S.C. Bhattacharya

A comprehensive procedure for performance evaluation of solar food dryers

Solar food dryers are available in a range of size and design and are used for drying various food products. Testing a dryer is necessary to evaluate its absolute and comparative performance with other dryers and the test results provide relevant information for the designer as well as the user. Literature reviews on existing testing procedures reveal that a comprehensive procedure for evaluating the performance of solar food dryers is not available. Therefore, selection of dryers for a particular application is largely a decision based on what is available and the types of dryers currently used widely. This paper presents a detailed review of parameters generally used in testing and evaluation of different types of solar food dryers. The inadequacies of the parameters generally reported are highlighted and additional parameters have been suggested. Based on this review, a procedure has been proposed, giving the methodology, test conditions and a sample evaluation sheet. This would assist in an unambiguous evaluation of solar dryer performance and facilitate comparing different solar food dryers.

Low greenhouse gas biomass options for cooking in the developing countries

Large quantities of biomass fuels are used for cooking in the developing countries. Although biomass is a renewable source of energy, traditional biomass-fired stoves cause significant greenhouse gas (GHG) emissions due to formation of products of incomplete combustion; also, exposure to smoke from these stoves causes serious health problems. This paper presents an analysis of a number of selected options available for developing countries in the context of reducing total greenhouse gas emission per unit of useful energy for cooking. It is assumed that biomass as an energy carrier is CO2—neutral. However, other GHGs emitted from biomass combustion cause a net greenhouse effect; accordingly, in this study only the non-CO2 greenhouse gases i.e. CH4 and N2O are considered in estimating GHG emission for different biomass-based cooking options. The total GHG emission from traditional wood-fired stoves is estimated to be about of CO2 equivalent per mega joule of useful energy (g CO2-e MJuseful−1) delivered to the cooking pot; this can be compared with 42, 5, 2, 350, 166 and -e MJuseful−1 in case of improved wood-, biogas-, producer gas-, kerosene-, natural gas- and LPG-fired stoves, respectively. Modern biomass based cooking options such as improved biomass-, biogas- and producer gas-fired stoves can potentially play an important role in mitigating GHG emission from domestic cooking by providing an alternative to kerosene-, natural gas- and LPG-fired stoves.

Emission factors of wood and charcoal-fired cookstoves

Abstract In the developing countries, energy required for cooking often has the biggest share in the total national energy demand and is normally met mostly by biomass. This paper presents the results of experimental studies on emission conducted on a number of traditional and improved cookstoves collected from different Asian countries using wood and charcoal as fuel. The emission factors from this study are comparable to those reported in the literature. In the case of wood combustion, CO 2 emission factor is in the range of 1560– 1620 g kg −1 . The emission factors for pollutants CO, CH 4 , TNMOC and NO x were in the ranges 19–136, 6–10, 6–9 and 0.05– 0.2 g kg −1 , respectively. In the case of charcoal combustion, CO 2 emission factor is in the range of 2155– 2567 g kg −1 . The emission factors for pollutants CO, CH 4 , TNMOC were in the ranges 35–198, 6.7–7.8, 6– 10 g kg −1 , respectively. Comparison between wood and charcoal fired stoves shows that, CO 2 and CO emission factor values for wood are lower as compared to charcoal. CH 4 and TNMOC emission factors for wood are with the same range as compared to charcoal. Emission factors for NO x using wood is slightly lower than charcoal. The emission of all the pollutants per unit of useful heat was found to decrease with increasing stove efficiency for both wood and charcoal fired stoves.

Emissions from biomass energy use in some selected Asian countries

In this paper, an attempt has been made to estimate the annual emission of certain greenhouse and other gases and substances from biomass energy sources in selected countries of Asia. For this purpose, the reported values of the different emission factor for biomass combustion have been compiled from an extensive literature review. From the compiled values, a set of emission factors of different gases/pollutants for each fuel-combustion system combination is obtained for each country. The emission factors for the carbon containing gases, i.e. CO2, CO and CH4, are corrected by multiplying each emission factor by a correction factor to avoid over- or under-estimation of total carbon emission. Estimated biomass energy use by technology and the corrected emission factors are used to estimate the total emissions in the selected countries.

Upgrading of biomass by means of torrefaction

We present results on upgrading of wood and briquettes by means of torrefaction. The torrefied products showed significantly less smoking during combustion and a relatively faster rate of combustion. The weight and energy yeilds of torrefied wood are 66.7–83.3 and 76.5–89.6%, respectively; the corresponding values for sawdust briquettes are 76.3–93.8 and 83.1–95.3%, respectively.

