Chapter 1
CASE STUDIES (contd.)

ACKNOWLEDGEMENTS

Work described in this case study was carried out under the project sponsored by the Swiss Development Co-operation, New Delhi. The authors are grateful to Dr. Urs Heierli and Dr. Veena Joshi of SDC for their sustained encouragement and guidance throughout the course of this study. The authors also wish to thankful to Mr. P. Jaboyedoff, SDC consultant, for fruitful discussions and valuable suggestion during the course of the study. The support provided by CSTRI personnel in carrying out the field survey and experiments was crucial for the succesful and fruitful completion of the study. Special thanks are due to Dr. T.H. Somsekhar, Director, CSTRI for his support and encouragement throughout the course of this study. The support and encouragement of Dr. R.K. Pachauri, Director, TERI, and the help provided by Mr. H.V. Dayal, Dean, TERI Bangalore office, is gratefully acknowledged. Thanks are due to Mr. R.B. Guptha for his help in conducting the survey.

Annexure - A

Calculation of flue gas flow rate through chimney

In the thermal analysis of any chulha, the thermal losses through the chimney in the form of hot flue gases in the major fraction. During the operation of chulha/oven, a lot of excess air is supplied to the fuel (i.e. more than the stoichiometric air requirement for complete combustion of the fuel). This is to make up for the draft created by the chimney. The quantity of air flow is quite low and therefore, difficult to measure with conventional techniques of flow measurement, like pilot tube or anemometer. The best and simplest way of estimating the flue gas flow rate in the field is to measure the volume fraction of easily measurable flue gas components such as CO₂ or O₂ along with flue gas temperature and then estimate the excess air and hence the flue gas flow rate. During the course of study a simple software was developed using lotus 1–2–3 spreadsheet to estimate the flue gas quantity for the burning of fuel from its composition, and by knowing the flue gas temperature and volume function of either CO₂ or O₂ The basic calculation procedure used is described below through sample calculation for tamarind wood fuel by measuring the O₂ fraction in the flue gas using a fyrite kit.

Fuel composition

Composition of the fuel used, tamarind wood, on weight basis is

Moisture = 7.23% ; Ash = 8.43%

Composition of the majority of the biomass fuel on a moisture and ash free weight basis is more or less consistent as C = 50%, H = 12% and O = 38%, therefore the actual weight of constituents (C,H,O) in the fuel works out to be:

C = 0.4217 kg = 0.0351 kmol
H = 0.1012 kg = 0.0506 kmol
O = 0.3205 kg = 0.0100 kmol

Theoretical oxygen requirement

From the basic combustion reaction equations for complete combustion of 1 kg of fuel, the theoretical oxygen required will be :

O₂ =(C × 1) + (H × 0.5) - (0) = 0.0504 kmol

Knowing the fact that air consists of 21% O₂ (oxygen) and 79% N₂ (nitrogen) by volume, the theoretical air required for complete combustion of 1 kg of fuel works out to

Air required = 0.2401 kmol

Actual combustion reaction

In actual practice, the amount of air supplied during the combustion of fuel is greater than the theoretical air requirement of the fuel. This excess air is responsible for high flue gas losses through the chimney. If ‘X’ is the excess air factor, the chemical combustion reaction becomes,

Reactants = Products

Reactants = 0.0351 C + 0.0506 H₂ + 0.0100 O₂ + (1+X) 0.0504 (O₂+3.762 N₂) + (0.0723/18) H₂O

Product = 0.0351 CO₂ + 0.0546 H₂O + 0.1897 (1+X) N₂ + 0.0504 × O₂

Balancing the various constituents C,H,O,N on both the sides, one gets a set of equations in the form of X. Thus, the value of X can be calculated if one knows any one fraction of gas in the product of combustion. As CO₂ and O₂ can be absorbed quickly, its volume fraction in the flue gas can be measured easily using the fyrite kit. Here the case is considered where O₂ volume fraction in the flue gas is measured using a J N Marshal Fyrite Kit. It gives the volume fraction in the moisture free gas.

O₂ volume fraction in the moisture flue gas = 10.0%(measured)

Thus through oxygen balance in the combustion reaction equation one gets.

Solving for X, one gets

X = 0.8665 = 86,65 %

Thus quantity of flue gas under given operating conditions can be determined by substituting the value of X in the products.

Flue gas = 0.4329 kmol on moisture free basis

= 0.4875 kmol including moisture

Knowing the molecular weight of different flue gas components (CO₂ = 44, O₂=32, H₂O= 18, N₂ = 28), the quantity of flue gas can be calculated as,

Flue gas = 13.8421 kg (including moisture) per kg of fuel

Therefore, flue gas flow rate for burning rate of 14.3 kg/hr works out to be

= 197.97 kg/hr

Annexure - B

Sample calculation for energy balance of cooking oven

In this annexure the procedure for carrying out an energy balance of a cooking oven, used in silk reeling units, is described in detail. The energy balance of stifling units and charka ovens can be carried out using similar procedures. The cooking oven performance was monitored for a batch operation.

Oven measurements

Complete oven details (geometric dimensions, construction material, etc.) required for the calculation of areas, weight of oven, heat transfer coefficient were measured and noted down. The dimensions used here in sample calculations are

Based on the above parameter, the calculation of various heat streams is described below

Heat input (Qin)

The total heat input through combustion of fuel in the oven can be calculated from the fuel consumption and its calorific value.

Qin = 71.5 (kg/batch) × 4845 (kcal/kg) = 346417.50 kcal/batch

Theoretically, the net heat input will be less, as the heat content of the balance char should be deducted. But since the char obtained is utilized from time to time for re-reeling operation as well as for igniting fuel in a stifling oven, it was difficult to quantify the exact amount of char obtained in a batch. Therefore this loss is put in the unaccounted heat loss.

