WO2020261286A1

WO2020261286A1 - A domestic cooking burner for piped natural gas

Info

Publication number: WO2020261286A1
Application number: PCT/IN2019/050482
Authority: WO
Inventors: Pankaj Kumar Arya; Satish Kumar; Gananath Doulat Thakre; Amar Kumar Jain; Surendra Pratap
Original assignee: Council Of Scientific And Industrial Research; Petroleum Conservation Research Association
Priority date: 2019-06-26
Filing date: 2019-06-26
Publication date: 2020-12-30

Abstract

A domestic cooking burner is designed for the efficient and safe application of Piped Natural Gas (PNG). The burner comprises of a gas injector with diameter suitable for injecting PNG at a range of flow rate at subsonic conditions. The injector is in alignment with mixing tube; throat has been designed for minimum 50% primary aeration to allow entrainment of primary air thus leading to air fuel mixing. The mixing tube is made divergent and smooth enough to prevent frictional pressure losses. The burner is conventionally arranged so that the head portion extends upwards towards the loading utensil with the mixing tube portion formed at 90° to the head portion so that the axis of inlet is perpendicular to the vertical axis of the burner. The top portion of the burner head has holes (flame ports) to support flames. There are three circular rows of holes with similar diameter designed to deliver a range of heat output; all the holes are drilled on the tapered faces of burner head so as to spread the flame in a larger circular area. The burner head and gas manifold have circular body with central hole to support secondary air entrainment. The loading height has been optimized for improved heat transfer from flames to cooking vessel that ensures minimum 55% of thermal efficiency. The invented PNG burner may also be used for commercial cooking and industrial heating applications.

Description

A DOMESTIC COOKING BURNER FOR PIPED NATURAL GAS

FIELD OF THE INVENTION

The present invention relates to a burner designed for Piped Natural Gas (PNG) as fuel for domestic cooking application. The present invention also relates to an atmospheric burner that confirms to a repeatable performance of thermal efficiency and safety when evaluated under controlled test conditions. Further, the burner is designed to fire PNG to deliver a range of power output (1.5 kW to 2.25 kW) with minimum 55% of thermal efficiency.

BACK GROUND OF THE INVENTION

Atmospheric burners used in cooking application are usually premixed type where fuel and air are premixed before passing through burner nozzle / injector. It is further understood that with proper mixture of fuel and air, the mixture is combustible and under ideal conditions a stable flame is generated through burner. Various domestic cooking burners have been designed previously, [US 3825404] refers to gas burner with one injector and two successive chambers to generate stable flame at low gas flow rates, [US005899681A] refers to atmospheric gas burner assembly for improved flame retention and stability, [US6263868 Bl] refers to gas stove burner having high heat, warming flame, [US6332460B1] refers to gas burner having high power generated from small head dimensions with short flames. Similarly, few other burner designs are prevalent e.g. [US3627462], [US4757801], [US2010/0279238 A1], [US2013/0199513 A1] in which major focus is given on innovative burner design to have better mixing of fuel-air and to establish stable flame.

Reference is made to [US 6093018] that presents an improved gas burner comprising of combination for controlled feeding and subsequent admixing of secondary air directly to the base of the flame in the form of a cap coaxially surrounding the head of burner comprising lateral apertures for issuing air-fuel mixture to form a flame. The present arrangement ensures efficient combustion of fuel which is lead to the intimate mixing of controlled secondary air with fuel gas. However, it may not result into improved thermal efficiency which is a function of thermal energy utilization during the heating application. Moreover, the above cited prior art has no mention of gas fuel for which the burner has been designed. Different fuels e.g. Propane, LPG, Natural Gas, Biogas, Producer gas etc. have different characteristics, therefore the burner design should be based on specific fuel characteristics as interchangeability of fuels in burner dose not confirm efficient performance and is also unsafe.

Reference is made to Boggavarapu et.al. [1] that presents the theoretical and experimental studies performed on a conventional domestic burner to investigate various strategies to improve thermal efficiency when fired with LPG and PNG. The prior is focused at optimizing loading height (distance between burner top and vessel bottom ) than design modification for improving performance of burner fired with PNG. However, no burner design concept is presented in the prior art for PNG. On the other hand we are presenting a burner design which is based on the characteristics of PNG which generates a stable flame of PNG and ensures safe operation. For enhanced thermal efficiency, both burner design and loading height are equally considered.

