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About 70% of the electrical power currently produced in Alabama is produced by burning coal. Some is produced from natural gas, but most of the rest is derived from hydro and nuclear sources, and this is fairly representative of other Southeastern states.
Most of the coal fired power plants in Alabama are old, and involve pulverizing the coal into a powder and blowing it into the furnace of a boiler where it is used to produce steam. The steam is then used to drive a steam turbine that generates electricity. This process is about 30% efficient: in other words, only 30% of the energy contained in the coal is converted to electricity. The rest is lost, mainly as heat.
Electrical power can also be produced by using natural gas to drive a gas turbine which generates electricity. This technology is cleaner than combustion of coal, and more efficient, and has been the process of choice for many of the newer power plants. However, the recent increase in the price of natural gas has substantially increased production costs of this approach.
Combustion of coal results in harmful emissions, including sulfur dioxide, nitrogen oxides and mercury. These emissions can be reduced by using “scrubbers,” but this technology is expensive. As a result, there is considerable interest in renewable sources of electrical power. So what are our options?
Forms of Renewable Power
Renewable power is electricity that can be produced without depleting a finite resource of energy, such as coal or natural gas. The five forms of renewable power are hydro, wind, geothermal, solar and biomass. Besides being renewable, these sources of energy are considered to be clean, mainly because they do not add to greenhouse gases and increase the risk of global warming, as do fossil fuels. However, each has its own set of problems.
Hydro-electric power is generated by building dams on rivers and allowing water to drive turbines that generate electrical power. While rivers are abundant in Alabama and the rest of the Southeast, there are actually very few remaining suitable sites to build new dams. Furthermore, the public has become very sensitive about the environmental impact of building dams. These are the two main reasons for lack of development of hydro power in the Southeast over the last several decades.
Since there is no geothermal activity in the Southeast, this is not an option for Alabama. Intuitively, wind and solar power might sound very appealing, but these options also have limitations. Wind power is generated by windmills that drive electrical turbines. Of course, most of the Southeast does not receive the regular wind needed to make this technology viable. Furthermore, even where the wind does blow on a regular basis, it does not blow continuously. Therefore, production of wind power is intermittent.
Similarly, solar power is produced during the day, but obviously not at night, and it is substantially reduced in cloudy weather. It is also still relatively expensive, and difficult to produce on a large scale. At this point, therefore, solar power has very limited potential to meet a major portion of the electrical power demand in Alabama. Clearly, this leaves only biomass power, or “biopower” as a significant option.
Biopower
Biopower is electricity produced from biomass. As with burning coal, electricity can be produced by simply burning biomass in a boiler that produces steam which drives a steam turbine. In fact, a considerable amount of biopower is already produced by this method, mainly at pulp mills. Even though the process is relatively inefficient, it pays pulp mills to do this because they are using a byproduct (mainly bark) that is low cost and that would need to be otherwise disposed of, and they are using the power produced internally, thus offsetting the retail price of electricity (typically about 5-6 cents/kilowatt hour).
Sugar mills in Florida and Louisiana are in a similar position. They use a considerable amount of electricity and can generate much of this by burning the bagasse, which is the fibrous residue that remains after extraction of the sucrose. Sawmills are another sector of private industry that can use biomass effectively because they have the biomass fuel on site, the need for heat in their lumber drying kilns, and expensive natural gas as the competitor. However, if electricity produced from biomass is sold to the grid, the price paid is typically no more than 2.5 cents/kilowatt hour, and this is not economically viable.
Biopower can also be produced by co-firing biomass with coal in existing coal fired power plants. This involves delivering biomass in a mixture with coal, or separately into the boiler, and requires some retrofitting of the plant. The Southern Company and Alabama Power have demonstrated this technology at their coal fired plant in Gadsden, and continue to produce a small amount of green power at this location for their customers who want it. It is possible to co-fire probably about 10% by weight of biomass with coal. This is because of the low bulk density of biomass compared to coal, which means that 10% by weight is about 50% by volume.
Here’s how the Alabama Renewable Energy program works. The Renewable Energy Rate is a premium offered to residential customers. Participants can purchase one or more 100 kilowatt-hour blocks of renewable energy per month for $6/block. Because of the higher cost of renewable energy, the cost of each block is in addition to the customer’s regular price. Customers participating must agree to purchase their subscribed number of blocks/month for 12 months. To sign up for this program customers who are interested can call 1-800-245-2244. The source of fuel for this green power is Alabama grown switchgrass and other biomass products.
Another technology for producing biopower is to generate methane from lagoons or landfills by anaerobic digestion, and then to use this gas to power engines that drive power generators. This process is widely used in various settings, but again, its economic viability is usually dependent on internal use of the power that is produced, and it is not viable if power is sold to the grid. Finally, biopower can also be produced by gasifying biomass (burning under starved air conditions, to produce a synthesis gas) and using the gas to drive a gas turbine, or by means of fuel cells. These technologies are more efficient, but are mostly still in the developmental stage. |