Heat loss through flue gas (Qf)

From the calculation procedure described in the earlier Annexure - A the flue gas flow rate works out to be

where,

Mg = flue gas flow rate (kg/hr)
Cpg = sp. Heat of gas = 0.26 kcal/kg °C
Tg = flue gas temperature (°C)
Tamb = ambient dry bulb temperature (°C)

Surface heat loss (Qs)

The heat loss from the oven surface takes place through two types of heat transfer mode,

1. convection (natural)
2. radiation

Here the sample procedure for calculation of surface heat loss is given for one surface (right hand vertical side). Similarly, the heat loss from other oven surfaces can be worked out to arrive at total surface heat loss.

a) Convection heat loss (Qs,c)

For air as fluid, the natural convection heat transfer coefficient (Hc) can be calculated using folllowing equations

where,

Hc = convective heat transfer coefficient = BTU/hrft 2°F
C & m = constants
D = geometric dimension (ft)

The values of C, m and D for various oven surfaces are as follows (Ref. Process Heat Transfer by Kern): Thus for the right vertical side surface the heat transfer coefficient can be calculated as,

Hc = 0.46653 Btu/hr ft2°F = 2.2766 kcal/hr m2°C

Therefore,

Qs,c = hc A T
= 38.9172 kcal/hr = 194.58 kcal/batch

b) Radiation surface heat loss (Qs,r)

Heat loss from the surface through radiation mode (Qs,r), by virtue of temperature difference between wall surface (Ts) and surrounding (T amb), can be calculated as

Qs,r =ó A s (Ts - Tamb )

where,

Ó = Stefan Boltzman constant = 4.88× 10-8 kcal/hr m2 K4
= Emissivity of wall surface

Ts' Tamb = Surface and ambient temperature in °K

Therefore,

Qs,r = 67.5 kcal/hr = 337.5 kcal/batch

Therefore, total surface loss from the right hand side vertical surface becomes,

Qs = Qs,c + Qs,r = 532.12 kcal/batch

In a similar manner the surface heat loss from other oven surfaces can be calculated. Thus total surface heat loss becomes

Qs = 32398.60 kcal/batch

Heat loss from oven opening (Qo)

In order to estimate the amount of heat loss from red hot fuel bed on the grate, through oven fuel port opening, it is necessery to calculate the view factor (also called as radiation shape factor) between the fuel bed (grate) area and fuel port opening of the oven. This can be determined using the following two ratios.

Then, referring to the graph given in figure 4.9 of ‘Process Heat Transfer’ book by Kern and Krause, for the above two ratios, the view factor (VF) works out to be 0.085. With fuel bed temperature ( Tbb ) of 1300 °C (1573 °K), the radiation heat loss through oven opening becomes

Qo = ó × A × VF × (Tb - Tamb )

Qo = 8402.9 kcal/hr = 42014.66 kcal/batch

Heat loss due to thermal mess of oven (Qm)

During the operation of the oven throughout the day, the oven gets heated up by absorbing the heat due to the thermal capacity property (specific heat) of its various structural components. This accumulated heat energy is liberated back to the surrounding atmosphere when the oven is not operational. Hence it is assumed, and this normally happens in many chulhas, that the oven temperature returns to the original temperature by liberating all the accumulated heat at the time of start by calculating weight of each component of the oven, and by knowing its specific heat. Here a sample calculation is done for the right side vertical wall of the oven.

This heat is lost throughout the day. Since the oven under consideration operates for 10 hrs/day, and the batch under study is of 5 hrs duration, the contribution of heat loss due to thermal mass for the batch under study can be calculated as,

Qm,rhs = 2547 63 kcal/batch

Similarly, the heat loss due to thermal mass of other oven components can be calculated. The total heat loss due to thermal mass of the oven under consideration amounts to

Qm = 9216.97 kcal/batch

Useful heat (Qu)

The useful heat, for cooking/stifling the cocoon, is calculated by a detailed water (and heat balance) exercise as described in Annexure - C. Thus the useful heat for the cooking process works out to be

Qu = 864.3 kcal/kg cocoon = 43065 kcal/batch

Heat recovered in water preheater drum (Qdr)

The amount of heat recovered from the gases for heating the water in the drum is calculated separately as follows.

Rate of evaporation of water from drum surface (gm/hr m²) can be as

Relative humidity of air can be calculated from the measured values of DBT and WBT measured values using psychometric charts.

Various heat streams calculated are summarized in table B-1.

Table B-1 : Summary of energy balance calculation

Annexure - C

Sample calculation for water balance of cooking basin

As described in earlier section 4.1, to estimate useful heat of a cooking oven, it is essential to estimate the various water streams. This is not an easy task as water carry-over takes place from cooking to reeling basins and vice versa. Therefore, in order to arrive at a net quantity of water going out from cooking basin to reeling basin, the weight of cocoons before putting into the cooking basin and after cooking (before taking it to reeling basin) was monitored continuously for one batch. For the traditional cottage basin under consideration (for sample calculation earlier and in this annexure), the ratio of water taken out from cooking basin to that going into it worked out to be 2.16.

In order to monitor water flow, the main water supply was stopped and reelers were forced to take water from the tank with graduations for monitoring water consumption. Reelers were asked to give the cocoons for weighing before and after cooking. Also the pupae waste, water drained, jute waste produced, pupae recycled, etc. were measured during the batch. The summary of the data collected during monitoring is given below for one batch.

Water evaporated from the open surface of the cooking basins is calculated as follows:

Rate of evaporation = Constant × 45.8 × DP gm/hr m²

The relative humidity for prevailing air temperatures (DBT = 27.5°C, WBT = 30.3°C) works out to be 65%

There are 6 cooking vessels of 235 mm dia each. Thus the total area of all cooking basins works out to be equal to 0.26 m².

Various water streams coming and going into the control volume (cooking basins) are shown in Figure C-1.

Figure C-1: Water balance of cooking basins

Assuming that fresh cocoons are at 27°C (feed water temperature) and specific heat of pupae waste, cooked cocoon same as that of water (considering the fact that moisture content is the major fraction in it) the heat balance across the control volume can be carried out as follows to arrive at the value of useful heat.

Case Study - Indonesia

CASE STUDY ON TAHU (SOYA-BEAN CAKE)
SMALL INDUSTRY IN YOGYAKARTA, INDONESIA

Sukamto
Yayasan Dian Desa
Yogyakarta, Indonesia

I. BACKGROUND

Soya-bean cake is known in Indonesia as ‘tahu’. It is a daily staple food which is rich in protein, relatively cheap, and delicious. Tahu is consumed by all people regardless of their economic status. It can be prepared and consumed in many different ways. Tahu was originally brought to Indonesia by the Chinese centuries ago.

In Yogyakarta all tahu industries are small scale or cottage industries. Production is usually scattered in order to serve the market. However, due to the specific characteristics of the tahu making process, especially with regard to its waste products, the household industries usually from into tahu industrial centers. Most are located near where they can dispose of the waste water.