Reference is made to Yung-Chang et.al. [2] that presents the experimental results of emissions and efficiency of gas burner fired with different compositions of natural gas. The burner used in the study is a double ring burner which is an adjustable burner in which both fuel and air flow rates can be controlled manually. The burner comprises of two rings where outer ring is used for primary heat input, whereas inner ring is used for auxiliary heat input. Both the outer and inner rings can be regulated separately. The burner can be used to generate stable flame but has low thermal efficiency. In our case the PNG burner consists of a single ring where both air and PNG mixes and directed towards the burner cap / top where flame is generated. There is only one thermal input provided through single ring in our case. Only the fuel flow rate is controlled whereas air is entrained through pressure difference in our case. Therefore the burner used in the prior art is different in design and in operation.

Reference is made to paper, Chen, Zhiguang_et. . . [3] that presents experimental study pertaining to flame stability of partially premixed combustion of PNG and LNG and also their interchangeability. The burner used in prior art is called the Precision Test Burner PTB, which is designed primarily for experimental studies pertaining to flame stability. The burner comprises of two air inlet and one fuel gas inlet that further goes into an expansion chamber and through a low pressure ejector to the burner head. There is a fundamental difference between the burner (PTB) used in the prior art and our burner. The PTB is a partially premixed burner (compressed air is fed through inlet alongwith fuel gas) whereas our burner is a self aerated burner where air is entrained inside the mixing tube due to pressure difference at throat (venturi effect). Besides it, a low pressure gas ejector is used in PTB to supply gas-air mixture to burner head, whereas a gas injector (jet) is used to supply PNG to mixing tube in our case.

Based on the review of many prior art, it is evident that heating value of LPG and PNG is different; PNG has lower heating value compared to LPG. The heating value of a fuel, which depends on its composition, strongly affects burner performance. Using the same burner to burn different heating values gases is inappropriate and hazardous due to possible occurrence of incomplete combustion (i.e. increase of CO emission and / or soot formation), flame lift off, flash back and inadequate heat input [2]

PNG as domestic cooking fuel is already in use in many parts of India. However, due to unavailability of dedicated PNG burner / stove, the available LPG stove is being modified to use PNG by changing the gas injector to maintain the heat input. This is an unsafe practice and is an act of tampering a standard product as Influence of parameters like variation of gas composition, primary aeration, gas supply pressure and loading height are important to be studied and optimized for the optimum safe and efficient performance [4]

The present invention provides a domestic cooking burner designed specifically for PNG. It is an atmospheric burner consisting of designed gas injector; mixing tube and burner head. The burner components are designed based on the characteristics of PNG (density, specific gravity, molar mass, dynamic viscosity, ratio of specific heats, and calorific value etc.). The throat and mixing tube is designed to have minimum 50% of primary aeration. Mixing tube and burner manifold is designed to have low frictional gas pressure losses. Further, the overall burner is designed to for a range of power output at a loading height of 17 mm with minimum 55% of thermal efficiency. The present invention therefore, provides a dedicated PNG burner that can be used for efficient and safe usage in domestic cooking application.

References:

[1] Boggavarapu, Prasad, Baidurja Ray, and R. V. Ravikrishna. "Thermal Efficiency of LPG and PNG-fired burners: Experimental and numerical studies." Fuel 116 (2014): 709-715. [2] Ko, Yung-Chang, and Ta-Hui Lin. "Emissions and efficiency of a domestic gas stove burning natural gases with various compositions." Energy Conversion and Management 44.19 (2003): 3001-3014.

[3] Chen, Zhiguang, Chaokui Qin, and Yangjun Zhang. "Flame stability of partially premixed combustion for PNG/LNG interchangeability." Journal of Natural Gas Science and Engineering 21 (2014): 467-473.

[4] Junus, R., et al. "The effects of the design of the cap of a natural gas -fired cooktop burner on flame stability." International journal of energy research 22.2 (1998): 175-184.

OBJECTIVES OF THE INVENTION

Since there is no dedicated burner available for the application of PNG in India, it is an object of this invention to design a dedicated burner for the application of PNG in domestic sector through the design of essential parts, for example, a gas injector, a mixing tube, a gas manifold, and a burner top.

