18 Abstract Biogas technology is a technology based on the digestion of various organic ...

126 Pages·2017·2.71 MB·English

Abstract
Biogas technology is a technology based on the digestion of various organic
substances by the action of bacterial organisms at suitable temperature and in absence of
oxygen. Although biogas is seen to be one better rural energy option, many factors have
made an effect on its spread and popularity in rural part. Considering on site practice and
use of biogas plant, it is observed that problems have arisen from installing too large a
capacity plant. Larger plants were unable to perform due to unavailability of required
quantity of feed material and also they fail to produce gas from it. Under feeding was also
found to occur due to the improper collection of dung as well as error during calculating
theoretical potential of biogas plant. As biogas production depends on various factors like
HRT, temperature, type of feed, density of feed, biogas generation of feed m3/ kg, mixing
ratio of feed to water, co-digestion and mixing of substrate. Besides knowing gas
production ability, one of the important factors of biogas plant construction is type of
design to be selected for construction and its financial viability. The important parameters
for design of biogas plant are material required, material available and cost of material. In
such a case, it is required to calculate amount of material required according to capacity
of plant.To plan and design biogas plants, several calculations should be carried out; this
requires time, effort and have possibility of making mistakes. The objective of this study
was to develop a tool to assist designers in planning and designing family size biogas
plants by providing a mathematical model and software program to save time and effort.
A mathematical model was developed to plan and design family size biogas plants i.e.
KVIC and Deenbandhu biogas plant models and their brick masonry and concrete
structures. Subsequently, flow charts were developed, and the mathematical model was
integrated into the flow charts to prepare a code of software. Afterwards, VB (VB.NET)
programming language was used to develop a software program by integrating the flow
charts and the mathematical model, and making the user interface. The developed
software is able to plan and design biogas plants, specify the dimensions of the different
types of biogas plant, and compute the required amounts of construction materials (brick,
wire mesh, iron rods, cement, sand, and gravel) required to build the designed structures.
Furthermore, it calculates the capital investment and total costs of the construction. Data
from Indian standards and actual biogas plants was used to carry out the model validation
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and to evaluate the software program. The differences between actual and calculated
values were determined. The coefficients of variation range between 0 % and7 %.
Furthermore, the calculated accuracy of the software program is 98%.
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CHAPTER- I
INTRODUCTION
1.1 Biogas Technology in India
Biogas technology is a technology based on the digestion of various organic
substances by the action of bacterial organisms at suitable temperature and in absence of
oxygen. It is an eco-friendly technology in era of modernization. The biogas technology
had existed over a longer period of time and is being still in use. In situation of global
energy crisis interest has been generated to use animal waste as an energy substitute for
fossil fuels. The production of biogas from animal waste in an oxygen free environment
is one of the best possible options, which can fulfill the growing demand of energy in
rural part of India.
In India, development of biogas technology started more than 60 years ago. Till
March 2011, four million domestic biogas plants have been constructed in whole country.
Basically these plants are fed with cow dung in rural areas. But nowadays mixed feed
stocks and agriculture residues are also used as alternative feed to biogas plants looking
to the reduction in cattle population per household.
According to Ministry of New and Renewable Energy (MNRE) many designs of
biogas plants are approved under National Biogas and Manure Management Programme
(NBMMP). The designs which are most popular in India are KVIC (Khadi and Village
Industries Commission’s) design and Deenbandhu Biogas design. Among above two
KVIC is floating drum type design while Deenbandhu is fixed dome biogas plant.The
designs of these biogas plants are variable according to the capacity, substrate, retention
time, digester conditions and temperature. The other approved designs are popular in
selective areas as per the climatic and geographical conditions.

1.2 Points hindering spread of Biogas Plant:-
Although biogas is seen to be one better rural energy option, many factors have
made an effect on its spread and popularity in rural part. Considering on site practice and
20
use of biogas plant, it is observed that problems have arisen from installing too large a
capacity plant. Larger plants were unable to perform due to unavailability of required
quantity of feed material and also they fail to produce gas from it. Under feeding was also
found to occur due to the improper collection of dung as well as error during calculating
theoretical potential of biogas plant. In some areas, the plant may not be technically
feasible all year round due to lowwinter temperatures that inhibit methanogenesis, and
also due to seasonal availability of waste material.
