This thesis constitutes fundamental experimental and computational investigations on gasification and combustion in a packed bed of biomass. Packed bed gasification-combustion in counter-current mode is used in two applications -(1) Gasifier stove in reverse downdraft mode (or equivalently, top-lit updraft mode) that constitutes the idea behind efficient and clean burning domestic stoves. (2) Combustion-on moving grate for boiler application, studied widely in Europe. While a large part of the present study is around domestic stoves, a crucial part of the study aims to address the second application as an extension of the approach taken in the first part to clarify conflicting conclusions of earlier studies and explain the aero-thermochemical behavior over the entire range of superficial velocities, V s (this is velocity of air through the empty cross section of the reactor). Operational differences between the two applications lie in the range of superficial velocity -3.5 to 6 cm/s for domestic stoves and 15 to 30 cm/s for grate combustion. Lower values of Vs are chosen for domestic stoves to limit the particulate emissions; higher values of V s for combustion-on-grate to maximize the conversion rate. Present work deals with a fan based gasifier stove, Oorja, built by BP, India (currently transferred to FEPL, Pune) and disseminated to over 400,000 households between 2005 and 2009. The technology was developed at CGPL, IISc and transferred to BP for commercialization. Work reported in this thesis was started to resolve issues of higher CO emissions in char mode operation and occasional smoking during transition from flaming to char mode. The contribution of the thesis is split into two parts. (a) Use of the principles of gasification to improve the performance of the stoves to the highest possible level, balancing between efficiency and ash fusion issues for domestic and industrial applications and (b) fundamental studies to unravel the flame structure in the two-phase gasification-combustion process over the entire range of Vs. Improving the stove performance It has been known that in most free-convection based stoves, like three stone fire and others developed over the last two decades, the amount of energy extracted from the stove by a cooking pot, usually measured as water boiling efficiency, is between 15 to 35 % with CO emissions of more than 1.5 g/MJ. Oorja stove had demonstrated water boiling efficiency of 50 % and CO emissions of 0.75 g/MJ. Operational issues noticed in the field provided an opportunity to further improve the performance by conducting detailed thermo-chemical studies. Towards this, the components of water boiling efficiency in different phases and from different modes of heat transfer were determined. Optimizing the ratio of air flow rate between combustion air from top and gasification air through the grate (denoted by R) was the key to improving the performance. The maximum water boiling efficiency obtained was 62% with 0.53 g/MJ CO for a 320 mm diameter vessel; under these conditions, the first phase, termed flaming mode, involving pyrolysis-gasification-gas phase combustion contributed 45% to the total efficiency and 0.4 g/MJ CO at R = 4.8 and the second phase, termed char mode, involving char surface oxidation-gasification-gas phase combustion contributed 17% and 0.13 g/MJ CO at R = 1.9. Under optimal air flow conditions, efficiency depends on the size of the vessel used; reactive flow calculations were performed with fast chemistry (using mixture fraction approach) in a zone that includes the free space of the combustion chamber and the vessel to obtain the heat transfer efficiency and bring out the effect of vessel size. Experiments aimed at evaluating the performance of the stove on either side of stoichiometry, revealed that while the stove could be operated on the rich side, it was not possible to operate it on the lean side -it was always tending towards the stoichiometric point with enhanced power. Computational studies showed that increased air flow from the top caused enhanced recirculation around the fuel bed bringing more oxygen that reacted closer to the surface and transferred additional heat enhancing the pyrolysis rate, explaining the observed shift towards stoichiometry. An examination of literature showed that the energy balance for stoves had long remained unexplained (unaccounted losses in stoves were up to 40 %). Using the different components of efficiency obtained from experiments and computations, a heat balance was established to within 5%. This vast improvement in the heat balance is due to the fact that the unaccounted loss in the earlier estimates was essentially due to poor combustion, but was not so recognized. The very significant increase in combustion efficiency in this class of stoves allowed the possibility of estimating other components reasonably accurately. This is a direct consequence of the two stage gasification-combustion process yielding steady flow of gases which contain 80% (gasification efficiency) of the input energy enabling near-stoichiometric combustion with the help of controlled supply of combustion air. Fundamental