Performance and Emission Analysis of a Novel Porous Radiant Burner for Domestic Cooking Application

Present study focuses on the performance and emission analysis of a novel porous radiant burner for domestic cooking application using liquefied petroleum gas (LPG) as fuel. The porous radiant burner (PRB) used here is a novel ceramic porous radiant burner which is designed and developed in the University laboratory for this present study. Two kinds of PRBs as circular porous radiant burner and square porous radiant burner have been developed and hence the thermal efficiency and emission analysis of these burners are tested for their performance. The test results are very encouraging as the thermal efficiency of the circular porous radiant burner and square porous radiant burner are much higher as compared to the conventional metallic burners or other types of burners. The emission characteristic also shows that the emission of CO and NOx values are much lesser than the conventional burner and are well within the world health organization standard. The experimental setup used here is a flexible one that contains PRBs, LPG cylinder, K- type thermocouple, data acquisition system, flue gas analyzer, Infrared camera and a computer. The maximum thermal efficiency obtained in that test for the PRB is about 72% which indicates its bright future prospect.     

Thermal efficiency improvement of an LPG gas cooker by a swirling central flame

The present study proposes a swirling central flame technique to improve the thermal efficiency of a conventional open‐flame atmospheric gas cooker which is now widely used as a domestic appliance. More extensive studies were done in an effort to improve the thermal efficiency of the cooker by reducing thermal inertia of the pan support and using the proposed porous medium technology to recover heat from flame radiation to preheat the secondary air entrained from the bottom of the burner. The experimental results showed that the thermal efficiency of the swirling central flame burner with conventional support is approximately 15 per cent higher than that of the conventional radial flow burner. This can be attributed to the higher heat transfer coefficient between hot flue gas and vessel surface of the swirl burner than that of the conventional one. By replacing the conventional support of the developed swirl burner with a lighter one, whose mass was reduced by a factor of 3.7, the thermal efficiency could be increased by about 3 per cent. By using the proposed preheating secondary air support instead of the light support, the thermal efficiency could be further improved by 3 per cent. The predicted thermal efficiency obtained from the proposed model showed good agreement with the experiment. Copyright © 2001 John Wiley & Sons, Ltd.     

Biomass availability, energy consumption and biochar production in rural households of Western Kenya

Pyrolytic cook stoves in smallholder farms may require different biomass supply than traditional bioenergy approaches. Therefore, we carried out an on-farm assessment of the energy consumption for food preparation, the biomass availability relevant to conventional and pyrolytic cook stoves, and the potential biochar generation in rural households of western Kenya. Biomass availability for pyrolysis varied widely from 0.7 to 12.4 Mg ha⁻¹ y⁻¹ with an average of 4.3 Mg ha⁻¹ y⁻¹, across all 50 studied farms. Farms with high soil fertility that were recently converted to agriculture from forest had the highest variability (CV = 83%), which was a result of the wide range of farm sizes and feedstock types in the farms. Biomass variability was two times lower for farms with low than high soil fertility (CV = 37%). The reduction in variability is a direct consequence of the soil quality, coupled with farm size and feedstock type. The total wood energy available in the farms (5.3 GJ capita⁻¹ y⁻¹) was not sufficient to meet the current cooking energy needs using conventional combustion stoves, but may be sufficient for improved combustion stoves depending on their energy efficiency. However, the biomass that is usable in pyrolytic cook stoves including crop residues, shrub and tree litter can provide 17.2 GJ capita⁻¹ y⁻¹ of energy for cooking, which is well above the current average cooking energy consumption of 10.5 GJ capita⁻¹ y⁻¹. The introduction of a first-generation pyrolytic cook stove reduced wood energy consumption by 27% while producing an average of 0.46 Mg ha⁻¹ y⁻¹ of biochar.     