The power output of the domestic burners available in India is in the range of 1.5 kW to 2.25 kW. It is therefore another object of the present invention to design a PNG burner of above mentioned power range, so that it can match the requirement of domestic consumers and can be readily commercialized.

Experimental evaluation of PNG stoves available in market confirms its low thermal efficiency when compared to LPG stoves (refer Fig.15). Considering the large number of domestic users, 10% improvement in efficiency can result into huge savings in terms of quantity and investment. It is therefore another object of the invention to design an energy efficient PNG burner through improved thermal efficiency, which is established through new burner design and optimum loading height that will result into minimum heat losses in the cooking application.

SUMMARY OF THE INVENTION

Accordingly the invention provides a domestic cooking burner designed for the efficient and safe application of PNG in domestic cooking. In an embodiment, a domestic cooking burner designed specifically for PNG is disclosed. The domestic cooker includes a gas injector designed to deliver PNG at a range of power output and at a range of pressure, a divergent mixing tube having throat in the form of a sectional cut located axially to entrain primary air and make mixture with PNG, a burner manifold to further mix air and PNG, and a burner head with three rows of holes (two on the outer face and one on inner face) with specific diameter pitch and depth to support flames with a defined loading height for cooking utensil. Further, the left side of the burner gas manifold is provided with a single hole to fix the PNG burner to the hob.

In an embodiment, the gas injector of inner diameter of 1.0 mm is provided to inject PNG into the central axis of mixing tube.

In an embodiment, the domestic cooker burner includes a divergent mixing tube of length 122 mm with throat in the form of a sectional cut of 180 degree and a divergent mixing tube with outer diameter of 16 mm and inner diameter of 21 mm.

In an embodiment, the PNG burner includes a burner head of outer diameter 68 mm having two rows of holes on outer face (PCD 62.5 mm & PCD 55.2 mm) and one row of holes on inner face (PCD 39.5 mm). Each hole has a diameter of 2.0 mm and a pitch of 2.8 mm.

In an embodiment, the PNG burner includes a burner head of inner diameter 24 mm and burner head faces inclined at 102 degrees with the central vertical axis and inclined at 12 degree with horizontal axis.

In an embodiment, the PNG burner has burner head holes of depth 6 mm and has a loading height of 17 mm for cooking utensil.

In an embodiment, the PNG burner has brass as material of construction for the burner head and the gas injector. The PNG burner has aluminum as material of construction for the mixing tube and burner manifold.

In an embodiment, the PNG burner is designed for domestic cooking application. In another embodiment, it may also be used for commercial cooking and industrial heating applications. In an embodiment, the mixing tube is designed for minimum 50% of primary aeration. In another embodiment, the mixing tube is designed for a range (1.5 kW to 2.25 kW) of power output operated at a range (17 - 21) mbar of inlet pressure.

In an embodiment, the PNG burner delivers minimum 55% of thermal efficiency, when evaluated under standard test conditions.

In an embodiment, the burner includes means for forming and subsequent introducing the mixture of PNG and primary air under a specific pressure at the predetermined ratio.

In an embodiment, the burner includes the gas injector for supplying PNG to an inlet of the mixing tube to compose the mixture with primary air at a predetermined ratio.

In an embodiment, the flow of air-PNG mixture directed from the injector through the throat introduced at a high speed into mixing tube where the speed is converted to the pressure of the particular corresponding value.

In an embodiment, a combustible air-PNG mixture is introduced under the prescribed pressure into the inlet port and then dissipates within the receiving chamber of the burner head, which is positioned adjacent the mixing tube.

In an embodiment, the burner head is provided with lateral apertures intended to issue and consequently uniformly distributes the combustible mixture all around the surface of the burner head.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.1: Top view of the invented PNG burner

In the drawings accompanying the specification, Fig.1 is a perspective top view of the improved PNG domestic burner detachably mounted thereon and a gas injector 1 mounted on the end of a gas supply conduit 2; supported in a fixed position to the burner inlet in accordance with the present invention; A divergent mixing tube 3 is located along the same axis fitted laterally on one side of the burner manifold 4, burner head 5 is mounted on the gas manifold 4 having plurality of holes of similar diameter located circumferentially in three rows. The left side of the burner gas manifold is provided with a single hole 6 to fix the PNG burner to the hob.

