B3 - Biofuels Flashcards
What is fermentation?
When bacteria or yeast break down substances like sugar using anaerobic respiration
How is ethanol made as a biofuel?
Yeast makes ethanol (along with carbon dioxide and energy) by breaking down glucose by anaerobic respiration
How is the glucose for the fermentation obtained?
Sugar cane juices can be used and glucose can also be derived from maize starch by the action of carbohydrase
What is done to the ethanol after being formed?
It is distilled to separate it from the yeast and remaining glucose before it’s used
What is gasohol?
A mixture of ethanol and petrol that can be used by adapted cars
How is biogas made?
Anaerobic fermentation of waste materials
What is the composition of biogas?
70% methane and 30% carbon dioxide
What are the 2 specific ways that biogas is made?
Bacteria can ferment plant and animal waste containing carbohydrates
Sludge waste from places like sewage works and sugar factories are used to make biogas on a large scale
What is a digester / generator?
The simple fermenter that makes biogas
What about the conditions of a biogas generator has to stay the same and why?
Must be kept at a constant temperature to keep the bacteria respiring
What are the 2 types of biogas generators?
Batch generators
Continuous generators
What is the main disadvantage of biogas?
It needs too high a pressure so it can’t be stored as a liquid so it has to be used straight away
What are the by-products of biogas generation used for?
Used to fertilise crops and gardens
What is a batch generator?
A generator that makes biogas in small batches
They are manually loaded with waste which is left to digest and the by-products are cleared away at the end of each session
What is a continuous generator?
They make biogas all the time
Waste is continuously fed in and biogas is produced at a steady rate
Describe the biogas generator
There is an inlet for waste material
The inside of the generator is has gas at the top and waste at the bottom of the container
There is an outlet at the top for the biogas and an outlet at the bottom for the by-products
What are the 4 factors to consider when designing a generator? (Explain each factor)
Cost (continuous generators are more expensive because everything has to be mechanically pumped in and removed
Convenience (batch generators are less convenient because they always have to be filled, emptied and cleaned manually)
Efficiency (the gas must be produced at 35% to get the fastest gas production)
Position (the waste will smell during delivery meaning the generator must be away from homes and close to the waste source)
What are 6 main advantages of biofuels?
They are carbon neutral because the carbon dioxide released into the atmosphere was taken in by plants which lived recently
Not much sulphur dioxide or nitrogen oxide is produced so there is less acid rain
Methane is given off from untreated waste, this is stopped by making it into biofuels
The raw material is cheap and available
The digested material is a better fertiliser than the undigested material
Biogas generators act as waste disposal systems
What is the main way that biofuels are made?
Fermentation
