A light bulb moment! Converting hot bulk solids into electricity
How indirect heat transfer tech can integrate with ORC to reduce energy consumption
Author: Jamie Zachary
It’s a novel concept – the ability to use hot bulk solids to generate electricity.
Yet many in the heat transfer world regard this concept as a modern-day lightning rod for industrial processes, particularly when the technologies involved have been around for decades.
We recently sat down (virtually) to discuss the idea with Neville Jordison, Chief Executive Officer with Solex Energy Science, a new Canadian-headquartered company focused on solving heat transfer needs from renewable energy solutions such as solar power, waste heat recovery and carbon capture.
He was joined by Gerald Marinitsch, Global Director of Industrials for Solex Thermal Science, who specializes in tailored and process-integrated solutions within industrial applications such as chemicals, metals and minerals and sands.
Explain the concept behind using bulk solids to generate electricity
Jordison: Industries have been recovering heat from exhaust gases for decades. Yet they’ve never looked at high-temperature bulk solid materials as a potential source of thermal energy that can be converted into electrical energy. Instead, those hot solids have often been left on the ground to air cool or be water quenched.
Marinitsch: Think about the slag coming out of steel mills, for example. It’s a byproduct from the smelting process, and is just being quenched with water to cool it down. This represents millions of gigajoules of energy that’s just dissipating as vapour into the air. All of this energy can be turned into electricity.
Jordison: Once you recognize that there’s energy potential within these hot materials, the next question is what are you going to do with that energy? And there are two answers to that: The first is, ideally, there’s a use for that waste heat elsewhere in the plant. It could be to pre-heat combustion air, for example. The second is, if there is not an obvious need for hot air, there’s an opportunity to tie in with an Organic Rankine Cycle (ORC) process in which you can convert that waste thermal energy into electrical power.
Marinitsch: That’s what’s new. That’s what’s exciting. We’re talking about the combination of two established technologies in a way that’s never been done before. The technology behind the indirect heating and cooling of bulk solids has been around for decades. ORC, meanwhile, has been similarly used around the world – primarily to convert low-temperature heat sources into mechanical energy that’s then used to produce electricity. More recently, ORC technology has been successful in geothermal power plants. But it’s never been combined with heat recovery from a hot bulk solid stream.
How does it work?
Jordison: At a high level, we have a moving bed plate-based heat exchanger with a high-temperature solid coming in. We put a relatively cold working fluid (e.g. thermal oil at around 150°C) to indirectly cool the solids, with a relatively hot working fluid (e.g. 250°C) coming out. The working fluid stream then goes to the ORC plant, which takes the energy out of the 250°C and returns it at 150°C.
Marinitsch: Whether that be a steel or cement plant or some other process, they could become producers of their own electricity to offset the electricity purchased, or else feed it into the grid and generate a revenue stream. However, in many cases the owner of the energy source (or with the cooling demand) does not necessarily need to be the operator of that plant. The likely scenario is that the thermal energy is going over the fence to the ORC plant, and would be financed and operated by somebody else on a contractual basis.
What are the benefits?
Jordison: The most obvious is the opportunity to reduce overall energy consumption by using waste heat. There are some sound economics in play where a company can realize a fairly realistic payback period with almost no risk. Both technologies are proven, with the ORC side located “across the fence,” so to speak.
Marinitsch: The other benefit is that subsidies are being provided for this type of technology combination as many jurisdictions around the world support the decarbonization of the economy. Reduced energy consumption – and even reduced water consumption if the bulk solids were previously being water quenched – plays right into these opportunities that are just waiting to be realized.
What industries are best suited?
Marinitsch: Larger industries that have solids throughputs greater than 20 tonnes per hour, or cooling demands around 2.5 megawatts (MW/h) at the indicated temperature range – for example, the iron and steel industry and slag granulation (dry slag), cement plants or even the refractory industry. The cement industry is particularly interesting given its reputation as a major contributor to global CO2 emissions. It’s now looking for innovative ways to reduce its GHG footprint and become a net-zero-emissions industry. Basically, all kinds of industries where you have a huge amount of solid product that is processed with temperatures between 400°C and 800°C.
Jordison: The reason behind needing such large volumes of solids throughput is the capital costs become uneconomical otherwise. There’s a difference between thermal heat and electrical. It’s not a 1:1 conversion. It’s a more like a 4:1 to 5:1 ratio. That means 4 MW of thermal energy, for example, will translate into 1 MW of electrical energy.
Want to learn more?
Visit Solex Energy Science to discover more about how the company is applying creative heat transfer solutions to applications involving high temperatures.
Ready to talk specifics? Contact a Solex Energy Science team member today.
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About the experts
Neville Jordison, Chief Executive Officer, Solex Energy Science
Jordison brings 30 years of experience to the table, including most recently as CEO of Solex Thermal Science. His focus is on combining innovation with a willingness to take on new and challenging applications to create equipment that is robust in design, has strong CAPEX and OPEX economics and is suitable for the rigors of large-scale, industrial plants.
Gerald Marinitsch, Global Director, Industrials, Solex Thermal Science
Marinitsch joined Solex in 2014 with a broad and comprehensive background in process engineering. Working with a team of experts at Solex, he now leads the company’s efforts in creating tailored and process integrated solutions within industrial applications such as chemicals, metals and minerals and sands.
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