Experimental investigation of the performance of a liquid fuel-fired porous burner operating on kerosene-vegetable cooking oil (VCO) blends for micro-cogeneration of thermoelectric power

Studies related to porous burner for thermoelectric (TE) power generation have mainly focused toward achieving a specific range of power output for various applications. However, detailed analyses on the performance and emission aspects of the porous burner are lacking. In addition, physical integration between the burner and TE modules has added further complexity in this research area. Thus, this work aims to comprehend the effects of fuel–air equivalence ratio on the performance and emission characteristics of a liquid fuel-fired porous burner for micro-cogeneration of TE power. A catalytically inert Al₂O₃ porous medium was incorporated into a liquid fuel-fired porous burner operating on four mixtures of kerosene-vegetable cooking oil (VCO) blends: 100 kerosene, 90/10 KVCO, 75/25 KVCO, and 50/50 KVCO. Ten bismuth-telluride TE cells were arranged in a ten-sided polygon that, together with finned dissipators, formed a TE module electrically connected in series but thermally connected in parallel. The performance aspects at various fuel–air equivalence ratios were thoroughly evaluated with the corresponding temperature profiles, voltage, current, power output, and electrical efficiency. Results indicated that the surface temperature of the porous media was generally higher than the developed and exit flame temperature of the burner. Varying the fuel-air equivalence ratio significantly affected the electrical efficiency, with a maximum and minimum value of 1.94% and 1.10%, respectively. The power output steadily increased in the lean region, but stabilized as the fuel–air equivalence ratio slowly increased beyond the stoichiometric ratio. The CO emission was relatively lower at the lean region; however, significant amount was recorded in the rich combustion region. Moreover, NOx fluctuated between 1 ppm and 4 ppm over the entire range of fuel–air equivalence ratio.     

The influence of swirl burner structure on the gas/particle flow characteristics

Improvements were made to a low-NO_x axial swirl burner (LNASB), aimed at mitigating slagging in a 600-MWe boiler burning bituminous coal. The new design is referred to as improved low-NO_x axial swirl burner (ILNASB). This paper describes investigations of the influence of swirl burner structure on the gas/particle flow characteristics using a three-dimensional particle-dynamics anemometer. In comparing results from both ILNASB and LNASB, a central recirculation zone is seen to form in the region x/d = 0.1–0.3 within the ILNASB. This zone had shifted from the region between primary and secondary air in LNASB to a region between inner and outer secondary air. In the vicinity of the burner outlet, particle volume flux is reduced significantly in the central recirculation zone. In contrast, this flux is high near the central axis in ILNASB, thus concentrating a great fraction of pulverized coal near the central axis. Form the study, the gas/particle flow characteristics of the ILNASB show that the improved burner has the ability to ease slagging and reduce NO_x emissions.     

Development of energy efficient porous medium burners on surface and submerged combustion modes

Two compact premixed LPG burners based on submerged and surface combustion modes in porous medium (abbreviated as MSB and SSB respectively) are developed and their combustion and emission characteristics are compared to those of the CB (conventional burner). The preheating and reaction zones of MSB are made from porcelain form and Alumina spheres of 30 mm size, respectively, and the corresponding zones in SSB are made from Alumina (Al₂O₃) foams of pore densities 26 ppcm and 8 ppcm. NO_x emission is reduced by 76% and 75% by the use of MSB and SSB, respectively, compared with the CB, with acceptable CO and SO₂ emissions. For a thermal load of 0.62 kW, the thermal efficiencies of CB, MSB and SSB are estimated to be 47%, 59% and 71%, respectively.     

Measurement of gas species,temperatures, char burnout,and wall heat fluxes in a 200-MWe lignite-fired boiler at different loads

We measured various operational parameters of a 200-MW_e, wall-fired, lignite utility boiler under different loads. The parameters measured were gas temperature, gas species concentration, char burnout, component release rates (C, H and N), furnace temperature, heat flux, and boiler efficiency. Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has two ring recirculation zones that start in the secondary air region of the burner. With increasing secondary air flow, the air flow axial velocity increases, the maximum values for the radial velocity, tangential velocity, and turbulence intensity all increase, and there are slight increases in the air flow swirl intensity and the recirculation zone size. With increasing load gas, the temperature and CO concentration in the central region of burner decrease, while O₂ concentration, NO_x concentration, char burnout, and component release rates of C, H, and N increase. Pulverized-coal ignites farther into the burner, in the secondary air region. Gas temperature, O₂ concentration, NO_x concentration, char burnout and component release rates of C, H, and N all increase. Furthermore, CO concentration varies slightly and pulverized-coal ignites closer. In the side wall region, gas temperature, O₂ concentration, and NO_x concentration all increase, but CO concentration varies only slightly. In the bottom row burner region the furnace temperature and heat flux increase appreciably, but the increase become more obvious in the middle and top row burner regions and in the burnout region. Compared with a 120-MW_e load, the mean NO_x emission at the air preheater exits for 190-MW_e load increases from 589.5 mg/m³ (O₂ = 6%) to 794.6 mg/m³ (O₂ = 6%), and the boiler efficiency increases from 90.73% to 92.45%.     

