Vision 21 Foresees Pollution-Less Power
By Bill Moore
Pittsburgh, PA -- August 2000. It has been estimated that the world will run out of oil in 80 years and natural gas in 70 years. But coal, of which America has the largest known reserves in the world, can last three more centuries.
The problem with is coal it is dirty, often dangerous to get at, and when burned to generate electricity produces devastating amounts of carbon dioxide, not to mention a toxic brew of other health-harming, environment damaging emissions. CO2 is an important greenhouse gas and is directly linked to global warming.
So, the question is do we simply ignore it or can we find a way to use it without creating pollution and adding more CO2 into our already over-burdened atmosphere. Clearly this is an important issue if we are to shift from a petroleum-based transportation system to one that is electrically-powered.
Forty percent of all electric energy in the US comes from the burning of coal and electric-power generation is the single largest man-made contributor of greenhouse gas. The emissions from coal-fired power plants are known do measurable damage to lakes and forests hundreds of miles downwind, so burning more coal using conventional, 20th century technology to meet America's future energy needs isn't an option.
New ways will need to be found to safely utilize coal before we can count on it for America and world's future energy needs. That's the objective of the US Department of Energy's newly formed Vision 21 program. According to Dr. Lawrence Ruth, product manager for the National Energy Technology Laboratory in Pittsburgh, Pennsylvania, there has been sufficient progress in the last twenty years to warrant optimism that it will be possible to build pollution free power plants, even those fueled by coal.
He points to the fact that between 1970 and 2000, sulfur dioxide emissions from coal-powered generation plants has been cut by a factor of three. "But that's not nearly enough," he told EVWorld. "The Vision 21 energy plants that we're working on will actually have emissions at near-zero level. These plants that use coal would be as clean as the cleanest gas-fired plants today."
Ruth said that there are now technologies available or in development that will bring both SO2 and NOx emissions from these future power plants down to near zero. Also in the works are ways to prevent the release of any carbon dioxide by capturing it before it leaves the plant and sequestering it either underground or in the ocean beds.
Can't Rule Any Energy Resource Out
While the Vision 21 program has its sights set on zero-pollution electric power generation from coal, biomass and even municipal waste, Ruth said that America cannot afford to ignore any potential energy source including solar and wind, as well as nuclear energy. He also emphasized that while there might be cases where a Vision 21 plant would also produce fuels and chemicals where economically feasible, for now the program is focused on electric power generation.
Ruth explained there are two ways to attack the problem of using coal in the future. One is to reduce the amount of coal used by improving the overall efficiency of the plant. At present the best coal-fired plans are 35% efficient. Vision 21's target is 60% efficiency thus reducing CO2 emission, for example by 45%. If the Vision 21 plant is natural gas fired, CO2 emissions can be cut by 75% prior to sequestration.
As Ruth went on to elaborate, if sequestration of CO2 were required, it would then make economic sense to shift from a combustion process to a gasification process to capture the carbon dioxide. Using gasification, CO2 could be simply and cost-effectively separated from water that is also the by-product of the process.
Gasification in a Vision 21 plant might work something like this. Coal lumps measuring about 3/4 of an inch in diameter are injected into a fluidized bed reactor which is also being force-fed pure oxygen (not atmospheric oxygen with its high nitrogen component) and steam. This converts the goal into a gas that can be cleaned of all pollutants and burned in a gas turbine.
Technologies such as fluidized bed reactors that use high-press steam and pure oxygen to turn coal into a gas will someday offer the potential of better controlling and then dramatically reducing the amount of pollutants now being forced into the atmosphere from 20th century power plants.
By combining best-of-bred technologies, some of which are still in development, the Vision 21 program hopes to nearly eliminate virtually all pollutants like sulfur dioxide, nitrous oxide, carbon monoxide, as well as carbon dioxide from the power generation process, according to Dr. Lawrence Ruth with the Depart of Energy's National Energy Technology Laboratory in Pittsburgh, Pennsylvania.
