Methodology_2019_Energy_gerneration_from_animal_farm_waste_Alexej_Vnukov

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COURSE:  
METHODOLOGY FOR PRODUCING, 
PRESENTING AND MANAGING 
TECHNICAL WORKS 
 
 
4th Grade Year

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METHODOLOGY FOR PRODUCING, PRESENTING AND MANAGING TECHNICAL WORKS 2019 Page. 1/22 
 
TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
Assignment nr. 1 
Technical Report on Energy generation from 
animal farm waste 
 
 
Lecturer:  Jorge Cerqueiro Pequeño 
Student:  Alexej Vnukov 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Vigo, April 2019 
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METHODOLOGY FOR PRODUCING, PRESENTING AND MANAGING TECHNICAL WORKS 2019 Page. 2/22 
 
TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
0.  ABSTRACT 
For the desired expansion of renewable energies on the basis of biomass, the 
energetic  use  of  liquid  slurry  as  an  agricultural  waste  material  is  an  attractive 
option. Compared to the use of renewable raw materials, it does not compete with 
food  production  and  has  the  potential  to  reduce  greenhouse  gas  emissions 
relatively cheaply. In Germany, the manure bonus for renewable raw materials in 
biogas  plants  has  therefore  been  granted  since  the  beginning  of  2009  if  the 
proportion  of  manure  is  at  least  30%  of  the  fresh  substrate  mass  used.  This 
incentive can lead to an increase in the use of manure.  
 
 
 
 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
 
Table of contents 
 
1. Introduction ......................................................................................................... 4 
2. Excrements from animal farming ........................................................................ 5 
3. Thermo-chemical transformation (burning) ......................................................... 8 
4.1 Production and use of biogas ........................................................................... 9 
4.2 Anaerobic degradation .......................................................................................................... 10 
4.2.1 Hydrolysis ............................................................................................................................ 11 
4.2.2 Acidogenesis ....................................................................................................................... 11 
4.2.3 Acetogenesis (acetate formation) ...................................................................................... 12 
4.2.4 Methanogenesis.................................................................................................................. 12 
5.1 Biogas ............................................................................................................. 14 
5.1.1 Methane (CH4) .................................................................................................................... 14 
5.1.2 Carbon dioxide (CO2) .......................................................................................................... 15 
5.1.3 Water (H2O) ........................................................................................................................ 15 
5.1.4 Hydrogen sulphide (H2S) .................................................................................................... 15 
5.1.5 Nitrogen and nitrogen compounds .................................................................................... 16 
5.1.6 Trace elements.................................................................................................................... 16 
6.1 Gas utilisation ................................................................................................. 16 
6.1.1 Heat supply ......................................................................................................................... 17 
6.1.2 Use in combustion engines ................................................................................................. 17 
6.1.3 Vehicle fuel.......................................................................................................................... 18 
6.1.4 Feeding into natural gas networks ..................................................................................... 18 
6.1.5 Further possibilities ............................................................................................................. 19 
7.  BIBLIOGRAPHICAL AND DOCUMENTAL REFERENCES ............................. 20 
APPENDIX /APPENDICES ................................................................................... 21 
 