Fig.2: Sectional elevation of the invented PNG burner

Fig. 2 is the cross sectional view taken along axis X-X of Fig.1 ; referring to the drawing in detail, burner indicated in Fig. l, has a burner head portion 5 mounted on the gas manifold 4 and a mixing tube 3. The burner is conventionally arranged so that the head portion 5, extends upwards towards the loading utensil, with the mixing tube portion 3 formed at 90° to the head portion so that the axis of inlet is perpendicular to the vertical axis Y-Y’ of the burner.

Fig.3: Front and side view of gas injector

Fig.3 shows a thimble shaped gas injector, with screw threaded end portion 7 that fits into a round tubular supply conduit 2. The open end of the gas injector 1 is provided with a hexagonal portion 8 to facilitate turning the gas injector with a wrench. The injector has an orifice drilled therein with a tapered approach bore leading thereto. Brass is the material of construction for the gas injector.

Fig.4: Top view with sectional elevation of burner head

Fig.4 shows the top view of burner head with its sectional elevation, having two rows of holes on outer face of burner head 9 and one row of holes on inner face 10. The outer face 9 is at an angle of 106° with the central axis 4-4’. Rows of burner holes are oriented in a manner to cover the entire utensil bottom surface for uniform heat distribution. The central part of the burner head 12 is open for the entrainment of secondary air. The burner head is made of brass, however, cast iron may also be used.

Fig.5: Top view with sectional elevation of burner manifold

Fig. 5 is top view of burner manifold with cross sectional view along axis 5-5’, the burner manifold 5 has circular collars 13, 14 to seat burner head 5 to prevent any leakage. A support arm 4 with a hole is provided to fit the burner axially with screw and nut on the stove body. The other side 15 of the burner manifold is provided with bore with internal threads for connecting the mixing tube 3. The material of construction of the burner manifold is aluminum; however, Mild Steel may also be used. Fig.6: Elevation with sectional end view of mixing tube

Fig.6 is the cross-sectional view taken along 6-6’ of mixing tube, mixing tube 2, a tapered tube with one end opened towards injector orifice 1, called the throat 16, has smaller diameter, the other end having larger diameter 17 with screw threaded top portion 18, so as to snugly fit into the gas manifold 4 at bore 15.

DETAILED DESCRIPTION OF THE INVENTION

The burner is designed for PNG, which as per GC (Gas Chromatography) analysis is found to be natural gas (more than 90%). Based on the fuel characteristics, the gas inlet pressure was determined based on critical pressure ratio and outflow conditions. Further, based on the relation of mass flow rate through injector at subsonic condition, diameter of gas injector was determined which was based on actual PNG density, ratio of specific heats, molecular weight and operating temperature. However, Mach No. and speed of sound in gas is calculated theoretically using standard values. Mixing tube of the burner is designed for an entrainment ratio, calculated for 50% primary aeration and for stoichiometric air-fuel ratio calculated for the actual PNG composition. Based on, the throat diameter of mixing tube is calculated using Prigg’s relation. However, for the entrainment of excess air, the throat diameter is taken 2 times of the calculated value. A divergent mixing tube of length 6 times the diameter of throat is taken to have low pressure drop in mixing tube. Finally, based on the flow rate of air -fuel mixture coming from mixing tube, area of burner top, diameter of holes and no. of holes are calculated. Flame stabilization is required for safe operation of burner during the prolonged application. The major concerns of flame stability is to avoid“flame lift” and “flash back” phenomenon that occurs when the speed of air-fuel mixture through the burner port is either high or low compared to the speed of the flame burning in the gas. Burning velocity of natural gas is 0.30 m/s, for a stable flame, velocity of air-fuel mixture at burner port should be less than this. Velocity of mixture at burner port is calculated to 0.12m/s which diminish the chances of occurring“flame lift”. Also, no“flash back” is observed during long hour operation of invented PNG burner. Loading height is the height between burner top and vessel bottom. This height is crucial for heat transfer between flame and cooking vessel and to supply secondary air. Large cooking height gives space for secondary air entrainment but heat loss occurs. However, low loading height minimizes heat loss at the cost of poor fuel combustion. Therefore, an optimum loading height is essential for an improved burner performance. Temperature profile around vessel bottom is examined theoretically; however thermal and combustion efficiency is determined experimentally at different loading heights. Finally, a loading height suitable for the invented PNG burner is determined.

