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Emissions from high altitude stoves: a case study in Nepal
[top] [end]Background informationNepal is a mountainous country with a climate that varies from one part to another. In the hills and mountains it is severely cold in winter and heating homes at high altitudes is important. Generally, one room is heated in order to keep it warm and comfortable and many household activities, besides cooking and sleeping, tend to be carried out in this room. Traditionally, open fires and closed or semi-closed stoves are used for cooking and heating (Figure 1); the use of cast iron or mild steel stoves at high altitudes is a recent phenomenon. These stoves have multiple uses and benefits, such as cooking, heating and boiling water etc. The concern about emissions from high altitude stoves is quite significant as the fire is kept burning in an unventilated environment round the clock through the six winter months.Using a household stove intermittently, or using one that does not burn efficiently, causes incomplete combustion, resulting in larger amounts of the 'Products of Incomplete Combustion' (PIC) being generated. It also reduces the heat energy available for space heating. In the hills and mountains of Nepal, various authors have compared the indoor air pollution experienced by cooks using traditional cooking stoves with those using improved ceramic cooking stoves. These studies have found that improved stoves reduce human exposure to pollutants in the kitchen. This paper deals exclusively with high altitude cast iron or mild steel stoves.
[top] [end]Metal stove technology, innovation and evolution in NepalIn Jumla (mid-western Nepal, 2500m altitude), the Karnali Technical School (KTS) established with support from United Mission to Nepal (UMN), introduced heavy two-pot cast iron stoves, with or without water heating and flue control systems into the schools (see Figure 2).
In Mustang (western Nepal 2850 m altitude), local blacksmiths produced metal stoves from thin sheet/scrap metal, using indigenous technology. A Chinese model stove found in Mustang has been brought from Tibet (see Figure 4).
The Mustang indigenous technology has been transferred to Ghandruk (Western Nepal, 1980 m latitude), where the Annapurna Conservation Area Project (ACAP) has introduced a 'back-boiler' water circulating system exclusively for the tourist lodges (see Figure 5).
[top] [end]Analysis of stove efficiencyField experiments were carried out in Jumla, Mustang and Kathmandu with various types of metal stoves used for heating and cooking. Heat losses were calculated and are shown in Table 1.Heat carried away in dry flue gas normally accounts for most of the loss, ranging from 19% to 43%. Unburnt carbon and formation of carbon monoxide (CO) are the results of incomplete combustion. At high altitudes, mostly softwoods are burnt. The results show that losses due to unburnt carbon are low in these stoves. However, fuel only converted to CO rather than carbon dioxide (CO2) causes rather high losses (1.8%-5.2%). [top] [end]Experimental study of emission factors in the fieldIn field tests, a portable Testo 3423-1 Combustion Efficiency Analyzer was used to measure the emissions. The emission of pollutants from each stove was measured at five minute intervals by inserting a probe into the chimney. The cooking stove was operated at high altitude in a rural kitchen. The inlet air velocity was calculated, based on the quantity of air required for combustion.Table 1: Heat losses in stoves used for cooking and heating
Where: Q1 = heat loss due to unburnt carbon Q2 = heat lost in dry flue gas Q3 = heat loss due to moisture in fuel Q4 = heat loss due to moisture from burning hydrocarbons Q5 = heat loss due to formation of carbon monoxide Q6 = heat loss due to moisture in the air Table 2: Variation in emission factor as a function of airflow rate
The variation in the concentration of emission products in the flue gas was measured during the experiments. Observations showed that a strong draught was produced, which caused a large heat loss in the dry flue gas. Table 2 shows the variation of emission factor as a function of airflow rate. From this table it can be seen that high airflow rates increase production of CO, which reduce the amount of useful heat produced, and increase the amount of heat lost through the chimney. [top] [end]ConclusionIn high altitudes, cast iron and mild steel stoves have been introduced to replace traditional stoves for cooking and heating purposes. Metal stoves, unlike clay stoves, lose a great deal of heat to the surroundings. In some metal stoves in Jumla, their low cooking efficiencies are thought to be due to excess space heating caused by the large combustion chamber, and high draught creating excess air flow etc. During summer, cooks feel uncomfortable and may vomit because of excess heat in the kitchen.Adding refractory stones into the stove's combustion chamber increases the heat capacity of the system and can reduce heat loss due to unburnt carbon and minimize formation of CO. The red-hot refractory stones in the combustion chamber facilitate cracking of the unburnt volatiles for subsequent combustion. Further improvements include insulating the combustion chamber, reducing the diameter and height of the combustion chamber, introducing a grate, and improving the way the air mixes with the fuel by providing a small volume of primary air and more secondary air. Heat lost in the dry flue gas can be reduced and heat transfer to cooking pots and pans can be improved by introducing a baffle. Proper use of a damper can reduce excess air intake and can minimize evaporation losses from the cooking pots. Advising the cook to use well-dried fuel can minimize heat losses due to moisture in fuel. Optimizing air intake will reduce heat losses, as measurements have shown that excess air intake was a major problem. Products of incomplete combustion, such as CO and other suspended particles represent the major health risks from wood combustion. The quantity of emissions depends on a number of variables, such as the composition of the fuel, operating conditions, the stove design and combustion conditions (eg feed rate and amount of excess air). Proper drying of fuel must be used to reduce the high moisture content of the fuel before combustion; otherwise the combustion temperature will be lowered causing incomplete combustion with high emission of particulates and carbon monoxide. [top] [end]Contents: Boiling Point 40: Household energy and health
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Page created:
02 August 2007; Last edited:
02 August 2007; Version: 0 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Pagename: EmissionsFromHighAltitudeStoves-ACaseStudyInNepal @HEDON: EEGA | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
