We discussed in the last article how expensive energy is in Brazil. Among the measures recommended for efficient energy use is the assessment of the equipment's thermal insulation, which is one of the main components of thermal processing equipment. In addition to maintaining process energy, it also has the function of personal protection.

This article aims to assist those who want to assess how much thermal insulation on their furnace can be improved. First, data collection. These four pieces of information must be collected:

- Cold face temperature of equipment (casing), in operation;
- Equipment external area;
- Energy costs;
- Equipment operation time, in operation;

The temperature can be assessed through thermographic cameras or radiometers. As there are usually significant temperature variations along the surface, it is important to consider the areas where they occur. That is, after mapping information for items 1 and 2, there is a table with two columns: temperature (in degrees Celsius) and area where it happens (in square meters). The sum of the areas shall be the total equipment area.

With the assistance of the attached chart, we can obtain the thermal losses relative to cold face temperatures. For example, 80 °C of cold face temperature equals 615 W/m2 of thermal loss. These thermal losses compose the third column of the information mapping process. The fourth column is then calculated by multiplying the thermal loss by the area where it occurs. The total thermal loss of the equipment is the sum of the areas' thermal losses and its unit is W.

The next step is calculating the financial impact of this thermal loss, which results from multiplying the total thermal loss by the energy cost (in R$/MWh) by the operation time of the equipment.

And finally, to estimate how much the equipment could be spending, we suggest considering the temperature of 60 °C as a reference (350 W/m2).

As an example: a continuous steel thermal treatment furnace is 6 m x 2 m x 2 m, with two openings of 0.5 m2. Energy costs in the plant are 350 R$/MWh and the furnace operates 10h/day, 240 days/year. From the thermography, area calculation and chart, the following table is obtained:

Temperature | Area | Thermal Loss by Area | Thermal Loss |

^{o}C |
m^{2} |
W/m^{2} |
W |

70 | 10 | 475 | 4.750 |

80 | 20 | 615 | 12.300 |

90 | 15 | 765 | 11.475 |

100 | 10 | 926 | 9.260 |

55 |
37.785 |

Therefore, the cost of this thermal loss is:

Actual cost = 37,785 W x 350 R$/MWh x 10 h/day x 240 days/year = R$ 317,394/year

Considering a well dimensioned insulation in perfect state of repair, we would have cold face temperature of 60 °C (350 W/m2), that is:

Estimated cost = 350 W/m2 x 55 m2 x 350 R$/MWh x 10 h/day x 240 days/year = R$ 161,700/year

That is, a savings percentage of approximately 50% and absolute savings of R$ 155,694/year.

Considering that the insulation of this furnace costs R$ 110,000, and that the insulation will last for at least 5 years, there is an excellent return on investment.