Technical sources about industrial fuel furnaces let know that the furnaces are operated with rather low thermal efficiency not exceeding 20-30 %, i.e. 3-4 times lower than, for example, efficiency of the modern boiler plants.

The above mentioned factor are determined, in general, by great heat losses with exhaust gases, reaching sometimes 50 – 65 % of total heat amount supplied into the furnace. To increase the furnace thermal efficiency the method of air heating in the furnace heat exchangers is used for the air supplied for burning into fuel-burning arrangements. At air heating in the furnace heat exchanger the air volume supplied into furnace increases in direct proportion to the temperature of its heating, i.e. the proportion (or percentage) of the heat supplied with the air increases in the receipt section of the furnace heat balance and, accordingly, the fuel consumption for the furnace reduces. The furnace plant efficiency increases in general due to reduced heat loss with exhaust gases.




Note that the caloric unit entered with the preheated air supplied for fuel combustion has more value than the caloric unit generated by fuel combustion. In this case the part of the caloric unit generated by fuel combustion in the furnace is used in its working space, as the other part is discharged with the flue gases. The heat containing in the preheated air (fuel gas) is fully used in the working space, as the exhaust gas volume doesn’t rise in this case.

Consider next which heating-performance parameters are influenced by the preheated air supplied to the furnace fuel-burning arrangements.

The preheated air facilitates flame temperature increase, as its calorimetric temperature rises. According to the technical specifications at excess ratio factor a=1.0 and its temperature 20°С the calorimetric temperature of natural gas burning is 2050°С, bit at the same a= 1.0 and at the preheated air temperature up to 400°С the calorimetric temperature is 2320°С.

As a result, the calorimetric temperature rises causes increase of the radiation constituent during heat transfer from heating agent to the heating units in the furnace working area. Increase of the radiation constituent results from the fact that radioactive heat transfer depends to the forth power from the flame temperature.

  1. Preheated air mixed with fuel in the fuel-burning arrangements provides fast heating of the fuel improving combustion procedure effectiveness and reducing incomplete combustion.
  2. At heat exchangers installation the flue gas temperature decreases at heat exchangers outlet and, as consequence, gas actual volume also decreases followed by decrease of the chimney flue air pressure. Therefore the power costs for the exhauster motor operation are reduced.
  3. At air heating and therefore at increased fuel combustion efficiency its toxic components are burned more fully stipulating reduction of the emission payments for the toxic elements.

Here we specify the general heating-performance aspects of justification of industrial heat exchangers application in industrial fuel furnaces and furnace plants, but together with the abovementioned heating-performance processes providing usage effectiveness it is necessary to point out that there are a number of other parameters of the heat exchangers designed by Termo Nord Stream considered as decisive factors for application feasibility of one or another industrial heat exchanger design. The article of Termo Nord Stream specialists regarding «Comparative analysis of design parameters of metal heat exchangers with different design with the heat exchangers designed by Termo Nord Stream», considers in depth the performance and parameter analysis for different types of heat exchangers.

Substantial contribution to justification of OPT type heat exchangers application is made by the fact that the specified heat exchangers enable to recover heat of slag and ash and severe dusty gas streams if installed after thermal generating unit combusting solid fuel.

Hot air supply to the burner for solid fuel combustion speeds up fuel ignition and intensifies its burning process reducing heat losses arising from chemical and mechanical incomplete burning. The recommended air preheating at in-chamber combustion of different fuel types in furnace units is given in the following table.

Fuel Temperature of the preheated air
Brown coals, milled peat, wood wastes350°C
Bituminous and lean coals 300°C
Oil and gas250-300°C

The most frequent cases of the heat exchanger application.

Air heating supplied to the furnace burners (blast) (burning efficiency increase and heat energy saving)

Application effect

  • Heat energy return
  • Fuel saving
  • Decreased costs for equipment and increased service life (gad ducts, chimney stacks, etc.)
  • Environmental standards are provided
  • Requirements of the Law No. 261 FZ «Concerning Energy Conversation» are met
  • Reduced ordering costs
  • Reduced costs for gas cleaning
  • Chemical and mechanical fuel afterburning
  • Increased efficiency of production process
  • Short payback period
Air heating for process tusks of allied production

Application effect

  • Heat energy return
  • Fuel saving
  • Reduced costs for the equipment used in the technological cycle and increased service life due to decreased operating temperature (gas ducts, chimney stacks, injectors, smoke exhausters, valves, etc.)
  • Environmental standards are provided
  • Requirements of the Law No. 261 FZ «Concerning Energy Conversation» are met
  • Reduced ordering costs
  • Reduced costs for gas cleaning
  • Process parameters consistency is provided
  • Chemical and mechanical fuel afterburning
  • Increased efficiency of production process
  • Short payback period
Combined use of heated air

Application effect

  • Heat energy return
  • Fuel saving
  • Reduced costs for the equipment used in the technological cycle and increased service life due to decreased operating temperature (gas ducts, chimney stacks, injectors, smoke exhausters, valves, etc.)
  • Environmental standards are provided
  • Requirements of the Law No. 261 FZ «Concerning Energy Conversation» are met
  • Reduced ordering costs
  • Reduced costs for gas cleaning
  • Process parameters consistency is provided
  • Chemical and mechanical fuel afterburning
  • Increased efficiency of production process
  • Operational comfort is provided
  • Reduces investment costs for heating system arrangement
  • Short payback period
Process gas (air) heat recovery

Application effect

  • Heat energy return
  • Fuel saving
  • Reduced costs for the equipment used in the technological cycle and increased service life due to decreased operating temperature (gas ducts, chimney stacks, injectors, smoke exhausters, valves, etc.)
  • Environmental standards are provided
  • Requirements of the Law No. 261 FZ “On Energy Saving” are met
  • Reduced ordering costs
  • Reduced costs for gas cleaning
  • Process parameters consistency is provided
  • Increased efficiency of production process
  • Operational comfort is provided
  • Reduces investment costs for heating system arrangement
  • Short payback period
Air heating for room heating system and other domestic needs

Application effect

  • Heat energy return
  • Fuel saving
  • Reduced costs for the equipment used in the technological cycle and increased service life due to decreased operating temperature (gas ducts, chimney stacks, injectors, smoke exhausters, valves, etc.)
  • Environmental standards are provided
  • Requirements of the Law No. 261 FZ «Concerning Energy Conversation» are met
  • Reduced ordering costs
  • Reduced costs for gas cleaning
  • Process parameters consistency is provided
  • Increased efficiency of production process
  • Short payback period




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