How carbon capture works and the debate about whether it’s a future climate solution

Power plants and industrial facilities that emit carbon dioxide, the primary driver of global warming, are hopeful that Congress will keep tax credits for capturing the gas and storing it deep underground.

The process, called carbon capture and sequestration, is seen by many as an important way to reduce pollution during a transition to renewable energy.

But it faces criticism from some conservatives, who say it is expensive and unnecessary, and from environmentalists, who say it has consistently failed to capture as much pollution as promised and is simply a way for producers of fossil fuels like oil, gas and coal to continue their use.

Here’s a closer look:

Carbon dioxide is a gas produced by burning of fossil fuels. It traps heat close to the ground when released to the atmosphere, where it persists for hundreds of years and raises global temperatures.

Industries and power plants can install equipment to separate carbon dioxide from other gases before it leaves the smokestack. The carbon then is compressed and shipped — usually through a pipeline — to a location where it’s injected deep underground for long-term storage.

Carbon also can be captured directly from the atmosphere using giant vacuums. Once captured, it is dissolved by chemicals or trapped by solid material.

Lauren Read, a senior vice president at BKV Corp., which built a carbon capture facility in Texas, said the company injects carbon at high pressure, forcing it almost two miles below the surface and into geological formations that can hold it for thousands of years.

The carbon can be stored in deep saline or basalt formations and unmineable coal seams. But about three-fourths of captured carbon dioxide is pumped back into oil fields to build up pressure that helps extract harder-to-reach reserves — meaning it’s not stored permanently, according to the International Energy Agency and the U.S. Environmental Protection Agency.

The most commonly used technology allows facilities to capture and store around 60% of their carbon dioxide emissions during the production process. Anything above that rate is much more difficult and expensive, according to the IEA.

Some companies have forecast carbon capture rates of 90% or more, “in practice, that has never happened,” said Alexandra Shaykevich, research manager at the Environmental Integrity Project’s Oil & Gas Watch.

That’s because it’s difficult to capture carbon dioxide from every point where it’s emitted, said Grant Hauber, a strategic…