Sometimes the plants are faulty in their construction, or develop problems that
lead to thenon-functioning of the plant, due to shoddy construction (more relevant to the
fixed-domemodels, than the floating dome, which comes pre-cast). Often, specially
trained masons in biogas plant construction were overlooked, due to their higher cost, in
favor of cheapertrainees, or those with no training at all.
Economically, biogas systems have been shown to be cost-effective. Despite the
positivecost-benefit of biogas technology, the 'macro-environment', may discriminate
against theuptake of biogas. The macro-environment which determines price structures of
conventionalfuels most likely acts as a disincentive to adopt renewable technologies.
Subsidizedconventional fuels, such as electricity, along with free connection to the grid
for farmers, willcontinue to make non-renewable technology the cheapest option, unless
subsidies for biogascan be brought into line, or prices of conventional fuels are raised. In
order to calculate economic viability of biogas in accordance with the conventional fuel
has got so much importance which may help to overcome problems in spread of biogas
plant.

1.3 Importance of proposed work:
Biogas production of different substrates is different and biogas production in
different places also varies with temperature giving different retention times. The HRT is
an important factor while making the use of alternate feed materials for biogas plants as it
changes from feed to feed. Also in case of alternate feeds like crop residues and plant
materials, it is important to have precise planning of available material to be utilized as
they are available seasonally. So by use of Simulation modeling it can be possible to have
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number of designs available with respect to parameters affecting production of biogas
plant using different feed stocks. Simulation models based on design procedures and
available data can be best utilized to give optimum designs which can suit conditions of
different places and situations. For designing of biogas plants in India normally the gas
production capacity of biogas plant is noted as design capacity of biogas plant not the
volume of digester capacity.
Besides knowing gas production ability, one of the important factors of biogas
plant construction is type of design to be selected for construction and its financial
viability to be affordable to beneficiary. After selection of type of biogas plant important
parameters for design of biogas plant are material required, material available and cost of
materials to be used for construction. In such a case it requires to calculate amount of
material required according to capacity of plant.
Biogas plant can be constructed with various materials and in different shapes and
sizes. Construction of plant structure forms a major part of investment cost. Planning and
designing of biogas plant is a sophisticated work requiring multiple procedures of
calculations which take long time and lots of efforts; moreover, making mistakes is also
possible. Various design procedure consists of solving polynomials which may be cubic
or of fourth degree also. They take longer time and it requires mathematical knowledge to
solve equations. For designing the biogas plants having capacity in fractions like 0.5 m3,
1.5m3, 2.75m3 etc. calculations becomes more hectic and for the same standard
dimensions are not been given in various standards which are followed for designing
biogas plants. In case of KVIC biogas plants, models are available for 30,40 and 55 days
HRT but in case of Deenbandhu biogas plantdesign and dimensions for 30 days HRT are
not available in standards. It is important to have design specifications for deenbandhu
biogas plant for zone having 30 days HRT consideration.
Economic analysis of any system requires deep knowledge about economics and
pricing of different systems. Their comes terms like fixed cost, variable cost, capital cost,
IRR, benefit cost ratio, payback period and inflation-deflation factor which are
complicated to calculate in accordance withdifferent types of materials used in biogas
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plant construction as well as considering biogas as replacement for different conventional
fuels.
So to avoid an error prone method and to accelerate and improvise decision
making, it is necessary to develop computer based tools (program or software) that have
ability to process data and give an optimum output or solution. The important perspective
behind taking this study is that software can be easily updated with latest information
available regarding to the biogas plant and latest developments.
Taking into account the requirement of a system for designing and planning of
biogas plant along with its financial evaluation; study has been undertaken with an aim to
design a computer based expert system (software) for selection and design of proper
family size biogas plant.
Hence, the study was attempted with following objectives:
1. Development of biogas potential assessment model.
2. Development of Simulationmodel for design of Deenbandhu biogas plant
model for sizes 1 to 6 m3.
3. Development of Simulationmodel for design of KVIC biogas plant model
for sizes 1 to 10 m3.
