(168b) The Long and the Short of Energy Consumption in Distillation

We all feel it every time we go to the gas pump, or pay an electric bill, or a home heating bill. Energy costs are continuously rising ? and there seems to be no relief in sight. The global demand for energy has and will continue to grow at an unprecedented rate as the US becomes more addicted to oil and gas and as China and India become industrialized nations. We are all also aware of the impact that burning fossil fuels has on the environment ? putting large amounts of carbon dioxide into the atmosphere and potentially contributing to global warming and climate change. This rather bleak picture has prompted renewed interest in energy conservation throughout the private and industrial sectors in the US since using less fuel has the two-fold advantage of reducing consumption and carbon dioxide emissions. One place where significant energy can be saved is in the chemical process industries where reaction and separation abound to produce all of the modern conveniences we now take for granted (e.g., the synthetic fibers, plastics, and polymers). Distillation is a widely used and versatile separation process that is used throughout the petroleum, chemical, pharmaceutical, and other industries to separate products, by-products, solvents, and raw materials. However, it is also a very large energy consumer with an estimated 40,000 distillation columns in the US that use approximately 24 % of the energy consumed by the manufacturing sector.

In this talk, I will give an overview of the recent unifying approach to energy consumption and energy efficiency proposed by Lucia and co-workers as it relates to distillation and, more generally, to multi-unit chemical processes that involve distillation. This novel methodology is based on differential geometry and the view that longest and shortest metrics (i.e., distances, surface areas, and volumes) associated with distillation paths give insight into the energy required for a given set of separation tasks. I will outline what can be demonstrated through example as well as what can actually be proved rigorously. I will show how this new approach encompasses all existing methods for determining minimum energy requirements for distillation ? such as the McCabe-Thiele method, Underwood's method, boundary value methods, and so on. I will also show that it provides a rigorous and implementable way of finding energy efficient solutions that other methods cannot find ? such as non-pinched minimum energy solutions. Throughout this talk, I will emphasize the facts that this new methodology can be applied to mixtures with any number of components, that it is applicable to multi-unit processes, and that it has a rigorous theoretical foundation rooted in differential geometry. Finally I will use many geometric illustrations to elucidate key features of this new approach to energy consumption in the synthesis and design of chemical processes.