studies Experiments with wood chips (615 kg/m3) and pellets (1260 kg/m3) showed that particle density has no effect on single particle and packed bed combustion in flaming mode beyond the role played through the surface energy balance (involving the product of fuel density and propagation rate, ˙r). Same is true for single char particles. A transport controlled combustion model taking into account the ash build up over the char surface confirmed this behaviour and showed that the phenomenon follows d2 law, where d is the equivalent diameter of the fuel particle, consistent with the experimental results. But packed bed of char particles showed distinct dependence on particle density. Differences were traced to poor thermal environment faced by low density wood char pieces compared to pellet char leading to variations in the volumetric heat release rate. A composite picture of the operational behaviour of the packed bed flame propagation was obtained from the measurements of exit gas composition, bed temperature, temperature of gas phase and condensed phase surface using 100 µm thermocouples, O 2 drop across the flame front using lambda sensor as a function of Vs. The packed bed studies were conducted in insulated steel and glass reactors. These studies clearly showed distinctive regimes in the bed behavior. In the first regime from Vs = 3 to 17 cm/s, (a) the propagation rate increases with Vs, (b) the fractions of CO, H2 are at least 10%, CH4 drops from 3 to 1%, (c) the oxygen fraction is near zero, (d) the gas phase temperature in the bed is constant at about 1600 K, (e) the condensed phase surface temperature increase from 850 K to 1600 K and (f) oxygen fraction drops from 0.21 to 0.0 within a single particle depth and coincides with the gas phase ignition. The inferences drawn from these data are that (i) the process is diffuusion controlled (ii) the bed operates in fuel rich mode, (iii) char participates only in reduction reactions. In the second domain from V s = 17 cm/s up to about 50 cm/s, (a) the propagation rate is nearly constant (b) the mass fractions of CO and H2 drops to less than 5%, CH4 decreases further, (c) oxygen fraction remains near zero, (d) CO 2 increases, (e) gas phase and surface temperatures are nearly equal and increase from 1600 K to 2200 K and match with the equilibrium temperature at that equivalence ratio, (f) oxygen fraction drops from 0.21 to 0 in one particle depth like in the first regime indicating diffuusion limitedness in this regime as well, (g) unlike in the first regime, volatiles from biomass are convected up to the next layer suppressing a local flame and char oxidation dominates. Beyond Vs = 50 cm/s, the propagation ceased to occur. The precise value of the extinction V s depended on the rate of increase of Vs in this range. A faster change initiated the extinction earlier. Observations showed that extinction began at some location around the periphery and spread laterally. Extinction at one layer was adequate to complete the extinction process. To explain the observed behaviour a simple zero-dimensional model tracking the heating of a fresh biomass particle upstream of the propagating flame front because of radiative heat transfer was set up. This equation was coupled with the equation for single particle flaming combustion to explain the behavior in the first regime. In order to explain the observed flattening of propagation rate in the second regime, it was found essential to account for the effect of the ash layer building on the oxidizing char particle and the temperature dependence of ash emissivity, on the radiative heat transfer to fresh biomass. The results of the model coupled with the experimental data from all sources on a corrected propagation rate vs. V s showed a universal behaviour that is considered a very important recognition of the packed bed propagation behaviour. Combining theory and experiments was essential to explain the extinction. The features are: (a) the presence of ash layer over the surface is shown to be responsible for maintaining a steady char conversion in a single particle at low stream speeds, (b) the feature that the ash layer would be blown away at stream velocities of 2.5 to 3 m/s in a single particle combustion, (c) with V s close to 50 cm/s, local velocities of air flow through the bed can reach 2 to 3 m/s, this value being sensitive to the bed arrangement (with slight shifting or settling of one particle leading to increase of the local velocity at the periphery). Thus, the high local speeds of flow through the bed (more than 2 m/s) was considered responsible for removal of ash layer such that radiation losses would be dominant and cause local extinction of the reaction front at the char surface. Thus, this study has led to a comprehensive understanding of the gasification-combustion behavior of packed bed in stoves and on grates. It has also led to the evolution of parameters for obtaining high efficiency and low emissions (HELE) from stoves -both domestic and industrial. Most interestingly, it has resulted in recognition of an universal behavior of flame propagation rate through packed bed of biomass.