Tahu is made of soya beans. The soya bean is finely ground and then boiled to make an extract that looks like milk. Some people like to drink this liquid as soya-milk. The extract is then strained through a fine cloth to produce the finest grade solution. This extract is then boiled for a long time. A small amount of acetic acid is added to act as a coagulant with the protein in the solution. Once the solution has settled, the water is removed and the white soft part is pressed so it becomes dense and hard. The tahu is then cut into small pieces and prepared for the market.

Tahu production flow diagram

Biomass fuel is an important part of the tahu industry because making tahu requires sustained boiling of large quantities of solution.

In Yogyakarta, there are two techniques for processing tahu: direct boiling and steam boiling. Steam boiling is actually a technique created by Mr. Taryono, a former trained mechanic who is now a tahu producer.

Biomass fuel is an important part of tahu industry because majority (90%) of the industries still use biomass as fuel. The fuel used includes wood, rice husk, coconut shell, leaves and sawdust. The type of fuel used depends on several considerations such as: fuel availability, cost, taste preference, efficiency (durability of utensils). Some producers have tried to change their fuel to kerosene but the woks do not last as long as those heated by biomass fuel.

The size of the production team varies from 2 to 25 workers and their production also varies from 25 kg of soya bean to 5000 kg/day.

The following case studies reflect the differences between direct boiling and steam boiling processing techniques.

II. THE PROCESSING TECHNIQUES

2.1. Tahu Making by Direct Boiling

The Stove

The stove used in direct boiling tahu production is a massive structure made of bricks and clay. The stove has a chimney which is also made from bricks and constructed up to the roof. A clay pipe, which is more resistant to the weather, extends the chimney above the kitchen roof.

Most of the stoves have two cooking holes, the first hole is used for boiling soya bean milk and the second hole is for boiling water. The diameter of the first is usually smaller depending on the size of the wok used. Small producers normally used single pot hole stoves with a smaller wok diameter.

The chimney is usually built at the corner of the stove with bricks. The height of the chimney is approximately 2.5 – 3 meters; and leads to the roof where the smoke can escape via a clay pipe from the work area. The chimney has no cap on its tip and smoke can easily be released from it.

The stove is usually made by local artisans. The materials used are as follows:
The body : bricks, clay, sand and cement
The grate : strip metal
The foundation : stones with a cement mix ture as plaster

The outside body of the stove is also sealed with cement mixture for increased strength and durability.

The size of the two-pot-hole stove is 280 cm × 140 cm × 80 cm. The average height of the chimney is 3 meters.

Typical of stove for Tahu making by direct boiling

According to Mr. Rasimun(63 years old) - one of the tahu producer at Pendowoharjo, Sewon, Bantul, Yogyakarta; local artisans can make the stove. There is no shortage of stoves or maintenance materials for anyone who wants to start tahu production. At the present price, one stove with two holes costs approximately Rp. 271,000. This consists of the following:

The boiled solution is screen with fine cloth	Acetic acid is added to act as coagulant

The stove takes 3 days to produce and can be used after 10 days. The stove he is using presently already more than ten years old and is still operating quite well. The main maintenance is required on the edges of the holes while the other flaws are cosmetic. Mr. Rasimun prefers using rice husk to saw dust for fuel, although both give good results.

The stove utensils in most cases consist of cast iron wok(s), which are affixed to the holes of the stove using a clay mixture.

The Fuel Used

Saw dust is the main fuel used for tahu processing in Yogyakarta. Fuel is collected from local saw mills using a big sack and transported by bicycle. The weight of each sack is approximately 80 kg.

Mr. Rasimun said that he has made tahu since he was 18. At the start he helped his father. After his father passed away he continued the family business. He said that when he was young, they used rice husks as the main fuel for making tahu. However, rice husks are getting more difficult to obtain. Mr. Rasimun attributes the scarcity of the husk to increased demand from brick and tile industries which are responding to increases in fuel wood prices. Tahu manufactures have started to use sawdust, or a combination of sawdust and rice husks, because it is more readily available. In terms of price, however, rice husk and saw dust are comparable at around Rp. 3,500 (US$ 0.50)/ bag of around 40 kg.

The Production Process

In general the making of tahu by direct boiling comprises the following steps:

If two woks are used, the second wok is usually used to boil water so that the cooking process does not need to start with cold water. Therefore, the tahu making process becomes more efficient and can continue without interruption.

Cutting Tahu into pieces	Ready to market or consumed

The stove is lit by pouring saw dust into the combustion chamber and using a little kerosene for ignition. The flames create a draft that goes into the chimney. The water in the two works warms up to 60° C while the workers grind the soya beans. The grounded soya bean is poured into the hot water in the first wok. More water is added to the wok until it is full. The solution has to be stirred so that the solution will not burn. Once the solution thickens and reaches a temperature between 110° C – 125° C (which usually takes about 30 minutes), it is removed and screened with a fine cloth. During this process, the fire in the combustion chamber is reduced or even extinguished to avoid cracking empty woks due to over-heating.

Economic Aspects

In one day Mr. Rasimun processes 100 kg of soya bean. He prepares ten batches of solution which provide 7000 pieces of tahu. The whole cooking process takes around 3 hours continuous cooking. The total working hours though is 5 – 6 hours (including pressing, cutting and cleaning). To process 100 kg of soya beans into tahu, he needs 4 bags of saw dust.

Mr. Rasimun has 4 workers and is also helped by his wife who usually cuts the tahu. One piece of tahu is sold for Rp. 75.

The following is a simple financial calculation of Mr.Rasimun's tahu industry

2.2 Tahu Making by Steam Boiling System

The steam boiling system was invented by Mr. Taryono. His former job was to repair trains or locomotives. He began making tahu in 1996. He estimated a 5 kg loss for every 100 kg of soya bean processed due to burnt solution at the bottom of the wok. From his experience as a mechanic working with steam engines, he reasoned that if the soya bean solution was boiled with steam, there would be no losses due to burning. He developed steam boiling cookstove for tahu production that is the first of its kind.

The Stove

The stove is made of metal attached to the steamer pot. The unit also has a pipe to channel the steam to the four pots which are part of the system. A complete stove including the steamer, the pipes and the pots (4) costs Rp. 10,000,000. For a small scale industry, the start up capital is rather high.

