Ch 9: Energy from Biomass Flashcards
What is the definition of biomass?
Biomass is a general term for material derived from plants or animal manure.
What are examples of categorised types of biomass?
- Organic materials
- Wood
- Agricultural crops
- Agricultural and municipal waste
What are the main plant crops that are grown commercially to produce biomass?
- Willow
- Poplar
- Elephant grass (miscanthus)
- Maize
- Sugar cane
What are the advantage of using biomass as a fuel source?
- Renewable (provided the wood is replaced when cut down)
- Lower carbon emissions (during the growth stage of biomass, cardon is absorbed from the atmosphere which can add to carbon emissions as well as cutting down and transportation of the biomass)
What are the disadvantages of using biomass as a fuel source?
- Land usage (transition of farmers from production of food crops to biomass crops can cause a drop in availability of food crops)
- Lower efficiency (than fossil fuels)
- Costs (more expensive to use than coal)
What accounts for the majority of energy obtained from biomass?
Combustion accounts for 90% of all energy obtained from biomass.
What are the advantages of cutting wood into wood chips?
- Transport (more wood can be transported)
- Accelerated drying (larger surface area per unit volume so dry faster)
- Automatic feed boilers (removes need for constant refuelling by the owner)
What is the first property of different types of woodchip?
Moisture content - the amount of what that is present in the biomass expressed as a percentage.
Lower moisture content allows the wood to burn faster as higher moisture content has to evaporate the water before burning.
What is the second property of different types of woodchip?
Energy density - the quantity of energy per unit mass (typically per tonne).
Moisture content of the wood can affect the energy density as a lower moisture content produces more energy per tonne of wood chip.
What is the third property of different types of woodchip?
Particle size - Smaller boilers require smaller more uniform wood chips while larger boilers can be supplied with larger less uniform wood chips.
What is the fourth property of different types of woodchip?
Porosity - a measure of the quantity of voids existing in the wood compared to its overall volume.
High porosity wood ships have larger voids where water can infiltrate when the tree is growing.
What is the process of gasification?
Char is gasified by reacting it at extremely high temperature and injecting controlled amounts of steam and or oxygen. A mixture of carbon monoxide, carbon dioxide and hydrogen are produced, which together are referred to as synthesis gas or more commonly syngas.
What is syngas?
A mixture of carbon monoxide, carbon dioxide and hydrogen. it can be produced via gasification of char. this syngas has approximately half the energy density of natural gas.
What are the principle uses of syngas?
- Used in the production of ammonia.
2.Used in the production of methanol.
3.Used as an intermediate in producing synthetic petroleum. - Can be used as a lubricant in chemical processes.
5.Syngas is combustible and is often used as a fuel of internal combustion engines.
What is aerobic digestion?
Digestion in which oxygen is present.
What is anaerobic digestion?
Digestion in which oxygen is not present. Anaerobic digestion is a biological process that results in the breakdown of organic matter by naturally occurring bacteria in an environment that has an absence of oxygen.
What is biogas?
When biomass is broken down through AD a gas called biogas is produced. This biogas consists of methane and carbon dioxide (as well as trace gases such as hydrogen sulfide). This biogas can then be captured and used to produce heat, fuel internal combustion engines and for electricity production.
What are the advantages of using commercial anaerobic digesters?
- Waste is treated and reduces greenhouse gas emissions including the potent methane.
- AD tanks can be located within close proximity to the waste source. This can reduce transportation requirements in getting the waste to the AD tanks. This can also help in creating jobs locally.
3.Biogas can be produced from AD which can be used for many purposes such as heating, internal combustion engines and electricity production.
What are the disadvantages of using commercial anaerobic digesters?
- Requires a steady supply of consistent feedstock.
2.The quality and relative concentrations of the biogas produced will vary. This may then require further gas cleaning if the gas is to be used by internal combustion engines.
3.The process is slow in colder temperature environments. This can be counteracted by using some (or all) of the biogas available to heat the slurry, to a sufficiently high temperature. This results in the maximum throughput of the system. In colder weather there is no net output of biogas from the plant. This means that no profit is generated. However, the owner of the facility does save money as they do not have to transport the waste off site or pay any waste disposal fees.
