Optimized heat transfer solutions to meet emission reduction requirements
Vertical plate technology helps plants reduce carbon footprints
Author: Jean-Marc Reichling
(Originally appeared in Infovrac, September 2020)
Evolving environmental considerations are placing newfound pressure on bulk solid processors to improve operational efficiencies while simultaneously reducing their collective carbon footprint.
Over the past decade, jurisdictions around the world have implemented increasingly stringent NOx reduction targets, as well as limitations on solid particles being released into the environment. This is requiring industry to pay more attention to in-stack emissions than ever before.
The path to increased sustainability has, likewise, renewed the need to reduce the amount of energy consumed per tonne of product produced. This makes sense given that any conversation revolving around carbon reduction leads back to the energy sources that keep today’s processing plants running. Most of the carbon monoxide and dioxide that is emitted from stacks come from the use of hydrocarbon energy resources. A reduction in energy consumption therefore makes it possible to reduce the amount of gC02/kWh being emitted by a plant.
Advances in indirect heat exchange technology for bulk solids are providing operators with efficient heat transfer solutions that reduce energy consumption and virtually eliminate emissions.
How it works
Pioneered by Canadian-headquartered Solex Thermal Science, the technology heats, cools or dries powders, crystals or granules indirectly. Typical applications include fertilizer, potash, sugar, polymers, oilseeds, salts and biosolids, to name a few.
The proprietary heat exchanger technology utilizes vertically oriented plates with internal channels through which the cooling or heating fluid flows. The configuration provides a large heat transfer area within a compact unit. The bulk solids flow by gravity between the plates, while a heat transfer fluid (e.g. hot water, steam, thermal oil) or refrigerant fluid (e.g. cold water, glycol water) flows counter-current through the plate’s internal channels. A mass-flow discharge device guarantees the uniform flow of the product through the exchangers, thereby producing a uniform temperature product at the discharge.
Solex uses a proprietary thermal modelling software to calculate product temperature profiles at every point through the heat exchanger to accurately predict performance. Capabilities include steam systems, multiple heat exchanger banks, co-current and counter-current flow of heat transfer media, drying evaporation loads, continuous flow and batch operations and more.
Indirect heat transfer eliminates any contact between the bulk solids and the cooling fluid, thereby eliminating potential contamination (e.g. bacteria and odours). And because air flow is typically minimal, dust emissions are low.
Air requirements are also significantly less when compared to traditional technology used for heating or cooling, meaning the need for sophisticated air handling and cleaning systems is eliminated. The infrastructure, equipment and operating energy that are typically required with other technologies such as rotating drums or fluidized beds is not required with vertical heat exchangers.
In some cases, it is still necessary to use low volumes of dehumidified air to prevent the condensation of moist air during the heating or cooling process. Condensation must be prevented to avoid avoids products (fines) caking at the plate surface and, in turn, minimizes frequent cleaning and maintenance. It also minimizes caking during storage and shipping, particularly in the fertilizer (e.g. urea, NPK, AN, MAP, DAP, potash) and sugar industries.
Solex has extensive experience handling numerous different types of bulk solids, with more than 600 installations in 50-plus countries over the past 30 years – including numerous successful applications in France.
Because bulk solids flow by gravity through the exchanger, very little energy is required to move the product. In studies completed by Solex, vertical plate technology can reduce energy consumption by up to 90% when compared with fluid beds or rotary drums.
Waste heat recovery
Indirect plate-type heat exchange technology has the additional benefit of being able to use low-grade energy that would otherwise go to waste. In plants processing oilseeds such as rapeseed, soybean and sunflower, it is possible to recover low-grade heat from several sources and re-use that heat in the heat exchanger in a pre-heating step before the flaker or cooker.
In the polymer industry, heat exchangers are used to heat polymer granules in a step to remove most of the residual solvents. This eliminates the need for large holding silos that have traditional been used for this.
Most recently, Solex has leveraged its decades of experience in bulk solids heat transfer to develop proprietary vertical plate conditioning technology. The equipment incorporates indirect heat transfer together with air injection into the moving bed of solids to provide not only the heating or cooling needed, but also drying. Significant reductions in the solids moisture content can be achieved in this way.
About the author: Jean-Marc Reichling is a Global Sales Director with Solex Thermal Science. Over the past two decades, he has worked in variety of on-the-ground application roles in industries such as biosolids, fertiilzer, sugar and oil and gas. Since 2001, he has helped to establish Solex as a global leader in heat transfer solutions for sugar beet, cane and refining applications. In addition, Jean-Marc is also leading Solex’s work in Africa.
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