 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
1. Introduction 
Fossil fuels are the main source of energy for the world. Energy consumption will 
continue to increase in the future. While it is unclear how long fossil fuels will last, 
so much is clear that they are limited. As the easily accessible resources of fossil 
fuels are increasingly exhausted, the price of oil reaches new highs almost every 
year.  Unconventional  sources,  such  as  tar  sands  and  oil  shale,  are  becoming 
economically interesting. Biofuels have been predicted to be a future alternative 
energy source and are already being used as an energy source in the fast-growing 
transport sector (an  average  annual increase  of  3%  is expected  over the next 
twenty  years,  largely  due  to  growing  mobility  in  China  and  India).  Transport 
represents 20% of global primary energy use and 70% of all liquid fuels. However, 
currently only bioethanol, biodiesel and regenerative diesel are produced on an 
industrial  scale.  Biofuels  are  produced  from  vegetable  biomass  consisting  of 
carbohydrates (starch, sucrose, cellulose, and hemicellulose), protein, fats, oils, 
nucleic  acids  (DNA,  RNA)  and  lignin.  The  relative  composition  of  these 
components depends not only on the plant species but also on the part of the 
plant from which they originate. For example, trees contain more lignocellulose 
than cereals and fruits and seeds contain more starch and protein than stems. On 
average, more than 70% of the total plant biomass is lignocellulose. Of the plant 
biomass,  protein,  starch,  sucrose  and  lipids  are  relatively  easily  degradable, 
whereas lignocellulose is not. Humans are not able to digest cellulose or lignin, 
which  is  why  they  depend  mainly  on  starch,  lipids  and  protein  as  food.  Until 
recently, biofuels were largely produced from easily degradable starch, sucrose 
(bioethanol) and fats (biodiesel and regenerative diesel), which also serve humans 
as  food  (first  generation  biofuels).  This  competition  (fuel  versus  food)  has  a 
negative  socio-economic  impact,  which  is  why  the  main  focus  is  now  on  the 
production of biofuels from the lignocellulosic part of plants (second-generation 
biofuels). However, second-generation biofuels are currently in a pre-commercial 
phase,  and  if  they  meet  the  2015-2020  targets  at  all,  there  are  still  significant 
technical barriers to the chemical transformation of biomass. Biofuels that can be 
produced from biomass through biological processes include biogas (methane), 
bioethanol  (ethanol),  biodiesel  or  regenerative  diesel  (diesel-like  compounds), 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
butanol, methanol and hydrogen. In addition, electricity can be generated from 
biomass  using  biofuel  cells.  In  the  following,  the  production  and  use  of  these 
energy sources are compared, bytheir energy efficiency and the feasibility of their 
use  compared  and  the  limited  availability  of  biomass  as  a  general  source  for 
biofuel production discussed in detail. 
 
2. Excrements from animal farming

Figure 1: Mass animal husbandry [6] 
 
Manure  from  animal  husbandry  mainly  occurs  in  agriculture,  the  terms  farm 
manure  or  farmyard  manure  are  also  used  for  this  organic  material.  The  raw 
materials for these biomass fractions are manure, which is more or less solid and 
the  liquid  urine.  Depending  on  the  type  of  housing  of  the  animals,  both  raw 
materials  may  accumulate  together with  the  bedding  material (usually  straw  or 
wood shavings), this is known as solid manure. If excrement and urine accumulate 
together without other additives (except for water, e.g. in the case of split floor 
cultivation),  the  resulting  mixture  is  called  liquid manure.  In  modern  housing 
concepts, water is normally added to these excrements for transport and cleaning 
purposes, the resulting mixture is then called full slurry. This solid slurry may also 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
contain other components (e.g. feed waste) or may be added (e.g. straw, kitchen, 
garden waste and leaves).

Figure 2: Animal farm waste [4] 
 
The quantity and composition of the excrement vary significantly depending on the 
feed  and  other  variables. For example,  with  the  same  dry  matter content  (DM 
percentage), the excrements of cattle are more viscous than those of pigs and in 
particular  chickens;  this  is  due,  among  other  things,  to  the  different  digestive 
systems  or  the  different  types  of  feedstuffs  that  are  usually  fed  to  these  farm 
animals. However, there may also be considerable differences within the same 
species. For example, cattle manure is thinner in summer when grass is fed than 
in winter when dry hay and silage are fed. Pig manure is also thinner when feeding 
liquid  feed  (e.g.  whey,  thick  stillage)  than  when  feeding  dry  feed  (e.g.  silage 
maize). Full slurry is thus a heterogeneous mixture of liquids of different origin, 
which may contain a wide variety of solids. The liquid consists mainly of water and 
dissolved salts as well as organic acids and other soluble components. The solids 
can be divided into three categories according to their physical behaviour.  
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
- Suspended particles that remain more or less in suspension (e.g. certain   
excrement particles, bacteria, cellulose fibres).  
- Floating solids which, due to their low density or the gas bubbles they 
produce,  can  accumulate  on  the  surface  and  form  a  floating  layer  (e.g. 
straw, roughage residues). 
- Sediments that accumulate at the bottom of the collection container as a 
result of  sedimentation  (e.g.  unwanted  sand  particles,  but  also  organic 
material). 
 
