Renewable Energy

Classification on origin

There are four main categories:

1. Woody plants
2. Herbaceous plants
3. Aquatic plants are plants that grow underwater. Biomass is produced in freshwater and marine environment. Most current aquatic plant biomasses include:
   • Seed plants: actively propagating due to acceleration of eutrophication in various places of low latitudes (Africa), used in anaerobic digestion, used usually in fertilizer and soil amendment agent
   • Seaweeds: used for dried feed, human food, and fertilizer
   • Micro-algae: contain high percentages of protein, biomass is prepared by artificial cultivation tank, used for health care supplements and feed for aquatic organism
4. Wastes: it can have different origins such as agricultural residues, wooden residuals, animal waste, sewage sludge, municipal solid waste, food processing waste

Biomass fuels are characterized by what is called the PROXIMATE AND ULTIMATE ANALYSIS.

The PROXIMATE analysis gives:

1. Moisture content
2. Volatile content
3. The ash in the sample
4. The high heating value based on the complete combustion of the sample

The UTILMATE analyses gives the composition of the biomass in % of carbon, hydrogen, and oxygen, as well as sulphur and nitrogen.

Moisture content: 7

Heating value:

It is the amount of heat released during the combustion of a specified amount of it. Heating values are commonly determined by use of a bomb calorimeter (works in adiabatic condition). It is measured in units of energy per unit of the substance (kJ/kg). It can be:

• Higher (HHV) = can be obtained when the water at the end of the combustion is in the liquid state
• Lower (LHV) = can be obtained when the water at the end of the combustion is in the gaseous state

Available heat Q = Q (1-w) - 1000w - flue heat adsorption - ash heat adsorption

Classification on supply chains:

Starting from land, we can follow four flows:

1. The primary that will go directly to the processing plant in which it can be transformed into power
2. Harvest

residuals flow can be considered secondary flow and even in this case it entered in the processing plant and ended in the same way as before- Waste flow- Other uses flow 8 Biomass conversion technologies Pre-processing Conversion to heat and/or power 9 Chemical routes to biodiesel from oils Biological routes to bioethanol from carbohydrates Thermochemical routes to fuel and power–PART 3 A FOCUS ON PROXIMATE AND ULTIMATE ANALYSES Ex of food processing waste 1. First thing that can be performed is the evaluation of total solid TSo Weight of raw sample 68.51 g Weight of dried sample 4.8 g Calculate the moisture content referred to raw sample and dried sample– o TS = 1 MC of raw sample 2. Second thing is the evaluation of volatile solids VS content (important parameter for evaluating biomass for anaerobic digestion) Weight of remaining residue (ashes) 0.83 g 3. Ultimate analysis in order to define the element composition Performed a lot of analysis for being representative Need to be

Use a elemental analysers in order to evaluate the composition of the gas coming out from the sample. Each peak on the graph represents an element.

Oxygen is obtained by subtraction because it is used for combustion, so when I find the other elements, oxygen is easy to find.

Heating value:

For the estimation, we can use a bomb calorimeter. It is a closed device filled by tap-water to maintain the temperature constant during the experiment. There is a stirrer that keeps in movement all the content. Then we have a sealed bomb, inside of it there is a sample older and the ignition wires that bring electricity inside the chamber. Furthermore, there is a thermometer that is used to record the value.

Dulong's formula.

Another value to evaluate the heating value is the EX verify the claim of sugar producers that one teaspoon of sugar (4.8 g) contains only 19 kcal.

We know:

• Mass = 1.010 g
• Chemical composition of sugar
• T1 = initial temperature = 24.92 C
• T2 = final temperature = 28.33 C

Heat capacity of the calorimeter assembly = 4.90 kJ/C

Evaluating HV with bomb calorimeter

If we use Dulong's formula the result will be different. Final result is quite higher (40.9 kcal)

PART 4 ANAEROBIC DIGESTION

Anaerobic digestion (AD) is a natural process of bacterial fermentation that operates in an oxygen-free environment and results in a biogas containing mostly methane and carbon dioxide. AD is also the principal decomposition process occurring in landfills.

Field of application

• Sludge line
• Wastewater treatment facilities for sludge degradation and stabilization and are used in engineered anaerobic digester to treat high strength industrial and food processing wastewater prior to discharge
• In animal feeding operation and dairies to mitigate some of the impacts of manure and for energy production
• Municipal solid waste to reduce the amount of material being landfilled, for recovery energy, to reduce CO2 emissions and to stabilize organic

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Material Stage of the overall process

1. Starting with pre-treatment, perform before the digestion process in order to have properly biomass and allow the digestion during fermentation phase. The aim is to make the carbon available to the organism that carry out the AD for a faster process
2. Digestion phase
3. Post treatment related with the transformation of digested substances in a fertilizer for landscaping use
4. Updating relate to two different scenario: one to prepare the combustion phase in order to produce energy and one related to biogas in order to separate carbon dioxide from methane and upgrade biogas for producing fuel

Phase of digestion process

It is an accurate balanced ecological system. It is composed by several phases:

1. Hydrolysis = conversion of non-soluble biopolymers to soluble organic compounds
2. Acidogenesis (fermentation) = conversion of soluble organic compounds to volatile fatty acids and CO2
3. Acetogenesis = conversion of volatile fatty acids to acetate and H2

Methanogenesis

Methanogenesis is the conversion of acetate and CO2 plus H2 to CH4 gas. It requires wet substances at the beginning of the process.