However, because his design gives good results, people are starting to adopt his innovatory stove with some modifications of their own.

Mrs Hardi, for instance, has also been in the tahu making business for a long time. When she heard about the steam boiling system, she wanted to adopt it but she still wants to use the old brick stove because it reduces the cost of the system. The steamer is then placed horizontally instead of vertically across the brick stove top. Mrs. Hardi uses coconut shells as the main fuel source.

The Fuel Used

The main fuel used are rice husks. However, close to production center there is a eucalyptus oil production factory which produce leaves as waste products. Mr. Taryono also uses eucalyptus leaves whenever possible available because he only needs to cover the cost of transportation.

The Production Process

The production process for preparing tahu with steam is similar to the previously described method.

First the main tank is filled with water until it is around 80% full. Then the stove is ignited. While waiting for the water in the main tank to boil and produce steam, workers grind the soya beans. The ground soya beans are mixed directly with water. Once the water in the main tank starts boiling, each pot is filled with 4/5 ths of the way full with soya bean solution. After all the pots have been filled, the valve is opened and the steam is allowed to get into the solution. This heat of the steam heats the solution. It usually takes around 7 minutes for the solution to start boiling.

Typical of steamer stove used in Tahu production using steam boiling system	Pouring the rice husk into burning chamber

According to Mr. Taryono, this system produces better quality tahu without burning the base of the pots. He also explained that less fuel is required because whenever steam is not needed, the valve is closed and the steam is kept in the steamer. In addition, he says using this system saves approximately ⅓ (one third) the fuel that would have been used by a traditional stove with the direct boiling method.

Economic Aspects

Mr. Taryono explained that to cook 350 kg soya bean to make tahu, he needs 10 bags of fuel (rice husks). Compared to the traditional stove it saves 4 bags (160 kg) of fuel. Yet, the tahu produced is better quality because it is free from dust that can enter the unsealed pots or from the residual ash at the bottom of the pot.

Grinding the soya bean using grinder machine

The solution in the tanks are heated by the steam

The following is the financial analysis

Sometimes, Mr. Taryono is able to use the eucalyptus leaves waste from the eucalyptus oil production plant near his place. This source of fuel is virtually free. If he uses eucalyptus leaves, the cost for fuel spent is around Rp. 13,500/day. He usually hires a truck for Rp. 40.000 to pick up the eucalyptus leaves; one truck load of leaves will supply three days of production.

The working hours are from 7:00 to 15:00. Looking at the total working hours, the steam boiling system seems to work faster.^₦

Case Study - Nepal

A. BIOMASS STOVE FOR KHUWA INDUSTRY

K.M. Sulpya
RECAST
Kirtipur, Kathmandu, Nepal

I. BACKGROUND

Khuwa (whole milk solids) consists of the solid constituents of milk, including the milk fat. Milk fat is the main ingredient of many varieties of sweetmeat. The sweetmeats are deep fried in ghee (fats from milk) or edible oil while colours, flavours and toppings are added before or after frying. Sweetmeats are often used as offerings to the gods and goddess in Hindu culture. It is common in Nepal to eat sweetmeats with breakfast.

Nepal's main source of income in rural areas is buffalo or cow milk. Small scale khuwa industries are found in many rural areas of Nepal, particularly in villages surrounding the urban centres where sweetmeat shops are widely available.

The khuwa processing industry is generally a small scale cottage industry stewarded by household members. However, additional labour is hired for transporting Khuwa to the urban sweetmeat shops.

Khuwa production flow diagram

These industries provide a good source of income for rural entrepreneurs and extra income for households. However, these industries are endangered by dairy development programmes being launched in the rural areas as well as by lack of fuelwood for milk processing.

Milk, the raw material, is bought from the community in the vicinity of the villages. The cost of the milk depends upon its fat content as that determines how much khuwa can be produced. In general, the supply of milk is met regularly. However, supply is better during August to November and is worse during April to July.

Fuelwood is the major source of energy for this industry. The bulk of the fuelwood comes from the forests of the far west, more than 600 km from Kathmandu. These forests are being rapidly depleted. Therefore, the reliability of the fuel stock is decreasing while the price is increasing. In the absence of fuelwood the industries use root stocks which are drawn from the degraded forests. Sometimes, fuelwood is also purchased from urban areas.

The fuelwood purchased in the rural areas is transported by foot while if it is purchased in the urban areas it is transported by tractor.

II. THE STOVE

2.1. Stove Design and its Features

The traditional wood burning stoves used in Khuwa production vary from place to place. The size, shape, number of pot holes, etc. depends on the skills available as well as on the requirements of the cook. In Bhaktapur districts, three-pot-hole rectangular stoves are used for milk processing. The wood feeding hole is in the front. The first and second-pot hole are inverted cone shaped and the bottom of the round bottomed cast-iron pots( karai) sinks into the fire box. Because of this, the pots are tightly sealed on the pot holes. Only in the third-pot hole, there are three pot supports (piece of bricks) where the flue comes out from the stove.

The three-pot-hole stoves do not have baffles or chimneys. The combustion chamber is straight so that the cooks can add as much fuelwood as they want. The first and the second chambers both act as a fire box or combustion chamber, however the first chamber provides more fire than the second and third chambers. Even without a chimney, the third pot hole receives adequate heat to keep the milk warm.

2.2 Stove Construction Materials

The materials needed to construct one three-pot hole stove are 180 bricks, 2 buckets of cow dung, and 2 buckets of rice husk and mud.

Mud is mixed with cow dung for plasticity and rice husks for clay binding until the consistency of the mixture seems appropriate. There is no fixed proportion. The interior walls of the stove are lined with firebricks.

The internal configuration is rectangular. The pot hole configurations of the first and second- pot hole are shaped like an inverted cones so that round bottomed pots like karai can fit into them. This cone shape increases the surface exposure of the cooking pots to the fire, thus increasing the speed and efficiency of fuel use. No baffle is installed.

The dimensions of the stoves vary considerably from 74 cm by 158 cm to 84 cm by 167 cm and with a height of about 38 cm to 44 cm. The stove has a single opening of about 22 cm × 25 cm to 26 cm × 29 cm that serves as a fuel feeding hole.

