A new technology could mean the end of air pollution from fossil-fuel power-generating facilities.

In the early industrial world, people could burn all the coal, oil or gas they wanted with no regulatory consequences. It the goal was power without concern for the world's health, the Industrial Revolution approach would work just fine: a big box, burn the coal, make the power.

As we progress through the electronic and biotech eras, the world's population desires an air quality environment closer to the pre-Industrial Revolution condition. With that in mind, a team at ThermoEnergy, along with support from the Department Of Energy and EPA, have created a patented process called TIPS: ThermoEnergy Integrated Power System, designed to enable existing power plants to burn fossil fuels with virtually no air emissions.

With many groups searching for solutions to pollution, the team at ThermoEnergy recognized that traditional pollution control techniques had been perfected and a different physical process was needed for zero air emissions from the combustion of fossil fuels.

"The initial direction we went in was different" says Alex Fassbender, inventor of the TIPS process. "We observed that the capture of CO₂ in a useful form changes the thermodynamic endpoint of combustion-fueled power generation. The capture of CO₂ in a useful form requires a compression step at some point. Rather than combust fossil fuel and then use capital and parasitic power to clean up particles, acid gases, mercury and CO₂ sequentially, TIPS integrates all of these functions into a system that simultaneously recovers the heat of vaporization from both the entrained and produced water from fossil fuel combustion.

"TIPS pays the capital and parasitic power costs up-front by separating the air. The CO₂ capture compression step is performed during the air separation process. When we implement TIPS as envisioned, we have a power plant with no air emissions and facilities that can clean up their own solid and liquid wastes. The ash becomes a product, the acids are recovered and the water cleaned. By controlling all of the emissions, the regulatory risk from a combustion standpoint is also controlled."

Necessity strikes again

The TIPS process works by elevating the pressure at which combustion and exhaust gas cleanup occurs. The elevated pressure increases the temperature at which steam condenses into water to a temperature significantly above the ambient temperature of the cooling water used at power plants. This elevated pressure also raises the temperature at which CO₂ will condense into a liquid to a temperature above the ambient temperature used at most power plants.

The combustion exhaust gases are cooled with hot water, a portion of which becomes steam. Once cooled, particles are removed by steam hydroscrubbing or nucleate condensation. The cleaned exhaust gases are further cooled and the nucleate condensation process repeats as the CO₂ is condensed into a liquid. Volatile mercury compounds and acid gases such as NO_x or SO_x condense at pressure and temperature regimes between water and CO₂, and are removed as the CO₂ condenses.

Brian Rustia, senior program manager for Civil Engineering Research Foundation, which has a contract with EPA to look at environmental technology, sees TIPS as a promising technology.

"Coal is an abundant resource but its power generating technology is a hundred years old" Rustia says. "To switch to a system like this that will meet all air standards and create a resource makes sense and is a great alternative."

TIPS came about in the midst of an existing expertise in hydrothermal technologies. Fassbender previously invented a dual shell pressure balanced reactor and had been working in the area of pressurized systems for some time. When asked to look into energy production, Fassbender noticed that many of his peers were looking at super critical water oxidation (SCWO), which uses an enclosed pressurized system and offered the potential for different physical processes and unit operations.

"The more we looked at it, the more challenging it became from an engineering standpoint;' Fassbender says. "When you traverse the critical point of water, the pressure is quite high. Then the properties of water change radically and dissolved solids can cause a lot of problems."

Fassbender then asked himself, what if, rather than super critical water, we used super critical CO₂?

"Basically, it all fell out from there" Fassbender says. "We did the math, put some balances and flows together and looked at the equipment required. It was all pretty much do-able."

So far, everyone Fassbender's team has talked to believes it can be done. Each individual piece of process equipment either in or similar to those in the TIPS process has been built and operated at industrial scale. Large pressure vessels in the oil refining and chemical industries handle both higher temperatures and pressures.

Of course, TIPS is going up against technology that has billions of dollars of development over generations to get to the current state of development and, according to Fassbender, this is not where it needs to be.