No More Smoke Stacks
EVWorld asked Dr. Ruth to envision what a 21st century power plant might look like and how it might function. In his scenario, set some 15 to 20 years from now assuming all the necessary technologies can be perfected and market conditions permit it, two of the most noticeable differences will the absence of coal piles and smoke stacks.
"It's probably going to look very different than the plants you have today. I would not be surprised if you don't even see a coal pile. I envision that the coal might be transported to the plant through a pipeline of some type." While he thinks rail cars might still be used for some portion of the transportation cycle, especially in the case of Western coal where water rights and usage is already a rancorous issue among states, he believes pipelines will carry the coal underground to those power plants that might be located near urban centers.
"You wouldn't have the 300 foot stacks because you don't have an emissions," he continued. You would not be using air anymore for combustion or gasification process. You would be using oxygen, so the volume of exhaust would be much less, which means the stacks would be much smaller."
Ruth also explained that these future plans would be highly automated and computer controlled. "Computers would be tied to a network of sensors that would monitor virtually every aspect of the plant's operation including, of course, all the emissions." The same computers would be programmed the continuously optimize the performance of the plant, reducing the chance of human error.
The Role of Distributed Generation
While the Vision 21 program does use improved technology to clean up a power plant's "act", it is still based on the turn-of-the-20th-century model of the central station power plant. In the last ten years, increasing interest has begun to be expressed in a new, decentralized power generation model called distributed generation.
DG, as it is called, makes use of small, more efficient generators closer to the end-user. Until now most of these were limited to gas-fired co-generation plants that powered factories. However, the recent development of new types of fuel cells and microturbines now promises to put electric power generation right in the home, a far different model than that envisioned by Vision 21.
"We do think that distributed generation is going to be an important factor," Dr. Ruth admitted, " I really don't know and it's hard to predict how big a factor this is going to be in the future."
"We still feel there is going to be a need for a central station power generation and Vision 21 is focused on central station generation power, but I do believe also that distributed generation will also have its applications. Just as we should not depend on one particular energy resource to fuel our power plants, but rather a diverse mix of energy sources, I think the same principle can be applied to distributed vs. central generation. I think we're going to do both," he stated.
Coal may not be the only fuel used to power the plants of the future. Vision 21 plants may also, under the right conditions, also use municipal solid waste, as well as landfill generated methane gas, as a supplemental fuel, Ruth explained.
Wanted: Revolutionary Breakthroughs
While some aspects of the Vision 21 program have their roots in earlier Department of Energy programs, Vision 21 itself is a relatively new effort in the last year stated Ruth.
"Vision 21 is focused on improvements in the technology that we feel is going to be needed in these advanced energy plants. We work with industry to identify what these key technologies are and we're going to try to make not evolutionary but revolutionary breakthrough types of improvements in these critical technologies."
Ruth elaborated on what the target technologies are including gasification, high performance combustion turbines, fuel cells, gas separation and purification, high temperature materials, computational modeling and virtual simulation. "All of these and other technologies will be very important."
Despite it's recent start up, Vision 21 has already identified several key technologies including the ability to drastically reduce NOx emissions from highly-efficient gas turbine generators. The program has also developed materials and technologies for very high temperature heat exchangers, Ruth added.
Some important new technologies in the works include new membrane materials which will separate nitrogen and oxygen from air. "They may be able to do this at much less cost then conventional technology today, which is a cryogenic technology," Ruth stated. Low cost oxygen is one of the necessary "ingredients" of a Vision 21 power plant.
Beside the oxygen separation membranes, the program is also looking for membranes which can separate hydrogen from the fuel gases produced by coal gasification. This hydrogen would be used to either power fuel cells in the plant or distributed for use by homes, businesses or vehicles.
Cutting the First Ribbon
Ruth said the goal of Vision 21 is to have the necessary technologies in place by 2015, so that construction of the first Vision 21-inspired power plants could be built, assuming market conditions at the time permit it, sometime between 2015-2020.
However, pieces of the technology are likely to find their way into the power plants of the next decade, Ruth said. While these early generation, pre-Vision 21 plants won't be as efficient or as clean as a Vision 21 plant, they will still be significantly better than today's power plants.
blog comments powered by Disqus