2.3. Cooking Utensils and Design

Round bottom pans (karai) without lids are used for khuwa processing because continuous stirring is required during the process. The pans are made out of iron or cast iron. The round bottom makes it easier to stir the milk during the boiling or cooking process. The pans are 43 cm in diameter and 14 cm in height.

III. THE FUEL

Two different fuelwood types are the main fuels source for milk processing. The root stocks that are used are normally around 27 cm long and 3 to 8 cm in diameter while the timber production wastes (bakal) that are available in the market are normally around 210 cm long and 3 to 7 cm wide but they are not uniform in size.

During stove operation, 2 to 4 firewood sticks (depending on the size of the firewood) are kept burning. During the cooking process the fire requires constant vigilance to prevent the milk from burning. The root stocks are used for kindling. No pre-treatment nor chopping is done as the bakal firewood is used as it is. Based on measurement, the average moisture content of the firewood was 12 percent. Normally, after the milk processing is completed, the firewood to be used the next day is stored on the warm stove that the firewood will be dry to some extent and thus easier to light. Green wood is never used because the moisture produces too much smoke.

3.1. Heat and Combustion

In the process of khuwa making, three big cast iron round bottomed pans (karai) with a capacity of 6 litres each is placed on a three-pot-hole stove. Each pan is filled with 2.3 litres of milk leaving enough space for the handling and boiling of milk. The pans are heated by burning firewood. The boiling temperature of the milk reaches around 96° C. The cook has to continuously stir the milk in the first and second pans to prevent the milk from burning. The process continues until the milk in the first pan solidifies. The first pan is then replaced with the second pan in which the milk is slowly boiling, and the second pan is replaced with the third pan containing warm milk. The thick milk paste (khuwa) is taken out from the first pan, and the pan is placed on the third-pot hole and filled again with 2.3 litres of fresh milk. The process continues until all the milk has been processed into khuwa.

For efficient processing, some entrepreneurs have designed three-pot hole stove so that they can use the excess heat in second and third pot holes.

The milk is stirred continuously to prevent from burning

During the cooking process, the temperature at the combustion chamber is between 540 to 804° C. Normally, the temperature is around 715°C. The temperature lowers when firewood is added. The temperature in the second chamber is similar to the first one, i.e. between 517 to 800°C and the maximum temperature attained in the third chamber is 570°C. During the combustion period, the colour of the flame is yellowish red and the hot flue gases pass directly under the round bottomed pan and towards second-pot hole and remain in the third-pot hole.

Charcoal and ash are by-products of the fuelwood used after the processing. Thus the stove remains hot and they utilize the heat of the stove to dry the fire wood that they will use the next day

3.2. Operation and Maintenance

During the cooking process, heat is controlled by adjusting the amount of fuel. The stove is very simple. It has no secondary air hole, grate, door, etc. The stove is well maintained by the users. The pans fit tightly on the pot holes to prevent the milk from burning. This also reduces the amount of heat that reaches the cook who is responsible for stirring the milk.

IV. THE PRODUCTION PROCESS AND COOKING PRACTICE

Khuwa processing technique is similar throughout Nepal. It is processed by boiling milk in a half-circle-metal pot until it solidifies. During the boiling the milk is stirred continuously to prevent burning. For efficient processing, some entrepreneurs have designed three-pot-hole stove so that they can use the excess heat in second and third-pot hole. The stove allows them to use three pans at a time. This helps them to reduce processing time and create more conformable working conditions. In a one-pot-hole stove 4.5 litres of milk take 80–90 minutes to process into khuwa (1 kg of khuwa) while in a three-pot-hole stove, it takes about 25– 30 minutes. The general condition of the kitchen is not well maintained.

The kitchen has proper lighting and ventilation but it is not well maintained. The cook remains seated during the cooking process.

During processing, continuous firing was observed in two processing units. Both the stoves are of the same design but differ in dimensions. The firing process is similar. The cooks are well trained and have processed khuwa for many years. They are quite experienced in controlling over-heating or under heat by adjusting the firewood. They never allow flames to lick the side of the pans as it will cause heat loss and burn the milk, as well as expose the cook to too much heat.

V. PROBLEMS AND CONSTRAINTS IN THE UTILIZATION OF THE STOVES

At present, the stoves that are being used are three-pot-hole stoves. These stoves are improved versions of the single-pot-hole stove. stove users prefer these stoves because they consume less fuel. However, the stove users still feel that the stoves consume too much fuel. They would like to have a more fuel efficient cookstove alternative.

The khuwa production process takes a long time, that is between 10 to 12 hours. The conditions in the kitchen are worse during summer as the kitchen becomes very hot, especially those that have no chimney installed.

The scarcity of fuelwood supply in rural areas is a growing problem in Nepal. Many milk processing industries have an uncertain future due to the increases in the price of fuelwood.

VI. ECONOMIC ASPECTS

Producers collect milk every day and pay on monthly basis. The price of milk depends on the ratio of khuwa production. According to the entrepreneurs, 3.8 litres of milk give 1 kg of khuwa. The khuwa production cost is minimal as presented below:

6.1. Cost Calculation of Stove Production

The existing traditional stoves cost around Rs.400 only. Cost calculation of stove production is given below.

6.2. Expected Durability of Stove

The stove is made of locally available materials and there is hardly any cost needed for maintenance. During use, the walls may crack but are quickly patched with a mixture of mud, cow dung, and rice husk. The stove is quite durable and may last for 10 years if properly maintained.

6.3. Capital Input Vs. Economic Output

As seen from the calculations, khuwa industries have a high rate of return on their initial investment (profit amounts to 169%) or a profit equal to 23.2% of the production cost. Even with that good profit, the production of khuwa is decreasing because of lack of fuelwood in the rural areas.

6.4. Fuel Used in Total Production Process

An economic analysis has been carried out for reference purpose. The analysis is based on case studies. The calculations are given below. The case studies show that specific fuelwood consumption varies within the range of 3.560 to 3.710 kg of fuelwood per kg of khuwa produced. On average, 3.635 kg of fuelwood is consumed per kg of khuwa production (Table 1). And the cost of fuelwood per kg of khuwa is about Rs. 14.54 (14.5% fuelwood cost per kg of khuwa).