Small scale porous medium combustion system for heat production in households

For heating purposes in modern households, gas burners are normally applied due to their simplicity, low cost and easy handling. On the other hand, practical experience showed that conventional, open flame gas burners compared to porous medium systems have low dynamic range, i.e. low power modulation capability and, additionally, higher production of pollutants such as carbon monoxide (CO) and nitrogen oxides (NO_x). This is especially notable when the burner operates at low thermal power regimes. In order to avoid the above-mentioned difficulties and disadvantages of conventional burners, new porous medium gas burner system with maximum thermal output of 8 kW has been developed. The objective of the presented work is focussed on better understanding and enabling further developing of porous medium burners (PMB) for household heating systems. The aim of the work is also to develop a compact and highly efficient combined heating system based on the 8 kW gas PM burner coupled with a new heat exchanger incorporated into an electro-fossil fuel system considering space and domestic water heating in one-family house. The final result was the heating system with modulation of the thermal power up to approximately 1:8 and low emissions of CO and NO_x.     

Experimental study of the processes in hydrogen-oxygen gas generator

The paper presents a hydrogen-oxygen gas generator, which could be a key element of a novel scheme of hybrid hydrogen-air energy storage system, which proposes to store energy in both compressed air and hydrogen. At a power generation mode, hydrogen is combusted in oxygen, the produced steam is mixed with air and the gas mixture is used in a conventional gas turbine. The experimental hydrogen-oxygen gas generator has produced gas with temperatures 953–1163 K at pressures 2–4 MPa and has reached the thermal capacity up to 210 kW and thermal efficiency up to 95–99%. Separation of the combustion zone and air injection has helped to reduce NO_x content in the product gas to 11 mg/st.m³.     

Experimental study of ultra-rich thermal partial oxidation of methane using a reticulated porous structure

Performance of SiC porous burner used in a non-catalytic partial oxidation reformer for syngas production was experimentally investigated in this study. Premixed combustion of ultra-rich methane-oxygen mixtures was conducted at thermal loads of 6 and 8 kW. In order to have a comprehensive analysis, temperature distribution along the burner and product compositions were measured. Moreover, a thermodynamic analysis was performed using Gibbs free energy minimization method to calculate equilibrium concentrations prior to the experimental work. The results showed that the highest syngas mole fraction of 0.67 and H₂/CO ratio of 1.86 can be achieved at higher power. The CH₄ conversions were found to be in the range of 79–96%, while the equilibrium data indicated complete consumption of methane.Eventually, this study proved high reforming efficiency of partial oxidation process within SiC porous burner, with a good methane conversion and syngas purity. Therefore, due to highly efficient characteristics of this burner, it may be a good solution in development of reformers, particularly for small-scale applications.     

Induction stoves as an option for clean cooking in rural India

As part of a programme on ‘access to clean cooking alternatives in rural India’, induction stoves were introduced in nearly 4000 rural households in Himachal Pradesh, one of the few highly electrified states in India. Analysis of primary usage information from 1000 rural households revealed that electricity majorly replaced Liquid Petroleum Gas (LPG), generally used as a secondary cooking fuel, but did not influence a similar shift from traditional mud stoves as the primary cooking technology. Likewise, the shift from firewood to electricity as a primary cooking fuel was observed in only 5% of the households studied. Country level analysis indicates that rural households falling in lower monthly per capita expenditure (MPCE) classes have lesser access to electricity and clean cooking options than those falling in higher MPCE classes. Again, only three states in India with high levels of rural household electrification report consumption statuses more than 82 kWh per month (the estimated mean for electricity consumption by induction stoves). Overall, the results of the study indicate that induction stoves will have limited potential in reducing the consumption of firewood and LPG if included in energy access programmes, that too only in regions where high levels of electrification exist.     