Hydrogen partial pressure (13NB) needs to be maintained within a precise range. Hydrogen is continuously created and needs to be removed for the methanogenesis phase to be balanced.

Factors affecting the process:

• Total solid content: different types of processes depending on the wetness, such as wet, semi-wet, and dry processes.
• Temperature: thermophilic bacteria work best at 45-60°C, mesophilic bacteria work at 25-45°C, and psychrophilic bacteria work below 25°C.
• Retention time: how long the biomass remains in the digester.
• pH and alkalinity: used to evaluate problems.
• Carbon to nitrogen ratio: the optimum ratio is between 20-30. A decrease can cause low efficiency or low production.
• Mixing.
• Organic loading rate: the quantity of biomass that is put into the reactor.
• Volatile solids.

Methods

If I want to estimate if a certain amount of biomass is good...

Per la valutazione della produttività del biogas posso utilizzare diversi metodi: - Valutazione preliminare per comprendere quanto substrato può produrre. Un parametro è il COD (Chemical Oxygen Demand) o la valutazione del contenuto di solidi volatili. La valutazione del COD richiede poca materia organica, ma per la valutazione dei solidi volatili l'analisi sarà più rappresentativa. - L'equazione di Busweel stima la quantità di biogas prodotto e la qualità di questo biogas. Richiede un composto organico completamente biodegradabile per poter stimare un valore teorico (sovrastima). Panoramica schematica dei sistemi di digestione: - Se il contenuto di solidi totali nel substrato è inferiore al 10%, mi trovo in una situazione di fermentazione umida. - Se il contenuto di solidi totali è superiore al 20%, mi trovo in una situazione di fermentazione secca. Sistemi di fermentazione umida: Possono essere chiamati anche reattori a serbatoio a mescolamento continuo (CSTR) perché la miscelazione interna è continua e avviene sempre. Funzionano con un contenuto di solidi totali compreso tra il 2% e il 10%. Le tecnologie utilizzate sono: - Ricircolo del biogas per muovere il fango e mantenerlo continuamente mescolato all'interno.Mechanical stirred inside the reactor- Take biogas and let inflow at the bottom so this can moved the sludge- Low stirrer placed just below the surface of the reactor so it moves the upper part of the reactorin order to move the sludge homogeneously CONVENTIONAL ADSystem present several stratification, it has an intermittent feed, it has atemperature between 30/35, HRT is based on liquid input and it is 30/60days and the organic loading rate is fixed from 500/1600 kg/m3 day.Old type of system HIGH RATE AD The system is homogeneous due to mixing, ithas a continuous or intermittent feed, it has atemperature between 30/35, the HRT is based on the liquid input is 15 days orless and the organic loading rate is fixed at 1600/8000 kg/m3 day. Moreeffective and have high quality of biogas. Dry fermentation systemMore difficult to manage. Substrate comes in the reactor in direct contact with microorganism.Mixing homogenously make the time permanent in the reactor lower. Three different design: 1.DRANCO high solids reactor that allow ORL of 15 kgVSS/m3d. It has a single stage, it works under thermophilic range and has SRT equal to 15 day. The digester is feed from above. Shape is similar to a silos. At he beginning it has a mixing and digestate recirculation pump and also steam to heat the feed in order to maintain the temperature optimal.

1. KOMPOGAS the system is prefabricated in two size, used for municipal waste, need careful control of moisture content between 72/77%, it has HRT of 15/20 days and it used to manage the biogas in the prefabricated silos rectangular reactor. Plug flow for mixing, inside there is a stirrer that moves very slow and moves from one side to the other of the reactor
2. VALORGA high solid load, it has continuous single stage modified plug flow reactor, works in mesophilic or thermophilic condition and it has SRT equal to 18/23 days.

Single stave VS multi stage Splitting and separately stage optimizing hydrolysis/acetogenesis and methanogenesis.

could:

• Enhance the overall reaction rate
• Maximize biogas yields
• Make the process easier to control both in meso and thermophilic conditions

Mesophilic VS thermophilic process

If we work under 30/35 C HRT is higher and after 30 days my biogas production is similar to the production in thermophilic condition. In thermophilic process work with low HRT and I can have smaller reactor or I can process higher quantity of biomass in the same period.

Role of the nitrogen → Important parameter is carbon to nitrogen ratio