
Biomass does not contribute very much to our electricity supply in the U.S. at only about 2%. However, agricultural and timber wastes are used to generate steam and heat for industries. As a source of energy, biomass offers a host of positive qualities; It is fairly plentiful, relatively inexpensive to use, and helps reduce agricultural waste problems. Most importantly, however, biomass is a renewable energy source, thanks to the carbon cycle and solar energy.
Solar energy is used by plants to generate energy in chemical form (glucose).
6CO2+6H2O + solar energy → C6H12O6+6O2
When plants die, this process simply works in reverse.
C6H12O6+6O2 → 6CO2+6H2O + energy
Walking through almost any forest is the best way to witness the decaying process in action. The ground is generally strewn with dead and decaying leaves, limbs, branches, and sometimes entire trees. If they did not decay, we would be faced with a serious dead-tree problem in our forests. Then, imagine the scope of this problem over millions of years. This helps illustrate the nature and value of the carbon cycle.
However, in Pennsylvania, about 320 million years ago (and even today), the forests did not decay. Instead, the trees fell into swamps (bogs) and were protected from the decay process. Eventually, these trees formed coal, and in the oceans, plankton and algae went through similar processes. There, the stored solar energy eventually formed oil (protection from oxygen at the bottom of the ocean, with sediment burial). Now as we use the fossil fuels (combustion), we release CO2 back into the atmosphere.
So, instead of allowing the biomass to rot naturally as explained above, we can harvest it and combust the biomass for home heating, industrial use, or electricity generation.
Let Dr. Mathews tell you the full story in the (:46) video below:
[Video opens with Dr. Mathews standing in front of a display of biomasses.] Dr. Mathews: Biomass, if it is an agricultural waste or even a plant deliberately grown for use in biomass, then we have an excellent source of free energy. We just have to harvest it; it is free solar energy being stored in the plant. The plant grows, and we can come and harvest it. And one of the other nice things about it is it's CO2 neutral. Even though when we combust it we produce carbon dioxide, when you grow the tree again, or we grow the plant again, or even livestock, that CO2 is stored back in that animal or that plant. And, really, there are 4 classifications behind me which we are going to look at. There are the grasses, there are the woods, there are the proteins, and there are the fats and lards. We are going to have a look at each one of those. [Video ends.]
Now that you've been introduced to the idea, you're ready for the details.
Weeds and Grasses (:32) Video
[Video opens with the caption: Biomass - Weeds and Grasses.] Dr. Mathews: This is switchgrass. [Dr. Mathews holds up a small bottle.] Dr. Mathews: Things like this are wonderful. They are more or fewer weeds but they are going to grow very quickly. And that is also desirable. You wouldn't want to have to plant an oak tree and wait 30 years before you could harvest it. But things like switchgrass are harvestable within 6 months. So you can get a couple of crops a year. And so anything like this that will grow quickly is possibly something that we use. [Video ends]
Wood Products (1:00) Video
[Video opens with a caption: Biomass - Wood Products.] Dr. Mathews: Wood again is another one. [Dr. Mathews picks up a small bottle.] Dr. Mathews: This is a tree of heaven. It is again a very quickly growing small tree, but like a bush. It is somewhat of a problematic plant. It grows on the sides of the roads and some parts of the south they have a major weed status. But again, quickly growing, we can crush it up and fire it either by itself or we can add this, to say, a pulverized coal facility and burn perhaps up to 10 percent the material being this biomass, this wood. Doesn't have as much energy content as coal because it is not concentrated, it has a lot of oxygen. But it is still very useful. But remember one of the main advantages of the biomass is that it is CO2 neutral. And so you plant the seed, you grow the seed, you cut it down, and you burn it. Provided you go and replant the seed, you are going to keep that CO2 locked away. [Video ends showing 4 bottles of this woody biomass.]
