft.

13. The kiln (100) according to claim 12, wherein the sheet metal material comprises a corrugated sheet metal (124).

14. A method for the production of lime from limestone, the method comprising:

- providing a vertical lime kiln (100) according to claim 1;

- stacking limestones within the vertical shaft, and

- burning firewood within the burner section.