Excrements  from  livestock  farming  are  usually  used  on  farms  untreated  as 
fertiliser and spread in this form on farmland; in the case of area-adapted livestock 
farming, the aim is to recycle the nutrients contained therein and thus close the 
internal nutrient cycles. In the case of non-adapted animal husbandry, such use 
on the farm's own land may not be possible, as there may then be a surplus of 
nutrients on the land used for the production of the animals; this implies the risk of 
nitrogen leaching in groundwater and surface water. Different treatment options 
are possible for the treatment that may then be necessary for transport to more 
distant arable land and for improving the application properties (e.g. minimisation 
of smell, improved distribution capability, reduction of water content). For example, 
chicken excrements can be dried, composted or pelletised and pig excrements 
can  be  separated  by  solid-liquid  separation.  Such  agricultural  substrates  (i.e. 
slurry, manure) are typical substrates that can be used for biogas production in 
agriculture.  They  are  relatively  easy  to  ferment  from  a  technical  point  of  view. 
However, there may be problems with chicken excrements due to the relatively 
high nitrogen content. This leads to the formation of high NHC 4 concentrations 
during  anaerobic  treatment,  which  can  inhibit  the  fermentation  process.  In 
Germany, liquid manure and slurry are already partly used for biogas production. 
However,  since  such  agricultural  substrates - unlike  municipal  or  industrial 
organically contaminated waste and waste water - do not necessarily have to be 
treated (anaerobically) and can therefore be applied to the fields without additional 
(aerobic  and/or  anaerobic) treatment  (i.e.  after  simple  interim  storage  and 
consequently without additional costs), anaerobic fermentation only takes place if 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
this is economically viable (e.g. in Germany on the basis of the Renewable Energy 
Sources  Law).  An  additional  advantage  of biogas  production  from  the 
environmental and climate protection point of view is that the use of excrements 
from animal husbandry in biogas plants can significantly reduce the often strong 
release of greenhouse gases from the storage of this group of substances (i.e. 
positive  contribution  to  climate  protection);  the  same  applies  to  the  odorous 
substances  that  are  degraded  to  biogas  in  biogas  plants  (i.e.  fermented  slurry 
"stinks" much less). In the case of thermophilic process variants, hygienisation of 
the material can also be achieved to a certain extent. [1] (2009): Energie aus Biomasse, p. 301- 
303; [2] (2016): Energie aus Biomasse, p. 158 
 
3. Thermo-chemical transformation (burning) 
For biogenic solid fuels (e.g. wood, straw), direct combustion in furnaces is still by 
far  the  most  important  energy  conversion  process  and  procedure.  Incineration 
plants are used to produce heat. This thermal energy can be used as secondary 
energy (e.g. steam, which can then be further converted into electrical energy), as 
final  energy  (e.g.  district  heating)  or  as  useable  energy.  Combustion  is  the 
complete oxidation of a (biogenic) (solid)-fuel by releasing energy. This produces 
off-gases and ash. Against this background, the technical aspects related to the 
direct  thermal  conversion  of  biogenic  solid  fuels  will  be  discussed  below. The 
focus of this part is on the description of combustion plant technology. In addition, 
the  possibilities  of  electricity  generation - both  within  the  framework  of  mono-
combustion of biogenic solid fuels and in co-incineration (i.e. the joint thermal use 
of solid biomass and fossil solid fuels such as hard coal) - or combined heat and 
power generation (CHP) are addressed. [1] (2009): Energie aus Biomasse, p. 375; [2] (2016): Energie 
aus Biomasse, p. 646 
 
 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
4.1 Production and use of biogas 
The generation of biogas from residues, by-products and waste on the one hand 
and  renewable  raw  materials  on  the  other  hand  is  an  option  for  biomass 
conversion  which  has  gained  considerable  market  importance  in  recent  years. 
Biogas  and  the  resulting  bio-methane  is  characterized  by  a  relatively  simple 
production and use of the through high flexibility with regard to possible usage 
options in the energy system i.e. use in the heat, electricity and fuel markets is 
possible.