This study examines the adoption of clean cooking technologies in developing countries with a focus on the ACE-1 advanced biomass stove (ABS). Marginalized communities in rural environments are often exposed to high levels of Household Air Pollution (HAP) due to the common use of traditional cookstoves. The United Nations (UN) has recognized the adoption of clean cooking technology like the ABS as a key driver and high-impact opportunity in the context of the 2030 Agenda for Sustainable Development. Nonetheless, the context for adoption is complex. Adoption depends on numerous variables, that can enable or hinder the uptake of modern cookstoves. This study is based on the assumption, that adoption starts with the decision-making process and acquisition of the stove. Based on a field study in rural Cambodia, this research focuses on users at the initial stage of adoption. By means of questionnaire-based interviews, this study identifies how variables related to ‘fuel and technology’ and ‘household and setting’ affect the likeliness of adoption and what opportunities can be identified to facilitate the process of adoption. The study finds, that ABS-suitable biomass fuels are available and accessible in rural Cambodia. Besides, the production of renewable biomass fuels like pellets is growing, which provides opportunities for collaboration with stove distributors. The study confirms the common practice of stove stacking and points out the strong market presence of Liquefied Petroleum Gas (LPG) stoves. Market activities need to consider these factors and highlight the competitive advantages of AB, namely fuel efficiency and cost savings. Finally, the impact of social influence and peer relations should be further researched and taken into consideration for sales and marketing activities.