PNG Burner Design:

5 The burner is designed for PNG, which as per GC (Gas Chromatography) analysis is found to be natural gas (more than 90%), Table.1. Gas inlet pressure was determined based on critical pressure ratio and outflow conditions. Further, based on the relation of mass flow rate through injector at subsonic condition, diameter of gas injector was determined which was based on actual PNG density, ratio of specific heats, molecular weight and operating temperature. 0 However, Mach No. and speed of sound in gas is calculated theoretically using standard values of natural gas. Mixing tube of the burner is designed for an entrainment ratio, calculated for 50% primary aeration and for stochiometric air-fuel ratio calculated for the actual PNG composition. Based on, the throat diameter of mixing tube is calculated using Prigg’s relation. However, for the entrainment of excess air, the throat diameter is taken 2 5 times of the calculated value. A divergent mixing tube of length 6 times the diameter of throat is taken to have low pressure drop in mixing tube. Finally, based on the flow rate of air and fuel mixture coming from mixing tube, area of burner top, diameter of holes and no. of holes are calculated. 0 Table.1 PNG composition and characteristics

Burner Design: heat release of PNG burner: The amount of power output from a burner, referred to as burner heat release, depends on how much fuel the burner consumes and how much chemical energy the fuel has (heating value), which is referred to as the heating value of the fuel and can be written mathematically as:

Diameter of injector d_o:

The amount of gas used by a burner is controlled by the size of injector orifice or jet. Besides it, it separates the burner from the gas supply and also works as a flame arrestor.

Critical pressure P_c:

In the present case fuel flow is subsonic:

For subsonic condition, mass flow rate through nozzle is given by following relation:

Putting all the values in eq. 2 the diameter of injector is calculated for the PNG

Diameter of throat d_t :

Using the prigg’s relation, diameter of throat d_t is calculated for PNG

The entrainment ratio r is calculated for 50% primary aeration P_a .

However for excess entrainment of air, throat area is taken as 2 times d_t

To reduce the pressure drop in the mixing tube the length of mixing tube L_m = 6 X d_t

Burner port:

Based on the above values, the burner port area is calculated based on following relation;

Whereas, no of holes (burner ports) are calculated based on below relation

Also the output per no. of hole is determined.

Burner Hydrodynamics

Velocity of fuel at exit V:

Velocity of PNG stream coming out of nozzle injector is calculated theoretically using below mentioned relation

Pressure drop in throat P_t :

Pressure drop at throat is calculated using the below mentioned relation. The pressure drop at the throat is crucial for primary air entrainment.

Flow of mixture Q_m :

For 50% primary aeration, flow of fuel air mixture is calculated using the below relation

Reynolds no. & Pressure drop in mixing tube:

The flow behavior of fuel (PNG) - air mixture and pressure drop in the mixing tube is calculated using below mentioned relations

In the present case, the flow is laminar, for laminar flow pressure drop across the mixing tube can be calculated using following relation,

In the present case, the pressure drop in mixing tube is very less compared to driving pressure of 230 Pa

Flame stability

Flame lift is the phenomenon commonly observed during fuel interchangeability, it occurs when the speed of fuel - Air mixture through the burner port is higher than the speed of the flame burning in the gas. Pure methane has a flame speed of 0.30 m/s, therefore for the design of stable flame velocity of mixture (Fuel + Air) should be less than this value. Following relation is used to calculate mixture flow rate;

In the present case, = 0.12 m/s , which is less than flame speed of methane. Therefore there shall be no flame lift in our design. The fact is also validated through long test runs on the designed PNG burner.

Fig.7 isometric view of PNG burner with sectional cut

Design Novelty:

Gas injector (Injector Orifice): Diameter of the gas injector in the present invention has been calculated based on the mass flow rate, density of PNG and other properties like Mach No. and speed of sound in PNG. Further, the diameter of the injector is designed for an inlet gas pressure (17 - 21 mbar). The diameter of gas injector in the present case is 1.00 mm. As existing LPG burner / stoves are being used for PNG firing in India, the gas injector has diameter designed for LPG and for an inlet pressure (30 mbar). The diameter of gas injector is around 0.6 mm in case of LPG. Since, the diameter of gas injector has been calculated theoretically and tested practically for PNG in the present case, it is non- obvious. However for manufacturing simplicity, the outer shape of the gas injector has been kept as per prevailing gas injector design.

