Currently available designs of metal heat exchangers have serious disadvantages which often determine lack of these devices in production units and processes. To begin with, they are the following:

  1. Unsatisfactory mass and dimensions parameters;
  2. Complicated or impossible repair of the heat exchange construction;
  3. The constructions are subjected to buckling and destruction due to thermal stresses arising from significant variation in elements thickness, uneven heating and cooling of elements, i.e. because of low thermal plasticity of constructions. Local overheated zones are often appeared in tube recuperators due to uneven airflow distribution in tubes. More air is supplied to short tube loops considering its lower resistance, and less air is supplied to long loops. As a result additional thermal stresses arise in the welding joint areas due to uneven airflow distribution.
  4. Traditional designs are characterized by uneven gasflow distribution through cross section of breechings, chimney flues, exhaust ducts which also has a negative effect on the heat exchange surfaces heating process directly within the heat exchanger. In this case uneven heat expansion of subunits takes place, i.e. thermal stresses appear resulting in damage of welding joints and heat exchange surfaces.



Significant disadvantage of traditional heat exchangers is low density factor, i.e. ratio of the heat exchange surfaces area to the volume(m2\m3). This parameter represents rationality of the unit arrangement and, consequently, heat exchange efficiency between heating and heated gaseous mediums.

As follows we consider the mentioned density parameter during comparative analysis of metal heat exchangers of different designs with OPT heat exchangers.

Special and specific design of the heat exchange surfaces in OPT heat exchangers provides equal distribution of inlet flows (as in the flue gas, so in the air side). Gas flows at the heat exchanger inlet are evenly distributed to numerous mini streams and these streams move through tight slot channels. These circumstances essentially increase degree of the heat exchange surfaces uniform heating both by heating and heated surfaces. This, in turn, prevents thermal stresses and, accordingly, construction damage. Equal thickness of OPT heat exchanger elements has the same impact.

OPT heat exchangers are made out of thin sheet stainless steel, thickness of all heat exchange surfaces is generally 1.5 mm.
OPT heat exchangers have a number of essential advantages as compared with the devices generally used, they are the following::

  1. Low mass and dimensions parameters ( 2-8 lower than traditional analogues)
  2. It is possible to configure any heat power for heat removal.
  3. Simple maintenance, transportation, installation and repair.
  4. Equal gas flow distribution directly in the heat exchanger.
  5. Low heat retention of the heat exchange surfaces.
  6. High structural thermoplasticity
  7. Heat exchange surfaces can be operated in aggressive gaseous mediums.
  8. Cleaning and self-cleaning of gas-air circuits from combustion materials can be performed, as the structural channels are linear and low air resistance provides significant speed.
  9. Each modular section is available for installation, repair and inspection.
  10. The design doesnt provide the tube sheet; this prevents thermal stresses as all heat exchange surfaces have equal small thickness.
  11. Different sorts of steel can be used in heat exchanger modular sections depending from operating conditions.
  12. Seal internal balance of thermal expansion thereby in some cases they can be installed without expansion joints.
  13. Low cost value of OPT heat exchanger and low operating costs and, consequently, short payback period (generally less than one year).

You can choose effective specifications of OPT heat exchangers for specific customers requirements and change it in wide range depending on:

  • gaseous medium speed (heating, heated);
  • ribbing interval and rib height in the heat exchanger basic element (ribbed panel);
  • irection of gaseous medium movement;
  • number of air circuit ways;
  • modular sections arrangement.