Probabilistic single box approach for modeling PAHs associated with combustion aerosols in a typical indoor environment

Firewood, coal, dung cake, kerosene and Liquefied Petroleum Gas (LPG) are the most commonly used fuels for cooking and heating purposes in developing countries. Combustion of such fuels leads to high concentrations of pollutants in the indoor environment. Polycyclic aromatic hydrocarbons (PAHs) are emitted during residential combustion, and have carcinogenic and genotoxic properties. In this study, data from an experimental setup for estimation of emission rate of particulate-bound PAHs generated during combustion of such fuels are used. PAHs emission rates were used in a probabilistic single box model for prediction of time average particle associated indoor B(a)P equivalent (B(a)P_eq) concentrations of PAHs resulting from typical Indian cooking. Model parameters such as fuel consumption rate, stove power and cooking time were also evaluated experimentally. Particle bound B(a)P_eq PAH emission factor was found to be highest (0.96 mg kg⁻¹) for dung cake, and lowest for LPG (0.48 mg kg⁻¹) among tested fuels. The time averaged B(a)P equivalent concentrations in indoor environment were found to be 0.82, 0.45, 0.87, 0.30, and 0.14 μg m⁻³ for firewood, coal, dung cake, kerosene and LPG respectively. Results reveal that there was higher B(a)P equivalent concentration during combustion of biomass (dung cake, fire wood) as compared to fossil fuels (coal) and non-solid fuels (kerosene, LPG). Predicted time averaged indoor air B(a)P_eq concentrations of PAHs were found to be much higher than the WHO indoor air guideline values for all tested fuels.     

Experimental study of hydrogen production and soot particulate matter emissions from methane rich-combustion in inert porous media

A detailed experimental study of stationary Thermal Partial Oxidation (TPOX) within inert porous media has been conducted. The reaction zone of the tested TPOX reformer is designed so as to enable stationary conversion of fuel/air mixtures for a wide range of operational conditions. Operating characteristics of the process have been examined for two different porous matrices, with different thermal and transport properties, namely SiSiC open foam structure and a packed bed of pure Al₂O₃ packing material in the form of cylindrical rings. The influence of reactants preheating was also examined since the reformer is meant for integration within high temperature fuel cell systems. The operating regime was scanned for reactants' inlet temperature of 400 °C and 550 °C, varying the thermal load in a range from 350 kW/m² up to 2600 kW/m² and the equivalence ratio from 1.9 up to 2.9. Temperature profiles within the reaction region of the reformer were recorded for all tested conditions while gas samples were on-line analyzed for the major species H₂, CO, CO₂, and minor species CH₄, C₂H₂. At reactants' inlet temperatures of 400 °C and 600 °C, for a fixed thermal load of 1540 kW/m² and for selected equivalence ratios around the sooting limit of the process (φ = 2.2–2.6), soot particle size distributions were measured in the exhaust gas with a Scanning Mobility Particle Sizer (SMPS). The results show that the better thermal properties and the higher porosity in the case of the SiSiC matrix enables longer residence times for slow reforming reactions to evolve towards equilibrium and yields syngas with significantly less soot in terms of particle numbers and mass concentration.     

Energy performance of wood-burning cookstoves in Michoacan, Mexico

There have been few detailed assessments of the actual impacts of improved stove interventions in rural communities, although many improved stove projects have reported overall efficiencies from tests in simulated kitchens using water-boiling tests (WBTs). This paper presents an integrated energy evaluation of the Patsari cookstove, an efficient wood-burning cookstove developed in Mexico that has recently obtained international recognition, in comparison to traditional cookstoves in rural communities of Michoacan, Mexico. The evaluation uses three standard protocols: the WBT, which quantifies thermal efficiency and firepower; the controlled cooking test (CCT), which measures specific energy consumption associated with local cooking tasks, and the kitchen performance test (KPT), which evaluates the behavior of the stoves in-field conditions and estimates fuel savings. The results showed that the WBT gave little indication of the overall performance of the stove in rural communities. Field testing in rural communities is of critical importance, therefore, in estimating the benefits of improved stoves. In the CCT for tortilla making, the main cooking task in Mexican rural households, Patsari stoves showed fuelwood savings ranging from 44% to 65% in relation to traditional open fires (n=6; P<0.05). These savings were similar in magnitude to the average energy savings from KPT before and after Patsari adoption of 67% (n=23; P<0.05) in rural households exclusively using fuelwood. Similar energy savings of 66% for fuelwood and 64% for LPG, respectively, were also observed in households using mixed fuels. With sound technical design, critical input from local users and proper dissemination strategies, therefore, improved stoves can significantly contribute to improvements in the quality of life of rural people with potential benefits to the surrounding environment.     