Fig.8 Gas Injector Mixing Tube: Mixing tube in the present case is designed to have throat for min. 50% primary aeration in the form of a sectional cut. Where the cut section provides throat area (opening for primary air entrainment) the uncut part provides support for gas injector. The mixing tube is divergent in shape with section having throat with lower diameter and section opening into burner manifold has larger diameter. Due to the divergent structure of mixing tube, the length of the tube is small compared to other conventional / prevailing gas burner where long mixing tubes are used. The material of construction for mixing tube in the present case is aluminum, however cast iron, mild steel is used in conventional / prevailing gas burners. Both the geometry and material of the mixing tube is designed with the aim to have minimum frictional losses for PNG - Air mixture that helps in generating stable flames. On the other hand controlled mixing of air and fuel provides proper combustion and therefore improves combustion as well as thermal efficiency. The design of mixing tube is therefore novel as well as non obvious.

Fig.9 Mixing tube

Burner head (cap): Burner head design plays a very important role as it generates or holds a stable flame. In present case, diameter of hole on burner head, depth of hole, area of head and its angles has been designed to generate stable flame (no flame lift) for a range of gas flow rates. The diameter of hole is 2.00 mm with a pitch of 2.8 mm and depth of 5 mm in the present case. Whereas, burner hole diameter in case of prevailing LPG and PNG burners is comparatively lower and flame lift is observed both theoretically and experimentally when PNG fired in conventional burner head hole.

LPG flame Natural Gas flame

Fig.10 Flame lift observed theoretically in a single hole burner

Fig.11 Burner head

Hole diameter in the present case is designed to provide sufficient thermal output, as calorific value of PNG is lower as compared to LPG. The pitch (distance between holes) is designed for have proper cross flame ignition (burner ignition). Hole depth designed for flame stability over a range of gas flow rates. Overall the burner head design provides a stable flame of PNG that result in improved thermal efficiency.

Loading height: Loading height is the distance between burner head top and cooking vessel bottom. The loading height is important for the heat transfer from flame to cooking vessel. However, it is not the part of burner design. In the present case loading height is determined both theoretically and experimentally. A loading height of 17 mm is kept for the present burner design. In some prior arts, different loading heights are reported for Natural Gas burners. The optimized loading height in the present case has contributed to further improvement in thermal efficiency.

Fig.12 Loading height

8. EXAMPLES / PERFORMANCE EVALUATION

The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.

Performance of the fabricated PNG burner is evaluated on the basis of its thermal efficiency. A standard procedure followed as per prevailing Indian standards to evaluate the invented PNG burner, gas inlet pressure is kept as per design to attain stable flame with appropriate height. Thermal efficiency of the invented PNG burner is evaluated as per following relation:

Where, G is the weight of water, W is the weight of utensil, Ti and T2 are initial and final water temperature, M is the volume of fuel (PNG) consumed and K is the calorific value that was determined theoretically based on composition. The experiment is conducted at 12 mbar of inlet pressure and the calorific value of PNG is taken as 8360 cal/lit.

To assess the performance, the thermal efficiency results of invented PNG burner is compared with the standard LPG burners available in market and also with the burners modified for PNG of same power capacity. It is clearly observed from the experimental data mentioned in Fig.6 that the performance of invented PNG burner (Blue bars) is 15% more than the burner modified for PNG (Green bars). However, the performance of the invented burner slightly lower than the commercially available standard LPG burner (Red bars) Performance of developed PNG burners are compared with PNG burners of same capacity, and it is found that average thermal efficiency of developed PNG burner of 1.53 kW (a) and 1.82 kW (b) power capacities is 55.90% and 56.54% respectively. The current performance of developed burners indicates an improvement of approximately 15%. Fig.13

(b)

Fig.13 Comparative performance of invented PNG burner

Performance of developed PNG burners of 2.06 (c) and 2.25kW (d) capacity was found to be 10% more than the available PNG burners of same capacity, Fig.14.

(d)

Fig.14 Comparative performance of invented PNG burner Modification of a standard LPG burner to a PNG burner by retrofitting with different gas injector is not a correct approach. Experimental evaluation of different capacity LPG burners modified for PNG clearly indicates reduction in thermal efficiency. Comparative result mentioned in Fig.15 shows significant difference in performance. Moreover, modifying LPG burner is an act of tampering a standard product.