"If clean coal were a solved problem, natural gas would probably not account for 90 percent of all new power plants being built," he adds. "We'll do a lot more optimization, but we don't believe we have to invent a whole new technology to make this work.

Birth of a process

TIPS' first step is to separate the air and pressurize the system--then combust. Although there is a parasitic power loss to separate the air and pressurize the system, the flipside is all the down-stream side (cleanup) is prepaid for. Everything is a lot easier.

"We use different physics" Fassbender explains. "The physics of the condensing heat exchanger is not reduced if there is a small number of particles. If you have a filter system, you get diminished returns. With TIPS, the small number of particles doesn't matter." CANMET has demonstrated essentially complete removal of particles using this technique at atmospheric pressure.

An example of a basic application for TIPS is a coal-fired boiler that has some pretreatment and aftertreatment, and no emissions. The two main products that will result from the process are CO₂ in a form that's useful, a reasonably pure liquid and of course, electricity.

"We see it appropriate for the retrofit market," Fassbender says. "We could probably build much of the TIPS plant onsite while the existing plant is still running."

An example of a TIPS retrofit: For existing coal-fired plants, the only modifications required are the addition of an air separation plant and replacing the combustion boiler and exhaust train--the remaining portions of the plant would still be usable.

Since the process does condense water, there is less penalty for wet fuel. This means wet coal and even municipal solid waste can recover the latent heat of vaporization of both the entrained and produced water. When a wet fuel is burned, part of the energy has to go into vaporizing the water, which usually goes up the stack. Coal doesn't have much hydrogen or produce much water but municipal solid waste produces water in gaseous form. TIPS will recover the heat of vaporization of that water, according to Fassbender.

"Recent studies in the last five years showed that CO₂ sticks to coal better than methane," Fassbender says. "You can actually push CO₂ down into the coal seams and you can displace the methane. The use of CO₂ for enhanced oil recovery is well known. If one has a large stream of very cheap CO₂ in a useful form, pressurized to the point where one can inject it into the ground, it is possible to sequester a large amount of CO₂ on coal seams and generate coal-bed methane in collection wells."

Using CO₂ to saturate the coal seam will reduce the amount of methane in the atmosphere in the vent the coal is mined. Less methane gets into the atmosphere and no CO₂ since the liquid CO₂ is directly used and not emitted into the atmosphere. With the amount of CO₂ this system would produce, CO₂ could quickly become a low-cost commodity.

Rustia agrees that switching to clean technology should be a no-brainer.

"Even if TIPS were more expensive than existing technology, the benefits might make people change their minds because it creates a commodity" adds Rustia. "Not to mention that it is a dean technology. Who wants to be downstream of a coal plant with all that pollution?"

Fassbender agrees that the CO₂ commodity will be an incentive.

"The technology exists to change the way a lot of things are done if one uses CO₂ as a solvent instead of water," Fassbender adds. "There are a lot of smart people out there working on uses for CO₂ and with a technique like TIPS, vast quantities would be produced. Even if the CO₂ still winds up in the atmosphere, a CO₂ solvent system will displace other pollutants."

Currently, ThermoEnergy is working to get funding to develop several different computer models of the technology in action. The model should be well under-way in a year.

"The first model we do will be an overall process model," Fassbender says. "With a process-model software, we will answer a lot of `what ifs,' this coal vs. that coal, if the coal was wet, etc., and see what this does to flow and equipment so we could do some preliminary sizing. Based on this, we can go out and get preliminary bids on equipment and estimate cost. Second, is to do a computational fluid dynamics model CFD, of combustion at pressure. After that, we're ready to go into testing and design."

ThermoEnergy plans to participate in a TIPS testing program through the Environmental Technology Evaluation Centers, a non-profit organization partially funded by EPA once the pilot plant is implemented. Optimism is high for all parties.

The feeling of having invented what may be a key solution to power-generating emission pollution does have its human rewards also.

"I feel, when I talk to another scientist who has an open mind, it's surprising how positive the responses have been," Fassbender explains. "Elation comes from constituency acceptance and that we might be on the track to contributing to the future solutions to providing energy to our economy with minimal consequences to the environment."