11. Conversion of Organic Wastes to Biochar and Clean Energy- If bio-media are converted to “biochar”, a material, mostly carbon, like charcoal (plus other compounds, possibly of value) (C 6 H 10 O 5 ) n - + heat 6n C + 5n H 2 O __ biochar The biochar may be incorporated into soil and remains inert for an indefinite amount of time with very beneficial affects on soil productivity. Thus, CO 2 is removed from the atmosphere and converted to an inert solid which does not return to the atmosphere in forseeable times.
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13. The Energy Balance - Some external energy is required to produce heat for start-up. After that, the heat for the process can be provided by burning producer gas (H 2 + CO) that can be generated from a portion of the biomedia. This produces some CO 2 , but the amount is less than the amount of the CO 2 that gets removed from the atmosphere. If desired, some of this producer gas can be used to supply energy for other use.
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15. Is there enough biomass? The US Department of Energy (DOE) and the US Department of Agriculture (USDA) estimated that by 2030, the US could sustainably produce 1.3 billion metric tons of dry biomass/year consisting of cellulosic biomass. This amount of biomass has the energy content of 3.8 billion BOE (barrels of oil energy equivalent), and the US consumes 7 billion barrels of oil/year. In the US it has been estimated that the cost of cellulosic biomass is $5 to $15/BOE, which is significantly below the current cost of crude oil of $56/bbl (average cost in 2005).
So why does more CO2 in the atmosphere to global warming? The atmosphere is transparent for much of the light that we receive from the sun. (That’s why we can see the sun.) The earth absorbs this radiation, and send out it’s own radiation. Since earth is colder than the sun, it radiates light at a different wavelength. This radiation is infra-red, and humans cannot see this. Infra-red radiation is absorbed by CO2 in the atmosphere and a fraction does not make it back to space. The absorbed radiation heats the atmosphere. This is called the greenhouse effect, which is a perfectly natural phenomena. If the CO2 content in the atmosphere increases, the greenhouse effect becomes stronger, and this leads to an additional heating of the atmosphere. This is thought to be a contributor to current global warming. In the next slide I show how much the CO2 concentration has increased.
A warming climate causes sea level rise because (I) ice on continents melts (Greenland, Antarctica), and (ii) sea water expands when it warms up. Sea level rise predicted by IPCC report from 2000-2100 (Fig. TS.27) is about 0.4 m. This means that the dark-red areas will be under water. This is, for Florida a thin strip along the coast, but this is where the people live! What is not taken into account here is that warmer sea water leads to stronger and more frequent hurricanes.
Removal of CO2 from a gaseous state is rather difficult task. It may require significant energy to collect and change the state from a gas to a liquid or solid. The practice has not been perfected to the point that it could be classed as a commercial possibility. Natural removal of CO2 from the air occurs normally in plants during photosynthesis. There are two major types of plants when one considers their ability to collect and hold carbon. They are the plants with herbaceous or annual above ground stems, and those that have perennial long lasting above ground structures. When one considers the requirements for annual collection of plant parts from those that are not long lived, there is a necessary parallel with agricultural techniques. This means that the land that can be used for annual energy production must be relatively flat and have unfettered access during the collection period. Any plant energy material that is not collected during this short window of time is lost. The energy used for this annual collection may be a significant part of the energy produced by the crop plants. If there is any undesirable competition from weeds, herbicides may need to be applied periodically. Deciding what process to use for conversion of one form of energy to another is very important.
This assumes that none of the O2 is consumed as CO, all of the carbon remains in the structural envelope of the plant material. I have heard that it is more likely that much of the O2 is used by oxidation of the carbon and that it is difficult to get more than 30% by weight of the material to be converted to bio-char.
Using organic wastes as a source of co-products, clean energy, a source of bio-char to detoxify or remove pollution from farm and neighborhood waste streams, and a long lasting soil amendment provides a win-win-win situation at a time when we all are aware that things have to change. This is a good approach.