The future of fossil fuels

The specter of hundreds of new, carbon-belching coal-fired power plants has added urgency to the task of figuring out how coal can be burned more cleanly. The same challenge applies to reducing the emissions of power stations that burn oil, gas or even biomass (wood). One straightforward approach is to increase the efficiency of such plants. To an extent, this has already been happening for some time. For example, incremental improvements in technology over the years have raised the efficiency with which coal-plants can pulverize and burn their fuel by several percent. This is no small achievement, but even in modern plants only about a third of the energy in the burned coal is actually translated into electricity.

Another approach to cleaning up coal is gasification. Instead of burning the coal directly, a gasification plant heats the furl to a high temperature with just a dash of oxygen. The resulting gases are either burned or further refined into synfuels – synthetic versions of oil-based fuels such as petrol or diesel. This isn’t a new idea; Hitler was driven to synfuels when Germany’s oil supplies ran low during World War II. On the face of it, gasification might seem like an inefficient way to use an already problematic fuel, but there are benefits to the process. Chief among them, in terms of greenhouse gases, is that CO2 can be easily separated out of the stew of gases after combustion.

Sequestration: capturing carbon

The attraction of isolating CO2 created in a coal gasification plant – or any other power station – is the possibility of capturing the gas before it has a chance to escape into the atmosphere. This process is known as carbon capture and storage (CCS), or sequestration.

A more promising solution is to put the carbon underground. If it’s pumped to depths of more than 800 m below ground, CO2 takes on a liquid-like form that greatly reduces the chance of it rising to the surface. Given the right geological formations, the gas could remain underground almost indefinitely. Among the possible locations being explored are:

• Depleted oil and gas wells. This technique has been used on a limited basis for decades in the practice called enhanced oil recovery, which has the economic – if not climatic – benefit of prolonging production from aging reserves (as the CO2 is pumped down into the wells, it helps push out remaining oil or gas).
• Saline aquifers. Found in basaltic formations and other types of rock, these typically hold salty water that’s separate from the freshwater found in other aquifers. There may be enough saline aquifers to hold centuries’ worth of CO2.

This technique holds real potential as part of the world’s climate-protection package.

There are two pieces to the CCS puzzle that haven’t yet come together but should very soon. One is the industrial-scale testing of sequestration. To date, there have been only a handful of such projects – one in the North Sea, where millions of tons of CO2 have been injected into an undersea aquifer from a natural-gas drilling platform, and another in North America, where CO2 from a synfuel plant in North Dakota is being piped to Saskachewan and used to enhance recovery at an aging oil field.

The other puzzle piece is next-generation coal plants that are designed from the start to make CCS a real option. The leader in this realm is a type of coal plant dubbed integrated gasification and combined cycle (IGCC). As of early 2006, there were two IGCC plants up and running in Europe and two in the US. These plants employ gasification but also use the waste heat to make steam, which drives a second turbine. Although it would be a fairly simple matter to capture the CO2 from an IGCC plant, it hasn’t happened yet. There’s now a $ 1 billion initiative under way in the US to do just this. The goal of FutureGen fulfils its promise; it’ll bring coal far closer to being carbon-neutral.

Дата добавления: 2015-11-16