Putting industrial waste heat to work
How Solex heat exchange technology solves the problem of recovering heat from solids
Authors: Lowy Gunnewiek, Gerald Marinitsch and Scott Harris
Value-added products produced by industrial processes such as cement, chemicals, packaging, food and drink all use energy – generally in the form of heat and electricity. Yet not all of that thermal energy is used for production; what isn’t used is rejected and referred to as industrial waste heat.
Waste heat can be found in many different thermal carrier streams:
- Gas such as flue gas or hot gas exhaust
- Liquid such as cooling water or wastewater
Solid thermal carrier streams are generally the end-user products, such as steel, or the intermediate or by-products of the production process such as slag from iron making.
How much waste heat is there?
In a 2018 study by Papapetrou et al, researchers found the sum of the industrial waste heat potential in the EU, excluding power generation, is about 305 terawatt-hours per year (TWh/yr). This represents 16.7% of the industrial consumption of process heat, and 9.5% of the total energy consumed by industry in the EU.
Of the 305 TWh/yr, they further calculated the amount of waste heat that is available at different temperature ranges, as follows:
- 25 TWh/yr at temperatures less than 100°C. This is considered low-grade heat that is technically difficult to recover and is often found in the food and drinks industry where the energy is used for drying and pre-heating.
- 100 TWh/yr in the range of 100°C to 200°C. This is considered low-temperature waste heat that is found in most industries such as chemical, minerals and paper. There is an opportunity to recover and re-use a portion of this waste heat.
- 78 TWh/yr in the range of 200°C to 500°C. This is generally considered high-grade waste heat with high potential to recover and re-use.
- 124 TWh/yr at temperatures more than 500°C. This waste heat is available from high-temperature processes such as steel making. It is generally difficult to economically recover and re-use the waste energy coming from these processes.
In the United States, Market Resource Future has produced a comprehensive report on the waste heat recovery market. Based on a compound annual growth rate (CAGR) of 9.21% from 2021-28, it’s estimated the waste heat recovery market will be worth $114.67 billion US by 2028.
The study’s authors note there has been a steady growth of energy use in the U.S. manufacturing sector. According to the US Energy Information Administration, energy use in this sector is 97 quadrillion BTU.
What is being done to monetize the waste heat?
Given continuing economic development, rising energy use, rising electricity prices and the growing cost of carbon, the U.S. government has implemented various initiatives and rules to save energy through energy efficiency and energy conservation. The energy efficiency resource standards (EERS) are an example of this.
A.SPIRE is an initiative of the European Process Industry with, “the mission to ensure the development of enabling technologies and best practices along all stages of large-scale existing value chain productions that will contribute to a resource efficient process industry.”
The organization is committed to implement a Process4Planet partnership. The objective is to support European process industries in becoming frontrunners in the transition to climate neutrality and circularity in alignment with the EU Green Deal Goals.
One of the program’s focus areas is heat reuse – a continuation of the SPIRE project Etekina, which has demonstrated cost-effective waste heat recovery in non-ferrous, steel, and ceramic industries with technologies at TRL7. The project anticipates deployment at TRL9 in 2024 will deliver 0.4 MtCO2 in greenhouse gas (GHG) reductions and 200 GWh/yr reduction in energy use per installation.
While this is encouraging, it is acknowledged there are various barriers that inhibit the use of industrial waste heat. For example, when the heat is contained in a solid material, it is generally difficult to transfer that heat to fluid so the heat can be transported to another application and re-used.
Making a difference
When waste heat is available in free-flowing granular solids streams – such as those found during many of the intermediate processing steps in the ceramic industry – moving bed heat exchangers (MBHEs) provide an opportunity to transfer that heat to another fluid.
For example, we at Solex Thermal Science have developed a vertical tube configuration of our heat exchangers (VT-MBHE) wherein the heat can be transferred from solids to air. That hot air is available for use in a variety of different ways, including:
• Space heating
• Pre-heating combustion air
• Steam generation using a heat recovery steam generator
• ORC cycles to produce electricity
• Brayton cycle to produce electricity
Alternatively, we have also developed heat exchangers based on vertical plate or horizontal tube configurations that can transfer heat from solids to a liquid such as water or thermal oil. This approach makes it practical and efficient to not only go after the recovery and reuse of high-grade waste heat, but also low-grade. In turn, it becomes for practical for a wide variety of process industries to reduce the amount of waste heat escaping from their operations.
Once the heat is recovered from the solids, it can be transported and used in ways similar to the hot air generated from the VT-MBHE.
Vertical plate, horizontal tube and vertical tube MBHEs can also be used in processing applications where a product undergoes a thermal processing step. Heat is recovered from the solids after the thermal processing step. It is then recycled back to the front end of the process to pre-heat the solids. This reduces the primary energy required for the thermal processing step. In some cases, the heat recovered can be further enhanced with heat pump technology.
Solex Thermal Science is the global market leader and developer of high-efficiency, indirect heat exchange technology for the heating, cooling and drying of free-flowing granular materials such as solid granules, pellets, beans, seeds and particles.
Over the past 30 years, our company has installed more than 900 advanced heat exchangers in more than 50 countries worldwide with applications such as fertilizer, oilseeds and industrial materials such as minerals/sands, chemicals and polymers.
In recent years, Solex has expanded into the energy-transition sector with key collaborations globally on decarbonization applications such as industrial waste heat recovery, concentrated solar power (CSP) and carbon capture.
Want to learn more about how our moving bed heat exchangers can help decarbonize your operations? Contact a Solex team member today.
About the authors
Lowy Gunnewiek, Chief Executive Officer
Lowy has more than 30 years of experience as a senior executive and professional engineer in the international energy, mining and minerals and infrastructure sectors. Contact Lowy
Gerald Marinitsch, Global Director, Industrials & Energy
Gerald leads Solex's efforts in creating tailored and process integrated solutions within industrial applications such as chemicals, metals and minerals and sands. Contact Gerald
Scott Harris, Regional Director, Americas
Scott is a career-long technical sales specialist for electro-mechanical industrial equipment with extensive experience providing engineered solutions for heat exchangers and energy systems. Contact Scott
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