Figure 3: Example of a biogas plant [7] 
 
In the following, the biochemical basics of anaerobic digestion for the production 
of  biogas  are  described.  In  view  of  the  resulting  requirements  and  boundary 
conditions  for  a  process  engineering  implementation,  selected  application 
examples  will  be  presented.  With  the  aim  of  using  biomass  as  efficiently  as 
possible,  the  material  and/or  energetic  utilisation  concepts  of  the  other 
fermentation products will be explained in addition to the options for using biogas 
or biomethane. [8] 
 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
4.2 Anaerobic degradation 
During methane formation, microorganisms decompose organic substances in an 
oxygen-free environment, releasing biogas. This is a gas mixture saturated with 
water vapour, which essentially consists of methane (CH4) and carbon dioxide 
(CO2).  Other  components  besides  steam  are  trace  gases  such  as  nitrogen, 
oxygen, hydrogen, hydrogen sulphide and ammonia. 
This  biogas  is  naturally  produced  by  anaerobic  microorganisms  in  moors, 
sediments, soils and rumen of ruminants. But such microbial methane formation 
also occurs in anthropological systems such as solid manure deposits, slurry pits 
or domestic waste landfills. In biogas and sewage gas plants, these anaerobic 
fermentation processes are technically applied and an energetically usable biogas 
is produced with the highest possible efficiency. 
This anaerobic degradation of organic material is realized by a complex network of 
microbial communities (biocenosis) in which the microorganisms are in different 
relationships and dependencies to each other. The different phylogenetic groups 
show individual activities and growth rates. As a consequence, the rate of total 
degradation  is  determined  by  the  microbiological  group  with  the  lowest  total 
activity. The diversity of microorganisms decreases over the stages of anaerobic 
degradation and thus their specialization increases.  
 
- When  using  stackable  or  puncture-resistant  substrates,  the  hydrolysis  is 
often the speed-determining step. Above all cellulose and hemicellulose, 
which  are  frequently  found  in  plant  substrates,  can  only  be  hydrolyzed 
comparatively slowly. 
 
- In  the  case  of  lignocellulose,  degradation  is  further  complicated.  An 
anaerobic  degradation  of  lignin  is  not  known  and  the  degradable 
substances cellulose and hemicellulose are built into a lignin skeleton and 
therefore difficult to access for hydrolytic bacteria. 
 
 
 
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- If  large  amounts  of  easily  degradable  compounds  are  involved  (e.g.  in 
waste water from distilleries or dairies, in kitchen waste, in some renewable 
raw  materials),  acetoclastic  methane  formation  may  become  the 
determining step for the rate, as the growth rates of syntrophic bacteria and 
methane formers are lower compared to fermenters. 
During substrate degradation, active biomass is newly formed by the reproduction 
of  microorganisms.  The  proportion  of  the  substrate  that  is  converted  into 
microorganism  biomass  is  quantified  very  differently.  For  the  individual  groups 
involved in degradation, the figures vary between 3 and 10 %. In the following, the 
different interdependent metabolic steps of anaerobic digestion are described in 
more detail. [2] (2016): Energie aus Biomasse, p. 1610-1613 
 
4.2.1 Hydrolysis 
In a first step, hydrolysis, the fermentation substrate, which consists of complex 
polymeric  compounds  (e.g.  carbohydrates,  fats,  proteins),  is  broken  down  by 
hydrolytic  bacteria  into  its  oligomeric  and  finally  di- and  monomeric  units  (e.g. 
sugars, fatty acids, glycerol, amino acids). Hydrolytic bacteria form exoenzymes 
from  the  group  of  hydrolases  (e.g.  amylases,  lipases,  proteases,  cellulases, 
hemicellulases), which are enriched on the membrane outside of the bacterial cell. 
These  are  partially  released  into  the  environment  as  large  enzyme  complexes 
(cellulosomes). The bacterial production of adhesion proteins supports hydrolysis. 
[2] (2016): Energie aus Biomasse, p. 1612 
 
