WO2018131026A1

WO2018131026A1 - Gasifier stove with vortex

Info

Publication number: WO2018131026A1
Application number: PCT/ID2018/000001
Authority: WO
Inventors: Nurhuda MUHAMMAD
Original assignee: Muhammad Nurhuda
Priority date: 2017-01-12
Filing date: 2018-01-10
Publication date: 2018-07-19

Abstract

A gasifier vortex stove of solid biomass fuel comprising of at least the following components: an outermost tube, a bottom floor, at least one pre-heating tube, a fan and its speed control system, a stove table with potstands on it, and a combustion tube with the construction of a secondary air holes that allow the flame to rotate vertically or horizontally. In particular, the toroidal vortex flame occurs due to combustion of smoke by using downward difracted secondary airflow expelled by stacks of the secondary air holes and lower pressure on the lower combustion tube, while the horizontal rotating flame is created by the secondary airflow passing through a series of inclined slits. To improve efficiency and prevent the stove from overheating, more than one preheating tube may be installed, or an insulating layer may be added to the outermost tube, the preheating tubes or to the outer surface of the combustion tube. The optimization of fuel utilization can be achieved by transferring the remaining charcoal from the biomass combustion to a charcoal combustion tube.

Description

GASIFIER VORTEX STOVE FIELD OP THE INVENTION

The invention relates to a gasifier cookstove that applies the force draft airflow, preheating and vortical combustion either vertically or horizontally, and a method for efficiently using the fuel.

BACKGROUND OF THE INVENTION

Biomass refers to all non-fossil organic compounds of living things that can be used as fuel. The sources of biomass may vary from wood, plants, leaves, grass, agricultural waste, household waste, garbage and others. It is estimated that more than 40% of the world's population still rely on biomass and coal as fuel.

In most rural communities, firewood is still the main fuel used for cooking. People cook using open flames or with simple stoves. This method is not only inefficient, but also produces harmful exhaust gases that can potentially trigger various diseases such as asthma, lung cancer, heart disease, and premature and low birth weight babies. An efficient method to use biomass as cooking fuel is probably a gasifier cookstove. In principle, the biomass is converted by a thermal process into a gas or smoke, where the smoke is then burnt with an excessive secondary air supply, so that it produces a much cleaner flame. The smokes comprise of gases like ¾, CO, CH₄, CO₂, SOx, NOx, water vapour, where among that gases, i.e. hydrogen (¾) , carbon monoxide (CO), and methane (CH₄) are highly flammable. Such combustion models are referred to as two stages burning mechanism. The cookstove operating under the two-stage combustion mechanism is known as a gasifier cookstove. The objectives in the development of gasifier cookstoves are to make the combustion cleaner and fuel usage as efficient as possible, characterized by low carbon monoxide (CO) emissions, low particulate matter (PM) emissions and high combustion efficiency. In general, the methods include the following attempts:

Preheating mechanism. The air used for gasification and smoke combustion is heated by the radiant waste heat of the combustion chamber.

- Adding an air supply. A low-power fan is normally used to drive the airflow.

Introduction of a mechanism that mixes smoke and secondary air as turbulent as possible. The effort is realized, for example by introducing a special design of the combustion tube, adding a flame concentrator to the top of the burner or introducing the vortex combustion scheme.

Some of the patents relating to forced draft biomass cookstove are: WO2007 / 036720A1, W02010 / 029567A2, US2009 / 0025703A1 and US2012 / 0060819A1. However, none of the above inventions deals with the scheme for optimizing the role of secondary air in improving combustion.

The present invention relates to a gasifier cookstove using a forced draft airflow, an air preheating mechanism for the gasification and the smoke combustion, and vortex combustion. Fuels are preferred in granules, such as biomass pellets, palm kernel shell, hazelnuts, grains, etc, although bulky fuels may also be used. The vortex combustion is created by manipulating the secondary airflow to produce a rotating flame. The invention also describes how the fuel, in particular biomass, can be used as optimally as possible. SUMMARY OF THE INVENTION

The aim of the present invention is a portable, forced draft gasifier cookstove which has a high thermal efficiency and low exhaust emissions, and which is easy to use, by implementing the vortical combustion mechanism. For the sake of simplicity, the term gasifier vortex stove is used to refer the aforementioned cookstove.

The gasifier vortex stove according to the present invention comprises at least the following components: an outermost tube, a combustion tube, at least one preheating tube disposed between the outermost tube and the combustion tube, a stove table with potstands thereon, and a forced draft airflow system with a speed control panel.