Fig.15 Performance of LPG and modified PNG burners

Theoretical study on interchangeability of LPG and PNG indicates that interchangeability of fuels depends on the Wobbe No. of the gasses. Wobbe No. of gas depends on composition and physico-chemical properties. Since the Wobbe Number of LPG and PNG are different, PNG cannot be directly used in the same burning appliance without design modifications.

Changing supply pressure in atmospheric burners affects the flame characteristics. Supply pressure may be varied to match Wobbe Number of two different gases used in same appliance. However, the different burning velocity of gases may cause“Flame Lift” or“Flash Back” during application.

The above mentioned conclusion points clearly indicate that PNG is a different fuel gas and a dedicated burning appliance (Burner) is required for its safe and efficient application. Minor modification in the existing burners can be made to burn PNG but it is unsafe and also very inefficient. The PNG burner designed in the present case is based on specific fuel (PNG) properties and the design of its mixing tube, jet size and burner head is different as compared to other prevailing burners. The designed (invented) PNG burner has shown significant performance improvement when compared to other domestic gas burners. The improved performance is the results of new burner design. Therefore, the PNG burner presented in this document is novel and non-obvious.

Nomenclature :

ADVANTAGES:

The main advantages of the present invention are:

The present invention provides a standard product designed for safe and efficient use of PNG in domestic cooking application.

The developed PNG burner has thermal efficiency of minimum 55%, which is 15% more than the prevailing modified PNG burners.

The improved energy efficiency may lead to significant reductions in energy consumption in the household sector and enable delivery of energy to household for cooking via lower PNG supply per household for the same energy duty.

The present invention provides a standard design of PNG burner for the commercialization

The present art also provides evaluation criteria for domestic PNG burners that can be helpful in formulating Indian standards on PNG burners.

Claims

We Claim:

1. A domestic cooking burner designed specifically for PNG, comprising a gas injector (1) designed to deliver PNG at a range of power output and at a range of pressure, a divergent mixing tube (3) having throat in the form of a sectional cut located axially to entrain primary air and make mixture with PNG, a burner manifold (4) to further mix air and PNG, a burner head (5) with three rows of holes (two on the outer face and one on inner face) with specific diameter pitch and depth to support flames with a defined loading height for cooking utensil, The left side of the burner gas manifold is provided with a single hole (6) to fix the PNG burner to the hob.

2. The domestic cooking burner as claimed in claim 1, wherein the gas injector of inner diameter of 1.0 mm is provided to inject PNG into the central axis of mixing tube.

3. The domestic cooking burner as claimed in claim 1, comprising a divergent mixing tube of length 122 mm with throat in the form of a sectional cut of 180 degree and a divergent mixing tube with outer diameter of 16 mm and inner diameter of 21 mm.

4. The domestic cooking burner as claimed in claim 1, comprising a burner head of outer diameter 68 mm having two rows of holes on outer face (PCD 62.5 mm & PCD 55.2 mm) and one row of holes on inner face (PCD 39.5 mm), each hole having a diameter of 2.0 mm and a pitch of 2.8 mm.

5. The domestic cooking burner as claimed in claim 4, comprising a burner head of inner diameter 24 mm and burner head faces inclined at 102 degrees with the central vertical axis and inclined at 12 degree with horizontal axis.

6. The domestic cooking burner as claimed in claim 4, comprising burner head holes of depth 6 mm and having a loading height of 17 mm for cooking utensil.

7. The domestic cooking burner as claimed in claim 1, having brass as material of construction for burner head and gas injector, and aluminum as material of construction for mixing tube and burner manifold.

8. The domestic cooking burner as claimed in claim 1, wherein the domestic cooking burner is designed for at least one of domestic cooking application, commercial cooking application, and industrial heating applications.

9. The domestic cooking burner as claimed in claim 4, wherein the mixing tube is designed for minimum 50% of primary aeration, and for a range (1.5 kW to 2.25 kW) of power output operated at a range (17-21) mbar of inlet pressure.

10. The domestic cooking burner as claimed in claim 1, wherein the domestic cooking burner delivers minimum 55% of thermal efficiency, when evaluated under standard test conditions.