Effects of selected parameters on performance and emission of biomass-fired cookstoves

The effects of different parameters on performance and emissions of three biomass-fired stoves have been investigated. The parameters considered were moisture content of fuel, size of fuel, size of pot and method of ignition, while the selected stoves were an improved Indian stove, a Vietnamese traditional stove and an improved stove developed by the Royal Thai Forestry Department. It was found that increase in fuel moisture content resulted in decrease in stove efficiency, increase in the emission factor of CO and decrease in the emission factor of NOx; a slight decrease in CO2 emission factor was also observed, while emission of CH4 was not significantly effected. The fuel size did not show any significant influence on the efficiency of the stove, however, it showed significant influence on the emission of CO for the size range investigated. The size of pan did not affect the efficiency of the stoves tested. Two methods of stove ignition—conventional bottom ignition and top ignition—were investigated. In general, emission of CO and NOx was significantly less in case of top ignition in comparison with conventional bottom ignition.

A study on wood gasification for low-tar gas production

We present results of an experimental study on two-stage wood gasification and attempts to reduce the tar content of the gas. Increasing the wood-chip moisture content resulted in an increase of CO2 and H2 but a decrease of the CO concentration without significantly affecting the tar content in the producer gas. For a particular primary air flow rate, an increase in the secondary air flow of the two-stage gasifier resulted in decrease of the tar content and the CO2 and H2 concentrations while that of CO increased. A charcoal gasifier and a floating-drum gas-storage system were coupled to a two-stage wood gasifier. The tar content of the product gas was in the range 19–34 mg/Nm3 for a charcoal gasifier coupled to a two-stage wood gasifier. With a floating-drum gas-storage system and a 3.5 h retention time, the tar content was reduced to 9.24 mg/Nm3, which is 85% less than that obtained by using the a two-stage wood gasifier alone.

Multi-stage reactor for thermal gasification of wood

Tar is the most undesirable contaminant of producer gas. Production of tar-free gas from uncarbonized biomass seems to be rather elusive, and removing tar from the gas remains a daunting task requiring bulky, expensive equipment and considerable operational effort. A new multi-stage reactor design has been developed in order to separate the flaming-pyrolysis zone from the reduction zone. Tar vapors generated in the first zone are burned or cracked to simple molecules by high temperature in the second zone. Data obtained from experimental tests show that the two-stage reactor has improved gas quality and conversion efficiency. The tar content of the gas is about 40 times less than that obtained with a single-stage reactor under similar operating conditions.

Greenhouse gas mitigation potential of biomass energy technologies in Vietnam using the long range energy alternative planning system model

The greenhouse gas (GHG) mitigation potentials of number of selected Biomass Energy Technologies (BETs) have been assessed in Vietnam. These include Biomass Integrated Gasification Combined Cycle (BIGCC) based on wood and bagasse, direct combustion plants based on wood, co-firing power plants and Stirling engine based on wood and cooking stoves. Using the Long-range Energy Alternative Planning (LEAP) model, different scenarios were considered, namely the base case with no mitigation options, replacement of kerosene and liquefied petroleum gas (LPG) by biogas stove, substitution of gasoline by ethanol in transport sector, replacement of coal by wood as fuel in industrial boilers, electricity generation with biomass energy technologies and an integrated scenario including all the options together. Substitution of coal stoves by biogas stove has positive abatement cost, as the cost of wood in Vietnam is higher than coal. Replacement of kerosene and LPG cookstoves by biomass stove also has a positive abatement cost. Replacement of gasoline by ethanol can be realized after a few years, as at present the cost of ethanol is more than the cost of gasoline. The replacement of coal by biomass in industrial boiler is also not an attractive option as wood is more expensive than coal in Vietnam. The substitution of fossil fuel fired plants by packages of BETs has a negative abatement cost. This option, if implemented, would result in mitigation of 10.83 million tonnes (Mt) of CO2 in 2010.

Performance analysis of multiple effect vertical still with a flat plate solar collector

The paper presents an analytical model for predicting performance of a multiple effect vertical still having a flat plate solar collector as a heat generator. The solar radiation, the ambient temperature and the wind speed are used as the input and the output are the temperature-time history of the evaporating and the condensing surfaces in the distillation unit and the distilled water production. The results agree quite well with the experiment. Simulation of long term performance of the system shows that as the ratio of the evaporating surface area to the solar collector area, Aevap/Acoll increases, the distilled water output also increases but when the ratio is over 5 the productivity output increases slightly. When the last condensing plate is covered with a wetted cloth, the system performance is better than when the surface is cooled by ambient air.