The specific fuelwood consumption varied within the range of 0.880 to 0.928 kg of fuelwood per litre of milk process. In one-pot-hole stove, the specific fuelwood consumption varied within the range to 2.8 to 5 kg of fuelwood per kg of khuwa production in lkudole village of Lalitpur District. In lkudole village, fuelwood is collected by family members. Based on the cost of wages and food, one kg of fuelwood costs around Rs. 1/50 per kg which is about 3% fuelwood cost per kg of khuwa (in lkudole on average 1 kg khuwa costs Rs.50 per kg.).

Table 1. Results of Khuwa Production Tests

Remarks: Pan balance is used for the tests. Fuelwood with 12% moisture content was used.
Stove A: Water Boiling Test (WBT) gave 16.08 HU with 37.59 m/min.
Stove B: WBT - 18.21 HU with 25..9 gm/min Burning Rate (BR)

6.5. Economic Analysis of Small Scale Khuwa Industry

Production Cost per Month

VII. SUGGESTIONS FOR FUTURE DEVELOPMENT

Khuwa production is impaired by the lack of reliable, affordable fuelwood. Therefore a more efficient stove may be needed by the khuwa producers

Based on analysis of stove used, same suggestions for future development are recommended as follows:

• The one-pot-hole stove, should be made into a three-pot-hole stove and the pot holder should be converted into an inverted cone shape as done in Sudal village of Bhaktapur District. This will help to use waste heat and to make the work environment more comfortable.
• In three-pot-hole stove, the combustion chamber should be reduced, baffles should be introduced. During the summer, the cooks suffer excess heat while they use the stove. They also suffer from smoke, thus a smoke extractor is recommended. The smoke extractor will not be directly coupled with the stove. The smoke extractor offers many advantages not generally associated with chimney stoves. The smoke extractor works on the principle that sufficient waste heat is available to rise up a chimney supported above the heat source. Smoke and other emissions are drawn from the cooking process into the chimney air above the heat source.^₦

B. BIOMASS STOVE FOR CANDY INDUSTRY

K.M. Sulpya
RECAST
Kirtipur, Kathmandu, Nepal

I. BACKGROUND

Candy Lapsi (Spondais sps.) plant is a special kind of tree that is available in some parts of Nepal only. The fruit is small and contains a seed. From generation to generation, the fruit has been mixed with salt and water to make a drink during feasts and festivals. The drink is sour because it contains citric acid. Lapsi is believed to help digest food.

Lapsi candy is prepared from the lapsi fruit. This candy is popular mainly among young women and girls. Because of product diversification, the industry is growing very fast and high quality candy is exported to India, Australia and Saudi Arabia. The export quantity is very small however, and domestic demand is often so high that producers can not meet the domestic demand.

Lapsi fruit processing and candy preparation is classified as a small scale cottage industry in Nepal. It is also identified as a traditional food processing industry. These industries provide a good source of income for rural entrepreneurs and extra-income for households. More and more people are involved in these businesses because of the high demand for the processed products.

Candy Lapsi processing flow diagram

The raw materials used in this industry are lapsi fruit, salt, pepper, sugar, chilli powder, preservatives (bechi, chakuwasa) and all are readily available in the local market.

The lapsi fruits are collected from the rural areas. Middlemen travel to rural areas when fruiting starts and give advances of Rs.400 to Rs.500 per plant to the farmers. When the fruits are ready to be harvested, the middlemen collect the fruits and supply them to the industries. The supply of fruits is more or less regular because of the involvement of middlemen in this business. The price of and demand for lapsi fruit is increasing each season. Thus, growing it generates a good income for the rural people.

The industry is a small scale cottage industry. It is also a labour intensive business which requires the help of all available family members. Additional labour may be needed for firing the stove, screening the pulp and seeds, cutting, packaging, transporting, etc.

The government's Food Research Laboratory provides training on candy making techniques. Most of the people who run this candy business do not have any formal training from any institute but instead learn the process from family members.

Biomass fuel is the main source of energy for this industry. Agri-residues like wheat straw, rice husk are obtained as agricultural by-products. These residues are collected from different sources and stored until needed. The cost of agri-residues (wheat straw) is about Rs.4.80 per kg. which is more expensive than fuelwood. Similarly, the cost of rice husk is Rs.1.60 collected from local areas. During seasons when agri-residues are scarce, the lapsi industry depends on fuelwood. The supply of fuelwood from local areas has lessened due to the scarcity of available forests. Thus, for fuelwood, the industry has to depend on timber offcuts (bakal) which are supplied to Kathmandu from the southern parts of Nepal. The cost of bakal is about Rs.3.50 per kg.

II. THE STOVE

2.1. Stove Design

The brick stove used for lapsi fruit processing has an open fire, thus during firing a lot of heat is lost. Heat is also lost from the wood feeding hole. Normally one industry will have 5 to 10 stoves and light the stoves one at a time. Because of this it is difficult to control the fire and it is worst if agri-residues are used as fuel.

Half cut drums are used for cooking the Lapsi fruit

2.2. Stove Construction and Materials

The stove is generally made out of bricks. Some are made simply using mud and bricks. The stove has one-pot hole and the interior is rectangular. The internal dimensions of the stoves are 25 cm height, 36 cm wide. The stove has one wood feeding hole but there are two other small openings for removing ash.

III. FUEL USED AND PREPARATION

Agri-residues and fuelwood are the main fuels used for cooking lapsi fruits. Agri-residues include wheat straw, rice husk, maize cobs, and other bushes and twigs. Timber off-cuts (bakal) fuelwood are also used and are around 210 cm long and 3 to 7 cm wide but they are not uniform in size.

A single brick stove for Lapsi processing

During cooking operations, one small bundle of wheat straw of about 62 g. is kept for burning. Then after that 31 g of wheat straw is added at a time. The wheat straw is spread inside the combustion chamber so that the pot is evenly heated. When using fuelwood, the pot must be fired otherwise the fruits may not be fully cooked.

During the rice husk season, a bed of rice husks is prepared and then fuelwood or agri-residues are burned. This combination of fuel provides continuous heat and also saves money.

3.1. Heat and Combustion

In the process of lapsi cooking, half cut drums of 90 litres capacity each are kept on an open fire (made out of bricks or mud bricks) and filled with 75 kg of lapsi fruits and 5 litres of water. Each is covered by a jute sack. The boiling and simmering is done with agri-residue fuel. The boiling temperature was found to be around 96 degrees Celsius. The fire requires continuous attendance. The contents are never stirred and firing is continued until all of the lapsi fruits are cooked properly. The cooks say that agri-residues ensure a steady, stable flame whereas firewood requires continuous attendance lest the fruits burn.

