BIOGAS AND FUEL CELLS Flashcards
How much waste per year
250kg of food waste per year 1/3 of food purchased
This food waste could be divrted from the landfill to an AD plant
Biomass for anaerobic digestion
- energy crops
- livestock manure
- food waste
- sewage sludge
- glycerol
STEPS OF AD
biomass in a 40 degreee pressurised container, biogas comes off along with byproducts.
- Anaerobic digestion of biodegradable material to make soluble organics
- Soluble organics hydrolysed to make acetic acid and propironic acid butyric acid and long chain VFA’s.
- Acidogenesis of proprionic acid, butyric acid Long chain VFA’s to acetic acid and H
+ CO2 - Acetogenesis of acetic acid into CH4 + CO2
AD benefits
reduces GHG emissions by using the methane
beneficial use of biofertiliser displacing mineral fertiliser
reduces transport waster
produces renewable energy
on farm AD PLANT
-planning straightforward
environmental permitting supposedly light touch
- scale typically from £500k to £2.5m
- annual income typically from £120k to £1.2 mill
-revenue costs depend on feedstock
oil got too high in price for farmers
sell gas to cattle waste back to grid
and they can use waste heat around the farm
£14 million to make tho
AD process
biogas 60% CH4 and 40% CO2
then goes to boiler
85% gos to heat
15% lost
Biogas CombinedHeatPower process
biogas -> CHP:
- electricity 40%
- heat 45 %
- losses 15%
Biogas upgrade process
biogass –> upgrade to biomethane by removing CO2 H2S H2O
A biogas upgrader is a facility that is used to concentrate the methane in biogas to natural gas standards. The system removes carbon dioxide, hydrogen sulphide,[1] water and contaminants from the biogas. One technique for doing this uses amine gas treating. This purified biogas is also called biomethane. It can be used interchangeably with natural gas.
Raw biogas produced from digestion is roughly 60% methane and 29% CO2 with trace elements of H2S; it is not high quality enough to be used as fuel gas for machinery. The corrosive nature of H2S alone is enough to destroy the internals of a plant.
cOMMERCIAL ad PLANT
- processing domestic food waste commercial waste, possibly with farm materials
- Land required for beneficial use of digestive
- planning a challenging and lengthy process
- environmental permitting very stringent scale typically from 1.0MW to. 2.0MW
- Capital cost typically from £5.0m to £10.0m
Annual income typically from £2.0 to £4.0m
High revenue costs
Fertiliser
once the biogas had been taken off minerals are still left in the sludge and is basically fertiliser
Energy required to stir tank
but if too much energy putting in then you don’t get as much revenue
HYDROGEN FUEL CELL
A fuel cell is an electrochemical cell that converts the potential energy from a fuel into electricity through an electrochemical reaction of hydrogen fuel with oxygen or another oxidizing agent.[1] Fuel cells are different from batteries in requiring a continuous source of fuel and oxygen (usually from air) to sustain the chemical reaction, whereas in a battery the chemical energy comes from chemicals already present in the battery. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.
Waste Water Treatment Plants
- Anaerobic Digestion generates high quality fuel (>50 vol% methane)
- Easily accessible and collection costs prepaid
- Methane is 23 times more powerful GHG than CO2
- WWTP gas fuel cells systems would only supply a small fraction of our energy needs but would stop a significant amount of GHG emissions
Challenges to using biogas
for a fuel cell
Hydrogen sulfide removal Initial concentration 3000-5000 ppm Need concentration < 25 ppb Moisture removal Need dry gas Dewpoint < -30 degrees Celsius Carbon dioxide removal Need concentration < 5 ppm
Technical Feasibility of Biogas Fuelled Fuel Cells
Numerous demonstrations have already proven the technical feasibility
- phosphoric acid fuel cell (PAFC) on landfill gas
- PAFC on waste water treatment gas (WWTG)
molten carbonate fuel cell (MCFC) on WWTG
- solid oxide fuel cell (SOFC) on AD gas
Most technical problems have been overcome
wide array of contaminants to clean up
high degree of variability in fuel quality
