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Examples from Audit Report
Contents:
Air Ratio Adjustment of Boilers
Heat Insulation Reinforcement
Waste Heat Recovery by Recuperators
Air Preheating with Exhaust Gas
Heat Recovery with Air-to-air Heat Exchangers		 2
3
4
5
6
Air Ratio Adjustment on Boilers
Existing problem
  • Because the air ratio of the boilers (2t/h x 2 boilers) is high (Exhaust gas O2 = 7, 9%), the exhaust gas heat loss is large.
Improvement
  • Adjust the air ratio to the standard value (1.2) under the Law Regarding the Rationalization of Energy Use.
Advantage
  • Fuel (Fuel oil A) reduction amount = 16.6kL/year (¥680,000/year)
    When:
    Exhaust gas temperature = 220oC Current fuel usage amount = 520kL/year/2 boilers Fuel reduction rate due to air ratio adjustment = 3.2%
Reference
Harmful effects of an excessive air ratio:
  • Increase in heat loss due to exhaust gas
  • Reduction of heat insulation combustion temperature, causing reduction in furnace temperature
  • Increase in power required by combustion air fan
  • Increase in draft resistance in flue
Heat Insulation Reinforcement
  • Existing problem
    • Non-heat insulated parts are contained in steam pipes, drain pipes and hot water pipes.
  • Improvement
    • Install simple insulation to prevent heat radiation.
  • Advantage
    • Reduction in boiler LPG = 1,096m3/year = 2,268kg/year
      (¥125,000/year)
      • When:
      • 150°C steam pipe 50A: Piping x 3m + Valve (corresponding length 1.28m) x 6 units + Flange (0.49m equivalent) x 20 units = Total corresponding length 20.48m
      • 90oC drain pipe 25A: Piping x 5m + Valve (corresponding length 1.21m) x 4 units + Flange (0.54m equivalent) x 10 units = Total corresponding length 15.24m
      • Heat radiation amount from non-insulated piping (from graph): 50A piping = 400W/m, 25A piping = 100W/m
      • LPG specific weight = 2.07kg/m3
Reference
  • Because valves and flanges have large surface areas, insulation will be required as for piping.
  • Beyond a certain thickness of insulation material, the additional insulating effect will be small.
Waste Heat Recovery by Recuperators
  • Existing problem
    • The exhaust gas temperature of kilns (5 kilns) is high at 1000°C. In the current situation, temperature reduction is carried out by external air aspiration before discharge.
  • Improvement
    • Install an exhaust gas recuperator and implement pre-heating of the combustion air to achieve a fuel reduction.
  • Advantage
    • LPG fuel reduction amount = 76.8t/year/kiln x 5 kilns x reduction rate of 16.8% = 64.5t/year (¥3,225,000/year)
    When:
    • Air ratio = 1.2
    • Recuperator inlet exhaust gas = 500°C
    • Recuperator heat recovery rate = 25%
    • Recuperator input/output air temperature = 25/300°C
    Reference
    • Characteristics of radiant type air preheater
      • The heat source gas is passed through the inside of the cylinder, and the pre-heated air is passed through the gap between the inside cylinder and outside cylinder.
      • Since the heat transmission in the inside cylinder is mainly radiant heat transfer, it will be possible to obtain very high temperature air due to convection heat transfer in the outside cylinder (gap)
      • Response is possible to up to 1200°C class temperature bands.
      • Even in locations with high dust concentrations, blockages will not occur, and a stable performance can be achieved.
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