New generation OPT recuperator is a plate-type heat exchanger made of finned panels - steel sheets with fins welded longitudinally by high frequency currents. Heat exchange surfaces are arranged in layers – channels of heating heat-medium are located between channels of heated medium. The medium runs through the channels crosswise.

Options of recuperator module assembly
The figure schematically shows the options of recuperator modules assembly

OPT Recuperators Finned Panels Welding Process

The following sequence of assembly operations for OPT recuperators is possible:

The set of base panels forms the module element:

  1. two base panels are inserted into each other, forming a double finning of the channel (having a finned cover);
  2. the base plate is covered with a sheet without finning (having a cover without fins);
  3. one base panel is covered with another base panel oriented transversely with respect to the first one (crosswise arrangement of panels).

The first two options are applicable for cases, when one of gas paths is finned.

The third option is used for cases, when both paths are finned.

Studies have shown that new recuperators have additional advantages due to small thickness of elements:
- low response rate;
- high thermal plasticity.

Module elements are assembled (welded) in package (module):

  • For the first two assembly options the elements are welded together with transverse spacers;
  • For the third assembly option the package is welded from cross-arranged panels;
  • In all cases two mutually crosswise channels are formed for heated and heating medium.

Heat exchange head is assembled from the modules. This head together with diffusers, confusers of gas paths, transition and connecting ducts and air tubes, as well as fitting, fastening and assembly elements forms the recuperator. The recuperator elements can be connected by bolted or welded joints. If necessary, thermal expansion joints are also installed between the elements.

It should be noted that inner compensation of thermal expansion occurs due to this design of recuperator modules, so …

The required recuperator capacity is determined by the volume of base panel cells and the set of modules.

Modular design allows using demountable design of recuperators that together with relatively low weight compared with similar tube recuperators makes it possible to simplify assembly, maintenance and repair processes.

The recuperator design allows using one or more runs through the heated medium (air). Changing the number of runs significantly impacts performance parameters of the recuperator. Increasing the number of runs improves its thermodynamic performance, but also leads to increase of air resistance through the path of heated medium. Permissible values of aerodynamic resistances (as through the heating medium channel, so through the heated medium channel) largely determine the size and weight of the recuperator.

Worked out technological and design methods allow using OPT recuperators in significant dust level environments, including abrasive component.

The design can have one or more air runs (heated medium).

Changing the number of runs significantly impacts the recuperator parameters and its aerodynamic resistance (the resistance sharply increases with increasing the number of runs).

Permissible values of aerodynamic resistances largely determine the size and weight of the recuperator.

Studies have shown that OPT recuperators made of sheet steel of 1.5 mm have additional advantages:

  • low response rate;
  • high thermal plasticity.

These conditions are extremely important for such devices, as if the recuperator is formed by elements of different thickness (for example, tubes and tubular grid in tube recuperators), significant thermal stresses, which destroy the structure, appear in its elements during transient processes (beginning and ending of furnace operation, sharp change of temperature mode and operating conditions of the recuperator, etc.).

Because of small and almost equal thickness of all structural elements OPT recuperator warms up quickly, providing designed capacity (due to low response rate), without causing the appearance of thermal stresses at that (due to high thermal plasticity).

The comparison of technical characteristics of OPT recuperators and traditional recuperators shows that under the same operating conditions and equal performance the weight and size parameters of OPT recuperators are 2-10 times greater than the performance of traditional devices (see Table 1).

The table below (as an example) presents the comparative characteristics of shell-and-tube recuperator and OPT recuperator (data for actual heat exchangers).

Comparative performance of recuperators.

  Shell-and-tube recuperator OPT recuperator
Length, mm 3340 1000
Width, mm 5655 2000
Height, mm 2090 1500
Weight, t 12 3

The following parameters were taken as initial data for the calculation of recuperators:

  • Flue gas temperature: 1000 °C
  • Heated air temperature: 400 °C
  • Flue gas flow rate: 34 000 Nm3/h
  • Heated area flow rate: 34 000 Nm3/h
  • Capacity of recuperator in these conditions: 2780 kW

New generation OPT recuperators not only successfully replace the existing devices, but also due to their features can be installed in those places, where traditional recuperators cannot be installed or where such installation is impractical (due to their technical and economic characteristics). It will provide colossal savings in energy and resources within the scope of different industries.

Technologies Used during Recuperator Operation under Increased Dust Level of Flue Gases.

At recuperator operation in conditions of increased dust level of gases the following changes to the standard project design should be made:

  1. Wear-resistant steels should be used. The steel can increase the wear resistance by 3-5 times in comparison with ordinary corrosion resistant steels and by 5-10 times in comparison with low-carbon steel applied for gas ducts;
  2. The section of recuperator channels should be chosen so that the velocity of Flue gases was above the velocity of channel self-cleaning;
  3. The screens should be installed at the inlet of gas paths that significantly reduces wear of recuperator end surfaces;
  4. The modular design of the recuperator increases its repairability. If one of its sections is worn, the rearrangement of the most and the least worn sections or its complete replacement should be performed. At that other sections of the recuperator can be left unchanged, if they are operable;
  5. The recuperator paths should be equipped with mounting ports to provide the access to the most loaded sections;
  6. The recuperator should be installed in the gas path area after partial (or full) gas cleaning.

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