The gasifier vortex stove according to the present invention is a cookstove, in which the combustion tube is a cylinder with a closed cross section in the bottom floor, where there are at least two stacks of holes annularly punched along the upper side provided for the secondary air inlets / burners, and in the lower part there are holes for the primary air. The gasifier vortex stove of the present invention is a cookstove which applies the following combustion mechanisms: (i) gasification of the fuel to produce smoke with limited air supply to the bottom of the combustion tube and (ii) combustion of smoke using secondary airflow expelled from the stacks of the secondary air holes, through which a strong toroidal vortex is created due to the diffraction of the expelled airflow. In addition, a lower gas pressure in the lower tube also contributes to a stronger vortex.

Another alternative for generating vortex combustion is the use of secondary air inlets in the form of inclined slits punched annularly along the upper side of the combustion tube. In this respect, the generated vortex is a horizontal circular vortex.

In accordance with the broad scope of this invention, the following variants may be included: the primary- and secondary airflow are separated and the respective air supply rate are adjusted by panels such that it can be used for different combustion phases: pyrolysis, gasification, and as well as for different types of fuel such as coal and charcoal,

addition of the insulating layer to the outermost tube or to the preheating tube, or an to outer surface of the combustion tube,

make the combustion tube in such a way so that it can be easily removed even when the stove is in use,

inclusion of the combustion tube whose diameter and length are shorter than its maximum dimension to facilitate the cooking purpose at a relatively low power or short cooking time,

incorporation of combustion tubes for burning charcoal, so that the residual charcoal can be used for further cooking purposes. In accordance with the broad scope of the invention, the stove housing may be formed in a box, cylinder or other geometrical shapes, provided that the principles of combustion refer to the aforementioned combustion principles. Accordingly, the drawings and explanations in this description are illustrative, and it is possible to design other variations as long as the basic idea of the present invention is not changed. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the trajectory of airflow occurring in (a) a single hole, (b) stack of 2 holes, (c) stack of 3 holes and (d) stack of 4 holes. Figure 2 (a) shows the pattern of toroidal vortex formation in the combustion tube. Figure 2 (b) is a three-dimensional embodiment of the combustion tube.

Figure 3 (a) shows the pattern of horizontal vortex formation in combustion tube, and Fig. 3 (b) is the embodiment of the respective combustion tube.

Figure 4 shows a schematic representation of an embodiment of a gasifier vortex stove with a preheating tube between the outermost tube and the combustion tube.

Figure 5 illustrates a schematic embodiment of a gasifier vortex stove with a ratio controller for primary and secondary air.

Figure 6 is a schematic illustration of an embodiment of a gasifier vortex stove having two preheating tubes between the outermost tube and the combustion tube. Figure 7 shows a 3-D cut view of the gasifier vortex stove according to the drawing scheme 6.

Figure 8 shows how to remove the biomass combustion tube and transfer the residual charcoal to a charcoal combustion tube . DETAILS OF THE INVENSION One of the expectations of the bioraass stove designers is to provide a stove that yields cleaner combustion and has high efficiency. This clean and efficient combustion is achieved when the air required for gasification and combustion is properly fulfilled and the mixture of smoke and preheated air is proper and made as turbulent as possible. The vortex combustion is one of the methods to improve the quality of combustion.

The fuel for the stove is preferably in granular form, for example, biomass pellet, palm kernel shell, hazelnut, coconut shell, although it is also possible to use fuels in pieces, such as wood chips, briquettes and others. Other solid fuels, e.g. coal in raw or processed form can also be used.

Figure 1 describes the mechanism of airflow coming out of the holes. Figure 1(a) shows the trajectory of airflow from a single hole. The airflow trajectory of a single hole is a straight line. Figure 1(b) is the path of the airflow from stack of 2 holes. Here, the airflow coming out from the upper hole is bent upwards, while that of the lower hole is bent downwards due to the diffraction. Figure l{c) shows the trajectories of the airflows emerging from stack of a 3 holes, and figure 1(d) refers to those coming out from a stack of 4 holes. In the 3- hole stack, the airflow in the central path undergoes virtually no deflection, while in the 4-hole stack, the upward and downward airflows exhibit greater diffraction power due to mutual interference.

Figure 2(a) describes how the diffraction mechanism is implemented to create a toroidal vortex in a combustion tube. The collision of the diffracted airflow with that of the opposite direction strongly pushes the movement of the air downwards. Next, the smoke is burnt with the diffracted secondary airflow, so that the temperature in the center of the combusti on tube increases, and as a result, the pressure increases. This higher pressure causes the exhaust gas to flow to the peripheral zone, which then rises through the sidelines between the secondary air holes. To obtain the diffraction that 5 allows the toroidal vortex combustion, the stack requires at least two arrays of secondary air holes are.