During the boiling period the temperature of the combustion chamber was found to be around 628 degrees Celsius. The temperature lowers when the agri-residues are added. During the combustion period, the colour of the flame was yellowish to yellowish red and hot flue gases and flames emanated from the pot. The stove produced smoke.

3.2. Operation and Maintenance

The heat is controlled by adjusting the fuel and requires continuous attendance. The cook decides how to adjust the fuel levels.

3.3. Cooking Utensils and Design

For lapsi fruit processing, half-cut drums are used. Some processors use cylindrical aluminium pots. The half-cut drums have a diameter of 54 cm and are 60 cm high, while the aluminium pots have a diameter of 62 cm and are 45 cm high.

IV. PRODUCTION PROCESS

Lapsi fruits are cooked in the half circle shaped drum. 75 kg of lapsi fruit are cooked at a time. Only 5 litres of water is kept during cooking. During the boiling period, the fruits are covered by a jute sack to prevent evaporation. The cooking is done above an open fire. The entrepreneurs use 6 to 10 open fire at a time so that one or two persons can monitor the fire. After the fruits have been boiled, 5 kg of salt are added to the mixture. The salt makes it easier to peel the fruit skin, increases weight and acts as a preservative of the processed product.

The cooked fruits are kept in a machine which kneads the cooked fruits and separates the fruits from the seeds. After two to three times, the remaining seeds are removed by hand. The processed fruit is like pulp and is stored underground inside plastic covered receptacles for more than 8 months. The use of salt extends the storage life of the pulp beyond 8 months.

The pulp is the main raw material for candy preparation. Depending on the quality of the candy, fine pulp without fruit skin is taken out and mixed with sugar, pepper, chilli as desired, and dried in the sun or in a solar drier or electric oven. For normal candy preparation, the pulp is plastered on wooden planks and dried in the sun. It takes 3–5 days to dry and process the pulp into candy products. Some preservatives are also added to the finished products.

Workers are seated for the duration of the production process.

4.1. Tricks Employed During Processing

During cooking, continuous firing was observed in two processing units. Both the stoves had the same design and size. In one stove the firing was done by the owner and in the other by the labourer. The labourer added more fuel than was needed but the lapsi cooked fast The owner controlled the fire in the hope of minimising the fuel consumption during and after the cooking process. He lowered the fire so that the minimum amount of heat needed was used.

V. ECONOMIC ASPECTS

For reference purpose the economic analysis of the small scale lapsi candy industry has been given. To run this industry a stock of raw materials and processed raw materials are necessary because it is seasonal work and because there is a good market for the product.

5.1. Cost Calculation of Stove Production

The existing traditional stove costs about Rs.40 only. The traditional stove has three stones/bricks stove.

5.2. Capital Input Vs. Economic Output

As seen from the calculations, candy industries have a better return on their investment (profit amounts to 214.5% of the total investment). Because of the profit, these industries are growing and some entrepreneurs are producing high quality candy for export.

A simple machine for kneads and separates the fruits from the seeds

Typical of improved stove for cooking the Lapsi fruit	The lapsi pulp is plastered in wooden plank and dried under the sun

5.3. Biomass Used in Total Production Process

Based on the case studies, fuel consumption depends on the discretion of the cooks. On average, boiling 75 kg of lapsi fruits in two stoves of the same size but with different cooks consumed 10.2 kg and 7.3 kg of biomass fuel respectively. On average, the specific fuel consumption is 0.117 kg of biomass per kg of fruit cooked The cost of biomass fuel (wheat straw) per kg of raw candy is Rs.2.39 (4.78% biomass fuel cost per kg of candy).

The cost of wheat straw fuel is more expensive than fuelwood. The cost of wheat straw comes to Rs.5 per kg, while the cost of fuelwood in the study area is Rs.3.75 per kg.

VI. PROBLEMS AND CONSTRAINTS IN THE UTILIZATION OF THE STOVE

This rural industry is labour intensive and needs considerable space. Because of this, the stoves are installed outside the house or in an open field. Because the stoves have open fires, a lot of heat is lost during the cooking of lapsi fruits and it is difficult to work nearby the stoves. To avoid excessive heat, cooking starts either in the early morning or after 3 PM.

Normally the industry uses 5–10 stoves at a time and requires about 2 to 3 hours to complete the cooking process. It is difficult for one or two people to maintain the fire if they use agricultural residues. Depending on the season, they use a combination of fuelwood, agri-residues and seeds of the lapsi fruits. If agri-residues are used, the cook must remove the ash frequently to ensure a steady temperature.

These small scale industries are hampered by the unreliable supply of good quality fuelwood. When coupled with the rise in the price of fuelwood, many processors may feel compelled to substitute fuelwood by kerosene. Some entrepreneurs have already swithched to kerosene.

6.1. Production Cost and Economic Analysis of Small Scale Candy Industry

Tabel 1. Results of Lapsi Fruit Cooking Tests

Remarks: Local measurement ‘Pathi’ is used and converted in into kg.
An balance is used for fuel (wheat straw) measurement.
Stove A: WBT - 11.82 HU with 138.9 gm/min BR.
Stove B: WBT - 10.06 HU with 160.9 gm/min BR.

VII. SUGGESTIONS FOR FUTURE DEVELOPMENT

Candy processing is a profitable business which must grow quickly to keep up with the demand for the processed products. However, the irregular supply of biomass fuel (including fuelwood) is making it difficult for entrepreneurs to maintain their level of productivity.

Based on analysis of stove used, suggestions for future development are as follows:

In candy processing occurs during the early morning or after 3 pm to avoid excessive heat; if the open fire is contained, production can occur at more flexible hours. The pot used for the fruit processing is cylindrical, so if the pot is sunk into the combustion chamber, more heat will transferred around the pot. Therefore the cook will be exposed to the less heat. Metal grate should also be introduced so that the cook can easily removed the ash below the grate without disturbing the fire and increase air circulation in the combustion chamber. This type of stove will be 28% more efficient.

At present, most fruit processing centres in open fields are not hygienic. If possible, the cooking facilities in the open fields should be enclosed and provided with the necessary infrastructure for sanitation. Proper production methods will help secure a market for exports.^₦

C. BIOMASS STOVE FOR SWEETMEAT INDUSTRY

K.M. Sulpya
RECAST
Kirtipur, Kathmandu, Nepal

I. BACKGROUND

Sweetmeats are identified as a traditional food and primarily processed within villages or household groups (as a cottage industry). Production provides a good source of income and employment.

