According to the Lawrence Livermore National Laboratory, in 2020, in the US alone, 67.5% of the energy produced ended up being rejected energy - energy returned to the environment and lost due to its low temperature.

It makes us wonder, is there a way to reduce the amount of rejected energy? The answer is a solid yes. Energy efficiency and better technologies help reduce the amount of energy lost and the overall energy consumption in residential and commercial areas, and the transportation sector. But in industrial processes and power generation, there are specific processes in which heat losses to the environment happen anyway. These account for 37.7% of the rejected energy from the following graph.

Figure 1. Estimated U.S. Energy Consumption in 2020

What if I told you that there's a technology that enables you to use this low-temperature heat to produce electricity and thermal energy. If you could profit from this, shouldn't you?

How?

There are at least eight different technologies that allow the production of energy from waste heat. The following figure, developed by Waste Heat EU, shows the major waste-heat utilization technologies for various temperature ranges and their thermal capacity.

Figure 2. Waste Heat technologies

Wasted energy results in an indirect cost for companies, and we all know we can't afford such losses. So regardless of whether you can use extra energy internally or you have it as surplus to commercialize it externally, what are you waiting for?

Our proposed solution today is: Organic Rankine Cycle (ORC).

What is ORC?

The Organic Rankine Cycle's principle is based on a turbogenerator working as a conventional steam turbine. The turbine transforms thermal energy into mechanical energy and finally into electric energy through a generator. In comparison to the Rankine Cycle, instead of generating steam from water, the ORC system vaporizes an organic fluid. This fluid is characterized by a molecular mass higher than that of water, which leads to a slower rotation of the turbine, lower pressures, lower burning point, and no erosion of the metal parts and blades. Examples of organic fluids are pentane, cyclopentane, R134, hexane, and toluene. What's curious is that we can produce electricity from fluids with temperatures as low as 70 °C / 158 °F!

A typical ORC unit consists of an evaporator, an expansion device, a pump, and a condenser like it can be seen in the figure below:

Figure 3. ORC parts

What are the benefits of using ORC?

There's a wide variety of advantages regarding ORC, but the main one is the vast quantity of applications it has. You can use ORC units wherever you have a source of waste heat that is at least 70°C if fluid or 150°C if gaseous.

Another great advantage is that ORC produces clean energy. Given the fact that the units work in closed-loop systems, they can generate emissions-free energy that can help you reduce your carbon footprint while at the same time boosting your company’s energy efficiency as a whole.

Let's not forget that energy savings lead directly to lower costs. Many countries even provide tax credits or funding for users that want to purchase such technologies. Germany, for instance, grants up to 40% CAPEX for an efficiency project. Still, case studies have shown that the payback time is between 2.5 and 4 years. Additionally, units are designed and manufactured so that maintenance tasks are not expensive nor complicated.

Finally, the last advantage is the modular design. Modularity allows the connection in series to produce more energy. In some cases, companies can generate up to 20 MW! Additionally, some units have the advantage to be plug-and-play. So, they can easily be transported from one place to another with minimal costs.

Let's get a little bit into the possible applications, is there really a wide range of applications?

Well, the answer again is yes! At least 12 different companies are producing and commercializing ORC units worldwide nowadays. This gives the added value of choosing which company is closer to you, which unit admits your temperature inlet, or even which one fits better for your needed application. To be more precise:

• Location: In general, the companies in the scope can deliver ORC units almost anywhere in the world. However, only a few companies work in the African continent.
• Temperatures: some units can produce energy from temperatures as low as 70°C to temperatures as high as 900°C. It all depends on the clients' needs. Several case studies show there are companies that have "small" units connected in series and can turn them on and off according to their needs. Exergy and Turboden have developed big ORC units that enable the generation of up to 2MWel. Others, like ElectraTherm, Climeon, and Orcan Energy aim to the low-hanging fruit. They developed units that can produce from 1 kWel to 150 kWel and connected in series can reach 20MW.
• Applications: As previously mentioned, waste-heat recovery units only need a source of heat to produce energy. Since the units are modular, they can fit small areas such as an engine room in a vessel. Some examples of the main applications we've been seeing are in the following industries: maritime, geothermal, steel plants, power plants, methane optimization projects, combined cycles, high-temperature CHP, O&G (up-, mid-, and downstream), biomass, and concentrated solar power.

Do you already have a waste-heat source in your company in mind? Are you curious about what the economics of such projects would look like? Follow up next week for deeper dive into more statistics, case studies, and economics. Also, comment and add possible questions we should be answering in next week's post or during our July forum!

References

• The Organic Rankine Cycle: Thermodynamics, Applications and Optimization
• Lawrence Livermore National Laboratory
• Waste Heat EU