Effects of dual-inlet on premixed hydrogen/air combustion characteristics and thermal performance for micro thermophotovoltaic application

Premixed H₂/air combustion in the micro-combustor with dual-inlet is investigated. Effects of the second-inlet settings on the combustion characteristics, thermal performance and radiation efficiency are discussed and compared. The results indicate that the second-inlet can efficiently modify burning characteristics and heat transmission, improving the burner thermal performance. With the increase of the distance between second-inlet and inlet, the mean outer wall temperature T_m is first risen and then down with a fixed reactants ratio of second-inlet Q_in. It also affects the flow field and radiation temperature, and combustor C3 achieves the highest T_m 1180.9 K and radiation efficiency 28.231% at the total flow rate m_f = 3.376 × 10^?5 kg/s and Q_in = 10%. For an augment of m_f, the radiation temperature is improved while radiation efficiency is declined, and the combustor C2 obtains the highest radiation power 42.3 W at m_f = 5.626 × 10^?5 kg/s and Q_in = 20%.     

Burner-heated dehydrogenation of a liquid organic hydrogen carrier (LOHC) system

For a hydrogen-based economy, safe and efficient hydrogen storage is essential. Compared to other chemical hydrogen storage technologies, such as ammonia or methanol, liquid organic hydrogen carrier (LOHC) systems allow for a reversible storage of hydrogen while being easy to handle in a diesel-like manner. In our contribution, we describe for the first time the successful utilization of the exhaust gas enthalpy of a porous media burner to directly supply the dehydrogenation heat for a kW-scale dehydrogenation of the hydrogen-rich LOHC compound perhydro dibenzyltoluene (H18-DBT). Our setup demonstrates the dynamics of the dehydrogenation unit at a realized maximum hydrogen power of 3.9 kW_th, based on the lower heating value of the released hydrogen. For the intended applications with fluctuating hydrogen demand, e.g. a hydrogen refueling station (HRS) or stationary heating in buildings, a dynamic hydrogen supply from LOHC is important. Methane, e.g. from a biogas plant, is utilized in our scenario as a fuel source for the burner. Hydrogen is released within 30 min after cold start of the system. The dehydrogenation unit exhibits a power density relative to the reactor volume of about 0.5 kW_therm l⁻¹ based on the lower heating value of the hydrogen and a catalyst productivity of up to 0.65 g_H2 g_Pt⁻¹ min⁻¹ for hydrogen release from H18-DBT. An analysis of the by-products and reaction intermediates shows low by-product formation (e.g. maximum 0.6 wt.-% for high boilers and 0.9 wt.- % for low boilers) and uniform distribution of intermediates after the reaction. Thus, a relatively homogeneous temperature distribution and a uniform LOHC flow in the reaction zone can be assumed. Our findings illustrate the dynamics (heating rates of about 10 K min⁻¹) and performance of direct heating of a release unit with a burner and represent a significant step towards LOHC-based hydrogen provisioning systems at technically relevant scales.     

Identification and characterization of trace metals in black solid materials deposited from biomass burning at the cooking stoves in Bangladesh