Oils, Grease, Animal Fat & Lard (2:10) Video
[Video opens with a caption saying: Biomass - Oil, Grease, Animal Fat, and Lard.] Dr. Mathews: McDonald's grease, something else that you can use. It is a waste product; it was already been used to fry french fries or various other components in it. You are not going to use it anymore to fry food in, but it still has calorific value. Remember, the difference between vegetable oils for cooking and oils for combustion is very little. Is just about length, but we can still burn these things. [The camera pans past several bottles of oil.] Dr. Mathews: This is choice white grease, we have coconut, you can crush coconuts and extract their oil. That again is something you can use for cooking purposes and once you have fried things in it you can go ahead and use it for other things - combustion. [Dr. Mathews holds up a small bottle.] This is poultry fat. We kill an amazing number of chickens every year. Not much is wasted. This fat is something else that you can think of as a waste product; something else you would need to dispose of, or you can use it as a fuel. [Dr. Mathews puts that bottle down and picks up another one.] Dr. Mathews: Ah, pork. There is a saying that you use everything from the pig, including the squeal. [Sound of a pig plays in the background.] Dr. Mathews: Well that is pretty much true. In the old days you could use the pork fat to make candle. You could use the liquid fuel for lighting prior to kerosene. Now pork oils have a value. Lard has a value. But if, for say, we were looking at having lower cholesterol, and going with a non-fatty, non-high cholesterol fat, then the pork market might go away for lard. In which case it would have to be disposed of. It is a beautiful boiler fuel. We heat it up to melt it and turn it into a liquid, and inject it into our boilers. It has very low sulfur content. And so pollution really isn’t an issue and it burns very nicely. It isn't quite as nice as, or have as much energy content as fuel oil, but you just have to burn a little bit more. Again, if it ever came to a problem that we had to dispose of it, combustion is one way we could dispose of it very cleanly and get a useful product at the same time. [Video ends showing several bottles of the fats, greases, and lards.]
Animal Proteins (1:15) Video
[Video opens with a caption saying: Biomass - Animal By-Products.] Dr. Mathews: Here are some other rather strange biomasses. [Dr. Mathews picks up 2 containers.] Dr. Mathews: This is feather meal. Again the chickens, we have no use for the feathers. If you grind them and extract them down this can be fed to other animals. Although with the Bovine Spongiform Encephalopathy scare, mad cow disease to you and I, we have gone away from feeding some of these other animal products to animals. And because I ate beef in England for a couple of years before coming here, I can't even give blood anymore because they are frightened that I have mad cow disease. [A caption reads: ...mad professor maybe...] Dr. Mathews: They might be right. Again, pork meal. It is essentially animal proteins that we can extract. There is still a lot of energy in these so we can go ahead and burn them. Manure would be something else we could use. And we have certainly looked into chicken litter (which is really chicken poop) and other manure. Obviously, in Africa they use certain manure for biomass applications and so we can certainly do the same things here if we had the desire to. [Video ends]
Biomass does not contribute as much to electricity as it does to industrial heat generation where industries that produce a combustible biomass waste product and require heat use the waste. Paper mills are a good example of this. The whole tree does not go into the paper manufacturing; bark, leaves, and small branches are combusted to generate the heat to drive off the water from the water/cellulose slurry.
When we discussed lighting, sperm whale oil was the fuel of choice for some of our ancestors. Candles would have also been produced from animal fat (pig fat worked well), and if the need arose, we could combust fats (currently pig fat is too valuable to burn; it is used in frying potato chips.)
Advantages of Biomass
- It is renewable
- There is no net carbon dioxide released into the atmosphere (greenhouse gas)
- Stimulate American jobs in agricultural areas
- Can be co-fired with coal to reduce the greenhouse gas emissions
Disadvantages of Biomass
- Biomass requires large plots of land, increased fertilizer (produced mostly from natural gas!), and more insecticide use (perhaps)
- In a world where starvation occurs, using food as fuel (such as corn) is an abuse
- Biomass is heavy (high water content), so transportation costs can be high, influencing the economic feasibility of biomass use
- Energy demand is constant, but only a percentage of biomass crops can yield harvests year-round, requiring the need for storage. Harvests will also be weather and disease dependent
The bottom line: Expect to see biomass being integrated into existing utilities that burn other fuels, rather than the creation of large biomass-only utilities. It is already a requirement in many states that renewable energy contributes to electricity generation. (This is known as the renewable portfolio standards.) In Pennsylvania, this can include photovoltaic energy, solar thermal energy, wind, low-impact hydro, geothermal, biomass, biologically-derived methane gas, coal-mine methane, coal-waste (those culm/gob piles), and from using fuel cells.