4.2.2 Acidogenesis 
In a second step, the water-soluble hydrolysis products in the cell interior of the 
bacteria  are  fermented  essentially  with  the  formation  of  various  low-molecular 
organic  acids  (mainly  acetic  acid,  propionic  acid,  n-butyric  acid,  lactic  acid), 
alcohols, carbon dioxide and hydrogen. The fermentations do not always result in 
a direct degradation of the substrates up to the final fermentation product; thus 
microbial chain extensions can also temporarily form e.g. butyric acid from acetic 
acid or valeric acid from propionic acid. This leads to a meandering rather than 
linear metabolic process during anaerobic fermentation. The diversity of bacterial 
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fermenters  is  high  and  can  contain  several  thousand  different  facultative  and 
strictly  anaerobic  species,  mainly  from  the  classes  Clostridia,  Bacteroidia, 
Gammaproteobacteria, Actinobacteria and Bacilli. [2] (2016): Energie aus Biomasse, p. 1612 
 
4.2.3 Acetogenesis (acetate formation) 
In the third step, the products of the acidogenesis are converted to acetate. If 
alcohols or organic acids such as short-chain fatty acids (e.g. propionic acid, n-
butyric  acid)  are  used  as  substrates,  hydrogen,  carbon  dioxide  and  other  C1 
compounds  are  also  produced.  For  the  activity  of  acetogenic  bacteria  low 
hydrogen  partial  pressures  is  essential,  since  the  degradation  process  is  only 
thermodynamically possible under these conditions. In order to maintain such low 
hydrogen partial pressures, the bacteria are therefore closely related to hydrogen-
consuming  microorganisms.  It  is  assumed  that  instead  of  the  direct  so-called 
interspecies hydrogen transfer, hydrogen can also be transferred from one cell to 
another in the form of formate. This dependence between the microorganisms is 
called syntrophy. Syntrophic partners of acetogenic bacteria can be, for example, 
sulfate-reducing  bacteria  or  methanogenic  archaea.  A  special  form  of 
acetogenesis is the formation of acetate from hydrogen and carbon dioxide. This 
is  the  reverse  reaction  of  syntrophic  acetate  oxidation,  which  is  part  of  an 
alternative route of methane formation from acetate. 
The  diversity  of  syntrophically  living  bacteria  is  less  than  that  of  acidogenesis. 
Thus  different  representatives  of  the  synergistales,  syntrophobacterales, 
clostridiales and Thermoanaerobacteriales are identified as abundant acetogens. 
[2] (2016): Energie aus Biomasse, p. 1612 
 
4.2.4 Methanogenesis 
In the last step methane is finally produced by the activity of specialized strictly 
anaerobic microorganisms  from  the  group of Euryarchaeota, the methanogenic 
archaea.  The  methanogenic  organisms  are  divided  into  three  groups,  the 
hydrogenotrophs,  methylotrophs  and  acetotrophs,  according  to  the  metabolic 
physiology of their substrates.  
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- In  the  hydrogenotrophic  process,  carbon  dioxide  is  reduced  using 
hydrogen.  The  methane  formers  compete  with  other  hydrogen-using 
microorganisms (e.g. sulfate reducers). 
 
- Methylotrophic  methanogenesis  uses  methylated  compounds  (e.g. 
methanol) as substrate. 
 
- In acetoclastic methanogenesis, acetate is split directly to form methane 
and carbon dioxide. 
 