In this study we have reported the emissions of trace metals from biomass burning at the cooking stoves. Black solid materials deposited from two different types of biomass (rice husk coils – type 1; mixed (straw, bamboo, cow dung, leaves and plants) biomasses - type 2) burning at the cooking stoves were collected from the top of the stoves (but inside the roof of the kitchen) in Narsingdi, Dhaka, Bangladesh. Systematic chemical analysis was done for both samples. Lead, mercury, iron and calcium were identified in sample type-1, and lead, iron and magnesium were identified in sample type-2. The concentration of the trace element was determined with an atomic absorption spectrophotometer. The average concentrations of lead, iron, cadmium calcium, potassium and magnesium were 95.6, 11520, 8.33, 1635, 17.1 and 443.1 mg kg⁻¹, respectively in sample type-1. The average concentration of lead, iron, cadmium calcium, potassium and magnesium were 125.2, 12360, 12.0, 1648, 21.5 and 534.2 mg kg⁻¹, respectively in sample type-2. However, the average concentrations of the determined trace elements followed the sequences, Fe > Ca > Mg > Pb > K > Cd. The emission of lead, iron, cadmium, calcium, potassium and magnesium were much higher from mixed biomass (type-2) compared than the rich husk coils (type-1). The mixed biomass produced about 31% higher lead, 44% higher cadmium, 26% higher potassium, and 21% higher magnesium compared than the rice husk coils. This is the first systematic analysis for the trace metal emissions from different types of biomass burning at the cooking stoves in Bangladesh.     

An experimental study of a cylindrical multi-hole premixed burner for the development of a condensing gas boiler

This study experimentally examined a cylindrical multi-hole premixed burner for its potential use for a condensing gas boiler, which produces less NO_x emissions and performs better. In this study, the hole diameters and the arrangement of a multi-hole burner were investigated using a flat burner model. The combustion characteristics for the flame stability as well as the NO_x and CO emissions were examined using a cylindrical burner. For an optimal operating condition, the equivalence ratio for the cylindrical burner was between 0.70 and 0.75. For this condition, the turn-down ratio was 3:1 or higher, which was suitable for appropriate control of the boiler operation. The NO_x and CO emissions were less than 40 ppm and less than 30 ppm, respectively, for a 0% O₂ basis. The LPG and LNG were able to be used in this type of burner because there was no phenomenal difference in the stable combustion region between them.     

Determination of characteristic parameters for the thermal decomposition of epoxy resin/carbon fibre composites in cone calorimeter

Present study concerns to the thermal degradation of two carbon fibre/epoxy composites, which differ by their volume fractions in carbon fibre (56 and 59 vol%), investigated in cone calorimeter (under atmospheric condition with a piloted ignition). In order to study the influence of the carbon fibre amount on the composite thermal decomposition, the cone calorimeter external heat flux was varied up to 75 kW m⁻². Thus, main parameters of the thermal decomposition of two different composites determined were: mass loss, mass loss rate, ignition time, thermal response parameter, ignition temperature, critical heat flux, thermal inertia and heat of gasification. As a result, when carbon fibre fraction decreases from 59 to 56 vol%, an increase of the thermal parameters was observed: 14–18 kW m⁻² for critical heat flux, 370–435 kW s^1/2 m⁻² for thermal response parameter, 2.25–5.07 kW² s m⁻⁴ K⁻² for thermal inertia and 16–18 kJ g⁻¹ for gasification heat. By analysing the mass loss rate evolutions, a four phases thermal decomposition mechanism is proposed. In the first phase, epoxy resin is cracked to form low molecular weight gaseous species and epoxy-derived compounds. For two next phases, the combustion of epoxy resin and liquor monomer solvent is observed that induces the formation of carbon char. In the last phase, char oxidation and carbon fibre decomposition are identified. Further, during the composite decomposition process, thermal behaviour of solid matrix is changed from a thermally thick material to a thermally thin one when sample is exposed at high external heat flux above 20 kW m⁻².     

Wood fuel use in the traditional cooking stoves in the rural floodplain areas of Bangladesh: A socio-environmental perspective

A study was conducted, using a multistage simple random sampling design, to determine the structural characteristics of the traditional cooking stoves, amount of wood fuel consumed in the rural floodplain areas in Bangladesh, and also to figure out the socio-economic and environmental consequences of wood fuel usage in the traditional cooking stove. The study showed that family size, income, amount cooked and burning hours significantly affected the amount of wood fuel used per family per year. Taking into account different family sizes, the study observed that 4.24 tonne fuelwood were consumed per family per year. The study showed that 42% of families used only biomass fuel, 5% used liquefied petroleum gas (LPG) and 53% used kerosene along with biomass fuels. The main source of biomass fuel was homestead forests (40%). It has been figured out that the incomplete combustion of biomass in the traditional cooking stove poses severe epidemiological consequences to human health and contributes to global warming. The study also showed that 83% of the respondents would prefer improved cooking stoves over traditional cooking stoves.