In this video, we'll be looking at biomass energy assessment. In this video, we'll be taking a look at biomass for electric power generation, including categories of biomass, energy from biomass, dry biomass resources, thermal power generation and its pros and cons, and wet biomass resources, anaerobic digestion for power. We'll look at some examples and pros and cons of wet biomass resources. Types of biomass useful for electric power include dry biomass waste. This is forest waste, manufacturing waste, woody manufacturing waste, agricultural waste, and municipal solid waste. Sources of wet biomass waste include livestock manure, such as shown to the right, food processing waste, sewage sludge, and municipal landfill waste again. Let's move on. Methods to convert biomass to electric power include fuel for geothermal plants. This is dry biomass, it's direct burning, we just use it in place of coal or natural gas. Biomass can be the sole fuel or we can co-fire where biomass is combined with typically coal to reduce the amount of coal needed in a particular power plant. Or we can engage in anaerobic digestion where we have liquid biomass, we let it ferment to produce methane, and this methane can then fuel gas turbine generators to generate electricity. Typically not always, this is done onsite where very large facilities can clean the gas and then put it into natural gas pipelines to serve a community. What are the types of dry biomass that are used for electricity generation? Well, first there's forestry waste and this is the energy density of about 18 kilowatt hours per kilogram. That's the embodied energy, not the electricity you get out after you process it and run it through a generator. This is the embodied energy in the waste. This waste can be forest slash, wood chips, sawdust, wood pellets from sawdust, or any other woody product that will burn. It can also be agricultural waste, same energy density, such as straw or stover. Stover is the leftovers from a harvest after you harvest corn or wheat or some other grain. Finally, there's municipal solid waste as shown to the right. It has a very low energy density of about 1.5 kilowatt hours per kilogram. This is for sorted municipal waste, where things that won't burn, such as metals or other things are already taken out, and all that's left is combustible material. It has a very low energy density. What are the pros and cons of using dry biomass for electricity generation? Well, first off, it's a byproduct of other processes, so we reduce waste and use waste rather than just throwing it away. It can mix with coal or use it alone reducing the amount of coal we need. It can reduce methane emissions and it diverts waste from landfills. Disadvantages are that most of dry biomass has low volumetric energy densities. It requires preprocessing in many cases, and acquiring it requires energy and equipment time. Oftentimes if we're using forest slash for instance, it has to be collected and transported to and then processed in order to use it in a power plant, so there are these energy equipment and transportation expenses that go along with dry biomass. There's often uncertain supply streams due to seasonality, weather, and distances traveled. Finally, there are combustion byproducts from dry biomass including ash, carbon dioxide, and other pollutants. It's not too similar to coal. That brings us to wet biomass feedstocks. These are used for anaerobic production of methane. It can be cattle manure from cattle hogs, chickens and turkeys. It can be food processing waste, vegetable waste, it can also be animal processing waste such as fats and other byproducts. We can use municipal biowaste sludge, basically sewage. We can't use woody biomass because cellulose will not digest easily, so it has to be material that they will ferment easily and create methane. The types of biomass used for anaerobic digestion and then used to generate electricity include animal manure, which has an embodied energy of about 200 kilowatt hours per tonne. Again, this is the energy embodied in the material. Landscape waste of about 130 kilowatt hours per tonne. Waste fruits and vegetables have 113 kilowatt hours per tonne. In municipal biowaste, again at about 200 kilowatt hours per tonne. On the right is a one megawatt biowaste methane digester in Australia. Here's an example for an anaerobic digester on a small dairy farm. You can see the pits on the right that hold the manure, and then you can see one of the pits covered with plastic to contain the methane. Let's suppose we have 100 dairy cows. These cows produce about 62 kilograms of manure per day per cow, which will translate to about 22.6 metric tons per year per cow. The energy out after we generate the electricity in turbine generator, we get to 54.2 megawatt hours of electricity per ton. This translates to about a 122.7 megawatt hours per year in electricity and $18,405 annual electricity savings. If we're paying $150 per megawatt hour for that electricity, and that's the global average. You can see that this reasonable amount of electricity can be generated even in a relatively small application like a dairy farm. What are the pros and cons of liquid biomass for power generation? Well, advantages include that it reduces and uses natural waste. Waste is a byproduct of raising livestock, it's going to exist one way or another so better that we can use it to generate electricity. It also reduces the odor of livestock farms. Reduces methane emissions. Methane is a powerful greenhouse gas, so burning it, if we're to generate electricity is positive. It does create CO_2 and water when it's burned, but CO_2 is a less potent greenhouse gas than is methane. It produces onsite electricity and it's burned in a gas turbine to produce electric power, which reduces grid power demand. Digestates, that's what's leftover after anaerobic digestion, it can be used for fertilizer and soil enhancement. Even what's leftover has as utility, doesn't have to be thrown away. Disadvantages include large upfront investments, impractical for small farms, because it may not be cost-effective. It requires constant monitoring. You can't just build it and walk away. You have to monitor it pretty closely to make sure it's working properly, and that you're getting the energy out that you expect. Requires substantial land area. Those are some disadvantages. In this video, we've been assessing biomass for electricity power generation. We've looked at the categories of biomass, we've looked at energy from biomass, we've looked at dry biomass resources and how they're used for thermal power generation, and we've looked at wet biomass resources and how they're used for anaerobic digestion to create methane for power. At the right is the world's largest anaerobic digestion plant , it's in Penkun, Germany and it's 20 megawatt hours in capacity, large plant. In the next video, we'll be taking a look at ocean energy. We'll see you there.