Acetate  can  also  be  degraded  to  methane  and  carbon  dioxide  by  syntrophic 
acetate  oxidation.  First,  both  methyl  and  carboxyl  groups  of the  acetate  are 
oxidized to carbon dioxide (CO2) by bacterial syntrophic acetate oxidizers to form 
hydrogen. This reaction is thermodynamically unfavourable. However, it can occur 
in combination with hydrogenotrophic methanogenesis. The entire process then 
becomes  exergonic.  Which  of  the  metabolic  pathways  to  methane  formation 
predominates in biogas production depends on the particular process conditions.  
Six different orders of methanogenic archaea are possible: 
Methanobacteriales,  Methanococcales,  Methanocellales,  Methanomicrobiales, 
Methanosarcinales and Methanopyrales. Most known methane formers are able to 
use  the  latter  two  pathways  (hydrogenotrophic  and  methylotrophic 
methanogenesis)  for  methane  formation,  while  only  a  few  use  the  acetoclastic 
pathways. Acetoclastic methanogenesis is performed by Methanosarcina at high 
and  by  Methanosaeta  at  low  acetate  concentrations.  Both  belong  to  the 
methanosarcinales  order.  Methanosaetaceae  is  the  only  known  family  whose 
members  can  only  catalyse  acetoclastic  methanogenesis.  In  methanogenic 
microorganisms, a large number of novel coenzymes involved in redox reactions 
or the transfer of C1 units have been identified. One of these is the coenzyme F420, 
which  is  responsible  for  the  autofluorescence  of  methanogenic  archaea  after 
excitation with 420 nm light. [2] (2016): Energie aus Biomasse, p. 1612 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
5.1 Biogas

Figure 4: Biogas production [5] 
 
Biogas is a gas mixture that consists of approximately half to a maximum of two 
thirds  methane (CH4) and  from  about  one  third  to  at  most  one  half  of  carbon 
dioxide (CO2) as well as various trace gases. 
Gas properties. For the combustion of biogas with 60 % methane 5.71 m3air/m3gas 
are required. The flame migration velocity of this mixture is 0.25 
 maximum. 
There  is  a  risk  of  explosion  if  an  explosive  biogas/air  mixture  and  an  ignition 
source are present. A methane/air mixture with a methane content of between 5 
and 15 % by volume is explosive; a CO2 content of for example 35 % narrows 
these  limits  to  5  to  12  %  by  volume.  There  is a particular risk of explosion in 
closed and poorly ventilated rooms into which the biogas can escape. Biogas can 
contain disturbing components (water, hydrogen sulphide, ammonia and carbon 
dioxide as well as various trace elements), the elimination of which can expand 
the possible uses. These individual gas components are briefly discussed below. 
In addition, the operation of the fermenter (e.g. charging, use of agitators) can 
lead to additional, but time-limited, fluctuations of the quantity and quality of gas. 
[2] (2016): Energie aus Biomasse, p. 1722 
 
5.1.1 Methane (CH4) 
Methane is a colourless and odourless gas whose density is lower than that of air. 
It is particularly flammable in mixtures with air and burns with a bluish, non-sooty 
flame.  The  calorific  value  is  35.89 [MJ/m3].  The  critical  temperature  for  the 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
liquefaction  of  methane  is  161.5  °C.  Above  this  temperature  there  is  no 
liquefaction even at very high pressures. This means that long-term storage in the 
smallest possible space (Liquefied Natural Gas) for later use is only possible at 
very low temperatures. [2] (2016): Energie aus Biomasse, p. 1723 
 
5.1.2 Carbon dioxide (CO2)  
Carbon  dioxide  is  an  inert  component  of  biogas.  The  solubility  of  CO2  in 
condensate and the resulting formation of carbonic acid lead to acidification and 
thus  to  corrosiveness  of  the  condensate.  However,  CO2  elimination  is  not 
absolutely  necessary  for  the  thermal  utilisation  of  the  gas.  However,  in  some 
applications (e.g. fuel for motor vehicles, feeding into the natural gas network) the 
carbon  dioxide  must  be  removed for quality assurance or volume reduction. [2] 
(2016): Energie aus Biomasse, p. 1723 
 
5.1.3 Water (H2O) 
Water is also a component of biogas. Depending on the temperature, different 
amounts of water can be contained in the biogas in the form of water vapour. The 
condensate produced during cooling can be converted into cause blockages in the 
pipes  and  promote  corrosion,  as  certain  biogas  components  dissolve  in  the 
condensate and  only  then  they  have  a  particularly  corrosive  effect. The  lines 
should  therefore  be  laid  with  a  gradient  in  the  direction  of  a  steam  trap.  The 
remaining water vapour does not affect many possible applications (e.g. use in a 
CHP  unit). The amount of condensate increases with increasing gas pressure. 
The  stronger  this  rises,  the  more  aggressive  the  condensates  are,  since  the 
solubility equilibria also shift to the corrosive products dissociated in water. [2] (2016): 
Energie aus Biomasse, p. 1723 
 