Household air pollution (HAP) is responsible for almost 4 million premature deaths every year, a burden that is primarily carried by women and children in developing countries. The mortality and morbidity impact of HAP can be significantly alleviated through clean cookstove interventions. However, for these interventions to be effective, the new intervention stove must be a substantially cleaner technology and adoption should be high and sustained over time. Woody biomass is the fuel of choice in many developing communities, and contributes substantially to HAP. Several organizations have launched clean cooking interventions to address this issue. However, the majority of those interventions do not address adoption related challenges, that they often face. This thesis explores previous studies on Human-Centered Design (HCD) and the impact of feedback and data access on behavior change. It details a HCD process and methodology applied during the design process of an air quality feedback system, to improve adoption of liquefied petroleum gas (LPG) cookstoves in Rwanda. The feedback system is intended to provide real-time air quality information to stove users and potentially encourage them to abandon traditional biomass cookstoves in favor of the cleaner LPG stoves.

Background: Three billion individuals worldwide rely on biomass fuel (crops, dung, wood) for cooking and heating, mostly in the developing world. Incomplete combustion of these biomass fuels in inefficient cookstoves leads to high levels of household air pollution (HAP). Health conditions resulting from HAP are responsible for approximately 1.6 million premature deaths each year. Of the diseases associated with HAP exposure, lower respiratory infections (LRIs) are the leading cause of death for children under five worldwide. There is a great need to understand the etiology of HAP-associated LRIs to inform health interventions and to improve treatments. Ultimately, however, the only way to prevent the disease burden from HAP is to stop exposure. Policies and programs to promote the use of clean fuels for cooking are a pivotal prevention strategy. Methods: All three studies draw from an established cohort in Ghana. The Ghana Randomized Air Pollution and Health Study (GRAPHS), was a cookstove intervention trial in Kintampo, Ghana. Participants were randomized to a more efficient biomass cookstove arm, a liquefied petroleum gas (LPG) stove arm, or the traditional cookstove arm (baseline). The principal outcome of GRAPHS was childhood pneumonia. The first chapter utilizes banked nasal swabs from GRAPHS to assess the relationship between HAP exposures and a panel of known respiratory pathogens. In the second chapter we leverage data on stove use during GRAPHS, and then follow a sub cohort 6 months prior to and 6 months after the GRAPHS termination date. We employ a novel construct, suspended use, to understand the factors associated with people stopping LPG use. The third chapter tests a new randomized intervention on a subset of the GRAPHS participants. We provide free cookstoves, and allocate participants to one of four arms: a behavior change intervention, an intervention where LPG fuel is directly delivered to their home, a dual intervention of behavior change and fuel delivery, or a control arm. We track their stove use to identify the most effective intervention on sustained use. Results: In Chapter 1, we find that the traditional cookstove users had a higher mean number of microbial species than the LPG (LPG: 2.71, 3-stone: 3.34, p<0.0001, n = 260). This difference was driven by increased bacterial (p<0.0001) rather than viral species presence (non-significant). Adjusted exposure-response analyses, however, produced null results. Chapter 2 identifies several factors associated with reduced or suspended LPG use of intervention cookstoves, including: experience of burns, types of food made, and access to biomass fuels. Finally, in Chapter 3 results show increased use for all three intervention arms, the largest for the direct delivery arm with an increased weekly use of 4.7 minutes per week (p<0.001). Conclusions: Transition away from traditional biomass stoves is projected to curb the health effects of HAP by mitigating exposure, but the full benefits of newer clean cookstove technologies can only be realized if use of these new stoves is absolute and sustained. This work enhances our understanding of the etiology of HAP-associated pneumonia, the drivers of clean cookstove suspension, and informs policies designed to promote clean cookstove sustained use, thus reducing the burden of disease associated with exposure. We recommend future use of the suspended use paradigm in research to inform future household energy interventions. Additionally, we encourage policymakers to incorporate health behavior change theory and approaches in cookstove intervention and promotion efforts.

This project examines the efficiency of a biochar-producing stove in meeting the needs of households in rural of Kenya. The stove has been tested and evaluated by five household in Embu, Kenya and compared with two other common cooking methods. The main parameters were time consumption, fuel consumption and emissions of carbon monoxide and particulate matter. Usability and energy use efficiency have also been evaluated. Three potential feedstocks have been examined for use in the biochar-producing stove; Grevillea prunings, maize cobs and coconut husks. The biochar-producing stove was well received by the households. It has potential of saving time, it saves fuel and it has a significantly lower level of emissions than other examined stoves. Despite some challenges related to the usability and the handling of the stove, an implementation of the biochar-producing stove can contribute to an alleviation of the women’s burdens, save fuel and contribute to a healthier indoor air climate.

Thesis (M.Soc.Sc.) - University of KwaZulu-Natal, Pietermarizburg, 2009. / Full text also available online. Scroll down for electronic link.

Home based interventions are advocated in rural areas against a variety of diseases. The combination of different interventions might have synergistic effects in terms of health improvement and cost effectiveness. However, it is crucial to ensure cultural acceptance. The aim of the study was to develop an effective and culturally accepted home-based intervention package to reduce diarrhoea and lower respiratory illnesses in children. In two rural Peruvian communities we evaluated the performance and acceptance of cooking devices, household water treatments (HWT) and home–hygiene interventions, with qualitative and quantitative methods. New ventilated stove designs reduced wood consumption by 16%. The majority of participants selected solar water disinfection as HWT in a blind tasting. In-depth interviews on hygiene improvement further revealed a high demand for kitchen sinks. After one year of installation the improved chimney stoves and kitchen sinks were all in use. The intervention package was successfully adapted to local customs, kitchen-, home–and hygiene management. High user satisfaction was primarily driven by convenience gains due to the technical improvements and only secondarily by perceived health benefits. / Revisión por pares.