It should be emphasized that toroidal vortex combustion takes place when the airflow at the lower combustion tube is much smaller than that at the upper side, so that it does not

10 affect significantly the trajectory of the diffracted secondary airflow. In principle, the primary air required for gasification must be less than its stoichiometry' s need. In such a case, the primary air deficiency is then satisfied by the diffracted secondary airflow downwards, whereby the toroidal vortex effect

15 is further strengthened. Therefore, it is important to limit the amount of primary air inlet. In simple terms, this can be expressed in a parameter η as:

Secondary airflow

Primary airflow

In cases where the primary and secondary airflows are 20 inseparable and the diameter of the secondary air holes and the primary air holes are the same, η can be approximated by:

Number of secondary air holes

jj— £ 2 )

' Number of primary air holes '

If the diameters of secondary and primary air holes are not equal, η can be approximated by:

„ . Total area of secondary air holes

25 ΊΊ— , ( 3 )

' Total area of primary air holes g

The value of η depends on the type of fuel. For relatively small fuels such as palm kernel shell, η is in the range of 2 to 4. For biomass pellets with a diameter of, for example, 8 mm, the optimum η is in the range between 8 and 12. From observation we found that the higher the value of η is, the stronger the vortex is. However, if η is very high (η> 12), then the vortical flame resulting from the smoke combustion cannot reach the fuel in the lower space, and therefore, not all the fuel is burnt.

In the case where the primary airflow is separated from the secondary airflow, the value of η in equation (2) can be chosen at the lowest value, e.g. 2. The variation from η to a higher value then can be achieved by reducing the primary airflow rate with the help of a control panel.

The diameter of the holes for the secondary air is determined with respect to the diameter of the combustion tube and the airflow rate. If the diameter of the combustion tube is too large while the flow velocity is small, the diffraction effects that occur then are too weak to cause a toroidal vortex. From the observation we found that, for 10 cm diameter and 21 cm length of combustion tube, the best configuration of the secondary air inlet holes can be made as follows: diameter of the holes in the range of 2.5 mm to 3 mm, the stack consists of 4 columns of secondary air holes and they are vertically separated by a distance of 0.75 cm, the horizontal distances between the holes are approximately 1.5 cm and are arranged alternately, as shown in Fig. 2(b).

Figure 2(b) shows a 3D cut view of the combustion tube. In general, the combustion tube is comprised of a combustion tube body 101T, a combustion tube flange 102T, a combustion tube bottom floor 103T and a combustion tube holder 104T used to easily remove the combustion tube. The holes in the upper side of combustion tube are the secondary air inlets or burners 105T. The holes at the bottom act as primary air inlets 106T. There is no standard rule for placing holes for the primary air inlets. If the combustion tube is quite long, another series of primary air holes 107T may be added. These additional holes are intended to assist the gasification process at the bottom of the combustion tube. The positions of holes 106T and 107T may be reversed to find the best configuration, and this usually depends on the type of fuel. Another alternative, the holes for primary air may be made at the bottom of the combustion tube. Other configuration that can also be made is a combination of holes at the lower side and at the bottom floor. The suffix T on the label indicates that the type of vortex is toroidal.

An alternative to the toroidal vortex is the horizontal rotating vortex or simply horizontal vortex. Here, the secondary air inlets consist of a series of inclined slits along the upper side of the combustion tube. The inclination of the slits may vary from 15 degrees to 80 degrees. Figure 3(a) shows how the horizontal vortex is created in the combustion tube. According to Figure 3(a), the airflow entering the inclined slits has a different velocity and depends on the altitude position of a point in the slit where the lower position experiences a higher velocity than that in the upper one due to the lower pressure. Therefore, the flame in the upper position is less energetic and moves slowly away behind the flame in the lower position. This creates a horizontal vortex flame that rotates against the inclination of the slits. From the observation we found out that for the diameter of the combustion tube of 10 cm, the inclination of the slits should be between 45-60 degrees, the width of the slits should be 2 mm, the length of the slits should be 1.5 cm and the number the slits that must be made along the upper side of the combustion tube should be 22. Figure 3 (b) shows a 3D view of a combustion tube that generates a horizontal vortex flame. Here, the suffix H refers to the term "horizontal" to distinguish it from the previous combustion tube that creates the toroidal vortex. In summary, the combustion tube comprises a combustion tube body 101H, a combustion tube flange 102H, a bottom floor 103H and a combustion tube holder 104H which allows easy removal of the combustion tube. On the upper side of the combustion tube is a series of inclined slits 105H that serve as burners. In the lower side, these are holes that serve as primary air inlet 106H. There is no standard rule that determines the position of the primary air holes. Optionally, a series of primary air holes 107H may be added to assist the gasification process in reaching the lower fuel level. Other option, the primary air inlet can also be made as a combination of holes in the bottom floor and the holes on the lower sidewall.