4. Development of economic analysis model for Deenbandhu and KVIC
biogas plant models.
5. Development of expert system for Deenbandhu and KVIC biogas plant
models.

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CHAPTER- II
REVIEW OF LITERATURE
A number of studies have been conducted in the field of biogas technology. Many
scientists and microbiologists have worked on various aspects of energy production from
various substrates and various designs of biogas plants throughout the world. This
chapter deals with the work done by several scientists, microbiologists, economists and
engineers on biogas technology, expert systems and designs of different types of biogas
plants. The work has been studied critically and reviewed under following headings-
2.1 Gas production ability of different substrates
2.2 Biogas plant designs based on feeds other than cattle dung
2.3 Simulation and Mathematical models related to biogas plants
2.4 Computer based design systems of biogas plant
2.5 Economic analysis of biogas plants
2.6 Characteristics of an Expert system

2.1 Gas production ability of different substrates:
The reviews under this heading describe the work done to determine the biogas
production potential from different feedstock substrates at different conditions in single
or mixing of dung conditions.
Werner et al., (1989) in their study suggested that the average gas production
from cow-buffalo manure, pig manure, sheep manure, poultry manure were 0.0414,
0.054, 0.04 and 0.0782 m3/kg feedstock respectively.
El-Shinnawi et al., (1989) studied biogas generation and changes in total and
volatile solids, total and NH + -N, available P monitored during a 120-day fermentation
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period, in laboratory biogas digesters, of maize stalks, rice straw, cotton stalks, and water
hyacinth, each enriched with partially digested cattle dung. Maize stalks gave the greatest
values of cumulative yield of biogas (65 l/2.5 l fermented material) and its methane
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component (39 l), whereas rice straw, water hyacinth, and cotton stalks produced
progressively less biogas.
Cho et al., (1995) conducted batch digestion tests of food wastes at 37 °C and 28
day retention time. The methane yields were 0.48, 0.29, 0.28, and 0.47 l/g VS for cooked
meat, boiled rice, fresh cabbage and mixed food wastes, respectively.
Singh and Maheshwari, (1995) reported that dung to water ratio of 1:1 was
optimum for gas production and smooth flowing of charge. But they also cited that 3:2
dung to water ratio is equally good.
Deivanai et al., (1995) studiedanaerobic digestion of banana trash and coir pith
for a period of one month by batch digestion. During biomethanation, reduction of total-
and volatile-solids was, respectively, 25.3 and 39.6% in banana trash and 13.6 and 21.6%
in coir pith. A production of 9.22 l and 1.69 l (per kg TS added) of biogas with average
methane content of 72 and 80% was achieved from banana trash and coir pith,
respectively.
Steffen et al., (1998) studied “Feed stocks for Anaerobic Digestion”, in which
they studied different feed stocks for anaerobic digestion in European perspective. They
used bovine i.e. cow and buffalo manure and reported that the average biogas production
from bovine manure was 0.033-0.0497 m3/ kg of feedstock.
Jagadish et al., (1999) reported that use of commonly available herbaceous
biomass feedstock, in addition to the existing potential of 12 million biogas plants
operating on cattle dung; it might be possible to meet the cooking energy needs of all the
rural families.
Zang et al., (1999) studied the anaerobic digestion of garlic waste with a batch-
fed anaerobic phased solids digester system and concluded that after digestion 51% of TS
and 62 % of VS in the garlic waste were converted in to biogas a yield of 58 l/g of VS.
Nagamani, B. and Ramasamy, K.,(1999) in their studied reported that average
yield of Dung from cow is 10 kg/day/head. They also reported that from buffalo, pigs and
poultry we get average yield of dung as 15, 2.25, 0.18 kg/day/head respectively.
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Ramchandra et al., (2000) in their work reported that dung availability from cow
is 3 and 10 kg/day/head as lower and upper values. They also suggested that average
yield of dung from cow in India is 6.5 kg/head/day. They also reported that the gas
production from cow and buffalo was 0.036 m3 per kg; that of pigs and sheep was 0.058
and 0.047 m3per kg feedstock respectively.