Performing analysis of the above mentioned information about excising metal heat exchangers and OPT heat exchangers we give the technical parameters of these heat exchangers in the tables where we specify initial and designed parameters according to the technical literary sources - (1), (2), (3), calculations for OPT heat exchangers were performed with the program developed by Termo Nord Stream, LLC -TERMO ( version 4.1)

Explanation:

  1. U shape tube heat exchanger
    OPT heat exchanger
  2. Gas-tube heat exchanger with straight tubes and two tube sheets
    OPT heat exchanger
  3. Tube radiation heat exchanger
    OPT heat exchanger
  4. Needle-like one-sided heat exchanger
    OPT heat exchanger
  5. Thermo block type heat exchanger
    OPT heat exchanger


Table 1.Comprehensive analysis of U-shape tube heat exchanger and OPT heat exchanger


U-shape tube heat exchanger

OPT heat exchanger
Flue gas inlet temperature, ° 1 000 1 000
Flue gas outlet temperature, ° 845 834
Flue gas consumption, m3/hour 14 500 14 500
Air inlet temperature, ° 0 0
Air outlet temperature, ° 400 430
Air consumption, m3/hour 7 000 7 000
Approximate dimensions, mm*mm*mm 1750*4513*1115 1680*840*1000
Approximate structural volume, m3 8,8 1,4
Approximate tubing weight, kg 3 940 1 080
Number of smoke ways 1 1
Number of air ways 2 2
Resistance in the air way, mm w.g. 117 164
Resistance in the flue gas mm w.g. 5 4
Heat transfer surface area, m2 75 78
Heat flow (heat removal)KW 1 032 1 090


Table 2.Comparative analysis of the gas tube heat exchanger with straight tubes (with two tube sheets) and OPT heat exchanger


Gas tube heat exchanger with straight tubes

OPT type heat exchanger
Flue gas inlet temperature, ° 1 100 1 100
Flue gas outlet temperature, ° 690 787
Flue gas consumption, m3/hour 5 300 5 300
Air inlet temperature, ° 20 20
Air outlet temperature, ° 500 500
Air consumption, m3/hour 4 200 4 200
Approximate dimensions, mm*mm*mm 1100*1620*2200 848*840*570
Approximate structural volume, m3 3,92 0,4
Approximate tubing weight, kg 2 700 630
Number of smoke ways 1 1
Number of air ways 4 2
Resistance in the air way, mm w.g. 231 289
Resistance in the flue gas mm w.g. 21,4 15
Heat transfer surface area, m2 56,2 36
Heat flow (heat removal)KW 756 755




The following should be noted after analysis of the main parameters specified in this table:

  1. The geometric scope of the tubing in the gas tube for-way heat exchanger almost 10 times exceeds the OPT geometric scope.
  2. The weight of the gas tube heat exchanger with two tube sheets 4 times exceeds the OPT weight. The flue gas inlet side of the gas tube type heat exchanger is equipped with expansion joint for compensation of structural thermal expansion at its height of 2200 mm.
  3. The density index for OPT heat exchanger is 13 m2/m3 = 36/0.4 = 90, and the density index for the gas tube heat exchanger is 13 m2/m3 = 56.2/3.92 = 14, i.e. OPT heat exchanger is 6 times more compact than the gas tube one.


Table 3.Comparative analysis of the tube radiation heat exchanger and OPT heat exchanger


Tube radiation heat exchanger

OPT type heat exchanger
Flue gas inlet temperature, ° 1 200 1 200
Flue gas outlet temperature, ° 916 962
Flue gas consumption, m3/hour 2 200 2 200
Air inlet temperature, ° 20 20
Air outlet temperature, ° 350 352
Air consumption, m3/hour 2 000 2 000
Approximate dimensions, mm*mm*mm 960*960*1800 420*840*440
Approximate structural volume, m3 1,2 0,16
Approximate tubing weight, kg 270 228
Number of smoke ways 1 1
Number of air ways 1 1
Resistance in the air way, mm w.g.
Resistance in the flue gas mm w.g. - 1
Heat transfer surface area, m2 7,3 13
Heat flow (heat removal)KW 243,5 244




The following should be noted after analysis of the main parameters specified in this table:

  1. The geometric scope of the tube radiation heat exchanger 7.5 times exceeds the OPT geometric scope. The density index for the tube radiation heat exchanger is 6, and the density index for OPT heat exchanger is 81, i.e. PT heat exchanger is 13 more nominally compact.