Figure 4 shows one of the embodiments of a gasifier vortex stove, in which at least one preheating tube is disposed between the outermost tube of the stove and the combustion tube. The main components include at least the combustion tube 101, the outermost tube of the stove 201, the bottom of the stove 202, the downward extension of the outermost tube of the stove, which is provided with a series of holes 203 serving as air inlet into the stove, the fan casing 204 with the fan 205 therein. At the top is a stove table with potstands 207 on it. The preheating of the air is facilitated by a preheating tube 208 where the upper part is open while the lower part is closed 203a. The trajectory of airflow is indicated by the gray curve with arrow. In this figure, the component used to hang the preheating tubes is not shown. Here the label 101 refers the combustion tube of figure 2(b) or the combustion tube of figure 3(b) with all parts therein. The airflow controller is not shown. Figure 5 shows another embodiment of the gasifier vortex stove with preheating. In this embodiment, the ratio between the secondary airflow rate and the primary airflow rate is not only determined by the ratio between the number of secondary air holes to the primary air holes, but also by the control panel. With the addition of such panel, various types of fuels such as granules of different sizes, e.g. palm kernel shells, pieces of wood, hazelnuts and various grains can be used. This control also facilitates different phases of combustion: pyrolysis, gasification and combustion of charcoal. For relatively small fuels, the primary air control can be set to maximum, while for relatively large fuels, the primary air control can be set to half the maximum or even lower. Similarly, for fuels with very high volatile matter content, the position of the primary air panel can be set to the zero position, resulting in pyrolysis.

Referring to Figure 5, the gasifier vortex stove comprises a combustion tube 101 and the stove housing. The stove housing includes the following parts; the outermost tube of the stove 301, the bottom floor of the stove 302, the stove legs 303, the stove table 306 with potstands 307 thereon, the fan casing 304 with the fan 305 fixed herein. Inside the outermost tube, there is a preheating tube 308, which is closed at the lower cross section 308a and blocked by stove table at the upper cross section, and equipped with holes for the primary and secondary air inlet. To separate the primary air from the secondary air, there is a horizontal skirt 309 positioned between the outermost tube and the preheating tube, and the horizontal skirt 311 between the preheating tube and the combustion tube. The ratio of secondary to primary airflow in this scheme is regulated by a flap 310. When the flap is moved upward, the air driven by the fan is more to flow as primary air and vice versa. Here, the label 101 designates the combustion tube of Figure 2 (b) or the combustion tube of Figure 3(b) with all parts inside. The primary and secondary airflows are represented by gray arrow curves . The ai rf low controller is not shown .

To prevent the heat from being wasted in terms of radiant heat, and to prevent the outermost wall of the stove from being very hot, it is important to add an insulating layer according to the diagram of figures 4 and 5. Such an insulating layer can be manufactured as an inner layer of the outermost tube of the stove, or as a part of preheating tube- or as an outer surface of combustion tube. In this way, the risk of overheating can be minimized.

Another way to reduce wasted heat is to install more than one preheating tube. Thus, more heat from the combustion tube is absorbed and returned as a hot airstream. Figure 6 shows the embodiment of a vortex stove with a double preheating tubes and figure 7 shows the respective 3D view. By using such a dual preheating tubes, the radiant heat loss in the environment can be further reduced and used to preheat the air before being introduced into the combustion tube, thus resulting in higher combustion efficiency. Here, the arrows of the gray curves represent the trajectory of the airflow.

The components of the gasifier vortex stove of figures 6 and 7 are the following. The outermost part is the stove body 401, the bottom floor of the stove 402, the extension of the stove body downwards which serves as a stove leg provided with the holes for the air inlet 403, the fan casing 404 with fan 405 installed therein, a preheating tube 408 disposed inside the outermost tube whose lower cross section 408a. is blocked and the upper section is open, the preheating tube 409 whose upper cross section is connected to the table of the stove, while in the lower section 409a there is a hole 410 as an air duct. The preheating tube 408 is hung with the support 411 to the outermost tube, the preheating tube 409 is hung with the support 412 to the preheating tube 408. The support for the preheating tubes can be made in terms of a bracelet and is connected to the inner wall of the respective outer tube. With such a configuration, the preheating tubes can be disassembled. Here, the label 101 refers to the combustion tube of figure 2 (b) or to the combustion tube of figure 3 (b) with all the parts inside .