5.1.4 Hydrogen sulphide (H2S) 
Hydrogen sulphide is already effective at low contents in the biogas (up to 2 000 
ppm) corrosive to copper and copper compounds. For gas discharge only plastic 
or stainless steel pipes should therefore be used. For use of biogas containing 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
H2S as fuel, corrosion-resistant material (e.g. stainless steel) must also be used 
for the chimney system. In addition, the energetic use of a gas containing H2S for 
SOx-formation and thus for emissions whose release to the atmosphere is legally 
limited in many countries. At the same time, the accidental inhalation of biogas 
containing H2S is dangerous, since a content of 1,000 ppm H2S and more can be 
fatal for humans. [2] (2016): Energie aus Biomasse, p. 1724 
 
5.1.5 Nitrogen and nitrogen compounds 
Elementary nitrogen in biogas may have entered the plant in the form of air as a 
component of the starting material. In this case, the additional oxygen introduced 
is  immediately  converted  by  facultative  aerobic  organisms.  In  general,  the 
simultaneous  presence  of  nitrogen  and  oxygen  indicates  the  entry  of false air, 
which may have entered the gas chamber of the plant or the gas pipeline. On the 
other hand, nitrogen-containing compounds can occur in biogas, since nitrogen 
compounds released during bacterial degradation from proteins or nucleic acids 
are converted to ammonium in the reductive environment of a biogas plant. The 
ammonium  dissolved  in  the  liquid  phase  is  again  in  equilibrium  with  gaseous 
ammonia. In the pH value range between 7.0 and 7.6, in which biogas formation 
preferably  takes  place,  this  equilibrium  is  very  sensitive  to  changes  in  the  pH 
value. An increase of the pH value by a few tenths of a unit already significantly 
increases the ammonia content in the biogas. [2] (2016): Energie aus Biomasse, p. 1724 
 
5.1.6 Trace elements 
Depending  on  the  input  substrate,  higher  hydrocarbons,  chlorine  and  fluorine 
compounds, organic sulphur compounds or siloxanes may also be present in the 
biogas. 
 
6.1 Gas utilisation  
Biogas can be used energetically by a variety of different possibilities. The main 
variants are for the provision of heat, electricity and fuel. 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
6.1.1 Heat supply 
Over a  wide  range of composition, biogas can easily be used in most biogas-
compatible industrial combustion plants. In the case of existing oil burners, the 
burner must be converted to a two-material system. 
Also,  plants  originally  intended  for  other  fuels  (e.g.  natural  gas)  can  often  be 
adapted to biogas. Usually only the burner nozzles and/or the actual burner need 
to  be  modified.  If biogas  containing  H2S  is  also  used,  a  corrosion-resistant 
material must also be used for the chimney system (e.g. stainless steel). In this 
case, more corrosion-resistant cast iron boilers are preferable to non-ferrous metal 
boilers. The same applies analogously to gas condensing boilers. 
In  industrial  furnaces,  the  combustion  air  supply  can  be  controlled  using 
continuous monitoring of the biogas calorific value to ensure optimum combustion. 
In  practice,  however,  the  biogas  composition  fluctuates  only  slightly  if  the 
fermentation reactor is operated stably. The firing system is also usually regulated 
in such a way that safe operation is ensured even with fluctuating composition. 
 
