Abstract

Rotary heat exchangers have been widely used in paint shops, combustion power plants, and in heating, ventilation, and air conditioning systems in buildings. For these processes, many types of heat exchangers are available in the market: Tube-shell heat exchangers, plate heat exchangers, and rotary heat exchangers, among others. For the rotary heat exchangers, the problem is that there is no net present value method and lifecycle assessment method-based optimization found in the literature. In this work, we address this issue: An optimization is carried out with help of an empirically validated simulation model, a life-cycle assessment model, an economical assessment, and an optimization algorithm. The objective function of the optimization simultaneously considers economic and environmental aspects by using different CO2 pricing. Different CO2 pricing scenarios lead to different optimization results. The ambient air empty tube velocity va, 2.1 optimum was found at 1.2 m/s, which corresponds to a specific mass flow msp of 5.4 kg/(m2·h). For the wave angle β, the optimum was found in the range between 58° and 60°. For the wave height h* the optimum values were found to be between 2.64 mm and 2.77 mm. Finally, for the rotary heat exchanger length l, the optimum was found to be between 220 mm and 236 mm. The optimization results show that there is still potential for technical improvements in the design and operation of rotary heat exchangers. In general terms, we recommend that the optimized rotary heat exchanger should cause less pressure drop while resulting in similar heat recovery efficiency. This is because the life cycle assessment shows that the use phase for rotary heat exchangers has the biggest impact on greenhouse gases, specifically by saving on Scope 2 emissions.

Highlights

  • 100 years ago, in 1922, the Swedish engineer Frederick Ljungström invented the first rotary heat exchanger (RHX) made of steel for power plants [1]

  • Since heat is to be recovered from a specific gas stream, this stream flows through one sector of the RHX

  • The values of the thermal efficiency η, internal rate of return (IRR), GHG emissions savings, and RHX design and operational parameters are shown for each scenario

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Summary

Introduction

100 years ago, in 1922, the Swedish engineer Frederick Ljungström invented the first rotary heat exchanger (RHX) made of steel for power plants [1] This is a type of heat exchanger whose compact design works efficiently, and it was patented in 1930 [2]. According to Warren, “The story of this development work is a good example of how a basically simple idea can be developed and refined by coordinated efforts in countries around the world into the carefully engineered product that it is today” [1] Until today, it has been used intensively in specific industrial processes [1] and in heating, ventilation, and air-conditioning (HVAC) in buildings [3] as a key element in heat recovery systems (HRS). Heat exchangers in general have been optimized over the years in order to improve their

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