M.Phil. / The combustion of fuels in poorly designed cookstoves is a major anthropogenic source of atmospheric emissions with severe environmental and health implications. It is widely acknowledged that these challenges are best addressed with the development and dissemination of clean cookstoves. Widely used stove testing protocols (UCB Water Boiling Test and variants) are often single task-based and not representative of real-world uses or likely combinations of the manner in which fuels, stoves and pots may be used. The hypothesis of this study is that a stove testing procedure that provides for testing of stove/fuel/pot combinations, in a sequence of heterogeneous tests, provides a better representation of thermal performance and emissions than existing protocols based on prescribed fuels and fuel loads, and single tasks. The study aimed to develop and evaluate a set of testing protocols for determining thermal efficiency and emissions performance of domestic fuels and cooking devices to satisfy the rigorous performance specifications expected for claims under the Clean Development Mechanism (CDM) carbon trading market. The Heterogeneous stove Testing Protocol (HTP) was developed and documented as a complete set of standard operating procedures (SOPs), using a template derived from the Desert Research Institute (DRI), Reno, Nevada, and used for performance evaluation of fuel/stove combinations. The effect of pot size on the performance of two paraffin wick stoves and a pressurised paraffin stove was assessed and was found not to be a major factor, which affected thermal efficiency only at the high power setting. Power setting was found to influence the thermal efficiency and combustion performance of all stoves tested, indicating the need for assessment of the devices across the full range of power settings (where feasible). The HTP was also employed in characterising the combustion performance of coal stoves, using three different ignition methods, giving qualitative and quantitative results. Compared to the bottom-lit up-draft (BLUD) ignition method, the Basa njengo Magogo, also referred to as the top-lit up draft (TLUD) method, proved to be a better method of coal fires ignition, in terms of reduced CO:CO2 ratio and less smoke generation than in conventional braziers. The bottom-lit down-draft (BLDD) ignition method, incorporated in the SeTAR prototype coal stove, was found to be effective in fuel utilisation and improved combustion efficiency compared to the TLUD and BLUD methods, with CO:CO2 emission factors below 1% for 230 minutes. A number of parameters employed by the Water Boiling Test (WBT) were examined and compared with the HTP (e.g. turn-down ratio; simmer process; hot-start phase; use of standardised fuels and test pots). The HTP was found to provide more representative performance data over a wide range of use scenarios, the equivalent of providing performance curves rather than the minimum and maximum performance points provided by the WBT. The findings of this study have shown that the Heterogeneous stove Testing Protocol is consistent, robust, and transportable; making it a valuable tool for stove design improvements, and for the assessment of stoves under voluntary and compulsory carbon markets.

Energy poverty is defined as the lack of access of households in developing countries to modern energy sources, and their consequent reliance on solid biomass fuels for cooking. So-called “Improved stoves” have been promoted by various public and private actors since the 1970s to tackle various environmental and health challenges associated with biomass use. Impact studies of such projects are usually based on on-site surveys about the stoves’ use, and thus are extremely site-specific, and difficultly generalizable. This thesis project aims to introduce a novel approach to impact assessment of improved cooking stoves on both local energy needs and deforestation in the area. This approach will base most of its figures and assumptions on calculated energy needs rather than survey reports. This will result in a highly flexible energy model, which can be used and adapted to help decision and policy makers in their function. The area of Nyeri County, Kenya, where the author completed a one-month field study, is used throughout the thesis as a case study in order to validate the model.

Household air pollution annually kills around 14 300 people in Kenya, due to the hazardous smoke of incomplete combustion coming from inefficient stoves. Exposure to this smokeleads to lethal health issues for the women and children staying in these kitchens, but the smoke also leads to a contribution to global warming. Which makes it important finding are placement for the inefficient traditional cooking methods. This report presents results from a field work situated in Kibugu, Embu in central Kenya. It includes testing of three stoves, the traditional Three stone open fire and two biochar producing stoves, the previously tested stove Gastov made by KIRDI and the MiG|BioCooker made by Make It Green Solutions AB. The data was collected using participatory cooking tests where five households got to cook the traditional meal Ugali with Sukuma wiki and Githeri (maize and beans). Firewood consumption, emissions of CO and PM, user experience and char production were measured during the test, to be able to compare the stoves. The results indicate that the MiG|BioCooker can decrease the emissions of PM2.5 and CO in the kitchens and produce biochar. But on the other hand, cooking with three stone open fire more effective in terms of cooking time. Even though the MiG|BioCooker could improve the conditions of the household’s indoor air, the users seems to prioritize the practical characteristics of the three stone open fire that gives them more time and making it easier to cook. But with some modifications and by further use of the MiG|BioCooker, it might be apossible substitute to the three stone open fire in the future.