Is there such a thing as clean coal
The abundance of coal makes it the most logical choice for energy independence, however the impact of coal on greenhouse gas emissions makes it a troublesome choice. The United States has more coal than the rest of the world has oil, with enough coal underground to provide energy for 200 to 300 years, compared with roughly 100 years of oil. We’re not going to break away quickly and easily from our coal habit, with more than 600 coal powered plants in the United States, and roughly half of our energy coming from this source.
Coal is becoming an increasingly contentious issue among environmental and energy factions, but with this abundance, it’s going to be frankly impossible to put a close on this energy source. Coal is troublesome because of the sulfur and nitrogen that are released as it burns – combining with water in the atmosphere to form acid rain. Microscopic coal particulates are also released into the air, which is an issue for human health because it can lead to asthma and other respiratory diseases. And, there’s the issue of carbon emissions, so called greenhouse gases, that are contributing to the warming of our planet. All three of these issues must be addressed if we’re going to make coal a more sustainable energy source.
Coal found in the eastern United States can contain as much as 10 percent of sulfur, while western coal is cleaner with less than 1 percent. In order to rid coal of this acid-making matter, it needs to be cleaned. One step is pre-processing plants that crush coal and put it through a water bath where the coal floats and the sulfur particles sink. It also takes scrubbers in the smoke stacks of power plants to bind to the remaining and combusted sulfur and eliminate it before it can escape into the air.
The issue of nitrogen in coal, which combines with oxygen to for nitrogen oxide (NOx), causes visible brown clouds around our cities. To combat NOx, scientists have devised a two-stage combustion where smaller amounts of oxygen are introduced in relation to the amount of fuel, which makes it tough for the nitrogen to combine with oxygen to form NOx. This method has proven to reduce NOx by 50%.
Both of these steps have been improvements over how we burn coal to make energy, but they’re not good enough to call coal clean.
A more efficient means of stripping coal of contaminants is to turn it into gas. Blasting hot, but not burning, coal with steam turns it back to a mixture of component parts – carbon monoxide and hydrogen – both gases. These gases are then burned in turn to spin turbines at the first pass, and then the hot gas exhaust from this process can be channeled for second-stage energy generation by turning water into steam that turns another turbine.
One of the best outcomes of gasification is that scientists have come up with ways to strip more than 90 percent of the sulfur and dirt particles from coal through this process. The detailed diagram of the integrated gasification combined cycle (IGCC) power plant process below gives you a sense of the complexities of this process.
While gasification solves a few of the problems, there’s still the issue of carbon. Coal is the second leading source of carbon dioxide emissions in the United States, a key contributor to global warming. The prevailing answer to dealing with carbon dioxide emissions is called carbon sequestration, the process of pumping the carbon dioxide gas underground for long term storage. Carbon sequestration projects are now underway all around the world.
Our ability to store carbon underground with out any harmful side effects is still untested. Some scientists fear leakage through sils, the contamination of aquifers that might harm drinking water, and the potential for geological instability. The technical feasibility will take time and testing to fully understand.
What is Clean?
Even with all of these scientific advancements, coal is inherently a dirty energy source that needs to be mined, hauled and handled with biproducts such as ash and mercury to be dealt with after energy is extracted. When compared with harnessing the power of sun, wind or water, coal is definitely at a clean energy disadvantage.
Coal has thrived for decades because it is plentiful and cheap to burn. Efficiency hasn’t really factored into the process until recently, because we can no longer tolerate harmful practices that jeopardize the longevity of humankind’s existence on our planet. Now that all the costs of this energy source are becoming apparent, we’re going to need to break out all of our scientific and engineering skills to make coal cleaner even if it can’t be considered clean.