6.1.2 Use in combustion engines 
Biogas can be used in stationary and mobile combustion engines and converted 
into  mechanical  energy.  The  most  commonly  used  spark ignition  engines  (gas 
Otto engines) are those in which the flammable air-gas mixture is ignited with one 
spark. In the case of compression-ignition engines (diesel engines), in addition to 
biogas, the use of an additional fuel with a low ignition temperature is required. 
Diesel gas engines are so-called dual fuel engines. The air-gas mixture is sucked 
in by the engine, compressed and ignited by injecting approx. 8 to 10 % diesel 
fuel.  Alternatively,  many  new  engines  can  also  use  biogenic  fuels  such  as 
vegetable oil or biodiesel as ignition oil. The gas mixture used in a gas engine 
must  be  anti-knock.  The  knock  resistance  of  a  gas  during  combustion  in  gas 
engines is indicated by the methane number, which is approximately comparable 
to  the  octane  number  for  petrol.  The  methane  number  is  the  percentage  by 
volume  of  methane  in  a  methane-hydrogen  mixture  which,  under  standard 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
conditions,  has  the  same  knocking  characteristics  in  a  test  engine  as  the  gas 
mixture to be tested. It is defined by the following two cornerstones. 
 
- Methane by definition has a methane number of 100 and is anti-knock. 
- Hydrogen by definition has a methane number of 0 and is knock resistant. 
 
6.1.3 Vehicle fuel 
Natural gas - and so methane - can also be used as a vehicle fuel in the form of 
CNG  (compressed  natural  gas).  Currently,  there  are  vehicles  available  on  the 
market that can run on CNG as standard, from cars to buses or trucks. For these 
vehicles to have an acceptable radius of action, the gas must be compressed to 
200 to 250 bar. 
Due  to  this  high  compression,  prior  treatment  of  the  biogas  is  absolutely 
necessary,  since  compression  of  the  gas  components that cannot be used for 
energy  purposes  (e.g.  carbon  dioxide),  for  example,  would  involve  a  generally 
unacceptable  amount  of economic effort. At the same time, further cleaning is 
necessary. 
Water  vapour  has  to  be  removed  as  well  as  hydrogen  sulphide.  If  the  biogas 
meets the natural gas specifications after such treatment, any CNG-compatible 
vehicle can also be operated with treated biogas without any problems. Such a 
treatment  of  the  biogas  to natural gas quality also has the advantage that the 
biomethane can be fed into the existing natural gas network. Since it is chemically 
identical to natural gas and can therefore be taken from any existing CNG filling 
station or refueled by the corresponding vehicles. 
 
6.1.4 Feeding into natural gas networks 
A flexible option for the use of biogas is the upgrading of biogas to natural gas 
quality with subsequent feeding into the existing natural gas network. This allows 
all natural gas applications with biogas or biomethane to be accessed (i.e. heat 
market,  power  generation,  mobility  sector,  material  use,  for  example  in  the 
chemical industry).  
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
 
6.1.5 Further possibilities 
 
Biogas  can  also  be  used  for  lighting,  cooking  and  cooling.  These  fields  of 
application  are  generally  used  in  micro-plants  (e.g.  in  households  in  India  or 
China).  Local  biogas  networks  can  also  be  set  up in  addition  to  generating 
electricity to supply heat and cooking gas. Particularly when used as cooking gas, 
however, it is important to note that biogas may contain higher levels of hydrogen 
sulphide,  which  are  hazardous  to  health.  For  this  reason,  the  gas  should  be 
desulphurised beforehand when used in a closed kitchen. 
 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
 
7.  BIBLIOGRAPHICAL AND DOCUMENTAL REFERENCES 
  
[1] Kaltschmitt, Martin / Hartmann, Hans / Hofbauer, Hermann (2009): Energie aus Biomasse 
[2] Kaltschmitt, Martin / Hartmann, Hans / Hofbauer, Hermann (2016): Energie aus Biomasse 
[3] Tippkötter, Nils (2016): Grundlagen der biochemischen Umwandlung   
[4] https://modernfarmer.com/2014/08/manure-usa/ 
[5] https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy 
[6] https://www.br.de/  
[7]https://www.werra-rundschau.de/lokales/wanfried/biogasanlage-bei-wanfried-soll-erweitert-
werden-10690880.html 
[8] https://www.heizsparer.de/energie/gas/biogas/was-ist-biogas 
 
Vigo, 29 of April 2019 
 
 
The Engineer international degree environmental engineering 
Alexej Vnukov 
 
 
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TECHNICAL REPORT ON ENERGY GENERATION FROM ANIMAL FARM WASTE 
APPENDIX /APPENDICES 
 
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