Proven tech improves industrial catalytic cooling process
Indirect heat transfer exchangers reduce energy consumption, stack emissions
Author: Jamie Zachary
They’ve been hailed as the unsung heroes that help make our society tick – the movers and shakers behind countless everyday products ranging from plastics and pharmaceuticals to paper pulp and liquid fuels.
Catalysts speed up chemical reactions to convert raw materials into everyday products. The petroleum refining sector, for example, relies heavily on fluid-cracking catalysts to break down large hydrocarbon molecules into smaller sections that, in turn, create value-added products we use in our vehicles, aerosol sprays and barbecues.
“In these situations, refineries are essentially breaking it down to the boiling point of different grades such as gasoline, butane, distillate and propane,” says Gerald Marinitsch, Global Director, Industrial for Solex Thermal Science.
During the cracking process, material will collect on the surface of catalysts (which come in powder, cylinders, spheres and trilobes). The catalysts then need to be regenerated to maintain their catalytic activity for the next round of cracking.
“The catalysts are heated to essentially force whatever is stuck in the pores to evaporate and ‘let go,” says Marinitsch, noting the “fresh catalyst” that comes out can be re-used until it eventually degrades from mechanical or thermal breakdown.
Once regenerated, the catalysts are then cooled – a process that has traditionally been handled by fluid bed technology, which involves passing a gas (most commonly air) through a perforated distributor plate and then through a layer (bed) of solids.
However, the premise behind fluid bed technology is that large volumes of air – and, in turn, significant energy requirements – are needed to both fluidize the material and act as the heat exchange medium. The fluidized bed keeps all the particles in motion and creates a tremendous mechanical impact between all the “dancing particles,” meaning the catalyst surface is suffering in terms of surface wear and erosion. In addition, the air leaving the fluid bed cooler is discharged through an emissions stack.
“Indirect plate heat transfer technology offers a much more efficient and gentle alternative to cooling catalysts that simultaneously allows operators to significantly reduce emissions and almost eliminates mechanical impact,” says Marinitsch, noting the proprietary technology optimized by Solex can be used both in the production and regeneration of catalysts.
Plate-style technology works by cooling catalysts indirectly using fluids such as water instead of air. Catalysts flow through Solex’s coolers by gravity, with a discharge device at the bottom creating uniform mass flow and even outlet temperatures.
Chilled water is pumped counter-current to the catalyst flow through a vertical bank of hollow stainless-steel plates while catalysts pass between the plates at a specified velocity to achieve the required cooling.
Advantage of indirect cooling
This offers several advantages when cooling catalysts, which, in the petroleum industry, is typically from 300-400 C to 50-70 C. The most significant is reduced energy consumption, notes Marinitsch.
While a typical fluid bed will require an estimated four to five kWh/tonne of energy, indirect plate cooling technology requires just 0.4 kWh/tonne – primarily because it forgoes the need for an electrical fan.
And because fluid beds require a large quantity of air for direct cooling, the result is significant dust and emissions that need to be cleaned up before being emitted into the air. In plate-style exchangers, the cooling media does not come into direct contact with the product, so dust or emissions are not created.
Dynamic forces are also not needed to move the particles through the vertical exchangers. Instead, they are fed by gravity at such a low velocity that the heat transfer process causes almost no wear on the catalysts nor the exchanger plates.
“The other advantage worth mentioning is that plate technology is better suited to recover and re-use low-grade energy,” says Marinitsch.
“The heat from the catalyst can be recovered in a wide range of input mediums, including steam, condensate or hot water — allowing for energy savings. Heat recovery loops can be optimized for maximum energy recovery and operational flexibility.”
Did you know?
The mass flow design of indirect heat transfer technology also ensures catalysts pass through the exchangers at low velocities, which minimizes product abrasion.
Learn more by visiting our catalysts page for applications, videos and more.
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