Sweetmeats are deep fried in ghee (fats from milk) or edible oil. Colours, flavours and toppings are added before or after frying. There are many varieties of sweetmeats using different raw materials. The nature of the products varies in form, texture or moisture content, etc. Some of the most popular sweetmeats in the rural as well as in the urban communities are: jilebi, sel and lalman. Some sweetmeats are mixed with khuwa (whole milk solids).

In Nepalese society, sweetmeats such as jilebi, swari or sel are consumed along with tea for breakfast. There is a special caste called the ‘Rajkarnikar’ whose main job is to cook sweetmeats. They are normally economically sound in comparison to other castes. But nowadays other castes also produce sweetmeats because it is profitable.

Sweetmeat production flow diagram

Every roadside restaurant, sells these items. Sweetmeats are also used as offerings during morning prayers. Sweetmeat are consumed in many areas of society and are widely available.

Fuelwood is the major source of energy used, however in places where it is expensive and where alternatives are available such as in Kathmandu and other cities, fuelwood is replaced by kerosene and LPG fuel.

The source of fuelwood for sweetmeat production is mainly from the country's progressively dwindling forest stock. In cities, timber offcuts are also used. In rural areas, fuelwood is transported mainly by human labour (or by foot). Only hard wood species of wood are used. The availability of hardwood species such as Sal (shorea robusta), Chilaune (Schima wallichi), Karma (Adina cardifolia), Katus (Castonopsis sps.), etc. is inconsistent, which has resulted fuel price hikes.

Sweetmeats are often produced and sold on site. These small scale businesses generally employ one or two labourers. The owner is responsible for training his employees.

II. THE STOVE

Normally, the stoves used for sweetmeats production have one-pot hole without a chimney. The stove is well-built. To reduce heat loss, very small pot supports are used. The round bottomed pan also sinks into the combustion chamber for better heat transfer to the pan. When a flat bottomed pan is used, small bricks are placed around the pot to prevent heat loss and also shield the cook from the heat. In some stove designs, a grate is used for better wood burning.

2.1. Stove Construction and Materials

The stoves are made of the following materials : 40 pcs of bricks, mud, agri-residues, dung, metal supports, and wood support.

To construct the stove, mud is mixed with cow dung and some agri-residues. In some stoves, a metal frame is used in the wood feeding hole.

The interior of the stove is shaped like a cylinder. Pot supports are used in the stove to protect the cook from the heat. Temporary bricks/tiles are kept surrounding the pot support. The dimensions of the stoves vary considerably from 24 cm to 30 cm inside diameter and with a height of about 30 cm to 40 cm. The stove has a single opening of about 16 cm that serves as fuel feeding hole.

III. THE FUEL

Fuelwood is the main fuel used in sweetmeat processing. Waste wood from timber processing is available in the market, size ranges from 60–210 cm long and from 3 to 7 cm wide.

During operation, between 2 and 4 firewood sticks are kept for burning depending on the size of the firewood. Kerosene or small pieces of firewood are used for kindling. If the combustion chamber becomes too hot, firewood is removed.

Typical of stove used in sweetmeat production

3.1. Heat and Combustion

In the process of sweetmeat production, the pan is filled up with about 5 litres of ghee or edible oil. The pan is heated by burning fuelwood with high intensity; when the ghee begins to boil, the cooking process starts.

Normally, well-dried wood is used for fuel. On average the moisture content was 13 percent during the author's observations. The wood burns yellowish red and the hot flue gases pass directly under the pan. During the study, the combustion was better and produced less smoke. The cook said that sometimes he has to use wet fuelwood which produces a lot of smoke.

During the stove use, the maximum temperature of the fire was estimated at 812 degrees Celsius; the temperature lowered when the fuelwood was added.

After completing the cooking process, the charcoal and ash are removed. Water is sprinkled on the charcoal and it is reused for space heating, tobacco smoking, or cooking meals in a special stove. Ash is used as a cleaning powder for plates, pans, pots, etc. After the cooking process, the temperature of the stove was around 520 degrees Celsius and slowly reduced.

3.2. Stove Operation and Maintenance

During production, heat is controlled by adjusting the amount of firewood. The stove does not have any mechanisms of secondary ventilation like an air hole, grate, gate. The stove is well-maintained by the cook.

3.3. Cooking Utensils and Design

For sweetmeats production, big pans (round bottomed or flat bottomed) are used. For deep frying round bottomed pans are preferred because the bottom part is embedded in the combustion chamber.

IV. SWEETMEAT PRODUCTION PROCESS

The raw materials used to make sweetmeats include buffalo meat, wheat flour, yeast, ghee, sugar, edible oil, khuwa, edible colours, etc. The ingredients are purchased in local markets and the cost varies from region to region. The supply of ingredients is not regular and the prices are increasing.

For jilebi cooking, wheat flour is mixed thoroughly with water, sugar, edible colour and fermented yeast in a bowl by stirring vigorously. After standing for one hour, the semi-liquid mixture is poured into the boiled ghee (milk fat) or edible oil according to the size of the jilebi required. Depending on the size of the pan, many jilebi can be cooked.

After some time, the jelebi is cooked and removed. The process continuous until they finish the mixture.

The general condition of the kitchen is messy but there is sufficient light and ventilation. The workers sit for the duration of the production process.

4.1. Tricks Employed During Processing

During processing, continuous firing was observed in two processing units. Both the stoves are the same design but differ in dimensions. The cooks are well-trained. However, in one stove, the cook used a metal support around the wood feeding hole to protect it from wear and tear during use. The combustion chamber is also smaller and has a grate for better burning. But the metal grate lasts for one and a half months only.

Both the stoves use small bricks around the pot ring to protect against heat loss from the pot hole.

V. PROBLEMS AND CONSTRAINTS IN THE UTILIZATION OF STOVE

The main problems faced by the shop keeper are the smoke emissions from the stove and the consumption of fuelwood which is increasingly difficult to obtain use.

For some sweetmeats, the cook prefers to use fuelwood to produce a strong heat and speed up the cooking process. Some cooks use both fuelwood and LPG in their stoves.