The control of the fire intensity is done by adjusting the speed of the fan. Referring to Figure 7, the fan level controller 413 is installed on the sidewall of the stove body. On this panel, a button 414 is mounted to adjust the fan speed as well as to turn on or off the fan.

The combustion residue of the gasifier vortex stove is charcoal. According to the observation, it is very difficult to use the remaining charcoal for further cooking. This is because charcoal combustion requires more air than biomass combustion. However, if the charcoal remains in it, it will be slowly burnt and ashed. The heat produced is less sufficient to be used for cooking and therefore not effective. This certainly reduces the efficiency of fuel consumption. That is why it is important to replace the combustion tube with a tube specially designed for burning charcoal so that the charcoal can be used for further cooking. Figure 8 shows how the remaining charcoal is used to continue cooking. Figure 8(a) shows how the hot combustion tube is removed using a hook, followed by replacement with a charcoal combustion tube. Figure 8(b) shows how charcoal is poured into a combustion tube. With this method, the use of biomass as fuel for cooking can be optimized. It should be noted that a gasifier vortex stove with removable combustion tube is an option with an advantage that allows optimal utilization of the charcoal residues. Another possible option is a gasifier vortex stove with a permanently installed combustion tube attached to the stove body.

It should also be noted that although the stove housing shown in this patent specification has a cylindrical shape, but in its implementation, other housings such as the box, the hexagon, the octagon or other geometric shapes may be developed. Similarly, any kind of variation of the stove table and its potstands, the position of the fan whether it is installed on the bottom or on the sidewall, is always open. Accordingly, the drawings shown in this description are illustrations, as long as the essence of the present invention is unchanged.

Claims

A gasifier vortex stove that generates a toroidal vortex flames comprising a stove housing with components at least :

an outermost tube 201 and bottom floor 202,

at least one preheating tube 208 disposed within the outermost tube 201,

a fan 205 and its flow rate controller

a stove table 206 and potstands 207 on it,

and a combustion tube 101T in the form of an open-top cylinder with primary air holes in the lower part and stack of at least two arrays of secondary air holes on the upper wall side, where the combustion mechanism comprises the following stages;

gasification of the fuel with primary air supply, - combustion of smoke by using difracted secondary air that is enhanced by low pressure in the lower combustion tube to produce a toroidal vortex flame. A gasifier vortex stove in claim 1 where the ratio of secondary airflow to primary airflow is as low as two. A gasifier vortex stove in claim 1, wherein the primary air holes can be selected on the lower wall side, bottom floor or a combination of both.

A gasifier vortex stove in claim 1, wherein the combustion tube can be fixed to the stove or made as a removable component.

A gasifier vortex stove in claim 1, wherein a heat insulating layer may be added to the outermost tube, preheating tube or combustion tube.

A gasifier vortex stove in claim 1, wherein the fan position can be attached on the bottom floor of the stove or on the sidewall of the stove.

7. A gasifier vortex stove in claim 1, where the primary airflow and the secondary airflow is optionally installed separately and their ratio is controlled via a control panel .

8. A combustion tube for generating a horizontal rotating flame in a gasifier vortex stove comprises at least:

combustion tube body 101H and combustion tube bottom floor 103H,

the primary air holes 106H and 107H at the lower side and the secondary air inlet, which are inclined slits, punched circularly along the upper sidewall of combustion tube with an inclination of between 15 degrees and 80 degrees.

9. A gasifier vortex stove generating horizontal rotating flame, in which the stove housing is provided with claim

1 and its derivatives, and the combustion tube is specified in claim 7.

10. A gasifier vortex stove according to claim 1 and 9, wherein its stove housing can optionally be formed in a different geometric shape than in the cylinder.

11. A gasifier vortex stove according to claim 1 and 9, for which fuel consumption can optionally be optimized, using a method that requires components :

additional combustion tube for burning charcoal, - a hook for removing the combustion tube when the stove is in operation,

where the procedure contains the following steps:

combustion tube for biomass fuel is removed from the stove body by using provided hook,

- inserting the combustion tube for burning charcoal in place of the biomass combustion tube,

charcoal from biomass combustion residue is poured into a charcoal combustion tube.