Table 4. Comparative analysis of the needle-like heat exchanger made out of one-way needle pipes with the length of 800 mm and OPT heat exchanger


Needle-like heat exchanger

OPT type heat exchanger
Flue gas inlet temperature, ° 750 750
Flue gas outlet temperature, ° 470 477
Flue gas consumption, m3/hour 1 330 1 330
Air inlet temperature, ° 20 20
Air outlet temperature, ° 320 332
Air consumption, m3/hour 1 340 1 340
Approximate dimensions, mm*mm*mm 3200*880*510 848*840*310
Approximate structural volume, m3 1,44 0,22
Approximate tubing weight, kg 3 740 1 470
Number of smoke ways 1 1
Number of air ways 4 2
Resistance in the air way, mm w.g. 92 91
Resistance in the flue gas mm w.g. 2 1
Heat transfer surface area, m2 9 19
Heat flow (heat removal)KW 147,5 154




The following should be noted after analysis of the main parameters specified in this table:

  1. The mass dimensional parameters of the needle-like heat exchanger, especially its weight, at least 3.5 times exceeds OPT heat exchanger weight.
  2. The density index for the needle-like heat exchanger is 6.25m2/m3, and for OPT type heat exchanger - 95 m2/m3, i.e. OPT heat exchanger is approximately 19 times more compact than the needle-like heat exchanger.
  3. The needle-like heat exchanger design gas the significant disadvantage with regard to gas tightness of the entire structure, as the insufficient installation quality and bad sealing can lead to the reduced heat exchanger operating efficiency due to partial air leakage into the flue gas flow. In this case the needle-like has 4-way airflow arrangement and the cross flow probability is rather high; according to the technical literature data (1) the cross flow probability can reach 15%.


Table 5.Comparative analysis of thermo block(cast iron-steel) type heat exchanger and OPT heat exchanger


"Thermo block" type

OPT type heat exchanger
Flue gas inlet temperature, ° 1 000 1 000
Flue gas outlet temperature, ° 785 808
Flue gas consumption, m3/hour 220 220
Air inlet temperature, ° 20 20
Air outlet temperature, ° 215 215
Air consumption, m3/hour 268 268
Approximate dimensions, mm*mm*mm 400*600*400 210*210*230
Approximate structural volume, m3 0,1 0,01
Approximate tubing weight, kg 600 17
Number of smoke ways 1 1
Number of air ways 1 2
Resistance in the air way, mm w.g. 44 43
Resistance in the flue gas mm w.g. 0,55 1
Heat transfer surface area, m2 1,92 1
Heat flow (heat removal)KW 19 19




At OPT heat exchanger installation on the furnaces the smoke-discharge pipe (minichimney) should be mounted above the heat exchanger to provide elevation head and chimney effect above the heat exchanger. The smoke-exhaust pipe with the height of 2.5 m. provides the chimney effect equal to 2 mm w.g., which will be enough to overcome resistance in the way of flue gases in OPT heat exchanger.

The following should be noted after analysis of the main parameters specified in this table:

  1. The mass-dimensional parameters of thermo block heat exchanger at least 35 times exceeds OPT heat exchanger weight.
  2. The density index for thermo blockis 11 m2/m3 and for OPT is 100 m2/m3, i.e. OPT nominally about 9 times more compact than the thermal block heat exchanger. It should be noted that the thermoblock type heat exchangers are not considered at all in the modern technical literature (2), as today they are not used at construction of new industrial furnaces due to its low technical efficiency in the terms of heat removal and due to its difficult manufacture using casting technology. This applies especially to design of thermo block heat xchangers with large dimensions.




The technical parameters for existing designs of metal heat exchangers as related to initial and designed data are considered according to the following information and technical sources:

  • (1)Industrial furnace heat exchangers. Tebenkov B.P., Metallurgiya publishing office, Moscow, 1975.
  • (2) Modern heating and heat-treating furnaces Gussovskiy V.L., Ladygechev M.G., Ussachev A.B., Mashinostroyeniyepublishing office, Moscow,2001.
  • (3) Reference book for rolling furnaces designer. Tymchak V.M., Gussovskiy V.L., et al. Metallurgiya publishing office, Moscow, 1969.




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