Bouallagui et al (2003) tested semi-continuously mixed mesophilic tubular
anaerobic digester for conversion of fruit and vegetable waste (FVW) into biogas. The
effect of hydraulic retention time (HRT) and the feed concentration on the extent of the
degradation of the waste were examined. Varying the HRT between 12 and 20 days had
no effect on the fermentation stability and pH remained between 6.8 and 7.6, but an
inhibition of methanogenic bacteria was observed at HRT below 12 days. The overall
performance of the reactor was depressed by changing the feed concentration from 8% to
10% TS (dry weight). By applying a feed concentration of 6% and HRT of 20 days in the
tubular digester, 75% conversion efficiency of FVW into biogas with a methane content
of 64% was achieved.
Heo et al., (2003) co-digested the food waste with activated sludge generated
from a municipal water waste plant in a single anaerobic digester. Increased fraction of
food in feed mixture resulted in improve in C: N ration and decreased methane contain at
shorter HRT. The optimum operating conditions was found at an HRT of 10 days with a
feed mixture of 1:1.
Xuet al., (2003) compared a single pass reactor (R1), a leachate recycled reactor
(R2) and coupled solid/liquid bioreactor (R3-Rm) for anaerobic digestion of food waste
in terms of their digestion process and treatment efficiency. The coupled solid/liquid bio
digester was an enhanced two phase system and distinctive from traditional two phase
system with an UASB reactor as the methanogenic process. In comparison with R1 and
R2, R3-Rm enhanced the digestion process and increased the methane content of biogas.
100% of R3-Rm methane yield was from the methanogenesis phase with average
methane content of 71%.
Heo et al., (2004) evaluated the biodegradability of a traditional Korean food
waste consisting of boiled rice (10–15%), vegetables (65–70%), and meat and eggs (15–
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20%) and showed that the methane yield was 0.49 l/g VS at 35 °C after 40 days retention
time.
Annimari (2006) evaluated the feasibility of utilizing energy crops and crop
residues in methane production through anaerobic digestion in boreal conditions.
Potential boreal energy crops and crop residues were screened for their suitability for
methane production, and the effects of harvest time and storage on the methane potential
of crops was evaluated. Co-digestion of energy crops and crop residues with cow manure,
as well as digestion of energy crops alone in batch leach bed reactors with and without a
second stage up-flow anaerobic sludge blanket reactor (UASB) or methano-genic filter
(MF) were evaluated. The methane potentials of crops, as determined in laboratory
methane potential assays, varied from 0.17 to 0.49 m3 CH4 kg-1 VS (volatile solids
added
added) and from 25 to 260 m3 CH4 t-1 ww (tons of wet weight).
Elango et al., (2007) investigated the production of biogas from municipal solid
waste (MSW) and domestic sewage by using anaerobic digestion process. The batch type
reactor was operated at room temperature varying from 26 to 36 °C with a fixed
hydraulic retention time (HRT) of 25 days. The digester was operated at different organic
feeding rates of 0.5, 1.0, 2.3, 2.9, 3.5 and 4.3 kg of volatile solids (VS)/m3 of digester
slurry per day. Biogas generation was enhanced by the addition of domestic sewage to
MSW. The maximum biogas production was of 0.36 m3/kg of VS added per day
occurred at the optimum organic feeding rate of 2.9 kg of VS/m3/day. The maximum
reduction of total solids (TS) (87.6%), VS (88.1%) and chemical oxygen demand (COD)
(89.3%) found at the optimum organic loading rate of 2.9 kg of VS/m3/day. The quality
of biogas produced during anaerobic digestion process was 68–72%.
Rongping et al., (2007) conducted a study on co-digestion of food waste and dairy
manure in a two-phase digestion system in laboratory scale. Four influents of R0, R1, R2,
and R3 were tested, which were made by mixing food waste with dairy manure at
different ratios of 0:1, 1:1, 3:1, and 6:1, respectively. For each influent, three runs of
experiments were performed with the same overall hydraulic retention time (HRT) of
13 days but different HRT for acidification (1, 2, and 3 days) and methanogenesis (12,
11, and 10 days) in two-phase digesters. The results showed that the gas production rate
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