>Energy-intensive manufacturing

In an increasingly competitive environment, manufacturers are seeking to cut their costs. Fluctuating energy prices often channel this investment into cost-effective energy-saving technologies and practices that will reduce operating costs while maintaining or increasing product quality and yield.

Energy-efficient technologies often bring other benefits, such as higher productivity or environmental gains, reducing the regulatory ‘burden’. Waste heat can be captured from many industrial processes through waste heat recovery technology. […]

Waste heat recovery represents the greatest opportunity for reducing energy loss in these industries while simultaneously reducing their carbon footprint and associated greenhouse emissions with improved overall energy production efficiency.[…]

The outlook for scCO2

Supercritical CO2 heat engines are scalable across a broad system size range, from 250 kWe to 45 MWe and above, with net electrical output to support the widest possible variety of industrial and utility-scale applications.

The sCO2 Cycle is thermal source neutral − suitable with a wide range of heat sources from 200°C to 500°C with efficiencies up to 30%. New energy production can be offset with recovered energy without increasing greenhouse emissions while improving overall energy production efficiency. The scCO2 heat engine can add up to 35% more power to simple-cycle gas turbines, 10–15% more power to reciprocating engines, and can significantly improve the energy efficiency and bottom line performance at steel mills, cement kilns, glass furnaces and other fuel-fired industrial processes by converting previously wasted exhaust and flue gas energy into usable electricity.

Alex Kacludis is an Application Engineer at EPS LLC; www.echogen.com

>Because of its physical properties as a liquid, it has become a target fluid of opportunity to run turbines and thus make electricity. Steven Wright, Ph.D., who recently retired from Sandia National Laboratory (SNL), has set up a consulting company called Critical Energy LLC to bring this technology to a commercial level.

The objective of using supercritical CO2 (S-CO2) in a Brayton-Cycle turbine is to make it much more efficient in the transfer of heat. Wright points out that a steam turbine is about 33% efficient, but that an S-CO2 turbine could be as high as 48% efficient, a significant increase.

A closed loop supercritical CO2 system has the density of a liquid, but many of the properties of a gas. A turbine running on it, “is basically a jet engine running on a hot liquid,” says Wright.

“There is a tremendous amount of scientific and industrial interest in S-CO2 for power generation. All heat sources are involved…<

>Chen et al. [1-3] did a comparative study of the carbon dioxide supercritical power cycle and compared it with an organic Rankine cycle using R123 as the working fluid in a waste heat recovery application. It shows that a CO2 supercritical power cycle has higher system efficiency than an ORC when taking into account the behavior of the heat transfer between the heat source and the working fluid. The CO2 cycle shows no pinch limitation in the heat exchanger. Zhang et al.  [4-11] has also conducted research on the supercritical CO2 power cycle. Experiments revealed that the CO2 can be heated up to 187℃ and the power generation efficiency was 8.78% to 9.45% [7] and the COP for the overall outputs from the cycle was 0.548 and 0.406, respectively, on a typical summer and winter day in Japan [5].

Organic fluids like isobutene, propane, propylene, difluoromethane and R-245fa [12] have also been suggested for supercritical Rankine cycle. It was found that supercritical fluids can maximize the efficiency of the system. However, detailed studies on the use of organic working fluids in supercritical Rankine cycles have not been widely published.

There is no supercritical Rankine cycle in operation up to now. However, it is becoming a new direction due to its advantages in thermal efficiency and simplicity in configuration.<