**3. Traditional and improved biomass cookstoves**

**Figure 2**(**a** and **b**) shows images of traditional biomass cookstove and improved mud cookstove. Average efficiency and CH4 emissions of traditional biomass cookstoves used in Asian countries were reported to be about 11% and 0.52 g/MJ of energy delivered by wood fuel [18]. Since early 1980s, some researchers reported ways of improving thermal performance of the traditional biomass cookstoves by modifying their designs [19–24]. These ways include: use of metals as cookstove materials, provision of grate for better air circulation, air preheating, provision of

**Figure 2.** *Images of traditional biomass cookstove and improved mud cookstove.*

swirl and secondary air, provision of insulation, use of chimney and baffles [18]. Average efficiency and CH4 emissions of improved biomass cookstoves used in Asian countries were reported to be about 24% and 0.408 g/MJ of energy delivered respectively with the wood fuel [18]. Thermal performance of improved biomass cookstoves was found to be better than the traditional cookstoves; but there was not much improvement in their emission performance as compared with traditional ones. Researchers have found that improvement in efficiency of biomass cookstove does not always ensure reduction in emissions. There exists a certain range of power levels where the correlation between efficiency and emissions is positive, while elsewhere it will be negative [18].

Improved biomass cookstoves are known as fuel efficient cookstoves as they reduce fuel consumption by 20–50% as compared with the traditional biomass cookstoves [25]. Some of the examples of improved biomass cookstoves are: *Swosthee* cookstove [26], rocket cookstove [27], *Patsari* cookstove [28], Envirofit cookstove [29], *Jiko* cookstove [30] etc.

#### **4. Advanced biomass cookstoves**

To improve thermal and emission performance of metal biomass cookstoves, efforts have been made by the researchers which include: application of scientific principles for designing the cookstoves, insulating the combustion chamber, supplying correct amount of primary and secondary air at right place into the combustion chamber, use of fan to create draft, use of gasification techniques, use of high density pellets as fuel etc. [31–34]. Such efforts have helped in accelerating the process of design of advanced metal biomass cookstoves, both in natural and forced draft versions, across the globe.

According to method of combustion of biomass fuel into combustion chamber, advanced biomass cookstoves can be classified into two types *viz.* normal combustion cookstoves and gasifier cookstoves. The best example of the biomass cookstove which can efficiently operate in both these modes is Philips forced draft biomass cookstove [34].

During normal combustion mode, the biomass is fed in terms of small batches to the combustion chamber (oven). The pyrolysis products burn near the top of the combustion chamber using secondary air whereas the char combustion occurs using primary air at the bottom of the oven. During gasification mode, the whole combustion chamber is filled with the biomass fuel. The cookstove is lit at the top and the fire slowly passes to the bottom of the combustion chamber. Unlike the combustion mode, no fuel is added to the cookstove until the fire goes off. This gasification mode of operation of cookstove is also known as Top Lit Up Draft (TLUD) gasification, as the cookstove is lit at the top and the flow of both primary as well as secondary air goes in upward direction. **Figure 3** shows schematic diagram of Philips forced draft cookstove.

Jetter et al. [35] conducted experimental studies on 22 biomass cookstoves and reported that the efficiency of Philips forced draft cookstove was about 38% where as its CO and PM2.5 emissions were very small. The authors also reported that cookstove operating on TLUD mode showed the lowest CO and PM2.5 emissions. Some examples of TLUD gasifier cookstoves are rice husk gas cookstove [36], Oorja cookstove [37], pellet-fed gasifier cookstove [38] etc. The main advantages of using TLUD type of gasifier cookstoves are: highly efficient operation, clean combustion with negligibly small levels of emissions, use of densified pellets made up of crop residues and other biomass wastes for waste to energy conversion.

*Energy Efficiency, Emissions and Adoption of Biomass Cookstoves DOI: http://dx.doi.org/10.5772/intechopen.101886*

#### **Figure 3.**

*Schematic diagram of Philips forced draft cookstove [34]. [© 2006, Royal Philips. Password, Philips Research innovation magazine, issue#28].*


#### **Table 2.**

*Default values of voluntary performance targets for biomass cookstoves [40].*

Research groups, non-government agencies and some government departments have developed protocols for testing the thermal and emission performance of biomass cookstoves. Comparative studies on testing protocols for biomass cookstoves are available in literature [9, 39]. An ISO technical committee comprising of experts from 45 countries and 8 international organizations published voluntary performance targets for biomass cookstoves in 2018 [40] in the form of a document called ISO Workshop Agreements (IWA) [41]. These targets cover five performance indicators *viz*. thermal efficiency, fine particulate matter emissions, carbon monoxide emissions, safety, and durability of biomass cookstoves. For each indicator, laboratory test results are rated along 6 tiers (0: for lowest performing cookstove to 5: for highest performing cookstove). **Table 2** reports default values of these voluntary performance targets. The three types of biomass cookstoves *viz.* traditional, improved and advanced can easily be categorized as per the tier rating. Most of the traditional cookstoves fall in tier 0 to 1 categories. The improved biomass cookstoves will have tier rating of 2–3 whereas the advanced biomass cookstoves shall be given the tier rating of 3–5. With increase in tier rating of the cookstove, its efficiency increases, CO and PM emissions decrease, its safety score increases i.e., it can be operated safely and its durability score decreases i.e., it becomes durable.
