Technical Note #33 Energy Efficiency Technologies - Flue Heat Recovery

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This study focuses on the feasibility and energy efficiency benefits of using “waste” flue gas energy to heat Heavy Furnace Oil (HFO) instead of electricity generated by South Africa’s coal-fired power stations.  The demonstration is of national significance because the opportunity to recover energy from flue gas exists at most fixed kiln plants.

Results

The raw data shows that the heat exchanger provided a 2.2% reduction in electrical consumption by the heaters equivalent to an annual energy saving of 3,682kWh. At the current electricity tariff structure available to Algoa Brick, this calculates to an annual electricity cost saving of approximately R3 331 and a simple payback of 69 years.

Notwithstanding, a closer look at the data shows that after the heat exchanger was installed, a statistical correlation can be seen between the average daily exhaust temperature of the kiln and the electrical energy used by the heaters. In brief, the hotter the flue gas temperature, the better the heat exchanger works. For this reason, if the dataset is filtered to remove days with average exhaust temperatures lower than 117oC, the filtered dataset provides an electrical energy consumption reduction at the heaters of 18.7% or 31 557 kWh per annum worth an estimated R28 553 annually. If the brickmaker is able to maintain the kiln exhaust temperature consistently in the range of 120 – 130oC, the filtered data shows that payback on the heat exchanger would be reached in <7 years in addition to the fan and ducting lasting the maximum time possible.

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